Thermodynamic and economic analysis of a supercritical and an ultracritical oxy-type power plant without and with waste heat recovery

Thermodynamic and economic analysis of two variants (W1 and W2) of an oxy-type power plant (with or without waste heat recovery) are presented in this paper. This plant consists of: a hard-coal-fired pulverized-fuel boiler, a steam turbine unit, a CO2 capture and compression unit and an air separation unit (with a four-end-type high-temperature membrane). A steam turboset gross electric power of 600 MW was assumed. Variants of the oxy-type plant have different live steam parameters (W1-650 °C/30 MPa; W2-700 °C/35 MPa), reheated steam parameters (W1-670 °C/6 MPa; W2-720 °C/6.5 MPa) and structures of the steam turbine unit. Two methods of utilization of waste heat were analyzed: replacement of regenerative feed water heaters and implementation of an additional ORC unit. The characteristics of the thermodynamic and economic analysis of the analyzed plant were determined as a function of the air compressor pressure ratio (β) and oxygen recovery rate (R). The values of these quantities were determined to ensure maximal net efficiency of the plant and the best value of the economic indicator. The results show that utilization of waste heat is essential for efficiency and economic indicator values of the oxy-type plant and optimal values of β and R. The net efficiency of the oxy-type plant can be 4.06 p.p. lower than the analogous efficiency of the reference plant (consisting of a classic pulverized-fuel boiler and steam turbine unit). This decrease of the efficiency is one of the lowest among the CO2 capture technologies.