Is Bulk CO2 Shipped Cryogenically To Minimize Tank Weight, Or For Some Other Reason?

[crshears]

Originally posted in the Railroad Equipment Engineering forum...but that seems to be a low traffic location, and probably the wrong forum considering the question...maybe here is a better fit?

My interest in railroads has been revived since I started volunteering aboard the retired / legacy steam ship SS Keewatin [www.sskeewatin.com], formerly an asset of the Great Lakes Steamship Service of the Canadian Pacific Railway...

Question: for bulk transportation of CO2 by rail [or large tanker truck] in North America, is liquid CO2 usually shipped cryogenically in heavily insulated tankers so the pressure rating and overall weight of the tank needn't be as high as if it were shipped at ambient temperature and higher pressure? My thought is that with the latter there would be less net loss en route due to expansion & blow-off, but that doesn't appear to be the way it's usually done.

For answers to the above, what reasoning is applied and/or what regulations prevail to dictate doing this one way or the other? My Internet search results to date have proven less than stellar...

Thanks!

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[racookpe1978]

From pv=nRT gas laws, consider how very little mass of CO2 you are shipping as a very high pressure gas (then add the dead weight of pressure vessel and its extra expense and the hazard increase of high pressure gas cross-country!) + the gas compression tooling and expense of compressing then bleeding off the CO2 as you fill empty transport tanks.

OK, now, consider CO2 is 'fabricated" commercially by cryogenic separation from air .. so low pressure systems already exist in the "factories" that already provide the CO2 at very low pressure and very low temperatures. To ship it using room temperatures but high pressure systems, you'd have to heat the liquid CO2, then compress it. Easier to ship cold and keep cold.

 

[EdStainless]

And a lot more tons of it in a single load, the liquid is much denser than even a high pressure gas.
And after all we ship liquid oxygen, nitrogen, argon, and hydrogen for some of the same reasons.
Another advantage is that the cryogenic sourced gases are much higher purity (dew points of -100F are common).

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P.E. Metallurgy, Plymouth Tube

 

[zeusfaber]

I'm curious. Is it shipped as a cryogenic gas, or just as liquid CO2 at ambient temperature and 55ish bar?

A.

 

[EdStainless]

Most CO2 is usually shipped as a refrigerated liquid, large bulk transports are usually designed at -50C and 7bar

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

The term cryogenic is usually limited to low temp ops < -100degC, with -100degC being the lower limit for C2= refrigerant. On a glance through T vs Psat curves for CO2, it should be possible to store CO2 at low pressures say at 7-10barg with a CO2 refrigerant condensor operating at -50degC / 7barg, if you want to limit materials of construction to charpy impact tested low temp A333 grades.

 

[crshears]

Sorry for my misuse of the term "cryogenic," georgeverghese; I guess I should've asked "Is Bulk CO2 Shipped As A Low-Temperature, Moderate Pressure Liquid To Minimize Tank Weight, Or For Some Other Reason?"

Continuing research following my OP led me to a webpage that gave the particulars of storing liquid CO2 at ~300 psig [see

https://kidde-fenwal.com/Media/Data Sheets/LP CO2 SPEC SHEET.PDF

]; despite its being a product promo, reading through this document made it clear how much more steel it would take to make a railroad tank car [and therefore how much higher the charges would be for returning the empties] to transport liquid CO2 at ambient temperatures [due to its much higher vapour pressure] instead of at zero Fahrenheit or colder, thick insulation still being much lighter than steel.

This being the case: the above-referenced document refers to instances where, in the event of failure of the AC-powered re-compressing and cooling machinery, how the refrigerant effect of flashing off excessive CO2 in the case of tank overpressure helps to limit further loss of CO2.

This makes me wonder: are or could refrigerated liquefied Class 1 gas rail cars, not having cooling machinery, be equipped with a cooling coil that routes the flashed gas down through a coil in the remaining liquid before venting said gas to atmosphere, in order to both take maximum advantage of said refrigeration effect of the flashed gas and minimize loss of remaining liquefied gas?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[dhengr]

Crshears:
It seems to me that I have seen tanks, probably tank cars too, with coils wrapped around the tank, under the insulation covering. These might be heating or cooling coils, and of course the tank car will then have an other skin of steel to cover and protect the insulation. I’ve never designed or built any tank cars, but I have been involved with them, in an engineering capacity, on several occasions. That’s why I suggested that you talk with some tank car manuf’ers. You might also add to my list of contacts, the people who make CO2, how do they ship their product, any rail shipment?

 

[Compositepro]

The CO2 vapor cannot be used to cool the liquid any further. It has already cooled the liquid by simply vaporizing in the tank it and is at the same temperature as the liquid.

 

[crshears]

Um . . . am i missing something? Obviously the vapour and liquid IN the tank are at the same temperature and pressure; but would not any vapour exiting the tank via an expansion valve and falling [from, say, 300 psig] to about atmospheric pressure undergo an isenthalpic expansion and drop to a yet lower temperature such that it could be passed through a coil in the liquid [or around the tank] and absorb at least some heat from the liquid before being released to atmosphere?

Also, thanks, dhengr, for the additional info [and just to let the rest of you know, dhengr was the only respondent to reply to the OP on this topic in the Railroad Equipment Engineering forum].

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[zeusfaber]

(Lurking, listening and learning here: please keep going).

A.

 

[EdStainless]

What do you get when you release high pressure CO2 through a throttling valve? Solid CO2, which is a little hard to use in heat exchanger.

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P.E. Metallurgy, Plymouth Tube

 

[crshears]

What do you get when you release high pressure CO2 through a throttling valve? Solid CO2, which is a little hard to use in heat exchanger.

True, dry ice will form...but would it not impinge on the walls, absorb heat, and sublimate? Especially if the dry ice generation rate is not crazy excessive...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Compositepro]

You get solid CO2 when you release pressure from liquid CO2, not vapor. The amount of cooling obtained from expanding a gas from 300 psi is not economical or it would be done already.

 

[georgeverghese]

Dry ice can form when pure CO2 pressure is less than 5barg or so.

 

[dhengr]

Why not ship the CO2 as dry ice, in a refrigerated box car. It is then saleable in two forms, dry ice or CO2, when you get to the destination.

 

[EdStainless]

The liquid is much easier to handle, you can pump it and such.
I haven't looked up densities, but it wouldn't surprise me if the liquid was denser.

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P.E. Metallurgy, Plymouth Tube

 

[crshears]

The CO2 vapor cannot be used to cool the liquid any further. It has already cooled the liquid by simply vaporizing in the tank it and is at the same temperature as the liquid.

This is the part I don't get; obviously the heat of vaporization has been supplied to transform the liquid to gas, but in the scenario under consideration the gas is still at ~ 300 psig, so to my view expansion of same to atmospheric pressure will cause a further drop in temperature below the saturated pressure/temperature within the tank, meaning that at the very least the gas should become somewhat superheated by absorbing thermal energy from within the tank before escaping to atmosphere.

The amount of cooling obtained from expanding a gas from 300 psi is not economical or it would be done already.

The refrigerating effect might not be huge; but 'uneconomical'? The equipment that would be used to accomplish the stated objective borders on the primitive, and I would not expect it to cost so an exorbitant amount as to preclude the possibility from being considered, which was precisely the reason for the OP...


CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[LittleInch]

Expansion of the gas occurs outside of the tank resulting in cold gas in the atmosphere which often then condenses water to appear as "steam" or "smoke". This has no impact on the fluid left in the tank.

In theory yes that cold temperature could be used to cool a liquid which then passes into the tank via a coil, but the power to run the pump and weight of the cooling system is probably more than it would take to simply add a small refidgeration unit, compared to the amount of cooling undertaken by the gas volume. Remember the purpose of transport is to transport the gas, not let it all leak out on the way there....

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

 

[crshears]

Hello LittleInch,

Earlier in this thread I wrote:

This makes me wonder: are or could refrigerated liquefied Class 1 gas rail cars, not having cooling machinery, be equipped with a cooling coil that routes the flashed gas down through a coil in the remaining liquid before venting said gas to atmosphere, in order to both take maximum advantage of said refrigeration effect of the flashed gas and minimize loss of remaining liquefied gas?

All I was inquiring about was using the endothermic effect of expanding gas to provide some cooling so as to possibly mitigate, not eliminate, the loss of CO2 during its transportation; chances could be that such a low-cost unit might be of value during the summer season when there would be increased heat transfer through the tank car insulation, all without the trouble of adding a refrigeration unit with its attendant capital, operating and maintenance costs.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]