Vortex Breaker on Axial Flow Pump

[vancitygd]

I have been asked by a client to look at a failure of a vortex breaker they have in service and to recommend a new design or welding procedures if necessary.

The vortex breaker is on an axial flow pump on a caustic evaporation loop in a chemical plant. I was sent photos of the failure and one leg of the vortex breaker "cross" had sheared off. Some analysis had been done and preliminary indications are that it was a poorly prepared weld. Note that both the pipe and the vortex breaker are made of Nickel.

I went to the site to investigate. Much to my surprise I discovered that the vortex breaker is installed on the discharge of the axial flow pump instead of the suction.

The pump handles caustic solution with a flow rate of 28,000 gpm at 16 ft of head. The pump discharge is 30". This increases immediately to 42". Less than two feet after this the vortex breaker (if that's what it is) is installed. The vortex breaker is your typical "cross" design. However, it is only 18" long. It is my experience that vortex breakers are usually 1.5 X pipe diameter. This also makes me wonder if this item is really meant to be a vortex breaker. I should also mention that although the staff at the plant refer to it as a vortex breaker, it is not called this on any of the drawings. The design is over 30 years old and I don't think there is much of a chance to contact the original design engineer to find out what the intent of this item is.

Does anybody have any idea what the purpose of this "vortex breaker" might be? Maybe it's not a vortex breaker, but is in fact a "flow straightener". But that doesn't seem to make sense either. The pump feeds into a shell and tube heat exchanger which is about a 12' vertical run from the pump to the heat exchanger. I don't know of any need to straighten the flow when feeding a heat exchanger. There is also no instrumentation between the pump discharge and the heat exchanger.

Does anybody have any ideas?

 

[FMJalink]

vancitygd,

From your message I understand this pump forms part of an evaporation loop. An axial flow pump will give a rotational component to the flow downstream of the impeller. In a loop will this vortex component return to the inlet of the pump, when the fluid completes a cycle in the loop. This rotational component of the flow at the inlet of the pump is disadvantagous, due to wrong inlet direction of the fluid on the blades.

The "vortex breaker" will kill this rotational aspect. In case there would be only one fluid speed (capacity), inlet vanes could be considered, but as it is an evaporation system, the fluid will be near to its boiling point, with the risk of cavitation.

 

[rmw]

I'd like a little bit of a better explaination of "axial flow" pump, since this term can be used ambiguously and means different things to different people. If this is intended as a flow straightener, depending upon the pump type, there can be issues at this point with blade passing frequencies acting on the surfaces of the "vortex breaker???"

rmw

 

[vancitygd]

Sorry I did not respond earlier, but I took some time away over the holiday season. I'll try to clarify some things. The pump is an axial flow elbow design with open impeller. It is an Ingersoll-Rand APL pump (more accurately, it is a jobber copy of one). The original 1967 drawings show the cross-type "vortex breaker" installed on the discharge side of the pump. This entire design was duplicated when the original pump finally wore out in 2005.

I have attached a partial scan of the P&ID showing the pump and related equipment. The pipe after the "vortex breaker" or "flow straightener" goes into a nozzle on the bottom of a shell & tube heat exchanger, so I don't see that removing rotational velocity would be a concern.

 

[Artisi]

Nothing there when I open the file.

 

[vancitygd]

Let me try that again

 

[vancitygd]

Still didn't work

 

[vancitygd]

I don't know what I am doing wrong trying to attach this file. Is there a Q&A or tutorial somewhere for this? It seems straight forward enough, but it doesn't work.

 

[whammett]

Depending on the viscocity of the liquid being pumped, it could be very important to have laminar flow going into a heat exchanger. I agree with you thinking it is more of a "flow straightener". I haven't ever bought any from an industrial vendor, or seen any for that matter, but I'm sure someone sells them. Typically we just run more pipe or run it through a venturi tube or orfice to make a laminar flow, but maybe this is how they did it in the mid 60's?

"I came, I saw, I made it better."
-Ode to Industrial Engineers
Will ChevronTexaco Corp.

 

[Compositepro]

Rotational velocity in the flow leaving the pump is lost energy - it does not contribute to pump flow. It will eventually be dissipated but it may also create more energy losses in passing through elbows or other geometries. A flow straightener after a propeller pump is a good idea. Ideally it would have some airfoil type curvature to turn the rotational flow into axial flow.

 

[EdStainless]

An this is an environment where there is a risk of erosion, so minimizing the swirl would be good.

There are a few grades of Ni, not all are readily weldable. Was the original cast or fabricated?
Maybe using 301 with higher strength would help.
The welds have to be very clean. Very clean.


= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Artisi]

It is not a vortex breaker, it is a flow straightener or to be more precise an energy recovery component. All axial and (very) mixed flow pumps will have energy recovery blades after the impeller. These will have been (or should have) been designed with the same care as the impeller blades, especially on large units when a lot of energy can be recovered.