Simultaneous production of CH4-rich syngas and high-quality tar from lignite by the coupling of noncatalytic/catalytic pyrolysis and gasification in a pressurized integrated fluidized bed

Abstract

An integrated fluidized bed (IFB) reactor with a two-stage configuration has been developed to process small-size coal particles for the simultaneous production of CH4-rich syngas and high-quality tar, in which coal pyrolysis occurred in an upper transport bed (TB) within an atmosphere mixing steam and syngas generated by steam-oxygen gasification of coal or char in a lower fluidized bed (FB). The coupling effect was investigated by combining non-catalytic/catalytic pyrolysis and gasification in a pressurized IFB. Having TB pyrolysis obviously raised CH4 yield (also its content in producer gas) and tar yield. The respective contributions to CH4 formation from the TB pyrolysis and FB gasification were mainly relevant to operating pressure and Ca(OH)2 catalyst. Raising pressure facilitated CH4 formation. When lignite was treated without catalyst, the contribution from TB pyrolysis was greater than that from FB gasification as hydropyrolysis was intensified by pressure in H2-rich gas atmosphere from the FB gasifier. Adding catalyst into lignite reversed their contributions. The FB catalytic gasification formed more CH4 because Ca(OH)2 functioned well asa catalyst for CH4 formation in pressurized gasification. With elevated pressure or/and the addition of Ca(OH)2, pyrolysis tar yield decreased in different degrees but its quality was improved. With the combination effect of pressure and Ca(OH)2, producer gas from the tested IFB reactor was highly rich in CH4 to reach 10.8vol%, with as well a high H2/CO ratio of 2.3 that is suitable for making SNG. The obtained tar had its light tar content as high as 95wt%.