PD or Centrifugal, which pump should be used for Oil Road Tanker unloading?

[aashim]

I have to select the type of pump to be used for ASL (Arabian Super Light Crude) road tanker unloading station. Viscosity of ASL is 1.5 to 2.2 cP and vapor pressure is high and at 50 degree C it is 92.3 kPa. Our company standard is to use rotary screw pump for similar application. However, we are facing problem in one of our project (still under commissioning) where screw pump used. Can i use centrifugal pump for this service? What are the problem may face if i select centrifugal pump instead PD?

 

[LittleInch]

Basic centrifugal pumps prefer a flooded suction and have an NPSH requirement of around 3m. You can get self priming units and slightly lower NPSHR pumps, but not much and given your fluid is so close to boiling it's not going to make much difference.

However most centrifugals don't like running on a mixture of liquid and gas, like you might get at the end of the unloading operation.

Hence for unloading you might need either a can type pump or place your pump in a pit below the road tanker.

If you can it might be a lot easier to simply gravity feed into a buried tank and then pump out from there in more controlled conditions? Doesn't have to be the same size as the tanker, but simply act as a buffer between the tanker and the pump and then use a submerged pump (vertical shaft) inside the tank and have pump stop on LL liquid level. Just an idea.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

To completely empty a tanker, the system needs to be designed to have a sump that permits total drain-out of the liquid from the lowest point. Where a pump is mounted above the liquid, it will probably cavitate at tank liquid levels. For an tank unloading pump installation it is best to install a buffer tank between the tank and the pump to let the road tanker completely drain-out before the pump starts cavitating. Tanker load-out pumps must have a very low net positive suction head requirement

 

[MJCronin]

I believe that a PD pump suitable for fuel oil delivery would be best.

That would be a sliding-vane pump such as those produced by Blackmer or IDEX.

Please respect us ...... Tell us of your final decision and the reasons for it

http://www.corken.com/sliding_vane_technology

http://www.psgdover.com/assets/blackmer/MC/atk3533-001.pdf

MJCronin
Sr. Process Engineer

 

[ahmadsalah]

I agree wth MJ. PD pump slidin vane is best for this applicaiton because first it has a good suction lift capability and second it has a very stable flow rate and NPSH. We use it all the time for fuel delivery.

 

[aashim]

Thank you all for your valuable inputs. Client ask us to install Centrifugal Pump or Self Primed Centrifugal with Air Release valve. The skid will be installed in a pit of 4m depth from FGL. The calculated NPSHA is 2.4mWc considering the liquid level at 0m (i.e FGL). My question is when i should stop the pump and how? I have thought a flow switch at truck end of the suction pipe which will stop the pump immediate after truck is empty. Due to tight schedule,I am asking bidder for centrifugal pump as base offer and self priming centrifugal as an alternate offer.

 

[LittleInch]

If your pump is in a pit 4m below Ground level(FGL?) then you shouldn't need a self priming pump. I would still go for either a tank or in the vertical leg down into the pit, make this from very oversized pipe, e.g. 24 or 36" pipe which feeds into your pump at the bottom. Then you could simply put a pressure transmitter on the bottom adjusted to be a level transmitter and stop the pump when the liquid level gets down to about 1 to 2m from the pump inlet.

Getting the last 5% out of the tanker can take some time so this would allow you to control flow based on a minimum level of say 2m in your oversized down pipe.

Flow switches are notoriously inaccurate, especially when a mixture of liquid and gas is coming through.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ahmadsalah]

put a pulser on the discharge side of the pump, send the signal to a plc that would start counting when no flow is coming. set it to count 30 seconds of no pulse and after that shut the pump. same thing with flow switch (paddle style) setting. set it for some time of no flow to make sure you got everything in the truck. If your pump is that low under the truck then you should easily empty it. It is just preferred to put the flow switch on pressure side and put 5D of pipe length before it and after it. cheers