Numerical Simulation Of Flow Field And NO_x Distribution In NST Calciner

As the core equipment of the new dry cement technology,the decomposing furnace is responsible for the decomposition of raw materials and pulverized coal combustion,but also produces a large amount of nitrogen oxides.With the increasing attention to environmental protection,it is urgent to reduce the nitrogen oxide emissions in the cement industry.Oxygen content and combustion state of coal are the main factors affecting nitrogen oxides in calciner.In this paper,numerical calculation of NST calciner of 4800t/d cement production line in a factory is carried out by CFD simulation technology combined with field thermal testing.The effect of different excess air quantity on the distribution of nitrogen oxides in the calciner was studied.The effect of pulverized coal to the total coal volume in the coal injection area of three air pipe coal injection zones on the nitrogen oxide distribution in the calciner is studied.The main conclusions are as follows:The test results show that on the coal injection pipe platform at the cone of the calciner,the high temperature tertiary air quickly confluence with the coal powder in the coal injection pipe0.3m away from its upper boundary,and the combustion reaction is rapid.The measured temperature here is about 1300℃,and the concentration of NO is as high as 1000 ppm.Numerical calculation shows that local high temperature occurs in the coal injection area near the tertiary air duct(0.3m away from the upper boundary of the tertiary air duct).The oxygen content at the outlet of the calciner was 2.1% and NO was 502 ppm by numerical calculation,while the oxygen content at the outlet of the calciner was 2.5% and NO was 523 ppm by measured calculation.The NO distribution of the calciner is affected by the third wind motion trajectory.In the NST calciner,the third air enters the calciner horizontally and is squeezed by the ascending kiln gas,and the trajectory of the third air rises spirally.As the amount of excess air increases,the velocity of the third wind increases,and the spiral degree increases.The movement trajectory of pulverized coal is also affected by the third wind,and the region with high NO value is in a spiral distribution.Near the third wind,the coal powder is moved by the third wind,and the movement trajectory is concentrated in the center of the calciner,resulting in a 1000 ppm NO high value area.The distribution of NO on the horizontal surface of the calciner is uneven,and the performance is "high in the middle,low around".With the increase of pulverized coal in this region,the uneven distribution of NO becomes worse.