Temperature difference issue in the thermal siphon reboiler of the butane stripping tower
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This post was last edited by chengkang on 2009-11-8 at 10:42. It relates to the debutanizing column of a reforming unit; the bottom of the column is equipped with a horizontal thermal siphon reboiler, with the process fluid flowing through the shell side and the heating steam flowing through the tube side. What I would like to ask is that, under normal operating conditions, the temperature of the material returning to the tower from the reboiler is 123°C, while the temperature of the material entering the reboiler from the bottom of the tower is 126°C; the tower pressure is controlled at around 1 Mpa. What’s not clear is why the temperature of the material after heating is actually 2–3°C lower than before heating. There might be an issue with enthalpy here, but I’m not quite sure; I hope everyone can provide an authoritative explanation. And the material after being heated should be a gas-liquid mixture, right? ! I don’t know whether there is more gas or more liquid. Thank you all.
There is a problem with the setting; the pressure loss is too high, which is equivalent to vaporization due to pressure reduction. As a result, the temperature value that meets your specified vaporization rate conditions decreases
Reply to 2# leiyu85639: Is the compression too high? What is the concept? I think this is related to the temperature measurement point; the outlet of the reboiler is a gas-liquid mixture, and it’s possible that the measurement point does not capture the actual temperature at the reboiler outlet.
Sharing the same view as the third floor, even in a gas-liquid mixture, such problems should not occur. If the temperature returning to the tower is lower than the temperature before it enters the reboiler, what will happen to the thermal balance within the tower? Isn’t it getting lower and lower?
Thank you all for the discussions; to this day I still don’t understand it.
It’s likely a problem with the thermocouple measurements. The material at the bottom of the tower consists of the liquid phase at the outlet of the reboiler, plus an additional layer of liquid phase that flows down from a higher tray, and therefore the temperature at the inlet of the reboiler is definitely lower than that at its outlet. In some systems, such as those used in gas fractionation, the material at the bottom of the tower is nearly pure; in such cases, the quality of this material is not controlled based on the temperature at the reboiler outlet, but rather by the temperature of a sensitive tray located in the middle or lower part of the tower, which is used to regulate the heating power of the reboiler. Therefore, it is necessary to carefully inspect the thermocouples, or pull out the cores of the two thermocouples and replace them on-site.
It’s the issue with the thermocouple measurement position; please check it again.