Ap1_02.vp 1 Introduction As a result of illogical trends in power prices, the competi- tiveness of district heating has greatly decreased in recent years in Košice. This situation is aggravated by the fact that a part of the heating plant is already reaching the end of its working life. If this part were to be closed, it would result in a shortfall of 200 MW heat output. The long term develop- ment plan for the Košice district heating system focuses on solutions to this problem. It also takes into account the demands of the national electricity supply network, and is therefore considering three possibilities. An alternative is needed because of Slovakia’s extremely high (90 %) de- pendence on imported energy sources, and the need for a lower level of the emission of pollutants. It is planned to es- tablish a new gas-steam cycle-based CHP plant-module with a 100 MW thermal output, and to supply 100 MW ther- mal output from geothermal sources. However the efficiency parameters (net present value, internal rate of return and payback period) indicate that competitiveness of this alterna- tive is rather low. 2 Current plan for geothermal energy utilization in the district heating system for Košice The current plan for geothermal energy utilization is based on direct feeding with this energy into the district heating system. This is justified by its relatively high tempera- ture (115–130 °C at a depth of about 2 000–2 500 m and 130–150 °C in the depth of about 2 500–3 000 m). According to the plan, nearby villages such as Bidovce, Ďurkov, Ruskov and Slanec will have two pairs of production and reinjection wells (doublets) and one heat exchanger plant. Thermal water will be pumped into the heat exchanger plants from the pro- duction wells. The thermal will infuse its thermal energy into the secondary mains water situated in the heat exchangers, and then the water will be returned to the earth’s crust through two reinjection wells. The thermal energy thus ac- quired will then be transported to the heating plant by the secondary mains water. This will be done with the help of pumping stations, and the CHP plant will enable it to be used in the district heating system. According to the plan, more than 2 500 TJ can be obtained this way to supply the town with heat from geothermal energy sources. 3 More rational utilization of the geothermal energy An examination of this conception of geothermal energy leads us to an important and to some extent surprising real- ization: according to the plan, the temperature of the thermal water compressed back into the reinjection wells should be higher than 60 °C. This means there will be an extremely low degree of exploitation of the available geothermal energy capacity. It seems justified to assume that an increase in the utilization degree would be the most efficient way to im- prove the economic efficiency parameters. Approximately 9 mil. USD could be saved on investment costs in the case of upgraded utilization of the available goethermal energy ca- pacity. About 70 MW heat output could be gained from direct utilization and about 30 MW from indirect utilization. The indirect utilization stage would be implemented by a heat pumping plant, which would utilize the heat output produced by cooling down the returning secondary mains water by about 20 K at a higher temperature level. Thus the tempera- ture at which the thermal water is compressed back would decrease to a similar extent. This conception can lead to some 44 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ Acta Polytechnica Vol. 41 No. 2/2001 Some Problems of the Integration of Heat Pump Technology into a System of Combined Heat and Electricity Production G. Böszörményi, L. Böszörményi The closure of a part of the municipal combined heat and power (CHP) plant of Košice city would result in the loss of 200 MW thermal output within a realtively short period of time. The long term development plan for the Košice district heating system concentrates on solving this problem. Taking into account the extremely high (90 %) dependence of Slovakia on imported energy sources and the desirability of reducing the emission of pollutantst the alternative of supplying of 100 MW thermal output from geothermal sources is attractive. However the indices of economic efficiency for this alternative are unsatisfactory. Cogeneration of electricity and heat in a CHP plant, the most efficient way of supplying heat to Košice at the present time. If as planned, geothermal heat is fed directly into the district heating network the efficiency would be greatly reduced. An excellent solution of this problem would be a new conception, preferring the utilization of geothermal heat in support of a combined electricity and heat production process. The efficiency of geothermal energy utilization could be increased through a special heat pump. This paper deals with several aspects of the design of a heat pump to be integrated into the system of the CHP plant. Keywords: geothermal energy, ejector, heat pump. improvement in the competitiveness of geothermal energy. However the main reason for unsatisfactory economic effi- ciency (the conflict between cogenerated heat and geothermal heat) cannot be set aside, since this comes from the concept of geothermal energy utilization. Cogeneration of electricity and heat, the bases of the relatively efficient heat supply of the town at a present time be very strongly limited if geothermal energy were to be fed into the district heating network. The conception of integrating geothermal energy sources into a system of combined electricity and heat production in the municipal CHP plant would be an excellent solution to this problem. The principal scheme is illustrated in Fig. 1. In this conception the utilization of geothermal energy in support of a combined electricity and heat production process would be preferred. The stream of the secondary geothermal energy medium into the CHP plant would be divided into two parts. The higher flow would be used for heating the feed water in the steam cycle. The lower flow would be used directly in the district heating network: • for domestic heating and hot water in winter period, • for absorption cooling in the summer period. After that, the streams would be mixed and cooled down by about 20 K in a heat pumping plant. The resulting flow of the secondary geothermal energy medium could be used for cooling the condenser in the steam cycle. The advantage of this solution would be that the primary geothermal water would be injected back into the earth’s crust at a lower tem- perature than without using the heat pump. Moreover a part of the energy losses from the condenser would be stored in this water in the earth’s crust. The thermal output of the heat pumping plant could be utilized the following way: • for domestic heating and hot water in two housing estates near the CHP plant in the winter period, • for domestic hot water preparing throughout the city in the summer period. Implementing this conception could reduce investment costs (by about 9 mil. USD) as well as operating costs, and could increase the benefits of geothermal energy utilization in the Košice district heating system. 4 Selection of the heat pumping technology One of main conditions for efficient geothermal energy utilization in this conception is the correct selection of the heat pump technology and its integration into the combined electricity and heat production system. Heat pumping technology can be classified according to: • the number of stages of evaporation and condensation – the most probable method would be to implement these processes in at least two stages. • the coolant that is used. Water can be used as a coolant. In addition to water, refrigerants R134a and R717 (ammonia) were analyzed, for lower dew and evaporation tempera- tures. • the method of compression. Steam can be compressed mechanically in turbocompressors in two stages, or by thermocompression in an ejector in a single stage. R134a and R717 vapors can be compressed mechanically in two stages. This system could work the following way. In summer, all the required heat power (~45 MW) would be produced by the heat pump. Consequently, the gas-steam cycle would produce mostly electricity. In winter, only one housing estate in Košice city would be supplied with heat power (~65 MW) by the heat pump. The most of the heat power would be produced in the gas-steam cycle. One possible solution of the heat pump conception is the three-stage alternative version in Fig. 2. This alternative is a combination of direct (first stage) and indirect (second and third stage) processes of evaporation and condensation. In the first stage, steam is compressed in a one-stage ejector by the motive steam acquired from the steam turbine of the © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 45 Acta Polytechnica Vol. 41 No. 2/2001 Fig. 1: Scheme of the integration of the geothermal source into the combined heat and electricity production system based on a gas-steam cycle gas-steam cycle. The evaporation temperature in the first stage is 39 °C and the dew temperature is 80 °C. Because of the direct processes in the first stage, the temperature dif- ference in the heat exchangers is negligible. In the second Acta Polytechnica Vol. 41 No. 2/2001 46 TV condenser I ·· mchIIImchII · mol · mol · mpl · mpl R a134 R a134 E 2 E 4 E 3E 1 45 °C 25 °C 45 °C 80 °C evaporator I Fig. 2: The three-stage alternative version of the heat pump integrated into combined heat and electricity production using the geother- mal source of the Košice basin TV condenser I R a134 · moI · mk · moI · mcII E 1 E 2 80 °C 45 °C 45 °C 25 °C evaporator I Fig. 3: The two-stage alternative version of the heat pump integrated into combined heat and electricity production using the geother- mal source of the Košice basin and third stages indirect processes are implemented. In this heat pump, the secondary water is cooled down from 45 °C to 25 °C and the water that is used for heating is warmed from 45 °C to 80 °C. This conception of a heat pump is advanta- geous due to possibility of heat power regulation. The heat power produced by this alternative is 55 MW. The coefficient of performance (COP) is relatively low because of the huge heat power of the motive steam. This energetic valuation does not take into consideration various exergetic qualities of the energies used for vapor compression. This fact could be re- spected by equal electrical power which is identical to the power we would get from the expansion of the motive steam. Using this assessment the COP reaches significantly higher values. Another possible solution of the heat pump is the two- -stage alternative shown in Fig. 3. Analogous to the previous solution, this version consists of direct processes (in the first stage) and indirect processes (in the second stage) of evapora- tion and condensation. In the first stage, the steam is com- pressed mechanically in two stages with intercooling after the intermediate stage. Because of the enormous specific volume of the steam, the process of compression could fake place in axial turbocompressors. In the second stage, vapors of cool- ant R134a are compressed mechanically. The temperatures of the water cooled down and heated up are as before. In this case the heating power is about 37 MW and the power required for compression is about 7 MW. Clearly this variant has a higher COP. However, it has the great disadvantage of problematic steam compression in turbomachinery, result- ing from the extremely low partial pressure of steam at low temperatures. 5 Conclusions The three-stage variant has advantageous characteristics both in terms of heat-power regulation and in terms of eco- nomic performance. A simplified economic analysis, based on the difference between the selling price of the heat and the cost of providing it, shows the promise of this variant. It is too early to state that this variant could be the final version of the heat pump technology. It will be necessary to analyze the synergies between the steam turbine of the gas-steam cycle and the heat pump. 6 List of used symbols HE, E heat exchanger CP condensate pump HP heat pump C condenser GT gas turbine cycle ST steam turbine G generator SS service system TV throttle valve m mass flow References [1] Böszörményi, G.: Využití hydrogeotermálního potenciálu Košické kotliny. Diplomová práce, Praha, 2000 [2] Bussmann, W. (Hrsg.): Geothermie – Wärme aus der Erde. Verlag C. F. Müller GmbH, Karlsruhe, 1991 [3] Austmeyer, K., E.: Mechanical Vapour Recompression. VDI-Society for Energy Technology, Düsseldorf, 1993 Ing. Gabriel Böszörményi e-mail: G.Boszormenyi@sh.cvut.cz Czech Technical University in Prague Faculty of Mechanical Engineering Vaníčkova 5, Koleje Strahov Bl. 6./301 169 00 Praha 6, Czech Republic Doc. Ing. Ladislav Böszörményi, CSc. e-mail: boszla@ccsun.tuke.sk tel.: +421 95 6024241 fax: +421 95 6321558 Technical University of Košice Faculty of Civil Engineering Vysokoškolská 4, 042 01 Košice, Slovak Republic © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 47 Acta Polytechnica Vol. 41 No. 2/2001 << /ASCII85EncodePages false /AllowTransparency false /AutoPositionEPSFiles true /AutoRotatePages /None /Binding /Left /CalGrayProfile (Dot Gain 20%) /CalRGBProfile (sRGB IEC61966-2.1) /CalCMYKProfile (U.S. Web Coated \050SWOP\051 v2) /sRGBProfile (sRGB IEC61966-2.1) /CannotEmbedFontPolicy /Error /CompatibilityLevel 1.4 /CompressObjects /Tags /CompressPages true /ConvertImagesToIndexed true /PassThroughJPEGImages true /CreateJobTicket false /DefaultRenderingIntent /Default /DetectBlends false /DetectCurves 0.0000 /ColorConversionStrategy /CMYK /DoThumbnails false /EmbedAllFonts true /EmbedOpenType false /ParseICCProfilesInComments true /EmbedJobOptions true /DSCReportingLevel 0 /EmitDSCWarnings false /EndPage -1 /ImageMemory 1048576 /LockDistillerParams false /MaxSubsetPct 100 /Optimize true /OPM 1 /ParseDSCComments true /ParseDSCCommentsForDocInfo true /PreserveCopyPage true /PreserveDICMYKValues true /PreserveEPSInfo true /PreserveFlatness true /PreserveHalftoneInfo false /PreserveOPIComments true /PreserveOverprintSettings true /StartPage 1 /SubsetFonts true /TransferFunctionInfo /Apply /UCRandBGInfo /Preserve /UsePrologue false /ColorSettingsFile () /AlwaysEmbed [ true ] /NeverEmbed [ true ] /AntiAliasColorImages false /CropColorImages true /ColorImageMinResolution 300 /ColorImageMinResolutionPolicy /OK /DownsampleColorImages true /ColorImageDownsampleType /Bicubic /ColorImageResolution 300 /ColorImageDepth -1 /ColorImageMinDownsampleDepth 1 /ColorImageDownsampleThreshold 1.50000 /EncodeColorImages true /ColorImageFilter /DCTEncode /AutoFilterColorImages true /ColorImageAutoFilterStrategy /JPEG /ColorACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /ColorImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000ColorACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000ColorImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasGrayImages false /CropGrayImages true /GrayImageMinResolution 300 /GrayImageMinResolutionPolicy /OK /DownsampleGrayImages true /GrayImageDownsampleType /Bicubic /GrayImageResolution 300 /GrayImageDepth -1 /GrayImageMinDownsampleDepth 2 /GrayImageDownsampleThreshold 1.50000 /EncodeGrayImages true /GrayImageFilter /DCTEncode /AutoFilterGrayImages true /GrayImageAutoFilterStrategy /JPEG /GrayACSImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /GrayImageDict << /QFactor 0.15 /HSamples [1 1 1 1] /VSamples [1 1 1 1] >> /JPEG2000GrayACSImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /JPEG2000GrayImageDict << /TileWidth 256 /TileHeight 256 /Quality 30 >> /AntiAliasMonoImages false /CropMonoImages true /MonoImageMinResolution 1200 /MonoImageMinResolutionPolicy /OK /DownsampleMonoImages true /MonoImageDownsampleType /Bicubic /MonoImageResolution 1200 /MonoImageDepth -1 /MonoImageDownsampleThreshold 1.50000 /EncodeMonoImages true /MonoImageFilter /CCITTFaxEncode /MonoImageDict << /K -1 >> /AllowPSXObjects false /CheckCompliance [ /None ] /PDFX1aCheck false /PDFX3Check false /PDFXCompliantPDFOnly false /PDFXNoTrimBoxError true /PDFXTrimBoxToMediaBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXSetBleedBoxToMediaBox true /PDFXBleedBoxToTrimBoxOffset [ 0.00000 0.00000 0.00000 0.00000 ] /PDFXOutputIntentProfile (None) /PDFXOutputConditionIdentifier () /PDFXOutputCondition () /PDFXRegistryName () /PDFXTrapped /False /CreateJDFFile false /Description << /ARA /BGR /CHS /CHT /DAN /DEU /ESP /ETI /FRA /GRE /HEB /HRV (Za stvaranje Adobe PDF dokumenata najpogodnijih za visokokvalitetni ispis prije tiskanja koristite ove postavke. 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