7 replies to this topic

[Propacket]

Hi Everybody,

I am working on simulation of LNG Plant. I have a De-Ethanizer which is operating under cryogenic conditions. I nedd to check CO2 freeze out on each tray. Hysys utility 0f "CO2 Freeze Out" works only for Streams and not for Trays. Is there any method to check CO2 freezing on Trays.

[Zauberberg]

Is this a turboexpander plant?

If you have concerns with respect to CO₂ freezing, the best place to check are: feed streams to the De-C₂ tower, and the overhead stream. There you can get CO₂ freeze-up. If temperature of these streams is sufficiently above the solidification points of CO₂, I can't see any issues in other locations in the tower.

http://www.bre.com/p...ation Paper.pdf
http://www.rivercity...p/CO2Freeze.pdf

[Propacket]

Is this a turboexpander plant?

If you have concerns with respect to CO₂ freezing, the best place to check are: feed streams to the De-C₂ tower, and the overhead stream. There you can get CO₂ freeze-up. If temperature of these streams is sufficiently above the solidification points of CO₂, I can't see any issues in other locations in the tower.

http://www.bre.com/p...ation Paper.pdf
http://www.rivercity...p/CO2Freeze.pdf

Thanks for the literature.
We have a propane chiller and then a low temp separator for condensate recovery. I have checked the feed stream and overhead stream. Temperature of ovhd gas from de-ethanizer is close to co2 freeze out temperature. I am working for worst conditions. I just wanted to know the co2 freezing temp on each tray if it occurs.

[Zauberberg]

You've already done the work if the coldest streams are outside of CO₂ freezing envelope. As you move towards lower trays in the tower, the temperature is higher and CO₂ freezing potential decreases.

Just be aware of freeze prediction methods. Articles attached above are very illustrative.

[Padmakar Katre]

Dear,

Please let us know the actual CO2 content and the lowest temperature you have.In case of De-Ethanizer and propane chiller I consider temperature is not less than (-)35C if your gas stream has molecular weight in the range of 20-22, the CO2 Freeze-out temperature is in the range of (-)80 to (-) 90 Deg C.(Pure CO2 freezing temp is (-)78.3 Deg C)whereas If you have De-methanizer and temperature is say (-) 120 Deg C then you need to keep less than 50ppm of CO2 in feed gas.
As far as my experience of LNG simulation is concerned I have seen the limit of CO2 content in Amine Absorber Ovhd is as low as 7 ppm.

[Propacket]

Dear,

Please let us know the actual CO2 content and the lowest temperature you have.In case of De-Ethanizer and propane chiller I consider temperature is not less than (-)35C if your gas stream has molecular weight in the range of 20-22, the CO2 Freeze-out temperature is in the range of (-)80 to (-) 90 Deg C.(Pure CO2 freezing temp is (-)78.3 Deg C)whereas If you have De-methanizer and temperature is say (-) 120 Deg C then you need to keep less than 50ppm of CO2 in feed gas.
As far as my experience of LNG simulation is concerned I have seen the limit of CO2 content in Amine Absorber Ovhd is as low as 7 ppm.

We have -90F lowest temperature and percentage of CO2 is 6.6%.

[Padmakar Katre]

Dear,
Could you just elaborate your scheme further. From where the DC-2 feed comes. As well give us the feed composition and de-ethanizer product specifications required. As it's not possible and even good to suggest you based on limited information you have given here.

[Zauberberg]

CO2 is not a concern in any De-ethanizer tower. But for the LNG process I doubt you can allow more than 50-80 ppm CO2 max.

http://www.ortloff.c...l/nglpapers.htm