Method for directly producing reduced iron and DRI production equipment

Abstract

1. A method for producing direct reduced iron, in which iron ore is reduced in a DRI shaft by a reducing gas comprising hydrogen obtained by extraction from coke oven gas through a hydrogen separation unit, and a remaining portion of such coke oven gas is at least partially injected into a transition section of the DRI shaft to set the carbon content of the direct reduced iron to 0.5-3 wt. %, as well as a DRI production plant comprising a DRI shaft (1) and a hydrogen separation unit (5), the inlet of which is connected to a coke oven gas source (6), a first outlet connected to the DRI shaft for injecting hydrogen separated from the coke oven gas, and a second outlet connected to a transition section of the DRI shaft (1) for injecting at least a portion of the remaining portion of such coke oven gas.

Description

Technical Field

[0001] The present invention relates to a method for producing direct reduced iron (DRI) and DRI production equipment.

Background Art

[0002] Currently, steel can be produced through two major manufacturing routes. Today, the most commonly used production route is to produce pig iron in a blast furnace using a reducing agent, mainly coke, to reduce iron oxide. In this method, about 450 - 600 kg of coke is consumed per metric ton of pig iron, and this method emits a large amount of CO2 in both the production of coke from coal in a coking plant and the production of pig iron.

[0003] The second major route involves the so-called "direct reduction method". Among them, there are methods by brands such as MIDREX, FINMET, ENERGIRON / HYL, COREX, FINEX, etc., and sponge iron is produced in the form of HDRI (hot direct reduced iron), CDRI (cold direct reduced iron) or HBI (hot briquetted iron) from the direct reduction of an iron oxide carrier. Sponge iron in the form of HDRI, CDRI, and HBI is usually further processed in an electric arc furnace.

[0004] Each direct reduction shaft with low-temperature DRI discharge has three zones: a top reduction zone, a central transition zone, and a conical bottom cooling zone. In high-temperature discharge DRI, this bottom part is mainly used for homogenization of the product before discharge.

[0005] The reduction of iron oxide occurs in the upper section of the furnace at a temperature of up to 950°C. Iron oxide ores and pellets containing about 30% by weight of oxygen are charged to the top of the direct reduction shaft and dropped by gravity through a reducing gas. This reducing gas enters the furnace from the bottom of the reduction zone and flows countercurrently to the charged iron oxide. The oxygen contained in the ores and pellets is removed by the stepwise reduction of iron oxide in the countercurrent reaction between the gas and the oxide. While the gas is moving to the top of the furnace, the oxidized body content of the gas is increasing.

[0006] Reducing gases generally contain hydrogen and carbon monoxide (synthesis gas) and are obtained by catalytic reforming of natural gas. For example, in the so-called MIDREX process, the first methane is converted into a reformer through the following reaction, producing synthesis gas or reducing gas: CH4 + CO2 → 2CO + 2H2 Iron oxide reacts with reducing gases, for example, according to the following reaction: 3Fe2O3 + CO / H2 → 2Fe3O4 + CO2 / H2O Fe3O4 + CO / H2 → 3FeO + CO2 / H2O FeO + CO / H2 → Fe + CO2 / H2O At the edge of the reduction zone, the ore is metallized.

[0007] The transition section is located below the reduction section and is long enough to separate the reduction section from the cooling section, allowing for independent control of both sections. In this section, carbonization of the metallization product occurs. Carbonization is a process that increases the carbon content of the metallization product inside the reduction furnace through the following reaction: 3Fe+CH4→Fe3C+2H2 (endothermic) 3Fe + 2CO → Fe3C + CO2 (exothermic reaction) 3Fe + CO + H2 → Fe3C + H2O (exothermic reaction)

[0008] Injecting natural gas into the transition zone promotes hydrocarbon cracking and carbon deposition by utilizing the sensible heat of metallization products within the transition zone. Due to the relatively low concentration of oxidizers, the natural gas in the transition zone is more likely to be cracked into H2 and carbon than reformed into H2 and CO. Natural gas cracking provides carbon for DRI carbonization and simultaneously adds a reducing agent (H2) to the gas, increasing its reduction potential.

[0009] Given the significant increase in atmospheric CO2 concentration since the beginning of the last century and the subsequent greenhouse effect, it is essential to reduce CO2 emissions in places where large amounts of CO2 are generated, and therefore especially during DRI production. [Overview of the project] [Problems that the invention aims to solve]

[0010] Based on the above, there is a need for a direct method of producing reduced iron that is CO2 neutral, environmentally friendly, and easy to implement, while demonstrating good yield. [Means for solving the problem]

[0011] This problem is solved by a method for producing directly reduced iron, in which iron ore is reduced in a DRI shaft by a hydrogen-containing reducing gas obtained by extraction from coke oven gas through a hydrogen separation unit, and the remaining portion of such coke oven gas is at least partially injected into the transition section of the DRI shaft to set the carbon content of the directly reduced iron to 0.5 to 3% by weight.

[0012] The method of the present invention may also include the following optional features, which are considered separately or in all possible technical combinations: - The reducing gas further comprises top gas from the DRI shaft, which is mixed with the hydrogen obtained by extraction from the coke oven gas. - The reducing gas further comprises an additional reducing agent gas selected from hydrogen and biogas, which is mixed with the hydrogen obtained by extraction from coke oven gas. -Such reducing gases are heated after mixing, - Heating of reducing gases is performed using CO2-neutral electricity. - The reducing gas is injected into the reducing section of the DRI shaft. -The top gas coming from the DRI shaft is scrubbed to remove water before being mixed with the reducing gas. -The remaining portion of such coke oven gas is partially injected into the cooling section of the DRI shaft, - The carbon content of directly reduced iron is set to 1-2% by weight.

[0013] Within the framework of this invention, directly reduced iron covers so-called DRI, but also covers high-temperature briquette iron (HBI), low-temperature directly reduced iron (CDRI), and high-temperature directly reduced iron (HDRI). Such materials can be subsequently used in different processes, such as the process of producing pig iron in a blast furnace, or the process of producing steel in a BOF or electric arc furnace. They can also be used as flammable materials or as electrodes in batteries.

[0014] The present invention also relates to a DRI production facility including a DRI shaft and a hydrogen separation unit, wherein the inlet of the hydrogen separation unit is connected to a coke oven gas supply source and includes a first outlet connected to the DRI shaft for injecting hydrogen separated from the coke oven gas, and a second outlet connected to a transition section of the DRI shaft for injecting at least a portion of the residual portion of such coke oven gas.

[0015] The equipment may also include the following optional features, which are considered separately or in all possible technical combinations: -A mixer is provided, which includes a first inlet connected to the first outlet of the hydrogen separation unit and a second inlet connected to the top gas outlet of the DRI shaft. - The mixer includes a third inlet connected to an additional reducing agent gas supply source. - The mixer is connected to the reduction section of the DRI shaft, -A scrubber is provided connected to the gas outlet at the top of the DRI shaft.

[0016] Other features and advantages of the present invention will become apparent from the description of the invention, which is given below as reference to the accompanying drawings and is not in any way limiting. [Brief explanation of the drawing]

[0017] [Figure 1] This is a diagram showing the DRI manufacturing equipment according to the present invention.

Embodiments for Carrying Out the Invention

[0018] The elements in the figure are for illustration and may not be drawn to scale.

[0019] Figure 1 is a schematic diagram of the DRI manufacturing equipment according to the present invention. The DRI manufacturing equipment includes a DRI shaft 1 having, from top to bottom, an inlet 10 for iron ore that moves through a shaft by gravity, a reduction section located at the upper part of the shaft, a transition section located at the central part of the shaft, a cooling section located at the bottom, and an outlet 12 from which direct reduced iron is finally extracted.

[0020] At the top of the shaft, the top gas exiting the DRI shaft is collected in a pipe 20 that can be optionally connected to a scrubber 2 located at the top gas outlet of the DRI shaft. The top gas exiting the DRI shaft usually contains H2, CO, CH4, H2O, CO2, and N2 in various proportions. The top gas scrubbing operation makes it possible to remove water vapor from the rest of the stream and improve its reduction potential.

[0021] In a preferred embodiment, after scrubbing, the top gas contains 40 - 75% by volume of H2, 0 - 30% by volume of carbon monoxide CO, 0 - 10% by volume of methane CH4, 0 - 25% by volume of carbon dioxide CO2, up to 5% by volume of H2O, and the remainder is nitrogen N2. After scrubbing, the H2 / N2 ratio in such top gas is preferably 1.5 - 3.

[0022] When the top gas exits the scrubber 2, it can be optionally compressed and either sent back to the DRI shaft or sent to one of the inlets of a mixer 4 through a connecting pipe 21.

[0023] Another inlet of the mixer 4 can be connected to a reducing gas supply source 3. Such a reducing gas may consist of hydrogen or hydrocarbon gases, such as methane. In a preferred embodiment, the hydrogen supply source is supplied with green hydrogen produced without emitting CO2 by water or steam electrolysis, which can be powered, for example, by CO2-neutral electricity.

[0024] CO2-neutral electricity, in particular, includes electricity from renewable resources but does not emit CO2, thus enabling the use of electricity derived from nuclear sources. CO2 from renewable resources is defined as energy collected from renewable resources that are naturally replenished on a human timescale, including sources such as sunlight, wind, rain, tides, waves, and geothermal energy.

[0025] In another embodiment, the reducing agent gas source consists of biogas, which is a renewable energy source that can be obtained by the decomposition of organic matter in the absence of oxygen inside a closed system called a bioreactor. Biogas can be produced from raw materials such as agricultural waste, fertilizers, municipal waste, plant materials, sewage, biological waste, food waste, or any biodegradable material. A preferred biogas is, for example, biomethane.

[0026] The third inlet of the mixer 4 is connected to the outlet of the separation unit 5. Such a separation unit 5 is connected to a coke oven gas supply source 6. The coke oven gas composition typically contains 3-6 volume% CO, 1-5 volume% CO2, 36-62 volume% H2, 16-27 volume% CH4, and the remainder being nitrogen. Coke oven gas is produced as a byproduct of coke production and is typically used to sinter coke oven batteries or simply burned. In most cases, its further use results in CO2 emissions into the atmosphere.

[0027] The separation unit 5 allows hydrogen to be extracted from such a flow and sent to the mixer 4 through the connecting pipe 50.

[0028] The separation unit may be based on any suitable industrial process for gas separation, such as physical and chemical absorption steps, adsorption steps, or membrane steps.

[0029] In a preferred embodiment, the separation unit is pressure swing adsorption (PSA).

[0030] In another embodiment, the separation unit is a membrane, preferably a ceramic microporous membrane.

[0031] The reducing gas produced in the mixer 4 by the addition of top gas, additional reducing agent gas, and hydrogen from the coke oven gas can optionally be heated through a heating means provided in the mixer, which is powered, for example, preferably by CO2 neutral electricity or by burning a portion of the coke oven gas. In a preferred embodiment, the temperature of the reducing gas is set in the range of 700°C to 1000°C, preferably 800°C to 1000°C.

[0032] Next, this reducing gas is returned through the tube 11 to the DRI shaft, preferably its reduction section.

[0033] Upon returning to the separation unit 5, the residual portion of the gas obtained after hydrogen extraction is sent back to the transition section of the DRI shaft 1 through the connecting pipe 51.

[0034] This gas injection is performed to increase the carbon content of the directly reduced iron to a range of 0.5 to 3% by weight, preferably 1 to 2% by weight, thereby making it possible to obtain directly reduced iron that is easy to handle and maintains good combustion potential for its future use.

[0035] The DRI manufacturing equipment may further include a recycling loop in the cooling section that allows for the extraction of a portion of the gas present at that level, sending it to the scrubber 30 and compression unit 31, and then reinjecting it into shaft 1.

[0036] In a preferred embodiment, a portion of the gas transported in the connecting pipe 51 may also be injected into such a recycling loop in the cooling section after the compression unit to increase the carbon content of the directly reduced iron in the cooling section.

[0037] Since such gases have reducing power thanks to their content in CO and residual H2, it is also possible to inject a portion of the gas transported in the connecting pipe 51 into the reduction section in the DRI shaft.

[0038] By using the method according to the present invention, reduced iron can be directly produced with appropriate quality and yield while keeping CO2 neutral and optimally utilizing gas by-products from coke production. It is also possible to reduce the use of fossil energy sources such as natural gas.

Claims

1. A method for producing directly reduced iron, wherein iron ore is reduced in a DRI shaft by a reducing gas containing hydrogen obtained by extraction from coke oven gas through a hydrogen separation unit, and the residual portion of the coke oven gas is at least partially injected into the transition section of the DRI shaft to set the carbon content of the directly reduced iron to a range of 0.5 to 3% by weight. A method wherein the reducing gas produced by mixing the hydrogen obtained by extraction from coke oven gas with an additional reducing gas selected from hydrogen and biogas is supplied to the DRI shaft by a mixer connected to an additional reducing gas source.

2. The method according to claim 1, further comprising top gas exiting the DRI shaft, wherein the reducing gas is mixed with the hydrogen obtained by extraction from coke oven gas.

3. The method according to claim 2, wherein the top gas is scrubbed to remove water before being mixed with the reducing gas.

4. The method according to claim 2 or 3, wherein the reducing gas is heated after mixing.

5. The heating of the reducing gas is CO ２ The method according to claim 4, which is carried out using neutral electricity.

6. The method according to any one of claims 1 to 5, wherein the reducing gas is injected into the reduction section of the DRI shaft.

7. The method according to any one of claims 1 to 6, wherein the residual portion of the coke oven gas is partially injected into the cooling section of the DRI shaft.

8. The method according to any one of claims 1 to 7, wherein the carbon content of the directly reduced iron is set to 1 to 2% by weight.

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