Module 8 – Process Control & Automation

Objective:
By the end of this module, a trainee will be able to:

1. Understand the purpose of process control in a butadiene or petrochemical plant.

2. Recognize types of control systems: manual, semi-automatic, and fully automatic.

3. Understand basic concepts of PID control, interlocks, and alarms.

4. Operate control panels safely and effectively.

5. Interpret control loop trends and respond to abnormal situations.

8.1 – Introduction to Process Control

Definition:

• Process control = maintaining process variables (temperature, pressure, flow, level) within desired ranges to ensure safe, efficient, and quality production.

Importance:

• Prevents process upsets, safety hazards, and equipment damage.

• Ensures product consistency and quality.

Analogy:

• Process control = “cruise control in a car”: automatically adjusts speed to stay on target, but operator monitors road conditions.

8.2 – Types of Control Systems

1. Manual Control:

   • Operator adjusts valves, pumps, or heaters directly.

   • Suitable for simple or small-scale operations.

2. Automatic Control:

   • Control system adjusts process automatically using sensors and actuators.

   • Types:

     • On-Off Control (simple, e.g., level switches)

     • PID Control (Proportional, Integral, Derivative)

     • Advanced process control (APC, multivariable, model-based – conceptual)

3. Semi-Automatic / Supervisory Control:

   • Operator supervises automatic control, intervenes during abnormal conditions.

Analogy:

• Manual = “driving car without cruise control”

• Automatic = “car with cruise control and lane assist”

• Semi-automatic = “cruise control with manual override when needed”

8.3 – Basic PID Control Concept

Purpose:

• Maintain process variable close to desired setpoint.

Components:

1. Proportional (P): reacts to current deviation from setpoint.

2. Integral (I): reacts to cumulative error over time.

3. Derivative (D): predicts future trend based on rate of change.

Operator Concept:

• Most operators observe trends and alarms, not tune PID themselves (unless trained).

• Recognize over/under-shoot or oscillations as signs of control issues.

Analogy:

• P = immediate reaction, I = correction for accumulated drift, D = anticipates change.

• Example: driving car: P = brake when too close, I = adjust if consistently too close, D = anticipate curve ahead.

8.4 – Control Loops & Operator Role

Types of Control Loops:

1. Temperature Control Loop: heater, reactor, exchanger

2. Pressure Control Loop: reactor, distillation column, storage tank

3. Flow Control Loop: feed, product, utilities

4. Level Control Loop: tanks, columns, separators

Operator Responsibilities:

• Monitor loop trends and alarms.

• Verify control action responds appropriately.

• Notify control room or maintenance if loops behave abnormally.

Analogy:

• Control loops = “nervous system”: sensors = senses, controller = brain, actuator = muscles

8.5 – Interlocks & Alarms

Interlocks:

• Automatic safety devices that prevent unsafe operation.

• Types:

  • Hard interlocks: shutdown process automatically if unsafe condition detected.

  • Soft interlocks: alarm operator to take corrective action.

Alarms:

• Indicate abnormal conditions.

• Levels: warning, critical, shutdown.

• Operators must respond promptly according to SOP.

Operator Tips:

• Never bypass interlocks or alarms.

• Verify plausibility of alarm; cross-check with field observation.

• Record alarm responses in logbook.

Analogy:

• Interlocks = “seatbelt interlock preventing car from moving without buckled seatbelt”

• Alarms = “car dashboard warning lights”

8.6 – Operator Panel Basics

Control Room Panels:

• Display process variables, alarms, control loops, and unit status.

• Include:

  • Trend displays

  • Push buttons for start/stop

  • Emergency shutdown buttons

  • Alarm indicators

Field Panels:

• Local switches and indicators for pumps, valves, compressors.

Operator Tips:

• Understand panel layout and color coding.

• Monitor trends, not just instantaneous readings.

• Report abnormal or unresponsive instruments.

Analogy:

• Control panel = “cockpit of the plant”

• Field panel = “local controls for specific equipment”

8.7 – Trend Analysis & Corrective Actions (Conceptual)

Operator Practices:

• Observe trends for temperature, pressure, flow, and level.

• Identify deviations early: drift, oscillation, spike, or drop.

• Take safe corrective action or notify supervisor.

• Record in logbook for shift handover.

Analogy:

• Trend analysis = “monitoring your health vitals daily”: notice small deviations before serious illness

8.8 – Quiz / Knowledge Check

1. What is the purpose of process control in a chemical plant?

2. Name three types of control systems.

3. Explain the role of proportional, integral, and derivative in PID control.

4. What is an interlock, and why is it important?

5. What should an operator do when an alarm activates?

6. Why is trend observation important for operators?

8.9 – Media Sites Integration

• Videos:

  • PID control animation

  • Control loop monitoring demo

  • Operator panel walkthrough (conceptual)

  • Alarm and interlock demonstration

• Diagrams / Infographics:

  • PID loop diagram

  • Trend analysis examples

  • Alarm hierarchy & interlock diagram

  • Operator panel layout

• PDF Downloads:

  • Control loop monitoring checklist

  • Alarm response guide

  • Trend observation log template

• Interactive:

  • Embedded quizzes

  • Scenario exercises: interpret trends and recommend actions

8.10 – Summary & Key Takeaways

1. Process control ensures safe, efficient, and consistent production.

2. Operators monitor control loops, trends, alarms, and interlocks.

3. PID control maintains process variables close to setpoint automatically.

4. Interlocks prevent unsafe operation; alarms alert operators to abnormal conditions.

5. Operator panels and trend observation are essential tools for proactive intervention.