| Abstract |
The paper presents corrosion and scaling studies in an EGS power plant located in the Upper Rhine graben: the ORC power plant located at Soultz-sous-Forêts, in France. The Soultz project is an experimental long term research dealing with Enhanced Geothermal System (EGS). Three deep wells have been drilled to 5 km into a granite reservoir, cased between the surface and 4,5 km depth and hydraulically stimulated. An ORC (Organic Rankine Cycle) power plant has been built with a net power capacity of 1,5 MWel. At Soultz, corrosion and deposits creation were investigated based on on-site test setting by using P110, N80 and P265GH steels, in order to determinate the reaction of those materials to the geothermal brine (having a salinity of 100 g/l and a pH of ~4,8). An innovative corrosion pilot was set up on the geothermal loop at the surface and tested for the first time between September 2008 and February 2009. Steels samples were introduced in the corrosion chambers, where the geothermal fluid circulates, and remained there for different time intervals. A series of physico-chemical parameters, such as pH, Eh, conductivity and temperature, was measured in the meantime. After their extraction, samples were analyzed by various chemical techniques. The main results consist in a significant action of geothermal brine on all studied steels. Newly created deposits, mainly sulfates (barite, celestite) formed on the surface of samples and were characterized by SEM analysis giving access to their structure. Corrosion occurred beneath the deposits and corresponds to pits. Beneath the deposits layer, an interface region was identified, in which various chemical elements (As, Ca, Pb, Si, etc.) were identified.. Corrosion products such as iron oxides (rust were found inside the deposits layer, too. There are no standard procedures available for on-site corrosion tests at geothermal power plants. Thus, the giveninvestigation methods, results and conclusions could be very helpful for defining comparable and standardized corrosion tests for future geothermal plants within the upper Rhine Graben. |