Questions regarding forced-circulation reboilers seeking answers.
Thread Content
1. Regarding the vaporization rate of forced-circulation reboilers, Sun Lanyi’s book \"Heat Exchanger Process Design\" states that it is <1%； A forced-circulation reboiler is used because the temperature rises due to pump pressure but does not exceed the boiling point; thereafter, a flow-limiting orifice plate or control valve is installed near the end of the tower to reduce the pressure and facilitate vaporization I’ve seen that in some processes, the material pipeline after a forced circulation is empty; obviously, that material must have vaporized in the reboiler. Can’t understand. 2. For the head of a pump used for forced circulation, my understanding is that it is required to move the fluid from one bottom of the tower to another; all that’s needed is to overcome the pressure losses in the pipes and heat exchangers. Additionally, this pressure ensures that the material stays in a liquid state and does not vaporize in the reboiler, thereby improving the heat transfer efficiency. So, isn’t a very high head necessary? But I saw some people on the forum saying it’s very high, even up to 2.5 MPa; I don’t understand why 3. In the process system design of the distillation tower forced-circulation reboiler, is it stated that forced-circulation reboilers are suitable for high vacuum? There is also Sun Lanyi’s \"Process Design of Heat Exchangers\", which is suitable for thermosensitive materials (below 1300 Pa). What is the reason? I’m a complete newbie; I hope the experts here can guide me.
Is there such a process where, although a pump is used, the vaporization rate is that of a thermosyphon reboiler? I’ll check the pipe diameter – the difference between the outlet and inlet of the reboiler is quite large. Moreover, there is no throttling element at the reboiler outlet, so the pump should serve only to provide the driving force for circulation.
It would be best to include a small flowchart; it’s easier to understand things when looking at a diagram. A rough understanding suggests that the liquid on one side of the reboiler is forced to circulate in order to cause the fluid at the other end of the reboiler to evaporate, right? Evaporation requires the absorption of heat, which is achieved by cooling the liquid that is in forced circulation; heat exchange helps to maintain a constant temperature of this liquid. The liquid that is being evaporated is continuously replaced as it evaporates. I’m not sure if this is the case; just for reference. It is recommended that, until it is clear what is going on, it is best not to refer to things using personal names. This isn’t anything high-tech. Since it is a device in operation, there is a reason for its existence. Before understanding it fully, it’s best to focus on one’s own comprehension. With all due respect.
Comments related to the questions I asked are acceptable, but the claim that I’m referring to things using my personal name is unacceptable. It’s completely normal to say that a book was written by Sun Lanyi – just as it’s normal to mention that a novel was written by Gu Long or that a poem was written by *,; it’s simply a way of indicating the source, showing that what I say is based on evidence. I just have some questions about the differences between the methods described in the book and those used in engineering. In practice, many reboilers equipped with circulation pumps have very large vapor-phase pipes, with a vaporization rate of around 20%; moreover, no throttling device is installed at the end of the reboiler where the material flows. In books and literature, however, the vaporization rate is much lower, with flow-limiting orifice plates placed at the end of the reboiler where the material flows. I believe that the forced circulation pump in engineering merely serves to provide a driving force, and the vaporization rate should be designed based on that of a thermosyphon reboiler.
In engineering, many reboilers are equipped with circulation pumps, but the outlet diameter of the reboiler is quite large; I estimate that the vaporization rate is around 20%, which is similar to that in a thermosiphon system. In books and literature, for forced-circulation reboilers, this value is <1%, or the vaporization rate after entering the reboiler bottom is 3%~8%, or the temperature difference is 10°C. I conclude that the low vaporization rate is due to the high pressure at the reboiler outlet. The high pressure is due to the action of the throttle orifice plate. Also, I mentioned that Sun Lanyi’s books do not deal with matters using personal names, just like Gu Long’s novels or Zhu Ziqing’s essays. It’s a normal thing. I mentioned the name because my source is reliable; after all, Sun Lanyi is an authority in the field of heat exchangers.
It’s a quite standard process. My questions are: why is it a forced-circulation reboiler? Why isn’t there a throttle orifice at the reboiler’s outlet? Why is there such a large difference in the diameters of the inlet and outlet pipes of the reboiler? The vaporization rate must be greater than 1%; should the circulation volume be calculated based on the vaporization rate of a pump-plus-thermosyphon reboiler?
If the diagram is rotated upside down, it seems to be a distillation tower, or perhaps a washing tower or an absorption tower. The function of this reboiler is to generate the required rising vapor within the tower, thereby enabling mass and heat transfer with the liquid flowing downward. Part of it should be taken as the product, while another part is forced to circulate back to the reboiler to be vaporized, serving as rising steam. I’m not sure if this is the correct way to understand it; I’d like to hear what professionals think. If this diagram is placed in this position right now, I really can’t understand it. For reference.
It seems you are learning the principle of this diagram from a designer’s perspective. If that is the case, it is recommended to understand it from a macroscopic perspective. Focusing too much on microscopic design parameters can backfire. It’s best to focus on the matter, not the person. I’m just giving a suggestive reminder; if you think it’s appropriate, go ahead and stick with it. I think it’s best not to contact anyone or refer to any relevant standard theories until the issue is fully understood. From this diagram, it’s clear that what’s presented here is something well-developed and standardized; one just needs to find a way to understand it. With all due respect.
This post was last edited by Wang Genrong on 2020-4-18 09:24. This image looks really awkward; is it upside down? Is that E211 a top condenser or a bottom heater?
Firstly, after adding a pump, your flow rate increases significantly, while the amount of gasification does not change much, resulting in a very low gasification rate； Secondly, since the material is close to its boiling point, the pump needs to take cavitation into account; I’m not entirely sure about the details. Thirdly, forced circulation is used to improve fluidity and reduce the adhesion of coked materials, so it is suitable for heat-sensitive materials, and heat-sensitive materials are generally processed using high-vacuum distillation
What is the purpose of keeping the forced circulation gasification rate at <1%?