Reboiler Selection and Design

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• Reboiler Selection and Design

Presented to the Auburn University Dept. of
Chemical Engineering Senior Design Class
Jeffrey R. Seay, P.E. Senior Process
Engineer Evonik Degussa Corporation 19 February
2008
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Types of Column Reboilers
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19 February 2008 Senior Design Class Lecture
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Principle Types of Column Reboilers

• The reboiler to a column serves to provide vapor
  flow up a column, and acts as an additional
  theoretical stage below the trays or packing.
• In general, there are three principle types of
  column reboilers, which will be discussed in
  detail
• -Thermosyphon
• -Forced Circulation
• -Kettle
• Other types include the internal reboiler, but
  these are rarely used in continuous columns and
  wont be discussed here.
• Proper reboiler design is critical to the optimum
  operation of a column!

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19 February 2008 Senior Design Class Lecture
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Thermosyphon Reboiler

• Return piping to the column must be sized for
  two-phase flow.
• Thermosyphons operate based on thermodynamic
  principles, rather than gravity.
• Therefore, design detail is important.
• Thermosyphon operation is simple, but they are
  often difficult to design for a wide operating
  range.
• Proper elevation is critical!

2-Phase Flow Region
All-Liquid Flow Region
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19 February 2008 Senior Design Class Lecture
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Forced Circulation Reboiler

• Forced circulation reboilers are designed to
  operate liquid full.
• Flashing occur as the liquid crosses the control
  valve.
• Valve should be located close to the column
  shell.
• Forced circulation reboilers offer greater
  operational flexibility than thermosyphons, yet
  have a smaller footprint than kettle reboilers.
• Elevation is less critical due to pump and
  control valve.

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19 February 2008 Senior Design Class Lecture
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Kettle Reboiler

• Vapor-Liquid disengagement occurs in the vapor
  space, therefore return piping is sized for
  all-vapor flow.
• Proper elevation is critical to kettle reboiler
  operation.
• Kettles have a large footprint, but require less
  elevation than a thermosyphon.
• Works by gravity, rather than thermodynamics.

Cross Section of Kettle
All-Vapor Flow Region
All-Liquid Flow Region
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19 February 2008 Senior Design Class Lecture
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Reboiler Design Considerations
Cost Comparison of Reboiler Types
Reboiler Selection Flowchart
Thermosyphon
Kettle
Forced Circulation
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19 February 2008 Senior Design Class Lecture
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Reboilers in Aspen Plus
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19 February 2008 Senior Design Class Lecture
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Questions and Comments
Thank you!