The major assumptions regarding the moving bed (updraft gasifier) model are as follows:

• There is no temperature or concentration distribution radially.

• The solid hydrodynamic is considered as a plug flow flowing downward.

• The gas flows upward as a plug flow.

• The mass transfer between two phases takes place by diffusion [14].

The mass balance equation ofjth-gas species can be written as (10.6):

Also, the energy balance of the gasifier in the z direction is expressed as follows:

These equations will be solved simultaneously with the appropriate kinetics discussed in section 3.