Less than a year after announcing that up to half the UK's homes could be heated with renewably generated 'biogas' derived from food waste, National Grid has unveiled a bold plan for how the gas could be produced on a local level.

In a new report released today, the grid operator sets out how a series of 'Urban Energy Centres' could take delivery of separated food and household waste.

The food waste would be fed straight into an anaerobic digester, which breaks down the sludge to produce a methane-rich gas and a nutrient-rich liquid slurry, that can be used as an agricultural fertiliser.

The household waste would be fed into a Mechanical Biological Treatment (MBT) plant, which sorts the waste to remove recyclable materials, and then submits the remaining fraction to high pressure steam, sterilising the waste and reducing its volume.

This waste is then heated to high temperatures in the absence of air to drive off 'syngas' - a mixture rich in hydrogen - which can be upgraded and then injected into the gas mains along with the gas from the anaerobic digester for use in home boilers and cookers.

Because the process does not incinerate waste in the presence of air, harmful combustion byproducts should be kept to a minimum.

National Grid calculates that 10 plants could deal with all of London's waste, reducing CO2 emissions by some 146,365 tonnes a year by displacing fossil natural gas.

However, although the report calculates that the Energy Centres would make better economic sense than incinerators (costing £62.50 per megawatt hour of energy produced, as opposed £110.25 per megawatt hour of energy from an incinerator), the Grid's executives believe that the project will not succeed unless the Government introduces promised financial incentives.

'This only becomes feasible if the Government introduces a renewable heat incentive (RHI) payment for renewable gas that makes it commercially viable,' said Mark Fairbairn, executive director of gas distribution for National Grid. 'Also support will be needed to develop gasification technology alongside a review of waste policy to ensure that energy recovery from waste is maximised at all plants in the UK.'

Useful links
National Grid report

See also

• Biogas: is your council about to waste your waste?
• First island power grid being used in Wales
• UK losing £650m a year by burning and binning our waste