【作者】 高攀；

【导师】 路春美；

【作者基本信息】 山东大学 ， 热能工程， 2008， 博士

【摘要】 我国是世界上最大的煤炭生产国和消费国，电力生产以火力发电为主，发电用煤占原煤消耗总量近50％。煤燃烧排放出大量有毒气体，十多年来我国火电厂NO_x放总量逐年增加，污染日趋严重，我国酸雨污染也正在由过去的硫酸型向硫、硝酸混合型转变。目前虽已经采取了低NO_x燃烧器、分级配风、火上风等技术措施，但降低NO_x排放能力有限，难以满足日益严格的环境标准要求。目前，我国拥有自主知识产权且成熟的脱硝技术较少，而燃煤电站烟气脱硝迫在眉睫，急需成本低廉、高效的脱硝技术。先进再燃及选择性非催化脱硝技术具有脱硝率高、运行成本适中、易于实现对中老锅炉改造等诸多优点，突出的技术、经济性优势使其有望成为我国燃煤电站脱硝的主流技术。本文建设了多功能脱硝实验平台及模拟气氛反应炉，实验研究了基本工况参数对SNCR脱硝反应的影响，重点研究了5种钠添加剂、3种含氧有机物、3种可燃气及SO₂对SNCR脱硝过程的影响；综合考虑氨水、尿素脱硝反应，增补钠添加剂、乙醇添加剂脱硝增效反应机理，提出了适用于添加剂协同氨水、尿素SNCR脱硝反应的机理模型，并对比分析实验与模拟结果，验证了动力学模型的合理性。实验研究了基本工况参数对3种气体燃料、4种生物质、3种煤粉以及生物质煤粉混合燃料再燃脱硝过程的影响，得出了不同种类燃料再燃脱硝特性；重点研究了氨剂、添加剂协同再燃脱硝过程，对比分析再燃、先进再燃及第二代先进再燃脱硝特性差异；建立了气体第二代先进再燃脱硝的机理模型，模型以GRI-Mech 3．0机理为基础，完善了氨水的脱硝反应，增补尿素的高温分解、水解反应以及钠、铁添加剂反应机理，实现了不同种类氨剂、添加剂协同气体再燃脱硝过程的动力学模拟，为优化先进再燃实验研究及完善动力学机理模拟提供参考和依据。（1）采用实验研究与动力学模拟相对应的方法系统研究了基本工况参数对SNCR脱硝过程的影响，明确了SNCR脱硝反应基本特性。研究发现氨水SNCR脱硝的最佳温度为1000℃，对应最大脱硝率89．2％，温度窗口为950℃-1067℃。尿素SNCR脱硝的最佳脱硝温度1000℃，最大脱硝率为90．1％，对应温度窗口为967℃-1057℃。在最佳脱硝温度下，氨水与尿素脱硝率相差较小，但低于最佳脱硝温度时，尿素SNCR脱硝受到分解及水解反应程度的限制，脱硝率明显低于氨水。氨水与尿素SNCR脱硝最佳氨氮比均为1．5，模拟SNCR脱硝过程达到反应平衡所需时间略小于实验条件所需时间，增加反应区氧浓度，使得氨水、尿素脱硝率均有所下降。（2）向反应区喷入Na₂CO₃添加剂明显提高了700℃-900℃温度区域SNCR脱硝率。Na₂CO₃进入炉膛后迅速分解并与H₂O反应生成稳定的钠化合物NaOH，利用含钠物质参与的脱硝反应对NO进行敏感性分析，得到含钠物质问的转化规律，发现NaOH经由NaOH→NaO₂→Na→NaO→NaOH链式转化，将H₂O和惰性的HO₂转化为活性的OH基，提高了活性基浓度，从而在较低温度时就激发了SNCR脱硝反应链，提高了低温下SNCR脱硝率。在最佳脱硝温度窗口内，Na₂CO₃参与反应生成的OH基与N-H-O反应系统自身产生的OH基浓度相比较小，因此高温条件下Na₂CO₃的促进作用不明显。实验研究了5种钠添加剂900℃时对SNCR脱硝反应的影响，发现各含钠物质具有相似的促进作用，其中NaOH、CHCOONa、CH₃COONa作用最为明显，脱硝率提高了23％，Na₂CO₃次之，脱硝率提高了19．6％，NaCl的效果最差，仅提高了10．8％。脱硝率随烟气中Na₂CO₃浓度的增大先升高后降低，Na₂CO₃的最佳浓度为400×10^-6。钠添加剂通过NaO+CO→Na+CO₂，NaO₂+CO→NaO+CO₂反应明显降低了尾气中CO浓度。（3）C₂H₅OH协同SNCR脱硝机理研究发现，C₂H₅OH能与O₂发生反应生成CH_i、OH等活性基，明显提高了750℃-850℃温度区域的脱硝率，并使最佳脱硝温度由1000℃降至850℃，但在高温条件下C₂H₅OH又一定程度降低了NO还原率。添加C₂H₅OH使SNCR脱硝反应温度窗口向低温方向移动约100℃，但并没有拓宽温度窗口。温度低于850℃时，脱硝率随C₂H₅OH浓度的增加而增加，温度高于850℃时，脱硝率随C₂H₅OH浓度的增加而降低。实验选用C₂H₅OH、C₃H₈O₃、C₃H₆O₂三种有机添加剂，研究其对SNCR脱硝过程的影响，发现添加含氧有机物均能明显提高800℃-900℃温度区域的脱硝率，而温度高于950℃后又不同程度削弱了NO的还原反应。实验还发现添加含氧有机物增加了尾气中CO的排放浓度，温度低于950℃时尤为明显，这是由含氧有机物在温度较低时不完全氧化造成的。含氧有机物是否适合用作SNCR脱硝添加剂需要慎重考虑，因为在其促进脱硝最明显的温度区域，增加了另一种污染物CO的排放量。（4）实验研究了CO、天然气（NG）、液化石油气（LPG）以及SO₂等4种气体添加剂对SNCR脱硝过程的影响。CO在水蒸气存在条件下的氧化反应能够产生H、OH等活性基，使得反应温度窗口向低温方向移动约100℃，并使氨水、尿素SNCR脱硝最佳温度由1000℃分别降为850℃和900℃，但CO没有拓宽SNCR脱硝反应温度窗口，最佳脱硝效率没有变化。天然气、液化石油气的加入改变了SNCR脱硝反应的温度特性，烟气中可燃气浓度越高，SNCR脱硝对温度的依赖程度越低，但反应区温度低于850℃，可燃气／NO摩尔比大于1．0时会造成CO排放增大。SO₂使SNCR温度窗口向高温方向移动，降低了最佳脱硝温度附近氨剂的还原效率，并削弱了Na₂CO₃和Ca（CH₃COO）₂对SNCR脱硝过程的促进作用。（5）利用高温气氛反应炉、多功能脱硝实验台以及改进的GRI-Mech 3．0脱硝反应机理系统研究了再燃区温度、过量空气系数、再燃比、停留时间等工况参数对再燃脱硝的影响。研究发现液化石油气和天然气再燃最佳过量空气系数为0．8。延长再燃区停留时间有利于提高脱硝率，当再燃温度低于1100℃时尤为明显；天然气再燃所需停留时间较短，约为0．68s，液化石油气、压缩天然气由于所含高分子碳氢化合物较多，再燃区停留时间应不低于1s，延长停留时间可缩小3种碳氢气体再燃脱硝率差异。模拟发现增加反应系统压力有利于提高脱硝率并能降低再燃区出口TFN（TFN=NO_x+HCN+NH₃）排放。由于不饱和烃键能较低，容易断裂，低温条件下不饱和烃含量较高的可燃气再燃脱硝率明显高于饱和烃含量高的可燃气。（6）在典型再燃温度1000℃～1300℃范围内，先进再燃脱硝率要比基本再燃脱硝率高出20％-38％，加入氨水、尿素和氰化氢均能明显促进再燃脱硝过程，结合TFN排放及还原剂经济性，氨水及尿素作为先进再燃还原剂优于氰化氢。尿素需要分解为NH₃和HNCO才能参与NO的还原反应，再燃区温度低于1100℃时，尿素对再燃脱硝的促进作用低于氨水，1100℃之后尿素为还原剂的先进再燃脱硝率基本保持不变，而氨水对再燃脱硝的促进作用则随再燃区温度增加而降低，因此再燃区温度低于1100℃应选择氨水为还原剂，高于1100℃时应选择尿素。动力学模拟及实验发现先进再燃脱硝率随氨氮比增大而提高，结合脱硝率及再燃区出口TFN排放，建议氨氮比取1．5-2．0。（7）Na₂CO₃、Fe（CO）₅添加剂对再燃脱硝过程的影响受再燃温度及添加剂浓度的共同制约，添加剂浓度越大，低温时抑制作用越明显，出现促进作用的温度点越高，在添加剂作用下最佳再燃温度向高温方向移动。当Na₂CO₃、Fe（CO）₅与氨剂共同喷入再燃区时，Na₂CO₃对先进再燃脱硝过程起促进作用，尤其是在1050℃之后，Na₂CO₃的促进作用更为明显：Fe（CO）₅在温度低于1100℃时对先进再燃脱硝起抑制作用，但温度高于1100℃之后，又起到明显的促进作用，在较高的再燃温度下，添加剂浓度对脱硝率几乎没有影响。（8）C₂H₅OH不适合用作先进再燃添加剂，它对氨水和尿素还原性能均有不同程度的削弱作用，并且增加了CO的排放浓度。SO₂对气体再燃脱硝影响微弱，但会削弱添加剂对再燃的促进作用。主要原因是SO₂与添加剂阳离子结合成稳定的硫化物，从而削弱金属离子与活性基的反应，并降低了金属氧化物的催化作用。实验发现氨水为氨剂时，先进再燃结合SNCR技术脱硝比仅先进再燃脱硝率高出10个百分点，而尿素作为氨剂时同比高出5个百分点，碳酸钠对二级喷入氨剂促进作用微弱。（9）实验发现700℃-900℃时，生物质再燃脱硝率随反应温度增加而提高，900℃之后脱硝率呈下降趋势，相同实验条件下生物质再燃脱硝率远高于煤粉。与单一煤粉再燃脱硝相比，掺混生物质可使再燃脱硝率提高15-27个百分点，并使煤粉再燃脱硝适宜温度区间由1100℃～1200℃拓宽至900℃～1200℃；与单一生物质再燃脱硝相比，1000℃～1200℃时掺混煤粉可使脱硝率提高5个百分点。为保证高脱硝率以及宽广的适宜再燃温度区间，掺混比λ应大于1。生物质再燃最佳过量空气系数为0．8，生物质掺混煤粉再燃过量空气系数最佳范围为0．6-0．8。实验固体燃料最佳再燃比均为20％。反应气氛中NO初始浓度越大，生物质粒径越小，再燃脱硝效果越好，较大的再燃比可以一定程度上缩小再燃物料粒径及初始NO浓度带来的脱硝率差异。（10）氨水、尿素均能明显提高生物质再燃脱硝率，AR-lean方式下先进再燃脱硝率高于AR-rich。钠添加剂对先进再燃脱硝的促进机理与反应气氛有关。在还原性气氛中钠添加剂通过消耗活性基，减弱羟基的氧化反应，增强NO的还原；在氧化性气氛下，钠添加剂的促进机理与还原性气氛相反，是通过H₂O（?）H+OH反应形成活性OH基，促进氨剂脱硝反应从而提高了脱硝率。向再燃区喷入Na₂CO₃，对先进再燃脱硝的促进作用要高于向燃尽区喷入添加剂，因为Na₂CO₃在再燃区和燃尽区均发挥了促进作用。更多还原

【Abstract】 As the largest coal producer and consumer in the world, electricity generated by coal-fired power plants keeps the dominant in China. Coal consumption by power plants accounts for nearly 50% of the total. The combustion of coal releases abundance of poisonous gas. In recent 10 years, total amount of NO_x emission from coal-fired plant increases year by year, pollution becomes severe gradually. The acid rain pollution of China is converting to mixed type of sulfuric acid and nitric acid from the past sulfur-based acid rain. Although some low-NO_x technology such as low-NO_x burners, over fire air has been used to control the emission of NO_x, the limited ability of NO removal is difficult to meet the increasingly stringent environmental standards. At present, our country owns few mature NO_x control technologies with self-dominated intellectual property rights. Facing the urgent task of NO_x emission control of coal-fired plant, it is required to develop the low cost and high efficiency NO_x control technology. Advanced reburning（AR） and selective non-catalytic reduction（SNCR） technology gain some advantages of low cost, high efficiency, easy to be accepted by old type boiler which may become dominating NO_x control technologies of coal-fired plants.In this paper, a multi-purpose equipment and a simulation atmosphere reactor were established to study the effect of basic conditions parameters on NO removal of SNCR, focusing on performances of the 5 kinds of sodium additives, 3 kinds of oxygen-containing organic compounds and 4 kinds of gas additives on SNCR process. A mechanism model is set up to simulate the SNCR process which considers not only ammonia and urea reaction but also additives reaction. The results of model simulation and experiment are compared to verify the rationality of mechanism model. The basic reburning process of 3 kinds of gas fuel, 4 kinds of biomass, 3 kinds of pulverized coal and the mixture of biomass and coal were studied on multi-purpose equipment. The denitrification characteristics are compared for different reburn fuel. The performances of N-agents and additives co-reburning process were studied meticulously. The features of basic reburning, advanced reburning and second generation advanced reburning were analyzed to optimize the advanced reburning technology. Based on GRI-Mech 3.0 mechanism, NO_x reduction mechanism by ammonia and pyrolysis and hydrolysis reaction of urea is remedied and also the effect of HCO, HNCO and NCO. Besides, additive mechanism of sodium carbonate and iron pentacarbonyl are also taken into consideration. All of the research aims to optimize experimental and modeling study of advanced reburning and SNCR process.（1） The NO reduction performances of SNCR process have been systemically studied by theory analysis, chemical kinetics modeling and experiments. The NO removal characteristics of SNCR process are clearly summarized. The SNCR process with ammonia as agent achieves maximum NO removal efficiency about 89.2% at 1000℃accompanying the temperature windows within 950℃to 1067℃. While, the top efficiency of urea is 1000℃and corresponding maximum efficiency about 90.1% with temperature windows for 967℃to 1057℃. The NO removal efficiency of ammonia and urea is similar at optimum reaction temperature. However, below the reaction temperature windows, the efficiency of urea is obviously lower than that of ammonia for the decomposition limitation of urea at low temperature. The experiments and modeling simulation both verify the best NSR of ammonia and urea is 1.5. The modeling simulation achieves a little short time for reaction balance than that of experiments. The efficiency becomes lower with increasing the oxygen concentration of flue gas.（2） The NO removal efficiency of SNCR is improved drastically at 700℃to 900℃with sodium carbonate additive. Sodium carbonate is decomposed instantly since it is injected into furnace and will be translated into the steady phase sodium hydroxide under the effect of moisture. Based on the sensitive analysis of sodium compound on NO reduction, it is found that sodium hydroxide goes through chain reactions via NaOH→NaO₂→Na→NaO→NaOH, the result of net reaction equal to convert H₂O and HO₂ to active OH. The increasing of active OH excitated the NO reduction at low temperature. Within the optimal temperature zone, concentration of active OH generated by sodium carbonate is small compared to N-H-O system self, so the promotion of sodium carbonate is feeble at high temperature. 5 kinds of sodimu compounds additives were chosen to investigate the promotion of additives on SNCR process at 900℃. It is observed that all of the sodium compounds promote the SNCR process. Among of additives, sodium hydroxide, sodium formate and sodium acetate present best performances and the efficiency is improved by 23%. The following is sodium carbonate which improves the efficiency byl9.6%. While sodium chloride acts the poorest result accompanying a 10.8% enhancement. There is a peak concentration value of 400×10^-6 for sodium carbonate, and exceeds this concentration a little prohibitive performance was observed. In addition, carbon monoxide concentration is reduced obviously by adding sodium additives mainly for the reactions: NaO+CO→Na+CO₂, NaO₂+CO→NaO+CO₂.（3） Investigating reaction mechanism of cooperating ethanol with SNCR process founds that active radicals like CH_i、OH are produced by the reaction of ethanol and oxygen. NO reduction is enhanced evidently from 750℃to 850℃and the optical temperature is removed from 1000℃to 850℃. However, the NO removal efficiency is compromised at high temperature. As a result, adding ethanol shifts the temperature window towards low temperature by 100℃, but the range of temperature window broadens hardly. NO reduction will be strengthened as the ethanol concentration increasing under 850℃, but it presents opposite when the reaction temperature exceeds 850℃. Ethanol, glycerol and methyl acetate were selected to investigate the effect of oxygen-containing organic additives on SNCR process. It is observed that all of the organic compounds could improve NO reduction evidently from 800℃to 900℃and then weak the process when reaction temperature exceeds 950℃. It is also found that carbon monoxide concentration of the flue gas is increased at the present of the additives especially when temperature lowers than 950℃.It is caused by the incomplete oxidation under low temperature . So more attention should be paid to the rationality of oxygen-containing organic compounds used as SNCR additive for generation of carbon monoxide generation. （4） Experiments were also conducted using carbon monoxide, natural gas（NG）, liquefied petroleum gas（LPG） and sulfur dioxide as additives respectively to investigate the effect on SNCR process. Carbon monoxide could produce H, OH etc, via oxidation reaction at the present of vapor which removes the temperature window towards low temperature by 100℃. The optical temperature shifts from 1000℃to 850℃and 900℃respectively for ammonia and urea. However, carbon monoxide does not broaden the temperature windows and maximum NO removal efficiency changes feebly. The NO reduction characteristic depend on temperature of SNCR is changed as injecting NG and LPG into reaction atmosphere. The more content of gas fuel, the more independent of temperature of SNCR was observed by experiments. But carbon monoxide emission increases obviously when the reaction temperature is lower than 850℃and the mole ratio of fuel gas to nitrous monoxide exceeds 1.0. The present of sulfur dioxide in the flue gas shifts the temperature window towards higher temperature and reduces the maximum efficiency around the optical temperature. It is also found that the promotion of sodium carbonate and calcium acetic on SNCR process is weakened by the effect of sulfur dioxide.（5） Operating parameters influencing the NO reduction including reburn temperature, reburn stoichiometric（SR₂）, reburn fuel fraction（Rff） and residence time, et al, were investigated by experimental system and the improved GRI-Mech 3.0 model. There exists best SR₂ value 0.8 of reburn zone for LPG and NG. Prolonging the residence time of reburn zone is favorable to for NO reduction, especially when the reburn temperature under 1100℃. The indispensable residence time of NG reburning is short which is about 0.68s and values of LPG and compressed NG should be exceed 1.0s for its abundant in hydrocarbon-macromolecules. The NO reduction performance of experimental gas fuel become accordantly by prolonging the residence time of reburn zone. The modeling simulation shows that heightening pressure favors in NO reduction and reducing the quantity of TFN（TFN=NO_x+HCN +NH₃） at exit of the reburning zone. The NO removal efficiency of gas fuel which contains unsaturated hydrocarbon is obviously higher than that of which mainly containing saturated hydrocarbon for chemical bond energy of the unsaturated hydrocarbon is low and easily to be ruptured.（6） Injecting ammonia, urea and HCN could promote the denitration process of reburning evidently. NO removal efficiency of advanced reburning is higher than basic reburning by 20%-38% at the representative reburning temperature from 1000℃to 1300℃. Consideration emissions of TFN and the economically of N-agents, ammonia and urea are more suited as N-agents of advanced reburning than hydrogen cyanide. The promotion of urea is lower than ammonia under 1100℃, because urea must be decomposed to NH₃ and HNCO which can react with NO directly, but the low temperature limit the decomposition. NO removal efficiency of urea is invariable when the reburn temperature exceeds 1100℃, but the promotion of ammonia falls. So ammonia should be selected as N-agents when the reburn temperature lower than 1100℃, otherwise urea would be chosen. Both of modeling simulation and experiments proved that the raise of NSR benefits the NO reduction process. Consideration of the TFN emission and NO reduction, the value of NSR about 1.5-2.0 is suggested.（7） The performance of sodium carbonate and pentacarbonyl iron on rebuning process is dominated by reburn temperature and the concentration of additives. The higher concentration of additives in the flue gas, the more prohibitive of NO reduction was observed at low temperature. The optimum reburning temperature moves to high temperature with the effect of additives. When the additives injected with N-agents together, sodium carbonate promotes advanced reburning process effectively at the whole reburn temperature especially after 1100℃. Pentacarbonyl iron restricts the NO reduction below 1100℃, but acts opposite contrarily when reburn temperature exceed 1100℃. The concentration of pentacarbonyl iron affects NO reduction feebly after 1150℃.（8） Ethanol is unfitted additive for advanced reburning for its imperfect NO reduction of ammonia and urea, and increases the carbon monoxide emission. Sulfur dioxide hardly affects the reburning process, but it can weaken the promotion of the additive for the reaction of sulfur dioxide with additive which generates steady sulfide. NO removal efficiency of advanced reburning combining with SNCR than advanced reburning by 10% and 5% respectively. Sodium carbonate hardly promotes the secondary ammonia injection.（9） The NO reduction characteristics of reburning and advanced reburning with biomass, pulverized coal and the mixture as reburn fuel were studied by experiments. The experimental results indicate that NO removal efficiency increases rapidly with the reburning temperature at 700℃-900℃and NO removal efficiency declines slightly after 900℃. The efficiency of pulverized coal reburning increases with the raise of temperature, but it is much lower than that of biomass at the same conditions. The mixture of coal and biomass in different ratio can promote the NO reduction of pulverized coal distinctly from 900℃to 1000℃. To achieve high denitration efficiency and large eligible reburning temperature range, the mixing ratio （λ） should be greater than 1.0. There is an optimum SR₂ value of 0.8 and 0.6-0.8 for biomass and the mixture. All experimental solid reburning fuel achieves optimal efficiency when the reburn fuel fraction is 20%.（10） Both ammonia and urea could promote the NO removal efficiency of biomass reburnng and the efficiency of AR-lean is higher than that of AR-rich. Adding sodium carbonate to reburning zone can urge active hydrogen atom and hydroxyl radical integrate to water and the net reaction is H+OH（?）H₂O. The present of sodium carbonate could weaken the reaction of hydroxide radical with hydrogen atom and hydroxyl radical, and raise the reaction probability with NO. As a result, NO removal efficiency is promoted. The stimulative mechanism of injecting sodium carbonate into burnout zone is adverse. It is suggested that the effect of sodium carbonate on NO reduction for can be explained by the ability of additive to increase hydroxyl radical by reverse reaction. Sodium carbonate co-injection with the reburning fuel is more effective than injecting it into the burnout zone. Because the additive promotes NO reduction both of reburn zone and burnout zone, and in the latter case the time of the additive evaporates and mixes with flue gas is relative short which is another reason.更多还原