An experimental investigation of high-ash coal gasification in a pilot-scale bubbling fluidized bed reactor

Gasification of low-grade, sub-bituminous coal with a high-ash content above 45% is carried out in a pilot-scale bubbling fluidized bed reactor using air and steam as the fluidizing gases. For a stable autothermal operation of the gasifier, the effects of equivalence ratio (phi) and steam/coal ratio (psi) on syngas composition, carbon conversion, cold gas efficiency, and agglomeration behavior are investigated. The chemical composition of the ash samples is analyzed using X-ray fluorescence, whereas a scanning electron microscope, coupled with energy-dispersive spectroscopy, is utilized to inspect agglomerates formed during the gasification. The optimum range of phi is found in the range of 0.19-0.28, which maintains bed temperature in the range of 800 - 900 degrees C. Steam injection increases heating value, carbon conversion, and gasification efficiency, however beyond a threshold value of psi, no additional gain is observed. The highest heating value of the syngas obtained from the experiments is found to be 3 MJ/Nm(3), whereas the corresponding carbon conversion and cold gas efficiency are found to be 85%, and 48%, respectively. At low fluidization numbers, agglomerates are formed due to local hotspots, as the collected ash sample has small alkali content. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study investigates the gasification of low-grade, sub-bituminous coal in a pilot-scale bubbling fluidized bed reactor. The effects of equivalence ratio and steam/coal ratio on the composition of the syngas, carbon conversion, cold gas efficiency, and agglomeration behavior are studied.