Heat Integration in Multipurpose Batch Plants: II. Indirect Heat Integration

Overview

This chapter is, in essence, an extention of Chapter 10 which focused on direct heat integration as encountered in the absence of heat storage (Majozi, J. Cleaner Prod., 17: 945–950, 2006). The inclusion of heat storage in the exploration of energy saving opportunities through heat integration adds more degrees of freedom in the analysis, which is likely to improve the optimum point. The necessity of heat storage arises from the time dimension that is inherent in batch plants as mentioned severally in the foregoing chapters. Storage of heat allows the time dimension to be bypassed by allowing the task that serves as the heat source to take place before the task that is appropriate to serve as the corresponding heat sink without losing the opportunity for heat integration. Heat transfer fluids, e.g. water, are normally used for this purpose. The presented mathematical formulation exhibits an MILP structure for the fixed capacity of storage. Application of the proposed method to an agrochemical facility demonstrates savings of more than 75% in external utility steam consumption.