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SPM Instrumentation Series
SPM-1600 Instrumentation II - Basic Control Concepts

Click to view schematic display A Click to view schematic display B Click to view schematic display C Click to view schematic display D

Process Description

The SPM-1600 Instrumentation II - Basic Control Concepts Process Simulation consists of four identical but independent process loops. Each one of these process loops is configured to demonstrate one of the four basic control concepts seen in most typical chemical processing plants. Each of the four process loops consists of a countercurrent tube and shell type heat exchanger. Cold water on the shell side is to be heated up with hot water on the tube side. The process variable to be controlled is the cold fluid outlet temperature.

The first process loop is the Manual (Open-Loop) Control. This loop demonstrates how difficult it can be to control the process variable in question in the absence of an automatic control strategy.

The second process loop is the Automatic Feedback (Closed-Loop) Control. This type of control strategy requires a deviation in the process variable in question before the instrumentation can take corrective action.

The third process loop is the Feedforward Control. With this type of control strategy the instrumentation can take corrective action before a deviation in the process variable in question occurs. This is accomplished by taking a number of process measurements (in this case the cold fluid flow rate and the cold fluid inlet temperature) and performing a calculation (in this case a simple heat balance). However, since it is usually not practical to take every required measurement and since it is usually not feasible to take every possible variable into consideration, the corrective action of this type of control strategy, depending on the type of process upset, may not always be able to maintain the process variable in question on target.

The fourth process loop is the Feedforward Control with Feedback. This type of control strategy, as the name indicates, takes the best of both worlds. The feedforward part of the control strategy takes corrective action before a deviation in the process variable in question occurs, while the feedback part of the control strategy ensures that the process variable in question will always be maintained on target.


Instrumentation

Each of the four process loops consists of a cold fluid flow controller (FIC-X01), hot fluid flow controller (FIC-X02), cold fluid inlet and outlet temperature indicators (TI-X01 and TI-X02), and hot fluid inlet and outlet temperature indicators (TI-X03 and TI-X04). The variable in question (the variable to be controlled) is the cold fluid outlet temperature. In the case of the Automatic Feedback (Closed-Loop) Control Process and the Feedforward Control with Feedback Process the cold fluid outlet temperature is outfitted with a temperature controller.