CaCO3 scale inhibition in paper making processes – evaluation of testing methods and inhibitor performance

The formation of an adherent layer of inorganic deposition on the surfaces of process equipment is called scaling. Scaling is a major problem in many industries using large quantities of water. One of these industries is the paper making industry and the most common scale forming compound is calcium carbonate. The scaling problem in the paper making industry can be eased or in the best case completely solved by the use of chemical additives referred to as antiscalants or scale inhibitors. The most common an-tiscalant compounds are phosphonates and polycarboxylates. The formation of calcium carbonate scale and its inhibition are widely studied themes but few of the studies are linked in the conditions of paper making. The objec-tives of this thesis are to establish laboratory testing methods for the evaluation of the performance of different scale inhibitors in the paper making conditions and to evaluate the performance of different antiscalants in these conditions. The thesis comprises an extensive literature survey and an experimental part. The literature survey covers the precipitation process of calcium carbonate, factors affecting this process and chemistry of different antiscalants. Also the theory of a computational model of French Creek’s WatSIM software is covered. In the experimental part three different laboratory test methods are utilized to conclude the performance of different antiscalants in the condi-tions of paper making. These laboratory test methods are a static jar test, a dynamic ro-tating disk procedure, and a dynamic tube blocking procedure. The WatSIM software is utilized to calculate different scaling potential indices in the conditions of paper making. The results of this thesis show that the differences between different antiscalants can be distinguished with the used laboratory testing methods and that the differences are significant. The phosphonate antiscalants might function better than polycarboxylate antiscalants in certain operating conditions but even a little change in the conditions, for example in the pH or temperature, can completely block the ability of the phosphonate antiscalants to function. The polycarboxylate antiscalants are more resistant to changes in the operating conditions, which extend their range of use. The computational results yielded with WatSIM were somewhat conflicting which indicates that the software is not fully optimized for the conditions of paper making /Kir1