Scottish Water in AD CHP move

Scottish Water Waste Services has signed a contract for the design and construction of an anaerobic digestion plant at their Deerdykes facility, outside Cumbernauld, in Scotland.

Gas generated by the facility will be used in reciprocating engines to supply electricity to the grid and heat used on-site and potentially in neighbouring industrial estates. A local company has a heat demand with a good match to the planned facility’s output and currently Scottish Water is examining the feasibility of making a connection to the heat network, with confirmation on the decision due in June.

Processing some 30,000 tonnes of food waste annually, material from the digester will be supplied by the local authority under its Landfill Directive obligations, together with waste from local food retailers and producers.

The CHP facility will comprise two gas engines and associated heat recovery systems, the supplier of which has not yet been determined. The engines are rated 500 kWe each and collectively are expected to supply 1.1 MWth. Total electrical output is expected to be some 6 GWh annually while the heat will be used in the digestion process, including a requirement to pasteurize the material at 70oC.

Planning permission for the site, a redundant sewage works, has been awarded and application for a grid connection permit is underway. Construction is anticipated to begin in April and operations are due to commence in April 2010. HBS Construction Ltd and Monsal Ltd are to design and build the plant.

In addition, two similar developments are under consideration, one at a redundant sewage works west of Glasgow, now a green waste composting site, and another in south west Scotland at a redundant Scottish Water depot with good proximity to waste sources as well as a large local heat demand.

Scottish Water has been composting on the Deerdykes site since 2004 and currently processes some 42,000 tonnes of green waste annually there, employing existing tunnel structures to compost the material. The company is currently examining the possibility of using the heat generated by the composting process to supply the on-site offices.

The company is also examining potential alternative used for the woody fraction removed from screened compost. Currently cleaned and send to a biomass power plant, Scottish Water is considering using the material in a potentially local application.

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