Abstract
Gas leak detection is an important issue in infrastructure monitoring and industrial production. In this context, infrared (IR) absorption spectroscopy is a major measurement method. It can be applied in an extractive or remote detection scheme. Tunable laser spectroscopy (TLS) instruments are able to detect CH4 leaks with column densities below 10 ppm·m from a distance of 30 m in less than a second. However, leak detection of non-IR absorbing gases such as N2 is not possible in this manner. Due to the fact that any leaking gas displaces or dilutes the surrounding background gas, an indirect detection is still possible. It is shown by sensitive TLS measurements of the ambient background concentration of O2 that N2 leaks can be localized with extractive and standoff methods for distances below 1 m. Minimum leak rates of 0.1 mbar·L/s were determined. Flow simulations confirm that the leakage gas typically effuses in a narrow jet. The sensitivity is mainly determined by ambient flow conditions. Compared to TLS detection of CH4 at 1651 nm, the indirect method using O2 at 761 nm is experimentally found to be less sensitive by a factor of 100. However, the well-established TLS of O2 may become a universal tool for rapid leakage screening of vessels that contain unknown or inexpensive gases, such as N2.
Highlights
Gas leak detection is an important issue in production processes to prevent safety hazards and to ensure functionality of many products
As a rule of thumb we assume that a 1% reduction of the effective absorption length d by dilution of the background gas by the leakage gas has to be measured with a laser spectroscopic setup
We have shown that gas leaks can be detected by the dilution of ambient O2
Summary
Gas leak detection is an important issue in production processes to prevent safety hazards and to ensure functionality of many products. Available handheld TLS instruments in the NIR are able to detect CH4 leaks with column densities >1 ppm·m via remote detection They can be used from a distance up to 30 m and have measurement rates up to 10 Hz [3]. A TLS remote detection device was able to identify a CH4 leak flux of 15 mL/min from a distance of 37 m [6] All these systems rely on infrared absorption of the target gas, which is the case for hydrocarbons, for example. Remote leak detection of any target gas— of non-IR-active gases—should be feasible by a sensitive tunable laser spectroscopy (TLS) measurement of the background gas concentration. We shall always compare experiments with direct (positive) detection of CH4 and with corresponding experiments on indirect (negative) detection of O2
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