低温干馏煤气/富氧大当量比燃烧热力学分析

为明确煤气/富氧大当量比燃烧过程中煤气各可燃组分间氧化剂竞争机制及其对内热火焰温度和干馏介质成分的影响,对该反应体系进行了热力学分析.结果表明:各组分的燃烧优先度随反应温度而变化,低温(<849 K)下CO优先燃烧,高温(>1143 K)下CH4优先燃烧;除选择性燃烧外,甲烷化和甲烷重整反应在800 K～1000 K发...     

低变质煤富氧低温干馏试验研究

用富氧代替空气与煤气燃烧提供热源,利用燃烧废气与低温干馏过程产生的干馏煤气混合形成高温循环气,对煤进行富氧干馏。试验结果表明,在不改变现行低温干馏炉结构的情况下,富氧干馏完全可行,可大幅提高煤气的有效成分,降低氮含量,煤气热值是空气助燃干馏的2倍以上,煤气放散量减少约3/4。     

预混富氧燃烧火焰特性的实验研究

对预混富氧燃烧的火焰特性进行实验研究,结果表明:富氧浓度在21%～30%的范围内变化时,随着氧含量的增加,燃烧反应速率和火焰传播速度逐渐增加,进而引起燃烧区的缩小和温度梯度的增加。并且火焰高温区逐渐缩小,最高火焰温度逐渐增高,并且最高温度点向烧嘴口方向移动。     

SJ型低温干馏炉燃烧影响因素研究

采用计算流体动力学(CFD)方法,在不同条件下对低温干馏炉内温度分布进行数值模拟.通过单因素试验确定了最优燃气比和入口流速;同时为了提高兰炭质量、煤气热值和焦油产量,研究富氧干馏对兰炭生产工况的影响.研究结果表明:燃气比和流速对干馏炉内温度的分布有较大的影响,当燃气比为0.6时,干馏炉内气体充分燃烧,温度达到最高;当燃...     

高炉煤气燃烧数值模拟在LOMA-MLB热风炉调试中的应用

LOMA-MLB热风炉为适用于高炉煤气的炉型，通过计算机建模和网格划分，使用Fluent软件数值模拟高炉煤气在热风炉中的燃烧情况，验证热风炉调试时配风所需的空燃比及烟气温度参考值。模拟结果表明，燃烧反应质量传递过程基本完成，实验数据比模拟数据计算的热值稍高，模拟燃烧燃尽率高，燃烧火焰中心最高温度为1 595K，出口处NOX含量仅为0.008 6ppm，高炉煤气钝体的设计有利于燃料与空气的混合和保持火焰的连续稳定。     

梭式窑预混富氧燃烧预热阶段换热特性的模拟研究

通过计算流体力学(CFD)软件—FLUENT研究了富氧浓度对预热阶段梭式窑内换热特性的影响。结果表明火焰最高温度随富氧浓度的增加非线性增大。梭式窑内的富氧燃烧可以减少高温高速烟气射流直接对窑墙的冲刷。由于烟气不能充分冲刷烧嘴附近区域和烟气射流顶部回流的影响,窑炉断面出现温差。为使窑内温度尽量均匀,预热阶段也可通过控制燃料量,点燃全部烧嘴。富氧助燃可以使窑内换热增强,减小窑内温差。     

辊道窑烧成带富氧燃烧及火焰空间数值模拟

采用FLUENT软件对气烧明焰陶瓷辊道窑烧成带的火焰空间进行数值模拟研究,并对不同氧气浓度下以天然气和炉煤气为燃料时辊道窑烧成带的燃烧特性进行对比.数值模拟结果表明:当燃料种类和燃料量一定时,富氧燃烧可以提高燃烧的火焰温度,随氧气质量分数百分比增加,平均温度呈上升趋势,但35%时有所减少;随氧气质量分数百分比增加,以发生炉煤气为燃料时炉内CO浓度逐渐减少,而采用天然气时,CO浓度逐渐增加;相同气氛下,以天然气为燃料时炉内温度高于发生炉煤气,CO浓度较低.本文结果为辊道窑的富氧燃烧运行提供了有益的参考.     

乙醇荷电喷雾对冲燃烧的火焰特性

研究液体燃料雾化燃烧的火焰特性,有助于理解整个燃烧的变化过程。基于对冲火焰结构,以无水乙醇为燃料,设计了乙醇荷电喷雾对冲燃烧装置。通过对喷雾和火焰进行拍摄,并对火焰温度进行测量,得到了不同燃料流量下的喷雾形态、火焰形态和火焰温度变化,探讨了不同当量比、应变率对火焰形态和温度的影响规律。结果表明：随着乙醇流量的增加,喷雾的雾化核心区域和卫星区域的分界逐渐消失,当乙醇流量增加到13 ml/h时,喷雾出现液柱。当量比小于1时火焰保持稳定,当量比大于1时火焰出现振荡,火焰的无量纲直径随当量比的增加呈减小趋势。随着应变率的增大,火焰的无量纲直径减小,温度降低。     

以甲醇为辅助燃料的超临界水热燃烧反应器数值模拟研究

对容积式超临界水热燃烧反应器内的燃料与氧化剂的混合与燃烧反应的物理化学过程进行模拟研究,揭示了反应参数、燃料特性及反应器喷嘴尺寸对反应器内温度场、浓度场和燃烧反应速率场的影响规律。研究结果表明,同轴喷射的非预混水热火焰发生化学反应的区域是狭窄的,并且反应器内的最高温度出现在以轴线上出现化学当量的轴向距离定义的火焰长度位置处。初始燃料浓度的增加会使反应器内的火焰温度升高、火焰长度延长;氧化系数的增大,不仅降低了火焰温度,并且可以缩短水热火焰长度;随着入射速度的增加,反应器内开始出现最高温度的位置远离反应器入口,火焰位置延迟。     

乙醇荷电喷雾对冲燃烧的火焰特性

研究液体燃料雾化燃烧的火焰特性,有助于理解整个燃烧的变化过程。基于对冲火焰结构,以无水乙醇为燃料,设计了乙醇荷电喷雾对冲燃烧装置。通过对喷雾和火焰进行拍摄,并对火焰温度进行测量,得到了不同燃料流量下的喷雾形态、火焰形态和火焰温度变化,探讨了不同当量比、应变率对火焰形态和温度的影响规律。结果表明:随着乙醇流量的增加,喷雾的雾化核心区域和卫星区域的分界逐渐消失,当乙醇流量增加到13ml/h时,喷雾出现液柱。当量比小于1时火焰保持稳定,当量比大于1时火焰出现振荡,火焰的无量纲直径随当量比的增加呈减小趋势。随着应变率的增大,火焰的无量纲直径减小,温度降低。     

低阶煤低温热解半焦在模拟高炉喷吹条件下的燃烧性能

采用自制固定床热解装置在隔绝空气的条件下制备神木长焰煤热解终温分别为400℃、450℃、500℃及550℃的热解半焦,利用管式沉降炉模拟高炉喷吹条件研究神木长焰煤低温热解半焦的燃烧性能,并考察了热解终温、半焦喷吹粒径以及燃烧反应温度对半焦燃烧性能的影响。研究表明：低温热解半焦的燃烧性能优于实验所选用无烟煤的燃烧性能,半焦的燃烧性能与其燃料比之间存在负相关关系,即燃料比越高,燃烧性能越差;降低热解终温、减小半焦喷吹粒径以及提高燃烧反应温度均能改善半焦的燃烧性能,当热解终温为400℃、喷吹粒径100～200目、燃烧反应温度为1100℃时半焦的燃尽度最佳为96%。本实验半焦制备及燃烧条件与现有低温热解和高炉喷吹工艺相符,且热解半焦各项性能均符合喷吹用煤指标。     

Chemistry and radiation in oxy-fuel combustion: A computational fluid dynamics modeling study

In order to investigate the role of combustion chemistry and radiation heat transfer in oxy-fuel combustion modeling, a computational fluid dynamics (CFD) modeling study has been performed for two different oxy-fuel furnaces. One is a lab-scale 0.8 MW oxy-natural gas flame furnace whose detailed in-flame measurement data are available; the other is a conventional 609 MW utility boiler which is assumed to be operating under oxy-fuel combustion condition with dry flue gas recycle. A new model for gaseous radiative properties is developed, validated, and then implemented in the CFD simulations. The CFD results are compared to those based on the widely used model in literature, as well as the in-flame measurement data. The importance and advantage of the new model for gaseous radiative properties have been well demonstrated. Different combustion mechanisms are also implemented and compared in the CFD simulations, from which significant difference in the predicted flame temperature and species is observed. This difference is consistent with those expected from the equilibrium calculation results. As a conclusion, the appropriate combustion mechanisms applicable to oxy-fuel combustion modeling are identified. Among the key issues in combustion modeling, e.g., mixing, radiation and chemistry, this paper derives useful guidelines on radiation and chemistry implementation for reliable CFD analyses of oxy-fuel combustion, particularly for industrial applications.     

CFD modelling of air-fired and oxy-fuel combustion of lignite in a 100 KW furnace

In this paper, a comprehensive computational fluid dynamics (CFD) modelling study was undertaken by integrating the combustion of pulverized dry lignite in several combustion environments. Four different cases were investigated: an air-fired and three different oxy-fuel combustion environments (25 vol.% O₂ concentration (OF25), 27 vol.% O₂ concentration (OF27), and 29 vol.% O₂ concentration (OF29) were considered. The chemical reactions (devolatilization and char burnout), convective and radiative heat transfer, fluid and particle flow fields (homogenous and heterogenous processes), and turbulent models were employed in 3-D hybrid unstructured grid CFD simulations. The available experimental results from a lab-scale 100 KW firing lignite unit (Chalmer’s furnace) were selected for the validation of these simulations. The aerodynamic effect of primary and secondary registers of the burner was included through swirl at the burner inlet in order to achieve the flame stability inside the furnace. Validation and comparison of all the combustion cases with the experimental data were made by using the temperature distribution profiles and species concentration (O₂, CO₂, and H₂O) profiles at the most intense combustion locations of the furnace. The overall visualization of the flame temperature distributions and oxygen concentrations were presented in the upper part of the furnace. The numerical results showed that the flame temperature distributions and O₂ consumptions of the OF25 case were approximately similar to the reference combustion case. In contrast, in the OF27 and OF29 combustion cases, the flame temperatures were higher and more confined in the closest region of the burner exit plane. This was a result of the quick consumption of oxygen that led to improve the ignition conditions in the latter combustion cases. Therefore, it is concluded that the resident time, stoichiometry, and recycled flue gas rates are relevant parameters to optimize the design of oxy-fuel furnaces. The findings showed reasonable agreement with the qualitative and quantitative measurements of temperature distribution profiles and species concentration profiles at the most intense combustion locations inside the furnace. These numerical results can provide useful information towards future modelling of the behaviour of pulverized brown coal in a large-scale oxy-fuel furnace/boiler in order to optimize the burner’s and combustor’s design.     

富氧燃烧方式下煤中砷的挥发行为

选取SJS烟煤,利用高温管式炉模拟富氧燃烧,在600~1400℃温度范围内研究了O₂浓度、CO₂浓度及温度对砷挥发的影响,并进行了空气燃烧模式下的对比实验。对不同工况下的灰样进行FTIR表征并结合化学热力学软件模拟进行分析,结果表明:富氧气氛和空气气氛下煤中砷的挥发比例均随温度升高不断增大,并在低温区间(<900℃)和高温区间(>900℃)分别出现了砷的剧烈失重,但O₂浓度和CO₂浓度影响了不同气氛下砷的具体挥发行为。低温下(<900℃)O₂浓度是影响砷挥发的主要因素,O₂浓度越高,砷的挥发比例越大;相同O₂浓度下,CO₂浓度越高,砷的挥发比例越低,CO₂的存在抑制了煤中砷的挥发。高温下(>900℃)CO₂浓度是影响砷挥发的主要因素,富氧气氛下高CO₂浓度对热量的阻碍导致相同条件下砷酸盐发生分解需要更高的温度,因此富氧气氛下砷的挥发较空气模式滞后;此外CO₂在煤颗粒表面形成还原性气氛,高价态砷化合物向不稳定的低价态砷化合物转变,低价态砷化合物的快速分解导致高温下富氧气氛中砷的挥发速率较常规空气模式快。     

稀薄燃气多孔介质燃烧二维火焰数值模拟

对稀薄低热值气体在多孔介质燃烧中的二维火焰温度分布进行了数值模拟。在一定工况参数下,考察了多孔介质二维火焰峰面和温度分布特性,以及火焰峰面传播过程。详细分析了当量比、燃气流速、及壁面热损失等工况参数对燃烧火焰和高温峰值的影响。结果表明,在火焰传播过程中,火焰峰面形状逐渐变化,导致高温区域分布逐渐改变;随着当量比增加,近壁面处的火焰峰面倾斜程度逐渐减少,火焰峰面逐渐向上游传播,火焰峰面形状由梯形分布逐渐转变成两侧向下倾斜的直线分布;燃气流速对火焰峰面形状和位置的影响与当量比相反;壁面热损失引起火焰峰面倾斜,对火焰位置影响较小。     

高浓度丙酮VOCs高温预热近极限贫燃预混火焰特性的数值分析

为进一步对一种丙酮挥发性有机化合物（VOCs）焚烧炉进行设计优化和运行参数调节,本文对其在不同的燃料当量比、预热温度下的火焰特性进行了数值模拟,分析了其绝热火焰温度、着火延迟时间、火焰传播速度和一维火焰产物分布特性。研究结果表明：典型当量比（约0.113）下的绝热火焰温度为850~900℃,属于中低温燃烧,绝热火焰温度随预热温度和当量比（0.06~0.4）的升高均线性升高。预热温度和化学当量比对着火延迟时间的影响十分敏感。在其典型贫燃条件下,层流火焰传播速度随预热温度升高呈指数函数关系增大,随化学当量比增大而缓慢升高,且其层流火焰传播速度不超过150cm/s。反应过程首先发生丙酮的分解和部分氧化,并持续时间较长,仅当混合物的温度升高一定程度后才发生较剧烈的CO氧化。     

氨气/甲烷贫预混旋转湍流火焰稳定性及NO生成

为了研究氨气/甲烷掺混燃气在贫预混旋转湍流状态下的火焰稳定性及NO的排放特性,设计建造了一个可视化的旋转湍流燃烧装置,开展了一系列的实验测量研究。研究表明：随着当量比增大,氨气火焰稳定燃烧的范围有所扩大,但当氨气掺混比大于0.60时火焰出现上下振荡现象,继续增加将导致火焰吹熄;NO的排放水平随当量比增加而提高;但在相同的当量比下,NO的排放随氨气掺混比的增加先升高再下降。此外,分别采用化学反应器网络（CRN）方法和一维层流预混火焰计算方法,对相应的火焰状态进行了数值计算分析,虽然计算结果与实验结果误差较大,但其预测的NO排放特性随氨气掺混比、当量比的变化趋势是一致的,对三者之间误差的来源进行了分析。     

氨气/甲烷贫预混旋转湍流火焰稳定性及NO生成

为了研究氨气/甲烷掺混燃气在贫预混旋转湍流状态下的火焰稳定性及NO的排放特性,设计建造了一个可视化的旋转湍流燃烧装置,开展了一系列的实验测量研究。研究表明：随着当量比增大,氨气火焰稳定燃烧的范围有所扩大,但当氨气掺混比大于0.60时火焰出现上下振荡现象,继续增加将导致火焰吹熄;NO的排放水平随当量比增加而提高;但在相同的当量比下,NO的排放随氨气掺混比的增加先升高再下降。此外,分别采用化学反应器网络（CRN）方法和一维层流预混火焰计算方法,对相应的火焰状态进行了数值计算分析,虽然计算结果与实验结果误差较大,但其预测的NO排放特性随氨气掺混比、当量比的变化趋势是一致的,对三者之间误差的来源进行了分析。     

Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface

The structure and dynamics of a natural buoyant turbulent diffusion flame near a vertical surface with combustible gas exhaustion are numerically studied by using the FDS model and computer code. The flame is considered near the surface through which gaseous propylene is injected with a prescribed flow rate. Requirements are determined for the grid cell size in the near-wall region, which ensure sufficient spatial resolution of the boundary layer structure. It is shown that the predicted value of the total heat flux at the surface agrees with the measured results. Investigations of ignition and combustion of a vertical plate of non-charring thermoplastic (polymethylmetacrylate) with allowance for the material pyrolysis reaction show that the ignitor parameters determine the duration of the transient period, but weakly affect the growth of the heat release rate and the height of the pyrolysis region at the stage of developed burning. Significant effects of the ignitor shape, size, and temperature, as well as lateral entrainment of air on the velocity of the upward flame spread rate over the plate surface and on the shape of the pyrolysis front are revealed. The existence of critical parameters of the ignitor separating flame decay from developed burning is demonstrated. Three flame spread regimes with different pyrolysis front shapes are identified.     

高碹顶玻璃熔窑全氧燃烧火焰空间的三维数值模拟

以优化玻璃熔窑结构,提高全氧燃烧玻璃熔窑寿命为目的,建立了高碹顶玻璃熔窑全氧燃烧火焰空间中燃烧过程的三维数学模型。从模拟结果可以看出,与普通碹顶全氧燃烧玻璃熔窑相比,高碹顶熔窑改善了窑内气体流动与温度分布,碹顶温度低且分布均匀,窑内烟气环流多、在窑内停留时间长,热效率高,减少了碹顶水蒸气浓度,很好地保护了窑墙和碹顶耐火材料,延长了全氧燃烧玻璃熔窑的使用寿命;有利于促进全氧燃烧技术在玻璃工业上广泛应用。