Average Railcar Heel? 2

[TiCl4]

We top off-load railcars of monomers and have been experiencing variances in our inventory management system on these materials. We recently compared tank level via gauge as well as stick measurement before/after emptying a railcar and found the storage tank to be light 700-1,200 gallons.

I'm not that knowledgeable about railcar design, but the top-offload configuration has a well at the bottom that should allow the dip tube to remove most of the material.

Compared with the other offloading station, this station usually takes much longer to offload; 4-6 hours as opposed to 2.5-3 hours.

I've been told by maintenance that the gear pump was replaced in the past with no discernable improvement. We'll start looking for vacuum leaks, especially around the swivel joint in the unloading arm.

However, 700-1,200 gallons of heel is a lot more than I'd expect so I wanted to get other's experience on railcar emptying and issues with overly large heels. Is that a normal heel in a railcar for top-offload, or am I looking at a likely vacuum leak?

 

[TiCl4]

Thank you all for your continued help. I'll be looking to further diagnose the issue and report back here. A few responses to comments so far:

I don't think this is a right technology for a like water product.

Gear pumps are not ideal, no, (I'd prefer a sliding vane pump), but that is the currently installed pump type that I have to work with.

He's looking to diagnose a problem with an under-performing station while providing insufficient information to do so. The "heel" appears to be a red herring. No car would be designed to allow that amount of material to remain.

Unfortunately there is not much documentation on the system. No isometrics, dP meter setup details, etc. The original question of this thread was to identify if the remaining heel that was measured was in-line with what a normal top-offload arrangement would be. It appears the consensus is that this is indeed an issue. I have no idea if the other station leaves a similar heel; all I do know is that the unloading times are quite different between the two.

It's really not clear why this station would continue to be used rather than diagnosed and repaired.

There are no other options. This station is the only one connected two two bulk material tanks - there are no secondary options.

Just my view, but your operation team and finance controller are not doing very well in term of stock taking/yield performance

Historically, I agree. However, it is the ops/finance that led me to looking at this in the first place this year due to the constant "losses" during cycle counts with these bulk materials.

The DP transmitter reports the hydrostatic head in pressure units.

This is why I prefer to have dP's report out in weight. The density value cancels out in the calculation, eliminating that source of error. I've done that on a new bulk installation, but these are legacy meters.



For those interested, below is a rough sketch I made this morning of the relative elevations.

 

[LittleInch]

What exactly is lowered into the tank?
I assume the dimensions are inches?
That hose thing doesn't look long enough so I assume there is some other tube which goes in?

what vapour pressure do you have here?
I'm seeing about 5.5m of lift at the lowest point of the liquid so are you getting vapour in the highest part of the system?

Plus anything with a strainer in before the pump is generally a bad move. When was the last time anyone opened it? Does it have DP guages?

Do you have pressure / vacuum gauges anywhere?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TiCl4]

LI - Nothing. The hose is on a swivel arm that lowers and connects to the top valve of the railcar. Dimensions are inches, sorry.

This station handles two monomers, one with a s.g. of 0.91 and a vapor pressure of 0.01 bar at standard conditions and the other with a s.g. of 0.89 and a vapor pressure of 0.007 bar at standard conditions. The suction lift (~50 kPa) should not get even close to the vapor pressure of the liquid, even when the railcar is near empty.

No, no gauges anywhere on the system. We will be leak checking the system on the pump suction side and opening the strainer this week.

FYI the pump OEM maximum recommended lift for water at 80 F is 23' of water, or ~ 69 kPa available lift. Again, the pump shouldn't be losing prime during pumping, which is what it appears to be doing.

 

[LittleInch]

That strainer would worry me for sure.

Oh hold on - "top valve of the rail car"?? Then you really need to get hold of the rail car supplier to get a drawing of what's inside the rail car....

I though that looked a bit strange....

Now to be fair UTLX have a nice looking website where this

https://www.utlx.com/tank-car-overview/

- go to build sequence page 9 - where it says the siphon line "extends to a sump a the bottom of the car".

I'd still like to see a detail drawing myself. The bottom bit of the pipe on the website looks odd - maybe it is flexible and has some holes in it?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[LittleInch]

I know this is about LPG, but it has some nice diagrams.

https://www.eng-tips.com/viewthread.cfm?qid=484077

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

Seems simple enough - cap the end of that hose and turn on the pump and see what the maximum draw is. If there's not a leak the pump should draw down to the 69kPA rapidly. Otherwise it will start drawing air at some lower pressure difference.

Since the stations are not the same they are not comparable.

As the tank fills it produces additional pressure the pump needs to overcome - so there's another feature to look at - what pump pressure is required to fill the tank and what delta-P the pump can produce.

So you'll need to check that also.

I suppose no one has checked the swivel for leakage yet. If it was leaking there it would likely be wet from styrene. I'd be more inclined to start with the hose as not every crack would allow liquid to drain to the outside but a complete inspection would be handy. The lowest pressure will be found near the top of the hose when the tank is nearly empty.

Littleinch - I think the siphon pipe has an anti-whirlpool guard on it to keep the shallower material along the sides from easily swirling and introducing gas/air into the siphon.