Process Control: Designing Process and Control Systems for Dynamic Performance Chapter 2. Control Objectives and Benefits Copyright © Thomas Marlin 2013 The copyright holder provides a royalty-free license for use of this material at non-profit educational institutions

CHAPTER 2 : CONTROL OBJECTIVES AND BENEFITS When I complete this chapter, I want to be able to do the following. Recognize examples of the seven (7) control objectives in chemical processes Calculate indicators of variability in a process variable Be able to calculate the economic impact of variability

CHAPTER 2 : CONTROL OBJECTIVES AND BENEFITS Outline of the lesson. Seven (7) Control Objectives 1. Safety 2. Environmental protection 3. Equipment protection 4. Smooth operation 5. Product quality 6. Profit 7. Monitoring and diagnosis Variability measures Economic impact of variability Workshop

EXAMPLE PROCESS: FLASH SEPARATION Feed Methane Ethane (LK) Propane Butane Pentane Vapor product Liquid Process fluid Steam F1 F2 F3 T1 T2 T3 T5 T4 T6 P1 L1 A1 L. Key Let’s discuss this process P  1000 kPa T  298 K

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES High pressure in drum is dangerous 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES To flare Never release hydrocarbons to atmosphere 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES No flow could damage the pump 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Always keep the production rate smooth 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Achieve L.Key by adjusting the heating 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Use the least costly heating 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Give example 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

SEVEN CONTROL OBJECTIVES Calculate & plot key parameters, e.g., UA. 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis UA time

SEVEN CONTROL OBJECTIVES All seven must be achieved. Failure to do so will lead to operation that is unprofitable or worse, unsafe. 1. Safety 2. Environmental Protection 3. Equipment protection 4. Smooth operation production rate 5. Product quality 6. High profit 7. Monitoring & diagnosis

BENEFITS FROM PROCESS CONTROL Without feedback control When we control a process, we reduce the variability of key variables to achieve the seven objectives. Without feedback control Composition (% H. Key) 50 100 150 200 250 300 350 400 450 500 2 3 4 5 6 time (min) outlet concentration 49 49.5 50.5 51 valve position (% open) Reflux valve

BENEFITS FROM PROCESS CONTROL When we control a process, we reduce the variability of key variables to achieve the seven objectives. With feedback control Composition (% H. Key), note smaller scale 50 100 150 200 250 300 350 400 450 500 2.5 3 3.5 time (min) outlet concentration 20 40 60 80 valve position (% open) Reflux valve Variability is moved from controlled to manipulated variable!

BENEFITS FROM PROCESS CONTROL When we control a process, we reduce the variability of key variables to achieve the seven objectives. What statistics can we calculate from this data? How do we relate variability to process performance?

BENEFITS FROM PROCESS CONTROL Process performance = efficiency, yield, production rate, etc. It measures performance for a control objective. Calculate the process performance using the distribution, not the average value of the key variable!

A B Example of Benefits of reduced variability for chemical reactor Goal: Maximize conversion of feed ethane but do not exceed 864C Which operation, A or B, is better and explain why. B

A B Example of Benefits of reduced variability for chemical reactor Goal: Maximize efficiency and prevent fuel-rich flue gas Which operation, A or B, is better and explain why.

CHAPTER 2: GOALS AND BENEFITS WORKSHOP 1 Determine one example for each of the seven control objective categories. Flue gas The feed flows through a pipe and is heated by the combustion of fuel feed product air fuel

CHAPTER 2: GOALS AND BENEFITS WORKSHOP 2 Squeeze down the variability Two process examples show the benefit of reduced variability, the fired heater reactor and the boiler. Discuss the difference between the two examples. Can you think of another example that shows the principle of each? Squeeze down the variability

CHAPTER 2: GOALS AND BENEFITS WORKSHOP 3 In both the flash drum and the fired heater examples, temperature measurement is very important. Describe several methods for measuring temperature and recommend the most appropriate for the flash drum example. How hot is it?

CHAPTER 2: GOALS AND BENEFITS WORKSHOP 4 Here is your chance to investigate a problem! Research the design of a vapor-liquid separator vessel. Determine the equipment included, how to determine the diameter and height, how to select the materials of construction, and how to change the operating variables to achieve the desired product purity as feed composition changes Figure source: Mbeychok, public domain, http://en.wikipedia.org/wiki/File:Vap-Liq_Separator.png

CHAPTER 2 : CONTROL OBJECTIVES & BENEFITS When I complete this chapter, I want to be able to do the following. Recognize examples of the seven (7) control objectives in chemical processes Calculate indicators of variability in a process variable Be able to calculate the economic impact of variability Lot’s of improvement, but we need some more study! Read the textbook Review the notes, especially learning goals and workshop Try out the self-study suggestions Naturally, we’ll have an assignment!

CHAPTER 2: LEARNING RESOURCES SITE PC-EDUCATION WEB - Instrumentation Notes - Interactive Learning Module (Chapter 2) - Tutorials (Chapter 1/2) www.pc-education.mcmaster.ca/

SUGGESTIONS FOR SELF-STUDY CHAPTER 2: SUGGESTIONS FOR SELF-STUDY 1. Discuss the importance of consistent quality in your decisions to purchase food, clothing, etc. 2. A P&I drawing of a distillation process is given in Woods*. Determine at least one example of each of the seven control objectives for this process. Evaluate the control designs given; do they achieve your objectives? 3. Find process examples in your previous textbooks and determine the advantage for reduced variability in each. Can you provide quantitative values for the economic benefit? * Woods, D. Process Design and Engineering Practice, Prentice-Hall, 1995 (page 2-65).