Process & Instrumentation Diagram (P&ID) Purpose. Howitisdone? Methodology?

Transcription

1 Process & Instrumentation Diagram (P&ID) Purpose 1. To indicate the instruments or control devices attached to the process. 2. To indicate the control system architecture associated with the process. Howitisdone? Standard symbols and notations representing instruments or control devices are placed to the pipings and vessels. Standard symbols and notations are available from ISA-5.1(1984) standard. Methodology? Process piping and sub-piping A thick straight line represent main process piping A thin straight line represent process sub-piping either to instruments or by-pass process line. PG Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 1

2 Naming rule P T L F A Measurement Device Device / Condition Condition Pressure Temperature Level Flow Analysis C T R I A S G Controller Transmitter Recorder Indicator Alarm Switch / Safety Gauge C T R H L V Controller Transmitter Recorder High Low Valve H L High Low Complete guide on P&ID symbols & notations are available from ISA 5.1 (R1984) Examples PC PIC LG FR TAL TALL TAHL Pressure Controller Pressure Indicating Controller Level Gauge Flow Recorder Temperature Alarm Low Temperature Alarm Low Low Temperature Alarm High Low PCC PTC PTR PIR TRR TRA TAV No such devices yet. Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 2

3 Symbols Instruments / control devices: A circle representing locally mounted instrument A circle with horizontal line representing control room panel mounted instrument. A circle with horizontal line inside a square representing its function in DCS. Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 3

4 Follow the standard published by the Instrument Society of America (ISA) Instrument Line (Signal) Symbols Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 4

5 Final control elements Control valves = Manual valve = OR Not darkened Always open Manual valve = Darkened Always closed OR NC Solenoid valve = NO NC NO Normally open NC Normally closed Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 5

6 Device names Devices (hardware) Notations Symbols Current to pneumatic transducer I/P I/P Pressure relief valve / Pressure safety valve PSV PRV Thyristor TY TY Inverter VY VY Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 6

7 Examples PG = Pressure Gauge PIC = Pressure Indicating Controller FT = Flow Transmitter TT = Temperature Transmitter TE = Temperature Element (RTD/TC) Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 7

8 Can you read the following P&ID? ❶ Main process line ❷ Process instrument piping ❸ Temperature transmitter product ❹ Temperature controller ❺ Flow controller Feed TT ❸ TC ❿ ❻ Current to pnuematic transducer ❼ Control valve ❽ Electrical signal ❾ Pneumatic signal ❼ ❶ Fuel ❾ ❷ ❻ I/P ❽ ❺ FC FT TC SP ❹ ❿ Temperature controller DCS function 12 ASD Automatic shut down PLC unit 12 Solenoid valve Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 8

9 SP, Set point Controller Final Control Element Process PV, Controlled Variable PV, Controlled Variable Sensor What is feedback control? Outcome of an action is fed back to the controller for corrective action. Merit? Simple design. Easy to tune (for linear, fast & short dead time processes: flow, level& pressure). Demerits? Slow recovery for slow process upon load disturbance or change in set point (such as temperature control). A process with long dead time may exhibit oscillatory process response and with longer settling time. Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 9

10 SP, Set point Controller 1 Controller 2 Final Control Element Process 2 Process 1 PV, Controlled Variable PV, Controlled Variable Sensor 2 PV, Controlled Variable Sensor 1 What is cascade control? The inner loop controller obtains its set point from the outer loop controller. The purpose is to eliminate the effect of disturbances. Merit? Faster recovery time as compared to SISO feedback control. Demerits? Controllability will be worst than SISO if both controllers were not properly tuned. Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 10

11 D, Disturbance Feedforward Controller Disturbance Sensor SP, Set point Feedback Controller Final Control Element Process PV, Controlled Variable PV, Controlled Variable Sensor What is feed forward control? A method of control based on process model: mass and energy balances. Purpose To compensate disturbances (D) before they affect the controlled variable(pv). Demerit a) Fail to work if any of the sensor broke down. b) Poor process controllability due to inaccurate process model. Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 11

12 TC I/P TT Heated product out Steam in Product in Steam out Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 12

13 TC FC I/P Heated product out TT FT Steam in Product in Steam out Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 13

14 TC Σ X FC I/P TT FT Heated product out L/L Steam in Product in TT FT Steam out Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 14

15 X FC I/P FT Heated product out Steam in Product in FT Steam out Abdul Aziz Ishak, Universiti Teknologi MARA Malaysia (2011) 15

16 Using correct P&ID symbols, draw the following instruments to the reboiler as shown in figure below. (i) Steam pressure gauge (ii) Reboiler vapor pressure gauge Reboiler vapor (iii) Steam temperature gauge (iv) Vessel over pressure relief valve (v) Steam over pressure relief valve Steam (vi) Liquid level gauge at overflow compartment (vii) Liquid level gauge at liquid boiling compartment (viii)temperature gauge at liquid boiling compartment. Bottom product Tower bottoms Condensate

17 Install appropriate control systems for the following tasks: (i) Liquid level control at over flow compartment (ii) Reboiler vapor pressure control Reboiler vapor (iii) Liquid temperature control (iv) Reboiler vapor pressure alarm high (v) Liquid temperature alarm high Steam (vi) Low and high level liquid alarm at liquid over flow compartment (vii) Low liquid level alarm at boiling liquid compartment Condensate (viii) Steam flow cut upon low liquid level. Bottom product Tower bottoms