Study on the reactions and alkali metals radiation characteristics from different coal ranks of a single coal particle flame

Abstract

In this work, the combustion progress and alkali metals radiation characteristic of the different coal ranks (NaoMaoHu (NMH) lignite coal, YangChangWan (YCW) bituminous coal and SiHe (SH) anthracite coal) are studied in a visualization drop tube furnace (VDTF) by a high-speed camera and a hyper-spectral camera. The effects of different coal ranks on the alkali metal (Na*, K*) radiation characteristics in the volatile and char reaction stage are explored at the oxygen concentration (Xi,O2) ranging from 0.2 to 1.0. In addition, the flame temperature of the different coal ranks is further calculated by alkali metal spectral intensity. The results show that in the volatile reaction stage, the NMH Coal is homogeneously ignited and the coal particle shows the fragmentation behavior. The YCW coal shows a hetero-homogeneous ignition, and SH Coal particles are heterogeneously ignited with a black spot in the center of the particle. During the char reaction stage, the three coal particles are ignited heterogeneously. As the reaction proceeds, the flame size and brightness of the three coal particles first increase and then decrease. The Na* and K* peak intensity and volatile reaction time of the different coal ranks have the relationship that NMH Coal > YCW Coal > SH Coal, because the volatile content of YCW Coal and SH Coal is lower than that of NMH Coal. Besides, the trend of flame temperature variation agrees with the alkali metal spectral intensity for different coal ranks. When Xi,O2 is 0.2, only one release peak of Na* and K* occurs, and the flame temperature varies from 1600 K to 1950 K. When Xi,O2 is greater than 0.4, the three coal particles show two Na* release peaks and the flame temperature varies from 1650 K to 2100 K. This paper provides insight on the effects of flame temperature and alkali metals radiation characteristics on reaction process of different coal ranks.