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Geothermal
GeoHex project : Novel coatings for geothermal heat exchangers
An example of a geothermal power plant . Source : Dreamstime
Heat exchangers are critical components for geothermal applications but prone to damage from scaling and corrosion . The GeoHex consortium has been working to develop materials for heat exchangers that offer improvements in anti-scaling and anticorrosion properties as well as heat transfer performance . These materials will afford improved efficiencies and reduced costs .
This project has received funding from the European Union ' s Horizon 2020 research and innovation programme . Grant agreement : 851917
Text and images provided in collaboration with GeoHex
The proposed way to realise the needed improvements is to use amorphous coatings . The initial challenge therefore lay in finding / developing coating materials which provide anti-corrosion and anti-scaling properties . This has led to the investigation of materials capable of not only providing the required anti-corrosion properties but also able to withstand the high temperatures associated with geothermal applications . GeoHex plans to achieve reduced scale formation in geothermal heat exchangers by using a variety of different coating types , including amorphous coatings . The project aims to take development from lab scale to full equipment scale ; from working on small coupons , to heat exchanger test rigs , to relatively small but still representative heat exchangers , composing of proper geometry , corrugated plates , and pipes .
Project focus The GeoHex project has centred its focus on Organic Rankine Cycle ( ORC ) powerplants due to their usability for low to medium thermal resources . In these applications , heat exchangers are used with a geothermal fluid on one side and a working fluid on the other . The working fluid is boiled and the vapour transfers energy to turbines to then generate electricity . The working fluid is then condensed to repeat a continuous cycle . The outcome of GeoHex ’ s coating research intends to increase the heat exchanger performance for such applications , as well as to enhance anti-scaling and anti-corrosion properties . The project relies on work carried out by a consortium ( see box text ). Tæknisetur undertook single-phase testing analysis for multiple types of coatings manufactured using different processes , including :
• Thermal sprayed aluminium coating ( TSA )
• Physical vapour deposition ( Amorphous 1 & 2 )
• Electroless nickel plated coatings ( ENP )
• Chemical vapour deposition ( MWCNT )
• High velocity oxygen fuel coatings ( nanoporous ) The Tæknisetur team assessed heat transfer performance and durability of each coating with an in-situ heat exchanger rig , installed at ON Power ’ s Hellisheiði geothermal power plant , fitted with temperature and flow sensors , and performed microstructural analysis of tested samples using SEM / EDX and XRD , and pull-off adhesion tests .
16 Heat Exchanger World May 2023 www . heat-exchanger-world . com