Investigation of Gasification Chemical Looping Combustion Combined Cycle Performance

Abstract

A novel combined cycle based on coal gasification and chemical looping combustion (CLC) offers a possibility of both high net power efficiency and separation of the greenhouse gas CO2. After pressurization, a coal slurry enters a pipe-type gasifier immersed in the CLC air reactor and takes in the heat released from the air reactor. After removal of particulates, the syngas is used as the fuel of the CLC fuel reactor or the supplementary firing. The technique involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from the combustion air to the fuel, and the avoidance of direct contact between fuel and combustion air. The fuel gas is oxidized by an oxygen carrier, an oxygen-containing compound, in the fuel reactor. The oxygen carrier in this study is NiO. The reduced oxygen carrier, Ni, in the fuel reactor is regenerated by the air in the air reactor. In this way, fuel and air are never mixed, and the fuel oxidation products CO2 and water vapor leave the system undiluted by air. All that is needed to get an almost pure CO2 product is to condense the water vapor and to remove the liquid water. When the technique is combined with gas turbine and heat recovery steam generation technology, a new type of combined cycle is formed which gives a possibility of obtaining high net power efficiency and CO2 separation. The performance of the combined cycle is simulated using the ASPEN software tool in this paper. The influence of the water/coal ratio on the gasification and the influence of the CLC process parameters such as the air reactor temperature, the turbine inlet supplementary firing, and the pressure ratio of the compressor on the system performance are discussed. Results show that, assuming an air reactor temperature of 1200 °C, a gasification temperature of 1100 °C, and a turbine inlet temperature after supplementary firing of 1350 °C, the system has the potential to achieve a thermal efficiency of 44.4% (low heating value), and the CO2 emission is 70.1 g/(kW h), 90.1% of the CO2 captured.