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CHE 185 PROCESS CONTROL AND DYNAMICSOPTIMIZATION AND PRIMARY LOOP ELEMENTS

TYPES OF CONTROLOPTIMIZATIONINTENTION IS TO GET THE BEST ECONOMIC/QUALITY CONDITIONSCONTROL IS THE MORE GENERAL FORM OF RESPONDING TO CHANGE

Control & optimizationFor a bioreactor

http://www.automation.siemens.com/wcmsnewscenter/details.aspx?xml=/content/10001666/en/as/Pages/PN-200201-06-Alles_unter_Kontrolle.xml?NoRedirect=true&xsl=publication-en-www4.xslEXAMPLE OF OPTIMIZATIONOptimization and Control of a CSTR

EXAMPLE OF OPTIMIZATION

OPTIMZATION exampleMethod of solution 1. Select initial guess for reactor temperature, T*2. Evaluate CA, CB, and CC3. Evaluate F4. Choose new reactor temperature and recycle through step 2 until T* is identified.

EXAMPLE OF OPTIMIZATION

EXAMPLE OF OPTIMIZATIONGraphical Solution of Optimum Reactor Temperature, T*

Other TYPES OF CONTROLSUPERVISORYRESPONDS TO THE SIGNAL FROM THE OPTIMIZATION CONTROLLERSENDS A SIGNAL TO THE REGULATORY CONTROL LOOPTYPES OF CONTROLREGULATORYRECEIVES A SIGNAL FROM THE SUPERVISORY CONTROLLERACTUALLY ADJUSTS A PROCESS VARIABLE TO MAKE NECESSARY CHANGES FOR OPERATION.REGULATORY CONTROL EXAMPLETemperature Control for a Heat Exchanger

CATEGORIES OF LOOP COMPONENTSFEEDBACK LOOP THE PRIMARY COMPONENTS ARE SHOWN SCHEMATICALLY

LOOP COMPONENTS - SENSORSMEASURE THE VALUE OF THE TARGET AND MANIPULATED VARIABLESTYPICALLY P, T, L, D, ,, COMPOSITION, MASSLOCATED IN-LINE, EVEN IF THEY DO NOT CONTACT PROCESS FLUIDSLOOP COMPONENTS - SENSORSTYPICALLY ANALOG DEVICES WITH FULL SCALE RANGES:20 mA CURRENT SIGNAL mV VOLTAGE SIGNAL3 - 15 psig PNEUMATIC SIGNALLOOP COMPONENTS - TRANSMITTERSANALOG DEVICESCONVERT SIGNAL INTO A VALUE THAT CAN BE TRANSMITTED WITHOUT SIGNIFICANT LOSS IN VALUETYPICAL OUTPUT IS 4 - 20 mA CURRENT FULL SCALE RANGELOOP COMPONENTS - TRANSDUCERSCONVERT THE ANALOG SIGNAL FROM THE TRANSMITTER INTO A DIGITAL SIGNALLABELED A/D FOR ANALOG TO DIGITALLABELED D/A FOR DIGITAL TO ANALOGCAN TRANSFER ELECTRONIC TO PNEUMATICLOOP COMPONENTS - CONTROLLERSRECEIVES DIGITAL SET/POINT AND MEASURED SIGNALS FOR A VARIABLEMAKES A COMPARISON BETWEEN THE SIGNALS USING A BRIDGEPRODUCES A DIGITAL OUTPUT SIGNAL TO ADJUST THE MEASURED VALUE TO THE SET/POINT VALUE

LOOP COMPONENTS - ACTUATORSRECEIVES THE OUTPUT SIGNAL FROM THE CONTROLLER, VIA THE TRANSDUCERADJUSTS THE POSITION OF A DEVICE (FINAL CONTROL ELEMENT) TO CHANGE A PROCESS VARIABLELOOP COMPONENTS - FINAL CONTROL ELEMENTCHANGES A PROCESS VARIABLE TO OBTAIN A CORRECTION TO THE MEASURED VARIABLEFOR CHEMICAL PLANTS, MOST OF THE TIME THESE DEVICES ARE VALVESSOURCE OF SET/POINTSFOR A SIMPLE PROCESS, THESE MAY BE ENTERED MANUALLYFOR CONTEMPORARY SYSTEMS, THESE SIGNALS COME FROM A COMPUTERPLC - PROGRAMMABLE LOGIC CONTROLLERDCS COMPUTER - DISTRIBUTED CONTROL SYSTEM COMPUTERDCS FUNDAMENTALSDCS HAS THE FOLLOWING GENERAL COMPONENTSLOCAL CONTROLLERS INPUT/OUTPUT PANELS (I/O PANELS) TO RECEIVE PROCESS VARIABLE VALUES FROM THE CONTROLLER AND SEND SET/POINT VALUESDATA HIGHWAY/MULTIPLEXER TO SAMPLE THE VALUES ON A REGULAR FREQUENCY

DATA HIGHWAY/MULTIPLEXER

DCS FUNDAMENTAL COMPONENTSHOST COMPUTER TO ENTER SET/POINTSALARM COMPUTER - PLCs TO INITIATE ALARMS AND/OR INTERLOCKSDATA STORAGE COMPUTERKEEPS TREND DATALOGS ALARMSOTHER COMPUTERS THAT HAVE ACCESSFINAL CONTROL ELEMENT CHARACTERIZATION - VALVESVALVES ARE USED FOR EITHER ON/OFF OR THROTTLING OPERATION - SEE PERRYS 7TH PAGE 8-64ON/OFF VALVE CHARACTERISTICSHAVE A COMPLETELY OPEN AND COMPLETELY CLOSED POSITIONHAVE A TIGHT SHUT-OFF CAPABILITYHAVE LIMITED VALUE FOR THROTTLINGPLUG VALVES AND BALL VALVES90 RANGE FROM OPEN TO CLOSEDUSE PNEUMATIC OR MOTOR ACTUATORS

GATE VALVESTYPICALLY USED FOR ISOLATION VALVES - FOR MAINTENANCE AND AS BACK-UP FOR CLOSED THROTTLING VALVES

GATE VALVESMAY HAVE SEVERAL TURNS BETWEEN OPEN AND CLOSEDMAY HAVE MOTOR OPERATORS BUT MORE FREQUENTLY USE MANUAL OPERATIONThrottling (control) valvesVARIOUS FLOW CHARACTERISTICS BASED ON THE SHAPE OF THE PLUG AND THE SEATFLOW THROUGH THE VALVE DEPENDS ON THE FRACTION OPEN AND THE NET PRESSURE DROPHAVE COMPLETELY OPEN AND COMPLETELY CLOSED POSITION, BUT DESIGNED FOR INTERMEDIATE POSITION FOR CONTINUOUS OPERATION - NOT TIGHT SHUT OFFGeneral Reference - http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf

Globe (THROTTLING) Control Valve

Cross-section of a Globe Valve

Throttling (control) valvesGlobe Valve TYPESQuick Opening- for safety by-pass applications where quick opening is desiredEqual Percentage- for about 90% of control valve applications since it results in the most linear installed characteristicsLinear- when a relatively constant pressure drop is maintained across the valve

Globe Valve FLOW CHARACTERISTICS

GLOBE VALVES - LINEARPLUGS/SEATS DESIGNED TO HAVE THE FRACTION OF FLOW BE LINEAR WITH THE VALVE STEM POSITION FOR A CONSTANT pf(x) = xWHERE x IS VALVE POSITION DESIGN POSITION IS ABOUT 50% OPEN

GLOBE VALVES - EQUAL PERCENTAGE

GLOBE VALVES - QUICK OPENING

GLOBE VALVES - OTHER TYPESECCENTRIC PLUG VALVESCOMBINATION OF PLUG AND GLOBE IN THEIR CHARACTERISTICSCLAIM TO BE TIGHT SHUT OFF

Reference:

http://www.millikenvalve.com/pdf/plug2011.pdf

CHARACTERIZATION OF CONTROL ELEMENTStIME CONSTANTSTIME IT TAKES FOR A UNIT TO RESPOND TO A SIGNAL AND COMPLETE A CHANGEFOR VALVES THIS IS THE TIME TO STROKE TO A NEW POSITIONDEADBANDRANGE OF SIGNAL THAT REQUIRED TO INDICATE AN ACTUAL CHANGECHARACTERIZATION OF CONTROL ELEMENTSPOSITIONDEADBANDRANGE OF SIGNAL THAT REQUIRED TO INDICATE AN ACTUAL CHANGEFOR THERMOCOUPLES THIS MIGHT BE +1 C.

CHARACTERIZATION OF CONTROL ELEMENTSTURNDOWN RATIOSPECIFIES THE RANGE OF STABLE OPERATION FOR THE DEVICE, MINIMUM TO MAXIMUMNORMAL OPERATING RANGE SHOULD NOT BE AT EITHER EXTREME POSITION

Control Valve DesignControl Valve DesignChoosesmallest valve that meets the range criterion for the minimum capital investmentthe largest valve to allow for future throughput expansion.CV versus % open for different valve sizes.Available pressure drop across the valve versus flow rate for each valve. Note that the effect of flow on the upstream and downstream pressure must be known.

http://www.norriseal.com/files/comm_id_47/Valve_Size_Manual.pdfControl Valve design ExampleSize a control valve for max 150 GPM of water and min of 50 GPM.Use the valve flow equation to calculate CvFor DP, use pressure drop versus flow rate (e.g., Table on page 82)

Control Valve design ExampleEquation at limits

Valve Position for Max and Min Flows based on size

Analysis of Results2-inch valve appears to be best overall choice: least expensive capital and it can provide up to a 50% increase in throughput.3-inch and 4-inch valve will work, but not recommended because they will cost more to purchase. The 2-inch valve will provide more than enough extra capacity (i.e., something else will limit capacity for it)

Adjustable Speed Pumps for flow controlUsed extensively in the bio-processing industries to maintain sterile conditions and relatively low flow rates.Fast and precise.Do require an instrument air system (i.e., 4-20 mA signal goes directly to pump).Much higher capital costs than control valves for large flow rate applications.

Chart1-0.2391024-0.2188701-0.1973783-0.1745807-0.1504331-0.1248938-0.09792406-0.06948884-0.03955746-0.0081042110.024890870.059441270.095553240.1332250.17244590.21319580.25544410.29914870.34425610.39069950.43839910.4872610.53717640.58802160.6396570.69192720.74466020.79766810.8507460.9036730.95621251.0081121.0591061.1089141.1572451.2037991.2482681.2903411.3297061.3660561.3990931.4285321.4541111.4755941.4927771.5054981.5136421.5171421.5159921.5102431.5000061.4854571.4668271.4444021.4185181.389551.3579031.3240061.2882941.2512051.2131671.1745891.1358531.097311.0592731.0220190.98578110.95075430.91709380.88491830.85431270.82533120.79800110.77232630.74829110.72586330.70499760.68563850.66772280.65118190.63594350.62193370.60907780.59730190.58653330.57670170.56773920.55958090.55216530.54543420.53933270.53380950.52881670.52430970.5202470.51659020.5133040.51035550.50771470.5053539

&APage &PT*Reactor Temperature (K)Economic Objective Function, F

F132.50E+02-2.39E-012.51E+02-2.19E-012.52E+02-1.97E-012.53E+02-1.75E-012.54E+02-1.50E-012.55E+02-1.25E-012.56E+02-9.79E-022.57E+02-6.95E-022.58E+02-3.96E-022.59E+02-8.10E-032.60E+022.49E-022.61E+025.94E-022.62E+029.56E-022.63E+021.33E-012.64E+021.72E-012.65E+022.13E-012.66E+022.55E-012.67E+022.99E-012.68E+023.44E-012.69E+023.91E-012.70E+024.38E-012.71E+024.87E-012.72E+025.37E-012.73E+025.88E-012.74E+026.40E-012.75E+026.92E-012.76E+027.45E-012.77E+027.98E-012.78E+028.51E-012.79E+029.04E-012.80E+029.56E-012.81E+021.01E+002.82E+021.06E+002.83E+021.11E+002.84E+021.16E+002.85E+021.20E+002.86E+021.25E+002.87E+021.29E+002.88E+021.33E+002.89E+021.37E+002.90E+021.40E+002.91E+021.43E+002.92E+021.45E+002.93E+021.48E+002.94E+021.49E+002.95E+021.51E+002.96E+021.51E+002.97E+021.52E+002.98E+021.52E+002.99E+021.51E+003.00E+021.50E+003.01E+021.49E+003.02E+021.47E+003.03E+021.44E+003.04E+021.42E+003.05E+021.39E+003.06E+021.36E+003.07E+021.32E+003.08E+021.29E+003.09E+021.25E+003.10E+021.21E+003.11E+021.17E+003.12E+021.14E+003.13E+021.10E+003.14E+021.06E+003.15E+021.02E+003.16E+029.86E-013.17E+029.51E-013.18E+029.17E-013.19E+028.85E-013.20E+028.54E-013.21E+028.25E-013.22E+027.98E-013.23E+027.72E-013.24E+027.48E-013.25E+027.26E-013.26E+027.05E-013.27E+026.86E-013.28E+026.68E-013.29E+026.51E-013.30E+026.36E-013.31E+026.22E-013.32E+026.09E-013.33E+025.97E-013.34E+025.87E-013.35E+025.77E-013.36E+025.68E-013.37E+025.60E-013.38E+025.52E-013.39E+025.45E-013.40E+025.39E-013.41E+025.34E-013.42E+025.29E-013.43E+025.24E-013.44E+025.20E-013.45E+025.17E-013.46E+025.13E-013.47E+025.10E-013.48E+025.08E-013.49E+025.05E-013.50E+025.03E-01

&APage &P

AAATTTCCondensateProduct StreamSetpointSteamFeed