Mathematical model of sulphate ion concentration in a closed cooling system of a power plant

Abstract

In commercial power plants, water is used in many processes and its physical and chemical properties have a significant impact on the efficiency of energy and heat production as well as failure-free operation. One of the largest consumers of water in a power unit is the cooling system consisting of condensers and cooling towers. In cooling towers, the main mechanism for the decrease in temperature of the water is its partial evaporation, which causes a gradual decrease in the amount of circulating water and, on the other hand, a continuous increase in the concentration of chemical compounds in the closed system. Among others, an uncontrolled increase in the sulphate ion concentration in cooling water may cause the corrosion of the concrete parts of the hydraulic system as well as an increase in the deposition of calcium salts on the surfaces of the heat exchangers, thereby worsening the heat exchange processes inside the condenser. The daily demand for fresh water in power plants often reaches tens of thousands of cubic metres and so the amount of wastewater released also has a significant influence on the environment. Therefore the Polish Ministry of Environment and EU directives have introduced, from the beginning of 2016, new limits on the physical and chemical parameters of wastewater released to natural reservoirs. Taking into account the previous regulations, the authors present a mathematical model which allows the prediction of the daily changes of the sulphate ion concentration in the circulating water in a condenser - cooling tower closed cooling system and the calculation of the minimum wastewater flow rate fulfilling legal restrictions.