A clean coal utilization technology based on coal pyrolysis and chemical looping with oxygen uncoupling: Principle and experimental validation

The coal poly-generation system offers the possibility to produce value-added chemicals, synthetic gas fuels and electricity simultaneously, which can improve the coal utilization efficiency. To realize the multi-generation of gas, tar and heat/electricity with CO2 capture, a new clean coal utilization technology integrating coal pyrolysis and CLOU (chemical looping with oxygen uncoupling) process was proposed. Both thermodynamic process simulation and batch-scale fluidized bed CLOU experiments were conducted to verify its feasibility and obtain some fundamental features. From simulation results, the total exergy efficiency had been improved by 0.82 percent points compared to the typical coal poly-generation system. Based on CLOU experiments of two pyrolytic semicokes of SL lignite (SL-20 and SL-60), it was found that the reactor temperature and the semicoke characteristic were two key factors in determining the CLOU process, in which higher fuel reactor temperature and semicoke with shorter pyrolysis time were favorable to the conversion process. In addition, both the semicokes showed very high CO2 gas yield (higher than 99%) and relatively low unburned gas yields, whilst the combustion efficiencies reached to higher than 93%. The results suggested that SL-20 with CLOU temperature of 900 °C was more favorable for the operation of the new system.