SELCHP energy recovery plant

My visit to a rubbish plant! It is actually an energy recovery plant. SELCHP is located in SE London, the name stands for SE London Combined Heat & Power and it is an advanced energy recovery facility.

It receives household waste and converts it into energy. The rubbish trucks arrive with the waste, drive up a ramp and tip the waste into a huge bunker.

This bunker holds 6000 tonnes. Here 2 huge grabs on semi-automatic cranes pick up the waste and put it into the feed hopper. Each grab lifts up to 5 tonnes of waste.

new grab

This process is carefully monitored by two men who check to ensure no large items such as mattresses, large metal objects, gas cylinders, tree trunks, etc, are picked up, as they would block the hopper.

The rubbish then drops down a feed chute onto a sloped incineration grate, where it is constantly turned to allow all combustion phases (such as drying, ignition and combustion itself) to happen simultaneously and a constant high temperature to be maintained. We were able to look through viewing windows at the 'furnace'. Temperatures are over 850° C.

The ash that is produced from the burning is transferred to the ash pit -

and is sent for reprocessing into recycled material for road building or construction use. Ash from SELCHP was used in the construction of London's Olympic Park. Ferrous metals are removed for recycling -

After combustion, the volume of the original refuse is reduced by 90% and the mass by 70%. Apart from the ash, a further 1.5% ferrous metal and up to 1.5% non-ferrous metal such as aluminium, copper and brass are recycled.

Hot gases produced in the combustion process pass through a water tube boiler where they are cooled; the heated water is transformed into steam. This steam is at a temperature of 395°C. It is fed into a steam turbo-generator, this rotates and produces electricity which is then sent to the National Grid. Steam from the turbine is also used to pre-heat the combustion air for the waste burning process.

A bank of air cooled condensers condense the exhaust steam from the turbine and recycle the water back into the process.

Many people assume these power plants produce smelly or even noxious gases. This is not so. The gases from the boiler go through a complex flue gas cleaning process, involving the injection of dilute ammonia solution to reduce nitrogen oxides to nitrogen and water; lime milk to neutralise acid gases and activated carbon to absorb heavy metals and any remaining dioxins.

Finally the particulate dust is removed from the gas stream by bag filters before the cleaned gas is released to air through the chimney. There are 3,000 individual bag filters (like hoover bags!).

The bags have to be cleaned periodically using compressed air to remove the dust. The resultant material known as Air Pollution Control Residue (APC residue) is sent for disposal at a licensed hazardous waste site.

The whole plant runs on just refuse with the controlled addition of air. Nothing else is needed.

The whole system is carefully monitored from the control room where a bank of computer screens can be constantly watched to ensure everything is running smoothly.

The small box on the right is the home of a peregrine falcon. Apparently it feeds on seagulls and pigeons in the area.

Heat is sold to Southwark Council and used to supply 2,500 Southwark properties.

SELCHP is just one of several plants in the UK, owned by the French company Veolia.

See more on SELCHP website.