Questions regarding the process of the atmospheric pressure tower condenser, reflux tank, and reflux pump
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May I ask, regarding the process of the top condenser, reflux tank, and reflux pump in an atmospheric pressure tower: 1. How is the outlet temperature of the hot stream from the top condenser determined and set? From a design and operational perspective, should the hot stream outlet stream from the tower top condenser always be subcooled? Otherwise, flashing will occur due to heat absorption, operating condition fluctuations, and other reasons? If it is indeed supercooled, by how many degrees Celsius is a supercooling amount generally appropriate? 2. For atmospheric pressure columns, the condenser and its outlet should be under vacuum conditions ； Since a liquid cannot exist independently, even in a supercooled state, there is always a saturated vapor pressure at a certain temperature; are the outlet pressure of the condenser and the operating pressure of the return tank therefore that saturated vapor pressure? 3. Is the return pump downstream of the return tank prone to cavitation? How can cavitation be avoided? Please help me find an answer, thank you!
I don’t understand what you mean by 1 subcooling? What comes out of the top of the tower is a gaseous phase, which is a saturated gas; after condensation, it becomes a saturated liquid. Subcooling is not understandable in this context. The condenser reflux should also be at the bubble point. If further cooling of the product is required, another condenser can be installed on the product flow path. I don’t understand what subcooling means, and I also don’t see how you arrived at the conclusion that the outlet of the atmospheric pressure tower is in a vacuum state. It seems you don’t understand. Vapor condensation does indeed result in a decrease in pressure, but you need to realize that this is a continuous process – gas is continuously fed in, so how could there be a vacuum condition? It’s not negative-pressure distillation after all. 3. Saturated liquid reflux certainly prone to cavitation; for details, you can refer to the pump’s cavitation head design, and it has nothing to do with whether it is a reflux pump or not
The last edit to this post was made by chemengineering on 2016-7-13 at 17:53. 1. I think that whether it’s the dew point or the saturation point, it’s just a single value, not a temperature range； The bubble point reflux seems good in theory, but in actual production, is it difficult to ensure that cooling and condensation occur exactly at the bubble point? And it’s unlikely to condense into a two-phase gas-liquid flow, which would be very troublesome ； From this perspective, it is more convenient to cool below the bubble point, that is, to supercool ； Operation and control are both very convenient. I don’t know; what is an appropriate degree of subcooling for the material? 2. It seems this is indeed something I haven’t figured out ； In this case, the outlet pressure of the hot fluid stream from the condenser is still equal to the inlet pressure minus the pressure drop ； Additionally, do the heat exchanger calculation software HTRI and EDR take into account the pressure drop caused by condensation during calculations? 3. Recirculation pumps used to transport saturated liquid are prone to cavitation.
What you’re saying now is all speculation; you should ask the people who were there what actually happened. It’s useless to imagine things like this. You say it’s unlikely to cool down to the bubble point for feeding, but you should know that many feed streams are also at the bubble point; according to your reasoning, that wouldn’t be very accurate either, right? The condensate water in the reboiler is also a saturated liquid, so what you say isn’t correct either, right? I think you shouldn’t rely on assumptions; either you need practical experience or a theoretical foundation. I suggest you start by reading books on the principles of chemical engineering