Proceedings European Geothermal Congress 2007 Unterhaching, Germany, 30 May-1 June 2007

The Concept of Hybrid Power Plants in Geothermal Applications

Bernd Kapp and Horst Kreuter Baischstraße 7, D-76133 Karlsruhe [email protected] and [email protected]

Keywords: hybrid concept, geothermal, biogas, power about 115°C or more depending on the arrangement of the plant heat exchanger in the cycle and the value of the geothermal energy. In addition to the higher heat input in the rankine ABSTRACT cycle the temperature increase of the fluid leads to a higher In many regions of Germany, the temperature of efficiency in the cycle. Both, ORC and Kalina Cycle, show a strong transient of the efficiency in the temperature range geothermal brine that can be tapped in natural reservoirs between 100°C and 120°C. generally is below 120°C. The production of electricity is economically not feasible in most of these areas, because Different thermodynamic calculations with the software with low temperatures the degree of efficiency and thus the Thermoflow were performed to investigate the influence of amount of produced power is too small. With the new the hybrid concept compared to the common stand-alone hybrid concept, it is now possible to feed in energy from a solution of a geothermal power plant (figure 2). A second renewable energy source into the geothermal power comparison between the different cycles (Kalina and ORC cycle while raising the temperature at the same time. using isobutane) is shown in figure 3. 1. INTRODUCTION Electricity generation out of a geothermal energy source depends on the local geological situation. Reservoir temperatures lower than 120°C are usually found if reservoir rocks are not deep enough or if the temperature gradient is too low.

The hybrid biogas-geothermal power concept (figure 5) which was developed by GeoThermal Engineering GmbH in 2004 helps a community in the Upper Rhine Valley to realize a geothermal power project in spite of these unfavourable circumstances.

2. TECHNICAL REALIZATION OF THE HYBRID CONCEPT Figure 2: Geothermal Kalina power plant Husavik, In Neuried, the geothermal power plant will be coupled Iceland (Exorka) with a biogas power plant. This project is now being implemented in this village for the first time worldwide.

Figure 1: Biogas power plant (Schmack Biogas)

In a fermentation process, methane is produced and then combusted in gas engines (CHP). These engines drive a generator which feeds in electricity into the grid. With the help of heat exchangers, the waste heat of both the exhaust and the cooling system of the engines are fed into the low Figure 3: Efficiency of ORC - and Kalina cycle temperature power-cycle of the geothermal power plant. Based on a Kalina cycle configuration in figure 6a the The exemplary calculation shows different effects on the increase of gross power in the hybrid cycle in figure 6d capacity factor: Based on geothermal power with an inlet reached a value of about 360 kWel. The power increase in temperature of e.g. 110°C and a amount of waste heat up to the hybrid ORC isobutane cycle in figure 6c achieved even 3 MW from biogas engines, the cycle can be heated up to a value of 400 kWel. 1 Kapp and Kreuter

In addition to this improvement of efficiency and power, By combining a geothermal power plant with another more synergy effects arise: The waste heat of both, the renewable energy source, the generation of geothermal thermal power and the biogas power, can be sold to energy can be extended regionally. Geothermal reservoirs neighbouring customers. The heat can be used in many with temperatures below 120°C can thus be made different ways: for example for private or office heating, profitable. This doesn’t only apply to parts of the favoured swimming pools or even for vegetable production in geothermal reservoir of the Upper Rhine Valley but even greenhouses. Heat is mainly needed during winter time. In more so to other regions in Germany and Europe. contrast to this seasonal usage, the waste heat of the biogas Especially in the Molasse basin in Bavaria, where the plant can be fed into the geothermal power plant cycle temperatures of the brines in the Malm karst reservoir during the whole year. average between 100°C and 120°C, the hybrid concept provides a high potential. Hence, projects, that wouldn’t be To guarantee a constant heat supply, back-up systems need profitable being based on geothermal energy only, can now to be installed, usually based on conventional heat sources be realized by using the hybrid concept. like oil or gas. By combining these two renewable energy sources, there will always be a renewable back-up system REFERENCES available in case one of the two sources shouldn’t be, e.g. in case of servicing. Hence, there is no more need for a THERMOFLOW: Comprehensive Thermal Engineering conventional back-up system if the waste heat is sufficient. Software. Thermoflow Inc., Sudbury. Ma, USA. If the geothermal power plant is down, the biogas waste Kapp. B., Kreuter, H., Borchert, G. & Treyer, H.: Das heat, which is normally being fed into the geothermal cycle, Geothermie-Biogas Hybridkraftwerk in Neuried. can then be used for direct heating. The waste heat of the Geothermische Vereinigung e. V., Tagungsband, geothermal power plant itself suffices for the direct heat use Geothermische Jahrestagung, Unterschleißheim, system. (2005). Both renewable energy systems produce base load electricity. An uptime of more than 8,000 hours a year is possible. Therefore, a complex control system is necessary which has to adjust the geothermal power circuit to the variation in load of the biogas system, of the direct heat use system and to the variation of the ambient temperature.

Figure 4: Geothermal power plant detail (exorka)

A hybrid power plant like the project in the Upper Rhine Valley can generate up to 44,000 MWh of power per year supplying up to 28,000 people with electric power. In comparison to a conventional natural gas power station, the emission of CO2 can be reduced by up to 18,000 tons per year.

3. CONCLUSION

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Figure 5: Flow diagram of a hybrid geothermal-biogas power plant

116 kWe Pump[18] CT[7] M1 14,5 105,8 17,2 kWe 30,5 204 kWe

B B A A 2,5 17,44 360

1 1.610 kWe 2,55 9,156 G1 360

B A 3 19,78 9,612 75,93 10 110 1 30,5 100 318,6 100 462

Ambient pressure 0,9547 bar Ambient temperature 8,5 C Ambient RH 50 % Ambient wet bulb temperature 4,16 C bar C THERMOFLOW Inc. Gross power 1610,4 kW kg/s kJ/kg 3,06 62,63 Gross electric efficiency(LHV) 11,23 % 30,5 Net power 1256,3 kW Plant auxiliary 354,1 kW

Figure 6a: Geothermal ORC – cycle with isobutane

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0 20 105,7 A 7,026 61,7 6,867 37,47 6,799 37,18 6,732 36,9 17,89 1518,3 B 17,89 1384 20 15,04 20

B A A B G1 2.239 kWe 1,328 22,69 350 6,957 74,71 2,112 245,4

6,799 37,18 4,958 20,2 106 CT[25] 20 203 kWe 20,6 53,11 20

B A

21,59 13,96 20

10 110 9,804 55,33 6,6 13,2 100 100 20 98,2 kWe M2 Ambient pressure 0,9547 bar Ambient temperature 8,5 C bar C Ambient RH 50 % THERMOFLOW Inc. Ambient wet bulb temperature 4,16 C kg/s kJ/kg Gross power 2238,6 kW Net power 1896,4 kW Plant auxiliary 342,2 kW

Figure 6b: Geothermal Kalina – cycle

17 54° 23° 14 11 14,65 106,4 1 31,6 Power kW 29 49 40 5 3 4 3 CT[7] 28 16 B B 228 kWe 10 11 18° 26 12 6 19 49 A A 16 13 14,5 106,3 37,8 7° 8 50 4 2 38 25 23 17 144 kWe 22 21 31 11 M1 36 41 A bar C 19 55° B 24° kg/s kJ/kg 15 12 2.003 kWe 9 1 32 2 9 12 2,55 9,157 1 G1 20 17 400 30 50 42 10 14 7 9,612 74,63 10 110 5 29 18 100 313,2 100 462 B

52 46 27 A 3 19,78 17 1 37,8 48 47 26 6 8

11 12 43 14,65 107 3,06 63,17 6,199 bar C 13 37,8 24 56° 36 34 25° 15 14 kg/s kJ/kg 16 13 15 B B Ambient pressure 0,9547 bar 47° 31 51 44 A A Ambient temperature 8,5 C 20 14 Ambient RH 50 % 30 20 35 33 Ambient wet bulb temperature 4,16 C 39 Gross power 5195 kW Gross electric efficiency(LHV) 22,88 % 2,403 80,04 28 Net power 4744 kW 17,82 40 Plant auxiliary 451,6 kW 15 27 37

2,5 119 17,82 13 16 45

Figure 6c: Hybrid ORC – cycle with isobutane

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4 1 0 20 105,2 A 7,026 61,1 6,867 37,47 6,799 37,18 6,732 36,9 20,79 1515,9 20,79 1381,8 B 23,3 17,52 23,3

20,2 105,5 B A 23,3 2.600 kWe bar C A kg/s kJ/kg B 4 G1 A 2,55 119 6,957 74,17 Jenbacher JMS320GS-B.L - No. 1: 17,82 1064 kWe 2,509 B 1 5

174,1 10 7 1,45 5 2 6 10 A 6,799 37,18 B 5,776

20,2 105 2,973 80 2,55 20,6 53,09 17,82 23,3 7 20,2 105,5 B 1,356 23,72 Jenbacher JMS320GS-B.L - No. 2: 20,75 380 1064 kWe A Ambient pressure 0,9547 bar 2 Ambient temperature 8,5 C Ambient RH 50 % Ambient wet bulb temperature 4,16 C 0,9547 8,898 Gross power 5792 kW 380 21,59 13,96 CT[33] 6 3 Net power 5376 kW Plant auxiliary 416,5 kW 23,3 218 kWe 9,804 53,25 10 110 6,6 13,2 100 100 23,3 114 kWe bar C kg/s kJ/kg M2

Jenbacher JMS320GS-B.L - No. 3: 1064 kWe 3

Figure 6d: Hybrid Kalina – cycle

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