World Geothermal Congress
May 21-26, 2021

Scale and Corrosion Mitigation: Economic Feasibility of Combined Mitigation Measures


[BESTEC GmbH, Germany]

Today, five binary geothermal plants are operating in the Upper Rhine Graben (URG), a geothermal low enthalpy region at the German – French border. Several new projects are planned and two of them are close to realization. Typical scales in geothermal plants of the URG consist of barium/strontium sulfates and other deposits, rich in lead, arsenic and antimony. Barium/strontium inhibition has already been realized successfully with an overall efficiency of more than 98% but it leaves the heavy metal deposits untouched. Currently, additional product tests are conducted at three of the geothermal plants within the framework of the research project SUBITO, funded by the German Federal Ministry for Economic Affairs and Energy (BMWi). The project aims to reduce total scale mass of lead, antimony and arsenic deposits and to limit or eliminate the accumulation of toxic and radioactive elements by using chemical inhibitors. Additionally, corrosion phenomena like localized corrosion should be reduced to a minimum. All inhibitor tests are accompanied by investigating the economic feasibility by balancing inhibitor related investment and operational costs with cost savings by improved plant availability and efficiency and reduced follow-up costs. The first approach of SUBITO targeted commercially available antiscalants which held the potential to inhibit barium sulfate AND lead sulfide in one product. Results of lab and on-site tests showed some improvement related to scale mass reduction but the limited efficiency in combination with some compatibility issues were not satisfactory. Moreover, scale characterization highlighted the importance of electrochemical reactions like corrosion as a trigger of heavy metal scale formation. Therefore, best results for scale inhibition of both types, sulfate scale and heavy metal scales were obtained by combining scale and corrosion mitigation measures. After careful pre-selection, corrosion inhibitors were applied at all three geothermal plants in combination with the barium sulfate inhibitors. As a result, the total mass of deposits was significantly reduced as well as corrosion related maintenance operations. Even considering the relatively high operational costs for continuous scale and corrosion inhibition the positive effect of cost savings by improved availability and operational performance as well as significantly reduced follow-up costs lead to a decrease of the total average operational costs.

        Topic: Corrosion and Scaling Paper Number: 27066

         Session 14G: Corrosion and Scaling 4 -- Corrosion Inhibitors [Monday 24th May 2021, 10:20 am]
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