Selection of heat source for distillation column reboiler.
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I was wondering if you could advise me on the principles for selecting a heat source for a distillation column reboiler. Generally, low-pressure steam seems to be used; I happened to notice that in some designs, waste heat recovery from the converted gas is utilized. In this way, it is necessary to ensure both the top temperature of the distillation column and the efficiency of cooling the conversion gas – isn’t this requirement too demanding in terms of logic? How should the system be handled when its load is reduced? Do any of you have any relevant experience in this regard?
The choice of heating medium depends mainly on the operating temperature and pressure of your tower. If the operating temperature is too high, low-pressure steam is not sufficient to reach such high temperatures; in such cases, it is necessary to use a higher-grade heating medium, such as medium-pressure steam, high-pressure steam, or heat transfer oil
Regarding the utilization of waste heat, considerations regarding load increases and decreases must be taken into account during the design phase. Generally, two systems are used simultaneously: even when no waste heat is available, original steam or hot oil is still used for heating, thereby providing a means of compensation when waste heat is insufficient. The same principle applies to the condensation and cooling of materials containing waste heat; even if no waste heat is needed for heating the distillation tower, there must still be a way to cool these materials down, which results in increased investment in equipment. Of course, if the device that generates waste heat and the device that utilizes it are part of the same process, then no additional equipment investment is required – when one device reduces its load, the other device does the same as well, eliminating the problem of insufficient heat or inability to cool.
Replying to floor 3: Personally, I think that if conversion gas isn’t used, all that’s needed is to add a low-pressure boiler; waste heat can be used to generate low-pressure steam, which in turn can be used to heat the distillation reboiler. If conversion gas is used directly, there’s an issue during startup, as the converter, acting as a heat source, cannot have a bypass system. It means there is too much stress on the tube side of the reboiler, which can easily lead to a reduced lifespan of the heat exchanger. If the heat exchanger starts leaking, it becomes a serious problem.
4th floor, I don’t know what you mean. Such a setup requires careful planning and the addition of additional equipment. The reboilers in the distillation tower should be operated in parallel, with one using waste heat and the other using steam as a supplement. At the beginning of operation, steam is generally used alone. Of course, an additional cooling device is also needed for the waste heat. When using this system, it’s necessary to consider plans for dealing with leaks; leaks could lead to safety hazards, and in such cases, waste heat must not be utilized in the distillation tower reboilers. Also, how the medium-temperature control system should be operated to ensure stability is something that requires careful consideration; the utilization of waste heat is not a simple issue. Judging from your description, your device isn’t very large, so you might not encounter many such problems; therefore, it’s important to pay close attention during the design phase.
Low-temperature heat transfer water and low-pressure steam are commonly used as heat sources