How dry is dry?
How dry is dry or it depends
on what your definition of is, is.
All natural gas contains some amount of water. This is most evident when you first light your stove top burner and see a small whiff of condensation on the stove. This is the water in the gas and at a burner tip, can not cause any problems. But compress this same gas and use it for fueling your natural gas powered vehicle and it is a different story.
Gas companies typically deliver gas with a 7#MMSCF which means 7 pounds of water per million cubic feet of gas. This is sufficiently low enough to avoid condensation, hydrate formation and freeze-ups at normal pipeline operating pressures. But 7#/MMSCF water content will cause problems for your refueling station and vehicle.
Many times we asked just how dry does the
natural gas have to be. Gas companies typically deliver gas with a 7#MMSCF
which means 7 pounds of water per million cubic feet of gas. This is
sufficiently low enough to avoid condensation, hydrate formation and
freeze-ups at normal pipeline operating pressures.
But, what does 7#/MMSCF mean for NGV
applications? It means a +52 degree F. Dew point @ 3,600 psig. This can
translate into potential condensation, hydrate formation and freeze ups
during gas expansion due to the Joule - Thomson effect.
To eliminate any potential problems for
your station or your customers, the gas should be dried to a pressure
dew point (PDP) that is well below the minimum ambient temperature that
will occur at the highest storage pressure.
The society of Automotive Engineers has
issued a fuel specification
(SAE J1616) that specifies the gas be dried to a local dew point
temperature of -10 degrees F. below the 99.0% winter design dry-bulb
temperature as found in the 1989 ASHRAE handbook at the maximum
operating tank pressure.
Here in Pittsburgh, PA the winter design
dry bulb temperature is 1 degree F., therefore, we must dry our gas to a
PDP of -11 degree F in order to meet fuel spec J1616. In San Diego, CA,
the winter design dry bulb temperature is 35 degrees F., we then need to
dry to a PDP of 25 degree F to meet J1616.
Contact us for the recommended PDP in