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Solar thermal power plants - parabolic gutter technology

In order to use solar energy independently from sun, engineers have developed a technology to accumulate solar energy.

Fluid salt serves as storage medium. Such a power plant has many thousand tons of a special salt-mixture available that is being pushed via pumps back and forth between two well insulated tanks. On the way from one boiler to the other the molten salt reaches a pipe section that is surrounded by thermo-oil. During the sun-flooded daily hours the 400° C hot oil releases its heat to the fluid salt. If no sun is available the heat transfer process is being reversed. The hot salt solution flows back into the adjacent tank. This time the salt releases its heat surplus to the oil.

Expansion joints are being applied everywhere in such power plants where saliferous process pipes lead into the tanks.

Image source: Siemens AG, Pictures of the Future, www.siemens.com/pof

Operating parameters for expansion joint design

In the present case besides the thermal extensions and highly corrosive medium also the problem of subsidence of the immense tank came up. During the initial fill and during the time short after the commissioning of the power plant such an event had to be taken into account and to be compensated for with a compensating solution.

Duct dimenisons Ø 1200 mm
Medium Molten salt
Operating temperature 550°C
Cycles/year 10000
Pressure [bar] ±0,05
Tightness
Flue gas tightness according
RAL - TI 002
Movement
axial:        -83/+80mm
lateral x: 0mm
lateral y: 90mm

Design solution: DEKOMTE Expansion joint

The possible subsidence and the expected thermal extension during operation provided for that the expansion joint had to be designed for an axial movement of more than 160mm.

The aggressive medium also presented specific conditions for the expansion joint. DEKOMTE solved this issue sustainably in using high-quality material, special welding technologies and by means of a condensate dissipating flow plate.

DEKOMTE design solution: high-tech expansion joint
Installed DEKOMTE special expansion joint