How Long Does It Take for CO2 to Diffuse in a Nitrogen-Filled Vessel?

[rad10k]

Ok so I wish to try solve a problem at work I will try explain as best I can .

Problem Definition;
Filling of a bundle of cylinders 17 x 50litre ( 850 000 k/m^3). 30 % Co2 in the cyindrical vessal followed by input of Nitrogen 70% to a final pressure of 200 bar

Due to production requirements it is often required to analysis the gas straight away after filling and more often than not the analysis for CO2 is reaching only 24 - 26 % which is under spec

If the vessals were left for instance 4 hours then upon anaylsis a reading of around 30% CO2 would be found.

.
My thoughts are with the diffusion of the CO2 in nitrogen as CO2 rate of diffusion is 1.25 to n2 is this causing the CO2 to take time to uniformly distribute throughout the vessal.

I would like to know how to calculate the time it will take for the CO2 to diffuse in the vessal given the final pressure and temperature of the vessal? if possible

Solution:

My current thought on solutions;

1. Fill a much smaller vessal as well at the same time and use that for analysis since the cylinder will get hotter causing the gases to diffuse quicker.

2. Increase pump speed to increase the temperature of the 17x50 bundle which in turn will increase the rate of diffusion.

3. heat the CO2 liquid before it enters the vessal increase the rate of its diffusion once inside the vessal

Any help and advice ie am I on the right track please

thanks

 

[Q_Goest]

I wonder how you're filling these bundles. Are they being weighed and a specific amount of CO2 added or are they filled to a specific pressure? Once filled to that limit, I assume you're adding the nitrogen.

The critical pressure and temperature of CO2 is 1071 psia and 87.9 F respectively. It's very possible the partial pressure and temperate of CO2 is below that, in which case there can be liquid CO2 in equilibrium with the gas. So if you can better define the gas mixture, it would help.

 

[rad10k]

Hi they are filled to pressure and temp. Liquid is cooled then vapourised. Co2 goes in first as you say then n2 upto specific pressure and temp to reach thre required final pressure (190 b)