Thermodynamic Study On Slagging Characteristics Of High Alkali Coal Under Oxygen-enriched Combustion Conditions

Coal has become a major source of energy in China,a typically gas-poor,oil-poor and coal-rich country,as the country’s economy has grown rapidly and its energy consumption has grown at the same time.Burning coal inevitably brings with it the problem of carbon dioxide emissions,and to solve this problem,oxygen-enriched burning technology has been born that can greatly reduce CO₂emissions.At present,scholars have not reached a unified conclusion on the slagging characteristics of high-alkali coal ash under oxygen-enriched conditions,so this paper selects a typical high-alkali coal——Zhundong coal,and studies its slagging characteristics under oxygen-enriched conditions through the change of low-temperature eutectic in the solid phase and the change of sodium sulfate in the gas-phase.Firstly,Factsage thermodynamic simulation software was used to simulate the effects of oxygen concentration,excess air coefficient and pressure on the main minerals in the solid phase of Zhundong coal ash in the temperature range of 800-1600℃under oxygen-enriched conditions.The results show that the main minerals that change in the solid phase are Ca SO₄,melilite and Ca₃Mg Si₂O₈,the increase of oxygen concentration and pressure and the decrease of excess air coefficient will increase calcium sulfate and melilite,and decrease Ca₃Mg Si₂O₈,indicating that the low-temperature eutectic is increasing at this time.And the reduction of excess air coefficient will also lead to an increase in nepheline,and Ca₃Mg Si₂O₈will disappear when the pressure increases to5atm,and the amount of slag liquid will increase before equilibrium.Secondly,the effects of Ca O——the main minerals in the Si O₂-Ca O-Fe O-Al₂O₃slag system,temperature and partial pressure of oxygen on the physical phase and liquidus were analyzed by using thermodynamic data and phase diagram,and the activity calculation model of the Si O₂-Ca O-Fe O-Al₂O₃slag system was constructed.The results show that the high Ca O content will make the dissolution of the slag system more difficult,and the increase of temperature will expand the range of liquid phase region,and make hematite convert to spinel,and the increase of oxygen partial pressure will delay this process and reduce the liquid phase region.Finally,Chemkin kinetic simulation software was used to simulate the effects of oxygen concentration,excess air coefficient,and pressure on sodium sulfate in the gas phase of Zhundong coal ash under oxygen-enriched conditions.The results show that after changing these conditions,the primitive reaction and its sensitivity coefficient affecting the formation of sodium sulfate at the maximum formation of sodium sulfate are changed,and the increase of oxygen concentration and pressure and the decrease of excess air coefficient will increase the formation of sodium sulfate,only the pressure change does not change the main formation path of sodium sulfate.