Results from Optimization Studies of Multistage Binary Cycles for Utilization of Low-Temperature Geothermal Heat Carrier

The creation of efficient technologies for converting low-temperature heat into electricity using binary power units operating on the organic Rankine cycle is an urgent problem of modern energy. Interest in these technologies is steadily growing since they make it possible to utilize the heat of waste heat carrier in various industries and geothermal power plants (GeoPPs). Currently, low-temperature resources, which are widespread throughout the world, are increasingly used as sources of geothermal heat carrier for generating electrical energy. One of the ways to increase the efficiency of binary technologies can be the use of multicascade binary energy complexes, which are several binary circuits connected in series. Due to the possibility of optimal selection of the working fluid in each circuit, the highest efficiency of an individual cascade and the energy complex as a whole is ensured. Preliminary estimates showed that the additional power that can be obtained by adding a new cascade decreases as the number of cascades increases. Optimization calculations were limited to comparing two- and three-stage binary power complexes with a single-stage binary power unit. The results of studies into the influence of the choice of an organic working fluid and the temperature of a geothermal heat carrier on the technical and economic characteristics of multicascade binary energy complexes with the utilization of a geothermal heat carrier with a temperature of 70°C are presented. It has been established that the efficiency of heat transfer to the binary cycle of multicascade energy complexes decreases with an increase in the temperature of the initial geothermal heat carrier. It is shown that the greatest decrease in the specific consumption of the geothermal heat carrier and the simultaneous increase in power during the transition from a single-stage power unit to two- and three-stage power complexes are achieved at low values of its temperature.