Synthesis of water-using network with central reusable storage in batch processes

The starting and finishing times of water-using operations in batch plants are dependent on the production planning and scheduling. For maximizing the possibility of water reuse/recycle, or for minimizing the freshwater consumption, central storage facilities in a batch water-using system can collect the reusable water from the earlier operations and then supply the remaining water to the later operations. For a predefined production schedule, this paper presents a mathematical formulation for the synthesis of batch water-using networks with central storage tank(s). Superstructures that incorporate all possible flow connections are built to facilitate the problem modeling. The design problem is formulated as a nonlinear program (NLP) if there is no limitation to water reuse/recycle, or a mixed-integer nonlinear program (MINLP) when forbidding water reuse between assigned water-using units and water recycle of certain water-using units is considered. A published literature example and some adaptation examples are provided to demonstrate the good expectation of the proposed, superstructure-based NLP and MINLP formulations.As supported by the results, superstructures with the design scheme can effectively accomplish the objective of solving the design problem for minimum freshwater consumption and offering the optimal network configuration.