6 replies to this topic

[Sue N]

I was asked to select a pump used to push liquid propane from a storage tank to a process vessel.   The pump is used intermittently - for perhaps an hour at a time every few weeks.  

 

Currently, the application uses a sliding vane pump.   It is a simple set up - the propane travels from the storage tank, through the pump, to the process vessel.  There is no recirculation line.  

 

The storage tank is not heated, so in winter, the low vapor pressure in the tank means that the suction pressure to the tank is low, and the discharge pressure from the pump does not get high enough to push the propane into the process vessel.  

 

I contacted the original pump vendor, but there are no upgrades that we can make to the existing sliding vane pump to increase the discharge head.  Instead, the vendor recommended a multi-stage centrifugal pump. 

 

Is it common to use multi-stage centrifugal pumps in intermittent service?  It seems like I would at least need to add a recirculation line to ensure minimum flow for the start-up and shut-down.  

 

I appreciate any advice you have, as I don't have a lot of experience with multi-stage centrifugal pumps.  I've only seen them in continuous flow applications.    

 

 

 

[Bobby Strain]

What is the required capacity and head?

 

Bobby

[Sue N]

80 GPM, 1415 ft (275 psig discharge pressure). 

[Bobby Strain]

Head is the differential pressure, not the discharge pressure.

 

Bobby

[Sue N]

My apologies.  The winter time differential is 1335 ft (~260 psi).  In summer, when we have a much higher vapor pressure head on the storage tank, the differential is closer to 150 ft (~30 psi).  

[J_Leo]

Sue,

 

For your reference, I saw one propane pipeline pump, a vertical can pump with 20 stages and DP 1835 psi. My understanding is this type of pumps are commonly used in light hydrocarbon services to provide sufficient NPSH because you can low the Can underground. Does it matter if it continuous or intermittent? 

 

It seems your vendor proposal is reasonable. If you have doubts, maybe you can call another vendor for verification.

 

Leo

[Sue N]

Since I haven't used the multi-stage pumps except in continuous service, I wasn't sure if they presented operational difficulty when being used for intermittent service.  (For example, being prone to instability/vibration during start-up or shutdown, or if parts tend to fail if started/stopped frequently, or left powered off for any length of time).   

 

I appreciate your help with this.