Reboiler calculation
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The last edit to this post was made by The Man in Black with a Knife on 2024-8-26 08:41. There is a device; the reboiler at the bottom of the absorption tower originally used distillation Unit 1 as its heat source. During startup and shutdown, Unit 1 is not operational, and since there is no heat source available, the system needs to operate for a long time. Now, consider adding a steam heat source to the reboiler of the desorption tower, to be used during startup and under abnormal operating conditions. The author uses steam for calculations. Taking this opportunity, the author created a PPT on reboilers, providing a brief introduction to reboilers and this specific example. Let’s learn together*.
This post was last edited by The Man in Black with a Knife on 2024-8-27 20:46. Today, as a newcomer, I presented this PPT at a meeting; an expert then provided comments on knowledge related to reboilers. Many things were learned, which are recorded below for future reference. I hope everyone will discuss more. 1. When the vaporization rate of the reboiler increases, it can be reduced by increasing the tower height, enlarging the diameter of the reboiler outlet pipe, increasing the diameter of the tower bottom, and lowering the height of the reboiler return pipe opening. However, increasing the tower height creates a problem: the pressure generated by the static liquid column at the bottom of the tower increases, and as a result, the pressure at the reboiler inlet also increases. At this point, a certain situation may occur. As the pressure increases, the bubble point temperature of the liquid in the reboiler rises, which affects the choice of heat source. 2. Why is a thermosyphon reboiler “dangerous” when approaching the critical pressure? Under high pressure, the difference between the gas density and the liquid density decreases, which reduces the driving force generated by that density difference; as a result, it is likely that the reboiler circulation will cease. 3. Why is a thermal siphon reboiler “dangerous” in high vacuum? Generally, a vacuum is chosen for the pressure at the bottom of the tower, mainly because the material is relatively heavy and difficult to vaporize; under vacuum, the bubble point of the material is lower, making it easier for it to vaporize to some extent. The pressure generated by the static liquid column at the bottom of the tower causes the pressure at the reboiler inlet to be slightly higher than the pressure at the bottom of the tower, resulting in a bubble point temperature for the material that is slightly higher than that at the bottom of the tower. If the pressure generated by the static liquid column at the bottom of the tower causes a significant increase in the bubble point of the material inside the reboiler, it will result in a very high temperature required from the heat source, making it difficult to select an appropriate heat source. The key is to maintain an appropriate ratio between the pressure generated by the static liquid column in the bottom of the tower and the vacuum pressure there, so that the elevation of the bubble point remains within a controllable range.
Thank you so much for sharing; it’s perfect for reviewing and learning from.
Increasing the outlet diameter of the reboiler is a matter for consideration; it would be possible to increase the inlet diameter in order to reduce the gasification rate