ABSTRACT
Direct combustion has been the traditional role of biomass in many economies to generate useful heat and energy. Combustion is the most efcient thermal conversion process for useful energy, such as for cooking, drying food products, or for producing electricity. This pattern of activity is still prevalent in many developing countries but is slowly changing owing to concerns for the environment. Deforestation is a common issue with most developing countries. Many countries have started banning the combustion or incineration of biomass for this reason. Combustion is a process of utilizing the carbon and hydrogen in biomass to generate carbon dioxide, water, and heat. The heat may be used to provide energy to a furnace or to produce steam to run a turbine, which generates electricity. For electricity production, the most common process is shown schematically in Figure 13.1. In this schematic diagram, the biomass is rst dried before being combusted in a furnace. The heat energy generated is used to boil water and produce steam that is required to run the steam turbine. The rotating shaft of the turbine is attached to an electrical generator, thereby producing electricity. This is not the only process that is used for the production of electricity from biomass. Various other processes are possible, such as utilizing hot gases to run the
turbines, instead of steam. Usually, the efciency of conversion is the ratio of the electrical energy produced divided by the rate at which biomass is used per unit of time. Efciency calculations have been introduced in previous sections. The overall thermal conversion efciency of an ideal steam cycle (or Rankine cycle) is around 25-30% (Wark, 1983).
