High-Precision <sup>13</sup>CO<sub>2</sub>/<sup>12</sup>CO<sub>2</sub> Isotopic Ratio Measurement Using Tunable Diode Laser Absorption Spectroscopy at 4.3 μm for Deep-Sea Natural Gas Hydrate Exploration
2019
Hanquan Zhang | Mingming Wen | Yonghang Li | Peng Wan | Chen Chen
For the detection of deep-sea natural gas hydrates, it is very important to accurately detect the <sup>13</sup>CO<sub>2</sub>/<sup>12</sup>CO<sub>2</sub> isotope ratio of dissolved gas in seawater. In this paper, a <sup>13</sup>CO<sub>2</sub>/<sup>12</sup>CO<sub>2</sub> isotope ratio sensor is investigated, which uses a tunable diode laser absorption spectroscopy (TDLAS) technique at 4.3 μm. The proposed sensor consists of a mid-infrared interband cascade laser (ICL) operating in continuous wave mode, a long optical path multi-pass gas cell (MPGC) of 24 m, and a mid-infrared mercury cadmium telluride (MCT) detector. Aiming at the problem of the strong absorption intensity of the two absorption lines of <sup>13</sup>CO<sub>2</sub> and <sup>12</sup>CO<sub>2</sub> being affected by temperature, a high-precision temperature control system for the MPGC was fabricated. Five different concentrations of CO<sub>2</sub> gas were configured to calibrate the sensor, and the response linearity could reach 0.9992 for <sup>12</sup>CO<sub>2</sub> and 0.9996 for <sup>13</sup>CO<sub>2</sub>. The data show that the carbon isotope measurement precision was assessed to be 0.0139‱ when the integration time was 92 s and the optical path length was 24 m. The sensor is combined with a gas−liquid separator to detect the <sup>13</sup>CO<sub>2</sub>/<sup>12</sup>CO<sub>2</sub> isotope ratio of CO<sub>2</sub> gas extracted from water. Results validate the reported sensor system’s potential application in deep-sea natural gas hydrate exploration.
Show more [+] Less [-]AGROVOC Keywords
Bibliographic information
This bibliographic record has been provided by Directory of Open Access Journals
