WEEK 1-Introduction to Chemical Process Control

Chemical Process Control

Definition

  • Chemical Process Control: Methods used in industries to control process variables while refining raw materials to create end products.

Types of Control

Manual Control

  • Performed by humans before automation.

  • Control operations where human intervention is required.

Automatic Control

  • No human intervention needed.

  • Control operations are automated, focusing on maintaining desired variables throughout the chemical process.

Importance of Process Control

  • Safety: Reduces risks and ensures safety in operations.

  • Product Quality: Maintains consistent quality of output.

  • Production Rates: Optimizes efficiency during manufacturing.

  • Reduce Energy: Minimizes energy consumption and costs.

Dynamics of Process Control

Characteristics of Processes

  • Processes are dynamic; they always change.

  • Control Systems: Maintain certain variables at desired levels.

Control System Functions

  • Control systems are essential for applications involving:

    • Temperature

    • Pressure

    • Flow

    • Level

    • Composition

    • Others

Control Variables

Types of Variables

  • Controlled Variables: Must be maintained at desired values (set points).

  • Manipulated Variables: Adjusted to maintain the controlled variables.

  • Disturbances: Factors that affect the controlled variable.

  • Uncontrolled Variables: Variables that remain unaffected by control mechanisms.

Everyday Examples of Process Control

Example 1: Room Temperature

  • Control Objective (Setpoint): Maintain temperature at 27°C.

  • Controlled Variable: Current temperature.

  • Manipulated Variable: Fan speed.

  • Disturbance: Changes in the weather outside.

Example 2: Driving a Car

  • Control Objective (Setpoint): Maintain car in lane.

  • Controlled Variable: Location of the car on the road.

  • Manipulated Variable: Orientation of front wheels.

  • Disturbance: Curves in the road.

Exercise

  • Select a simple control objective, identify the controlled variable, manipulated variable, and disturbances in the process.

Heat Exchanger

Description

  • Illustrates the flow of steam and fluid for effective heat exchange.

  • Ti: Inlet temperature; T desired: Desired temperature.

Variables in Heat Exchanger

  • Controlled Variables: Temperatures entering and exiting the heat exchanger.

  • Manipulated Variables: Input/set points for steam.

  • Load Disturbances: Changes in fluid conditions.

  • Uncontrolled Variables: Environmental and operational factors affecting performance.

Basic Components of Control System

  • Measurement (M): Sensors measure controlled variables.

  • Decision (D): Controllers evaluate data to maintain variables.

  • Action (A): Actuated by control valves, executing the controller's decisions.

Control System Terms

  • Set Point (SP): Desired value for controlled variable.

  • Open Loop System: No feedback or control action.

  • Closed Loop System: Feedback compares set point and controlled variable for corrective action.

Maintaining Control

  • Considerations for keeping T at set points involve assessing inputs, outputs, and dynamics affecting performance.