SCR脱硝烟气中硫酸氢铵的生成机理研究

发布时间：2018-05-19 00:11

  本文选题：SCR + 硫酸氢铵/硫酸铵　； 参考：《浙江大学》2017年硕士论文

【摘要】：氮氧化物(NOx)是燃煤锅炉的主要大气污染物之一,对环境以及人体健康有多重危害。选择性催化还原法(SCR)是脱除燃煤烟气中NOx的主要方法。随着烟气温度的下降,未反应完全的还原剂NH3易与烟气中的SO3反应生成硫酸氢铵。液态硫酸氢铵具有极强的粘性以及腐蚀性,凝结在空气预热器表面并不断捕捉飞灰,导致空气预热器的积灰、堵塞和腐蚀。当前燃煤机组的超低污染物排放技术不断推广,其中增加一层SCR催化剂是进一步脱除NOx的主要途径,不仅增加S03浓度,且随着机组运行时间的增加,催化剂老化失活,氨逃逸浓度也会上升,进一步增加硫酸氢铵的生成量,加剧空气预热器的积灰堵塞现象。因此本文研究脱硝烟气中硫酸氢铵的生成机理,为空气预热器设计和运行提供理论依据。本文先从化学热力学的角度计算NH3和S03反应过程中吉布斯自由能的变化,并判断反应进行的方向。研究表明,由于S03易与H20反应生成H2SO4,烟气中S03更多地以H2SO4形式反应生成硫酸氢铵,且SO3和NH3反应更易生成硫酸铵。在硫酸氢铵沉积温度的实验研究中发现,NH3和SO3对沉积温度有相同的影响。在实验的浓度积Φ[NH3]·Φ[SO3]范围内(20～11000μL2·L-2),硫酸氢铵的沉积温度与反应物浓度积的对数呈线性正相关关系,沉积温度的变化范围在225-251℃之间。在相同浓度积的情况下,摩尔比(NH3/S03)偏离1:1时,硫酸氢铵的沉积温度略有上升。随着烟温的越低,硫酸氢铵/硫酸铵生成率不断增加。S03和NH3浓度的增加导致硫酸氢铵的生成率上升;NH3浓度的增加导致硫酸铵的生成率增加,而SO3浓度增加则导致硫酸铵生成率的下降。根据分析结果推断硫酸氢铵的生成进度由反应平衡控制,不考虑硫酸氢铵状态,反应平衡常数K1在各温度下数据集中性都较好,随着温度的下降,lgK1在120-200℃和200-260℃两个温度区间基本呈线性增加,且高温段增加速度更快。根据硫酸氢铵完全凝结假设的反应平衡常数集中性较好,lgK11在120-220℃之间随着温度的下降呈线性增加趋势。K1和K11均有较强的实际应用价值。据分析推断硫酸铵由硫酸氢铵和NH3反应生成。
[Abstract]:Nitric oxide (no _ x) is one of the main atmospheric pollutants in coal-fired boilers, which is harmful to the environment and human health. Selective catalytic reduction is the main method to remove NOx from coal-fired flue gas. With the decrease of flue gas temperature, NH3, which is not a complete reductant, can easily react with SO3 in flue gas to form ammonium bicarbonate. Liquid ammonium hydrogen sulfate is very viscous and corrosive, which condenses on the surface of air preheater and continuously captures fly ash, resulting in ash accumulation, blockage and corrosion of air preheater. At present, the ultra-low pollutant emission technology of coal-fired units is popularized, and the addition of a layer of SCR catalyst is the main way to further remove NOx. It not only increases the concentration of S03, but also deactivates the catalyst with the increase of unit operating time. The concentration of ammonia escape will also increase, further increase the amount of ammonium hydrogen sulfate, and aggravate the fouling and blocking phenomenon of air preheater. Therefore, the formation mechanism of ammonium hydrogen sulfate in denitrification flue gas is studied in this paper, which provides a theoretical basis for the design and operation of air preheater. In this paper, the change of Gibbs free energy in the reaction of NH3 and S03 is calculated from the point of view of chemical thermodynamics, and the direction of reaction is judged. The results show that because S03 reacts with H20 to produce H2SO4, S03 reacts more in the form of H2SO4 to produce ammonium hydrogen sulfate, and SO3 and NH3 react more easily to produce ammonium sulfate. It is found that NH _ 3 and SO3 have the same effect on the deposition temperature of ammonium hydrogen sulfate. In the range of 桅 [NH3] 桅 [SO3], the deposition temperature of ammonium hydrogen sulfate has a linear positive correlation with the logarithm of reactant concentration product, and the range of deposition temperature is from 225 鈩，

本文编号：1907829