Download dynamics files

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Download dynamics files

• F\tmpfiles\Chapter6
• \\speedy\sdsmtshare\tmpfiles\chapter6\

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ChE450/550 Dynamics

• Optimization Lectures
• November 13th
• Gable Rhodes, Instructor

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Todays Example

• Constantly Stirred Tank Reactor (CSTR)
• This system mixes Analine and Hydrogen and reacts
  them to produce cyclohexalamine at a conversion
  of 76mol
• New blocks today
• CSTR
• Lag time
• Use Aspen to determine fake reaction constant
• Aspen Dynamics method of autotuning controllers
  to control the reactor temperature and prevent
  runaways

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1 Set up steady state model

• Create flow sheet with only
• CSTR reactor, control valves
• Analine and hydrogen fresh feed
• One product stream and one vent stream
• Feed 100lbmol/hr
• Analine 100mol
• T100F, P650psia
• Feed 400lbmol/hr
• Hydrogen 100mol
• T10F, P650psia

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2 Add valves and pump

• Pressure reducing and increasing equipment must
  specify
• the pressure drop/outlet pressure for valves,
  pipes, unit ops
• Feed valve outlet is the oeprating pressure of
  the reactor, P595psia

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2 valves and pump

• Valve parameters
• All adiabatic
• CV-nitro, CV-eth, CV-pent outlet P110psia
• Pump parameters
• Pressure increase ?
• Mixer _at_ 110psia

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3

• CSTR specification
• Operating pressure is 595psia
• Operating temperature is 250F
• Vapor and liquid phases with the reaction in the
  liquid phase
• Volume of 1200 ft3, with 80 liquid level

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3 continued
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3 continued

• Define a reaction for the Analine to
  cyclohaxalamine (CHA)
• Kinetics (fake)
• Reaction activation energy is 20,000btu/mol
• First order dependence of both reactants
• Setup Spec/Vary to solve for the pre-exponential
  factor
• Goal of 76 single pass conversion.

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Reaction definition
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4 Vessel sizing

• Vessels are sized according to steady state
  (average) flow conditions
• Using rule-of-thumb, Luyben p.14
• Maximum velocities
• Equipment specifications
• Use the LARGEST value of the above methods

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4 Vessel sizing

• Separator size
• V1200ft3
• D9.14ft
• H is calculated automatically by Aspen

18.28ft
9.14ft
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Dymanics

• 5 Run simulation to converge values
• 6 click on pressure driven button to check the
  simulation
• Fix errors
• 7 save as a .bkp file before attepting to
  convert to Aspen Dymanics!
• Save as regular APW also.

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Convert to Aspen Dynamics

• Check to make sure the blocks are available
• Setup
• Reports Option
• Block tab
• Include all blocks
• Export
• Go to File and click Export
• pressure-driven simulation
• Save

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Aspen Dynamics

• Close Aspen
• Open Aspen Dynamics file
• Make initialization run
• Set communication time to 0.001

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Add controllers

• Controllers can be added in many ways, but
  generally we need controls
• on all pressure reducing valves
• on liquid level
• Temperatures and pressures

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Controllers

• Luyben p68
• Dynamics tab
• Control Models
• PID, drag to the location you want to
  control.arrow will pop out on the flowsheet
• Measurement coming off of a block or stream is
  the PV (process Variable)
• The signal is the OP coming off of the controller
  and into the valve

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Controller-Analine, Hydrogen

• From Chapter 4, the flow controllers use
• Gain 0.5/
• Integral time .3 min
• No derivative control
• Reverse Acting!
• Filter Time constant 0.1 min

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Controller-Liquid Level

• Gain 2 /
• Integral Time 60000min
• Direct Acting

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Controller-Tank Pressure

• Gain 2 /
• Integral Time 2 min
• Direct Acting

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Lag

• The Lag simulator in the controlmodels box
• Connect with control signals, selecting PV as the
  output to the OP controller input.
• Open AllVariables and input 1.0 as the gain, 1.0
  as tau
• Two are used for second order lag effects

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Controller-Temperature

• We have no idea what to put in this controller,
  so just initialize and run.
• Action
• Reverse for constant Q
• Reverse for isothermal
• Direct for LMDT

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How do we tune temperature controller?

• Calculations could be used.
• The Lags makes system oscillations possible is
  too tight control is used.
• Aspen Dynamics has a built in controller tuning
  that can be used.
• Set up a plot showing PV and OP of the
  temperature controller

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Auto Tuning

• Achieve steady state and initialize the run (no
  easy task).
• Open the faceplate for the composition
  controller.
• Click the musical note icon to open the tuner.
• Specify 100 / gain and 99999 integral time
• Run the simulation, then hit the start test button

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When to stop?

• When the simulation is oscillating regularly, you
  can stop the test, then pause the run.
• Go to the results tab and record the constants
  given there.
• These are the recommended constants for the
  controller.

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Homework

• Submit Aspen Dynamics plots of variables other
  two CSTR models
• CSTR temp, pressure and level, conversion
• Controller OP and PV
• CSTR modes
• Constant duty
• LMTD