PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
(OP)
The scenario is this --- PD pumps (Gaso triplex plunger) pump crude oil via a 6" pipeline into a breakout tank (crude gathering system). From this point, 2 centrifugal pumps in series (mult-stage pipeline pumps) are used to draw from the tank (using a booster pump) and into another pipeline (8") for delivery downstream.
The tank now needs to be placed out-of-service for inspection/repairs. The operator wishes to bypass the storage tank and feed the centrigugal pumps directly from the PD pumps.
I am concerned due to the puslations of the PD pumps (even though the last pump is 15 miles upstream) and the the elaborate controls likely to be required, e.g., PRV on suction side of centrifugal pumps, startup and shutdown philosophy. The centrifugal may "want" to pump more, but will be deprived by the PD pumps's steady flow - even with a programmed control valve on the pumps' discharge.
I've always tried to avoid this due to what I feel would be an unstable hydraulics scenario, however, I've never tried it. Before I suggest against it and instead suggest the more expensive installation of a replacement breakout tank, has anyone tried this or have any thoughts to share on this.
Thank you in advance.
The tank now needs to be placed out-of-service for inspection/repairs. The operator wishes to bypass the storage tank and feed the centrigugal pumps directly from the PD pumps.
I am concerned due to the puslations of the PD pumps (even though the last pump is 15 miles upstream) and the the elaborate controls likely to be required, e.g., PRV on suction side of centrifugal pumps, startup and shutdown philosophy. The centrifugal may "want" to pump more, but will be deprived by the PD pumps's steady flow - even with a programmed control valve on the pumps' discharge.
I've always tried to avoid this due to what I feel would be an unstable hydraulics scenario, however, I've never tried it. Before I suggest against it and instead suggest the more expensive installation of a replacement breakout tank, has anyone tried this or have any thoughts to share on this.
Thank you in advance.





RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
Efficiency is the only concern but you may sacrifice this for the short term the tank is out of action.
Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
Either use the recirculation configurations mentioned above if you can, or another option would be a control valve in the centrifugal's discharge closing% to hold minimum suction pressure. Not very elaborate.
http://virtualpipeline.spaces.msn.com
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
A spill-back line would work, also. But I would suggest a controlled spill-back that is set to hold constant suction pressure to the centrifugals. An orificed spill-back could be a trial and error process that might take several iterations. And if there is any change in product conditions, it might not work well over time.
Johnny Pellin
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
If a pulse ever makes it that far (doubtful, they are reduced by line friction and pipe expansion along the way), you will simply, momentarily and probably minutely lift the suction and discharge pressure a bit. The flow through the pump will also increase, perhaps reducing the differential pressure as well (with no net change in discharge pressure (?).
This is something that I do all the time and I highly doubt you need to be worring about this at all.
http://virtualpipeline.spaces.msn.com
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
http://virtualpipeline.spaces.msn.com
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
Without knowing more, your most likely scenario is a bypass control valve back to the centrifugal suction to keep suction pressure from dropping too low, as discussed above. Depending on the PD flow suppying this pump, you will have to watch for overheating due to recirculating much of the flow.
As this system will not be very forgiving of flow swings without the surge tank, you might want to consider tripping the centrifugal pump on low suction pressure. (loss of pd pump)
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
As rzrbk suspects, with VERY good reason, I also doubt the recips capacity are greater than the centrifugals. Once again, It doesn't look like you will have a problem. However to be sure, it would be an excellent idea to know a little about your system before you even think of modifying anything. I thought you might have divulged some details by now. So then, what exactly do you know about it?. Recip's flowrate, recip discharge pressure, centrifugal curve, centrifugal's shutoff pressure, discharge pipe diameter off the centrifugal, or do you only know you have 15 miles of 6"? If you don't know any of this stuff, you don't really need to be thinking about modifying the system ....and, with that in mind, so far your asking all the questions in the wrong place. We don't have those answers. Maybe better to come back later when you've got the details.
http://virtualpipeline.spaces.msn.com
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
PS - Regarding pump flow rate capacities, the PD pumps on average are lower than that of the centriful pump. However, there are peak periods when a high number of PD pumps are running simultaneously and the total flow rate would exceed that of the centrifugal pump's capacity.
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
As you will only be in the modified configuration for a short time, I suggest you intentionally limit the capacity to that of the 1 centrifugal. Too bad you simply can't just turn down the speed of the recips, or are they constant speed electric driven?
In any case don't accept peak ops when in the temp configuration.
http://virtualpipeline.spaces.msn.com
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
RE: PD PUMPS TO CENTRIFUGAL PUMPS - SERIES OPERATION
When reaching MAOP (of the downstream pipeline), centrifugal discharge pressure would probably be held constant by a control valve, the net head in the system (might remain the same, but) would not therefore increase and the downstream pipeline would not increase flow, so no movement on any curve would occur.
http://virtualpipeline.spaces.msn.com