TBCFB system simulation and optimization for pyrolysis-gasification-combustion of low rank coal
(2.College of Chemistry and Biological Engineering, Taiyuan University of Science and Technology, Taiyuan, Shanxi, China 030021)
(3.North Japan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, Aomori 030-0813, Japan)
【Abstract】The quality-based utilization technology of low rank coal has attracted much attention due to its advantages in energy saving and emission reduction. A novel triple-bed combined circulating fluidized bed (TBCFB) system, which includes a pyrolyzer, a gasifier and a combustor, is developed to minimize energy loss. A new process is proposed to use char particles instead of sand particles as heat-carried circulating medium and an Aspen Plus process simulation is established to obtain optimum operating conditions for material conversion and energy utilization among three bed reactors. The results show that 40% char combustion can provide enough energy for both low rank coal pyrolysis at 600 °C and gasification of water over 60% residual char at 800.9 °C. The high-heat-capacity char particles significantly reduce the amount of heat-carried particles needed to circulate in the system. To meet the requirements of heat transportation, the mass ratio of char to low rank coal is 5.5, whereas the mass ratios of quartz and ash to low rank coal are 11 and 12, respectively. Comprehensive analysis of syngas composition, cold gas efficiency (CGE) and lower heating value (LHV) indicates that the optimal ratio of steam to char (St/C) is 1.5 in gasification. The simulation results provided some guidance on the industrial application of TBCFB system with char as heat-carried particles.
【Keywords】 quality-based utilization; circulating fluidized bed; simulation; gasification; optimization;
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