4.2. Thermochemical conversion
Thermal conversion is one component in a number of integrated waste management solutions proposed in various
strategies. Four main conversion technologies have emerged for the treatment of both dry and solid wastes: combustion,
gasification, pyrolysis, and liquefaction (to produce an intermediate liquid or gaseous energy carrier) and are as follows:
Combustion is the burning of biomass in air. It is used over a wide range of commercial and industrial combustion plant
outputs to convert the chemical energy stored in the solid waste into either heat or electricity. Combustion uses various
items of process equipment, such as boilers and turbines. In theory, any type of biomass can be burned in practice;
however, combustion is feasible only for biomass with a moisture content o50% unless the biomass has been pre-dried
[16].
The gasification process involves treating a carbon-based material with either oxygen or steam to produce a gaseous fuel.
Gas produced can be either cleaned and burned in a gas engine or transformed chemically into methanol that can be
used as a synthetic compound.
Pyrolysis is the heating of biomass in the absence of oxygen to produce liquid (termed bio-oil or bio-crude), solid, and
gaseous fractions in varying yield. Pyrolysis depends on a range of parameters such as heating rate, temperature level,
particle size, and retention time.
Liquefaction is the low-temperature cracking of biomass molecules as a result of high pressure to produce a liquiddiluted
fuel. Liquefaction employs only low temperatures of around 200 1C to 400 1C.