Liquid CO2 2

[cfuller]

I've installed a liquid CO2 system but keeping getting gas CO2 at the discharge rather than liquid. I've tried various things such as bringing the supply/return closer to the machine and increasing the line size but for some reason I can not get the system cold enough to get liquid. It's running at about 285 psi at 20 F. I have no experience with CO2. Is there a consultant or applications engineer who could help?

thanks

 

[LittleInch]

You need to draw a diagram of your system to be able to see what is going on and describe it a bit more.

What is the pressure at the discharge?

It looks to me like you are right on the liquid / gas phase line.

If you're taking as off and dropping pressure then it will gasify.

CO2 is interesting stuff, but I don't understand your system at present.

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

 

[Compositepro]

300 psi storage uses refrigeration to keep the CO2 liquid. To keep the lines filled with liquid requires insulated pipes and constant recirculation of liquid back to the storage tank designed so that all vapor generated in the piping flows back to the tank.

 

[LittleInch]

Actually looking closer you seem to be in the gas phase part of the phase diagram.

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

 

[cfuller]

Thanks for the response. The system has 1-1/2" piping with 1-1/2" insulation and the loop is 700' so the supply/return are 350 ft each. We're using a Blackmer CRL 1.5 (Sliding Vane) pump. The pressure at discharge is 285 psi and 20 F.

 

[Latexman]

285 psig (20.7 bara) and 20 F, you are far into the gaseous phase.

Good Luck,
Latexman

 

[LittleInch]

I agree. You might have installed a liquid CO2 system but don't appear to have put enoughCO2 into it to keep it liquid.

Is this a circulating loop for cooling or something?

what's the pressure and temp on the inlet of the pump?

At 20F (~-5C) you need to be at about 30 bar (450psi) or more to be in liquid CO2.



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

 

[csk62]

If you have no experience with liquid co2, you need to be very careful, there are some serious hazards that you may be unfamiliar with, such as ice blocking during system depressurization.

The saturation temperature at 285 psig is about -1F, so at 20F you definitely have gas. If you are using a blackner recirculation pump you will need an external refrigeration system to recondense gas being sent back to the tank. Most bulk liquid co2 tanks have ports which allow for refrigerant to flow through copper coils located in the headspace of the tank.

----------------------------------
Not making a decision is a decision in itself

 

[dik]

Is ice blocking the formation of 'dry ice' on depressurisation? I couldn't find anything on google.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Latexman]

dik,

Yep.

Good Luck,
Latexman

 

[dik]

Thanks, first I've heard the expression... kinda an educated WAG...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[pierreick]

Hi,
Consider this pamphlet about CO2 properties.
Good luck
Pierre

 

[cfuller]

Thanks everyone for responses. I don't think this is a problem that can be solved through a forum. As I said in my original post, is there a consultant or applications engineer who could help?

 

[LittleInch]

Oh ye of little faith. It's mainly because you've only told us 10% of the story.

"but for some reason I can not get the system cold enough to get liquid." Well what are doing at the moment?

"closer to the machine " - what machine?

What are you trying to do? Get to liquid at a certain pressure?
Use the CO2 for cooling?
Or can you increase the pressure?
How is pressure being maintained in the loop?
what's the flowrate / velocity in your 1 1/2 " pipe?
Temperature at start and stop of your loop?
Pressure at start and stop
Pressure in the reservoir

285 psi you need to get to <0F.
And then a bit more to keep it liquid

Can you draw a diagram, post a drawing, give us the whole picture?

If you don't need it to keep this thread going then any consultant will just be asking you the same questions.

But who designed this? Can't you ask them?

Where in the world are you located?

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

 

[cfuller]

What are you trying to do? Cool rubber on a mandrel
Get to liquid at a certain pressure? No set process pressure but need to be discharging liquid CO2 for the rubber
Use the CO2 for cooling? Yes
Or can you increase the pressure? No, it's a set pressure at the tank
How is pressure being maintained in the loop? Mainly with the tank pressure (285 psi)
what's the flowrate / velocity in your 1 1/2 " pipe? I don't know
Temperature at start and stop of your loop? 0 F and 20 F
Pressure at start and stop 285 F
Pressure in the reservoir 285 F

It's closed loop system but pull off liquid when we need to wrap rubber.

Here's what we found. We opened the supply valve at the bottom of the tank and by the pump and it had gaseous CO2. I'm thinking the return line is liquid CO2 judging by the frost and in similar processes the pump is frozen over. In this case there is no frost on the pump. I'm thinking the supply line is piped to gas side of the tank inside. Tried to get drawings from the manufacturer but the tank is too old. In the picture below the line on the right is the return and the line on the left is the supply. If I swap lines, is there a problem putting liquid CO2 on the gas side of the tanks.

Thanks

 

[Latexman]

Check out the Liquified Gas Handbook and Blackmer Liquified Gas Pumps . Together, they explain a bit about what’s going on in your CO2 system.

I believe you have a two phase coolant system, but I don’t know what other components you have that I’ve seen mentioned. The only place you have near 100% liquid CO2 is the point it comes out of the tank. Immediately after that, due to frictional losses and heat gain, you have a two phase mixture. The further down the line it goes and the more heat it picks up, the greater the gas content in the two phase mixture.

Link to possible Consultant1 or Consultant2

Google something like using two phase carbon dioxide as coolant or two phase carbon dioxide coolant consultants

Good Luck,
Latexman

 

[MortenA]

@pierreick,

Thanks for posting that co2 "pamphlet" - i have been looking for it since i "lost" it. UNION dont have it on the web pages these days (unfortunately). A star for you

Best regards, Morten

--- Best regards, Morten Andersen

 

[LittleInch]

Now we're getting somewhere.

What I don't think any of us understand at the moment is how do you cool the returning gaseous CO2?

Somewhere if you want a substance to stay below a certain temperature then you need to have a cooling mechanism. This can be boiling off the liquid or some mechanical means such as a chiller loop.

Can you actually sketch out your complete loop system with pressures and temperatures where known. A consultant will ask for this in the first instance or charge you to create one.

Some confusing things - you say you tried to get drawings from a manufacturer but it was too old - but in the OP it said you had just installed it??

What is the pressure and temperature in the tank in the tank??
When you know that you can find out where on the phase diagram you are.
You state the pressure at the discharge of the pump as 285 but not it's inlet pressure ( though you state storage pressure is 285 so what is the pump doing??)

To understand CO2 you need to use the phase diagram I posted above and annotated below.

It sounds to me that in your storage tank (285 psi @ 0F) you may just be at point A where there is liquid CO2 in the tank. But it might be a tank of gas as this is right on the line. Even if it's a liquid if you maintain the same pressure ( how do you get it to flow?) and the temperature increases as you go along your line, then the liquid CO2 will boil as it moves right on the graph but at the same or similar pressure. Therefore you will get gas at your mould at point B.

Then somehow it returns to the tank as a gas. There needs then to be some mechanism to cool it back down to 0F to liquify it.

Long and short of it is that if you want to get liquid CO2 at 285 psi to the mould the temperature needs to be 0F or lower. Or if the temperature is 20F then you need to arrive at point C - about 400 psi.

Does this make sense?

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

 

[pierreick]

Hi,
You may consult your supplier of Co2 to get support .
I've attached a document from Praxair using N2 to cool reactor ( Indirect cooling) .
What is not clear to me in your description is the recycling of CO2 gas to the storage tank , something is missing here .How do you intend to liquify this gas prior to return to Storage .
My 2 cents
Pierre

 

[Caloooomi]

What material is the tank? If it is carbon steel and the pressure control has been a bit suspect, then I'd worry that you'll have dipped below the MDMT...
Typically, a LCO2 tank would need to be > 9 barG at all times to avoid this.