| Abstract |
Inhibitors are used in many geothermal production systems around the world to prevent scale formation, for example in various geothermal plants in the Upper Rhine Graben (ORG), Iceland (Krafla), the Netherlands, Austria, and Turkey. So far no inhibitors have been used in the geothermal plants of the southern German Molasse Basin. However, some plants in this region are prone to scaling which mainly consist of calcium carbonates and iron sulfides and undesirably occur almost everywhere including the submersible pump, riser pipe, above ground pipes, filters, and heat exchanger. The occurrence of these scales makes the operation of geothermal energy production difficult and by using precipitation inhibitors these problems can be solved. Because these inhibitors are sent together with the cooled groundwater back into the geothermal reservoir, the inhibitors must be harmless and biodegradable in all respects according to the German and European water law. Investigating the use of NC47.1B (Niederrhein Chemie) as a biodegradable inhibitor in geothermal plants in the Bavarian Molasse basin is the major aim of the BMWi (Federal Ministry for Economic Affairs and Energy) funded joint research project EvA-M. As part of the project, pilot plants were used onsite to perform static and dynamic investigation of the stability of the inhibitor and its interactions with the reservoir. Changes to the aquifer rock, the chemical and isotopic composition of the geothermal water and the inhibitor were also examined. Thermodynamic and kinetic modeling of calcite precipitation, complexation of calcium/ or slowing calcite precipitation by means of NC47.1B as well as degradation of the inhibitor over time was done by means of PHREEQC and TOUGHREACT. By using data from batch and bypass experiments, reliable numerical models can be used to determine optimal inhibitor concentrations and predict outcomes. The results of this research allow for the use of biodegradable inhibitors in southern German Molasse Basin and similar carbonate aquifers, which will lower production costs due to minimizing plant downtimes and breakdowns as well as damages to system components such as pumps, valves and measuring instruments. |