STOVES FOR RICE HUSK AND OTHER FINE RESIDUES

Rice husks and other fine residues have historically been regarded as worthless wastes, disposed of by being burnt on site or, on occasions, flushed away into rivers. By converting them into a resource, they become an asset rather than a liability. However, fine particles have particular characteristics that make them impossible to burn in a standard stove. The major sources are rice-husk and sawdust, but other residues, such as millet husk and peanut shells can often be burnt. Common to all fine residues is the need to get the mix of fuel to air correct. Where residues are densely packed, air cannot reach the middle of a heap of residues, smouldering occurs, along with lots of smoke. Ways must be adopted to burn this smoke before it leaves the stove. If residues are too widely dispersed, they are impractical to burn, but another approach allows fuel to trickle down, mixing with the air in the correct proportions. For residues such as rice husk, there is the added problem of low calorific value. This means that each small particle produces a lot of ash for a small amount of heat. Getting rid of the ash must be addressed in the stove design. One way to deal with such residues is to convert them into briquettes. In some circumstances this is a good solution and a lot of research has been done on how to make and burn briquettes. However, briquetting is an extra process and adds cost to the fuel, and is not always appropriate. This document looks at using the raw material directly in the stove.