Dual bed pyrolysis gasification of coal: Process analysis and pilot test
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Via isolating the fuel pyrolysis and char gasification, the so-called dual bed pyrolysis gasification (DBPG) was proposed to realize the co-production of pyrolysis products and gasification gas. The process simulation with Aspen Plus shows that the DBPG process can run autothermally using air as the gasification reagent, but the complete conversion of char in the gasifier requires relatively high O/C ratio due to the absence of steam in the reactor. This would make the higher heating value (HHV) of the produced gasification gas below 1000 kcal/Nm3. Adding steam to the char gasifier can realize full char conversion at lower O/C ratio to improve the gasification gas quality. The effect of air preheating on the gasification performance was further analyzed to optimize the operating conditions of DBPG. A pilot scale plant (100 kg-coal/h) of DBPG was established and tested by using air as the gasification reagent plant to verify the technology feasibility. At the steady operating temperatures of 600 °C for pyrolyzer and 850 °C for gasifier, the produced pyrolysis gas was rich in hydrocarbons and the tar yield reached 8.4 wt% and was rich in phenols and its derivatives, but the HHV of the gasification gas was only 510 kcal/Nm3, much lower than the simulated value. A laboratory test on char–air gasification in a fluidized bed reactor further showed that the short residence time of char inside the gasifier and thus the low carbon conversion and the burning of the produced gas in the reactor was the cause for this lower heating value of the gasification gas.
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