Energy can be recovered from waste by various (very different) technologies. It is important that recyclable material is removed first, and that energy is recovered from what remains, i.e. from the residual waste. Energy from waste (EfW) technologies include:

• Combustion in which the residual waste burns at 850°C and the energy recovered as electricity or heat
• Gasification  and pyrolysis, where the fuel is heated with little or no oxygen to produce “syngas” which can be used to generate energy or as a feedstock for producing methane, chemicals, biofuels, or hydrogen (see also landfill gas and sewage gas)
• Anaerobic digestion, which uses microorganisms to convert organic waste into a methane-rich biogas that can be combusted to generate electricity and heat or converted to biomethane. This technology is most suitable for wet organic wastes or food waste. The other output is a biofertiliser.

Harnessing energy from waste has many benefits:

• It helps the UK reduce its dependency on energy imports
• It contributes towards reducing carbon emissions and meeting renewable energy targets
• When used for electricity generation, these technologies have a steady and controllable output, sometimes referred to as providing “baseload” power
• It has very good sustainability and greenhouse gas saving characteristics, as it makes further use of materials that have already been discarded.

For more detailed information on EfW technologies and their current use in the UK, please download our EfW leaflet.

Gasification and Pyrolysis

Gasification, as applied to solid waste materials and biomass, is a relatively new application of this technology that is increasingly being used for the disposal of wastes. It is a thermo-chemical process in which wastes, including their biomass content is heated, in an oxygen deficient environment to produce a low-energy gas containing hydrogen, carbon monoxide and methane. The gas can then be used as a fuel in a turbine or combustion engine to generate electricity.

Gasifiers fuelled by fossil sources such as coal have been operating successfully for many years, but they are now increasingly being developed to accept more mixed fuels, including wastes. New gas clean-up technology ensures that the resulting gas is suitable to be burnt in a variety of gas engines, with a very favourable emissions profile. Gasifiers can operate at a smaller scale than an incineration plant, and can also be provided in modular form to suit a range of different scales of operation. A number of British companies are leading in this emerging technology.

Pyrolysis is another emerging technology, sharing many of the characteristics of gasification. With gasification partial oxidation of the waste occurs, whilst with pyrolysis the objective is to heat the waste in the complete absence of oxygen. Gas, olefin liquid and char are produced in various quantities. The gas and oil can be processed, stored and transported, if necessary and combusted in an engine, gas turbine or boiler. Char can be recovered from the residue and used as a fuel, or the residue passed to a gasifier and the char gasifed.

For more detailed information and to find out more about this technology sector group, please email Tricia Wiley, Senior Policy Analyst, on twiley@r-e-a.net.