SOLUTIONS FOR UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES

Transcription

1 SOLUTIONS FOR UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES Ana-Maria BIANCHI*, Sorin DIMITRIU**, Florin BĂLTĂREŢU* * TECHNICAL UNIVERSITY OF CIVIL ENGINEERING, Bucharest **UNIVERSITY "POLITEHNICA", Bucharest Rezumat. Lucrarea analizează posibilitatea utilizării resurselor geotermale existente pe Valea Oltului, în perimetrul Călimăneşti - Cozia, pentru modernizarea şi eficientizarea sistemelor de alimentare cu energie electrică şi termică din zonă. Cele trei foraje existente furnizează apă geotermală de entalpie joasă cu temperatura la gura sondei de o C şi cu un conţinut mare de gaze, 2..2,5 m 3 N/m 3 apă produsă. Debitul disponibil al celor trei foraje de 50,4 l/s echivalent unui potenţial termic de 13,2 MW este utilizat pentru încălzirea unor unităţi hoteliere, pentru tratamente balneare şi în sistemul de alimentare cu căldură al oraşului Călimăneşti. Gazele asociate, cu un conţinut de peste 88% metan şi având PCI de cca. 32 MJ/m 3 N nu sunt utilizate în prezent, fiind evacuate în atmosferă. Lucrarea face o analiză a modului actual de utilizare al acestor resurse şi propune soluţii de valorificare completă a potenţialului lor energetic prin utilizarea pompelor de căldură pentru epuizarea potenţialului termic al apei până la temperatura de cca 30 o C şi prin utilizarea unor instalaţii de cogenerare cu motoare cu ardere internă sau cu turbine cu gaze. Cuvinte cheie: energie geotermală, cogenerare, pompă de căldură, eficienţă energetică, apă geotermală. Abstract. The paper concerns the possibility to use the geothermal resources from Olt Valley, in area Calimanesti - Caciulata - Cozia, for modernization and increasing of efficiency of the local electric power and heat supply systems. The three existing drills provide low enthalpy geothermal water, with temperature at the exit of well o C and with a high content of gases, of m 3 N/m 3 water. The available volume flow for the ensemble of the three drillings of 50.4 l/s, equivalent with a thermal potential of 13.2 MW is used for heating of several SPA hotels and for heat supply system of the Calimanesti town. The associated gases with a content of methane over 88% and having a low heating value about 32 MJ/m 3 N, actually are not used, being exhausted in atmosphere. The paper analyses the current use of these resources and proposes full recovery solutions using heat pumps for heat recovery from geothermal water and using gas engines or gas turbines cogeneration units for recovery of the associated gases thermal potential. Keywords: geothermal energy, cogeneration, heat pump, energy efficiency, geothermal water. 1. INTRODUCTION Romania has a high economic potential of the renewable energy sources. Among these, the geothermal energy resources which were identified by drills represent an annual potential of about 10 7 GJ ( toe - tons oil equivalent); by using approximately 60 functioning wells an annual contribution of GJ (energy economy, equivalent to toe) is achieved [1], [2]. This energy is successfully used to produce thermal energy needed for technological processes, or, especially, for the heat supply of various residential areas. The distribution of these resources on the Romanian territory is presented in fig.1. Only 2/3 of the existing potential is used in Romania, mainly because of the lack of a corresponding financial support to sustain the development of this energy sector. This paper proposes a modern solution for the utilisation of the energy potential of the geothermal resources from the area around the localities Calimăneşti - Caciulata - Cozia from the Valcea County, in order to include them in a district heating system. In this area, the geothermal water is provided by three drillings having more than 3000 m in depths, and located on the right side of the Olt River [5], at about 1-2 km one from each other, in the neighbourhood of the mentioned localities, as presented in the figure 2. The three existing drillings stand out deposits of medium/high enthalpy geothermal water (the temperature at the exit of the well being o C). The available flow volume of the three wells is 50.4 l/s, equivalent to a thermal potential of 13.2 MW, when the geothermal water is cooled to 30 o C. TERMOTEHNICA 2/

2 UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES Fig. 1. The distribution of the geothermal resources on the Romanian territory. [1] 2. THE ENERGY POTENTIAL OF THE GASES FROM GEOTHERMAL WATER The energy potential of the geothermal sources from Olt Valley is very promising. The measurements made at the commissioning of the thermal water drillings, pointed out a great ratio of gases in produced water, about m 3 N/m 3 water, containing over 85% methane. The heating value of the combustible gaseous mixture captured from hot water produced by the three existing geothermal water wells, established by additional measurements, is comprised in range of MJ/m 3 N. Table 1 presents the composition and ratio of gases associated with geothermal water, measured at wells from Calimanesti - Caciulata - Cozia perimeter [5]. Table 2 presents the raw energy potential possible to be recovered by burning gas associated with hot water produced by three existing water wells from Calimanesti - Caciulata - Cozia perimeter [5]. The simplest solution to utilise this potential consist to burn the gases directly in the actual hot water boilers, replacing completely the liquid fuel. Considering an efficiency of the hot water boilers of about 90%, the value of the utilisable thermal potential is of about 3.2 MW, the existing heating system having the possibility to work without liquid fuel and to be extended based only on the burning of combustible gases. However, the best solution is to use the combustible gases to put into action small gas engine or gas turbine cogeneration units. In this way is possible to combine production of thermal energy delivering the consumers, with production of electricity used for pumping the thermal agent and to cover their own consumption. Excess electricity can be injected into the local electricity network. Fig. 2. Olt Valley working geothermal perimeter [5]. 50 TERMOTEHNICA 2/2011

3 Ana-Maria BIANCHI, Sorin DIMITRIU, Florin BĂLTĂREŢU Composition and ratio of gases from geothermal water [5] Table 1 water well The water well working parameters during the sample gathering Caciulata Volume flow 32,4 m 3 /h Temperature 87 o C 1008 Cozia Volume flow 57,6 m 3 /h Temperature 89 o C 1009 Calimanesti Volume flow 28,8 m 3 /h Temperature 85 o C The ratio of gases associated with geothermal water (m 3 N/m 3 water) Nitrogen (N 2 ) Carbon dioxide (CO 2 ) Methane (CH 4 ) Ethane (C 2 H 6 ) Propane (C 3 H 8 ) i-butane (C 4 H 10 ) n-butane (C 4 H 10 ) Total from which: Combustible gases ratio (88%) (84%) (86%) Low Heating Value (MJ/m 3 N) Table 2 The raw energetic potential possible to be recovered from gases associated with geothermal water [5] Water volume flow Gas temp. Low Heating Value Gas ratio Thermal power water well l/s Nm 3 / m 3 water o C MJ/Nm 3 MW toe/h Caciulata 9,4 2, ,0 0,743 0,064 Cozia 23,0 1, ,5 1,392 0,120 Calimanesti 18,0 2, ,0 1,476 0,127 TOTAL 50,4 2,311 * 92,7 * 30,9 * 3,611 0,311 * Mean value. 3. THE PRESENT UTILIZATION OF THE GEOTHERMAL RESOURCES The drilling located in the neighbourhood of Căciulata and Cozia are used for local needs. The geothermal water provides a group of hotels and SPA treatment units, for heating, domestic hot water supply and thermal pools. The high thermal potential of the geothermal water leads to its direct exploitation, the basic scheme of the geothermal water distribution being presented in figure 3. In the cold season, the geothermal water (having a temperature of o C) is cooled in a plate heat exchanger, producing the thermal fluid for the district heating system. A second heat exchanger produces domestic hot water. The geothermal water, cooled in the two heat exchangers, feeds the thermal pool, after that being discharged in the Olt River at a temperature of about 30 o C. In the warm season, the mass flow extracted is reduced, only the heat exchanger for domestic hot water and thermal pool being in use. The third drilling is situated at a distance of 1,2 km from Calimaneşti, providing a volume flow of 18 l/s at the same temperature values o C [2]. This locality, beside the tourists which are staying in hotels, has about 8500 permanent habitants; 20% of the habitants are living in apartments connected to a centralized system for thermal energy supply. In the winter of , 529 apartments were branched to centralized heating system. This system has to ensure a thermal need of about 3500 kw for heating and about 500 kw for domestic hot water supply (taking into account the conventional climatic parameters); it was initially designed with three thermal units, equipped with hot water boilers using light liquid fuel. The geothermal water from the nearby well was initially used only for the thermal energy supply of the SPA treatment units and for the thermal pools. The project of geothermal energy supply was started in 2002 year with internal financing, and was later supported by European funds. Initially, the project included the three wells to provide the centralized heating of TERMOTEHNICA 2/

4 UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES Calimanesti town. Later it was utilized only the available water from the well 1009, situated in vicinity of town. The available volume flow is of 18 l/s, from which about 8 l/s is utilized by a SPA centre and a hotel; the rest of volume flow (about 10 l/s) being used in the centralized district heating system of Calimanesti. In order to include the geothermal water into the district heating system, a geothermal heating station was built just near the geothermal well; the geothermal water produces, by using plate heat exchangers, the primary thermal fluid for the district heating system, having a temperature of about 85 o C. This primary thermal fluid serves to partially cover the heating demand and to completely cover the sanitary hot water preparation. Fig. 3. The basic scheme of geothermal water utilization in the SPA hotels. Fig. 4. The basic scheme of the geothermal station. The geothermal heating station with its scheme presented in the figure 4, uses a continuous functioning heat exchanger, that completely covers the thermal needs for the sanitary hot water preparation, and another heat exchanger working only in the cold season, when the heating system is on. Because the temperature of the thermal fluid returned from the both domestic hot water preparation system and heating system is about 45 o C, the geothermal water cannot be cooled below 50 o C, being discharged in the Olt River at this temperature. In this way, the thermal potential of the geothermal water is not entirely used. Even in these conditions, the use of the geothermal water leads to the complete elimination of the liquid fuel for domestic hot water preparation and to the supply of about 1/3 of the thermal energy needs for heating in the locality of Calimaneşti. In order to cover the peaks and the rest of the thermal energy needs, the oil-fired hot water boilers were maintained. The really cost of thermal energy produced from geothermal water, is about 155 lei/gcal, compared with 500 lei/gcal if the energy is produced in oil-fired plants. The old three district heating plants was transformed in thermal distribution points. 52 TERMOTEHNICA 2/2011

5 Ana-Maria BIANCHI, Sorin DIMITRIU, Florin BĂLTĂREŢU Fig. 5. The scheme of centralized heating system based on geothermal water [5]: 1 geothermal water collector distributor; 2 plate heat exchangers (3x1.24MW); 3 hot water circulating pumps; 4 closed expansion vessel; 5 softening plant; 6 7 hot water collector distributor; 8 9 heat meters; 10 hot water collector for urban distribution heating points; 11 plate heat exchangers for domestic water. DHW 500 kw 13% DHW 500 kw 12% Thermal energy from liquid fuel 2180 kw 54% heating 1320 kw 33% Primary energy of liquid fuel 2422 kw 57% heating 1320 kw 31% a) b) Fig. 6. The energy balance of the geothermal heating station: a the energy delivered in the district heating system; b the primary energy consumption. The coefficient of performance of the combined thermal energy supply system (geothermal energy and thermal energy produced by using liquid fuel), reported in primary energy consumption from classical energy sources, can be determined with the expression: Q COP CAF Q INC CAF, (1) where: Q is the estimated thermal power [kw]; CAF Q INC the supplementary energy needs for heating, provided by the hot water boilers [kw]; CAF the efficiency of the hot water boilers ( CAF ). In these conditions we obtain a value of efficiency COP about This means an improvement of about 83% to the previous situation, when the thermal heating is produced using only liquid fuel. The comparison was made without taking into consideration the electrical energy consumption associated to pumping and lighting. The energy balance of the combined thermal energy supply system for the standard cold season conditions is presented in figure FULL RECOVERY OF THE ENERGETIC POTENTIAL OF GEOTHERMAL WATER BY USING A HEAT PUMP To turn to the best account the thermal potential of the geothermal water, it is proposed a solution to recover the available thermal energy from the water discharged in the Olt River, by using a water/water vapour compression heat pump. The TERMOTEHNICA 2/

6 UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES insertion of the heat pump in the functioning scheme of the geothermal station is presented in figure 5.The heat pump works only in the cold season, when the thermal power required by the district heating system overcomes the thermal power of the geothermal station heat exchanger. In the heat pump evaporator, the geothermal water is cooled off to a temperature of about 30 o C, after that being discharged in the Olt River. The heat pump condenser operates in parallel with the geothermal water heat exchanger, multiplying the thermal fluid flow sent into the thermal energy supply system, increasing therefore the heat provided to the system. In this way, it can be covered about 2/3 from the estimated thermal energy needs; the rest of thermal energy and the peaks are covered by hot water boilers using liquid fuel or by using thermal energy recovered form the combustible gases associated with geothermal water. In order to integrate into the temperature range corresponding to the thermal energy supply system, the heat pump must operate with an evaporating temperature of about 25 o C and with a condensation temperature of about 90 o C. The working fluid must fulfil the following conditions: the fluid must be environmental friendly. the saturation pressure that corresponds to the evaporation temperature must be closed to the atmospheric pressure; the critical temperature must be superior to 100 o C; the maximum pressure (at the condenser) must not reach very high values; Fig. 7. The scheme of geothermal heating station with GHP heat recovery. From the field of currently used refrigerants, these conditions are fulfilled by R123 (2,2-dichloro-1,1,1- trifluoroethane) and by some hydrocarbons (pentane, isobutane). From the thermodynamic point of view, these refrigerants determine similar performances. For big refrigeration power machines, the quantity of refrigerant is important; therefore the hydrocarbons are not recommended for this application, due to their flammability. By consequence, the refrigerant R123 is the best fluid for the given conditions. The option regarding R123 is also justified by the its reduced environmental impact, having an ODP closed to zero (0,02) and a very small value of GWP (120). The refrigerant R123 can be used without any restriction until 2030, when the production of HCFC will cease, according to the Montreal Protocol. It is a high temperature refrigerant with high stability, fireproof, non explosive, having the advantage of low pressures in installation and small compression ratios. Also, it is very accessible, the price being about 15 EUR/kg. In the table 3 are presented the properties at saturation state for R123, and in the figure 8, the simulation results of heat pump operation, according to conditions imposed by its use in geothermal installation. The simulation was made by EES software. The temperature variation in evaporator of the geothermal water was considered 50/30 o C, and the temperature variation of the thermal fluid prepared in condenser 45/85 o C. For the maximum available volume flow of geothermal water of 10 l/s, the thermal power at evaporator was 840 kw, the thermal power of condenser was 1060 kw and the electric power consumption of compressor 230 kw. 54 TERMOTEHNICA 2/2011

7 Ana-Maria BIANCHI, Sorin DIMITRIU, Florin BĂLTĂREŢU The properties of R123 ( CHCl 2 CF 3 ) at saturation state Table 3 t [ o C] p [bar] v' [dm 3 /kg] v'' [m 3 /kg] h' [kj/kg] h'' [kj/kg] s' [kj/kgk] s'' [kj/kgk] 20 0,759 0,6777 0, ,44 391,62 1,0650 1, ,550 0,7019 0, ,42 403,87 1,1307 1, ,873 0,7298 0, ,71 416,01 1,1963 1, ,919 0,7625 0, ,98 427,73 1,2608 1, ,898 0,8020 0, ,83 438,65 1,3231 1,6817 Fig. 8 The simulation of heat pump operation by EES. The efficiency coefficient of installation is about 4,7 resulting a price of thermal energy delivered in the heating system about 100 lei/gcal, the price of electric energy being considered 0,4 lei/kwh. Taking in account the maintenance cost and depreciation rate of investment, it is estimated a price of energy comparable to that of geothermal energy actually delivered in the centralized heating system. As a result, a clean thermal power of about 2880 kw (2650 kw from geothermal energy and 230 kw, electrical energy needed by the heat pump compressor) will be introduced into the heating system; this represents 72% from the total thermal heating (3500 kw). Adopting this solution, the thermal heating, considering standard cold season conditions is covered in a proportion of 68 %, generating an important economy of liquid fuel; in the same time, an important reduction of carbon dioxide and other polluting gases is obtained. Really, the effect is more important because the estimations were made for extreme climatic conditions, this situation having a little probability in zone. Considering a value of the electrical energy production efficiency of 30 33% (corresponding to the disadvantaged solution, in which the electrical energy is produced in classical thermal power stations), the system coefficient of performance compared to the primary energy consumption from classical sources can be determined with the expression: Q COP, (2) CAF Q INC PC CAF EE where: P C is the mechanical power required for the compressor [kw]; η EE is the efficiency of the electrical energy production. The value obtained in this case is COP 2. 1, which means an improvement of about 133 %, as compared to the situation in which only liquid fuel for heating is used. In figure 9 is presented the energy balance of the thermal energy production system using the heat pump, considering peak consumption. If the electrical energy required by the heat pump can be also obtained from renewable energy sources (like the micro-hydraulic potential of the Olt River), then the system can operate almost the entire cold season only by using green energy. In this case, the hot water boilers are retained only for peaks or breakdown. 5. RECOVERY OF THE ENERGETIC POTENTIAL OF THE GASES SEPARATED FROM GEOTHERMAL WATER. The recovery of the energetic potential of the gases separated from geothermal water can be achieved using several solutions: direct burning in hot water boilers; low power gas engines cogeneration units; low power gas turbines cogeneration units Direct burning in hot water boilers. The simplest recovery solution of the energetic potential of the combustible gases separated from geothermal water is direct burning in hot water boilers. Figure 10 shows the scheme of the geothermal heating station using a heat pump and a gas- TERMOTEHNICA 2/

8 UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES fired hot water boiler. Taking into account only the gases collected from 1009 Calimanesti well (see table 2), we obtain a supplementary thermal power of 1300 kw (for available volume flow of 18 l/s), the complete covering of the thermal load peak of the centralized heating system; in this case, we totally eliminate the liquid fuel. The system efficiency is similar to that using liquid fuel, but the price of energy delivered in system is much lower. If both heat pump and hot water boiler are made in modular construction, the operation of the system becomes very flexible; it can tracks the variation of the thermal load, only by changing the flow geothermal water over the well. Thermal energy from liquid fuel 1120 kw 28% DHW 500 kw 13% Primary energy of liquid fuel 1244 kw 27% DHW 500 kw 11% Electrical energy 230 kw 6% energy recovered 830kW 21% heating 1320 kw 32% Primary energy of electrical energy 697 kw 15% energy recovered 830 kw 18% heating 1320 kw 29% a) b) Fig. 9. The energy balance of the geothermal heating station using heat pump: a the energy delivered in the district heating system; b the primary energy consumption. Fig. 10. The scheme of the heating geothermal station using heat pump and gas-fired HWB. PHE plate heat exchanger; HP heat pump; HWB hot water boiler; CT cooling tower. Economically, the solution is very attractive; the necessary investments for capture, distribution and burning of these gases are recovered quickly, and the price of energy delivered in system decreases, being determined solely by the price imposed by the geothermal water well owner (FORADEX SA Bucharest), and maintenance and operation costs of the system Low power gas engine cogeneration units This kind of cogeneration implies the existence of one or more internal combustion motors using as fuel the gases separated form geothermal water, which are connected to an electric generator. Also, thermal energy is produced by cooling the exhaust gases, lubricating oil and engine jacket (figure 11). The advantages of the gas engine cogeneration are: a) the use of the thermal motors imply much simpler systems, less voluminous, cheaper and fully controlled; b) a large range of cogeneration units is possible (from some kw to more than 20 MW); c) a simple operation, a quick start with a short time constant (about 30 s to attain the nominal regime). d) this kind of cogeneration units can be located in the vicinity of energy consumers, resulting small losses in transport lines. 56 TERMOTEHNICA 2/2011

9 Ana-Maria BIANCHI, Sorin DIMITRIU, Florin BĂLTĂREŢU The main disadvantage of using thermal motors is related to their vibrations and noise (about dba); this fact involves the use of silencers on the intake and the delivery lines, as well as a special mounting on heavy supports. The gas engine cogeneration units can be integrated into a centralized heat supply network, or used like in this case - for covering the local thermal needs; the generated electrical energy can be used for local needs and / or for the public grid. It is important to mention that the global efficiency of such a system is about 90%, the energy balance being shown in figure 12. The figure 13 presents the comparison of the separated production of the electrical and thermal energy with their combined production in a gas engine cogeneration unit, using as fuel the combustible gases contained in the geothermal waters from the considered area, and taking into account only the available thermal potential (1450 kw) corresponding to gases possible to be separated from 1009 geothermal well Calimanesti. Electricity 580 kwe (40%) 1450 kw Losses A Thermal 145 kw (10%) 725 kwt (50%) Power Gas engine cogeneration unit Electricity 1660 kw 580 kwe (35%) 860 kw B 2520 kw Losses 1215 kw C Thermal Power 725 kwt (85%) Classic production of electricity and heat Fig. 13. Combined and separated production of electric end thermal energy: A steam power plant; B hot water boiler plant; C gas engine cogeneration unit. Fig. 11. The principle of gas engine cogeneration unit: 1 inlet cold water; 2 oil cooler; 3 inlet gases; 4 thermal engine; 5 electric generator; 6 exaust gases cooler; 8 hot water boiler. Combustible gases Electric energy Thermal Energy Loses T 1 Heat recovered from exhaust gases T 2 Heat recovered from cooling system T 3 Heat recovered from lubricating system T 4 Heat recovered from air cooler Fig. 12. Energetic balance of a gas engine cogeneration unit. It can be observed a reduction of 42.3% of the primary energy consumption from fossil fuel by using the gas engine cogeneration solution, for the same energetic effect. Figure 14 presents the scheme of the heating geothermal station using heat pump and gas engine cogeneration unit. Taking in account only the gasses collected from 1009 Calimanesti well (see table 2), it obtains a supplementary thermal power of 725 kw (for available volume flow of 18 l/s), complete covering the peak thermal load of the centralized heating system. The produced electric power covers the consumption of heat pump, and the exceeding power covering the consumption for thermal fluid pumping in the heating system and some local consumption. This solution can be achieved in modules with small units; it results an economic and flexible system operation, in according to thermal need of the consumer. The price of the gas engine cogeneration units is nowadays about EUR/kWe, which makes the investment to recover quickly, and determines a low cost for the energy delivered in system. Such solution ensures energy independence, the cost of delivered energy including only the cost of geothermal water and for maintenance and operation Low power gas turbine cogeneration units The small gas turbine cogeneration units, using gaseous or liquid fuel, have become commercial and operationally about ten years ago. The efficiency TERMOTEHNICA 2/

10 UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES of electric energy production is about 28 30%, and global efficiency of combined electric and thermal energy production is about % (exhaust gases temperature of 90 o C). The advantages of gas turbine cogeneration are: a) very low polluting emissions, without chemical treatment or afterburning installation; b) one element in motion - the impeller; c) air bearings and air cooling; d) possibility for using a great variety of liquid and gaseous fuels, including high content of H 2 S gases; e) optimization for permanent full load operation (24x7); f) ability to track the load variations of the consumer; g) full automation and unattended operation; h) maintenance at great intervals of time (about 8000 hours) and guarantee operation over hours; i) low level of noise (60 70 dba at 1 m). The main disadvantage of using gas turbines is related to their lower electric efficiency and to their price, greater than that of gas engines. Fig. 14. The scheme of the heating geothermal station using heat pump and gas engine cogeneration unit. PHE plate heat exchanger; HP-heat pump; GECU-gas engine cogeneration unit; CT-cooling tower. Fig. 15. Gas micro turbine cogeneration unit. 1 power converter and command and control unit; 2 high frequency electric generator; 3 centrifugal turbo-compressor; 4 air admission; 5 delivery pipe of compressor; 6 annular combustion chamber; 7 micro gas turbine; 8 exhaust pipe of turbine; 9 intake fuel pipe; 10 economizer; 11 by-pass valve; 12 hot water boiler; 13 hot water delivery pipe; 14 by-pass pipe; 15 hot water return pipe; 16 exhaust manifold; 17 fuel pump/gas compressor. The operating scheme of a gas micro turbine cogeneration unit is shown in figure 15. The atmospheric air is aspired by the centrifugal compressor 3 through pipe 4. The compression ratio is about 4, the value of internal compressor efficiency about %, and compressed air temperature about 250 o C. In the recovery heat exchanger 10, the air is warmed to about 500 o C temperature, before being introduced into combustion chamber. The combustion chamber, annular type, ensure formation of a homogeneous mixture, with an excess air factor about 5 6. The exhaust gases have a very low content of polluting emissions (up to about 24 ppm) and an oxygen content about 15 %. The output temperature of the combustion chamber is about o C. The rotation speed of the turbine-compressor group is very high: rpm, the value of internal turbine efficiency is about %, and the exhaust gases temperature about 650 o C. The temperature of gases after the heat exchanger 10 is about 280 o C. These gases cross the hot water boiler 12, which prepares hot water at 70/90 o C, then being exhausted into atmosphere. The hot water boiler has an electronic controlled by-pass on gases part, its thermal load being very easy to modify according to consumer needs. 58 TERMOTEHNICA 2/2011

11 Ana-Maria BIANCHI, Sorin DIMITRIU, Florin BĂLTĂREŢU In the figure 16 is presented a 250 kw gas micro turbine cogeneration unit, MT250 Ingersoll- Rand. Overall dimensions are 213x372x228 cm, and mass of 5500 kg. The scheme proposed for energetic potential recovery of the gases separated for geothermal water drill 1009 Calimanesti, using a heat pump and a gas micro turbine cogeneration unit is shown in figure 17. The figure 18 presents the comparison of the separated production of the electrical and thermal energy with their combined production in a gas micro turbine cogeneration unit, using as fuel the combustible gases contained in the geothermal waters from the considered area, and taking into account only the available thermal potential (1450 kw) corresponding to gases possible to be separated from 1009 geothermal well Calimanesti. Control and metering panel Generator Hot water boiler Economizer Combustion chamber Micro turbine Fig kw gas micro turbine cogeneration unit, Ingersoll-Rand. Fig. 17 The scheme of the heating geothermal station using heat pump and gas micro turbine cogeneration unit: PHE plate heat exchanger; HP heat pump; GMTCU gas micro turbine cogeneration unit; CT cooling tower kw kw A B C Electricity Losses Thermal Power Gas micro turbine cogeneration unit Electricity 435 kwe (30%) 290 kw (20%) 725 kwt (50%) 435 kwe (35%) 2105 kw Losses 945 kw Therma l 725 kwt (85%) Classic production of electricity and heat Fig.18. Combined and separated production of electric end thermal energy: A steam power plant; B hot water boiler plant; C gas micro turbine cogeneration unit. The efficiency of heat production by the gas micro turbine cogeneration unit is the same order of magnitude as that of the gas engine cogeneration unit (50 %), so it gets the same heat in system. The electrical efficiency of gas turbine cogeneration unit being smaller, a smaller amount of electricity is produced, but sufficient to ensure the operation of heat pumps and circulation pumps. Also, this plant can operate autonomously in terms of energy. The cost of gas micro turbine cogeneration units is compared to that of gas engines, EUR / kwe, making investment in this case to recover quickly. Unlike gas engine installations, maintenance costs are very low, at EUR/h, and the staff are virtually nil, because operation is completely automatic. 6. CONCLUSIONS The thermal potential of geothermal water and associated combustible gases composition of the analyzed area is a significant primary energy reserve. It may allow operation of an autonomous heating system of Căciulata-Călimăneşti Cozia localities. TERMOTEHNICA 2/

12 UPDATING THE URBAN ELECTRIC POWER AND HEAT SUPPLY SYSTEMS, USING GEOTHERMAL SOURCES The solution using the heat pump can cover winter over 80% of heat peak required, the rest of it (for extreme weather conditions / severe) can be produced in oil-fired hot water boilers, or by using the energy recovered from the combustible gases coming from reservoir with geothermal water. Using as fuel the combustible gases separated geothermal water, we obtain the hot water boilers efficiency of similar value to that obtained for the operation of liquid fuel; the price of thermal energy produced is however much lower, given the removal cost fuel. This solution of direct burning has the lowest investment cost compared to those involving gas engine or gas micro turbines cogeneration. If the heat pump and hot water boilers are made in a modular structure, functioning is very flexible and can track changes in thermal load of consumers, only by changing the flow of geothermal water taken from wells. The advantages of cogeneration are well emphasized by the use of gas engine or gas micro turbine units using the combustible gases associated with geothermal water as fuel. Worthy to note is that both solutions allow a great operational flexibility due to selective use of the heat pump. Thus, in summer, when thermal heating load decreases, the heat pump can be kept in partial operation; in this case it is reduced significantly geothermal water flow over the well, thus contributing to conservation of the geothermal source. The proposed solution of using a combustion engine cogeneration system fueled by combustible gas leads to a reduction of 42.3% of primary energy consumption for the same amount of heat and electric power produced separately. The initial investment is high, but the recovery period (4-5 years) is very reasonable; accordingly the price of delivered heat unit are very favorable, due to the elimination of electricity consumption to drive the heat pump and circulation pump. Maintenance and operating costs are high due to the need for technical revisions and replacement equipment. The use of gas micro turbine cogeneration units leads to an efficiency having the same order of magnitude as that of gas engine cogeneration units, so it gets the same energy in the heating system. In this case, a smaller amount of electricity is produced, enough however to ensure the operation of heat pumps and circulation pumps. The proposed solution with gas micro turbines has the advantage of lower maintenance costs and higher reliability. Both solutions involving cogeneration, both gas engine and one with gas micro turbines, have the major advantage of autonomous operation of respective plants that feed on themselves. They may also be designed with a modular function, allowing a dynamic response according to variable needs of consumers, thus ensuring geothermal resource conservation, exigency imposed by the requirement of sustainable development of the area. REFERENCES [1] * * * Strategia de valorificare a surselor regenerabile de energie din România (The strategy for the renewable energy resources in Romania), ISPE study nr. I B0-002 (2007). [2] * * *. Studiu privind evaluarea potenţialului energetic actual al surselor regenerabile de energie în România (solar, vânt, biomasă, microhidro, geotermie), identificarea celor mai bune locaţii pentru dezvoltarea investiţiilor în producerea de energie electrică neconvenţională, ICEMENERG Res. study for Economy Ministry (2006). [3] Bianchi A.-M., Băltăreţu Fl., Drughean L., Teodorescu D., Energétique Urbaine et Energies Renouvelables, - INP, Grenoble, [4] Radcenco, Vs., Florescu, Al., Dimitriu, S., et al., Instalaţii de pompe de căldură, Editura Tehnică, Bucureşti. [5] Burchiu N., Burchiu V., Gheorghiu L., (2006), Sistem centralizat de alimentare cu căldură, bazat pe resurse geotermale, în oraşul Călimăneşti Judeţul Vâlcea, The 4th Nat. Conf. of the Hydroenergeticians from Romania - Dorin Pavel, Paper Nr Proc. Conf. CD. [6] Strachan N., Dowlatabadi H., Distributed generation and distribution utilities, Energy Policy, 30 (2002), [7] Devine M., Chartok M., Gunn E., Huettner D., Avoid cost rates: economic and implementation issues, Energy Systems and Policy, 11 (1987), [8] ANRSC - Date privind starea serviciilor energetice - [9] INGERSOLL-RAND Industrial Technologies - MT250 Series Microturbine, technical specification, [10] Khisamutdinov N. - Gas Engine and Gas Turbine Cogeneration Units - EEICT sbornik 03, 2010, Brno, Cz. 60 TERMOTEHNICA 2/2011