Effects of Pyrolysis Heating Rate on Intrinsic Reactivities of Coal Chars

Abstract

The main objective of this work was to determine the effects of pyrolysis heating rate on intrinsic O2 reactivity of coal chars. Relationships of intrinsic reactivity to other pyrolysis conditions and char physical and chemical structure were also investigated, and empirical correlations were obtained. Two different entrained flow reactors (a flat flame methane/air burner and a drop tube reactor) were used to prepare chars under a variety of different pyrolysis conditions at maximum particle temperatures and heating rates of 840−1627 K and 104 to 2 × 105 K/s, respectively. Intrinsic reactivities of a lignite and two bituminous coal chars decrease with increasing preparation heating rate. Maximum particle temperature and heating rate are difficult preparation 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 coal char reactivity has utilized vast residence time differences, comparing data from fixed bed (residence time of ∼1 h) and entrained flow reactors (residence time of ∼100 ms). It is concluded from this work that observations made on the basis of such experimentation are a function more of residence time and reactor variations (packed or fixed bed, as opposed to entrained flow) than particle heating rate. This work also provides evidence that intrinsic reactions of O2 with coal char (for the three coals observed in this study) are not significantly influenced by large differences in char meso- or micropore surface area obtained by varying pyrolysis conditions.