Why do you Need Dew-Point Sensors to Measure Moisture in Natural Gas? 

How dew-point sensors help you meet your gas quality and custody transfer obligations 

Natural gas is an invaluable resource, powering industries, homes and vehicles worldwide. Transporting and supplying natural gas on such a broad scale involves a complex web of operators, pipelines and regulations.  

Two critical aspects of this network are custody transfer tariffs and sales contracts.  These agreements define gas quality as it passes between operators along the transport and supply network.  Failure to meet any of these specifications can result in significant financial penalties.

Natural gas quality is normally determined by measuring the levels of oxygen, hydrocarbon dew point and water dew point.  You can read more about oxygen measurement and hydrocarbon dew point in our related blogs.  In this article, we focus on the importance of measuring water dew point in natural gas.

How moisture contamination affects gas quality and pipeline safety 

Water generally enters the natural gas stream at the wellhead, where it is already mixed with a range of other contaminants.  In both liquid and gaseous forms, it can also contaminate natural gas during subsequent processing and transportation. 

To reduce contamination to a safe level, water is removed using adsorption, absorption, membrane separation or refrigeration processes, which are used singly or in combination. In a glycol dehydration system, for example, water is removed by binding it to liquid glycol with a suitable trace moisture analyzer, such as our new Multi-Channel Process Monitor (MCPM). This is fitted downstream of the final drying stage and allows the moisture content to be precisely measured, confirming that the dehydration system is functioning correctly and, thus, that the natural gas is within specification. 

If water is allowed to enter the downstream pipework and transportation system, it creates a number of problems: 

• Pipeline corrosion: Water condensing in pipelines and transportation equipment can lead to corrosion.  This can be especially problematic if dissolved gases such as CO2 and H2S are also present.  In each case, corrosion damage can weaken the structural integrity of pipeline systems, potentially resulting in leaks, pressure loss and increased maintenance costs. 

• Pipeline blocking: When water pools at low points in pipelines and then freezes as temperatures drop, it can cause pipeline blockages.  In extreme cases, this can lead to pressure fluctuations and the risk of particles of ice being carried into downstream equipment.  A similar situation can occur if water combines with hydrocarbons to form solid hydrates, which can again lead to pressure build-ups, pipeline blockages and, if they occur close to the combustion stage, the risk of damage to turbine blades. 

• Gas quality and energy values: Water entrained in the natural gas at the combustion stage will adversely affect its heating value, reducing the efficiency of gas turbines, increasing operating costs and potentially infringing tariff specifications. 

How do dew-point sensors measure the water content in natural gas?

The water content in natural gas is calculated by measuring water dew point.  This is the point at which, at a given pressure, water vapor entrained in the natural gas begins to condense.  Best practice is to take measurements using dew-point or moisture sensors, connected to a suitable moisture analyzer.  These devices are extremely accurate, repeatable and reliable, and are normally positioned at key locations in the gas processing, transportation and combustion network.

Although there are several technologies for measuring water dew point, the most widely used are ceramic metal-oxide moisture sensors, such as our Easidew Intrinsically Safe Dew-Point Transmitter.  This compact device has a low copper alloy or stainless-steel construction, is certified to IECEx, QPS, ATEX and UKCA standards and is accurate to ±2° Cdp.   

The output from each dew-point sensor, along with those from optional oxygen sensors, can be fed directly to our new Multi-Channel Process Monitor.  This unit is designed to provide real-time, multi-parameter displays from up to six input channels for the measurement of high-pressure process gases and vaporized liquids in natural gas systems.

The MCPM features a bright 7” color touchscreen LCD, has three 4…20 mA configurable outputs per channel, process and status alarms and offers Modbus RTU over RS485 and Modbus TCP/IP communication. 

Used in combination with our latest in-line dew-point sensors, the MCPM provides an ideal solution to the challenges of ensuring the safety, efficiency and quality of natural gas processing, transportation and combustion systems. 

We are the world’s leading experts in moisture monitoring and dew-point measurement.  We have eight different technologies covering all moisture applications, backed by unrivalled technical and customer support.  To learn more, talk to one of our application specialists today. 

Related Information

Natural Gas

Related Blogs

Critical Quality, Safety and Reliability Measurements in Natural Gas

Oxygen Measurement in Natural Gas

Hydrocarbon Dew-Point Measurement in Natural Gas

Related Categories

Trace Moisture Analyzers for Natural Gas Quality and Petrochemical Applications