Experiments and modeling studies on the gasification of wood-char

Abstract

In this chapter, the experimental data on the reactivity of wood char spheres with steam at high temperatures are presented. The earlier model is extended to include both kinetic and transport aspects of char-steam interactions, and good agreement with experimental results is demonstrated. The need to employ a detailed kinetic reaction mechanism is also emphasized.

Data on wood char reactions with CO /N , O /N , and H O/N mixtures are combined to obtain correlations for CO /H O/O /N mixtures. The single-particle model is further extended to a packed bed of particles. Packed-bed analysis is used to determine the propagation front movement, gas temperature, and solid temperature within the bed. The composition of the exit gas is also predicted.

The predictions are compared with the present experiments as well as with the experimental results of Reed and Markson (1983) and Groeneveld (1980). Peak propagation rate is obtained at a flux of 0.1 kg/m²·s, while peak CO formation is observed at higher flux. Beyond a certain flux, i.e., 0.3 kg/m²·s, propagation ceases and extinction occurs. This feature has been examined using the analysis proposed by Dosanjh et al. (1987).

From the analysis, it is shown that extinction occurs when all the energy released in the reaction zone is consumed in heating the incoming gas. The model also demonstrates that increasing the heat release in the reaction zone can delay extinction and sustain propagation.