【作者】 季俊杰；

【导师】 罗永浩；

【作者基本信息】 上海交通大学 ， 热能工程， 2008， 博士

【摘要】 燃煤链条锅炉是我国重要的热力设备,量大面广,但效率却十分低下。在链条锅炉中,燃烧优化的3T+E要素,即Time(停留时间),Temperature(温度),Turbulence(混合),Excess air(空气过量率)主要由配风和炉拱来调节控制,优化配风和炉拱是提高链条炉燃烧效率的常用手段。然而,长久以来,无论是传统炉拱还是双人字拱等新型节能炉拱都依赖于经验设计,配风也往往由司炉人员根据经验调节,存在很大的盲目性,常造成燃烧效果不佳,甚至出现不明机理的正压燃烧问题。针对燃烧优化设计缺乏理论预测的问题,本文旨在建立基于煤质分析和供风配置的燃煤链条锅炉燃烧数值模型。该模型主要由三部分组成,即床层燃烧模型,炉膛气相燃烧模型,以及两者的流动传热耦合。床层模型中,考虑到我国燃煤颗粒大、灰量高的特点,建立了包含煤块内部温度梯度和灰层扩散阻力的二维床层燃烧模型,然后基于煤层和炉膛的整体网格,将其与炉膛气相燃烧模型结合,耦合两者的流动、辐射、对流等条件,集成为一体化的链条炉燃烧模型。为验证模型的准确性,采用气相色谱测量了实际链条炉中煤层表面的气体成分分布,并与模型预测结果校对。研究结果显示,模型具有较好预测结果,且精度较一般的等温模型有所提高。为进一步对不同煤种的预测结果进行分析,搭建了单元体实验炉,利用红外烟气分析仪,对三种不同挥发份等级的煤种的煤层表面气体组分进行实时测量记录,通过与模拟结果的对比,发现本文的模型在整体上具有合理的精度,可以满足配风和炉拱辅助设计的要求。在成功建立模型的基础上,对影响煤层燃烧的基本因素,如炉排前进速度、煤层厚度进行了研究,揭示其影响机理,为运行提供理论指导。将模型用于配风和炉拱优化分析,研究了不同配风方式对不同挥发份等级煤种煤层燃烧的影响,及作用机理。并针对新型双人字节能炉拱,研究了其工作原理,配风搭配,及拱型设计原则。随后,针对某20t/h锅炉炉拱存在的问题,通过辅助计算确定改良炉拱形状和配风,经实测,获得了较好的节能效果。最后,针对炉拱设计不当引起的非阻力型正压燃烧这一局部特殊问题,建立挥发份燃烧炉内脉动压力测试实验台,研究其发生机理。采用动态压力传感器数据采集系统测量了不同配风下炉内压力的波动。通过大涡模拟结果与实验比对,并对炉内的燃烧分析表明,非阻力正压是由于周期性的涡脱落诱导挥发份不正常燃烧引起的。根据得出的机理,提出了避免非阻力型正压的炉拱设计方式。更多还原

【Abstract】 Coal-fired travelling grate boilers are important thermal facilities in China with a huge number and wide distribution. The efficiency, however, is relatively low. The“3T+E”combustion optimization factors, i.e., time, temperature, turbulence and excess air in travelling grate boilers are mainly adjusted by arch in the furnace and air distribution under the grate. Optimization of arch and air distribution is the common method to improve the combustion efficiency.However, the design of arches, either conventional arch or novel arches such as double-herringbone arch, are based on experience. Air distribution is also mainly determined by the experience of stokers. These empirical methods are greatly blindfolded, which usually leads to low improvement of combustion efficiency, even unclear puffing combustion in the furnace.In consideration of the lack of prediction method in the combustion optimization, this paper aims to develop a coal-fired travelling grate boiler combustion numerical model using coal analysis and air supply as the input conditions. The model comprises three parts, i.e., bed model, furnace model and their coupling model. In the bed model, a non-isothermal two-dimensional method considering the temperature gradient and ash diffusion resistance in particles is established in view of the special features of domestic coals (large-diameter and high-ash). Then the bed model is combined with the furnace model based on an integrated grid. After the couplings between the furnace and the bed, such as flow, radiation and convection are added, the integrated travelling grate boiler combustion model is achieved.In order to verify the model, the gas components along the grate length in a 20t/h boiler are measured by a gas chromatograph and the data are compared with those predicted by the model. The result shows that the model is in reasonable agreement with the experiment. Additionally, the precision is improved compared with the conventional isothermal model. To further verify the model ability for different coals, a lab-scale furnace is set up. The gas components at the bed surface when burning three coals of different volatile level are measured by an infrared gas analyzer. The data are used for the verification and the result shows that the model has a reasonable precision on the whole, which is satisfied for the design of arches and air distribution. On this base, some influencing factors, such as grate velocity, bed thickness are analyzed and influencing mechanisms are revealed.Next, the influences and mechanisms of different air distribution modes on the beds of various volatile level coals are studied. For the novel double-herringbone arch, the working principle, suitable air distribution and arch shape are analyzed. Later, the arch and air distribution in a 20t/h boiler are improved with the aid of the numerical model. The efficiency measurement shows a good energy-saving result. Finally, a pulsating micro-pressure test rig of volatile combustion is set up to study the mechanism of non-resistance puffing combustion led by inappropriate arch design. A dynamic pressure transducer is used to measure the pressure fluctuations in the furnace under different air distribution modes. Large eddy simulation is performed to compare with the experiment and analyze the combustion features in the furnace. The result shows that non-resistance puffing combustion is led by the abnormal volatile combustion induced by periodic vortex shedding. The arch design scheme to avoid the non-resistance puffing combustion is suggested based on the mechanism.更多还原