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[process_persia]

Dears,

I have a question regarding the propane reflux pump as attached to this post. as you can see, the pump is protected by minimum flow. I cannot figure out completely the pump configuration so I drew a circle around the parts that seemed ambiguous to me. first, what are those tappings at pump suction? second, what is the difference between nozzles N03 and N08? third, what is the reason for that tapping from top at condenser outlet?

more information that sound necessary: the pump is a canned motor, minimum flow protection via by pass, pump medium: liquid propane returning to depropanizer tower.

Thank you in advance

Attached Files

•  reflux pump.xlsx   1.01MB   70 downloads

[Nikhiln]

Hi,

Your first and third questions are one and the same. This line is called a pressure-equalisation/balancing line (usually seen where there is considerable difference in elevation between the condenser and reflux pump. The most common setups involve placing the condenser at some height above the reflux drum (to facilitate gravity flow into the drum) and the drum itself much above the reflux pump to satisfy NPSH requirements. This results in considerable elevation difference between the condenser and pump. Consequently, the head gained by this elevation difference results in pressure at pump suction being higher than condenser outlet. To overcome this, the balancing line is provided. What it does is that it makes the pump suction see the same pressure as the condenser outlet. Then the only pressure gradient is gravity, which allows flow downwards. Infact, thats why the valves on those lines are locked open. If you close those valves, there will be no flow to the pump suction, since drum will be at lower pressure than pump suction. It becomes all the more critical in vacuum applications.

For your second question, I am not sure about this explanation I am giving. I hope others will validate my thoughts. Nozzle N03 is clearly for minimum circulation. (by the way, it shouldnt be called bypass, recirculation is more appropriate). The other line (1") from the NRV, is actually what I believe to be a NRV bypass line that is used to keep the standby pump in hot standby (in this case, cold temperature standby actually). The standby pump casing is generally kept at the same temperature as that of the running pump, by providing a bypass across the NRV. Even if the suction valve is kept open, stagnation could cause the temperature of fluid to drop or rise , as the case may be. The way this has been represented in this drawing is pretty confusing, since it seems as if the line is originating from the NRV body, though thats not the case usually. The only thing I couldnt figure out is why it needs to be connected back to the drum via nozzle N08. That is why I am not sure about this logic that I gave. Hope others will clear it for me.