ESDU 90033 is primarily concerned with the application of process integration to batch processes and other time-dependent systems, for example, the start-up of a continuous process, a multi-plant complete site, or even a building. Methods are described for determining energy targets, for identifying possibilities for heat storage (within or between batches) and for rescheduling process operations to maximise heat exchange, and for designing heat recovery networks. In addition, consideration is given to the use of process changes in continuous systems that will reduce energy targets, for example, changing a distillation column temperature, adding a pumparound or an intermediate boiler, or changing the number of stages in an evaporator. The techniques described are developed and explained through case studies that illustrate their practical application. ESDU 87030 should be consulted for the basic principles of process integration while ESDU 89001 shows how it is applied to combined heat and power supply on a site and for the selection of utility systems for heating and cooling.