Combustion

It is estimated that around 3 billion people worldwide rely on wood, stubble, dung and leaves for cooking fuel. Burning biomass fuels on open fires and in inefficient stoves releases many harmful pollutants. These pollut­ants result in excess respiratory illnesses and death in women and children. Known as a "silent killer", over

1.6 million children die annually throughout the devel­oping world from the consequences of exposure to biomass fuel smoke (Edelstein et al., 2008). Improved stoves reduce the fuel consumption and indoor pollu­tion by 50% (Ravindranath et al., 1997; Halim, 2008). Co-combustion of solid biomass and coal is reviewed by Cremers (2009).

Combustion—steam cycle. This combustion of solid biomass and the use of a steam cycle is not very energy efficient (32%, Yang et al., 2006). The maximum temper­ature is limited as potassium and calcium together with silicon form at high temperatures glasslike deposits on the furnace walls. Corrosion problems occur in straw — based furnaces at 500 °C (Hansen et al., 2000).

Gasification

Gasifying cook stoves are described by Field (2012). A high-pressure liquid ash gasifyer has an efficiency

of 50%. These are large installations with capacities of over 200 MWe. At present only 15% biomass is cogasi­fied with coal (Drift, 2008).