蜂窝陶瓷蓄热体格孔壁面应力变化特性的数值研究

介绍了高温空气燃烧过程中蜂窝陶瓷蓄热体的工作原理和损毁原因，采用代数雷诺应力模型和修正的速度-压力耦合算法SIMPLEC，耦合蓄热体内流体的流动和换热过程，运用有限元分析方法，对蜂窝陶瓷蓄热体格孔壁面上的应力变化规律进行数值研究，并根据计算结果对操作参数进行了改进。结果表明，频繁的蓄热和释热过程变换，使得蓄热体格孔壁面交替地受到拉应力和挤压应力的作用。流体的流速越大，应力变化越大；换向时间越短，应力交替作用的影响越大。适当地调低烧嘴负荷，延长四通阀的换向时间，有利于提高蓄热体的使用寿命，计算结果为蓄热体结构设计和操作参数的优化提供了依据。     

蜂窝型陶瓷蓄热体换热器的热动态特性实验研究

对高温空气燃烧技术中的关键设备——蜂窝型陶瓷蓄热体换热器的热动态特性进行了实验测试。结果表明:蜂窝型陶瓷蓄热体换热器的压力损失随着空气流速以及蓄热体长度的不同而变化,但总体上说,其压力损失并不大;四通换向阀的换向周期和蜂窝陶瓷蓄热体换热器的体积等是影响其温度效率和热回收率等热性能的重要因素。     

蜂窝蓄热体温度特性数学解析

基于蜂窝蓄热体气固传热精确解，研究蓄热体温度变化和切换周期设计方法，忽略沿气流流动方向的固体导热影响，建立了周期传热数学模型，并求出了气固温度分布精确解。和数值计算相比，半解析解可信，按炉内低氧稳定燃烧和蓄热体低温端不结业的要求，可进行切换周期优化设计，从而为低氧弥散燃烧设计和操控优化提供一种高效、经济、准确的解析研究方法。     

用拉普拉斯变换法求解蜂窝蓄热体气固温度分布

提出一种蜂窝蓄热体气固耦合周期传热数学解析研究方法。忽略沿气流流动方向的固体导热影响,建立了薄壁蓄热体周期传热数学模型,并对线性偏微分方程组进行无量纲化处理;借助Matlab的符号运算功能,用拉普拉斯变换法,求出了蜂窝蓄热体气固温度连续分布函数精确解,并获得了温度分布数值解;和文献纯数值计算对比,半解析结果吻合。证实高效、经济、准确地获取蜂窝蓄热体传热半解析数值解的可行性。     

稀薄氨气的燃烧特性及动力学研究

文章通过稀薄氨气在固定床反应器中的燃烧,研究了反应温度、停留时间、氨气浓度和氧气浓度对低浓度氨气燃烧特性的影响,并描述了氨气在氧气过量条件下在陶瓷蜂窝蓄热体中燃烧的动力学过程。研究结果表明:提高反应温度、延长停留时间以及增大氧气浓度和氨气浓度均可以提高NH3转化率,氧气浓度过高会促进NO生成;当反应温度为740~770℃、氨气浓度为1%、氧气浓度为15%时,氨气在陶瓷蓄热体中燃烧的活化能为253.56 kJ/mol;与氨气在自由空间内的燃烧相比,氨气在陶瓷蜂窝蓄热体中主要发生表面燃烧反应。     

不同蜂窝蓄热体的性能对比及能耗分析

蜂窝蓄热体对于改善空气燃烧过程,降低NOx起着至关重要的作用。本文通过Pointwise和Fluent软件建立了蜂窝蓄热体三维数值模型,从不同的换向时间、孔型、边长、材料的角度对比了蜂窝蓄热体的换热特性,并对实际工作中节能效率进行了理论计算。结果显示,当换向时间从15s增长到45s时,正方形蓄热体的温度效率从78.5%降低到63.1%。当边长、壁厚相同时,圆形蓄热体的温度效率最高,压降也最大;六边形蓄热体的温度效率最低,但压降最小。总结发现,孔隙率的减小可以有效的提高温度效率,但是同时会增大流动的压力损失。在实际应用中可据此选择合适的孔隙率。同时得到,在实际运行中,当a=2mm时,圆形蓄热体的节能效率最高（26.9%）,六边形节能效率最低（24.4%）。     

高温空气燃烧新型锅炉及特性分析

好采用高温空气燃烧技术的新型锅炉,其关键部件包括蜂窝陶瓷蓄热体,实现分级燃烧和炉内烟气再循环的燃烧器及四能视频切换阀。详述了其工作原理及过程,探讨了开发该锅炉的基本思路,对其基本特性进行了分析,最后讨论了在我国推广应用该新型锅炉的意义。     

蜂窝陶瓷蓄热体的热应力场数值模拟

对普通正方形格孔蜂窝蓄热体和夹角圆弧过渡正方形格孔蜂窝蓄热体的热应力场进行了数值模拟计算与对比分析.结果表明,夹角圆弧过渡正方形格孔蜂窝蓄热体的低应力区域更大,应力分布也更均匀;数值模拟结果能够指导蓄热体的结构优化设计.     

陶瓷蓄热体的流动与传热特性模拟研究

为了选用合适的蓄热陶瓷体填充乏风氧化装置氧化床,首先对方形、圆管形和六边形蓄热陶瓷体的几何结构进行理论分析,得出特征长度对蓄热陶瓷体孔隙率和比表面积的影响规律。然后利用FLUENT软件对方形、圆管形和六边形蓄热陶瓷体进行模拟,得出在相同孔密度和开孔率条件下,选用方形孔可以获得较好的蓄热能力,选用圆管形、六边形孔可以降低其压强损失。在同孔隙率、比表面积和当量直径条件下,方形陶瓷体的阻力损失较低,六边形陶瓷体的传热效率较高。     

蓄热体余热回收换热器强化传热实验研究

利用蓄热式热热交换理论和高温空气燃烧技术的原理,在热态实验基础上建立了蜂窝陶瓷蓄热体的性能研究实验.结果表明,热效率及温度效率随换向时间的增加均呈现先上升后下降的趋势,存在一个最佳换向时间,即热效率和温度效率随着长度的增加而增大,但阻力损失也随之增大;同时存在一个最佳气体流速使蓄热体效率与经济效益达到最佳值;蓄热体的平均温度与气体出口温度均随着换向周期数的增加而升高;对于给定几何外形尺寸的蓄热体,四边形孔格结构的蓄热体具有较大的比表面积,流动性更好,具有更高的温度效率和热效率.     

Thermal performance analysis on a two composite material honeycomb heat regenerators used for HiTAC burners

Honeycomb heat regenerators do not only reduce the fuel consumption in a high temperature air combustion (HiTAC) burning system but also provide the necessary high temperature of combustion air. A two-dimensional simulation model was developed to numerically determine the dynamic temperature and velocity profiles of gases and solid heat-storing materials in a composite material honeycomb regenerator. Consequently, the energy storage and the pressure drop are calculated and the thermal performance of honeycomb heat regenerator is evaluated at different switching times and loading. The model takes into account the thermal conductivity parallel and perpendicular to flow direction of solid and flowing gases. It considers the variation of all thermal properties of solid material and gases with temperature. Moreover, the radiation from combustion flue gases to the storage materials was considered in the analysis. The results are presented in a non-dimensional form in order to be a design tool as well. These analyses were applied on a regenerator made of two layers of ceramic materials, one is pure alumina and other is cordierite. This regenerator is contained in a 100 kW twin-type regenerative-burning system used for HiTAC. The effectiveness and the energy recovery rate were 88% and 72% respectively at nominal operating range of the regenerator and the pressure drop across the twin regenerator system was 1.16 kPa. The periodic steady state condition is reached after about 11 min and it takes only 2 min of operation until the temperature of combustion air remains above the self-ignition temperature that is required for HiTAC. Furthermore, these mathematical analyses show good agreement with experiments made on the same regenerator. In the experiments, the dynamic behavior of the heat regenerator operation was considered in order to compensate measurement readings for this effect.     

Unsteady thermal flow analysis in a heat regenerator with spherical particles

Heat regenerator occupied by regenerative materials improves thermal efficiency of regenerative combustion system through the recovery of sensible heat of exhaust gases. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of regenerator with spherical particles, were numerically analysed to evaluate the heat transfer and pressure drop and to suggest the parameter for designing heat regenerator. It takes about 7 h for the steady state in the thermal flow of regenerator, where heat absorption of regenerative particle is concurrent with heat desorption. The regenerative particle experiences small temperature fluctuation below 10 K during the reversing process. The thermal flow in heat regenerator varies with inlet velocity of exhaust gas and air, configuration of regenerator and diameter of regenerative particle. As the gas velocity increases with decreasing the cross-sectional area of the regenerator, the heat transfer between gas and particle enhances and pressure losses increase. As particle diameter decreases, the air is preheated higher and the exhaust gases are cooled lower with the increase of pressure losses. At the same exhaust gases temperature at the regenerator outlet, the regenerator length need to be linearly increased with inlet Reynolds number of exhaust gases. It is confirmed that inlet Reynolds number of exhaust gases should be introduced as a regenerator design parameter. Copyright © 2002 John Wiley & Sons, Ltd.     

燃烧参数影响高温空气燃烧特性的数值分析

高温空气燃烧技术具有高效节能和低NOx排放等多重优越性，是一种新型燃烧技术。为了深入研究高温空气燃烧机理和低氮氧化物排放特性，将湍流N—S方程与扩散燃烧模型和热力型NO生成模型相结合，研究了低氧浓度条件下，燃烧参数，如燃气供应量，过量空气系数，进口空气预热温度以及进口空气氧含量对燃烧的影响，为发展高温空气燃烧技术提供了理论依据。     

大加速度场中层流扩散火焰流场的数值计算

通过对大加速度场中层流燃烧室流场的数值计算，建立了大加速度场中二维层流燃烧的数学模型，对控制方程组进行离散，采用SIMPLE算法和交错网格设计并调试程序。在调试成功的程序上对甲烷和空气在大加速度场中的扩散燃烧过程进行了数值模拟。计算结果表明，沿燃烧室轴线方向的均匀大加速度场会对扩散火焰的速度场和温度场等产生明显影响。一方面使得燃料与空气的扩散混合过程得到强化，扩散火焰的形状变短变粗，火焰面温度升高．因而能够提高其燃烧速度；另一方面，由于浮力作用驱动高温气流的流动方向与燃料射流的方向相反，将形成一种不稳定的流场结构，并同时诱发燃烧过程的不稳定。     

Laminar flow with combustion in inert porous media

This work presents one-dimensional numerical results for combustion of an air/methane mixture in inert porous media using laminar and radiation models. Comparisons with experimental data are reported. The burner is composed by a preheating section followed by a combustion region. Macroscopic equations for mass, momentum and energy are obtained based on the volume average concept. Distinct energy equations are considered for the porous burner and the flowing gas. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to relax the entire equation set. Inlet velocity, excess air, porosity and solid-to-fluid thermal conductivity ratio were varied in order to investigate their effect on temperature profiles. Results indicate that higher inlet velocities result in higher gas temperatures, following a similar trend observed in the experimental data used for comparisons. Burning of mixtures close to the stoichiometric conditions also increased temperatures, as expected. Increasing the thermal conductivity of the preheating section reduced peak temperature in the combustion region. The use of porous material with very high thermal conductivity on the combustion region did not affect significantly temperature levels in the combustion section.     

600 MW偏转二次风系统锅炉炉内结渣特性的数值模拟

偏转二次风系统已广泛应用于大型四角切圆燃烧锅炉，用以报制炉内结渣，防止水冷壁高温腐蚀等。为降低炉膛出口扭转残余，通常采和下部二次风大角度正切、上部二次风和OFA风反切的布置方式。本文对某台采用偏转二次风系统的600MW燃煤四角切圆燃烧锅炉的炉内结渣过程进行模拟，对炉内气固相流动、温度场、气固相燃烧、固相向水冷的输运过程和灰粒在水冷壁上的附生长过程进行了数值模拟，结果表明，偏转二次风系统具有较强的防结渣性能，这一点也被锅炉的实际运行所证实。     

Performance analysis for glass furnace regenerator

Glass manufacturing is an energy intensive process where fossil fuel is used to maintain high temperature (about 1700 °C) for glass melting. Heat recovery from flue gas (1350–1500 °C) is usually in the form of combustion air pre-heating (900–1200 °C) using a regenerator. Dust from flue gas which is carried over from the furnace gets deposited in the regenerator storage matrix path. This leads to a deterioration of regenerator efficiency. A regenerator model is developed to estimate the actual performance of the regenerator and to compare it with the target performance. The proposed model is based on mass and energy balance of streams along with heat transfer characteristic equations. The model is illustrated for a 130 TPD (Ton per Day) furnace regenerator of an industrial glass plant at Mumbai, India. Model results for the regenerator studied indicate a blockage of 50% on the doghouse side and 22% on the non-doghouse side of the regenerator. The actual performance of the regenerator is found to be 7% lower than its target performance for the doghouse side regenerator. The model developed can also be used in other industrial sectors like steel, chemical etc.     

Energy and exergy analysis of a new hydrogen-fueled power plant based on calcium looping process

A novel hydrogen-fueled power plant with inherent CO₂ capture based on calcium looping process is proposed in this paper. The analyzed system has been evaluated from the energy and exergy points of view, it enables determination of the contribution of main component to the total exergy loss. The results show that energy and exergy efficiencies of the system are 42.7% and 42.25% respectively, combustion chamber and regenerator are responsible for large exergy destructions, mainly due to irreversibilities associated with the combustion reactions, they have great potential for system efficiencies improvements. The effects of various air pressure ratios and gas turbine inlet temperatures on the system thermodynamic performance are also presented. The thermodynamic efficiencies increase with the increase in air pressure ratios and gas turbine inlet temperatures.