RIVERSIDE RESOURCE RECOVERY PLANT,
Norman Road, Belevedere.
The firm established Cory Environmental Trust in 2003 to provides grants to community schemes local to its business.
Cory are now commissioning their “Energy From Waste Facility". The latest methods are used to minimise flue emissions of dioxins, N0x, halogens and sulphur, keeping them below European limits. The chimney produces no visible emission apart from a slight shimmer. The plant takes 670 000 tonnes per annum of residual waste which would otherwise go to landfill that is left after various London Boroughs have done their recycling and produces on average 72 MW, 66 MW exported to the grid. Their main preoccupation is to burn waste in an environmentally friendly manner and avoid polluting the atmosphere - not to maximise generation - although they achieve 27'% efficiency, currently an industry best for such a facility. There are plans to improve this by selling waste heat. Heat is recovered in a water tube boiler, which produces superheated steam for the turbine whose exhaust is condensed, producing water that is recirculated to the boiler and warm air to feed the furnaces. Equipment is duplicated so that the plant can continue working even if something breaks down or needs maintenance. Only the electrical generator is unduplicated and even if that is not working the waste can still be burnt.
Only Bexley Council delivers residual waste by road, about 15% of the total. The rest comes from upriver boroughs by barge (which otherwise passed by on the way to landfill sites in Essex) for which a new jetty was needed. This is 201m long, connected to the plant by a 160m long pier (apart from the Thames Barrier it is the largest structure built in the river since the 19C). Even so the effect of the outflow from the sewage works means the jetty is not far enough into the river to avoid the occasional need for dredging. Two travelling cranes on the jetty take waste containers from 'barges moored alongside and put them on tipper trailers. These are towed by diesel tractors, across a weighbridge at the foot of the pier, into the plant. They had looked at other ways of transferring the waste, but had settled for one where failure of an individual unit would not cause a stoppage. Neither would failure (or maintenance) of one crane.
At the plant the containers are backed onto one of several tipping bays and the waste is shot into a vast storage bunker, 25m high (partly below ground level - the whole building is only 27m high), The containers taper slightly, being wider at the mouth, to ease discharge but even so there are hydraulic pokers to dislodge stuck waste. Occasionally, when a container is emptied a lump of hot waste will spontaneously combust in air - there is a water hose to quench it. An exit weighbridge checks the amount delivered. The bunker normally holds 8000 tonnes, but 11000 on a Friday, and as much as they can get in on Christmas Eve, to give a four day supply. Depending on the quality of the waste (that from Kensington & Chelsea is better, with much restaurant waste) they might do a crude sort, using a grab crane (again one of two) over the bunker. Air is sucked down through the waste bunker and into the furnaces to prevent dust flying and to control odours. (At the end of the row of tipping bays is an unloading bay that juts into the bunker, and can be used to remove decomposing waste if the plant were to be shut down.)
However the grab cranes main task is to load 30 tonnes of waste per hour into three high level hoppers, each feeding a furnace line, Below the hopper a hydraulic ram pushes the waste onto a moving grate, in several sections, agitated to ensure even combustion, This operation is controlled automatically, maintaining the furnace temperature above 8500C, typically 950°C. When the waste is burnt out (after a transit time of about an hour) the grate feeds the ash residue (about 26% of the in feed) including large unburnt lumps (e.g. of resolidified glass or aluminium, even charred tree trunks) into a bottom ash hopper. This has to be emptied on a two-daily basis; special blue containers are used, and taken away in barges for recycling. This involves extraction of various metals etc., glass lumps are crushed and sorted into sand at 4mm; aggregate; and coarse aggregate at 1Omm, for road foundations. Glass is no longer colour sorted for recycling to glassworks but, crushed, to the construction industry.
Richard Buchanan .