Study On The Capture Of Alkali Metals By Liquid Slag From High Alkali Coals

Xinjiang has a large quantity of coal resources.Among them,Zhundong coal field is the largest,with a reserve of 390 billion ton.The coal from Zhundong shows the features of high moisture content,high volatile,medium to high calorific value and low ash content.However,the alkaline oxides contained are significantly higher than typical bituminous coal in China,which brings great difficulties to the safety operation of the boiler in the power plant.How to reduce the influence of alkali metal on slagging during burning process is an urgent problem to be solved.Aiming at the situation,this paper firstly studied the melting and release characteristics of a typical Xinjiang high alkali coal----Zhundong coal,which can provide basic features for capturing alkali metals like Na and K in high alkali coal,then use liquid slag and kaolin to study the capture characteristics of alkali metals.Based on the experiments and researches,this paper forms the following conclusions on aspects of melting and release characteristics of high alkali coal ash,the capture mechanism of Na and K by liquid slag and kaolin additions and the element migration law.1.Based on the study of melting and release characteristics of high alkali ash,it can be seen:The melting characteristic temperatures of Wanxiang high alkali coal are:DT=1250?,ST=1295?,HT=1310?,FT=1321?;The rate of volume change after the melting is 39%;The comprehensive judgment of clinkering R=4.15,which is higher than 2.5,thus Wanxiang coal is seriously clinkered.Because of the high content of CaO in high alkali coal,the melting characteristic temperatures are higher than non-high alkali coal;Because of the effect of helping melting by alkali metal oxides,the volume change rate of high alkali coal is higher.The release of Na and K increases with the temperature goes higher.When the temperature reaches 1200?,the release finishes.2.Through the capture of NaCl by liquid slag,it is found that the highest capture ratio by 5g of liquid slag is 34.34%.The best reaction time is 30min.The addition of kaolin can increase the capture ratio by 35%in maximum,the add ratio of kaolin is 5%.Most of the Na is fixed near the capture surface,there is a little amount of Na goes to the deep layer.3.By researching on the mechanism of alkali metal capture,it is found that the slag captures the alkali metal and forms some alkali metal salt like Na₄Ca(SO₄)₃·2H₂O,which reduces the staining and slagging.