In my March 14 posting on process simulation I addressed some of the some basic technique that may be used to integrate process simulation into a control system. The P&ID often serves as the starting point in the development of a process simulation for control system checkout or operator training. In most cases, one process simulation module should be developed for multiple modules that support control or monitoring functions associated with a piece of equipment. Thus, as outlined in Chapter 15 of Control Loop Foundation – Batch and Continuous Processes, a first step in developing a process simulation is to break the equipment and piping shown on the P&ID into multiple processes that may be simulated in one or more simulation modules.
Each simulated process represents a small portion of the plant equipment and interconnecting piping shown on a P&ID. The calculated output of one process simulation may be an input to another process simulation. An example of how the equipment and piping shown on the P&ID may be broken into smaller sets of equipment that represent processes is illustrated in the Recycle Tank example shown below.
In this example, the areas of the P&ID circled in black will be simulated processes that are interconnected and can be documented in a Simulation Diagram as illustrated below.
Once the P&ID has been analyzed in this manner, the simulation diagram is implemented as a simulation module that references the existing control modules. The processes on the simulation diagram are implemented as composite blocks in the simulation module. Process inputs from final control elements are added as external references to the setpoints of the analog output blocks in the existing control modules. Unmeasured inputs to a process should be added as parameters. Outputs of the process simulation that represent field transmitter measurements are implemented as external references that write to the simulate parameter of the analog input
blocks of the existing modules.
The simulation module for the recycle tank example is shown below.
Examples of how process simulation implementation may be explored on the ControlLoopFoundation web site.