There are situations in which process integration is detrimental to the capacity of batch process plants. In such cases heat storage provides a flexible alternative. The use of reactor jackets and coils is also inefficient. Where possible, external exchangers should be used for feed preheating and product cooling of batch reactors. The use of external heat transfer leads to the heat storage problem being steady state. Procedures are presented for the design of heat storage systems under both steady and unsteady states.