The reboiler for this distillation column is a thermosiphon reboiler with stainless steel boiling tubes and a glass shell. This reboiler mimics an industrial scale distillation reboiler in terms of its design, boiling heat transfer, and liquid level control. Process steam with regulated pressure and controlled flow rate, enters the bottom of the reboiler and is evenly distributed throughout 18 vertical condensation tubes. The steam condenses onto the inner wall of the tubes, and the heat of condensation transfers to the outer wall of the tubes by conduction. The outer wall temperature is typically very close to the steam temperature. The liquid on the shell side of the reboiler evaporates and vapour bubbles form at the surface of the heating tubes. These vapour bubbles float and coalesce to form bigger bubbles at the top of the liquid level. It is important to note that the boiling side of the reboiler is a mixture of liquid and vapour bubbles, while the right-hand side of the loop only takes liquid from the column, which is slightly denser. This density difference drives liquid circulation in the reboiler, resulting in a uniform concentration and boiling condition in the reboiler without the need for forced circulation.
The reboiler operating conditions are closely related to the distillation column performance. For a specified distillation performance, the liquid flow stream coming into the reboiler and the vapour flow that needs to be generated are specified. The boiling rate is determined by heat transfer calculations using the steam temperature and flowrate.
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