Experimental evaluation of the performance of humidity analyzers in natural gas under industrial conditions

Abstract The work reported is the continuation of the extensive comparison performed in controlled laboratory conditions using natural gas from the Spanish grid, as part of the European Metrology Research Project (EMRP) “Characterisation of Energy Gases” (ENG01-Gas, 2009). One of the outcomes of the project was the good performance of a laser absorption spectrometer with respect to other measurement technologies, in particular the absence of appreciable drift effects, exhibited by aluminium oxide (Al 2 O 3 ) sensors that are traditionally used in the natural gas industry. The investigation was performed over a wide range of humidity content (13 ppm v to 250 ppm v ) in ambient conditions of 23 °C ± 3 °C, at Enagas central laboratory in Zaragoza, Spain (Gallegos et al., 2015). We report the subsequent comparison of two laser absorption analyzers, from different manufacturers, and a conventional Al 2 O 3 installed on site in real industrial conditions, at an underground gas storage (UGS) and drying plant of Enagas in Serrablo, Spain. The performance of sensors is reported and discussed for all production stages of the plant (extraction, injection and shutdown), during which extreme ambient temperature values took place (from −15 °C up to 40 °C) and at line pressures up to 6.7 MPa. A purpose built sampling system was designed and constructed to accommodate the different instrumentation requirements and ensure an optimum metrological analysis. The new results are compared with those previously obtained under more ideal laboratory conditions in the context assuring compliance with the contractual specifications that are to be met in Europe (EASEE-gas, 2005).