In times past, this used to be called incineration, and the mood of the nation was against it as fear of toxic materials trucked in by night, and dioxins produced by day, stalked the land. Although it's now called energy from waste [EfW], the nation's mood has hardly improved. Even those mildly in favour don't want EfW facilities anywhere near them: No Waste In My Back Yard.
So, putting EfW plants on industrial estates makes sense in many ways, especially as the energy generated can be used in the immediate locale. The Devon County Council site in Exeter, operated by Viridor, is one such facility. When a second site, in Plymouth, opens in 2015, 27% of Devon's residual rubbish (after composting, recycling, upcycling, etc) will be diverted from landfill to these plants. This will be about 8000 tonnes a week. Last month, SWLSC held its AGM at the Viridor site. This included a tour and insights into the educational work at the facility.
It's an impressive place with more dials in the control room than in an Apollo spacecraft. Now that the landfill tax escalator has reached £80/tonne, the incentive for local authorities to reduce material going to landfill has increased dramatically. Once upon a time, there was an real incinerator on the site, but this was closed in 1996, and it became a waste transfer station. There was strong political support for its reincarnation for EfW because of the site history and location. It now takes 60k tonnes/year. It cost £45m to build: there is a lot of concrete.
The energy extraction (not to be called incineration on pain of having to leave Devon for ever) takes place @ 1100 degrees C, giving rise to a 20% ash residue. Flue gases spend at least 2 seconds @ 850 degrees C in a post-combustion chamber to ensure that all the nasties (dioxins, etc) get burnt; they are then mixed with activated carbon and lime and passed through Goretex filters before being released into the 60m stack to head off for Somerset and Wiltshire on a typical blowy, south-westerly, sort of day. Rather to my surprise, it seems that there is sufficient caloric value in the waste without having to have plastics in the mix. All told, 4mw of electricity can be generated, 3mw of which are typically exported. There is also the potential for 13mw of heat for district heating, if that ever gets off the ground.
I confess that I really wanted to have a go with the big grabber thing which took the dumped waste, churned it up, and them dropped it onto conveyors en route to the furnaces. Sadly, I didn't have the qualifications.
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