Homogeneity in biogas processes: pioneering project in the German town of Mühlacker
How innovative substrate preparation with the Wangen Pumps BIO-ROXX improves the efficiency of the Mühlacker biomethane plant
Efficient preparation of heterogeneous and complex substrates represents an increasing challenge in the biogas sector. The Mühlacker biomethane plant has overcome this obstacle using the Wangen Pumps BIO-ROXX module. Its precise mixing processes and reliable separation of foreign matter open up new substrate preparation options. Greater operational flexibility, higher efficiency, and improved gas quality: the results of the new infeed solution speak for themselves.
Mühlacker biomethane plant is more than just an energy generator – it embodies the innovative power of the biogas industry. Established in 2007 as a subsidiary of the Mühlacker Department of Public Works, it was one of the first plants in Baden-Württemberg to incorporate its own gas preparation plant. With a capacity of 5 MW of gas power and 2 MW of electrical power, it has established itself as an industrial benchmark in this industry.
The plant is the prototype of a functioning regional circular economy: in the absence of its own agricultural land, it co-operates with some 120 local raw material suppliers and produces high-quality universal fertilisers for horticulture alongside biomethane. The treated biogas is fed directly into the public natural gas network and is thus available as a flexible energy source – a significant contribution to decentralised energy supply.
With an annual processing capacity of 30,000 tonnes of fresh material, the plant handles a wide variety of substrates: from traditional maize silage, grass and cattle manure to straw and landscaping management materials. This versatility is especially important given the industry’s shift away from energy crops towards biological residues – a change that brings significant technical challenges. In particular, the increased use of long-fibre substrates such as straw and manure, which often contain contaminants like stones, require a different engineering approach.
From screw conveyance to liquid infeed
The need to replace obsolete solids dispensers while ensuring a high level of operational reliability led to a decisive change of direction at Biomethan Mühlacker. The existing process of using dry infeed by screw conveyors, which led directly into the fermenter, was rapidly reaching its limits.
“Our plant was designed with a clear focus on redundancy and two solids dispensers to ensure continuous energy supply even in the event of a fault,” explains Matthias Naun, Operations Manager at Biomethan Mühlacker. “We faced the challenge of modernising our plant, but definitely wanted to maintain redundancy. Conventional screw conveyors are susceptible to blockages and problems at the transitions between the screws, making the redundancy concept considerably more difficult. This gave rise to the idea of switching from solid infeed to liquid infeed – uncharted territory for us at the time.”
The transition to liquid infeed requires precise co-ordination of several components (metering system, infeed and discharge pump) to minimise the risk of leaks and operational malfunctions.
More efficient substrate management mixes and protects
A search for a suitable solution led Biomethan Mühlacker to Wangen Pumps, a company known for its robust and reliable pumping and mixing systems. The team at Mühlacker had already had positive experience with various pumps supplied by the manufacturer. The BIO-ROXX module is a new substrate preparation system in the Wangen Pumps product range, specifically developed for the efficient treatment of solid substrates in biogas plants. This module optimises the input for the biogas process and protects downstream plant components, such as pumps and agitators, by combining technologies to homogenise the substrate and separate foreign matter.
“The BIO-ROXX system is based on an ingenious mixing process in which an agitator ensures intensive mixing of the liquid and solid substrates to produce a homogeneous mass that can be pumped.” explains Lukas Geiger, Project Engineer at Wangen Pumps. “The system, equipped with an active stone discharge outlet, reliably removes unwanted components from the substrate before it enters the fermenter”.
Two redundant BIO-ROXX modules act as central interfaces between the solids infeed and the fermenter in the Mühlacker biomethane plant. Solid substrates, such as manure or landscaping management material, are fed in through two solids dispensers and are conveyed by screws into the BIO-ROXX modules. Parallel to this, a substrate pump (Wangen Pumps product KL65) feeds digestate from the post-fermenter into the system as a liquid substrate. BIO-ROXX then mixes the two substrate phases into a homogeneous mass. Controlled addition of the liquid substrate ensures optimum consistency for efficient fermentation and ease of further treatment. A second corresponding discharge pump (Wangen Pumps product KL80) then feeds the mass to the fermenter.
Successful implementation during operation
The changeover to the BIO-ROXX system was initially a challenging project for the Mühlacker biomethane plant, as it was one of the first practical applications of the new substrate preparation system. However, the innovation has now proved itself to be extremely successful. The modernisation of the plant was carried out while it was still in operation and was completed in less than six months.
Use of the BIO-ROXX module has significantly improved gas values. Homogeneous mixing of the substrate provides for more uniform and efficient fermentation, which has a direct impact on methane production. In addition, it prevents the formation of sinking and floating layers in the fermenter, improving the efficiency of the entire fermentation process.
The technical robustness of the BIO-ROXX system is yet another benefit. The module is designed with only a few wearing parts, resulting in minimal maintenance costs – a factor that contributes to the long-term efficiency of the system.
Mühlacker is contributing to dynamic biogas production
“The BIO-ROXX project was undoubtedly a challenge, but the positive results underpin our strategic decision,” concludes Matthias Naun. “Thanks to the integrated safety mechanisms of the modules, the leaks I had feared have not been an issue. Overall, the new infeed system, deliberately oversized from a redundancy aspect, has significantly improved our workflows and increased our operational flexibility. We are now able to respond more effectively to changing requirements and potential faults, compensate for bottlenecks, and adapt more quickly to changes in the substrate mix - factors that increase the overall efficiency of our plant in the long term.”
The flexibility of biogas production is a key factor in the industry, and is becoming increasingly important. A central challenge lies in the storage of biogas, and in on-demand production. Biomethan Mühlacker has implemented a pioneering concept with its modernisation of the infeed system that allows for demand-led adjustment of substrate infeed. This dynamic plant control contributes significantly to network stability.
BIO-ROXX
The system is suitable for the optimum preparation of the substrate by intensively mixing the solid and liquid together, and efficiently separating contaminants. The BIO-ROXX increases the gas yield by means of accelerated fermentation, reduces the formation of floating layers, and prevents the accumulation of foreign matter in the fermenter.
(Subject to change at short notice)
