| Blast furnace slag is the main by-product of the blast furnace ironmaking process,which releases a large amount of heat from the high temperature melting state to the complete cooling process.One ton iron produces 0.3 to 0.4 ton of iron slag,of which temperature is above 1500?.It is a hot and difficult point that how to effectively use this part of heat in the current metallurgical industry.The treatment process of molten blast furnace slag directly affects the recovery of heat and the utilization of solid slag.Compared with the previous slag treatment processes,the dry centrifugal granulation technology of high temperature liquid slag has many advantages;The core works of high-temperature slag treatment process is the centrifugal granulation and the rapid cooling of the liquid slag balls.In order to achieve good recovery of waste heat and increase the additional value of granulated slag,it is necessary to granulate the molten blast furnace slag into spherical slag particles which have uniform and controllable size and cool those particles rapidly.The sustainability of the process is the key technology in the dry centrifuge granulation process.The theoretical basis of research,numerical simulation research,laboratory research,semi-industrial experimental study was used in this paper.The mechanism of centrifuge granulation,the phase evolution and heat transfer process were performed for the granulation sustainability of the blast furance slag by the design of the test program,the construction of the test platform and the implementation of the test process.The evolution rules of the phases in the granulation process are clearly defined sand the key control parameters are obtained.Through the pilot test,the feasibility of the process is verified,and high-added industrial raw materials are obtained for the dry granulation treatment of high temperature slags.The industrial application of sensible heat recovery technology provides basic data and theoretical support.The process of dry centrifugal granulation of high temperature slag is divided into five stages,including dilution,crushing,contraction,flight and curing.First,it is assumed that high temperature melt is composed of liquid spherical particles with specific diameter.The process of centrifugal granulation of high temperature slag is studied in terms of force analysis and wave theory of liquid slag.Secondly the process of solid-liquid phase transition during the flight process was studied.The effects of temperature and relative velocity on the solid-liquid phase are studied based on themathematical model of heat transfer and mass transfer in liquid-solid phase.Lastly the mathematical model of centrifugal granulation curing treatment capacity calculation is established.The five stages of high temperature slag were numerically simulated by ANSYS,and the three stages of dilution,fracture and solidification of high temperature melt were simulated.The changes of slag temperature,viscosity and solid fraction in time were The effects of factors such as granulation temperature on the phase transition interface were analyzed.The factors influencing the process of slag oxidation were as follows: particle diameter>temperature field strength>relative velocity.The most typical metallurgical performance index of blast furnace slag is viscosity,which directly affects the granulation process of high temperature melt.The main factors affecting the slag viscosity are the chemical composition and physical temperature of slag.Through the experimental study on the performance of blast furnace slag,the influence of slag composition and temperature on the slag viscosity is obtained.The the influence of The viscosity of high slag on granulation process is analysed,especially the interaction between the high temperature slag and the metal granule in the continuous operation process;the establishment of the slag viscosity,the diameter of the pellet and the angular velocity affect the centrifugal granulation process of the liquid slag model.Based on the mechanism analysis and numerical simulation results,the reasonable operating parameters of the centrifugal granulator,the ability to treat high-temperature molten slag,and the heat exchange efficiency were calculated and tested.The high proportional spherical particles of diameter 1~2mm shape can be obtained with the high temperature slag viscosity coefficient of 0.2 to 0.65 Pa.s,the slag temperature of1450°C~1480°C,?200mm granulation plate and the speed of 1600~1800r/min.In the condition of granulated slag particles and cooling air relative speed 5m/s and the air temperature below 200 °C,the proportion of the spherical slag grain vitrification degree and heat transfer efficiency can reach the highest.Based on theoretical research,laboratory research platform and test platform in the field of blast furnace are established.After a contrastive research on experiment condition of these two platforms and multi-dimensional system optimizations to granulating device,dry centrifugation has achieved a breakthrough in terms of sustainability.A number of technology innovations were achieved to ensure the drygranulation device operate sustainably,such as "overfull slag for high enough temperature,constant diameter for steady performing,rotary flowing air for cooling down quickly,slag film quenching for not bonding,water atomization for safety and slag cover for continuous maintenance".At the same time,during the pilot test,a two-stage heat exchange idea that combines dry centrifugal granulation and vulcanization heat transfer technology was attempted,achieving a heat transfer efficiency of 29%.There are a few conclusions derived from the experimental research results,the Qingdao steel's molten slag viscosity coefficient is around 0.3 Pa.s,the temperature is around 1470 ?,phi 200 mm of granulating disc,the rotation speed round 1740 r/min.We can get a high proportion of 69.4%(1~2 mm diameter)spherical particle shape rules;The environment temperature in Granulating device can reach to 185? and be affected weakly by the speed change.The parameters of consistency with the calculated value is higher. |
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