Qualifying Geothermal Applications For Fouling Repellent Sol-Gel Coatings With A Proven Track Record In The Offshore Oil Industry

Abstract

Geothermal energy has a lower environmental footprint than any other renewable energy source, and the European Council recognize geothermal energy’s essential role in the European energy transition towards net-zero greenhouse gas emissions in 2050. Currently, geothermal energy provides 0.2 % of EU final electricity demand and 0.8 % of the energy generated by renewable sources. In order to expand the potential for geothermal power production, focus should be made on overcoming the existing technical barriers that limit the utilization of the geothermal resources. To overcome these barriers, the sector has to pursue collaborations with other industries to generate new ideas and identify crossover technologies that offer potential solutions. The economic feasibility of geothermal installations relies on continuous and constant operation of the geothermal loop. Constraints of operational performance like unscheduled shut-down periods, maintenance operations and follow-up costs reduce their reliability. To be competitive and reduce costs, operators must pay attention to proper maintenance of critical equipment, especially the heat exchangers transferring heat from the geofluid to the working fluid. The chemical nature of the geothermal fluids, high temperatures and pressures create very harsh environments that forces the use of very resistant high alloying materials. Those high-quality materials can perform well in very aggressive environments, but economic aspects must be taken into account, and this leads to a trade-off between performance and costs. Thus, if cheaper materials (i.e carbon steel, low alloying stainless steels) could be coated with cost-effective coatings, providing the same corrosion protection as the exotic materials, minimizing fouling, and having limited impact on the heat transfer, this would improve the installation economic factors by engendering a considerable reduction in capital investment, and a decrease in the costs of operations and maintenance. One purpose of the MATChING project is to examine whether the know-how gained from the development of anti-fouling sol-gel coatings for oil & gas (O&G), at Danish Technological Institute (DTI), could be applied to the geothermal sector. DTI’s protective anti-fouling sol-gel coatings have proved to be a cost-effective remedy to reduce fouling problems in the O&G sector. DTI’s coatings have for a number of years been utilised on plate heat exchangers in the North Sea, proving a good track record within the offshore oil industry. While uncoated plate heat exchanger units typically have an operating time of about 6 months before fouling issues demand onshore cleaning, coated units achieve 3 years of operation without the need for any cleaning procedures. This significant increase in operation time allows operators to maintain a high output from their equipment. In MATChING, we upgraded the corrosion resistance of different DTI sol-gel coatings, which were initially developed for the O&G sector and tested their performance in the laboratory under conditions that mimic those encountered for heat exchangers in geothermal installations. For the tests, we employed a custom-designed device in which samples were exposed to synthetic brines at high temperatures and pressures for long time periods. The heat transference across the coatings was also estimated to evaluate the resistance factor introduced by the coating. Results showed that several of the coating candidates effectively protect the substrates, do not deteriorate, and could provide alternative material solutions for heat exchangers in geothermal installations.

AAPG Datapages/Search and Discovery Article #90346 ©2019 AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop, Geneva, Switzerland, April 9-10, 2019