Reasonable Ore Blending And Process Optimization For Pellet Preparation From Imported Iron Concentrate

In recent years,Chinese iron and steel enterprises mostly use imported iron concentrate as the main raw materials,and use grate-kiln to produce oxidized pellets for blast furnace ironmaking.Due to the unreasonable selection of pellet ore blending and process system in the production process,the pellet oxidation is insufficient,which is easy to produce black core structure,low strength of preheated ball and finished ball,excessive amount of pelletizing binder and other problems,which reduces the grade and performance of pellet,and it is difficult to play the role of concentrate in the smelting process of blast furnace.In this experiment,based on the study of pelletized basic characteristics of four imported iron concentrates A,B,C and D,the optimization of pelletized ore blending structure and grate process system was studied by taking the strength of preheated balls as the assessment index.It provides theoretical and technical support for reducing the amount of pellet binder,eliminating the black core structure of pellet,ensuring the strength of preheated and finished pellets,and improving the reduction performance of pellet.The experimental results show that In the P series blending structure,the comprehensive performance of the pellets under P6 blending structure is the best,the particle size of mixed ore is more reasonable through ore blending,and the properties of raw pellets meet the standards.The compressive strength of preheating Ⅱ section is the highest,which is 967N/P,and the compressive strength of finished pellets is relatively high,which is 3032N/P.The reduction expansion rate is the lowest,which is 5%,and the reducibility is the highest,which is 71%.The compressive strength after reduction is the highest,which is 1466N/P.In the K series blending structure,the comprehensive performance of the pellets under K1 blending structure is the best.Under this structure,the particle size of mixed ore is more reasonable and the performance of raw pellet is better.The compressive strength of the preheating Ⅱ section is high,which is 971N/P,and the compressive strength of the finished pellets is 2813N/P.The reduction expansion rate is relatively low,which is 10%,and the reduction is high,which is 70%,The compressive strength after reduction is relatively high,which is 1163N/P.When optimizing the grate-kiln process,the effect degree of grate process on the strength of P6 preheating pellets is as follows: preheating temperature of the second state > exhaust drying temperature > preheating temperature of the first state > blast drying temperature.The optimal technological parameters of grate are that,drying temperature of the blast state is 250℃,drying temperature of the exhaust state is 300℃,preheating temperature of the first state is 720℃,preheating temperature of the second state is 990℃.Under the optimal chain grate process system,it can accelerate the evaporation of water and oxidation of sulfur in the drying section,and is conducive to the oxidation of magnetite and the migration of hematite microcrystals.The process system can make the preheating pellets fully oxidized.the strength of preheated pellets can reach 1105N/P,Fe O content is 3.26%;The roasting temperature of 1270℃ and the roasting time of 25 min are the suitable technological parameters for kiln,the strength of pellets can reach 3710N/P,Fe O content is less than0.5%,the magnetite can be further oxidized at reasonable roasting temperature,pellet ore is fully oxidized,and the formation of black core can be inhibited.The effect degree of grate process on the strength of K1 preheating pellets is as follows: exhaust drying temperature > blast drying temperature > preheating temperature of the second state > preheating temperature of the first state.The optimal technological parameters of grate are that,drying temperature of the blast state is 200℃,drying temperature of the exhaust state is 360℃,preheating temperature of the first state is 720℃,preheating temperature of the second state is 990℃.The higher drying temperature accelerates the evaporation of water,which is beneficial to the oxidation of magnetite in the preheating section,and the higher preheating temperature accelerates the oxidation of magnetite and the migration of hematite microcrystals,the process system can make the preheating pellets fully oxidized.The strength of preheated pellets can reach 1056N/P,Fe O content is 2.31%;The roasting temperature of1250℃ and the roasting time of 30 min are the suitable technological parameters for kiln,the strength of pellets can reach 3519N/P,Fe O content is less than 0.5%,the magnetite can be further oxidized at reasonable roasting temperature,pellet ore is fully oxidized,and the formation of black core can be inhibited.Iron concentrate K1 was selected as raw materials to explore the influence of the ratio of A,B and C pellet additives on the performance of pellets.The results show that with the increase of the ratio of a and b bentonite,the drop strength,compressive strength of pellets and the compressive strengthof roasted pellets all increase,the optimum ratio of a bentonite is 2.5% and b bentonite is 2%.When using mixed additives,the appropriate ratio is: With 1.5% a + 0.5% c,When bentonite a and organic binder c are mixed,organic compounds volatiliz,gangue content decreas,porosity is moderate,and pellet structure is reasonable.The pellet drop strength is 6.9 times/(0.5m),compressive strength of the pellet is 13.6N/P,the compressive strength of the finished pellet is 3099N/P,the reducability is 70%,and the TFe content is 64.01%,which is about 0.5% higher than that of the bentonite pelletwith a alone.