Prediction And Operation Optimization For NOx Emission Property Of Large-scale Mixed Coal-fired Utility Boiler

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.