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Sunday, November 2, 2008

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A loyal reader in Chemical Process Technology raised a question. I have a dry gas composition. As the gas is produced from reservoir, it is saturated with water. How to simulate in the HYSYS simulator ? How to calculate water content in wet gas ?

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From hydrocarbon - water equilibrium analysis, you will find that as you increase water content in dry gas, the water will mix with dry gas until the dry gas is saturated with water. Once it is saturated with water, any addition of water into the water saturated gas (normally called wet gas) will knock-out as free water in aqueous phase. This can be easily modeled in any process simulator like HYSYS.

Below image shows Dry gas stream is mix with Water in a 3-phase Separator unit operation. To saturate the Dry gas with water, the only requirement is increase the Free Water flow until the aqueous flow (Free Water) starts to knock off free water. In this case, an ADJUST unit is used to adjust the water flow until zero flow.



To find water content (in lb/mmscf), first check out the Water Mass Flow in Wet gas from composition, change the basis to mass flow. See following image.




Then find the Molar flow in MMSCFD. See following image.



In above example, the Water Mass Flow is 1233.6 kg/h (2719.6 lb/h) and Molar Flow is 1005 mmscfd. Thus,

Water content = (2719.6 x 24) / 1005 = 64.93 lb Water / mmscf Gas.

If you have better method, let us know.

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posted by Webworm, 2:27 PM

4 Comments:

Anonymous Anonymous said...

Dear all,

Nice article regarding dry gas saturation. But, in my opinion there must be a 2nd adjust function to keep wet-gas [saturated gas]temperature same as the dry gas has. In existing model gas temperature will decrease as we add water contents to it [owing to heat energy requirement for evaporation of water droplets to saturate the dry gas].

Best regards.

Muhammad Adnan Hanif
Process Engineer
Fauji Fertilizer Company Limited
adnan_hanif@ffc.com.pk

November 7, 2008 at 1:31 PM  
Blogger Webworm said...

Muhammad,
Thanks for your comments.

You may set the Wet gas at required temperature and leave the Water temperature free. The Water temperature will be adjusted automatically by HYSYS module so the Dry gas temperature same as Wet gas temperature.

November 7, 2008 at 3:35 PM  
Blogger dhiraj said...

Dear all,
i have another method. I need inputs if this is correct.
Mix the the dry gas stream with water stream at same process conditions. there might be a dip in temperature, so add a hypo heater. Then separate the gas and liquid water(excess) stream with two phase separator. Then check for the water at the bottoms of the separator. Add an adjust operation to the stream after hypo heater and the input water stream. Set the target value for HC stream as 0.9999 vapor frac. and adjust the mass flow of water that is input to mixer.
That should also work.

Regards

Dhiraj

May 22, 2010 at 1:16 AM  
Anonymous JoeWong said...

It works.

May 22, 2010 at 8:47 AM  

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