Biogas technology has been undergoing rapid development in Germany since the introduction of the country's Renewable Energy Sources Act (EEG). The number of plants in agriculture has more than doubled from about 1,000 in 2000 to more than 9,300 currently. Most of the biogas produced in Germany is converted into electricity directly at its source, and the majority of farmers who have invested in the technology use cogeneration units that generate electricity and heat at the same time – known as combined heat and power, or CHP. Most of the electricity generated is fed into the grid and about a third of the heat goes back to biogas production. Thanks to modern local heating networks, however, the remaining surplus heat can be used to warm agricultural buildings or to dry products such as grain.
Future-oriented technology for bioenergy
Germany is still the world market leader and pioneer in the use of biogas, and to defend this top position one thing is vital: technical innovations that result in more efficient bioenergy plants. It is not surprising, therefore, that these are the focus of EnergyDecentral. In addition to manufacturers of complete systems and CHP plants, suppliers of components, mixing technology and gas treatment will also be represented at Hanover's Exhibition Center in November.
In response to recent amendments to the EEG that apply stricter regulations to large biogas plants, Germany's renewable energy industry has reacted by developing smaller and modular plants with a capacity of less than 75kW. These convert waste and residual materials such as liquid manure, solid manure, biowaste and green waste into energy. The heart of every system is the fermenter. Here, microbial decomposition of the organic substances take place and biogas is produced. In the simplest case, the manure flows from the barn into the pre-pit and from there directly into the fermenter. Solid substrates can be introduced by means of stationary feeders.
Straw as a substrate alternative
Because of its high levels of lignin, cellulose and hemi-cellulose, and low levels of macro and micronutrients, straw has not traditionally been considered an ideal raw material for fermentation. As many of EnergyDecentral's exhibitors and market players are impressively demonstrating, however, that situation is changing. With eight to 13 million tonnes of cereal straw produced annually, the economic potential of being able to use it as substrate in biogas plants is promising.
The co-digestion of straw is always a viable solution if there are also sufficiently nutrient-rich liquids such as manure or liquid manure to feed the fermenter. Currently, the methane yield achieved from the fermentation of straw is about 50 to 70 percent of that achieved by using corn silage as a feedstock. This year, several EnergyDecentral exhibitors will present energy-saving processes for digesting straw to further increase the gas yield. These include mechanical and biochemical treatment of the straw before it enters the fermenter to help dissolve the lignocellulose structures.
Information about steam explosion
Biogas Systems will exhibit the Economizer SE system that presents a solution for the hydrolysis of pulp-rich biomass at the Hanover trade fair. The fibrous or viscous raw substrate is heated in two stages up to 180 Celsius and treated at up to ten bar of pressure in a hydrolysis reactor. After completion of the hydrolysis process, optimal substrate disintegration is achieved by means of "steam explosion". This is where the material is shredded with saturated water vapor under pressure, with a subsequent sudden release of the pressure resulting in the coarsely fractionated starting material being transformed into a homogeneous, easily usable substrate pulp. This means the subsequent fermentation benefits from constant and stable reaction conditions, and the material spends less time in the fermenter. This patented technology can be also be used to help process other agricultural residues such as manure, grass and shrubs into biogas.
Microbes from the deep sea crack lignin
Another approach is pursued by the BMT process from MWK Bionik. Through the targeted interaction of biological, mechanical and thermo-catalytic processes, it promotes the fermentation of lignin-dense materials, such as straw or wood residues. The BMT system is integrated in the substrate flow between substrate storage and fermenter so that existing plants can also be retrofitted. Up to 90 percent of the organic dry matter is converted into biogas, which is made possible by using a special mixture of enzymes and herbal active ingredients, as well as natural deep-sea microorganisms. They crack the sturdy and waterproof lignin layers and release the trapped and fermentable carbohydrates from the straw.
New tasks in the energy transition
As the transition in energy production continues, biogas will take on an increasingly important role in the supply of sustainable electricity. In addition to the requirements of the Renewable Energy Sources Act, farmers and plant manufacturers must keep an eye on the regulations on fertilization and plant safety.
Many operators are upgrading their existing plants with gas storage facilities and more-efficient CHP plants – trends that will also be reflected among the exhibits and the supporting technical program at this year's EnergyDecentral.
At the same time, researchers continue to explore the potential for making alternative substrates available. For example, scientists at Fraunhofer IKTS, in Dresden, want to open up new potential for the biogas industry with straw pellets. These sink in the fermenter and dissolve within 60 minutes, and this chemical-mechanical treatment reults in a gas yield that is 40 percent more than that achieved from untreated straw – without converting the existing biogas plant.
EnergyDecentral 2018 takes place at Hanover's Exhibition Center from 13 to 16 November. More information about the event can be found online at www.energy-decentral.com
