| Abstract |
Increase of geothermal heat implementation for power production can be provided by usage of binary energy installations, which at low temperatures of geothermal fluids can be more efficient than stem turbine plants. In the paper a generalized scheme of a geothermal power plant (GeoPP) is described, which includes various options of the geothermal fluid utilization: power production by a steam turbine, which use the steam separated from the geothermal fluid; use of this fluid heat to produce vapor of a low temperature boiling substance and production of power in a turbine fed by this vapor; a combined power production scheme using both working fluids and turbines. The elaborated mathematical model can be used to analyze the main energy indices of various schemes at prescribed initial parameters of the geothermal fluid (temperature, steam quality, flow rate from the well) and ambient temperature defining the thermodynamic cycle lowest temperature as a function of the back pressure at the steam turbine exit, kind of low boiling working fluid, its maximum pressure and flow rate in the low boiling loop. Variants are investigated when to the low boiling loop only the heat of the separated geothermal vapor is transferred, as well when the heat of the separated geothermal water is taken into account. In this last case the cooling down of the geothermal liquid is limited to avoid precipitation of salts from the fluid in the vapor superheater. Freons R12 and R134a, as well as propane, isobutane, butane, pentane, isopentane and ammonia are considered as low boiling fluids. Proper equations of state are used in each case. Calculations are made with reference to the design of the unit for the Verchne-Mutnovskaya GeoPP with temperature of the geothermal fluid 162?—, vapor quality 0,3 and flow rate of the well 36,6 kg/s. It is concluded that a GeoPP, which use only a steam turbine can produce about 8 MW of electric power, only a low boiling working fluid can produce some 5.5 up to 7 MW depending on kind of the working fluid and limits of cooling down the geothermal water. When the combined scheme is used for most low boiling liquids candidates a flat optimum is obtained (about 8.5 MW) when the back pressure of the steam turbine is close to atmospheric. The influence of the geothermal fluid steam quality upon the GeoPP energy indices is also considered. The research work was carried out in close co-operation with the JSC ìGeothermî and ìNaukaî ñ leading institutions in the field of GeoPP imolementation in Russia. The study is supported by the Russian Foundation for Basic Research (grant 03-02-16637). |