Numerical Simulation Of Nitrogen Oxides Formation And Control Technology For Four-channel Burner In Rotary Cement Kiln

Nitrogen oxides are one of the major sources of air poulltion and rotary kiln is the main production source of Nitrogen oxides in the cement industry. At the same time, developing low NOx technology and low NOx equipment have become an inevitable trend with the continuous increase of NOx emission standards. In order to improve the performance of the burner and reduce the emission of pollutants, a design & research institute developed a new four-channel burner, but there are some problems in practical application, such as too much NOx emissions. Because the restrictions of measuring method in rotary cement kiln, it is significant to solve the problems in the actual operation process through numerical simulation. This paper mainly study the NOx formation and control method of rotary cement kiln, and tried to find the method of NOx control by changing the burner operating parameters.Firstly, this paper summarized and compared the mathematical models used in the numerical simulation of the pulverized coal combustion in rotary cement kiln. Emphasize introduced the principles of the mathematical model, compared the accauracy of Kinetic/diffusion-limitted model and CBK model, two-competing reaction model and CPD model, and established a set of mathematical model for NOx formation in a full-scale rotary cement kiln. The results indicated that the optimization mathematical model suitable for the numerical simulation of the pulverized coal combustion in rotary cement kiln.Next, based on the commercial FLUENT software, this paper studied the combustion performance of burner on the designed conditions by numerical simulation. At the same time, this paper detailed analysis the gas phase velocity field and the distribution of internal and external backflow. The results can accurately express internal flow pattern of burner, achieve the purpose to understand gas flow field. In addition, this paper emphasize discusses the distribution of the temperature field, important gas components concentration and NOx concentration. The result show that temperature distribution and the position of high temperature agree well with measurement in the site. Qualitative analysis, the distribution trend of oxygen,NOx and other important components concentration is correct, which provides a theoretical support for the research and development of burner.Finally, by changing the parameters of the axial and the swirling velocities of the wind, we studied the important impaction to the flow structure and the generation of NOx. And the results show that the larger the axial velocity, the closer to the axis the high temperature zone, and the more reasonable the distribution of the gas temperature. When the swirling velocity gets larger, the flame become shorter and thicker, which is agree well with the observations from the industry. In addition, as the axial and swirling velocities increase, the formation of the NOx increases slightly in the initial part of the combustion. At the same time, we find a reduction of the peak of the concentration of NOx, which effectively controls the emission concentration of NOx in the export. Moreover, the trend of the distribution of the concentration of NOx is qualitatively correct, which can be taken as a reference in the industry.