Chemical Looping Gasification of Coal in a 5 kW_(th) Interconnected Fluidized Bed with a Two-Stage Fuel Reactor

摘要

Chemical looping gasification (CLG) is a novel technology using lattice oxygen in a solid oxygen carrier (OC) for syngas production. The present work investigated the CLG performance of coal in a 5 kW(th) interconnected fluidized bed, in which the fuel reactor was designed as a two-stage-based circulating bed. The fresh OC from the air reactor entered into the upper stage of the fuel reactor, in which it was reduced by syngas. Then, the partial reduction of the OC was circulated to the bottom stage of the fuel reactor to be reduced further to low-valence metal oxide and catalyze the process of coal gasification. Afterward, the reduced OC was transported to the air reactor for regeneration. The influences of the coal feeding rate, gasification temperature, and gasification agent on the performance of CLG were evaluated in detail. The syngas yield and gasification efficiency were remarkably influenced by the coal feeding rate, with an optimal value of 487.5 g/h in the current unit. The high temperature promoted the coal gasification process with the maximum gasification efficiency and syngas yield corresponding to 75.2% and 0.97 Nm(3) kg(-1) of coal, respectively, at a gasification temperature of 915 degrees C. Steam, CO2, and a mixture of them were used as gasifying agents separately. The experimental results demonstrated that carbon conversion, syngas yield, and gasification efficiency increased with the proportion of steam in the gasifying agent. The OC particles in the upper and bottom stages of the fuel reactor were analyzed by X-ray diffraction. The main phase of the OC particles in the bottom stage was FeO, which has a high catalytic activity on coal gasification and tar cracking. Serious particle agglomeration was observed under the low fluidization flow of 20 L/min and high temperature of 950 degrees C at which the system cannot be stably operated.