Power plants with CO2 capture using integrated air separation and flue gas recycling

Natural gas (NC) and synthetic gas (SG) fired power plants are investigated Both, NG and SG are burned in highly enriched oxygen (99.5%+) and recycled CO2 from the flue gas. Both use the combined gas turbine-steam turbine cycle. SG is obtained from a conventional coal gasification process. Oxygen for coal gasification and oxygen/fuel combustion is obtained from an air separation unit (ASU). Liquid oxygen from the ASU is used to condense part of the CO2 from the flue gas. The condensed CO2 can be resold or sequestered in terrestrial or deep ocean reservoirs. The rest is recycled into the combustor of the gas turbine. By cross-integrating the ASU and the CO2 capture, the overall efficiency, defined as electricity out/heat in, is estimated at 45% for the NC fired plant, compared to a plant without CO2 capture of 54%. The thermal efficiency of the coal gasification-SG fired plant is estimated at about 36.6%, compared to a plant without CO2 capture of 47.8%. The efficiency estimates include the energy spent on air separation and coal gasification. The relatively modest efficiency loss is amply compensated by producing salable byproducts (Ar and N-2) and capturing CO2, thereby avoiding carbon taxes, if levied. The efficiency of the coal gasification plant with CO2 capture is of the same order as modem pulverized coal fired, single cycle plants without CO2 capture. Furthermore, these plants emit no NOX, SO2 and particulate matter. In fact, the plants require no smokestack.