Draft PPS18: Renewable Energy
Annex 1 Energy from Waste (Thermal Processes) Technology: Direct Combustion
The majority of MSW incinerators burn the waste stream essentially in the form it is collected. This process is called direct combustion. The combustion gases are cleaned in a sequence of processes which remove particulates, acid gases and trace organic compounds. The ash exits the process as two distinct streams – bottom ash that falls from the combustion grate, and fly ash that is separated from the flue gases. Bottom ash is considered to be inert and, after the separation of metals, is either taken to general landfill or used as aggregate. Fly ash can contain heavy metal contamination and so should be disposed of in a controlled landfill.