The Effect Of Different Coal Injection Locations On NO_x Formation And Raw Meal Decomposition Rate In KDS Precalciner

The decomposition furnace uses the high-temperature flue gas provided by the rotary kiln and the heat provided by the combustion of the pulverized coal in the decomposition furnace to preheat,pre-decompose and separate the raw materials.The decomposition furnace makes full use of pulverized coal combustion to release energy to improve the thermal efficiency of the entire system and reduce system energy consumption.At present,the working condition of the decomposition industry of the cement industry still stays on the surface basic data(temperature,air volume,gas composition at a certain point),and the actual production control of the decomposition furnace is basically based on experience.Accurately obtaining the distribution of temperature field,velocity field,pressure field,material trajectory and gas composition inside the decomposition furnace can vigorously advance the cement production technology.The NO_x emissions of the cement industry are large.The national “ 13 th Five-Year Plan” document on emission reduction pollutants points out that various industries should vigorously reduce NO_x emissions.The decomposition furnace is the main equipment for generating NO_x in the cement production process.Research can provide theoretical basis and guiding direction for NO_x emission reduction work.In this paper,the CFD simulation technology is used to carry out parametric modeling and analysis of the decomposition furnace.The formation mechanism and process of NO_x are analyzed by changing the angle of injection and the height of the position.The following results are obtained.Before the simulation calculation of the decomposition furnace,the traditional thermal calibration is carried out,the basic data is collected,and the basic operation status is grasped.The results show that the internal temperature field and velocity field of the decomposition furnace are unstable.There is an insufficient position of pulverized coal combustion,high CO content,and low NO content.The overall O2 content of the decomposition furnace is too high,resulting in an excessive NOX content.The final decomposition rate of raw meal is over 91%.The basic data provides initial calculation conditions and accurate boundary conditions for the simulation calculation of the decomposition furnace.The research on the basic model of the decomposition furnace found that the structural mesh and the unstructured mesh division model are used,and the mesh quality of each part meets the research requirements,and the simulation results are consistent with the actual situation.The tertiary air enters horizontally from both sides of the decomposition furnace,collides with the rising kiln tail gas phase,and forms two symmetrical recirculation zones in the furnace.The pulverized coal residence time increases,which promotes the combustion of pulverized coal and the decomposition of raw materials.The production of NO_x is mainly affected by the concentration of O2.The NO_x content at the large O2 concentration is high,and the NO_x at the outlet of the decomposition furnace is 546 ppm.The temperature distribution in the decomposition furnace is uniform,the edge temperature is high,the intermediate temperature is low,and the temperature is up to 1600k,which satisfies the raw material decomposition demand,and the final decomposition rate of the raw meal is 90.5%.The simulation of the spun coal pipe rotating counterclockwise by 10°,20°,30° and 40° shows that the larger the angle of the coal injection pipe is,the more chaotic the pulverized coal trajectory is,which can be better dispersed in the interior of the decomposition furnace,and the tertiary wind Adaptability is enhanced.After the rotation of 40 °,the coal injection pipe and the third air pipe have the best adaptability,and the raw material decomposition rate is also up to 91.7%.As the moving angle increases,the NO_x emissions of the decomposition furnace decrease.According to the research and analysis of different coal injection heights,the lower the position of the coal injection pipe,the more disordered the distribution of the cone velocity of the decomposition furnace,and the worse the compatibility of the coal powder and the tertiary wind.In the movement of the decomposition furnace,the pulverized coal in the coal injection pipe with the third air duct is better than the pulverized coal in the coal injection pipe far from the tertiary air duct,which is beneficial to reduce the NO_x content in the decomposition furnace.The lower the position of the coal injection pipe,the lower the decomposition rate of the raw meal,and the lower the NO content at the outlet of the decomposition furnace.Through the simulation study on the angle and height of coal injection in the decomposition furnace,the structural characteristics of the decomposition furnace and the formation mechanism of NO_x were mastered,which provided theoretical basis and guidance for the NO_x reduction of this type of decomposition furnace.