某600MW燃煤机组脱硝装置喷氨优化效果评价

某600 MW机组脱硝装置经过长时间运行,出口NOx浓度无法有效跟踪烟囱入口NOx浓度,判断脱硝装置存在NOx浓度场分布不均,局部喷氨过量的情况,通过对喷氨支管手动调门开度多轮优化调整,最大程度提高反应器出口NOx浓度分布的均匀性,调整后反应器A侧出口相对标准偏差从42.4％下降至13.7％,降低了28.7％,反应器B...     

660MW燃煤机组SCR烟气脱硝系统的研究

以某电厂660MW级燃煤机组SCR脱硝装置为例,在保证SCR系统以及燃烧条件稳定运行的情况下,主要研究了入口NO_x浓度对出口NO_x浓度、脱硝效率、氨逃逸率等运行参数的影响。结果表明:出口NO_x浓度随着入口NO_x浓度的提高而提高,线性拟合的R2值可达0.97,满足线性关系;脱硝效率总体随入口NO_x浓度的变化不大,稳定浮动在81%左右,证明此机组脱硝效率具有稳定性;入口NO_x浓度与氨逃逸率呈正相关,且入口浓度存在一个最佳值(280mg/m~3),使氨逃逸率最低。     

SCR脱硝系统精准喷氨改造

随着国家环保政策要求的不断严格,氮氧化物排放的限值不断降低.为满足环保要求,各火电厂纷纷进行脱硝超低排放改造,但因传统的选择性催化还原技术(SCR)脱硝工艺无法精确控制喷氨量,机组虽达到了氮氧化物超低排放控制的投运要求,但也因过量喷氨产生了一系列问题.本文对电厂SCR脱硝超低排放改造后,机组运行存在的一些问题进行分析,...     

烟气脱硝装置喷氨流场模拟分析

对装置动力站脱销单元氨逃逸问题,结合现场实际排查氨逃逸的原因.根据现场分析,针对供氨母管的喷氨阀组不能动作,可能引起喷氨格栅各喷口流速不均匀,致使烟气和氨气在烟道内的流场分布不均从而引起氨逃逸的问题,借助FLUENT开展喷氨系统单模块流场模拟,重点考察喷氨系统喷氨流量以及烟气上升过程的流场分布问题,从减小流体流动阻力和...     

涡流混合式SCR脱硝系统喷氨优化调整试验研究

针对脱硝系统氨逃逸量大造成除尘器无法投运的问题,对涡流混合式脱硝系统进行喷氨优化试验。试验发现,脱硝出口NOx浓度在烟道宽度方向分布不均。通过调整喷氨支管手动蝶阀降低了脱硝出口NOx浓度分布的不均匀度。满负荷下,烟道A侧出口不均匀度由48.3%降低到19.4%; B侧出口不均匀度由62.7%降低到21.8%。经过调整,NOx分布不均匀度显著下降。两侧烟气流量在高低负荷下不存在明显的偏差,流场分布也较为均匀。电厂采用新型涡流静态混合器,有助于解决脱硝出口NOx浓度沿烟道深度方向分布不均的问题。利用SIS数据分析发现脱硝出口NOx浓度CEMS测点不准确,导致喷氨自动投运时喷氨量过大,氨逃逸量变大。CEMS测点取样不具代表性,建议采用网格法取样,并对CEMS测点进行定期标定。喷氨控制策略中,喷氨量跟随性差,导致喷氨量与脱硝入口NOx浓度变化存在一定的延迟,建议优化喷氨控制逻辑。净烟气NOx排放浓度值不宜设置得过低,设定值越低,氨逃逸量越大。综合环保性和经济性,推荐净烟气NOx排放浓度控制在25～35 mg/m3。经过喷氨优化后,整体的氨逃逸量控制在3×10-6以下。     

百万机组脱硝系统AIG喷氨控制分析与优化

本文结合某电厂3号机组SCR脱硝系统AIG喷氨实时优化项目,分析了机组不同工况下脱硝系统AIG喷氨自动回路的调节效果,介绍了AIG喷氨自动回路的调节原理及特点,并结合实际工况在线优化AIG喷氨控制逻辑和调整前馈量修正系数。优化后的SCR脱硝系统AIG控制回路通过分区自动调整效果很好,反应器出口氮氧化物均匀性明显改善,可为供氨母管自动调节回路提供准确的氮氧化物参考值。     

SCR脱硝系统运行过程中存在的问题分析

选择性催化还原(SCR)工艺是目前燃煤机组中广泛应用的高效脱硝工艺,长期应用以来出现了流场不均、喷氨格栅堵塞、脱硝效率达不到设计值、氨逃逸浓度超标、压降过大、烟温过低等问题.针对上述问题,文章研究了其产生的原因,分析了其造成的影响,并且提出了可行性建议和解决方案.     

SCR系统流场优化数值模拟研究

为提高选择性催化还原脱硝系统(SCR)的烟气气流均匀性,进而提高SCR反应器的催化效率、减少催化剂的冲蚀和损耗、提高催化剂使用寿命和提高催化反应反应物的接触程度,针对SCR反应器的流场开展数值模拟以及导流板和整流板的结构优化,基于Realizable k-ε模型和多孔介质模型,通过对全尺寸SCR反应器模型的速度场的模拟,研究导流板结构、整流板数量对于SCR脱硝系统的流场组织和气流均匀性的影响。通过模拟SCR反应器内的颗粒分布,研究飞灰颗粒对流场的影响。通过计算整流板前截面的相对速度偏差和分析不同优化方案下的SCR反应器的速度场,评估导流板和整流板的导流效果,进而确定最佳方案。结果表明:在弧形、直弧形、弧形、直弧直4种导流板方案中,直弧直形导流效果最好,这是因为弧形导流板前的水平直板和竖直直板可以更好地引导气流流动;结合反应器采用斜顶设计的几何特点,基于流场调整导流板形状与速度梯度方向相同,可以显著优化烟气的气流组织,减少转弯处的能量耗散;催化剂层前的整流板可进一步引导气流流动,极大改善气流均匀性;但过多的整流板提高近壁面处的烟气气流阻力,加剧能量耗散和速度不均匀性,反而降低整流板的整流效果。本研究整流板数量15较为合适。经过对导流板和整流板结构及数量的调整,最终可将催化剂上层的速度偏差降至6.68%,符合工业要求。针对烟气颗粒场的分析表明,飞灰颗粒主要沉积在烟道右壁面和上升通道上壁面处;同时,对颗粒沉积处必要的飞灰处理可减少烟气飞灰对于催化剂的冲蚀作用。     

350MW机组锅炉SCR脱硝系统优化

准东煤田是我国目前最大的整装煤田,但准东煤在锅炉燃烧过程中易发生结焦问题,一般掺烧高岭土缓解结焦。某燃用准东煤350 MW机组,锅炉燃煤掺烧高岭土后烟气携带灰尘颗粒及灰尘量增大,出现SCR脱硝系统烟道积灰严重和喷氨量明显偏大问题,同时在空气预热器形成硫酸氢氨堵塞,使机组不能长周期稳定运行。通过与国内同类型多台机组锅炉对比后发现,脱硝系统均存在易产生积灰的脱硝转向室、催化剂上方及空气预热器入口斜坡积灰状况等情况。针对存在的问题,通过建立改造前、后的模型计算分析,进行了导流板布置的优化设计、CFD流场分布、优化SCR系统导流板设计、声波与蒸汽吹灰器结合吹灰和氨注射栅格优化升级等工作,应用德图480风速仪实测风速试验,发现脱硝烟道原导流板设计不合理及施工安装偏差;原导流板水平段跨距大,支撑不足,造成导流板压塌变形,影响烟气流场分布;锅炉所烧煤质为高钠煤,为防止锅炉结焦掺烧高岭土后,增加了烟气飞灰颗粒及灰尘量,飞灰具有很大黏性,易沉积在烟道导流板及烟道壁面上。因此,提出对脱硝内部各处导流板进行优化改造,对脱硝系统烟道易产生积灰的部位增加声波吹灰器,对喷氨格栅喷嘴数量及氨空混合器升级,同时开展锅炉SCR脱硝喷氨热态优化调整试验工作。通过开展相关工作,SCR烟气系统的烟气流场相对标准偏差优化5%,相同负荷下液氨消耗量降低45%,彻底解决脱硝系统积灰和空气预热器堵塞问题,实现机组满负荷达标稳定运行。锅炉长期运行半年后停炉检查,发现前期脱硝系统烟道高达1 m的积灰部位彻底解决,催化剂表面干净无杂物,解决了脱硝系统积灰问题,同时配合提高空气预热器冷端综合温度的措施,彻底解决锅炉空气预热器堵塞问题。同时,经济效益显著,每年可以分别节约液氨费用70万元,节约风机电耗费用100万元,节约检修清理积灰及检修费用80万元,节约空气预热器冲洗治理费用20万元,综合节约费用270万元/a,达到预期效果实现机组长周期安全经济稳定运行。     

燃煤电厂真实烟气条件下SCR催化剂脱硝性能

制备了具有工业应用价值的V₂O₅/TiO₂负载WO₃与MoO₃的蜂窝状SCR催化剂,并在某燃煤电厂烟气环境下,对其催化性能进行了测试,结果表明:增大催化剂体积能够提高脱硝效率,但活性增量逐步下降,当脱硝效率达到80%以上时,继续增大催化剂体积其活性提高不显著。催化剂的脱硝活性随着积灰时间的延长而降低,脱硝系统运行4 h后,催化剂脱硝活性减少9.4%。在燃煤电厂尾气飞灰浓度约为0.031 kg·m^-3环境下,为满足尾气中NO_x浓度排放要求(<200 mg·m^-3),每连续运行6 h需进行一次吹灰。催化剂的脱硝性能随着运行时间的延长,先急剧下降,后缓慢降低。在连续运行48~168 h范围内,脱硝活性下降值小于1%,SO₂氧化率下降值小于0.1%。在12个月内,平均每连续运行700 h,脱硝活性降低1%。     

Modeling and simulation of the injection of urea-water-solution for automotive SCR DeNOx-systems

The evaporation of water from a single droplet of urea water solution is investigated theoretically by a Rapid Mixing model and a Diffusion Limit model, which also considers droplet motion and variable properties of the solution. The Rapid Mixing model is then implemented into the commercial CFD code Fire 8.3 from AVL Corp. Therein, the urea water droplets are treated with Lagrangian particle tracking. The evaporation model is extended for droplet boiling and thermal decomposition of urea. CFD simulations of a SCR DeNOx-system are compared to experimental data to determine the kinetic parameters of the urea decomposition. The numerical model allows to simulate SCR exhaust system configurations to predict conversion and local distribution of the reducing agent.     

Modeling and simulation of urea-water-solution droplet evaporation and thermolysis processes for SCR systems

A reliable mathematical model of urea-water-solution(UWS) droplet evaporation and thermolysis is developed.The well known Abramzon–Sirignano evaporation model is corrected by introducing an adjustment coefficient considering the different evaporation behaviors of UWS droplet at different ambient temperatures. A semidetailed kinetic scheme of urea thermolysis is developed based on Ebrahimian's work. Sequentially, the evaporation characteristics, decomposition efficiency of a single UWS droplet and deposit formation are simulated. As a result, the relation of evaporation time, relative velocity, exhaust temperature and droplet initial diameter is presented. Synchronously, it indicates that temperature is the decisive factor for urea thermolysis. Different temperatures result in different deposit components, and deposit yield is significantly influenced by temperature and decomposition time. The current work can provide guidance for designing urea injection strategy of SCR systems.     

Formation and emission characteristics of VOCs from a coal-fired power plant

On-site measurements of volatile organic compounds (VOCs) in different streams of flue gas were carried out on a real coal-fired power plant using sampling bags and SUMMA canisters to collect gas samples,filters to collect particle samples,Gas chromatography-flame ionization detector/mass spectrometry and gas chromatography-mass spectrometry was the offline analysis method.We found that the total mass concentration of the tested 102 VOC species at the outlet of wet flue gas desulfuration device was (13456 ± 47) μg·m-3,which contained aliphatic hydrocarbons (57.9％),aromatic hydrocarbons(26.8％),halogen-containing species (14.5％),and a small amount of oxygen-containing and nitrogen-containing species.The most abundant species were 1-hexene,n-hexane and 2-methylpentane.The top ten species in terms of mass fraction (with a total mass fraction of 75.3％) were mainly hydrocarbons with a carbon number of 6 or higher and halogenated hydrocarbons with a lower carbon number.The mass concentration of VOC species in the particle phase was significantly lower than that in the gas phase.The change of VOC mass concentrations along the air pollution control devices indicates that con-ventional pollutant control equipment had a limited effect on VOC reduction.Ozone formation potential calculations showed that aromatic hydrocarbons contributed the highest ozone formation (46.4％) due to their relatively high mass concentrations and MIR (maximum increment reactivity) values.     

660MW燃煤机组百万吨CO_2捕集系统技术经济分析

为了解常规燃煤机组碳捕集系统的技术经济性,以基准情景为基础,根据国内某10万t CO_2燃烧后捕集系统的投资情况,利用生产能力指数法对5种脱碳情景的投资进行估算。在保证内部收益率为8%的前提下,分析了5种脱碳情景的上网电价、CO_2综合减排成本及其敏感性。结果表明,CO_2综合减排成本中,厂内碳捕集成本比例最大;随着燃料价格的上涨,CO_2综合减排成本逐渐增加;随着CO_2综合收益的增加,上网电价可以逐渐下降。     

基于CFD的三相分离旋流器流场分析与结构优化

基于计算流体动力学(CFD)方法,采用FLUENT软件对三相旋流分离器进行了流场分析和结构优化。通过对该旋流器的脱气和除砂功能开展数值模拟分析,研究了不同结构参数对脱气和除砂效果的影响。研究发现,溢流管伸入长度、倒锥结构高度、入口截面面积以及出液孔高度等的变化对脱气除砂效果均有较大影响。     

Modeling and simulation of a smart catalytic converter combining NOx storage, ammonia production and SCR

Dynamic simulation of the smart catalytic converter, proposed by Daimler AG, is presented. The smart catalytic converter combines NOx storage, on-board ammonia production and selective catalytic reduction (SCR) and functions in a dual-mode operation, alternating between lean burn and rich burn. It relies on intrinsic dynamic operation and synchronization of all units and its development demands a reliable dynamic simulator. A platform capable of simulating the dynamic behavior of multiple-unit aftertreatment system was developed based on COMSOL package. Predictive kinetic models were developed for NOx storage unit that includes ammonia formation function and for NH₃-SCR unit. Using these kinetic models, two-unit smart catalytic converter was simulated on the developed simulator. The results of the simulator were validated using two-unit experimental data. The simulator was also employed to control and optimize the performance of smart catalytic converter. It was shown that the simulator is vital for optimization of lean and rich periods in order to ensure stable lean–rich cycles.     

Experimental and numerical analysis of droplet deformation in a complex flow generated by a rotor-stator device

The deformation behaviour of single drops suspended in a second immiscible liquid undergoing a complex laminar flow is analysed both experimentally and numerically. The flow is generated in a channel formed by two rotating concentric cylinders with teethed walls as a model for extruding flow. The transient drop deformation and position in the device is captured by a twin-camera system in which one camera captures the drop deformation and the other camera captures the position of the drop. Results from an experiment consist of the transient drop deformation and the particle track of the drop. In our data analysis we define a geometry-based apparent shear rate which we compare to time-averaged drop deformations. Results indicate that for small deformations the relation between the time-averaged drop deformation and time-averaged apparent shear rate can be described by Taylor's small deformation theory.Furthermore we have used the particle track data obtained from a number of experiments to numerically calculate the local flow experienced by the drop. The numerically calculated local flow is then used as input to a computational algorithm for simulating the transient drop deformation. Comparison between numerical calculations of the drop deformation and experimental results generally agree well although calculations predict a somewhat higher deformation than experimentally observed.