CHE 448

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CHE 448 Chemical Engineering Design
Spring 2006
We are not in Kansas Dorothy!
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Announcement!

• Tuesday April 4 Mr. Garnett on Human Errors in
  Design
• Thursday April 6 Second Midterm

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Stream splitting

• Stream splitting must be used when
• The number of hot streams on the cold side of the
  pinch is smaller than the number of cold streams.
• The number of cold streams on the hot side of the
  pinch is smaller than the number of hot streams
• Stream splitting helps to reduce the number of
  exchangers without increasing use of utilities.

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Example stream splitting
Stream Ts C Tt C mCp kW/C Q kW
H1 200 100 5 500
H2 150 100 4 200
C1 90 190 10 1000
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Heat Integration of a Reactor System
Stream Ts F Tt F mCp Btu/s F Duty Btu/s Cost/Btu
C1 100 580 1 -480 0
C2 100 580 2 -960 0
H1 600 200 3 1200 0
Steam 650 650 2/106
Hot Wat 250 gt 130 1.5/106
Cooling W 80 lt 125 1/106
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Temperature IntervalReversible (Ideal) System
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Temperature interval I
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Temperature Interval II
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Cost of heat exchanger network system
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Heat integrated system I
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Heat Integrated System II
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Cost of system without heat integration
Unit Str 1 Str 2 Duty Btu/s A(ft2) Cost utility Cost unit
HU-1 1 Steam 480 825 28300 62000
HU-2 2 Steam 960 1650 56700 82000
CU-1 3 CW 1200 4650 35500 145000
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Cost of Integrated System
Unit Stream 1 Stream 2 Duty Btu/s Area ft2 Cost utility Chex
HU-1 C1 Steam 80 138 4700 45000
HU-2 C2 Steam 160 276 9400 48000
PU-1 C1 H1/3 400 1550 0 80000
PU-2 C2 2H1/3 800 3100 0 114000
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Heat Integrated Distillation Trains
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Multiple Effect Distillation
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Multiple effect distillation alternativesSingle
column 2.12 107 kcal/h
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Heat and Power Integration
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Heat Engine Carnot cycle
1-2 Isothermal expansion 2-3 Adiabatic
expansion 3-4 Isothermal compression 4-1
Adiabatic compression
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Heat pump/refrigerator cycle
Work Wc is done by compressor
Heat Qe leaves the system at condenser Tc
Tb of reboiler is smaller than Te of condenser.
Heat Qb enters the system at reboiler Tb
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Heat pumps and heat engines
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Example of heat and power integration
Distillation of propylene-propane mixture
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Propylene-propane distillation example
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Alternative I Reboiler flashing
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Reboiler flashing
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Positioning of heat engines
Not a good design
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Positioning of heat pumps