14 May, 2002 – UK-based ash handling specialists Clyde Bergemann Materials Handling Limited (CBM) has successfully commissioned an important contract from Scottish Power Generation Limited for the provision of a Waste Derived Fuel (WDF) storage and transportation system at its coal fired Longannet Power Station.
WDF is a dry, biologically benign and virtually odourless granule made from sewage sludge and although of a lower calorific value than coal, it represents a useful and valuable fuel. The benefits of processing this otherwise waste material into a renewable energy source cannot be overstated. With a growing population, the re-use of sewage sludge is an increasing problem since the ban on dumping at sea in 1999 and the current option of using landfill becoming difficult due to cost, environmental concerns and pending legislation.
By mixing the WDF with coal, then pulverising it before co-firing it into two of four 600MWe Units, it will provide a useful fuel component for Longannet. In a wider context it overcomes an environmental problem by providing the means to burn WDF in an efficient, large scale generating plant.
In terms of a handling system for this material, two major factors had to be overcome. The system needed to be totally enclosed and it had to be capable of dosing (and monitoring) measured amounts of material into the process.
The answer was a new transportation system from CBM, using the company’s well-proven Rotofeed Injection Technology. The WDF is transported from the customer’s road tankers into six new storage silos and from here, two CBM Multi-Outlet Rotofeeds continuously inject metered amounts of WDF material along 400 metre long pipe runs into the coal feeders at the coal mills where it is mixed with the coal and pulverised prior to be co-fired into two 600MWe boilers.
CBM originally developed the Rotofeed System for injecting granular coal into blast furnaces. It’s dual advantages of keeping the material totally enclosed whilst allowing very accurate feed rates makes it ideally suited to handling WDF.
Whilst the use of the Rotofeed in this application is new, CBM’s association with Scottish Power and Longannet is not. In 1996 the company completed work on a £5m turnkey contract to supply replacement ash handling systems on the plants 4 x 600 MWe boilers.
The WDF project means that as well as providing a fuel source for Scottish Power Generation Limited, Scottish Water, from where the sludge arises, is provided with a sustainable re-use for this often-wasted material. In addition, generating electricity from renewable energy sources like WDF may attract renewable energy benefits for the generating company. Renewable Energy Certificates may make electricity from renewable sources worth as much as double the price of that from fossil fuels.