The Continued Evolution of Hydrocarbon Dew-Point Measurement

When to use automatic or manual hydrocarbon dew-point measurement in natural gas

Let’s face it – few natural gas engineers enjoy the prospect of taking on-site hydrocarbon and moisture dew-point measurements. Carrying around and setting up a manual cooled mirror device, such as the Standard Bureau of Mines’ Dew-Point Tester conforming to ASTM D1142, is time consuming and requires considerable experience if readings are to be recorded accurately and consistently.

Nonetheless, precise measurement of hydrocarbon dew point is a vital process parameter – one that is growing in importance with the increasing integration of pipelines and use of non-traditional forms of gas being injected into the network.

In North America, manual ASTM D1142 dew-point instruments are widely used to collect data. By comparison, in Europe it is normal for custody transfer agreements to be applied for control of gas quality, often under the guidelines provided by the EASEE-gas Common Business Practice 2005-001/01 standards. Many European countries impose strict criteria for gas quality, with automated dew-point measurement instruments being the norm. The calibration and operation of these devices is mandated under ISO/TR 12148:2009, supplemented by ISO 6570, while ISO 6327 specifically covers water dew-point measurement.

Traceability and contract compliance

Measuring hydrocarbon dew point is a prerequisite of all tariff specifications and custody transfer agreements between producers, pipeline operators and utility companies. Hydrocarbon dew point provides a key parameter to show that gas quality meets the required criteria at each stage of the supply chain, thereby avoiding costly disputes or reputational damage. It also confirms that pipeline and combustion conditions are suitable to ensure operational efficiency and safety, for example:

Differences in hydrocarbon dew-point measurement

Different countries and regulatory regimes standardize on either manual spot measurements or in-line automated chilled mirror measurement of hydrocarbon dew point. Although each approach has its advantages – such as the simplicity and lower cost of manual versions, verses automation and consistency of measurement with in-line systems – there is now a new generation of chilled mirror dew-point instruments that may, in time, replace both techniques.

The latest chilled mirror technology has been incorporated in two recent devices from Michell Instruments: the Condumax CDP301 manual dew-point tester and the Condumax CD603 fully automated online analyzer. Both use an innovative method of measuring hydrocarbon dew point: a semiconductor-grade silicon mirror with integrated PT1000 temperature element which, in the case of the CDP301, is used in conjunction with advanced high-definition digital camera sensors and color touchscreen displays. The sensors capture still and video images of the mirror surface, detecting subtle changes in the RGB channels within the image reflected from the mirror to produce extremely accurate measurements, within ±0.5 °C hydrocarbon dew point.

CDP301 Portable Dew-Point Tester

The manual version is compact and portable, making it ideal for occasional, on-site spot measurements, with full analyses being available on screen within minutes. Unlike existing manual techniques, which rely heavily on experienced operators, this system allows measurements to be taken and interpreted by relatively unskilled staff, with the option for further expert analyses to be carried out once the unit has been returned to the laboratory.

By comparison, the CD603 uses a single cooled-mirror sensor cell with greater than 65 ˚C (149 °F) measurement depression range with automated HCdp and Wdp measurement modes and novel measurement algorithm to provide superior sensitivity to the previous generation of HCdp analysis products. In applications such as custody transfer, where reliable and repeatable measurements are required 24 hours a day, this new sensor technology allows automated, continuous online measurements to be taken. This system also incorporates customizable alarm options, is designed for easy set-up and low maintenance, and is supplied with both analog and digital connections for a SCADA DCS or a similar process network.

CD603 Dew-Point Analyzer

Hydrocarbon measurement with peace of mind

These two new systems conform to both ASTM and ISO standards for dew-point measures and are ATEX, UKEX, IECEx and North American hazardous area approved, making them ideal for use worldwide, regardless of the preferred type of data collection techniques. In each case, the CD603 and CDP301 provide precise hydrocarbon dew-point measurement, eliminating the challenges associated with traditional cooled mirror devices and offering far greater peace of mind for applications across the natural gas sector.

We are the world’s leading experts in moisture monitoring and 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.

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