Synthesis of maximum energy recovery networks in batch processes

Abstract

In the heat integration problem for batch processes, there are two differences in treatment from continuous operations. The first is the occurrence of cocurrent heat exchange, this case may happen when a process can not be transferred to another process. The second is that time must be considered as a variable. We divide the problem into two cases, namely co-current heat exchange and counter-current one, and then intend to find the rules to satisfy the requirement of each case. For the former, a matching rule and a MILP formulation had been proposed but any method did not obtain the optimal solution. The latter including the time as a variable often occurs in the practical industry. The limitation of time has been reduced by changing the schedule of processing or using the heat storages. However, the systematic rule considering the batch cycle time has not been presented for the rescheduling and heat storage is not usually practical although it is reasonable concept. Therefore this paper presents general method for optimal rescheduling to maximize heat recovery and reduce batch cycle time when heat exchanges occur as counter-current type. In the exchanges of co-current type, the heuristic, called the modified H/H which can be used to find the optimal match sequence of heat exchange between hot and cold tanks, is proposed. The proposed heuristics have the advantages of simple calculation and small computation time.