Regarding the bottom reboiler issue
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The bottom reboiler of the fractionation unit in my company is heated by steam. When the temperature is low, even with the steam control valve fully open, the temperature doesn’t rise; however, by closing part of the manual valve located after the control valve, the temperature does increase. What could be the reason for this? Logically, the larger the hand valve is opened, the greater the steam flow and the higher the temperature.
Mainly, the steam does not condense, and its heat of vaporization is not released.
I agree with the view from the second floor: the insufficient capacity of the steam trap or flash tank prevents an increase in the amount of heat supplied by the steam
Is that steam flow control valve located on the steam inlet pipeline or on the condensate outlet pipeline? If it is a steam inlet pipeline, there must be non-condensable gas accumulated on the steam side; the total pressure inside is high, but the steam partial pressure is not high. Turning up the steam valve doesn’t have much effect (but it also shouldn’t be turned down, as that would increase the heating capacity). It can only be said that it’s more or less the same.) In the case of condensate pipelines (I’ve seen many such systems, where the phase-change heat transfer area is controlled by the condensate level, thereby indirectly controlling the amount of steam consumed), it’s possible that if the valve is too large, the condensate level gets emptied, and the pressure inside drops too low; as a result, a sufficient temperature difference for heat exchange cannot be established. Once the liquid level is adjusted lower, the pressure on the steam side will be relieved.
The temperature of saturated steam is directly proportional to its pressure; if the temperature doesn’t rise, then it’s certain that the pressure in the steam pipeline won’t increase either. Another possibility is that condensate water in the steam pipeline isn’t removed in time, which also causes the temperature to drop
Current reboiler designs make use of the latent heat of steam; when a large amount of steam is available, only the sensible heat is utilized, and the latent heat remains unexploited. As a result, the boiling cannot be intensified when the flow rate is increased, since the latent heat of steam is much greater than that of equivalent sensible heat. I don’t think this type of reboiler is suitable for use in places with strict temperature requirements, as it’s difficult to control the latent heat.