COMPARATIVE ANALYSIS OF EXTERNAL COMBUSTION SCHEMES IN THE THREE-STEP COAL GASIFICATION TECHNOLOGY WITH CO₂ RECYCLING

Chemical energy conversion has a great influence on the cold gas efficiency of coal gasification technology. In this paper, a three-step gasification technology with CO₂ recycling is introduced and two external combustion schemes (CO-fueled chemical looping combustion and unconverted coke combustion) are compared. Results showed that the CO-fueled chemical looping combustion scheme has a higher cold gas efficiency of 90.1%, while cold gas efficiency of the unconverted coke combustion scheme is 88.4%. Before the water gas shift subprocess, the chemical energy conversion efficiency in the unconverted coke combustion scheme is 93.2%, which is 1.6 percentage points higher than that in the CO-fueled chemical looping combustion scheme. However, more chemical energy is consumed for CO₂ regeneration in the unconverted coke combustion scheme, which results in chemical energy conversion efficiency decreases from 93.2% to 88.4%. Therefore, better energy matching between reactions can effectively improve the cold gas efficiency of the coal gasification technology. Besides, chemical energy consumption for CO₂ regeneration should be reduced for gasification technology adopting CO2 as a gasifying agent.