(599m) Simultaneous Optimization of Energy and Water 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 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.

In the past, wastewater minimization and energy optimization in batch plants have mainly been treated as separate problems in literature. For instance, mathematical formulations that addressed wastewater minimization maximized revenue by minimizing wastewater generation while those developed for energy optimization maximized revenue by minimizing utility usage in the facility. 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 energy separately.

Presented in this study is a formulation that addresses wastewater minimization and energy optimization concurrently, while simultaneously optimizing the batch process schedule. With respect to wastewater minimization, opportunities for direct water reuse and indirect water reuse utilizing wastewater storage and wastewater regeneration are explored. With respect to energy 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.