SCREW PUMPS OR CENTRIFUGAL PUMPS 2

[mfakharmechanica]

Does anyone know when screw pumps are used. In the project we had lots of hydrocarbon like Naphtha, gas oil, gasoline….
For Fuel oil with the viscosity of 950 CP and flow rate of 1250m3/hr, I used twin screw pumps which now the client ask us to use the centrifugal ones or explain whay centrifugal pumps can not be used.
For the mentioned condition of fuels centrifugal pumps can be used?

 

[MortenA]

Screw pumps may give better flow control (semi PD and VFD)?

Especially if the flowing conditions changes as your high visvosity fluid also often see a strong temperature dependency of the viscosity.

Best regards

Morten

 

[BigInch]

Your refined products have low viscosities. Centrifugal pumps are the norm.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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

 

[mfakharmechanica]

As I mentioned before, the Min./Normal/Max. visscosity will be 57/300/950 CP respectively for Fuel oils with capacity of 1250m3/hr and discharge pressure of 17 barg.
Also the design case will be maximum viscosity(950 CP). The pumps will be used in Tank farms to transport the products into the ships.
Our client want to have the chipest pumps for this applications. Screw manufacturers submitted suitable offer with force loblication (external lobrication system).

Can we use the centriugal pumps for this application?

 

[BigInch]

You could still use centrifugals for all your products.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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

 

[mfakharmechanica]

With the viscosity of 95 CP (Centi pose)?
It realy will be appicable?

 

[BigInch]

Yes, in fact you don't need to consider increased viscosity effects of a product on pumps for most cases until you are into the 400-500 cP range. You should apply a correction factor to pump characteristic curves when cP is going above 500.

See

http://www.engineeringpage.com/technology/pumps/viscosity_correction.html

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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

 

[Artisi]

If pumping gasoline you need to be careful with your pump selection - check with the local authority re any specific requirements for gasoline pumping.

 

[mfakharmechanica]

Hello BigInch agin,
Thanks so much for your kindd hepls,
I have problem with the pump selection, let me explain to you,
Actually for pump type selection I used Exxon Mobil Corporation guids. They mentioned for viscosity over 600 CP centrifugal pumps are not suitable, then I used screw pumps (according to API 676) for this condition (940 CP, 1375m3/hr, Discharge pressure=16.5barg). I also searched throughother references (shell...) and I found that screw is the best chose. Also, I calcuated voscositycorrection factor for this condition and it is near 0.6, Ifound that the total required power will increased for centrifgal 1.2times rather than screw pumps.
I searchmuch reference projects and I found that in many similar projects, the screw was used (for the same condition..)
Finally the client asked for centrifuga pumps! I would like toknow which option (my select or client request)isthe best one withconsidering commercial and technical matters.
Thanks

 

[BigInch]

Many times pump selection can be decided by preference alone, maintenance considerations, or on a fabrication and delivery time issue, rather than on optimum energy cost over the project's lifetime. I like being an idealist, but when you can get one pump 3 months sooner than another and you can make $ millions a day x 90, selecting on an energy cost alone basis might not tell the whole story.

In your case the optimal selection may depend on how much time you spend pumping gasoline versus how much time you spend pumping heavy crude.

My e-mail; Google "virtualpipeline" and its #1.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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

 

[mfakharmechanica]

The pumping fluid is FUEL OIL with viscosity of 940 CP.
The required power will increase because of the efficiency correction factor of 0.6!
Is it usual to use centrifugal pumps for such viscose fluid and mentioned condition? On the other hand, many operational problems will be raised during the operation or not?

 

[BigInch]

No worries. If they can afford the extra energy cost, let them use the centrifugals. If I were you, I'd turn in my evaluation stating that the most technically suitable are the screw pumps, due to the lower energy costs, then let them decide, but discuss that with your boss first.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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

 

[Unotec]

Another point to consider, whether it is relevant on your application or not I do not know, centrifugal pumps might emulsify your fluids. For that reason I sometimes choose PD pumps instead. If this is not an issue for you, I'd abide to BigInch's recommendations.

<<A good friend will bail you out of jail, but a true friend
will be sitting beside you saying ” Damn that was fun!” - Unknown>>

 

[GaTechTheron]

I would highly recommend against a centrifugal pump with at 950cP! Consider cold start conditions, and the torque required just to move the impeller. Go with a 3 Screw.

 

[BigInch]

Cold start would better be accomplished with diesel, naptha or another diluent in the line, then switching to the heavy crude.

I've also used two pumps, in series for start, switching to parallel when things get moving.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

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