The range of application of ORC power plant in power stations fed with low and medium thermal sources

West-Pomeranian University of Technology, Szczecin, Department of Heat Engineering, al. Piastów 17, PL-70-310 Szczecin, Poland

^* Corresponding author: tomasz.kujawa@zut.edu.pl

Abstract

The work presents the diagrams of the applied power plant solutions with a description of their operation and calculation algorithm. In the latter case, the cycle of thermodynamic transformations of the Rankine cycle presented in the T-s coordinate system was used, which reflects the subsequent transformations occurring in individual devices of the power plant, including the method of determining unit quantities characterizing their operation. The energy balance equations of the evaporator and the heater are presented, which among other things will be the basis for determining the coefficient that plays an important role in determining the range of applications of the single-circuit sub-critical power plant in the power plant/CHP plant. The coefficient ϕ was defined as the ratio of the mass stream of water flowing through the counter-current heat exchanger in which the liquid of the working medium is heated within the limits of condensation and evaporation temperatures, to the mass stream of water leaving the evaporator according to the dependence ϕ = ṁ_s1/ṁ_s. It has been assumed that a given mass stream of water ṁ_s at a given temperature T_s1 is heated in a heat exchanger which is the upper heat source. The calculations of the power plant for selected working fluids (R227ea, RC318, R1234ze and R1234yf) were made for different evaporation temperatures taking into account near-subcritical temperatures for selected supply water temperatures. On this basis, the figures ϕ = f(T_EVAP) illustrating the application ranges of a single-circuit power plant in a power plant/CHP plant were drawn up. The analysis of the above figures became the basis for formulating final conclusions.