Incorporating a District Heating/Cooling System Into an Existing Geothermal Power Plant

Abstract

Geothermal energy has been used for power generation, space and process heating, and to a lesser extent, space cooling. However, it is rarely used for cogeneration. This paper shows how a district heating/cooling system can be incorporated into an existing geothermal power plant to make the best use of extracted hot brine. In the power plant analysis, exergy destruction throughout the plant is quantified and illustrated using an exergy cascade. The primary source of exergy destruction in the plant is determined to be the reinjection of used brine into the ground, which accounts for 48.1 percent of the total exergy destruction. The overall first and the second law efficiencies of the plant are calculated to be 5.6 and 28.3 percent, respectively, based on the exergy of the geothermal fluid at downwell, and 5.7 and 28.6 percent, respectively, based on the exergy of the geothermal fluid at wellhead. A binary system is considered for the heating/cooling district to avoid corrosion and scaling problems. The heating system, as designed, has the capability to meet the entire needs of the Reno Industrial Park under peak load conditions, and has 30 percent reserve for future expansion. An absorption system will be used for the cooling of the intended 40 percent floor space of the industrial park. An economic analysis shows that the incorporation of the district heating/cooling system with 2,785,000 m2 of floor space connected to the geothermal grid appears to be feasible, and financially very attractive. Further, using the returning freshwater from the district heating/cooling system for partial cooling of the binary fluid of the power plant can save up to 15 percent of the fan work.