Positive suction head

[21121956]

Hello everybody:

I would like to hear comments or to find documents, papers or a site in the web, where the subject of the suction pipe of a pump (movable pipe submerged in a storage tank) is approached.

If we make an analogy and we suppose that the tube is like the arm having the closed fist, the connection between the tube and the entrance of the pump is in the elbow (by a sort of swivel or pivot joint) and the fist is where the liquid enters to be pumped.

The fist (the intake of the submerged pipe) is always in the free surface of the liquid and travels along with it until the level reach an almost horizontal height.

When the tank is full of liquid, the submerged pipe ("the arm") is almost in vertical position.

Thanks a lot in advance for your advice and/or comments.

 

[unclesyd]

If I may ask why would you want such an arrangement?

 

[21121956]

Hello everybody:

The liquid to be pumped out is heavy fuel oil (Bunker C or distillate Nº 6) with a viscosity of around 600 cSt @ 50º C. This fuel oil normally has important amounts of impurities and water as well.

In order to obtain some settling effect, the fuel is stored in the tanks at 60÷65º C (with the help of steam heaters). With that floating intake, the idea is to send clean fuel oil to the transfer pumps, avoiding to suction fuel from the bottom of the tanks.

 

[vpl]

21121956

1) You would need to calculate the NPSH with the suction hose at its lowest level, no matter what.

2) You would need to ensure that the suction hose would always drop as the fuel level dropped, or you could end up with situations where the hose was above the fuel level (not a good thing). This would seem rather hard because the hose can't be buoyant (or there would be air not fuel in the hose) and it can't be too heavy (or it would just sink to the bottom).

3) You would need to ensure the hose "retracted" smoothly without developing any kinks or bends. Otherwise you might end up with a voided suction line even though there was plenty of fluid in the tank. (also not very good).

4) You might want to consider whether a more feasible design would be using a fixed standpipe located off the tank floor by some reasonable amount.

Patricia Lougheed

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[unclesyd]

We have three tanks for #6 oil storage and I have noticed that anything in contact with the material slowly develops a coating which could affect the buoyancy and operation of the swing arm.

Another problem would be if the inlet is close to the liquid level there is strong possibility of creating a vortex, even with fuel oil.

As posted vpl I would look to taking the suction off the bottom for normal operations and have a nozzle at the bottom to drain the tank.

On our fuel oil tanks we have one with a shallow sump to take care of the water and the other two have small nozzles at the bottom to remove the water. All our tanks have bayonet heaters that are 2 feet off the bottom. The suction nozzles are approximately 90 degrees from the heaters and are at the same level.

 

[BigInch]

Don't put the nozzle all the way at the bottom, that lowest volume will have the crud and water.

There should be a drain in the bottom of the tanks to remove the settled water after a sufficient volume of water has accumulated.

Your nozzle should be above the highest allowed water level + a vortexing safety allowance.

http://virtualpipeline.spaces.msn.com

 

[21121956]

Hello everybody:

Thanks to all for your comments. With the ideas that you have given to me, I will reinforce a proposal to the direction of the company, in order to consider a change in the decision making.

At its moment, I will tell you what was the final result.

Once again, thanks.