【作者】 杜振；

【导师】 高翔； 施正伦；

【作者基本信息】 浙江大学 ， 工程热物理， 2011， 硕士

【摘要】 煤的燃烧过程中排放多种污染物,其中SO2和NOx对人类健康和生态环境存在着严重的危害,其排放控制已经成为环境研究热点。虽然常采用干法和湿法等技术来进行NOx和SO2的脱除,但是经济的脱除NOx和SO2仍然是环保行业的一大挑战。考虑到设备投资、运行成本以及设备的占地面积,越来越多研究部门尝试着研究出能够在同一温度区间同一设备对NOx和SO2同时脱除的技术。由于湿式氨法脱硫技术能够在脱硫的同时达到协同脱硫脱硝的目的,且脱除后的副产物可以作为氨肥进行利用,所以该技术在中国受到越来越多的关注。本工作的研究重点就是湿式氨法脱硫脱硝过程中NOx的吸收过程上,研究NOx在脱硫吸收液中的吸收机理,同时对NOx吸收的影响因素进行了初步探索。本文通过双搅拌反应釜研究湿式氨法脱硫脱硝过程中气液相组分对NOx吸收的影响。NO2和NO在(NH4)2SO3溶液中的吸收速率要高于其在同浓度下的NH4HSO3溶液中的吸收速率。液相组分中HSO3-含量对NO2吸收速率的影响效果要高于其对NO的影响。而在液相浓度一定时,在(NH4)2SO3和NH4HSO3溶液中,NO吸收速率受NO2入口浓度的影响,NO的吸收速率随NO2入口浓度的增加刚开始会不断增加,当增加到一定程度时,NO的吸收速率会随NO2入口浓度的增加而下降；同时气相中存在NO对NO2在(NH4)2SO3和NH4HSO3溶液中的吸收有促进效果；另外气相中存在SO2对NO和NO2的吸收都有促进效果,在气相中SO2能和NO2直接反应生成NO,而气相中O2的存在对NO的吸收有促进效果,而对NO2的吸收有抑制作用,主要是由于O2能同时对NO和SO32-进行氧化。总的研究结果是在一定程度上NO与NO2共存及SO2与NOx共存对彼此的吸收有促进效果。本文通过双搅拌反应釜对NOx在湿式氨法脱硫吸收液中的吸收特性进行试验研究,通过对工艺条件的影响与分析,确定试验的工艺条件。通过进一步的试验得到NOx和(NH4)2SO3的气液反应是受气膜和液膜共同控制的,而当(NH4)2SO3溶液浓度大于临界值时,NOx和(NH4)2SO3的气液反应主要受气膜控制。同时建立一个简化的数学计算模型来模拟NOx整个吸收过程,得到NO、吸收的传质方程,并通过对试验结果的拟合来确定传质过程中反应级数及反应的速率常数与NO2/NOx比值的关系,进而确定传质方程中气相组分的热物性参数,从而可以得到NOx吸收的总传质方程式。通过传质方程对NOx吸收过程进行相应的计算,并对计算结果与试验结果进行比较,发现计算值和试验值能够较好的吻合,进而验证了NOX的传质方程的准确性,同时说明数学计算模型对NOX的模拟具有可行性。更多还原

【Abstract】 The combustion of coal lends to the emission of pollutions, because SO2 and NOx have serious effects on human health and the ecosystems, their emission have been the major environmental concern. Although the removal of NOx and SO2 in flue gas is usually achieved by means of dry as well as wet techniques, the economical removal of NOx and SO2 still represents one of the greatest challenges in environmental protection. Recently, considering the capital investment, operation cost and space for equipment, attempts have been made to find an effective method to remove SO2 and NOx simultaneously in the same temperature rang and in a single reactor. As the ammonia-based wet process can remove SO2 and NOx simultaneously and has the ability to generate ammonium fertilizer, thus ammonia-based desulfurization and denitrification technology has drawn an increasing attention in China. The main objective of the paper is to study the absorption of NOx in ammonia-based wet flue gas desulfurization and denitrification process, and to study the absorption mechanism of NOx into absorption solution, meanwhile, to investigate the influence factor of NOx absorption.The gas-liquid phase compositions on NOx absorption in ammonia-based wet flue gas desulfurization and denitrification process is investigated in the double stirred tank reactor. The absorption rate of NO2 and NO in (NH4)2SO3 is higher than them in NH4HSO3 solution, and the effect of molar ratio for HSO3- to the total salt concentration on the NO2 absorption rate is larger than that for NO. Then, as the (NH4)2SO3 (or NH4HSO3) concentration is constant, the NO absorption rate increases with the increase of NO2 inlet concentration, and when the concentration of NO2 is large enough the NO absorption rate reduces with the increase of NO2 concentration, and that the presence of NO in the gas phase is favorable to the absorption rate of NO2. Meanwhile, the presence of SO2 in the gas phase is also favorable to the absorption rate of NOx, that because of NO generated by the reaction between NO2 and SO2. However, the presence of O2 in the gas phase is also favorable to NO absorption, but it is unfavorable to NO2 absorption, that because of the oxidation of NO and SO32- by O2. The total results suggest that the coexistence of NO and NO2 (or SO2 and NOx) in the flue gas could enhance the absorption of each other to some extent.The absorption of NOx into ammonia-based wet flue gas desulfurization and denitrification absorption solution have been investigated in the double stirred tank reactor, and determine the experimental conditions by optimizing the process conditions. The experimental results demonstrate that NOX absorption reaction is controlled concurrently by gas-and liquid-film, and the reaction may be mainly influenced by gas-film when the (NH4)2SO3 concentration is above some critical value. Meanwhile, a simplified mathematical calculated model is applied to simulate the total absorption process. Using the experimental data the relationship between reaction orders (or reaction rate constants) and the ratio of NO2/NOx also can be achieved, Then through the experiment the property parameters can be determined and a kinetic equation for total NOx absorption can be obtained. The comparison between calculated values (calculated by the kinetic equation) and experimental values of the NOx absorption rate, and it can be seen that the calculated values fit the experimental data well. So it is feasible definitely to simulate NOx absorption using the simplified mathematical calculated model.更多还原