In situ H2O and temperature detection close to burning biomass pellets using calibration-free wavelength modulation spectroscopy
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The design and application of an H2O/temperature sensor based on scanned calibration-free wavelength modulation spectroscopy (CF-WMS) and a single tunable diode laser at 1.4 µm is presented. The sensor probes two H2O absorption peaks in a single scan and simultaneously retrieves H2O concentration and temperature by least-squares fitting simulated 1f-normalized 2f-WMS spectra to measured 2f/1f-WMS signals, with temperature, concentration and nonlinear modulation amplitude as fitting parameters. Given a minimum detectable absorbance of 1.7 × 10−5 cm−1 Hz−1/2, the system is applicable down to an H2O concentration of 0.1 % at 1,000 K and 20 cm path length (200 ppm·m). The temperature in a water-seeded laboratory-scale reactor (670-1220 K at 4 % H2O) was determined within an accuracy of 1 % by comparison with the reactor thermocouple. The CF-WMS sensor was applied to real time in situ measurements of H2O concentration and temperature time histories (0.25-s time resolution) in the hot gases 2–11 mm above biomass pellets during atmospheric combustion in the reactor. Temperatures between 1,200 and 1,600 K and H2O concentrations up to 40 % were detected above the biofuels.
KeywordsWheat Straw Tunable Diode Laser Absorption Spectroscopy Energy Wood Wavelength Modulation Spectroscopy Absorption Path Length
We gratefully acknowledge financial support by the Swedish Energy Agency (36160-1), the Kempe Foundations (JCK-1316) and the Swedish strategic research program Bio4Energy.
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