Thermodynamic analysis of the 2nd generation pressurized fluidized-bed combustion cycle utilizing an oxy-coal boiler and a gasifier

Abstract

This study proposes the 2nd generation hybrid pressurized oxy-coal combustion power cycle that utilizes both fluidized-bed combustion coupled with the Rankine cycle and gasification connected to the Brayton cycle. The fluidized-bed boiler and gasifier are thermally connected by a flue gas stream flowing from the former to the latter. This improves thermal integration carbon conversion in the gasifier. The Rankine cycle is thermally connected to the Brayton cycle through the reheating process of intermediate pressure steam. This hybrid cycle enables the system to recover thermal energy from the pressurized flue gas with effective thermal integration in a way that it balances heat flow rates between hot and cold streams and increases the degree of freedom for heat flow control. The proposed system also reuses cold boiler exhaust gas as a diluent of the Brayton cycle to control its gas turbine inlet temperature, which raises the gas turbine flow rate and hence the gross power. The results indicate more than 9%-point and 1%-point increases in the gross and net efficiency, respectively, as compared to a single Rankine cycle system. The proposed hybrid system exhibits the net efficiency of 34.39% (HHV) higher than 33.04% (HHV) of the single oxy-PFBC cycle.