Four cats go to waste21 February 1999
Four Caterpillar G3516 SITA generators fitted with the new Techjet fuel system have been installed at Coxhoe in Durham in the UK. The project was awarded under tranche 4 of the Non Fossil Fuel Obligation (NFFO), making use of for 1030 kWe generators which are fuelled by methane gas derived from landfill waste for Durham County Waste Management Co.
Coxhoe will be able to generate full power between methane levels of 35-55 per cent, and will be able to run as low as 30 per cent methane if necessary.
Each generator has spark ignition, along with turbo-charging and after-cooling, and these are fitted with a direct drive three-phase 400 V alternator via an automatic synchroniser to a step-up transformer. The plant then sells the 4 MWe to the grid.
"In the long-term, it will out-perform the old system with improved efficiency, wider scope for methane fluctuation and greater power output," says Malcolm Johnson, Technical Adviser for Durham County Waste. "While carrying out modifications to the gas collection system, I had to close down one of the carrier mains, which resulted in an average methane content of only 35.5 per cent. All four engines maintained full power for two weeks until repairs to the bore-holes were completed."
Coxhoe is a full landfill site containing about 3 million m3 of household waste that is undergoing restoration, while the adjoining Joint Stocks site currently accepts up to 180 000 tonnes of waste per year. Eighty one extraction wells from the two sites provide the landfill gas for the Coxhoe plant, which is estimated will be operable for 15-20 years.