CHAPTER 9

• Reboiler


  Heat exchangers typically used to provide heat to the bottom of industrial distillation columns to generate a flux of vapor
• Reboiler


  • Forced circulation
  • Thermosiphon, natural circulation
  • Kettle type
  • Internal Reboiler
• Boiling


  Liquid boils at a temperature at which its vapor pressure is equal to the pressure of the gas above it
• Choice of reboiler type

  • Nature of the process fluid; viscosity and fouling
  • Operating pressure, vacuum or pressure
  • Equipment layout
• Forced Circulation Reboiler


  1. Fluid is pumped through the exchanger

  2. Vapour formed is separated in the base of the column

  3. Disengagement vessel needed if used as a vaporiser
• Vertical or Horizontal Thermosyphon

  1. Evaporation taking place inside tubes

  2. Evaporation taking place inside shell
• Vertical or Horizontal Thermosyphon


  • Less susceptible to fouling
  • Additional height required
• Kettle Reboiler


  1. Boiling takes place on tubes immersed in a pool of liquid

  2. No circulation of liquid through the exchanger
• Kettle Reboiler


  • Also called submerged bundle reboiler
• Internal Reboiler


  Boiling takes place in the pool of liquid at the bottom of column
• Internal Reboiler


  • Simplest
  • Limitation by the size of column
  • Mounting problem
• Fired Heater


  Fuel gas and/or fuel oil is burned in a furnace to heat and vapourise the bottom liquid
• Fouling mechanisms


  • Particulate fouling
  • Crystallization fouling
  • Biological fouling
  • Chemical reaction fouling
  • Corrosion fouling
• Pool boiling/nucleate boiling


  Boiling in a pool of liquid such as in a kettle-type reboiler or jacketed vessel
• Convective boiling


  Vaporizing fluid is flowing over the heated surface, heat transfer by forced convection & nucleate boiling, e.g. forced circulation or thermosiphon reboilers
• Pool Boiling


  1. Foster-Zuber (1955) equation to estimate heat transfer coefficient

  2. Mostinski (1963) equation for convenience when fluid properties not available
• Critical Flux


  Design and operating should be below the critical flux, important to check
• Film Boiling


  Heat transfer controlled by conduction through film of vapor, Bromley (1950) equation
• Advantages and disadvantages of reboilers