Rate Expression and Evaluation of Reactivity for Gasification of Various Coal Chars with Steam and Oxygen

Abstract

Fundamental study of gasification of 19 kinds of coal chars was carried out gravimetrically with steam (H20 (24%)-N2) at 850°C and oxygen (O2(10%)-N2) at 900°C. The fuel ratio of original coal ranged from 1.2 (brown coal) to 7.9 (anthracite), and each sample char was prepared under the same conditions. The main results obtained were as follows: 1) The fractional gasification f, vs. gasification time θ, curves could be fitted very closely with the equation, f=l — exp(—aθb); (a, b=constant), independent of coalification rank, gasifying conditions and sigmoidal character of fvs. θ curves. This rate equation was derived by assuming that a rate constant k was dependent on the extent of gasification as k(f) = a1/bb(-ln (1-f))(b-1)/b. 2) An average rate constant, k = ∫01k(f)df, which was nearly equal to k at f=0.5, and θ to be f=0.5 (θf=0.5) were found to be useful for evaluation of gasification reactivity of char, and to be correlated with fuel ratio of coal and atomic ratio of H/C of coal and/or char with fairly good approximation. 3) By normalizing gasification time 0 with θf=0.5 to be τ, rate-curves (f vs. θ) of steam or oxygen gasification over 19 kinds of chars were correlated to a characteristic curve shown as f=1— exp(—aτB); (A, B=constant) respectively. © 1982, The Society of Chemical Engineers, Japan. All rights reserved.