大型电站锅炉配煤掺烧的NOx排放特性预测与优化运行
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摘要
能源是当今世界经济发展的重要基础,随着能源消费的增长,我国污染物排放量持续增长,而煤燃烧的污染排放已成为中国最大的大气污染源,所以如何实现煤种变化、煤质波动情况下燃煤电站锅炉的高效低污染燃烧,是我国可持续发展的一个重要课题。本文围绕大型燃煤电站锅炉配煤掺烧优化运行开展研究,所提出的锅炉燃烧优化则是通过调整锅炉运行参数,以达到兼顾降低NOx排放和提高锅炉燃烧效率的目标,具有一定的现实意义。
     首先,综述了燃煤电站锅炉NOx生成机理、人工神经网络和遗传算法,同时介绍了配煤掺烧技术及本文大型锅炉的掺烧方案,为后文建立模型提供了基础。
     然后,在某台700MW四角切圆燃煤电站锅炉的NOx排放特性及锅炉效率多工况热态测试的基础上,应用人工神经网络建立大型四角切圆燃煤电站锅炉NOx特性及锅炉效率预测模型并进行预测,检验样本NOx和锅炉效率预测值与实测值的平均相对误差分别为3.63%和0.23%,证实模型的可行性。
     最后,在所建立的700MW四角切圆燃煤电站锅炉配煤掺烧NOx排放特性和锅炉效率预测模型基础上,综合考虑NOx排放特性和锅炉燃烧效率两方面的影响,结合遗传算法建立了锅炉燃烧优化模型,并结合锅炉测试试验,分别以不掺烧第1组、掺烧比分别为1:4和2:3的第7和18组试验工况为例,利用该优化模型寻优。不掺烧的第1组优化后NOx浓度为421.44mg·m-3,降低了37.56%,锅炉效率为94.56%,提高了0.09%;掺烧C磨的第7组优化后NOx排放浓度为255.05mg·m-3,降低了29.43%,,同时锅炉效率为94.13%,提高了0.42%;掺烧B和C磨的第18组优化后NOx排放浓度为215.40mg·m-3,降低了30.56%,,同时锅炉效率为94.80%,提高了0.88%。
     该模型可在掺烧非设计煤种情况下寻找出最优运行参数,降低锅炉NOx排放浓度并提高锅炉效率;同时结果表明国产煤掺烧印尼煤随掺烧比增大,NOx排放浓度降低,实际工程中掺烧情况复杂,降低NOx排放量的同时还必须考虑到锅炉效率等其他因素;当国产掺烧印尼煤,选择掺烧D磨煤机和E磨煤机有利于降低NOx排放量。
Energy is an important foundation for today's world economy, with the growth of energy consumption, emissions continue to grow in China, while the pollution from coal combustion has been the biggest pollution source in China, how to achieve boiler combustion with high efficiency and low pollutants emission in the condition changes in coal or fluctuation in coal quality becomes the very key task for our country’s sustainable development. This work was mainly involved in the technology about combustion optimization of large-scale mixed coal-fired boiler, boiler combustion optimization is to give attention to improve boiler efficiency and reduce nitrogen oxide emissions from boiler through adjustment of boiler operation parameters. It has great practical significance.
     The paper mainly contains mechanisms of NOx formation,, artificial neural networks and some optimizing algorithms. This paper also introduced blending technology and large-scale boilers blending program. It provides a theoretical basis for the establishment of model.
     In this paper, the NOx emission property and boiler efficiency of a 700MW utility tangentially firing coal burned boiler are experimentally investigated, an artificial neural network model on NOx emission property and boiler efficiency of large-scale boiler is developed to predict the NOx emission, and the predicted result indicates the mean relative error of NOx emission and boiler efficiency is 3.63% and 0.23% between experimental value and the calculated value, respectively , which proves the feasibility of the model.
     Finally, the boiler combustion optimization model based on the neural network prediction model of 700MW tangentially coal-fired boiler blending NOx emission and the boiler efficiency, considering the impact of the NOx emission characteristics and boiler combustion efficiency, combined with the genetic algorithm was established. This model combined with boiler tests is used to serch the optimization operating parameters of group 1 with no blending, group 7 with blending C and group 18 with blending B and C. The optimized NOx concentration of group 1 is 421.44 mg·m-3, decreased 37.56%, the boiler efficiency is 94.5%, increased 0.09%; the optimized NOx concentration of group 7 is 255.05 mg·m-3, decreased 29.43 %, the boiler efficiency is 94.13%, increased 0.42% and the optimized NOx concentration of group 18 is 215.40 mg·m-3, decreased 30.56%, the boiler efficiency is 94.80%, increased 0.88%.
     The result shows that the combustion optimization model can be used to reduce boiler NOx emissions and improve boiler efficiency through adjustment of boiler operation parameters when the boiler blending non-design coals; and shows that when domestic coals blending Indonesian coals, more the mixing ratio, less the NOx emission; the actual blending project is much more complicated,so reducing NOx emissions must also take into account other factors such as boiler efficiency; and Blending D and E coal mill is helpful to reduce NOx when domestic coals blending Indonesian coals.
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