Choked flow and Joule-Thomson in a valve for CO2 injection

[AndreaSagninese]

Hello everyone,

nice to join the forum! I've recently started a R&D, ChemEng post, even if my background is in Numerical Analysis and Applied Maths. So I will ask you a couple of questions more related to the Engineering/Thermodynamics.
Suppose you are transporting CO2 in a pipe and then you want to inject it in the ground through a well. The C02 is arriving with certain pressure and temperature. At the wellhead the injection flowrate is regulated through a valve.

1) How would you model the choked flow? Consider that upstream pressure in the pipe is 120bar (liquid C02), while at the top of the well we see 38bar (gaseous CO2) as initial condition.
2) How would you model the JT expansion? Physics tells me that C02 will cool down.

I am a bit confused. In my CFD code I need to initialise the internal cells of the domain (so far, so good) and the ghost cells. But I need to talk into account the choke and the JT expansion. What is the correct way of doing it?

Cheers,
A.

 

[LittleInch]

With all due respect there is so little understanding here of what is going on that it is not possible to answer based o the data given.

You really need to talk to / hand this over to a chemical or process engineer that actually understands the actions.

CO2 is strange stuff and going from liquid to gas isn't really J-T, but a change of state. Doing what you're trying to do will result in very low temperatures and a huge increase in volume.

Choked flow is a well understood thing - just google a bit to get some idea. All good flow simulation programs will understand this.

What is "CFD code" and ghost cells? Sounds like some sort of science fiction to me....

Please get some help with this from someone who can spend a few hours explaining it.

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

 

[zdas04]

Most of us here will understand that CFD is Computational Fluid Dynamics.

As LittleInch says, CO2 is strange stuff. Take a look at a pressure vs. temperature enthalpy map and see if you can answer your own question. There is a big area in the upper right hand corner of the map that should be labeled "Abandon Hope, all yee who enter here".

CO2 can be successfully transported as liquid, gas, or as "dense phase" (also called "super critical" which lies in the upper right of the map). Doing what you are doing with liquid upstream of the choke is really risky, since the transition from liquid to gas is hugely exothermic and results in cryogenic temperatures before pressure gets very low. Transporting it as a gas gives you J-T cooling, but it is pretty squirrelly because it is pretty easy to transition to dense phase, where J-T doesn't work.

In terms of transporting, storing, and using CO2 is just about as hard a fluid as is possible to have. To get a great education on CO2 search eng-tips.com for user "Montemeyer" (it may end in "yor", I'm not certain). He is likely the world expert in real-life CO2 issues and has given a number of seminars here in the guise of answering posts.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[georgeverghese]

Before you start the CFD modelling, would suggest you get some graphs or charts that show pressure vs enthalpy for the gas, liquid and solid phases for CO2. That will also give you a second indication of what goes on with this CO2 as it drops down isenthalpically from 120bar to the built up backpressure at the surface elevation of the injection well.

 

[LittleInch]

Ok, I knew what CFD was, but unclear how it is being used in this instance.

The main point was this - "a R&D, ChemEng post, even if my background is in Numerical Analysis and Applied Maths." It is more than a bit unrealistic in my view to expect someone to undertake work for which they are not qualified or experienced in and the risk is that an answer will be found that is in fact very wrong. Pressurised fluids can kill when they go wrong and it should not be treated lightly.

As zdas04 explained, CO2 has a particular set of properties at different pressure and temperatures and going from a "liquid" or dense phase state to a gaseous one is something that can result in temperatures well below freezing resulting in ice formation and material becoming brittle and being stressed by contraction.

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