Chapter 1 Introduction to Process Instrumentation and Control

Chapter 1 Introduction to Process Instrumentation and Control

• 1.
  Introduction
• 2.
  Topics ▪ Basic ofprocess instrumentation and control (PI&C). ▪ Symbols identifications in piping and instrumentation diagram (P&ID) drawing. 2
• 3.
  Topic outcomes ▪ Explainthe basic instrumentation and process control. ▪ Construct a complete P&ID including alarm system for a particular process or equipment. 3
• 4.
  Process Control 4 Why How What Where
• 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 Howto 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 tankhas 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 levelwill 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? ▪ Steadyoperation (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 objectiveof 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 controldone? 13
• 14.
  Where is controldone? 14
• 15.
  DCS Main Competitors 15
• 16.
  How is controldesign documented? • Piping and Instrumentation Diagram (P & ID) • Use standard symbol 16
• 17.
  Control system elements 17 Receives informationfrom 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 Blockdiagram – shows the flow of information in the control system
• 19.
  Control terminology ▪ Controlled/Processvariables - 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 InstrumentationDiagram (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 InstrumentationDiagram (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 TableA.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 FigureA.1. Fraser (2001).Process measurement and control
• 26.
  Example liquid flowand level control loops 26
• 27.
  Example liquid flowand level control loops 27
• 28.
  Example liquid flowand 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 orfunctions • 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 orfunctions 30
• 31.
  Jigsaw Activities 31
• 32.
  Exercise 1 You’re givena 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 acontrol 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
• 36.
  Exercise 2 Flash separation 36
• 37.
  37 Thanks!