HW 3 Additional Points

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HW 3 Additional Points

• Heat Duty of Reboiler ? Steam Requirements
• QJ/h/?Hvap J/kg kg Steam/h
• Not the gross heating value of the stream going
  to the reboiler
• Heat Duty of Concenser ? CW Requirements
• QJ/h/(?H2O CpJ/kg/º ?Tº) m3 CW/h
• ?T 30ºF/1.8 ºF/ºC 16.67 ºC
• Use Cheapest Utilities you can
• Electricity is very expensive per J

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Cost of Utilities Last HW
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HW 3 Additional Points

• Can you heat integrate the Reboiler and
  Condenser?
• Generally not!

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Distillation Columns
Typically two separate temperatures Condenser is
colder than reboiler 0th law violation heat
can not go up hill
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Position a Distillation Column Between Composite
Heating and Cooling Curves
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Heat Integration
Columns in series and parallel have potential for
heat integration
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Multi-effect DistillationAdjust Pressure in C2
for ?Tmin
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• Heat Pumps in Distillation

Closed cycle Heat Pump
Open cycle Heat Pump
Heat pumps make heat flow up hill
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Dealing with Impurities in Processes and Process
Simulators

• ChEN 5253 Design II
• Terry A. Ring
• There is not chapter in the book on this subject

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Impurity Effects

• Heat Exchange
• Reactors
• Separation Systems
• Recycle Loops

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Impurities in Heat Exchange

• Impurities effect heat capacity
• Lower Cp
• Various options
• Raise Cp
• Increase H2
• Impurities effect the enthalpy of stream
• Total heat of condensation is less due to
  impurity
• Total heat of vaporization is less due to impurity

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Impurities in Heat Exchange

• Impurities in Steam Trouble shooting
  (MicroPlant) Lecture
• Heat exchanger with Steam Trap
• Build up of Impurity with Time
• Kills Heat Exchange with Time.
• To Overcome This Problem
• Clean up steam
• Purge to remove impurity build up
• How to determine the purge flow rate?

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Impurities in Heat Exchange

• Impurities in Fuel
• Vanadium in Venezuelan Crude Oil
• Vanadium follows the heavy oil product that is
  burned to supply heat for the refinery
• Vanadium gives low temperature eutectic in weld
  beads
• Welds failed in process heaters
• Welds failed in process boiler
• Crude Processing to remove heavy metals before
  entering the refinery

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Impurities in Heat Exchange

• Impurities that lead to high corrosion rates
• e.g. HCl in steam
• Heat exchangers are hot so corrosion is fast
• Corrosion of Heat Exchanger surfaces
• Decreases heat transfer coefficients in U
• Heat Exchange is not as effective with time
• Cooling towers are easily corroded
• Lower heat transfer coefficients
• Heat Exchange is not as effective with time

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Corrosion

• Pitting Corrosion
• Galvanic Corrosion
• Corrosion in General

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Galvanic Series
Least Noble metal corrodes when two metals are in
contact
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Corrosion Products

• Fe2(aq) 2e- ? Fe(s)
• -0.44 V
• Fe with Stainless Steel
• Corrosion Potential 0.14 V
• Fe with Copper
• Corrosion Potential 0.3 V

Rust
Pourbaix diagram
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Corrosion Rates-OLI Corrosion Analyzer
D 0.1m
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Aluminum Corrosion

• Al3(aq) 3e- ? Al(s)
• -1.68 V
• Connection with Iron
• Corrosion Potential
• -1.2 V

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Aluminum Corrosion Rates

• Increase with salt concentration
• Increase with temperature
• Increase with decrease in pH