Online Detection of Water Vapor in an Industrial Gasifer Using Terahertz Spectroscopy

Abstract

A terahertz spectrometer was set up for the monitoring of product gas in a thermal gasifer. The goal was to measure temperature and H2O concentration, and preferably also CO concentration. This environment presents several difficulties such as high temperature,toxic gases, high H2O content and a high concentration of particulate pollutants. Spectroscopy using IR Lasers tend to be obstructed by the high absorption of H2O as well as the scattering by the particulates, and so does not produce satisfactory results. It was hoped that these problems could be avoided by using terahertz radiation, with a lower absorption by water and a longer wavelength possibly avoiding scattering by particulates. A system operating in the range 300-500 GHz was built and tested in laboratory as well as in an industrial gasifer at Chalmers Power center, yielding promising results. Our results indicate that monitoring of H2O, and probably other gases, in the rugged environment of gasifer rawgas can be done with response times on the order of a few minutes. This has applications in biomass gasifcation, where variable quality of the fuel results in a need for continous monitoring and tuning of the gasification process.