Combined Generation of Electricity and Heat Based on a Low Temperature Geothermal Source

The article points out the relevance of and prospects for integrated use of geothermal resources for solving various problems, first of all, in the field of electricity and heat generation, which is connected with the fact that a significant potential for the development of geothermal energy sources is available in a number of regions in Russia. The article describes the Khankala geothermal power plant as a unique facility for implementing pilot commercial operation of electricity generating units operating based on the organic Rankine cycle (ORC) with applying a low-grade heat source, the use of which in power units of other types is inexpedient. A thermal cycle circuit arrangement for combined use of a geothermal resource is proposed: for electricity generation in an ORC power unit (with using isopentane as working fluid) and for supplying heat to greenhouses. The electric energy obtained in such power unit is consumed to cover the external energy expenditures, namely, for driving the greenhouse facility network pump. Calculations for different geothermal fluid flowrates were carried out, in the course of which the power capacity of the ORC power unit itself and energy expenditures for geothermal fluid reinjection into the well were evaluated, and the optimal parameters of the system considered were determined. For the proposed thermal cycle circuit arrangement implemented at the Khankala geothermal power plant, the geothermal fluid flowrate at which the minimal amount of electric energy is consumed from the external grid, was adopted as the optimal one. In that case, the additional capital outlays for implementing the ORC power unit, which are mainly characterized by the increase in the heat transfer surface sizes of the power plant’s existing delivery water heater and condenser are also minimized. A conclusion has been drawn that incorporation of such power units into low-grade heat recovery systems for electricity generation purposes is very promising, whereas separation of heat supply and electricity generation is less preferred.