一次风叶片倾角对旋风液态排渣锅炉燃烧及NOx释放特性的影响

针对纯燃高碱煤旋风液态排渣锅炉,采用数值模拟方法研究了不同一次风叶片倾角下该锅炉炉内空气动力场、温度场及各组分质量分数分布特性,分析了一次风叶片倾角对炉内燃烧及NOx排放特性的影响.结果表明:旋风液态排渣锅炉炉内空气动力场良好,烟气充满度高,错列逆向布置的旋风燃烧器可强化燃烧;在所选工况范围内,随着一次风叶片倾角的减小,炉膛出口烟温降低,炉膛出口NOx质量浓度先降低后升高;一次风叶片倾角为30°时,炉内整体温度和煤粉燃烧效率较高,炉膛出口NOx质量浓度最低.     

350MW煤粉锅炉低氮燃烧改造与参数优化设计

对某350 MW煤粉锅炉的低氮燃烧改造方案进行分析,采用数值模拟方法研究了不同工况下气流的速度场、炉膛温度场和NOx排放质量浓度,并与实测结果进行了对比.结果表明:延长并调整旋流燃烧器二次风的扩锥可降低NOx的排放质量浓度;改变燃尽风喷口结构,增大燃尽风风量,使主燃区总体处于还原性气氛,既有利于NOx的还原,又能有效控制炉膛出口烟气温度,缓解屏底结焦状况;数值模拟结果与实测结果吻合较好.     

燃尽风射流形式对墙式对冲煤粉锅炉低氮燃烧改造的影响

采用数值模拟方法对某330 MW亚临界墙式对冲煤粉锅炉低氮燃烧改造进行了研究,在燃尽风风率、喷口中心距最上层煤粉燃烧器的高度及喷口面积保持一致的条件下,分析了不同燃尽风射流形式对炉内高温黏性火焰的穿透能力及改造工况燃尽率和NOx生成情况的影响.结果表明:圆形直流燃尽风的穿透能力最强,矩形直流燃尽风次之,同心圆式的内直外旋燃尽风最弱;圆形直流燃尽风在炉膛高度横截面上射流根部的覆盖范围和沿烟气流程的气流层厚度综合水平最低,CO浓度最高;内直外旋的燃尽风射流形式由于射流后期与高温烟气混合剧烈,燃尽特性最好,炉膛飞灰含碳量最低;3种射流形式的燃尽风对NOx浓度几乎没有影响.     

生物质(气)耦合燃煤锅炉燃烧特性数值模拟

为了研究不同类型生物质对煤粉耦合生物质再燃锅炉燃烧特性的影响,基于FLUENT模拟软件,选取某超超临界660 MW锅炉作为研究对象,搭建煤粉锅炉耦合生物质(气)再燃模型,对锅炉进行改造,在最顶层二次风喷口和燃尽风之间增添生物质(气)再燃喷口,分别对纯煤燃烧,生物质固体再燃,生物质气体再燃等不同工况的燃烧特性进行数值模拟,研究燃烧区温度场,组分分布以及炉膛出口烟气中CO2和NOx质量浓度分布的变化规律.结果 表明:生物质再燃降低锅炉煤粉消耗量,使得主燃区燃烧温度降低,同时使得炉内燃烧火焰中心上移,炉膛出口CO体积分数上升,增加了排烟热损失;相比于纯煤工况,生物质固体和生物质气再燃均可以使炉膛出口CO2和NOx的体积分数降低,但是生物质气效果要明显高于生物质固体.其中食物垃圾气体再燃减少CO2排放与降氮效果最好,CO2减排率可达13.87％,降氮率可达24.13％.     

生物质(气)耦合燃煤锅炉燃烧特性数值模拟

为了研究不同类型生物质对煤粉耦合生物质再燃锅炉燃烧特性的影响,基于FLUENT模拟软件,选取某超超临界660 MW锅炉作为研究对象,搭建煤粉锅炉耦合生物质(气)再燃模型,对锅炉进行改造,在最顶层二次风喷口和燃尽风之间增添生物质(气)再燃喷口,分别对纯煤燃烧,生物质固体再燃,生物质气体再燃等不同工况的燃烧特性进行数值模拟,研究燃烧区温度场,组分分布以及炉膛出口烟气中CO2和NOx质量浓度分布的变化规律.结果 表明:生物质再燃降低锅炉煤粉消耗量,使得主燃区燃烧温度降低,同时使得炉内燃烧火焰中心上移,炉膛出口CO体积分数上升,增加了排烟热损失;相比于纯煤工况,生物质固体和生物质气再燃均可以使炉膛出口CO2和NOx的体积分数降低,但是生物质气效果要明显高于生物质固体.其中食物垃圾气体再燃减少CO2排放与降氮效果最好,CO2减排率可达13.87％,降氮率可达24.13％.     

超超临界锅炉炉内燃烧过程的数值模拟

采用计算流体力学软件PHOENICS，选择合理的数学模型，对1台1000 MW超超临界单炉膛双切圆煤粉炉内的燃烧过程进行数值模拟．着重研究了单炉膛双切圆燃烧特性、炉内焦炭燃烧特性及NO生成特性。结果表明：燃烧器前后墙布置导致炉内气流呈椭圆形，NO生成总体水平较低，焦炭燃尽效果较好，但在炉膛高度方向40m以上的区域，烟气高温区及大量未燃尽焦炭偏向前墙附近，且未燃尽焦炭在辐射屏区逐渐燃尽。针对这一问题提出了解决方案，结果表明：改进后的工况明显提高了焦炭的燃烧速度．使其在屏区以下基本燃尽，NO2排放量也有所降低。     

燃尽风速的改变对锅炉炉膛内燃烧过程影响的数值模拟

借助计算流体力学软件Fluent,选择合理的数学模型,对1台600MW燃煤锅炉的燃烧过程进行的数值模拟。研究燃尽风风速改变对炉内温度场和混合特性的影响。结果表明:燃尽风风速增大时,炉内气流的旋转强度随之增强,燃尽风的穿透程度随之加强,相对容易穿透到炉膛中心,从而使得烟气与煤粉的混合加剧,有利于增加煤炭燃烧的效率;在一定条件下,随着燃尽风速的增加,炉膛中心的高温区域面积增加,而且相对集中;当燃尽风速增加时,锅炉烟气出口温度随之降低;燃尽风风速为50m/s时炉内燃烧状况最佳。     

800MW旋流对冲燃烧锅炉低NOx改造的数值模拟

针对某800MW超临界锅炉NOx排放量较高的问题,设计了配风方式不同的3种工况．利用CFD软件,对3种工况进行了炉内燃烧、传热及污染物排放等方面的数值计算,并分析了炉内的温度、NOx及cO组分的分布情况．结果表明：计算结果与实测数据吻合较好,空气分级燃烧使主燃区温度降低,CO体积分数升高,N0x质量浓度明显降低;燃尽风对燃料的燃尽率和炉膛出口烟温产生了不利影响,从而影响机组的经济性和安全性．通过对各个工况燃料的燃尽率及炉膛出口烟温进行综合比较分析,得出工况3为较理想的改造方案．     

1000MW超超临界锅炉燃烧调整的试验研究

对某电厂1000MW燃煤锅炉进行了燃烧优化调整试验,分析了一次风配风均匀性、煤粉细度、燃烧器配风、运行中氧的体积分数以及燃尽风率对锅炉效率的影响．结果表明：对同层燃烧器外二次风采用两端和中间开度大的配风方式可以改善由于大风箱两端进风引起的沿炉膛宽度方向氧气的体积分数偏差,随着炉内氧气的体积分数增加,锅炉的热效率先提高后降低．当氧气的体积分数在3．0％左右时,锅炉热效率达到最高．随着燃尽风率的逐渐降低,锅炉热效率和NOx排放质量浓度逐渐提高．综合考虑锅炉效率、NOx排放质量浓度以及屏式过热器管壁金属温度,在额定负荷下,燃尽风率以保持在25％左右为宜,此时锅炉热效率为93．9％,NOx排放质量浓度为306．1mg／m^3．     

210MW煤粉炉燃烧系统改进的数值模拟

运用CFD软件对某210 MW煤粉锅炉的燃烧过程进行三维数值模拟,针对锅炉实际存在温度分布不好、燃烧效率不高、结渣问题严重,对炉膛进行偏二次风、反切燃尽风及两者联用改进。结果表明:与设计工况相比,单独的小角度偏二次风改进下的炉膛燃烧区温度降低约300 K,水冷壁附近氧气浓度提高,减少了水冷壁的结渣和高温腐蚀;单独小风率反切燃尽风改造后的配风方式更合理,烟气的停留时间增加0.6 s,燃烧区温度提高约373 K,高温区域扩大,炉膛出口烟气热偏差系数减小约0.7%,提高了锅炉的燃烧效率和运行的安全性,但可能加重炉内结渣;二者联用改进既能够很好地改善炉膛的温度分布,扩大炉膛高温区域,提高燃烧区温度约353 K,同时能够减少燃烧器区域的结渣和高温腐蚀,减小炉膛出口烟气热偏差,采用二者联用改造对锅炉运行最为合适。     

Experimental investigation on the conversion of fuel-N to NOx of quasi-particle in flue gas recirculation sintering process

Flue gas recirculation sintering process is a potential technology to decrease fuel consumption and NOx emissions compared with conventional sintering process. In present work, a vertical quartz tube reactor was used to investigate the combustion characteristics and conversion of fuel-N to NOx of quasi-particle. The mass conversion rate of quasi-particle increases with higher temperature. It was found that D₁ model is more appropriate than other models to describe quasi-particle combustion process through comparing correlation coefficients calculated by different mechanism models. Effects of temperature, coke size and proportion, circulating flue gas components on the conversion of fuel-N to NOx of quasi-particle were studied. The conversion rate of fuel-N to NOx of quasi-particle increases with higher temperature. With increasing coke size and proportion, the conversion rate of fuel-N to NOx decreases obviously. O₂ has a positive impact on the conversion of fuel-N to NOx of quasi-particle. CO could decrease the conversion rate of fuel-N to NOx by reducing NO directly or reacting with char to decrease NOx indirectly. CO₂ has an obviously inhibitory effect on the conversion of fuel-N to NOx of quasi-particle because it reacts with char to generate CO. The results were conducive to further understanding the combustion behavior and NOx formation mechanism of quasi-particle during flue gas recirculation sintering.     

链条炉区段烟气再循环对锅炉运行及NOx排放特性影响的工业试验研究

针对一台采用尽早配风方式的29MW链条炉进行分区段烟气再循环对锅炉运行及NOx排放特性影响的工业试验。在挥发分析出及燃烧区段煤层下的一次风室混入再循环烟气将有效强化该区段煤层燃烧,降低该区段煤层以上燃烧空间的氧浓度,控制及消减挥发分N向NOx的转化,同时降低了穿过该区段煤层一次风的氧浓度,抑制焦炭N向NOx转化,NO消减效果最高达到25%。在焦炭燃烧区段煤层下的一次风室混入再循环烟气,能够降低穿过床层气流的氧浓度,抑制焦炭氮向NO的转化过程,该区段烟气再循环低氮效果有限,最大降幅9%。再循环烟气可以替代部分一次风,以维持足够的风室风压,进而降低穿过煤层气流的O2浓度,从而强化链条炉区段燃烧特性的低氮特征,实现链条炉的NOx减排。随着工业锅炉NOx排放指标的不断提高,烟气再循环作为一项有效的前置低氮环节,能有效降低整个低氮系统的投资,进而取得较好的经济性。     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

Experiment and numerical simulation investigations of the combustion and NOx emissions characteristics of an over-fire air system in a 600 MWe boiler

Several numerical simulations are conducted to investigate the influence of pulverized-coal combustion characteristics and NO_x emissions with different configurations of nozzle and arrangements of an over-fire air device for a 600 MWe boiler unit. It is found by a series of comparisons that the numerical simulation results are almost in agreement with the in-situ experimental results, including the flue gas temperature of the burner outlet, the flue gas temperature along the furnace height, the NO_x concentration, and combustible content in the fly ash of the air preheater outlet, which indicates that the numerical model and the grid are reasonable. Numerical simulation results show that setting the over-fire device in which the inner is straight flow and the outer is swirl flow and the staggered arrangement of two layers of over-fire air (OFA) in the boiler are both conducive to the pulverized-coal combustion in the furnace and to the reduction of NO_x emissions. The results also show the values of 241.64?mg/m³ @ 6% O₂ for the lowest NO_x concentration at the furnace outlet. Compared with the boiler without OFA, the NO_x concentration decreased by 60.4%. Using the staggered arrangement of two layers of OFA in the practical 600 MW boiler unit, the gas temperature can reach 1100?K at the height of 100?mm away from the burner outlet, leading to coal particle ignition immediately; moreover, the NO_x emission concentration reduced to 284?mg/m³ @ 6% O₂ and heat loss due to unburned carbon in refuse of the air preheater outlet is 3.17%.     

污泥掺烧方式对燃煤锅炉燃烧影响的模拟研究

为了确保燃煤锅炉掺烧污泥后炉内燃烧安全稳定并控制NO_x的生成,以国内某典型1 000 MW超超临界燃煤锅炉为研究对象,利用CFD软件计算研究了不同的污泥掺烧方式对锅炉温度场和NO_x生成的影响。结果表明：在燃煤锅炉不同层的燃烧器掺烧污泥,掺烧污泥的燃烧器对应高度均出现了温度的下降和NO_x排放浓度的降低;随着污泥分别由下往上在B,D,F层燃烧器进行掺烧,在炉膛出口处烟温升高,NO_x排放浓度降低;在保持F层燃烧器总热值不变的情况下进行掺烧时,能保证锅炉整体温度水平,掺烧污泥比例越高,炉膛出口烟温越低,NO_x生成量越少;在F层燃烧器掺烧污泥燃烧效果较好,有利于NO_x减排,是最适合污泥掺烧的燃烧器层。     

双通道浓淡与乏气OFA组合煤粉燃烧器的试验研究

为解决某电厂100 t/h四角切圆煤粉炉燃烧效率低、燃烧不稳定的问题,采用双通道浓淡与乏气OFA(燃尽风)组合煤粉燃烧器进行技术改造,其特点为上一次风双通道上下浓淡、下一次风水平浓淡并且集中布置,乏气通过OFA送入炉内。冷态结果表明;该改造方案炉内气流充满度好,气流量不偏斜刷墙;一次风喷口有明显的回流区,并随着腰部风开度的增大向炉膛中心移动,回流区半径减小;热态测试结果表明:热效率提高了3个百分点,50%低负荷稳燃,NOx排放量为260 mg/m3(折算到氧量6%)。     

Fundamentals of coal combustion during injection into a blast furnace

The efficiency of coal combustion is important for the blast furnace process. Incomplete combustion of coal does not reduce coke consumption as can be expected and decreases burden permeability which results in improper gas flow and temperature distribution. Consequently, this reduces the throughput of the blast furnace.

This paper describes combustion conditions and mechanisms of coal combustion in the blast furnace, and discusses factors affecting coal combustion such as injector location, coal type, injection rate, maceral composition, and air blast parameters. Also, mathematical models of coal and coal/coke combustion in the blast furnace are considered.     

超细煤粉再燃低NOx燃烧技术的数值模拟

为了验证超细煤粉作为再燃燃料的有效性,使用FLUENT软件对元宝山褐煤在燃烧试验研究装置中的进行了4个工况的数值模拟;1 个为常规燃烧,3 个为超细粉再燃工况。计算结果表明:超细粉再燃可以有效的降低NOx 排放,与常规燃烧相比,脱除率为58.2%~72.5%;再燃区过量空气系数越小,越有利于NOx 的还原;超细粉再燃工况中出口NOx 排放量不仅与再燃区NOx 的还原率有关,而且还与燃尽区新的NOx 生成有关。图5表3参7     

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。