Small vessel pressure transfer help

[MatthewL]

Hi all, looking for some design help with a proposed change.

We currently have a small (~3 gallon) additives tank on an upper level used for small charges to ~1000 gallon premelt vessels. The tank is pressurized with 60 PSI N2 to transfer the contents (RO water and additive) to the premelt vessels. The problem is the tank is on the 4th level, while the control room is on the 2nd level (much up and down steps and the heat on the upper levels doesn't help). I am looking at relocating the tank to the second level, but am worried about the N2 "tunneling" through the water/additive mixture instead of transferring it to the premelt vessel. The elevation change from the 2nd to 4th level is ~20 ft, and the pipe is 1" sched 80 (0.0376 gal/foot). The operators currently use ~1 gallon of water mix for the charge. I was considering having them use 2 gallons of water to help with having a "liquid full" condition at start. Would a check valve on the line help? The actual charge to the vessel is handled by automation (two control valves and pressure rise on destination vessel to indicate transfer is finished), the operators just have to fill the tank. Any advice or suggestions?

Thanks in advance,

Matt

 

[gr2vessels]

Sorry, what has to do 2 gallons of fluid with the check valve? Would 2 gallons make a 'full charge' in the 3 gallon vessel? Is the older operator's name Henry and he does manual charge of the small vessel, walking up and down the stairs? I am a bit confused here...

 

[MatthewL]

gr2vessels, the check valve is to prevent the liquid from flowing back into the tank if the nitrogen "tunnels" past it on the 20 ft vertical rise and leaves liquid in the line once the transfer "completes" per programming. The additional gallon of water should be enough (by calculation) to fill the 1" line before the tank is empty, which should help the transfer. The problem with the location of the tank is that it feeds multiple vessels, needs charged before each batch (maybe 7 or 8 times a shift), and is located between two premelts running at ~650 F, giving air temps of over 140 F and 90+% RH most of the time-I know it gets that hot because I was a shift supervisor before moving back into engineering. I don't know about you, but I don't like having an OSHA recordable for heat prostration when it could be solved by some piping. And yes, the operators are older (most have 25+ years experience) and if you want to make an issue of it you can handle the age discrimination suit not to mention the slew of grievances that would start.

 

[gr2vessels]

Take my word, I am better with H&SE than your predecessors who designed the plant and is commending that you want to improve it.
Provided the nitrogen exerts pressure downwards, it will not tunnel in the pipe, hence the check valve has no use. Keeping the line full with liquid will prevent the running dry and nitrogen filling the premelt vessels.
Cheers,
gr2vessels

 

[Compositepro]

It sounds to me that you are changing the tank from an elevated location to a lower one, so your pipe will no longer gravity drain. So you suggesting to push liquid up the pipe with nitrogen pressure.
A check valve will do nothing to help. You have a couple options.

You can put a float valve in your tank so that it always empties to the same level. The pipe will always stay full and you will not be injecting nitrogen into the other tank (which may have some safety problems). In this case you may need a check valve after the float valve for when you release nitrogen pressure to refill the tank.

You can use a small diameter tube rather than pipe. Nitrogen will still tend to tunnel through the liquid, but there will be less liquid residue, and this residue will be swept through the tube by high velocity gas flow when the gas breaks through the liquid.