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The Fibrowatt poultry-litter-fired power station in Thetford, Norfolk was opened in 1998 and is the third power station of this type to be built in the United Kingdom. It is also the largest, with 38.5MW output capacity.
The plant works by direct combustion of some 400,000 tonnes of poultry litter per year. Poultry litter is a mixture of chicken droppings and materials like straw or wood shavings. It typically has an energy content of about 9 to 15MJ per kg. This energy is used to turn water to steam, which spins a turbine and generator to produce electricity.
The Holsworthy Biogas plant is an anaerobic digester. Anaerobic digestion is the process by which organic matter is broken down by bacteria in the absence of air.
Organic matter is placed in a digester (a warmed sealed airless container) for 10–25 days. The materials ferment and produce methane gas and a solid called the digestate. The gas is cleaned and can then be used in a furnace, gas engine or turbine. The digestate is returned to the farms for use as a fertiliser.
Holsworthy Biogas processes 146,000 tonnes of cattle, pig and poultry manure and organic food waste per year. The manure is collected from 30 local farms, all within 10 kilometers of the plant. The plant has an output capacity of 2.1MW.
It is planned that any excess heat produced by the plant will be used to heat the hospital, schools and other public buildings in Holsworthy.
The sewage treatment works at Minworth, near Birmingham, is completely self-sufficient in electricity and exports a 12 per cent surplus to the National Grid. The sewage plant serves 1.3 million people. Minton's bio-energy system uses anaerobic digestion to process more than 4,000 litres of sludge a day, producing 75,000 cubic metres of sewage gas, mostly methane.
The methane is compressed and then piped to a combined heat and power plant and burnt in five gas engines, each capable of producing 1.5MW of electricity. A CHP (combined heat and power) engine unit is the ideal system for a bio-plant. CHP burns bio-gas to produce both electricity and heat, some of which is re-used in the treatment process.
Bio-waste in this process includes food, vegetable waste, cooking oils and bones.
The average household produces 4.2kg of kitchen waste per week. Pre-treatment includes pasteurization (heat treatment), and shredding to reduce the materials to pellets.
