Reboilers and Reboiler Type Selection (with PDF)

What is a Reboiler

Reboilers are a typical heat exchanger that produces vapor to drive fractional distillation separation. In classical fractional distillation services, all the vapor to drive the separation comes from the reboiler. (Alternatively, externally generated vapor, feed preheat, or inter-reboiler systems may be used). Proper reboiler operation is vital to effective distillation.

The selection of the proper type of reboiler for any specific service is the most difficult job of reboiler design. Reboilers normally are shell-and-tube exchangers that heat up the fractionation column fluid utilizing the heat transfer from steam. Specific services may use other specialized designs including stab-ins, plate-fins, spiral-plate and others. The purpose here is not to go into the design details of each specific type but rather to examine the selection criteria that favor one configuration over another. Since shell-and-tubes are so common, most of the discussion focuses on them but some factors favoring other designs are covered as well.

Factors influencing Reboiler Type Selection

Many factors influence reboiler type selection. In the end, all these factors reduce economics. Every plant will weight the trade-off between these factors differently. No one-size-fits-all selection exists. Major factors include:

  • Plot space available
  • Total duty required
  • The fraction of tower liquid traffic vaporized
  • Fouling tendency
  • Temperature approach available
  • Temperature approach required

Reboiler Configurations

All of the above-mentioned factors affect the desired configuration of the Reboiler. The major configuration selections include:

  • Forced versus natural circulation
  • Tube side versus shell side vaporization
  • Once-through versus process recirculation
  • Single-shell versus multiple-shell systems
  • Vertical versus horizontal orientation
  • Stab-in bundles
  • Other types

Figures 1 to 4 shows common types of reboilers. Figure 1 shows two horizontal, shell-side boiling configurations. Figure 1A is a recirculating thermosyphon. Figure 2A is a once-through thermosyphon. Figure 2 shows vertical configurations. Figure 2C is a tube-side boiling configuration with the once-through flow and Figure 2D is a shell side boiling recirculating thermosyphon. Figure 3E shows a kettle reboiler and Figure 3F shows a forced-circulation reboiler. Figure 4G illustrates a stab-in bundle and figure 4H shows a forced-circulation, fired heater. Table 1 includes the major factors in making an exchange system choice.

Horizontal Reboiler
Fig.1: Horizontal Shell Side Boiling Reboilers
Vertical Reboilers
Fig. 2: Vertical Reboilers
Flooded bundle reboilers
Fig. 3: Flooded bundle reboilers
Stab-in and fired heater reboilers
Fig. 4: Stab-in and fired heater reboilers

Reboiler Type Selection Table

 FactorFavored typesDisfavored types
Low bottoms product fraction compared to boil-upRecirculating
Kettle
Once-through
High bottoms product fraction compared to boil-upOnce-throughRecirculating
Low relative volatility systemsRecirculating 
High relative volatility systemsOnce-throughRecirculating
Large exchanger size or high duty requirementsHorizontalVertical
Small exchangersVertical
Stab-in
 
Leaks hazardous or difficult to deal withStab-in 
Exotic materialsStab-in 
Tight temperature approachSpiral-plate
Plate-fin
Shell-and-tube
Solids presentKettle
Spiral-plate
Plate-fin
Thermally unstable productsRecirculating (no baffle)Kettle
Once through
Tight plot planVerticalHorizontal
Ample plot planHorizontal 
High temperaturesFired heaters 
High heat fluxesForced circulation
Flooded bundles
Natural circulation

Other systems in addition to the ones shown here are also possible. Of course, every system’s final choice will depend upon specific design details involved. Many systems have specific characteristics that favor designs that might not be immediately apparent.

Few more resources for you…

Piping Design and Layout
Piping Stress Analysis
Piping Materials
Piping Interface

Further Studies

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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

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