Thermodynamic Analysis of Ways to Modernize CHP Plants with Back-Pressure Turbines in the Absence of an Industrial Steam Consumer

Thermal power plants with back-pressure turbines have been widely used for the combined production of electricity and industrial steam. Due to the decline in industrial production by more than 50% between 1990 and 1998, the demand for industrial steam decreased, as a result of which some of the pressure turbine units lost their load and were decommissioned. In order to resume the operation of thermal power plants with back-pressure turbines, it is possible to modernize existing power units. This article presents the results of a comparative thermodynamic analysis of various ways to modernize thermal power plants with P-type turbines: a superstructure of a condensing turbine and a superstructure of a heat exchanger heating carbon dioxide used as a working fluid of a closed Rankine or Brayton cycle. Calculated estimates of the influence of ambient temperature on the energy efficiency of the proposed circuit solutions have been obtained. It has been established that the use of a circuit with a carbon dioxide working fluid proves to be a thermodynamically effective solution at outdoor temperatures below 7°C. In turn, the payback period for modernization by adding the carbon dioxide cycle is 13.5 years.