Reduction of CaSO4 oxygen carrier with coal in chemical-looping combustion: Effects of temperature and gasification intermediate

Chemical-looping combustion (CLC) has been suggested as an energy efficient method for the capture of carbon dioxide from combustion. Thermodynamics and kinetics of CaSO4 reduction with coal via gasification intermediate in a CLC process were discussed in the paper, with respect to the CO2 generating efficiency, the environmental factor and the surface morphology of oxygen carrier. Tests on the combined process of coal gasification and CaSO4 reduction with coal syngas were conducted in a batch fluidized bed reactor at different reaction temperatures and with different gasification intermediates. The products were characterized by gas chromatograph, gas analyzers and scanning electron microscope. And the results showed that an increase in the reaction temperature aggravated the SO2 emission. The CO2 generating efficiency also increased with the temperature, but it decreased when the temperature exceeded 950 °C due to the sintering of oxygen carrier particles. The use of CO2 as gasification intermediate in the fuel reactor had a positive effect on the sintering-resistant of oxygen carrier particles. However, increasing the steam/CO2 ratio in gasification intermediate evidently enhanced CO2 generating efficiency and reduced SO2 environmental impact.