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CHE 185 – PROCESS CONTROL AND DYNAMICS

CHE 185 – PROCESS CONTROL AND DYNAMICS. ELEMENTS FOR OPERATION, OPTIMIZATION AND SAFETY. TEMPERATURE SENSING DEVICES. A GOOD GENERAL REFERENCE IS AT http://www.temperatures.com/sensors.html

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CHE 185 – PROCESS CONTROL AND DYNAMICS

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  1. CHE 185 – PROCESS CONTROL AND DYNAMICS ELEMENTS FOR OPERATION, OPTIMIZATION AND SAFETY

  2. TEMPERATURE SENSING DEVICES • A GOOD GENERAL REFERENCE IS AT http://www.temperatures.com/sensors.html • SENSORS ARE NORMALLY INSTALLED IN THERMOWELLS OR OTHER UNITS SO THEY CAN BE REMOVED FOR MAINTENANCE, CALIBRATION, OR REPLACEMENT

  3. TC’s -THERMOCOUPLES • BASED ON THE RESISTANCE AT A JUNCTION OF TWO DISSIMILAR METALS • SIGNAL IS NOT NECESSARILY LINEAR WITH TEMPERATURE • APPLICATION RANGE VARIES ACCORDING TO TEMPERATURE RANGE http://www.electrical-res.com/constantan-thermocouple-table/

  4. TC WIRING CONFIGURATIONS • THE OPTION DEPENDS ON THE SERVICE www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps

  5. TC’s -THERMOCOUPLES • USE A BRIDGE FOR MEASUREMENT (DELTA) SO NEEDS A REFERENCE JUNCTION • RESPONSE TIME DEPENDS ON THE METAL GAUGE AND HOW THE MATERIALS ARE IN THERMAL CONTACT WITH THE SYSTEM • The Seebeck effect causes an electrical potential when two dissimilar wires are joined and the junctionis heated. www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  6. TC’s -THERMOCOUPLES

  7. TC’s -THERMOCOUPLES

  8. TC COLOR CODES • STANDARDIZED IN MANY COUNTRIES www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  9. TC VOLTAGE/TEMP CURVES • TYPICAL VALUES • LETTERS REFER TO TC TYPES www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  10. REFERENCE VOLTAGE • CAN BE BASED ON RESISTANCE IN ICE WATER www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  11. COMPLETE TC CIRCUIT • INCLUDES LEADS TO TC – TYPICALLY COPPER www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  12. INTERMEDIATE JUNCTIONS AND TC VALUES • AS LONG AS THE NON-MEASURING JUNCTIONS ARE AT THE SAME TEMPERATURE, ONLY THE PRIMARY JUNCTION DETERMINES THE MEASUREMENT. LAW OF INTERMEDIATE METALS. www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  13. resistance temperature detector - rtd • contains a resistor with a resistance that INCREASES with temperature www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  14. RTD’s - RESISTANCE THERMOMETERS

  15. RTD’s - RESISTANCE THERMOMETERS • BASED ON THE INCREASE IN RESISTANCE IN A SINGLE TYPE OF METAL (LONGER TIME LAG THAN TC’s) • ABOUT 10 TIMES MORE SENSITIVE THAN TC’s • TYPICALLY NICKLE, PLATINUM, OR COPPER

  16. RTD’s - CONSTRUCTION • precision wires wrapped around an insulator and encapsulated in a protective sheath (TYPICALLY glass) in the form of a bulb. www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  17. THERMISTERS • OPERATE ON THE BASIS OF CHANGING RESISTANCE IN SEMICONDUCTORS • CAN BE QUITE SMALL, SO HAVE VERY RAPID RESPONSE TIMES • VERY NON-LINEAR RESPONSES • RESPONSES ARE CONSISTENT OVER A CONSISTENT DESIGN, SO INTERCHANGEABLE http://www.amwei.com/

  18. THERMISTER APPLICATIONS • IT IS POSSIBLE TO USE A THERMISTER AS A SWTICH www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps

  19. PYROMETERS • DEVICES THAT OPERATE ON THE BASIS OF RADIATION FREQUENCY RELATED TO THE TEMPERATURE OF THE BODY. • ALLOWS FOR NON-CONTACT OPERATION • CAN BE USED AT A DISTANCE • ACCURACY IS NOT HIGH • FOR A CONCISE REFERENCE http://www.lumasenseinc.com/EN/products/infrared-thermometers-and-switches/

  20. OTHER THERMOELECTICAL PHENOMENA • Peltiereffect is where heating and cooling occurs at the junctions of two dissimilar conductive materials when a current flows through the junctions. www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  21. OTHER THERMOELECTICAL PHENOMENA • Thomson effect causes heating or cooling when there is current flow through a temperature gradient in a wire. www.go2atp.com/RG_Demo/INS5RG/PPT/INSRG06.pps‎

  22. TEMPERATURE MEASURING DEVICES (GAUGES) • THESE PROVIDE AN INDICATION OF THE LOCAL TEMPERATURE BUT ARE NOT SENT TO CONTROLLERS • LIQUID IN GLASS THERMOMETERS • ARE THE CLASSICAL BULB THERMOMETER BASED ON THERMAL EXPANSIVITY OF FLUIDS • USE DIFFERENT FLUIDS FOR INDICATORS

  23. TEMPERATURE MEASURING DEVICES (GAUGES) • BIMETALLIC THERMOMETERS • STRIPS OF TWO DIFFERENT METALS THAT CONTRACT AND EXPAND AT DIFFERENT RATES • THESE ARE THE CIRCULAR TEMPERATURE GAUGES IN MOST FIELD INSTALLATIONS • USED FOR THERMOSTATS

  24. PRESSURE SENSORS (GAUGES) • STRAIN GAUGES - FOR A GENERAL TUTORIAL http://zone.ni.com/devzone/cda/tut/p/id/3642 • STRETCHING A WIRE RESULTS IN CHANGES IN RESISTANCE THAT CAN BE RELATED TO FORCE • THIS RESISTANCE CAN BE CONVERTED INTO A PRESSURE SIGNAL • PIEZORESISTIVE TRANSDUCERS ARE A STRAIN GAUGE BASED ON SEMICONDUCTOR MATERIALS

  25. OTHER PRESSURE MEASUREMENT TECHNIQUES • ELASTIC TUBE ELEMENTS • ELASTICALLY DEFORM IN RESPONSE TO CHANGES IN SYSTEM PRESSURE • BOURDON TUBES ARE HELICAL UNITS THAT DEFLECT TO ALLOW A FACE DIAL TO ROTATE • http://www.instrumentationtoday.com/bourdon-tube/2011/09/

  26. OTHER PRESSURE MEASUREMENT TECHNIQUES • BELLOWS ELEMENTS • USE A DEVICE THAT HAS ACCORDION FOLDED METAL THAT EXPANDS AXIALLY WITH PRESSURE • http://www.georgin.com/us_technologies.php • CAN BE USED FOR EITHER ABSOLUTE OR RELATIVE PRESSURE MEASUREMENTS

  27. OTHER PRESSURE MEASUREMENT TECHNIQUES • DIAPHRAGM ELEMENTS • LIKE A BELLOWS, EXCEPT THEY HAVE A SMALLER RANGE OF OPERATION • THEY HAVE A HIGH SENSITIVITY AT LOW PRESSURE DIFFERENCE • http://www.georgin.com/us_technologies.php

  28. LEVEL SENSING • DIFFERENTIAL PRESSURE • USES PRESSURE MEASUREMENT BASED ON THE LEVEL ABOVE A SENSOR RELATIVE TO EITHER THE HEAD PRESSURE OR EXTERNAL PRESSURE • CAN USE ANY OF THE ELECTRONIC PRESSURE DEVICES MENTIONED ABOVE • FLOAT VALVES • MEASURE THE DISPLACEMENT OF A FLOAT TO DETERMINE THE LEVEL IN A VESSEL • CAN BE EITHER HORIZONTAL OR VERTICAL MOUNTED • CAN BE EITHER ON/OFF OR CONTINUOUS OUTPUT DEVICES.

  29. LEVEL SENSING • SKETCHES FROM http://www.ksr-usa.com/sensors.htm

  30. LEVEL SENSING • CAPACITANCE PROBES • PROBE IS INSERTED VERTICALLY OR HORIZONTALLY IN A TANK AND A CAPACITOR IS SET UP BETWEEN THE PROBE AND THE TANK WALL • LEVEL IS BASED ON PRESENCE OF FLUID BETWEEN PLATES OF A CAPACITOR • CAN BE USED TO MEASURE SOLIDS AS WELL AS FLUIDS

  31. LEVEL SENSING • CAPACITANCE PROBES SKETCH FROM http://www.omega.com/literature/transactions/volume4/images/13_Fig_04_ l.GIF

  32. LEVEL SENSING • ELECTROMAGNETIC SENSORS • USE RADIO WAVES, ULTRASONIC WAVES, OR RADIATION TO MEASURE LEVEL BASED ON REFLECTANCE FROM THE SURFACE ON ATTENUATIONS OF A SIGNAL • THESE DEVICES HAVE THE ADVANTAGE OF NON-CONTACT WITH THE MATERIALS. SKETCH FROM http://www.omega.com/literature/transactions/volume4/images/14_Fig_01_ l.GIF

  33. LEVEL INDICATION • MOST OF THE ELECTRONIC DEVICES MENTIONED ABOVE CAN BE EQUIPPED WITH FIELD MOUNTED GAUGES • MANOMETERS • U-TUBE • SIGHT GAUGES • DIP STICKS http://www.mepinc.net/shop/ViewCategory/32/9900sightlevelgauge

  34. FLOW SENSING • FLOW IS TYPICALLY MEASURED WITH A DEVICE IN DIRECT CONTACT WITH THE MEDIA AND THAT SIGNAL IS SENT TO A TRANSDUCER. • DELTA PRESSURE DEVICES - CONNECTED TO ΔP CELLS • ORIFICE PLATE • VENTURI • PITOT TUBES • VORTEX SHEDDING FLOWMETER (ANNUBAR)

  35. FLOW SENSING • Orifice plate/DP cell most common approach. Good repeatability and fast dynamic response. • Magnetic flow meters and vortex shedding flow meters are also used in certain situations. They are more expensive but more reliable and require less maintenance. • A straight run of pipe required for good accuracy for all flow meters.

  36. FLOW SENSING • Orifice Plate/DP Cell Flow Indicator in a Flow Control Loop

  37. FLOW SENSING • Paddle Type Orifice Plate

  38. FLOW SENSING • Sizing an Orifice for a Differential Pressure Flow Indicator • bis the ratio of the orifice diameter to the pipe diameter. • 0.2 < b < 0.7 • Pressure drop at minimum flow should be greater than 0.5 psi. • Pressure drop across the orifice should be less than 4% of the line pressure. • Choose the maximum value of bthat satisfies each of the above specifications.

  39. FLOW SENSING • TURBINE METERS • FLOW RATE IS BASED ON THE RATE OF ROTATION • USE MAGNETIC PICKUPS • ULTRASONIC FLOWMETERS - USE THE DOPPLER EFFECT • MAGNETIC FLOWMETERS - ARE USED FOR CONDUCTIVE MEDIA SKETCH FROM http://www.ncinter.net/~fgtc/mag_pg.html

  40. FLOW SENSING • CORRIOLIS MASS FLOWMETERS • USE THE CORIOLIS EFFECT WITH FLUID FLOWING THROUGH VIBRATING TUBES • VIBRATION IS IN THE DIRECTION NORMAL TO THE FLOW STREAM • VERY ACCURATE AND RELATIVELY EXPENSIVE • FLOW INDICATION IS OBTAINED BY GAUGES ADDED TO THE FLOWMETERS OR ROTAMETERS

  41. OTHER CONTROL VARIABLES • VISCOSITY • DENSITY • POSITION • MASS FLOW • CHEMICAL COMPOSITION • USING A PROPERTY OF MIXTURES • USING INFRARED, UV-VIS OR OTHER RADIATION DEVICE • USING CHROMATOGRAPHY • THERMAL CONDUCTIVITY • DIELECTRIC CONSTANT • PARAMAGNETISM • pH • MOISTURE

  42. Analyzer Sensor Systems • GC- most common composition analyzer. Based on plug flow of a volatile sample through a packed bed-behaves as deadtime. Deadtime and repeatability depend on the particular components being measured. • Radiation absorption- infrared, ultraviolet, and visible. Can be effective for certain components. • Sample system can affect dynamics and reliability of composition measurement.

  43. Bio-Sensors

  44. Common Bio-Sensors • Flow measurements: Coriolis meters and rotameters. • Off-gas analyzers: mass spectrometers (one mass spec can provide online measurements for up to 32 bio-reactors), O2 electrode for O2 concentration and infrared spectrometer for CO2 concentration. • Fermentation product analysis: HPLC and Flow Injection Analyzer • Ion-specific electrodes • pH sensor • DO sensor • Redox sensors

  45. Typical Ion-Specific Electrode

  46. SAFETY DEVICES AND SYSTEMS • PRIMARY SAFETY SHOULD BE INHERENT IN THE DESIGN OF THE FACILITY • EQUIPMENT IS DESIGNED TO AVOID UNSAFE CONDITIONS • THE SYSTEM IS BUILT TO EXCEED THE ANTICIPATED CONDITIONS • SAFETY SENSORS • SAFETY LOOPS FALL INTO ALARM, INTERLOCK, AND SELF-ACTUATING CATEGORIES.

  47. SAFETY DEVICES AND SYSTEMS • ALARMS - INDICATE TO THE OPERATOR THAT A SYSTEM IS OUTSIDE OF THE NORMAL CONTROL RANGE. • LOW OR HIGH ALARM LEVELS. • IN THIS SKETCH, x REPRESENTS THE ALARMED VARIABLE. • IT IS ANTICIPATED THE OPERATOR CAN MAKE CORRECTIONS FOR THESE OUT-OF-RANGE CONDITIONS • ALARM CIRCUITS CAN USE OUTPUTS FROM THE PRIMARY CONTROL LOOP OR HAVE INDEPENDENT SENSORS.

  48. SAFETY DEVICES AND SYSTEMS • INTERLOCK ALARMS INITIATE ACTIONS THAT WILL PROTECT THE PERSONNEL AND THE PROCESS • LOW-LOW OR HIGH-HIGH ALARM LEVELS • IN THIS SKETCH, x REPRESENTS THE ALARMED VARIABLE. • IT IS ANTICIPATED THAT AUTOMATIC CORRECTIONS FOR THESE OUT-OF-RANGE CONDITIONS ARE TO BE MADE BY THE SYSTEM, SO OUTPUT FROM THESE SENSORS GOES TO INTERLOCK CONNECTIONS.

  49. SAFETY DEVICES AND SYSTEMS • INTERLOCK ALARM CIRCUITS SHOULD ONLY USE OUTPUTS FROM INDEPENDENT SENSORS • INTERLOCK ALARMS ARE ALWAYS INDICATED ON THE OPERATOR MONITOR. http://blog.svconline.com/briefingroom/wp-content/uploads/2010/03/ipixpanel-jpeg.jpg

  50. SAFETY DEVICES AND SYSTEMS • SELF-ACTUATED SYSTEMS • THESE ARE DEVICES THAT ARE INCLUDED TO PROTECT WITHOUT HAVING EXTERNAL INTERLOCKS • PRESSURE RELIEF DEVICES • PRESSURE RELIEF VALVES • THESE HAVE VARIOUS TYPES OF DESIGNS ACCORDING TO PRESSURE RANGE, CAPACITYAND RESET CAPABILITIES • TAKEN FROM http://www.conbraco.com/products/safety/safindex.asp

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