Natural gas poses a unique situation since it can have very high levels of solid and liquid contaminants as well as corrosives in varying concentrations.
Water measurements are made in parts per million, pounds of water per million standard cubic feet of gas, mass of water vapor per unit volume, or mass of water vapor per unit mass of dry gas. That is, humidity is the amount of “vapor-phase” water in a gas. If there are liquids present in the gas, they are often filtered out before reaching a gas analyzer to protect the analyzer from damage.
Measurements of moisture in natural gas are typically performed with one of the following techniques:
* Color indicator tubes
* Chilled mirrors
* Electrolytic
* Piezoelectric sorption, also known as Quartz Crystal Microbalance
* Aluminum oxide and silicon oxide
* Spectroscopy
Other moisture measurement techniques exist but are not used in natural gas applications for various reasons. For example, the Gravimetric Hygrometer and the “Two-Pressure” System used by the National Bureau of Standards are precise “lab” techniques but are not practical for use in industrial applications.