Numerical simulation on optimization of structure and operating parameters of a novel lean coal decoupling burner

Due to its low volatile characteristics of lean coal, it is difficult to catch fire and burn out. Therefore, high temperature is needed to maintain combustion efficiency, while, this leads to high nitrogen oxide emission. For power plant boilers burning lean coal, stable combustion with lower nitrogen oxide emission is a challenging task. This study applied the 3D numerical simulation on the analysis of a novel de-coupling burner for low-volatile coal and its structure and operation parameters optimization. Results indicate that although it was more difficult for lean coal decoupling burner to ignite lean coal than high volatile coal, the burner formed a stepwise ignition trend, which promoted the rapid ignition of lean coal. Comparison of three central partition plate structure shows that in terms of characteristics of the flow field distribution, rich and lean separation and combustion, the structure with an inclination of 0° showed good performance, with its rich-lean air ratio being 0.85 and concentration ratio being 22.94, and there was an apparent decoupling combustion characteristic. Finally, the structure of the selected burner was optimized for its operational conditions. The optimal operating parameters was determined as the primary air velocity of 24.9 m·s^-1 and the mass flow rate of pulverized coal of 2.5 kg·s^-1, in which the pyrolysis products were utilized as reductive agent more fully. Eventually, the nitrogen oxide was efficiently reduced to nitrogen, which emission concentration was 61.88% lower than that in the design condition.     

Microwave plasma combustion of coal

Microwave plasma is studied as an alternative to oil or gas fuel for ignition and stabilisation of burning of lean coal. The study is performed on an experimental set-up, which includes a burner with a microwave plasma generator, coal and air supply systems, and measurement equipment. Power and thermochemical characteristics of the coal-plasma interaction have been measured and analysed. The obtained results indicate an essential intensification of ignition and combustion processes in the microwave burner compared to those in conventional burners. In particular, it has been demonstrated that the microwave energy consumption is only about 10% of the required expenditure of oil or gas, measured in heat equivalent. A design of an industrial microwave-plasma burner is proposed. Prospects of such burner for applications at industrial boilers of power plants are discussed.     

超细煤粉NOx和SO2排放特性与燃烧特性

将合山煤分别制成常规粒度的煤粉与超细化煤粉 .在单只水平直流燃烧器燃烧室内进行了常规煤粉与超细化煤粉的燃烧特性、空气分级燃烧NOx 排放特性、炉内喷钙对超细化煤粉与常规煤粉燃烧SO2 排放特性的影响的燃烧试验研究 .试验研究表明 ,超细化煤粉与常规煤粉比较 ,着火提前 ,着火稳定性好 ,燃尽效果好 ;分级燃烧对超细煤粉的NOx 排放量的降低效果更显著 ;在Ca/S摩尔比相同的条件下 ,超细化煤粉的固硫特性明显优于常规煤粉 .     

煤粉富氧燃烧着火温度预测的优化随机森林(GA-RF)模型

二氧化碳排放是造成温室效应的主要原因之一,富氧燃烧作为一种有效的碳减排与封存技术具有广泛的研究前景。在燃煤电厂中煤粉富氧燃烧的着火温度是燃烧器设计和运行安全的重要指标,并且与煤粉组成成分、煤粉粒径以及燃烧氛围都有复杂的相关性。因此,对煤粉富氧燃烧着火温度的预测模型研究意义重大。采用滴管炉分别测量了5种煤粉在O2体积分数为30%、35%、40%、50%、60%、70%、80%、90%、100%富氧条件下的着火温度,分析了氧气体积分数和煤粉的组成成分与着火温度之间的关系。研究发现,随着氧气体积分数分数的增加,5种煤样的着火温度均显著下降,且挥发分越高的煤,下降幅度越大。将45组试验着火温度数据与其他研究者采用同样方法测得的69组着火温度数据组成机器学习样品库,以煤粉的元素分析、工业分析、煤粉粒径及氧气体积分数为输入条件,以着火温度T为目标输出,构建了遗传算法优化的随机森林模型(GA-RF模型),准确预报了煤粉富氧燃烧的着火温度,其预报精度为:R2>0.99,RMSE<16,MAE<8。通过模型参数重要性分析发现,氢组分超过5%后,着火温度出现阶跃式上升,现有煤粉着火数据也证实了该现象。     

Induction-heating ignition of pulverized coal stream

Induction-heating ignition burner for the pulverized coal fired boiler is introduced. Some experiments were conducted on an experimental set-up, which includes alternative current power system, induction-heating system, pulverized coal and air supplier system, and measurement system to study the ignition process of coal powder and air mixture stream. Some results are presented. An industrial induction-heating burner for a 220 t/h boiler, which was designed on the basis of a series of researches, is described. This kind of oil-free ignition burner is characterized by its stable operation performances, and the lower cost in its maintenance.     

NO emission on pulverized coal combustion in high temperature air from circulating fluidized bed – An experimental study

High temperature air was adopted by combustion in high excess air ratio in a circulating fluidized bed. Experiments on pulverized coal combustion in high temperature air from the circulating fluidized bed were carried out in a down-fired combustor with the diameter of 220 mm and the height of 3000 mm. The NO emission decreases with increasing the residence time of pulverized coal in the reducing zone, and the NO emission increases with excess air ratio, furnace temperature, coal mean size and oxygen concentration in high temperature air. The results also revealed that the co-existing of air-staging combustion with high temperature air is very effective to reduce nitrogen oxide emission for pulverized coal combustion in the down-fired combustor.     

Comparison of flame propagation properties of petroleum coke and coals of different rank

Ignition and flame propagation characteristics of 18 kinds of coal and a petroleum coke were investigated through a laser ignition experiment. Flame stability was strongly influenced by amount of volatile matter and pyrolysis rate. Lean limit of flame propagation was strongly influenced by amount of volatile matter. Flame propagation was observed when pyrolized volatile matter was mixed with surrounding air or oxygen, until the concentration of pyrolized volatile matter reached a constant value. Flame propagation velocity was strongly influenced by pyrolysis rate. As the pyrolysis rate increased, the flame propagation velocity increased. The flame propagation velocity of petroleum coke was higher than that of coal with the same volatile content. The flame propagation of petroleum coke was superior to what was expected based on the volatile content, primarily because the high pyrolysis rate caused a shorter ignition delay than what would be expected given the volatile content. A database for the lean limit of flame propagation was used to develop a flame stability model to estimate lean flammability of a large-scale burner. The model could predict the effect of the coal rank, the particle diameter distribution for lean flammability limit. The estimated lean flammability limit of petroleum coke (volatile content 11.5%) was equal to that of lv bituminous coal with volatile content of about 15%.     

Numerical simulation of oxy-coal combustion for a swirl burner with EDC model简

The characteristics of oxy-coal combustion for a swirl burner with a specially designed preheating chamber are studied numerically. In order to increase the accuracy in the prediction of flame temperature and igni- tion position, eddy dissipation concept （EDC） model with a skeletal chemical reaction mechanism was adopted to describe the combustion of volatile matter. Simulation was conducted under six oxidant stream conditions with dif- ferent OjN2/CO2 molar ratios： 21/79/0, 30/70/0, 50/50/0, 21/0/79, 30/0/70 and 50/0/50. Results showed that 02 en- richment in the primary oxidant stream is in favor of combustion stabilization, acceleration of ignition and increase of maximum flame temperature, while the full substitution of N2 by CO2 in the oxidant stream delays ignition and decreases the maximum flame temperature. However, the overall flow field and flame shapes in these cases are very similar at the same flow rate of the primary oxidant stream. Combustion characteristics of the air-coal is similar to that of the oxy-coal with 30% 02 and 70% CO2 in the oxidant stream, indicating that the rear condition is suitable for retrofitting an air-coal fired boiler to an oxy-coal one. The swirl burner with a specially designed preheating chamber can increase flame temperature, accelerate ignition and enhance burning intensity of pulverized coal under oxy-coal combustion. Also, qualitative experimental validation indicated the burner can reduce the overall NOx emission under certain 02 enrichment and oxy-coal combustion conditions against the air-coal combustion.     

预燃室对逆喷旋流煤粉燃烧器流场特性作用研究

煤粉高效低氮燃烧技术是煤炭高效利用领域持续关注的热点。煤粉燃烧器作为煤粉锅炉的核心设备,研究适合多煤种、宽负荷条件的煤粉燃烧器设计原理及技术至关重要。逆喷射流稳燃机理大都应用在航空发动机和燃气轮机领域,在煤粉燃烧领域应用极少。前人大量研究了预燃室对旋流燃烧器流场特性的影响,但鲜见预燃室对逆喷旋流燃烧器流场影响的相关研究。为了探究预燃室对逆喷旋流煤粉燃烧器流场特性的影响规律,笔者针对一款20 t/h逆喷旋流燃烧器,基于等温模化原理建立冷态燃烧器模型,利用热线风速仪和飘带法进行了流场测试和分析,结果表明:预燃室的存在不改变逆喷旋流煤粉燃烧器回流区环形的形状,但在逆喷旋流煤粉燃烧器内形成一个有利于煤粉着火的轴向速度低和湍流强度大的回流区。在X/D<1.3区域内,由于圆锥形预燃室对气流的挤压作用,预燃室的存在对回流区的面积起到抑制作用;在1.32.3区域内,预燃室对燃烧器内部流场的作用减弱,可忽略不计。在预燃室的作用下,回流区最宽处的直径从0.97D降至0.86D,最大相对回流率位置从截面X/D=1后移到截面X/D=1.6处,相对回流率从1.17减小至0.99。预燃室的存在对二次风区域内的轴向平均速度和湍流度分布规律影响较大。无预燃室工况下,在X/D<0.6区域内,速度和湍流度均出现峰值,在X/D>1.6区域内峰值消失,内外二次风完全混合;有预燃室工况下,在X/D<0.6区域速度沿着径向方向逐渐增大,湍流度沿着径向方向逐渐减小,在X/D>1.6区域,速度和湍流度沿着径向方向分布均匀。预燃室的存在有利于回流区煤粉的稳定燃烧,工程应用中起到煤粉迅速着火以及难燃煤稳定燃烧的作用。另外预燃室壁面气流速度较大,刚性强,避免预燃室壁面超温或结焦现象的发生,延长了煤粉燃烧器无故障运行时间和整体的使用寿命。     

煤粉工业锅炉技术发展及应用

中国煤粉工业锅炉借鉴油气锅炉和德国煤粉工业锅炉技术理念,经历立项研发、中试验证和工业示范,系统技术逐步成熟,自2010年起,实现规模化工业应用。煤粉工业锅炉系统具有高热效率、低烟气污染物排放等优点,有效带动了燃煤工业锅炉产业发展。笔者论述了煤粉工业锅炉技术与发展,重点介绍了煤粉工业锅炉的关键技术,并对主要技术进行对比,分析了煤粉工业锅炉的工业应用情况,最后提出了煤粉工业锅炉技术发展方向。煤粉工业锅炉系统由燃料煤粉生产、储供、油气点火、燃烧、锅炉本体、烟气净化以及自动化控制等系统构成。锅炉热效率大于91%,烟气污染物达到国家超低排放标准,系统技术符合国家煤炭清洁利用方向。燃料煤粉生产采用一步法工艺,通过强化流动性和安全措施,现可实现最大为1 000 m^3安全存储量。锅炉供粉采用气动活化、无脉动给料及高速引射流浓相输送技术,已实现输送阻力低于20 kPa,粉风固气比大于2.5 kg/m^3,供料精度在±3.0%以内,最大供料量为5 t/h的浓相供料技术与装备,广泛应用于锅炉供料系统。供料量在2.5 t/h,供料精度在±2.0%和±1.0%以内的第三代和第四代供料器也分别开展了工业验证和样机的试制工作,并取得了阶段性的成果。煤粉燃烧器采用逆喷式回流式结构,设计工作依据其结构特征,通过模拟气流扩展角、回流区域范围、回流量、旋流强度以及温度和速度场等研究开展,再经过实际工程应用,进一步验证优化设计参数,最终实现燃烧器的逐级放大。天然气/煤粉双燃料燃烧器具有便捷切换和快速着火功能。风冷燃烧器采用内外双级旋流供风燃烧技术,具有点火迅速、燃烧稳定、燃烧效率高和初始NOx排放低等优点。随着煤粉锅炉系统测控技术向智能化、网络化和集成化方向发展。锅炉烟气脱硫除尘采用NGD高倍率灰钙循环脱硫技术,具有占地小,运行成本低等特点,在低钙硫摩尔比下,系统脱硫和除尘效率分别达到90%和99.95%以上。低温炭基预氧化脱硝耦合NGD协同烟气净化技术具有工艺简单,耗水少,废物资源再利用,无二次污染产生等优点,更加适合于煤粉工业锅炉的烟气净化。煤粉工业锅炉在发展历程中通过关键技术和装备优化升级,在大型化、模块化和系列化方向已取得成效,在节能性、环保性和经济性等方面较常规工业锅炉具有显著优势,技术已达到世界先进水平。未来随着国家能源结构优化,天然气/煤粉锅炉、低氮燃烧、生物质复合半焦粉及协同化烟气净化等技术的开发与成熟,煤粉工业锅炉技术将成为煤炭清洁燃烧利用主要技术之一。     

典型煤炭燃料在民用解耦炉中的燃烧实验研究

实验对比研究了烟煤块状半焦及烟煤型煤等煤炭燃料在民用解耦炉中燃烧时的污染物排放特性和炊事能力,并基于解耦测试炉对烟煤型煤的特征尺寸进行优化,验证了解耦炉具对不同种类民用煤炭燃料的适应性。结果表明,民用解耦燃煤炉具特有的结构特征和通风方式有利于NOx和CO的同时减排。若在解耦炉中燃烧烟煤洁净型煤,可进一步实现对SO2和颗粒物(PM)的有效控制。型煤尺寸对炉具污染物排放影响显著,尺寸优化后的烟煤洁净型煤在解耦炉中稳定燃烧时NO, SO2, CO和PM的平均排放浓度按基准氧含量9vol%折算后,分别低于190, 300, 380和30 mg/m3,炊事功率可达1.65 kW。     

In situ diagnostics of Victorian brown coal combustion in O2/N2 and O2/CO2 mixtures in drop-tube furnace

Experimental investigation of the combustion of an air-dried Victorian brown coal in O₂/N₂ and O₂/CO₂ mixtures was conducted in a lab-scale drop-tube furnace (DTF). In situ diagnostics of coal burning transient phenomena were carried out with the use of high-speed camera and two-colour pyrometer for photographic observation and particle temperature measurement, respectively. The results indicate that the use of CO₂ in place of N₂ affected brown coal combustion behaviour through both its physical influence and chemical interaction with char. Distinct changes in coal pyrolysis behaviour, ignition extent, and the temperatures of volatile flame and burning char particles were observed. The large specific heat capacity of CO₂ relative to N₂ is the principal factor affecting brown coal combustion, which greatly quenched the ignition of individual coal particles. As a result, a high O₂ fraction of at least 30% in CO₂ is required to match air. Moreover, due to the accumulation of unburnt volatiles in the coal particle vicinity, coal ignition in O₂/CO₂ occurred as a form of volatile cloud rather than individual particles that occurred in air. The temperatures of volatile flame and char particles were reduced by CO₂ quenching throughout coal oxidation. Nevertheless, this negative factor was greatly offset by char-CO₂ gasification reaction which even occurred rapidly during coal pyrolysis. Up to 25% of the nascent char may undergo gasification to yield extra CO to improve the reactivity of local fuel/O₂ mixture. The subsequent homogeneous oxidation of CO released extra heat for the oxidation of both volatiles and char. As a result, the optical intensity of volatile flame in ∼27% O₂ in CO₂ was raised to a level twice that in air at the furnace temperature of 1273 K. Similar temperatures were achieved for burning char particles in 27% O₂/73% CO₂ and air. As this O₂/CO₂ ratio is lower than that for bituminous coal, 30-35%, a low consumption of O₂ is desirable for the oxy-firing of Victorian brown coal. Nevertheless, the distinct emission of volatile cloud and formation of strong reducing gas environment on char surface may affect radiative heat transfer and ash formation, which should be cautioned during the oxy-fuel combustion of Victorian brown coal.     

燃气燃烧器在灰融聚流化床粉煤气化炉上的创新设计及应用

针对燃气燃烧器在灰融聚流化床粉煤气化炉上首次应用时需进行配套技术设计的问题,介绍了灰融聚流化床粉煤气化的技术特点、工艺流程以及配套技术创新设计方案;论述了燃气燃烧器配套灰融聚流化床粉煤气化炉的工艺流程特点、点火程序要求以及气化炉的结构布置和安装要领;总结了采用创新设计后燃烧器的应用效果.     

民用解耦燃煤炉中的NO x 和CO同时减排

典型民用解耦燃煤炉具有底部连通的两个分别被称为热解室和燃烧室的并列炉膛，煤炭从热解室上部加入，空气通过热解室底部的倾斜炉排引入。结合煤炭燃烧过程中的氮转移路线与解耦炉中的气体循环流动特征，定性分析了民用解耦燃煤炉中的NO _x 和CO同时减排机理，并在此基础上对配风和煤种等因素对NO和CO排放的影响进行了定量实验研究。结果表明，民用解耦燃煤炉特有的结构特征和通风方式有利于NO _x 和CO的同时减排，解耦炉具与洁净型煤匹配可显著降低综合污染物排放。     

石油焦与煤粉燃烧性能差异的研究

石油焦作为石油工业副产品,具有低灰分质量分数、高挥发分质量分数、高发热值等特点,但对其燃烧价值的利用还很不充分。文中利用X射线衍射及扫描电镜对石油焦及烟煤和无烟煤进行微观结构的研究,同时利用热重分析方法对其燃烧性能进行系统研究发现:石油焦的芳香片层堆砌结构与无烟煤接近,但其丰富的气孔结构又有利于改善其燃烧过程。无烟煤中加入石油焦后,着火点温度从527℃降低到482.6℃;总质量分数从71.95%提高到76.82%,其燃烧效率得到提高。     

Shell煤气化装置点火烧嘴与开工烧嘴的试验及应用

点火烧嘴和开工烧嘴的正常投用是Shell煤气化装置顺利试车的重要环节。针对其他先期试车的装置曾出现的点火烧嘴无火焰检测信号、开工烧嘴易烧坏等问题,进行了点火烧嘴和开工烧嘴的模拟试验。通过调整进入点火烧嘴的煤气流量和空气流量,确定点火烧嘴头部火焰的强度,取得最佳测试数据;用清水代替柴油,用中压洁净氮气代替氧气,进行开工烧嘴的炉外试验,获得最优化操作参数。结果表明,点火烧嘴点火成功率为100％,火焰检测强度信号反馈时间为2s;开工烧嘴点火成功率为100％,烧嘴烧坏次数为0,火焰强度保持在90％以上。点火烧嘴和开工烧嘴的正常投用为Shell煤气化装置一次点火投煤成功奠定了基础。     

风速对骨料烘干煤粉燃烧器排放特性的影响

基于煤粉燃烧机理,结合骨料烘干工艺,建立了骨料烘干煤粉燃烧器内部场的控制模型,采用Fluent软件模拟煤粉燃烧器内部燃烧状况,考察了一、二、三次风的风速对煤粉燃烧器中心轴线处CO, CO2, NO和SO2浓度的影响。结果表明,在研究的风速范围内,一、二、三次风风速越大燃烧越充分,一、二、三次风风速越小,产生的NO越少;三次风风速为40 m/s时,SO2浓度最低;较合理的控制参数为一次风风速30~35 m/s,二次风风速45~50 m/s,三次风风速30~40 m/s。     

Computational modeling of a utility boiler tangentially-fired furnace retrofitted with swirl burners

The paper presents 3D numerical investigation of OP-380 boiler tangentially-fired furnace utilizing bituminous coal. The boiler was retrofitted by replacing traditional jet burners with RI-JET2 (Rapid Ignition — JET) swirl burners. This kind of solution is unique in power generation systems. The purpose of this work is to show how the flow, combustion performance and heat exchange in the furnace are affected by introducing rapid ignition phenomena in RI-JET2 burners instead of delayed ignition associated with the traditional jet burners. Results were compared to simulations of similarly designed boiler equipped with traditional jet burners. Furnace simulation was preceded with a single RI-JET2 burner simulation at the inlet to a virtual combustion chamber. The results have shown that pulverized coal (PC) concentrator separates the PC into two streams: concentric with fine particles and axial with coarse particles. Stable flame operation was noticed even without secondary and tertiary air swirl. 3D simulations of combustion chamber have shown that in a burner zone a visibly isolated, concentrated flame exists in the furnace axis. This kind of flame shape reduces corrosion risk and furnace walls slagging as a result of RI-JET2 burner's long range.     

A numerical study of accelerated moderate or intense low-oxygen dilution (MILD) combustion stability for methane in a lab-scale furnace by off-stoichiometric combustion technology

Moderate or intense low-oxygen dilution (MILD) combustion has become a promising low-NOX emission technology, while the delayed mixing of reactants and slower oxidation rate could potentially cause igni-tion instability in some scenarios. This paper proposes a new idea for enhancing the ignition stability for methane MILD combustion by combining with off-stoichiometric combustion (OSC), and its perfor-mances have been numerically assessed through a comparison against the original MILD combustion bur-ner. The results reveal although non-premixed pattern has the lowest NO emission, it suffers from a larger liftoff distance, thus less ignition stability. Contrarily, both partially-premixed and fully premixed patterns exhibit excellent ignition stability. Among the considered OSC conditions, the pattern of Inner ultra-rich and Outer lean produces the lowest NO emission while maintains a high ignition stability. Furthermore, the enhancement of the combustion stability by implementing OSC to the original MILD combustion burner is shown by comparing the operational range of furnace wall temperature (Tf), CO and NO emissions, as well as the evolution of chemical flame. The comparison reveals that OSC can extend the lowest operational Tf from 900 K to 800 K. More importantly, OSC can significantly improve the ignition stability in the whole range of Tf as compared to the original MILD combustion burner.     

煤粉着火燃烧过程光学诊断研究发展

煤炭储量丰富,尽管新能源和可再生能源快速发展,煤炭资源在未来几十年仍将作为我国一次能源重要组成部分。同时煤炭利用带来很多环境污染问题,因此未来煤炭资源的利用逐渐向高效、低碳、低污染物排放利用方式转变。随着光学技术的不断发展,涌现出多种适用于煤粉燃烧诊断的原位非接触式光学诊断技术,极大地促进了燃烧学的发展,为煤炭清洁高效利用提供了更多试验手段。介绍了国内外煤粉着火、不同方式下燃烧特性的光学诊断研究进展,对煤粉单颗粒和煤粉颗粒流的着火燃烧过程的光学诊断研究进行总结。目前常用的煤粉燃烧光学诊断技术主要包括全光谱成像、CH*/C2*化学发光成像、平面激光诱导荧光(PLIF)、双色/三色高温计、米氏散射、激光诱导白炽光、相干反斯托克斯-拉曼光谱、激光诱导击穿光谱等多种先进的光学诊断技术,可对煤粉单颗粒、颗粒流的着火延迟、脱挥发分、挥发分燃烧、着火模式、环境因素(环境温度、氧浓度、气氛)、富氧燃烧、水-氧燃烧、煤中碱金属释放等多方面关键问题进行光学诊断研究,为煤炭清洁高效利用提供了理论和试验基础。采用OH-PLIF和三色高温计对热解半焦和神华烟煤混合燃料共燃的着火和燃烧特性进行研究。综合考虑着火延迟和混合物的燃尽率,热解半焦的最佳掺混比为20%,为热解半焦的实际工业应用提供了参考。同时采用500 Hz、5 k Hz高时间、空间分辨率的OH-PLIF技术探究煤粉颗粒流中单颗粒挥发分燃烧的发展过程和挥发分着火的时序演变过程,通过二者的结合获得煤粉颗粒流从着火到挥发分燃烧的时间特性。采用OH-PLIF技术对烟煤和褐煤煤粉颗粒流燃烧火焰的脱挥发分和挥发分燃烧行为进行探究,提出采用OH信号径向分布的相对标准偏差探究火焰稳定性的方法。相同燃烧条件下,烟煤煤粉颗粒流燃烧的稳定性高于褐煤。基于OH-PLIF和CH*化学发光诊断技术,提出一种用于探究煤粉颗粒流中颗粒挥发分燃烧振荡特性分析方法——动态模态分解方法(DMD)。随着氧浓度的增加,挥发分火焰振荡增强。颗粒的聚集可能导致煤粉挥发分燃烧的低频振荡。相反,单独或分离的颗粒燃烧会产生较大的振荡频率。但目前取得的成果还不够完善,需要继续深入开展煤粉燃烧的光学诊断试验研究,对污染物NOx的生成及排放、新型水氧燃烧技术中水蒸气作用机理等方面深入探索,开发出新型清洁煤燃烧技术,为我国煤炭资源清洁高效利用做出贡献。