Gasification describes the process by which material is converted into a synthetic gas (and ash) in a low oxygen environment. The process is similar to that used for making town gas from coal. The gas is then combusted and the heat generated used in a boiler to raise steam for a turbine, where electricity is generated. In addition, heat is generated which can be supplied for use.
Most gasification processes require residual waste to undergo some degree of pre-treatment before it can be processed. > RDF/SRF
How it works
Waste is heated with insufficient oxygen to minimise combustion. This causes decomposition of the waste and production of thermal decomposition gases, sometimes called a “syngas”. The syngas produced is then combusted to generate heat and to produce electricity. It is important to differentiate between ‘true gasification’ (where the syngas produced is cleaned and fed to a higher efficiency thermodynamic process) and ‘staged combustion’ (where the syngas is subsequently combusted in a steam boiler within the same installation). Some gasification plants have been developed to burn the gas in a gas engine in place of a boiler and steam turbine. Other concepts include the use of gas in gas turbines or supply to gas grid networks, but these are currently not well proven as commercial applications.
Gasification technology has been used for over 100 years, and was the basis of town gasworks using coal before their replacement by North Sea gas. It has been applied to various waste streams for some decades, mainly well-defined industrial wastes. Its application to mixed wastes, such as municipal waste, is more recent, although several commercial scale plants have been constructed in the last 20 years. It is significantly less common at a commercial scale than combustion EfW.
Gasification processes seek to separate the various stages that also occur in the more common single stage combustion EfW process. When combined with combustion of the gas generated, the energy from the waste can be recovered.