1. INTRODUCTION CONCEPT ERT 210/4 Process Control & Dynamics
Introduction to Process Control
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MISS. RAHIMAH BINTI OTHMAN (

3. Chapter 1 Course Outcome 1 (CO1)
Ability to derive and develop theoretical model of chemical processes, analyze Laplace transform techniques to simplify first order and second order processes and create transfer functions and state space models.
Introduction Concepts
Introduction to Process Control:
Basic concepts of process dynamics and process control.
Theoretical Models of Chemical Processes:
2. Laplace Transform
3. Transfer Function Models
4. Dynamic Behavior of First-order and Second-order
Processes
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4. Process Dynamics Chapter 1
Refers to unsteady-state or transient behavior.
Steady-state vs. unsteady-state behavior;
Steady state: variables do not change with time
c) Continuous processes : Examples of transient behavior:
Start up & shutdown
Grade changes
Major disturbance;
e.g: refinery during stormy or hurricane conditions
iv. Equipment or instrument failure (e.g., pump failure)
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5. Process Dynamics
* Example: Typical Continuous Processes
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6. Process Dynamics Chapter 1 d) Batch processes
Inherently unsteady-state operation
Example: Batch reactor
Composition changes with time
Other variables such as temperature could be
constant.
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* Example: Typical processes whose operation in noncontinuous.

7. Process Control Chapter 1 1. Objective:
Enables the process to be maintained at the desired operation conditions, safely and efficiently, while satisfying environmental and product quality requirements.
2. Control Terminology:
Controlled variables (CVs)
- these are the variables which quantify the performance or quality of the final product, which are also called output variables (Set point).
Manipulated variables (MVs)
- these input variables are adjusted dynamically to keep the controlled variables at their set-points.
Disturbance variables (DVs)
- these are also called "load" variables and represent input variables that can cause the controlled variables to deviate from their respective set points (Cannot be manipulated).
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8. Process Control Chapter 1 Large scale, continuous processes:
Oil refinery, ethylene plant, pulp mill
Typically, 1000 – 5000 process variables are measured.
Most of these variables are also controlled.
Examples: flow rate, T, P, liquid level, composition
Sampling rates:
Process variables: A few seconds to minutes
Quality variables: once per 8 hr shift, daily, or weekly
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9. Process Control Chapter 1 Manipulated variables
We implement “process control” by manipulating process variables, usually flow rates.
Examples: feed rate, cooling rate, product flow rate, etc.
Typically, several thousand manipulated variables in a large continuous plant
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11. Bioprocess Control Chapter 1
In the production of biopharmaceutical products (human therapeutics) and fermented foods, such as bread products and yogurt.
Fermentation process needs to be maintained for acceptable operation.
With modern technology, batch bioprocess go through a systematic events such as sterilization, filling a vessel, maintaining T, pH, DO concentration, emptying vessel & washing vessel.
FDA regulations: cGMP, a basic principles, procedures and resources to ensure a manufacturing environment which is suitable for producing bio-pharmaceuticals of acceptable quality.
This required good process sensors.
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12. Justification of Process Control
Specific Objectives of Control
Increase product throughput
Increase yield of higher valued products
Decrease energy consumption
Decrease pollution
Decrease off-spec product
Increase Safety
Extended life of equipment
Improve Operability
Decrease production labor
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13. Objectives of Control Chapter 1
1. Maintain the process at the desired operating point.
A process is expected to operate at the steady-state condition as prescribed by its design.
But, the process may be unstable, implying that process variables may not remain within their physical bounds
A process operating at steady-state experiences frequent upsets due to various changes in its operating environment.
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14. Objectives of Control Chapter 1
2. Move the process from one operating point to another
In many process operations, the plant personnel may want to change the operating point that a process is at for a variety of reasons.
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15. CLASSIFICATION OF CONTROL STRATEGIES Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Ratio Control
Split Range Control
Cascade Control
Differential Control
DESIRED OUTPUT

16. Closed-loop Artificial Pancreas (Feedback Control)
glucose setpoint
controller
sensor
pump
patient u y r
measured glucose
Bob Parker has integrated this example throughout his course (different levels of modeling, etc.

17. FEEDBACK CONTROL Chapter 1
Distinguishing feature: measure the controlled variable
It is important to make a distinction between negative feedback and positive feedback.
Negative Feedback – desirable situation where the corrective action taken by controller forces the controlled variable toward the set point
Positive feedback – controller makes things worse by forcing the controlled variables farther away from the set point.
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18. FEEDBACK CONTROL Chapter 1 Advantages:
Corrective action is taken regardless of the source of the disturbance.
Reduces sensitivity of the controlled variable to disturbances and changes in the process (shown later).
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19. FEEDBACK CONTROL Chapter 1 Disadvantages:
No corrective action occurs until after the disturbance has upset the process, that is, until after x differs from xsp.
Very oscillatory responses, or even instability…
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20. FEEDFORWARD CONTROL Chapter 1
Distinguishing feature: measure a disturbance variable
Advantage:
Correct for disturbance before it upsets the process.
Disadvantage:
Must be able to measure the disturbance.
No corrective action for unmeasured disturbances.
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21. Chapter 1 1.1 Illustrative Example: Blending system Notation:
w1, w2 and w are mass flow rates
x1, x2 and x are mass fractions of component A

22. Chapter 1 Assumptions: w1 is constant x2 = constant = 1
(stream 2 is pure A)
Perfect mixing in the tank
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Control Objective:
Keep x at a desired value (or “set point”) xsp, despite variations in x1(t). Flow rate w2 can be adjusted for this purpose.

23. Chapter 1 Terminology: Controlled variable (or “output variable”): x
Manipulated variable (or “input variable”): w2
Disturbance variable (or “load variable”): x1
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24. Chapter 1 Some Possible Control Strategies: Control Question.
Suppose that the inlet concentration x1 changes with time. How can we ensure that x remains at or near the set point, xsp ?
Some Possible Control Strategies:
Method 1. Measure x and adjust w2.
If x is too high, w2 should be reduced
If x is too low, w2 should be increased
Can be implemented by a person (manual control)
More convenient and economical using automatic control
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25. Design Question. What value of is required to have
Overall balance:
Component A balance:
(The overbars denote nominal steady-state design values.)
At the design conditions, Substitute Eq. 1-2, and , then solve Eq. 1-2 for :

26. Development of Dynamic Models Illustrative Example: A Blending Process
Figure 2.1. Stirred-tank blending process.
An unsteady-state mass balance for the blending system:

27. Some Possible Control Strategies:
Equation 1-3 is the design equation for the blending system.
If our assumptions are correct, then this value of will keep at But what if conditions change?
Control Question. Suppose that the inlet concentration x1 changes with time. How can we ensure that x remains at or near the set point ?
As a specific example, if and , then x > xSP.
Some Possible Control Strategies:
Method 1. Measure x and adjust w2.
Intuitively, if x is too high, we should reduce w2;

28. Manual control vs. automatic control
Method 1 can be implemented as a simple control algorithm (or control law):
Proportional feedback control law,
where Kc is called the controller gain.
w2(t) and x(t) denote variables that change with time t.
The change in the flow rate, is proportional to the deviation from the set point, xSP – x(t).

29. Chapter 1

30. Chapter 1 Method 2. Measure x1 and adjust w2.
Measure disturbance variable x1 and adjust w2 accordingly
Thus, if x1 is greater than , we would decrease w2 so that
If x1 is smaller than , we would increase w2.
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31. Chapter 1

32. Because Eq. (1-3) applies only at steady state, it is not clear how effective the control law in (1-5) will be for transient conditions.
Method 3. Measure x1 and x, adjust w2.
This approach is a combination of Methods 1 and 2.
Method 4. Use a larger tank.
If a larger tank is used, fluctuations in x1 will tend to be damped out due to the larger capacitance of the tank contents.
However, a larger tank means an increased capital cost.

33. Table. 1.1 Control Strategies for the Blending System
Classification of Control Strategies
Table. 1.1 Control Strategies for the Blending System
Method
Measured Variable
Manipulated Variable
Category 1 x w2
FBa 2 x1 FF 3
x1 and x
FF/FB 4 -
Design change
Feedback Control:
Distinguishing feature: measure the controlled variable

34. It is important to make a distinction between negative feedback and positive feedback.
Engineering Usage vs. Social Sciences
Advantages:
Corrective action is taken regardless of the source of the disturbance.
Reduces sensitivity of the controlled variable to disturbances and changes in the process (shown later).
Disadvantages:
No corrective action occurs until after the disturbance has upset the process, that is, until after x differs from xsp.
Very oscillatory responses, or even instability…

35. Feedforward Control:
Distinguishing feature: measure a disturbance variable
Advantage:
Correct for disturbance before it upsets the process.
Disadvantage:
Must be able to measure the disturbance.
No corrective action for unmeasured disturbances.

36. Figure 1.7 Hierarchy of process control activities.

37. Figure 1.9 Major steps in control system development

38. Summary
Control allows us to regulate the behavior of process systems.
Good control performance has the potential to yield substantial benefits for safe and profitable plant operation.
Expanded role of process control represents an integration of the traditional role with plant information management.
Objectives of control include stability, performance and optimization.
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39. By applying the fundamental process control principles, the engineer can design plants and implement control strategies that can achieve the control objectives set forth by plant operations.
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40. Prepared by, MISS RAHIMAH OTHMAN
Thank you
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Prepared by,
MISS RAHIMAH OTHMAN

41. QUIZ1 Feedback and feedforward control both require measured variable.
Which of the following statements are true?
Feedback and feedforward control both require measured variable.
The process variable to be controlled is measured in feedback control.
Feedforward control can be perfect in the theoretical sense that the controller can take action via the manipulated even while the controlled variable remains equal to its desired value.
Feedforward control can provide perfect control; that is, the output can be kept at its desired value, even with an imperfect process model.
Feedback control will always take action regardless of the accuracy of any process model that was used to design it and the source of a disturbance.
False/True
False/True
False/True
False/True
False/True

42. QUIZ1 Feedback and feedforward control both require measured variable.
Which of the following statements are true?
Feedback and feedforward control both require measured variable.
The process variable to be controlled is measured in feedback control.
Feedforward control can be perfect in the theoretical sense that the controller can take action via the manipulated even while the controlled variable remains equal to its desired value.
Feedforward control can provide perfect control; that is, the output can be kept at its desired value, even with an imperfect process model.
Feedback control will always take action regardless of the accuracy of any process model that was used to design it and the source of a disturbance.
False/True
False/True
False/True
False/True
False/True