某超临界循环流化床锅炉NOx排放与问题分析

针对超临界循环流化床锅炉在机组负荷50％以下时NOx达不到超低排放要求的情况,以某电厂350 MW循环流化床机组为例,分析了该机组在实现超低负荷下NOx超低排放要求中存在的NOx超标、氨耗量过多和播煤风结构不合理等问题.结合循环流化床锅炉自身特点,对锅炉部分结构提出了改造方案:新增一层二次风喷口同时进行二次风喷口改造、...     

循环流化床锅炉降低NO_x排放浓度试验与优化改造研究

NOx排放浓度低是循环流化床锅炉的主要优点之一,但国内一些循环流化床锅炉的NOx排放浓度不能满足《火电厂大气污染物排放标准》(GB 13223—2011)的要求,给电厂的环保、经济运行带来了不利影响。在研究分析了各种影响循环流化床锅炉NOx排放浓度的运行控制因素后,对循环流化床锅炉进行了降低NOx排放浓度的燃烧优化调整试验。结果显示:NOx排放浓度会随氧量、一次风率、床温的增加而增加,同时其还与上、下二次风比例、SO2排放浓度有关联。对于NOx排放浓度较高的循环流化床锅炉,可以采取二次风系统改造、增加烟气再循环措施,必要时增加SNCR脱硝系统。     

浅谈循环流化床锅炉的气体污染控制

通过对循环流化床锅炉SO2和NOx的生成机理及影响因素的简单分析，提出循环流化床锅炉炉内脱硫及控制NOx的排放措施。     

燃煤改烧石油焦CFB锅炉改造与运行特性研究

介绍某项目循环流化床锅炉完成的燃煤改烧石油焦改造设计和运行特性.运行结果表明,锅炉通过实施纯烧石油焦针对性改造后,纯烧石油焦情况下,锅炉运行状态非常稳定,运行参数满足设计要求,NOx原始排放达到超低排放要求.     

大型循环流化床锅炉NO_x排放的研究

近年来循环流化床锅炉技术得到了迅速发展.基于由国内某锅炉厂生产并投运的大型循环流化床锅炉的实际运行及试验数据,对锅炉的NOx排放特性进行了分析和研究.分析了锅炉的NOx排放量与锅炉负荷,空预器进口氧量,上、下二次风配风量及配风方式,燃料特性及脱硫剂之间的关系.研究表明:锅炉运行过程中应合理调整燃烧工况,以优化运行,减少污染物排放.研究为电厂循环流化床锅炉的优化和调整运行参数提供借鉴和参考,从而实现锅炉NOx排放的环保达标.     

620t·h-1循环流化床锅炉提效 及低NOx改造的实践

针对国产620 t·h-1循环流化床锅炉效率及NOx排放浓度不能达到性能保证值的现状,分析了锅炉的热损失情况以及NOx排放浓度与平均床温等参数间的规律,得出排烟热损失及固体未完全燃烧热损失过大、平均床温偏高、因风帽磨损引起的流化质量下降是造成锅炉效率及NOx排放浓度超性能保证值的主要原因.在此基础上提出了提高空预器吸热量、降低床温、提高流化质量的改造思路,对改造思路逐项分析,得出了回转式空预器改造、加长水冷屏和屏式过热器以及风帽改型等具体改造措施.对改造后参数作了分析,并提出改造完成后可能出现的热风管磨损及浓相区上移等问题.通过改造实现了锅炉提效和减排的目标.     

循环流化床锅炉运行节能技术的实践

总结了宁波光耀热电厂循环流化床锅炉生产运行中遇到的问题,对解决堵煤、点火及合理控制调整运行等一系列循环流化床锅炉运行中的常见问题进行了详细分析,经过探索和实践。提出优化运行和设备改造方案。通过实施有效的节能措施,提高了循环流化床的效率,达到了节能降耗的效果。     

循环流化床锅炉节能环保一体化改造技术研究与应用

针对某厂240 t/h循环流化床锅炉存在的问题进行了深入分析,制定了相应的节能环保一体化改造方案。改造实施后,锅炉各项运行指标大幅改善,锅炉效率提升1.22%,一次风机和引风机电耗下降10%,氮氧化物原始生成浓度稳定降至180 mg/Nm~3以下,较改造前下降40%以上,有效提升了锅炉低负荷脱硝能力。通过节能环保一体化改造,实现了循环流化床锅炉节能环保的协同治理。     

循环流化床锅炉节能环保改造研究

针对某厂240 t/h循环流化床(CFB)锅炉存在床温高、NOx原始排放浓度高的问题,提出了节能环保综合改造方案,具体内容包括:布风均匀性改造、旋风分离器提效改造、冷态试验及燃烧调整优化。通过改造解决了锅炉存在的问题,使得锅炉运行参数回归设计值,实现了锅炉的安全、稳定、经济运行。改造后锅炉烟气的NOx原始排放浓度低于200 mg/Nm~3(6%氧浓度,干基),依托原有SNCR脱硝系统,最终NOx排放浓度可控制在50 mg/Nm~3以内,满足超低排放限值要求。     

煤粉炉改造循环流化床锅炉及运行研究

循环流化床燃烧技术以其独特的燃烧理念越来越受到重视，将小煤粉炉改造成循环流化床锅炉并燃用劣质燃料，符合国家的产业政策及环保政策。本根据丁程实践，对煤粉炉改造循环流化床锅炉(CFB)的方案及改造后的运行情况进行研究。对改造后锅炉运行中存在的主汽温度偏低、飞灰含炭量偏高等问题进行了分析，并提出了相应对策，对今后继续用循环流化床燃烧技术改造煤粉炉有一定的指导意义。     

一种控制燃煤机组SCR烟气脱硝系统氨逃逸的优化调整方法

以某烟气脱硝工程3号机组为例,针对选择性催化还原(SCR)脱硝反应器出口NO_x质量浓度偏差大、氨逃逸率高的问题,提出了一种喷氨均匀性调整优化方案。采用该方案对喷氨格栅每路供氨支管上的手动调节阀进行调整,最终在反应器出口建立均匀、稳定的NO_x分布。优化调整前后系统A、B两侧的NO_x不均匀度分别从55.1%和19.2%,降至27.6%和14.7%;SCR脱硝系统的平均氨逃逸率从3.289 6 m L·m~(-3)降至1.265 7 mL·m~(-3),表明采用该优化调整方法可使反应器出口NO_x分布均匀,降低氨逃逸率,有利于系统的安全、稳定运行。     

NOx formation and reduction mechanisms in staged O2/CO2 combustion

The purpose of this study was to investigate the NO_x formation and reduction mechanisms in staged O₂/CO₂ combustion and in air combustion. A flat CH₄ flame doped with NH₃ for fuel-N was formed over the honeycomb, and NO_x formation characteristics were investigated. In addition, chemiluminescence of OH^* distribution was measured, and CHEMKIN-PRO was used to investigate the detailed NO_x reduction mechanism. In general, the NO_x conversion ratio decreases with decreasing primary O₂/CH₄ ratio, whereas NH₃ and HCN, which are easily converted to NO_x in the presence of O₂, increases rapidly. Therefore, a suitable primary O₂/CH₄ ratio exists in the staged combustion. Our experiments showed the primary O₂/CH₄ ratio, which gave the minimum fixed nitrogen compounds in O₂/CO₂ combustion, was lower than in air combustion. The NO_x conversion ratio in O₂/CO₂ combustion was lower than in air combustion by 40% in suitable staged combustion. This could be explained by high CO₂ concentrations in the O₂/CO₂ combustion. It was shown that abundant OH radicals were formed in O₂/CO₂ combustion through the CO₂ + H → CO + OH, experimentally and numerically. OH radicals produced H and O radicals through H₂ + OH → H + H₂O and O₂ + H → OH + O, because a mass of hydrogen source exists in the CH₄ flame. O and OH radicals formed in the fuel-rich region enhanced the oxidation of NH₃ and HCN. NO_x formed by the oxidation of NH₃ and HCN was converted to N₂ because the oxidation occurred in the fuel-rich region where the NO_x reduction effect was high. In fact, the oxidation of NH₃ and HCN in the fuel-rich region was preferable to remaining NH₃ and HCN before secondary O₂ injection in the staged combustion. A significant reduction in NO_x emission could be achieved by staged combustion in O₂/CO₂ combustion.     

Removal of NOx by microwave reactor with ammonium bicarbonate and Ga-A zeolites at low temperature

Microwave reactor with the mixture of ammonium bicarbonate (NH₄HCO₃) and Ga-A zeolites was set up to study the removal of nitrogen oxides (NO_x) from waste gas with excess oxygen concentration (14–19%) at low temperature (80–120 °C). The results showed that the microwave reactor filled with NH₄HCO₃ and Ga-A zeolites could reduce NO_x to nitrogen with the best purifying efficiency of 95.45% and the best denitrification amount of 89.28 mg h⁻¹. The optimal microwave power and residence time (RT) on denitrification was 259–280 W and 0.259 s, respectively. Microwave denitrification effect of the experiment using ammonium bicarbonate and Ga-A zeolites was much higher than that using ammonium bicarbonate or Ga-A zeolites only. The mechanism for microwave-induced NO_x reduction can be explained as the microwave-induced catalytic reaction between NO_x and ammonium bicarbonate with Ga-A zeolites being the catalyst and microwave absorbent.     

燃气锅炉低氮排放的经济性分析

简要阐述了燃气锅炉低氮排放技术,并对烟气再循环（FGR）技术进行了详细介绍。从经济性方面分析,选择合适的烟气再循环率可减小FGR对锅炉效率的影响,并可实现减排的目标;提出燃烧器和锅炉的研究方向是如何提高锅炉传热效率,并将FGR对锅炉热效率的影响降到最低,以便更好地实现节能减排的目标。     

Study on the NOx release rule along the boiler during pulverized coal combustion

Numerical simulation and experimental study on NO _x release along the boiler during pulverized coal combustion have been conducted. With the increase of temperature the NO _x emission increased and the peak value of NO _x release moved forward. But when the temperature increased to a certain degree, NO _x emission began to reduce. NO _x emission increased with the increase of nitrogen content of coal. The peak value of NO _x release moved backwards with the increase of coal rank. NO _x emission increased obviously with the increase of stoichiometric ratio. There existed a critical average diameter of the pulverized coal (d _c ). If d ⩽ d _c , NO _x emission reduced with the decrease of pulverized coal size. If d > d _c , NO _x emission reduced with the increase of the pulverized coal size. The results showed that the simulation results are in agreement with the experimental results for concentration distribution of NO _x along the axis of the furnace. Translated from Proceeding of the CSEE, 2006, 26(1): 35–39 [译自: 中国电机工程学报]     

NOx emission and thermal efficiency of a 300 MWe utility boiler retrofitted by air staging

Full-scale experiments were performed on a 300 MWe utility boiler retrofitted with air staging. In order to improve boiler thermal efficiency and to reduce NO_x emission, the influencing factors including the overall excessive air ratio, the secondary air distribution pattern, the damper openings of CCOFA and SOFA, and pulverized coal fineness were investigated. Through comprehensive combustion adjustment, NO_x emission decreased 182 ppm (NO_x reduction efficiency was 44%), and boiler heat efficiency merely decreased 0.21%. After combustion improvement, high efficiency and low NO_x emission was achieved in the utility coal-fired boiler retrofitted with air staging, and the unburned carbon in ash can maintain at a desired level where the utilization of fly-ash as byproducts was not influenced.     

New trends to grow the n-CdZn (S1−xSex)2/p-CuIn(S1−xSex)2 heterojunction thin films for solar cell applications

The n-CdZn(S_1−xSe_x) and p-CuIn(S_1−xSe_x)₂ thin films have been grown by the solution growth technique (SGT) on glass substrates. Also the heterojunction (p–n) based on n-CdZn (S_1−xSe_x)₂ and p-CuIn (S_1−xSe_x)₂ thin films fabricated by same technique. The n-CdZn(S_1−xSe_x)₂ thin film has been used as a window material which reduced the lattice mismatch problem at the junction with CuIn (S_1−xSe_x)₂ thin film as an absorber layer for stable solar cell preparation. Elemental analysis of the n-CdZn (S_1−xSe_x)₂ and p-CuIn(S_1−xSe_x)₂ thin films was confirmed by energy-dispersive analysis of X-ray (EDAX). The structural and optical properties were changed with respect to composition ‘x’ values. The best results of these parameters were obtained at x=0.5 composition. The uniform morphology of each film as well as the continuous smooth thickness deposition onto the glass substrates was confirmed by SEM study. The optical band gaps were determined from transmittance spectra in the range of 350–1000 nm. These values are 1.22 and 2.39 eV for CuIn(S_0.5Se_0.5)₂ and CdZn(S_0.5Se_0.5)₂ thin films, respectively. J–V characteristic was measured for the n-CdZn(S_1−xSe_x)₂/p-CuIn(S_1−xSe_x)₂ heterojunction thin films under light illumination. The device parameters V_oc=474.4 mV, J_sc=13.21 mA/cm², FF=47.8% and η=3.5% under an illumination of 85 mW/cm² on a cell active area of 1 cm² have been calculated for solar cell fabrication. The J–V characteristic of the device under dark condition was also studied and the ideality factor was calculated which is equal to 1.9 for n-CdZn(S_0.5Se_0.5)₂/p-CuIn(S_0.5Se_0.5)₂ heterojunction thin films.     

The effects of injection timing on NOx emissions of a low heat rejection indirect diesel injection engine

Higher NO_x is one of the major problems to be overcomed in a low heat rejection (LHR) diesel engine as insulation leads to an increase in combustion temperature about 200–250 °C compared to an identical standard (STD) diesel engine. High combustion temperatures alter optimum injection timing of a LHR engine. With the proper adjustment of the injection timing, it is possible to partially offset the adverse effect of insulation on heat release rate and hence to obtain improved performance and lower NO_x. However, the injection timing and brake specific fuel consumption (BSFC) trade-off must be considered together in performance and NO_x emission point of view. In this study, optimum injection timing was found with 4 crank angle (34° CA) retarded before top dead centre (BTDC) in LHR diesel engine in comparison to that of STD diesel engine (38° CA BTDC). When the LHR engine was operated with the injection timing of the 38 crank angle, which is the optimum value of the STD engine, it was shown that NO_x emission increased about 15%. However, when the injection timing was retarded to 34° CA in the LHR case, it was observed a decrease on the NO_x emissions with about 40% and the brake specific fuel consumption (BSFC) with about 6% compared to that of the STD case. Thus, by retarding the injection timing, an additional 1.5% saving in fuel consumption was obtained.     

Combustion and NOx emissions characteristics of a down-fired 660-MWe utility boiler retro-fitted with air-surrounding-fuel concept

Air-surrounding-fuel is a well-known concept used within tangential and wall-fired boilers. Here, we report for the first time on industrial experiments performed to study the effects of this concept on a 660 MW_e full-scale down-fired boiler. Data are reported for the gas temperature distributions along the primary air and coal-mixed flows, furnace temperatures, gas compositions, for example O₂, CO and NO_x, and gas temperatures in the near-wall region. The influence of concentration control valve (CCV) opening on combustion and NO_x emission in the furnace were determined. The results show that the flame stability, temperature distribution, unburnt carbon are influenced by both concentration ratios and fuel-rich flow velocities. As CCV opening increases, NO_x emissions decrease from 2594 mg/m³ to 1895 mg/m³. Considering altogether economic benefits and environmental protection issues, 30% is the optimal value for the CCV opening.     

Acoustic excitation effect on NOx reduction and flame stability in a lifted non-premixed turbulent hydrogen jet with coaxial air

The effects of acoustic excitation on the reduction in nitric oxidant (NO_x) emission were experimentally investigated in non-premixed lifted hydrogen jet flames with coaxial air. The purpose of the present work was to analyze the acoustic forcing effect on the flow field, the reaction zone, and NO_x emission, and to study the mechanisms of NO_x reduction and flame stabilization. To analyze of the flow field, a PIV method was used that incorporated two Nd-YAG lasers and a CCD camera. The reaction zone was visualized by taking OH* chemiluminescence images with a 307.1 ± 5 nm narrow band pass filter and an ICCD camera. A flow condition was carefully selected at u_F = 150, 200, 250 m/s and u_A = 12, 16, 20 m/s, which was sustainable for acoustic excitation in a lifted flame region. The frequency was swept from 150 to 1000 Hz in 5 Hz steps. From the measurements of the flow field, the reaction zone, and NO_x emission, we concluded that NO_x emission was reduced and minimized at the resonance frequency. The vortex that was generated by acoustic forcing promoted air entrainment and enhanced the fuel-air mixing rate. This premixing effect resulted in a lower flame temperature, and thus lower NO_x emissions. In addition, the liftoff height periodically fluctuated due to the stretch effect as the vortex interacted with the flame base.