Power plants with CO 2 capture using integrated air separation and flue gas recycling

Abstract

Natural gas (NG) and synthetic gas (SG) fired power plants are investigated. Both, NG and SG are burned in highly enriched oxygen (99.5%+) and recycled CO 2 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 CO 2 from the flue gas. The condensed CO 2 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 CO 2 capture, the overall efficiency, defined as electricity out/heat in, is estimated at 45% for the NG fired plant, compared to a plant without CO 2 capture of 54%. The thermal efficiency of the coal gasification-SG fired plant is estimated at about 36.6%, compared to a plant without CO 2 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 CO 2, thereby avoiding carbon taxes, if levied. The efficiency of the coal gasification plant with CO 2 capture is of the same order as modern pulverized coal fired, single cycle plants without CO 2 capture. Furthermore, these plants emit no NO x, SO 2 and particulate matter. In fact, the plants require no smokestack.