The Impact Of O₂/CO₂ Atmosphere On The Ash Melting And Ca-containing Minerals Production And Transformation Of Blended Coal

As one of the main greenhouse gases,CO₂ is an important cause of global warming.In order to reduce CO₂ emissions from thermal power plants,the application of oxygen-enriched combustion technology in boilers has been widely valued.Because the combustion medium in oxygen-enriched combustion is pure oxygen mixed with flue gas,the component of flue gas discharged from thermal power plants is mainly CO₂,which facilitate the economic and efficient capture,storage and utilization of CO₂.The ignition characteristics,flame stability,coke burnout,NOx emission,sulfur transformation,radiation characteristics,ash deposition and slagging characteristics of pulverized coal will change in oxygen-enriched combustion atmosphere.This paper studies the foul and slagging characteristics of single and mixed coals in oxygen-enriched combustion atmosphere.The differences of ash fusion characteristics and mineral formation and transformation between O₂/N₂ and O₂/CO₂ atmosphere are explored.The formation and transformation characteristics of calcium-containing minerals in blended coal ash under different atmosphere are mainly studied.The ash fusion temperature?AFT?of blended coal has a non-linear relationship with the mixing ratio.The melting point of blended coal ash is lower than that obtained by linear weighting according to the mixing ratio.The reason is that the minerals in blended coal ash react with each other and melt at low temperature.The non-linear change rule of blended coal AFT is in good agreement with the change of liquidus of ternary phase diagram,and ternary phase diagram can well reflect the melting characteristics of blended coal ash.There is no obvious influence on the blended coal AFT when changing atmosphere from O₂/N₂ to O₂/CO₂.Because of the limitation of AFT test methods,the AFT results can not well characterize the influence of atmosphere on the ash melting characteristics and mineral transformation.The difference between O₂/N₂ and O₂/CO₂ atmosphere may affect the formation and transformation of calcium-bearing minerals in fly ash,which depends on whether the calcium in raw coal is easily carbonated by CO₂.If the calcium in the blended coal ash is not easily carbonated in CO₂ atmosphere,the transformation of calcium minerals will not be significantly affected by different atmosphere.If the calcium in the blended coal ash is easily carbonated in CO₂ atmosphere,more CaCO₃ will be formed in the O₂/CO₂atmosphere than in the O₂/N₂.The lower decomposition temperature of CaCO₃ makes it easier to produce CaO and react with other aluminosilicates in the blended coal ash.More CaO produced by CaCO₃ will prevent the conversion of aluminosilicates to high melting point minerals.Thus,the carbonation of Ca in O₂/CO₂ atmosphere makes it easier for Ca elements to react with other silicates to form feldspar,calcareous feldspar and eutectic which will make blended coal ash higher slagging tendency.