When SEL finally got its CHP: The launch

Written by: RWW | Published:

Originally built in the early 1990s, the South East London Combined Heat and Power (SELCHP) plant has finally achieved the district heating aspect of the project for which it was intended. Geraldine Faulkner reports.

For people of a ‘certain age’ the borough of Deptford in South East London was best known as the birthplace of actress Lorraine Chase, TV presenter Danny Baker and musician Steve Harley, not forgetting it was also the site of the first ever royal naval dockyard, founded by Henry VIII in 1513, however, from this month it will hopefully be better known as the site of South East London Combined Heat and Power (SELCHP). Thus began the introduction by Simon Bussell, managing director for Veolia Environmental Services, at the official launch ceremony of London’s first energy from waste district heating network which took place at the Deptford-based facility last week.

Originally built in the early 1990s by CNIM SA, the facility was opened in 1994, but due to various political and legislation changes the district heat part of the project was shelved; only coming back on to the agenda in 2008 when Southwark Council forged a PFI relationship with Veolia Environnement. 

Working in partnership, the London Borough of Southwark and Veolia Environnement, who manages the facility, conceived a plan to supply 2,500 Southwark properties on a 5km pipe work system with heat and hot water. The aim of which is to make the heat generated at SELCHP cheaper than gas and, since the waste that SELCHP burns is about 60% renewable carbon, provide low carbon heat.

Now that the £7m district heating project - £5m of which was invested by Veolia into the pipe network and boiler house modifications and £2m by SELCHP Ltd into plant related investments at SELCHP - has been completed and the system commissioned, it is being put into full service this month and means that more than 60% of homes in Southwark will be supplied by district heating.

“Heat accounts for a third of the total UK output [of energy],” said Greg Barker, minister of state for climate change at DECC, at the launch. “Solutions should be local and low carbon heat networks are the way forward. We [the government] are already taking steps to establish a delivery unit turning proposals into live projects, however, it will take pioneering projects like SELCHP to identify and seize opportunities,” emphasised the minister before adding that: “In SELCHP we have a real glimpse of the future.”

Drivers for the project

So what were the drivers that got the district heating aspect of SELCHP going?

“It was all down to having strong planning conditions,” said Barrie Hargove, cabinet member for transport, environment and recycling at Southwark Council. 

“It was a policy that was vigorously enforced along with strong political will and helped along with the introduction of the Renewables Obligation. We published a carbon reduction strategy which proposed making the heat network function; after which three things were needed. Those were energy from waste, the requirement for energy and the political will to drive it through.”

Capable of handling 420,000 tonnes of waste per annum, SELCHP uses the mass-burn process to incinerate waste and supplies enough power for 48,000 homes (For details of the thermal process, see text below).

But why has it taken 20 years to get the district heating system up and running?

“I do not know why it took so long,” is the frank response from Estelle Brachlianoff, executive vice-president UK and Northern Europe, Veolia Environnement. She points to Scandinavia as the way forward with its high recycling rates and well established district heating network. “We believe the UK could follow in the footsteps of countries in Scandinavia; it is the way forward and an opportunity for the UK not to miss. The district heating in SELCHP is a very long awaited event and a small start but a good one. What is so exciting is that we talk a lot about the circular economy and here we are producing green calories out of waste which creates local energy. Indeed, 10% of the UK’s renewable energy could be provided by waste.”

Stressing that she didn’t want district heating to begin and end at SELCHP, Brachlianoff went on to say: “We want to expand around the 2,500 homes. We have very big ambitions for the future and we are committed to creating more facilities. 

“Our facility in Staffordshire is about to open and Leeds has just started so we welcome any new customers who want to connect to our new plants.”

Nor was the pipe laying project without its challenges. According to Deborah Collins, strategic director of environment and leisure at Southwark Council, an extensive consultation was carried out with Southwark residents who were worried about the disruption of the works. 

As well as concern over a gap in supply, the main worry was over the planned route for the pipework (which was originally going to be laid through the 19th century Southwark Park) residents expressed concern for the old London plane trees in the park.

“So we altered the proposed route,” recalls Collins. “However, Southwark is a historic borough with an old historic infrastructure and it was a case of plugging in a new system to old fashioned boilers. On one occasion we had to tackle a 22-storey block with its boilers on the roof. All in all, it has been an interesting challenge.”  

The technology: How does the thermal process work?

SELCHP receives waste from households and some businesses. Waste is tipped into a bunker where a crane collects it and places it into the feed hopper. It then drops down a feed chute into a sloped 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 is maintained.

Ash from the burning process is transferred by an ash discharger and residue handling system to the ash pit. 

During the transfer, ferrous metals are removed for recycling and the remaining ash is sent for reprocessing into recycled material for road building or for use in construction. Hot gases produced in the combustion process pass through a water tubed boiler where they are cooled and the heated water is transformed into steam. A turbo-generator uses the steam to produce electricity which is then exported to the National Grid.

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 matter is removed from the gas stream by a bag filter before the cleaned gas is released to air. 

The resultant material known as air pollution control residue (APCR) is sent for disposal at a licensed hazardous waste site.

How is the power generated?

Steam leaves the boilers at a temperature of 395 degrees Celcius and pressure of 46 bar and is fed directly into a single 35mW (megavolt or 1,000,000 volts) steam turbine generator.

The turbine rotates the generator to produce electricity. 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.

Electricity is generated at 11kV (kilovolt or 1,000 volts) and transformed up to 132kV for export to the London Electricity system which passes very close to the SELCHP facility.

No supplementary fuel is required to maintain combustion, just refuse and the controlled addition of air.

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