Preventing Winter Weather Woes with Moisture Analysis

As headlines speak of the polar vortex and many cities in the northern hemisphere are covered with snow and ice, staying warm becomes a daily necessity for many.  Most of us don’t think much about turning the thermostat up in our homes or plugging in the space heater in our office.  The seamless demand for heat and power is almost taken for granted.  However, behind the scenes, the oil and gas industry support our needs for heat and power by continually providing natural gas safely and reliably to residential, commercial, and industrial users.  As temperatures plunge, the natural gas infrastructure from exploration to processing to underground storage to pipelines continues to deliver gas for heat and power. For the system to operate so effectively, the operators of these facilitates need sensors and analyzers that can also perform under extreme conditions.

As many of us learned in science class in elementary school, water freezes at 0oC (32oF). Moisture, or water vapor, is a common contaminant in natural gas.  Operators of gas processing plants, pipelines, and underground storage facilities must ensure that the natural gas is dry to properly process, transport and sell the gas to end users. While moisture is continuously important to measure, extremely cold temperatures place added pressure on the system to prevent freezing of critical components, damage to the infrastructure, and a reduction in or loss of gas flow. 

A variety of technologies are available to measure the moisture content in natural gas. Over the past decade, tunable diode laser absorption spectroscopy (TDLAS) has become one of the preferred methods for moisture measurement in natural gas due to its fast response, high specificity to the measured analyte (in this case moisture), excellent sensitivity, high measurement accuracy, and low maintenance.  With TDLAS, a diode laser generates light at a specific wavelength where water molecules absorb energy. The natural gas flows through a measurement cell which contains the laser and detector at one end and a mirror at the other end. The light beam is transmitted into the measurement cell where the water molecules absorb the light energy.  The detector measures the amount of light energy lost which is related to the moisture concentration. 

Since only light contacts the natural gas, TDLAS-based moisture analyzers are not susceptible to interference from common contaminants in natural gas, such as glycol or methanol.  Additionally, TDLAS analyzers do not require annual calibration as is the case with some contact-based sensor technologies, such as impedance sensors and thus have very low total cost of ownership, providing years of nearly maintenance-free operation. TDLAS analyzers respond quickly, typically in seconds to minutes, to changes in the moisture content in the natural gas in both dry-to-wet and wet-to-dry conditions.  If a moisture upset occurs, TDLAS analyzers will quickly alert the operator to the problem, allowing a process correction to be made. Once the upset is correct, the analyzer provides a rapid dry down response reducing the amount of time a producer may be “locked out” of a transmission pipeline.  Users adopt TDLAS technology for moisture measurement for the benefits of interference-free, fast responding measurements and low ownership costs.

Learn more about how our 5100 series TDLAS analyzers could help prevent moisture problems in your natural gas processes.

John Kerney is the Natural Gas Marketing Manager for AMETEK Process Instruments.

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