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Chem Eng Lab II

by: Alfonzo Bednar

Chem Eng Lab II CHE 460

Alfonzo Bednar
GPA 3.5


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This 11 page Class Notes was uploaded by Alfonzo Bednar on Thursday October 29, 2015. The Class Notes belongs to CHE 460 at University of Michigan taught by Staff in Fall. Since its upload, it has received 11 views. For similar materials see /class/231607/che-460-university-of-michigan in Chemical Engineering at University of Michigan.

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Date Created: 10/29/15
BROWN INDUSTRIES INDIRECT HEATING CONTROL SYSTE1I Department of Chemical Engineering University of Michigan Ann Arbor MI 48109 September 3 2008 INDIRECT HEATING CONTROL SYSTEM I EQUIPMENT DESCRIPTION This apparatus was designed to provide a variable ow of clean heated city water at constant temperature to a downstream process Cold water from the Ann Arbor City water supply is heated in the tube side of a shellandtube heat exchanger The shell side of the heat exchanger is heated by a recirculating water loop which in turn is heated by a PICK1 direct injection steam heater Figure l is a schematic of the apparatus and its instrumentation For the system to work a recirculating water loop has to be established in the shell side of the heat exchanger Steam is injected into this water loop and immediately condenses providing the heat necessary to heat the water Heat Exchanger Standard2 shellandtube heat exchanger model BCF No 503003014005 This is a fourpass heat exchanger with a 3quotdiameter brassshell 14quot OD copper tubes and 43 sq ft of exchange surface area Water Supply City water is available for equipment testing This water ows trough a main shutoff valve a owregulating valve a lter to provide protection to the ow meter a ow meter and into the tube side of the heat exchanger In addition warm water from the building hot water line is available to produce small temperature disturbances in the inlet water stream The hot water outlet from the heat exchanger will be connected to the process which temperature we aim to regulate Currently this water discharges into the drain A small water line is also available to re ll the recirculating loop when necessary Steam Supply Steam from the G G Brown building supply is available at pressures up to 50 psig The Steam supply line is provided with a main shutoff valve and a steam trap return leg to remove any condensing water from the piping This setup provides for saturated steam with minimal liquid water to enter the steam pressurereducing valve The pressurereducing valve can be adjusted manually to pressures between 6 and 60 psig although pressures above 50 psig can not be sensed by the steam supply pressure sensor The steam ow reaching the steammixing chamber is regulated by a direct acting pneumatically operated valve air to open l2inch Pick brand model 3224588 which is activated by the output from the controller Recirculation Loop This loop consists of the heat exchanger shellside a watersteam mixing chamber a recirculating pump and an orificeplate ow meter All the piping in this recirculation loop is standard linch brass pipe schedule 40 A connection to the cold 1 Manufactured by Pick Heaters Inc West Bend Wisconsin 2 Manufactured by ITTStandard Cheektowaga Buffalo NY 14227 472 water supply is provided to ll the recirculation loop with water A drain valve is also available to drain the water if needed Controller VP 61L supply Steam Mixing Chamber Control Pressure Valve reducing va ve Cond return Orifice Plate Recirculating lgtltl Pump Hot Water Cold Water D ain Figure 1 Temperature Control Apparatus Piping and Instrumenta tion Diagram Instrumentation The apparatus is equipped with the following instruments 0 Four platinum resistance temperature detectors or RTDs Omega Engineering model PRll2100146E to monitor the inlet and outlet temperatures from both sides of the heat exchanger A turbine ow meter Cole Parmer model E3225020 to monitor the ow of water in the tube side of the heat exchanger A sharpedge orificeplate ow meter is installed in the 1inch schedule 40 brass pipe to detect the ow rate in the recirculating loop The bore size of the ori ce is 0746 inches The recirculation loop is equipped with ow and temperature switches The object of these two switches is to shutoff the steam supply to the mixing chamber in case there is not sufficient recirculating ow of water or the water heatsup to above 95 0C A Dell computer used for data acquisition and process control Control Implementation The temperature of the water outlet from the heat exchanger is monitored by a lOOohm platinum Resistance Temperature Detector RTD The signal from this RTD is sent to the controller The controller a software program resident in the computer uses this temperature signal to produce a calculated analog output in the range of 0 to 5 volts This output is sent to a voltagetopressure VP converter that produces an air pressure linearly related to the voltage The air pressure is directed to the steam control valve actuator that regulates the ow of steam into the steammixing chamber The steam control valve is an airtoopen valve which is fully closed when the air pressure is 3 psig and fully open when the air pressure is 15 psig These pressures correspond to voltage signals of 0 and 5 volts respectively II PROCESS CONTROL SOFTWARE There are currently three programs available to the users to control the process These programs run in the control computer and they are based on LabVIEW data acquisition and control software Manual Control Manualvi This program controls the voltage to the steam valve actuator manually by direct input from the user SingleLoop feedback Control PIDControlwithFFvi This program performs a ProportionalIntegralDerivative PID control algorithm on the measurement of the temperature to be controlled and calculates the voltage required for the steam valve actuator This program also allows the user to implement Feedforward Control based on measurements of disturbances to the process The feedback and feedforward modes of this program can be used independently of each other ie only PID control or only feedforward control or in conjunction to improve the controller response Dual Loop or Cascade Control Cascadevi This program utilizes two PID feedback loops the Master Controller performs a PID control algorithm on the measurement of the temperature to be controlled and calculates the required temperature in the shell side of the heat exchanger The Slave Controller uses this calculated temperature as the set point 3 LabVIEW is a trademark ofNational Instruments Corp Austin TX for a second PID control loop to determine the voltage required for the steam valve actuator Theory The PID control algorithm used by the computer is based in the following PID equation UKC cti I et dt 7D 16 139 F0 dt 1 ea SP 7 Mt 2 Where et error as function of time SP Setpoint F Wt Feedback variable at time t U Controller output Kc Proportional constant 239 Integral gain TI 00 gt no integral action TD Derivative time constant TD 0 gt no derivative action The feedback variable FV in this case is the signal from the temperature sensor RTD located at the tube outlet of the heat exchanger Implementation of Manual Control The Program Manalvi produces a constant output voltage to the control valve actuator This value is selected by the user and can be any value between 0 and 5 volts Zero volts correspond to the steam valve fully closed 5 volts correspond to the valve fully open Implementation of the PID Algorithm The program PIDControlwithFFvi implements the PID control algorithm using the temperature set point and the water outlet temperature controlled variable as the inputs to calculate the error and generates a voltage output to manipulate the steam ow to the shell recirculation loop The equations used in this control algorithm to produce the outputs at any time n are Mums 11V011i9 KC 6 SI 7 At 3 en Temperature SetPt 7 Water outlet Temperature C 4 S1quot 7 SW 1 en At 5 Aen en 7 e0 6 0 3 S1quot 3 5 volts 7 0 S uquot S 5 volts 8 Where K C Prop Gain dimensionless I Integral Frequency seconds39l I 117 and r Integral gain as described in Eq 1 TD Derivative Gain seconds At Time Interval between measures seconds In this control program At 1 second um Feed forward component of the controller Default value for una 0 until another model is implemented Equation 7 limits the integral term to the limits of the control valve actuator to prevent unlimited values of the integral term also known as reset windup Equation 8 limits the total output of the controller to the same limits of 0 and 5 volts The feed forward component of the control equation requires a model of the process created by the user based on the operation of the control equipment Cascade Control Implementation The program Cascadevi implements the control algorithm using 2 PID control loops as follows Master Control loop uses the temperature set point and the water outlet temperature controlled variable as the inputs to calculate the error and generates a temperature set point for the shell side of the heat exchanger as an output Slave control loop uses the shell side inlet temperature and the set point generated by the Master Control loop to calculate the error and generates a voltage output to manipulate the steam ow to the shell recirculation loop The equations used in this control algorithm to produce the outputs at any time rt are Master Control Loop SbeIISetpt C K4122 em Sm Lyon 9 enm Water SetPt 7 Water Temperature C 10 SIMquot SIn1m t 1menmAt C 11 ABMquot emquot arm1Wquot C 12 0 s S1nm s 98 C 13 0 3 Shell Setptn s 98 C 14 Slave Control loop u volts 195 es Ss 755 15 ens Shell Setpt 7 Shell Inlet Temperature C 16 SIMS SIM125 15 en At C 17 AEMS en govMS C 18 0 S S1SS 5 volts 19 0 S uquot S 5 volts 20 Where KJm Master Control Prop Gain dimensionless Hm Master Control Integral Frequency seconds39l TDm Master Control Derivative Gain seconds At Time Interval between measures seconds In this control program At 1 second KJS Slave Control Prop Gain Volts C 13 Slave Control Integral Frequency seconds39l TDS Slave Control Derivative Gain seconds Equations 13 and 14 limit the integral term and the total output of the master controller to just below the boiling point of water Equation 19 and 20 limit the integral term and the output to the control valve to within the limits of 0 and 5 volts corresponding to the full range of the steam ow control valve III DATA ACQUISITION AND DATA LOGGING A computer is connected to the water heater hardware and instrumentation for purposes of Process Control and Data Logging The computer monitors the output of all the RTDs ow meter and pressure sensors using LabVIEW 4 software All the analog signals from the instruments are sent to a MCC PCIDAS 1002 analogtodigital N D conversion card in the computer The LabVIEW program converts the digital signals from this card corresponding to the volts to the value of the measured variables in the desired engineering units ie galmin mS etc This card also converts the digital output 4 Produced by National Instruments Austin Texas 477 signals generated by the LabVIEW program to analog voltage signals from 0 to 5 volts and sent to the eld instruments Monitoring and Controlling Process Conditions LabVIEW operates under Microsoft WINDOWS XP operating system To start the program turn the computer on if it is not already and select the Chelab user account Doubleclick on the quotCONTROLquot folder if it is not open already This folder contains icons for the four control programs mentioned above and a file folder named DATA for storage of the data files generated during the experimental runs To start the data acquisition and control functions doubleclick on the desired iconeither Manual PIDControlwithFF or Cascade A product identification screen will appear and the LabVIEW setup will start the data acquisition program The setup produces a display screen with the values for all the sensor outputs on the righthand side of the screen and analog traces for some of the sensor outputs on the lefthand side of the screen Figures 2 and 3 show details of the user interface created by the PID ControlwithFF control program The quotTemperaturequot frame on the left side shows the traces of the four RTDs The quotFlowquot frame shows the water ow rate through the heat exchanger tubes The Pressure frame shows the pressure of the steam supply and the air pressure to the valve actuator The quotOutputquot shows the output from the controller and the partial components of that output Also on the right side of this display there are four control fields to select the values of the four control parameters Set point K0 1 and T c for the process note that the value of I correspond to the reciprocal of the integral gain I 11quot or I 0 correspond to no integral action All values displayed on the screen are updated every second The Cascade control setup shows the output of the two control loops in two separate windows see figure 3 for details A file named Manualimmxls PIDandFFimmxls or Cascadeirmnxls is generated every time the data acquisition program is invoked The 111m indicate the numerical order of the file and it is incremented by one each time a new file is saved All the temperature ows Pressures controller output and time values are stored in this file every second To start the data acquisition click on the Start button a small rightpointing arrow located on the leftmost position of the menu bar See figure 2 for details To stop the data acquisition click on the red STOP located on the upper left comer of the user interface A new file is created each time the Start button is pressed and saved when the Stop button is pressed To retrieve these files at the end of your work doubleclick on the DATA icon in the quotCONTROLquot folder The files list can be sorted by date with the most recently created file at the top of the list Your files can be recognized by their creation date and time and by the File Name shown in the user interface window Controller Setup Parameters Wat Tempn Wate Temp Out 2 E a a E a g 38 unions 9 77 LL 5 g 5 5 Pg 0 r at in D 11100 539 000000 M00000 58 m 9 4000000 1 5 o 9 E 7 o o ruewamaom Time 10 7 7 7 7 7 77 77 7 Fzgure 2 User interfa cc for the PZDCOHIIOIWz jFF program en you are done with the computer please Log Off the Chelab account but do not shut down the computer There is an automatic upgrade program that is set to run every night at midnight so it is important that the computers be left on for this event Controller Outputs Controller Parameters Seconds From Start 0 I aim an ONYROLLER rm 2 quot1 I m J m Jm i nnnnnn Qinmnnnn Shell 51 Pl SLAVE ONYROLLER W I Kc I gnmmnn rinnnmm v V FIgure 3 User mterface y the Cascade Contra Setu His Name 0mg V Sensor Calibration electronic signals produced by the instruments are converted to a standard 0 to 5 volts signal and sent to the computer The sensor calibration is done by means of a regression Al e instrumenm ve been calibrated and fitte with a linear equation If there is any concern about these calibrations please notify the laboratory personnel in order to ascertain the nature of the problem In addition to Microsoft Excel the computer connected to the process control equipment also has Po y and Mathematica software for those users interested in creating simulations of the process control equipment IV HEATING SYSTEM STARTUP AND SHUTDOWN PROCEDURE a Startup Pr ooedure 1 Close the Drain valve if it is open 2 Fill up the recirculation loop with water open the fillup valve until water leaves the recirculation loop over ow line 5 V39 509080 959 3 Turn on the recirculation pump Allow a few seconds for the recirculation ow to become established When a steady ow of water leaves the recirculation loop over ow no more air present in the loop shut the water supply to the recirculation ow Turn on the data acquisition and control software and choose the desired control parameters Establish a desired water ow rate through the tube side of the heat exchanger Open the main steam supply valve Regulate the steam pressure as desired Modify the setpoint and control parameters as desired Shutdown Procedure Shut the main steam supply valve Shut the water supply to the tube side of the heat exchanger Shut the recirculation pump off Shut down the data acquisition and control software Log off from the Chelab computer account There is no need to drain the recirculation loop 4711


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