Chapter 1 Introduction to Process Instrumentation and Control
- 1. Introduction
- 2. Topics ▪ Basic of process instrumentation and control (PI&C). ▪ Symbols identifications in piping and instrumentation diagram (P&ID) drawing. 2
- 3. Topic outcomes ▪ Explain the basic instrumentation and process control. ▪ Construct a complete P&ID including alarm system for a particular process or equipment. 3
- 5. What is control? ▪ “measurement & adjustment” ▪ Everyday example bounds ▫ Room temperature (air conditioning) ▫ measure room temperature ▫ adjust thermostat ▫ cruise control in car ▫ measure speed of car ▫ adjust gas flow rate to engine 5
- 6. Example: Buffer tank 6 h Qin Qout H How to keep the level at desired value, H? What happen if the level is too high/low? Overflow – may create safety and environmental hazard Too low – may effect the next process equipment
- 7. Example: The buffer tank has a relationship between flow and level given by 𝑄𝑜𝑢𝑡 = 𝐾 ℎ . where h is in feet and K is 1.156 (gal/min) ft1/2. Suppose the input flow rate is 2 gal/min. At what value of h will the level when the system stabilize at steady state condition? 7
- 8. ▪ The level will stabilize when Qin = Qout. Thus, solve for h, 8
- 9. Human Aided Control 9 • The equipment has the local gauge/ side tube • Controlled variable-liquid level • Manipulated variable-Qout • What will cause the level high/ low? Qin h Qout H
- 10. Automatic control 10 • Machine, electronic, or computer replace human operation h Qout Controller Actuator Sensor s u Qin
- 11. Why control? ▪ Steady operation (main reason) ▫ consistent product despite disturbances ▪ Optimal operation ▫ minimise cost of production, use of resources, increase throughput ▪ Safety ▫ protect people, environment, plants 11
- 12. “ The primary objective of process control is to maintain the process at the desired operating conditions, safely, efficiently, while satisfying environmental, and product quality requirements. 12
- 13. Where is control done? 13
- 14. Where is control done? 14
- 16. How is control design documented? • Piping and Instrumentation Diagram (P & ID) • Use standard symbol 16
- 17. Control system elements 17 Receives information from measuring devices and decides what action to be taken Thermocouples, flow meters, gas chromatography Implement the decision taken by the controller Sensor Controller Final control element
- 18. Control system elements 18 Block diagram – shows the flow of information in the control system
- 19. Control terminology ▪ Controlled/Process variables - these are the variables which quantify the performance or quality of the final product, which are also called output variables. ▪ Manipulated variables - these input variables are adjusted dynamically to keep the controlled variables at their set-points. ▪ Disturbance variables - these are also called "load" variables and represent input variables that can cause the controlled variables to deviate from their respective set points. 19
- 20. Piping and Instrumentation Diagram (P&ID) • Process control employs a standard set of symbols and definitions to represent a plant and its associated control systems. • This standard was developed and approved by a collaboration between the American National Standards Institute (ANSI) and the Instrumentation, Systems and Automation (ISA) Society. • The P&ID depicts the entire plant and associated control system. • This includes plant operating units, product flow lines, measurement and control signal lines, sensors, controllers and final control elements. 20
- 21. Piping and Instrumentation Diagram (P&ID) • A complete control loop includes instrumentation for measurement and control of a process variable. • The complete loop includes: ▫ Equipment i.e. reactor, column etc ▫ Valves ▫ Instrumentation i.e flow, temperature, pressure sensor ▫ Controllers ▫ Piping i.e. process pipe, utilities (steam, water, fuel, air etc) pipe 21
- 22. The identification format • Each loop on P&ID used ISA symbols to show the particular devices that perform certain functions. • The first letter of tag number is correspond to the measured process variables. • The succeeding letters in the tag number describe the function of the elements in the loop such as T for transmit, I for indicate, R for record, and or C for control. 22
- 23. Instrumentation identification letters Table A.1. Fraser (2001).Process measurement and control 23
- 24. Typical tag number • TIC-103 Temperature Indicate Control (loop number) 103 • Where ▫ TXX-103 identifies the loop by first letter and number and IC in place of XX identifies the functions by succeeding letter. ▫ Hyphens are optional 24
- 25. Instrument line symbols 25 Figure A.1. Fraser (2001).Process measurement and control
- 26. Example liquid flow and level control loops 26
- 27. Example liquid flow and level control loops 27
- 28. Example liquid flow and level control loops • Flow loop F-212 includes both flow element and flow transmitter. • Level loop needs only the level transmitter. • The P&ID shows all the instrument functions so that the detailed drawings will reflect the complete loop and so that any engineering cost estimates will be complete. • The dotted line coming from the flow and level measuring sensors to their controllers represent the electrical feedback signal. 28
- 29. General instruments or functions • The ballons, rectangles, hexagons, and diamonds are used to denote the instrumentation. • A line through a symbol means it is accessible to an operator, such as being in a panel in the control room. • No lines means that the instrument is located in the field and is not accessible to the operator in the control room. • A dashed line means that the device is inaccessible by virtue of being located within other equipment, such as behind the panel of a control room. 29
- 30. General instruments or functions 30
- 32. Exercise 1 You’re given a process that includes a chemical reactor, a flash separator, heat exchangers, and associated piping. Propose one control configuration for this process to control the following variables: a) Feed reactor temperature (T4) b) Reactor liquid level ▪ Draw the P& ID. 32
- 33. Exercise 1 33
- 34. Exercise 1 34
- 35. Exercise 2 Suggest a control configuration to satisfy the following constraint. Draw the P&ID and justify your answer. ▪ Case a: High pressure is dangerous. ▪ Case b: No flow could damage the pump ▪ Case c: High temperature may cause thermal loading in the column ▪ Case d: Quality of product at the bottom column is the most critical 35
- 37. 37 Thanks!