Pressure of stream to a tank

[shahyar]

Assume we have a tank with 5 meter water in it(atmospheric tank). The minimum pressure of an stream to get into the tank is (roughly) 50 KPag.
What is the MAXUMUM allowable pressure of such stream? Can we send an stream with pressure of (eg)1000 KPag into it?

Thanks for your responses.

 

[sshep]

shahyar,

If the tank is clear liquid, then the back pressure at the tank base will be 50kPa as you reason. Note: if the tank is well aerated, then it could be somewhat less. In any event this pressure is fixed- your supply pressure does not change this boundary condition.

If you start with 1000kPa air, then the flow of air into the tank will be determined by the piping and valve design which establishes a pressure drop vs flow relation (the system head curve). The airflow into the tank will be that required to use up the pressure drop (1000-50). You can control the airflow to some approximate value by sizing the pipe for the required pressure drop (950kPad) at design airflow; by including a control valve to control the air flow to a setpoint by using up the excess pressure drop; or by variable speed fan that will change the flow by varying the inlet pressure to the piping feeding the tank.

I think that once you understand the relationship between flow and pressure drop, the answer to your question will be clear.

best wishes,
Sean

 

[MJCronin]

Shamere,

The question you are really asking is about the venting capacity of the atmospheric tank. Is it truly vented to the atmosphere, and if so, what is the size of the vent ?

When you deliver a high pressure stream into the tank, when the stream hits the liquid in the tank there will be turbulence and a drop in pressure. There will be a forced venting from the tank. The tank may have to be strengthened to sustain such an event.

In the USA, we have API guidelines that describe the sizing of the tank and vents for such an event.

Where are you and your tank located ?

-MJC

 

[DeltaCascade]

Your concern is likely with superheat of the steam. If the steam does not condense in the short rise of 5 m, it will vent. For safety, assume no condensation as a first approximation, at least, regardless of how much sparging and mixing you may do.
Also, once the water gets to boiling, all the steam will vent, and you will even generate additional steam (per enthalpy balance).
So, yeah, potential for dangerous situation as the tank is not a pressure vessel.
Perhaps steam pressure let down and desuperheat is required for that 1000 kPa steam, before it sees the tank.
Good luck...

 

[jte]

Delta-

The OP spoke generically about a process stream. Steam is not necesserely the fluid he's asking about...

jt

 

[sshep]

Gentlemen,

Looking back I can see no reason why I thought we were sparging air into the tank and started us off on the wrong track. I thought this a rather novice question about pressure flow relationships. Still I am puzzled how a general statement of pressure got us into vent rates, tank strength, and steam superheat.

MJC, even when designing jet mixing using high pressure kinetic energy nozzle, I don't recall ever ever having to increase the vent size. Presumably this is additional energy input to be theoretically handled in the same manner as thermal breathing, but I have never even seen calculations that took the kinetic energy of the feed stream into account. Rather I have seen velocity and submergence guidelines, grounding for static electricity, and nozzle reinforcement. If you have some API guidelines for jet mixing then I would like to get a refresher.

best wishes,
sshep

 

[JStephen]

API-2000 includes allowances for inflow, but it doesn't matter what the velocity is- just volumetric flow rate is used. If blowing air or any gas into a tank, it would be the volume at atmospheric pressure that was needed.

The question is a little misleading. If you take some sort of high-pressure line and attach it to an atmospheric tank, you won't have that high pressure at the tank inlet- you'll have a (presumably) high flow rate and a massive pressure drop through the piping and nozzle system. There is not a specific limit on the pressure where it enters the tanks.

 

[shahyar]

Sorry I was away for long time.
Thank you all for your time.
Yea, as SSHEP said my question was a simple question.
What will happen if I introduce 500 KPag WATER into the tank.
I think the answer is in last sentence of JStephen: "There is not a specific limit on the pressure where it enters the tanks."
I feel he is completely right:"If you take some sort of high-pressure line and attach it to an atmospheric tank, you won't have that high pressure at the tank inlet- you'll have a (presumably) high flow rate and a massive pressure drop through the piping and nozzle system."

Thanks all again

 

[mbeychok]

shayar:

It seem to me that you have not given us enough basic information:

1-- The word "tank" describes a great many different types of tanks. Is it a vertical, cylindrical tank with a flat bottom and a cone roof? And does the roof have a vent line to the atmosphere or to somewhere else?

2-- If not a tank as decribed above, describe the geometry of your tank.

3-- What is the design pressure of the tank?

4-- Does the vent line (if there is a roof and a vent) have a pressure control valve or not?

4-- If the tank has a roof, does it also have a pressure relief valve of any sort?

It seems to me that without the above information, it is virually impossible to answer your question accurately.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[jeap]

"Assume we have a tank with 5 meter water in it(atmospheric tank). The minimum pressure of an stream to get into the tank is (roughly) 50 KPag.
What is the MAXUMUM allowable pressure of such stream? Can we send an stream with pressure of (eg)1000 KPag into it?

Thanks for your responses,"

May be there is a misconception in some comments from above. In order to make clearer my explanation let's assume that:

1.- You have a source of pressure that will mantain 1000 KPa after you open the valve to feed the tank.

2.- You have a steel line of, say, 4 in diameter to feed the tank from the source located 100 m away.

3.- Consider water as the fluid.

Calculations will show that flowrate through the line is about 320 m3/h and velocity is abt 11 m/s, very high, and you problably observe vibration and some noise in the line. That's the velocity you fluid enters the tank and may be it generates a high turbulence in the tank (depending on the size) but, there is no other problem unless that the tank can't evacuate a equivalent flowrate of gas (air) through a vent valve, in such a case the tank could be overpressurized to a value of pressure that allows to evacuate the gas on the top. If this value of pressure is higher than the design pressure of you tank you have a problem....

Thus you have to calculate the flowrate for you specific case and see what happens. Remember always conceptualize flow problems in order inverse to the direction of flow, I mean consider that your main condition is the pressure at the point of discharge.

Regards,
jeap

 

[pipehead]

Keep it simpleer yet. The pressure in the tank is just that, something is keeping that presure ther and its ability to relieve the pressure sets what will happen when a stream is added. NEXT, you open a valve, that valve controls the pressure on the stream until a point where the thing on the tank takes over.

Simply, the maximum pressure on a stream entering the tank is infinite, until we hit limits that the OP didn't specify, almost, its atomospheric pressure and no limits so I'd assume a tank with a 1KM diameter open top..

 

[jeap]

Pipehead,

Sorry, but I completely disagree with the concepts you wrote in the last paragraph.

What do you mean with infinite pressure?

 

[mbeychok]

Pipehead:

You "would assume an open tank with 1 KM open top"?? Did you mean a 1 kilometer(km) open top??? Wow!!!

Why should we assume anything? The original poster (OP) has already been asked to provide the shape of his tank, whether it has a roof or an open top, whether or not it has a vent, and whether or not it has pressure controller on the vent (see my previous message above). He has chosen to not respond. Until he does, there is absolutely nothing to gain by continuing this thread based on guesses and assumptions. It is a waste of time.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[pipehead]

OK, the tank is completely closed, in any case, keep it simple, can the OP send a stream to the tank with 1000Kpag, it doesn't matter, the only thing that matters is the tanks outlet (if any). You could pump up the inlet stream to 100,000 Kpag, but the system will always get to whatever the tank outlet will allow.

The OP didn't say what the 5 meter was depth, width, diameter, just atmoshereic. If the tank had 1mm hole to the atmosphere, then once the valve was opened, the pressure would rise quickly to the supply pressure behind the valve. If the tank had 1 KM opening, no matter what pressure that was on the line, the tank pressure stay at atmosheric pressure, even if the feed line was 1 meter in diameter.

This reminds of a fliuds test I took, the question was, what is the pressure on top of the fluid in a tank that was opened to the atmosphere. There were pumps and lines and valves and filters all drawn going into the tank. I looked at it, wrote 14.65 psig and walked out of the class and waited 10 minutes before the next person. Only 3 of us got it right and the other two did all the head loss, pump junk before they realized it.