Methane-rich syngas production in an integrated fluidized bed by coupling pyrolysis and gasification of low-rank coal

An integrated fluidized bed which combines a fluidized bed gasifier and a transport bed pyrolyzer was proposed to produce CH4-rich syngas from coupling pyrolysis and gasification of low-rank powder coal below 10 mm. This study investigated the effects of major operating parameters on CH4 content in the syngas produced from processing a kind of subbituminous coal in a laboratory facility. It was found that the formation of CH4 was facilitated under the conditions of lower overall excessive oxygen ratio (ER), lower temperature of gasification (830–970 °C), higher temperature of pyrolysis (500–700 °C) and higher holdup of coal in transport bed. The CH4 content in the produced syngas increased with elevating the operating pressure but decreased with increasing the steam to carbon ratio (S/C) for gasification. Coupling transport bed pyrolysis with fluidized bed gasification at atmospheric pressure caused the CH4 content in the syngas to be 7.1 vol.% under the conditions of ER = 0.1, S/C = 0.1, gasification temperature of 900 °C and pyrolysis temperature of 700 °C, which was higher than 5.1 vol.% for the case without coupling coal pyrolysis. At the operating pressure of 1.4 MPa the CH4 content reached about 11.2 vol.%, about six times higher than 2.0 vol.% for the usual fluidized bed gasification and close to 12.0 vol.% for the Lurgi gasifier.