Biogas at IFAT 2008: Optimisation strategies in all areas

28 dicembre 2007
Right across the spectrum of producing and processing the input material, fermentation and then the creation of electricity and heat, there is still plenty of scope for innovations and efficiency improvement in the use of biomass. IFAT 2008, which takes place from 5 to 9 May 2008 in Munich, will for the first time be including the new focal theme of biogas, and looking at current developments in the segment.

Every biogas project has to prove its cost-effectiveness in competition with other concepts. When it comes to agricultural produce, for example, biogas stands in direct competition to the production of food- and feedstuffs. Against a background of rising prices for the raw materials, the only biogas plants that are cost-efficient are those that produce as much biogas as possible with as little material, energy and financial input. As a result the suppliers of the technology and systems are coming up with many new ideas to boost the efficiency of biogas plant.

One way of optimising the fermentation process is to precisely control the addition of the often difficult-to-handle renewable raw materials to the fermentation vat. One idea here is to use a newly developed, highly energy-efficient special container made of plastic, which facilitates the process.

Another way of increasing efficiency is to improve the conditions for the methane-producing bacteria. The microbes derive their energy from polysaccharide chains. First the polysaccharides have to be divided by enzymes before they can be used. Normally the quantity of the enzyme occurring in a biogas plant is too low for optimum ‘feeding’ of the microorganisms. This can be boosted by adding to the fermenter an enzyme preparation developed by a Berlin-based biotechnology company. This promotes the division of polysaccharides into mono- and oligosaccharides. The improved supply of sugar means the microorganisms can multiply faster and biological activity increases. Following extensive field tests by the distributing company, the use of this preparation has been shown to improve biogas volumes by an average of 18 percent.

A higher rate of breakdown for the input material also has positive effects on the process management. As polysaccharides play a key role in the viscosity of the content of the fermentation vat, the increased division of these polysaccharides produces a much more liquid substrate. This means less energy is required to stir the contents, which also brings cost savings. An economic feasibility study shows that through the increased electricity production an added yield is achieved which is significantly above the costs for the use of the enzyme.

In another technique, a comparatively simple physical method is used to increase the number of bacteria in the biogas plant. Under the system currently used, the microorganisms are removed from the fermenter in large quantities along with the fermented material. This is an unwanted effect. The now decimated bacteria concentration in the vat is only capable of acting more slowly on the material to be fermented and thus performance is reduced. In the new technique small quantities of magnetic particles are added to the system, the particles being taken from the bacteria flakes in the substrate. By applying magnetic forces, for example with the use of a permanent magnet, the bacteria can be separated from the outflow from the biogas plant and returned to the reactor. To magnetise the bacteria flakes only 0.1 grams of ferrite per gram of organic dry substance of reactor content is needed, for example. The primary application for magnetic biomass recovery is in fermenting water-rich substrates, such as for example distiller´s wash.

The most popular use of biogas is in a combined heat-and-power generation plant (CHP). However the environmentally-friendly fuel varies enormously in its composition. Values such as knock resistance and flame speed can change within seconds by 30 to 50 percent. In order to generate energy efficiently in CHPs under such changing conditions, one option is to use appropriately adapted pilot injection engines as well as spark-ignition gas engines. The pilot injection engine is based on the principle of a diesel engine. In such engines, when operated with biogas, the combustion air drawn in is mixed with the aid of an electrically controlled gas regulator valve and compacted in the engine. Injecting a small quantity of vegetable oil starts the ignition of the lean-gas-and-air mix in the combustion chamber. A key role is played here by an innovative electronic control mechanism which regulates the ideal injection time, the required injection quantity and the best combustion temperature. According to the manufacturers’ instructions efficiency can be improved by up to 44 percent – and at the same time emission values are reduced and the lifetime of the engine increased.

As an alternative to direct combustion in a combined heat-and-power generation plant, another idea that is becoming more and more popular is to process the biogas to natural gas quality before feeding into the natural gas network. Thermal-driven cogeneration plants that are linked up to the natural gas network achieve an efficiency level of over 80 percent. It must be said, however, that before this can be achieved considerable technical and financial input is required in terms of drying, desulphurisation, methane-enrichment and odorisation. This concept, too, aims at achieving improved efficiency through new technology. According to sector experts, it could even be possible in five years to deliver processed biogas at the same price as classic natural gas.

The technology and services associated with biogas will form a new section at IFAT 2008, the world’s most important trade fair for the environment and waste disposal – for water, sewage, refuse and recycling. For five days, this well-established environmental trade fair held in Munich will present a compact review of the products and services from across the industry – from system manufacturers, full-service suppliers, manufacturers and distributors of individual components, plus service specialists.

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