Response Behavior And Removal Mechanism Of Slagging Metal Elements In High Alkali Coal Under Ionic Liquid System

Zhundong coal is an ideal power coal and chemical raw material with low mining cost,high reserves,low ash content and good reactivity.Due to the specific coal-forming environment,Zhundong coal has become a typical high alkali coal.The content of alkali and alkaline earth metal elements metals（AAEMs）such as sodium and potassium in Zhundong coal is high,and accompanied by the characteristics of high iron content.During combustion,AAEMs and iron not only produce sub-micron air pollutant particles,but also cause boiler contamination,slagging and high-temperature corrosion problems,threatening the production safety of power plants.Therefore,it is of great significance to study the slagging metal elements in high alkali coal of Zhundong.In previous studies,the control methods of slagging metal elements in high alkali coal are faced with such problems as low efficiency,harsh reaction conditions or unfriendly reagent environment,and generally only focus on sodium element,lack of systematic research on other metal elements that lead to fouling and slagging.Therefore,it is urgent to find a green and efficient treatment solvent to conduct a comprehensive study on the purification and quality improvement of high alkali coal in Zhundong.In view of the influence of ionic liquid on the chemical structure and reactivity of coal,this thesis studies the response behavior and removal mechanism of slagging metal elements in Zhundong high alkali coal under ionic liquid system,aiming at exploring the purification and quality improvement effects of four ionic liquids（[PMIm]Cl,[BMIm]Cl,[PrSO₃HMIm]Cl and[BSO₃HMIm]Cl）on Zhundong high alkali coal.The removal mechanism of slagging metal elements in high alkali coal under ionic liquid is described.The results show that:Ionic liquid can destroy the electrostatic force and coordination between metal cations and organic functional groups in coal,and H⁺can replace metal cations,carboxylate and phenol salts are protonated to form new carboxylate and phenol hydroxyl groups.At the same time,the swelling effect of ionic liquid on coal is conducive to the release of inorganic minerals embedded in coal matrix,which further strengthens the purification effect of high alkali coal in Zhundong.The main mechanism of non-acidic ionic liquid removal of slagging metal elements is swelling,but the ion exchange is weak.The removal mechanism of slagging metal elements by acidic ionic liquid includes swelling,ion exchange and double decomposition.In addition,ionic liquids with longer cationic side chains interact more violently with coal.In addition,ionic liquids with long cationic side chains interact with coal more strongly than those with short cationic side chains.The response behavior of slagging metal elements in high alkali coal under ionic liquid system is analyzed.The results show that:Under the optimal conditions of ionic liquid concentration of 0.5 mol/L,reaction temperature of 80℃,reaction time of 60min,solid-liquid ratio of 25 g/L and stirring speed of 300 r/min,ionic liquid[BSO₃HMIm]Cl solution shows the highest removal rates,with the removal rates of sodium,potassium,magnesium,calcium and iron being 83.51%,52.73%,44.58%,67.77%和35.76%,respectively.The removal of slagging metal elements in non-acidic ionic liquid system is controlled by internal diffusion,while the removal of slagging metal elements in acidic ionic liquid system is controlled by internal diffusion and chemical reaction.The evolution of thermal reaction and fouling slagging characteristics of ionic liquid enhanced coal is investigated.The results show that:After the treatment of ionic liquid,the H/C atomic ratio of coal decreased,while the O/C atomic ratio was close to that of raw coal.The possibility of oxidation reaction of ionic liquid improved coal through spontaneous combustion was reduced and the safety of storage and transportation was improved.Compared with raw coal,the silica-aluminum ratio and ash viscosity index of coal ash of ionic liquid enhanced increased,while the alkali-acid ratio,scaling index and slagging index decreased significantly.The melting characteristic temperature of coal ash enhanced by[PMIm]Cl and[BMIm]Cl increased by 0～50℃,and the characteristic melting temperature of coal ash enhanced by[PrSO₃HMIm]Cl and[BSO₃HMIm]Cl increased by 50～100℃.The tendency of coal ash fouling and slagging was improved.Ionic liquid treatment is an effective method to purify and improve the quality of high alkali coal.There are 55 figures,25 tables and 119 references in this thesis.