CO2 Storage 4

[GSgopi]

I am using liquid co2 in my setup for cooling inside the oven.I use the liquid co2 only once or twice in a month
The 300psi regulated Co2 gas is passed into VT-300 satellite reservoirs which gives liquid co2 as output.
Problem:
In idle situtaion,
The 300psi builds upto 450 psi inside the reservoir cyclinder due to temperature variations (30 to 40 deg celcius in INDIA).Due to increase of pressure the rupture disk blows off, co2 is wasted out. If we condense the Vapour co2 we end up with liquid co2 again the inventory is wasted.

I am in need of a solution to minimise the wastage of co2.

Pardon me if my understanding on co2 is wrong .

 

[Compositepro]

To keep the CO2 liquid in the VT-300, it must be on continuously. That is not very economical if you only need it once or twice a month. It is cheaper to vent the CO2 between uses. I hope it is a relief valve that is lifting and not a rupture disc blowing. For your case high pressure CO2 cylinders may be a better choice than the VT-300. Venting the CO2 in the VT-300 should be a normal part of the shutdown procedure. Have you read the manual?

 

[GSgopi]

I thank you for the reply.
Its the rupture disk blows off.
I havent gone through the manual for draining procedure. will sure go through it.
I am bascially an electronics engineer, I am not able to figure out the properties of co2 with variation in temperature.As far as my understanding,The liquid Co2 in the tank gets expanded due to variations in the surrounding temperature and thereby increase in Co2 vapour pressure.
Is there any linear relationship between the conversation from liquid state to vapour state and vapour state to liquid sate of Co2.

 

[Compositepro]

Google "vapor pressure of CO2". And "RTFM", too, while your at it. It is 60 atm at room temp. and 10 atm at -40C. You won't be draining CO2, you will be venting it, preferably outside. Operating this type of equipment with your level of knowledge is dangerous. You can get someone killed.

 

[MortenA]

Dont be hard on the fellow - but you are right: You wont have any liquid co2 at atm P - but ice or vapour.

For your reference this document caontains a lot of hard data re co2 - but you need to be a chemist to understand most of it:

http://www.union.dk/media/CO2-GB.pdf

I think you should consult with somebode re. this to make sure that you are safe.

Best regards

Morten

 

[chicopee]

You can always replace the VT 300 with higher pressure reservoirs rated for a MAWP based on the highest ambien temperature expected.

 

[Montemayor]

There are basic hazardous conditions and misunderstandings within this topic and I am forced to repeat some facts that I’ve made known in past threads regarding the storage, use, and application of liquid and gaseous CO2.

Gsgopi makes some misleading (?) statements in his/her original post. This is understood as a lack of necessary process training and understanding of phase equilibria and thermodynamics. Both subjects have a lot to do with the application (which is not accurately described). Gsgopi states: “I am using liquid co2 in my setup for cooling inside the oven”. This doesn’t say what are the conditions of the liquid CO2. It makes a big difference in understanding what he is doing without a flow diagram or P&ID resource.

It is further stated: “The 300psi regulated Co2 gas is passed into VT-300 satellite reservoirs which gives liquid co2 as output.” This then implies that the liquid CO2 fed to the oven must be low pressure, liquid CO2 at approximately 250 – 300 psig and -8 to +1 oF. This cold, liquid CO2 pick up latent heat of vaporization and is recovered as a saturated gas by the “VT-300” apparatus described in the referenced website.

The VT-300 is apparently nothing more than a recovery unit comprised of a refrigerating unit and a liquid reservoir and it recovers the generated CO2 vapors for temporary storage and subsequent use later. It apparently lacks the refrigeration capacity to maintain the captured CO2 in the liquid state when subjected to heat gain from the surrounding ambient conditions. The OP fails to state this and this has to be assumed. This badly described data has caused misconception and wrong advice from the subsequent posts. This just causes confusion, but the most important point here is that the VT-300 unit apparently has been either badly specified prior to purchase or has been sadly designed.

No low pressure liquid CO2 tank (which is the international norm for storing CO2) should be equipped with a low-cost rupture disc. The reason for this is clearly seen and understood by studying the thermodynamic properties on the valuable information furnished by our old friend, Morten. This basic data should be well-understood because it is the underlying information necessary to avoid a hazardous situation or to mitigate it when dealing with a liquefied, compressed gas such as CO2. Morten is almost correct in his comment referring to the result of venting liquid CO2. Whenever liquid CO2 is vented, the result will be DRY ICE (solid carbon dioxide at -107 oF). This is the same effect that is seen when a CO2 fire extinguisher is actuated during a fire. However, the fire extinguisher is at ambient temperature (80 oF) and consequently at approx. 1,000 psig. In this case, the liquid CO2 is at 300 psig (and +1 oF) and when it expands due to the sudden release of a rupture disc, the liquid in the reservoir is converted to dry ice at -107 oF. This is OK, as long as the parent metal of the reservoir is made with properties to resist such a low temperature without undergoing subsequent brittle fracture (as is the case with normal carbon steels). This is a “stealth” type of hazard that can occur if the reservoir metal cannot withstand such a temperature “shock”. Normally, design engineers take this into consideration when confronting this type of possible scenario and fabricate the vessel out of low-temperature steel or stainless steel (more expensive!). Another solution is to install safety pressure relief valves (two) that reseat after relieving the excess pressure. However, these are more expensive than a simple rupture disc. One can quickly conjure up what a supplier would supply if left to sell the most “competitive design” due to a lack of specifications or data sheets from the buyer. The lack of demonstrated process knowledge in this application raises my concern and my writing this post.

In my opinion, both Compositepro and Morten raise a valid and important safety issue regarding this application. I recommend that VA-Tran Systems be advised what is happening with regards to their equipment and an inquiry made as to what is their opinion and what can be the consequences of these over-pressure incidents. Certainly a PSV can replace the rupture disc; but what has occurred with the ability of the reservoir to safely continue to store the liquefied CO at 300 psig? If there is a justifiable reason for continued storage of LP CO2 liquid, then additional storage refrigeration is required – which translates into more capital monies.

The comment by chicopee does not apply because what is clearly being used here is low pressure, saturated liquid CO2 at 300 psig and not high pressure liquid CO2 at ambient temperature. The HP CO2 would not work in this process.

 

[Compositepro]

Montemayor, I do not believe that the VT-300 is designed to, or capable of, recovering ambient pressure CO2 after it has been used for cooling an environmental chamber or whatnot. It is used to replace an insulated recirculating liquid CO2 loop, which is traditionally used for rapid chilling in test labs. The constant energy losses from hundreds of feet of piping are expensive. Instead simple piping can be used to transfer 300 psi CO2 vapor from bulk storage (which is liquid CO2) at some distance away from the lab. The CO2 is refrigerated to liquify and store it in the VT-300. It does not recover any CO2. It fits a niche market of medium volume CO2 users.

High pressure CO2 bottles can be used for this application but it gets expensive if much CO2 is needed. And handling bottles is a hassle.

 

[GSgopi]

Hi all,
First I apologise for providing misleading statements as Montemayor said in his post.
I thank all for your valuable suggestions.
The process diagram is attached with this post for your reference.

I am doing a temperature (heating and cooling) testing for an electronic component inside the oven.The heating is achieved by increasing the oven temperature and cooling is achieved by venting liquid CO2 from VATRAN reservoir into the Oven.

The operating temperature of my lab system is 75Deg Farenheit and ambient temperature in India is 96.8Deg Farenheit.We do have a relief valve and rupture disc in our system.On all our working days we will maintain 75 Deg and on saturday and sunday it will be the ambient temperature which is causing the increase in vapour CO2 pressure inside the storage reservoir of VT300.Due to increase in vaprour pressure the relief valve allows the co2 out.

We are planning to switch ON the refrigrant whenever there is an increase in co2 vapor pressure of above 350PSI(The co2 Vapor input to resevoir is closed in idle state) thereby preventing increase in vapor pressure.will there be any safety issues in this automation.

I am not able access the link

http://www.union.dk/media/CO2-GB.pdf

what MortenA has qouted . Please help me out in getting this pdf file