Thermodynamic analysis and optimization of low-boiling fluid parameters in a turboexpander

Abstract

The influence of the initial parameters of a low-boiling working fluid on the thermodynamic efficiency for two turbo-expander cycles (with a heat exchanger at the outlet of the turbo-expander and without a heat exchanger) is considered. For each of the studied cycles, the dependences of the exergy efficiency on the temperature of the low-boiling working fluid before the turboexpander at a constant pressure and the dependence of the exergetic efficiency on the pressure of the low-boiling working fluid before the turbo-expander at a constant temperature were obtained. The dependences of exergy losses on the elements of the studied cycles on the parameters of a low-boiling working fluid are constructed and their analysis is carried out. For the considered schemes, the dependences of the exergy efficiency on pressure are constructed at various temperatures of the low-boiling working fluid in front of the turboexpander. An analysis of the results showed that at any temperature of a low-boiling working fluid, it is possible to determine the pressure at which the exergy efficiency of the investigated circuit will be maximum. Graphic dependencies are obtained that are characterized, from a thermodynamic point of view, by the optimal parameters of a low-boiling working fluid. Comparison of these dependences revealed that, over the entire range of studied temperatures (from 100 °C to 300 °C), a cycle with a heat exchanger at the outlet of the turboexpander has a large exergy efficiency. These graphical dependencies make it possible to determine the optimal parameters of the working fluid in the turboexpander cycle, as well as to predict the change in the exergy efficiency of the installation with changing parameters of the working fluid.