Some Insights into the Tube Blocking Test Method to Evaluate the Efficiency of Mineral Scale Inhibitors

Abstract

Abstract The Dynamic Tube Blocking Test (TBT) method is used to evaluate the efficiency of chemical inhibitors to prevent the formation and deposition of mineral scales such as calcium carbonate, as well as calcium, barium and strontium sulfates. The TBT method aims at (1) determining the Minimum Inhibitor Concentration (MIC) required to prevent the formation of scale, and (2) performing comparative tests with different inhibitors in the same conditions. Inhibitor efficiency is measured by the ratio of the time needed to block the tube in the presence of inhibitor divided by the time needed to block the tube without inhibitor, i.e. blank time. Conditions for the blank test are adjusted to induce a significant precipitation in a reasonable time frame. Main adjusting parameters are solution degree of saturation of scaling species and flow rate. Other parameters such as capillary length and diameter can be chosen arbitrarily. The purpose of this study is to check the accuracy of the TBT method and to compare the MIC values obtained in various experimental conditions. Three types of inhibitors were used, namely, phosphonates, polyacrylates, polyaspartates and a carboxymethylated polysaccharide. Scales were calcium carbonate, calcium sulfate and barium sulfate. The results show that the TBT method is very sensitive to the effect of flow rate and capillary dimension. A careful control and monitoring of the temperature is also required. The TBT method is shown to give information on the physical mechanisms acting on the scale inhibition process.