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。     

燃天然气浮法玻璃窑炉的三维数值模拟

建立了具有实用意义的浮法玻璃熔窑三维数学模型,将火焰空间燃烧模型、配合料熔化模型、玻璃液流动模型进行耦合计算,求解出玻璃熔窑火焰空间、玻璃液流的温度场、速度场分布及配合料堆的长度分布。以日产400t的燃天然气浮法玻璃熔窑为对象研究了其火焰空间内气体、窑池内玻璃液的流动情况及各自的温度场分布。从模拟结果可以看出,该三维耦合数学模型能够比较客观地反应燃天然气浮法玻璃熔窑的速度场和温度场的分布规律,对燃天然气浮法玻璃熔窑的设计和运行具有一定的实用价值。     

Effects of air excess control in a heat storage solid fuel-fired household furnace

Due to a significant increase in electricity prices during the last decade and insufficient production capacity of the electric power industry in Serbia, many households that are currently using electric heat storage furnaces for heating have been forced to find an alternative solution for heating. A possible solution is replacing electric heating appliances with similar solid fuel-fired ones. Existing solid fuel-fired furnaces are often unsatisfactory with respect to their efficiencies and flue gas emissions. A prototype of a new concept of heat storage, solid fuel-fired furnace has been developed to meet these growing needs, providing electricity saving together with considerable environmental benefits. In order to examine furnace performance, efficiency and environmental aspects, and to assess the influence of air excess control in the furnace on the efficiency and flue gas emissions, numerous experimental tests were conducted. The amount of combustion air, the flue gas flow rate and the fuel feeding regime have been adjusted in order to keep the flue gas oxygen content in a relatively narrow range, thus obtaining controlled combustion conditions and, correspondingly, lower carbon monoxide emission and higher furnace efficiency. In this way, the furnace was made able to respond to the changes in heating needs, fuel quality and other parameters, which is considered to be advantageous in comparison with similar solid-fuel fired furnaces.     

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。     

Numerical simulation of the combustion processes in a W‐shaped boiler furnace under different operating conditions

Numerical simulations of gas–solid flows, heat transfer and gas–particle turbulent combustion have been conducted for a three‐dimensional, W‐shaped boiler furnace. The gas–particle flow, distributions of temperature and concentrations of gaseous constituents, distributions of the rates of heat release, burnout rates of coal particles, and formations of volatiles have been predicted. The results indicate that a steady high‐temperature zone is formed under the arch of the W‐shaped flame boiler, this zone would be of benefit to the ignition and carbon burn‐out and suggest that the W‐shaped flame boiler is suitable for burning low‐quality coals and can operate well under different operating conditions for full and partial loads. Copyright © 1999 John Wiley & Sons, Ltd.     

A statistical model for predicting the fluid displaced/added mass and displaced heat capacity effects on transport and heat transfer of arbitrary-density particles in turbulent flows

The objective of the paper is twofold: (i) to present a new statistical model for predicting the transport and heat transfer of arbitrary-density particles suspended in turbulent flows and (ii) to examine the performance of this model in an isotropic velocity flow field without and with a mean temperature gradient as well as in a near-wall turbulent flow. The model presented is based on a kinetic equation for the probability density function (PDF) of velocity and temperature distributions and coves the entire range of the particle-to-fluid density ratio (from heavy particles in a gas to bubbles in a liquid).     

Instrumentation techniques for studying heterogeneous combustion

Diagnosis of heterogeneous combustion systems requires the measurement of physical and chemical properties in flames laden with liquid and solid particles. For liquid-fuelled combustors, the characteristics of the spray require to be determined, including the trajectories of individual droplets and their interaction with gas streams. Vaporization rates can be determined from measurement of the rate of change of diameter of individual droplets. Particulate matter emitted from combustion chambers is mainly in the solid phase and consists of both unburned fuel and non-burnable material. With heavy fuel oils, particles of the order of 100 μm can be emitted while, for the lighter fuels, particulate emissions are mainly in the sub-micron size region. The laser anemometer can be used for simultaneous measurement of velocity and particle size of individual droplets and particles in spray flames. Laser diffraction techniques can be used for measurement of over-all size distributions. Laser Raman spectroscopy offers the possibility of simultaneous measurement of temperature and species concentration in flames. Presence of particles results in laser irradiated particulate heating and incandescence, which can lead to the swamping of signals. The use of coherent anti-Stokes Raman and near-resonant Raman offers possibilities for making laser Raman measurements in particle laden flames.Solid probes for measuring temperature and species concentration require special adaptation when used in particle laden flows. Particles may damage probes by direct impingement and cause blockage of orifices. Thermocouples can be used in sprays, but the effects of direct droplet impingement must be considered. Diagnostic techniques have been developed in which thermocouple signals are digitized and recorded on a computer. This system permits the rapid measurement of time constants and, subsequently, digital frequency compensation of temperature time histories, providing a frequency response of the order of 1 kHz. Information on spray boundaries is provided by both laser anemometer and thermocouple measurements. Gas sampling probes, specially designed to separate liquid and solid particles from the gas, are used for removal of samples from within the flame. Size analysis of particles is made by microphotography and computer image analyser. Species concentration in the gas is measured by gas phase chromatography, flame ionization detectors, non-dispersive infrared and ultraviolet detectors and chemiluminescent analysers.All measurement diagnostic techniques are affected by the presence of large-scale coherent eddy structures in the turbulent flow systems. The need for increasing frequency response, recording and analysis of variations with time, and the use of conditional sampling in intermittent flows is emphasized. The coupling of high-speed movies with laser optical proves to give simultaneous recording of visual and signal events is recommended.     

An investigation of the combustion of pulverized coal-air mixture in different combustor geometries

A two-dimensional theoretical study of the flow and combustion of pulverized coal by diffusion flames is presented. The model predicts gas flows, species concentrations, and temperatures in combustors having specific geometries. The conservation equations are solved utilizing the κ-ε turbulence model. Coal devolatilization is modeled by the two-competing-reactions scheme, which generates two sets of volatiles and char, each by a specific rate constant, described in Arrhenius form. Char combustion from devolatilization occurs by reaction with oxygen, carbon dioxide, water, particle dispersion, and radiative heat transfer between furnace wall and particles. The model is used to investigate the interaction between flow and combustion in flames produced by arranging the locations of the primary inlet and the secondary air inlets in a furnace. The predictions, which could be valuable for designing furnaces, indicate that a centered primary inlet and a minimum recirculation are some of the criteria that could favorable for combustion.     

Computational model to predict thermal dynamics of planar solid oxide fuel cell stack during start-up process

Solid oxide fuel cell (SOFC) systems have been recognized as the most advanced power generation system with the highest thermal efficiency with a compatibility with wide variety of hydrocarbon fuels, synthetic gas from coal, hydrogen, etc. However, SOFC requires high temperature operation to achieve high ion conductivity of ceramic electrolyte, and thus SOFC should be heated up first before fuel is supplied into the stack. This paper presents computational model for thermal dynamics of planar SOFC stack during start-up process. SOFC stack should be heated up as quickly as possible from ambient temperature to above 700 °C, while minimizing net energy consumption and thermal gradient during the heat up process. Both cathode and anode channels divided by current-collecting ribs were modeled as one-dimensional flow channels with multiple control volumes and all the solid structures were discretized into finite volumes. Two methods for stack-heating were investigated; one is with hot air through cathode channels and the other with electric heating inside a furnace. For the simulation of stack-heating with hot air, transient continuity, flow momentum, and energy equation were applied for discretized control volumes along the flow channels, and energy equations were applied to all the solid structures with appropriate heat transfer model with surrounding solid structures and/or gas channels. All transient governing equations were solved using a time-marching technique to simulate temporal evolution of temperatures of membrane-electrode-assembly (MEA), ribs, interconnects, flow channels, and solid housing structure located inside the insulating chamber. For electrical heating, uniform heat flux was applied to the stack surface with appropriate numerical control algorithm to maintain the surface temperature to certain prescribed value. The developed computational model provides very effective simulation tool to optimize stack-heating process minimizing net heating energy and thermal gradient within the stack.     

Convective heat transfer to water containing bubbles: Enhancement not dependent on thermocapillarity

Upstream injection of small gas bubbles causes increases of up to 50 per cent in heat-transfer coefficient for water flowing upward in a channel of rectangular cross-section. The increase depends on gas flow rate and liquid phase Reynolds number but not on heat flux, indicating that thermocapillary flows do not contribute to the heat transfer. A possible mechanism for the increase is secondary flow production by the interaction of bubbles with the shear flow near the wall.     

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.     

阳极焙烧炉燃烧煤气和天然气的数值比较

针对燃烧低热值煤气的阳极焙烧炉炉内情况，采用数值模拟的方法和CFD软件进行了计算和分析，并探讨了将燃料改为高热值天然气的可行性．通过比较煤气和天然气的燃烧计算结果，指出燃烧煤气的阳极焙烧炉改为燃烧天然气，可以解决煤气燃烧速度过快导致的炉内温度分布不均匀的问题．     

不同富氧含量玻璃熔窑火焰空间温度场的对比

建立了玻璃熔窑火焰空间温度场的三维数学模型，通过对某日产400t燃油浮法玻璃熔窑火焰空间在三种富氧情况(氧含量分别是24％，27％，30％)下用图像模拟直观的表述出计算结果。模型包括气相流动与传热模型，雾化油滴燃烧的轨道模型，和辐射传热模型。程序采用MS-FORTRAN语言，绘图采用Stanfordgraphic软件。对比结果表明，随着富氧含量的增加，各小炉火焰长度明显缩短，温度显著提升，模拟结果对窑炉设计与富氧燃烧组织有一定的参考价值。     

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     

板坯加热炉内常规燃烧与富氧燃烧数值计算对比分析

以某公司热轧厂板坯加热炉为研究对象,建立该加热炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,重点对比分析了常规燃烧和富氧燃烧特性,得到了各自的炉内速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与“黑匣子”实验测量数据吻合良好.总结出的富氧燃烧...     

CFB垃圾焚烧炉绝热炉膛热平衡计算及燃烧特性分析

针对降低CFB垃圾焚烧炉辅助燃煤掺混比例的实际需要,提出垃圾焚烧炉绝热炉膛燃烧方案,通过炉膛热平衡计算,计算出热值在3 558～4 605 kJ/kg(850～1 100 kcal/kg)范围内6组不同热值垃圾在绝热炉膛内的燃烧温度,结果表明:有无外置式换热器时的炉膛燃烧温度相差40～60℃,无外置式换热器时,垃圾热值3 768 kJ/kg即可达到850℃燃烧温度;有外置式换热器时,垃圾热值4 396 kJ/kg才能达到。这对于纯烧生活垃圾焚烧炉设计有重要指导意义。     

全燃和掺燃高炉煤气炉的比较研究

由于高炉煤气中含有大量的惰性气体 ,可燃成分少 ,发热值低 ,燃料产物的体积流量大 ,因而使大容量高压燃煤气锅炉各受热面的传热特性与燃煤锅炉相比发生很大的变化。针对 5 0MW高压锅炉全燃和掺燃高炉煤气2种炉型的特点进行了详细的分析讨论 ,并与燃煤锅炉进行了比较研究 ,阐述了燃用高炉煤气锅炉的热工参数、传热特性以及受热面布置的特点 ,为研究和设计燃用高炉煤气炉提供了可靠的实践数据和理论依据。     

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.     

Numerical study of different gas–solid flow regimes effects on hydrodynamics and heat transfer performance of a fluidized bed reactor

In this study, a two‐?uid Eulerian–Eulerian model has been carried out applying the kinetic theory of granular flow (KTGF) to study the hydrodynamics and heat transfer behavior of a fluidized bed reactor simultaneously. The effects of different gas–solid flow regimes on the operating conditions and heat transfer rate between the hot air and two types of low and high‐density inert particles are investigated in a fluidized bed dryer. Different gas–solid flow regimes for wood and glass particles of groups A, B, and D of Geldart's classification are simulated to introduce the most optimal flow regime in terms of heat transfer rate and operating costs. The compromise between the heating rate, the height required for the reactor, and the ratio of the final mass to the initial mass of solid particles, which specifies the need for a cyclone separator showed that the bubbling regime of Geldart B powder for low‐density particles and the turbulent regime of Geldart D powder or bubbling regime of Geldart B powder for high‐density particles are the optimal operating conditions and flow regimes. Furthermore, it was concluded that the convective heat transfer is the dominant mechanism, which increases with increasing the air velocity and decreasing the particle diameter in each group.     

玻璃池窑的热平衡测试及节能评价

通过对玻璃池窑的热平衡测试、计算及分析,得到了该池窑玻璃液带出显热、潜热,池窑表面散热、观察孔口辐射散热、溢流气体显热以及烟气带走的显热等各项热指标。计算了玻璃液单位耗热、热效率、重油单耗及熔化率等主要技术经济指标。在此基础上,对该玻璃池窑的技术特点进行了分析和评价,给出了今后进一步提高热效率的技术措施建议。