Restoring Grout on Footings of an HTF Tank

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HTF liquid tanks are subjected to continuous temperature changes and variations in the amount of liquid they store, causing cyclic efforts in the supports. The anchoring and insulation system used for the moving supports on this tank had deteriorated, with the steel base plates acting as stress concentrators. Alphatec Engineering was called upon to rehabilitate the system and prevent further degradation of the insulating material.

 

The Problem and Solution

 

The anchoring and insulation system used for the moving supports of the Andasol concentrated solar power station’s Heat Transfer Fluid tanks was thoroughly deteriorated, leading to movement of the tanks due to the contraction-dilatation cycle and variations in HTF level. This causes considerable loads in the footings. This movement resulted in progressive cracking of the insulating material due to the loose anchor bolts and frictional forces which led to the degradation of the insulation layer.

Alphatec Engineering carried out repairs to restore the integrity of the interface between the grout and the sliding plates situated beneath the footings. The team used pneumatic chippers to remove enough material from underneath the sliding plate to place Alphapadยฎ sized D2, ensuring a properly levelled surface with healthy concrete. The repairs were completed using epoxy grout ALPHATECยฎ 800 and the hydraulic levelling system ALPHAPADยฎ, which allowed the tank to be realigned in situ.

Features

Client
UTE Andasol III
Final user
Marquesado Solar
EPC
MAN Solar Milennium Duro Felguera s.a. energรญa
Project
Restoring Grout on Footings of a HTF Tank
Equipment
31WTE22 BB001 VESSEL 400 m3
Work period
February 2015
Location
Aldeire Granada, Spain

The Background

 

The Andasol concentrated solar power station was the first Parabolic Trough power plant in Europe. It consisted of three projects:

  • Andasol-I (completed 2008)
  • Andasol-II (completed 2009)
  • Andasol-III (completed 2011)

The Andasol power plant uses a thermal storage system to capture heat from the solar field during the day. This heat is then stored in molten salts in two HTF tanks.

The insulation system consists of two insulation plates and one cement grout with a total thickness of approximately 110mm. The tanks can move up to 4 cm on each footing due to temperature changes, producing loads on the footings. Assuming a friction coefficient for a steel-steel interface of ฮผ=0.7 and a net weight of P=170 tonnes, the shear stress can be calculated using ๐œ= Pยทฮผ/A = 0.35 MPa. Any good cementitious grout can withstand a shear stress resistance of 1.75 MPa. However, the shear forces, together with the laminated disposition installed without any bonding agent and loose anchor bolts, induced progressive cracking on the insulating material.

 

The Procedure

 

The repair process began by using pneumatic chippers to remove enough material from underneath the sliding plates to place the first Alphapadยฎ sized D2, ensuring a properly levelled surface with healthy concrete, without changing the position of the saddle. After surface preparation was complete, the Alphapadsยฎ were set in place and adjusted to the appropriate height, allowing the hydraulic levelling system to work with the tanks in place.

Once the Alphapadsยฎ were set, the team conducted a complete regrout with the use of ALPHATECยฎ 800 epoxy grout. The grout was applied to the interface between the grout and the sliding plates, situated beneath the footings. After taking off the pressure on the Alphapadsยฎ, the whole weight of the tank rested on the epoxy grout.

ย A final inspection was carried out to ensure that the grouted areas were properly aligned and there were no sharp edges. The repaired tanks were left to cure for the appropriate amount of time, ensuring that the tanks were stable and would continue to perform as intended. The repairs were conducted on all six footings of the two parallel tanks to restore the interface between the sliding plates and the grout located beneath the footings.

 

Conclusion

 

At Alphatec Engineering we take pride in our ability to provide innovative and effective solutions for complex machinery foundation problems. With our advanced epoxy resin-based grouts and hydraulic levelling systems, we can restore damaged foundations and ensure reliable and efficient operation.

Whether it’s for the power generation, oil and gas, or renewable energy industries, we offer customised solutions that meet the unique needs of our clients. By choosing Alphatec Engineering, you can be confident in maximising your productivity and reducing downtime. Contact us today to learn more about our services and products.