The difference between dry and wet gas: -
Dew Point
wet or dry - is based on the operating temperature corresponding to its dew point.
Some reference state when operating temperature 10F higher than the dew point temperature, it is considered as dry gas.
To be conservative, the operating temp. should be the minimum operating temp. possible.
Dry gas --------> Min. operating temp. - dew point = at least 10F
The difference can be in % or 30-40F higher than the dew point. The more the margin the safer it is to make sure there is no condensation.
The reasoning behind it that the operating temperature shall high enough to prevent condensation due to pressure drop along the pipeline.
BTU
The difference is the amount of water vapor it hold and consequently the amount of BTU produce.
Dry Gas is defined as being less than 1050 BTU
West Gas - 1050 BTU to 1350 BTU Super Rich - greater than 1350 BTU.
The super rich will contain more condensate and high API oil. The wet gas, typically more LNG’s.
HC content
When natural has a high methane concentration, the gas is considered dry.
When natural gas contains ethane, butane, pentane or natural gasoline, collectively referred to as natural gas liquids (NGL) or condensates, the gas is considered wet.
Wet gas:
This usually refers to unprocessed gas. Basically as it comes from the well. Even after it has gone through the gathering stations process (removing BS&W) it is still considered “wet” due to the H2O content it still has.
Not all gas that comes from the well is “wet”. There are places that produce very dry gas.
Dry gas:
The finished, ready for sales gas (mostly methane) at the end of the process.
- Usage
NGLs are currently more valuable than natural gas and typically follow oil prices. Wet gas ia more valuable than dry or sales gas. Sales gas is used for home heating.
To extract the NGLS, the wet natural gas is transported through pipeline to a processing plant. At the plant, the liquids are first extracted from the natural gas and then separated into their base components.
The remaining portion of the gas after the methane (used for such things as home heating) has been separated out. There can be a number of different products here, such as; ethane, propane, gasolines, butanes, iso-butanes, etc… They will be processed further.
The boiling points for the different products in the stream are different and to separate out the product you are looking for you must reach the temperatures that give you both liquids and gas (that’s how they separate…then the gas goes out the top of a vessel and the liquids fall to the bottom).
In order to reach the temperature necessary to keep the methane in gaseous state while putting the others into a liquid state you are reaching temperatures of roughly -140 degrees Fahrenheit. Were there to be water or CO2 in the stream you would freeze up your process. Potential catastrophic damage to equipment and piping.