The main combustible components of wood are cellulose and lignine
which are compounds of carbon, hydrogen and oxygen. Other minor combustible
components in wood are resins and waxes. The major non-combustible component of
wood is water which is present upto 50 % in freshly cut wood. Though the ash
content is low (less than 1 %), but because of high oxygen content, the
calorific value is low (16-20 MJ/kg).
Next to charcoal, wood is quite suitable fuel for fixed bed
gasifiers. As wood contains high volatile matter, updraft gasifier system
produce the gas containing tar, which need to be cleaned before using in
engines. Cleaning of gas is difficult and labour intensive process. Hence, wood
is not suitable in updraft gasifier coupeled with internal combustion engines.
However, the gas containing tar from updraft gasifier can be used for direct
burning. Downdraft can be designed to produce relatively tar-free gas. After
passing the gas through simpel clean-train, it can be used in the internal