Evaluation of oxygen as oxidant in coal fired open cycle MHD-steam power plants

This study compares the thermal efficiency and economics of using oxygen rather than air as the oxidant in large coal-fired MHD-steam energy conversion plants, using a computer model to calculate thermal efficiency. The systems compared are a coal-air system with a thermal input of 2000 MW_th and two coal-oxygen systems, one with an input of 2000 MW_th and one with 6600 MW_th. The paper describes the process; compares flame temperature, electrical conductivity, and specific enthalpy; and presents Mollier diagrams for the two systems. At an oxidant preheat temperature of 1644 K, the net thermal efficiency of the coal-oxygen system is 8 to 9 percentage points lower than that for the coal-air system, if the power required to produce the oxygen is taken into account; however, despite its lower thermal efficiency, the coal-oxygen system has a lower cost of electricity. At a preheat temperature of 1644 K, the cost advantage is small, but at temperatures below 1200 K, the cost advantage is significant.