Gasification is a process that chemically and physically changes biomass through the addition of heat in an oxygen-starved environment. The end products of gasification include solids, ash and slag, liquids and synthesis gas, or syngas. The gas has a calorific value, or potential heat content, equivalent to 25% that of natural gas if ambient air is used or 40% if oxygen-enriched air is used.2 Figure 1 on the following page illustrates the process: combustion chambers, power boiler, pollution controls, and pollution by-products: bottom ash and slag, fly ash, and air emissions

http://www.bredl.org/pdf/wastegasification.pdf