Experimental investigation on ignition and burnout characteristics of semi-coke and bituminous coal blends

Ignition and burnout characteristics of semi-coke and bituminous coal blends were investigated by thermogravimetric analyzer and drop tube furnace. The results showed that the ignitability index and the comprehensive combustion characteristic index of the blends decrease as the blending proportion of semi-coke increases, but the average activation energy of the blends increases gradually. Ignition mode of bituminous coal is changed from homogeneous to hetero-homogeneous ignition with the increasing of semi-coke content in the blends. When the mixing proportion of semi-coke is lower than 45%, the burnout rate is lower than the weighted value in the early stage of combustion and gradually higher than the weighted value with the development of combustion process. However, the burnout is always lower than the weighted value to mix with 67% semi-coke. Increasing furnace temperature from 850 °C to 1050 °C can improve the mid-term reaction process, alleviate the negative effects of semi-coke on the co-combustion process and increase the burnout rate. So less than 45% semi-coke blending ratio and increasing furnace temperature are recommended for semi-coke and bituminous coal co-combustion.     

不同煤种混煤燃烧时NO_x生成和燃尽特性的试验

在一维沉降炉上对无烟煤、贫煤、烟煤及其混煤的燃烧特性进行了研究,分析了不同因素对NOx排放量的影响,并讨论了不同过量空气系数、掺混比及一、二次风比例对燃尽率的影响,试验结果表明：当烟煤的掺混比例为25％,NOx的排放量较低,混煤燃烧时沿程分析结果表明,煤种特性的不同导致NOx排放时有不同的峰值。     

Characteristics of co-combustion of anthracite with bituminous coal in a 200-MWe circulating fluidized bed boiler

The effect of co-combustion of Vietnamese anthracite with Australian bituminous coal on the performance of a commercial circulating fluidized bed boiler was observed in the Tonghae thermal power plant.The temperature in the cyclone exit of the boiler increased slightly, which caused a decrease in the desulfurization efficiency as the co-combustion ratio of the bituminous coal increased from 40 to 100%. The unburned carbon fraction also increased. Consequently, the fine particles of the bituminous coal had lower combustion reactivity than those of the anthracite.NO_x emissions decreased as the bituminous coal ratio increased, although the fraction of nitrogen in the bituminous coal was higher than that in the anthracite. However, the emission of dust was found to increase due to an increase in the amount of CaO and MgO in the fly ash, which could lower the efficiency of the electrostatic precipitator.From these results, we concluded that the complete switch from the anthracite to Australian bituminous coal was possible, although the efficiency and the operation stability became lower than before. Additionally, as a future study, it is necessary to monitor the instability of the temperature increase and its effect on the prolonged clinker formation in the boiler.     

低NOx排放燃烧技术及燃烧优化的试验研究

介绍了煤燃烧过程中NOx生成机理和电站锅炉采用低NOx燃烧技术.通过对某电厂670 t/h锅炉进行炉膛出口氧量、一次风速、二次风配风方式、燃烧器上、下组的给粉方式、一次风煤粉浓淡比等对NOx排放量、飞灰可燃物含量和锅炉再热蒸汽温度的影响规律的试验研究.得出水平浓淡风煤粉燃烧技术能降低NOx排放量,确定了给出锅炉优化运行方式.试验结果表明燃烧优化调整是提高锅炉运行的经济性和降低NOx排放量的有效方法.     

燃煤机组耦合固废焚烧关键技术研究进展

[目的]燃煤与固体废弃物混合掺烧不仅可以实现固废的能量回收利用,也是实现燃煤发电的碳减排的路径之一。[方法]文章综述讨论了燃煤电站掺混固废的研究工作,主要介绍了基于目前主流的电站锅炉为反应器开展燃煤与不同固废掺混的燃烧应用与技术发展;从燃料经济性、混合燃料的飞灰特征、污染物排放以及碳税角度评价燃煤掺混固废的燃烧技术发展;最后讨论了直接掺混和间接掺混的技术的特点。[结果]燃煤直接掺混固废燃烧时需要尽可能减少对锅炉运行的影响,特别是气体污染物的排放以及飞灰对换热面的影响和飞灰无害化处置。间接掺混可以避免混合燃料燃烧对炉膛的影响,但是需要较高的硬件成本投资且耦合技术较为复杂。富氧燃烧技术依旧需要对现有锅炉结构优化来提高该技术的适用性。[结论]直接掺混可实现性与成本优于间接掺混,且循环流化床燃料适应广的特点有利于燃煤直接掺混固废燃烧技术的应用,随着基于循环流化床的富氧燃烧技术的发展将更有利于实现火电厂的碳减排。     

利用CCD测量炉膛温度场及NOx排放特性试验研究

炉膛火焰中的局部高温是NOx排放量升高的重要原因，利用CCD摄像机对炉膛温度进行了测量，测温原理为双色法。在各种不同工况下。对锅炉负荷、过量空气系数、煤种、炉膛温度和燃烧器运行方式等因素同锅炉NOx排放特性之间的关系进行了实验研究。实验结果表明：随着各种影响因素的改变，炉膛温度相应发生变化，NOx排放亦表现为不同的变化规律。CCD能有效地实时监测炉膛温度，诊断局部高温，从而有助于改进燃烧，调节运行工况，有效降低NOx排放。     

锅炉燃烧调整对NOx排放和锅炉效率影响的试验研究

在2台典型的1025 t/h锅炉上进行了燃烧调整降低NOx排放浓度的试验研究,通过改变过量空气系数、辅助风配风方式、运行负荷和制粉系统运行方式等,测定了锅炉尾部烟道NOx排放浓度,分析了锅炉运行工况、运行方式对NOx排放的影响.结果表明:降低过量空气系数,烟煤锅炉NOx减排效果比贫煤锅炉好得多;降低负荷,烟煤锅炉的NOx排放量降低值较大;缩腰式配风的NOx排放浓度比均匀配风方式约降低10%,制粉系统的运行方式影响炉内燃料的燃烧状态和温度分布,也影响NOx的生成和排放.在不降低锅炉效率的前提下,调整燃烧工况,可降低锅炉排放NOx浓度1O%～20%.     

神华煤粒径在分级燃烧中对NOx排放的影响

在多路进风一维炉上,研究不同粒径的神华煤在分级燃烧中氮氧化物的排放规律.结果表明:不分级燃烧时中等粒径煤粉氮氧化物的排放较高;分级燃烧时,分级的程度越大,氮氧化物排放越低;普通分级燃烧时粒径的影响很明显,但仍是中等粒径的氮氧化物的排放明显较高;深度分级燃烧时粒径的影响被削弱;在主燃烧区固定风量时,燃尽风的增加会导致氮氧化物的排放略微升高;并且分级燃烧会减少神华煤的飞灰含碳量.     

低NOX燃烧技术及其在我国燃煤电站锅炉中的应用

针对我国以煤为主的电力状况，对我国电站锅炉目前采用的低氧燃烧、空气分级和燃料分级燃烧的各影响因素进行了分析和总结，根据采用某些低NOx燃烧技术后尚不能使燃用低挥发份无烟煤、贫煤和劣质烟煤的电站锅炉NOx排放达到国家标准要求的事实，指出了进一步进行降低燃用以上煤种NOx排放水平的空气分级和燃料分级燃烧技术研究的必要。图2参12     

Effects of coal properties on the production rate of combustion solid residue

The production rates of furnace bottom ash in a pulverized coal-fired power plant were monitored for a two-year period and its variations with respect to coal properties were analyzed. The power plant was originally designed to fire the coal sludge generated from a washing process; however, the coal sludge and its mixture with low-rank bituminous coal have been started to be used as the main fuel with time. The results of the hardgrove grindability measurements have shown that the grinding properties of sludge or its mixtures could not be predicted based on proximate analysis (moisture, ash, carbon and volatile contents); it could only be determined by experiments. The production rate of bottom ash in this particular power plant remained relatively insensitive to the high ash and moisture contents and could be estimated almost only by knowing the calorific value of the source coal. The evaluated dependency was linear.     

Numerical calculation on combustion process and NO transformation behavior in a coal-fired boiler blended ammonia: Effects of the injection position and blending ratio

Ammonia (NH₃), as a potential carbon-free alternative fuel, can be blended into coal-fired boiler to achieve significant pollution reduction and carbon reduction, but there are concerns about high NOx emissions due to high nitrogen content. According to the characteristics of coal/NH₃ co-combustion, a dual-fuel co-combustion model with strong adaptability and high accuracy was established in this study through Chemkin software to study the influence of different injection positions and blending ratios on combustion characteristics and NOx generation process. Then, the co-combustion model was applied to the three-dimensional CFD calculation process of a 330 MWe front-fired boiler, and the combustion characteristics, NOx distribution and reaction process were calculated when cal. 20% NH₃ was blended in the primary air. The results show that when cal. 20% NH₃ is blended, the change of NO content mainly occurs in ignition zone and flame zone, and the transformation behavior of N in NH₃ is optimized to a 15-step elementary reaction; The temperature distribution in the furnace is similar, and the average temperature at the furnace outlet decreases from 1033 °C to 988 °C, while NH₃ have a preferential combustion reaction with air than coal, resulting in a decrease in the burnout rate of coal; The NOx concentration at the furnace outlet decreases from 355 mg/Nm³ to 281 mg/Nm³, which is 20.85% lower than that under the pure coal burning condition, and the variation range of O₂ concentration and unburned NH₃ concentration is small.     

基于正交设计的分级分区头部流动特性研究

针对某650 MW超超临界燃煤锅炉在深度调峰过程中燃用大同烟煤时无法稳定燃烧的情况开展研究,就如何提高锅炉在低负荷运行中稳燃性的问题,对原煤种进行掺混改良,改变不同富氧燃烧配风方式,利用计算流体力学模拟软件模拟了不同工况的炉内燃烧情况。模拟结果表明：由于锅炉降低负荷运行增加了原煤种的着火难度,固定碳含量低且挥发分高的煤种可以较好适应锅炉运行调整;富氧燃烧可以提高锅炉低负荷运行时的出口烟温,能满足后续脱硝处理的要求;随着富氧燃烧程度的增大,煤粉燃烧耗氧量增加,每秒燃烧的煤粉颗粒数增加,加剧了炉内的燃烧,使燃烧更稳定;当富氧浓度大于27%时,不能高效提高炉内温度,NOx排放量增多;当富氧浓度为27%时,炉膛出口NOx排放量按6%O2折算为负增长的最小值,是该锅炉低负荷投运较为理想的工况。     

不同燃烧条件下煤粉锅炉NOx排放特性的试验研究

以1台670 t/h煤粉锅炉为对象进行了热态试验,研究了煤粉锅炉在不同燃烧条件下NOx 的排放特性.采用在线烟气分析仪对烟气成分进行分析,并通过化学分析获得了飞灰中的可燃物含量.改变二次风配风方式、炉膛出口氧量、周界风风门开度以及磨煤机组合方式等影响因素,对锅炉热效率、飞灰可燃物以及NOx排放浓度进行测量和分析,获得了可减少NOx排放并保持较高燃烧效率的合理燃烧方式:采用均等配风,炉膛出口氧量为2.25%左右,周界风风门开度为15%,采用ABC层的磨煤机组合方式.     

Modeling of thermal characteristics for a furnace of a 500 MW boiler fired with high-ash coal

An advanced zonal computational method has been used to determine the temperature and heat flux profiles and other thermal characteristics for a furnace of the 500 MW boiler fired with high-ash, medium-volatile Ekibastuz coal. The predicted temperature profiles for a 100% boiler load and different methods of fuel distribution through the burner tiers were compared with respective data obtained in experimental tests. The effects of the fuel dust fineness and excess air on the furnace temperature pattern were studied. The cases associated with the reduced boiler loads were considered as well. The lower limit for the boiler load has been established, based on the predicted results.     

自动可调叶栅煤粉分配器在富拉尔基发电总厂锅炉的应用

富拉尔基发电总厂1号～4号炉均已成功地改造安装了自动可调叶栅煤粉分配器。此分配器能在运行中对空气和煤粉分配进行调节,实现了风粉分配由不可控制到有效控制,有效调整炉膛出口温度,避免或减轻炉内结渣,使锅炉的低负荷不投油稳燃能力得到大大增强,并且由于燃料在炉内燃烧被分为过浓燃烧和过淡燃烧两部分,使NOx排放量低于373mg／m^3,机械不完全燃烧损失降低了1．166％,具有良好的经济效益和社会效益。     

空气分级燃烧低NO_x排放数值模拟研究

由煤燃烧产生的NOx引起的污染受到世界各国的重视.因此研究降低污染物排放成为燃烧研究的重要课题.对某电站锅炉的实际情况,进行了空气分级燃烧降低NOx的数值模拟研究,并和改造后的运行结果进行了比较.结果表明,分级燃烧可有效降低NOx排放,为电站锅炉清洁燃烧提供了依据.     

木粉与塑料粉循环流化床中共燃的NOx生成研究

为减少废塑料在焚烧过程中NOx的生成及充分利用生物质能,提出在循环流化床中将废塑料和生物质进行共燃的处理方法.在实验室循环流化床装置上进行了木粉和塑料粉的共燃实验,研究了温度、木粉和塑料粉混合比例对NO和NO2生成浓度的影响.实验结果表明:随温度升高,NO生成浓度升高,而NO2生成浓度迅速降低;随木粉和塑料粉混合比例增加,NO和NO2生成浓度均降低;共燃时NO的生成量低于2种物料单独焚烧时其生成量的线性叠加,实验条件下NO的减少量最高达43.3%.为寻找二者共燃时NOx生成的一般性规律,采用径向基神经网络建立了NO生成的预测模型,预测结果表明该模型具有很高的准确性.     

CFB锅炉节能降耗改造及其应用效果

文中针对某135MW CFB锅炉存在的排烟温度高、点火启动用油量大问题,采用低温省煤器改造降低了排烟温度、延长了布袋除尘器使用寿命,采用给煤系统改造减少了锅炉启动物料上料时间,通过对锅炉炉前煤仓补充点火用烟煤大大降低了点火启动用油,上述两项技术有效实现了CFB锅炉的节能降耗。     

300MW烟煤/高炉煤气混燃锅炉掺烧褐煤燃烧特性的数值模拟及经济性分析

对某300MW烟煤/高炉煤气混燃锅炉掺烧褐煤的燃烧特性进行数值模拟和经济性分析,分析了褐煤完全取代烟煤、部分掺烧褐煤和不同高炉煤气掺烧比例等因素对炉内温度场和CO摩尔分数分布的影响.结果表明:褐煤完全取代烟煤后,炉内温度显著降低而炉膛出口烟气温度明显升高,影响了锅炉运行的安全性;褐煤取代部分烟煤后,随着褐煤掺烧比例的增大,炉内温度逐渐下降,炉膛出口烟气温度升高但CO摩尔分数变化不大;在褐煤掺烧比例一定时,随着高炉煤气掺烧比例的增大,炉膛最高温度明显降低且炉膛出口温度升高,CO摩尔分数的峰值逐渐减小;纯烧烟煤的发电成本为117 090元/h,当掺烧40%褐煤和20%高炉煤气时,发电成本降为80 107元/h,发电成本比纯烧烟煤降低了31.59%.     

Experimental study of the combustion efficiency and formation of NOx in an industrial pulverized coal combustor

With horizontal bias combustion burners, experiments have been carried out on a 670 t h^?1, corner‐fired, pulverized‐coal fired boiler burning bituminous coal. At 200 MWe load, the furnace excess O₂ remains stable. The different horizontal fuel biases are obtained by changing the tilt angle of all the Louvre enrichers' regulating blades. The tilt angles of the blades are 0, 15, 24, 32°; the result is that the enriching ratios of the fuel‐rich primary air increase from 2.2 to 2.6 at No. 2 corner, and from 1.2 to 4.2 at No. 3 corner. The gas temperature increases in the burner region. The application of the horizontal bias combustion burners results in a reduction in NO_x formation from 545.7 mg Nm^?3 (O₂=6%) to 287.9 mg Nm^?3, and a substantial reduction in carbon in ash content from 5.24 to 2.48%. The boiler operated stably at a load of 80 MWe without auxiliary fuel oil. Copyright © 2004 John Wiley & Sons, Ltd.