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CHEMICAL PROCESS CONTROL FUNDAMENTALS. CONTROL CATEGORIES OPERATING MODE –CONTINUOUS –BATCH –SEMI-BATCH OPERATING CONDITIONS –START-UP –STEADY-STATE OPERATION.

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Presentation on theme: "CHEMICAL PROCESS CONTROL FUNDAMENTALS. CONTROL CATEGORIES OPERATING MODE –CONTINUOUS –BATCH –SEMI-BATCH OPERATING CONDITIONS –START-UP –STEADY-STATE OPERATION."— Presentation transcript:

1 CHEMICAL PROCESS CONTROL FUNDAMENTALS

2 CONTROL CATEGORIES OPERATING MODE –CONTINUOUS –BATCH –SEMI-BATCH OPERATING CONDITIONS –START-UP –STEADY-STATE OPERATION –CONTROLLED SHUTDOWN –EMERGENCY SHUTDOWN MONITORING –MAINTENANCE –OPTIMIZATION SEE PERRY’S 7 TH ED., CHAPTER 8 ergs.com/images/FM%20 operator%20desk.jpg

3 CONTROL DESIGN OPERATOR CONTROL AUTOMATIC CONTROL ALARMS INTERLOCKS DATA LOGGING AUTOMATIC TUNING SEQUENCING PROGRAMMABLE LOGIC CONTROLLERS FIELD MONITORS 6_255.htm

4 STEADY STATE OPERATION SYSTEM SHOULD RUN RELIABLY WITH MINIMAL SUPERVISION SYSTEM SHOULD MAKE ON-SPECIFICATION PRODUCT ROUTINELY MONITORED BY OPERATOR WITH A MINIMUM NUMBER OF VARIABLES CONTROL LOOP INTERACTIONS AUTOMATIC rchive.com/images11/ jpg

5 START UP SYSTEM SHOULD BE ABLE TO SAFELY REACH PRODUCTION AND QUALITY LEVELS THROUGH A STANDARD SEQUENCE OF EVENTS CONTROL SYSTEM SHOULD INCLUDE ASSESSMENT (CHECKS TO CONFIRM STEPS IN THE START UP SEQUENCE HAVE BEEN CORRECTLY COMPLETED) EFFFECTS OF CHANGES SHOULD BE ANTICIPATED es/milling/milling_startup_offline.gif

6 START UP PROCEDURES REACTORS CONTINUOUS MAY BE STARTED WITH A HEEL OF MATERIAL FROM THE PREVIOUS SHUTDOWN OR SOME PRODUCT RECYCLED TO THE REACTOR TO APPROXIMATE STEADY STATE CONDITIONS BATCH FOLLOW NORMAL START UP SEQUENCE

7 START UP PROCEDURES SEPARATION PROCESSES –TYPICALLY ARE STARTED ON TOTAL RECYCLE UNTIL SPECIFICATION QUALITY MATERIAL IS PRODUCED. –THIS MAY REQUIRE DELAYING START UP OF REACTION SYSTEM OR ADDING A SURGE TANK TO COLLECT PRODUCT DURING SEPARATION START UP.

8 CONTROLLED SHUT DOWN CAN BE PARTIAL OR COMPLETE PARTIAL –PUT SYSTEM IN STANDBY MODE TO ALLOW RAPID AND SAFE RESTART –DISTILLATION COLUMNS ON TOTAL RECYCLE COMPLETE –SHUT DOWN PROCESS WITHOUT CREATING OFF-SPEC PRODUCT OR PRODUCING A HAZARDOUS SITUATION STANDARD PROTOCOLS FOR BOTH

9 TYPICAL SHUTDOWN DESIGNS REACTORS –SHORT TERM STOP FEEDS MAINTAIN COOLING, BUT KEEP MATERIALS FROM CRYSTALLIZING MAINTAIN AGITATION. –LONG TERM POSSIBLY DRAIN REACTANTS TO A SEPARATE VESSEL IF REACTION CANNOT BE STOPPED AT THE STEADY STATE CONDITIONS OTHERWISE, SAME AS SHORT TERM SUPERPRO

10 TYPICAL SHUTDOWN DESIGNS SEPARATION PROCESSES –SHORT TERM - PLACE SYSTEM ON TOTAL RECYCLE AND MAINTAIN OPERATION. –LONG TERM - DRAIN SYSTEM TO SAVE UTILITIES. ROTATING EQUIPMENT –DEPEND ON NEEDS OF PROCESS WHILE SHUTTING DOWN –COOLING AND AGITATION ARE TYPICALLY MAINTAINED. SIMSCI PROSIM II

11 EMERGENCY SHUT DOWN ONE BUTTON SHUT DOWN BY OPERATOR –PROCESS SHOULD BE PROTECTED AGAINST CATASTROPHIC FAILURE DURING AN UNMONITORED SHUT DOWN –PROCESS SHOULD BE FAIL-SAFE ALARMS AND INTERLOCKS SHOULD PROTECT LOCAL PROCESSES –FIRST LEVEL ALARMS ALERT THE OPERATOR TO TAKE ACTION –SECOND LEVEL ALARMS AUTOMATICALLY INTITIATE PROTECTIVE ACTION afe-explanation.gif

12 MONITORS INSTRUMENTATION THAT IS NOT REQUIRED FOR NORMAL OPERATION –USED FOR FIELD OBSERVATION –USED FOR START-UPS –USED FOR MAINTENANCE –USED FOR OPTIMIZATION PTPT PT PT HEAT EXCHANGER

13 SAFETY & ALARM SYSTEMS OPERATOR ALARMS AND INTERLOCK ALARMS –(LO, LOLO, HI, HIHI) –SHOULD BE ON LOOPS THAT ARE INDEPENDENT FROM CONTROL LOOPS RELIEF SYSTEMS NEED TO BE DIRECTED TO FACILITIES TO SAFELY PROCESS THE RELEASE SAFETY SYSTEMS SHOULD BE INTERLOCKED TO SHORT OR LONG TERM SHUTDOWN LOOPS, AS APPROPRIATE.

14 CONTROL DESIGN REQUIRES PFD’S P&ID’S ARE THE PRIMARY DOCUMENT –SHOW LOOPS –SHOW INTERLOCKS –SHOW PLCs STANDARD DIAGRAMS CAN BE USED FOR SOME SYSTEMS SPECIAL CONTROL DIAGRAMS - LADDER LOGIC, AND INTERLOCKS ARE ALSO DEVELOPED

15 CONTROL LOOPS SENSORS - TO MEASURE CONTROL VARIABLE AND ADJUSTED VARIABLE THERMODYNAMIC PROPERTIES PRESSURE TEMPERATURE FLOW –VOLUMETRIC –MASS TRANSPORT PROPERTIES DENSITY VISCOSITY SYSTEM INVENTORY - LEVEL ANALYTICAL SENSORS MEASURE SPECIFIC CHEMICAL PROPERTIES CONTROL STATION

16 CONTROL CONFIGURATION FEED BACK CONTROL

17 CONTROL CONFIGURATION FEED FORWARD CONTROL

18 CONFIGURATION COMPARISON FROM PERRY’S CHAPTER 8 STEAM TO HEAT EXCHANGER FEEDBACK BASED ON PROCESS EXIT FLOW TEMPERATURE FEEDFORWARD BASED ON PROCESS FEED FLOW

19 LOOP RESPONSE DYNAMIC RESPONSE IS MEASURED BY HOW QUICKLY A SYSTEM RETURNS TO CONTROL AFTER A PERTURBATION. –CONVERGENT –DIVERGENT –CYCLING –AT STEADY STATE, THE IDEAL CONTROL PATTERN IS LINEAR

20 ANALOG AND DIGITAL SIGNALS CONTINUOUS SENSORS AND CONTROLLED DEVICES TYPICALLY ARE ANALOG CONTROLLERS ARE TYPICALLY DIGITAL DISTRIBUTED CONTROL –USES LOCAL I/O PANELS –DATA HIGHWAY IS USED TO CONVEY ACTUAL AND SET POINT CONDITIONS TO AND FROM THE CONTROL ROOM PANEL

21 DATA HIGHWAY DESIGN SYSTEM CAN ALSO BE CONNECTED TO PROGRAMMABLE LOGIC CONTROLLERS FOR BATCH OPERATION AND INTERLOCK FUNCTIONS SYSTEM CAN HAVE PARALLEL DATA HIGHWAYS

22 INSTRUMENTATION SYMBOLS ISA SYMBOLISM IS TYPICALLY USED FOR LABELING DEVICES FOR LABELING LOOPS POSITIONS POSITION 1 - VARIABLE CONTROLLED –P, V, T, F, L, ρ, μ, ETC. POSITION 2 - FUNCTION –INDICATION, GAUGE, CONTROLLER, ALARM, CAN BE SAME AS POSITION 1 FOR RATIO DEVICE. POSITION 3 - FUNCTION –CONTROL, RANGE (HIGH OR LOW FOR ALARMS), RATIO FOR RC POSITION 4 - FUNCTION AGAIN –FFRC, e.g.

23 CHARACTERISTICS OF CONTROL MODES STEADY STATE CAN BE DIRECT OR INDIRECT

24 CASCADE EFFECTS FOR THIS EXAMPLE THE FEEDS TO THE REACTOR ARE SET BY ONE MASTER FLOW WITH THE SECOND FLOW FED BY RATIO.

25 CASCADE EXAMPLE USING A FLOW CONTROL TO THE FLASH TANK –WOULD REQUIRE THAT IT CHANGE ACCORDING TO THE MASTER FEED –THE EXTENDED LAG TIME WOULD MAKE THIS CONTROL INEFFECTIVE. USING A FLASH FEED BASED ON LEVEL CONTROL –PROVIDES A MORE IMMEDIATE RESPONSE TO CHANGES IN THE REACTOR FEED –THE GAIN WOULD NEED TO BE ADJUSTED TO ALLOW FOR THE CAPACITANCE OF THE SYSTEM.

26 GENERAL INSTRUMENTATION DESIGN COMMENTS CONTROL LOOP SENSORS - LOCATE AT THE POINT OF CONTROL ON ALL DIAGRAMS CONTROL VALVES - LOCATE ON PUMP DISCHARGE LINES PUMP TANKS AND SUMPS - SHOULD BE PROVIDED WITH LEVEL CONTROL, HI/HIHI/LO/LOLO ALARMS AND RELIEF SYSTEMS. ng.com/pumpTankStations/ind ex.php

27 GENERAL INSTRUMENTATION DESIGN COMMENTS STORAGE, SURGE AND OTHER PROCESS TANKS - SHOULD BE PROVIDED WITH LEVEL CONTROL, HI/HIHI/LO/LOLO ALARMS AND RELIEF SYSTEMS. HEAT EXCHANGER CONTROL - SHOULD TYPICALLY CONSIST OF A CONTROL VALVE ON THE HEATING/COOLING MEDIA WITH A SENSOR ON THE TEMPERED FLOW DISCHARGE. SOLIDS FLOW CONTROL - GENERALLY OBTAINED BY VARIABLE SPEED DRIVES FOR CONVEYING EQUIPMENT, CONNECTED TO A WEIGHING DEVICE; BELT SCALE OR WEIGH TANK.

28 GENERAL INSTRUMENTATION DESIGN COMMENTS CONTROL ROOM DISPLAY - ALL PROCESS VARIABLES AND ALL ALARMED POINTS SHOULD BE ON THE CONTROL ROOM PANELS. ONLY LOCAL GAUGES AND NON-PROCESS ITEMS SHOULD BE EXCLUDED. 03.ibm.com/ibm/hist ory/exhibits/tucson/i mages/5403PH15.j pg


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