Numerical Simulation Of Particle Segregation Behavior During The Sintering Charging Process And The Combustion During The Sintering Process

The sintering burden charging and combustion process are two important links during the sintering process,for the sintering burden charging process,the segregation distribution with the small particles decreasing while the large ones increasing along the vertical direction of the sintering pallet is beneficial to improving the permeability of the bed and avoiding the under-burning at the upper part or over-burning at the bottom part because of the uneven temperature distribution;the coke combustion is the main source of heat in the whole sintering process,the simulation of coke combustion in the sintering process is a better method to know the temperature distribution than the measurement in the practical process because the sintering pallet is a “black box” and it is difficult know its inner temperature distribution.As a result,there are two parts in this paper.The first part is the sintering burden charging process,a nine-roller burden distribution model with respect to the NO.2 sintering machine in Shougang China was established to simulate the burden charging process,the segregation degree(SD)and segregation tendency(ST)are defined to describe the ternary-sized particle size segregation behaviors,the main conclusions are:(1)The mass fraction of ternary-sized particle first fluctuate apparently during the initial and then approaches to and stable value by calculating the mass fraction of ternarysized particle changing with time in the four areas and the stable value of the ternarysized particles at four areas shows a good agreement with the measured results in the practical production process.(2)In the base case study,the SD at upper layer is larger than then initial SD by 0.147,while that at layer 3 is smaller than the initial SD by 0.002,and that at layer 2 and layer 4 is almost the same with the initial SD.For the ST,the results shows that the largesized particles are mainly locates in the bottom layer of the sintering pallet while the small-sized particles are mainly locates at the upper layer and the medium-sized particle distributes evenly along the vertical direction,the maximum ST of the large-and smallsized particle can reach as great as 0.347 and 0.178,the reason of which are mainly the horizontal velocity difference at the exit of the NO 1 roller and the velocity of the largesized is larger than the small-sized particles’ by 0.3 m/s,while the vertical velocity of ternary-sized are all about-1.7m/s.(3)The ST at the upper and bottom part shows the opposite changing tendency with increasing the nine-roller rotating speed and the former decreases to 0.295 and the later increases to 0.256,while that middle layer do not change obviously.The segregation of ternary-sized particle changes little except for the upper and bottom layer,they also show the opposite change regular,the segregation of the large-sized particle is improved at the upper layer as the ST increases from-0.175 to-0.121 while worsen at the bottom layer as the ST increases to 0.238;on the other hand,the segregation of the small-sized particle is improve as the ST decreases by 0.054 at the upper layer while almost fluctuate around 0 at the bottom layer.(4)The friction coefficient between particle and wall makes much influence to the SD at the upper and bottom layer.Obviously,the SD at layer decreases with increasing of the friction coefficient and the minimum value is 0.116,while that at layer 4 shows the opposite regular and the maximum value can reach as great as 0.473.The SD at layer 2 and layer 3 both show the increasing tendency with the increase of the friction coefficient and the maximum value of SD are 0.216 and 0.359 respectively.The ST of the large-sized particle increases with the increase of the friction coefficient at all layers and the maximum of ST can reach 0.472,while the small-sized particle shows the opposite regular and the minimum is-0.260,and the medium-sized particle also shows different changing tendency.Besides,the mass fraction difference of the large-sized and smallsized particle between the upper and bottom layer increases with increasing the friction coefficient can the maximum difference can reach as great as 0.732.The second part is the coke combustion process simulation of the sintering process,a 1-dimensional sintering model was established based on the sintering pot in the laboratory and the combustion process during the sintering process was simulated by using the Fluid Dynamics code Fluent and the User Define Function(UDF),the main conclusions are:(1)The temperature contours distribution of the bed indicates the temperature distributes evenly along the horizontal direction while the highest temperature increases with the time along the vertical direction and the highest temperature can reach as great as 1621 K and the thickness of the high temperature beyond 1373 K is about 8cm.The temperature at different height changing with time shows that the temperature at the same height of the bed first increases and then decrease with time and the higher the height is,the higher the temperature,and the duration time of high temperature zone increases.The temperature contours distribution of the section of the sintering pallet can be divided into three zone apparently,namely sintering completion zone,combustion zone and unreacted zone.Finally,there shows agreement between the simulation and measured result and the parameters can be used to the following simulation.(2)The temperature of the whole bed increases with the increasing of the carbon content and the duration time of high temperature zone increases and the highest temperature can reach as great as 1707 k when the carbon content is 3.5%.The increasing of the ignition temperature makes much influence to the temperature of the upper part while the bottom part can be neglected and there is little changing in the temperature contours distribution.The highest temperature of the bed increases with the increase of the bed porosity and the maximum is 1801 K,while the duration time of high temperature zone and the time of the sintering process are both shorten and the area of high temperature zone in the temperature contours distribution decreases.(3)Deep bed sintering is simulated by adding the height of the model,when the height of the model is 80 cm,the highest of the bed can reaches as great as 1697 K and the time of the sintering process increases by 414 s and the production efficiency increases by 13.08% as well.After changing the adding zone of the model into wider zone,the temperature distribution of the bed along the horizontal direction demonstrates that the temperature of the edge zone is higher than that of the center zone and the highest temperature difference can reaches as great as 222 K,while the time reaching the highest temperature of the center zone is faster by 260 than that of the edge zone.After changing the adding zone of the model into trapezium with different angles,the results shows that the increasing of the angle of the trapezium will increase the highest temperature of the edge zone and the time reaching the highest temperature,the highest temperature of the edge zone can reach 1962 K and the time is 2754 s when the angle of the trapezium is 33.7°.On the other hand,the temperature at different depth under different angle of the trapezium is also calculated and the results that the time reaching the highest increasing in the center zone with the increase of the angle and the highest value decreases,while that in the edge shows the opposite regular,and the temperature difference between the center and edge zone gradually increase with the angle of the trapezium.