Measuring moisture in high pressure gas

Michell Instruments have announced an increase in the maximum pressure rating for their Easidew and Cermet II ranges of dewpoint instruments

Michell Instruments have announced an increase in the maximum pressure rating for their Easidew and Cermet II ranges of dewpoint instruments.

These on-line hygrometers are already able to withstand an impressive 300 barg and this has been extended for use in gases with pressures up to 400 barg, believed to be the highest pressure rating of any dewpoint or moisture measurement instrument on the market.

All of the Michell Instruments hygrometers that utilise the Ceramic Moisture Sensor feature a glass/metal seal capable of withstanding high-pressure gas.

This high integrity seal allows the sensor to be installed in the process with no possibility of gas leaking from the system through the instruments sensor.

Dewpoint (or dewpoint temperature) is the most common measurement used to determine the amount of water vapour in a gas and is widely used in industries such as compressed air, natural gas, power generation and industrial/medical gas.

Dewpoint is a pressure dependant variable and as the pressure of a gas increases, so does the dewpoint, making condensation more likely to occur and thus heightening the importance of reliable dewpoint measurement.

Measurement of dewpoint in very high-pressure gas is commonly seen in the following applications:.

* Breathing Air: Users of high pressure breathing air cylinders such as firemen or divers appreciate the importance of keeping the dewpoint of their breathing air within specified limits.

Failure do this can cause condensation at the exit valve: the liquid formed, combined with the Joules Thompson cooling effect associated with expanding gases, can cause the valve or regulator to "ice up".

Michell Instruments portable dewpointmeters can be used for spot-checking of the dewpoint within cylinders, whilst the filling of such cylinders can be continuously monitored using the Easidew or Cermet II product ranges.

* Natural Gas Filling Stations: Recently there has been an increase in the number of road vehicles powered by Compressed Natural Gas (CNG).

The gas is taken from a supply of typically 1-1.5 barg which has a dewpoint of around -30 degC.

This gas is compressed to more than 200 barg before being used to fill the gas tank on the vehicle and therefore needs to be dried to prevent condensation in the tanks.

The dryers used for this application are often supplied with a Michell Instruments intrinsically safe dewpoint transmitter to ensure consistent performance.

* Military: Current military machines such as jet aircraft, ships and submarines utilise high-pressure gas for various applications including purging of optical systems and pneumatic actuation of guidance systems.

Portable and on-line dewpointmeters are widely used by military technicians for ensuring that the dewpoint of such gas is below the lowest expected ambient temperature, thus preventing fogging of optical systems (such as periscopes or radar waveguides), or liquid damage to pneumatic actuators.

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