Commercial VW/Ti catalyst used in selective catalytic reduction (SCR) process is one of the major sources of SO3 in coal-fired boiler, and modification of VW/Ti catalyst by adding catalytic promoter has been demonstrated to be an effective way to inhibit SO3 generation. In this study, the effect of P addition on the activity of NOx conversion and SO2 oxidation over VW/Ti catalyst was investigated. The results showed that the P-modified VW/Ti catalyst not only enhanced the catalytic activity at low temperature, but also reduced the oxidation rate of SO2. The 1.5PVW/Ti catalyst exhibited the lowest SO2 oxidation rate at 360 degrees C and achieved about 30 % reduction in SO2 oxidation rate when compared to 0PVW/Ti catalyst, whereas the conversion of NOx was still above 95 %. The physicochemical properties of catalysts were comprehensively characterized with N-2 adsorption, XRD, H-2-TPR, NH3-TPD, XPS and DRIFTS. The results illustrated that the W-O-W structure was also the main reason for SO2 oxidation on P-modified VW/Ti catalyst, which oxidized SO2 to form intermediate products HSO4- and constantly replenished in the presence of O-2. The oxidation of SO2 was weakened by the generation of VOPO4 on P-modified VW/Ti catalyst surface, which inhibited the formation of VOSO4 by reducing the adsorption of SO2 on the catalyst. In addition, the release of P-OH and W=O were promoted with the addition of P, which led to a significant increase in the intensity of the Bronsted and Lewis acid sites, resulting in the increase in the conversion of NOx at low temperatures.

The V 2 O 5 -TiO 2 catalyst produced by ultrasonic impregnation method was used to study the effects of different V loadings on the formation of SO 3 at the catalyst surface.The samples were characterized by N 2 adsorption,X-ray diffraction（XRD）,Raman analysis（Raman）,X-ray photoelectron spectroscopy（XPS）,NH 3 temperature programmed desorption（NH 3 -TPD）,H 2 temperature programmed reduction（H 2 -TPR）methods.Results show that with the increase of active component V loading,the content of V 4+ and V 3+ formed on the catalyst during the reaction also increases,and when the acidity of the catalyst surface increases,the amount of oxygen（Oα）adsorbed by the V=O bond on the catalyst surface will increase as well.After introduction of SO 2 ,it will react with V=O on the surface of the catalyst.V 5+ is reduced to V 4+ and can provide more surface that allows adsorption of oxygen（Oα）,so that SO 2 can be ox idized to VOSO 4 .On the other hand,SO 2 will also react with the [V5+] -OH groups on the catalyst surface and produce HSO 4 - ,and simultaneously,V 5+ is reduced to V 4+ .During the reaction,O 2 dose not directly provide O atoms to oxidize SO 2 but reacts with VOSO 4 to regenerate V= O,transforming V 4+ oxidized to V 5+ again.

为进一步降低现有燃煤机组烟气污染物排放质量浓度,实现大气污染物的协同深度治理,选取现役的选择性催化还原(SCR)催化剂作为研究对象,对不同条件下HCl/HBr等卤素成分对现役SCR催化剂脱硝协同汞氧化效果进行实验研究,并设计卤素溶液喷射系统,依据实验室研究结果,在现场脱硝过程中进行了不同浓度NH4Cl/NH4Br溶液喷射的工程应用与试验.结果表明:脱硝过程合理添加NH4Cl或NH4Br溶液均可有效提高现役SCR脱硝催化剂对单质汞氧化能力,HCl/HBr共同作用可以提高单一HCl在SCR催化剂表面对单质汞的氧化效果,进一步通过脱硝、下游脱硫、除尘等环保设施实现汞污染物的高效协同脱除.

针对某电厂300 MW燃煤机组超低排放条件下电除尘器极线出现的严重裹灰、板结现象,通过分析积灰样品烧失量、可溶性离子浓度、灰成分、粒径以及比电阻特性,结合锅炉超低排放运行特点,研究了电除尘器极线裹灰形成的关键影响因素.结果表明,低低温电除尘器极线上裹灰样品的NH+4、SO24-及灰样中SO3含量均较高,证实了电除尘器极线裹灰的主要原因是SCR脱硝系统逃逸氨与烟气中SO3反应生成硫酸氢铵,且由于低低温电除尘器工作温度较低,烟气中硫酸氢铵一旦形成后难以分解,造成电除尘器极线裹灰严重.同时由于除尘器入口烟气湿度过大,导致飞灰黏性增加,加剧了电除尘器极线裹灰与板结现象.硫酸氢铵使飞灰性质发生改变,飞灰粒度降低,同时硫酸氢铵的附着会影响电除尘器荷电,导致电除尘器除尘效率下降,进一步加剧极线积灰现象.因此,为减少电除尘器裹灰、板结现象,必须有效控制电除尘器入口烟气含水率,同时严格控制脱硝系统氨逃逸及SO3生成浓度等关键影响因素.

采用超声浸渍法制备了不同W负载量的WO3/TiO2催化剂,研究了 W负载量、温度及SO2浓度对催化剂表面SO2氧化过程的影响.结果表明,催化剂表面SO2氧化率随W负载量及温度的升高而增大,当W负载量由1％增至7％时,SO2氧化率由0.034％升高至0.210％;而当温度由280℃升高至 400℃时,SO2氧化率由 0.043％升高至 0.240％.通过N2吸附、XRD、Raman、NH3-TPD、H2-TPR及XPS等方法对催化剂样品进行表征.结果表明,活性组分W的增加会导致WOx增加,该结构能够减弱催化剂表面Br?nsted酸性位点强度,增强SO2在催化剂表面的吸附,同时导致催化剂表面吸附氧(Oα)增多,促进SO2氧化;针对W负载量5％的催化剂原位红外试验结果表明,通入SO2后会与催化剂表面W—O-W结构反应形成HSO4,同时将W6+还原为W5+.反应过程中,O2并不直接氧化SO2,而是与中间产物反应重新生成W—O—W,使得W5+再次氧化为W6+;另外,O2会促进HSO4-向吸附态的SO3转化,促进SO3在催化剂表面的脱附.

贫煤锅炉燃烧过程中,保证贫煤燃料的稳定着火、燃烧及燃尽特性,必须充分满足和保证燃烧过程温度、氧量等要求,这一定程度上与NOx生成控制要求的低氧、低温条件存在矛盾.因此在贫煤锅炉应用低氮燃烧技术过程中,如何保证锅炉低氮燃烧,又不影响锅炉燃烧性能,一直以来都是低氮燃烧技术的难点.在锅炉低氮燃烧技术初步方案的基础上,通过系统分析与设计,提出了切实可行的低氮燃烧技术深度优化改造方案.针对某300 MW贫煤锅炉,通过数值模拟分析了空气分级低氮燃烧方式以及底二次风喷口面积对锅炉燃烧及NOx排放的影响.在锅炉增设3层新型SOFA风进行低氮燃烧改造初步方案基础上,通过进一步计算与分析,提出了增大底二次风喷口面积1.5倍的低氮燃烧深度优化改造方案.模拟结果表明,NOx排放量由原先的473.4 mg/m3减少为265.3 mg/m3,改造后NOx排放量减少了40％以上,同时能保证锅炉温度场和氧量场分布均匀.改造后锅炉实际运行结果表明,NOx排放量由优化前的481.6 mg/m3降至269.1 mg/m3,NOx排放量减少了44.1％,有效实现了贫煤锅炉安全、高效、低污染运行.

Under various combustion process, CO2 and H2O both would exist in flue gas, the understanding of the influence mechanism of high concentration of CO2 and H2O on V2O5-WO3/TiO2 catalysts can provide needed information for the achievement of ultra-low emission. This study predominantly investigated NH3 adsorption and catalytic performance of V2O5-WO3/TiO2 catalyst under high concentration of CO2 and H2O conditions. Analyses of XRD, NH3-TPD, XPS and DRIFTS were performed to characterize the catalyst properties. Results show that the reaction between NO and NH3 followed E-R mechanism, CO2 and H2O mainly affect NO conversion by influencing the proportion of O alpha, proportion of V4+ and NH3 adsorption, which would hardly change the physical and crystalline structure of the catalyst. NH3 adsorption on catalysts is complicated under CO2 and H2O conditions. The net effect of CO2 on NH3 adsorption was negligible, and H2O inhibited NH3 adsorption generally. Although the addition of 25%H2O increased the proportion of O alpha on catalyst by forming hydroxy groups, the decreasing of V4+ proportion and NH3 adsorption play dominant roles in NO removal process, resulting in the significantly decrease of NO conversion under H2O-containing atmospheres.

在燃煤烟气中选择性催化还原(SCR)技术由于脱硝效率高、选择性好被广泛应用,然而SCR催化剂的催化作用会使烟气中的SO2氧化成SO3,SO3会与NH3等反应生成硫酸氢铵(ABS)和硫酸铵(AS),当烟气温度低于硫酸铵盐的凝结温度时,其会沉积在催化剂、空预器及其附属设备上,引发诸多严重的问题,对电厂的运行和环境造成了不利影响.本文综述了燃煤烟气中SO3与硫酸氢铵的生成特性及其控制方法最新进展,分析了SO3在锅炉和SCR系统中的形成机理、迁徙转化特性,阐述了控制SO3与硫酸氢铵生成的方法,介绍了不同活性组分对催化剂表面SO3和硫酸氢铵生成的影响.最后提出了开发新型催化剂是燃煤烟气中SO3与硫酸氢铵生成控制的重点研究方向.

选择性催化还原(SCR)技术由于脱硝效率高、选择性好而被广泛应用于烟气氮氧化物排放控制;然而,目前广泛采用的钒钛系SCR脱硝催化剂会使烟气中SO2氧化成SO3,烟气中过高的SO3对电厂安全运行会造成严重影响,也会对环境造成污染.以典型V2O5-WO3/TiO2催化剂为研究对象,系统研究了SCR脱硝过程中烟气流量、温度、O2浓度、SO2浓度等对催化剂表面SO3生成特性的影响,并进一步对SO3生成的反应动力学特性进行了分析.研究表明:催化剂表面SO3生成反应中SO2的反应级数为0.59,当O2浓度大于3％时,O2的反应级数为0,该反应的表观活化能为70.39 kJ/mol;实验条件下,烟气中SO2浓度增加会使SO3生成的反应速率提高;O2浓度对催化剂表面SO3生成影响并不显著;烟气温度对催化剂表面SO3生成具有显著影响,高温会促进SO3的生成.

以不同热解条件下制取的陕西烟煤(YL)半焦为原料,使用预糊化淀粉为黏结剂冷压成型制取成型燃料,分析不同热解条件下获得的煤焦成型后的物理特性,研究热解条件对半焦挥发分和表面含氧官能团的影响规律,揭示热解半焦特性对其成型的影响机理.结果表明:热解停留时间和热解终温对半焦成型特性具有显著影响.热解停留时间增加和热解终温升高会降低半焦挥发分含量和表面含氧官能团,影响黏结剂颗粒和半焦颗粒之间的黏结作用,从而会降低半焦成型后的冷压强度和跌落强度.结果表明:挥发分质量分数在16％以上的半焦成型后冷压强度大于450 N,适宜成型;热解终温小于600℃且热解停留时间小于5 min的半焦表面含氧官能团含量较高,成型后冷压强度大于450 N,可用于成型.半焦的成型特性受其挥发分含量和表面含氧官能团的综合影响.

基于燃煤烟气SO3·生成与排放给电厂运行及大气环境带来的严重影响,研究了一种在役典型商用蜂窝型V/W/Ti系脱硝催化剂表面的SO3生成反应动力学及反应机理.结果表明,反应温度与SO2浓度是影响催化剂表面SO3生成的关键因素.在SO2浓度为400×10-6时,当反应温度从300℃升至360℃,SO2-SO3转化率从0.2％提高至0.65％,温度达到400℃后,催化剂表面V2O5活性增加更为显著,SO2-SO3转化率从0.65％增2.3％,SO3生成反应的表观速率常数增加近3倍.SO3在催化剂表面的生成路径为:SO2与V5+-OH反应生成中间产物VOSO4与HSO4-,随后进一步反应生成SO3.SO2主要通过其在催化剂表面的吸附、转化过程影响SO3的生成,其本征动力学反应级数为0.52.O2的本征动力学反应级数为0,SO3生成反应可以在无O2条件下进行,O2存在会促进反应进行,但不会改变反应路径.

The transfer characteristics and removal capability of Hg in ultra-low emission facilities such as selective catalytic reduction (SCR), low temperature electrostatic precipitator, seawater desulfurization and wet electrostatic precipitator in a 300 MW coal-fired boiler of a power plant were studied under different working conditions and different types of coal. The results show that under different working conditions, the total emission concentration of mercury is basically 1.16-2.90 μg/m3. The final release of mercury into the atmosphere is mainly composed of elemental mercury and a small amount of oxidized mercury, the particulate mercury was completely removed. Most mercury is removed in seawater flue gas desulfurization. The overall removal efficiency of mercury of low temperature electric precipitator, a seawater flue gas desulfurization scrubber and wet electric precipitator is 25%, 62% and 37% respectively on average. The proportion of Hg2+ is the key to affect the efficiency of mercury removal in flue gas, and the higher proportion of Hg2+ in flue gas is beneficial to obtain higher efficiency in electrostatic precipitators and seawater flue gas desulfurization devices. In the 300 MW coal-fired boiler of a power plant equipped with a selective catalytic reduction unit, a low temperature electrostatic precipitator, a seawater flue gas desulfurization scrubber, and a wet electrostatic precipitator and other ultra-low emission facilities, the average removal rate of total mercury is about 83%, which can achieve greater levels of mercury removal.

The char samples were prepared from the coal impregnated with NaCl under different steam concentrations and temperatures. The mode of occurrence of sodium and the contents of sodium in different chars with the same conversion ratio were analyzed by inductively coupled plasma mass spectrometry. The effects of steam and temperature on the migration and transformation of sodium in the coal during the thermal conversion processes were studied. The results showed that the increase of steam concentration enhanced the release of water-soluble sodium during the thermal conversion of coal and promoted the transformation of water-soluble sodium into ammonium acetate, hydrochloric acid and insoluble sodium. As a result, the release of sodium was suppressed to a certain extent. It was also observed that increasing the reaction temperature could promote the release of water-soluble sodium and promote the transformation of water-soluble sodium to the other soluble forms of sodium. The evolution of char structure was an important influence on the release of sodium. The results revealed that the degrees of char condensation increased with the steam gasification reaction. The formation of large aromatic ring structures from the condensation of the small aromatic rings played the important role in the encapsulation of sodium, which would inhibit the release of sodium.