Research On Rotary Kiln Structure Optimization And Indirect Measurement Of High Temperature Flue Gas Temperature

Rotary kiln is an important high temperature calcination equipment in industry.It is widely used in cement,metallurgy and other production links.The internal temperature control is directly related to the stable operation,product quality and production cost of the entire production line.However,direct measurement of fuel gas temperature in calcination section of rotary kiln is always a difficult problem.As the same time,the heat utilization rate of the traditional rotary kiln is less than 80%,and there is some space for energy saving.Aiming at the problem that the heat utilization rate of the rotary kiln needs to be improved,this paper conducted a further structural optimization study on the 9 m pellet roasting variable diameter rotary kiln for Jiugang.That is,by using CFD numerical simulation technology,simulate the internal combustion temperature field of the 9 m variable diameter rotary kiln with the improved structure of Jiugang,and compare with the traditional straight 9 m rotary kiln.It is found that the variable diameter rotary kiln is superior to the straight rotary kiln,because the temperature is higher in the preheating section.Than under the appropriate working conditions,through structure adjustment of the kiln head and kiln tail structure,changing the length of variable diameter section,and changing the position of the variable diameter section,further structural optimization research on the structure of the variable diameter rotary kiln was made.It is found that the nozzle is installed at the end with a large inner diameter,the length of the variable diameter section is set to 1 m,and the position of the variable diameter section is close to the nozzle,which is the optimal structure of the variable diameter rotary kiln.The simulation shows that the optimal structure of the rotary kiln is 5%energy saving compared to the traditional straight rotary kiln.If calculated according to the pellet production volume of 100,000 t/a,the annual LNG saving can be about 18,000 m³.Aiming at the problem that the maximum temperature of fuel gas in the calcining section of the rotary kiln is difficult to measure directly,an indirectly measurement method is proposed.That is,analyze the thermal equilibrium in a pellet kiln,and based on two points of simplification,a new thermal equilibrium equation is proposed:Q_{secondary air}+Q_fuel=Q_{fuel gas}+Q_wall+Q_mineral.By using the formulas to deduce the relationship between flue gas temperature fluctuations in the calcination section and kiln exhaust temperature during stable operation of the rotary kiln.Then,put forward the theoretical relation equation.Finally,establish a 3D model of?5×33m pellet rotary kiln,by using numerical simulation to test the theoretical relation equation.The linear relation is t_y=0.468t_r+573.029,R²=0.997.The practical significance of this equation is that we can measure the maximum temperature of fuel gas in the calcination section which is unable to be measured directed by indirect measuring kiln exhaust temperature.It provides the basic theoretical guidance for on-line temperature monitoring and automatic adjustment of flame temperature in calcining section of rotary kiln.