Sulfide stabilization in geothermal applications

Abstract

Scale formation is commonly observed in geothermal power plants due to high salt content, high temperatures, and varying pH conditions altering the solubility of salts. Scaling at surface facilities impairs the heat transfer, reduces the overall plant efficiency, limits the total power output, and in severe cases leads to equipment losses. Despite the common scale types of carbonates and silicates, sulfide deposition is considerably encountered. This type of deposition is mainly observed in binary cycle geothermal power plants. Among various sulfide scales, including arsenic and iron, this contribution will focus on antimony and lead-rich sulfide scales in geothermal utilization.

Sulfide scale formation is more geographically dependent and is greatly affected by the characteristics of the reservoir. Looking at the geothermal plants worldwide, antimony sulfide precipitation is mainly reported on the west coast of Turkey, Italy and New Zealand, whereas the PbS is reported primarily in Japan, North-West Turkey, Upper Rhein Graben, and Greece.
Despite the widely conducted research on carbonate and silicate scaling, studies concerning sulfide mitigation strategies are limited.
This contribution will present the effect of successful stabilizers for antimony sulfide and lead sulfide mainly dedicated to geothermal applications. In addition, laboratory studies will be shown for both deposit types. A case study for antimony sulfide stabilization will be demonstrated with physical parameters observed during the treatment program in the field.