Winning Bio-gas from Organic Waste
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 SOME 5,000 tonnes of organic waste are used each year in Volketswil, Switzerand to produce electricity  |
ENERGY & SUSTAINABILITY:
Nickel-containing stainless steels are being used to make processing facilities that extract
renewable fuels from household wastes. By Alfred Bauer
Nickel magazine, Mar. 01 -- Imagine taking all of the table scraps from our kitchens and the
organic wastes from our gardens and making fuel for our cars, and even generating electricity from it. This
renewable-energy idea was taken seriously some 10 years ago by the Swiss company, Kompogas, which has since
developed the technology to the point where 20 bio-gas facilities are now operating in Europe and Asia. What
makes these plants economic are nickel-containing stainless steels, which help reduce maintenance costs and
increase plant availability.
In many communities, organic wastes from kitchens and gardens are typically collected and disposed of by
incineration or composting, a process that produces heat and a moderately strong fertilizer for re-use in the
garden.
The Kompogas process extracts much more usable energy. Just one tonne of organic waste produces 80 to 140 cubic metres of so-called bio-gas, which contains enough energy to fuel the average passenger car for about 1,000 kilometres. In Europe, at least 12 models of cars, from 8 different manufacturers, are commercially available that use gas or a combination of gas and gasoline or gas and diesel. Gas-operated cars have successfully participated in 24-hour races
In the Kompogas process, organic matter is first shredded and then fermented anaerobically in an insulated reactor at 55 to 60°C. This moderately corrosive process produces a valuable gas containing about 60% methane, the balance of which is carbon dioxide, water vapour and several other minor gases. Methane is valuable because it can be burned in the uncleaned condition in an integrated heat-and-power block unit, or if the solid particles and the water vapour are removed, it can be used as a fuel for road vehicles, as a fuel for generating electricity, or fed into a natural gas distribution system.
In a plant that processes 10,000 tonnes of acidic organic matter a year, about seven tonnes of nickel-containing stainless steel are needed for the critical components, such as heat exchangers, piping, pumps, filters and for many items inside the reactor. Nickel-containing stainless steel is used for its corrosion resistance and low life-cycle costs, and to increase the longevity of the plant.
One-quarter of the electricity generated by a Kompogas plant that is designed to generate electricity only is used to operate the plant itself, and the remaining electric power goes into the local power grid. Heat generated by the process is used for the production of hot water or the heating of buildings. Organic matter removed from the reactor is de-watered in a filter press. The organic matter is then aerated and used as a fertilizer in gardens, thus completing the cycle.
A Kompogas plant that processes the organic wastes from a city of 200,000 people (about 20,000 tonnes per year) produces the equivalent amount of energy as is contained in 1.4 million litres of fuel oil, in addition to 7,500 to 9,000 cubic metres of compost per year.
The water removed from the organic matter contains all the necessary ingredients for fertilizer for use in agriculture or in the production of aquatically grown vegetables. After this stage, the water still contains nutritious elements and can finally be used in a pond for raising fish before it is sent to a wastewater treatment system.
The full process cycle takes 18 days, of which one day is needed for the preparation of the supplied organic waste material, 15 days are taken for the fermention process and intermediary storage, and two days for the aerobic treatment to turn the processed waste material into compost.
An additional benefit of using bio-gas that is obtained from organic waste is that it is carbon-dioxide-neutral. That's because the amount of carbon dioxide produced by combusting the bio-gas is the same as that absorbed from the atmosphere by the plants during growth.
On balance, bio-gas is a sustainable source of energy. If only there were enough for us all.
Alfred E. Bauer is a Switzerland-based consultant to the Nickel Development Insitute.
Photo: Wolfgang Stråuli, Winterthur
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Kompogas AG |
