(599ah) An Integrated Platform for Optimization of Heat and Water Use in Multipurpose Batch Plants

Utility and water requirements in many batch plants, such as in the food industry, breweries, dairies, biochemical plants and agrochemical facilities, contribute largely to their overall running costs. Process equipment cleaning is usually associated with large amounts of water, due to the inherent sharing of equipment by different tasks. Hence, efficient use of water for process equipment cleaning is pursued to ensure that the amount of freshwater consumed as well as the amount of wastewater generated is minimized. Similarly, heating and cooling are unavoidable aspects of many chemical processing facilities, with operations where heat is generated and others where heat is required. It is because of this occurrence that heat integration becomes a possibility.

Heat optimization and optimization of water use have mainly been treated as separate problems in literature. The batch production schedules resulting from each of these formulations do not guarantee that the plant is operated optimally. Consequently, it is required to develop a formulation that caters for opportunities that exist for both wastewater minimization and heat integration. This may result in production schedules that improve the operation of the batch plant when compared to optimizing water and heat separately.

Presented in this study is a formulation that addresses the optimization of both water and heat, while simultaneously optimizing the batch process schedule. The scheduling framework used in this study was based on the formulation by Seid and Majozi (2012).  This formulation was shown to result in reduced computational time, an improvement of the objective function and required much fewer time points compared to published techniques. In the case of wastewater minimization, opportunities for direct water reuse and indirect water reuse utilizing wastewater storage are explored. On the other hand, in the case of heat optimization, both direct and indirect heat integration are explored for reducing external utility requirements. The objective is to improve the profitability of the plant by minimizing wastewater generation and utility usage.

Keywords: Wastewater minimization, heat integration, heat storage, multipurpose batch plant