2.5. DIRECT APPLICATION TECHNOLOGIES AND PROJECT …...PRITISKA REGULATION PANEL 64ºC 30ºC Deaeration HOT WATER BOILER 4 MW SOLENOID VALVE Sensors of the ex-ternal climate: tem-perature,

Kiril Popovski, Sanja P. Vasilevska: DIRECT APPLICATION TECHNOLOGIES AND PROJECT DEVELOPMENT

91

2.5.DIRECT APPLICATION TECHNOLOGIES

AND PROJECT DEVELOPMENT

Kiril Popovski, Sanja Popovska VasilevskaSt. Kliment Ohridski UniversityFaculty of Technical SciencesBitola, Republic of Macedonia

Key words: Application technologies, development, exploitation

Summary: Normal uses of low enthalpy geothermal energy are related with heating pur-

poses as are (Fig.1):_ Space heating and domestic hot water._ Agricultural applications of heat;_ Aquaculture._ Industrial applications of heat, like hot water,

drying etc._ Desalination of sea or brackish water._ Combination of some or all listed consumers

(district heating systems).

_ Some other non characteristic uses (snow melting, etc.).However, there is not only one technology for

extracting the heat from the geothermal resourceand its supply to concrete user. Each one of listedpurposes uses particular sets of already developedtechnology(ies) in order to meet the concrete users’requests.

Some of the particularities connected to thecomposition of optimal technology chains for geo-thermal energy use for concrete uses but also with aconcrete resource on disposal are discussed in thispaper.

(Lund, Freeston, 2000)

Fig.1. Different direct uses of geothermal energy in the world

INTRODUCTION

Direct application of geothermal energy beca-me the main line of development of geothermalenergy use during the recent decade. Differentapplication technologies have been developed orthe existing ones for classic fuels use have beenaccommodated, enabling very wide field of pos-sible use (Fig.1). However, still, it is not possible(and it shall not be) to speak about some kind of

common technology for the use heat from the earthbecause also a list of local particularities influencethe composition of a concrete project and economyof its application.

The factors that must be considered when as-sessing the economic viability of a geothermal pro-ject vary from project to project, from conversiontechnology to conversion technology, and especial-ly from electrical generation to direct use. There

International Geothermal Days POLAND 2004. Zakopane, September 13-17, 2004Imternational Course on Low Enthalpy Geothermal Resources – Exploitation and Development

92

are, however, a number of factors common to allprojects, although actual cost and impact on projecteconomics will be, to a large extent, dependent up-on resource characteristics and national or evenlocal political and economic circumstances.

Therefore, when speaking about the techno-logy of direct application of geothermal energy, weare dealing more with chains, composed of differ-ent technologies, than for one technology. Ele-ments of such chains are:- Technologies of extraction the heat from the

earth, i.e. its production for the needs ofconsumer(s);

- Technologies of transportation the heat fromthe source(s) to the consumer(s);

- Technologies for monitoring and regulation ofheat supply to different users;

- Technologies for monitoring and regulation ofthe heat use by concrete user(s);

- Technologies for protecting the environmentof possible negative impacts of geothermalenergy use.Final quality of a technology chain depends

on the local possibilities, used “know-how” for itscomposition and economical factors.

Fig.2. Technologies for heat extraction from the earth (hydro-convective systems)


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Pump

water table

a) Groundwater heat pump (doublette

Connection in series

Connection in parallel

Pipe in trench

b) Horizontal ground heat exchanger types

trench collector

"Slinky" collector

Manifold inside or at the building

c) Borehole heat exchangers (double-U-pipe)(Sanner, 2004)

Fig.4. Principles of GHP heat extraction

1. TECHNOLOGIES FOR HEATEXTRACTION

Presently, three groups of heat extractiontechnologies are in use, i.e.:- Hydro-convective systems;- Geo Heat pumps; and- Systems for effluent heat of power generation

use.Elements of the listed technologies are:

a) Hydro-convective systemsThree main technologies are in use, i.e.:

- Thermal water extraction from geothermal

wells (Fig.2-a);- Down-hole heat extraction from geothermalwells (Fig.2-b and Fig.3);- Hot-dry rock system (Fig.2-c), i.e. heat ex-traction from dry subsurface heat sources by addi-tion of surface water as heat transfer fluid and itsdirect or indirect (with down-hole HE) use

b) Heat pump systems

Three main technologies for heat extractionare in use:

- Ground coupled heat pumps (Fig.4-1) withhorizontal vertical or spiral pipe heat exchangeruse;- Ground water heat pumps (Fig.4-2) with orwithout reinjection of effluent water; and- Surface water heat pumps (Fig.4.3) with clo-sed or open loop system.

c) Effluent heat of geothermal powergeneration (Fig.4 and 5)Two main technologies for heat extraction are

in use:- Closed loop system with heat extraction bythe use of heat exchanger put at the effluent hotfluid flow.- Open loop system with the use of effluentfluid as heating fluid (possible only with con-venient chemistry of the fluid).

It’s necessary to underline that most of thetechnologies in question (except the ones with theuse of down hole or ground coupled heat exchan-gers, condition careful handling of the geo-thermalreservoir in order to preserve it from the overload-ing, i.e. water or heat extraction over its natural ca-pacity. Re-injection of effluent water for hydro-convective geothermal resources is a part of the re-servoir engineering (returning back the water to thereservoir from which is extracted) and play rolepreserving the reservoir water level but also in theenvironmental protection of possible negative im-pact of high mineralized (and often hot) waters.

This part of the whole technology chain forgeothermal energy use is the most risky andcomplicated one. Its proper composition, comple-tion and exploitation conditions a multi disciplinalknowledge.

(Bloomquist, 2003)

Fig.5. Scheme of a single flash geothermal powerproduction plant


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(Bloomquist, 2003)

Fig.5. Schemes of the binary and Kalinageothermal power production plants

2. TECHNOLOGIES FOR TRANSPORT-ATION OF HEAT FROM THE HEATSOURCE TO THE HEAT USERS

Normally, heat is transported by the use of:- Thermal water as transportation fluid (con-ditioning low mineralized or chemically treatedwater in order to preserve the transportation pipesfrom scaling or corrosion); and- Soft water as transportation fluid, i.e. beforetransport, heat is extracted from the thermal water

with the use of heat exchanger.- In both cases, a pump station is necessary inorder to enable movement of the transportationfluid from the source to the user.

Transportation of the water is going throughpipe-lines (Fig.6) positioned directly in the ground(Fig.6.a), or in beton channels below (Fig.6.b) orabove (Fig.6.c) the ground surface. The use of pi-pelines above the ground surface without betonchannels is not recommended because being vulne-rable to the unprofessional handling or stilling ofits parts.

In principle, when low temperature direct ap-plication is in question, transportation of heat tolonger distances is not economically viable, i.e.distance between the source and users should be asshorter as possible in order to decrease the pump-ing costs.

3. TECHNOLOGIES FOR MONITORING AND REGULATION OF HEAT SUPPLY TO DIFFERENT USERS

The problem is connected to the daily andseasonal changes of heat consumption, due to theclimate changes (different heatings) or seasonalcharacter of use (drying agricultural products). Inorder to follow the changes of heat needs, it isnecessary to change the flow of the heating fluid.

When a geothermal system is in question, mo-nitoring and regulation of heat supply to the usersconsists three main problematics, i.e.:- Monitoring and regulation of heat extractionfrom the geothermal field in order to enable properuse of it and proper following of changeable heatneeds. That is particularly important for the hydro-convective systems where overpumping resultswith decrease of the water level in the reservoir.Regulation itself is connected to the work of pumpsin the well(s) and the water distribution pumps.

Fig.6. Pipe-lines for transportation of geothermal heat (Bloomquist, 2003)


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- Proper completion of the heat source in orderto enable proper maintenance of the requested pa-rameters of the user(s) but also economical use ofgeothermal heat. Normally, at least when differentcentral heatings are in question, daily and seasonalclimate changes result with short lasting of maxi-mal loadings of the system (Fig.7). Peak loadingsabove 50% of the maximal heat power participatewith less then 5% of the total annual heat con-sumption.

Therefore, high investments in completion ofthe geothermal resource for covering this part ofannual heat consumption shall not be economically

justified and shall result with production of expen-sive heat. Normally, short morning peak loadingscan be covered by introduction of a hot water ac-cumulator (Fig.8 and Fig.9). It is filled during thelasting of low heat consumption and emptied du-ring the peak loadings. However, for some users(greenhouses) that is not enough and additional hotwater boiler using fossil fuels should be incor-porated (Fig.8) in order to meet longer peak load-ings during the winter season. Capacity of the heataccumulator, type and power of the boiler are mat-ter of technical and economical calculations.

Fig.7. Annual heat loading curve of a greenhouse in middle European climate conditions

Fig.8. Economical composition of the heat source


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Fig.9. Heat accumulation reservoirs of the districtheating system in Reykjavik (Iceland)

Fig.10. Measurement of heat consumption

Fig.11. Geothermal plate heat exchanger

Connected to this part of the system is alsomeasurement of the heat supply and the use of openor closed loop system by the user.

Normally, so called “calorimeters” should beapplied (Fig.10), using multiplication of the water

flow and temperature difference for determinationof the “heat flow”. However, mostly, only measu-rement of water flow is in use because enabling tothe supplier to “press” the user to use also the low-er parts of temperature difference on disposal. It isrecommended to install the measurement of thethermal water flow even in the cases when it does-n’t serve for payment purposes because enablingorientation about short and long term thermal waterconsumption, i.e. necessary data for setting the re-gulation.

Dearation

SENZOR

PRITISKA

REGULATION

PANEL

64ºC

30ºC

Deaeration

HOT WATER BOILER 4 MW

SOLENOIDVALVE

Sensors of the ex-ternal climate: tem-

perature, humidityand velocity of air,

solar radiation in-

tensity

Computerizedsteering center

LIMITER OF THETEMPERATURE

OF EFFLUENTWATER

DISTRIBUTION OF THE HEATING FLUID

TO THE GREENHOUSE COMPLEX

Fig.12. Composition of the central connection stati-on of a large greenhouse complex

Regulationpanel

TS TS

TS TS

TSTS

25/30 ºC 60/90 ºC

25 ºC40 ºC

Clima station of

the internal cli-

mate: tempera-

ture, humidityand velocity ofair, intensity of

solar radiation

Fig.13. Composition of connection station of a con-sumer to the distribution network

The question of application of open or closedloop system by the heat users is a quite important


97

decision to be taken before the project completion.Closed loop system conditions installation of ex-pensive heat exchangers and escorting equipmentbut enable protection of the installations from sca-ling and corrosion. Plate heat exchangers (Fig.11)enable easy maintenance and cleaning of the geo-thermal water side. Also re-injection of the effluentwater is much easier and cheaper. On the otherhand, open loop system is much simpler and can beused even without any control equipment. It ismuch cheaper and in wide use by the small con-sumers. Both systems enable the use of hand orautomatic regulation of thermal water supply. Thechoice depends on results of economy analysis, i.e.requests of the heat user. At Fig.12 and 13examples of completion of connection stations withautomatic regulation for a larger greenhouse com-plex composed of several users are given.

4. TECHNOLOGIES FOR MONITORING AND REGULATION OF THE HEAT CONSUMPTION BY CONCRETE USER(S)

Heat requests and consumption of concreteconsumer depend on the changes of climate con-ditions, when central heating is in question, orchangeable technological requests of the processesusing geothermal heat. In both cases, a continualcontrol of reached parameters is necessary and re-gulation of the heat supply according to their chan-ges. Normally, hand regulation cannot fulfill suc-cessfully such requests and the automatic oneshould be mostly applied (Fig.13). However, theeconomy reasons are the background of a very wi-de use of the hand regulation, particularly betweensmall consumers.

Practically, this part of the technology chain isthe crucial point of the geothermal energy directuse in comparison with the fossil fuels. When aheat consumer is making decision for technicalsolution to cover his needs, most important ele-ments are the necessary investments, quality ofheat supply, simple handling and maintenance andcheap exploitation. If fossil fuels are in question, hehas on disposal excellent technologies enablingfulfilling of all the requests, except the last one. Hehas nothing to do with complicated technologiesenabling the use of some of renewable energiesand, if the cost of energy is not a crucial factor forhis work, he shall hardly make the decision to go tothem. Or, when small users are in question, he shalltry to avoid all the complications by simplifyingmaximally the technical solutions and, at the end,shall get a heat supply with weak quality. Therefo-re, a real development cannot be expected withoutoffering a solution which shall “divide” the consu-mer from the problems of heat “production”. Hisproblems should finish at the border of the connec-tion station, where to take the energy and pay for it

according to the measured consumption. That ispossible only with development of larger districtheating systems and is the background of their suc-cess everywhere where properly completed. How-ever, that also means incorporation of a another andrather complicated technology in the geothermalenergy technology chain.

5. TECHNOLOGIES FOR THE HEAT USEBY CONSUMERS

At the end of the chain come technologies forthe heat use by consumers. In principle, that shouldnot be a “special” case, differing from the techno-logies where fossil fuels are used, because whenbeing on disposal heat is heat, doesn’t matter fromwhat origin. However, there are differences due tothe fact that the heat source “offers” the heat withcontinual characteristics, i.e. temperature and floware not changeable according to the needs of theconsumer. In addition, temperatures on disposal arenormally lower than the ones conditioned by theclassical technologies base on the fossil fuels use.

The above listed resulted with development ofso called “low-temperature” technologies for heat-ing the rooms, drying agricultural products, indus-trial applications, etc. Some of them brought im-provements of the quality (heating of greenhouses,drying of agricultural products) and later on havebeen accepted also by the fossil fuels users. How-ever, common characteristic of all these techno-logies is that being more expensive than the clas-sical ones.

6. ENVIRONMENTAL PROTECTION

In addition to the technologies for productionand consumption of the heat, final and obligatorypart of the chain is the environmental protection. Ifnot incorporating it, geothermal energy utilizationshall have negative impact(s) to the environment,mainly thermal, chemical or with scaling of con-sisted minerals, plus the destroyed balance of geo-thermal reservoir. Different technologies for pro-tection can be applied, depending on the charac-teristics of concrete resource and type of appli-cation.

Some of them are incorporated by the appliedtechnology of heat extraction itself (down hole heatexchangers). However, for most of the others it isthe most complicated part of the technology ofapplication.

First problem, which often appears, is the sca-ling. Immediately after disturbing the pressure andtemperature balance of thermal water by its extrac-tion from the reservoir, a list of consisted mineralsbegin to scale on the internal pipes surface.

Second problem is the corrosion, resultingfrom the presence of corrosive minerals in manythermal waters, particularly when coming in touchwith the oxygen from the atmosphere.


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Technological solutions on disposal for bothproblems are quite complicated and expensive.They can be physical (taking measures not todisturb the pressure balance of the water) or che-mical (by addition of neutralization agences). Firstones condition expensive investments and thesecond expensive exploitation.

Additional problem is the re-injection of ef-fluent water back to the reservoir. It should not bewith a chemical composition which is very muchdifferent of the original one because can damagethe reservoir, Therefore, many times additionalmeasures are necessary in order to fulfill its re-quests, and that can increase significantly the ex-ploitation costs.

If the water is not re-injected back to the re-servoir, which is an often case when small users arein question, negative thermal or chemical impact tothe environment is immediately visible and causesa negative reaction of local people to further de-velopment of the source or application.

7. COMPOSITION OF VIABLE TECHNO-LOGY CHAIN(S)

Summary of the consisted problematics, madein 1-6, illustrates the complicate character of com-position, application and development of direct ap-plication geothermal projects. As already said, thatis not a question of completion of one, good or bad,technology for application but composition of aaccommodated chain of a list of technologies fordifferent parts of it. By intention it is not said anoptimal but an accommodated chain because eco-nomy reasons normally do not allow application ofthe best solutions on disposal, particularly not forsmaller projects with only one user.

Composition of the technology chain isnormally dictated by:- Nature of the geothermal resource whichshould produce the heat for the project;- Characteristics of the heat consumption whichshould be covered;- Existence or not of combination of users withdifferent heat consumption characteristics;- Distance between the heat source and heatconsumer(s);- Particularities of the technology(ies) of theheat use by the consumer(s);- Financial funds on disposal for investments inthe technology chain completion; and- Final prize of used heat which can be compe-titive for the user(s).

It’s obvious that it is a quite complicated mul-ti-disciplinal task. Normally, first comes the defini-tion of “minimal” limits of completion of each oneof technologies in question and definition of nega-tive technical and economy consequences of appli-cation of such “minimal” solutions. Then, it comesthe evaluation and estimation of resulting negative

consequences and positive implications of intro-duction of possible improvements. These ones arecompared afterwards in combination with the ne-cessary investments for their incorporation, influ-ence to the final price of used heat and financialfunds on disposal for completion for project com-pletion. Finally, not optimal but the viable com-bination is chosen, enabling a successful start withthe new energy source use. That is the reason whya geothermal project is never finished, i.e. based onthe experiences of running it, there are alwayspossibilities (and need?) for improvements and de-velopment. That is also the reason why the tech-nology chain applied for one project cannot beapplied for some other one.

In that way, we localized the weakest point ofthe direct application of geothermal energy andpossibilities for its further development. Very com-plicated character of the application technologychains conditions an expensive initial engagementof multi-disciplinal teams of experts in order toguarantee success of accepted solutions. Numeroustrials for simplification of small owners regularlyfinish with negative results and, in that way, stop-ping of initiatives for development of direct ap-plication of geothermal energy in many locations.

It’s quite clear now-a-days that a real widerdevelopment is possible only with application ofbigger district heating schemes. They justify theengagement of expensive experts for definition ofconcrete elements of the technology chain(s) andteam of professionals, able to perform a proper ex-ploitation and maintenance of the project. As big-ger it is and as better is the combination of heatusers, better are possibilities to reach a higher an-nual heat loading factor of the system and betterfinal economy results.

REFERENCES

Barbier, E. and Fanelli, M. (1977). Non-ElectricUses of Geothermal Energy, Prog. EnergyCombust. Sci., 3-2.

Boyd, T. L., and Rafferty, K. (1998). AquacultureInformation Package, Geo-Heat Center,Klamath Falls, OR, 106 p.

R. Gordon Bloomquist: Economic Factors Impact-ing Direct Use, 2004, Proceedings of ID Poland 2004

R. Gordon Bloomquist. 2003. Direct Utilization of Geothermal Energy, European Geothermal Conference, Szeged 2003

Kavanaugh, S. P. And K. Rafferty, 1997. “Ground-Source Heat Pumps”, ASHRAE, Atlanta, Georgia, 167 p.

Lund, J. W. and Freeston, D. H. (2001). World-Wide Direct Uses of Geothermal Energy2000, Geothermics, Vol. 30, No. 1, ElsevierSciences Ltd., United Kingdom, pp. 29-68.


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Lund, J. W., 2001a. “Geothermal Heat Pumps - AnOverview”, Geo-Heat Center QuarterlyBulletin, Vol. 22, No. 1, (March), pp. 1-2.

Lund, J.W. : Geothermal Direct-Heat Utilization,2004, Proceedings of IGD Poland 2004

Popovski, K. (1998). Geothermally-HeatedGreenhouses in the World, Proceedings of theWorkshop: Heating Greenhouses withGeothermal Energy, International SummerSchool, Azores, pp. 425-430

Popovski, K. (1993), Heating Greenhouses withGeothermal Energy – Engineering Hand-book, International Summer School, Pisa andSkopje

Rafferty, K. (1997). Fossil Fuel-Fired Peak

Heating for Geothermal Greenhouses, Geo-HeatCenter Quarterly Bulletin, Vol. 18, No. 1(January), Klamath Falls, OR, pp. 1-4.

Rybach, L., and B. Sanner, 1999. “Ground-SourceHeat Pump Systems - the EuropeanExperience”, Proceedings of the InternationalSummer School - Oregon 1999, Geo-HeatCenter, Klamath Falls, OR, pp. 159-170.

Schmitt, R. C. (1981). Agriculture, Greenhouses,Wetland and Other Beneficial Uses ofGeothermal Fluids and Heat, Proceedings ofthe First Sino/U.S. Geothermal ResourcesConference (Tianjin, PRC), Geo-Heat Center,Klamath Falls, OR, 12 p.

Documents

2.5. DIRECT APPLICATION TECHNOLOGIES AND PROJECT …...PRITISKA REGULATION PANEL 64ºC 30ºC Deaeration HOT WATER BOILER 4 MW SOLENOID VALVE Sensors of the ex-ternal climate: tem-perature,