【作者】 王志鹏；

【导师】 禚玉群；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2019， 博士

【摘要】 低温同时脱硫脱硝技术是在半干法脱硫基础上,实现NO_x和SO₂的协同脱除,为此需要详细研究NO_x、SO₂在Ca（OH）₂等吸收剂表面的脱除反应路径且要提高协同脱除效率,以此为背景本文研究了NO_x、SO₂协同脱除过程气固反应机制。首先通过原位漫反射装置测定Ca（OH）₂和NO_x、SO₂反应的产物的光谱,分析产物成分和结构;其次用固定床实验平台研究了协同脱除效率,反应物和产物生成和消耗比例,研究温度、O₂等的影响,通过间歇性通断气相反应物,研究NO_x/SO₂和Ca（OH）₂反应过程,本文提出了详细的气相转化反应路径,从气固反应的角度角度解释反应机理;然后建立了固定床脱硫脱硝的反应模型,拟合了实验数据,获得了扩散系数、反应速率常数、衰减因子等参数,验证了反应机理,用DFT计算从微观角度解释了NO_x和SO₂协同脱除机理;最后通过工业化试验和应用验证了协同脱除新工艺。本文发现NO₂的脱除是两个NO₂先发生歧化反应,然后再和Ca（OH）₂发生酸碱反应生成产物,反应前期生成Ca（NO₂）（NO₃）,随后被NO₂氧化成Ca（NO₃）₂。随着反应的进行产物结构经历了表面桥式硝酸盐→双齿硝酸盐→单齿硝酸盐→体相硝酸盐的变化。NO₂的反应级数约等于2,NO₂的脱除分两部分,N₂O₄反应以及两个NO₂的反应。NO₂能氧化Ca（NO₂）₂,但却很难氧化Ca SO₃。NO和Ca（OH）₂反应弱,产物为亚硝酸-硝基物种以及硝酸盐物种。NO_x、SO₂在Ca（OH）₂表面协同脱除时,产物主要是Ca（NO₃）₂和Ca SO₄,从反应物到终产物之间存在硫和氮的含氧酸盐的多分子的活性中间体,中间体分解生成终产物。1000～850cm^-1之间的红外光谱先快速上升然后下降,即Ca SO₃会部分的被氧化。NO和NO₂可形成协同脱除。无O₂时NO₂和SO₂协同脱除时,NO₂转化成NO。O₂对Ca（OH）₂和SO₂反应生成Ca SO₃的过程无影响,但有O₂时反应生成了更多的Ca SO₄。Ca（NO₂）₂和SO₂反应产物是Ca S₂O₆。SO₂脱除过程中能同时脱除NO,1分子的NO和1分子的SO₂结合。SO₂或NO₂时“倒扣”着吸附在Ca²⁺位上时,和Ca²⁺相邻的O^2-位能协同吸附NO₂或NO。在模型研究方面,提出了成核膨胀共模型用于修正反应面积,可以更好拟合有扩散影响的实验数据。本文提出了分段协同脱除工艺,形成高SO₂区域,实现了SO₂和NO_x的高效协同脱除,形成了基于半干法的同时脱硫脱硝新工艺。更多还原

【Abstract】 Low temperature simultaneous desulfurization and denitrification tech NOlogy is based on semi dry desulfurization to achieve the collaborative removal of NO_x and SO₂.Therefore,it is necessary to study in detail the removal reaction path of NO_x and SO₂ on the surface of Ca（OH）₂ and spent absorbent and improve the collaborative removal effi-ciency.Based on this background,this paper studies the gas-solid reaction mechanism of the collaborative removal of NO_xand SO₂.Firstly,the spectrum of Ca（OH）₂ reaction with NO_x and SO₂ was measured by in-situ diffuse reflectance device,and the composition and structure of the product were analyzed.Secondly,the synergistic removal efficiency,the ratio of reactant and product generation and consumption,the influence of temperature and O₂ were studied by using fixed bed experimental platform.The reaction process and mechanism of NO_x/SO₂ and calcium hydroxide were studied by gaseous reactant transient techniques.The detailed reaction path of gas-phase transformation was given,and the reaction mechanism was explained from the point of gas-solid reaction rather than solution ion reaction.Then the reaction model of fixed bed desulfurization and denitrification was established,the experimental data were fitted,the parameters such as diffusion coefficient,reaction rate constant,at-tenuation factor were obtained,the reaction mechanism was verified,and the synergistic removal of NO_x and SO₂ was explained from the micro point of view by DFT calculation.Finally,the new process was validated by industrial test and application.In this paper,we found that as regard to the NO₂ removal the disproportionation of two NO₂ occurs first,and then react with Ca（OH）₂ by acid-base reaction to produce the product.In the early stage of the reaction,Ca（NO₂）（NO₃）is formed,and then it will be oxidized by NO₂ to Ca（NO₃）₂.With the reaction going on,the product structure experi-enced the changes of surface bridge nitrate,chelating and bindentate nitrate,Monodentate nitrate and bulk free-like nitrates.The reaction order of NO₂ is about equal to 2.The removal of NO₂ is divided into two parts,N₂O₄ reaction and two NO₂ reactions.NO₂ can oxidize Ca（NO₂）₂,while it is difficult to oxidize Ca SO_3.NO reacts weakly with Ca（OH）₂,and the products are nitro-nitrito and nitrito species.When NO_x and SO₂ are removed on the surface of Ca（OH）₂,the main products are Ca（NO₃）₂ and Ca SO₄.The the formation of multi-molecular active intermediates contain-ing sulfur and nitrogen,which decompose into the final product are the key step form the from reactant to product.The infrared spectrum between 1000～850cm^-1rises rapidly and then decreases,that is,Ca SO₃ will be partially oxidized.NO and NO₂ has synergistic removal effect.When NO₂ and SO₂ are removed together without O₂,NO₂ is converted into NO.O₂ has NO effect on the reaction of Ca（OH）₂ and SO₂ to form Ca SO₃,however more Ca SO₄ is produced when there is O₂.The reaction product of Ca（NO₂）₂ and SO₂ is Ca S₂O₆.NO can be removed at the same time during the process of SO₂ removal.When SO₂ or NO₂"reversely buckled"on Ca²⁺site,the O₂ potential adjacent to Ca²⁺can syner-gistically adsorb NO₂ or NO.Referring to the model research,the nucleation expansion model is proposed to modify the reaction area,which can fit the experimental data better when there is diffusion effect.In this paper,a new technology of simultaneous desulfurization and denitrification based on semi dry method is proposed,which moves up the absorbent spout to form a high concentration area of SO₂,realizes the efficient collaborative removal of SO₂ and NO_x.更多还原