Abstract
In this study, two novel narrow bandpass filters (BPF) obtained from the high-resolution transmission molecular absorption (HITRAN) data for a carbon monoxide (CO) non-dispersive infrared (NDIR) analyzer were investigated and compared with a commercial BPF (4.64 µm). The new BPF was made using a two-cavity filter method with different center wavelengths and bandwidths from the commercial BPF. The wavelengths of the two BPFs were 4.5 µm and 4.65 µm. The gas emission pattern of a coal-fired power plant was used as a case study. Various concentrations of target gases were used to theoretically estimate the interference, and to practically determine it. It was found that although the transmittances of the two new BPFs were lower than that of the commercial BPF, the signal-to-noise ratio caused by two novel BPFs was approximately 20. In terms of interference effect, carbon dioxide (CO2) was found as a strong interfering gas on the commercial BPF at 4.64 µm and the new BPF at 4.65 µm. In contrast, the new BPF at 4.5 µm cut off the interference effect of all target gases. The measurement error of the NDIR analyzer applying the BPF at 4.5 µm was similar to that of gas filter correlation (GFC) NDIR and was less than 1%. This indicates that the novel BPF at 4.5 µm can be used instead of a GFC for a CO NDIR analyzer, thus overcoming the limitations of using a GFC.
Highlights
Carbon monoxide (CO), which is produced mainly from the combustion process, is a toxic gas when its concentration is >35 ppm [1]
I =1 n where ∑ ai is the integration of all line-by-line absorption intensities from high-resolution transmission molecular absorption (HITRAN) database of each i =1 gas from line 1 to line n within each bandpass filters (BPF) spectral range, Ngas is the number of molecules of that gas, T’ is the average transmittance of the BPF and L is the optical pathlength of the gas chamber
BPF_1 was applied for the Non-dispersive infrared (NDIR) analyzer, the measurement error was still less than 1%
Summary
Carbon monoxide (CO), which is produced mainly from the combustion process, is a toxic gas when its concentration is >35 ppm [1]. In the monitoring of CO, two main methods have been used: gas chromatographic technologies (e.g., gas chromatography-flame ionization detectors, gas chromatography-electron capture detectors, gas chromatography-mercuric oxide detectors and gas chromatography-mass spectrometry) and spectroscopic technologies (e.g., gas filter correlation (GFC)-NDIR, Fourier-transform infrared spectroscopy, tunable diode laser spectroscopy, and resonance fluorescence) [2]. Among these instruments, NDIR has been widely used for field monitoring of CO because its optics and detecting system are less complicated than that of other instruments [7].
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