Terahertz Spectroscopy for Real-Time Monitoring of Water Vapor and CO Levels in the Producer Gas From an Industrial Biomass Gasifier

In this paper, we present a study of THz transmission spectroscopy as a novel tool for the monitoring of the steam and CO contents of the raw gas from industrial biomass gasifiers. A THz gas spectrometer with a frequency range of 300-500 GHz was designed and constructed. Proof-of-principle testing was performed at laboratory conditions using mixtures of different gases at high temperatures (600-700 K). The results demonstrate the feasibility of applying strong rotational water vapor lines at 448 and 383 GHz, so as to obtain reliable online measurements of water vapor with an absolute precision of about 0.2 vol.% for the current device. CO lines were identified at 461 and 346 GHz, facilitating measurement of this gas. The gas spectrometer was integrated into an industrial gasifier and boiler, and its performance was tested in terms of online measurements of steam and CO in the hot raw gas and flue gases under real-life conditions. Considering the error intervals, the results are in complete agreement with data acquired by solving loose mass balances around the system. The onsite experiments demonstrate that THz gas spectroscopy is a promising tool for fast, robust, and reliable monitoring in industrial applications.