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The demonstrator was built in Nortorf, Schleswig-Holstein. It holds approx. 100 m³ and can be charged and discharged with an output of up to 230 kW.
© T. Urbaneck, TU Chemnitz
Storage tanks for heating network
Projektinfo 10/2018

Schematic structure of the demonstrator
© T. Urbaneck, Chemnitz University of Technology

Structure of the storage tank wall: The cladding panel is connected to the screwed segments via thermally decoupled stainless steel strips. The spaces in-between are insulated with a polyurethane bulk.
© T. Urbaneck, TU Chemnitz
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Cost-saving erection of large heat storage tanks

Scientists are testing a large overground hot water storage tank with lower production costs than comparable constructions thanks to its construction with prefabricated steel segments. The OBSERW research project is building on the experience gained from a large cool water storage tank that has been tried and tested in the district cooling network of the city of Chemnitz for more than ten years. For the first time, the construction principle, which is flexible in shape and size, could be transferred to hot water storage tanks that have to withstand high temperatures and temperature changes.

Overground cold water storage tanks with enameled and sealed segments can be inexpensively produced and work reliably. This has been shown by the construction and long-term operation of a storage tank for the district cooling network of the city of Chemnitz. In order to make the segmental construction also  eployable in heat storage tanks, a consortium from research and industry has further developed the construction principles with a multitude of detail solutions. We worked through the complex task in a three stage procedure,” explains Prof. Thorsten Urbaneck, who coordinated the joint project. “Starting from small scale material tests to laboratory tests on components, we have finally brought all partial results together and tested them in a pilot storage tank.” The demonstrator was built in Nortorf, Schleswig-Holstein. It holds approx. 100 m3 and can be charged and discharged with an output of up to 230 kW. “Perspectively, we could make storage tanks with storage sizes of between 500 and 6,000 m3,” states Thorsten Urbaneck. Therefore, when combined with the low heat losses and a stable temperature stratification, many possible applications for both short-term and longer-term storage cycles open up. In solar and district heating systems, the storage tank can contribute to maintaining the pressure and in this way, it performs ancillary services. The development objectives also included low investment and operation costs.

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Overview of structural features

In comparison to the existing flat-bottom tanks and cold water storage tanks, the construction concept was thoroughly revised. The overground storage tank consists of screwed together steel segments. The storage tank is thermally separated from the concrete foundation through the pressure-resilient foamed glass plate. Thewall and the floating roof are also insulated in order to avoid loss of heat. The thickness of the thermal insulation layer can be adapted according to requirements. As usual for short-term storage in networks with combined heat and power, the demonstrator is charged and discharged using two radial diffusers according to the principle of displacement. Using a radial channel widening they ensure a reduction of the initially high flow velocities meaning that hot and cold water hardly mix and the temperature stratification in the storage tank is maintained. A special feature is the free-form design of the radial diffusers with very low pressure losses. Therefore, a shortfall in the charger’s steam pressure is avoided and it is possible to discharge up to approx. 98 °C. The same construction is also suitable for solar thermal systems with variable or constant supply temperatures. In principle, storage tank volumes of up to 6,000 m³ and charging and discharging capacities of up to 56 MW are possible. It can also be used for long-term storage.

The pressure level in the storage tank’s roof area is the equivalent of the ambient pressure. The maximum storage temperature is determined by the boiling point of the water. That means that the storage tank is not designed for classic primary networks with supply temperatures of over 100 °C. However, this limitation is countered by important benefits: pressure vessel constructions with strong steel walls are not necessary; storage volumes with good thermal insulation and a small surface-volume ratio can be inexpensively produced and it reduces external heat losses; and the expense for piping and instrumentation is low.

Particular attention was paid to segments’ sealing and the screw connections. The sealant must be able to permanently withstand high water temperatures and changing temperature loads. The control of the steam and oxygen diffusion presented a challenge. Likewise solutions to minimise thermal bridges had to be found.

Projektinfo 10/2018:
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Addresses

Practice-based development and demonstration
farmatic tank systems

Coordination/scientific support
TU Chemnitz, Fakultät für Maschinenbau

Scientific support
Universität Stuttgart, IGTE

Service

BINE-Projektinfo 10/2018
(PDF, 4 pages, 242 kB)

Links

OBSERW
Project site of the research partner (in German)

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