单元熔窑燃烧过程数值模拟

对单元熔窑燃烧空间内的流动,燃烧及辐射传热等过程进行数值模拟研究,比较燃烧布置方式对火焰形状及传热过程中的影响,结果表明,对于所研究的宽度为3．2m的窑炉,燃烧器的布置应采用错排方式。     

内置稳燃热岛燃气锅炉内流动与传热数值模拟

1前言近年来,随着钢铁工业的迅猛发展,生产中的副产煤气大量增加。焦炉煤气和转炉煤气由于发热值高,可以在生产和生活中有效利用。而高炉煤气属低热值燃料,受到其燃烧特性的限制,很难作为远距离输送的生活用气,只能在企业内部转换利用[1]。为了充分利用自产的高炉煤气,国内钢铁     

Assessment of a novel numerical model for combustion and in-flight heating of particles in an industrial furnace

The key factors for efficient in-flight particle heating in a combusting flow were investigated within this paper for the development of a novel boiler slag bead production furnace. A natural gas fired industrial burner with a thermal input of 1.2?MW was thus evaluated using Computational Fluid Dynamics (CFD). The steady laminar flamelet model (SFM) and a detailed chemical reaction mechanism, considering 25 reversible chemical reactions and 17 species were used to account for the steady-state gas phase combustion. Measurements of gas temperature and flow velocity within the furnace were found to be in good accordance with the numerical results. In the second step, sintered bauxite beads were injected into the furnace as an experimental material and heated up in flight. The particle heating characteristics were investigated using the Discrete Phase Model (DPM). The computational results of the particle laden flow raised the issue that convective heat transfer is a key factor for efficient particle heating. At the burner chamber outlet, the temperature of a particle which had been injected into the burner flame was 178?K higher compared to a particle, which trajectory led through zones with lower gas temperatures.     

O2/CO2气氛下炉内煤粉切圆燃烧数值研究

对某电厂600 MW切圆燃烧锅炉进行了O2/CO2气氛下炉内流动、传热和燃烧过程的数值研究。结果表明:在O2/CO2气氛下,随着氧气摩尔浓度的增加,炉内温度升高,高温区变大,对煤粉的着火燃烧有利;但考虑到燃烧器安全和水冷壁结渣,氧气摩尔浓度不能太高,对燃用文中煤质的锅炉其极限摩尔浓度在40%至45%之间。O2/CO2气氛对现有切圆燃烧锅炉的上层燃烧器煤粉的燃烧影响较小,对下层燃烧器煤粉的燃烧影响较大。与空气气氛煤粉燃烧相比,炉内火焰中心上移,且在氧气摩尔浓度不太高时,炉内温度分布特性有利于防止水冷壁的结渣。     

马蹄形火焰玻璃熔窑燃烧空间流动与传热的数值模拟

对马蹄形火焰玻璃窑炉燃烧空间内的流动、燃烧及辐射传热等过程进行了数值模拟研究,得到了炉内燃烧空间的速度场、温度场、组分浓度分布及燃烧空间向玻璃液面传递的热流分布。探讨了燃烧空间入口的进气角度对炉内温度场和向玻璃面传递的热流的影响,模拟结果表明,当入口的进气角度在5°～10°之间时,传热效果较好。     

A study on the design of recuperative burner

Waste heat recovery from the exhaust gas of industrial furnaces and kilns that are high energy-consuming equipment is one of the effective energy conservation methods because of its high sensible heat contents. The recuperative burner integrated with a recuperator and burner is one of the combustion equipments with many advantages of simple installation, compactness and easy control which can be applied to various fields of industry. A recuperative burner with the capacity of 400 kW was designed using the design data from experimental results. Performance tests on this burner were made. The exhaust gas analysis, including NO_x, the measurement of the flame temperature, velocity, heat flux and heat flux analysis on the recuperative burner were the main topics of hot combustion tests. Design data from the experimental results are gas velocity, air velocity, air velocity, the tip-location of gas nozzle, the dimension of furnace suitable to burner capacity, the dimension of recuperator and the role of cross-shaped steel plate for increasing the energy efficiency in the recuperator. For uniform temperature distribution and good thermal efficiency, it is appropriate to maintain the furnace pressure at 2–3mmAq. © 1998 John Wiley & Sons, Ltd.     

Numerical studies on heat coupling and configuration optimization in an industrial hydrogen production reformer

Steam methane reforming furnaces are the most important devices in the hydrogen production industry. The highly endothermic reaction system requires reaction tubes in the furnace to have a large heat transfer area and to be operated under high temperature and pressure conditions. In order to enhance heat transfer efficiency and protect reaction tubes, the controlling and optimization of the furnace structure have increasingly received more and more research attention. As known from the furnace structure, it is essential to couple the exothermic combustion with the endothermic reforming reactions due to the highly interactive nature of the two processes. Thus, in this paper, the combustion process in the furnace was numerically studied by using computational fluid dynamics (CFD) to model the combustion chamber, coupled with methane steam reforming reaction inside the reaction tubes, defined by a plug flow model. A set of combustion models were compared for the furnace chamber and a plug flow reaction model was employed for reforming reaction tubes, and then a heat coupling process was established. The predicted flue gas temperature distribution showed that the heat transfer in the furnace was not uniform, resulting in hot spots and heat losses on the tube wall. Therefore, structure optimization schemes were proposed. Optimization on arrangements of the tubes and the nozzles promoted the uniform distribution of flue-gas temperature and then improved heat transfer efficiency, thereby enhancing performance of the steam reforming process.     

The study on the heat transfer characteristics of oxygen fuel combustion boiler

According to 350MW and 600MW boilers, under oxygen fuel condition, through the reasonable control of the primary and secondary flow and the correct option and revision of mathematical model, the temperature distribution, heat flux distribution and absorption heat distribution, etc. was obtained which compared with those under air condition. Through calculation, it is obtained that the primary and secondary flow mixed well, good tangentially fired combustion in furnace was formed, the temperature under air condition obviously higher than the temperature under O26 condition. The adiabatic flame temperature of wet cycle was slightly higher than that of dry cycle. The maximum heat load appeared on the waterwall around the burner area. The heat load gradually decreased along the furnace height up and down in burner area. The heat absorption capacity of the furnace under O26 was lower than that under the air condition. The heat absorption capacity of the platen heating surface under O26 was equal to that under air condition. And the heat absorbing capacity of waterwall under O26 was about7%~12% less than that under air condition.     

横火焰玻璃窑炉燃烧空间流动与传热的数值模拟

对横火焰玻璃窑炉燃烧空间内的流动、燃烧及辐射传热等过程进行了数值模拟研究,建立了玻璃窑炉燃烧空间内的综合数学模型,给出了诸控制方程的统一的数值解法,得到了炉内燃烧空间的速度场、温度场、组分浓度分布及燃烧空间向玻璃液面传递的热流分布。     

蓄热式连续加热炉内流动与换热特性的数值模拟

以某公司大方坯蓄热式连续加热炉为研究对象,对该炉建立了三维物理数学模型,分别采用可实现双方程湍流模型,PDF非预混燃烧模型、离散坐标法辐射模型(DO模型),应用Fluent数值仿真软件进行了模拟研究,得到了蓄热式连续加热炉内的流场和温度场的分布规律,并对炉内对流换热系数的分布进行了详细的分析研究.结果表明:钢坯表面局部对流换热系数在各加热段内分布不均匀,这主要是由于烧嘴进口射流所引起的局部流速的差异性,从整体上来看,预热段和加热1段的对流换热系数要高于其它各段.     

A simplified numerical approach to hydrogen and hydrocarbon combustion in single and double-layer porous burners

Motivated by the fuel hydrogen applications in porous combustors, as well as hydrogen production in syngas porous devices, this work shows a simplified one-dimensional, steady state heat and mass transfer model for stabilized premixed flames in porous inert media. Single-layer and double-layer porous burner are studied. The model has three conservation equations, describing the heat transfer in the solid and fluid phases and the mass transfer in the reacting flow. The model considers a plug flow and is solved numerically by using the finite volume method. The results are compared with benchmark data, depicting the superadiabatic flames and the heat recirculation process. A parametric analysis of the model reveals the effects of the porous media properties and the Lewis and Peclet numbers on the heat and mass transfer processes. Furthermore, the effects of the flame stand-off parameter in double layer porous burner are also analyzed. The results have considered the values of the dimensionless parameters based on reference data for hydrogen/air and methane/air combustion in porous burners built with SiC and Al₂O₃.     

Heating and Flow Analysis in Hot‐Rolled Stainless Strip Continuous Annealing Furnace Based on CFD Modeling

A three‐dimensional mathematical model was found for a continuous annealing furnace, the temperature field, and flow field of the furnace and the temperature of the stainless strip could be calculated by using this model. The simulation results were compared with measured data and the accuracy of the model was proved by the predicted temperature distribution. By using this model, the convective heat transfer coefficient and equivalent radiation heat transfer coefficient of the strip surface were also analyzed.     

蜂窝蓄热体易损原因分析及其解决措施

针对加热炉采用的蜂窝蓄热体出现的问题,从材质性能、炉内实际情况、结构等方面分析出其破损原因。并设计一种新型的蓄热式烧嘴,通过热态试验对其换热性能与普通蓄热烧嘴进行了比较,表明采用这种新型烧嘴是解决蓄热体破损的有效措施之一。     

Novel Approach to Estimate the Optimum Zone Fuel Mass Flow Rates for a Walking Beam Type Reheating Furnace

Three-dimensional numerical simulation is performed to predict the heat transfer performance in a walking-beam reheating furnace. The furnace uses a mixture of coke oven gas as a heat source to reheat the slabs. The fuel is injected into the furnace at four zones: preheating zone, first heating zone, second heating zone, and soaking zone. This numerical model considers turbulent reactive flow coupled with radiative heat transfer in the furnace; meanwhile, the conductive heat transfer dominates the energy balance inside the slabs. An initial iterative method is proposed to estimate the fuel mass flow rate at each zone of the reheating furnace, while the required heating curve of the slabs is specified. In addition, a simplified two-dimensional numerical model is performed to estimate the fuel mass flow rate for the consideration of computational time consummation. The results of the two-dimensional numerical simulations are compared with those of three-dimensional numerical simulation and the in situ data. Furthermore, velocity and temperature distributions are examined for two cases under different heating curves of the slabs.     

The impact of bed temperature on heat transfer characteristic between fluidized bed and vertical rifled tubes

In the present work, the heat transfer study focuses on assessment of the impact of bed temperature on the local heat transfer characteristic between a fluidized bed and vertical rifled tubes (38mm-O.D.) in a commercial circulating fluidized bed (CFB) boiler. Heat transfer behavior in a 1296t/h supercritical CFB furnace has been analyzed for Geldart B particle with Sauter mean diameter of 0.219 and 0.246mm. The heat transfer experiments were conducted for the active heat transfer surface in the form of membrane tube with a longitudinal fin at the tube crest under the normal operating conditions of CFB boiler. A heat transfer analysis of CFB boiler with detailed consideration of the bed-to-wall heat transfer coefficient and the contribution of heat transfer mechanisms inside furnace chamber were investigated using mechanistic heat transfer model based on cluster renewal approach. The predicted values of heat transfer coefficient are compared with empirical correlation for CFB units in large-scale.     

Numerical Study of the Performance of a Regenerative Furnace

In the present study, the numerical simulation of reactive turbulent flow and heat transfer in a regenerative gas-fired furnace has been carried out to investigate its performance. The effects of geometric and operating conditions on the performance of the furnace have also been studied. A moment closure method with an assumed g probability density function for mixture fraction is used in the present work to model the turbulent nonpremixed combustion process in the furnace. A comparison is made between the predicted results and the experimental data.     

热风炉提高风温的几点浅见

综述了热风炉提高风温的主要途径：采用空煤气预热和高效能陶瓷燃烧器技术提高理论燃烧温度和拱顶温度;增大单位体积格砖的换热面积和采用均匀配气技术加强蓄热室内的热交换;同时在热风炉的不同部位选用不同材质的耐火材料,实现良好的保温效果;在此基础上适当缩短送风周期时间,并采用合理的操作制度。适当评价了各种技术对提高风温的效果。     

圆形铝熔炼炉内非稳态热工过程数值模拟

针对铝熔铸过程中常用的圆形铝熔炼炉,利用FLUENT软件,根据能量守恒方程、动量方程建立铝熔炼炉内热工过程数学模型,采用标准k-ε湍流模型、P-1辐射模型对铝熔炼炉内非稳态传热及流动过程进行数值模拟研究。考虑到铝料熔化过程会消耗一部分能量,采用等效比热法将铝料的熔化潜热转换为相应的比热值进行计算。通过数值模拟得到了炉内流场、炉膛及铝料温度场分布情况。模拟结果与实际情况相符,为铝熔炼炉的设计与优化研究提供了理论依据。     

Assessment of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces

The present study investigates the application of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces and their economic potential for decreasing carbon dioxide emissions in this field of application. Doing so, a detailed technological analysis of several influencing parameters on the heating system was performed as well as a consideration of furnace heating technology challenges. Starting with an evaluation of the main thermophysical properties of the blends and their corresponding flue gases, requirements for the heating systems were identified. Potential ways of decreasing flue gas losses and increasing the heat transfer are shown. In the radiant tube application, an increased overall combustion efficiency of about 1.2% was measured at 40 vol% hydrogen in the fuel gas. Influences on the air to gas ratio control system of the furnace is a further important point, which was considered in this study. Two commonly used control systems were evaluated concerning their capabilities to regulate the gas flow rates of blends with varying hydrogen contents and combustion properties, such as Wobbe Index. This is important, since it shows the capability to retrofit existing furnaces. Two types of burners were tested with different natural gas/hydrogen blends. This includes an open jet burner with air-staged and flameless combustion operation modes. A recuperative burner for radiant tube application was considered as well in these tests. Doing so, the nitrogen oxide formation of both systems under different operating conditions and different fuel blends were evaluated. An increase by about 10% at air-staged combustion and about 100% at flameless combustion was measured by a hydrogen content of 40 vol% in comparison to pure natural gas firing. Finally, the additional fuel costs of natural gas hydrogen blends and different cases are presented in an economic analysis. The driving force for the use of hydrogen as a fuel is the price of the CO2 certificates, which are considered in the analysis at a current price of 25.2 €/t CO2.