Modeling and control of fluid transportation operations in production plants with Petri nets

In industrial plants various material flows take place, connecting processing and storing units to accomplish specific product routings. For example, chemical and batch plants are characterized by fluid exchange between tanks, reactors, filters, distillation columns, etc. Such fluid transportation operations may involve the use of many elementary transporting resources (e.g., pipes and valves), which can be extremely complicated to manage, especially in the case of concurrent material transfer and possibly conflicting commands. A systematic modeling and control approach for such operations is proposed based on Petri nets, which employs aggregate transportation resources denoted lines, for which suitable definitions of dependency and compatibility are provided. The actual management of valves is demanded to a specific control module, which computes valve commands with simple logical rules on the basis of the marking of resource places in the supervisor Petri net. The hierarchical and modular control architecture separates the resource allocation and deadlock avoidance problems from the physical device management, thus limiting system complexity. The general ideas discussed in this brief have been exemplified with a simple batch process example drawn from the literature