Numerical study of combustion in a cylindrical porous burner

Hybrid combustion waves in a two-section apparatus with cylindrical symmetry were studied using a two-temperature mathematical model. A program was written and a large series of numerical calculations was performed using an algorithm developed earlier. For one-and two-section apparatuses with various flow rates, characteristics of the process such as the position of the steady-state point, the maximum gas temperature, the gas velocity at the steady-state point, the width of the combustion zone, etc., were determined. It is shown that, in the two-section apparatus, there is a stabilization of the position of the combustion front near the interface. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 17–21, May–June, 2008.     

Velocity of combustion of a turbulent diffusion flame jet

Conclusions The investigation carried out showed that the velocity of transverse expansion of a reduced flow of combustion products can be used as the characteristic velocity of diffusion combustion, and the width of this flow can be used as a linear dimension, characterizing the degree of burnup.The physical basis for the velocity of diffusion combustion coincides completely with the well-known ideas in the literature concerning the velocity of laminar and turbulent homogeneous combustion, and therefore it is possible to compare the intensities of all three types of combustion. During the experimental investigations of turbulent homogeneous combustion, it was more useful to measure not the flame propagation velocity with respect to its leading edge, as is usually done, but the combustion velocity, which is unambiguously related to the rate of heat release.The preliminary comparison, carried out between the velocities of diffusion and homogeneous combustion, indicates the significant reduction of the heat-release intensity in a diffusion flame jet in comparison with a homogeneous flame jet, which, obviously, is explained by the complexity of the mixing process which precedes the chemical reaction.Institute of Problems of Mechanics, Academy of Sciences of the USSR, Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 12, No. 4, pp. 483–493, July–August, 1976.     

Characteristics of diesel fuel combustion in a burner with injection of a superheated steam jet

Basic characteristics of combustion of the diesel fuel in a novel autonomous burner with injection of superheated steam into the combustion region are studied. The temperature distribution in the flame is obtained. Calorimetric measurements of heat release and gas analysis of combustion products are performed. The environmental effects of fuel combustion are compared for regimes with injection of a steam jet and an air jet. It is demonstrated that the combustion regime with steam gasification ensures high combustion intensity and combustion efficiency; moreover, the combustion process becomes more environmentally friendly.     

Numerical simulation of aerodynamics and combustion of a gas mixture in a channel with sudden expansion

A physicomathematical model and results of numerical simulations of aerodynamics and combustion of a swirled flow of an aluminum-air mixture in an axisymmetric channel with sudden expansion are presented.     

Model of a two-phase turbulent jet with heterogeneous particle combustion taken into account

Kaliningrad. Translated from Fizika Goreniya i Vzryva, Vol. 24, No. 3, pp. 12–17, May–June, 1988.     

Numerical simulation of turbulent gaseous combustion in axially symmetric combustion chambers

A mathematical model and numerical algorithm are developed for the combustion of gaseous fuels in two dimensional turbulent flows. The model includes a system of basic differential conservation equations for the gaseous phase, supplemented by equations for the energy and dissipation rate of turbulent fluctuations for calculating the turbulent diffusion coefficient, as well as a mixing function for initially unmixed flows and its dispersion for describing the effect of turbulence on the concentration of the components, on the temperature, and on chemical reaction rates in terms of a probabilistic approach with a probability density function whose first moment is the mixing function and whose second moment is its dispersion. The calculations are compared with experimental data. The model is found to be effective for thermodynamic equilibrium and for finite kinetics. The results are in satisfactory agreement with the experimental data. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 4, pp. 3–12, July-August 1998     

Numerical analysis of pulverized coal combustion characteristics using advanced low-NOx burner

A three-dimensional numerical simulation is applied to a pulverized coal combustion field in a test furnace equipped with an advanced low-NO_x burner called CI-α burner, and the detailed combustion characteristics are investigated. In addition, the validities of the existing NO_x formation and reduction models are examined. The results show that a recirculation flow is formed in the high-gas-temperature region near the CI-α burner outlet, and this lengthens the residence time of coal particles in this high-temperature region, promotes the evolution of volatile matter and the progress of char reaction, and produces an extremely low-O₂ region for effective NO reduction. It is also found that, by lessening the effect of NO reduction in Levy et al.'s model and taking the NO formation from char N into account, the accuracy of the NO prediction is improved. The efficiency factor of the conversion of char N to NO affects the total NO concentration downstream after the injection of staged combustion air.     

Numerical investigation of turbulent non-premixed combustion of a wood pyrolysis gas

A fully compressible database of turbulent non-premixed flames of a wood pyrolysis gas is developed by means of direct numerical simulation (DNS). A reduced kinetic mechanism is used to model the combustion of a pyrolysis gas-air mixture. The instantaneous flame surface density evolution equation based on the concept of a displacement speed is examined. The normal component of the displacement speed is nearly constant with respect to curvature, while the curvature-related component tries to restore the flame front to a planar shape. The strain-rate term is mainly a source as the flame is mostly extended. The normal displacement is responsible for both positive and negative contributions to the flame area. The displacement/curvature term is primarily a sink, since it is dominated by its curvature component. Effects of strain and curvature are analyzed by considering their correlations with reaction rates. Reaction rates are enhanced with increased positive strain rates owing to an increase in the flame surface area and to a decrease in curvature. The analyzed results aid in the development of turbulent combustion models. Finally, a new model for a mean variance of the scalar dissipation rate, based on a scale similarity approach, is proposed and examined. A comparison with DNS results shows that the proposed model provides a significant improvement over existing models. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 3, pp. 15–34, May–June, 2007.     

燃烧器上摆角度对四角切圆锅炉再热蒸汽温度偏差影响的数值模拟

采用燃烧器上摆和附加风上摆角度偏差设置的方法来降低锅炉烟温偏差和再热蒸汽温度偏差。对一台700 MW四角切圆燃烧锅炉不同燃烧器上摆角度条件下的炉内燃烧过程进行了数值模拟,模拟结果与试验值符合较好。燃烧器上摆角度增加,炉内气流的旋转动量矩和屏区入口的残余旋转动量矩减小,水平烟道内烟气速度和温度偏差降低。附加风上摆角度的偏差设置可降低屏区入口的残余旋转动量矩,进而减小烟气速度和温度偏差。燃烧试验表明,燃烧器上摆11°和附加风上摆角度的偏差设置10°可将再热蒸汽温度偏差由20℃左右降低至4℃以下,是一种有效降低烟气和再热蒸汽温度偏差的手段。     

铝电解槽用矩形燃烧器燃烧过程的数值模拟

燃料加热启动法是铝电解槽加热启动的一种新方法,用燃料燃烧产生的高温烟气来加热启动铝电解槽,即烟气加热技术,可克服燃料加热法的不足,是较理想的铝电解槽加热方法,研究结构合理的燃烧器是保证烟气加热效果的关键.采用数值模拟的方法对烟气加热用燃烧器内的燃烧过程进行了研究,预测了燃烧器的燃烧性能及其影响因素.研究认为燃烧器设置预燃室有利于提高燃烧器的完全燃烧度,紧靠燃烧室壁面的三次风有利于降低燃烧室内壁温度,研究结果为燃烧器结构的优化设计提供了理论依据.     

Catalytic combustion in a domestic natural gas burner

Gastec and Vaillant developed a boiler in which the combustion is catalytically stabilised as well as a completely catalytic boiler. The catalytically stabilised boiler emitted about 5 ppm NO_x and 0 ppm CO. In this boiler the burner is replaced by a metal honeycomb. The honeycomb is partly coated with a catalyst washcoat. The coated part is at the flame side of the honeycomb. The coated length of the channels is an important parameter. A too long coating results in CO emissions, a too short coating in higher NO_x emissions.

The catalytic boiler emitted 0 ppm NO_x, 0 ppm CO and 0 ppm CH₄. The gas is combusted catalytically in two metal honeycombs. Most gas is converted in the first few millimetres from the entrance of the monolith. The heat that is produced is radiated to a heat exchanger. The remaining honeycomb and the secondary honeycomb convert the rest of the methane.

Comparing these boilers, the completely catalytic boiler shows lower emissions and a lower sensitivity to the gas quality. The partly catalytic burner is more reliable and can use a conventional security system. Production and development costs are thus smaller.     

A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream

A diffusion-kinetic model for pulverized-coal combustion and heat-and-mass transfer in a gas stream is proposed, and the results of numerical simulation of the burnout dynamics of Kansk-Achinsk coals in the pulverized state at different treatment conditions and different model parameters are presented. The mathematical model describes the dynamics of thermochemical conversion of solid organic fuels with allowance for complex physicochemical phenomena of heat-and-mass exchange between coal particles and the gaseous environment.     

Numerical modeling of nitrogen oxide formation in turbulent combustion of a premixed gas mixture

Based on the particle equilibrium approximation and introducing a prespecified probability density function of the bimodal type, we have developed a method for calculation of the rate of NO formation in turbulent combustion of a premixed gas mixture, taking into account the pulsations in temperature and composition caused by the chaotic motion of the thin reaction zone, the superequilibrium concentration of oxygen atoms, and the energy losses to radiation. Based on the numerical results, we have compared the effects of the listed factors on the rate of nitrogen oxide formation.Dolgoprudnyi. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 3, pp. 78–81, May–June, 1993.     

Reactivity of bituminous coal chars during the initial stage of pulverized-coal combustion

The reactivities of pyrolysed and partially burned char particles prepared in an entrained-flow reactor have been investigated. The results indicate that chars collected at the end of the active devolatilization stage are more reactive than those collected before or after this stage. Deactivation of the pyrolysed chars was accompanied by the development of micropores. The chars produced from a liptinite-rich fraction of an HVA bituminous coal showed higher reactivities than those generated from an inertinite-rich fraction. It is suggested that residual volatiles play a more important role in determining char reactivity than the microporosity and the optical anisotropy of the chars. A new expression for TGA reactivity is suggested for use in deriving char combustion kinetics. Relatively constant activation energies of ≈ 125 kJ mol⁻¹ were obtained for chars prepared from a wide range of coal precursors. Calculated char combustion rates at high temperatures extrapolated from such reactivity parameters were in agreement with experimentally determined rates.     

Numerical simulations of the slagging characteristics in a down-fired, pulverized-coal boiler furnace

Numerical studies of the slagging characteristics under different operational conditions in a 300 MW down-fired boiler were carried out using slagging models coupled with gas-solid two phase flow and combustion models. Combined with the real operating conditions; comparative and detailed analysis on the slagging position, extent, and causes is presented. The results show that the serious slagging is mainly on the side walls of the lower furnace. Because of the more rapid expansion of the flue gas under the higher temperature, the flue gas in the furnace center makes the flue gas on both sides deflect and flow to the side walls; and the pulverized-coal flame impinges on the side walls. This results in the slagging on the side walls. Under off-design operating conditions, such as stopping some burners, the local flow field is asymmetric and impinges on the local arch burner, front and rear wall regions where the stopped burners are located. It leads to slight slagging on the arch burner regions and the front and rear wall regions of the lower furnace. Based on the investigation, it has been found that the serious slagging on the side walls can be effectively alleviated by cutting off the burners close to the side walls, reducing boiler load and burning low slagging-tendency coals.