Numerical study of the fouling effect on wet cooling towers designed to CSP plants

Abstract

As fouling issues have been gaining more and more attention every day, understanding the fouling behaviour on heat exchangers is the main way to increase knowledge on fouling effect, then reducing the waste heat on an industrial process. Cooling towers are widely used in CSP plants for energy transfers and utilization. However, air-side and water-side are usually unclean. The mineral salts contained in cooling water are deposited on the surface of heat exchangers, which reduce the heat transfer performance significantly and threatens the operating stability of the system. Meanwhile, the additional economic losses are caused due to the failure of heat exchange tubes and the soot-blowing process. Therefore, fouling is a major issue for heat exchangers and it should be fully taken into account in the heat exchanger design process. In this purpose, an apparatus scale unit of cooling towers designed for CSP plant was installed in the Green Energy Park (GEP) research platform, located in Benguerir, Morocco, in the framework of the MinwaterCSP project. In this study, we investigated the effects of fouling in cooling towers numerically for cross-flow heat exchangers tube geometry. The equation system governing the problem has been based on the finite volume method. The studied flow considered turbulent and modeled by the K-ε standard model, known to generate satisfactory results for this type of flow. A mesh sensitivity study was also carried out to choose an optimal mesh. The obtained results show that the heat transfer efficiency with the polymer is greater than with galvanized steel in the absence of fouling.In case of dirty deposits, the efficiency drops for both materials, with the increase of the resistance of the fouling. For the polymer, the efficiency of the heat exchange decreases by up 4% and 3%for galvanized steel. Moreover, the fouling resistance is more higher on galvanized compared to polymer. This behaviour is due to the wall surface temperature of the two tubes, which are higher in the polymer than steel, which justified the rapid rate of deposition of the mass. The proposed model is validated by