EVALUATION OF REACTIVITY FUNCTIONS FOR COAL COMBUSTION FROM PARTICLE-SIZE ANALYSIS IN BACKMIX REACTORS

Data obtained by Campbell and Davidson on the particle size distribution (PSD) in a small fluid bed have been used to show that the equations for the PSD in a perfectly stirred reactor (PSR) can yield additional information on the PSD due to swelling and breakage of an entering stream that is nominally monosize. For monosize particles, the results with coke confirm that there is a reciprocal relationship between the PSD function in the bed and the equation for coke. With char, it is shown that the measured PSD function can be used to back out the effects of breakage, with a nearly linear increase found for the number of particles with decreasing diameter due to breakage. The trend obeys a normal expectation. With swelling coals, however, there is also breakage but of a different sort, with the number of particles declining instead of rising with falling diameter. In a considered extension of the PSD analysis to the char burnup region of a coal flame, the problem is shown to be more complex. Problems discussed include the effects of continuous removal, imperfect mixing, and changes in particle density by internal reaction. The problem may then become intractable when approached from the PSD point of view and a Monte Carlo procedure may be the best alternative. © 1990.