Modeling filtered heat transfer model by considering dimensionless temperature difference between gas and solid phases

Computational fluid dynamics–discrete element method is used to simulate gas–solid flows with heat transfer. The strategy of repetitively resetting the gas phase temperature is adopted to maintain the temperature difference between the gas and solid phases. The difference between the heat transfer characteristics produced by this strategy and the traditional heat source method is analyzed. It is found that heat transfer in dense regions is artificially enhanced by the heat source method. Therefore, the results obtained by the temperature reset method are filtered to develop a three-marker model for the filtered interphase heat transfer coefficient (IHTC). In the developed model, the filtered gas–solid temperature difference is nondimensionalized by the average gas–solid temperature difference in surrounding grids, which is shown to have an impact on the filtered IHTC. The developed model is demonstrated to be effective and accurate in both a prior and a posterior tests.     

热重分新法对不同粒度煤自燃过程特征温度的研究

选用3种煤分别制得3种粒度的试样。采用非定温测量法进行TG分析,得到相应的TG／DTG曲线,选定煤自燃过程中的6个特征温度,并确定其温度界限,分析不同粒度煤样特征温度的变化并总结规律。结果表明,高位吸附温度和着火温度基本保持不变,其余4个特征温度的变化规律不尽相同。     

天然气催化燃烧器独石通道内气体温度分布

研究了天然气催化燃烧器蜂窝状独石通道内气体温度分布。由于催化反应区在独石通道内10 mm左右基本结束,将催化剂独石长度减至20 mm进行实验,由于在高热强度下燃烧不易稳定,为降低独石入口前端腔内混合气温度,将一块20 mm长的无催化剂独石连接在镀钯催化剂独石的入口前组成组合催化剂独石,发现组合催化剂独石燃烧稳定。     

Determination of laminar burning velocities for natural gas

Spherically expanding flames of natural gas-air mixtures have been employed to measure the laminar flame speeds, at the equivalence ratios from 0.6 to 1.4, initial pressures of 0.05, 0.1 and 0.15 MPa, and preheat temperatures from 300 to 400 K. Following Markstein theory, one then obtains the corresponding unstretched laminar burning velocity after omitting the effect of stretch imposed at the flame front. Over the ranges studied, the burning velocities are fit by a functional form u_l=u_l0(T_u/T_u0)^α_T(P_u/P_u0)^β_P, and the dependencies of α_T and β_P upon the equivalence ratio of mixture are also given. The effects of dilute gas on burning velocities have been studied at the equivalence ratios from 0.7 to 1.2, and the explicit formula of laminar burning velocities for dilute mixtures is achieved.     

高温燃烧水解-电位滴定法测定固体生物质燃料中氯的试验条件初步研究

分析比较了国内外固体生物质燃料中氯的测定方法,选择以Ag—AgCl电位滴定法作为固体生物质燃料中氯的最佳测定方法,并通过试验研究初步确定了高温燃烧水解-电位滴定法测定固体生物质燃料中氯的试验条件,为下一步制定相应的国家标准奠定了基础。     

Effects of gas temperature fluctuation on the NO release from pulverized coal particle during char combustion

The effects of gas temperature fluctuation on the NO release from pulverized coal particle during char combustion are investigated. The computed results show that the NO formation through the heterogeneous oxidation and reduction reactions is influenced by the gas temperature fluctuation for the particles with initial diameters of 10-50 μm. The gas temperature fluctuation leads to faster NO release from the particle. The heterogeneous NO formation during the char combustion is further enhanced by the increase in the fluctuation amplitude of gas temperature.     

预测生物质颗粒热解时热损失影响的分析模型(英文)

This paper presents the combined influence of heat-loss and radiation on the pyrolysis of biomass parti-cles by considering the structure of one-dimensional, laminar and steady state flame propagation in uniformly pre-mixed wood particles. The assumed flame structure consists of a broad preheat-vaporization zone where the rate of gas-phase chemical reaction is small, a thin reaction zone composed of three regions：gas, tar and char combustion where convection and the vaporization rate of the fuel particles are small, and a broad convection zone. The analy-sis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number is large and the equivalence ratio is larger than unity （i.e. u 1？ ≥ ）. The principal attention is made on the determination of a non-linear burning velocity correlation. Consequently, the impacts of radiation, heat loss and particle size as the de-termining factors on the flame temperature and burning velocity of biomass particles are declared in this research.     

燃煤细灰的形成及微观形态特征

引 言 大气环境中的细小颗粒物不仅影响气象和气候,使空气质量变差,降低大气能见度,而且对人体特别是呼吸系统有严重危害.研究表明细小颗粒物极易进入人体肺部,被吸收进入血液,长期蓄积在体内,且颗粒越小,进入肺部越深[1].对我国大气中细小颗粒物来源虽有不同看法,但基本上认为煤燃烧是主要的来源之一[2],而且因为煤成分的复杂性,使得燃煤细灰含有各种矿物成分和多种痕量有毒元素,灰粒越细,富集越多,因此燃烧源小颗粒毒性更强,危害更深[3-4].由于现有的除尘设备,如煤粉炉普遍采用的电除尘器,虽然总除尘效率可以达到99%以上,但对细飞灰(PM2.5)的捕集效率也只有90%左右,而旋风除尘器更是在5%以下[5].因此,加强燃煤细灰的形成、细灰微观形态特征及其有害元素分布规律的研究,对开发燃烧源小颗粒控制技术有重要的指导意义.     

Modeling the temperature in coal char particle during fluidized bed combustion

The temperatures of a coal char particle in hot bubbling fluidized bed (FB) were analyzed by a model of combustion. The unsteady model includes phenomena of heat and mass transfer through a porous char particle, as well as heterogeneous reaction at the interior char surface and homogeneous reaction in the pores. The parametric analysis of the model has shown that above 550 °C combustion occurs under the regime limited by diffusion. The experimental results of temperature measurements by thermocouple in the particle center during FB combustion at temperatures in the range 590-710 °C were compared with the model predictions. Two coals of different rank were used: lignite and brown coal, with particle size in the range 5-10 mm. The comparisons have shown that the model can adequately predict the histories of temperatures in char particles during combustion in FB. In the first order, the model predicts the influence of the particle size, coal rank (via porosity), and oxygen concentration in its surroundings.     

低燃速低燃温双基推进剂燃烧性能的调节

为调节低燃速燃温双基推进剂的燃烧性能(燃速及压强指数)，探索铅、铜盐和碳黑等燃烧催化剂在该类推进剂中的催化效果，从理论燃温在900～1700K的低燃速双基推进剂中选出4种作为基础配方，分别加入不同种类的铅盐、铜盐及碳黑等燃烧催化剂，改变催化剂的加入量及搭配关系，进行了一系列试验研究。同时还研究了辅助增塑剂对推进剂燃烧性能的影响。结果表明，常规的铅、铜盐和碳黑等催化剂在低燃速低燃温推进剂中仍能发挥催化作用，作用效果与催化剂的品种及加入量相关，特别是使用复合催化剂时，对燃烧性能的调节更为有效。不同品种的辅助增塑剂对燃烧性能也有影响。     

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.     

海藻生物质颗粒流化床燃烧试验研究

在小型流化床试验台上研究了海藻颗粒(条浒苔与马尾藻)的流化床燃烧。海藻在流化床内的挥发分析出燃烧时间都在1 min左右。条浒苔颗粒在流化床中燃烧先进行脱水和挥发分的燃烧,接着发生焦炭燃烧,其燃烧过程符合缩核模型,炭核由外向内逐层燃烧,而灰层半径几乎不变。但马尾藻颗粒由于挥发分的大量快速释放而迅速膨胀破碎成屑。另外通过对条浒苔颗粒及不同燃烧时间后收集的焦炭颗粒剖面的SEM扫描电镜观察,发现随着燃烧的进行,颗粒内孔隙增大,微孔表面粗糙。进一步详细研究了两种海藻颗粒(条浒苔与马尾藻)在流化床内单次投料下的燃烧。随着床温的升高,条浒苔释放NO_x相对浓度增加,CO相对浓度减少。而马尾藻释放气体中SO₂与NO_x含量相对条浒苔有所增加;随着床温的升高,CO相对浓度减少。床温的升高使得床内传热速率加快,两种海藻挥发分的析出提前,燃尽时间缩短。风速、床高的升高使得两种海藻燃烧容易,燃尽时间缩短。     

Effect of the equivalence ratio on the effectiveness of inhibition of laminar premixed hydrogen-air and hydrocarbon-air flames by trimethylphosphate

This paper reports results of an experimental study and numerical simulation of the effect of the equivalence ratio (φ = 0.6–1.6) on the burning velocity of laminar, premixed atmospheric methane-air and propane-air flames without additives and with 0.06% trimethylphosphate (TMP). The effect of the equivalence ratio (φ = 0.7–4.5) on the burning velocity of hydrogen-air flames without additives and with 0.1% TMP was studied by simulation. The experimental and simulation results show that, in hydrocarbon flames doped with TMP, the inhibition effectiveness decreases sharply with a growth in φ from 1.2–1.3 to 1.4–1.6 and in hydrogen-air flames, the inhibition effectiveness increases with a rise in φ from 1.5 to 4.5. The reactions determining the dependence of the inhibition effectiveness on the equivalence ratio were found by analyzing the flame velocity sensitivity coefficients to changes in reaction rate constants. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 2, pp. 14–22, March–April, 2008.     

高渐增性发射药研究进展

列举出发射药燃烧渐增性判断的方法,阐述了燃速渐增性发射药、燃面渐增性发射药、变燃速发射药技术的实现方式。对这3种方式进行对比分析,表明变燃速发射药在燃烧渐增性实现上有较大的优势。     

Modeling of circulating fluidized beds systems for post‐combustion CO2 capture via temperature swing adsorption

The technology of circulating fluidized beds (CFBs) is applied to temperature swing adsorption (TSA) processes for post‐combustion CO₂ capture employing a commercial zeolite sorbent. Steady state operation is simulated through a one‐dimensional model, which combines binary adsorption with the CFB dynamics. Both single step and multi‐step arrangements are investigated. Extensive sensitivity analyses are performed varying the operating conditions, in order to assess the influence of the main operational parameters. The results reveal a neat superiority of multi‐step configurations over the standard one, in terms of both separation performance and efficiency. Compared to fixed‐bed TSA systems, CFB TSA features a high compactness degree. However, product purity levels are limited compared to the best performing fixed‐bed processes, and heat management within the system appears to be a major issue. As regards energy efficiency, CFB systems place themselves in between the most established absorption‐based technologies and the fixed‐bed TSA. © 2017 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1744–1759, 2018     

Problems in studying formation of smoke oxide particles in combustion of aluminized solid propellants

The present paper deals with properties of smoke oxide particles formed near the surface of burning aluminized solid propellants. The global physical picture of formation of this product is formulated. Based on this picture, it is demonstrated that smoke oxide particles are formed in two processes: combustion of non-agglomerating metal in the gas-phase layer above the surface and combustion of agglomerating metal in the surface layer of the propellant. Combustion mainly proceeds in the heterogeneous and gas-phase modes in these two cases, respectively. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 45–53, January–February, 2007. An erratum to this article is available at .     

Devolatilization and combustion of large coal particles in a fluidized bed

Devolatilization and combustion of large particles of Eastern Canadian coals (Evans and Minto), 5-50 mm dia., were studied in a bench-scale atmospheric fluidized bed reactor at 1023-1173 K with 0.5 mm sand particles as the bed material. The devolatilization time, mass loss history, changes in proximate volatiles content and C/H mass ratio, and temperature history at the centre of the particle during devolatilization were determined. The mass loss during devolatilization is correlated with the proximate volatiles content of the parent coal. The devolatilization time is correlated with the initial particle diameter by a power-law relation with an exponent of 1.54-1.64. The results show insignificant effect of superficial velocity on devolatilization.     

Fe2O3催化无烟煤燃烧燃点降低机理的实验研究

利用TG-DTG法和DTA法研究了无烟煤催化燃烧时燃点的变化情况,结果表明Fe2O3可使无烟煤的燃点降低。基于无烟煤燃点的形成原因和催化热解过程,研究了催化热解过程中热解转化率、热解气组成、半焦表面结构的变化情况,结果表明Fe2O3促进了无烟煤的热解,热解转化率、热解气的组成明显变化,热解气热值增加。催化热解产生的半焦表面形貌粗糙,颗粒细碎,比表面积大。由于热解过程直接影响到点燃过程,因此通过催化热解的研究,可知催化燃烧过程中均相燃烧（热解气燃烧）提供给异相燃烧（半焦燃烧）的热量高于非催化燃烧。同时催化热解所得半焦的吸附氧气能力强,在低温时吸附氧气的速率较快,缩短了达到点燃时所需氧气浓度的时间,进而降低了无烟煤的燃点。