【作者】 汪文辉；

【导师】 苏亚欣；

【作者基本信息】 东华大学 ， 热能工程， 2010， 硕士

【摘要】 高温空气燃烧（High temperature air combustion,HTAC）是一种采用高预热空气在超低氧浓度条件下的先进燃烧技术,它具有很低的NO_X（热力型）排放特性,并且通过采用高效的蓄热陶瓷材料极限回收燃烧后的烟气中的余热来加热进入炉膛内的空气,从而大幅度地节约了能量。高温空气燃烧技术在过去20年里得到了迅速发展,在钢铁冶金、玻璃、陶瓷、水泥等行业的工业炉中具有广阔的应用前景,被誉为21世纪最有发展前景的燃烧技术之一。高温空气燃烧技术在气体燃料的应用上可节能30%～70%,氮氧化物排放可控制在40～70mg/m³之间,已取得了良好的经济效益和环境效益。研究表明燃料和空气喷嘴的特殊布置方式及其射流在炉内引起的流场回流、燃料和气体成分间的混合、扩散等影响燃烧的稳定性、温度分布以及局部NO_X的生成。在高温空气燃烧技术中,设计合理的燃烧器可以降低氮氧化物的排放。如何调整燃烧器结构参数和操作参数,使得燃料在低氧氛围中进行燃烧,以降低氮氧化物排放,减少对环境的污染是实现高温空气燃烧的关键。本论文以工业炉的高温空气燃烧技术应用为背景,对一个新型轴向旋流式单烧嘴（HCAS burner）燃烧室内的高温空气燃烧特性以及氮氧化物排放进行了数值研究。采用数值模拟的方法研究了燃烧器结构参数和操作参数对燃烧特性和氮氧化物排放的影响。其中湍流采用Reynolds应力模型,气相燃烧模拟采用β函数形式的PDF燃烧模型,采用离散坐标法模拟辐射换热过程,NO_X模型为热力型与快速型。通过数值模拟,得到一下结论:首先,对预热空气采用旋转射流相比于直射流对降低NO_X生成量有着明显效果。对于HCAS型燃烧器,燃气的内直流使其具有一定的射流刚性,预热空气外旋流部分埘内、外侧气流的卷吸作用则使得流场捌有较好的回流、整体混合特性。在一定程度上,预热空气采用旋转射流可获得较好的流场、温度场、氧气浓度场和较低的氮氧化物排放。出口烟气中NO_X的摩尔分数由35.2×10^-4%降低到12.3×10^-4%,降低幅度达到200%左右。其次,研究和探索了喷嘴结构对高温空气燃烧特性的影响。随着肋片旋转角度的增加,燃烧室中的高温区移向入口,火焰长度缩短,宽度增大;NO_X排放量先减小,后增大。在此基础上,进一步分析了肋片伸展长度和空气燃气射流速度比对燃烧性能和NO_X排放的影响。通过几组数据的模拟结果比较,得出当肋片旋转角度为180°,肋片长度伸展因子为2时的较好的燃烧特性以及较低NO_X排放量。最后,在燃烧器结构参数不变的情况下,改变燃烧的操作参数,分别对预热空气温度、过量空气系数和空气含氧量等因素对对高温空气燃烧特性的影响进行了详细的数值模拟,分析和总结了在不同操作参数下高温空气燃烧的具体特点。研究结果为高温空气燃烧器设计提供了一定的理论参考。更多还原

【Abstract】 High Temperature Air Combustion （HTAC） is an advanced combustion technology developed for the industrial furnaces since 80s, 20^th century and has been applied successfully to the field of steel, glass, ceramic heating furnace. By recovering maximally the waste heat of the flue gas for the heating of the combustion air to approach or exceed the ignition point of the fuel, the fuel can be burnt at a super low oxygen level with a stable flame. HTAC conserves 30% to70% of the energy for gas combustion and emits very low nitrogen oxide pollutant, 40～70mg/m³.It’s shown that the burner design plays important role in keeping the steady combustion and low NOx generation if the jets of the fuel and air could produce a reasonable recirculation in the furnace. The interaction of the jets determines the distribution of the local oxygen, temperature, the mixing of the fuel and air, which determines the local production of the thermal NOx. Therefore, it’s very important to achieve low NOx emission by keeping the combustion of the fuel in a low oxygen atmosphere through a reasonable arrangement of the burner parameters and operation parameters.The objective of the thesis is to carry out a numerical simualton of the high temperation air combustion of natural gas in an industrial furnace with a swirling burner. A Homocentric Axial Swirling （HCAS） Burner was designed and the burner geometric parameters and operation parameters were intensively studied on how these parameters influenced the combustion process and the final NO eimission. The Reynolds Stress Model was used to calculate the flow field and PDF （Probability Density Function） combustion model based on aβfunction was selected to simulate the gas combustion. The radiation was simulated by a Discrete Ordinates method. The NOx was simulated by thermal NOx model based on the modified Zeldovich reaction model. The software FLUENT was used to carry out the simulation. The following conclusions can be drawn from the simulation results. First, the results show that the swirling injection of preheated air reduces NOx emission obviously when compared to direct injection of preheated air. For HCAS burner, the central jet of gas has rigidity characteristics, while the external swirling jets of the preheated air enhances the mixing of the gases and induces a good recirculation flow field in the furnace and leads to a better low oxygen distribution and low temperature field, resulting a low NO generation. The final NO mole fraction decreases from 35.2ppm to 12.3 ppm when a swirling burner was used.Second, the effect of the burener configuration was studied. The maximum temperature region will move toward the burner inlet, flame length will decrease and flame width will increase with the increase of the spiral angle of the swirling fin.The NOx emission will first decrease, then increase with the increase of the spiral angle of the swirling fin. Therefore by regulating the spiral angle of the swirling fin, NOx emission can be reduced. The simulated results showed that when the spiral angle of the swirling fin is 180°, the dimentionless stretch factor of fin length is 2, the better combustion characteristics as well as lower NOx emissions were achieved.Finally, when the burner structure parameters were fixed, the effect of the operation parameters was studied. Results were discussed and analyzed for the combustion character and NOx emission at different inlet preheated air temperature, excess air coefficient and oxygen concentration.The results and conclusion drawn from this thesis can provide useful references for engineering application of HTAC burner design.更多还原