Possibilities for improving the thermodynamic and economic characteristics of an oxy-type power plant with a cryogenic air separation unit

Abstract

In this paper the thermo-economic analysis of the oxy-type supercritical power plant integrated with the cryogenic air separation unit was presented, with the efficiency of the whole power plant of 32.26%. The reduction of energy intensity of ASU (air separation unit) was proposed by appending the membrane module. A hybrid air separation unit allows to decrease the energy intensity of oxygen production from the value of 0.226 kWh/kg O2 for the cryogenic ASU to 0.179 kWh/kg O2, for the analyzed hybrid membrane-cryogenic ASU, with an increase of the net efficiency to 33.84%. This solution causes the efficiency change by 8.7 percentage points in comparison with the reference air-fired power plant.A method of using the waste heat from the ASU and CCS (CO2 capture system) installations for the regeneration system of the steam turbine was proposed as a mean to decrease the efficiency drop. Using the waste heat in the steam turbine system causes an increase of the electric energy of the generator of turbine, and in the consequence leads to the improvement of the efficiency of the analyzed power plant by 0.5 percentage points. An economic analysis showed that the profitability of building of the oxy-type power plant in place of a conventional power plant will be higher with the price of CO2 emission allowances equal to 27.1 €/Mg CO2. All these effects of increasing the efficiency of the block can lead to lowering the cost of electricity generation by 5 €/MWh.