How to cool down liquid CO2 Tank 6

[Peter_Kim_niceman]

Hello, I'm Peter, Chemical engineer.
I have Liquid CO2 Tank (Tank dia is 30meter, carbon steel). I want to get a tip for tank (sphercial) cool down to perform safely.

Fistly, tank will be nitrogen condtion (oxygen content < 1%).
Tank is designed to be operated at approximatly 5.5barg, -55℃.
Tank design is 7.8barg, +80 ~ -60℃.

we have plan to fill the LCO2 (20barg, -19℃) to our tank using tank lorry.

I want to get method for cooldown of tank using tank lorry and precaoutions to perform safely.

 

[pierreick]

Hi,
Warning, this makes no sense! Your tank cannot withstand the pressure.
Check with your safety manager. Good also to contact CO2 supplier who can supply a well-designed tank to store liquified CO2.

https://www.eng-tips.com/viewthread.cfm?qid=145412

https://www.cheresources.com/invision/topic/17168-liquid-co2-storage-tank/

Pierre

 

[kremenco]

If you want cool down your sperical tank before introducing Liquid CO2 try to introduce gaseous nitrogen slowly at low temprature first to cool down the tank so that when the liquid CO2is introduced, there will not be any cold shock for the tank.
You should have liquid relief valves on the tank set at 7.8 barg with capacity to relieve liquid CO2 at pumping rate of your lorry pump.

 

[georgeverghese]

Do you have a PID of this sphere and feed / exit lines ? Can you list out internals in this sphere or post diagram with descriptors on nozzles ?

Think you can only cooldown sphere with vapor CO2 at 20barg / -19degC, not with liquid CO2. This is because you want to avoid solid Co2 from forming on the vapor exit line valve / backpressure PCV going to vent. It is also safer, since it also avoid potential blockage at sphere PSV in case of over pressurisation. So is there some vaporiser for this LCO2 ?

See Molliere diagram for CO2 for reference.

 

[LittleInch]

Peter Kim,

Are you sure about your numbers?

You are very very close to the triple point (5.1 bar, -56.6C) where your "liquid" tank could easily go solid. The margins are very low. Ditto design pressure is quite tight to the operating pressure.

However cooldown is fairly easy. Just flash your liquid CO2 from your tanker into your tank at a pressure of say 4 bar and then deal with all the gaseous CO2 that generates as it sweeps the nitrogen out of the

That's what everyone does for LPG and LNG and similar chilled liquids and vapours.



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

 

[georgeverghese]

On second thought, the process safety risk of using LCO2 straight off the bat for precooling this sphere are minimal, provided you have reliable level indication. This should be evident when you see the Mollier P-h diagram - LCO2 should not be present at the backpressure PCV or PSV inlet nozzle at sphere top due to risk of solid CO2 blockage. However, shock chilling a warm sphere with LCO2, though it is designed with LDT = -60degC, is not a good idea from a mechanical/ metallurgical view point. Temp drop rate should be kept to a max 50degC / hr, as with all prechilling operations to avoid thermal fatigue and localised cold spots, and this is best done with saturated vapor CO2 off the supply tanker. Suggest precooling with saturated V-CO2 at-20degC/20barg for about 12hours at a low rate with sphere pressure at 5.5-6barg, before introducing LCO2 at a low rate. Keep a close eye on level once LCO2 introduction begins. Presume you have a dedicated precooling spray header on this sphere.

 

[georgeverghese]

Drying out this sphere prior to precooling is equally critical to safety. Warm cryogenic quality N2 at about 50degC should be used to dry out the sphere, blow out impulse lines to pressure and level instruments, entrance lines to PSV to get rid of traces of moisture. Suggest warming the sphere for at least 12hours, and then check moisture content at purge points with a MSA or Shaw moisture meter.

 

[georgeverghese]

This is the clearest P-h diagram I see on the net. It is also in the GPSA in the section on thermodynamic props

https://www.imperial.ac.uk/media/im...es-and-groups/thermophysics/Chart-p-h-CO2.pdf

 

[Caloooomi]

.... GEP II?

Dry with warm N2
Purge with GCO2

You'll be flashing nearly all the LCO2 from a standard trailer tank due to their normal operating pressure. To use liquid for cooldown, the trailer tank pressure will need to reduce as much as possible (allowable by transport company), before introducing the LCO2 to the static storage. How much LCO2 there will be in the tank after reducing pressure (due to evaporation), will need to be figured out.

What I can see happening is that you'll be filling with saturated vapour from the trailer to cooldown (which will be slower than just liquid), until you can get LCO2 from the liquefaction at the low pressure required. If it is the project above, then maybe you can transfer from one sphere to another...

 

[Peter_Kim_niceman]

Dear Caloooomi

I really thank you for your kind reply. I want to check somthing more specifically, so i'm leaving addtional question.

Are you telling me to vaporize the LCO2 of the trailer and cool down the tank as lower as possible with gas CO2 and finally inject the LCO2 produced by our liquefier ?
So, do you mean our tank have only low temperature GCO2 until we produce LCO2 from our liquefier ?