Process Dynamics

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Process Dynamics

• Consider when variables change with time
• Many inherently dynamic processes
• Pharmaceuticals
• Specialty chemicals

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Why Dynamic Models?

• Start-up/Shutdown
• Process responses
• Improved Control
• Eliminate waste
• Cost savings
• Safety
• Time to achieve steady-state
• Training
• Process optimization
• Predictive control
• Improved understanding
• Experimental design

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Aspen Dynamics

• AspenPlus ? steady-state simulation
• AspenDynamics ? dynamic simulation
• Steps to setting up AspenDynamics
• Get steady-state simulation running
• Estimate equipment sizes
• Get plumbing setup
• Size control valves
• Install controllers and tune
• Save/convert to AspenDynamics files

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1. Get steady-state simulation running

• Flowsheet topology (types and positioning of
  units)
• Reactor types, sizes, and conditions
  (temperatures, pressures, catalyst amounts,
  heat-transfer area, cooling or heating medium,
  etc.)
• Reaction kinetic data
• Physical property data
• Phase equilibrium data
• Number of stages in all staged-operations
  (distillation columns, absorbers, liquid-liquid
  extraction columns, etc.) and operating
  conditions (pressures and temperatures)
• Heat-transfer rates, minimum approach
  temperatures, overall heat-transfer coefficients,
  flowrates of cooling or heating medium and areas
  in all heat exchangers
• Flowrates, temperatures, pressures and
  compositions of all process streams (input)

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2. Estimate Equipment Sizes

• Why?
• Think about idealized vs. real chemical reactors
• Idealized ? RSTOIC (specify conversion and solve)
• Real ? RCSTR
• Must specify volume ? determines response of
  system/equipment
• Mole balance
• Energy balance

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3. Get Plumbing Setup

• How things are hooked up
• Control valve location
• Type of AspenDynamics System
• Flow-driven
• Pressure-driven

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4. Size Control Valves

• What is pressure drop across valve?
• What is valve percent opening at steady-state?

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5. Install Controllers and Tune

• Set controller action
• Valve action
• Sensor/process deadtimes/delays (realism)

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6. Save/Convert to AspenDynamics Files

• Save steady-state simulation as .bkp
• Convert (export) to .dynf and .dyn files

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1. Get steady-state simulation running

• Will be given to you, or
• You develop yourself (first half of class)

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2. Estimate Equipment Sizes

• Surge tanks
• Flash tanks
• Heat exchangers
• Distillation Columns
• Need physical properties
• Luyben Chapter 2
• Equipment Sizing pdf on course website
• Examples

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3. Get Plumbing Setup

• Liquid pumping systems
• First law of plumbing Locate valves in liquid
  lines downstream of centrifugal pumps
• Second law of plumbing Use only one valve in a
  liquid-filled line
• Gas compression systems
• Do not throttle the discharge of a compressor

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3. Get Plumbing Setup
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3. Get Plumbing Setup