Evaporative Crystallization with Recycle

This Demonstration shows mass balances for an evaporative crystallization process. A 60% potassium chloride/40% water feed is mixed with a recycle stream and fed to an evaporator, which evaporates water and increases the KCl concentration in the exiting solution. This solution enters a crystallizer and filter. A filter cake of KCl crystals and a portion of the saturated KCl solution are removed from the crystallizer and filter. The rest of the KCl solution is recycled and mixed with the fresh feed. Use sliders to set the fraction of crystals in the product stream, and the temperatures of the evaporator and crystallizer/filter. The solubility of KCl increases linearly with temperature.

SNAPSHOTS

  • [Snapshot]
  • [Snapshot]

DETAILS

Overall material balances
= mass flow rate of fresh feed (kg/h)
= mass flow rate of water exiting evaporator (kg/h)
= mass flow rate of solid KCl crystals exiting the crystallizer and filter (kg/h)
= mass flow rate of slurry exiting the crystallizer and filter (kg/h)
= mass fraction of water in fresh feed
= mass fraction of KCl in saturated solution
= mass fraction of water in solution exiting crystallizer and filter
Material balance around crystallizer and filter
= mass flow rate of solution exiting evaporator (kg/h)
= mass flow rate of recycle (kg/h)
= mass fraction of KCl in stream exiting evaporator
= mass fraction of KCl in solution exiting crystallizer and filter
= mass fraction of KCl in recycle stream
Material balances around mixing point
= mass flow rate entering evaporator (kg/h)
= mass fraction of KCl in fresh feed
= mass fraction of KCl in stream entering evaporator
Material balance around evaporator
Dependence of solubility on temperature
= solubility of KCl in 100 kg
= evaporator operating temperature (°C)
= solubility of KCl in 100 kg
= crystallizer and filter operating temperature (°C)
Note that and , where is the stream.
View the screencast video at [1] for more practice with material balances on a crystallizer.
Reference
[1] Crystallizer Material Balance with Recycle [Video]. (Oct 29, 2013) www.youtube.com/watch?v=Dnfgc4_OFhI.
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