Pump and Seal for Liquid CO2
Pump and Seal for Liquid CO2
(OP)
We are having a lot of trouble with a pair of pumps used to transfer liquid CO2. The pumps are vertical in-line pumps that use a special type of gas seal designed for cryogenic service. The wear parts (bushing and wear rings) have been converted to a non-metalic material that is more tolerant of dry run. I am wondering what other pump or seal technology is being used successfully in similary services. Specifically, what other pump configurations are working well for others? Is anyone using seal-less pumps in services such as this? Any suggestions will be greatly appreciated.





RE: Pump and Seal for Liquid CO2
thread798-63268.
RE: Pump and Seal for Liquid CO2
RE: Pump and Seal for Liquid CO2
If you haven't pumped LCO2 before, I can relate to your concern and questions. But I can put your mind at ease by relating that it is an easy chore and it doesn't take a pump as sophisticated as what you describe.
Firstly, LCO2 is certainly not a "cryogen" and shouldn't be classed as one. Therefore, it doesn't need an expensive cryogen pump to be pumped successfully and with consistent results. Additionally, sealless technology is an over-kill as well. I've used gear pumps (Smith MC2) and common centrifugals with the expected success. No "fancy" or expensive seal arrangements or seal "systems" were employed. You don't mention your pump make or seal manufacturer or type so I can't comment on what I can't identify or relate to.
As Insult states, sometimes it's not the pump or the bells and whistles; sometimes it's just making sure that pure liquid is simply getting to the impellar.
RE: Pump and Seal for Liquid CO2
RE: Pump and Seal for Liquid CO2
I've run cast iron pumps on LCO2.
However, I believe you are using your vertical centrifugals on truck loadings from main storage tanks. If that's the case, I don't see how you can dead head the pump since both the storage tank and the truck tank are equalized -- at least, they should be. That makes it a case where you really must have dense (I mean really dense) truck drivers.
Even with a centrifugal I would install a "spill-back" valve and line in order to avoid dead-heading the pump (regardless of whether it is positive displacement or centrifugal). From what you describe, I wouldn't chase the pumps; I'd chase after the operating procedures and the drivers who are supposed to be applying them.
Basically, you've got a rather benign operation and from what I gather of your description, a very favorable hydraulic installation - positive, flooded suction head, good seals, API construction, centrifugal design, etc. You should be out playing 18 holes of golf instead of chasing around after this operation.
RE: Pump and Seal for Liquid CO2
I have never been involved in pumping LCO2 and if it's a product / seal material incompatibility problem then I will leave this to others - but would be interested if it is a problem coming from a mechanical / operation failure mode.
Naresuan University
Phitsanulok
Thailand
RE: Pump and Seal for Liquid CO2
RE: Pump and Seal for Liquid CO2
So really the failures appear to be application / operation type failures, not a pump design fault or inadequacy.
Mis-applications just go round in circles - overcoming one problem just transfers it somewhere else.
You might have overcome the problem of rubbing of componets - you might come up with a seal that can handle the shaft deflection and can run dry.
But next the shaft will fail from fatigue.
What do you do then? - change shaft material / stiffen it to overcome the breakages.
Then the bearings will start to fail from overload and so on and on and on .
This is stating the obvious but stop the pump running at shut-head -
change the mode of operation - make it "Paddy-proof" so the operators can not run the pump at "shut-head". - put in a recirc. line - a pressure switch to shut down the pump from over pressure - a 3 way valve to close the discharge line to the tankers and divert the flow back to the source.
Naresuan University
Phitsanulok
Thailand
RE: Pump and Seal for Liquid CO2
Just as a curiosity, can you advise what the original seal and flush type were?
RE: Pump and Seal for Liquid CO2
RE: Pump and Seal for Liquid CO2
I think I have seen some good advice from this forum. Any thoughts on the paragraph above? Agree or disagree?
RE: Pump and Seal for Liquid CO2
I know I know - the "bean counters - the figure fakers" just tell you it's a maintenance problem and you need to account for it from the maintenance budget - "Sorry we don't have any money available for capital equipment" - have you heard that before - the ongoing saga of plant engineers throughout the world.
Naresuan University
Phitsanulok
Thailand
RE: Pump and Seal for Liquid CO2
Inline pumps have come a long way in the last 15 years, but still have not overcome the stigma of their poor past performace. Your comment about the great distance to the first "true" bearing is absolutely correct. That's why pretty much all the vertical inline units now are made with a close clearance "throat bushing" that are in fact hydrodynamic product lubricated bearings - typically made of an upgraded metal impregnated carbon, with an operating clearance of .005"-.008" on diameter. I would suggest considering reworking the cover to fit one - be carful with the thermal expansion difference between the cover, shaft and the bushing. Should you go to a metcarb/graphalloy type bearing in the box, you should also use the old plan 11 to push some fluid through the bearing/throat bushing. This "could" be a relatively inexpensive fix. All this of course is just general speculation without knowing specifics - OK, here's the disclaimer - to be honest, I've no specific experience with liquid CO2. Feel free to abuse me.
Good luck with the pump