(747c) Optimizing Chlorine Dosage and Discharge In Industrial Seawater Cooling Systems

Using seawater in industrial cooling systems is a common practice in many parts of the world where they have limited freshwater resources. There are problems associated with the usage of seawater in the cooling system from the biological activities of the microorganisms in seawater. Those microorganisms tend to create a thin layer sticks to the inside surface of the tubes inside heat exchangers and pipelines. A layer thickness of only 250 is enough to reduce the heat transfer coefficient by fifty percent. Consequently, biofouling is one of the major operational problems caused by the usage of seawater as a coolant. Therefore, chlorine is added to seawater in order to eliminate or at least reduce those biological activities. The discharged seawater contains chlorine residual as well as chlorine-reaction byproducts. The discharged seawater is subject ot chemical and thermal regulations. One limit is controlling the average amount over some period of time. The other limit is for the maximum at any time.

In this paper, an optimization-based approach is developed to optimize seawater cooling systems and the usage and discharge of biocide (e.g., chlorine). The devised model simulates the chlorine behavior inside the cooling system starting from the basin where the chlorine is injected till the discharged point. A model is also developed for the reaction mechanism and kinetics of chlorine and its byproducts under different operating conditions of the plant. An optimal dosage strategy is used to determine the dynamics of chlorine dosage and the characteristics of the effluents. Additionally, the solution of the optimization problem determines necessary retrofits to process design and operation. A tradeoff is established between process economics, environmental performance, and seawater cooling performance. A case study is solved to illustrate the devised procedure and its usefulness.