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Performance of Thermal Spray Coatings in Phase Change Materials (PCMs) used in Geothermal Plants

Geothermal energy has been an integral part of the renewable energy mix for several decades. The total installed geothermal power generation capacity by the end of 2021 was 15,854 MW. Despite the challenges imposed by the pandemic, new capability was developed, and capacity was added in several countries. The capacity was increased by 246 MW from the figure in 2020.4

Product Number: 51323-18862-SG
Author: Shiladitya Paul, Catherine Leahy
Publication Date: 2023
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Corrosion is a major issue in several geothermal plants, and this has serious impact on the ability of the geothermal sector to operate economically. The ability to engineer surfaces to reduce corrosion offers a tool for engineers and plant operators to have better maintenance and repair. This paper explores the possibility of using thermal spray coatings on steel substrates and modify its corrosion behaviour in phase change materials (PCMs) used in geothermal plants. The thermal spray coatings were pre-selected based on the performance data in literature, ease of application, availability and cost. The philosophy was to select coatings that were anodic to the substrate in molten PCM that would protect the substrate in case of any damage to the coating. Carbon steel substrates with thermal spray coatings of Al were prepared and exposed to molten PCM at 165°C for 450h. After testing, the specimens were visually examined and detailed post-test characterisation [light and electron microscopy (SEM/EDX) etc.] of surface and cross-sections was carried out. These measurements provided an indication of performance of the coatings and allowed further understanding of the mechanism of degradation of materials in nitrate-nitrite PCM. The study showed that thermally sprayed aluminium (TSA) could provide a possible corrosion mitigation pathway for carbon steel structures in nitrate-nitrite based PCM systems.

Corrosion is a major issue in several geothermal plants, and this has serious impact on the ability of the geothermal sector to operate economically. The ability to engineer surfaces to reduce corrosion offers a tool for engineers and plant operators to have better maintenance and repair. This paper explores the possibility of using thermal spray coatings on steel substrates and modify its corrosion behaviour in phase change materials (PCMs) used in geothermal plants. The thermal spray coatings were pre-selected based on the performance data in literature, ease of application, availability and cost. The philosophy was to select coatings that were anodic to the substrate in molten PCM that would protect the substrate in case of any damage to the coating. Carbon steel substrates with thermal spray coatings of Al were prepared and exposed to molten PCM at 165°C for 450h. After testing, the specimens were visually examined and detailed post-test characterisation [light and electron microscopy (SEM/EDX) etc.] of surface and cross-sections was carried out. These measurements provided an indication of performance of the coatings and allowed further understanding of the mechanism of degradation of materials in nitrate-nitrite PCM. The study showed that thermally sprayed aluminium (TSA) could provide a possible corrosion mitigation pathway for carbon steel structures in nitrate-nitrite based PCM systems.

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