Mechanism on the Suppression of Sticking and the Fluidization Reduction of Fine Iron Ore by the Combination of Pressure and Plastic Particles

Author:Xu Qi Yan

Supervisor:wang jian jun

Database:Doctor

Degree Year:2018

Download:7

Pages:144

Size:7871K

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The direct fluidization reduction process has several advantages,including a large gas-solid contact area,uniform temperature and concentration,good heat and mass transfer conditions,and high operating efficiency.However,sticking can easily occur in the high temperature fluidization reduction of fine iron ore powder,thereby decreasing the reduction efficiency and hindering the continuous operation of the reduction process.To solve this problem,this paper systematically studies the fluidized reduction of fine iron ore powder under atmospheric pressure,the mechanism of restraining the bounding of fine iron ore particles by high pressure,the mechanism of inhibiting high pressure coupled with plastic particles on the sticking of fine iron ore particles,and the optimization of reduction pressure and reduction time in the reduction process.The main contents and conclusions of this work are outlined as follows:(1)The optimal operating parameters of the fluidized bed reduction of ORD-S fine iron ore under normal atmospheric pressure are systematically studied by using a fluidized bed thermal experimental device.The related kinetics are also analyzed.The optimal operating parameters include a reduction temperature ranging from 923K to1023K,particle size ranging from 0.63 mm to 1.00 mm,linear velocity of 0.6 m/s,and mixture of carbon monoxide and 80%hydrogen.MgO with a size of 2%of the total fine iron ore is selected as an additive.The average apparent activation energy E of the chemical reaction is 22.48 kJ/mol,while the speed control of chemical reaction is the internal diffusion control.(2)The sticking of fine iron ore in the fluidization reduction process can be ascribed to two reasons.First,the reduced iron atoms on the surface of the iron ore come in contact with one another.Second,recrystallization occurs within the Tammann temperature range of the iron atom,thereby leading to the sticking of fine iron ore particles.The mechanical properties of particles are analyzed from three aspects,namely,the drag force of gas to particles,the cohesive force between particles,and the gravity of the particles themselves.The mathematical model of reduction and the fluidizing fine iron ore sticking process can be expressed as (?) Where (?).(3)A high-pressure visible fluidized bed experimental equipment is designed,developed,and visualized to conduct an experimental study on the fluidized reduction process of fine iron ore powder.The optimal operating parameters and reduction effect of pure CO and pure H2 for reducing Australian ore powder under high pressure conditions are also systematically studied.The optimal operating parameters for the reduction of fine iron ore powder by pure CO include a line velocity of 0.8 m/s,reduction pressure of 0.2 MPa,reduction temperature of 1023K,and mineral particle size ranging from 0.18 mm to 0.66 mm.Meanwhile,the optimal operating parameters for the reduction of fine iron ore powder by pure H2 include a line velocity of 0.8 m/s,reduction pressure of 0.2 MPa,reduction temperature of 1073K,and mineral particle size ranging from 0.18 mm to 0.66 mm.The reduction effect of pure H2 is obviously higher than that of pure CO,but the fluidization performance of H2 is lower than that of pure CO.(4)The mechanism of CO and H2 that inhibit the sticking of fine iron ore particles under pressure has been studied.When CO is used as reducing gas,increasing the reduction pressure within an appropriate range can promote a carbon dioxide reaction,increase the precipitation amount of free carbon,effectively prevent the diffusion of iron atoms,prevent a direct contact between iron atoms,or obstruct the hooking of iron whiskers.When pure H2 is used as reduction gas,the reduction pressure can be increased within 0.2 MPa to promote the adsorption of H2 on the surface of fine iron ore,accelerate the reduction reaction,and improve the metallization rate.Chemical reaction resistance and internal diffusion resistance exist at the same time.Chemical reaction resistance is higher than internal diffusion resistance at the initial stage of the reaction,during which the chemical reaction controls the speed.Meanwhile,internal diffusion resistance exceeds chemical reaction resistance in the later stage,during which internal diffusion controls the speed.The relation between the contact area of the iron atom or iron whisker and the reduction temperature satisfies the curve equation Y=AX+BX2+CX3,where A=-0.39079,B=3.45083×10-4,and C=-1.01037×10-7.The contact area of the iron atom or whisker gradually decreases along with an increasing reduction pressure,and the tendency of bounding also gradually decreases.The optimal reduction pressure range is from 0.2 MPa to0.45 MPa.(5)The optimal operating parameters of pressurized energetic waste plastics are systematically studied through an orthogonal experiment and a comprehensive balance analysis.The optimal operating parameters for the reduction of fine iron ore added with waste plastics H2 include a reduction temperature ranging from 923K to973K,line speed of 0.8 m/s,reduction pressure of 0.15 MPa,energy waste plastic particle size ranging from 0.18 mm to 0.66 mm,and an 8%quality content of waste plastic.(6)The occurrence and changes in the content of carbon in the carbon precipitation reaction are studied via XPS,and their effects on sticking are analyzed along with the mechanism of inhibiting the sticking of fine iron ore particles by the coupling of pressurized and energy containing waste plastics.The occurrence states of carbon containing waste plastic cracking can be divided into free carbon and carbon in Fe3C.The carbon in Fe3C can decelerate the sticking of fine iron ore,while free carbon can block the contact between iron particles or restrain the binding of iron whiskers,thereby effectively inhibiting the occurrence of sticking.(7)The influences of reduction pressure and reduction time on the reduction effect are systematically studied under high temperature.After mastering the method for inhibiting the sticking,the fluidization process for treating Brazil,King,Zhangzhuang,Newman,and Gushan iron ores is examined.The optimal reduction pressure and reduction time for reducing fine iron ore by pure H2 are 0.2 MPa and 50 min,respectively,while the optimal reduction pressure and reduction time under the conditions of pressurized energy waste plastic are 0.1 MPa and 65 min,respectively.Under the conditions of pressurization and the coupling of pressure and plastic particles,the reduction of the aforementioned types of iron ores has demonstrated a great metallization and sticking ratio.The fluidized reduction process for the pressurization and coupling of pressure and energy-bearing waste plastics is expected to become an efficient,feasible method for processing domestic fine iron ores.