How to determine the temperature of the heating medium in the bottom reboiler?

Personal opinion: From the perspective of heat transfer, there needs to be a sufficient temperature difference for heat transfer to occur (for example, ten degrees). If this temperature difference is too small, a larger heat exchange area is required; whereas if it is too large, boiling or vibration, as well as coking, can occur

This is a very interesting issue in engineering; don’t focus only on the software requirements – it’s sufficient to follow these principles: 1. The temperature difference should be no less than 5°C ； 2. If there is excess heat, such as waste steam, make sure to make use of it. At this point, a temperature difference of just over 5°C is sufficient ； 3. Use waste steam (condensate) as much as possible, and secondly, excess heat fluid without phase change. Because the heat content of the waste steam (condensate) is high, the area of the reboiler at this time is generally smaller than that in the case of no phase change ； 4. If steam is to be used, there will be no waste steam; make use of the steam parameters of the existing steam boiler as much as possible, in case there is excess steam available ； 5. If you plan to install a new boiler, you can choose the steam specifications freely; in this case, a temperature difference of over 10°C is preferable, though the actual temperature and the cost of the boiler also need to be taken into consideration. Tip: Engineering design should take into account cost savings and energy conservation.

First, it is necessary to ensure an adequate temperature difference, so that a suitable heat exchange area can be selected; too small a temperature difference would result in an excessively large heat exchange area. Secondly, it depends on the properties of the material; for example, excessive temperature differences can lead to coking, polymerization, or decomposition, so the decision is made based on the process requirements. Third, make rational use of energy based on the available heating medium conditions, such as readily available steam or others.

Reply to 3# wiseboy: By the heat transfer temperature difference you mentioned, do you mean the difference between the low temperature of the hot medium and the high temperature of the cold medium, or the average convective temperature difference between the two? Also, what temperature difference needs to be considered to use a floating-head heat exchanger?

1. It is the logarithmic mean temperature difference; 5°C is quite low ； 2. There don’t seem to be many floating-head types for reboilers.

Well, in practical applications, reboilers usually use the simplest type of heat exchanger, which is the shell-and-tube type; floating-head types are rarely used as they involve high design costs and numerous sealing issues. . .

Is a temperature difference of 5 degrees sufficient? I’m also confused about this issue. Some people say that even if the temperature difference is large, it’s still very difficult to increase the temperature further. For example, if the material needs to be heated from 300 degrees to 350 degrees, raising those 50 degrees proves to be extremely challenging. I don’t quite understand why, but the designers on the furnace side say that the smaller the temperature difference, the harder it is to raise the temperature. We plan to use molten salt for heat exchange; the temperature of the molten salt is 450 degrees. Using this temperature to heat oil from 300 degrees to 350 degrees is said to be very difficult, and a large heat exchange area is required to make it possible. Why is that?~

Reply to 8# wufenghang: I’ve also considered this issue, but you can use simulation software to run simulations first, by setting different temperature differences, to see if there are significant changes in the requirements for the heating medium. I’m not entirely sure either; I hope experts can answer this

In my opinion, there should be sufficient temperature difference, heat exchange area, amount of heating medium consumed, as well as the properties of the liquid to be heated and its physical and chemical characteristics