1. Air Cooled Condenser
After combustion, the volume of the original refuse is reduced by 90% and the mass by 75%. From this remaining bottom ash an off-site, joint venture business recycles a further 1.5% ferrous metal and up to 1.5% non-ferrous metal such as aluminium, copper and brass. The off-site business also processes the bottom ash to produce a high performance aggregate, sold for use in road construction and other purposes.
2. Steam Turbine and Generator
Steam arrives from the boilers, driving the turbine, which rotates the generator to produce electricity. The electricity leaves via 11,000 volt cables that you can see passing though the floor.
3. Tipping Hall
Vehicles drive up a ramp into the tipping hall. They then reverse to the edge of the pit and empty their contents into it.
4. Refuse Bunker
Two semi-automatic cranes transfer refuse to boilers which burn up to 29 tonnes per hour. Each grab lifts up to 5 tonnes of refuse. Normally there is 4,500 tonnes of refuse in the bunker. The bunker can hold up to 6,000 tonnes.
5. Feed Hopper
The refuse from the crane grabs is dropped here and fed onto the incineration grate in a controlled manner.
6. Incineration Grate
Martin Reverse Acting Grate. Pull down handle on right hand side of viewing port, look up at 45 degrees to see combustion of refuse. Note ash falling into quench bath below.
7. Steam Boiler
Refuse is dropped into the chutes above. Hydraulic rams feed refuse onto the grate, where it burns at temperatures greater than 850C. Heat energy is released into a multi pass boiler where 78 tonnes per hour of steam is produced at 395C and 46 bar.
8. Gas Treatment Scrubber
As the hot combustion gases pass through here they are mixed and cooled with a measured amount of lime milk sprayed in at the top. The lime falls through the gases, reacting with and removing any acid gases present and reaching the bottom as a dry powder where it is removed. The incoming acid gas content is continuously measured to ensure the right amount of lime is added.
9. Bag House Filter
The bag house contains around 5,000 individual bag filters (like hoover bags!). All the gases from the waste combustion pass through the filter bags and any dusts are captured on the filter material. The cleaned gases are then emitted from the chimney stack. The dust is periodically dislodged from the bags by a pulse of compressed air. This removed dust becomes part of the Air Pollution Control residue.
10. Induced Draught Fan
A powerful adjustable fan draws all the gases through the plant, keeping the whole process under a slight vacuum and ensuring there are no leaks.
11. Residue Handling Crane
Transfers the bottom ash and recovered ferrous metal to loading chutes prior to discharge into lorries for removal from site.
12. Bottom Ash Handling
After combustion, the volume of the original refuse is reduced by 90% and the mass by 75%. From this remaining bottom ash an off-site, joint venture business recycles a further 1.5% ferrous metal and up to 1.5% non-ferrous metal such as aluminium, copper and brass. The off-site business also processes the bottom ash to produce a high performance aggregate, sold for use in road construction and other purposes.
13. Under Fire Fan
These large ducts are drawing air from above the waste pit which is through the concrete wall to the west. The air is fed into the furnace via fans from both below and above the flames. This air is vital to maintain the correct combustion of the waste. Drawing the air from around the waste pit also stops smells from escaping into the local area.
14. Water Treatment Plant
Two exchange units treat incoming mains water at the rate of 10 tonnes per hour per unit. The treated water is then used in the boilers for the production of steam to drive the turbine.
