All food waste is emptied into hoppers which act as mixing vessels before going through our depack process which separates packaging from organic waste. Plastics are recovered, cleaned and sent away to create refuse-derived fuels. Liquid is then added to the organic waste so it can be pumped.
All food waste is now passed through a heat exchanger and heated to 70°C using recycled heat.
The waste is held at 70°C for 1 hour to comply with ABP regulations.
It is cooled by passing it over the incoming material, taking it back to approximately 40°C.
Waste is moved to a mixing tank that holds 3 days of material and ensures a uniform product is transferred to the digestors.
Digestor tanks are fed in turn, with each holding 3,500 tonnes of material. Material stays here for 30 to 35 days and in the absence of oxygen, bacteria breaks it down and produces methane gas.
Gas is collected from the top of the digestors and then passed through a biological scrubber where bacteria filters it to remove hydrogen sulphide (and CO2 at our Widnes plant) which damages the engines.
At our Doncaster plant: Gas is stored in storage tanks until required, it is then pre-conditioned to remove water, cooled and pressurised before being fed to our engines, which produce enough electricity to power 10,000 homes a year. This power is fed into the National Grid. Excess heat is collected to produce approximately 2 tonnes of steam per hour.
At our Widnes plant: Once it is refined to pure biomethane, the gas odour (Mercaptan), is then injected into the National Grid – producing enough gas to power 10,000 homes a year.
Once all material is fully digested we are left with a liquid which is turned into bio-fertiliser, which we call ReGrow, for farming and agricultural use.
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