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Draft PPS 18: Renewable Energy
Annex 1 Energy from Waste (Biological Processes) Technology: Gas Collection & Use

C18. The gas collected through the AD process is primarily a mixture of methane (typically 65% of the total) and carbon dioxide (typically 35%). Trace gases are also produced, including hydrogen sulphide.
C19. The gas is collected at the top of the digester and piped to a holding tank. Because this tank will have a finite storage capacity, a flare stack is often located nearby to dispose of any excess gas. The gas can be used:
  • as a heating fuel for nearby buildings and for the generation of electricity;
  • in a range of industrial applications;
  • for the drying or incineration of sludge at sewage works; and,
  • to heat the digester itself and to power associated machinery.
The gas can also be bottled, after cleaning, for use as a domestic fuel or to power vehicles.
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