| Ferroalloy is an essential additive agent during steelmaking,which is offen used as alloying agent and deoxidizer,and for which it is called the “monosodium glutamate” in steelmaking industry.At present,in most steelmaking plant,ferroalloy is added to the converter must be met some requirements: moderate particle size(about 10 mm),regular shape(spherical),high purity(low oxidation and less impurities)and so on.However,the obtained ferroalloy particles are usually inhomogeneous particle size,serious segregation and irregular shape by traditional ferroalloy granulation process on the basis of crushing mechanism.In addition,the crushing process would result in a large proportion dust,which not only polluting the environment,but also is harmful to our body,and it will take much time and cost to process these dust.To solve these problems,a lot of ferroalloy granulation technologies had been developed and studied,and some of them had been used in industrial production.But there are still tow common problems in these granulation processes: one is that most granulation technologies are still crushing process,just the crushing method has changed,but problems caused by crushing still can not be solved.The other is that the water-cooling is almost used in these processes,although high cooling intensity can be provided,the oxidation,environmental pollution,safety,waste heat recovery and other issues can not be effectively resolved.For the above problems facing ferroalloy granulation,a new ferroalloy granulation process is introduced in this paper,and corresponding granulating devices are designed.The granulation mechanism,particle morphology,particle size distribution and particle surface oxidation state were systematically studied by means of experimental study and theoretical ananlysis.On this basis,the dimensional prediction model,the flight dynamics model and the cooling process model of granulated ferroalloy droplet were established,and the calculated model values are compared with the experimental results.In addition,granulation experiments are completed with different material cup,the effect rules of wettability between granulator and ferroalloy on granulation behavior had been studied.The main conclutions are as follows:(1)Under the laboratory conditions,through the novel ferroalloy high temperature granulation process of which granulator is multi-nozzle rotary cup,the obtained ferroalloy particles are well spherical,homogeneous particle size and small proportion fine particles,and granulated particles below 1 mm can be avoided effectively.(2)The rotating speed and nozzle diameter are important parameters affecting the morphology and particle size distribution of ferroalloy particles.In 10 mm and 12 mm nozzle diameter and 150~200rpm rotating speed,the average particle size of obtained particles is about 10 mm,and the ratio of particles below 4mm is less than 10%,in the current experimental conditions,which is the best granulation condition.(3)It is found that the surface oxidation degree of granulated ferroalloy particles is related to particle size and cooling medium.In the condition of water cooling,both the oxidation degree and oxide layer thickness decreased with the increse of particle size,oxygen content and surface oxide layer thickness of granulated FeSi75 particles are only 0.05% and 16?m respectively in the range of 10~13mm particle size,which is in accordance with the requirements of large size and high purity for steel plants.In the same particle size range,the particle oxidation degree by air-cooling is lower than that of water-cooling,the oxygen absorption is about 0.07% below 4mm particle size by air-cooling,however,the water-cooling is about 0.13%,moreover,compared with water-cooling,the air-cooling is more effective and economical for the next heat recovery process.(4)The microstructure of granulated particles is more fine than that of raw material,and the phase composition is relatively homogeneous,which means this novel ferroalloy high temperature granulation process can eniminate the segregation of raw material effectively.(5)It can be found that the splitting model of Fe Si75 by multi-nozzle rotary cup is mainly linear splitting through experimental observation and theoretical calculations.The droplet size prediction model was established by Rayleigh spoiler theory:(?),and the calculated results were in good agreement with the experimental results.The flight trajectory model was established by Newton's laws of motion:(?),and the distribution characteristic of ferroalloy particles was obtained.The cooling process model of droplet was established by Newton's law of cooling: 4 4(?),and the change of temperature with time,air volume and the relationship of air volume and solidification time were obtained during flight.These established models will have a significant guiding for industrial production and the selection of wast heat recovery methods.(6)The interfacial tension between FeSi75 and rotary cup is one of the important factors that affect the granulation behavior of ferroalloy.The larger interfacial tension,the worse wettability between ferroalloy and rotary cup,and ferroalloy is easier to get out of the rotary cup.It has a good wetting between FeSi75 and graphite,the apparent contact angle is about 7.5°,while the apparent contact angle is about 45° between FeSi75 and alumina.In contrast,the better spherical shape and more homogeneous particle size can be obtained by alumina cup,however,the average particle size is lower than that of graphite cup,which indicates that it is necessary to choose poor wetting material as the granulator for good spherical shape particles,and to choose well weeting material as granulator for large size particles.Considering into the cost and frangibility of alumina cup and other issues,comprehensive analysis,the graphite cup for ferroalloy granulation is economical and effective choice. |
PDF Full Text Request