There are four processes whereby biomass can be used to generate electricity or pro­duce fuels. These options are given in Fig. 4.5 and include direct combustion, co-firing, gasification and pyrolysis.

Combustion

Biomass has been used for many years to provide domestic heating using direct com­bustion in fires and stoves. These systems are normally not very efficient and produce some emissions of soot and dust. Small to medium-scale heating systems using pel­leted biomass have been developed for houses and larger buildings such as schools. These modern heating systems have improved efficiencies and reduced emissions. Large-scale combustion of biomass for the production of electricity is used in many countries. The technology involved in the combustion of wood and forest residues can be conventional pile burning, stationary, moving, vibrating, suspension and fluid­ized beds. Wastes can be incinerated to produce heat and power and are found widely distributed in Europe. Incineration is central to the treatment of domestic waste although there have been some concerns about emission from incinerators. The appli­cation of fluidized beds and advanced gas cleaning has given an efficiency of 30-40% for electricity production at a scale of 50-80 MW combined with flue gas cleaning.