ACS219 Process Control Group assignment Payam Soulatiantork October 2023 1 Introduction The assignment is linked to chemical engineering applications related to control scheme design, instru- mentation, control strategies and looking at the control of selected systems. Students work in groups of four students to produce a number of separate posters, one for each case study. The main purpose of each poster is to demonstrate the importance of a given control strategy or design in the context of chemical engineering. The poster should include context and numerical illustrations and, for high marks, should also include evidence of analysis and independent systematic design. A typical case study could either: (i) focus on the efficacy of different strategies for controlling a given system, or (ii) the efficacy of a given strategy for tackling particular scenarios, perhaps using several systems to illustrate. Most likely numerical evidence will be produced using Matlab or TSC although other software tools may be used. This is 45hr work per student and thus to achieve good marks, the submissions must not be superficial. Typical marking guidance is provided at the end for information. As this is a group work assignment, each group will also need to submit, as a group, an agreed peer assessment of the contribution of each group member with some explanation and evidence where the marks are not awarded equally. In order to ensure no group member is disadvantaged or excluded, groups will have a private discussion board on Blackboard they can use to communicate dates, locations and summaries of core meetings as well as to share interim documentation. The groups are self-enrolled so you can choose the students you want to work with on your project. Some possible scenarios are listed over the page, but students should feel free to explore other areas they find interesting which fall within the remit. Some good resources including some Matlab files are also available on the BB page -> Group assignment for ACS219 -> Coursework useful material. • Students are reminded that the substantive work submitted should be their own. Where resources have been used from elsewhere, these must be clearly and explicitly referenced. • Students are reminded of University policy on unfair means and moreover should ensure that any resource they use is fully cited. http://www.shef.ac.uk/ssid/exams/plagiarism. • Groups can meet with staff during the tutorials and lectures to discuss any queries. Please see staff immediately if special circumstances are affecting your performance http://www.shef.ac.uk/ ssid/forms/special. Group feedback will appear on Blackboard after marking is complete for the whole class. 2 Submission details Posters are submitted in soft copy onto Blackboard through the group assignment link. The deadline is the Friday of week 12 of semester 1, 15 December 2023 at 5pm. 3 Feedback Group feedback will appear on Blackboard after marking is complete for the whole class. Also, in a single hour lecture on Friday of week 11, the students will get a chance to bring their posters along and get some interim feedback. 1 4 A table of potential themes Case study scenario Low order systems for use in the case studies Systems in series and higher order dynamics Multi-input-multi- output systems Impact of constraints and actuation choices Impact of measurement and delays Advanced control strate- Develop an awareness of some alternative control strategies and why these gies are deployed in industry such as: cascade, feedforward, selective control, split-range control, ratio control, model predictive control, smith predictors and time delays, anti-windup strategies, inferential control, fault-tolerant control, optimal control, robust control, sequence control, on-off control. Discrete control Fault tolerant con- trol/safety Impact of design on con- trol performance Impact of uncertainty PID tuning Possible content 1st order in series, distillation column, multi-tank system, thermocouple delay, power generation, stirred tank with cascade. Valve sizing Higher order systems are less easy to control with PI. Students can explore through several case studies the consequences of more involved dynamics such as multi-1st-order in series, non-min phase. (Multi CSTR, multi-tank, distillation column, etc.) Discuss the challenges of controlling systems with interacting dynamics. Illustrate with case studies such as distillation columns and oil fired power generation. Use case study examples to demonstrate how constraints limit performance and impact on safety. Brief discussion of how these might be handled in practice (say with PID and predictive control). Use case studies to analysis the impact of actuator choices on controllability, constraint handling and performance. Consider the consequences on control performance (and safety) of poor measurement such as accuracy, repeatability, lag/delay, reliability. Use a few case studies illustrating different sensor choices to show how these impact on control loop performance. Include inferential control. What is the impact of discretising a control law that is implementing via a computer and thus involving sampling? Use some case studies to demonstrate the impact of actuator/sensor failure and discuss possible mitigation. Show through case studies how poor design effects control, e.g. Vaporizer, reboiler, knockout drums, ball mills, cooling towers, simple distillation tower, etc. How would you undertake control design when the system/model parame- ters are continually changing, or unknown? What is the impact on control of significant sensor noise or large input/output disturbances? Compare and contrast different tuning methods for PID, e.g.: Zeigler- Nichols, Cohen-Coon, Modified Ziegler-Nichols method, Tyreus-Luyben method, Damped oscillation method, C-H-R method, Fertik method, Ciancone-Marline method, Minimum error criteria (IAE, ISE, ITAE), etc. Identify, select and position different instruments appropriately within a control loop. 2 5 Marking criteria and Grade Descriptors for ACS219 group assignment 7-10 • Extensive knowledge of the subject area and the engineering context. A perceptive and focused use of the relevant material. Widespread evidence of independent sourcing and original thought. 5-6 6-7 • A sound knowledge of the subject area and engineering context. A comprehensive use of the relevant material with some evidence of independent sourcing and original thought. 4-5 • Shows an insight and depth of understanding, including an awareness of the complexities and subtleties. 3-4 ● Very high standard of critical analysis and evaluation. • Clearly structured presentation, showing logical development of arguments and properly referenced data and examples. • Shows an understanding of arguments, contribution and context, including some awareness of the complexities and subtleties. ● High standard of critical analysis of the source material. Evidence of some evaluation and synthesis. • Clearly structured presentation, showing logical development of arguments and properly referenced data and examples. • Some knowledge of the subject area and engineering context. Makes some use of the relevant material with little or no evidence of independent sourcing, or original thought. • Shows some understanding of arguments, contribution and context. • Attempts analysis of the source material but may include some errors/omissions. Little evidence of evaluation and synthesis. • Presentation reasonably clear with arguments not fully developed and data and examples not fully referenced. • Some knowledge and appreciation of the engineering context. Superficial use of the material provided. No evidence of independent sourcing, or original thought. • Some areas of understanding of the arguments, contribution and context. • Confused analysis including errors and omissions. No evidence of evaluation and synthesis. • Descriptive presentation based on confused arguments. Includes poorly referenced data and examples provided during lectures. • Limited and patchy knowledge and appreciation of the engineering context. Poor use of the material provided. No evidence of independent sourcing, or original thought. • Limited understanding of the arguments. No understanding of the contribution and context. • Confused analysis including a number errors and omissions. No evidence of evaluation and synthesis. • Descriptive presentation based on confused arguments. Poor use of data and examples provided during the lecture. No references 0-3 ● Inadequate knowledge and no appreciation of the engineering context. Poor use of the material provided. No evidence of independent sourcing, or original thought. 3 ● Inadequate understanding of the arguments, contribution and context. • Inadequate grasp of the analysis including many errors and omissions. No evidence of evaluation and synthesis. • Presentation that contains no data, examples or even class notes. 4

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ACS219 Process Control Group assignment Payam Soulatiantork October 2023 1 Introduction The assignment is linked to chemical engineering applications related to control scheme design, instru- mentation, control strategies and looking at the control of selected systems. Students work in groups of four students to produ

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A single-tank process has been operating with an inlet flow rate equal to29.4 m3 min-1. The operator increases the flow rate suddenly by 10%,resulting in a level change in the tank as recorded in Table Q3. Assuming that the liquid-level dynamics follow a first-order model, determine: (a) The Pl controller settings using the Ziegler-Nichols tuning relations. (b) The process gain and time constant using Sundaresan and Krishnaswamy's method. Compare these values against the values from the graphical method.

Two liquid storage tanks are shown in Figure Q2. For System I, the valve acts with a resistance R = 580 s m-2, so that the relation between the flow (F)and liquid level in the tank (h) is given by F = hlR. For System II, a pump is used instead of the valve, meaning that variations in liquid level do not affect the exit flow rate. The diameter of each tank is the same, D = 1.1 m. For each system determine the following information and show all your workings: (a) Process gain (Kp) and time constant (7). (b) New steady-state liquid levels in both System I and System II, if the inlet flow rate suddenly changes from 3.0x10-3 m³ s-1 to4.5x10-3 m3 s-1. The initial steady-state level in both systems is 1.8 m. (c) If each tank is 2.4 m tall, which tank overflows first? Calculate when this will happen.

A proportional controller operated pneumatically is used to control temperature within the range of 65°F to 100°F.The measured temperature goes for 71°F to 78°F with the set point held constant when he controller is adjusted so that the output pressure goes from 3 psi (valve fully open) to 15psi (valve fully closed). Find the Proportional band.

In the process presented in Figure Q1, tomato pulp is heated as it passes through a steam heat exchanger and then enters an evaporator where the water boils off. The purpose of this process is to produce tomato paste, which has a lower water content than the pulp. As a chemical engineer, you are tasked to control the liquid level and temperature in the evaporator.Considering this information, answer the following: (a) Define the process variables and the manipulated variables, as well as possible disturbances. (b)Propose feedback control loops by sketching a schematic diagram. (c) Propose any additional features in order to assure the safe operation of the process. Illustrate these features using a schematic diagram.

Question 1 An engineer uses a temperature sensor mounted in a thermowell to measure the temperature in a CSTR. The temperature sensor behaves as a first-order process with a time constant of 3 seconds, and the thermowell behaves as a first order process with a time constant of 9 seconds. Using Matlab: (a) Plot the open-loop response of the system to a step-change in the CSTR temperature. Comment on whether the response in under or over damped (b) Plot the closed-loop response of the system for proportional only control with a controller gain of unity. (c) The engineer notes that the measured temperature has been varying sinusoidally between 180 and 186°C with a period of 20 seconds for at least 10 minutes. Determine the likely temperature fluctuation in the CSTR contents to the nearest degree.

Consider a weight held in place by a spring. Initially suspended at rest, the height ofThe spring constant is kThis represents how "stiff" the spring is and is constant. The frictional losses areisthe weight is x=0The mass of the weight ismcharacterized by the constant b . The force applied to the weight after t=0 f(t) . This leads to the ODE m \frac{d^{2} x}{d t^{2}}+b \frac{d x}{d t}+k x=f(t) 2. (65 points) Imagine the spring is vertical. The weight is held by a platform atx=0 initially. If m=0.1kg , b=0.1 kg/ s , and k=1.0 kg/s . The platformis removed at t=0 O What are the initial conditions for this system? b. (15 points) What is the new steady-state position? That is, where willt - o ? Show this using the final-value theorem.the mass settle as c. (15 points) What is the maximum distance the mass will move from itsinitial position? (Hint: what is the force applied to the weight?)(15 peints) Whatvalue vwill recuultming d. (15 points) What spring constant value will result in the system comingto (and remaining within) 1% of its new steady-state position withoutovershooting that value as quickly as possible? e. (15 points) Imagine the spring system is now horizontal.represents how far the spring is from its resting position. If 1 N of forceis instantaneously transferred to the weight (in thedirection)described above att=0 ,what is the response? That is, what isx(t) when the weight is flicked with 1 N of force? Assume the weightis only free to move in one direction.

The process described by the transfer function GP(S) Kp (T₁S+1) e-TDS (T₂S + 1)(T3S + 1) Gp(s) = is controlled by a P controller with an arbitrary gain of Kc. a) If Kc = 2; Kp = 5; T₁ = 2; Td = 1; T₂ = 2; T3 = 3 determine whether the closed-loop response will be stable using frequency response techniques. What is the limiting value of the controller gain to ensure stability? b) For the following scenarios, generate the Bode plots for the open- loop behavior using Excel. Comment on the effect of the parameter changes on plots 2, 3 and 4 using plot 1 as the reference. 1. 2. 3. 4. Kc = 2; Kp = 5; t₁ = 0; TD = 0; T₂ = 2; T3 = 3 Kc = 2; Kp = 5; t₁ = 0; TD = 5; T2 = 2; T3 = 3 Kc = 4; Kp = 5; T₁ = 0; TD = 0; T₂ = 2; T3 = 3 Kc = 2; Kp = 5; T₁ = 0; TD = 10; T₂ = 2; T3 = 3 c) Using the same general transfer function, plot the Nyquist plots using Excel for the following parameters. Comment on the behavior. 1. Kc = 2; Kp = 5; T₁ = 1; TD = 0; T₂ = 2; T3 = 3 2. Kc = 2; Kp = 5; T₁ = 3; TD = 0; T2 = 2; T3 = 3

Question 5 Determine the controller gain (Kc) for a proportional-only feedback controller for the system comprising the following elements that ensures a gain margin of at least 2 and a phase margin of at least 30°. Plot the controlled and uncontrolled closed-loop response of the system to a unit-step change in set- point. Gc= Kc; Gp = 50 30s +1' G₂ = 0.016 3s +1' Gm = 1 10s + 1

Q.4 An electronic PID temperature controller is at steady state with an output of 12 mA. The set point equals the nominal process temperature initially. At t=0, the set point is increased at the rate of 0.5 mA/min. If the current settings are K₂= 2, t=1.5 min, Tp=0.5 min. (a) Generate the controller response in Simulink. (b) Repeat part (a) for a PI controller

Question #4 A system of three cylindrical tanks holding liquid is arranged as shown in Figure 1. Fint Fina Tank #1 R₁ F₁ h₁ h3 h₂ h₁ F₁ = R₁ Tank #2 R₂ F₂ Tank #3 Figure 1- Schematic showing layout of tanks. For all three tanks you can assume that the outlet flow rate is equal to the height in the tank divided by the valve resistance, i.e.: h3 hz F₂= F3: R₂ R3 a. Clearly derive the transfer function that relates the height in tank #1 (hi) to the inlet flow to the tank (Fin). [4 marks] b. Tank #1 is 0.5 m in diameter and the value of R₁ is 200 s m². At steady state the liquid height is 1 m. What is the flow rate of liquid entering the tank (i.c. what is Fin,1)? [1 mark] c. Calculate the gain and time constants for tank #1. [2 marks] d. Derive the transfer function that relates the height in tank # 3 (ha) to the flow entering the system (i.e. to Flis and F2.in). [5 marks] c. Tank #2 has the same diameter as Tank #1, but R₂ = 0.5R₁. Tank #3 has double the diameter of Tank #1 (i.e. it is 1 m in diameter), and R3= R₁. Fin1 = Fin2 = 0.01 m³ s¹. If the system is at steady state what is the liquid level in each of the tanks? [3 marks]