.

Top left: The floating roof in the roof area is flexibly sealed. For insulation the segments are filled with PU bulk. The outer layer form accessible XPS thermal insulation panels.
© T. Urbaneck, TU Chemnitz

The upper diffuser is integrated in the floating roof. Its form has been specially optimised.
© T. Urbaneck, TU Chemnitz
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Sealing, coating and insulating

A central task was to permanently guarantee the impermeability of the segment joints. In the laboratory, the scientists tested various sealants for their thermalmechanic durability. The best results were found with a condensation crosslinking silicone, which was then also used in the demonstrator.

For the corrosion protection of the steel segments, which at the same time guarantees the water quality, various coatings were tested in the laboratory and then tried out in practice on the demonstrator. Hardly any coatings showed any visible changes after approximately one year of operation with temperature loads of up to 92 °C and are therefore also suitable to be used as corrosion protection.

At the same time, the project partners tested and compared different insulation materials for the roof and wall insulation. The best choice turned out to be pourable polyurethane particles for technical, economic and ecological reasons. They were provided as recycling material at a comparably low price. The bulk material easily fills the spaces that occur between the cladding panel and the screwed wall. In contrast, the installation of thermal insulation panels would be much more costly because screwing together the segments, the spacers and other structural elements would make installation more difficult. Consequently, the filling technique also reduces the production costs.

Typical problems for insulation fillings have proven to be uncritical in tests under conditions close to those in real application. The starting material showed fluctuations in the product quality, however, in the observed application they did not impact the usability and only negligibly impacted the insulating effect. Fill heights of several meters, e.g. in the wall structure, can be achieved without any change to the properties or the settlement.

The hydrophobisation of the particles has proven to be extremely effective. Particles stored under water only absorb very little water, even over months. Particles with contact to the ambient air dry quickly. The scientists were unable to find any significant, moisture-caused degradation processes.

As with most insulation materials, the effective thermal conductivity increases with the temperature. However, in this case the increase is only slight and uncritical. The convection flows are more noteworthy for although hey are negligible in slab structures, they could reduce the insulating  effect in the vertical layer of the wall structure. However, by using convection breaks (XPS plates) the transport processes were effectively suppressed n the laboratory.

Segmental construction also for the floating roof

The storage tank is different to previous constructions, above all in the roof area. The roof made of folded metal sheets guarantees that the pilot storage tank is protected against environmental factors. For larger storage tanks, the use of raftered roofs is envisaged. In the case of the floating roof, the scientists also consistently adhered to segmental construction. Here they were also able to take advantage of the benefits of the lightweight construction and easy transportation. The roof is formed by individual components screwed together to make a fixed panel, whose stabilityallows the diffuser to be installed. A single diffuser is sufficient for a storage size of up to 6.000 m³. Since the radial diffuser is located directly on the underside of the floating roof, it allows the usage of the full storage zone. Furthermore, only low mix effects occur between the inflowing charging fluid of lower density and the fluid in the storage tank with a higher density. This is particularly important for high quality thermal stratification.

A film flexibly seals the edge area between the storage tank wall and the floating roof. This film was also selected from various brands after laboratory tests. The tested construction allows a height adjustment from approximately 70 to 100 cm. The height displacement is based on the requirements of bigger storage tanks. Therefore, the storage tank can compensate temperature- related changes in volume very well. Analogous to the wall structure, a particle bulk fill is used as thermal insulation. Hard foam plates laid on the planks of the floating roof make it possible to enter and inspect the roof area.

Structure of the base

The storage tank wall is attached directly to the foundation. Consequently, the load transfer of the storage tank wall occurs directly in the foundation. The thermal insulation made of foam glass plates is installed on the foundation. A stainless steel plate closes off the storage tank on the base and protects the interior insulation against penetration by storage tank water. The seal between the ground plate and the storage tank wall is implemented in the connection area with the same sealant that is used to seal the wall segments. When the temperature rises the complete wall structure expands and it contracts when the temperature falls. Therefore, the seals are particularly exposed to loads. However, no problems occurred in the test operation. Base and wall connection are practically free from thermal bridges and it is only the base plate that separates the thermal insulation layers from the storage medium. Therefore, there are no heating-up losses.

Conclusion and outlook

The project has shown that a new type of storage tank has been created by way of new developments and multi-faceted optimisations. The many tests in the laboratory and the innumerable simulations have not been presented here. On the basis of these tests and simulations the demonstrator was created and then intensively tested. In this regard, complex tests have proven its practicability or rather that the project’s objectiveshave been achieved. After the first presentations of the demonstrator, the project partners have experienced much interest from municipal utilities, planning offices and public institutions.

The researchers see two future fields of activity. Diverse constructional details (e.g. thermal bridges) could be further developed in order to further reduce external heat losses, to allow easier production and to guarantee cost-effective manufacturing. The next large step is then transferring the newly developed construction principles to very large tanks and the adaptation to the higher loads associated with them.

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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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