Analysis of the Single Coal Particle Combustion Process under O2/CO2 Atmosphere Based on Spectral Diagnostics Technology: Combination of Spectroscopic Characteristics and Flame Temperature

Abstract

This work studies the single coal particle combustion process in an O2/CO2 atmosphere based on spectral diagnostics technology in a visual drop tube furnace (VDTF). The chemiluminescence characteristics of OH*, CH*, Na*, and K* in single coal particles at two reaction stages and different oxygen fractions (Xi,O2) are investigated. The results show that both flame temperature and alkali metal spectral intensity increase first and then decrease, and the trend of temperature variation is consistent with that of alkali metal spectral intensity. Meanwhile, with Xi,O2 increases, Na* and K* peak intensities are enhanced because of the improvement in the oxygen flow rate. In the volatile reaction stage, the coal particle shows a typical envelope flame with high soot generation and luminosity. As the reaction time increases from 10 to 30 ms, the flame size increases and the flame temperature increases from 1550 to 1950 K. The spectroscopic results corresponding to the volatile reaction stage show that, as Xi,O2 increases from 30 to 50, the OH* and CH* intensity peaks increase linearly. Moreover, the intensities of the Na* and K* peaks increase by approximately 50.2 and 89.2%, respectively. During the volatile–char reaction stage, the coal particle exhibits a brighter luminous characteristic. As the reaction time increases from 40 to 70 ms, the flame size reduces and the flame temperature decreases from 1900 to 1700 K. The spectroscopic results corresponding to the volatile–char reaction stage indicate that, with the increase in Xi,O2, the positions of the OH* and CH* peaks change little and the intensities of the Na* and K* peaks increase by 21.3 and 75.1%, respectively. Our results prove that the flame temperature and alkali metal atomic emission spectroscopy exhibit the same trends as a function of the reaction time, and the alkali metal atomic emission spectroscopy can be used to characterize the flame temperature.