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MÉMOIRE
CONFIDENTIEL jusqu’en 2013
Présenté par : Ophélie TOUCHEMOULIN
Dans le cadre de la dominante d’approfondissement : IDEA (Ingénierie de
l’Environnement, Eau, Déchets et Aménagements durables)
Innovative and sustainable solutions to mitigate the carbon footprint of Seafield wastewater treatment plant
Pour l’obtention du :
DIPLÔME D’INGENIEUR d’AGROPARISTECH
Cursus ingénieur agronome
et du DIPLÔME D’AGRONOMIE APPROFONDIE
Stage effectué du 08/03/2010 au 10/09/2010
A : Veolia Water Outsourcing Ltd (AVSE)
20 Marine Esplanade
Seafield Road
Edinburgh
EH6 7RF
Enseignante-responsable : Claire CHENU
Maître de stage : Hélène Galy
Soutenu le : 30 septembre 2010
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Seafield WWTP: final settlement tanks – source: VWOL
Internship at Veolia Water Outsourcing Ltd, in Edinburgh, from March to September 2010
Ophélie TOUCHEMOULIN
Internship co-ordinator: Claire CHENU Internship supervisor: Hélène GALLY
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Executive summary
Veolia Water operates the Almond Valley, Seafield and Esk contract, whose client is Scottish Water. Within the framework of this contract, Veolia has to operate five wastewater treatment plants (WWTP), among which is Seafield, the biggest one. Although this activity enables the discharge of treated water into the environment instead of sewage, it has an important carbon footprint, mainly because of the large amount of energy required to run the plant (electricity and fuel represent about 70% of Seafield‟s total GHG emissions). Veolia is really committed to sustainable development and fighting against climate change, because of its name (Veolia Environment), its activities (waste & water management, energy supply, transport) and for its reputation. This is why the project on innovative and sustainable solutions to mitigate Seafield‟s carbon footprint was launched. Along with the environmental and reputational benefits, the project also represented a critical opportunity to reduce costs.
The question is how can we turn Seafield into a more sustainable and environmentally friendly WWTP? The focus was put on the energy consumption of the plant as it represents the highest contribution to the site‟s carbon footprint and thus the biggest opportunities to carbon reduction. Not only the site could reduce its energy consumption but also it could use energy from renewable sources. Among all the existing techniques to produce green energy, the first step was to select the most suitable technologies to the site characteristics and context. It appears that wind energy, hydro power, waste heat recovery and co-incineration of the rags are the most interesting solutions as they were technically suited to the site requirements but also developed enough to be considered as reliable. The second step was to analyse the electrical production potential of each of those solutions, their environmental benefit and their profitability.
Wind turbines could have been interesting because of the plant‟s location (near the coast), but in fact it appears that the wind resource is not strong enough to produce significant energy levels. Moreover, the reliability of the data can be questioned. Depending on the data source (national database or on-site measurements with the use of a production or power curve), the installation of one turbine is either profitable or not. Finally, planning permissions are difficult to obtain, especially in the context of the Seafield project where the plant is very close to the city. All those factors made the wind option very risky.
Using the water drop on the outfall to produce electricity is worth considering. However, only an Archimedean Screw is profitable, classical turbines such as Kaplan or Vortex turbine are too expensive. Hydro-energy appears as the most financially and environmentally interesting solutions for Seafield, provided that the amount of money given by the government to green producers and used for the calculations is confirmed.
Waste heat recovery from the CHP or the cooling down of the hot sludge after thermal hydrolysis could be used either for space heating or to produce electricity via an Organic Rankine Cycle machine. But it appears that the quantity (flow rate) and quality (temperature) of the hot water is not high enough for the second option. The profitability of the space-heating option depends on the energy consumption to heat the office. As it stands now, the uncertainty about this data (no monitoring per usage) makes it impossible to give a clear answer.
Screenings are one of the wastes produced by the plant‟s activity. They are currently sent to landfill, which is not the best way of disposal and is becoming more and more expensive too (increase of landfill taxes). As the Scottish government is encouraging the incineration and as an energy from waste plant will be build in the neighbourhoods, the co-incineration solution could be financially interesting, but only if Seafield is not eligible to the water discount, a discount on landfill taxes given when the waste is composed of a significant part of natural water.
Thus, this study shows that opportunities to minimize Seafield‟s carbon footprint exist. However, more detailed studies are needed to confirm these results.
Key word: wastewater treatment plant, carbon footprint, renewable energy, profitability
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Executive summary
Veolia Water opère le contrat AVSE (Almond Valley, Seafield and Esk), dont le client est Scottish Water. Veolia doit ainsi gérer cinq stations d‟épuration (STEP), parmi lesquelles Seafield, la plus grande de toutes. Bien que cette activité permette le rejet dans le milieu naturel d‟une eau traitée au lieu d‟eaux usées, elle a toutefois un important impact environnemental du fait de son importante consommation énergétique. En effet, l‟électricité et le fuel nécessaires au fonctionnement de la station représentent environ 70% des émissions totales de gaz à effet de serre du site. Veolia est réellement engagé en faveur du développement durable et contre le changement climatique, de part son nom (Veolia Environnement), ses activités (gestion-traitement des déchets et de l‟eau, production d‟énergie, transport) et pour sa réputation. C‟est pourquoi le projet sur les solutions innovantes et durables pour diminuer l‟empreinte carbone de Seafield a été lancé. Les objectifs sont triples : réduire les coûts, diminuer l‟impact environnemental et renforcer l‟image du groupe sur ce thème.
La problématique est la suivante : comment Seafield peut-elle devenir plus durable et plus écologique ? L‟accent a été mis sur la consommation énergétique, puisque cette dernière représente la part la plus importante dans l‟empreinte carbone de la STEP. C‟est donc dans ce secteur que les opportunités de réduction sont les meilleures, en termes de consommation d‟énergie et de recours aux énergies renouvelables. La première étape de l‟étude a été de sélectionner les technologies les plus adaptées au site. Ainsi, l‟éolien, l‟hydroélectricité, la réutilisation de chaleur et la co-incinération des refus de dégrillages se sont avérés être les plus appropriés et les plus fiables. La seconde étape a consisté en l‟analyse de la production d‟énergie pour chaque solution, son intérêt environnemental et sa rentabilité.
Le recours aux éoliennes aurait pu être intéressant car Seafield se trouve juste en bord de mer, où la vitesse du vent est plus importante. Cependant, il est apparu que la ressource éolienne n‟était pas suffisante pour assurer une production significative. En outre, la fiabilité des données est remise en question puisque selon leur provenance (base de données nationale, mesures sur site, utilisation de la courbe de production ou de puissance), l‟installation d‟une éolienne est ou non rentable. De plus, l‟obtention d‟un permis de construire est difficile, particulièrement dans un contexte urbain tel que celui où se trouve la STEP. Toutes ces raisons font de cette solution une option risquée.
Utiliser la chute d‟eau au niveau du point de rejet pour produire de l‟électricité est intéressant. Cependant, seule la vis d‟Archimède est rentable, les autres solutions plus classiques comme les turbines Kaplan et Vortex sont trop chères. La solution hydroélectrique s‟avère être la plus intéressante financièrement et écologiquement pour Seafield, à condition que le tarif de rachat de l‟électricité utilisé pour les calculs soit confirmé.
Réutiliser la chaleur produite lors du refroidissement des machines de co-génération ou de la boue après le traitement d‟hydrolyse thermique pourrait servir soit à chauffer les bureaux soit à produire de l‟électricité. Néanmoins, la quantité (débit) et la qualité (température) de l‟eau chaude disponible ne sont pas suffisantes pour la deuxième option. La rentabilité de l‟option « chauffage des bureaux » dépend de la consommation énergétique pour chauffer ces bâtiments. Pour le moment, l‟incertitude sur cette donnée ne permet pas de donner une réponse claire.
Les refus de dégrillage produits lors du traitement des eaux usées sont actuellement envoyés en centre de stockage des déchets ultimes (CSDU), ce qui n‟est pas la voie d‟élimination la plus écologique. De plus, cette solution va devenir de plus en plus chère avec l‟augmentation des taxes sur la mise en CSDU. Comme le gouvernement écossais encourage le recours à l‟incinération et qu‟un incinérateur va être construit dans les environs de la STEP, l‟opportunité de co-incinérer les refus pourrait s‟avérer intéressant financièrement, si la STEP n‟a pas le droit de bénéficier d‟une remise sur la taxe de mise en décharge, qui s‟applique aux déchets composés d‟une certaine part d‟eau naturellement présente.
Cette étude a donc permis de mettre en évidence les opportunités existantes pour réduire l‟empreinte carbone de Seafield. Toutefois, de plus amples études sont nécessaires afin de confirmer ces résultats.
Mots-clé: station d‟épuration, empreinte carbone, énergies renouvelables, rentabilité
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Table of contents
INTRODUCTION ____________________________________________________________ 7
I. INNOVATIVE AND SUSTAINABLE SOLUTIONS AT SEAFIELD WWTP: A
PROJECT IN PHASE WITH THE ENVIRONMENTAL AND POLITICAL CONTEXT _ 7
A. Almond Valley, Seafield, Esk (AVSE): a key contract for Veolia in Scotland ________ 7
1) The presence and work of Veolia Water in the UK and in Scotland _________________ 7
2) AVSE: five WWTP in Scotland operated by Veolia Water on behalf of Scottish Water _ 10
3) Seafield, a state-of-the-art WWTP __________________________________________ 13
B. Sustainable opportunities at Seafield: the objectives of such a project ____________ 15
1) The challenge: make Seafield a more sustainable WWTP ________________________ 15
2) The three main objectives of this project: environment, economy and communication __ 16
3) Expected results and the continuity of this study_______________________________ 17
C. The framework of the study: the reasons of this project ________________________ 17
1) The desire and obligation to comply with the government and Scottish Water
environmental targets ________________________________________________________ 17
2) A financial context difficult for AVSE _______________________________________ 18
3) Communication about Veolia corporate responsibility ___________________________ 19
II. THE METHODOLOGY ADOPTED TO CARRY OUT THE STUDY ___________ 20
A. From a broad range of possibilities to the selection of only four solutions _________ 20
1) The first step: a broad research on all the existing sustainable solutions to produce “green”
energy ____________________________________________________________________ 20
2) Information needed for each solutions of the broad list __________________________ 21
3) Selection of the four most interesting technologies suitable for Seafield _____________ 21
B. Business case for each selected solutions and final selection of only one project ____ 22
1) Technical analysis: resource available and expected production ___________________ 22
2) The choice of the company that will provide a quote and with which we will work later if
the project is kept ___________________________________________________________ 22
3) Comparison between the companies of a same sector and between the solutions thanks to
economical criteria __________________________________________________________ 23
C. Limits of the study _______________________________________________________ 26
1) Reliability of the company chosen __________________________________________ 26
2) The needs of complementary studies ________________________________________ 26
3) Gathering reliable information: relationship with the companies __________________ 27
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III. THE RESULTS OF THE STUDY: AN ARCHIMEDEAN SCREW AS THE BEST
TECHNICAL AND ECONOMICAL SOLUTION TO DECREASE SEAFIELD’S CARBON
FOOTPRINT _______________________________________________________________ 27
A. The four most interesting solutions and characterization of the resources available 27
1) Many solutions, only a few opportunities _____________________________________ 27
2) Localization of the highest resource and the best place for the installation of the engines 30
3) Characterization of the resource available ____________________________________ 35
B. The benefits of each solution in terms of costs savings and GHG emissions avoided 40
1) The companies selected and the equipment advised for each solution _______________ 40
2) Production of “green” electricity and minimisation of the carbon footprint ___________ 42
3) Economical analysis: the profitability of each solutions __________________________ 45
C. Choice of the best solution for Seafield WWTP by taking into account the risks of the
project _____________________________________________________________________ 49
1) Analysis of the risks _____________________________________________________ 49
2) The most suitable solution given financial and environmental results_______________ 51
3) Continuation of the study and implementation of the chosen project _______________ 53
CONCLUSION ______________________________________________________________ 54
ACKNOWLEDGEMENTS ____________________________________________________ 54
GLOSSARY _________________________________________________________________ 55
APPENDIX _________________________________________________________________ 55
REFERENCES AND BIBLIOGRAPHY _________________________________________ 120
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Introduction
Before the development of wastewater treatment, sewage was discharged in the nature, thus
resulting in pollution and sanitation problems for the local population. It thus had an ecological
impact. The construction of wastewater treatment plants was a huge improvement in terms of
hygiene and environment. Since then, laws have been created to ensure that the water discharged
is clean enough to be released in the milieu without polluting it. As awareness on environmental
issue increases, so do the standards on water treatment. In order to meet these requirements
(organic content, nitrogen and phosphorus content), treatment plants had to develop new
technologies and strengthen each step of the process, resulting in more energy consumption
(aeration, UV treatment…), more chemicals use and so a higher carbon footprint. Thus, water
companies use 7700 GWh of energy each year in the UK, about 2% of all UK industrial
consumption. The sector ranks fourth in terms of energy intensity, behind steel, cement and parts
of the chemicals sector. So, wastewater treatment has a positive and negative impact on the
environment, and today‟s goal is to minimize the negative impact while keeping and improving
the good one. This is the question this report deals with: what are the solutions to turn a specific
WWTP (Seafield plant, in Edinburgh, Scotland) into a more sustainable and environmentally
friendly activity.
The first part of the report presents the general framework of this project and the context in
which it was launched. The second part is about the methodology used and the limits of the study.
The last part describes the main results and the final decision that will be taken to mitigate the
carbon footprint of the plant.
I. Innovative and sustainable solutions at Seafield WWTP: a project in phase with the environmental and political context
A. Almond Valley, Seafield, Esk (AVSE): a key contract for Veolia in Scotland
1) The presence and work of Veolia Water in the UK and in Scotland
Veolia Environment is one of the leading companies in environmental services, with operations on
every continent and more than 312,590 employees. It is made of four main subsidiaries, each one
dedicated to a specific sector: Veolia Transport (passenger transport), Veolia Environmental
Services (waste management), Dalkia (energy) and Veolia Water (water supply and sewage
treatment).
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In the UK, the water sector is divided into two segments: the regulated and non regulated
markets.
In the UK, Veolia Water is present in both markets through its five companies: Veolia Water
Central, Southeast, East, Projects and Outsourcing, as shown in figure 1.1
Figure 1: Veolia Water locations in the UK
Source: http://www.veoliawater.co.uk/en/water-companies/
I completed my internship in the commercial part of the business, within Veolia Water
Outsourcing Ltd (VWOL).
The three first companies supply water for the South East of England and are part of the
regulated water market. . This means their operation is regulated by Ofwat (Office of Water
Services), which sets the price of water across the whole country and the standards to meet.
On the other hand, VWOL and Projects are deregulated. The price of the service is set by the
competition at the time of invitations to tender.
VWOL offers the following commercial services:
Building, operating and maintaining water-related assets that belong to other
organisations
Providing customised and sustainable solutions to optimise water cycle and wastewater
management for the industrial clients
Offering technological solutions for the treatment of potable, process; and utility water
and wastewater
Operations and maintenance activities in public sector water and wastewater treatment
plants
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Veolia Water entered the commercial market in the UK by acquiring the non regulated business
of Thames Water in December 2007. VWOL was created then to support all commercial
contracts.
VWOL has four divisions: England and Wales, Scotland, Northern Ireland and Republic of
Ireland, Customer Services division. I completed my internship in the Scotland division, within the
AVSE business unit (see organization chart below). Indeed, VWOL is organised into four
business units. A business unit is a segment of a firm representing a specific business function or
dealing with a specific client. For example, Nevis‟s client is the Ministry of Defense, AVSE‟s client
is Scottish Water. The functional area of Nevis is providing drinking water and treating
wastewater for its client. As an autonomous division, it is small enough to be flexible and large
enough to exercise control over most of the factors affecting its long-term performance.
Figure 2: VWOL and AVSE contract within Veolia Environment in the UK
As part of the acquisition of Thames Water businesses, Veolia Water entered the Scottish market
in 2007 with the aim of developing the commercial activities. Their aim is to double the size of
their business by 2012. Since 2007, two main steps have been made towards that objective.
The award of the Scottish Water Solutions contract: a joint venture between Scottish
Water (51%) and a consortium called Thistle Water which is composed of Veolia Water
(40%), Jacobs (design) and Laing O‟Rourke (construction). Solutions 2 main activity is to
upgrade Scottish Water infrastructures over a period of 5 years.
Veolia Environment
Veolia Transport
Veolia Water (UK)
VW Central VW Southeast VW East
VWOL (Veolia Water Outsourcing
Ltd)
VWOL England and
Wales
VWOL Scotland
Nevis (Ministry of
Defense)Stirling-AVSE
Engineering Services
(maintenance)
Scottish Water Solutions
VWOL Ireland
VW Projects
Veolia Environmental
ServicesDalkia
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The very recent acquisition of the commercial business of United Utilities (one of Veolia‟s
main competitor), including 3 PFIs (Private Finance Initiative) in Scotland
Combined with its existing activities, this will make Veolia Water the leading player in the non-
regulated water sector in the UK, with national coverage in a market expected to enjoy strong
growth and offering immediate synergies.
2) AVSE: five WWTP in Scotland operated by Veolia Water on behalf of Scottish Water
Scottish Water is a publicly owned company supplying drinking water and treating wastewater.
In some cases, Scottish Water outsources the operation of its facilities to private companies such
as Veolia Water. So Scottish Water is Veolia’s client.
AVSE stands for Almond Valley, Seafield, Esk. The contract began in 1999 and will last until
2029. The previous structure of this contract is shown in figure 3.
Figure 3: AVSE contract structure before 2009
It is a PPP (Public Private Partnership) between Scottish Water and Stirling Water. The Private
Finance Initiative (PFI), also called Public Private Partnership (PPP) describes a “partnership”
established between a public sector body and a private sector organization to deliver public
services. With this type of partnership, the government‟s strategy is to encourage the private
sector to invest in and deliver high quality public services where the financial risk remains with
Client
Stirling Water Service company
Design Construction Operator
Veolia bought their shares in 2009: Stirling Water is now a Veolia
company
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the investor. Stirling Water has made an investment of more than £120 million in the project and
continues to invest more than £1.2 million each year in renewing project assets.
Stirling Water was a joint Venture between the construction company (MJ Gleeson), the design
company (MW Harza) and the operator (Veolia Water). Initially, the operator was Thames Water
but it has been bought out by Veolia in 2007.
In 2009, Veolia Water bought the shares of Gleeson and MWH to control 100% of Stirling
Water. The company remains a separate entity from the AVSE operations.
Within AVSE contract, Veolia has to operate 11 storm water sites in the Esk Valley and 5
WWTP in Edinburgh and the Almond Valley. The map below located the different plants and
gives the capacity of each one. Seafield is the biggest plant and currently treat the sewage of 800
000 PE. It is in this WWTP that I have worked on innovative and sustainable projects. AVSE
covers the sewage treatment needs of 20% of the Scottish population.
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Wallyford
Pumping station
200 000 PE
EEddiinnbbuurrgghh
Esk
Valley
Blackburn WWTW
13 000 PE
Almond Valley
Newbridge WWTW
40 000 PE
East Calder WWTW
90 000 PE
Edinburgh
(Seafield) WWTW
600 000 + 200 000 PE
0 km 10 20
F i r t h o f F o r t h
Waste water treatment works
Storm water treatment works
Sewers
Sewers upgraded
Transfer pipeline
AVSEAVSE
Whitburn WWTW
10 500 PE
Source : VWOL
Figure 4: The Almond Valley, Seafield and Esk project
Source: VWOL
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3) Seafield, a state-of-the-art WWTP
Seafield treats the sewage of the Edinburgh population, industries and commerce as well as the
storm flow from the Esk Valley. It is a unitary network, so it collects rainwater too. On average
300 000 m3 are treated each day, the equivalent of 121 Olympic swimming pools.
The WWTP was built in the 1970‟s. The process is the classic one for wastewater treatment:
activated sludge (figure 5).
The first step is screening: the screens are made from a metal mesh which collects any item over
6mm in size. A mechanical process then cleans the screens and the rags are washed and
compressed to remove moisture. They are then deposited into skips for transportation to landfill.
The 2sd step is grit removal: to prevent damages to the equipments, small particles of grits and
sand that have been washed into the system from road drains must be removed from the
wastewater. This is achieved using natural settlement in the detritors tanks. The grits are then
removed from the tank and recycled into road construction.
The 3rd step is primary settlement: it occurs in primary settlement tanks (PFT). The suspended
solids settled at the bottom of the tanks and are removed.
The 4th step is the activated sludge (AS): the sewage is aerated into 6m deep tanks. The bacteria
use the O2 to consume the organic matter present in the wastewater.
The 5th step is final settlement: it occurs in final settlement tanks (FST), where any remaining
solid material is allowed to settle again. This biological sludge is rich in bacteria and so return to
the AS tanks to treat more incoming sewage. After FST, the water is cleaned enough to be
discharge in the sea via a long sea outfall tunnel of 1.8km.
However, during the bathing season (June-September), the sewage needs to undergo a 6th step:
UV treatment, to kill the remaining pathogens. This UV plant is the second biggest one after
Wellington, New Zealand. It means too that during the summer months, the electrical
consumption is more important.
The primary and biological sludge is digested into 6 giant digesters, each one containing 2 500t.
The biogas produced from the mesophilic (35˚C) anaerobic digestion is converted into electricity
and heat via two Combine Heat and Power (CHP). The power of the 2 CHPs is 2.3 MW and the
electricity produced is on average 10-11 GWh/year. The digestat (digested sludge) was
afterwards dried with a centrifuge (24 %DS) and thermal driers (96 %DS) and transformed into
pellets in order to have a pasteurisation (the sludge is not compliant after the AD). However, the
driers were not working efficiently and cost a lot to run, so this stage was abandoned last year.
More information on Seafield WWTP is available in appendix 1.
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Figure 5: Wastewater treatment process at Seafield
Source : VWOL
The innovative characteristic of this WWTP is the anaerobic digestion of the sludge since
2006. There are others ongoing improvements:
Improvements of the screening stage (there was a by-pass and so a part of the rags
entered the process)
Odour Improvement Plan: the channels and the edges of the FST will be covered and the
gas will be extracted and treated into an odour plant
Thermal hydrolysis (TH) project: currently the sludge is not compliant (only 1.2 log kill
after AD) and thus can not be spread on agricultural fields (need 2 log kill). The sludge is
either sent to landfill, to land restoration or for industrial crops. The TH process would
allowed to have a compliant sludge and thus be able to dispose of the sludge on fields,
which is cheaper than sending it to landfill and better for the environment too.
Co-digestion: at the present time, co-digestion (mixing of different fermentable biomass
in the digester) is not allowed in the UK, whereas it is widely used in the rest of Europe,
especially in Germany. Because the TH process will decrease the volume of sludge, there
Screens
Digester
Primary Settlement Activated Sludge Final Settlement
Effluent
Wastewater
Centrifuge
Sludge cake
Dryers
Pellets
UV
disinfection
This stage of the process does
not work anymore: it will be
replaced by thermal hydrolysis
CHPs Electricity +
heat
15
will be spared places in the digesters and they are looking at food waste to fill this empty
place. The addition of co-products will increase the biogas yield and its quality too
The purchase of a 3rd CHP to convert more biogas into electricity
So, Seafield WWTP is a dynamic plant and Veolia does not hesitate to invest in it to improve the
process.
B. Sustainable opportunities at Seafield: the objectives of such a project
1) The challenge: make Seafield a more sustainable WWTP
The question I was asked is what can we do to make Seafield more sustainable and to mitigate its
carbon footprint. This means achieving a balance between financial performance, impact on the
community and environmental benefits.
On the one hand, a WWTP helps the environment since it treats and removed the nutrients and
the pollutants from the sewage, but on the other hand the process requires a lot of energy and
produces wastes (sludge, rags). Because the energy consumption of the plant is very
important, so is its ecological and GHG footprint. In order to minimise environmental impact
through energy consumption, to options are available:
Reduce the energy consumption through process improvement
Replace fossil fuels by renewable energy
Decreasing the energy consumption can be done by either reusing an energy that is wasted or by
having better energy efficiency. In the first case, the waste energy that can be recovered is the
heat produced by the different processes. I had to look where we produce waste heat, and how we
can recover and promote this waste heat. The second case -energy efficiency- means that newer
and more efficient equipments have to be purchased, that these equipments have to be well
maintained so that they keep running at their best efficiency. The equipments in questions are
especially the pumps, the aerators for the activated sludge process, the UV plant, and the driers.
The engineers have already looked at reducing the aeration but the blowers are too big and are
fixed power. A solution would be to put a variable speed. The UV plant is under review and the
driers have been abandoned because they were too energy consumer. An alternative solution is
currently studied (thermal hydrolysis). Also, an additional CHP is going to be bought to valorise
the maximum of the biogas and have less biogas flared (biogas burned because the capacity of the
CHPs is full or because they are not running). I was not involved in that part.
But I have worked on the second possibility, that is to say using renewable energies. I looked at
the different renewable energies that exist today and saw how they can be applied to Seafield. This
includes solar, wind, hydro, and biomass.
On the waste side, improvements can also be made. The AD process uses the sludge as a resource
by producing biogas turned into electricity. However, the remaining sludge is still to be disposed
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after digestion. The current process produces a non-compliant sludge which cannot be fully
recycled and is sent to landfill. The Thermal Hydrolysis (TH) project should solve that issue. I
mainly focussed on the screenings products. They are currently sent to landfill, which is the most
harmful way of disposal if the biogas emitted by the wastes is not retrieved.
With this project in process, I focussed more on the rags than on the sludge. My work was to look
at other ways of disposal of the rags, how it can be adapted to Seafield and how much it would
cost compared to the current disposal.
Of course, these sustainable and innovative solutions have to be profitable, or at least not cost
money. This project is in line with the sustainable development strategy of Veolia Scotland and a
part of its implementation at AVSE.
2) The three main objectives of this project: environment, economy and communication
What are the benefits of my work for Seafield? What would they gain by reusing energy and
recycling waste?
The first benefit is environmental. The sustainable opportunities that will be chosen should
enable Veolia to reduce its ecological and carbon impact. At the moment, AVSE produces about 24
000t of CO2e because of its activity, of which 18 000t from Seafield. This tonnage takes into
account the electricity and fuels consumed for the sewage and sludge treatment (70% of the total
emissions), the energy for the administration (office heat, transport of people, travel…), the
emissions from the process and from the sludge disposal. The use of renewable energies and the
recovery of waste heat will decrease the GHG emissions, and thus the global footprint. Regarding
the rags‟ project (finding another way of disposal than landfill), the advantages are the same
(decrease in the GHG emissions: even if the biogas emitted in the cells is caught and valorised, the
efficiency is not 100% and a part is released in the atmosphere). Moreover, landfills are a risk for
groundwater (there may be leakage) and it takes a lot of space. Finding a better treatment
(incineration, composting, AD) will participate in decreasing these impacts.
There is also a financial benefit to that project. With the increase in energy prices (electricity,
natural gas, fuel oil), the need for finding cheaper sources is becoming more and more vital.
Renewable electricity should cost less than electricity from the national grid, and the financial
incentives implemented by the government (ROCs, FIT) ensure this is the case. Reusing waste
energy instead of buying new one is of course financially interesting, but the initial investment has
to be taken into account to carry out a relevant economical analysis. Because landfill taxes are
rising, finding another disposal solution for the screenings (and a more environmentally friendly
one) is of interest. However, the business case will make sure that each project is profitable.
Communication and corporate social responsibility will obviously benefit from the project too.
Installing for instance a wind turbine on the site can make a good example for Veolia Water to
17
show its involvement and concern for climate change and environment. The projects would
positively reflect on the company‟s image.
3) Expected results and the continuity of this study
My study aimed at assessing several potential projects (renewable energy, waste heat recovery,
rags):
how it integrates itself in the WWTP and the general context of the contract
which amount of energy has been saved or will be produced thanks to the project
which amount of GHG emissions will be avoided
how much it will costs and what is its profitability based on the analysis of economical
criteria such as the NPV (Net Present Value), the IRR (Internal Rate on Return), the
payback period
This assessment will enable Veolia to choose which project is the most interesting, and then to
implement it.
After I leave, the wok will be picked up by another intern and/or VWOL staff. They will be in
charge of dealing with the company of the chosen technology, manage the project and
communicate on it.
C. The framework of the study: the reasons of this project
1) The desire and obligation to comply with the government and Scottish Water environmental targets
Since Europe has acknowledged the reality of climate change and our impact on the environment,
measures have been taken and targets have been set.
In January 2008 the Commission published the 20-20 by 2020 package. This package announces the
commitment of the EU to reduce its GHG emissions by 20% and to achieve a target of 20% deriving
of the EU’s final energy consumption from renewables sources, both by 2020. In order to achieve the
overall EU renewable energy target of 20% the proposal includes individual targets for each Member
State. The UK’s proposed target is 15% of renewable energies in the final energy consumption.2
At the present time (2008), only 5.5% of the British electricity generated comes from renewables. 3
Scotland objectives are more ambitious: 50% of demand for Scotland's electricity to be met from
renewable resources by 2020, with an interim milestone of 31% by 2011.4
Concerning the GHG emissions, the DECC’s (Department of Energy and Climate Change) target for
2020 includes the goal to cut greenhouse gas emissions by 34% on 1990 levels. Greenhouse gas
emission has been cut by 28% since 1990 according to 2008’s figures. 5
18
The Scottish Government's Climate Change Act, which came into force in June, sets a target of
reducing emissions by 80% by 2050, including emissions from international aviation and shipping. It
also sets a world-leading interim target for a 42% cut in emissions by 2020.6
The UK government also seeks to decrease the amount of waste sent to landfill. It has launched this
summer the “Zero Waste Plan” (ZWP). Scotland’s targets will apply to all waste and are as follow:
70% recycled (currently 40-47%), and maximum 5% sent to landfill, both by 2025.7
So the British and Scottish governments are really focused on green energy with their targets
described above and the incentives in place for developing such sustainable technologies (Feed in
Tariff, Renewable Obligation Certificates).
Scottish Water, Veolia‟s client, is looking at minimizing the impact of its activities too. SW is
taking a number of actions including:
Developing hydro generation to meet a target of 25GWh in the minister‟s objectives
Taking opportunities for cost effective generation
Looking at the potential for wind power across their asset base and working with
partners to pilot some schemes
Amending their standards and specifications to promote more energy efficient pumps and
other kit
Developing tools to allow carbon to be fully appraised in our investment programme
Promoting energy efficiency across the business
Commitment to carbon reporting annually
Developing a carbon plan to promote and deliver more activity
They do not have a specific carbon emissions target at this stage; however they are planning to
outturn 2014 with the same emissions as at 2010 (whereas they are currently increasing emissions
by 10% each regulatory period).8
Veolia is engaged into being on the same line of conduct than the government and SW. The
sustainable and innovative projects at Seafield will help VWOL being in phase with SW and the
governments objectives, as well as his owns. Indeed, within its sustainable strategy, Seafield has
announced the following targets regarding renewable energies: 40% of the energy used should
come from renewables by 2010, 50% by 2011 and 100% by 2020. It is on the right track, since in
2009, 48% of the total electrical consumption comes from biogas converted into electricity.
2) A financial context difficult for AVSE
Veolia has bought the all AVSE contract in 2009. It is now responsible for the good operation of
the different sites. However, it is a difficult contract which is currently financially
underperforming. £1.7 million was lost last year and £800 000 should be lost for 2010 (budget
forecast). There are various reasons for that:
there were a lot of investment at the beginning of the contract and when buying Thames
Water, Veolia also inherited its loans
19
the design of the plant is old (1970‟s): Veolia has to make a lot of improvement because
the plant was not well designed
it is a very tight contract: there are a lot of controls from SEPA (Scottish Environmental
Protection Agency), the compliance standards are high …
the plant is located in the city, not in the countryside: so Veolia should not only satisfy
the client (Scottish Water) but also the stakeholders such as the community (odour issue
for example). Important investments (Odour Improvement Plan) are undertaken as a
response from Veolia.
The company is now trying to decrease the deficit by changing techniques and improving the
performances.
From January 2009 to June 2009, electricity has represented about 20% of the total costs at
Seafield (operational and maintenance). In 2009, the average electrical consumption was 12.8
GWh for £915 000. The monthly consumption is one third higher during the bathing season
(June-September) because the UV plant is running. VWOL can play on these 20% electrical costs
to reduce its deficit.
In a word, each solution that can bring money or reduce the expenditures is worth considering.
My project is one of this.
3) Communication about Veolia corporate responsibility
As for every other big company, showing a good image is very important. Since climate change hit
the public scene, the trend is to advertise your commitment to protecting the environment. In
essence, Veolia already acts in favour of the environment (water treatment, waste management
…), but they have to go further than relying on the nature of their activities to compete on
sustainable development.
At VWOL, internal and external communication is done about sustainable development. Internal
communication is done through workshops on sustainable development, to explain to the
employees what it is, and how each one can act in a more environmentally friendly way.
Delivering information and awareness about sustainable development is done too via the
organisation of the sustainable month, planned for October 2010. Quiz, e-mail, flyers … will be
organised to raise awareness across the staff. Furthermore, there is a sustainable team that meets
every month to discuss potential environmental improvements within Veolia Scotland. In order to
minimise Veolia environmental impact, this working group focuses its efforts on three main issues:
counting emissions and measuring environmental impact
reducing this impact
communicating on the benefits and the performance both internally and externally..
Counting is achieved through developing indicators and carrying out carbon footprints. Reducing
includes my project (renewable energies, waste heat recovery) and other actions like encouraging
employees to reuse drafts or to print both sides to decrease paper consumption, assessing suppliers
and contractors regarding their environmental performance, convince people to take the train
20
instead of the plane when they have to go to London …Communicating is made through setting a
strategy, writing newsletters and organising events as previously described.
The sustainable team is at the interface between internal and external communication . VWOL
sustainable strategy which is currently being written is aimed at the public as well as the staff
and the clients. This strategy is then implemented at the scale of the different business unit
(AVSE, Nevis, Engineering Services …). The sustainable and innovative solutions for Seafield
WWTP are an example of the implementation of the strategy in AVSE.
AVSE monitors its carbon footprint too by calculating the amount of tonnes of CO2 equivalent
emitted each year because of its activity. Systematic carbon footprinting started in Autumn 2009.
Furthermore, AVSE and Veolia Water Central have been selected by Jean-Michel Herrewyn,
Chief Executive of Veolia Water in Paris, to take part in a pilot programme to measure carbon
foot-printing. Previously, as the head of Veolia Water Solutions and Technologies (VWS), Jean-
Michel Herrewyn initiated a global programme of carbon management with the aim of calculating
the carbon footprint of services provided by VWS, so that the information could be used for
marketing and to create a commercial advantage. Now CEO of Veolia Water, Jean-Michel wanted
to launch a similar programme for operational activities. The pilot phase aims to determine
whether it‟s feasible and commercially useful to calculate the carbon footprint of different
operational activities. Carbone4 – a recognised carbon strategy consulting company – is assisting
with the programme and has already submitted its initial findings to AVSE and VWC. These are
now being reviewed.
The project I worked on will enable VWOL to show what it does for sustainable development,
and the impact of it (we have reduce our GHG emissions by x tonnes).
II. The methodology adopted to carry out the study
A. From a broad range of possibilities to the selection of only four solutions
1) The first step: a broad research on all the existing sustainable solutions to produce “green” energy
To begin with, I made a list of all the solutions that exist to decrease the impact on the
environment in terms of energy and waste. I used my previous experiences (internship in a wind
development company, internship about the renewable energies available in a region), my
knowledge, internet and persons from Veolia, Scottish Enterprise and Carbon Trust, two not-for-
profit companies that provide specialist support to help business and the public sector cut carbon
21
emissions, save energy and commercialise low carbon technologies. The next step was to gather
information on these solutions.
2) Information needed for each solutions of the broad list
Then, I found out more information for each solution, but without going into too precise details,
since the goal here was not to make a business case but to prepare the selection of the 3-4
projects that will be analysed further afterwards. The information I looked at for each solution
were:
How does it work?
What type of resource does it need? (sun, tide, wind, biomass)
What type of energy is produced? (electricity, heat, both – cogeneration)
How far is the technique develop, is it a new one, a proved and effective one or a new one
still in development?
How much does it cost on average? (especially if it is expensive)
What are the references for this technology?
Which person/companies work in that field?
3) Selection of the four most interesting technologies suitable for Seafield
Thanks to the information gathered on each technique, I was able to compare them and see which
ones would be the most interesting and suitable for Seafield. The criteria used to select the
solutions are the following:
State of development of the technology
Resources available at Seafield compared to the resources needed by the technique
Type of energy produced
Cost
As a result, all the technologies that are still under development, that need to be improved, that
are not reliable enough, that are too expensive (either because they are quite new or too expensive
given their efficiency), that does not produce the type of energy we require (mostly electricity, low
grade heat is not needed) were rejected.
Four solutions were kept: wind power, hydro power, waste heat recovery, co-incineration of the
rags.
22
B. Business case for each selected solutions and final selection of only one project
1) Technical analysis: resource available and expected production
The first part of the technical-economical analyse was to quantify with precision the available
resource at Seafield. For wind power, it means knowing the wind speed, for hydro power,
knowing the head and the flow rate, for waste heat recovery, it is necessary to have the
temperatures and the flow rate of the hot source (in our case it is hot water). For the rags, we need
to know the quantity and the biological characteristics (water content, composition …) of them.
Then, I had to decide, with the advice of the companies working in that field, where the best
location would be for each technology: where the resource is the maximum and where it would
not bother the activities of the WWTP. For wind power, it is better to install the turbines far
from high buildings (obstacles for the wind) and on top of hills because the wind is accelerated
there. But we have to take into consideration too the numerous technical and legislative
constraints that apply to wind turbines: proximity to residential areas, proximity to roads, rail and
airport, visual impact, presence of protected natural sites …
Regarding hydro turbines, the choice of the best location depends on where the head is the higher,
with a flow free of rags and in a place where the turbine will not disturb the process.
Concerning the waste heat recovery project, the identification of the heat sources gives at the
same time the location where the equipment to recover this heat will be put.
The next step was to choose the type of material, especially the size and power of it. This has
been done by the specific companies for the hydro turbines and the waste heat recovery. However,
for the wind turbines, the choice depends on the amount of energy we want to produce and the
size of turbine that will probably be allowed by the Edinburgh Council. As we need a lot of
electricity, we would have preferred a large turbine (1.5-2MW), but since the plant is located in an
urban area, a large turbine project would have probably been rejected by the council. So smaller
turbines have been chosen.
2) The choice of the company that will provide a quote and with which we will work later if the project is kept
Selecting the right companies for each solution is important for the quality of the work, the
reliability of the company, the price they offer. Whenever it was possible, three companies per
technology have been chosen, so that we can compare the costs afterwards. A Google search gives
a lot of companies in each sector, but we have to select them according to some criteria. The
criteria for the selection are:
If possible, chose a British company. It is better for sustainable development: we give
work to national companies, and we avoid having to import the material (even if it is not
23
always true since some equipment are manufactured abroad and imported by the
company itself) and make people travel a lot (which cost money to VWOL too).
Whenever it is possible, prefer companies that are located near Edinburgh: the reason is
environmental (less transport) and practical (if the distance is too important, it is likely
that the company will refuse to come on the site just to have a look without being paid).
Chose installers and suppliers that are MCS certified (Microgeneration Certification
Scheme). 9 Indeed, to apply for the Feed In Tariffs (FIT) (a financial help of the
government to encourage the development of renewable energies – for each kWh
generated with renewables, you receive money) installations less than 50 kW must be
installed by a an MCS accredited installer. In a first stance I did not know what the
power of the equipment will be, which is why I restricted the choice to MSC companies
when it applies.
Select approved companies that are recommended or have good references: either
because they are already used by other Veolia subsidiaries, or they have done with success
such work (especially for hydro power: it is not very common to install one in a WWTP
compared to run-of-river scheme) or they are part of a renown association (British Wind
Energy Association-BWEA, British Hydropower Association-BHA, Carbon Trust)
I then contacted the selected companies and ask them for advice and a quote. Some of them agreed
to do it for free (desktop study, meeting on the site), others wanted to do a site survey or a pre-
feasibility study before giving a quote. The quotes were never complete (civil works and some
electrical equipments like high voltage cables, grid connection, transformers were not taken into
account) so I had to go to the engineers at Seafield or to civil contractors to get the missing costs.
3) Comparison between the companies of a same sector and between the solutions thanks to economical criteria
Thanks to the figures given by the companies, I was first able to make a comparison between the 2
or 3 companies of a same technology in order to keep only the most interesting one. The
comparison was based on the economical results: NPV (Net Present Value), IRR (Internal Rate on
Return) and payback period.
The NPV will say if the profits will be higher than the initial investment. NPV compares the value
of a pound today to the value of that same pound in the future, taking inflation and returns into
account. A project is acceptable if the NPV is positive. However, if NPV is negative, the project is
rejected because cash flows will also be negative. The higher the NPV, the better is the project.
The IRR is the interest rate of a loan equivalent to the investment; it is the discount rate that will
give it a NPV of zero. You can think of IRR as the rate of growth a project is expected to
generate. Generally speaking, the higher a project's internal rate of return, the more desirable it is
to undertake the project.
The payback period is the time taken to recover the initial investment. Investments with a
shorter payback period are preferred to those with a long period.
24
I resorted to the model used by Veolia to do a business plan. A business plan is a document which
presents the projected flow of receipts and expenses for a project, year after year, to see if this
project creates value. The method used is based on the Expected Discount Cash Flow (EDCF).
The goal is to calculate the Free Cash Flow (FCF) and then to measure the IRR and the NPV on
these FCF. The figure 6 sums up the different parameters to calculate in order to get the FCF and
then the other economical criteria.
Figure 6: Method of the Expected Discount Cash Flow to judge the profitability of a project
Nonetheless, this analysis is not enough. Indeed, there are uncertainties within the project:
uncertainties on the initial investment, the annual revenues ….Thus, an analysis of the
sensibilities has to be done. The risks must be identified, a mean to minimize or remove them has
to be found, and the residual risks must be explained. For practical purposes, we recalculate the
IRR, NPV and payback period for a best case, a base case and a worst case, to have an idea of the
importance of the risks.
For example, regarding the projects I worked on, the main risks were on the initial investment (it
could be more expensive than the costs given in the quote) and the energy output (the electrical
production may be overestimated). As a result, the analysis of the base/best/worst cases enables
me to see which impact these uncertainties will have on the profitability, and so on which
parameters more studies must be done.
This economical analyse enables me to chose the most interesting companies for each technology
and then to compare the technologies and select the most profitable one that wil l later be
implemented. The steps of the methodology are described in figure 7.
Figure 7: simplified diagram of the method used to fulfil the study
Supplier credits
-- Customer credit
-- Inventories
WC
Discount factor
Χ FCF
Discount FCF
Total revenues
+ Total costs (OPEX)
EBITDA
+ ∆WC year
CFFO
-- CAPEX
-- Taxes
FCF
IRR
If IRR> WACC +
4.8% = 15%, project
is accepted
NPV
Calculated at the rate of the WACC
(not at the rate of inflation)
If NPV > 0, project is accepted
Discount payback
period If payback < 5 years,
project is accepted
25
IRR NPV
Payback period
Civil works‟
companies
Seafield
engineers
Knowledge
Previous experiences
Internet
Carbon Trust,
Scottish
Enterprise
Veolia staff
British company
MCS certified
References, renowned
Cost
State of development
Resource available
Type of energy produced
Reliability, efficiency
26
C. Limits of the study
1) Reliability of the company chosen
Choosing the right companies is important for the quality of the project (reliable equipment,
quality of the work provided).
The criteria presented before to select the best companies are very useful but in some cases they
could not be applied. This is the case for the waste heat recovery project. As the technologies in
that field are not supported by the government scheme for renewable energies, there is no list of
accredited suppliers. The specific type of job asking by the waste heat recovery project is not what
most of the firm in the heating field do. Here we do not ask them to install a boiler, but to create a
full heating network using another heat source.
As there are no clear references for firms in the heating sector (no association, no MCS list), I just
chose firms at random (the first to appear on the internet search), trying to focalise on firms that
manufacture or sell heat exchangers and heat recovery equipment. Most of them answered that
they do not do the work we require, but they recommended companies that will do such work and
who they already work with. This is how companies for waste heat recovery were chosen. We can
not guaranty the seriousness of these selected companies, although they can not be seen as
amateurs.
2) The needs of complementary studies
Further studies may be required after one of the solutions has been chosen. Indeed, this study
should be considered as a pre-feasibility study. The companies contacted to help me on the
different solutions provided only general and rough information and quote, because they were not
paid to do something more precise. They only based their quote on a site survey or a pre-
feasibility study or even just rely on the information I provided them with. As a result, the energy
output is often an average and there are a lot of uncertainties, especially for the wind turbines.
The same comment can be made for the quotes, all the more so as the prices will change a little by
the time the project will be implemented. Furthermore, the quotes were never complete; there
were always a part that was not taken into account (electrical equipment, grid connection, civil
works). The additional costs needed to do a full economical analyse were provided by the
engineers of Seafield given on their experience or by other companies, but again the costs are only
an estimation.
In order to minimize these uncertainties, an analysis of the risks was done and the calculation of
the NPV, the IRR, and the payback period was done for 3 cases: base case, worst case, best case.
To be sure of the profitability and technical feasibility of the chosen solution, as well as the
possible technical problems, specialists will have to do a detailed feasibility study.
27
3) Gathering reliable information: relationship with the companies
The challenges I faced at that stage of the project were:
Gathering information regarding the plant
Obtaining quotes from the companies
The operation of Seafield WWTP has changed many times of operator over the life span of the
contract (East of Scotland Water, Thames Water, and Veolia Water). As a result, a lot of
information has been lost. For instance, it was often difficult to find the appropriate drawings I
needed (the digitalisation of the drawings is not complete, some are missing). What is more, some
studies had already been done or people went on the site to look at the hydraulic potential a few
years ago, but I was not aware of that and discovered it later, which was a bit frustrating.
Another problem I have encountered is that companies were not always keen to provide a quote
without doing first an expensive feasibility study. Some of them were even not interested in
working with us. The ones that have been kept were not very reactive and took a very long time
before sending the quote, even with constant relaunch. This study could have been done much
more quickly if the companies had answered faster. While waiting for their answer, I was given
others small jobs which will not be described in this report. I especially worked on environmental
indicators for Seafield WWTP (energy consumed per litre of treated sewage, percentage of
renewable energy produced, the CO2e of biogas flared, destination of the sludge, amount of paper
used in offices…), on a quiz about sustainable development, on the analysis of the consultants‟
carbon footprint calculations and on a biodiversity project at East Calder WWTP (how we can
enhance the biodiversity there, how much it would cost).
III. The results of the study: an Archimedean Screw as the best technical and economical solution to decrease Seafield’s carbon footprint
A. The four most interesting solutions and characterization of the resources available
1) Many solutions, only a few opportunities
The first stage of the work was to identify all the solutions that exist to produce renewable
energy, to convert waste heat and wastes into a new source of energy.
28
Regarding renewable energies, the technologies are:
Wind power: UK is the windiest country in Europe. Seafield‟s location, near the shore, makes this
technology even more interesting, because the wind speed is more important near the coast. The
large choice of turbine‟s size, from micro (5 kW) to large scale (3MW) makes wind turbines a
flexible and adaptable solution.
Hydro power: micro hydro is less developed than large hydro power station. However, whenever
there is a water drop with enough flow, it can be envisaged. The hydraulic profile of treatment
plants sometimes offers the opportunity of putting a turbine.
Thermal solar power: these types of solar panels are used to produce hot water and heating. But
because of the poor solar resources in Scotland and the more important need of electrical energy
on the site, solar thermal does not seem to be the best solution.
Photovoltaic solar power: unlike solar thermal panels, PV panels produce electricity. However
the poor solar resource in Scotland and the costly price of panels do not make this technology a
suitable solution at the present time
Tidal/wave energy: The UK has the best wave and tidal resource in Europe. Nonetheless, not
every place is suitable and the Firth of Forth does not seem to provide the good conditions for this
marine renewable energy. Moreover the devices have to face a number of challenges before they
can meet their potential and reach large-scale commercialisation.
Geothermal: geothermal uses the heat stored in the earth, at the surface or very deeply, to
produce heat or electricity. Not every place has the potential for geothermal energy, and Seafield
is not suitable for geothermal electricity. Only geothermal heat could be considered
The technologies that convert wastes and wasted energy into suitable output are:
Fuel cells: fuel cells are an interesting technology to produce electricity and heat from hydrogen.
They are more efficient and less pollutant than classical power generator. However, their price
and early stage of advancement at the present time involves that it may be a good solution for
Seafield but only in a more or less near future, depending on its development.
Heat exchanger to extract the heat from the wastewater: special patented heat exchangers are
installed in sewage pipes for space heating and hot water production. This could be a solution at
Seafield, all the more so as the channels will be covered thanks to the Odour Improvement Plan
(the sewage temperature might be a little higher). However, we have to see if it really can be
interesting or if it would not be better to promote the waste heat at first.
Heat exchanger to extract the heat from the CHP and the thermal hydrolysis (TH) process :
cooling down the CHP engine is done by adding cold water which runs through the engine and
comes out at a higher temperature. This low grade heat can be used for space heating or by being
converted into electricity.
One technique to reduce the energy consumption of the treatment process is the use of specific
enzymes. These products are manufactured in order to help the quick degradation of pollutants in
29
wastewater. They are said by their producers to decrease the amount of sludge, accelerate the
treatment, enable odour control, save money and energy. However, this technique does not seem
really compatible with the production of biogas and its effectiveness can be questioned.
Concerning the energetic valorisation of the rags, the solutions are:
Pyrolysis/gasification: these technologies position themselves as an alternative to classic
combustion to get rid off municipal, commercial and industrial waste, and by recovering the
energy. They claim to be more efficient and environmentally friendly (less emissions). However,
the lack of feedback and impartial analyse of the processes make them still riskier for the moment
than classic solutions.
Incineration: burning the waste with energy recovery is an alternative to landfill. But standards
are very strict on incinerators and the amount of rags produce here is not important enough to
have our own plant.
Co-incineration: the working is the same as for incineration but here the waste comes from
different sources (municipal, industrial ...). The rags can be sent to an existing facility instead than
to landfill.
Wet Air Oxydation: hydrothermal oxidation is used to oxidize liquid waste such as sewage or
sludge. It has many advantages such as reducing the amount of sludge, treating very loaded
effluents with a very good yield, producing energy that can be recovered… It is an interesting
solution when other type of sludge‟s promotion (agriculture, incineration …) is not possible
Giving the selection criteria detailed in part II-A-3), only wind power, hydro power, waste heat
recovery from CHP & TH and co-incineration of the rags have proved to be the most suitable.
Table 1 summarises the drawbacks of each technologies and if it is worth considering it now, later
or never.
You can find for each technology that was not selected a sheet explaining its working, its
advantages and disadvantages in appendix 2.
30
Table 1: summary of the different sustainable and innovative solutions for Seafield
Project: To be
considered now To be considered
in the future To be
abandoned
In d
evel
opm
ent
Too e
xp
ensi
ve
Not
enoug
h
reso
urc
es
Not
tech
nic
ally
fe
asib
le
Ty
pe
of
ener
gy
pro
duce
d n
ot
inte
rest
ing
(h
eat)
Reasons:
Technologies:
Solar electricity (PV)
Solar thermal
Tidal-wave energy
Geothermal
Hydro-electricity
Wind turbine
Fuel cells
Heat exchanger (sewage)
Waste heat recovery (TH and
CHP)
Enzymes
Gasification/ pyrolysis
Incineration
Co-incineration
Wet Air Oxidation (WAO)
2) Localization of the highest resource and the best place for the installation of the engines
Now that the four best solutions have been identified, we need to know exactly which amount of
energy they may produce. To do that, we first need to identify and locate the resource and then
quantify and qualify it.
31
Wind energy
Wind speed and wind directions are the major elements to characterise the wind resource. The
best locations to install a wind turbine are where the wind speed is the highest and where there
will be no turbulences. The top of smooth hills is an ideal location, as shown on figure 9.
We also need to avoid high buildings that would be an obstacle for the wind and create
turbulences that might damage the turbine. As a result, I tried to find elevated areas far or without
any obstacles for the main wind direction. The main direction is given by wind roses like figure 8.
The main wind at Seafield blows from the SW, that is to say roughly form the earth to the sea. A
second dominant direction is NE: here the wind blows from the sea to the earth. These main
directions of the wind in the proximity of the sea are classic: it reflects the earth breeze during the
night (SW) and the sea breeze during the day (NE) because of the inertia of the water.
With this piece of information and the advice of wind companies regarding the facility of access,
six locations have been identified where wind turbines could be installed.
There are shown on the map below.
Figure 9: best places to install a wind turbine
Source: http://www.chrisrudge.co.uk/images/siting1.jpg
Source: http://citydev-
portal.edinburgh.gov.uk/portal/getEdmDoc?docid=55768910&e
xt=pdf&page=8
Figure 8: annual wind rose for Edinburgh harbour (10m
above ground)
32
f
Strom tank
Primary
settlement
tank
Transformers: connection to national
grid. Inside the building: distribution
substation
Digesters
Detritors
Activated
sludge tank
Final
settlement
tank
a
d
1
b
Sludge
building
a: location of turbines
Total number of turbines we could potentially installed on the site: 6
Main wind
Anemometer
c
1
Main electricity supply: a single cable
goes to the transformers and it is
distributed on the site from there
e
f
33
Hydro power
The electrical output of a hydro turbine depends on the head, the flow rate and the efficiency of
the turbine. Indeed, Pe (in W)= ρ.H.Q.g.k
where Pe is the electrical power in Watts
ρ is the density of water (~1000 kg/m3)
H is head in meters
Q is flow rate in m3/s
g is acceleration due to gravity of 9.8 m/s2
k the yield of the turbine
The head refers to the height that the water falls through the hydro installation. The flow rate is the
amount of water that will go through the turbine. The higher, the better the production will be.
The resource to measure is therefore the head and the flow rate. I identified on the WWTP
locations with a water drop and enough place to put a turbine (figure 10).
For these four potential locations, the water that go through the channels is cleaned, has been
treated and will be discharged via the outfall and a 2 km long channel into the sea. It was
important to choose locations where the water is cleaned in order not to damage the turbine (rags,
corrosion ...). Some measures could have been taken to use wastewater (like a screen to prevent
rags from entering the turbine), but it would have increased the initial investment.
The highest head is at the outfall: this location is therefore the best one for a hydro turbine.
Diagrams and photos can be seen in appendix 3.
34
A) Just after the UV plant B) Small drop in the channel C) Connection of the 2 streams D) Outfall shaft
Waste heat
Two sources of waste heat have been identified: from the CHP and from the TH.
Currently, the hot water that cools down the CHPs is used to keep to digesters at a constant temperature of 35˚C, to enable mesophilic digestion. A
simplified diagram of this circuit can be found in appendix 4.
But with the implementation of the thermal hydrolysis project, the digesters will not need to be heated anymore. Indeed, TH is a thermal treatment
of the sludge before AD. It pasteurized the sludge at a temperature of 170˚C. The pasteurized sludge is then digested, but it needs to be cooled down
before entering the digesters. The temperature is decreased to 42˚C, so that the digesters do not need to be heated anymore (with an entering sludge
at 42˚C and heat losses, the sludge staying in the digesters during 12 days should be at about 35˚C). So the current heat used for the digesters will be
available in the future (normally in summer 2012 when the TH will be implemented). Moreover, the hot water resulting from the cooling down of
the sludge leaving the TH reactors is another available heat source.
A B
D C
Clean flow
Storm flow
Figure 10: localization of the main water drops
35
3) Characterization of the resource available
Wind energy
Now that we know where wind turbines could be installed, we can find out about wind speed. The
wind speed is very important for the production of the turbine. Indeed, the energy produced is
equal to the cubic power of the speed (E=a.v3). That is to say that if the wind speed doubles, the
energy produced will be multiplied by 8! It is important to notice too that the wind speed changes
from one year to another, by 10% on average. The limit of commercial viability is said to be 5 m/s
at hub height.
3 sources of data are available:
National Wind Speed Database for the all country (NOABL)
Carbon Trust tool based on NCIC database
Veolia database (measurements on site thanks to the Odour Improvement Plan)
The Carbon Trust Wind Yield Estimation tool is the most rigorous of its kind. Other currently
available tools do not incorporate land use information, which is vital to accurately model wind
behaviour, particularly for urban areas. The tool has also been created using 30 years of data from
the Met Office‟s 220 weather stations. This data from NCIC is preferable to NOABL which rely
on observations for 56 stations during 10 years. The longer time period implies that the NCIC
data are more representative of long-term conditions, and the higher number of stations means
the data are also less reliant on interpolation, as Carbon Trust concludes in its report Small-scale
wind energy-Policy insights and practical guidance.
Both NOABL and NCIC provide fairly good estimates in general. The weakness of NOABL and
NCIC data is that, while orography is taken into account, local variations in roughness and
ground features are not. This means that both models give a very limited representation of local
topography and except for open, exposed rural sites surrounded by grassland, the data are
unlikely to be representative. Various adjustments are needed, particularly for built-up urban
areas.10
The on-site measurements should give more accurate results.
We can then deduct the wind speed at hub height thanks to this formula:
V1/V2= (H1/H2)a
with V1: wind speed at the altitude 1 in m/s
H1: altitude 1 in m
a: roughness length in m
For Seafield, we use a=0.15 as it is almost a flat area (only a few high buildings) and it was advised
by one of the wind company contacted. The results are presented in table 2.
36
Table 2: wind speed (m/s) at hub height for the 6 identified locations, depending on the database
used
Location a b c and d e and f
Elevation in m 5.5 11.5 12.5 1
Hub height (25m tower) 30.5 36.5 37.5 26
NOABL 6.6 6.6 6.6 6.4
Carbon Trust Tool 7.2 7.6 7.7 6.8
On-site measurement 4.9 5.0 5.0 4.8
Carbon Trust (CT) gives slighter higher results than NOABL (+6 to +14%), whereas on-site
measurements are respectively 30% and 50% lower than NOABL and Carbon Trust. As a result,
the expected production with Carbon Trust will be 3 times higher than with on-site measures
(because E=v3)
This can be explained because NOABL and Carbon Trust do not take into account roughness:
local obstacles for the wind will decrease these results. Regarding on-site measures, there is a
building that could create turbulences for the 2sd main wind direction, so the figures could be a
little higher than that. The other explanation is that the coefficient “a” used was not the good one:
with a=0.‟ 5small towns, rough and uneven terrain), the results are closed to NAOBL and CT
(respectively 11 and 1% of difference).
Hydro power
To define the outfall shaft as the best place for a hydro turbine, I had to measure the head with a
simple tape measure and gather the data about the flow rate.
Only the outfall is interesting, because for the others falls, the head is lower than 1m. The head in
the outfall changes between dry and wet weather and because of the tide too, since it is linked with
the sea through the long sea channel. The head during dry weather varies from a factor of 3
between low tide and high tide (max: 3.2m, min: 1.0m, average: 2.1m). The following chart
illustrates its variation.
Source: Spaans Babcock study
Figure 11: variation of the head at the outfall shaft due to the tide
37
During a storm, the head will decrease because the clean flow coming through this channel will be
at his maximum (5.88 m3/s) but there will be a storm flow too coming through the opposite
channel, when the storm tanks are full. (see darts on figure 10)
The variation of the head between storm and dry weather has not been measured but can be
estimated: as the storm flow represents 5% of the total flow, we can assume that the head and thus
the production would be decreased by 5%.
The flow rate is on average 3.5 m3/s, with a maximal capacity of 5.88 m3/s. However, it varies
during the day, according to the use of water by the inhabitants. (see the charts in appendix 5)
As a result, the electrical output of the turbine will vary during the day, in phase with the flow
rate and head variations.
Waste heat
Waste heat comes from CHP and TH. The energy that can be recovered is calculated with this
formula:
Q = V. ρ.Cp.∆T
With Q: heat content in kCal
V: flow rate in m3/h
ρ: density of the hot liquid or gas in kg/ m3
Cp: specific heat of the substance in kCal/kg.˚C
∆T: difference of temperature in ˚C
The hot substance in our case is water: we will take on average ρ =1 kg/ m3 et Cp=1 kg/ m3. So
ρ.Cp=1 kCal/m3.˚C. To have the heat content in kW, just multiply by
4.18*0.0002778*1000=11.622 because 1 Cal= 4.2 Joules and 1 J= 0.0002778 W
So the simplified formula is
Q=V. ∆T. 11,622
with Q in kW, V in m3/h and ∆T in ˚C.
Thanks to technical manuals, Seafield engineers and a report done by the firm Rowan House CHP
Engine Waste Heat Study for Veolia, I was able to quantify the heat from the 2 CHPs that can be
reused. For example for CHP 1, 45.5 m3/h of water at 75.5˚C is available, as shown in figure 12.
The hot exhaust gases will help producing steam, and thus are not available for this project. (its
energy is currently only used to achieved the desire temperature of the water, the excess energy is
wasted via the stacks)
38
Concerning the heat from the TH process, the diagram below presents the quantity of hot water
recoverable for another use.
The sludge leaving the buffer tank en route to the digester is cooled down. It is cooled down in
two stages. The first stage reduces the temperature from 110˚C to ~54˚C. The second stage
reduces the temperature from ~54˚C to ~42˚C or to whatever temperature is required,
Intercooler
1st stage
Lube oil Exhaust gas Engine
(jacket)
70˚C Max 80˚C Max 95˚C 445˚C 150˚C
64.8˚
C
60˚C 75.5˚
C
68.8˚
C
90˚C
Flow rate: 45.5 m3/h
256 kW 356 kW 768 kW 208 kW
Cold
sludge
30˚C
Hot
sludge
54˚C
Hot sludge
110-105˚C
Digesters
41˚C
TH
reactors
170˚C
22%DS
13.7%DS
13.7%DS 16%DS 13.7%DS 10%DS
Cold water
10˚C, 10 m3/h Hot water
85˚C, 5.9 m3/h
Hot water
85˚C, 4.1 m3/h
Recoverable thermal
output: 514 kW
Heating and dilution
with hot water
Cooling and dilution
with cold water
Cold water
10˚C, 6.5 m3/h
Figure 12: the four steps to cool down CHP and the potential power available (in blue)
Figure 13: the cooling down of the sludge after TH reactors and the waste hot water available
39
considering heat loss from the digester, to keep the temperature within the digester at 35˚C (the
54˚C is generally +/- ~1˚C)
The first stage from above, ie reducing the temperature from ~110˚C to ~54˚C is undertaken by
using a heat exchanger. The heated water doing the cooling is then used to pre-heat the sludge
entering the TH reactors (10˚C at 22% DS to ~32˚C at ~16% DS). The second stage, reducing the
temperature from ~54˚C to ~42˚C is undertaken with the addition of water. This also reduces the
solids concentration of the sludge before it enters the digester. It leaves the TH reactor at ~13.7%
DS and enters the digester at ~10% DS.
To sum up, the quantity of waste heat that could be recovered is as follow:
Table 3: waste heat available from the CHP and TH cooling system
CHP 1 CHP 2 TH
Water flow rate m3/h 45.5 44 5.9
Inlet temperature ˚C 60 68 10
Outlet temperature ˚C (at full load) 75.5 80 85
Power kW (at full load) 820 600 517
Average load 55% 67%
Outlet temperature ˚C (at current
load) 68.7 ?
Power kW (at current load) 459 ?
Percentage of operation/year 66% 77%
With the purchase of a 3rd CHP, it is said that CHP 1 and 2 should run at full load.
The waste heat can be used either to heat the nearest office or to produce electricity.
Rags
The information needed for this project is the amount of screenings produced each year by
AVSE and the characteristics of them. Table 4 gives the amount of screenings produced by the
different WWTP in AVSE in 2009
Table 4: amount of screenings products for AVSE plants
WWTP Seafield Newbridge East Calder Blackburn Whitburn
Quantity of rags in t 2500 58 300 58 58
Current destination
of the rags
landfill landfill landfill landfill landfill
At Seafield, an important part of the flow is by-passed and does not go through the screens
because they are blocked. Works are under way to improve the situation. Thanks to these
40
improvements, we will produce 10 to 15% more, that is to say between 2 750 and 2 875 t. The
screenings are washed and compacted (MegaWasher).
The composition of the rags is not known. However, a thesis done in France in 2009 by Ronan
Le Hyaric studied the composition of the rags and the different way of promotion.11
% of dry solid (DS) (in % of the humid solid) : 15% when no compacted, 30% when compacted
% volatile matter (VM) which can be seen as the organic matter content: 77 to 86 % (in % of
DS)
Biodegradable organic matter: 37 to 50% of the total DS content
Composition:
o 68 +/- 13% of sanitary textiles (tampon, sanitary towel, baby wipe …)
o 16 +/- 6% of filler (particles of less than 20mm: a mix of sand, glass, ash, vegetal
waste …)
o 6 +/- 5% of paper (newspaper, cardboard, packaging …)
o Vegetal waste, plastics … for less than 10% of the total weight
These characteristics are only a mean, and it would be useful to analyse the one produced at our
WWTP in laboratory. In Seafield, operators estimate that screenings are mainly composed of
papers, sanitary textiles and small plastic pieces.
B. The benefits of each solution in terms of costs savings and GHG emissions avoided
1) The companies selected and the equipment advised for each solution
The selection of the companies is based on criteria already described in part II-B-2).
Wind energy
At the beginning, companies for small wind turbines and large turbines had been chosen.
However, it quickly appears that large turbines will not be allowed on the site. Indeed, the
numerous constraints that come with wind turbines (proximity to residential areas, to airport, to
roads, noise, presence of natural protected areas, of Ministry of Defence sites, impact on landscape
and radars) will prevent us from having the planning permission for big turbine. So we focus on
smaller machines. Nonetheless, as the electrical consumption is huge, micro-scale would not be
interested. I try to find companies that supply turbines in the range of 15-100 kW.
Finally, the retained companies are:
Aeolus Power
Proven Energy Ltd
Segen Ltd
41
At the beginning, we were also thinking about small systems mounted on the roof of buildings.
However, the companies selected do not offer such type of turbine and furthermore, they advice
again turbine on the roof, because according to them, such systems are currently not reliable and
efficient enough.
Generally speaking, turbines producing the most power without being too big and high (not
higher than the light tower, that is to say ≈45m) have been chosen. The general manager did not
want to transform Seafield into a wind farm, and what is more, we will not get planning
permission for turbine mounted on too high tower. The turbines selected are:
Proven 35: a 15kW turbine from the firm Proven Energy Ltd
Endurance Wind Power E-3120: a 50kW turbine form the firm Aeolus Power
Wes 18: a 80kW turbine form the firm Segen Ltd
Hydro power
It appears that classic technologies for low head (<6m) such as Kaplan turbines, propeller
turbines or Banki turbines may be suitable for the poor hydraulic resource at Seafield, as the
report Low Head Hydro Power in the South-East of England explains, but these turbines are quite
expensive. To confirm that, we will see with one of the 2 companies present in the MCS and BHA
lists (RD Energy Solutions Ltd). I have also added Spaans Babcock Ltd, leader in the
Archimedean screw technology. This technique is well adapted to very low head and the firm is
part of the British Hydro Association suppliers‟ list. An explanation of the Archimedean Screw is
available appendix 6.
Spaans and RD Energy told us which turbine and which power should be installed:
A 110 kW Archimedean screw
A 100 kW vertical axis Kaplan or Vortex turbine
Waste heat
As explained in part II-C-1), it was not easy to find companies for this work. The selected firms
for reusing the heat to heat the Stirling office are Arthur McKay Building Services, recommended
by Daikin, and BMM Heaters Ltd recommended by Ambaheat.
For converting the low grade heat into electricity, the internet research gives Ener-G Rotor,
ElectraTherm, Turboden and DRD Consultants.
However, Ener-G Rotor answered that they “do not yet have a commercialized version of our waste
heat to electricity device”. DRD Consultant and Turboden devices‟ size are too big for our amount of
resource. Finally, only ElectraTherm has been kept. The working of his waste heat generator is
based on the Organic Rankine Cycle (ORC). A heat source (hot water) heats a special fluid which
boiling point is lower than that of water. This fluid then becomes vapour and turns an expander,
which drives a generator and puts out electricity.
All the sizing of the equipment will be done by these specialists.
42
Source: http://www.electratherm.com/waste-heat-generator.html
Rags
When the co-incineration solution was chosen, I looked for incinerators in the neighbourhoods.
Thanks to this website http://ukwin.org.uk/map/ which lists the existing and in project
incinerators, we know that the nearest incinerator under project is the one at Dunbar, at about
50km. This is a Viridor‟s project. Viridor is a waste management company which already operates
the landfill site at Dunbar. The firm is looking at building an Energy from Waste (EfW) plant
just near the cement works and the landfill site. Viridor started looking at this solution three years
ago. At the present time, the project is through the appeal stage and they hope to get an answer
from the Scottish Government within 3 months. They are quite confident because they think that
the project will be accepted.
The future plant will treat 300 000t/year of waste to serve the needs of Edinburgh, East and Mid
Lothian. It will produce heat, which will be recovered and used to generate up to 25.6 MW of
electricity. Of the electricity produced approximately 22.7 MW will be available for export to the
local electricity network, with the remainder used by the facility.
2) Production of “green” electricity and minimisation of the carbon footprint
Thanks to wind/hydro turbines and waste heat recovery, we will avoid CO2 emissions by not
importing electricity from the grid. Only the gross CO2e emissions avoided is calculated (the
carbon cost for the construction of the equipment is not taken into account because it is not
available from the manufacturers). The data used to calculate it is 0.54418 kg CO2e/kWh. 12
Figure 14: diagram of the Organic Rankine Cycle of ElectraTherm device
43
Wind energy
Now that the type of turbine has been selected and that we have an idea of the wind speed, we can
calculate the electrical output. This is done using the power curve of the turbine (Carbon Trust
Tool – kW in function of wind speed) or the production curve (kWh in function of wind speed).
Examples of power and production curves are available in appendix 7.
Three results are presented: Carbon Trust tool, NOABL + production curve, on-site measurement
+ production curve. Normally the figure for annual mean energy generation will have to be
reduced slightly to account for electrical systems losses and unplanned downtime and
maintenance. Because of the error and discrepancy between the results due to different wind speed
data, the results have not been decreased to take into account any losses. For Proven, we could not
find precise power curve so we use the Proven calculator.
http://www.provenenergy.co.uk/why_production.php
Table 5 shows the potential amount of electricity produced by each type of turbine and the
corresponding GHG emissions avoided
Table 5: electrical output for the three types of wind turbines, according to different data sources
Proven 35 Wes 18 (Segen) Endurance wind power
(Aeolus)
Nominal power of one
turbine in kW 15 80 50
Number of turbines
installed 6 4 4
Pro
ven
calc
ula
tor
NO
AB
L
On
-sit
e
mea
sure
s
Car
bon
Tru
st
NO
AB
L
On
-sit
e
mea
sure
s
Car
bon
Tru
st
NO
AB
L
On
-sit
e
mea
sure
s
Electrical production
MWh/year 136 297 189 797 790 423 731 770 463
Part into the 2009 grid
import (12 GWh) 1.1% 2.3% 1.5% 6.2% 6.2% 3.3% 5.7% 6.0% 3.6%
CO2e avoided per year
in t 74 162 103 434 430 230 398 419 252
Part into the carbon
footprint of AVSE (18
450t CO2e)
0.9% 0.6% 0.4% 2.4% 2.3% 1.3% 2.2% 2.3% 1.4%
Carbon Trust and NOABL gives quite similar results (difference of -3% to +10%), whereas
NOABL and on-site measurements have about 57 to 87% of difference! The main reason is that
the wind speed measured on site is 30% lower than NOABL, and as E=v3, the output is much
lower.
We can notice that for low wind speed, Endurance Wind Power is better than Wes 18, whereas Wes 18
will give better results on sites with a high wind speed. For Seafield, which has a low to medium wind
speed, Endurance Wind Power will be more interesting than Wes 18, all the more so as the cost of this
turbine is a little lower than Wes 18.
44
In the best case, only about 6% of the electricity would be produced by the turbines, resulting in
decreasing the GHG emissions of the plant by 2.3%, ie 430 t of CO2e.
Hydro power
The total annual output for the Archimedean screw and the hydro turbine has been estimated by
the companies (Spaans and RD Energy Solutions). Table 6 sums up the results in term of GHG
and electricity.
Table 6: production results for the hydro turbines
Archimedean Screw Hydro turbine
Nominal power of one turbine in kW 110 100
Electrical production MWh/year 414 429
Part into the 2009 grid import (12 GWh) 3.2% 3.3%
CO2e avoided per year in t 225 233
Part into the carbon footprint of AVSE (18 450t CO2e) 1.2% 1.3%
Both equipments provide approximately the same amount of energy, and so of GHG avoided.
Like for the wind turbine, benefit in term of GHG avoided and electricity produced is low
compared to the current needs of the plant. But if we compare the power installed with thus of the
wind turbines, the best results are encountered with the Archimedean Screw, the hydro turbine
and Endurance Wind Power (table 7)
Table 7: comparison of the efficiency of wind and hydro turbines
Archimedean
Screw
Hydro
turbine Proven 35 Wes 18 Endurance
power kW 110 100 90 320 200
production
MWh/year 414
429
189 790 731
t CO2e avoided 225 233 74 430 398
MWh/kW 3.8 4.3 2.1 2.5 3.7
t CO2e/kW 2.0 2.3 0.8 1.3 2.0
Waste heat
Concerning the option “space heating”, there is of course no electrical production. Still, GHG
emissions will be avoided. Because at Seafield the energy consumption is not split into each usage,
we do not know how much we buy for office heating. So to estimate it, I had to measure the
surface area of the office (no drawings for this old building) and use data from the government 13
(151 kWh/m2/). The Stirling office is supposed to use 85 MWh of diesel (9 971L) for heating. 1L
of diesel emits 2.669 kg CO2e.14
45
Concerning the option “converting low grade heat into electricity”, we can consider either using
only one source of heat (CHP 1 since it has the highest power) or a combination of the 3 sources
(see appendix 8 for the details of the calculations).
Table 8: GHG emissions avoided by reusing the waste heat
Office heating ElectraTherm
CHP 1 only
ElectraTherm
CHP 1&2 and TH
Nominal power in kWe / 30 81
Electrical production
MWh/year
/ 237 639
Part into the 2009 grid import
(12 GWh)
/ 1.8% 5.0%
T of CO2e avoided per year in t 27 129 347
Part into the carbon footprint of
AVSE (18 450t CO2e)
0.1% 0.7% 1.9%
The ecological impact of both options is really negligible in term of percentage, but still it can
help avoiding the emissions of 350 t of CO2e.
Rags
We can compare the carbon footprint of the incineration with this of landfill. Since the place
where the rags will be sent is the same (Dunbar), only the way of disposal will change the GHG
emissions, not the transport.
Their composition makes them close to municipal solid waste (MSW). However, there is not one
common figure for the GHG emissions of MSW that are burn or sent to landfill. I found different
data, each one very far from the others (see appendix 9). The environmental advantage of the
incineration is not that clear and depends on numerous parameters (type of waste, yield of the
energy recovery of the landfill and the incinerator …)
3) Economical analysis: the profitability of each solutions
The savings comes from the non importation of electricity from the grid and the money the
government gives to green energy producers. Renewable Obligation Certificates (ROCs) and
Feed in Tariffs (FITs) are the two governmental means to encourage the development of
renewable energies in the UK. The price of ROC is less interesting than FIT, so FIT have been
chosen. Indeed, new installations can apply either for ROC or FIT, with some eligible criteria.
The tariff depends on the type of technology and the size of the installation. The larger the
installed power is, the lower the FIT are. Solar PV has the highest purchase tariff, followed by
wind and hydro. A detailed explanation about ROCs and FITs is available in appendix 10 and in a
document made by Ofgem Renewables Obligation: Guidance for generators.
46
Electricity from national grid is purchased at a cost of 75.2 £/MWh in 2009.
Wind energy
The costs were provided by each companies, but fully installed costs are dependent on a number of
variables and at this stage in the process it is only possible for them to give rough estimates. It wi ll be
necessary to decrease the slope of the hills where the turbine will be mounted, for the diggers to be able
to go on top. This will add a cost, and the soil removed will need to be sent to land restoration. These
additional costs were estimated by Seafield senior project manager.
The results were first calculated for the 2sd best electrical production estimated (189 MWh/year
for Proven, 790 for Wes 18 and 731 for Endurance).
Installing 6 Proven turbines is not profitable (NPV negative). The same conclusion was found for
4 Wes 18 turbines or 4 Endurance turbines.
One of the reasons is that the installed power is high with 4 turbines, so we get less FIT. Thus I
calculated the economical criteria with only one turbine, installed on location “a” since there the
slope‟s angle is low enough for the diggers and does not need to be decreased, so the initial
investment is lower too. As Proven turbines are smaller, 2 could be installed (locations e and f) to
be in the 1.5-15kW range for the FIT.
Table 9: economical results for an installed power lower enabling to have the higher FIT
1 turbine Wes 18 1 turbine Endurance 2 turbines Proven
Initial investment
k£ excl. VAT
250 225 91.7
NPV 17.3 35.6 -26.3
IRR 11.1% 12.3 5.9%
Payback period 16.5 14.1 never
Wes and Endurance could be interesting, but we need to be very careful because the wind speed
data are very different form one source to another. This will be study in part III-C-1) with the
risks.
Hydro power
The costs for the screw were provided by the companies contacted and by Veolia engineers to
have a complete quote. Because the calculation of the declared net capacity (DNC) for the FIT is
not clear, we have assumed that the screw could get a FIT rate for a scale lower than 100kW,
which Spaans says would be possible if they label the turbine at 100kW. This will nonetheless
need to be confirmed by Ofgem, the department managing the FIT and ROC. If the installation
can not get into the 15-100 kW scale, but will be considered in the 100-2000 kW scale, then the
Screw project is not profitable anymore.
47
Table 10: comparison of the profitability of the 2 options for a hydro turbine
Archimedean Screw Vortex turbine
Initial investment k£ excl. VAT 330.3 522.5
NPV £97 720 £-177 800
IRR 14.1% 4.9%
Payback period 11.7 never
The Vortex turbine is more expensive than the Archimedean Screw for approximately the same
electrical production. As a result, it is less profitable than the screw. In fact, only the Archimedean
screw is worth considering
Waste heat
The costs were provided by Arthur MacKay and BMM Heaters for the material and the
installation and by Seafield senior project manager for the additional cost not included in their
quote (trenching).
The initial quote of Arthur McKay was very expensive (about £95 000), because they had added
unnecessary work and equipment. Indeed, they have assumed that the heating network of the
office was too old and should be replaced. They have also changed the current radiators for bigger
ones (because the temperature from the CHP and TH is too low for the radiators‟ capacity), but
the other company BMM Heaters, based on the size of the rooms and the size of the radiators,
think they will be suitable. As a result, the initial quote of Arthur McKay has been reduced by
about 2 by removing these unnecessary works.
Table 11 only presents the cheapest option (using the waste heat from the TH). For
ElectraTherm, only a very rough estimation can be made because neither the investment nor the
outputs are sure (a trial will be needed to get accurate production results, and the company only
gave us an average price for its machine). Economical criteria have been calculated only for the
recovery of CHP 1 heat, because using the three sources of heat (CHP 1&2 and TH) would add
costs for the installation of new pipes and connections that can not be estimated at the present
time.
Savings only come from the no purchase of electricity or fuel. There is no FIT for ElectraTherm
technology, but according to the company which will install such machine on a landfill site; this
new technology is eligible for 2 ROCs
Table 11: comparison of the profitability of reusing the waste heat either for space heating or
electricity production
Arthur McKay BMM Heaters ElectraTherm
Initial investment k£ excl. VAT 43.2 23.6 200
NPV -31 250 £ -3 820 £ -142 840 £
IRR -5.2% 7.6% -4.9%
Payback period never never never
48
None of the proposals are profitable. However, there is an important uncertainty about the fuel
consumption for the office heating. If the real consumption is higher than estimated, BMM offer
could become interesting. This will be analysed in the next part.
Rags
As the landfill taxes will increase, alternative treatment such as incineration could be economically
interesting. The current contract to dispose of the rags begins in June 2010 and is with Caleco. To
seriously consider this solution, a comparison between the current costs of disposal to landfill with
the proposed costs of incineration by Viridor has been done.
The cost of current disposal is made of 2 parts: Caleco’s charges (which is fixed during the duration of
the contract) and the landfill tax.. The tax is currently 48£/t (1st April 2010 until 31st March 2011). It
will increase by 8£/year until 2014 where it will reach a price of 80£/t. Moreover the government will
introduce a floor so that the rate will not fall below £80 per tonne until at least 2020.Because of
the nature of the screenings (water + organic matter), it is possible to have a discount on the tax. It is
called the water discount. If the water (that has not been added) is more than 25% of the waste by
weight it is eligible to water discount. 15
If we want to compare the prices of disposal to landfill and other disposal, we should take into account
the increase in landfill taxes and the discounting of water.
Viridor‟s proposal is:
transport of the material in their skips: £76/skip
receiving the rags into their EfW plant in Dunbar would cost £61/t. The price is fixed
until March 31st 2011. He adds that “Going forward as our new technology infrastructure comes
on stream we will be able to review this. The cost will definitely decrease once our new plant is
operational ”
There is no contract; their facility is there as long as we wish to use it.
If we compare this with the current contract with Caleco, Caleco is more interesting than Viridor
for the transport (55£/skip compared to 76£/skip). The choice between Caleco-landfill and
Viridor-incinerator will depend on the possibility to have the water discount or not (see table 12
below).
Table 12: Choice between Caleco and Viridor for the disposal of screening
Caleco Viridor
Year
Total cost
with water
discount
Total cost
without water
discount
Constant
price
Price
decreasing
by 2%
Price
decreasing
by 5%
Price
decreasing
by 10%
2010 30.9 64
61 59.8 58.0 54.9 2011 33.4 72
2012 35.8 80
2013 38.3 88
49
C. Choice of the best solution for Seafield WWTP by taking into account the risks of the project
1) Analysis of the risks
The value created by a project needs to be put into perspective with the risks taken. Risks have to
been identified, evaluated (high-medium-low), a mean to minimize them must be found and the
residual risk should be described.
The main risks common to each project are the uncertainties on the energy output and the initial
investment.
Wind energy
The main risks come from the uncertainty about the wind speed. On-site measurements, which
should be more precise than Carbon Trust and NOABL, are however 30 to 50% lower and thus
the production calculated is on average two times lower. An economical analysis for the base, best
and worst case has thus been done for one turbine Endurance (more interesting than one turbine
Wes 18) and 6 Proven turbines (we get 15% discount when buying more than 4 turbines, which is
why it is most interesting to have 6). The dead point is the value that gives an NPV equal to zero.
Table 13: Analyse of the sensibilities
MWh/year Base case Worst case Best case Dead point
Endurance 209 108 215 190
Proven 189 136 297 251
Table 14: Comparison of the economical results between the base case, the worst and the best one
Turbine NPV k£ IRR % Payback period
Endurance Base case 35.6 12.3 14.1
Worst case -148.7 -1.8 never
Best case 46.5 13 13.2
Proven Base case -113.3 4.2 never
Worst case -210.0 -3.0 never
Best case 83.7 13.9 11.9
As table 15 shows, having a right wind speed is very important. Endurance project seems less
risky than Proven, but Proven could be more profitable than Endurance if the best case is proved.
To get accurate results, the only solution would be to install a mast on the locations and monitor
the wind speed at hub height. However, this is costly (about £13 000 per turbine)
50
Hydro power
The electrical output calculated did not take into account the diminution of the head during storm
weather. Indeed, storm flow will come to the outfall too and thus decrease the available head. The
fall off has been estimated to 5%, as the storm flow represented 5% of the total flow in 2009. Other
uncertainties has been analysed (estimation of the civil costs: +/- 15%) but are not presented here.
For this risk, the project was still profitable. Impact of the risk coming from the storm flow is
presented in table 15.
Table 15: Comparison of the economical results between the base case, the worst and the best one
Number Base case Worst case Best case Dead point
lower production 414.3 MWh/year 391.8 MWh/year / 348 MWh/year
Parameter NPV k£ IRR Payback period
1 Base case 96.7 14.1% 11.7
Worst case 63.9 12.8% 13.4
Even if the electrical output is a bit lower, the project is still profitable.
Waste heat
BMM offer was the less expensive. However, it was still not profitable. Playing on the fuel
consumption of the office, we have a base, best and worst case.
Table 16: analysis of the sensibilities
Type of risk Assessment of the risk
(probability, scope)
Answers to that risk Residual risk
Wrong estimation of the
energy consumption to
heat the office
High Calculate the results with
different figures – better
monitor the fuel consumption
Medium
Base case Worst case Best case Dead point
151 kWh/m2
£5 930
100 kWh/m2
£3 929
300 kWh/m2 (opinion
of the heating engineer)
£11 788
170kWh/m2
6 680£
The base case indicates a consumption of 151 kWh/m2. The source of this information has been
given in part III-B-2). BMM engineers‟ opinion is that it could be twice higher, since the building
is very old. This gives the best case. The dead point is the value that gives an NPV equal to zero.
51
If the fuel consumption was a little higher than estimated, the project could become profitable and
with 300 kWh/m2, all Veolia requirements are achieved (an IRR higher than 15%, a payback period
lower than 5 years, see table 17).
It would be really useful to monitor the volume of fuel consumed to heat this office, instead of relying
on average figures. We could then have a precise idea of the savings and thus of the profitability of the
project. At the present time, with the uncertainties about the fuel consumption to heat the office, no
clear answer about the worthiness of this project can be given.
Table 17 Comparison of the economical results between the base case, the worst and the best one
NPV IRR Payback period
Base case -3 820£ 7.6% never
Worst case -14 430£ -1.7% never
Best case 27 204£ 25.1% 5.4
2) The most suitable solution given financial and environmental results
The figure 15 below shows the variation of the NPV depending on the discount rate, for the most
interesting companies of each technology (wind, hydro, waste heat). The base and best case are
presented (for hydro, the worst case becomes the base case since it takes into account the decrease
in the production because of storm flows). If we compare the base cases, the Archimedean screw
is the most profitable, followed by Endurance wind turbine. Comparing the best cases, it is still
the hydro project that is the most interesting, but this time the 2sd place is for the Proven turbines.
Proven project seems also more risky. Finally, the best choice is for the Archimedean screw, since
the base and the best case are the most profitable. To confirm that decision, we can have a look too
at the profitability index: it is the sum of the discounted FCF divided by the initial investment. It
takes into account the fact that the initial investment is not the same for the projects. It must be
higher than 1 (otherwise the project is not profitable) and the choice will be applied to the highest
index. Table 18 proves that the Archimedean screw project is the best one.
Moreover, the fact that there could be planning permissions issues from Edinburgh council to
install the wind turbines since Seafield is located in an urban area, near protected natural sites and
with the airport at 13km is another argument in favour of the Archimedean Screw.
52
Figure 15: comparison of the NPV and the IRR for projects with the same duration
-300 000
-200 000
-100 000
0
100 000
200 000
300 000
400 000
500 000
600 000
Comparison of the NPV and the IRR for projects of the same length
Endurance Base case
Endurance Best case
Hydro Best case
Hydro Base case
Proven Base case
Proven Best case
WACC = 10.2% minimum IRR for Veolia = 15%NPV = 97 k£, payback = 12
NPV = 84 k£, payback = 12
NPV = 64 k£, payback = 13 years
NPV = -113 k£, payback = never
NPV = 36 k£, payback = 14
NPV = 47 k£, payback = 13
discount rate
NPV in £
Table 18: comparison of the profitability index
Project Proven
best case Proven
base case
Endurance
best case
Endurance
base case
Hydro
best case
Hydro
base case
Profitability index 1.28 0.62 1.21 1.16 1.29 1.19
Comparing the Archimedean screw and BMM Heaters (office heating) can not been done like that
since the duration of the projects are different (19 years in one case, 17 in the other case). To be
able to compare them, we need to calculate the NPV ad infinitum. It supposes that the projects can
be renewed ad infinitum.
Table 19: comparison of two project with a different length thanks to the NPV ad infinitum
Project BMM best
case BMM base
case
Hydro best
case
Hydro base
case
NPV ad infinitum in k£ 33.7 -4.7 114.9 75.9
The table above shows that for the same length of the two projects, the hydro one is still the most
interesting. However, the profitability index for BMM best case is higher than for hydro (2.15).
The payback period is also very short (5 years). Nonetheless, as explained before, the BMM best
case has not been proved for the moment, it will need to have precise fuel consumption monitoring
before acknowledging its profitability.
53
Not only has the profitability had to be taken into account, but also the environmental benefit.
The electrical production and thus the amount of GHG avoided is the largest for the hydro project
(225 t of CO2 for a production of 414 MWh/year for the best case), whereas heating the office
with the waste heat only avoid the emissions of 53t of CO2e for the best case.
3) Continuation of the study and implementation of the chosen project
After reviewing the results of this study, the General Manager of the AVSE contract will be able
to take a decision and chose whether to implement or not the best solution to mitigate Seafield‟s
carbon footprint, that is to say installing an Archimedean Screw on the outfall. But some details
must still be sorted out:
Make sure that SEPA, the environmental agency, will agree to divert the discharge flow to
the short sea outfall. This means that during the time of installing the screw (about 2
weeks), the water will be discharged on the beach and not in the sea. SEPA decision will
probably depend on the way the ecological benefits of the project are enlightened to them.
Make sure with Ofgem and Spaans Babcock that the 110 kW installed screw will be
eligible to the FIT for the range 15-100 kW. Otherwise, to get the highest FIT rate, it
would be possible to install a 90kW screw, resulting in less electricity produced but also an
initial investment a little lower.
It is obvious that such renewable project cannot achieve Veolia economical requirements (IRR of
15% and payback of 5 years). However, it is a choice that the company will have to make between
high profitability and good brand image.
One of the limits for the implementation of the hydro project is the financial situation of AVSE.
Since the contract has not reached the breakeven point yet, the initial investment for the
Archimedean Screw may be too important to them at the moment. This can drive the choice
toward the waste heat recovery project, to heat the office. Indeed, the initial investment is 14
times lower. The BMM project could be very profitable if the energy fuel consumption is 170
MWh/year. Seafield staff will have to precisely monitor the volume of fuel purchased to heat the
office, so that an accurate economical analysis can be carried out.
Along with the purchase of the 3rd CHP and the TH implementation in 2012, the hydro project
will enable Seafield to reach its objective of producing 100% of its energy from renewables by
2020.
54
Conclusion
Many new technologies have been developed these past 20 years to produce renewable energies.
Among all of them, only a few seemed the most suitable for Seafield WWTP. By taking into
account the resources of the site, only wind turbine, hydro turbine, waste heat recovery and co-
incineration of the screenings products turned out to be worth considering. By studying more
precisely the profitability of each solution, it results that the hydro project with the Archimedean
Screw option was the best one, with the highest NPV, IRR, payback period and the lowest risks. It
is also the solution that produces the largest amount of electricity, an important point for Seafield
engineers who want the renewable project to produce a significant amount of the energetic needs
of the plant. Yet, it must be clear that with the available resources of the site, the output cannot be
compared to the needs. Nevertheless, the screw could produce 7% of the energy required by the
UV plant, as well as avoiding the emissions of ~220 t of CO2e.
Final decisions will need some further information, like the confirmation of the FIT rate for the
hydro project, the possibility to get the water discount for the co-incineration opportunity or the
real fuel consumption of the office for the waste heat recovery project. These last two solutions
could be interesting if the hypotheses made to calculate their profitability are confirmed.
This study also enlightened the fact that the engineer‟s methods are confronted with the reliability
of the data and above all, with the constraints of the business (economy, reputation, public
relations…)
Acknowledgements
This study would not have been possible without the help of Seafield engineers. I would like to
thanks especially Paul Banfield, Simon Wriggelsworth, Alex Kimble, Alex McTear, Roy Adam
and Craig Wylie for their advice and for providing me with the data I needed.
I would like to thank my internship supervisor too, Hélène Galy, for her support during these 6
months. I have enjoyed the welcome and help of Richard Johnson, General Manager for the AVSE
contract and of all his team, as well as the ones of Bertrand Masure, General Manager for VWOL
in Scotland.
55
Glossary
AD: Anaerobic Digestion
AS: Activated Sludge
AVSE: Almond Valley, Seafield, Esk
CAPEX: Capital Expenditure = initial investment
CFFO: Cash Flow From Operation
CHP: Combine Heat and Power
CO2e: CO2 equivalent
DECC: Department of Energy and Climate Change
EBITDA: Earnings Before Interest, Tax, Depreciation, Amortisement
EDCF: Expected Discount Cash Flow
EfW: Energy From Waste
FCF: Free Cash Flow
FIT: Feed in Tariff
FST: Final Settlement Tank
GHG: Green House Gases
IRR: Internal Rate on Return
MCS: Microgeneration Certification Scheme
NPV: Net Present Value
OPEX: Operation Expenditure = on-going cost for running the business (maintenance, renewal)
PE: Population Equivalent
PFI: Private Finance Initiative. It is the same thing as a PPP
PFT: Primary Settlement Tank
PPP: Public Private Partnership
ROC: Renewable Obligation Certificate
SEPA: Scottish Environmental Protection Agency
SW: Scottish Water
TH: thermal hydrolysis
WACC: Weighted Average Cost of Capital
WC: Working Capital
VWOL: Veolia Water Outsourcing Ltd
WWTP: WasteWater Treatment Plant
Appendix
56
APPENDIX 1: Seafield WWTP
Process Flow Diagram
PRELIMINARY
TREATMENT
PRIMARY
SEDIMENTATION
BIOLOGICAL
TREATMENT
FINAL
SETTLEMENT
ULTRA
VIOLET
TREATMENT
OUTFALL TO
FIRTH OF
FORTH
SITE RETURN
LIQUORS
TO SLUDGE
TREATMENT
PROCESS
STORM
TANKS
RETURNED
ACTIVATED
SLUDGE
STORM TANK
OVERFLOW
RAW SLUDGE
SURPLUS
ACTIVATED
SLUDGE
STORM
RETURN
AIR
57
Sludge Stream Process Flow Diagram
PICKET FENCE
THICKENERS
DIGESTION
TANKS
CENTRIFUGES
CAKE
STORAGE
SILO
SLUDGE
DRYERS
OVERFLOW
SUMP
IMPORTED
WET
SLUDGES
DISPOSAL
SAS
HOLDING
TANK
BELT
THICKENERS
RAG
SKIP
DIGESTER FEED
HOLDING TANK
CAKE
BREAKERS
PRIMARY
SLUDGE
DIGESTED
SLUDGE HOLDING
TANK
POLYELECTROLYTE
EAST
CALDER
IMPORTED
SLUDGE
CAKE
STORAGE
SLAB
ODOUR
CONTROL
UNIT
FOUL
SUMP
MAIN PS
OVERFLOW
OVERFLOW
RETURN
LIQUORS
P.S.
STEAM HEATING
NEWBRIDGE
IMPORTED
SLUDGE
58
View of Seafield WWTP from Arthur Seat
More information on the plant here
http://www.scottishwater.co.uk/portal/page/portal/SWE_PGP_INVESTMENT/SWE_PGE_I
NVESTMENT/WHAT_WWTW_SEA/WHAT_SEA_FACTS
http://www.lifesciences.napier.ac.uk/smaefiles/wwtw/seafield.htm
Map of the plant and location of the main buildings
59
f
Strom tank
Primary settlement tank
Digesters
Detritors
Activated sludge tank
Final settlement tank
Sludge building
CHPs
Biogas holding tank
Screening house
UV plant
Sludge storage tanks
60
APPENDIX 2: the different solutions to make Seafield more sustainable in term of energy
Biocatalysts and enzymes
These products are manufactured in order to help the quick degradation of pollutants in
wastewater. They are said by their producers to decrease the amount of sludge, accelerate the
treatment, to enable odour control, to save money and energy. However, this technique does not
seem to be really compatible with the production of biogas and its effectiveness can be questioned.
Input: a powder or liquid solution made of enzymes, co-enzyme, microbial, co-factors,
micronutrients, bacteria, micro-organisms, biocatalysts…
Output: improves the waste water treatment and decreases the amount of sludge
Principle and technologies:
These products content a mix of bacteria, enzymes and other biological components. Their goal is
to accelerate the degradation of the organic matter and pollutants (BOD, COD, N, P, fat, oil,
grease …) in the sewage.
Microorganisms and their enzyme systems are responsible for many different chemical reactions
produced in the degradation of organic matter. As the bacteria metabolize, grow and divide they
produce enzymes. These enzymes are high molecular weight proteins. Enzymes in biochemical
reactions act as organic catalysts. They are basically proteins which act to speed up various
biochemical reactions without being changed themselves. Since they are proteins, enzymes are
subject to the conditions that often affect proteins. They are very useful hydrolytic organic
catalysts. The enzymes actually become a part of the action, but after having caused it, split off
from it and are themselves unchanged. After the biochemical reactions are complete and products
formed, the enzyme is released to catalyze another reaction.
The rate of reaction may be increased by increasing the quantity of the substrate or temperature
up to a certain point, but beyond this, the rate of reaction ceases to increase because the enzyme
concentration limits it. What is needed is the addition of an enzyme manufacturing system right in
the sewage that can be pre - determined as to its activity and performance and which has the
initial or continuing capacity to reduce waste.
We have hold three products from three companies:
Biowish-AquaTM from Biowish Technologies
FortexTM from Utileco
Bac-Zyme® Waste Digester from Microtack
Biowish-AquaTM is composed of 3 bacteria (Pediococcus pentosaceus Mees, Bacillus subtilis,
Pediococcus acidilactici), 2 yeasts (Dekkera anomala, Yamadazyma farinose), metabolite substrates
(digestive/metabolic enzymes, organic acids, bacteriocines/ iturins / killer toxins, growth factors,
vitamins) and dried bran carrier (also provides nutrients for microbials). The concentrations to
61
apply in the WWTP are 4 ppm on the 1st day, 2ppm on the 2sd day, 1 ppm on the 3rd and then for
tne ongoing treatment 0,3 ppm/day or 2 ppm/week.
FortexTM includes products (natural micronutrients and biocatalysts) that enhance the
performance of any size sewage treatment plant in order to achieve compliance with regulation.
The FORTEX™ Pack is comprised of powders and solutions that can be dosed into sewage
catchment area pump stations or directly into the entrance tank of the sewage treatment plant.
This can be achieved using a mixing tank with a timer controlled automatic dosing system.
Bac-Zyme® contains powerful waste digesting enzymes, essential nutrients and specifically
selected strains of enzymes producing bacteria to degrade all the principle organic constituents
normally found in municipal and industrial wastewater treatment facilities. Initial treatment of
any waste system should be four times the volume of Bac-Zyme® Waste Digester required for
normal preventative maintenance. As a general rule, normal preventative maintenance is 2 ppm of
Bac-Zyme® Waste Digester per day, determined by the total weight of the wastewater in the
system
Advantages:
Accelerate the degradation of pollutants in the sewage
Reduces BOD, COD and SS in municipal and industrial wastewater treatment effluent
Improves floc settling formation, thus prevent bulking sludge
Enable to absorb the shock of toxic influent
Enhances odour control through natural organic acid oxidation
Environmental friendly,100% organic and biodegradable
Energy saving in aeration (potentially > 50% according to Biowish Technologies)
Sludge reduction (potentially up to 95% according to Biowish Technologies or up to 65%
according to Utileco) and less Returned Activated Sludge (RAS) (only 5% of the inflow
volume says Biowish Technologies)
Chemical saving
Process stability
Potential to increase plant capacity
Reduction in total operating costs
Improved plant carbon footprint
Suitable for all biological WWTP‟s and for plants with biogas generation (Biowish-Aqua)
Inconvenient:
What is the real effectiveness of these products?
By enhancing the degradation of OM, the sludge contains less fat and volatile matter. As a
result, its anaerobic digestion may produce less biogas
for Seafield: we can not take the risk to have a worse biogas yield as it may not balance the
potential gain of aeration. Moreover, the current aerators are too big and we can not decrease the
power of aeration. This solution could be interested in other WWTP of the Almond Valley in
order to reduce the quantity of transported sludge, but we have to be sure it will not have a
negative impact on the anaerobic digestion.
62
Fuel cells
Fuel cells are an interesting technology to produce electricity and heat from hydrogen. They are
more efficient and less pollutant than classical power generator. However, their price and early
stage of advancement at the present time involves that it may be a good solution for Seafield but
only in the future more or less recent, depending on its development.
Input: all hydrogen based liquid or gas (methane, natural gas, biogas, syngas from biomass
gasification, pyrolysis oil …)
Output: electricity, heat, water
Principle and technologies:
1- Extraction of H2 from the fuel: it is done with a fuel reformer. Water vapour is injected into the
feedstock in the presence of a catalyst to break down the fuel into carbon monoxide (CO) and
hydrogen (H2). The water vapour also breaks down into H2 and oxygen. The oxygen from this
reaction combines with CO to create CO2.
2- Electrochemical process to turn hydrogen and oxygen into pollution-free electricity and
heat: a fuel cell is made of a cathode, an anode and an electrolyte between them. At the anode, the
hydrogen atom loses an electron and its proton goes into the electrolyte. The electrolyte is
specifically made to conduct ions to the other pole of the fuel cell but not electrons. At the cathode,
when two ions enter it from the circuit, these join with an oxygen atom and create a water
molecule. Electrons, directed to flow through a wire from one electrode to the other, power an
electrical circuit for use.
Sources: http://toocan.com/lunog/media/blogs/misblog/images/pem_fuel_cell.jpg and fuel cell operation on
anaerobic digester gas, R. J. Spiegel, August 7 - 8, 2001
63
There are different types of fuel cells:
Type of fuel
cells
Composition of
the electrolyte
Efficiency Operating
temperatures
Characteristics Use
Phosphoric
Acid fuel cells
(PAFC)
Liquid
phosphoric acid
Only electricity:
37-42%
Cogeneration:
60-70%
160-200ºC PAFC power plants
are usually large,
heavy and require
warm-up time
stationary applications
Landfill/wastewater
treatment facilities: to
generate power from
biogas
Commercial: hospitals,
nursing homes, hotels,
office buildings, schools
Proton
Exchange
Membrane
fuel cells
(PEM) or
polymer
electrolyte
membrane fuel
cells
(PEMFC)
Polymer
electrolyte in the
form of a thin,
permeable
membrane
Only electricity:
40-50%
Cogeneration:
40% (the
temperature of
waste heat is
too low to
be used in the
fuel reforming
process)
80ºC rapid start-up
capability, light
weight, high power
density, low operating
temperature, low cost
relative to other types
Light-duty (50 to 100
kW), medium-duty
vehicles (200 kW), small
residential (2 to 10 kW)
and commercial (200 to
500 kW) power
generation,
small/portable
applications (cell phones,
video cameras, laptotp)
Solid Oxide
fuel
cells (SOFC)
Hard, non-
porous ceramic
compound
(mixture of
zirconium oxide
and calcium
oxide)
Only electricity:
45-50%
Cogeneration:
70-80%
700 - 980°C large, heavy and
require long start-up
time stationary
applications
SOFCs have lifetimes
of 10 to 20 years, two
to four times the
lifetime of other fuel
cells
Commercial: airport
terminals, public and
commercial office
buildings, hotels,
hospitals
Landfill/wastewater
treatment facilities: to
generate power from
biogas
Alkaline fuel
cells (AFCs)
Potassium
hydroxide
Only electricity:
60%
Cogeneration:
70-80%
120-260°C AFCs are susceptible
to carbon
contamination, so they
require pure hydrogen
and oxygen
terrestrial applications
are limited
Mainly space
applications
Molten
carbonate fuel
cell (MCFC)
Molten
carbonate salt
mixture
suspended in a
porous,
chemically inert
ceramic lithium
aluminium oxide
(LiAlO2) matrix
Only electricity:
50-60%
Cogeneration:
80%
650°C corrosive electrolyte
durability limited
Commercial: airport
terminals, public and
commercial office
buildings, hotels,
hospitals
Landfill/wastewater
treatment facilities: to
generate power from
biogas
For more technical information see http://www.nrbp.org/pdfs/pub31.pdf
64
Advantages:
Greenhouse emissions and particulates are very low since water is the only by-product of
the reaction between hydrogen and oxygen in a fuel cell, no pollutants are produced if pure
hydrogen is used to power fuel cells. Even when non-pure hydrogen sources are used as fuels,
most of the contaminants are removed prior to use of the fuel in the fuel cell. This fact,
combined with the fact that fuel cells do not rely on combustion, means that regulated air
pollutants, such as sulfur and nitrogen oxides, carbon monoxide, and unburned hydrocarbons,
are nearly absent from fuel cell emissions.
System is very quiet and less noisy than a diesel engine generator
Fuel cells systems have no moving parts: as a result, it requires little maintenance (only a
two-day annual maintenance shutdown), and fuel cell power plants are shut down less often
than conventional power plants
Fuel Flexibility
Fuel cells are more efficient than the typical cogeneration systems used at wastewater
treatment plants, converting on average 40% of the energy contained in digester gas into
electricity, compared to 32% for cogeneration.
Possibility to produce hydrogen in the future thanks to a tri-generation systems that produce
heat, hydrogen and power (CHHP)
Inconvenient:
Cost per kilowatt is very high: 4000-4500 $/kW just for the fuel cells
Biogas must be cleaned up to strict specifications. It adds cost and complexity while
consuming energy. Depending on the type of fuel cell to be utilized, these gases and
contaminants will have to be treated or removed to varying degrees: hydrogen sulfide
removal, moisture removal, carbon dioxide removal
After about 5 to 7 years, the fuel cell stack must be rebuilt
Fuel cell is an emerging technology
for Seafield: a sustainable solution that need to be considered but only in a few years when the
technology is more advanced and the cost economically interesting.
65
Alternative thermal treatments: pyrolysis and gasification
These technologies position themselves as an alternative to classic combustion to get rid off
municipal, commercial and industrial waste, and by recovering the energy. They claim to be more
efficient and environmentally friendly (less emissions). However, the lack of feedback and
impartial analyse of the processes make them still more risky for the moment than classic
solutions.
Input: any carbon-based waste such as paper, plastics, organic materials. So the screenings
produced on site could be treated by these technologies.
Output:
pyrolysis: a solid (the char or coke), pyrolysis oil, gas (syngas) electricity or/and heat
gasification: ash, gas (syngas) electricity or/and heat
Principle and technologies:
In contrast to incineration which fully converts the input waste into energy and ash, these
processes deliberately limit the conversion so that combustion does not take place directly.
Instead, they convert the waste into valuable intermediates that can be further processed for
materials recycling or energy recovery.
The conditions under which pyrolysis and gasification take place are a little different, and sot are
the products generated. However, the two processes are often combined; the majority of the
systems under development are based upon gasification in combination with either pyrolysis
or combustion.
input
air ash
fumes Incinerator
Excess of air
input
air ash
Poor syngas Gasification
plant
Lack of air
input Rich syngas Pyrolysis
plant
Absence of air
oils
char
Incineration Direct heating by the complete combustion of waste
Gasification Direct heating by the partial combustion of syngas or of the pyrolysis‟s char
Pyrolysis Indirect external heating
Increasing amount of
air
66
Pyrolysis (known as thermolysis too): thermal degradation of waste in the absence of air and in
medium temperatures (400-700˚C). There are different ways of doing pyrolysis:
Thermolysis alone: the char is not promoted directly
Integrated thermolysis: the char undergoes a combustion or gasification just after the pyrolysis
Slow thermolysis: 10 min at 400-500˚C
Flash thermolysis: a few seconds at 600-900˚C-complex technology limited to low capacity
Source: http://www.mbt.landfill-site.com/Pyrolysis___Gasification/pyrolysis___gasification.html
Gasification: breakdown of hydrocarbons into a syngas by carefully controlling the amount of
dioxygen present, at high temperatures (850-1000˚C). Different types of air can be used
(atmospheric air, water steam, O2, CO2) resulting in a syngas more or less rich.
Source: http://www.mbt.landfill-site.com/Pyrolysis___Gasification/pyrolysis___gasification.html
67
Gasification and pyrolysis processes have 4 stages:
1. Preparation of the waste
2. Heating the waste
3. Scrubbing the gas (cleaning)
4. Using the cleaning gas to generate electricity and in some cases heat (CHP)
The gases, oils and solid char from pyrolysis and gasification can be used as a fuel (RDF: Refuse
Derived Fuel), or purified and used as a feedstock for petro-chemicals and other applications, or
even produce hydrogen.
The syngas is composed of CO and H (85%) with smaller quantities of CO2, N2, CH4 and various
other hydrocarbon gases. It is combusted in a secondary process to generate energy.
Advantages:
Better efficiency than conventional fossil-fuel energy generation or incineration. For example,
gasification can be used in conjunction with gas engines, gas turbines, steam turbines or even
fuel cells in the future to obtain higher conversion efficiency.
More flexibility of scale: some processes can be used as local solutions at small scale (30
000t/year), others deal at a larger scale (150 000-500 000t/year)
The plants are modular: they are made of small units which can be added to or taken away as
the waste stream changes
The plants are quicker to built than an incineraor
A wide range of waste can be treated (Juniper‟s database lists over 50 different types of waste
for which systems are available or under development)
These processes can handle mixed waste feeds like MSW (municipal Solid Waste). Currently,
only incineration and landfill can do this
By using less oxygen, fewer air emissions may be produced. However, if the gases coming off
the process are then burnt (in a steam boiler for example), thus may also generated emissions
These technologies produce a more useful product than incineration (gases, oils and char can be
used as a fuel, as a feedstock for petro-chemical applications…)
Inconvenient:
These technologies are significantly less proven than conventional solutions such as
incineration
Project costs are rarely significantly lower than conventional alternatives
There is a few demonstrator projects at large scale in Europe. The technology is far more
developed in Japan
Most of the available data on the performance of these technologies come from the companies
themselves, which makes it difficult to establish the real performances
Unless they only deal with truly residual waste, theses processes can undermine recycling and
composting. But as they need a certain amount of particular types of materials in order to work
effectively (paper, plastic, food waste) they are unlikely to be able to deal with truly residual
waste
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There are uncertainty about the real practical and financial performances
Many of the commercial gasification systems actually follow the gasification with combustion. In
doing so, many of the key theoretical differences between pyrolysis, gasification, combustion
become blurred
Like incineration, pyrolysis and gasification produce solid residues (8 to 15% of the original
volume of waste) like inert mineral ash, inorganic compounds, unreformed carbon for which a
promotion has to be found
Syngas must be cleaned before being promoted in a gas turbine or turbine; it is considered by
Juniper as a major technical risk factor in integrated MSW gasification with high efficiency
energy recovery
The waste has to be prepared before (sorting, drying, grinding)
for Seafield: even if these processes can work at a lower scale than incineration, the quantity of
screenings produced in al AVSE sites is still too low for such processes (2916t in 2009). This has
been confirmed by 3 firms I contacted (Energos-38 000t, Ebara, Thermoselect-100 000t).
Moreover, the fact that these technologies are quite new restricts the use of them for the moment.
69
Geothermal energy
Geothermal uses the heat stored in the earth, at the surface or very deeply, to produce heat or
electricity. Not every place has the potential for geothermal energy, and Seafield is not suitable for
geothermal electricity. Only geothermal heat could be considered.
Input: groundwater and soil
Output: heat/hot water or electricity
Principle and technologies:
Depending on the type of resources, heat or electricity can be produced. This is why geothermal
energy is classified into three types:
Very low temperatures: it uses the groundwater that is less than 100 m deep and with a
temperature lower than 30˚C or the fact that the shallow ground, the upper 3 m of the Earth,
maintains a nearly constant temperature between 10° and 16°C (thanks to the solar energy
adsorbed at the surface). This ground temperature is warmer than the air above it in the winter
and cooler than the air in the summer. Geothermal heat pumps take advantage of this resource to
heat and cool buildings.
Source: http://www.mightyoak.co.uk/aqua-wordpress/wp-content/uploads/2009/01/heatpumpschematic.gif
Low temperatures: it uses the groundwater with temperatures between 30 and 150˚C and at a
depth between 1 500 and 2 500 m. Geothermal reservoirs of hot water provide heat directly. This
is called the direct use of geothermal energy. A well is drilled into a geothermal reservoir to
provide a steady stream of hot water. The water is brought up through the well, and a mechanical
70
system - piping, a heat exchanger, and controls - delivers the heat directly for its intended use. A
disposal system then either injects the cooled water underground or disposes of it on the surface.
As the energy here is more important, geothermal at low temperatures is used in heat network
(urban heating), for industrial processes, for agricultural drying …
Source: http://www1.eere.energy.gov/geothermal/pdfs/directuse.pdf
Medium and high temperatures : it uses the groundwater with temperatures higher than 180˚C.
Here it is possible to produce electricity through a turbine. A geothermal power plant is like in a
regular power plant except that no fuel is burned to heat water into steam. The steam or hot
water in a geothermal power plant is heated by the earth. It goes into a special turbine. The
turbine blades spin and the shaft from the turbine is connected to a generator to make electricity.
The steam then gets cooled off in a cooling tower. There are three types of geothermal power
plants: dry steam, flash steam, and binary cycle.
71
Source: http://visual.merriam-webster.com/images/energy/geothermal-fossil-energy/production-electricity-from-
geothermal-energy.jpg
. Advantages:
It needs no fuel
Geothermal heat pumps use much less energy than conventional heating systems, since they
draw heat from the ground
Low heating costs and low maintenance costs (only to change the heat pump unit‟s air
filter)
Very low levels (sometimes none) of the air pollutants and greenhouse gases (due to the
pumps which run on electricity not necessarily coming from a renewable source)
.
Inconvenient:
Geothermal heating are very high installation costs and its positioning, since it requires big
yard for horizontal installation and a bedrock-free ground for vertical installation or a well or
pond. The Department of Energy estimates that the installation cost on a retrofit can be
recouped in two to ten years and sometimes as some experts say payback can be even more
than 20 years long
In some cases, a site that has happily been extracting steam and turning it into power for
many years may suddenly stop producing steam. This can happen and last for around 10 years
There aren‟t many places where a geothermal power station can be set up. Besides, hot rocks
of a certain kind are needed that can go down a particular depth where they can be drilled
for Seafield: the geological structure of the ground is too much broken and cracked to allow a
medium/high temperature geothermal power. We have to investigate if a (very) low temperature
geothermal is possible, and yet heat is not really a need on the site. Firstly, it would be better to
promote the waste heat than installing a geothermal device.
72
Heat from the sewage
Special heat exchangers patented by a Swiss firm are installed in sewage pipes for space heating
and hot water production. This could be a solution at Seafield, all the more so as the channels will
be covered thanks to the Odour Management Plan (the sewage temperature might be a little
higher). However, we have to see if it really can be interesting or if it would not be better to
promote the waste heat at first.
Input: the wastewater, which temperatures is 15˚C in the sewer on an annual average basis
Output: heat and hot water
Principle and technologies:
The waste water has a medium temperature of over 25°C when leaving the houses. In drains the
annual average is 15°C (18-22°C in summer and 10-12° C in winter ). The waste water is a
constant, renewable energy source on a comparatively high temperature level. With modern heat
pumps one reaches thereby usable temperatures of 65-70°C, sufficient for warm water production
and for heating new buildings.
This is what the Swiss company Rabtherm has been developing for the last 10 years. The
Rabtherm system is a heat exchanger installed in the pipes to extract the energy of the
wastewater and supply it through an intermediary thermal unit heat carrier (ITUHC) to the heat
pump. The system can be used in winter for the production of heating water and domestic warm
water (whole year) and in summer with small additional investment for production of cold water
for air conditioning systems (6°/ 12°). The heat exchanger cools down the wastewater by 2°C
(maximum 0,5°C as a 24 hours average). The energy is then transferred with water pipes to the
boiler rooms where the heat pump raises the temperature for heating and hot water to maximum
65°C.
In existing or new sewers, heat exchangers can be installed and connected to a heat pump. Heat
exchanger elements, made from high-grade stainless-alloy, are hollow, sandwich-type elements
measuring approximately 14-mm thick. An anti-fouling system on the surface of the heat
exchanger was added to optimize the process. The company says the heat exchanger has a service
life of at least 50 years and can withdraw approximately 2 to 6 kilowatts (KW) per square meter of
heat exchanger. To produce 1 kWh heat, 420 litres waste water are necessary
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Source: http://www.rabtherm.com/index.php?option=com_content&task=view&id=27&Itemid=28
Criteria for optimal use of the system are:
sewer diameter: min 400 mm for an installation in a new sewer, min. 800 mm for an
installation in an existing sewer
minimum wastewater flow (dry weather): 12 L/s
minimum wastewater temperature in winter: 8 °C
heat exchanger lengths: 9 to 200 m
minimum heating power: 80 kW
maximum distance from the sewer to the boiler room: 200 m
maximum building heating temperature: 70°C
Veolia Water in France has just started looking at the same type of heat exchanger but with
different companies: Uhrig and Kasag. The requirement for their devices is practically the same
as for Rabtherm‟s device.
There is another system which recovers the energy contained in the wastewater but not in the
pipe, directly in the building, before the sewage goes in the sewer. The process recovers the
Heat
exchanger
to be
installed in
an existing
pipe
Heat exchanger incorporated in a new pipe
Source: Degrés bleus, Suez
74
domestic (shower, bathtub, washing machine and dishwasher-20-33˚C) or industrial wastewater
(washwater, any hot water). After the heat exchanger, it is discharge in the sewer at a temperature
between 8 and 9˚C. The company which has developed this technology is
Biofluides Environnement.
Advantages:
It needs no fuel
Primary energy cost reduction: 20-30 %
CO2 reduction: 30-85 % depending on the system of electricity
generation used to drive the heat pump
Return on investment: 1 to 8 years
The heat exchanger form is adaptable according to the physical
constraints of the pipes, the flow rate, the energetic promotion
wanted
Inconvenient:
It may need an additional heating
You have to find a use for this heat within a short distance
The sewage must not be cooled down too much in order to avoid bad treatment conditions
for Seafield: energy in the form of heat is not the most wanted in Seafield compared to
electricity. It could be used to heat AVSE office but not Stirling office (too far). This low
temperature heat can not be used in the process. So, before considering this solution, it may be
better to promote the waste heat already present on the site (sludge at 45˚C in the sludge tank and
the sludge after the thermal hydrolysis when this technology will be implemented)
75
Solar photovoltaïque (PV)
Unlike solar thermal panels, PV panels produce electricity. However the poor solar resource in
Scotland and the costly price of panels do not make this technology a suitable solution at the
present time.
Input: solar PV panel, the sun
Output: electricity
Principle and technologies:
A solar PV panel constitutes of a group of photovoltaïque
cells which are made of two silicon layer, a semi-conductor
material. These cells create an electrical courant when a
photon hit them. Different technologies share the market:
Mono-crystalline cells: they are the most efficient
(yield between 14 and 20%) and also the most
expensive.
Poly-crystalline cells: they are a little less efficient
than mono (12-14%) but are less expensive to
manufacture.
Amorphous cells: it is the less expensive
technology but its yield is much lower than
crystalline cells (5-10%). However, they perform
better than the other types in cloudy conditions.
It is possible too to install a tracking system which will enable the panels to follow the sun in his
trajectory. It improves the yield by 25-40 % but the cost of such systems is up to twice the price of
a classic panel.
Solar resources in the UK: to soak up the maximum amount of solar energy, the panels must be
well oriented and inclined as shown below (35˚, S). Even with optimally-inclined south-oriented
PV modules, the global irradiation in Scotland is quite low compared to the rest of Europe, about
900 kWh/m2.
Source:
http://www.rise.org.au/info/Tech/pv/image009.jpg
76
Source: http://re.jrc.ec.europa.eu/pvgis/
Advantages:
It needs no fuel
It is scalable: additional units will produce proportional energy increases and it is easily
expandable
Unlike wind generators, or electricity plants, solar energy production is silent
Very little maintenance is required
Inconvenient:
Intermittent power source - energy is not available at night and also may not be accessible
in case of bad weather conditions. This requires complementary power station
Solar energy can be influenced by the presence of water vapour, pollution etc. in the air, which
may cause complexities
Panels ideally need to be able to face a south west to south east direction and should not be
overshadowed by trees or other obstructions
Due to their low yield (10-20%), they require a lot of space. Moreover, solar cells produce DC
which must be converted to AC (using a grid tie inverter) when used in current existing
distribution grids. This incurs an energy loss of 4-12%
PV panels are expensive
77
A quick economical analyse:
o 800 m2 poly-crystalline panels (96 kWp) optimally situated (35˚ inclined, S
oriented) at Seafield
o Mean price of a PV solar panel which is more than 10 kWp (≈100 m2):
5 000£/kWp 480 000£ (without the cost of the loan)
o Electrical production of the 96 kWp PV panels: 76 100 kWh/year
http://re.jrc.ec.europa.eu/pvgis/apps3/pvest.php#
o Feed in tariffs for PV [10; 100 kW] for the electricity produced: 31,4 p/kWh
during 25 years 23 895£/year
o If all this electricity is exported, the export tariff is 3 p/kWh 2 283£/year
o Total income per year: 26 176 £
o Return on investment: 18 years lower than the life of the panel (25-30 years)
but still very long
o If all the electricity is used on site: 76 100kWh we do not need to import at an
average price of 0.075£/kWh (2009 price) a saving of 5 708£/year
o Total income per year: 5 708+23 895= 29 603£
o Return on investment: 16 years lower than the life of the panel (25-30 years) but
still very long
for Seafield: PV panels are interesting because they produce the maximum of electricity during
the summer when the needs of the WWTP are the hugest. Nevertheless, currently the technology
is not very profitable due to its price and low efficiency. I advise to reconsider this solution in a
few years when the technology will be more advanced.
78
Solar thermal
These types of solar panels are used to produce hot water and heating. But because of the poor
solar resources in Scotland and the more important need of electrical energy on the site, solar
thermal does not seem to be the best solution.
Input: solar thermal panel, the sun
Output: heat and hot water
Principle and technologies:
Solar thermal panels are used for water heating, space heating,
pool heating and drying. The two main technologies for water and
space heating are:
Flat plat collector: the most common solar collector. It is an
insulated metal box with a glass or plastic cover (called the
glazing) and a dark-colored absorber plate. It is used for
applications that require temperatures below 90°C.
Source: http://www.onosisolar.com/up_files/p/Flat%20Panel%20Collector%20.jpg
Evacuated tube collector: it is for applications that require
temperatures higher than 90°C. The collectors are usually made of
parallel rows of transparent glass tubes. Each tube contains a glass
outer tube and metal absorber tube attached to a fin. The fin is
covered with a coating that absorbs solar energy well, but which
inhibits radiative heat loss. Air is removed, or evacuated, from the
space between the two glass tubes to form a vacuum, which
eliminates conductive and convective heat loss. This panel is more
expensive than flat panels but they are more effective, especially
with low solar radiation.
Source: http://www.clearchain.com/blog/images//2009/11/Solar-Evacuated-Tube-Collector-Heatpipe.jpg
The diagram below shows a simple water heating circuit. The solar collector contains two
independent circuits. An heat-transfer fluid circuit in a closed system comprises a solar collector,
the tubes and a small pump (needed to move the fluid through the circuit ) and a U-tube heat
exchanger in the water tank.
The cold fluid is moved by the pump, collects heat energy in the solar collector, goes to the u-tube
heat exchanger and transfers some of its heat to the water in the tank.
The second circuit, starts in a cold water feed which fills up the thank and pick up energy from the
U-tube heat exchanger. Once the water is warm it can be used in a tap water circuit. A
conventional system providing additional heating may be necessary.
79
Source: http://www.petervaldivia.com/technology/energy/image/solar/Solar-Water-Heating-Diagram.gif
Solar drying enable to dry agricultural product or even the sludge. The roof is made of a double
wall with air inside. This double wall plays the role of the solar collector as the external wall is
dark to absorbe radiations. The air between inside the double wall is heated and directed inside the
building. Air movement can be by natural convection or can be assisted using fans.
Source: Heliantis®, solar
sludge drying, SUEZ
80
Advantages:
It needs no fuel
It is scalable: additional units will produce proportional energy increases and it is easily
expandable
Broad range of uses
Unlike wind generators, or electricity plants, solar energy production is silent
Very little maintenance is required
Solar thermal systems don‟t require a large area of roof space
Inconvenient:
Intermittent power source - energy is not available at night and also may not be accessible
in case of bad weather conditions. This requires complementary power station
Solar energy can be influenced by the presence of water vapour, pollution etc. in the air, which
may cause complexities
Panels ideally need to be able to face a south west to south east direction and should not be
overshadowed by trees or other obstructions
for Seafield: first, Scotland is not the more sunny place: solar resources are limited and so the
return on investment can be very long. Secondly, heat and hot water production is not the main
demand on the site. We better have to focus on other technologies.
81
Wave/tidal energy
The UK has the best wave and tidal resource in Europe. Nonetheless, not every places are suitable
and the Firth of Forth does not seem to provide the good conditions for this marine renewable
energy. Moreover the devices face a number of challenges before they can meet their potential and
reach large-scale commercialisation.
Input: the sea and its movements
Output: electricity
Principle and technologies:
There are different kinds of technologies, at different stage of development. Here are the main
technologies:
Tidal energy
Seaflow from Marine Current Turbines Ltd is a 2 bladed
rotor connected to an electrical generator mounted on a
steel mono-pile drilled into the seabed. The blades turn in
the tidal stream (like wind turbines are driven by wind) and
the greater density of water means that although the blades
are smaller and turn more slowly, they still deliver a
significant amount of power. This is the world's first
successful offshore tidal turbine
TidEL from SMD Hydrovision consists of two
turbines mounted on a buoyant crossbeam. A full scale
device would consist of 15m diameter blades driving
two 500kW generators. The unit is buoyant and
tethered to the seabed, allowing it freedom of
movement. The turbines can automatically align
themselves down-stream of the tidal flow as it changes
during the day. It is still in development.
Stingray from The Engineering Business uses a
hydroplane, similar to an aeroplane's wing but in
water, to collect energy from the tide. This is attached
to a mechanical arm which changes the position of the
hydrofoil each cycle, and is also connected to a pump
which pressurises oil. This oil passes through a
hydraulic turbine which drives a generator to produce
electricity. Stingray is a seabed mounted machine,
designed for use in water up to a depth of 100m.
82
Wave energy
The Pelamis Wave Energy Converter from Pelamis
Wave Power Ltd consists of several large, floating
cylinders connected by a hydraulic system. As waves
pass under the device the cylinder joints pivot and
move hydraulic rams, pressuring oil and storing
potential energy. This high-pressure oil is released
through hydraulic turbines, driving generators
inside the device. In August 2004 Pelamis was
connected to the UK grid at the European Marine
Energy Centre (EMEC) in Orkney to be tested. A
commercial development was completed in September 2008 at the Atlantic coastline of northern
Portugal. This was the world‟s first commercial wave farm.
Limpet (Land Installed Marine Powered Energy
Transformer) from Wavegen, on the coast of Islay
in the Highlands of Scotland, is an onshore
Oscillating Water Column (OWC). Waves surge
into a chamber open to the sea and force air
through a Wells turbine, which can generate
power from air flowing in either direction. As the
waves recede, air is drawn back into the chamber
via the turbines, generating more power. Rated at
0.5MW, this device has generated power for the
local grid since 2000.
For more information, see http://www.bwea.com/marine/devices.html and
http://www.bwea.com/marine/devices2.html
Advantages:
It needs no fuel
It is more predictable than solar and wind power
Offshore turbines and vertical-axis turbines are not expensive to maintain and do not have a
large environmental impact
.
Inconvenient:
Some technologies are expensive to built and maintain due to the corrosive nature of salt
water
There are relatively few coastal locations in the world where the tidal range (the difference
between high and low tides) is large enough to justify exploitation of the available tidal
energy: the Fith of Forth is probably not the best place for such technologies ( see the Marine
Renewable Energy Resource Atlas http://www.renewables-atlas.info )
83
Wave energy is dependant on the waves: sometimes there will be loads of energy and
sometimes almost nothing
Tidal devices only provide power for around 10 hours each day, when the tide is actually moving in
or out
The electricity has to be conducted from the sea to the land and if the distance is too
important, there might be loses
It is still a technology currently in development
for Seafield: at the moment wave and tidal energy do not seem to be a suitable solution because
of the poor resources of the Fith of Forth, but it is interesting to follow the development of these
technologies and see if they may be an economical and technical solution in the future
84
Wet Air Oxidation (WAO)
Hydrothermal oxidation is used to oxidize liquid waste such as sewage or sludge. It has many
advantages such as reducing the amount of sludge, treating very loaded effluents with a very good
yield, producing energy that can be recovered… It is an interesting solution when other type of
sludge promotion (agriculture, incineration …) is not possible.
Input: digested sludge, sewage
Output: electricity, heat + a solid (mineral matter) + a liquid (Organic Matter (OM), N) + gas
Principle and technologies:
Also known as hydrothermal oxidation, this technique enables the treatment of wet waste that is
very loaded. The waste is oxidized in liquid state at high temperatures (150-650˚C) and high
pressure (15-300 bars) in the presence of dioxygen (air, air enriched in O2 or pure O2):
OM + O2 CO2 + H2O
There are two types of WAO:
Sub-critical: commonly called wet air oxidation, this reaction occurs at temperatures between
200 and 300˚C and at pressure comprised between 30 and 150 bars. In these conditions, the
liquid and vapour phases are distinct and in equilibrium. The residence time in the reactor
lasts between 3min to 3 hours. The oxidation yield is about 70-95%. The remaining 5-30% of
organic matter that has not been transformed into CO2 and H2O stays in the liquid phase and
is then treated by the WWTP.
Supercritical: this reaction occurs at temperatures higher than 374˚C and at pressure higher
than 221 bars. This specific point (221 bars - 374˚C) is called the critical point of water.
Source:
http://www.granit.net/image
s/pOvhDiagrA.gif
85
Beyond this point, water is in a supercritical phase. Within these particular conditions, water
acquires specific physical properties:
o Organic compounds are soluble; oil mixes with water
o Oxygen dissolves totally in water
o Mineral salts precipitate whereas they are very soluble in sub-critical water
The residence time of this reaction is very quick (less than one minute) and the yield is very
important too (>99%). The remaining liquid does not need to be treated and can be discharged in
the natural milieu.
The only energy to provide to the process is the difference of enthalpy between the entering
sewage and the outgoing one, whereas for incineration, energy must be provided continuously to
heat the air and the waste. The oxidation reaction is exothermal, which means that it releases
energy that can be getting back. Indeed, with a 15-20 g/L of COD, the process is autotherm.
Energy can be recovered under three levels:
Maximal recovery of heat: the sewage is cooled down and heat is used through a heat
exchanger
Electrical recovery in order for the process to be self-sufficient
Co-generation
Advantages:
No need to dry the waste before the oxidation (3,5-5,5% DS for the sludge)
No need to treat the fumes as some potential gas pollutants do not appear to be formed
(particulates, NOx, and dioxins…)
WAO decreases the amount of sludge
It can treat the effluent that are very loaded and to much diluted to be incinerated
Auto-combustion is achieved with only 15-20 g/L COD compared with 300-400 g/L COD for
the incineration
The solid can be promoted as a building material (cf. Technosand of Veolia)
This process can be adapted to small scale
.
Inconvenient:
Sub-critical oxidation does not perform a complete mineralization. The high organic
content of the effluent water will require further processing (e.g., biological treatment).
Corrosion is expected to be a severe problem with both technologies, requiring control by
suitable choice of material and/or control of pH. Corrosion is a particular problem with
supercritical water oxidation, where pH control has thus far led to plugging problems
It is limited to wastewaters containing oxidizable organic and inorganic compounds. For
example, WAO cannot destroy PCBs, some halogenated aromatics and some pesticides
for Seafield: this technology could be an interesting alternative to the current process (thermal-
hydrolysis + mesophile digestion + centrifugation) if the promotion of sludge via agriculture is
becoming difficult
86
APPENDIX 3: the outfall shaft, the best location to install a hydro turbine
Clean flow
outfall
87
outfall
Clean flow
storm flow
Weir to short sea outfall (when the flow is too important)
88
A simplified diagram of the outfall shaft
Strom flow clean flow
Width of channel: 4.5m
Depth: 52m
≈ 5m (circular curve-radius 4.93m)
Long sea outfall (2.8 km)
penstock screens screens penstock
Diameter: 7m
89
APPENDIX 4: the digesters’ heating circuit
The hot water circuit keeping the sludge in the digesters at 35˚C uses the heat from the two CHPs
and an additional help from boilers running with natural gas
The CHP produces electricity (that is used on site) and heat. On average, the energy is split as
follow:
38% electricity
40% heat
22% losses
Because the sludge in the digesters needs to be at 35˚C (mesophilic digestion), the sludge is
reheated via “sludge heat exchangers” (SHE). The reheating is possible because we use the heat
from the cooling down of the 2 CHPs. Below is a simplified drawing of the different circuits to
keep the digesters at 35˚C using the waste heat from the CHP.
Boiler 1 and 2 only run when the CHPs are not running.
But as the sludge will be hot enough after thermal hydrolysis, there is no need to heat the
digesters anymore. So the hot water circuit will be of no use anymore
90
Boiler 1
D6
CHP 1 internal
cooling circuit Q=45.5 m3/h
Hot water circuit Q=207 m3/h
Cold water 60˚C
Hot water 90˚C
Cold water 50-55˚C
Hot sludge
37-39˚C
Hot water 60-70˚C
Cold sludge 32-35˚C
CHP 2 internal
cooling circuit Q=44 m3/h
Hot water 90˚C
lukewarm water 68˚C
6 digesters D D1 D2 D3
Sludge circuits
D4 D5
Q=34.5 m3/h
Boiler 2
By-pass
91
APPENDIX 5: daily and seasonal variation of the flow coming to the outfall
Generally speaking, the flow rate for the main channel going to the outfall is about 3.5 m3/s.
Annual average clean flow rate
Year Flow rate m3/s
2006 3.5
2007 3.7
2008 3.4
2009 3.6
The flow changes during the day, according to the use of water by the inhabitants.
Flow variation during a day (summer months)
1500
2000
2500
3000
3500
4000
4500
5000
5500
00:00:
00
00:45:
00
01:30:
00
02:15:
00
03:00:
00
03:45:
00
04:30:
00
05:15:
00
06:00:
00
06:45:
00
07:30:
00
08:15:
00
09:00:
00
09:45:
00
10:30:
00
11:15:
00
12:00:
00
12:45:
00
13:30:
00
14:15:
00
15:00:
00
15:45:
00
16:30:
00
17:15:
00
18:00:
00
18:45:
00
19:30:
00
20:15:
00
21:00:
00
21:45:
00
22:30:
00
23:15:
00
hours
L/s
14/04/2009 19/05/2009 15/06/2009 15/07/2009
15/08/2009 14/09/2009 15/10/2009
92
There is clearly a pick at 2pm (lunch time minus the duration for the water to flow to the
WWTP). After that, the consumption slightly decreases until it reaches its lowest value at 6am,
with a small increase at 9pm. The flow rate in winter is a little higher than in summer.
Consequently of this daily variation, the turbine production will not be constant through out the
day. The lowest production will occur early in the morning, because the flow rate is low at that
time.
Flow variation during the day (winter months)
2000
2500
3000
3500
4000
4500
5000
5500
6000
00:0
0:0
0
00:4
5:0
0
01:3
0:0
0
02:1
5:0
0
03:0
0:0
0
03:4
5:0
0
04:3
0:0
0
05:1
5:0
0
06:0
0:0
0
06:4
5:0
0
07:3
0:0
0
08:1
5:0
0
09:0
0:0
0
09:4
5:0
0
10:3
0:0
0
11:1
5:0
0
12:0
0:0
0
12:4
5:0
0
13:3
0:0
0
14:1
5:0
0
15:0
0:0
0
15:4
5:0
0
16:3
0:0
0
17:1
5:0
0
18:0
0:0
0
18:4
5:0
0
19:3
0:0
0
20:1
5:0
0
21:0
0:0
0
21:4
5:0
0
22:3
0:0
0
23:1
5:0
0
hours
L/s
15/01/2009 15/02/2009 15/03/2009
15/11/2009 15/12/2009
93
APPENDIX 6: the working of an Archimedean screw to produce electricity
Source: http://www.sep.org.uk/catalyst/articles/catalyst_19_3_411.pdf
94
Example of an Archimedean Screw installed by Spaans Babcock on a WWTP in England
95
Source: Spaans Babcock
96
APPENDIX 7: power and production curve of a wind turbine
Source: http://www.wes18.com/files/pdf/Complete%20Description%20WES18.pdf
97
Obtaining a POWER CURVE
The power curve of a wind turbine is a graph that indicates how large the electrical power output
will be for the turbine at different wind speeds. Power curves are found by field measurements,
where an anemometer is placed on a mast reasonably close to the wind turbine (not on the turbine
itself or too close to it, since the turbine rotor may create turbulence, and make wind speed
measurement unreliable).
Basic Equation
The equation for energy recovery from the wind is as follows:
Coefficient of Performance
Not all the energy can be recovered from a wind stream. The theoretical maximum value for the
coefficient of performance is 0.593. An "ideal" wind turbine with this maximum value is known as
a Rayleigh-Betz machine. In practice the value of the maximum values of coefficient is in the
range 0.25 to 0.45. In general, the larger the machine the higher is the value. Also the use of
variable pitch rotors can optimise the coefficient of performance for a range of wind speeds.
Conversion Efficiency
This is the fraction of the energy available at the turbine hub which is converted into electricity.
For simplicity, the example value has been set at 0.7. In practice, the value is composed of two
elements, mechanical and electrical. The mechanical element is quite high with losses coming
from items like bearings, gearboxes (if any) etc. whilst the electrical part would come from the
specification of the generator.
Very simply, we just divide the electrical power output by the wind energy input to measure how
technically efficient a wind turbine is. In other words, we take the power curve, and divide it by
the area of the rotor to get the power output per square metre of rotor area. For each wind speed,
we then divide the result by the amount of power in the wind per square metre.
98
Area
This is the area swept by the rotor blades, the example calculation shows the power generated per
square metre. The range of sizes for wind turbines is shown in the table below:
Description Diameter (m) Area (m2) Power (kw)
Small < 2.5 5 <1
Medium 5 - 15 20 - 200 10 - 50
Large > 50 2000 > 1000
Density of Air
The density of air at sea level is 1.23 kg/m3. However, this density declines with altitude as
shown in the graph below:
Thus a turbine located at an altitude of 1,000m would produce approximately 80% of the power an
equivalent installation would produce at sea level.
Wind Speed - Effect of Height
Wind speed varies with height. At ground level (zero metres) the speed is low and turbulent and
at some higher altitude (say, 100m) it is faster and smoother. This is due to friction as wind passes
across the earth's surface. Whilst the nature of surface varies, it is common practice to use an
empirical relationship between height and speed:
The exponent (sometimes referred to as the wind sheer factor) is an average value for onshore
locations. A lower value, says 0.1, might be appropriate for offshore locations and a higher one,
say, 0.25 for urban or forest locations.
The standard height for meteorological observation wind speed data is 10m. This type of data is
the most readily available. As the power generated is proportional to the velocity cubed, there is
99
an advantage to be gained by locating the turbine on some form of tower, typically in the range 10
to 120 metres high. If site specific data is not available at the proposed height, an initial estimate
can be gained from scaling up data collected at 10m to the height of the proposed tower. Using
the above equation, the effect of height is shown in the graph below:
The graphic below illustrates the increase in wind speed with height in the context of rated
output.
The sample calculation assumes that the turbine is mounded on a 30 metre tower, thus if the
Rayleigh wind speed is 5 m/sec at 10m, this can be expected to increase by a factor of 1.17,
allowing a value of 5.85 to be used for the estimate, giving a 60% increase in output.
100
Wind Speed - Operating Range
At very low speeds (say less than 2 m/sec) the turbine will not rotate at all whilst at high speeds
(say greater than 25 m/s) it is necessary to limit or stop the turbine to prevent damage from over-
speeding.
In the sample calculation, it has been assumed that the turbine has an operating range of 2 - 25
m/sec and does not generate any power outside this range.
Form of Calculation
The estimation of power output with varying Rayleigh wind speed has been performed using a
table based on intervals of 1 m/sec. This method makes it relatively simple to handle variations in
coefficient of performance and operating range.
Obtaining a PRODUCTION CURVE
To go from the power to the production, the
wind variations are needed: this is Weibull
distribution. The model describes the
distribution of wind speed over the period of a
year.
If you measure wind speeds throughout a year,
you will notice that in most areas strong gale
force winds are rare, while moderate and fresh
winds are quite common.
The wind variation for a typical site is usually
described using the so-called Weibull
distribution, as shown in the image. This
particular site has a mean wind speed of 7 metres per second, and the shape of the curve is
determined by a so called shape parameter of 2.
The area under the curve is always exactly 1, since the probability that the wind will be blowing
at some wind speed including zero must be 100 per cent.
Half of the blue area is to the left of the vertical black line at 6.6 metres per second. The 6.6 m/s is
called the median of the distribution. This means that half the time it will be blowing less than 6.6
metres per second, the other half it will be blowing faster than 6.6 metres per second.
As you can see, the distribution of wind speeds is skewed, i.e. it is not symmetrical. Sometimes you
will have very high wind speeds, but they are very rare. Wind speeds of 5.5 metres per second, on
the other hand, are the most common ones. 5.5 metres is called the modal value of the distribution.
101
If we multiply each tiny wind speed interval by the probability of getting that particular wind
speed, and add it all up, we get the mean wind speed
The statistical distribution of wind speeds varies from place to place around the globe,
depending upon local climate conditions, the landscape, and its surface. The Weibull distribution
may thus vary, both in its shape, and in its mean value.
If the shape parameter is exactly 2, as in the graph above, the distribution is known as a
Rayleigh distribution. The shape parameter, k, tells how peaked the distibution is, i.e. if the wind
speeds always tend to be very close to a certain value, the distibution will have a high k value, and
be very peaked.
k = 2 for inland sites at an average latitude
k=3 near the coasts
k=4 for islands (cyclonic area)
Wind turbine manufacturers often give standard performance figures for their machines using the
Rayleigh distribution. This is the case for the production curve presented at the beginning of this
appendix for Wes 18.
An underlying assumption in the calculation is that the annual distribution of the wind speed is a
Rayleigh Distribution (itself a special case of the Weibull distribution in which the shape factor is
set to 2.0). For a given project is important to determine that this assumption is valid. Depending
on the nature of the site, another form of model may be appropriate, common alternatives being
the Weibull with appropriate shape factors.
Source: http://www.brighton-webs.co.uk/distributions/rayleigh_wind_2.asp
http://www.talentfactory.dk/en/tour/wres/weibull.htm
102
APPENDIX 8: turning low grade heat into electricity
Calculations are based on the ElectraTherm Waste Heat generator performances
ElectrTatherm is an American company and it is Thistle Energy, a Scottish firm, that will sell its
device for the UK market. ElectraTherm has employed the proven organic Rankine cycle in its
Waste Heat Generator solution. It uses a non-flammable, eco-friendly refrigerant selected for high
performance at low temperature. Surplus heat captured by the evaporator is used to "boil" the
working fluid into a vapor. Under pressure, the vapor is forced through the screw expander,
turning it to spin an electric generator. The vapor is cooled and condensed back into a liquid in
the condenser. The working fluid liquid refrigerant is pumped to higher pressure and returned to
the evaporator to repeat the process.
ElectraTherm combines traditional components with patented, cutting-edge technology to create
electricity from waste heat. ElectraTherm power systems use a closed-loop organic Rankine cycle
(ORC) to create pressure by boiling EPA-approved chemical working fluids into gas. The gas
expands in a one way system and turns a patented Twin Screw Expander, which drives a
generator to ultimately put out electricity.
Historically, ORCs incorporating turbo-expanders have not been commercially viable in sizes less
than 1MW. By replacing turbo-expanders with ElectraTherm's patented, robust, low-cost Twin
Screw Expander, users benefit from short payback on systems that provide unattended operation
and negligible maintenance. [f]
Further information about this equipment:
A minimum temperature of 85˚C
A minimum flow rate of 27 m3/h
Power of the device: 50 kW
Average costs (supply, delivery,
installation, commissioning): £200 000
Life time: 20 years
ElectraTherm does not install a waste heat generator if the payback period is higher than 3
years
Maintenance: 1 time/year
Net efficiency: 12-15%
It runs 8 000 h/year (91% of the time)
After 7 years of development, the firm has started to sell their device this year (2010), mainly
to supermarket
To have a higher amount of heat, it is possible to combine the three waste heat flows. We have to
see how it is technically feasible. The temperature will not be higher but the flow rate will be more
Minimum requirements for the best efficiency. However, if one of
these requirements is not achieved, it can be compensated by a higher
value for the 2sd characteristics
103
important. As a result, according to the formula Q=V. ∆T. 11,622, the amount of heat available
will be higher.
We will take into account the fact that the 3rd CHP will have been commissioned. Seafield
engineers say that with this additional CHP, the 2 others will work at 100% load. We
acknowledge this hypothesis.
Connecting the three heat sources can be done with heat exchangers and a separate hot water
circuit or by connecting the internal cooling circuit of the CHPs with the same hot water circuit.
Solution 1: a separate hot water circuit and heat exchangers
Solution 1 uses a separate hot water circuit with heat exchanger. As the 2 CHP will work at full
load, the power from the CHPs is 1 420 kW. If we had the hot water from the TH, the total waste
heat is 1 937 kW. The temperature of this circuit can be chosen depending on the flow rate. The
Electratherm generator seems to be more efficient with high temperature than with high flow
rate. According to the results of devices currently installed by ElectraTherm, the average yield is
4.2% (but is varies depending on the flow rate and the temperature). As a result, we could expect
an electrical output of 81 kWe, so two machines will be needed.
Electricity 81 kWe
CHP 1
CHP 2
Electratherm Waste Heat
Generator
Cold water to dump
Hot water circuit Flow rate to choose (better
to have a lower flow rate and a higher temperature)
Hot water from TH
600 kW
820 kW
517 kW
Total: 1 937 kW
104
Energy output of ElectraTherm generators installed
Available heat in kW Temperature of the hot
water in ˚C
Gross output in
kWe Yield
420 88 18 0.043
545 82-93 24 0.044
640 88 24 0.038
775 82-93 26 0.034
675 110 35 0.052
732 110 37 0.051
1640 90 54 0.033
With the 3rd CHP, the two old CHP are supposed to run more often. We will suppose they run
90% of the time (7 884h, lower than the 8 000h of the ElectraTherm machine). The electrical
production would be around 639 MWh/year.
However, all these figures are only estimations and to get more accurate results, a trial will need
to be done.
Solution 2: a connected hot water circuit
: by-pass + cooling in case the waste heat generator is not working
ElectraTherm Waste Heat Generator
Electricity
79 kWe
Hot water from TH
85˚C, 5.9 m3/h
Cold water to dump
61˚C, 5.9 m3/h
CHP1
75.5˚C, 45.5 m3/h
CHP2
80˚C, 44 m3/h
Hot water circuit
78˚C, 95.4 m3/h
105
As the flows are connected, the total flow rate is the addition of the individual flow and the
temperature is a pondered mean: 95.4 m3/s and 78˚C. The available power would be around 1 885
kW (the difference of temperature before and after the machine is said to be 17˚C). With the same
hypothesis as for solution 1, the output would be 79 kWe, ie 623 MWh/year (with 2 machines).
Nonetheless, it is not likely to be this amount, since the temperature is lower than what the
machine require (78˚C ≠ 85˚C).
Recently, Thistle Energy, with which I was in contact about the ElectraTherm device, decides to
move away from the ElectraTherm machine, and instead use the Calnetix machine. The
ElectraTherm machine was having reliability problems and delayed shipments. Thistle Energy is
about to install a machine on a landfill site near Glasgow and with 2 ROCs and saving on climate
change levy the estimated income is £ 120,000 / year. The cost of the machine plus installation is
£ 300,000. However, this ORC machine requires to higher temperatures (min 121 ˚C, 125 kWe of
power).
106
APPENDIX 9: comparison of the GHG emissions of landfill and incineration
Screenings products have a composition close to the MSW. Here are different data for the GHG
emissions of 2 ways of disposal of MSW: incineration and landfill. When data for the UK were
available, we focused on them.
It is important to notice that the GHG emissions will depend on the performance of the landfill,
the characteristics of the waste, and the recovery yield of the EfW plant.
In landfills, the biogas produced can be recovered and valorised into CHP. According to IPCC
(Independent Police Complaints Commission), only 7.7% of the gas escaped British landfills.
Source: Carbon accounting in the UK water industry: methodology for estimating operational emissions, Report Ref.
No. 08/CL/01/5, p.35
GHG emissions of MSW in Ireland
Landfill 1 = with minimal gas flaring
107
Landfill 2 = with gas recovery for electricity production.
Nota:
L1 – Limited gas collection, typical of the majority of existing landfills in Ireland. Gas collection
occurs at site periphery with an efficiency of 20% and is subsequently flared with no energy
recovery. The oxidation rate of the remaining CH4
is assumed to be 10%.
L2 – Best practice in accordance with new EU Landfill Directive. Gas collection efficiency is
assumed at 70% and as with L1 the oxidation rate of the remaining CH4
is 10%. Of the collected
gas, 60% is used for energy production (with an energy conversion efficiency of 30%) and the
remaining 40% of the collected gas is flared.
The net climate change impact of thermal treatment is dependant on a number of factors including
the waste composition and the resulting CO2 released from materials of fossil carbon (C) origin
(i.e. plastics and some textiles). The other key factor is the percentage of energy recovered and
utilised from the WTT plant, and the energy mix which it displaces
Source: GHG benefits of using municipal solid waste as a fuel in a thermal treatment plant, Carly Green, Department
of Biological and Environmental Science, University College Dublin http://www.ieabioenergy-
task38.org/projects/task38casestudies/Ire2_fullreport.pdf
GHG emissions of MSW in Europe EU 25
108
Source: International conference on municipal waste, October 2008
http://www.isrcer.org/newweb/upload/eventos/lipor/Jan_Manders.pdf
GHG emissions of MSW in England
The present study assessed the GHG emission impacts of three technologies that could be used
for the treatment of Municipal Solid Waste (MSW) in order to recover energy from it. These
technologies are Mass-Burn Incineration (MBI) with energy recovery, Mechanical Biological
Treatment (MBT) via bio-drying and Mechanical Heat Treatment (MHT), which is a relatively
new and uninvestigated method, compared to the other two. MBT and MHT can turn MSW into
Solid Recovered Fuel (SRF) that could be combusted for energy production or replace other fuels
in various industrial processes. Moreover the study estimated the climate change impact of the
expected increase on the amount of MSW treated for energy recovery in England by 2020.
Source: Assessment of the climate change impact of the technologies used for energy recovery from municipal waste: a
case for England, A. PAPAGEORGIOU1, J.R. BARTON
2, A. KARAGIANNIDIS
1
http://www.wasteandclimate.org/DocumentDownloadServlet?id=32&language=en
109
GHG emissions of MSW in England
Source: 2009Waste to Energy Schemes; Are they Deliverable?, Neil Swannick, chair of Greater Manchester Waste
Disposal Authority
110
http://www.apse.org.uk/presentations/09/07/frontline-services-climate-change-carbon-
reduction/SESS%202c%20Cllr%20Neil%20Swannick.pdf
GHG emissions of MSW in England
The principal components of Global Warming power (GWP) are summarised in Table 3. Some
elements have not been quantified because they are too uncertain, such as the GWP of the wheeled
bins and disposal of the rejects from the centralised treatment site. Rejects from FWD (Food
Waste Disposal units: a grinder under the sink) will go to the residual waste; rejects from MSW
composting and AD will also go to residual waste but at a later point of entry to the route. The
GWP associated with the additional biogas yield at a WWTP with AD has been derived from two
sources; it is encouraging that they are in good agreement. A further apparent omission from
Table 3 is the GWP associated with wastewater treatment but this has been shown (Monteith et
al. 2005) to be trivial in the context of this study because emissions are mostly short-cycle CO2 in
well-managed plants.
Source: Environmental impact study of food waste disposers for the County Surveyors Society and Herefordshire
Council and Worcestershire County Council, Dr Tim Evans BSc MS PhD CChem CEnv FCIWEM MRSC
https://www.joneca.com/Environmental_Impact_Study_v-8_part_1_EIS.pdf
111
GHG emissions of wastes in the UK
Source: DEFRA http://www.defra.gov.uk/environment/business/reporting/pdf/20090928-guidelines-ghg-
conversion-factors.pdf
Conclusion
GHG emissions from the combustion of MSW vary from –129 to + 150 kg CO2e/t MSW,
depending on the data source. For landfill, it goes from +150 (the +743 surely does not take into
account the biogas recovery) to +81.
So the environmental advantage of the incineration is not that clear and depends on numerous
parameters (type of waste, yield of the energy recovery of the landfill and the incinerator …)
112
APPENDIX 10: economical advantages of renewable energies: ROCs and FIT
Renewable Obligation Certificates (ROCs) and Feed in Tariffs (FITs) are the two governmental means to encourage the development of renewable energies in the UK.
The Renewable Obligation Certificates
The goal and working of the RO
The RO (Renewable Obligation) is the main support scheme for renewable electricity projects in
the UK. The Renewables Obligation Order (Scotland) came into effect in April 2002. Eligible
renewable generators receive Renewables Obligation Certificates (ROCs) for each MWh of
electricity generated. These certificates can then be sold to suppliers, in order to fulfil their
obligation. Indeed, the Orders place an obligation on licensed electricity suppliers in England and
Wales, Scotland and Northern Ireland to source an increasing proportion of electricity from
renewable sources. In 2005-06 it was 5.5 per cent (2.5 per cent in Northern Ireland). In 2006-07
the obligation is set at 6.7 per cent (2.6 per cent in Northern Ireland). In 2008 suppliers should
provide 7.8% of electricity from renewable sources in 2008, rising to 10.4% in 2010 and 15.4% in
2015. Scotland has its own Renewables Obligation system, with targets to supply 18% of
electricity from renewables by 2010.
Suppliers meet their obligations by presenting sufficient Renewables Obligation Certificates
(ROCs). Where suppliers do not have sufficient ROCs to meet their obligations, they must pay an
equivalent amount into a fund, the proceeds of which are paid back on a pro-rated basis to those
suppliers that have presented ROCs. Suppliers can either present enough certificates to cover the
required percentage of their output, or they can pay a „buyout‟ price for any shortfall. All proceeds
from buyout payments are recycled to suppliers in proportion to the number of ROCs they
present. The buyout price is set each year by Ofgem, and in 2007/08 stands at £34.30/MWh, and
ROC trading is administered by Non-Fossil Purchase Agency Ltd.
These certificates can be sold on the open market to companies that need them to make up their
shortfall. Suppliers can then present enough certificates to cover the required percentage of their
output. According to the British Wind Energy Association (BWEA), ROCs have traded as high as
£47/MWh but there is no guarantee that they will remain at this price.
The Government intends that suppliers will be subject to a Renewable Obligation until 31 March
2027.
113
Example for the anaerobic digestion at Seafield:
Year Buyout price
£/ROC Recycle price £/ROC
Total price
£/ROC Sold for £/ROC
2008-09 35.76 18.61 54.37 48.93
Price decided by
the government
The fee that electrical
companies have to pay
if they do not have
enough “green”
electricity and that is
then redistributed to
generators
Since 2007, Veolia
Water sold its ROC on
the market to electricial
companies so that they
can achieve the required
percentage of “green”
electricity
The reform: ROCs banding
Since April 2009, the rules 1MWh produced receive 1 ROC is not true anymore for the new
installations: it is to encourage the new technologies such as wave and tidal energy, gasification,
pyrolysis, offshore wind ….
Generation type Definition ROCs/MWh
Hydro-electric Electricity generated by a hydro generating station.
NB The current restrictions on pre-existing hydro above 20MW in capacity will continue to apply.
1
Onshore Wind Electricity generated from wind by a generating station that is not
offshore (see offshore below). 1
Offshore Wind
Electricity generated from wind by a generating station that is offshore. A generating station is offshore if:-
(i) its turbines are situated wholly or mainly in offshore waters, and (ii) it is not connected with dry land by means of a permanent structure
which provides access to land above the mean low water mark.
1.5
Wave Electricity generated from capture of the energy created from the motion
of waves on the sea. 2
Tidal Stream Electricity generated from the capture of the energy created from the
motion of tidal currents in the sea. 2
Tidal Impoundment – Tidal Barrage
Electricity generated by a generating station driven by the release of water impounded behind a barrier using the difference in tidal levels and that barrier is connected to both banks of a river and is less than 1 GW
declared net capacity.
2
Tidal Impoundment - Tidal Lagoon
Electricity generated by a generating station driven by the release of water impounded behind a barrier using the difference in tidal levels and which is not a tidal barrage and is less than 1 GW declared net capacity.
2
Solar Photovoltaic
Electricity generated from the direct conversion of sunlight to electricity. 2
Geothermal Electricity generated using naturally occurring subterranean heat. 2
Geopressure Electricity generated using naturally occurring subterranean pressure. 1
Landfill Gas Electricity generated from the gas formed by the anaerobic digestion of 0.25
114
material in a landfill. “Landfill” has the meaning given in Article 2(g) of the Landfill Directive
(1999/31/EC).”
Sewage Gas Electricity generated from the gas formed by the anaerobic digestion of
sewage. 0.5
Energy from Waste with CHP
Electricity generated from the combustion of waste in a qualifying combined heat and power generating station.
1
Gasification / Pyrolysis
Electricity generated from the conversion of waste or biomass into a liquid or gaseous fuel, or both, for use in a generating station, by the
processes of gasification or pyrolysis or any combination thereof. 2
Anaerobic Digestion
Electricity generated from the gas formed by anaerobic digestion of material which is neither sewage nor landfill.
2
Co-firing of Biomass
Electricity generated from biomass by a generating station in a calendar month in which it has generated electricity partly from fossil fuel and
partly from biomass 0.5
Co-firing of Energy Crops
Electricity generated from energy crops by a generating station in a calendar month in which it has generated electricity partly from fossil
fuel and partly from energy crops “Energy crop” means a plant crop planted after 31st December 1989
which is grown primarily for the purpose of being used as fuel or which is one of the following:
(a) miscanthus giganteus; (b) salix (also known as short rotation coppice willow); or (c) populus (also known as short rotation coppice poplar).
1
Co-firing of Biomass with
CHP
Electricity generated from biomass by a qualifying combined heat and power generating station in a calendar month in which it has generated electricity partly from fossil fuel and partly from biomass, and where the
fossil fuel and biomass have been burned in separate boilers
1
Co-firing of Energy Crop
with CHP
Electricity generated from energy crops by a qualifying combined heat and power generating station in a calendar month in which it has
generated electricity partly from fossil fuel and partly from energy crops, and where the fossil fuel and energy crops have been burned in separate
boilers.
1.5
Dedicated Biomass
Electricity generated from biomass, except for electricity generated by a generating station in a calendar month in which it has generated
electricity partly from fossil fuel and partly from biomass 1.5
Dedicated Energy Crops
Electricity generated from energy crops, except for electricity generated by a generating station in a calendar month in which it has generated
electricity partly from fossil fuel and partly from energy crops 2
Dedicated Biomass with
CHP
Electricity generated from biomass by a qualifying combined heat and power generating station in a calendar month in which it is fuelled
wholly by biomass. 2
Dedicated Energy Crops with CHP
Electricity generated from energy crops by a qualifying combined heat and power generating station in a calendar month in which it is fuelled
wholly by biomass. 2
For more details, see http://chp.decc.gov.uk/cms/roc-banding/?phpMyAdmin=ff232c1d3b302ac6e951f554eeeaefdf
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The Feed in Tariffs (FITs)
The goal and working of the FITs
The government has introduced the FITs Order on 1st April 2010. This new scheme is intended
to encourage the uptake of small-scale low carbon technologies up to 5MW, though tariff
payments made on both generation and export of produced renewable energy. Suppliers play
the main customer-facing role for this scheme. Their role is to take generators through the
registration process, take regular meter readings and make payments. Not all suppliers will
offer Feed-in Tariffs. Generators are advised to contact their supplier in the first instance to
enquire about applying under the scheme. A list of participating suppliers can be found on the
Ofgem website.
http://www.ofgem.gov.uk/SUSTAINABILITY/ENVIRONMENT/FITS/RFITLS/Pages/rfi
tls.aspx
The Tariffs give three financial benefits:
A 'generation' tariff based on the total generation and the energy type; it is a payment for all
the electricity you produce
An 'export' tariff for any energy Exports when generating more than you need
Lower bills from your supplier for the energy you import from them because you are now
producing some of the energy you use
Eligibility
The maximum declared net capacity under the scheme is 5 MW and supports the following
technologies:
Photovoltaic
Wind
Hydro
Anaerobic digestion (beware, AD of sewage and landfill biogas are not covered by the FITs)
Micro CHP (less than 2kW)
Two categories of generators are recognized:
microgenerators (with a declared net capacity (DNC) of 50kW or less)
small generators (with a DNC greater than 50kW and up to and including 5MW)
Microgenerators (<50 kW)
Microgenerators in the following technologies covered by the FITs are no longer eligible for support under the RO:
Anaerobic digestion
Hydro
Photovoltaic
Wind
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Such installations are required to use Microgeneration Certification Scheme (MCS) eligible products instlled by a MCS accredited supplier. http://www.microgenerationcertification.org/Home+and+Business+Owners/Microgeneration+Technologies
Small generators (50kW- 5MW)
Operators of any new PV, wind, hydro or AD small generating stations that commissioned on or
after 1 April 2010 have the one-off option of applying under the RO Orders or the FIT scheme.
Generators will need to apply for accreditation through the ROO-FIT process via Ofgem‟s
Renewable and CHP Register.
http://www.ofgem.gov.uk/Sustainability/Environment/RCHPreg/Pages/RCHPreg.aspx
Multiple installations of the same technology type on a site will be viewed as one combined
installation regardless of whether any particular part of the installation is an eligible installation
under FITs or not, or if they have different owners. For example, if you install a two 1 MW wind
turbine the 1st year, you will receive only 4.5p/kWh (see table below) because the total power of
the installation is greater than 1.5MW. But if you install the first 1MW turbine the 1 st year and
then the second 1MW turbine the next year, the 1st turbine will receive 9.4p/kWh and the 2sd
one 4.5p/kWh.
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Source: Feed-in Tariff Scheme: Guidance for Licensed Electricity Suppliers
The rate of the FITs
They are 2 tariffs:
An export tariff: you get an extra payment of 3p/kWh for the electricity exported to the grid. It is index linked to the RPI (Retail Price Index).
A generation tariff: see the table below. The tariff is index linked with the RPI too.
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Table of Feed-In Tariff levels
Energy Source Scale
Generation Tariff
(p/kWh)[A]
Duration
(years)
April 2010-March 2011
April 2011-March 2012
April 2012-March 2013
Anaerobic digestion ≤500kW 11.5 11.5 11.5 20
Anaerobic digestion >500kW 9.0 9.0 9.0 20
Hydro ≤15 kW 19.9 19.9 19.9 20
Hydro >15 - 100kW 17.8 17.8 17.8 20
Hydro >100kW -
2MW 11.0
11.0 11.0 20
Hydro >2kW - 5MW 4.5 4.5 4.5 20
Micro-CHP[B] <2 kW 10.0 10.0 10.0 10
Solar PV ≤4 kW new[C] 36.1 36.1 33.0 25
Solar PV ≤4 kW
retrofit[C] 41.3
41.3 37.8 25
Solar PV >4-10kW 36.1 36.1 33.0 25
Solar PV >10 - 100kW 31.4 31.4 28.7 25
Solar PV >100kW -
5MW 29.3
29.3 26.8 25
Solar PV Standalone[C] 29.3 29.3 26.8 25
Wind ≤1.5kW 34.5 34.5 32.6 20
Wind >1.5 - 15kW 26.7 26.7 25.5 20
Wind >15 - 100kW 24.1 24.1 23.0 20
Wind >100 - 500kW 18.8 18.8 18.8 20
Wind >500kW -
1.5MW 9.4
9.4 9.4 20
Wind >1.5MW -
5MW 4.5
4.5 4.5 20
Existing generators transferred from RO
9.0
Notes:
[A]: These tariffs are index-linked for inflation as further described here.
[B]: This tariff is available only for 30,000 micro-CHP installations, subject to a review when
12,000 units have been installed.
[C]: These terms are defined as follows:
“Retrofit” means installed on a building which is already occupied “New Build” means where installed on a new building before first occupation “Stand-alone” means not attached to a building and not wired to provide electricity to an
occupied building
In the 3rd year, tariffs are likely to be lower; the estimation is a decrease of 7%. So to benefit from the present tariffs, we must hurry up.
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For more information on the FIT, see http://www.ofgem.gov.uk/SUSTAINABILITY/ENVIRONMENT/FITS/Pages/fits.aspx
http://www.ofgem.gov.uk/SUSTAINABILITY/ENVIRONMENT/FITS/Documents1/Ofgem-FIT%20Guidance%20Document%20for%20Licensed%20Electricity%20Suppliers%20(FINAL%20FOR%20PUBLICATION).pdf
The installed capacity and the declared net capacity
The scale of the FIT is based on the DNC. The following definitions come from the Statutory Instrument, by reference to the Standard Licence Conditions:
Total installed capacity (also called rated capacity): the maximum capacity at which an Eligible Installation could be operated for a sustained period without causing damage to it
Declared net capacity: the maximum capacity at which the installation can be operated for a sustained period without causing damage to it, less the amount of electricity that is consumed by the plant
However, for renewable energies, the input is not constant and will vary with the availability of the resource (wind, sun, water). Very broadly, the DNC is a measure of the equivalent capacity of base-load plant (coal, gas, nuclear) that would generate the same average annual energy output as the renewable plant. The ETSU, a unit supporting the UK Department of Trade and Industry, has defined factors to calculate the DNC.
DNC = (installed capacity – energy used by the plant)* factor
Type of renewable energy Factor
Solar 0.17
Wind 0.43
Tidal/wave 0.33
Others (hydro, …) 1
Source: http://www.tvenergy.org/pdfs/SEE-Stats%20MSc%20Thesis.pdf p.12
http://www.publications.parliament.uk/pa/ld199899/ldselect/ldeucom/78/7805.htm paragraphe 173
How to choose between ROCs and FITs?
You have the choice between the 2 schemes only for generators bigger than 50kW and installed
after April 2010. The advantages of the FITs are that it is a fixed tariff, only linked to inflation,
whereas the ROCs‟ prices fluctuate with the market because ROCs are sold on the market.
Moreover, ROCs will be available only until 2027, so if for example you install a wind turbine in
2011, you will be able to receive the FITs until 2031 or ROCs until only 2027. Furthermore, FITs
tariffs are most of the time more interesting than ROCs (on average, ROCs are sold at
0.5£/kWh)
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References and bibliography
1 http://www.veoliawater.co.uk/en/contact-us/
2 http://www.publications.parliament.uk/pa/ld200708/ldselect/ldeucom/175/175.pdf
3 http://www.restats.org.uk/statistics_national.htm
4 http://www.scotland.gov.uk/Topics/Business-Industry/Energy/Energy-sources/19185/17612
5 http://www.homeheatingguide.co.uk/blog/uk-falls-short-of-2010-renewable-energy-
target.html
6 http://www.scotland.gov.uk/Topics/Business-Industry/Energy/Energy-sources/19185/17612
7 http://www.zerowastescotland.org.uk/latest_news/scotlands_zero.html
8
http://www.scottishwater.co.uk/portal/page/portal/SWE_PGP_NEWS/SWE_PGE_NEWS/I
NFO_CLIM_CHANGE/NEWS_CLIM_QA
9
http://www.microgenerationcertification.org/Home+and+Business+Owners/Microgeneration+
Technologies
10 to calculate the average wind speed with the NOABL database http://www.renew-reuse-
recycle.com/noabl.pl?n=503
Carbon Trust tool http://www.carbontrust.co.uk/emerging-technologies/current-focus-
areas/offshore-
wind/_layouts/ctassets/aspx/windpowerestimator/WindPowerEstimatorIntro.aspx
Explanation of the databases: Small scale wind energy - Policy insights and practical guidance
(CTC738), p.12 and 28
http://www.carbontrust.co.uk/Publications/pages/publicationdetail.aspx?id=CTC738
11 Caractérisation, traitabilité et valorisation des refus de dégrillage des stations d‟épuration,
Ronan LE HYARIC, November 2009
12 Defra data, http://www.defra.gov.uk/environment/business/reporting/pdf/20090928-
guidelines-ghg-conversion-factors.pdf p.11
13 “Energy use in offices-energy efficiency best practice”: typical consumption of a naturally
ventilated cellular: 151 kWh/m2/year http://www.cibse.org/pdfs/ECG019.pdf).
14 Defra data, http://www.defra.gov.uk/environment/business/reporting/pdf/20090928-
guidelines-ghg-conversion-factors.pdf p.7
15 Water discount
http://customs.hmrc.gov.uk/channelsPortalWebApp/channelsPortalWebApp.portal?_nfpb=true&_pa
geLabel=pageExcise_ShowContent&propertyType=document&id=HMCE_CL_000509#P424_39279
121
Bibliography
Bacon Ian (TV Energy), Davison Ian (MWH), February 2004, Low Head Hydro Power in the
South-East of England – A Review of the Resource and Associated Technical, Environmental and Socio-
Economic Issues, p.20-35
Carbon Trust, 2008, Small-scale wind energy-Policy insights and practical guidance, p.12 and 28
Khan Zaffer (Rowan House), December 2008, CHP Engine Waste Heat Study
Le Hyaric Ronan, 2009, Caractérisation, traitabilité et valorisation des refus de dégrillage des stations
d’épuration
Ofgem, April 2010, Renewables Obligation: Guidance for generators
Complementary bibliography
Antonini Gérard, Hazi Mourad (étude Ademe/Procedis),2001, PYROLYSE – GAZEIFICATION
DE DECHETS SOLIDES-Etat de l’art des procédés existants-Faisabilité de traitement d’un déchet par
Pyrolyse ou Gazéification
Fontana André (Université libre de Bruxelles, Solvay Business School, Centre Emile Bernheim),
2007, Les techniques thermiques : Pyrolyse – Thermolyse et Gazéification
Office Wallon des Déchets, Aout 2003, Analyse des Plans Stratégiques des Intercommunales et de la
Gestion des Déchets Ménagers et Assimilés et des DIB en Région Wallonne
E. Piat, P. Camacho, W. Ewert, J. Kopp, K. Panter, S.I. Perez-Elvira, Combined Experiences of
Thermal Hydrolysis and Anaerobic Digestion-latest thinking on hydrolysis of secondary sludge only
