Vympel engineer using computer-based diagnostics as part of VympelCare service for a Hygrovision BL portable dew point analyzer. for example, and will be more comparable to measurements taken by other instruments. In addition, the calibration gas used by OGE is a representative multicomponent gas essentially similar to pipeline natural gas. As a result, the calibration is made using gas that behaves essentially similar to the way pipeline gas behaves, by slowly building up a layer of condensation. It is this condensation behavior that makes it possible to establish the 5mg/m3 threshold. This is opposed to a single component calibration gas, such as propane, which is often used to calibrate this type of instrument. Propane has a very different condensation behavior that results in so much condensate forming at once that it is not possible to limit the condensation to 5mg/m3. Because of this, it is not possible to discern the beginning of condensation. In other words, calibrating to 5mg/m3 ensures that the analyzer is set to the level of “best” evidence for registering the start of condensation. It is worth noting that ONLY Vympel instruments are sensitive enough to actually resolve 5mg/m3. Competitor devices can only discern a film that corresponds to 40mg/m3 or more, depending on the instrument. This lack of sensitivity represents a level of uncertainty that will not ensure the required degree of measurement accuracy. For these devices, the GERG calibration requires the incorporation of a correction factor, adding to measurement uncertainty. Vympel instruments are not subject to this uncertainty! The calibration for the water dew point
measurement channel is also not as straightforward as one might expect. Water vapor in a hydrocarbon matrix, such as natural gas, does not behave in quite the same way that it does in regular air. In 1995, the GERG group carried out a project for developing a mathematical correlation between the water content and water dew point in natural gas in order to more accurately define the behavior of water
condensation in hydrocarbon gas mixtures. GERG also realized that it was necessary to build a comprehensive and accurate database relating measured water content to water dew point values for a variety of representative natural gases. It was shown that there was a need to improve the existing correlation values. As a result, a more accurate, compositiondependent correlation was developed on the basis of GERG’s database. This research is the basis for the current ISO standard 18453:2004 “Natural gas — Correlation between water content and water dew point” which also incorporates. And it is this standard that OGE uses when calibrating the water dew point channel for VympelCare units. After calibration VympelCare analyzers are returned to the Vympel facility in Düsseldorf for a final check before being returned to their owners. The whole procedure usually is completed within seven to ten days, and the analyzer that is returned to service can be relied upon to operate well for another 12 months at least. From the beginning VympelCare was developed in response to three basic needs: to provide timely prevent maintenance to Vympel analyzers; to provide those analyzers with the best calibration; and to make it easy and economical for owners to take advantage of these services. The ultimate goal of VympelCare is to ensure that Vympel instruments in the field provide accurate quality control information for the entire service life of the instrument. •
Dr. Markus Wolf, Head of the Gas Quality Department at OGE delivering a presentation about calibration of dew point analyzers according to the GERG* project 1.64. * Groupe Européen de Recherches Gazières (European Gas Research Group).
If you would like to know more about the solutions discussed in this article please contact: SPA Vympel +49 211 21077391 info@npovympel.ru
