The desire to utilize waste heat from various industrial and technological processes leads to the search for new technical solutions and the development of technologies aimed at converting the thermal energy of low-grade heat carriers into electrical energy. Today, one of the most widespread technologies for generating electricity based on the use of low-grade heat is the organic Rankine cycle, which is implemented in binary cycle (ORC) power plants. The increased interest in these technologies is explained by the fact that significant initial capital costs for the creation of binary plants and their relatively low economic performance are in most cases offset by low operating costs for fuel. The use of multistage ORCs can become one of the ways to increase the efficiency of waste heat utilization. Specific examples and promising possibilities for the practical use of modular-staged ORCs in order to utilize the heat of waste heat carriers of various industries are presented. The features of multistage schemes are studied, the operation of which is based on the principle of incremental (step-by-step) energy conversion of a high-temperature geothermal single-phase water heat carrier in ORCs to increase the efficiency of using geothermal resources. Some results of computational studies of thermodynamic indicators and technical characteristics of two- and three-stage ORCs with a high-temperature (180°C) initial geothermal fluid are considered. The analysis of the technical characteristics of two- and three-stage ORCs is carried out in comparison with the traditional single-circuit ORC power unit when using various organic substances as a working fluid. It is shown that the use of a two-stage scheme makes it possible to increase the amount of heat transferred to a binary cycle by 15% in comparison with a single-stage scheme, and the use of a three-stage scheme by 18.9%. When implementing the developed methodology for numerical modeling of geothermal and binary circuits, it is possible to optimize the technological schemes of two- and three-stage ORCs according to the maximum installed power and minimum mass flowrate of the initial geothermal fluid.
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