In geothermal power plants, various types of scales can occur. Barite (BaSO4, barium sulfate) is the dominating mineral species of the scales in a region in middle Europe, acting as isolation material and leading to a reduction of the heat transfer and clogging of installations. Further, sulphide minerals like galena (PbS, lead sulfide) may be part of the scaling. As a consequence, cleaning for scale removal is required in regular time intervals to keep up the efficiency of the energy production. Another important counter measure is to prevent or reduce deposit formation by the addition of an antiscalant into the water.
State of the art antiscalants for the prevention of barite formation are based on phosphonates. Since they contain a non-negligible amount of phosphorous, combined with poor biodegradability, they become more and more a reason for concern.Hence, there is a need of an antiscalant having an improved environmental profile and/or an improved performance. Three different commercially available antiscalants were tested in the laboratory concerning their efficiency against barium sulfate scaling:a biodegradable product, a polyacrylate copolymer being free of phosphorous and nitrogen and a phosphonate.
Artificial water adapted from a geothermal brine was used in all tests. Preliminary turbidity tests were carried out as well as beaker tests with different concentrations of the inhibitors.
All three inhibitors showed a high compatibility with the artificial brine. Further, all three inhibited the precipitation of barite successfully. Nevertheless, the biodegradable product showed the best performance concerning the inhibition of barium sulfate, combined with an improved environmental profile.