^ The CSTR’s after installation, before insulation and cladding was installed.Text & images by Stallkamp

 The digester after in operation
The digester after in operation, fully wrapped in insulation and cladding.
A food manufacturer from northern Germany uses production waste in its own waste and sewage treatment plant in order to exploit the energetic waste in a biogas plant. This way, the company combines economic success with its ambitious ecological goals. The success of this endeavor meant that the expansion of the biogas plant had become a necessity.
The decision was made in favour of two tall digesters made of high-quality stainless steel – designed, manufactured and assembled by Stallkamp from Dinklage, Germany.

Challenging construction

The two identical tanks have a diameter of 15 m and a height of almost 20 m, each having a capacity of 3,300 m³. The construction of the stainless steel digesters was carried out using a segmented design. For this purpose, individual shell plates with thickness of 3 to 6 mm were rolled to diameter. These were screwed together then sealed to form large rings at the construction site.

The first fully assembled ring was lifted with electrical lifting supports that were especially developed for this project. This was followed by the assembly of the next ring, which was again lifted by the 30 synchronously running lifting supports. When lifting the tank to assemble the final ring, more than 40 tons were weighing on the lifting supports, which lifted the weight evenly and safely.
“We knew from multiple tests that the concept would work. Nevertheless, the calm and even lifting of the structure was a special moment,” reports Erich Stallkamp (managing partner), who followed the construction progress daily.

Duplex the optimal material

In order to minimise corrosion in the anaerobic fermentation process, the plant operator consistently uses stainless steel for the new digesters – in its highest quality. All side panels as well as the 4 mm thick stainless steel bottom are made of duplex 1.4462 sheets. The material has particularly high yield strength as well as a very high corrosion resistance and is therefore particularly suitable for use in the biogas plant. The roof is also made of stainless steel: stable rafters supported by an inner and an outer ring form the basic structure. An inner and an outer stainless steel skin was then attached to this structure. In the middle of the roof there is an opening for the central mixer. It constantly mixes and homogenises the fermentation mixture and thus ensures optimum process biology.

Three more under construction

For Stallkamp, the continuously stirred tank reactors are an important step, as they are the highest tanks of this type ever produced by the company.

“We are pleased with the successful completion of the project and showed that we can play along on this scale,” stated Christoph Heseding (Managing Director) and Patrick Wienken (Head of the Technical Office Tank Construction).
Currently, three further CSTR for a mega biogas plant are under construction in Denmark. A total of 14 tanks are currently being built to treat up to 600,000 tonnes of biomass per year. Three of these digesters have a height of 20 m and a diameter of 23 m. Further information is available at www.stallkamp.de/en.