Measurement And Analysis Of Emission Spectra From Flames Containing Alkali Metals

Alkali metals released from combustion of coal and biomass cause substantial problems with the fouling, slagging and corrosion of heat exchange surfaces.They affect the life of the boiler and reduce the heat efficiency. Studying and solving these problems has become one of the important research directions. However, the release of alkalis is a complex process, and effected by the fuel type, temperature and alkali metals concentration and so on. Studying the gas-phase alkalis in the flame is an important tache for understanding the release process, and essential for the improvement of combustion efficiency, the increase of security of boliers and the improvement of mechanism of alkali release. This dissertation used flame emission spectroscopy technique to measure and analyz flames containing alkali metals. The detailed decription is as below.A spectrometer system covered visible(VIS) and near-infrared(NIR) spectra from 200 nm to 1750 nm was developed.The calibration coefficients independent of temperature were obtained when the system was calibrated by a blackbody furnace. Different temperatures of blackbody were calculated using two-color method in different bands. The results show that the maximum relative errors for temperature were less than 2%, and the calculated results were consistent in no matter entire or partial band.A premixed burner was designed, and principle of alkali metal emission spectra and their concentration in the flame were introduced and calculated respectively. An experimental investigation was presented on the measurement of alkali metals radiation intensities using the spectrometer system. The results show that the peak intensities of alkali metals emission lines in the flame changed little and fluctuation error was less than 2%. The peak intensities of alkali metals emission lines will increase with the concentration of gas-phase alkali in the flame, the relationships between them were fitted.An experimental investigation of measuring and analyzing flame emission spectra in an industrial municipal solid waste(MSW) incinerator was presented. Based on spectra processing and non-gray emissivity model, the temperature, emissivity, and intensities of alkali metals emission lines were calculated from spectral radiation intensities. Experimental results indicate the MSW flame contains alkali metals including Na, K, and even Li and Rb, and shows non-gray characteristic in wavelength range from 500 to 900 nm and from 1150 to1320 nm. The temperatures derived from VIS and NIR range have a little difference, but both of them have similar variation trend with primary air, and approximately reflect the change of actual evaporative capacity. Besides that, peak intensities of alkali metals emission lines from VIS range will increase when primary air is high. Moreover, the spectral absorptivities of H2 O in NIR range have been estimated and show some relationship with water vapor content in flue gas. The results prove that flame emission spectroscopy technique is useful for combustion measurement in the MSW incinerator.