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

• An integrated fluidized bed was used for coupling coal pyrolysis and gasification.
• Coupling coal pyrolysis of the transport bed increased CH4 content in the syngas.
• The formation of CH4 was enhanced observably by raising the operating pressure.
• This study verified the technical feasibility for CH4-rich syngas production.

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.

This figure presents a comparison of CH4 content in produced syngas among the gasification in the integrated fluidized bed (IFB), usual fluidized bed (FB) and Lurgi gasifier. The produced CH4-rich syngas in IFB had the CH4 content of up to 11.2 vol.% under optimized conditions, which was about six times higher than 2.0 vol.% for the fluidized bed gasification and close to 12.0 vol.% for the Lurgi gasifier. Accordingly, we can summarize that the proposed IFB gasification process works like Lurgi gasifier to have different thermal regions in the reactor but the new process treats small-size coal particles below 10 mm to extend the application of the Lurgi's working principle for the production of CH4-rich syngas.Figure optionsDownload as PowerPoint slide