5 replies to this topic

[Doru]

Dear all,

can someone, please, tell me what is the minimum allowable temperature for the inlet natural gas when a dehydration process using silica gel is considered? I have an application where 9 mln. cubic meter / day of natural gas at -10 C must be dryed to a -15 C dew point. What dehydration process will be best suited? Thank you!

Best regards,
Anku

[ColinR33]

Dear Anku,

There are a couple of options available for you, for a -15C dewpoint a TEG unit would be acceptable, but a -10C inlet temperature is too cold.. Typically minimum inlet temperature for a TEG unit is 10-15C so you would have to pre-heat the gas before treating. If you have to do HC dewpoint control at the same time, a refrigeration unit with EG injection would work. For silica gel I personally have not seen or designed a unit for operation at -10C, so I can't comment, I typically see them running at 30-50C inlet gas temperature, maybe someone else can comment on that. What presure is the system operating at and why is the gas so cold coming in?

Cheers,
Colin

[Doru]

Dear Colin,

thank you very much for the reply. The system operates at a pressure from 20 to 55 bar. The gas is not allways so cold but the minimum inlet temperature required by the Client is -10 C.

[PaoloPemi]

for silica gel there are no real low temperature limits except those of materials and the efficiency of the dehydration process,
the dehydration process has the scope to remove the water but the maximum amount of water in gas (not condensate) reduces as you reduce the temperature so you'll get a limit where the efficiency becomes very low.
You may find useful the GPSA charts for natural gas + water or calculate natural gas + water equilibria with a software.

[Doru]

Thank you Paolo! We will provide a heating stage to ensure the gas will enter the TEG unit at temperature greater than 15 C. However, I'm wonder if there could be a cheaper solution. A different dehydration method?

[PaoloPemi]

it is not clear if gas is saturated with water at -10C,
if water dew point in inlet stream is below -15C (i.e. HC condensate) then you could consider a refrigeration unit (or equivalent system) as already suggested,
with physical adsorption an equilibrium exists on the adsorbent surface and for dehydration that depends from partial pressure of water which becomes very low as you reduce the temperature.