Effects of operating pressure on coal gasification

Abstract

Correlation of operating pressure with coal pyrolysis, coal caking, coal clinkering and coal char reactivity is very important as regards coal gasification. It is shown that irrespective of whether the pyrolysing atmosphere is N 2 or H 2, yields of CH 4 and C 2H 6 increase with increasing pressure, but the yields are much higher in H 2. The reactivities of coal chars obtained by pyrolysis under pressure tend to decrease with increasing pressure. The CH 2O and CCO 2 reactions are similar to each other, their reaction rates increase with increasing P H 2O and P CO 2 respectively up to 1–1.5 MPa, and then tend to have a zero order with respect to the partial pressure of reacting gases. Char combustion rates are 0.25–0.35 order with respect to P O 2 , Coal or char hydrogasification is very sensitive to P H 2 , a first order reaction being obtained in a broad range of operating pressure. When air flow rates are kept constant, the coal clinkering ratio increases with decreasing pressure. Trends of coal caking property change with increasing pressure depending on coal rank. Brown coals do not coagulate at normal pressure or under pressure; the caking properties of weakly caking coals increase smoothly with increasing pressure at first, and then remain constant above a characteristic pressure, while the caking properties of caking coals increase throughout the pressure range examined.