Biogas usage in agriculture:

straw fermentation and new technologies speed up the energy revolution

Storable, flexibly usable and : baseload capable with an electrical output of over 4,200 megawatts: biogas plants have become an important element of the energy revolution. At EnergyDecentral, visitors can engage in intensive discussions regarding the current situation and the future prospects of the technology. The specialist international trade fair for innovative energy supply, which will take place together with EuroTier from 09 to 12 February 2021 in Hanover, will provide answers as to which technologies are currently being focussed on, and how plant efficiency can be increased with new substrates. Increasing attention is being paid to straw as a source of energy in this respect.

Germany remains the global market leader and trailblazer in the use of biogas. First and foremost, defending this top position necessitates technical innovations for more efficient bioenergy plants and this  will form the focus at EnergyDecentral. In addition to manufacturers of complete systems and combined heat and power plants, suppliers of components, agitator technology and gas processing equipment will  be represented at the trade fair.. Not least due to the latest German Renewable Energy Act (EEG) amendment, the industry is responding with smaller and modular plants with  outputs of less than 75 kilowatts and the capability of converting into energy  waste and residual materials such as liquid manure, solid manure, organic waste and green waste.. The core element of each plant is the fermenter. Microbial degradation of  the organic materials resulting in the production of biogas takes place within. In the simplest case, liquid manure flows from the animal housing into the slurry store and from there directly into the fermenter. Solid substrates can be added using stationary loaders.

Straw as an alternative substrate

Due to its high content of lignin, cellulose or hemi-cellulose and  low content of macro and micro nutrients, straw is not actually an ideal raw material for fermentation. But interest in this material is growing, as many exhibitors and market players will be impressively demonstrating. The economic potential is very promising: an estimated eight to 13 million tonnes of cereal straw suitable  as  substrate in biogas plants, are produced each year. The cofermentation of straw is always a practical solution when sufficient nutrient-rich liquids such as slurry/ liquid manure are available. At present, a methane yield of  around 50 to 70 percent of that of maize silage can currently be achieved by fermenting straw. In order to further increase the gas yield, the exhibitors at EnergyDecentral will be presenting energy-saving methods for breaking down the raw material with, for example,straw mechanically  and biochemically processed for  lignocellulose degradation prior to fermentation.

Breakdown by means of steam flashing

Back in 2018 in Hanover, Biogas Systems presented the Economizer SE as a solution for hydrolysing cellulose-rich biomass. Here, in two stages the  fibrous or viscous raw substrate is heated to 180 degrees Celsius  and then processed  in a hydrolysis reactor at a pressure of up to ten bar. Once hydrolysis has been completed, steam flashing and expansion are used to achieve optimum substrate disintegration. In this process, the material is shredded under pressure with saturated water vapour and subsequent abrupt expansion – thus transforming the coarsely fractioned input material into a homogeneous, easily digestible substrate pulp. This gives consistent reaction conditions for  subsequent fermentation, , shorter residence times and stable, trouble-free operation. In addition to straw, usingf the patented technology enables  conversion into biogas of virtually all agricultural residues such as farmyard manure and grass, up to and including brush cuttings.

Deep-sea microbes crack lignin

The BMT method from MWK Bionik pursues a different approach. Through the specific interaction of biological, mechanical and thermocatalytic processes, it fosters the fermentation of materials with high lignin content such as straw or wood residues. The BMT system is integrated into the substrate flow between the substrate store and the fermenter, with the result that existing plants can also be converted. Up to 90 percent of the organic dry substance is converted into biogas. This is made possible by a special mixture consisting of enzymes and plant active substances as well as natural microorganisms from the deep sea. These break down the robust and waterproof lignin layers and release the enclosed and fermentable carbohydrates in straw and woody material.

New tasks in the energy revolution

As the energy revolution progresses, biogas takes on  new important tasks in supplying sustainable power. In addition to the requirements in the German Renewable Energy Act, farmers and plant manufacturers must also keep an eye on the fertilisation and plant safety regulations. Many operators therefore increase  flexibility and upgrade  their existing plants with gas storage systems and more high-performance combined heat and power plants – a trend that is also reflected by the products and supporting programme on offer at this year's EnergyDecentral. At the same time, researchers are working intensively towards making alternative substrates available. Scientists at the Fraunhofer IKTS in Dresden are aiming to open up new potential in the biogas industry with straw pellets. These sink down in the fermenter and dissolve within 60 minutes. The chemical/mechanical processing leads to a 40 percent higher gas yield in comparison with untreated straw – without converting existing biogas plants.