Reactivity of the fuel
The reactivity is an important factor determining the rate of reduction of carbon dioxide to carbon monoxide in a gasifier. Reactivity influences the reactor design insofar as it dictates the height needed in the reduction zone.
In addition certain operational characteristics of the gasification system (load following response, restarting after temporary shutdown) are affected by the reactivity of the char produced in the gasifier. Reactivity depends in the first instance on the type of fuel. For example, it has been observed that fuels such as wood, charcoal and peat are far more reactive than coal.
Undoubtedly, there is a relation between reactivity and the number of active places on the char surface, these being influenced by the morphological characteristics as well as the geological age of the fuel. The grain size and the porosity of the char produced in the reduction zone influence the surface available available for reduction and, therefore, the rate of the reduction reactions.
It is well known that the reactivity of char can be improved through various processes such as steam treatment (activated carbon) or treatment with lime and sodium carbonate.
Another interesting point is the assumed positive effect on the rate of gasification of a number of elements which act as catalysts. Small quantities of potassium, sodium and zinc can have a large effect on the reactivity of the fuel.