Natural Gas is used world-wide as a fuel. There are many applications for measuring its moisture content:
Offshore: The gas is usually dried offshore, before being compressed for transmission by pipe-line or tanker to the shore base. The excess moisture must be removed to prevent damaging condensation in the compressor.
On-shore: The measurement is needed for exactly the same reason, as the gas is compressed further for pipe-line transmission/distribution, or bulk storage in the liquid phase.
Re-gassing: When stored in bulk as a liquid, the refrigerated liquid passes through heat-exchangers in the evaporation stage. These heat-exchangers are prone to leakage - introducing unwanted moisture into the very dry gas, so the moisture content is monitored immediately after the heat-exchanger for leak-detection purposes.
The measurement in Natural Gas is not difficult, but there are several special considerations:
Offshore drying is often achieved by passing the gas over Glycol liquid (in a 'Glycol contactor'). The gas at the outlet will be dry, but may well contain some Glycol liquid residue, or carryover. This will not damage the sensor, but if the sensor is coated with a film of Glycol then its response will become very slow - it is therefore to be avoided by using a knock-out pot or coalescing filter in the sample line. In exactly the same way, hydrocarbon condensate liquid in the gas will contaminate the sensor and result in a very slow response.
Obviously an installation on Natural Gas must be safe because of the fire/explosion risk. The Automatic Dewpoint Meter is Intrinsically Safe as standard. In-line instruments may be made intrinsically safe by using the Zener Barrier Unit and, if there is no safe area for the instrument location, then the explosion-proof model SDAEXD makes a 'local safe area' for the instrument. The model SWM-SSNG has two-stage pressure regulation with condensate drain, and will deal with hydrocarbon condensate or Glycol contamination, while the model SWM-SSNGH has heated two-stage pressure regulation and is intended for installations where there may be heavy condensate/Glycol contamination or for light hydrocarbon liquids which will vapourise.