(288d) Optimal Synthesis, Scheduling, and Operation of Batch Water-Recycle Networks with Interception
AIChE Annual Meeting
Tuesday, November 6, 2007 - 4:33pm to 4:54pm
Increasing attention has been given to the conservation of natural resources in processing facilities. As such, reduction in water usage and discharge has received much interest as a means of sustainable operation. Towards this end, water reuse and recycle is an effective tools in the overall management of water systems. 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. The objective of this work is to introduce a systematic framework for the synthesis, scheduling, and operation of water recycle networks in batch systems. Direct recycle opportunities are first considered without the addition of new process equipment. A new source-tank-sink representation is developed to allow for storage and dispatch tanks. A mathematical formulation is developed for minimizing the total annualized cost of the system while providing sufficient targets for fresh-water usage, process-water recycle, and wastewater discharge. The solution also provides enough information to develop the scheduling strategy. The formulation is further simplified for a special case where a hierarchical procedure can be used solve the problem in interconnected stages. Next, interception devices (e.g., separation equipment) including unsteady-state units are introduced into the problem representation to adjust the characteristics (e.g., concentration of impurities) in the process-water streams. Several cases are addressed to determine the optimal separation tasks as well as the design, operation, and scheduling of the interception devices. Finally, the recycle network is integrated with the separation network to provide cost-effective water networks. A case study is presented to illustrate the efficacy of the developed procedures.