Modelling and design of gas-solid reactors

The basic approach is to consider the problem in two parts. Firstly, the reaction of a single particle with a plentiful excess of the gaseous reactant is studied. A common technique is to suspend the particle from the arm of a thermobalance in a stream of gas at a carefully controlled temperature the course of the reaction is followed through the change in weight with time. From the results a suitable kinetic model may be developed for the progress of the reaction within a single particle. Included in this model will be a description of any mass transfer resistances associated with the reaction and of how the reaction is affected by concentration of the reactant present in the gas phase. 

The second part of the problem is concerned with the contacting pattern between gas and solid in the equipment to be designed. Material and thermal balances have to be considered, together with the effects of mixing in the solid and gas phases. 

These will influence the local conditions of temperature, gas composition and fractional conversion applicable to any particular particle. The ultimate aim, which is diflicult to achieve because of the complexity of the problem, is to estimate the overall conversion which will be obtained for any particular set of operating conditions. 

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