CHE 448 Chemical Engineering Design

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CHE 448 Chemical Engineering Design
Spring 2006
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Chapter 10 Heat and Power Integration

• Determine minimum usage of heating and cooling
  utilities
• Design heat exchanger networks
• Reduce the number of heat exchangers
• Select and position the use of hot and cold
  utilities
• Revise the concept of minimum approach
  temperature
• Understand the approaches to design
  energy-efficient distillation trains.

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Heat and power integrationstatement of problem
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Design a heat exchanger network
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Working equations
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Cost evaluation
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Minimum temperature approach
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Minimum utility targets example
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Temperature-Enthalpy DiagramHohman (1971)
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Temperature-Enthalpy composite streams
PINCH
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Temperature interval methodLinnhoff Flower
(1978)
n
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Temperature interval Eliminate Pinch
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Minimum utilities in reversible network DT0
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The pinch depends on the value of DTmin
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Temperature interval eliminate pinch
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Minimum energy requirements

• Minimum from energy balance 0.10 Mbtu/h
• Minimum for reversible network DT0, 0.15
  Mbtu/h
• Minimum for small approach temp DT 10 F -gt
  0.6 Mbtu/hr
• Minimum for large approach temp DT 20 F -gt
  1.125 Mbtu/h

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Lessons to learn

• The value of Dtmin is a compromise between
  capital costs of heat exchangers and cost of
  utilities.
• Any amount of heat introduced above the minimum
  balance will have to be removed by a cold
  utility.
• A pinch indicates the presence of two subsystems,
  one that lacks energy (above) and one that has
  too much energy (below).
• The energy consumption found through the
  Temperature Interval Diagram is the lower bound
  for energy recovery.

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Finding the Heat Exchange Network
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Use heuristic to find matchAlternative I
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Alternative I 7 units