Investigation On Optimizing Permeability And Temperature Field Of Sintering Bed

As an important energy saving measure, deep-bed sintering is widely applied to the sintering process because of its heat-accumulation effect. However, when the bed depth exceeds700mm,sintering permeability goes bad and the distribution of temperature field through the bed depth is considerably uneven, making the sintering index decline and the depth of sintering layer difficult to rise further. Therefore, it is necessary to optimize the structure of sintering layer for the development of deep-bed sintering technology and decline of solid fuel consumption.For sintering mixture with irregular granular shapes and wide size distribution, fitting and modifying Ergun equation to obtain the formula to describe pressure dropping of sinter bed:The relationship between sintering permeability and properties of granulated mixture is studied, and the results show that, for constructing good sintering permeability, the mean size of mixture,-1mm powder content and the shape coefficient of granulated balls should be satisfied to be more than4.5mm,less than5%and above0.88respectively. Meanwhile, the influencing factors of sintering permeability also are studied, which indicates that sintering permeability is good when adhering fines content of mixture varies from45to50%and specific surface area of the adhering fines is above1000cm2/g.The characteristics of temperature field in sintering bed are studied, which illustrate that both the highest temperature and high temperature duration time increase, while the cooling speed slows down. Part of surface sinter is raw because of the highest temperature and high temperature duration time are not enough. Besides, the sinter tends to have more flaws, lower mechanical strength and finished product ratio as a result of having no time to crystallize for cold-blast air is sucked into the sinter bed leading to high cooling speed. Because of the heat-accumulation, the highest temperature of sintering bed is excess, so that the bottom sinter is burned excessively, giving rise to poor reducibility. Through mini-sintering experiment, the reasonable temperature field of sintering bed has been proposed in the paper:the highest temperature is about1300℃, the high temperature keep time should be no less than3min and the cooling speed should be under100℃/min.The comprehensive optimizing technology of building reasonable bed structure is studied. Through optimizing ore proportioning, the specific surface area of adhesive fines is increased from785cm2/g to1050cm2/g, and of which the content is reduced from52.54%to46.67%by optimizing ore-blending. Otherwise, the pressure dropping is reduced from759Pa to554.33Pa, the vertical sintering speed is faster by1.53mm/min and the utilization coefficient is higher by1.1t/(m2·h) Segregated feeding is used to optimize the temperature field distribution. The temperature of whole sinter bed tends to be uniform as well as the permeability and quality of sinter in the upper layer are improved as a result of the segregation of size distribution, fuel and flux so the sintering utilization coefficient is higher, the sinter quality of whole bed is more uniform, the appropriate bed height is increased from680mm to830mm and the solid fuel consumption is reduced from57.04kg/t to55.30kg/t.After optimizing the heat curves by using hot blast sintering, the highest temperature and the high temperature keep time of surface sinter is enhanced, the cooling speed is slowed down, the quality of surface sinter becomes better. The solid fuel consumption is reduced from57.04kg/t to55.91kg/t when the temperature of hot blast is400℃. On the basis of optimizing ore proportioning, combining segregated feeding with hot blast sintering benefits to achieve good sintering indexes compared with the referential scheme. The appropriate bed height is increased from680mm to830mm, the coke ratio is reduced from5.0%to4.7%, the vertical sintering speed、the sinter yield、the tumbler index and the utilization coefficient all become better, the solid fuel consumption is reduced from57.04kg/t to53.40kg/t, the quality of sinter through the sintering layer is more uniform and its microstructure is also more reasonable.