CN1114360A

CN1114360A - Method for producing direct reduced iron

Info

Publication number: CN1114360A
Application number: CN 94111002
Authority: CN
Inventors: 侯拥和; 黄焯枢; 薛生晖; 李华成; 陈刚; 刘小银; 姜淑芝
Original assignee: Changsha Research Institute Of Mining And Metallurgy ministry Of Metallurgical Industry
Current assignee: Changsha Research Institute Of Mining And Metallurgy ministry Of Metallurgical Industry
Priority date: 1994-05-23
Filing date: 1994-05-23
Publication date: 1996-01-03
Anticipated expiration: 2014-05-23
Also published as: CN1037193C

Abstract

A method for producing direct reduced iron, which is characterized by comprising the following steps: grinding iron ore raw material, solid carbonaceous reducing agent and binder are made into double-layer composite pellets, the inner layer is iron ore, the outer layer is carbonaceous reducing agent, the solid carbonaceous reducing agent in the outer layer pellets is used as reducing agent to reduce iron ore in the inner layer pellets on one hand, and is used as fuel to maintain the temperature of the rotary kiln on the other hand, the pellets are placed in the rotary kiln to be reduced, high-quality direct reduced iron with iron metallization rate of more than 94%, S less than 0.03% and C less than 2% can be obtained, and the capacity of the rotary kiln can reach 0.8t/m³D or more.

Description

Method for producing direct reduced iron

The present invention relates to a production method for obtaining direct reduced iron by reducing iron ore using a solid carbonaceous reducing agent.

At present, the industrialized process for producing direct reduced iron by reducing iron ore with solid carbonaceous reducing agent in the world mainly comprises an SL/RN method, an ARCAR method and the like, wherein the process principle is that a rotary kiln is used as a reactor, iron ore (lump ore) or pellet ore and part of coal are added from the tail of the rotary kiln, part of the coal is thrown from the kiln head, a fan is arranged on the kiln body, air is supplied to the inner part of the kiln section by section through an air pipe so as to maintain a longer high-temperature reaction zone in the kiln, the highest reduction temperature is kept at 1050-1250 ℃, and the iron ore can be reduced into the direct reduced iron with the metallization rate of more than 90%. The prior art for producing direct reduced iron by using a rotary kiln has the main problems that:

(1) the iron-containing material and the solid reducing agent are separated in the kiln, and the chemical reaction process is

(1)

(2) Since the reaction (2) is slower than the reaction (1), the reaction (2) becomes a control step that restricts the reduction of iron ore. Since the reduced coal exists in a lump shape and has a small specific surface, the increase of the reaction rate is limited, which restricts the increase of the reduction rate of the iron ore. In order to reduce iron ore within an industrially acceptable reduction time, the method for accelerating the reaction rate of the formula (2) is mainly to select high-reactivity bituminous coal, and the coal for the direct reduction process has to meet the requirements of high ash melting point and low S content, so that the selection of the coal for the process is greatly limited, and places have to be reserved for purchasing the coal meeting the requirements to meet the process requirements, which increases the arrival cost of the coal to the plant by a large amount.

(2) Because the granularity and the density of iron ore and coal particles are different in the process of moving the materials in the kiln and segregation is easy to occur, the reducing atmosphere in the kiln is distributed unevenly, and the reducing speed of the iron ore is limited at the position where the iron ore is concentrated and on the surface of a material layer because of low reducing atmosphere.

For the above reasons, the current industrialized production of rotary kiln using coal as reducing agent is directly carried outThe raw iron process has low productivity of the reactor, and the yield is generally 0.4t of direct reduced iron/m³D level, resulting in a large investment per ton of direct reduced iron with a corresponding increase in both labour and energy costs.

The invention aims to: the double-layer pelletizing process is adopted, so that the reduction rate of iron ore raw materials in the rotary kiln is accelerated, the productivity of the solid rotary kiln per unit volume is improved, the investment, cost and energy consumption of ton of direct reduced iron are reduced, and the selection range of a solid reducing agent is expanded.

The technical scheme of the invention is as follows: the method comprises the steps of preparing a double-layer composite pellet by adding a binder into a ground iron ore raw material and a solid carbonaceous reducing agent, wherein the inner layer is iron ore, the outer layer is the solid carbonaceous reducing agent, and the solid carbonaceous reducing agent in the pellet on the outer layer is used as a reducing agent to reduce the iron ore in the pellet on one hand and used as a fuel to maintain the temperature of a rotary kiln on the other hand. The pellets are placed in a rotary kiln for reduction, the reduction temperature of the rotary kiln is controlled to be 1000-1300 ℃, iron ore in the pellets is reduced into metallic iron, the pellets discharged out of the rotary kiln enter a cooling cylinder for cooling and are self-ground to remove residual solid carbonaceous reducing agent and ash thereof on the outer layer of the pellets, and high-quality direct reduced iron with the iron metallization rate of more than 94 percent, the sulfur of less than 0.03 percent and the carbon of less than 2 percent can be obtained. The method comprises the following specific steps:

1. preparing the double-layer composite structure pellet:

1) firstly, making finely ground iron ore or iron ore concentrate into an inner layer of a double-layer pellet;

2) the outer layer of the double-layer pellet is formed by wrapping the pellet with a layer of solid carbonaceous reducing agent, wherein the reducing agent can be anthracite, coke powder, bituminous coal, lignite, charcoal, petroleum coke or the combination of the anthracite, the coke powder, the bituminous coal, the lignite, the charcoal and the petroleum coke, and the amount of the reducing agent is 5-150% (dry basis) of the weight of the pellet in the inner layer. If the ash melting point of the solid carbonaceous reducing agent is low and the sulfur content is high, substances such as dolomite, limestone, lime and the like can be added into the reducing agent to adjust the ash melting point of the solid carbonaceous reducing agent to be higher than the carbothermic reduction temperature of iron ore in the pellets, prevent the pellets from forming rings in the rotary kiln at high temperature, fix the sulfur in the solid carbonaceous reducing agent, prevent the sulfur from diffusing into the pellets of the inner iron ore and polluting a reduction product (directly reduced iron), wherein the dosage of the sulfur is 0-100% of the weight of the solid carbonaceous reducing agent.

3) In order to ensure the strength of the pellets, a binder is added during ball making, wherein the binder can be one of or a combination of seven substances, namely asphalt, sodium humate, ammonium humate, water glass, sulfuric acid pulp waste liquid, syrup and lignin silicate, and the added weight is 0.2-15% (dry basis) of the total material amount.

4) The pellets are dried and consolidated at the temperature of 50-600 ℃ for 3-120 minutes, and the moisture is removed to 0-1.5% of the weight of the pellets.

2. Reduction in a rotary kiln:

feeding the double-layer composite pellets into a rotary kiln, and heating the pellets to a temperature higher than the carbothermic reduction temperature of iron ore in the pellets, wherein C in a solid carbonaceous reducing agent on the outer layer of the pellets and CO in kiln gas are firstly added₂The gasification reaction shown in the reaction (2) is carried out, part of CO generated by the reaction enters kiln gas, part of CO is diffused into the pellets on the inner layer, the reduction reaction shown in the reaction (1) is carried out with iron ore in the pellets on the inner layer, and CO generated by the reaction₂And (4) all the iron ore enters the outer layer pellets, and the reaction with the C is continued according to the reaction (2), and the process is circulated until the iron ore in the pellets is completely reduced into metallic iron. Meanwhile, the pellets are formed by pelletizing fine powder and then drying and consolidating, have large porosity, the inner layer and the outer layer can be regarded as porous structures, and because the finely ground iron ore raw materials and the solid carbonaceous reducing agent have large specific surfaces, the reaction can be simultaneously carried out in the whole pellet volume, so that the reaction rate is greatly increased, and the problem of slow reaction rate in the traditional production of direct reduced iron by reducing iron ore by using a coal-based rotary kiln is solved. Thereby improving the productivity of the reactor and greatly reducing the investment, energy consumption and cost.

In addition, the reducing agent is directly attached to the outer layer of the iron ore raw material, so that the reducing agent and the iron ore raw material do not have any segregation problem in a reactor, the problem of unbalanced reduction rate caused by the segregation of the solid carbonaceous reducing agent and the iron ore raw material in the traditional process is solved, and the fast and balanced reduction rate of the iron ore raw material in the industrial kiln is ensured.

And because the solid carbonaceous reducing agent of the pellets on the outer layer is the solid fuel, the part of the rotary kiln where the charging materials are contacted with the kiln gas is the solid fuel rather than the iron ore raw material all the time, so that the interference of the atmosphere in the kiln to the reduction of the iron ore in the pellets is not large, the reduction of the iron ore raw material is ensured to be carried out in high reducing atmosphere all the time, meanwhile, the solid fuel on the outer layer of the pellets can provide energy to maintain the temperature of the rotary kiln required by the reduction of the iron ore, and the energy does not need to be supplemented from the outside of the kiln, and only the oxygen-containing gas required by combustion needs to be provided to the inside.

3. The pellets are put into a cooling cylinder for cooling and self-grinding to remove the residual solid carbonaceous reducingagent and the ash content on the outer layer of the pellets:

the pellets enter the cooling cylinder after leaving the rotary kiln, the pellets can be cooled by spraying water to the cooling cylinder, and meanwhile, the pellets are self-ground in the cooling cylinder, so that residual solid carbonaceous reducing agent and ash thereof on the outer layer of the pellets are separated from the metallized pellets on the inner layer, and impurities cannot be brought into the direct reduced iron, thereby ensuring the quality of the direct reduced iron. And (4) carrying out fine screening and grading on the material discharged from the cooling cylinder and sorting the material by a magnetic separator to obtain the direct reduced iron product.

Example (b): the following tests were carried out according to the procedure described above, with the following results, the chemical composition of the iron ore raw material used being: TFe62.46%, FeO 0.53%, Mn0.065%, SiO₂4.43％、Al₂O₃0.34 percent of coke powder, 0.07 percent of CaO0.07 percent of MgO0.05 percent of S0.01 percent of coke powder, wherein the carbonaceous reducing agent is coke powder, the chemical composition is C72.16 percent, the volatile matter is 3.67 percent, the ash content is 24.17 percent of S0.5 percent, and the ash content is SiO₂66.47％、Al₂O₃23.90 percent, CaO1.12 percent and MgO0.73 percent, firstly grinding the iron ore by a ball mill until the particle size is more than 80 percent with minus 200 meshes, balling in a disc balling machine, adding 1.5 percent (dry basis) sodium humate binder when balling, wherein the moisture content of the ball is 10 percent, and the grain size of the ball is 8 mm. Carrying out secondary pelletizing on the pellets, wrapping a layer of-200 meshes of coke powder more than 80 percent, wherein the coke powderaccounts for 40 percent of the weight of the pellets, mixing-200 meshes of dolomite powder more than 80 percent into the coke powder, the dolomite powder accounts for 10 percent of the weight of the coke powder, drying and consolidating the pellets with the chemical components and physical specifications at 200 ℃, conveying the pellets into an axial ventilation rotary kiln with the diameter of phi 2 multiplied by 30 meters, controlling the highest temperature of materials in the kiln to be 1080 ℃, keeping the materials in the kiln for 2.5 hours, and cooling the pellets discharged from the kiln by a cooling cylinderAnd screening to obtain the direct reduced iron product. The product mass is TFe83.73%, metal iron 80.29%, pellet metallization rate 96%, S content 0.025%, C content 0.93%.

The invention has the advantages and the effects that: (1) the pellet with the double-layer composite structure of the iron ore and the carbonaceous reducing agent is adopted, so that the reduction rate of iron in the pellet is enhanced, the problem of segregation between the reducing agent and iron ore raw materials in a rotary kiln in the traditional process is solved, the reduction rate of the iron ore of the pellet is up to 40 minutes at 1100 ℃, and the metallization rate is 97%. The yield of the rotary kiln of the reactor is 0.4tDRI/m of that of the traditional process due to the improvement of the reduction rate of the iron ore³D is increased to 0.8tDRI/m³D, coke powder and anthracite with poor reactivity can be used as reducing agents, the selection range of process reducing agents is widened, and the invention can ensure that the energy consumption and investment of direct reduced iron of production units are largeAnd decreases. (2) Oxygen-containing gas is fed through the kiln head and the kiln body air pipe of the rotary kiln, oxidation reaction is carried out between the oxygen-containing gas and CO generated in the pellets in the area above the material layer, and heat is supplied to the material layer to meet the requirement of reduction reaction, so that the method of supplying fuel by the kiln head is eliminated, and the structure of the reactor is simplified. (3) The pellet strength is high, and the finished pellet strength index can reach: the falling strength is more than 25 times per meter, the compressive strength is more than 400N per ball, and the abrasion resistance index (-0.5mm) is less than 1.3 percent, thereby ensuring that the pellets are not pulverized in a reactor and ensuring that the process obtains high iron yield. (4) Compared with the internal carbon pellet preparation process, the residual solid carbonaceous reducing agent and ash content in the outer layer of the double-layer pellets after the double-layer pellets are discharged out of the reactor can be easily removed by an autogenous grinding method, so that the iron grade of the product metalized pellets cannot be reduced, residual impurities in the solid reducing agent cannot be brought into the product metalized pellets, and the product quality is ensured.

Claims

1. A method for producing direct reduced iron, comprising the steps of: the method is characterized in that iron ore and a solid carbonaceous reducing agent are ground, mixed and uniformly mixed to prepare pellets, the pellets are dried and consolidated, the pellets are placed in a rotary kiln for reduction, the maximum material bed temperature of the rotary kiln is controlled to be 1000-1300 ℃, and the iron ore in the pellets is reduced into metal iron, and the method is characterized in that: the pellet is made into double-layer composite structure, the inner layer is made into pellet from grinded iron ore or iron ore concentrate, the outer layer is made by wrapping a layer of solid carbonaceous reducing agent on the pellet, binder is added during the pellet making, and the pellet is dried and consolidated.

2. The method for producing direct reduced iron according to claim 1, characterized in that: the solid carbonaceous reducing agent in the outer layer pellet is one of or a combination of bituminous coal, anthracite, coke powder, charcoal, petroleum coke or lignite, and the proportion of the solid carbonaceous reducing agent is 5-150 percent (dry basis) of the weight of the inner layer pellet; one or the combination of dolomite, limestone, lime and silica can be added into the solid carbonaceous reducing agent of the outer layer pellets, and the adding amount is 0 to 100 percent of the weight of the solid carbonaceous reducing agent.

3. The method for producing direct reduced iron according to claim 1, characterized in that: the binder added during the ball making process can be one of or the combination of the following seven, namely asphalt, sodium humate, ammonium humate, water glass separation, sulfite pulp waste liquid, syrup and lignin xanthate, and the addition amount is 0.2-15% (dry basis) of the weight of the added materials.

4. The method for producing direct reduced iron according to claim 1, characterized in that: the pellet drying and solidifying temperature is 50-600 ℃, the solidifying time is 3-120 minutes, and the water is removed to 0-1.5% of the weight of the pellet.