| China is the country with the largest steel production in the world.In 2018,China’s crude steel production was 92.862 million tons,accounted for 51.1% of global crude steel production.At the same time,the energy consumption of the steel industry in 2017 accounted for 16.3% of the national energy consumption,which is the high energy consumption industry.The tapping slag temperature in the iron and steel industry is as high as 1450℃-1550℃,which consumes a considerable part from energy consumption of iron and steel industry.In 2018,the molten slag from China’s iron and steel industry contained 13.974 million tons of standard coal energy,of which the blast furnace slag accounts for about two-thirds of the molten slag.At present,the water quenching method is mainly used in the world to treat blast furnace slag,but the water quenching method have the disadvantages of wasting water and unable to recover waste heat.Therefore,the dry granulation method of blast furnace slag was proposed,which can also recover waste heat while used in resource utilization.Among them,the centrifugal granulation method has the greatest advantage as the current research focus.At present,in the process of centrifugal granulation,the mechanism of liquid film granulation at the edge of the granulator is relatively comprehensive.It is mainly believed that there are three modes of slag granulation,they are direct drop formation,ligament formation and sheet formation.A large number of studies have been conducted on the generation conditions of the three modes and the transformation conditions between them.However,at present,there are lack of research on the phase change heat transfer process on the surface of the rotary cup and the thermal protection method of the rotary cup.And there are insufficient understanding of the heat transfer mechanism.In this paper,the VOF model and the k-ω SST turbulence model are used to study the effects of rotary cup in experiment and other rotary cups with different structural parameters on the flow characteristics of molten slag.Then,based on the phase change heat transfer process of the slag on the surface of the rotary cup,the enthalpy model and the discrete ordination radiation model are used to study the characteristics of flow and heat transfer between the slag and the rotary cup at different rotational speeds by transient calculation.To simplify the physical model,without radiation model,obtained the characteristics of flow and heat transfer between the slag and the rotary cup at different tapping slag temperature and slag mass flow rate.Finally,based on the two ideas of setting the refractory and change the heat transfer conditions,the thermal protection effects of the different refractory thickness and thermal conductivity,different cooling air flow rate and heat transfer conditions at the bottom of the rotary cup were studied.And the temperature distribution in the rotary cup was obtained.The main conclusions of this paper are summarized as follows:(1)Compared with the rotary disc of same radius by simulation,the rotary cup used in the experiment can reduce the thickness of the liquid film at the edge by 14.5%,which obviously enhance the granulation.The radius and depth of rotary cup can significantly affect the thickness of the liquid film at the edge of rotary cup,but the inner angle of rotary cup has no effect on it.The radius and depth of rotary cup have a linear relationship with the thickness of the liquid film at the edge of rotary cup.As the radius increases,the thickness of the liquid film at the edge of rotary cup decreases by a maximum of 14.5%,and the granulation effect was enhanced.As the depth increases,the thickness of the liquid film at the edge of rotary cup increases by a maximum of38.4%,and the granulation effect was weakened.(2)During the initial operation of the rotary cup,slag crust were formed on the surface of the rotary cup.Both the thickness of the slag crust and the liquid film decreased with the increase of the rotational speed.At the same time,it was found that the slag crust can significantly reduce the temperature and heat flux on the surface of rotary cup.(3)After reaching steady state for a long time,the slag crust is completely remelted at different slag mass flow rate and the tapping slag temperature between 1450℃-1550℃.The larger mass flow rate and higher tapping slag temperature are both result the higher temperature and heat flux on the surface of rotary cup.(4)By setting refractory on the rotary cup and choosing a refractory with a suitable thickness and thermal conductivity,the highest temperature in the rotary cup can be reduced by 900℃,as can be seen,the thermal protection is effective.The temperature on the side wall of rotary cup can be significantly reduced by cooling air,and the temperature on the center of rotary cup can be significantly reduced by changing the heat transfer conditions at the bottom of rotary cup.Setting the refractory can greatly reduce the highest temperature in the rotary cup,but the stability of the adhesion to the rotary cup needs to be considered.While setting the cooling air and enhancing the heat transfer at the bottom of the rotary cup can not reduce the highest temperature in the rotary cup significantly,but the combination of these methods can play a certain role in thermal protection. |
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