Aerial photo of Könnern in Germany. Commissioned in 2009 with 16 digesters, 4 second stage digesters and 16 storage tanks, it is today one of the world’s biggest biogas plants.

It’s time for organic energy

Around the globe, governments, organisations and corporations are seeking ways to reduce carbon emissions, step away from their dependence on fossil fuels and at the same time ensure a reliable, sustainable energy mix. There surely has never been a better time to embrace biomethane plants – the very epitome of a sustainable, circular economy, says Wolfgang Bokern, Head of Plant Construction at WELTEC BIOPOWER.
^ Aerial photo of Könnern in Germany. Commissioned in 2009 with 16 digesters, 4 second stage digesters and 16 storage tanks, it is today one of the world’s biggest biogas plants.

Article by David Sear

The basic science behind biogas is easily explained. You take organic waste, such as left-overs from the food industry, grass silage and farmyard manure, and break this down into the simplest of hydrocarbons, namely methane. That methane (essentially the major component of natural gas) can then be fed into the natural gas system and used to heat houses, power industry and drive turbines to create electricity.

Of course the actual process is more complicated and requires various steps such as shredding and blending the feedstocks, anaerobic digestion in large tanks and removing the co-produced carbon dioxide In addition, reliable partners have to be sought to provide a steady stream of suitable organic matter.

Nevertheless biopower is certainly not rocket-science and moreover a long track record of successful applications has been demonstrated by companies such as WELTEC BIOPOWER, headquartered in Vechta, Germany. Indeed, when SSWN asked Mr. Bokern to mention just a few projects he quickly reeled of his top four case histories. “Take Könnern in Germany, which when built about a decade ago was one of the biggest biogas plants in the world. This gas-to-grid project is actually owned and operated by the WELTEC group. Then there’s Aurora in Australia which I would describe as an exemplary waste-to-energy project involving one of Australia’s largest enterprises providing water supply and sewerage services.

Biopower facilities can also be successfully installed at food production sites, such as at Sober, France, where they make potato chips. And coming right up to date, in late 2019 we completed work at Lanes Farm Energy in the UK, where biomethane is now produced in a very sustainable fashion.”

“Our tank rings are made of 1.4162 and 1.4462 duplex stainless steel”

Duplex grades

Central features in typical biomethane plants are the round tanks, or digesters. When it comes to materials of construction for these tanks Mr. Bokern is adamant that stainless steels are the perfect choice. “Stainless steel is a high quality material and is very stable against the aggressive acids in the gas. Most competitors use concrete for their tanks. That material may be cheaper but requires extra protection against aggressive ingredients in the biogas and has longer building times. Besides any dowels in concrete tanks could weaken the material. In stainless steel tanks all connections are securely bolted together.”

Another important advantage of stainless steels is that tanks can be built to a consistently high stand the world over. “We deliver the tanks in the form of ready-to-assemble plates which are all produced in Germany. Tanks made of concrete are always dependent on the locally-available materials and conditions –shipping concrete would be too expensive. Besides, stainless steel plates are quick to assemble which saves time and money during construction. Furthermore, the use of stainless steels means that each tank can be customised to individual requirements, such as for pipe access etc.”

Mr. Bokern further explained that WELTEC’s tanks are typically built up using five layers, or rings. “For our rings we use duplex stainless steel. The lower rings, which are around the liquid zone, are made with 1.4162 duplex. However, the top ring is in the gas zone so we select 1.4462 duplex as this material is more resistant to aggressive substances.”

Once each biogas plant has been designed, WELTEC procures necessary items such as pumps and valves from approved suppliers. Some additional components such as the MULTIMix entry system are designed in-house and then built locally by a mechanical engineering company. However, the manufacturing of the actual tanks plus sundry components is outsourced to mother company WEDA.

Mr. Bokern: “our tanks are designed and delivered according to a very practical modular concept. Here in Germany WEDA cuts the duplex stainless steel plates to size using a laser and creates all the necessary holes and perforations. Specially manufactured profiles are also prefabricated; these are used to reinforce the construction and to connect the tank with the base plate and the roof membrane. Other U-profiles are formed according to the required tank diameter. For the connection of pipelines or other components we use flanges or fittings made of stainless steel.”

All components are then shipped to the construction site for assembly by long-term partners, continues Mr. Bokern. “The U-profiles give the plates the required curvature to form rings. Hence we build up a WELTEC stainless steel tank ring by ring. Note that welding is not required: the plates are simply bolted together with sealant being used to create a tight finish between the overlaps.”

Although tank construction is relatively straightforward, WELTEC often sends out a foreman to keep an eye on assembly, especially for more complex elements or new designs. Project managers are also regularly on-site to assess progress and to coordinate agreements between various trades, such as electrical engineering, piping, etc.


In just under twenty years WELTEC has constructed more than 300 biogas plants on five continents. One change that Mr. Bokern indicates has taken place during these years is that plants are increasingly purpose-built to suit local conditions. “To date we have designed plants for over 120 different feedstocks! But all round I can report that we are seeing an increased demand for biomethane - the processed biogas- worldwide. Biomethane has the same properties as natural gas, but is a completely sustainable gas. We expect the demand to continue to increase in the coming years.”

Indeed, Mr. Bokern is convinced that biogas can make a huge contribution to creating a sustainable society. “The CO2 footprint of biogas plants is extremely positive - especially when manure and organic residues are used. According to the European RED II directive, there is even a negative CO2 balance for these input materials. Biogas plants are therefore the perfect energy supplier to achieve European and worldwide climate goals. Especially in the areas of heat and transport, the potential is far from being exhausted. Biomethane is the perfect fuel: It can be used as bio-CNG or LNG in all gas vehicles and convinces with its good climate balance, fast refuelling and a very long range. Biogas not only helps the climate, but also has economic advantages: on the one hand, cost-intensive disposal of certain waste materials becomes obsolete and, on the other hand, a company can save CO2 tax by using biogas.”

It is not for nothing that WELTEC’s mission is ‘Organic energy worldwide’, concludes Mr. Bokern. “We are actively looking for more sustainable projects around the globe and talking to various parties about how their organic waste can be converted into a valuable resource.”

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