Reactivity of heat treated coals in steam

Abstract

Reactivities of seventeen 40 x 100 mesh US coals charred to 1000/sup 0/C have been measured at 910/sup 0/C in 0.1 MPa of a N/sub 2/-H/sub 2/O mixture containing water vapor at a partial pressure of 2.27 kPa. Char reactivity decreases, in general, with increasing rank of the parent coal. The chars show a 250-fold difference in their reactivities. Results suggest that gasification of chars in air, CO/sub 2/ and steam involves essentially the same mechanism and that relative gasification rates are controlled by the same intermediate oxygen-transfer step. Removal of inorganic matter from raw coals prior to their charring or from chars produced from raw coals decreases the reactivities of lower rank chars whereas reactivities of higher rank chars increase. Addition of H/sub 2/ to steam has a marked retarding effect on char reactivity in most cases. However, in a few cases H/sub 2/ acts as an accelerator for gasification. The effect of particle size, reaction temperature and water vapor pressure on char reactivity is considered.