4 replies to this topic

[Wajid]

I am getting Dewpoint of natural gas -74 deg C at 0 psig. Water contents are calculated to be 1.4 ppmv.
At the line pressure of 680 psig dewpoint is calculated to be -45.6 deg C. Will the water concentration in ppmv remain same, increase or decrease?

Looks like what you've done is increased your pressure, kept ppm(v) constant ,and found your new dew point.

ppm(v) is proportional to the ratio of the water vapour partial pressure to the total system pressure.

[Wajid]

Thank You very much mbardfast, now I have a second opinion to convince my colleagues.

[DrDewLittle]

I am getting Dewpoint of natural gas -74 deg C at 0 psig. Water contents are calculated to be 1.4 ppmv.
At the line pressure of 680 psig dewpoint is calculated to be -45.6 deg C. Will the water concentration in ppmv remain same, increase or decrease?

By definition parts per million by volume does not change with pressure.

Edited by DrDewLittle, 14 August 2010 - 01:30 PM.

[Padmakar Katre]

Dear,
When it is said that the natural gas is at its dew point temperature or pressure it will have a certain saturated water unless you route your gas through an adsorbent bed to remove saturated water. Now when you alter the conditions like Temperature and Pressure, saturated water could become as free water e.g. in case-1 if the temperature falls down and case-2 pressure goes up (change is say substantial), you may find free water and subsequent change in water concentration in flashed gas. You have to judge the change in these parameters.