(341e) Optimization of Biofouling Control and Energy Supply Policies in Thermally Integrated Plants

One of the most important aspects of a process economy is the proper use of energy resources; in this context heat integration strategies have been widely used in order to reduce the amount of external heating and cooling utilities. Although the degree of integration may vary from one process to another, there is typically the need for additional external utilities. Cooling water is the most commonly used cooling utility; however, low salinity resources are limited and, furthermore, not homogeneously distributed in the planet, which has driven the interest for the use of seawater as a cooling fluid. Two main issues associated with the use of seawater are the formation of biofilms and the need for additional refrigerant utilities when the required temperature of any hot process stream is below room temperature. Two design strategies are considered in this work for these types of situations. One is the addition of biocides to control biofilm growth, and the other one is the inclusion of an absorption refrigerant system when cooling water is not feasible as a cooling utility. An integrated scheme of heat exchanger networks together with the use of seawater as cooling utility and an absorption refrigeration system is considered in this paper, so that energy integration aspects are tied to proper biocide dosing scheduling in the search for an optimal implementation policy.  A mathematical programming approach is developed to deal with this problem and obtain an optimal scheduling of biocide dosing, mechanical maintenance and energy supply for thermally integrated facilities. The resulting model is a multi objective mixed integer non-linear programming problem. A case study of an Acrylonitrile plant located in Musqat, Oman is used to show the applicability of the proposed approach. Pareto curves are obtained, which help devise attractive solutions considering technical, economic and environmental constraints for the selected process.