Hard-to-access lignocellulose
Straw and crop residues have resistant fibre structures. Without suitable size reduction, disintegration and hydrolysis, a substantial share of their energy potential remains unused.
Repowering existing biogas plants
Anaerobic digestion of straw and lignocellulosic residues
Targeted biogas plant repowering enables the anaerobic digestion of straw, crop residues and other fibre-rich organic residues. Energy crops and feed materials can be partly or fully replaced while much of the existing plant equipment remains in use.
Initial challenge
Why conventional biogas plants struggle to digest straw and fibre-rich residues
Unsuitable digester biology
Conventional microbial cultures and fully mixed digesters are not optimised for permanently high shares of lignocellulosic feedstocks.
Inhibitors in the process loop
When biofiltrates are recycled, ammonium and hydrogen sulphide can accumulate to process-inhibiting concentrations.
Dependence on energy crops
Maize silage and other high-value substrates occupy farmland, are exposed to price risks and compete with food and feed production.
Process concept
Biogas plant repowering instead of complete replacement
Store and reduce residue size
Existing silage stores are used for dry or ensiled crop residues. Straw and cleaning residues are reduced to particle sizes below approximately 10 mm.
Thermomechanical disintegration
Fibre-rich feedstocks can be mechanically and thermally disintegrated before suspension to make the lignocellulosic structure more accessible.
Biosuspension and aerobic hydrolysis
Process liquids and treated biofiltrates are used to produce a pumpable biosuspension. Upstream aerobic hydrolysis opens up the fibre components before methane formation.
Culture-retaining primary digestion
A hydraulically and only partially mixed primary digester retains a mesophilic mixed culture adapted to lignocellulosic materials and permits stable high solids contents.
Post-digestion and reuse of existing tanks
Existing stirred digesters can be reused as a second digestion stage and, where suitable, operated in batches to significantly increase minimum retention time.
Gas and nutrient loop
Biogas is biologically desulphurised. The resulting bio-acid supports inhibitor removal, while solid digestate fractions and fertiliser concentrates remain available as nutrient products.
Suitable feedstocks
Straw, crop residues and other lignocellulosic feedstocks
Crop residues
Cereal straw, maize straw, rapeseed and other oilseed straw – dry or ensiled where required.
Cleaning and processing residues
Cereal, maize and oilseed cleaning residues as well as other crude-fibre-rich by-products.
Animal residues
Solid and liquid manures can be integrated depending on the site, permitting conditions and material balance.
Client benefits
Commercial and operational benefits of conversion
Less dependence on costly energy crops
Locally available residues can replace maize silage and other high-value substrates and stabilise procurement costs.
Use of existing investments
Tanks, gas storage, digestate storage and other plant components are incorporated into the new concept wherever technically appropriate.
More energy from residues
Disintegration, hydrolysis, adapted cultures and extended retention times improve energy recovery from fibre-rich biomass.
Land-use and climate benefits
Farmland can be used more extensively for market crops, while transport volumes and dependence on fossil energy can be reduced.
Valuable fertiliser products
Nutrients are retained in solid digestate fractions and nitrogen- and sulphur-containing concentrates for agricultural use.
Project-specific repowering
The extension is tailored to the existing equipment, available material flows, permitting framework and intended gas use.
Technical background
The presented process solution is based on German published patent application DE 10 2014 005 270 A1. A specific conversion requires a site-specific plant assessment, material-flow analysis, permitting review and technical and economic design.
Your existing biogas plant