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Atmospheric Tank Incoming Pressure

Atmospheric Tank Incoming Pressure

Atmospheric Tank Incoming Pressure

(OP)
Hello Guys,
I have a tank with height 40 feet and 55 feet in Diameter. Currently we want to connect pump discharged line to this tank. Based on our reading on the pressure gauge near the the existing outlet of the discharged line, the pressure is about 70 Psig. What will be happen to my tank if I connect the pump line to my new tank with such 70 Psig incoming pressure ..??? We appreciate all of your help

RE: Atmospheric Tank Incoming Pressure

Well the tank will fill up with whatever you are pumping and at the same time the air inside the tank will have to displace via the overflow or whatever is open. However if the pumping rate is such that the "open" branches cannot accommodate the displaced air then you have a problem as the tank will become pressurised and could go "bang". What I really saying is you need to do the calcs to ensure that teh tank will not become overpressurised. Simples really!!!

RE: Atmospheric Tank Incoming Pressure

Depends on the diameter of the incoming line, but with that discharge pressure you may also want to check the "thrust" nozzle load where it is attached to the tank wall for excessive tank wall stress and deformations.   

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RE: Atmospheric Tank Incoming Pressure

If you have any reasonable outbreathing venting capacity at all in the tank, I would not expect that the affected tank nozzle will ever see a pressure higher than 20 psi, 17 of which would arise from static head alone at tank high level.  Your concern might not be tank inlet pressure so much as pump run-out (if centrifugal).  Again, your outbreathing capacity in volumetric flow has to be well in excess of your inlet liquid volumetric flowrate.

Regards,

SNORGY.

RE: Atmospheric Tank Incoming Pressure

(OP)
Dear All,
Tanks for your information. In my new line we will instaal 16 inch pipe line incoming to the atmoshperic tank i said before. The incoming flowrate and outgoing  flowrate from the tank will be same about 400,000 bwpd. Is it allowed to have such 70 Psig to the tank..??? If yes why..??? Sorry I'm still confuse. If we put 70 Psig on the tank inlet, does it will create water jetting on the tank..???

RE: Atmospheric Tank Incoming Pressure

I can only guess what you are trying to ask.

I assume that the 70 psig is the shut-in pressure of a valve adjacent to the tank.  As such, the pressure adjacent to the tank will be much less when the line is flowing.  Take a look at the exit loss for the flow to determine the pressure adjacent to the tank.

Otherwise, if you are flowing into the tank with the exit loss being 70 psig, you have some problems.  

How do you come up with the 400,000 bbl/day?  Is this a calculated number from a hydraulic analysis?  If so, you should be able to calculate the velocity of the fluid entering the tank and then determine the exit loss.  

Please provide the calculated flow rate and/or the velocity of the stream entering the tank.

    

RE: Atmospheric Tank Incoming Pressure

What will happen if you hook up your garden hose to the tank? It has roughly the same pressure...

A 16" line will simply have a higher flow rate.

If you are somehow concerned about the fluid impinging on the opposite side... use an inlet distributor / diffuser.

jt
 

RE: Atmospheric Tank Incoming Pressure

I hope I don't muddy the water with my comments.  You stated that your incoming flow will be 400,000 BPD.  You can only know that if the pump is positive displacement or if the flow is controlled with a control valve.  If the pump is positive displacement, then it will produce this amount of flow at any pressure. When you hook it up to the tank, it will run with about 20 psi discharge and produce the flow it was designed to produce.

If the pump is centrifugal, then you have two options.  Either you provide a control system to pinch the pump back to the target flow rate or you let the pump run out on the curve which will deliver much more flow than you want.  I assume that either the incoming or outgoing flow would be controlled to maintain the level in the tank.  But, there are a lot of different control schemes that could be used.   

The important point is this:  If you reduce the pressure on the discharge of a centrifugal pump from 70 psig to 20 psig, the flow will increase based on the pump performance curve.  If you don't want the flow to increase, you have to rerate the pump, or take up that extra pressure drop somewhere else.  I tend to assume the use of a control valve to take up the pressure drop.  Others might lean toward a speed reduction, impeller diameter change or a piping change that would result in the same pressure reduction.  
 

Johnny Pellin

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