(130a) A Practical Approach to the Synthesis and Scheduling of Optimal Batch Water-Recycle Networks

Responsible industries have begun to take considerable actions to identify ways to reduce fresh water consumption and wastewater generation. One effective approach has been to maximizing water reuse and recycle within the process plant. The numerous water sources and users must be simultaneously addressed. This leads to the need for efficient techniques to design water recycle networks to optimize the use of fresh water, recycle of process water, and discharge of wastewater. While significant contributions have been made in developing systematic approaches for synthesizing water networks in continuous processes, much less work has been done for batch processes. This work is aimed at developing a generally-applicable methodology for the optimal design of water recycle networks in batch processes. This is a challenging problem that requires the identification of network configuration, fresh-water usage, recycle assignments from sources to sinks, wastewater discharge, and a scheduling scheme. A new source-tank-sink representation is developed to allow for storage and dispatch tanks. A hierarchical procedure is developed to solve the problem in interconnected stages. Benchmarks for minimum usage of fresh water and wastewater discharge are determined by eliminating scheduling constraints. An iterative procedure is formulated to minimize the total annualized cost of the system by trading off capital versus operating costs. A case study is solved to illustrate the usefulness of the devised procedure.