Dynamics mode results for the G2 example simulation

The detailed engineering simulation provides the Dynamics mode results. The objective of the dynamic simulation is to study the behavior of the process control system for upset conditions in the feed stream. This scenario increases the feed stream flowrate from 13,500 kg/h to 15,000 kg/h by adjusting the setpoint of the feed flowrate controller (FC1) to 15,000 kg/h. The control loop responds by modulating XV1 to increase the flowrate. The following figure shows the resulting flowrate (FC1.PV) in comparison to the setpoint (FC1.SP).

Figure 5: Step response of the change in flow controller setpoint

The flowrate significantly oscillates around the setpoint rather than converging. For this scenario, the default controller values do not give the desired response.

As a result of the poor feed control, the reboiler duty and bottom product composition also oscillate rather than converging to a single value, as shown in the following figure. We observe a similar trend for the overhead condenser and product.

Figure 6: Response of the final products

Here we have an opportunity to modify the control scheme to yield a better response. There are a variety of ways to accomplish this, but the logical starting point is FC1. The default control range for FC1 is from 0 to 36,000 kg/h. With these default values, an increase of 1,500 kg/h represents less than 5% of the control range. To improve control performance for such a small change, you can adjust the gain (Kp) of the controller. Given the number of existing resources related to PID tuning, we do not include the controller tuning in this example.

Note: The detailed engineering simulation also includes Trends for additional process specifications and parameters. You can use these Trends to further investigate the process control responses, if desired.