Thermodynamic Characterization Of Coal Ash Melting Under O₂/N₂-O₂/CO₂ Atmosphere

As one of the major greenhouse gases,CO2 is an important cause of global warming.Under the background that thermal power plant has become the largest CO2 emission point,in order to reduce CO2 emission of thermal power plant,O2/CO2 technology provides a solution to reduce CO2 emission,which is very promising.However,the slagging problem of boiler coal ash fusing in coal-fired power plants has always been a difficult problem for coal-fired power plants.Different kinds of coal will produce different problems of slagging.Liquid phase characteristics,mineral transformation and high temperature volatile alkali metal gas deposition all affect the slagging process of coal ash fusing.In this paper,three typical coals,ZD,CG and SM,were simulated under O2/N2-O2/CO2 atmosphere,and the differences of liquid phase,solid phase and gas phase in ash melting under O2/N2O2/CO2 atmosphere were investigated.The following conclusions can be drawn:1)ZD coal and SM coal are easily slagged coal.There was no significant difference in the initial point of liquid phase between CG coal and ZD coal under the four atmospheres of O2/N2-O2/CO2,and the formation point of liquid phase for SM coal was delayed by about 50’C under O2/CO2.2)Under O2/CO2 atmosphere,the types of solid phase minerals are not changed,but the content of minerals is affected.The transformation of O2/N2-O2/CO2 may affect the formation and transformation of calcium-containing minerals in coal ash,which depends on whether the calcium in the original coal ash is easy to be carbonated by CO2.Compared with O2/N2 atmosphere,under O2/CO2 atmosphere more calcium carbonate formation in the coal ash,calcium carbonate with low decomposition temperature makes it easier to generate CaO and other silicon aluminate reaction of fly ash and prevent sialic acid salt to high melting point of minerals,resulting in O2/CO2 atmosphere generates more calcium feldspar,calcium feldspar and other calcium silicon aluminium acid salt and low temperature eutectic material,makes the high calcium coal under O2/CO2 atmosphere have higher tendency of slagging.3)In the presence of water-soluble alkali metals in coal,the gas phase products are mainly Na and K compounds.O2/CO2 atmosphere can form reducing gas CO,but it has no influence on gas phase products.When the temperature is less than 1000℃,the precipitation form of Na is mainly NaCl,and then Na2SO4(g)will gradually form at a higher temperature.With the increase of oxygen concentration,Na2SO4(g)in the gas phase will increase,which makes the high alkali coal have higher slagging tendency.