Abstract
Comparative studies were carried out on cycle efficiencies of five coal synthesized gas driven combined power plants. In the top gasification scheme, where the coal is gasified separately from the power generation units, we considered an oxygen combustion MHD topping cycle (Case I), a 40% oxygen enriched air combustion (Case II), a high temperature preheated air combustion (Case III) and a gas turbine topping cycle (Case V). The bottoming is a steam cycle in these four cases. The fifth case (Case IV) was a tail gasification scheme with oxygen combustion plasma MHD as the topper and a combined gas turbine and steam turbine system as the bottoming system, where the coal was synthesized by the high temperature MHD exhaust gas and both of the top and bottom units were driven by the synthetic fuel. Assuming the same enthalpy extraction for the MHD generator, the gas turbine cycle and the steam turbine cycle, the same inlet and outlet temperature at the wall separated type regenerator and the same exhaust temperature at the stack in five cases, we showed that the Case IV exhibited the highest plant efficiency of 62.5% which was higher than that of the Case V by about 10%.
