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 INTO REDUCTION CHARACTERISTICS OF NO IN HIGH TEMPERATURE COMBUSTION PRODUCTS

The characteristics of reducing NO in high temperarure combustionproducts are studied for the control of emissions of high concentration NO_x.It showsthat the main factors affecting the reduced characteristic of NO contained in hishtemperature gases are the combustion equivalent ratio, the coulins rate of the com-bustion gas and the tempoirature level when no reductants are added. A new methodof reducing NO by injecting hydrocarbon fuels has been adopted. It is found that theresults are very effective, and the method is simple and practicable. The chemical ki-netic models of reducing NO with and without injection of reductants are developed.

Effect of yttrium and manganese addition on catalytic soot combustion activity and anti-high-temperature stability of CeO_(2) catalyst

In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO_(2) catalyst,a series of Y/Mn-modified CeO_(2) catalysts were prepared.The effects of structural properties,textural properties,oxygen vacancies,Ce^(3+),surface adsorbed oxygen species,reduction properties and desorption properties of oxygen species on the activity were analyzed by various characterization methods.The results of the activity test show that the addition of manganese is beneficial to enhancement of the activity,while the addition of yttrium increases the amount of reactive oxygen species,but decreases the activity.After aging at 700℃,the activity of the CeMn catalyst decreases most sharply,while the catalytic activity of the CeY catalyst can be maintained to a certain extent.Interestingly,the addition of yttrium and manganese at the same time can stabilize the activity.The fundamental reason is that yttrium and manganese move to the surface of the solid solution after aging,which increases the reduction performance of the catalyst,thus contributing to the increase of activity.Although the activity of CeYMn catalyst decreases after aging at 800℃,it is still higher than that of other catalysts aged at 700℃.

Dissolution-precipitation mechanism of self-propagating high-temperature synthesis of TiC-Cu cermets

The mechanism of self-propagating high-temperature synthesis （SHS） of TiC-Cu cermets was studied using a combustion front quenching method. Microstructural evolution in the quenched sample was observed using scanning electron microscope （SEM） with energy dispersive X-ray （EDX） spectrometry, and the combustion temperature was measured. The results showed that the combustion reaction started with local formation of Ti-Cu melt and could be described with the dissolution-precipitation mechanism, namely, Ti, Cu, and C particles dissolved into the Ti-Cu solution and TiC particles precipitated in the saturated Ti-Cu-C liquid solution. The local formation of Ti-Cu melt resulted from the solid diffusion between Ti and Cu particles.

Quantitative temperature imaging at elevated pressures and in a confined space with CH4/air laminar flames by filtered Rayleigh scattering

Laminar methane/air premixed flames at different pressures in a newly developed high-pressure laminar burner are studied through Cantera simulation and filtered Rayleigh scattering(FRS).Different gas component fractions are obtained through the detailed numerical simulations.And this approach can be used to correct the FRS images of large variations in a Rayleigh cross section in different flame regimes.The temperature distribution above the flat burner is then presented without stray light interference from soot and wall reflection.Results also show that the extent of agreement with the single point measurement by the thermocouple is<6%.Finally,this study concludes that the relative uncertainty of the presented filtered Rayleigh scattering diagnostics is estimated to be below 10%in single-shot imaging.

Analysis of Aluminum Dust Cloud Combustion Using Flame Emission Spectroscopy

In this study,aluminum flame analysis was researched in order to develop a measurement method for high-energy-density metal aluminum dust cloud combustion,and the flame temperature and UV-VIS-IR emission spectra were precisely measured using a spectrometer.Because the micron-sized aluminum flame temperature was higher than 2 400 K,Flame temperature was measured by a non-contact optical technique,namely,a modified two-color method using 520 and 640nm light,as well as by apolychromatic fitting method.These methods were applied experimentally after accurate calibration.The flame temperature was identified to be higher than 2 400 Kusing both methods.By analyzing the emission spectra,we could identify AlO radicals,which occur dominantly in aluminum combustion.This study paves the way for realization of a measurement technique for aluminum dust cloud combustion flames,and it will be applied in the aluminum combustors that are in development for military purposes.

Mechanism of sulfur capture during coal briquette combustion

The mechanisms of sulfur capturing during coal briquette combustion was discussed. Various factors affecting sulfur removal efficiency have been studied. Characterization of the slag left after combustion has been carried out by using X ray diffraction (XRD), Messbauer spectroscopy (MS), scanning electron microscopy (SEM), energy dispersion X ray analysis (EDAX), and electron spectroscopy for chemical analysis (ESCA). No other sulfur containing species besides CaSO 4 was found. Small amount of CaFe 3(SiO 4) 2OH, some complexes of CaO SiO 2 Fe 2O 3 and vitreous iron oxides were identified on the surface of CaSO 4 grains. This might explain the mechanism of sulfur fixation during coal briquettes combustion.

Combustion Synthesis of h-BN-SiC Ceramic Composites

The feasibility was demonstrated to fabricate h-BN-SiC ceramics through combustion synthesis of the mixture of boron carbide and silicon powders under 100 MPa nitrogen pressure. The mass fraction of BN and SiC in the combustion products were found to be 72 % and 28 % respectively. The thermodynamics of the synthesis reaction and the adiabatic combustion temperature were calculated on the theoretical ground. The bending strengths of the ceramics were measured to be 65.2 MPa at room temperature and 55 MPa at 1350℃ The phase composition and microstructure of the combustion products were identified by X-ray diffraction （XRD） and scanning electron microscopy （SEM）.

Preparation of β-SiC by combustion synthesis in a large-scale reactor

The feasibility of 5 kg β-SiC synthesized in one batch was demonstrated through igniting the mixture of Si, C-black and polytetrafluoroethylene （PTFE） under different nitrogen pressures. The effect of experimental parameters, including the contents of PTFE, nitrogen pressure, preheating, and raw materials distribution forms were investigated. The results show that the products are β-SiC with equiaxed grains. The average grain size is less than 200 nm. The powders loaded loosely promote reaction heat dispersing, resulting in small grains. High purity β-SiC powders are obtained when the PTFE content is as low as 5wt%, which simplifies the process and decreases the cost effectively. The ceramic sintered from the obtained β-SiC powders presents the hardness of 22.20 GPa, the bending strength as high as 715.15 MPa and the fracture toughness of 8.179 MPa·m^1/2, which are higher than those of ceramics fabricated with α-SiC produced by combustion synthesis.

傅里叶变换离子回旋共振质谱技术在稠油高低温氧化评价中的应用

为了认识稠油开发过程中低温氧化与高温氧化阶段原油变化规律,利用静态氧化釜开展稠油的高低温氧化实验,借助傅里叶变换离子回旋共振质谱分析技术对高低温氧化前后的原油分子量及O、N、S杂原子化合物特征开展研究,结果表明:原油低温氧化阶段分子量分布特征与原样相似,相对分子量分布范围在200~750,整体呈平缓状单峰型分布,高温氧化阶段分子量分布范围前移,呈明显的前峰单峰型分布;杂原子化合物中的O元素在低温氧化阶段主要以无环的饱和二元酸形式存在,在高温氧化阶段受环化、芳构化及脱甲基作用的影响,伴随着侧链烷基及杂原子基团的断裂和芳构化过程,造成原油中杂原子化合物向着碳数更小、双键当量(double bond equivalents,DBE)值更低的方向演化。该研究探索了温度与原油结构及化学组成之间的关系,对于指导稠油开发现场具有重要意义。

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.

孟巴矿高地温环境煤孔隙及氧化动力学特征

为预防高地温煤层开采条件下煤自燃灾害,明确煤的自燃特性,以孟巴矿Ⅵ煤层1306工作面煤样为例,将煤样分别置于40、50、60℃控温炉中恒温处理30天,采用全自动比表面积和孔径分布分析仪测试煤的孔隙结构,利用同步热分析仪测试原煤样和高温预处理煤样的氧化动力学参数。结果表明:孟巴矿煤样经高地温作用后,煤的小孔比例减小,中孔和大孔比例增大,煤样经60℃处理后比表面积由原煤的2.351 m^(2)/g增至3.285 m^(2)/g,总孔容由原煤的0.00788 mL/g增至0.01001 mL/g;与原煤相比,高地温处理后煤样点火温度和燃尽温度显著降低,最大失重量、最大失重速率分别提高6.1%和23.3%;高温处理后煤样的活化能和指前因子均小于原煤,说明高地温环境显著提高孟巴矿煤样的氧化反应活性,增大煤自燃的危险性。

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.

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.

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.

地温对不同变质程度煤自燃特征影响的实验研究

地温影响煤的自燃特征,进而影响采空区煤自燃危险区域的分布。为了探究地温对煤自燃的影响,实验选取褐煤、长焰煤和1/3焦煤为研究对象,利用热重实验获得不同温度预处理煤样在燃烧过程中重量变化情况,通过TG/DTG曲线分析特征温度点,运用积分公式计算热解阶段的活化能。实验结果表明:在相同预处理温度条件下,同一特征温度随着煤样变质程度的增加而升高;相同变质程度煤样,预处理温度越高,燃烧时的特征温度越低,尤其是干裂温度、增速温度和着火点温度降低较为显著;热解阶段活化能也降低5%~30%,说明预处理温度越高,煤氧越容易达到临界着火温度,进而达到煤自燃所需的条件,加速煤自燃进程。研究结果对高地温环境开采条件下煤自燃灾害的防治具有指导意义。

高温高压条件下含瓦斯煤解吸-自燃演化特性研究

随着矿井开拓水平的延深,煤岩赋存环境呈现出高瓦斯压力、高地温特征,而温度、压力是影响含瓦斯煤吸附-解吸-氧化特性的重要因素。为了探究高温高压下遗煤中瓦斯解吸特征及自燃特性的变化,选用高瓦斯易自燃矿井不同埋深的煤样作为试验对象,设计不同温度和压力下煤中甲烷解吸的正交试验,并对原煤样和解吸煤样进行孔隙及表面积测试、TG-FTIR联用、程序升温试验。结果表明:在整个解吸试验过程中,温度的抑制都显著大于压力的促进作用;高温高压环境主要改变了煤中的微孔结构,致使煤体的比表面积和总孔容都出现增加;解吸后,标高320 m和标高343 m煤样的温度突变点提前了8.7%和4.9%,同时虽然煤中的官能团种类相同,但含量出现了不同程度的降低;标高320 m和标高343 m解吸煤样和原煤样CO生成的交叉温度点分别为78℃和74℃,C_(2)H_(4)、C_(2)H_(6)的浓度始终低于原煤样;同时解吸煤样的耗氧量在相同煤温下出现了下降,在170℃时差距最大,标高320 m和标高343 m解吸前后煤样的氧气含量为9.3%、13.1%和10.3%、14.3%,两者的耗氧量最大相差42.3%、41.2%。综合分析表明,煤体经过高温、高压解吸后煤样在氧化初期更易自燃,产生更多的CO,可以选择CO作为指标气体,而在高温阶段反应剧烈程度有所降低。此外推导出了煤中甲烷解吸对采空区气体环境的实时变化公式,并以1304综采工作面为模型,对“高瓦斯压力、高地温”特征下采空区遗煤中瓦斯解吸影响下的“氧化带”区域进行了更细致的划分,将范围缩小了63.5%。研究成果可为高瓦斯易自燃煤层瓦斯与火耦合灾害防控提供基础支撑。

大流量高压燃烧加热器振动加速度测试分析

针对不同采样频率下(10、20、50、100、200 kHz)大流量高压燃烧加热器振动加速度差异较大的问题进行了研究,开展了冷吹试验、敲击试验、点火试验。采用时域分析法中的均方根、偏度、峭度,频域分析法中的功率谱密度,时频域分析法中的小波变换,并结合模态参数识别中的多参考最小二乘复频域法重点分析了10 kHz和200 kHz采样频率下的振动数据。获得了传感器的安装谐振频率、安装底座和待测设备组合体的固有频率以及加热器运行的主要频段,与声振频率计算公式的结果偏差小于5%。研究结果表明,采用10 kHz的采样频率能够有效表征加热器的振动情况,该方法可为大型复杂燃烧设备振动测试采样频率的选择提供参考。

某700 MW锅炉水冷壁高温腐蚀原因分析及其防治措施

针对某电厂700 MW对冲式燃烧锅炉水冷壁腐蚀严重问题,对该锅炉高温腐蚀产生的原因进行了分析。在现场割取了腐蚀的水冷壁管,对其腐蚀垢层进行了X射线衍射(XRD)、能量色散X射线谱(EDS)和扫描电镜(SEM)分析,结果发现腐蚀产物中主要含有ZnS、FeS、Fe_(7)S_(8)、Fe_(3)O_(4)和α-FeOOH,推定此炉主要为硫化物型高温腐蚀,并制定了该锅炉的防治措施。