Abstract
An all-passive, multipoint, and multiparameter optical monitoring system was developed and deployed in an industrial environment for the simultaneous measurement of methane concentration and other physical parameters. Methane is detected via rapid wavelength modulation spectroscopy (WMS) at 1648.2 nm and 4 MHz frequency. An attenuation invariant quantity defined by the peaks at 0, 4, and 8 MHz of the fast Fourier transform (FFT) of temporal signal is employed, characterized, and validated. Other parameters can concomitantly be measured by fiber Bragg grating (FBG) sensors operating in the 1520-1590 nm range. In the deployed system, the tested parameter was the temperature, which is an important quantity for gas monitoring. The system features a modular architecture that enables scalability up to 16 384 sensing points with an estimated less than 20-min acquisition cycle. In its current deployment, it monitors methane and temperature at eight locations using a single optical network. The system is intended to be used onshore and offshore platforms where the usual monitoring protocol consists of manual measurements usually performed three to four times a year and involves personal displacement and risky situations. Field tests at an onshore natural gas treatment unit (NGTU) demonstrated reliable performance and effective event detection, including undocumented nocturnal emissions, maneuvers at main shut-off valve, and partial plant shutdowns and restarts.

Abstract

Abstract