Biogas – a German success story1 January 2009
Germany has built itself a world-leading position in biogas generation, backed by an industry that is building 800 plants a year. Now that investment is paying off as the profitability of bioplant increases.
Because it is derived from sources that would otherwise vent methane and other gases to atmosphere, biogas is regarded as a form of green energy and is able to call increasingly on leading edge technnologies. Undoubtedly, the produced kW cost is not yet a competitor against nuclear or fossil fuel based supply, but the systems installed are more and more efficient, and their financial profitability is increasing. In this field, Germany has built itself a world-leading position. German companies built 820 systems in 2006, increasing the number of installed production units to 3700. It now has more biogas based energy production than any other country and has become the technological leader. CIAT, with approximately a 35% share of the market, plays a major role, mainly through its acquired a expertise in gas treatment, enabling it to propose systems adapted to widening scopes of application. This has brought about specific developments in the field, a process illustrated by the two installations produced in partnership with two German companies SEVA AG and Siloxa AG.
European biogas electricity production in 2006 was 17272 GWh, of which 7338 GWh was by Germany alone. Biogas in Germany now represents 1.2% of the annual production of electricity and nearly 10% of renewable energy, with an installed power base close to 1500 MW. This success is due primarily to regulation intended to promote renewable energies. Biogas systems are very ‘clean’ from an environmental point of view because the contribution of a methane molecule (CH4) to the greenhouse effect is 21 times greater than that of a carbon dioxide molecule. Therefore burning methane, even though the process exhausts an equivalent volume of CO2, reduces its impact on the environment.
German law stipulates the purchase price per kWh paid by energy distributing companies for a period of 20 years. This price makes a special case of ‘green’ energy sources and recompenses operators accordingly, based on efficiency, technological innovation and agricultural re-conversion criteria. During the first year, in certain cases it may reach 0.18 r / kWh.
CIAT’s method is to work from a customer’s overall plant specification in choosing and sizing components to integrate in the optimum manner. This results in a very precise technical solution, according to customers such as SEVA.
There are several different types of biogas production systems, but they always lead to electricity production via a gas engine and alternator. In cogeneration systems process heat can also be recovered. Biogas is a gas produced by the fermentation (also called methanisation) of animal or vegetable organic matter without oxygen, or spontaneously in waste dumps containing organic waste, or artificially in digesters (when treating purification sludge, industrial organic waste or selected agricultural crops, etc...). Biogas can also be recovered from mines gas. In all cases, the biogas must be dehumidified and purified before combustion; otherwise it can damage the gas engine.
CIAT’s dehumidification technology has become a recognised standard for up-line treatment of the gas. Vapour is condensed out by cooling the gas to temperatures between 15°C and 5°C using a refrigeration unit and heat exchanger set optimised for the exact degree of cooling required. The advantage of this process is that it eliminates those impurities that are trapped in the condensates and carried off during the evacuation process. This treatment protects the engine, reducing the maintenance frequency and prolonging its service life.
Biogas is a mixture of methane (30 to 70%) and carbon dioxide, with varying quantities of water and hydrogen sulphide (H2S). Other contaminant gases can also be found, especially in biogas from waste material and landfill, namely ammonia, hydrogen, nitrogen and carbon monoxide. Only the methane and hydrogen can contribute to electricity production.