Dieng Geothermal Field: Testing of The Effectiveness of Ph Modification For The Mitigation of Silica and Arsenic-Sulfide Scaling In Heat Extraction Process Using A Pilot Plant.

A new mobile pilot plant unit was designed and built for Geo Dipa Energy in Indonesia. The unit’s purpose was to test different process cycles and find the most effective method of scale mitigation for present and future power plants in the Dieng geothermal field. The pilot plant was constructed in Indonesia and transported to Dieng geothermal field in central Java and connected to well HCE-7C. Tests, conducted for demonstrating the operability of the pilot plant provided conclusive results about the suitability of the proposed mitigation methods for the Dieng brine. Of four process options tested only high-pressure separation and hot injection proved satisfactory. The tests demonstrated that the proposed pH modification is not effective for scale mitigation in an ORC process using the hot brine as the energy source. This is because of high scaling rate of arsenic sulfide and silica. Because of the low solubility of arsenic sulfide at low pH, acidification for mitigation of silica scale is not beneficial. The tests demonstrated that the proposed pH modification is neither sufficiently effective for scale mitigation in a dual flash process operated at low secondary separator pressure. Diluting the brine with the condensate is less effective than expected because of the high ammonia content, and high pH of the condensate. Testing of injectivity with packed bed was demonstrated but due to the short duration of the tests the significance of the packed bed experiments is somewhat limited.