CO2 Sublimation

A client inquired why a CO2 vessel can be full by weight, but no product will come out. They mentioned that they'd been able to feed NF Nitrogen into the vessel and then get CO2 out.

"I think the principle issue here is one of pressure. CO2 is one of a few substances that go straight from the gas to solid phase and vice versa at atmospheric pressure. The only way to keep it in liquid form is to maintain adequate pressure as shown on this chart http://www.school-for-champions.com/science/dry_ice.htm.

We’ve found it necessary to use pressure to convert the sold back to a liquid once CO2 turns to dry ice (solid) due to a drop in pressure below the level needed to stay as a liquid. This can be done a number of ways and the addition of N2 as you have done is one. The key in your approach is to be certain that flow is tightly controlled and there are reliefs on all hoses and other trap points to prevent rupturing lines or tanks. Complete removal of all CO2 from the vessel can be pretty time consuming and take several days to accomplish. Once all CO2 is removed from the vessel, it is suggested that you use liquid nitrogen to test all functions of the vessel and perform a thorough leak check.

If you have a leak in a pressure building line or regulator, for instance, you get exactly the opposite result from the one desired when you open the PB isolation valve. The same can occur due to a leak in a valve stem or packing. When the valve is opened and a resultant leak occurs pressure will drop and then dry ice will form."

Low-Loss Liquid Fill- What Price Success?

Companies delivering liquid nitrogen, oxygen, and argon are fortunate these days to have some choices:

a) Pumped Systems- many of which have low transfer loss features

b) Pressure Driven Systems- some with MC-338 options allowing them to travel under pressure without venting between stops.

c) Pressure Driven Systems with Gas Use Capabilities- allowing them to be used not only for liquid delivery, but also for gas use for welding, purging, cutting, etc.

Which is best?

Of course- again we hit the millenium answer- It depends.

And it really does depend on what you are doing with the vessel- How much liquid you are delivering, what other uses (if any) you might have for the tank, and your budget.

The question crystallized after a client visit where it turns out they'd have been able to purchase two GOrilla 500s and a GOrilla 1500 (all tricked out with trailers) for what they paid for one low loss pumping truck. This is an irrelevant comparison where you need the pumping truck. Where you don't, it could be interesting to further explore where you get the most from your investment dollars.

DOT 4L Cryogenic Liquid Cylinder Pressure Relief Change

A large production and research facility has multiple uses for cryogenic liquid cylinders and keeps an inventory of DOT 4L-100, 4L-200 and 4L-292 vessels on site. The 4L-100s are set with 22psi reliefs and installed in labs and a few other locations where they are used strictly for liquid withdrawal. The 4L-200 “medium pressure” vessels are the most commonly used liquid cylinders throughout the facility and are fitted with standard 230psi reliefs. There are also some higher pressure applications at the site where 4L-292 vessels fitted with 350psi reliefs are needed.

Liquid nitrogen, oxygen and argon vessels are normally delivered to this site every Thursday. Mid-morning one Tuesday, they empty a 4L-200 oxygen liquid cylinder at a location that has a maximum feed pressure of 260psi. On arrival at the inventory area they find that their supply of 4L-200 (230psi relief) liquid oxygen cylinders has been exhausted. There are, though, a few 4L-292 (350psi relief) liquid cylinders still on hand. They call to find out if they can take a 230psi relief off an exhausted 4L-200 and put it on a 4L-292 in order to use the 4L-292 at the process area that cannot exceed 260psi.

What is the answer?

Why?

Are there any other questions or considerations that need to be reviewed related to this answer?

Tune in next time…….

West Cryogenics Manufactures New Cryogenic Equipment in the U.S.

Yes. West Cryogenics manufactures brand new GOrilla & Ultra Cryogenic Liquid Oxygen, Nitrogen and Argon Tanks and Dragon Vaporizers in their ASME Code plant in Willis, Texas. And- clients are welcome to come and watch the manufacturing work being done. You can see everything from welding nozzles on heads and then welding the heads to shells and performing ASME pressure tests to seeing how super-insulation wrapping is done and vessels are sealed and mass-spec tested to be sure they are leak free. Then you can see the heated and cool vacuum processing, sand blasting, painting, and piping…… not to mention also getting to see cleaning materials for oxygen service and performing tests and analyses.

When you really think about it this ranks with touring the Blue Bell Ice Cream and Dr. Pepper plants except that manufacturing brand new cryogenic vessels in the United States is a lot less common than ice cream or soda pop. I have to say this in a very qualified manner, though, because it is a bit of an understatement to refer to Blue Bell simply as “ice cream” or Dr. Pepper as “soda pop.” It is more likely that they, in fact, are the very real modern personification of “milk and honey.” And well, you know, GOrilla Tanks, Ultra Tanks, and Dragon Vaporizers are mighty fine, too. And- They are all manufactured new in the U.S.

Cryogenic Liquid Cylinder NER (Normal Evaporation Rate) Testing

Full NER Steps include:

- Make sure your pressure builder and gas use valve are securely closed
- Open the Vent valve and connect a fill source to the liquid connection on the liquid cylinder
- Fill the Vessel with liquid nitrogen to “full” level by weight and leave the vent open allowing the liquid to fully stabilize (ie- until venting stops)
- If the vessel vents continuously for several (3-4) hours after filling and shows no sign of slowing down then check to make sure your pressure building line is not leaking past the valve. If it is then your pressure building valve needs to be rebuilt or replaced. If the PB is fine then stop the test and save whatever product you can as you already know that your vessel needs to be sent in for service.
- Now, top off liquid level to replace initially vented product
- Log the weight of the filled vessel and leave the vent open
- After 24 hours, reweigh the vessel and log this (minus vessel tare weight) as “Net Starting Weight”
- Measure the weight of the vessel in two successive 24 hour periods
- Subtract the final weight from the starting weight to determine the total weight of product lost. In all cases subtract the tare weight of the vessel so that you are just logging the weight of the product. (net weight)
- Divide the net weight of product lost by the net starting weight to get the percentage of loss over two days.
- Divide that figure by two to get the daily NER.

Is Microbulk Cultural?

Seven or eight years ago U.S. Manufacturers were told that there would be no real reason for them to do much in the way of 250-500 gallon vertical bulk tank production. Reasons given included plentiful stocks of used equipment and the inability of suppliers to economically justify small volume cryogenic liquid deliveries. Yet, During the past few years, sales of microbulk vessels in the 1000 to 2000 liter range have been strong. These are the same sized vessels just packaged differently.

This might be ironic except for the fact that “Nature abhors a vacuum.” And- just because a major producer of liquid oxygen, nitrogen and argon has a business model that focuses their efforts on deliveries of 1500 gallons or more does not preclude the need of users. Posed with the question of how to fill the gap from liquid cylinders to 1500 gallon bulk tanks one producer eloquently responded “That’s what distributors are for.” And in the U.S. this has proven largely true.

Interestingly enough, though, I was informed that some of the same companies who have 1500+ models in the U.S. are actively involved in establishing a microbulk presence in Europe and Asia. Part of the answer given for this is a cultural aversion in other countries to soliciting a competitor’s clients for nearly identical services. For example- If Manufacturer X is buying 20-30 liquid nitrogen cylinder exchanges per month then it might be considered unseemly for a competitive supplier to come in and offer to provide the same service at a lower rate. But- A competitive supplier who offers the same liquid in a different package is offering an alternative that changes the rules of the game.

I’m told it would still be “unseemly” to go out directly soliciting microbulk business as an alternative, but there are means of finessing the approach so that the client calls the supplier to initiate discussion. Economic presentations at trade shows, article publication, web posting and general advertisement all become fair game along with referrals from other happy clients. Overall, this is sort of a retail walk-in approach to engaging clients vs. a more active direct approach in the U.S.

Good Fun and Good Ice Cream at Sub Zero

Our high school invites the parents of graduating seniors to attend the homeroom class Valentine’s Day Party and “do whatever you’d do when you were eight.” I come with my little bag of Valentines (“one for everyone regardless…..”) and a bag of candy to find a bunch of 17 and 18 year olds absolutely tickled to be exchanging sweets and treats. Of course, there are also the wistful thoughts wondering what it would be like if every day was a little party.

My next thoughts are of Jerry Hancock and Sub Zero Ice Cream where every day is a cryogenic ice cream party. Fortunately, Jerry is enjoying real success with his novel stores where you get to mix your own concoctions and then turn them to milk shakes, soft or hard ice cream right before your eyes. The difference in what you get is determined by how long you feed liquid nitrogen into your mix. A lot of the enjoyment comes from the fun mixed in with the magic of quick freeze and delightful presentations. Also- according to Jerry: “The faster you freeze the ice cream, the creamier it is, because ice crystals don’t have a chance to form.”

Starting from stereotypical humble beginnings Sub Zero is now taking their cryogenic ice cream into the potentially hot franchise market and has done some great web site upgrades in preparation. If you can’t get to one of his locations in Utah and enjoy the fun in person you can always visit the site at www.subzeroicecream.com. And, who knows- if Jerry’s plans for going mobile work out you might even find him at your next Valentines party. If you do, please say hi for me.

Vacuum Rupture Disk D- CSI Outer Leak

Another client met me at the door saying, “Your timing is perfect. Come back to the plant and see what you can tell us about this freshly rehabbed vessel that we are having some trouble filling.” The problem was apparent from about ten feet away. We walked on up to the vessel and found a neat hole (about welding wire diameter) that went through the plastic rupture disk cover, the “Do Not Remove” warning and apparently through the rupture disk. The plastic cover and label were removed to reveal the expected “sucked in” rupture disk. This was obvious tampering and one of the few times I’ve seen it done through the rupture disk cover.

Vacuum rupture disks plastic covers are put on cryogenic liquid cylinders both to prevent tampering and to protect the very thin disk material from welding and cutting sparks and corrosion. A supplier who is able to consistently assure that all liquids go out with rupture disk covers in place is both protecting their assets and providing a ready visual indicator for drivers to help with spotting potential problems.

Many of the liquid oxygen, argon, and nitrogen bottles that come in with blown rupture disks are clearly tampered with. Spotting problems at the user site and documenting them helps with the possibility for recovering the cost of repairs for damages.

A lot of people believe that “if you take care of the nickels the dollars will follow.” Here is a case in point.

Blown Rupture Disk C- CSI Inner Leak

Delivery Company Y makes a delivery to my shop. Two weeks later I call them and say I just got to this box, it is damaged and I want to place a claim. Unable to stand the sound of their laughter I hang up. Much is the same when a gas supplier tries to call their client two weeks after picking up liquid cylinders to say that some of them are damaged and they are going to bill the customer. The difference is that the reaction from the client can be a little rougher than laughter.

Having alert drivers who pay attention to what they are loading at pickups, note damage found and get customer signatures is priceless. Take for instance a cryogenic liquid cylinder that has a bent handling ring, piping and a dent on the head. Looking a bit further the driver finds that the vacuum rupture disk is blown out. This is pretty simple. The liquid cylinder has been dropped and there is now an inner leak at the neck or some other point. The contents (oxygen, nitrogen, argon or CO2) has escaped into the annulus, built pressure and blown the rupture disk.

Now the cryogenic liquid distributor is confronted with either a costly repair $750 to $1000 or more or replacement of the liquid cylinder $2000 to $3000 or more. In the case of a larger “micro-bulk” vessel that is set down too hard and snapped a neck connection the replacement cost can be well over $10,000 to $20,000. And- it is really hard to tell if that happened at the customer’s site or the fill plant without documentation at pick up.

Note that all inner leaks are not the result of abuse. Some do occur due to manufacturing or design issues, but the chance of recovering or even sharing costs with users are greatly diminished without documentation…… and reasonably so.

Vacuum Rupture Disk- Blown B

A client called upset that they’d just received 20 liquid cylinders back from rehab and now had 18 in the yard “bad.” They wanted immediate attention and got it. Two things were obvious on arrival. The first was that there were no DOT-4L repair “K” tags on the vessels indicating right away that we’d never seen the vessels in question. Number two, and most upsetting to the client, was the very apparent indication that someone had intentionally punctured the rupture disk on 18 of the 20 liquid cylinders. This was obvious as the protective disk covers were missing and the disks were blown “in” instead of “out.”

The purpose of vacuum rupture disks for cryogenic tanks and liquid cylinders is to prevent rupturing of the outer vessel which has no pressure rating. Vacuum rupture disks are very thin, concave and surrounded by knife edges which are lined up just over the surface. A very low pressure build up in the annular space of an oxygen, nitrogen, argon or carbon dioxide cryogenic tank will cause the disk to protrude against the cutting edges and rupture allowing free flow of the gas to atmosphere. So- any CSI investigator who sees the disk blown out can readily tell that a vessel with a disk blown “out” probably has some type of inner leak.

A disk that is blown “in” indicates a leak occurred in the disk and the vacuum in the annulus sucked atmosphere from outside pulling the disk in. There are slip-on plastic protective covers installed over most disks to prevent damage that would cause a leak. Many manufacturers and service companies also install a warning between the cover and disk noting that removal or tampering will void any warranty of the vessel. This cover helps protect the disk from welding or cutting sparks and corrosion that could cause a vacuum space leak in the cryogenic tank.

When there is a good vacuum on a tank then rupturing the disk will cause a great whoosh of flow into the annulus. It is an all too common occurrence for vandals to remove the covers and puncture the disks. Whether their intent is malicious or just for entertainment the result is the same. The liquid cylinder now has no vacuum and will have to be sent in for a rather expensive repair.

Next, we’ll talk about responsibility and how cryogenic liquid suppliers can save hundreds of dollars by training their drivers to be alert to damage and consistent in documenting it on site.

A Really Smart Fireman

Answering the phone I hear, “Hello, sir. This is ___ of the ___ Fire Department in __, California. I am responding to a call at ___ University Chemistry Department and hope you can help.”
“Of course, what’s up?”
“Well, sir. I am outside a lab that has a liquid nitrogen cylinder that has been venting off very hard for a good while and I’m trying to get a few answers before going in. I understand that liquid cylinders are supposed to vent, but we want to be sure there is no danger of an explosion.”

a) How’d he get my phone number?
b) Is there a potential danger?
c) How will we know?

a) He had a scope and was able to see the “K” tag that we and all other DOT-4L authorized repair centers are required to put on liquid cylinders that we repair. It also has our phone number.
b) Since he could see the “K” tag I asked if he could also see the data plate. He answered yes and reported the liquid cylinder was a 4L-200 rated vessel. And, he could even see the pressure gauge which was reading about 220psi.
c) We’ll talk more about DOT 4L ratings later, but for now suffice it to say that the cylinder was not likely to be an explosion hazard at that moment. So- all is OK? Not necessarily.

And just as I was about to tell him so he said “Oh, and don’t worry, sir. I’m very aware of the potential asphyxiation hazard in the room and have a breathing air pack on and an oxygen monitor. Thank you for your help” and hung up.

More like Thank You for Yours! I wish I had his name or even had the time to note the Department or University. He was smart , appropriately cautious and personified Falstaff’s statement in Henry IV:

"The better part of valour is discretion, in the which better part I have saved my life."