Method for producing direct reduced iron by coupling gas-solid dual reducing agent

Abstract

This invention belongs to the field of non-blast furnace ironmaking, and specifically relates to a method for producing direct reduced iron using a gas-solid dual-reducing agent coupling process. This invention is the first to propose a process for producing direct reduced iron using a carbon-based solid reducing agent and a hydrogen-rich gaseous reducing agent coupling process, which improves the product reaction rate, increases production capacity, and reduces energy consumption. Due to the addition of the gas reduction reaction, the kiln temperature can be quickly adjusted by controlling the gas injection flow rate, resulting in high process flexibility. In this invention, iron ore reacts with the gas-solid dual-reducing agent in a solid phase at a low reaction temperature. Only iron oxide is selectively reduced in the iron ore, with very little other metallic elements or harmful impurities entering the metallic iron, resulting in high iron purity and the production of high-quality direct reduced iron products.

Description

Technical Field

[0001] This invention belongs to the field of non-blast furnace ironmaking, specifically a method for producing direct reduced iron by coupling gas and solid dual reducing agents. Background Technology

[0002] Currently, China has an overcapacity in the steel industry, and the government is actively advocating for changes in the steel industry structure and the development of short-process steel production technology. This has led to a growing demand for scrap steel, especially scrap steel with lower impurity content. Scrap steel is the main raw material for short-process steelmaking, and almost 100% of the harmful impurities such as Sn, As, and Cu remain in the steel. Therefore, simply using scrap steel to improve steelmaking quality is extremely difficult. Direct reduced iron (DRI) has advantages such as fewer impurity elements, making it crucial for smelting high-quality and special steels, such as stainless steel, oil casing, automotive steel, nuclear power plant steel, and military steel. In fact, it can be said that the production of special and high-quality steels necessitates the use of DRI.

[0003] In 2021, global direct reduced iron (DRE) production reached approximately 100 million tons, with about 72% produced using gas-based shaft furnace processes and about 24% using coal-based rotary kiln processes. In gas-based DRE, the reducing gas is CO and H2, converted from natural gas, petroleum gas, coke oven gas, and coal gas through reforming, which is used to reduce iron concentrate into DRE in a shaft furnace. The coal-based rotary kiln process uses carbon from coal as a reducing agent to reduce oxidized pellets or chilled pellets into DRE in a rotary kiln. Other equipment for DRE production includes tunnel kilns and rotary hearth furnaces. Given my country's scarcity of natural gas and other resources, developing gas-based reduction processes using coke oven gas or other reducing gases, or coal-based reduction processes, has significant development potential.

[0004] Traditional rotary kiln direct reduction is a typical coal-based direct reduction process. Rotary kiln direct reduction offers advantages such as low investment costs and high product quality. However, traditional rotary kilns use coal exclusively as the reducing agent, resulting in problems such as poor temperature control precision within the kiln, high discharge temperature leading to ring formation, slow heating rate in the preheating zone at the feed end, high energy consumption, and low production capacity. Summary of the Invention

[0005] This invention aims to provide a process for producing direct reduced iron using a rotary kiln with gas-solid dual reducing agent coupling, which solves the problems of poor temperature control accuracy inside the existing rotary kiln, high discharge temperature, easy ring formation, slow heating rate of the preheating zone at the feed end, high energy consumption, and low production capacity.

[0006] A method for producing direct reduced iron using a gas-solid dual-reducing agent coupling process is provided, comprising the following steps:

[0007] Step 1: The iron-containing raw materials in the raw material silo are fed into the rotary kiln feed inlet via the batching belt.

[0008] Step 2: The large-particle solid reducing agent with a particle size of 16-30mm in the auxiliary material silo is fed into the rotary kiln feed inlet simultaneously with the iron-containing raw materials via the batching belt.

[0009] Step 3: Using air as a carrier, inject small-particle solid reducing agent with a particle size of less than 16mm from the auxiliary material silo into the rotary kiln at high speed at the discharge end.

[0010] Step 4: Inject the gaseous reducing agent into the rotary kiln at the discharge end;

[0011] Step 5: Secondary air is introduced into the kiln by blowers arranged in the kiln body, and the temperature inside the kiln is regulated by controlling the air volume.

[0012] Step 6: Inside the rotary kiln, the iron-containing raw material is reduced by a combination of solid and gaseous reducing agents at a temperature of 900-1300℃, and then discharged at the discharge end of the kiln.

[0013] Step 7: The material discharged from the outlet end is screened by a hot vibrating screen. The block material is hot-pressed to become the finished product, direct reduced iron hot-pressed block. The carbon-containing powder material is recycled and reused.

[0014] Furthermore, in step 1, the iron-containing raw material is one of the following: iron oxide pellets, lumpy iron ore, iron-containing solid waste, vanadium-titanium magnetite, laterite nickel ore, copper slag, and red mud.

[0015] Furthermore, in steps 2 and 3, the solid reducing agent is one of coal, coke fines, semi-coke, or semi-coke; in step 2, the weight ratio of the iron-containing raw material to the large-particle solid reducing agent is 10:3; in step 3, the weight ratio of the iron-containing raw material to the small-particle solid reducing agent is 10:1.

[0016] Furthermore, in step 4, the reducing gas includes one of natural gas, coke oven gas, petroleum gas, blast furnace gas, converter gas, or coal gas; the amount of coke oven gas added as the reducing gas agent is 300 Nm³. 3 / t of iron-containing raw materials.

[0017] Furthermore, in step 6, the coupling reduction time is 100 minutes.

[0018] Furthermore, step 7 can be replaced by: the material discharged from the discharge end is cooled by a water cooling cylinder, screened, the block material is sponge iron, the powder is magnetically separated, the magnetically separated powder is cold-pressed into direct reduced iron cold-pressed block product, and the remaining material is mainly carbon-containing powder, which is returned for reuse.

[0019] Compared with the prior art, the present invention can achieve at least the following beneficial effects:

[0020] (1) This invention proposes a method for reducing iron ore in a rotary kiln using a combination of gas and solid reducing agents. The solid reducing agent can be fixed carbon from one of the low-value-added energy sources such as coal, coke fines, semi-coke, and semi-coke, thus reducing the consumption of coal resources; the gaseous reducing agent can be one of natural gas, coke oven gas, petroleum gas, blast furnace gas, converter gas, and coal gasification, making full use of the high reaction efficiency of gases, improving energy utilization, and reducing energy consumption.

[0021] (2) In this invention, ambient temperature reducing gas is injected into the discharge end, which cools the material at the discharge end. This can prevent the local material from overheating and forming rings at the discharge end of the rotary kiln due to the exothermic reaction of carbon reduction, which is beneficial to improving the service life of the kiln.

[0022] (3) The gaseous reducing agent of the present invention decomposes into carbon and hydrogen at a temperature above 700°C after being injected into the kiln. The carbon and hydrogen can directly participate in the reduction reaction of iron ore. In particular, the addition of hydrogen reduction shortens the reduction reaction time and is conducive to improving the direct reduction metallization rate of iron ore.

[0023] (4) The gaseous reducing agent injected into the discharge end of the present invention participates in the reduction reaction in the high-temperature reduction section. The excess carbon and hydrogen flow to the feed end and mix with the combustion air injected into the secondary air blower of the kiln body to burn and release heat, which increases the temperature of the preheating section and heating section of the rotary kiln and is conducive to increasing the production capacity of the rotary kiln.

[0024] (5) The flow of the gaseous reducing agent from the discharge end to the feed end of the present invention drives the combustion air injected by the secondary air blower of the kiln to be evenly distributed in the kiln body, avoiding local high temperature caused by excessive local combustion air, which causes ring formation in the rotary kiln, thereby improving the uniformity of temperature distribution in the rotary kiln and helping to improve the service life of the rotary kiln.

[0025] (6) In this invention, iron ore reacts with a gas-solid dual reducing agent in a solid phase at a reaction temperature of 900-1300℃. The reaction temperature is low and the energy consumption is low. Furthermore, due to the addition of the gas reduction reaction, the kiln temperature can be quickly adjusted by controlling the gas injection flow rate, resulting in high process adjustment flexibility.

[0026] (7) In this invention, the iron ore reacts with a gas-solid dual reducing agent in a solid phase. Only iron oxide is selectively reduced in the iron ore, and very few other metal elements or harmful impurities enter the metallic iron, resulting in high iron purity. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0028] Figure 1 This is a flowchart of a method for producing direct reduced iron using a gas-solid dual-reducing agent coupling according to the present invention;

[0029] Figure 2 This is a process flow diagram of the gas-solid dual reducing agent coupling for the production of direct reduced iron, followed by a sieving-hot pressing process according to the present invention.

[0030] Figure 3 This is a process flow diagram of the present invention for the production of direct reduced iron by gas-solid dual reducing agent coupling, followed by a process of water cooling cylinder protection cooling, magnetic separation, and cold pressing. Detailed Implementation

[0031] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0032] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known structures, methods, apparatuses, implementations, materials, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0033] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention.

[0034] Example 1

[0035] A method for producing direct reduced iron using a gas-solid dual-reducing agent coupling process includes the following steps:

[0036] Step 1: The TFe70.2% iron oxide pellets are fed into the rotary kiln feed inlet via a batching belt.

[0037] Step 2: Solid reducing agent coke powder is fed into the rotary kiln feed inlet simultaneously with iron oxide pellets via a batching belt. It is used to reduce iron ore and provide heat for the reaction. The weight ratio of iron oxide pellets to large-particle coke powder is 10:3. The particle size of the large-particle reducing agent coke powder is 16-30mm, which includes 11wt% ash, 1.4wt% volatile matter, 86.31wt% fixed carbon, and others.

[0038] Step 3: The solid reducing agent coke powder is injected into the rotary kiln at high speed at the discharge end using air as a carrier. It is used to reduce iron ore and provide heat for the reaction. The weight ratio of iron oxide pellets to small-particle coke powder is 10:1. The solid reducing agent is one of coal, coke powder, semi-coke, or semi-coke. The particle size of the reducing agent coke powder is less than 16mm, and it includes 11wt% ash, 1.4wt% volatile matter, 86.31wt% fixed carbon, and others.

[0039] Step 4: Inject coke oven gas, the gaseous reducing agent, into the rotary kiln at the discharge end for reducing iron ore and supplementing the reaction heat. A preferred embodiment is that the coke oven gas injection rate is 300 Nm³. 3 / t iron oxide pellets; due to the addition of gas reduction reaction, the temperature inside the kiln can be quickly adjusted by controlling the gas injection flow rate, and the process adjustment is highly flexible; the gas reducing agent has an H2 content of 60.92%, a CH4 content of 21.03%, and a CO content of 8.87% in the coke oven gas.

[0040] Step 5: Secondary air is introduced into the kiln by blowers arranged in the kiln body, and the temperature inside the kiln is regulated by air volume control; the air volume control can be adjusted by a variable frequency motor, and the air distribution is based on the reduction situation during the operation of the variable frequency motor, and the air distribution is based on the needs of completing the combustion reaction.

[0041] Step 6: In the rotary kiln, the iron oxide pellets are reduced by a combination of solid reducing agent coke powder and gaseous reducing agent coke oven gas at a temperature of 1050-1150℃ for 100 minutes, and then discharged at the discharge end of the kiln body; preferably, the iron oxide pellets are reduced by a combination of solid reducing agent and gaseous reducing agent at a temperature of 1100℃.

[0042] Step 7: The material discharged from the outlet end is screened by a hot vibrating screen. The block material is hot-pressed to become the finished product, direct reduced iron hot-pressed block. The carbon-containing powder material is recycled and reused.

[0043] The hot-pressed direct reduced iron briquettes obtained had a total iron content of 97.6% and a metallization rate of 95.22%.

[0044] Example 2

[0045] A method for producing direct reduced iron using gas-solid dual reducing agent coupling, following the steps described in Example 1, but with changes to the reaction temperature and coupling reduction reaction time in step 6, yields hot-pressed direct reduced iron blocks with total iron content TFe and metallization rate ηFe, as shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049] Example 3

[0050] A method for producing direct reduced iron using a gas-solid dual reducing agent coupling method is described in Example 1, but the gaseous reducing agent in step 4 is changed. The gaseous reducing agent is adjusted to natural gas, petroleum gas, blast furnace gas, converter gas, and coal gas, respectively. The total iron content and metallization rate of the hot-pressed direct reduced iron briquettes are shown in Table 2.

[0051] Table 2

[0052]

[0053] Example 4

[0054] A method for producing direct reduced iron using gas-solid dual reducing agent coupling, following the steps described in Example 1, involves adjusting the iron oxide pellets in step 1 to have the following contents: iron ore TFe 57%; vanadium-titanium magnetite TFe 55.6%; iron-containing solid waste TFe 56%; laterite nickel ore 47%; copper slag TFe 40%; and red mud TFe 56%. The total iron content and metallization rate of the resulting hot-pressed direct reduced iron briquettes are shown in Table 3.

[0055] Table 3

[0056]

[0057] Example 5

[0058] A method for producing direct reduced iron using gas-solid dual reducing agent coupling, following the steps described in Example 1, wherein step 7 is adjusted so that the material discharged from the outlet is cooled by a water cooling cylinder, screened, the lumpy material is sponge iron, the powder is magnetically separated, the magnetically separated powder is cold-pressed to produce direct reduced iron cold-pressed briquettes, and the remaining material is mainly carbon-containing powder, which is returned for reuse.

[0059] The cold-pressed direct reduced iron briquettes produced had a total iron content of 96.7% and a metallization rate of 94.31%.

Claims

1. A method for producing direct reduced iron using a gas-solid dual-reducing agent coupling process, characterized in that: Step 1: The iron-containing raw materials in the raw material silo are fed into the rotary kiln feed inlet via the batching belt. Step 2: The large-particle solid reducing agent in the auxiliary material silo is fed into the rotary kiln feed inlet simultaneously with the iron-containing raw material via the batching belt; the particle size of the large-particle solid reducing agent is 16-30mm, and the weight ratio of the iron-containing raw material to the large-particle solid reducing agent is 10:

3. Step 3: The small-particle solid reducing agent in the auxiliary material silo is sprayed into the kiln at the discharge end of the rotary kiln using air as a carrier; the particle size of the small-particle solid reducing agent is less than 16mm, and the weight ratio of the iron-containing raw material to the small-particle solid reducing agent is 10:

1. Step 4: Inject the gaseous reducing agent into the rotary kiln at the discharge end for reducing iron ore and supplementing the reaction heat. The gaseous reducing agent is one of natural gas, coke oven gas, petroleum gas, blast furnace gas, converter gas, or coal gasification. The addition of the gaseous reducing agent can be used to quickly adjust the kiln temperature by controlling the gas injection flow rate. The coke oven gas containing the gaseous reducing agent has an H2 content of 60.92%, a CH4 content of 21.03%, and a CO content of 8.87%. Step 5: Secondary air is introduced into the kiln by blowers arranged in the kiln body, and the temperature inside the kiln is regulated by controlling the air volume. Step 6: Inside the rotary kiln, the iron-containing raw material is reduced by a combination of solid and gaseous reducing agents at a temperature of 1200℃-1300℃, and then discharged from the kiln outlet; the combined reduction time is 100 minutes. Step 7: The material discharged from the outlet end is screened by a hot vibrating screen. The block material is hot-pressed to become the finished product, direct reduced iron hot-pressed block. The carbon-containing powder material is recycled and reused. The direct reduced iron hot press block prepared by the method has a total iron content of ≥95% and a metallization rate of ≥93%.

2. The method for producing direct reduced iron using gas-solid dual reducing agent coupling according to claim 1, characterized in that: In step 1, the iron-containing raw material is one of the following: iron oxide pellets, iron ore, iron-containing solid waste, vanadium-titanium magnetite, laterite nickel ore, copper slag, and red mud.

3. The method for producing direct reduced iron using gas-solid dual reducing agent coupling according to claim 1, characterized in that: In steps 2 and 3, the solid reducing agent is one of coal, coke fines, semi-coke, or semi-coke.

4. The method for producing direct reduced iron using gas-solid dual reducing agent coupling according to claim 1, characterized in that: In step 4, the natural gas has a CH4 content of 94.56%, a C2H6 content of 2.74%, a C3H8 content of 0.54%, and an N2 content of 1.18%; the petroleum gas has a C3H8 content of 96.2%; the blast furnace gas has an H2 content of 1.6%, a CO content of 24.9%, a CO2 content of 14.9%, and an N2 content of 58.4%; the converter gas has a CO content of 62.2%, a CO2 content of 16.2%, and an N2 content of 13.4%; and the coal gas has a CO content of 29.3%, a H2 content of 12.5%, a CO2 content of 2.24%, a CH4 content of 2.2%, and an N2 content of 53.4%.

5. The method for producing direct reduced iron using gas-solid dual reducing agent coupling according to claim 1, characterized in that: In step 4, the amount of gaseous reducing agent added is 300 Nm³. 3 / t of iron-containing raw materials.

6. The method for producing direct reduced iron using gas-solid dual reducing agent coupling according to claim 1, characterized in that: Step 7 may further include: the material discharged from the discharge end is cooled by a water cooling cylinder, screened, the block material is sponge iron, the powder is magnetically separated, the magnetically separated powder is cold-pressed into direct reduced iron cold-pressed block product, and the remaining material is mainly carbon-containing powder.

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