Modeling Multi-period Operations using the P-graph Methodology

A new modeling technique is presented here for handling multi-period operations in process-network synthesis (PNS) problems by the P-graph (process graph) framework. Until now, the P-graph framework could only handle single-period operating units. It means that the operating conditions and the load of each unit remain unchanged throughout its operation. This assumption is usually true for the chemical industry but may be false in agriculture or in other areas where seasonal effects are important. Hence, the current work proposes the notion of multi-period operation wherein the load of an operating unit may vary from period to period. Subsequently, a modeling technique is proposed to represent operating units in the multi-period operation. The idea is to represent separately the physical body of an operating unit and the operations in each period. Surprisingly, to achieve these tasks, there is no need to dramatically change or augment the basic structure of the P-graph methodology, e. g. with a new type of multi-period unit, but the already available constituents are adequate.