The most commonly used gasification technologies are fixed bed and fluidized bed gasifiers. Fixed bed gasifiers are employed in the low-capacity range of some MWth, fluidized bed installations, typically in the range above 5 MWth.
The gas produced in the gasifier can be used in various ways for electricity production or for the production of process heat. The systems differ with respect to efficiency, costs, and demand on the gas quality. Engines are suited for electric capacities between ca. 50 kWe and 10 MWe in connection with atmospheric fixed-bed gasifiers. From a capacity of about 5 MWe gas turbines, often in combination with a fluidised bed gasifier, are an alternative. In order to avoid fouling and deposits in the engine, the gas should be to a large degree tar- and dust-free. The requirements for fuel cells are more stringent, however a clear concept about allowed concentrations in the product gas is not yet available.
The gasifiers available on the market today exceed the indicated values by far when operated without gas cleaning. The removal of both tar and particles is therefore a requisite. The use of the product gases for thermal purposes does not make such high demands on the quality regarding tar and dust content. So for those applications it is not necessary to provide for a special gas cleaning.