PASCHAL supplies round formwork and wall formwork for the Bürstadt Energy Park

The most modern biogas system in the world goes into operation

Our attitude to energy production has changed dramatically over the past few decades. Whilst combustion power plants were seen as large-scale evidence of prospering industry in the middle of the 20th century, they are now generally viewed as sources of pollution. The discovery that higher emissions of carbon dioxide can actually change our climate suddenly made them politically incorrect. For the past few years small power plants have been gaining in popularity as these work in a sustained fashion and use resources efficiently, i.e. they draw their energy from regenerative sources, or renewable raw materials.

In this field, Germany is a role model and pioneer for other nations, both technically and politically. And also the construction-related designs of these procedures are no longer in their infancy. According to a study by the consultants A.T. Kearney, between 2007 and 2030 a total of 25 to 39 billion Euros will be invested in systems that generate power and heat from biomasses. The renewable resources from agricultural operations will play the main role here.

This report looks at one of the most successful solutions: The Bürstadt Energy Park.

The inside formwork and outside formwork of the 8.5 metre high trapezoidal girder round formwork (TTR) with adjustable radii have various radii and sizes regardless of the respective wall thickness and are matched to each other centimetre by centimetre. The tie rods, of which there are comparable few, ensure perfect absorption of the pressure and run exactly vertically through the concrete.

Bürstadt (Hessen):

Regardless of how politically desirable an energy project may be, if it is financed privately, it must have a sound economic base, it must function in the long-term and also retain its value. These are all factors that play a role in the construction process: often the preliminary planning stage, assuming it is done properly, is decisive for the long-term quality and the level of costs required to maintain the system.

The Energiepark Bürstadt with its innovative 2.3-megawatt biogas system went online in September 2008. It supplies power made of renewable resources, namely residual agricultural materials that come from the immediate surroundings. The biogas power plant, which claims to be the largest in Hessen, is also the most modern in Germany and therefore probably the most modern in the world. Not surprisingly, it assumed a political importance before it was even built and became a magnet for both the media and political circles. This kind of news is very welcome in times where the prices for fossil fuels are rising rapidly; also, systems of this kind function as role models and set a standard for others and become an important work field for the construction industry.

Preliminary work

The start of the biogas power plant project on the green fields was complicated. Bürstadt is located between Mannheim and Darmstadt in the old Rheinaue wetlands on very peaty and cohesive grounds which are heavily affected by the groundwater; also they are not strong enough to support heavy constructions. The location however had been chosen because of its close proximity to the producers of the biomass - they all come from within a 5 km radius! - thus saving transportation costs and raising efficiency. In February 2007 work began on improving the ground by means of vibrated concrete pillars. Then base plates were laid down as flat foundations.

Skeleton building

In May 2007, the construction company Wilms GmbH & Co KG (Bürstadt) started the skeleton building work as commissioned by the company Energiepark Bürstadt GmbH & Co Biogas KG. The turnkey project was budgeted to cost 11 million Euros. This included the building for the power station, the office building and four "smaller" reservoirs with diameters of 18.0 metres and two "large" round reservoirs with diameters of 28.0 metres. Also, there is a 4,000 square metre sole plate for silage that is subdivided and surrounded by a 4 m high wall. A warehouse with 1,000 square metres holds the bio waste and also large biological solids.

The base plates contained concrete of the type C25/30, F3; the small reservoirs alone required 320 cubic metres each. The Modular universal formwork was used from PASCHAL, even for the base plates of the round reservoirs, although here the polygonal formwork was used to save costs.
The same round reservoirs serve as fermenters (bioreactors), the larger reservoirs as co-fermenters.

Walls

The straight walls were formed by the company Wilms GmbH using their own GE-elements. These large-surface elements come from the Modular/GE series; whilst the numerous different grid elements can also be used for manual formwork, the GE-elements are up to 2.75 metres high and 2.0 metres wide.
The trapezoidal girder formwork (TTR) with adjustable radii was met with great enthusiasm. The world’s leading technical product with 21 mm thick, 15-layer plywood made of Finnish birch that can be nailed is the only system that can be flexibly tightened to a radius of 2.5 metres where other systems would break or form waves. As a "dual support" it can even be used for radii up to 1 metre with an 18-mm plywood. The formwork here is stable, round and accurate and does not distort even if it is moved several times. The circumference can be formed to the exact centimetre and without any on-site compensation work. One square metre of formwork surface can absorb up to 60 kN of fresh concrete pressure even though there are only 0.28 ties per square metre. It is exactly these benefits that count especially when producing complex constructions such as round reservoirs. Thanks to the speedy relocation processes, the extremely low number of ties and the fact that the formwork does not need to be additionally supported with belts or re-rounded, all the work was performed comfortably, safely quickly and efficiently. The low number of ties also improves the quality of the concrete surface.

Phasing instead of ring-construction

The conscious decision to opt for the phasing method, i.e. concreting segments of the building in the required height phase-by-phase, as opposed to the ring method where several concreting processes are performed in a ring on top of each other, has the advantage that the reinforcements are covered with concrete in a more controlled and even manner. In turn this extends the service life of the construction making it more secure and less likely to require repairs. This is also the case with the joints that, in the tried-and-tested phasing method, are much shorter overall and statistically less likely to suffer corrosion.

The phasing method also has the advantage that, if required, much fewer formwork elements need to be used. This also reduces transportation costs and raises the overall level of efficiency on the building site itself.

The large round reservoirs were produced in eight phases, the smaller ones in five phases. The multiple use of the formwork reduces the overall quantity of formwork material and this is reflected in the final costs.

The formwork was delivered pre-rounded to the building site so that it only needed to be erected. The re-spindling service by a PASCHAL technician, i.e. the targeted resetting of the formwork to a different radius for another round reservoir, was used of so that an own team could understand the process.

The construction manager Dipl.-Ing. (qualified engineer) Michael Wilms is convinced: "All the concrete work went smoothly, right on schedule. And with the 8.5 metre high and 25 cm thick walls, we are definitely players in the top division now!" The use of radial pre-curved reinforcements made of steel mesh also helped to raise efficiency. "This alone helped us to save time by a factor of 4!"

The two block heating stations work with a ship’s engine that now supplies 16,000 households with "green" power.

Internet tip

http://www.energiepark-buerstadt.de

The round reservoirs look like huge pots of paint during the pressure test: Although they would never normally have to cope with loads of this kind, they are filled to the top with water for the construction acceptance procedure. Of course, they did not lose even one drop!