How it works
The energy-from-waste process
A large reception hall allows waste vehicles to manoeuvre and tip waste safely. Air needed for the combustion process is drawn into the furnace from here so that odour and dust do not escape from the building.
Waste vehicles tip their loads into a large concrete bunker, big enough to hold six days worth of waste. Bulky items, such as mattresses, go through a shredder first.
All of the facility’s equipment, including the grabber which mixes the waste in the bunker, is operated from the control room. Control systems check that equipment is working properly, continuously monitor the combustion gas and make sure the whole facility is working to maximum efficiency. All on-site functions are monitored both automatically and manually.
Grate and boiler
Air is blown under the moving grate through five computer-controlled zones. The thermal energy released from burning the waste is used to convert water to super-heated steam. At high pressure, this steam drives a turbine to generate electricity.
After leaving the turbine, steam goes through air-cooled condensers and is condensed back to water, which is then treated and reused in the boiler to produce more steam in a closed-loop system.
Control of emissions starts in the furnace with good combustion control to make sure the correct proportion of air is supplied and temperature is maintained. Combustion gases from the furnace are subject to a rigorous cleaning process. Nearly one-third of the facility is taken up with the cleaning process, which involves spraying carbon and lime into the flue gases to neutralise any pollutants. Monitors at the base of the chimney continuously check emission levels and if they start to rise, adjustments are made to the cleaning process. In the unlikely event that they continue to rise, or if the monitoring equipment fails, the facility will shut down. Monitoring information from the chimney will be displayed both at the facility and online.
Air Pollution Control Residue
The cleaned gas is passed through fine-fabric bag filters to remove solid particles. The resultant air pollution control residue (also known as fly ash) contains these solid particles, excess lime, salts and carbon dust. This is taken away in sealed containers for specialist treatment or recycling. Lime and carbon are reused in the process.
Ash left on the grate after incineration is cooled and carried along a conveyor to an on-site ash treatment building where the ferrous and non-ferrous metals are taken out for recycling. The remaining ash will be used in road building and construction.
Electricity will be generated at 11 kilovolts. Around three megawatts is used to power the facility, leaving around 20 megawatts (enough for 30,000 homes) to be fed into the National Grid. An underground cable will take the electricity from the facility to a sub‑station at Stowmarket, where it will be fed into the National Grid.
The facility has two lines (a shared bunker feeding into duplicate furnaces, emission control systems and chimneys) and each will shut down for servicing for around two weeks every year. During these times, household waste will continue to arrive at the facility and be processed. Business waste may be directed elsewhere.