EFFECTS OF PYROLYSIS HEATING RATE ON INTRINSIC REACTIVITIES OF COAL CHARS

The main objective of this work was to determine the effects of pyroly sis heating rate on intrinsic O-2 reactivity of coal chars. Relationsh ips of intrinsic reactivity to other pyrolysis conditions and char phy sical and chemical structure were also investigated, and empirical cor relations were obtained. Two different entrained flow reactors (a flat flame methane/air burner and a drop tube reactor) were used to prepar e chars under a variety of different pyrolysis conditions at maximum p article temperatures and heating rates of 840-1627 K and 10(4) to 2 x 10(5) Ws, respectively. Intrinsic reactivities of a lignite and two bi tuminous coal chars decrease with increasing preparation heating rate. Maximum particle temperature and heating rate are difficult preparati on parameters to separate and were closely coupled in this work, as in most entrained flow coal research. Indeed, much of the work described in the literature defining the effects of pyrolysis heating rate on c oal char reactivity has utilized vast residence time differences, comp aring data from fixed bed (residence time of similar to 1 h) and entra ined flow reactors (residence time of similar to 100 ms). It is conclu ded from this work that observations made on the basis of such experim entation are a function more of residence time and reactor variations (packed or fixed bed, as opposed to entrained flow) than particle heat ing rate. This work also provides evidence that intrinsic reactions of O-2 With coal char (for the three coals observed in this study) are n ot significantly influenced by large differences in char meso- or micr opore surface area obtained by varying pyrolysis conditions.