7 replies to this topic

[MFAHOS]

Hi there

Could you explant why the booster pumps are used in addition to the main pumps in LPG pipeline transport, while they are not requiered in truck/ship loading ?

is there a relation between the head and the NPSH required of a pump?

Thanks

[Zauberberg]

You haven't provided basic process data, but I assume that the reason is because there is no need for high-head during truck loading while there must be high-head requirement when you start pushing LPG product into the pipeline.

There is relationship between NPSHr and pump flow, suction head requirement increases with increased flow. You can see that on any pump manufacturer curve.

http://www.irrigatio...t.com/npshr.htm
http://www.pumped101.com/npsh.pdf
http://www.cheresour...galpumps4.shtml

[kkala]

Could you explain why the booster pumps are used in addition to the main pumps in LPG pipeline transport, while they are not required in truck/ship loading ?
is there a relation between the head and the NPSH required of a pump?

Usual diagrams (head < 200 ft) for single impeller pumps show (statistical) relation between pump flow rate and NPSH (increases with flow), but no dependence on head. Flow rate mainly affects NPSH; impeller type (and craftsmanship to some extent) can reduce NPSH for a pump of given flow & head, yet impeller type is usually use-defined, e.g. process pumps have a rather narrow range of suction specific speeds.
Multistage pumps can develop heads to 2000 ft and probably require higher NPSH than a single stage pump of same flow rate due to complexity. However I have not found any written evidence on this (advice is welcomed!).

I believe booster pumps are used to: (1) supply additional head to an existing pump (2) supply enough pressure for NPSH to the suction of main pump, if above "assumption" is true (some non centrifugal piston pumps need a rather high suction pressure to operate). In case of LPG transfer main centrifugal pump is most probably multistage, versus a single stage booster (or of few stages).

You do not clarify whether same LPG main pump is used for both pipeline transfer and truck / ship loading. If so, check (1) in case of pipeline transfer (flow rate may not meet requirement without the booster pump). Case (2) is rather improbable.

Edited by kkala, 08 March 2010 - 04:43 PM.

[MFAHOS]

Tnaks Gents

I guess we chare the same thoughts that NPSH of pumps with High heads is somewhat greater thant that of low head

I have an exemple on my own where : LPG Main Pump (Head = 700m, NPSHr = 7m)
LPG Booster Pump (Head = 75m, NPSHr = 3m)

but it still not enough to confirm what we said.


Again, I have another question

when using two pumps in series, Technicaly, How to select the discharge pressure of the first pump

exemple

Suction 1st pump 10barg
Discharge 2nd pump 30barg

which will be better? Discharge 1st pump 15barg or 20barg...


Thanks

[fallah]

Discharge pressure of 1st pump would be almost equal to suction pressure of 2nd pump.The value should match heads of each pump in BEP and on the other hand should cover the NPSHr of 2nd pump.

[kkala]

One thought would be to select two identical pumps to save spares of them in the storehouse. In this case discharge of the first pump would be about 15 barg (assuming almost zero suction pressure).
I have asked local advice (Athens) on the NPSH requirement of multistage centrifugal pumps, without a clear answer.

Another case needing booster pump is when distance between tank and pump is too long. A long suction would result in low available NPSH due to friction, flow may be even cut off in case of big ground ups / downs. So a booster pump is necessary to keep flow or to regain suction pressure drop. It is noted that there may be truck loading pumps 1-2 km far from their tank in a refinery.

Edited by Art Montemayor, 07 August 2010 - 08:26 AM.

[truckcarrier]

Hi..The new LPG booster pumps provided pressure for the mainexport pipeline initiating pump station when pumping LPG. System operations were very challenging as the suction pressure provided for the natural gasoline buffer..

Truckload carriers

[R NESAMANI]

Hi MFAHOS

We are operating LPG pipeline system. How do u evacuate the LPG in filter, during maintenance of filter...?
do u flare the LPG or extract and push LPG into process line...?