As we saw in Figures 6.4and 6.6, the cross-sectional area of a downdraft gasifier
may be nonuniform; it is narrowest at the throat. The hearth load is, therefore,
based on the cross-sectional area of the throat for a throated gasifier, and for a
throatless or stratified downdraft gasifier, it is based on the gasifier cross-
sectional area. The actual velocity of gas is, however, significantly higher than
the designed space velocity because much of the flow passage is occupied by fuel
particles. The velocity is higher in the throat also because of the higher temperature there. Table 6.6gives some characteristic values of these parameters.