Experimental Research On Dropping Strength And Compressive Strength Of Basicity Pellets

The energy consumption of sintering production is high,the emission of CO2,NOx and dust is high.The energy consumption of pellet production is 1/3-1/2 of sintering,and the exhaust gas emission is about 13%of that of sintering.In the winter heating season of 2017,some iron and steel companies were forced to limit their production.In fact,the production of sintering and the use of coal resources were limited and the proportion of sinter in blast furnace charge structure is reduced.In order to change the constitution mode of iron-making raw materials,high basicity sintering easily produces high melting point minerals such as Dicalcium silicate,which lead to poor sinter strength.Therefore,the development and application of fluxed pellets technology has important practical significance.Based on the raw materials provided by a large domestic iron and steel enterprises,the fluxed pellets were tested by disc pelletizer,muffle furnace and electronic universal.Iron ore is magnetite,limestone and calcined lime are used to adjust the basicity of pellets.The ratio of bentonite is 2%,the pelleting time is 33 min and in 1200? calcination temperature 30 min.The different stages pellet strength was studied by controlling the parameters such as pre-added moisture of mixtures,single feed consumption of disc pelletizer and digestion time of mixtures with different particle size and flux addition.The strength and influencing factors of fluxed pellets were discussed.Conclusions:(1)Balling parameters influence on green balls strength.a)By properly increasing the preadded moisture in the mixture improv fluxed pellets strength,but it is difficult to control the size of pellets when it is too high.b)Low moisture content of raw pellets will lead to low strength of pellets,when moisture content is too high,the size of pellets is difficult to control.c)Finer particle size of iron ore increases the strength of pellets at all stage.raw pellets is not obvious and the strength of finished pellets is obviously improved.b)By testing the strength of pellets with different sizes,the larger the diameter pellets with lower the drop strength,but the compressive strength is improved,due to the particularity of the force exerted.Under the experimental conditions,the optimum pre-added water content was 5%,and the optimum raw ball water content was 8-8.5%.Under this condition,the falling strength of fluxed pellets can reach 5.4 times,and the compressive strength can reach 9.6N.(2)Flux type influence on green pellet strength.a)Limestone reduces the fluxed pellets strength.But when the basicity is less than 1.1,pellets strength can still reach more than 2000N,which can produce pellets with strength meeting production requirements.b)Quicklime is added as flux,fluxed pellets strength increases with the increase of basicity,which is due to the positive and negative attraction of Ca(OH)2 and water molecule caused by the dipolarity of water molecule,which improves the capillary cohesion of fluxed pellets.c)Lime is used as flux,the pelletizing mixture with pre-added water digested for 2 hours,and the falling strength and compressive strength of fluxed pellets are improved.Which is due to water and calcium oxide have enough time to form excellent binder calcium hydroxide,but will reduce the production efficiency.(3)Strength of finished fluxed pellets.a)Limestone is used as flux,finished pellets Strength decreases with the increase of basicity,due to the decomposition of carbonate.The increasing of pore size and the formation of low strength silicate minerals.b)Quicklime is used as flux,finished pellets Strength decreases with the increase of basicity,caused by the formation of low strength minerals and the pore formed by cooling crystallization.In summary,different fluxes has different effect to the strength of pellets and the mechanism of action at different stages.According to the experimental conditions and results the optimum parameters of fluxed pellets are as follows:using quicklime flux,digesting for 2 hours,adding 5%water in advance,8.0%-8.5%water in raw pellets.Under this condition,the falling strength of fluxed pellets can reach 5.8 times,the compressive strength can reach 10.2N and the strength of finished pellets can reach 2000N...