Migration law of alkali metals during Zhundong coal combustion

Due to the wide range of Zhundong mining area,the properties of Zhundong coal are different in different areas.In order to explore the slagging mechanism of Zhundong coal,the combustion tests of Zhundong coal under different conditions were carried out in a horizontal tube furnace and one-dimensional drop furnace,and the alkali and alkali earth metals( AAEM) contents of Zhundong coal were measured by ICP-OES.The migration and deposition of AAEM in different reaction environments of Zhundong coal were investigated.The results show that with the increase of temperature,the amount of escaping sodium metal from coal samples increases and when the temperature exceeds 1 000 ℃,that comes to 2 760 μg/g,over 85%.The contents of the other same oxides of the same kind in coal ash are close at different temperatures,the proportion of Ca O and MgO in ash account for a lot.The O_2 fraction has little effect on sodium metal escape and the proportion of the same oxides,and the biggest difference is only 0.52%.The result of experiments of drop furnace shows that the color of ash deposit changing from light to deep and the deposition of gray gradually increases and ash deposit is difficult to be removed,which indicates that the increase of temperature promotes slagging.When the temperature exceeds 1 000 ℃,the volatilization of sodium metal finishes and the content of Na in ash remains at about 11%.What's more,at high temperature,oxide scales on ash deposit tubes fall off.When the excess air coefficient is large,the agglomeration in ash deposition is less than that in the other two atmospheres,but the difference is not obvious.The uniformity of pulverized coal becomes worse with the increase of pulverized coal fineness during combustion,resulting in the severe combustion in some location in the furnace,and that makes the local temperature higher than other conditions and aggravates the ash deposition.In addition,the number of large particles in ash increases with the increase of particle size,and the number of large particles adhering to slagging rods increases.