Booster for Positive Displacement Pump?

[eugen25]

Gentlemen, first of all I would like to salute everybody and to express my appreciations regarding this Forum. I’m a poor beginner, so, please, be patient with me. Currently, I’m involved in a concept regarding the transfer of oil from a tank to a storage area far away from our tank. I suggested a twin screw pump (positive displacement) which can provide the required characteristics (68 m3 @ 100 bar), obviously, with a VSD. The process guys jumped on me, saying that booster pumps are a must in such applications. Is it correct? And if it is correct, what type of pump should I choose for booster, because I don’t think a centrifugal one is recommended. And if it is recommended, what should be the characteristics for the booster pump(s)? The shaft power required by the twin screw pump is 400kW. Can anybody advise about the motor characteristics V / kW as the electrical guy is arguing with me.
Thank you very much in advance, and I hope to hear from you soon.
Eugen25

 

[JJPellin]

I do not understand your questions. Someone believes that you cannot run a positive displacement pump in any situation without a booster pumps on the suction side? This makes no sense. Evaluate the suction conditions for the new pump including the Net Positive Suction Head available. Make the evaluation over the full range of operating conditions (maximum flow, minimum tank level, etc.) If the selected pump has a Net Positive Suction Head required that is lower than the NPSHa, then it should work. It would be wise to maintain a minimum margin (NPSHa above NPSHr) of at least 3 feet. If you do not have adequate NPSHa, then a booster might be needed. Please provide additional details on the system and we can provide better answers.

Johnny Pellin

 

[eugen25]

JJ Pellin, thank you for your quick answer. First, I need to highlight: it's a concept, but, still there are some clear data. The NPSHa is more than 5 ft (I studied some manufacturers' datasheets and, as you said, the minimum should be 3ft). The problem is not that the suction conditions colud not be satisfactory. The problem is exactly your question formulated in the second phrase, and, as the process dpt suggestion is fixed, my problem is to suggest (in these conditions)the right type of pump for the booster position (as I don't think the centrifugal pump is the solution - maybe I'm wrong).
Thank you very much,
Eugen 25

 

[JJPellin]

I still don't understand the question. Are you asking if you can run a positive displacement pump without a booster pump in series, boosting the flow into the PD pump? Or, are you asking if it is appropriate to pump this stream with a positive displacement pump at all? Without additional details, it is impossible to answer your questions. If you have adequate suction head to support the screw pump, and if the screw pump is designed to deliver the flow and pressure you require, and if the variable speed drive you propose will allow adequate control of the flow to meet the variability in the process requirements, and if the system is properly protected against overpressure in the event that the screw pump is run against a blocked valve, then the screw pump should work. A positive displacement pump will generally be more efficient that a centrifugal pump. So, for a given flow rate, you will need less power from the motor driver.

I am sorry that I keep asking you to restate the question. I was originally born in Arkansas, so English is not my native language.

Johnny Pellin

 

[BigInch]

Just how far away are the tanks? Must be pretty far if you need 100 bars going to a tank, or the pipe is very small diameter. Is the tank pressured or atmospheric? You also have given 68 m3 but no time, so is that a flowrate, like m3/h or are you pumping into a tank with 68 m3 volume and you have all day to do it? Why do you think you need a PD pump?

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[CH5OH]

100bar seems very high to transfer oil to a storage tank

 

[micalbrch]

eugen25: Not every PD pump needs a booster pump under any conditions. That's what was written by JJPellin and that is correct. You have a given NPSHA and you have a given NPSHR from the pump supplier. If you do not have a NPSHR from the supplier, ask him what NPSH is required or what minimum inlet pressure they require at the pump's suction. Then it can be decided whether a booster pump is necessary.
You have a NPSHA of more than 5'. Is there a positive static head on the suction side or does the PD pump have to lift a head? I'm not 100 % sure but I think twin screw pumps can lift a head.
Booster pumps are usually centrifugals. Their head should be 30-50 psig (but that is only a rough guideline!!!). Their flow must be minimum the flow of the PD pump. That must be checked too with the PD pump manufacturer. The necessary flow of a booster pump can be higher than the flow of the PD pump.
Power requirement seems pretty high if the flow is 68 m³/h. That is an efficiency of 47.2 % which is rather poor.

 

[FACS]

The booster pump "they" tell you you need isn't for your pump, it's to maintain pressure and flow in your system.

If there is an occasional situation where your main pump can't keep up, a booster pump will kick in and take up the slack.

If your fluid is flowing over a long pipeline, then the pressure lost needs to be regained... with a booster pump down the line.

These people are probably experienced with long pipe lines, and they know that you need to return some pressure to the lines or the flow will stop.

Charlie

http://www.facsco.com

 

[BigInch]

FACS, I don't think we know much about this system yet, so let's don't tell him what his pump is for or where it is. Some people call pumps at an intermediate station 1/2 way down the pipeline, "booster pumps", instead of mainline pumps, and they call your booster pumps, "transfer pumps", and call the pumps at the first pump station, "shipping pumps". Some people run "booster pumps" all the time, if they can't make NPSHr without them, not just when they kick in on pressure loss. Some people use "booster pumps" "transfer pumps" to keep NPSH on the shipping pumps for some products, but when they are not shipping that product, they use the same transfer pumps to move that product from tank to tank. IMO, nobody seems to have made any sense of this system yet. So ... do you think we could just wait for the OP to answer the questions he's already got?

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[eugen25]

Gentlemen, first of all,thank you very much for your input to this thread. I will try to answer to the questions raised above and I will inform you about what I understood so far: downstream PD pump is a line of about 70km (not much info regarding the ground configuration along the line) which will be connected to a manifold having a certain pressure in (about 90bar, not confirmed yet). I consider that a PD is suitable because is able to maintain the flow against any "surprise" might get on the line. The NPSHa is satisfying the requirements of the PD I found.
Also, reading the characteristics of the twin srew pump, I understood that a booster pump should not be required unless there are some special requirements(and you cofirmed it). My concern is why the manufacturer stated that the max inlet pressure is 15bar as a booster pump should produce 2 - 3.5 bar on outlet (inlet for PD pump)? Micalbrch calculated a low efficiency. That is because I, deliberately, considered a low efficiency. Also, Micalbrch is stating that usually the booster pumps are centrifugal. Is our case "an usual one"? I'm asking this because the PD and the centrifugal are different types, different concepts... Can they work together? No conflicts?
JJ Pellin, the English language is not the native language for me. I'm from the Eastern Europe and the nearest English speaking country is about 2500km from my homecity...This is one more reason why I had to ask you for patience. Many thanks to everyone of you. Eugen25

 

[micalbrch]

eugen25: If your NPSHA meets the requirements of the twin screw pump manufacturer, then you will not need a booster pump unless the medium is extremely sticky. But that does not seem to be the case.
The twin screw manufacturer mentions someting about the max. inlet pressure, not something about the required inlet pressure. That is a big difference. And the limitation of 15 bar for the inlet pressure has technical (design) reasons. Such a high feed pressure occurs only under certain circumstances and with special fluids.
In general: A centrifugal pump as booster pump works fine with a PD pump if both are correctly sized.
Why did you calculate efficiency and motor power? Didn't you get the required motor power from the twin screw pump manufacturer?

 

[eugen25]

Micalbrch, thank you very much for yor answer. I highlighted at the begining that the whole this story is in coceptual stage. The requirement was to find out what is needed mechanical, electrical, instumentation, etc. wise. This is why I tried to appreciate the the power. I know the motor should be of higher voltage, but, I don't know what voltage and, in this phase, I can not "go out" to the manufacturer asking this kind of things (in the short description/datasheet was not mentioned). Once again, thank you very much. Eugen25

 

[TenPenny]

A 2 screw, or even a 3 screw, will certainly be a decent choice. Like this 3 screw, 900 gpm at 100 bar. 745 kW motors.

 

[BigInch]

First: I don't know why you think you need a PD pump. Tip: Go for a centrifugal, they're cheaper and easier to maintain. Your flow stoppage reason makes no sense. With a flow stoppage the PD pump would simply try to blow the pipeline or itself, or a relief valve, if the line stopped up.

Second: I don't know why you think you need a booster to feed the PD. Will you be pumping hot gasoline with a very high vapor pressure or something? If not, one centrifugal-type should work.

You also won't be able to define a real pressure until you have some idea of the line profile, so I think you're running a little ahead of yourself right now. At least get an idea of the profile from Google Earth or something.

Don't worry about voltages yet. If you don't know the profile, you don't know the power or the pressure. Once you know that, then let the EE guys figure out what voltage you need to run a motor with the power requirements you have. If they can't get the voltage ... you can always go with either a diesel driver or install a generator. What other choice would you really have... not build the pipeline? Right now today you need the pipe diameter, pressure and power requirements. Focus on that.



**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[micalbrch]

eugen25: The voltage of the motor is of minor interest now. You wrote you are from Eastern Europe. So, the voltage should be 400/690 V, 50 Hz. This together with flow and pressure enables any pump manufacturer to determine the motor size (power).

If you want to pump rather clean oil (low or even no solids content), BigInch' recommendation to look for a centrifugal pump as an alternative will be a good advise. Although I have no clue how much a centrifugal is in comparison to a twin or triple screw pump. But that is something you can compare when you will have the proposals. Do not forget to compare the motor sizes too as energy costs should be considered.

Who calculated the pressure of approx. 90 bar?

 

[micalbrch]

BigInch: What do you mean with " Your flow stoppage reason makes no sense"?

 

[eugen25]

BigInch, thank you for the answer. The PD will be able to cover all the "surprises" might apear. A relief valve with a return line is already in my mind for protecting the pipline and the pump. The booster is wanted (not by me). The motor power was required by EE for his estimations. The pipeline profile will be taken in consideration after a decision will be taken.
TenPenny, thank you for the info. It helps a lot. Actually it confirms my supposition.
Gentlemen, thank you for lighting my way. It is a pleasure and a honor to have you close. All the best to all of you.
Eugen25

 

[BigInch]

Exactly, he needs the power consumption now. Not even he's interested much in the voltage, as he probably knows what it will be already.

OK somebody wants a booster. Why? Is it heavy heavy crude and the suction line loss is very high, or you have a something?

Mical,

Yes, it makes no sense. What I mean is that you have a maximum pipeline pressure and both types of pumps supposedly will reach that, but they CANNOT go over that. If the PD runs up the pressure to max the relief goes off, or it bends a rod. If the centrifugal runs up the pressure to max, the relief goes off, or it overheats. So you won't get any more pressure on the pipeline with one type of pump than you would get with the other type of pump. So, there is no reason to chose a PD over a centrifugal for preventing flow stoppage.


**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/

 

[micalbrch]

BigInch: Thanks for the explanation. Now I understand what you meant.

I think eugen25's preference for a PD pump was to have some kind of pressure margin in case the pressure is not 90 but 100 bar and he still needs the full flow. But let's leave it as it is. He is satisfied so far.

 

[GaTechTheron]

BigInch, he has to be pumping something nasty, maybe even a crude since he is using a twin screw.

It has also been my experience that many process guys don't understand the concept of the twin-screw beast. Many of these monsters require little to no NPSHa, and this point might not be getting through in his organization.

-Theron