Frequency Drive Impeller Pump Question

[retrolefty]

It was named the 'Alky Plant' using sulfuric acid in a cracking process, output product was isobutane.

Right, that would be a sulfuric acid alkylation plant. It actually takes isobutane as one of the feeds and converts it into high value products for use in gasoline.

Some of these alkylation plants use hydrofluoric acid (HF) instead of sulfuric acid. You have to really hope such a plant does not develop any leaks when you are near it as HF is one of the most dangerous substances around...

 When I first went to work there around 1979 they had a even old at that time small HF alky plant. Lots of special training needed and special acid suits for anyone working in it. Lots of horror stories about HF acid burns (something about it being calcium seeking, right to the bone). Luckily they shut it down soon after I started working there and I never actually had to enter that particular plant.

[qno]

Reset your Drive.
Set the motor parameters correct.
Tune the motor.
Check the current limit. set it to 150%.
 

[strantor]

So it looks like something's jammed or rusted up inside the impeller. The company has suggested I attempt an across the line start of the motor.

Which I'm a little worried about doing. Switching 480v like that seems like it might cause problems?

So you verified that the motor/pump was locked up, and their advice in response was to throw it across the line? I would disregard anything they told you in the past, or that they may tell you in the future. I wonder where their head was on that one... were they thinking that by brute force you canmunch up whatever the blockage is, and free up the pump? That's pretty stupid.

[CaptnYellowShirt]

Yeah, the more I think about the situation the more I agree...





So to avoid something like this, I've fashioned this pin spanner socket that should mate up with the impeller. I'm going to attempt to turn the impeller by hand with this "tool". I should be able to apply around 200 ft-lb to the impeller this way. If this doesn't "free something up" I'm resigned to think that anything the motor could do at full torque is just going bend something. At that point, I'll be looking a full tare-down for the impeller housing. 

[retrolefty]

Even if you manage to free up the pump shafts there is a good chance that the bearings are shot and will soon destroy the pump or leak process out the pump seals if you just try and run them again.

 I would think it's time to have the pumps uncoupled from the motors and have some machinist types inspect the pump bearings and seals to determine what maintenance is required.

[CaptnYellowShirt]

Luckily that's not my department. And even if they do leak, a little HF never hurt anybody.... right?


Just kidding. They could very well be damaged at this point. I was able to free the impeller up tonight with my  spanner socket. It would seem a ring of rust had formed around the seal bearing surfaces. It took about 120 ft-lb to break the rust, but afterwords 20 ft-lb moves the impeller. I dry started the pump for 1/2 sec to check for sufficient start-up torque -- no problems there.

These pumps move plain water in an open system in a research environment, so leak safety's not a huge concern. If we had access to a machinist type, I'm sure I would have already called him. So now its a trade off between running the pumps in a potentially degraded mode, or shell out some big cash to have a contractor come in. I think the general consensus is to run what we can when we can. Not sure if that's the smartest thing, but that's what the budget says now.

I am wondering if I should try lubricating the seals now that I have access to them. I doubt it will do much good after a few thousand gallons of water is run though it, but  it couldn't hurt. Any ideas there? CorrosionX comes to mind.

[IanB]

You apparently need a fitter/mechanic/maintenance technician/commercial plumber.

Why were the pumps seized up in the first place? Have they been standing idle for a long time?

If you have equipment that is not in regular use you need a maintenance regime, for example start them once a week to keep them running.

If they are going to be out of use for a long period, drain the system and dry it out.

[SeanB]

The seals just need to run in water, they are probably a ceramic/graphite/cast iron sandwich that needs water for lubrication. They will work with water as lube, so if you run them dry they will overheat and burn out quite fast. Symptom is water leaking from the hole at the joint of the motor and pump body. Then you either ignore until it pours out in a stream or pull the pump body front and replace the seal. $500 job to do a $20 seal.

[peter.mitchell]

I'm honestly surprised the motor could not free itself, 15HP pumps even with soft starting can punch pretty hard...

Also, pretty much what IanB said; you've gotta look after your pumps.
For us (mainly industrial irrigation management), every 3~ hours of runtime in multi-pump setups, we stop the pumps, then open and close some valves and flush the pumps with the other pumps.

[CaptnYellowShirt]

If they are going to be out of use for a long period, drain the system and dry it out.

I'm pretty sure that's what caused the issue.

I'm in the unfortunate position of 'inheriting' this rig from another group. I couldn't tell you what the history of it it. But I think the water in the last run had several kinds of salts in it. Upon completion of that project, I'm assuming they didn't flush the system. Rather, it was just drained and left standing for 6 months.