Studies On Sodium Release And The Kinetics Of Sodium Sulfate Formation In Zhudong Coal Combustion

Zhundong coalfield in Xinjiang is currently the largest integrated coalfield in China.Zhundong Coal has the characteristics of high sodium,high moisture content,high volatile content,low sulfur,low ash content,etc.It has good burnout characteristics and is difficult to extract.It is an excellent power coal.However,the high content of alkali metal in the Jungdong coal is released during coal combustion and reacts with sulfur dioxide and fly ash in the flue gas to form a compound sulphate in a molten state at a lower temperature and condenses on the heating surface,causing a serious accumulation of equipment.Ash slagging and corrosion problems.Therefore,we must deepen the understanding of the following two aspects,one is the release characteristics of sodium in Zhundong coal combustion process,and the second is the change of sodium in flue gas,especially the formation process of sodium sulfate.However,there are few studies on the online monitoring of sodium in combustion flue gas and the change of sodium in flue gas.In-depth research can provide a theoretical basis for the search for economical and efficient alkali metal control methods.The thermogravimetric experiment platform was used to study the effect of heating rate on the weight loss characteristics of Zhundong coal.A variety of coal pyrolysis kinetics models were used to fit the weight loss data,and the kinetic parameters of the quasi-dong coal were calculated and analyzed.Applicability of various pyrolysis models.The results show that the FWO model in the iso-conversion model is suitable for describing the pyrolysis process of the quasi-dong coal,and the activation energy of pyrolysis under different conversion rates is calculated.It is found that the activation energy of pyrolysis increases with the conversion rate first and then decreases.Based on this,the distributed activation energy model was used to obtain the distribution of activation energy.It was found that the activation energy of the quasi-dong coal pyrolysis was mainly concentrated in the interval of 200 kJ/mol-225 kJ/mol,and the performance of the pre-exponent factor and activation energy.There is a clear"compensation effect."Aiming at the lack of analysis of bottom ash at present,the deficiency of sodium release behavior was studied.Using the on-line monitoring system of flue gas,the concentration of sodium released from the combustion of Zhundong coal at 750-900°C was monitored in real time,and the temperature and atmosphere were studied.The effect of chlorine content on sodium release.The results show that under the air and oxygen-enriched atmosphere,the increase of temperature will promote the sodium release in the Jungdong coal.At high temperatures?850°C,900°C?,the oxygen-enriched atmosphere is more conducive to sodium release,and at low temperatures?750°C,800°C?air atmosphere is more favorable for sodium release.The presence of Cl will promote the release of sodium from Zhundong Coal,and the effect is significant under the air atmosphere.According to the obtained instantaneous concentration curve,the sodium release kinetics was studied by the back-model method.It was found that the apparent activation energy of sodium release was 175.6 kJ/mol in air atmosphere,and the pre-exponential factor was 7.28×10⁶ mg·kg^-1·s^-1·m^-2.The apparent activation energy of sodium released under an oxygen-rich atmosphere was 304.7 kJ/mol,and the pre-exponential factor was 9.67×10¹² mg·kg^-1·s^-1·m^-2.The specific process of conversion of sodium forms in smoke is still unclear.The gas phase reaction mechanism of Na/H/O/C/S/Cl in high-temperature flue gas was established.The reaction mechanism was verified by simulation in CHEMKIN software.The effects of SO₂,H₂O,O₂ concentration and temperature on the formation of Na₂SO₄ in the gas phase were studied,and the reaction pathway for the formation of Na₂SO₄was analyzed.The analysis of the reaction pathway showed that there are two pathways for the production of Na₂SO₄:one depends on the direct oxidation of SO₂?NaCl?NaSO₃Cl?NaHSO₄?Na₂SO₄?,and the seconddependsontheindirectoxidationofSO₂?NaCl?NaO₂?NaSO₄?NaHSO₄?Na₂SO₄?.Sensitivity analysis results indicate that the formation of Na₂SO₄ is mainly sensitive to reactions that generate or consume free radicals in the system.