Moisture measurement is critical for gas companies to meet quality specifications and to protect pipelines from corrosion, but false positives are very costly because the gas cannot be delivered if it is ‘wet’. Now there is a method that improves the speed and reliability of this crucial measurement.
All natural gas contains water (moisture) which is measured in natural gas pipelines at production and gathering sites, custody transfer points, compression stations, storage facilities and in distribution markets. Several methods are used for dehydrating (drying) the natural gas such as pressurising, chilling and absorption processes that use liquid and solid desiccants. Commonly, dehydration is achieved in the field with triethylene glycol (TEG) contactors.
Natural gas streams may also contain high levels of solid and liquid contaminants as well as corrosive gases. This presents a challenge for the measurement of moisture because the contaminants can interfere with the readings or even destroy traditional moisture sensors.
Issues with traditional measurements
Moisture measurements have traditionally been performed using a chilled mirror to determine the dew point, but it is a slow and subjective measurement because many other components in natural gas can condense on the mirror. Additionally, a variety of electronic sensors have been used that rely on the adsorption of water onto a sensitive surface that is placed into the natural gas stream. In practice, however, sensors that are in contact with natural gas streams are adversely affected by natural gas components, causing errors, interferences and failures. Ultimately, they are too costly to operate, and the measurement is unreliable.
A reliable solution
Tunable diode laser absorption spectroscopy (TDLAS) was introduced to the natural gas industry by SpectraSensors, an Endress+Hauser company since 2013. The rugged nature of these laser-based analysers has allowed them to be used in natural gas pipelines with very little maintenance, no interference, and with no detrimental effects from glycol due to carryover to the analyser from the drying step, methanol, amine, H2S, moisture slugs etc. Since its inception, this technology has demonstrated its reliability in thousands of installations worldwide. SpectraSensors analysers require no calibration in the field and the calibration is stable for the life of the analyser.
For more information on our TDLAS solution, visit our analyser product pagehttps://eh.digital/2IaaOZ7