Performance of a down-draft charcoal gasifier

The gas composition and temperature profiles for charcoal, gasified in the down-draft mode, have been obtained from theoretical considerations. The prediction is based on kinetics and the heat and mass transfer mechanisms in an air-blown gasifier at atmospheric pressure. The charcoal has been assumed to be pure carbon, i.e. free from volatile matter and ash. Parametric studies were made on solid and gas flow rates, char reactivity and particle size, both with dry air and with steam in the system. The rate parameters used were those for anthracite coke and were taken from published literature, with appropriate reactivity corrections. The results showed the O2 consumption took place very rapidly, in a distance of about 10-15 cm from the level at which air entered; the CO2 concentration dropped after increasing to a maximum; the CO and H2 concentrations continually increased from zero. The model predictions agreed reasonably with experimental results.