Predictions obtained by using the accepted reaction model together with three different reactor models -plug-flow, complete-mixing and bubble-assemblage -are compared. In general, the three reactor models gave significantly different results. The bubbleassemblage model, therefore, represents a valid alternative when modelling fluidized-bed gasifiers. For small inverse space velocities, meaning high steam feed rates and shallow beds, the bubble-assemblage model predicts the lowest (among the three) steam conversions. For deep beds and low steam feed rates, the conversion predicted by the bubbleassemblage model becomes greater than that predicted by the completely mixed model and approaches, the values for the plug-flow model. However, this occurs only at very large height/diameter ratios which are not generally used in operating fluidized beds.
Increase in the reaction rate constant associated with the partial pressure of water, kl, caused a marked increase in conversion. The effect of k2,-associated with the partial pressure of hydrogen, was not so great, conversion decreasing as k2 was increased. Inclusion of the water-gas shift reaction when calculating the gas composition in the kinetic rate expression may be of significance in predicting steam conversion by reactor model 3. However, varying the value of Ke, did not have a significant effect.