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May/June 2013Issue 3 • Volume 4
Regional focus: Scandinavia
Shifting focusThe largest natural gas fuelling chain in the uS is investing heavily in renewables
Compare and contractRaw material scarcity is still impacting the pellet market in Scandinavia
This degression will not standa change to the RHI is needed to avoid the risk of unnecessary tariff degression
Issue 3 • Volume 4
May/June 2013
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ISSN 2046-2476Front cover image courtesy of ADBA
contents Bioenergy
Contents2 Comment3 Biomass news8 Biopower news9 Biogas news14 Biopellet news17 Technology news 25 Incident report 26 Green page 29 US House farm bill removes funding certainty A small round-up as the US moves towards sealing its
farm bills which will affect energy sectors30 IBTC: Setting the standards for torrefied biomass32 Plant update – Scandinavia34 Power to neutrality EnaEnergiCEOexplainswhyheisnotsatisfiedwith
simply being a ‘provider’ of renewable energy35 Looking long-term CoulddiversificationbeonthecardsatNorwegian
pellet company Pemco Trepellets36 Compare and contract In a region dense with forestry it’s surprising to learn that raw material scarcity
is still one factor impacting the pellet market in certain parts of Scandinavia 39 Danish power in the Far East An abundance of feedstock and change of attitude toward renewable
energy has made China the destination of choice for PlanEnergi 40 Denmark’s hot topic 41 This degression will not stand A small but important change to the Renewable Heat Incentive is
needed to avoid the risk of unnecessary tariff degression43 Hammering coal Biomassisfindinganicheasmoreandmorepower
plants look for alternatives to coal45 Retrofitting for the future 47 Hybrid theory A Germany-based paper mill needed a biomass system that seemingly
did not exist – so how did it get to where it wanted to go?49 Achieving renewable compliance50 Shifting focus The nation’s largest natural gas fuelling chain is investing heavily in renewables,
and wants to provide biogas producers access to an untapped market52 New additives address biomass boiler operational issues Fouling, corrosion and agglomeration issues related to
biomass combustion can be mitigated using additives54 The grass can be greener 55 Success is tough times 57 Cleaning up AUSgasificationplantchosetouseawetsyngas-cleaning
system as opposed to a solely dry technology59 Food waste digestion becomes reality in Somerset62 The coal copycat The start-up of two torrefaction plants could prove industry game-changers 64 Digesting the possibilities 65 Attention to detail 66 An Insight into ADBA 76 Event listing Ad index
Bioenergy Insight May/June 2013 • 1
Follow us on Twitter: @BioenergyInfo
Consulting Engineers First ChoiceHurst biomass fired systems lead the alternative energy boiler market with innovative “Hands Free” solid-fuel-feed and combustion designs.Complete modular construction for easy low cost installation. Husrt has 46 years specializing in custom design of biomass steam plants and cogeneration systems.
MAY/JUNE 2013Issue 3 • Volume 4
Regional focus: Scandinavia
Shifting focusThe largest natural gas fuelling chain in the US is investing heavily in renewables
Compare and contractRaw material scarcity is still impacting the pellet market in Scandinavia
This degression will not standA change to the RHI is needed to avoid the risk of unnecessary tariff degression
FC_Bioenergy_May/June_2013.indd 1 04/06/2013 17:09
Bioenergy Insight May/June 2013 • 27
• Value-adding solutions for boiler performance •
Aurora™ Solutions eliminateslagging, fouling & corrosion
www.imerys-aurora.com
Aurora™ Solutions treatthe entire fireside system
Aurora™ Solutions broadenyour fuel portfolio
A4_Propal_BioenergyV1:Mise en page 1 31/05/2013 15:16 Page 1
Bioenergy biomass boilers
52 • May/June 2013 Bioenergy Insight
Fouling, corrosion and agglomeration issues related to biomass combustion can be mitigated using additives
New additives address biomass boiler operational issues W hile
approximately 11% of the world’s total energy
is provided by biomass combustion1, operational problems in biomass boilers can arise from ash-forming elements in fuels. These include silicon (Si), calcium (Ca) and alkali metals, of which potassium (K) is the most prevalent in biomass.
Alkali metals are released during combustion as vapour phase alkali chlorides, hydroxides and sulphates. These cause fouling and corrosion, necessitating periodic tube cleaning or even replacement.
Additionally, alkali compounds also react with silica and form low melting
silicates which enhance slagging and the formation of sticky, agglomerated ash. This ash is problematic for bottom ash handling due to the creation of large clinkers which require additional work time for removal.
Feedstock
Biomass feedstocks are sourced primarily from wood yet a variety of agro-waste can also be used for combustion. Residual materials and byproducts including bark, sawmill residuals such as sawdust and wood shavings, and energy crops grown specifically to create biomass feedstocks such as willow and switchgrass, can all be viable materials. Pelletised wood
and agricultural residues are easy to handle making them a popular option, but they also contain the ash-forming elements that contribute to deposits and corrosion.
These non-wood feedstocks can pose increased challenges related to deposits. And the more ‘exotic’ fuel options show increasing tendencies to contribute to deposits such as slag, fouling, agglomerations and clinkers.
One option for avoiding these increased deposit-related issues could be to simply avoid materials containing significant amounts of alkali including short rotation crops such a straw or fast growing forest residues such as leaves and
twigs. This would, however, limit biomass flexibility and lessen the opportunity to utilise feedstocks that are economical by virtue of their proximity to the heat/power generating facility.
A more preferable countermeasure for dealing with these deposit-related issues is mitigation through dosage of additives.
Case study
Norbord is a global manufacturer of wood-based panels used in the construction, furniture and DIY sectors, headquartered in Toronto, Canada. At its UK-based medium density fiberboard (MDF) plant in Increasing tendency to form deposits utilising selected biomass feedstocks
Typical tube fouling after six weeks in operation
Source: Imerys
biomass boilers Bioenergy
Bioenergy Insight May/June 2013 • 53
Cowie, Scotland Norbord was experiencing fouling issues in a 15MWth travelling grate boiler used to heat thermal oil consumed in the ~280˚C MDF mat hot pressing process prior to final trimming and packaging of finished MDF sheets.
Fuel for the boiler, a mixture of wet wood fibres and dry wood fibre, is fed directly into the grate via dual feed screw conveyors. The fuel analysis indicated high alkali metal and chlorine content which was believed to be contributing to heat exchanger tube fouling and corrosion, ash accumulation, large bottom ash clinkers and high solids levels in the fly ash.
The boiler required shutdown every four to six weeks to address thermal oil heat exchanger tube fouling.
Also, large and coarse bottom ash clinkers caused plugging of the grate and, at times, blocked the bottom ash conveyor. Plant operators commonly had to open the boiler in difficult conditions during operation to break down the larger clinkers into
more manageable pieces.In addition, the high
level of suspended and dissolved solids in the boiler flue gas required a wet electrostatic precipitator (WESP) for removal. The volume of high solids in the fly ash contributed to unplanned outages and high maintenance costs for the WESP sludge pumps.
In October last year, a 54-day trial was conducted at the Cowie plant for the purpose of evaluating the effects of dosing Aurora, an additive manufactured by solution provider Imerys, headquartered in France, into the boiler with the fuel.
Aurora is a proprietary fuel additive which prevents the formation of slag, fouling and corrosion by reacting with the alkalis in the fuel. Once delivered into the boiler, Aurora is heat processed from a hydrous to a dehydrated form which in turn reacts with the vapour phase alkalis.
The alkalis are preferentially captured by the heat-processed Aurora, controlling the deposit mechanism by forming
compounds with melting points above the operating temperature of the boiler. This process prevents the formation of sticky alkali-silicate layers which bind deposits together. The resulting agglomerates are thus smaller and friable, allowing easy removal with the boiler ash.
During the trial period, Aurora was added onto the main fuel feed conveyors using an injection skid. Boiler availability, efficiency, heat output, fuel injection set point (feeding screw frequency) and WESP behaviour were monitored during the trial period and compared to a 76 day reference period just prior to the commencement of the trial.
Findings
Several improvements were observed, notably:• There were no boiler
shutdowns due to fouling, slagging or bottom ash agglomeration during the 54 day trial period. Boiler tubes remained clean
and backpass fouling was dramatically decreased.
• Boiler efficiency improved; the study compared the average heat output of the boiler and feeding conveyor screw frequency before and during the trial and found the average heat output of the boiler increased by 11% and the feeding conveyor screw frequency decreased by 10%.
• A reduction of suspended and dissolved solids in the WESP was observed. Aurora, by reacting with volatile alkali compounds released in the boiler, forms stable phases that become trapped in the bottom ash thus accounting for the reduction of solids.
• Finally, there was no blockage of the stoker grate or bottom ash conveyor. Examination of the bottom ash clinkers showed they were smaller and more friable. In addition to reducing maintenance costs for the bottom ash conveyor, this positively impacts health and safety as operators can avoid frequent opening of the boiler to break down large clinkers.
Norbord today also utilises Aurora to control fouling in biomass boilers at two of its oriented strand board plants in North America. Andrew Taylor, process and technology manager for Norbord Europe, says: ‘We continue to utilise Aurora to realise these benefits and evaluate added efficiency improvements.’ l
References:1Overand, R., Direct Combustion of Biomass, National Renewable Energy Laboratory, Golden, Colorado, USA Encyclopedia of Like Support Systems http://www.eolss.net/Eolss-sampleAllChapter.aspx
For more information:This article was written by Olivier Haerlingen, technical sales manager Europe, Power and Energy ([email protected]), and David Osby, global product manager, for Aurora, Imerys ([email protected])
Top (left) and bottom (right) of thermal oil heat exchanger following the 54 day trial period
