Numerical Simulation of High Temperature Air Combustion Flames Properties

High temperature air combustion (HTAC) is an attractive technology of saving energy and controlling environment. The mathematical models of turbulent jet flame under the highly preheated air combustion condition are conducted in the paper. The mixture fraction/probability density function model is employed. The results show that the maximum flame temperature is decreased, the temperature in the HTAC furnace is more uniform than that in the conventional furnace, and the NO x emission is low. The numerical results are partially validated by some experimental measurements.

Numerical simulation of high temperature air combustion in aluminum hydroxide gas suspension calcinations

The high temperature air combustion(HiTAC) process in gas suspension calcinations(GSC) was studied by using a CFD software FLUENT that can simulate the three-dimensional physical model of GSC with the k-epsilon turbulent viscous model, PDF non-premixed combustion species model, P1 radiation model, thermal and prompt NO pollution model. The simulation vividly describes the distributions of the temperature, velocity and consistency fields. Finally, the optimal operation conditions and igniter configuration of particular fuel combustion are obtained by analyzing and comparing the simulation results. And the emission quantity of NOx, CO and CO2 deduced from computation can play a role as reference. These optimal and estimated values are beneficial to practical operation.

Investigation on Combustion Characteristics and NO Formation of Methane with Swirling and Non-Swirling High Temperature Air

Combustion characteristics of methane jet flames in an industrial burner working in high temperature combustion regime were investigated experimentally and numerically to clarify the effects of swirling high temperature air on combustion.Speziale-Sarkar-Gatski(SSG) Reynolds stress model,Eddy-Dissipation Model(EDM),Discrete Ordinates Method(DTM) combined with Weighted-Sum-of-Grey Gases Model(WSGG) were employed for the numerical simulation.Both Thermal-NO and Prompt-NO mechanism were considered to evaluate the NO formation.Temperature distribution,NO emissions by experiment and computation in swirling and non-swirling patterns show combustion characteristics of methane jet flames are totally different.Non-swirling high temperature air made high NO formation while significant NO prohibition were achieved by swirling high temperature air.Furthermore,velocity fields,dimensionless major species mole fraction distributions and Thermal-NO molar reaction rate profiles by computation interpret an inner exhaust gas recirculation formed in the combustion zone in swirling case.

Numerical Simulation of Combustion Characteristics in High Temperature Air Combustion Furnace

The influences of air preheating temperature, oxygen concentration, and fuel inlet temperature on flame properties, and NOx formation and emission in the furnace were studied with numerical simulation. The turbulence behavior was modeled using the standard k-ε model with wall function, and radiation was handled using discrete ordinate radiation model. The PDF （probability density function） /mixture fraction combustion model was used to simulate the propane combustion. Additionally, computations of NOx formation rates and NOx concentration were carried out using a post-processor on the basis of previously calculated velocities, turbulence, temperature, and chemical composition fields. The results showed that high temperature air combustion （HiTAC） is spread over a much larger volume than traditional combustion, flame volume increases with a reduction of oxygen concentration, and this trend is clearer if oxygen concentration in the preheated air is below 10%. The temperature profile becomes more uniform when oxygen concentration in preheated air decreases, especially at low oxygen levels. Increase in fuel inlet tempera- ture lessens the mixing of the fuel and air in primary combustion zone, creates more uniform distribution of reactants inside the flame, decreases the maximum temperature in furnace, and reduces NOx emission greatly.

The Experimental Study on Regenerative Heat Transfer in High Temperature Air Combustion

For the purpose of decomposing the processing gases CF4 from semiconductor manufacturers, ceramic honeycomb regenerative burner system is suggested by using the principle of HTAC. A simulated high temperature air combustion furnace has been used to determine the features of HTAC flames and the results of the decomposition of CF4. The preheat air temperature of it is above 900℃. The exhaust gas released into the atmosphere is lower than 150℃. Moreover, the efficiency of recovery of waste heat is higher than 80%, the NOx level in exhaust gas is less than 198 mg/m3 and the distribution of temperature in the furnace is nearly uniform. The factors influencing on heat transfer, temperature profile in chamber and NOX emission were discussed. Also some CF4 can be decomposed in this system.

Numerical Simulation on Pulverized Coal Combustion and NO_x Emissions in High Temperature Air from Circulating Fluidized Bed

High temperature air combustion is a prospecting technology in energy saving and pollutants reduction. Numerical simulation on pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed was presented. The down-fired combustor, taken as the calculation domain, has the diameter of 220 mm and the height of 3000 mm. 2 cases with air staging combustion are simulated. Compared the simulation results with experimental data, there is a good agreement. It is found that the combustion model and NOx formation model are applicable to simulate the pulverized coal combustion and NOx emissions in high temperature air from circulating fluidized bed. The results show that there is a uniform temperature profile along the axis of the down-fired combustor. The NOx emissions are lower than those of ordinary pulverized coal combustion, and the NOx emissions are 390 mg/m3 and 352 mg/m3 in Case 1 and Case 2, respectively. At the range of 300-600 mm below the nozzle, the NO concentration decreases, mainly resulting from some homogeneous reactions and heterogeneous reaction. NO concentration has a little increase at the position of 800 mm below the nozzle as the tertiary air supplied to the combustor at the position of 600 mm below the nozzle.

Dynamic simulation on effect of flame arrangement on thermal process of regenerative reheating furnace

By analyzing the characteristics of combustion and billet heating process, a 3-D transient computer fluid dynamic simulation system based on commercial software CFX4.3 and some self-programmed codes were developed to simulate the thermal process in a continuous heating furnace using high temperature air combustion technology. The effects of different switching modes on injection entrancement of multi burners, combustion and billet heating process in furnace were analyzed numerically, and the computational results were compared with on-site measurement, which verified the practicability of this numerical simulation system. The results indicate that the flow pattern and distribution of temperature in regenerative reheating furnace with partial same-side-switching combustion mode are favorable to satisfy the high quality requirements of reheating, in which the terminal heating temperature of billets is more than 1 460 K and the temperature difference between two nodes is not more than 10 K. But since the surface average temperature of billets apart fi＇om heating zone is only about 1 350 K and continued heating is needed in soaking zone, the design and operation of current state are still needed to be optimized to improve the temperature schedule of billet heating. The distribution of velocity and temperature in regenerative reheating furnace with same-side-switching combustion mode cannot satisfy the even and fast heating process. The terminal heating temperature of billets is lower than that of the former case by 30 K. The distribution of flow and temperature can be improved by using cross-switching combustion mode, whose terminal temperature of billets is about 1 470 K with small temperature difference within 10 K.

An Experimental Study on High Temperature and Low Oxygen Air Combustion

High temperature preheated and diluted air combustion has been confirmed as the technology, mainly applied to industrial furnaces and kilns, to realize higher thermal efficiency and lower emissions. The purpose of this study was to investigate fundamental aspects of the above-mentioned combustion experimentally and to compare with those in ordinary hydrocarbon combustion with room temperature air. The test items were exhaust gas components of CO, NOx, flame shape and radical components of CH, OH and C2,which were measured with gas analyser, camera and ICCD(Intensified Charged - Coupled Device) camera. Many Phenomena as results appeared in combustion with the oxidizer, low oxygen concentration and extremely high temperature air, such as expansion of the flammable limits, increased flame propagation speed, it looked so strange as compared with those in existing combustion technology. We confirmed that such extraordinary phenomena were believable through the hot-test experiment.

深井酸性浸水煤层风干氧化自然发火特性分析

为探究深井酸性浸水煤层风干氧化自然发火的特性,选取陕西省某矿煤样,利用氧化模拟试验系统,对预氧化及浸水风干煤样和原煤样进行程序升温试验,对比分析了两者的耗氧量以及CO、CO 2、CH 4的产生量,进而分析这几种不同情况下煤样的氧化自燃特性。结果表明,酸性条件下浸水风干的煤样耗氧量最小,说明该煤样在氧浓度低时容易发生氧化自燃;酸性条件下浸水风干的煤样CO、CO 2、CH 4的产生量最大,说明该煤样发生氧化自燃的危险性越大。总之,当煤体处于高地温、弱酸性浸水风干条件下发生煤体氧化自燃的危险性最大,研究结论可为矿井高产高效和安全生产提供一定的指导。

预热温度影响甲烷高温空气燃烧特性的数值分析

为了深入认识近年发展起来的一种新型燃烧技术－高温空气燃烧的机理和超低氮氧化物排放特性，本文将扩散燃烧模型、热力ＮＯ生成模拟与完全湍流Ｎ－Ｓ方程相结合，数值研究了甲烷高温燃烧的火焰特性、空气预热温度对燃烧特性和ＮＯ排放浓度的影响规律。研究结果与实验数据符合良好，为在我国发展这项技术提供了依据。

低热值煤气高温空气燃烧数值模拟

采用k -ε湍流双方程模型、PDF燃烧模型以及离散坐标辐射传热模型 ,对低热值煤气高温空气燃烧过程进行了计算机辅助模拟试验 ,比较了不同预热温度和不同过量空气系数对低热值煤气燃烧过程的影响 。

高温空气燃烧NO_x排放特性的试验研究

通过两种结构烧嘴的热态燃烧试验对比,研究了烧嘴结构、燃气射流速度、过量空气系数对高温空气燃烧过程氮氧化物排放的影响特性。研究结果认为:在燃气喷口两侧布置两个矩形空气喷口的烧嘴,氮氧化物排放量低于圆形空气喷口烧嘴;随着燃气射流速度的提高,高温空气燃烧过程排放的氮氧化物逐渐减少。与普通燃烧过程不同的是,随着过量空气系数的提高,在一定范围内高温空气燃烧的氮氧化物排放量不断增加。分析认为,高温空气燃烧氮氧化物排放量与火焰体积、炉内氧气与燃气混合过程以及燃气射流和空气射流对炉内烟气的卷吸量有关。

甲烷／空气预混气体火焰的传播特征

利用高速纹影摄像等技术探讨了密闭管道内不同当量比的甲烷/空气预混气体火焰的传播特征。结果表明,当甲烷含量接近当量值时,预混气体火焰传播中会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程,逐渐由层流燃烧转变成湍流燃烧,并形成Tulip火焰结构;当甲烷含量偏离当量值一定程度时,预混火焰呈现出典型的层流燃烧特征,不会发生火焰阵面由向未燃区弯曲到向已燃区弯曲的转折过程。Tu-lip火焰结构形成于火焰传播速度迅速降低的区间里,且只有当减速阶段的最大加速度的绝对值大于某一数值时才能形成;Tulip火焰结构是预混火焰由层流燃烧向湍流燃烧转变的一个中间过程。

注空气开采过程中稠油结焦量影响因素

通过建立油藏高温、高压反应模拟实验装置,物理模拟了稠油注空气开采过程中焦炭的生成过程,研究了反应气氛、温度、压力以及空气通风强度对稠油生焦量的影响。研究表明:在空气气氛下,原油低温氧化显著促进了焦炭生成,5 MPa反应压力下,每克稠油最高焦炭生成量为0.375g,是氮气气氛下最高生焦量的2.5倍,焦炭初始生成温度受低温氧化影响比氮气条件降低了近200℃。随压力升高,加剧的低温氧化反应提高了焦炭生成量,但是5 MPa后压力影响不再显著。随空气通风强度增加,生焦量并非持续增加,而是在33.4 N·m3/(m2·h)附近存在极值。进一步对比分析了焦炭的高温氧化消耗与原油组分蒸馏失重对焦炭生成量的影响。其结果表明,焦炭氧化是空气气氛下温度自225℃升高至300℃过程中焦炭净生成量减少的主要原因。在氮气气氛下,随温度升高至450℃,加剧的原油热解缩聚反应增加了生焦量,但温度进一步升高引起焦炭自身热解失重,生焦量降低。另外,实验还发现,当温度超过200℃时,反应管内油砂中心温度超过外壁面加热控制温度。分析表明,超温现象由原油组分的低温氧化和部分活性较强的焦炭高温氧化引起,因此该稠油存在油层自燃点火的应用潜力。

低NO_x高温空气燃烧技术

低NOx高温空气燃烧技术将传统的低NOx 燃烧技术与高温蓄热式燃烧系统有机地结合起来 ,具有热效率高、炉内温度分布均匀、NOx 排放量低等特点。本文介绍了高温空气燃烧技术 ,重点分析了高温空气燃烧技术中的低NOx排放的原理 。

U型蓄热式辐射管表面温度分布数值模拟研究

以一支燃烧能力为 5 8kW的蓄热式辐射管为对象 ,利用商业CFD软件CFX4 3对蓄热式辐射管表面温度分布进行数值模拟 ,并进行试验验证 ,重点分析了辐射管沿长度方向温度分布的规律及其影响因素。结果表明 ,高速煤气射流产生的湍动燃烧动力 ,能搅拌炉膛、消除炉内的温差 ,有利于提高烟气的加热能力 ,改善其加热性能。但煤气喷射速度不能无限制增大 ,对于该类型的蓄热式辐射管燃烧器 ,煤气喷射速度可限制在 80m/s～ 1 1 0m/s。

高温空气发生器热态实验研究

介绍了高温空气发生器热态实验研究的实验方法和仪器，进行了高温空气发生器热态实验研究，实验结果表明：高温空气发生器的基本性能满足系统设计要求，并获得了大量的实验数据；根据实验数据分析了空气预热温度、排烟温度、炉温、切换时间之间的变化关系，研究了空气预热温度、切换时间对烟气中NOx排放的影响，并且获得了高温空气发生器重要的性能参数，为深入研究生物质高温空气气化系统作好了充分的准备。

高温空气燃烧新型锅炉及特性分析

介绍了采用高温空气燃烧技术的新型锅炉 ,其关键部件包括蜂窝陶瓷蓄热体、实现分级燃烧和炉内烟气再循环的燃烧器及四通高频切换阀。详述了其工作原理及过程 ,探讨了开发该锅炉的基本思路 ,对其基本特性进行了分析 。

换向方式对蓄热式加热炉热过程影响数值模拟

基于商业软件CFX4.3和自编程序,建立了三维非稳态HTAC加热炉内热过程的CFD仿真系统,并以国内某HTAC加热炉为对象,分析了不同的换向燃烧组织方式对HTAC加热炉内多烧嘴喷射射流的卷吸、燃烧现象以及钢坯在炉内的加热过程的影响。结果表明:采用分段同侧换向控制的HTAC加热炉能获得很好的流场和温度场分布,基本满足高质量的钢坯加热需要,但该炉在生产条件下的温度制度存在不合理之处,在今后设计和操作中应进一步优化和改进;全同侧换向控制的火焰布置方式不利于钢坯的均匀、快速加热;而采用交叉换向控制的火焰布置方式可以改善加热炉内的流场和温度分布,更有利于满足钢坯的加热工艺要求。

高温空气煤粉直燃技术的数值模拟

本文通过数值计算的方法,对高温空气煤粉直燃燃烧器的多种运行工况进行了数值试验研究,分析了煤粉气流入口速度、煤粉浓度和高温空气速度等主要因素对煤粉气流着火的影响,模拟结果还可以反映出高温空气无油点火燃烧器内的流动、燃烧和传热情况。与试验数据的对比分析表明,数值模拟结果与试验数据趋势一致。研究结果对此燃烧器的结构及运行参数的优化提供了指导。