The Syudy Of A New Additive In Reducing Slagging And Fouling During The Combustion Of Zhundong Coal

The Zhundong coal field,identified as the largest coal field in the world,plays an important role in energy development in China.Zhundong coal is characterized as a high-quality coal considering its medium moisture content,low-to-medium ash yields,high volatile matters,and low S content.At this stage,Zhundong coal combustion causes severe slagging and fouling in the off-design boilers,and it is generally believed that the high sodium content is the main cause.The additive injection technology has been effective in alleviating slagging and fouling during coal combustion.In this paper,the influences of vermiculite on the slagging characteristics during high-sodium and high-calcium Zhundong coal burning are investigated by experimental methods.The aim of this study is to assess the effectiveness of vermiculite as a new kind of coal additive and provide a theoretical foundation in industrial application.At first,the influences of vermiculite on element content,mineral matters and ash fusion point of standardized ash are investigated.Results show that sodium and calcium content in standardized ash decrease with vermiculite additive,on the contrary,kalium content increases slightly and magnesium content falls significantly.Ca₂Al₂SiO₇ is transformed into CaMgSiO₆ with vermiculite additive.The decomposition of anhydrite in ash to produce free CaO is inhibited by vermiculite injection which,however,has little effect on ash fusion point.Meanwhile,the influences of vermiculite on the ash deposition and the reaction between vermiculite and coal ash are investigated by drop tube furnace.Results show that vermiculite has positive impacts on reducing ash deposition,the mechanism difference between inner ash and outer ash can be explained as follows:the sodium tend to present as the form of NaCl in inner ash,and the viscosity of inner ash also decreases with vermiculite injection.When it comes to outer ash,the agglomeration of ash particles is inhibited by the partition of low-viscosity slices formed through vermiculite swelling after heat treatment.Intermetallic reactions occur on the surface of vermiculite particles,resulting in the formation of frizzle sheets,and these sheets are stacked in micro-scale to produce macro-scale polyporous structure.The surface of sticky and spherical ash particles are covered by high melting point and less sticky minerals including forsterite and Enstatite.More importantly,based on the experimental results,the optimal injection value and particle sizes of vermiculite are confirmed by 5-7%and 100-150?m,respectively.