Design and optimization of indirect energy storage systems for batch process plants

One of the main difficulties for handling heat integration problems in batch plants is the time-dependent existence of hot/cold process streams during time period p. This article aims at proposing a generic method for synthesizing an indirect heat exchange network and its associated, thermal storage policy for targeting the external utility in a batch plant. Therein, a heat transfer medium (HTM), originally staying in a cold tank, is used to absorb surplus heat from hot process streams, and the HTM with elevated temperature is temporarily stored in a hot tank. The accumulated hot HTM is then utilized to heat subsequent cold process streams, and the cooled HTM recirculates back into its source cold tank. The limitation of heat interchange between time-dependent hot/cold process streams can be relaxed by applying the recirculated heat transfer medium to carry out indirect thermal storage. A superstructure is proposed and the mathematical programming approach is applied for investigating the indirect heat exchange policy. Not using any heuristics that are based on the concepts of pinch limitations, the proposed superstructure-based representation for synthesis of indirect heat exchange networks (HEN's) for batch processes is formulated as a mixed-integer nonlinear program (MINLP). Numerical examples are explored to demonstrate the applicability of proposed indirect HEN synthesis method for batch processes. This method is verified by two examples with different numbers of storage tanks.