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Flender Helps Power Thetford Power Station

An unusual fuel is being used to power Thetford Power Station in Norfolk - and it's being helped along by Flender gear units!

A total of 12 screw conveyors have been constructed to feed chicken litter into the 38.5 MW plant, which is Europe's largest renewable electricity power station. It is the third and largest in a series of commercial power stations constructed by Fibrowatt Limited, an independent British power developer.

The screw conveyors, which have been manufactured by BAS Wagstaff Limited (Blackburn) feature Flender FZG B4SH size 8 gear units, which have a nominal ratio of 224:1. Input power is 11 kW 4-pole, with a speed of 1500 rpm, reducing down to a final speed of 6.7 rpm. Because the units are mounted vertically with Siemens motors, the top part of the gear housing had to be lubricated, so they were fitted with flange pumps for forced lubrication. The screws were also ceramic coated to prevent corrosion.

Thetford Power Station is situated in the centre of Thetford Forest, and is much smaller than a fossil fuelled plant, impacting less on the environment. This is because the use of a biomass fuel "closes" the carbon cycle, reducing net CO_ emissions by recycling carbon rather than producing new carbon dioxide.

The chemical composition of poultry litter also ensures that the level of noxious gases released, such as sulphur dioxide and nitrogen oxides, are a fraction of those emitted by the coal-fired generation process. The elimination of methane emissions from stored litter also helps reduce gas production.

The litter, which comes from surrounding poultry farms, is burned in high temperature furnaces, heating water to produce steam which drives a turbine linked to an electricity supplier. The electricity is exported into the local supplier's grid and the steam condensed back into water by an air-cooled condenser before being recirculated into the boiler.

There are no waste products from the process, as the ash produced, which is rich in potash and phosphate, is marketed as an environmentally friendly fertiliser. Poultry litter therefore makes an excellent fuel for electricity generation and Fibrowatt is already expanding into Europe and America, with new projects in several major poultry rearing areas.