What are some effective ways to implement a control system in a chemical process?

1 Process Modeling

The first step to implement a control system is to develop a mathematical model of the process, which describes how the process variables change in response to the inputs and disturbances. A process model can be derived from first principles, empirical data, or a combination of both. A process model can help you to identify the process characteristics, such as gain, time constant, dead time, nonlinearity, and coupling. A process model can also help you to simulate the process behavior under different scenarios and test the performance of different control strategies.

2 Control Objectives

The second step to implement a control system is to define the control objectives, which specify what you want to achieve with the control system. Control objectives can be related to safety, efficiency, product quality, or environmental compliance. For example, you may want to maintain the temperature of a reactor within a certain range, minimize the energy consumption of a distillation column, or ensure the purity of a product stream. Control objectives can be expressed as setpoints, constraints, or optimization criteria for the process variables.

3 Control Strategies

The third step to implement a control system is to select the appropriate control strategies, which determine how the control system will manipulate the inputs to achieve the control objectives. Control strategies can be classified into different types, such as feedback, feedforward, cascade, ratio, adaptive, or model predictive. The choice of control strategy depends on the process characteristics, the control objectives, the available measurements and actuators, and the complexity and cost of the control system. For example, feedback control is suitable for processes with moderate dynamics and disturbances, while feedforward control is suitable for processes with large and measurable disturbances.

4 Control Hardware

The fourth step to implement a control system is to choose the suitable control hardware, which includes the sensors, actuators, controllers, and communication devices that make up the control system. Control hardware should be selected based on the process requirements, the control strategies, the reliability and accuracy of the devices, and the compatibility and integration of the devices. For example, sensors should have adequate range, resolution, and response time for the process variables, actuators should have adequate capacity, authority, and speed for the process inputs, controllers should have adequate computing power and memory for the control algorithms, and communication devices should have adequate bandwidth and security for the data transmission.

5 Control Tuning

The fifth step to implement a control system is to tune the control parameters, which affect the performance and stability of the control system. Control tuning involves adjusting the values of the parameters, such as proportional, integral, and derivative gains for a PID controller, or weights and horizons for a model predictive controller. Control tuning can be done manually, by trial and error, or automatically, by using optimization or adaptive methods. Control tuning should aim to achieve the desired trade-off between the control objectives, such as setpoint tracking, disturbance rejection, robustness, and sensitivity.

6 Control Monitoring

The sixth and final step to implement a control system is to monitor the control system, which involves observing and evaluating the behavior and performance of the control system. Control monitoring can help you to detect and diagnose any problems or faults in the control system, such as sensor failures, actuator malfunctions, controller errors, or process changes. Control monitoring can also help you to improve and optimize the control system, by identifying and implementing any corrective or preventive actions, such as recalibrating the sensors, replacing the actuators, updating the controllers, or modifying the control strategies.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?