Method for producing low temperature direct reduced iron
By optimizing the flow rates and temperatures of reducing and cooling gases in the direct reduction process, the method enhances energy efficiency and maintains product quality in the production of direct reduced iron.
Patent Information
- Application Number
- JP2025515337
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-09-30
- Filing Date
- 2023-09-26
- Publication Date
- 2025-09-19
AI Technical Summary
Existing methods for producing direct reduced iron (DRI) using hydrogen gas are inefficient in terms of energy consumption, particularly due to suboptimal flow rates of cooling and reducing gases, which affect the quality and efficiency of the reduction process.
A method involving the direct introduction of a reducing gas heated to a specific temperature into the reduction section, followed by a cooling gas into the cooling section, with controlled flow rates to optimize heat exchange and minimize energy consumption, while maintaining product quality by adjusting gas temperatures and flow rates to achieve optimal metallization.
The method reduces energy consumption by optimizing gas flow rates and temperatures, ensuring efficient production of high-quality DRI by maintaining the metallization degree within acceptable limits.
Smart Images
Figure 2025531124000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention provides a method for producing direct reduced iron (DRI), comprising the steps of: a) introducing iron ore into an ore inlet of a direct reduction shaft; b) heating a reducing gas consisting essentially of hydrogen to a reducing gas temperature Tredgas and introducing the heated reducing gas into a reduction section of the direct reduction shaft to form a first component portion of a reducing gas that reduces the iron ore to high-temperature DRI at a reduction temperature Tred, wherein Tredgas>Tred; c) introducing a cooling gas consisting essentially of hydrogen and having a temperature Tcoolgas into a cooling section of the direct reduction shaft, wherein the cooling section is located downstream of the reduction section in the flow direction of the DRI, and the cooling gas is introduced adjacent to the reduction section. a) introducing the hot cooled gas into an end of the cooling section opposite the end of the cooling section where the hot DRI having a temperature Tdritop is introduced into the cooling section, thereby cooling the hot DRI having a temperature Tdritop upon entering the cooling section to the cold DRI and heating the cooled gas (by heat exchange with the countercurrent DRI) to a temperature Tcooltop, such that the cold DRI exiting the cooling section has a temperature Tdriout; b) allowing the hot cooled gas to enter the reducing section of the direct reduction shaft and mix with the heated reduced gas to form a second component portion of the reduced gas; and c) removing the spent reduced gas from an upper portion of the reducing section of the direct reduction shaft as top gas, said top gas having a temperature Ttopgas. [Background technology]
[0002] In connection with the reduction of iron oxide to iron using hydrogen gas, prior art, for example, CN111926135A, proposes using hydrogen gas both as a reducing gas that is heated and introduced into the reduction section of the reduction shaft, and as a cooling gas that is introduced into a cooling section downstream of the reduction section. The cooling gas is allowed to flow in the opposite direction to the flow direction of the direct reduced iron (DRI) passing through the cooling section, and is allowed to flow up to the reduction section, where it mixes with the externally heated reducing gas and contributes to the reduction process in the reduction section. Because the cooling gas has a significantly lower temperature than the DRI entering the cooling section from the reduction section, it undergoes heat exchange with the DRI, making the process more energy efficient.
[0003] However, CN111926135A is silent about how to optimize the flow rates of the cooling gas and the heated reducing gas, respectively, to achieve a more energy-efficient process while still obtaining a product that meets certain quality standards. Summary of the Invention [Problem to be solved by the invention]
[0004] It is therefore an object of the present invention to provide a method that improves energy efficiency compared to the prior art, as defined herein above and in the preamble of claim 1. In particular, the present invention aims to reduce the energy consumption associated with heating, by an external heater, a reduction gas that is introduced directly into the reduction section (without passing through a cooling section). [Means for solving the problem]
[0005] The object of the present invention is to provide a method for producing direct reduced iron (DRI), comprising the steps of: a) introducing iron ore into an ore inlet of a direct reduction shaft; b) Heating a reducing gas consisting essentially of hydrogen to a reducing gas temperature Tredgas, introducing the heated reducing gas directly into the reduction section of a direct reduction shaft to form a first component portion of the reducing gas for reducing iron ore to high-temperature DRI at a reduction temperature Tred, with Tredgas > Tred, c) Introducing a cooling gas consisting essentially of hydrogen and having a temperature Tcoolgas directly into the cooling section of a direct reduction shaft, the cooling section being located downstream of the reduction section as viewed in the flow direction of the DRI, the cooling gas being introduced into an end of the cooling section that faces an end of the cooling section adjacent to the reduction section, thereby cooling high-temperature DRI having a temperature Tdritop when entering the cooling section to low-temperature DRI, heating the cooling gas to a temperature Tcooltop, and the low-temperature DRI exiting the cooling section having a temperature Tdriout, d) Enabling a hot cooling gas to enter the reduction section of a direct reduction shaft and mix with the heated reducing gas to form a second component portion of the reducing gas, and e) Removing the used reducing gas as top gas from the upper portion of the reduction section of a direct reduction shaft, the top gas having a temperature Ttopgas including, the method being f) Measuring Tdriout and controlling the flow rate of the cooling gas to the cooling section so that Tdriout < Tdrioutmax, where Tdrioutmax is the set maximum allowable temperature of the DRI exiting the cooling section, [[ID=!2]]g) Measuring the temperature Tcooltop of the heated cooling gas and increasing the flow rate FRcoolgas of the cooling gas introduced into the cooling section until Tcooltop = Tcooltopmin, where Tcooltopmin is a predetermined minimum allowable temperature of the heated cooling gas and Tcooltopmin ≤ Tdritop, h) Adjusting the flow rate FRredgas of the heated reducing gas to form a first component portion, determining the metallization degree of the produced DRI, measuring the top gas temperature Ttopgas therebetween, and determining a minimum top gas temperature Ttopgasmin below which the metallization degree is less than the minimum allowable value, i) measuring the top gas temperature Ttopgas and controlling at least one of the flow rate FRredgas of the heated reducing gas and the temperature Tredgas to which the heated reducing gas is heated before being introduced into the reduction section so that Ttopgasmin≦Ttopgas≦Topgasmax, where Topgasmax is the set maximum allowable temperature of the top gas; This is achieved by a method further comprising:
[0006] Step g) results in an optimization of the heat exchange between the cooling gas and the DRI, allowing a relatively low flow rate of the externally heated reduction gas introduced into the reduction section, thereby contributing to less energy consumption by the heater or heaters used to heat the first component part of the reduction gas.
[0007] Step h) can be accomplished by adjusting the flow rate of the first component portion, measuring the corresponding top gas temperature, and performing laboratory measurements of the metallization degree of the DRI corresponding to different flow rate levels and top gas temperatures, and determining at which top gas temperature the metallization degree becomes unacceptable from a product quality standpoint.
[0008] Steps h) and i) prevent excessive total flow of reducing gas through the reduction shaft, thus contributing to a reduction in the flow rate of the first component portion of the reducing gas, and consequently to a reduction in energy consumption by the heater used to heat said first component portion. There is a relationship between the top gas temperature and the final metallization degree of the final product, i.e., DRI. By examining this relationship, it is possible to determine a minimum top gas temperature, Ttopgasmin, below which the metallization degree is below the minimum acceptable value. Therefore, at a top gas temperature above Ttopgasmin, an acceptable metallization degree is achieved. Step i) helps to achieve a sufficient top gas temperature, and thus a sufficient metallization degree.
[0009] Tdritop may be determined by indirect temperature measurement. The peak temperature of Tcooltop measured at a low cooling gas flow rate serves as an indicator of Tdritop.
[0010] According to one embodiment, Ttopgasmax = Topgasmin + 50°C.
[0011] According to one embodiment, Ttopgasmax = Topgasmin + 25°C.
[0012] According to one embodiment, Ttopgasmax = Topgasmin.
[0013] According to one embodiment, Tcooltopmin = Tdritop - 50°C.
[0014] According to one embodiment, Tcooltopmin = Tdritop - 25°C.
[0015] According to one embodiment, Tcooltopmin = Tdritop - 10°C.
[0016] According to one embodiment, Tcooltopmin = Tdritop.
[0017] According to one embodiment, the minimum allowable value of the degree of metallization is 90 wt%, preferably 94 wt%, more preferably 96 wt%, or even more preferably 98 wt%.
[0018] According to one embodiment, 850°C < Tredgas < 1200°C. According to another embodiment, 950°C < Tredgas < 1100°C.
[0019] According to one embodiment, 900°C < Tred < 1000°C.
[0020]
[0021] [Figure 1] 1 is a schematic diagram of a portion of an apparatus for the direct reduction of iron ore to sponge iron. [Figure 2] 1 is a flow chart illustrating an embodiment of a method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION
[0022] With reference to Figure 1, an apparatus for the direct reduction of iron ore to sponge iron is shown, to which the method according to the invention can be applied.
[0023] The apparatus includes a direct reduction shaft 1 having an inlet 2 for introducing iron ore into the shaft 1. The bottom of the shaft 1 is provided with an outlet 3 for removing pelletized sponge iron of the direct reduced iron (DRI). The direct reduction shaft 1 includes a reduction section 4 where the reduction of the iron ore takes place and a cooling section 5 where the DRI is cooled before exiting the shaft 1 through the outlet 3. The direct reduction shaft 1 is a vertical shaft, in which the reduction section 4 is located at the top of the cooling section 5, the inlet 2 for introducing the iron ore is located at the top of the reduction section 4, and the outlet for removing the DRI is located at the bottom end of the cooling section 5. In other words, the cooling section 5 is located downstream of the reduction section 4 in the flow direction of the DRI. As a result of the design, as will be disclosed later, cooling gas is introduced at the end of the cooling section 5 opposite the end of the cooling section 5 adjacent to the reduction section 4.
[0024] The apparatus further includes a hydrogen gas source 6 including an electrolyzer arranged to produce hydrogen gas from water. A first gas line 7 extends from the hydrogen gas source 6 to a heater device 8, which in a preferred embodiment includes a plurality of electric heaters. The first gas line 7 further extends from the heater device 8 to a reduction gas inlet 9, through which hydrogen gas heated by the heater device 8 and conducted through the first gas line 7 is introduced into the reduction section 4 of the reduction shaft 1.
[0025] The second gas line 10 extends from the hydrogen gas source 6 to the cooling gas inlet 11, through which unheated hydrogen gas from the hydrogen gas source 6 is introduced into the cooling section 5 of the direct reduction shaft 1. The cooling gas inlet 11 is provided at the bottom of the cooling section 5.
[0026] A top gas outlet 12 is provided at the top of the direct reduction shaft 1, through which the reduced gas from the reduction shaft 1 is removed from the shaft 1. A third gas line 13 extends from the top gas outlet 12 to a device 14 for top gas washing, which includes removing water and dust from the top gas, so that the washed top gas mainly consists of hydrogen gas. The third gas line 13 further extends from the gas washing device 14 and is connected to the first gas line 7 at a position upstream of the heater device 8. This allows non-used hydrogen gas from the direct reduction shaft 1 to be recycled.
[0027] The apparatus for direct reduction of iron ore also includes a first control valve 15 disposed in the first gas line 7 for controlling the flow rate of hydrogen gas heated by the heater device 8 and introduced into the reduction section 4 via the heater device 8. A second control valve 16 is also disposed in the second gas line 10 from the hydrogen gas source to the cooling section 5 for controlling the flow of hydrogen gas.
[0028] The apparatus for direct reduction further includes a first temperature sensor 17 configured to sense the temperature of the DRI leaving the cooling section 5. The first temperature sensor 17 is provided at the outlet 3 of the cooling section 5. A second temperature sensor 18 is also provided configured to sense the temperature Tcooltop of the cooling gas at the top end of the cooling section 5. A third temperature sensor 19 is provided for measuring the temperature Ttopgas of the top gas, and a fourth temperature sensor 20 is provided for measuring the temperature Tredgas of the hydrogen gas heated by the heater device.
[0029] The apparatus for direct reduction of iron ore further includes a control unit 21 configured to control operation of the heater device 8, the first control valve 15, and the second control valve 16 based on inputs from the first, second, third, and fourth temperature sensors 17-20.
[0030] The direct reduction apparatus also includes components such as compressors (not shown) for generating suitable gas pressures in the respective gas lines, and the process pressure in the direct reduction shaft may typically be in the region of 8 to 12 bar. Also provided is an input vessel 22 through which iron ore is introduced into the reduction section 4, and a discharge vessel 23 through which DRI is removed from the cooling section 5. The input vessel 22 and the discharge vessel 23 may be pressurized with any suitable gas, such as nitrogen gas, when they are open toward the reduction section 4 and the cooling section 5, respectively, to prevent the pressurized process gas (mainly hydrogen gas) in the reduction section 4 and the cooling section 5 from leaking into the atmosphere. According to one embodiment, the gas used to pressurize at least one of the input vessel 22 and the discharge vessel 23, and preferably both, mainly comprises hydrogen gas. This prevents the introduction of gases other than hydrogen, such as nitrogen gas, into the reduction section 4 and the cooling section 5.
[0031] The apparatus for direct reduction is configured to operate according to the following description of an embodiment of the method of the present invention, see Figure 2. The method comprises the following steps: a) Introducing iron ore into the iron ore inlet 2 of the direct reduction shaft 1. b) heating a reducing gas consisting essentially of hydrogen to a reducing gas temperature Tredgas and introducing the heated reducing gas into the reduction section 4 of the direct reduction shaft 1 to form a first component part of a reducing gas for reducing the iron ore to high-temperature DRI at a reduction temperature Tred, where Tredgas>Tred. The reducing gas is first taken from the hydrogen gas source 6 and, when the reduction starts, is taken from the top gas that has been partially washed in the scrubber 14 and is conducted to the heater device 8 via the third gas line 7 and the first gas line 7. c) A step of introducing a cooling gas that consists essentially of hydrogen and has a temperature Tcoolgas directly into the cooling section 5 of the direct reduction shaft 1 through the second gas line 10 and the inlet 11. Thereby, due to the countercurrent of the DRI passing through the cooling section 5 and the cooling gas, the hot DRI having a temperature Tdritop when entering the cooling section 5 is cooled to the outlet temperature Tdriout, and the cooling gas is heated to the temperature Tcooltop and reaches the upper part of the cooling section 5 or the bottom of the reduction section 4. d) A step of enabling the hot cooling gas to enter the reduction section 4 of the direct reduction shaft 1 and mix with the heated reduction gas delivered through the first gas line 7 to form a second component part of the reduction gas. e) A step of removing the top gas from the upper part of the reduction section 4 of the direct reduction shaft 1 through the top gas outlet 12, wherein the top gas has a temperature Ttopgas. f) A step of measuring Tdriout using the first temperature sensor 17 and controlling the flow rate FRcoolgas of the cooling gas to the cooling section 4 using the control unit 21 and the second control valve 16 such that Tdriout < Tdrioutmax, where Tdrioutmax is the set maximum allowable temperature of the DRI exiting the cooling section 5. g) A step of measuring the temperature Tcooltop of the heated cooling gas using the second temperature sensor 18 and increasing / adjusting the flow rate of the cooling gas introduced into the cooling section until Tcooltop = Tcooltopmin, where Tcooltopmin is the predetermined minimum allowable temperature of the heated cooling gas and Tcooltopmin ≤ Tdritop. Thereby, the control unit 21 controls the second control valve 16 based on the input from the second temperature sensor 18. h) adjusting the flow rate FRredgas of the heated reducing gas forming the first component portion and determining the degree of metallization of the produced DRI while measuring the top gas temperature Ttopgas using a third temperature sensor and determining the minimum top gas temperature Ttopgasmin below which the degree of metallization is below the minimum acceptable value. For the time being, the measurement of the degree of metallization is carried out in a laboratory, which means that step h) can be considered a key step for determining a specific limit value, and when step h) is used to determine that limit value, minimizing energy consumption by the heater device is mainly achieved through steps f), g) and i). i) measuring the top gas temperature Ttopgas and controlling at least one of the flow rate FRredgas of the heated reducing gas and the temperature Tredgas to which the heated reducing gas is heated before being introduced into the reduction section so that Ttopgasmin≦Ttopgas≦Topgasmax, where Topgasmax is the set maximum allowable temperature of the top gas. For this purpose, the control unit 21 controls the power of the first control valve 16 and the heater device.
[0032] In the embodiments disclosed herein, Ttopgasmax = Topgasmin, which means aiming for the lowest top gas temperature possible while still achieving satisfactory metallization.
[0033] In the embodiment disclosed herein, Tcooltopmin=Tdritop, which means that the heat of the DRI is optimally utilized for heating the cooling gas, thereby reducing the energy consumption associated with heating the reduction gas by the heater device 8 that is introduced directly into the reduction section 4.
[0034] In the disclosed embodiment, Tdritop=Tred as a result of the reduction section 4 and the cooling section 5 being directly connected to each other.
[0035] In one embodiment, Tredgas is about 1050°C and Tred is about 950°C.
[0036] In the disclosed embodiment, the minimum allowable metallization level is 98 wt%.
Claims
1. 1. A method for producing direct reduced iron (DRI), comprising: a) introducing iron ore into the iron ore inlet (2) of the direct reduction shaft (1); b) heating a reducing gas consisting essentially of hydrogen to a reducing gas temperature Tredgas and introducing the heated reducing gas into the reduction section (4) of the direct reduction shaft to form a first component portion of reducing gas for reducing iron ore to high-temperature DRI at a reduction temperature Tred, where Tredgas>Tred; c) introducing a cooling gas consisting essentially of hydrogen and having a temperature Tcoolgas into a cooling section (5) of the direct reduction shaft (1), said cooling section (5) being located downstream of the reduction section (4) in the direction of flow of the DRI, and the cooling gas being introduced into the end of the cooling section (5) opposite the end of the cooling section (5) adjacent to the reduction section (4), thereby cooling the hot DRI having a temperature Tdritop to a cold DRI on entering the cooling section (5) and heating the cooling gas to a temperature Tcooltop, the cold DRI leaving the cooling section (5) having a temperature Tdriout, d) allowing the hot cooling gas to enter the reduction section (4) of the direct reduction shaft (1) and mix with the heated reduction gas to form a second component part of the reduction gas; and e) removing the spent reduction gas as top gas from the upper part of the reduction section (4) of the direct reduction shaft (1), said top gas having a temperature Ttopgas; Including, f) measuring Tdriout and controlling the flow rate FRcoolgas of the cooling gas to the cooling section (5) so that Tdriout<Tdrioutmax, where Tdrioutmax is the set maximum allowable temperature of the DRI leaving the cooling section (5); g) measuring the temperature Tcooltop of the heated cooling gas and increasing the flow rate FRcoolgas of the cooling gas introduced into the cooling section (5) until Tcooltop=Tcooltopmin, where Tcooltopmin is a predetermined minimum allowable temperature of the heated cooling gas and Tcooltopmin≦Tdritop; h) adjusting the flow rate of the heated reducing gas FRredgas to form the first component portion and determining the degree of metallization of the DRI produced, while measuring the top gas temperature Ttopgas and determining the minimum top gas temperature Ttopgasmin below which the degree of metallization is less than the minimum acceptable value; i) measuring the top gas temperature Ttopgas and controlling at least one of the flow rate of the heated reducing gas and the temperature Tredgas to which the heated reducing gas is heated before being introduced into the reduction section so that Ttopgasmin≦Ttopgas≦Topgasmax, where Topgasmax is the set maximum allowable temperature of the top gas; The method further comprising:
2. 2. The method of claim 1, wherein Ttopgasmax = Topgasmin + 50°C.
3. 3. The method of claim 1 or 2, wherein Ttopgasmax = Topgasmin + 25°C.
4. 3. The method of claim 1 or 2, wherein Ttopgasmax = Topgasmin.
5. 5. The method according to claim 1, wherein Tcooltopmin = Tdritop-50°C.
6. 5. The method according to claim 1, wherein Tcooltopmin = Tdritop-25°C.
7. 5. The method according to any one of claims 1 to 4, wherein Tcooltopmin = Tdritop-10°C.
8. 5. The method according to claim 1, wherein Tcooltopmin=Tdritop.
9. 10. The method of any one of the preceding claims, wherein Tdritop = Tred.
10. 10. The method according to any one of the preceding claims, wherein the minimum acceptable degree of metallization is 90 wt%, preferably 94 wt%, even more preferably 96 wt%, or even more preferably 98 wt%.
11. 10. The method of any one of the preceding claims, wherein 850°C<Tredgas<1200°C.
12. 10. The method of any one of the preceding claims, wherein 900°C<Tred<1000°C.