Method and apparatus for preparing pre-reduced burden

Abstract

The application provides a method for preparing pre-reduced furnace charge, comprising the following steps: 1) directly feeding high-temperature pellets into a hydrogen-based shaft furnace through a charging system; 2) heating ammonia gas or mixing and heating ammonia gas and hydrogen-rich tail gas to form reducing gas; 3) introducing the reducing gas into the hydrogen-based shaft furnace to cool and reduce the high-temperature pellets, and obtaining pre-reduced furnace charge and post-reduction gas. Compared with the prior art, the method for preparing pre-reduced furnace charge by cooling and reduction with ammonia gas can realize heat utilization of the high-temperature pellets, reduce energy loss, improve the utilization rate of ammonia gas in the reduction process, and realize low carbon emission. The application further provides a device for implementing the above method.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and in particular to a method and apparatus for preparing pre-reducing furnace charge. Background Technology

[0002] Carbon emissions from the ironmaking process account for approximately 60% of the total carbon emissions in the steel industry, making its reduction crucial. Currently, the direct reduction process using hydrogen-rich or all-hydrogen sources in vertical shaft furnaces is gradually becoming a direction for emission reduction exploration by domestic steel companies, aiming to reduce carbon emissions by minimizing the output of the long blast furnace-converter process. However, the difficulty in storing and transporting hydrogen, as well as its endothermic nature during reduction, limits its widespread application in the metallurgical industry. Ammonia, a hydrogen-rich carrier, offers advantages such as high output, easy liquefaction, and high loading efficiency. Therefore, using ammonia as a direct reducing gas for the reduction of high-temperature pellets is beneficial for reducing energy consumption.

[0003] There are existing patents related to the direct use of ammonia for reduction.

[0004] For example, Chinese patent CN 112921143 A discloses "a method for producing hot sponge iron by direct reduction of iron with ammonia". The feature is that ammonia is introduced into a reaction device containing iron-containing raw materials. While the ammonia is catalytically decomposed by the iron oxides in the iron-containing raw materials to generate nitrogen and hydrogen, it directly participates in the reduction reaction of the iron oxides to reduce the iron oxides to metallic iron.

[0005] Chinese patent application CN 112813219 A discloses a system and process for achieving near-zero emissions in direct ammonia reduction of iron. The system includes a direct reduction shaft furnace, a regenerative heat exchanger, and an ammonia combustion and pretreatment device, enabling the industrial production of direct ammonia reduction of iron and achieving near-zero emissions of dust, wastewater, and slag. However, due to the significant heat absorption during ammonia reduction, maintaining a constant reduction temperature is difficult, requiring multiple heating and circulation of the gas, resulting in low ammonia utilization. Furthermore, the cold charge introduced into the shaft furnace requires further preheating to ensure smooth reduction.

[0006] Chinese utility model patent with publication number CN 214830449 U discloses "a preheating device for a direct reduction shaft furnace in the direct reduction iron process of ammonia". It is used to preheat the furnace charge in the shaft furnace. The high-temperature flue gas generated after the ammonia is burned by the mixed burner is directly introduced into the preheating section of the shaft furnace to preheat the furnace charge, realizing the recycling of heat and ensuring that no carbon dioxide is generated in the direct reduction iron process, thereby achieving near-zero emissions.

[0007] Furthermore, Chinese utility model patent CN218089652 U discloses a "Plasma-Assisted Direct Reduction Smelting Apparatus for Ammonia," which provides a plasma-assisted direct reduction smelting apparatus for ammonia. This apparatus utilizes plasma to directly crack ammonia into hydrogen or a hydrogen-ammonia mixture, producing a hydrogen-based reducing gas. Simultaneously, plasma-assisted ammonia combustion provides heat for the direct reduction smelting, avoiding the generation of carbon dioxide and other polluting gases during the smelting process. While these methods reduce smelting energy consumption to some extent, for cold furnace charges, auxiliary combustion or recycling of the reducing gas is still necessary to provide the heat required for reduction.

[0008] In practice, pellet production involves first adding appropriate amounts of water and binder to ore powder to create green pellets with uniform viscosity and sufficient strength. These green pellets then undergo drying, preheating, and calcination, resulting in pellets with a temperature between 1200 and 1300°C. This temperature is sufficient for direct reduction in subsequent hydrogen-based shaft furnaces. However, most manufacturers use water spray cooling and air cooling systems to cool the high-temperature pellets, recovering some heat through heat exchange before proceeding to the next smelting stage. However, these methods only achieve partial heat recovery, resulting in significant heat loss during the cooling process.

[0009] In summary, a new method is needed to solve the technical problems of heat loss during the cooling process of high-temperature pellets, how to supply heat for direct ammonia reduction, and the low utilization rate of direct reduction gas. Summary of the Invention

[0010] To address the aforementioned technical problems in the prior art, a first aspect of the present invention provides a method for preparing pre-reducing furnace charge, comprising the following steps performed sequentially:

[0011] 1) High-temperature pellets are directly fed into the hydrogen-based vertical shaft furnace through the charging system;

[0012] 2) Heating ammonia or mixing and heating ammonia and hydrogen-rich tail gas to form reducing gas;

[0013] 3) The reducing gas is introduced into the hydrogen-based vertical shaft furnace to cool and reduce the high-temperature pellets, thereby obtaining pre-reduced furnace feed and reduced gas.

[0014] In step 1, the high-temperature pellets obtained by direct feeding are not cooled but immediately loaded into the charging system, and then fed into the hydrogen-based vertical shaft furnace through the charging system. The method of this invention uses ammonia or ammonia-based reducing gas to prepare pre-reduced furnace charge. Compared with existing technologies, this method can realize the utilization of heat from the high-temperature pellets, reduce energy loss, and improve the utilization rate of ammonia in the reduction process, thus achieving low carbon emissions.

[0015] Preferably, the above method further includes step 4), where the reduced gas is discharged from the top of the hydrogen-based vertical furnace and separated by nitrogen to form hydrogen-rich tail gas and nitrogen. Preferably, the hydrogen-rich tail gas is reused in step 2); and / or, the above method further includes step 5): cooling the pre-reduced furnace material obtained in step 3) so that its discharge temperature is below 100°C.

[0016] Preferably, in step 4), before nitrogen separation, the reduced gas is subjected to waste heat recovery and / or cooling and washing; and / or the nitrogen obtained in step 4) is introduced into the charging system of step 1) for preliminary cooling of the high-temperature pellets and / or for pressure equalization control of the lower hopper in the charging system, so that the pressure of the lower hopper is equal to that of the hydrogen-based vertical shaft furnace; and / or the nitrogen obtained in step 4) is introduced into step 5) to cool the pre-reduced furnace charge.

[0017] Preferably, the temperature of the high-temperature pellets is 1200-1300℃; and / or the high-temperature pellets are metal oxide high-temperature pellets; and / or the temperature of the reducing gas is 600-700℃.

[0018] Preferably, in step 3), the flow rate of the reducing gas is 800-1000 m³ / h. 3 / t, and / or cooling and reduction time is 60-90min.

[0019] Preferably, the metallization rate of the pre-reduced charge is above 30%. The metallization rate is the ratio of metallic iron content to total iron content in the pre-reduced charge. A higher metallization rate indicates a better reduction effect on high-temperature pellets. Simultaneously, a higher metallization rate of the pre-reduced charge is more beneficial for its subsequent use in the blast furnace, reducing blast furnace operating costs (e.g., the amount of coke input). On the other hand, when using existing processes to reduce pellets at relatively low temperatures, high-temperature reducing gas is required to obtain the ideal metallization rate, increasing the energy consumption for preparing the pre-reduced charge.

[0020] In this invention, there is no particular upper limit on the metallization rate; the higher the metallization rate, the better. However, in practice, due to the operating cost considerations of the reduction process, the metallization rate of the pre-reduction furnace charge is usually below 50%.

[0021] Preferably, in step 2), ammonia and hydrogen-rich tail gas are mixed in a volume ratio of 3:1 to 4:1. Controlling the volume ratio of ammonia and hydrogen-rich tail gas within this range can achieve higher reducing gas utilization and better metallization rate of pre-reduction furnace charge.

[0022] Preferably, in step 3), the utilization rate of ammonia is 45%-55%.

[0023] In this invention, the ammonia utilization rate is the ratio of the ammonia participating in the reduction reaction to the total amount of ammonia fed into the hydrogen-based vertical shaft furnace. In the traditional pellet reduction process, high-temperature pellets undergo heat recovery before being fed into the hydrogen-based vertical shaft furnace to utilize their heat. Therefore, the pellet temperature is relatively low during the subsequent reduction process, resulting in a low ammonia utilization rate.

[0024] According to a preferred embodiment of the present invention, high-temperature pellets at 1200-1300°C are directly fed into a hydrogen-based vertical shaft furnace. Since the pellets themselves are at high temperatures, even when they are reduced by medium-temperature reducing gas at 600-700°C, a better reduction effect can be obtained. This can effectively utilize the heat of the high-temperature pellets and improve the utilization rate of ammonia during the reduction process.

[0025] A second aspect of the present invention provides an apparatus for preparing pre-reduced furnace charge, which can be used to implement the above-described method. The apparatus includes a charging system, a hydrogen-based vertical shaft furnace, and a cooling reduction system.

[0026] The charging system is located above the hydrogen-based vertical shaft furnace and is used to feed high-temperature pellets into the furnace.

[0027] Preferably, the charging system includes a distribution funnel, an upper silo, and a lower silo, wherein high-temperature pellets sequentially enter the hydrogen-based vertical shaft furnace through the distribution funnel, the upper silo, and the lower silo; more preferably, the upper silo is equipped with a gas vent pipe for introducing nitrogen gas, and the lower silo is equipped with a pressure equalization device to make the pressure of the lower silo equal to that of the hydrogen-based vertical shaft furnace, and valves are provided in the distribution funnel, the upper silo, and the lower silo;

[0028] The cooling and reduction system is used to introduce reducing gas into the middle of the hydrogen-based vertical shaft furnace, and to cool and reduce the high-temperature pellets through the reducing gas to obtain pre-reduced furnace charge and reduced gas;

[0029] Preferably, the cooling reduction system includes an ammonia tank and an electric heating device connected in sequence. The ammonia tank provides ammonia, and the electric heating device heats the reducing gas containing ammonia to 600-700°C. The electric heating device is connected to the inlet located in the middle of the hydrogen-based vertical shaft furnace to introduce the reducing gas into the furnace. More preferably, the cooling reduction system further includes a waste heat recovery device, a cooling scrubber, and a nitrogen separation device connected in sequence. One end of the waste heat recovery device is connected to the outlet at the top of the hydrogen-based vertical shaft furnace, and one end of the nitrogen separation device is connected to the electric heating device. The reduced gas is discharged from the outlet of the hydrogen-based vertical shaft furnace to the waste heat recovery device. After passing through the cooling scrubber and nitrogen separation device, it forms hydrogen-rich tail gas and nitrogen. The ammonia and hydrogen-rich tail gas are mixed in a conveying pipeline and then enter the electric heating device for heating to form reducing gas at 600-700°C. The reducing gas enters the hydrogen-based vertical shaft furnace from the inlet in the middle to cool and reduce the high-temperature pellets.

[0030] In this invention, the hydrogen-rich tail gas is formed after the medium-temperature reducing gas participates in the reaction in the vertical furnace and is discharged from the flue gas outlet at the top. The flue gas is then subjected to heat recovery by a waste heat recovery device, water vapor and dust removal by a cooling scrubber, and nitrogen separation by a nitrogen separation device.

[0031] Preferably, the above-mentioned apparatus further includes a cooling system located at the lower part of the hydrogen-based vertical shaft furnace for cooling the pre-reduced charge, ensuring that the discharge temperature of the pre-reduced charge is below 100°C. Preferably, a nitrogen separation device is used as the cooling system, with one end connected to the hydrogen-based vertical shaft furnace. Nitrogen gas is introduced into the lower part of the hydrogen-based vertical shaft furnace through an inlet located at the bottom to cool the pre-reduced charge, ensuring that the discharge temperature of the pre-reduced charge is below 100°C. The cooling system is used to cool the pre-reduced charge and prevent oxidation of the pre-reduced charge during the cooling process.

[0032] Preferably, the electric heating device includes an electric heating element and a temperature control element, the temperature control element being used to achieve real-time control of the reducing gas temperature. The technical solution of this invention relies on the heat generated by the electric heating element to heat the reducing gas through radiation, conduction, and convection. The electric heating element includes heating elements such as electric heating wires, silicon molybdenum rods, and silicon carbide rods that are heated indirectly by resistance.

[0033] Preferably, one end of the nitrogen separation device is connected to the upper silo and / or the lower silo, for preliminary cooling of the high-temperature pellets in the upper silo and / or pressure equalization of the lower silo, so that the pressure of the lower silo is equal to that of the hydrogen-based vertical shaft furnace.

[0034] In this invention, ammonia and hydrogen-rich tail gas are mixed in a conveying pipeline and then enter an electric heating device. Under the action of the electric heating device, the gas is heated to form a medium-temperature reducing gas at 600-700℃. The temperature control element can achieve real-time control of the reducing gas temperature during this process, thereby enabling the pre-reduced charge to achieve a specific metallization rate of 30-50%. This is beneficial for reducing blast furnace operating energy consumption during subsequent blast furnace smelting of the pre-reduced charge. If the metallization rate is lower than 30%, it will increase the operating pressure of the subsequent blast furnace reduction process, requiring more coke and wasting resources.

[0035] The beneficial effects of this invention are:

[0036] 1. The present invention eliminates the cooling process of high-temperature pellets used as furnace charge and the heating process of directly reducing high-temperature pellets, thereby reducing the cooling consumption of high-temperature pellets and achieving efficient energy utilization.

[0037] 2. The present invention directly utilizes the physical heat of high-temperature pellets to meet the heat required for the direct reduction of high-temperature pellets, thereby improving the utilization rate of reducing gas. Using the pre-reduced furnace charge prepared by the method of the present invention as blast furnace charge can reduce blast furnace fuel consumption and carbon emissions. Therefore, the method of the present invention is a new low-carbon and green process for preparing pre-reduced furnace charge.

[0038] 3. The present invention uses ammonia or ammonia as the main component as the direct reducing gas. Compared with hydrogen, ammonia has a higher energy density, is easier to store for a long time and transport over long distances, and can improve the utilization efficiency of hydrogen, reduce the footprint of storage equipment and reduce construction costs during use.

[0039] 4. This invention utilizes an electric heating device to preheat the direct reducing gas, solving the problem of insufficient heat during reduction, reducing the amount of reducing gas used in the vertical shaft furnace direct reduction iron process, improving the utilization efficiency of the reducing gas, and reducing costs and emissions. Attached Figure Description

[0040] Figure 1 A schematic diagram of the connection of the apparatus for preparing pre-reduced furnace charge in this invention is shown.

[0041] Figure label:

[0042] 01-Hydrogen-based vertical shaft furnace, 02-Waste heat recovery device, 03-Cooling scrubber, 04-Nitrogen separation device, 05-Ammonia tank, 06-Electric heating device, 07-Distribution funnel, 08-Upper silo, 09-Lower silo. Detailed Implementation

[0043] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0044] It should be noted that in this specification, similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0045] In the description of this embodiment, it should be noted that the terms "upper", "lower", "inner", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship that the product of the invention is usually placed in during use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0046] In the description of this embodiment, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment based on the specific circumstances.

[0047] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0048] According to one embodiment of the present invention, the method for preparing pre-reduced furnace charge by ammonia cooling reduction can be generally carried out as follows. (Reference) Figure 1 During the charging process, high-temperature pellets enter the charging system through the distribution funnel 07, then pass sequentially through the upper hopper 08 and lower hopper 09 before being distributed into the hydrogen-based vertical shaft furnace 01. After the high-temperature pellets are loaded into the upper hopper 08, they are purged with nitrogen generated from the flue gas separation at the furnace top to achieve initial cooling of the high-temperature pellets and remove oxygen from the hopper. Subsequently, the valve below the upper hopper 08 is opened, and after the high-temperature pellets have completely entered the lower hopper 09, the valve below the upper hopper 08 is closed. Then, the separated nitrogen is used to complete the pressure equalization process. After pressure equalization is completed, the valve below the lower hopper 09 is opened, and the high-temperature pellets are distributed into the hydrogen-based vertical shaft furnace 01.

[0049] During the cooling reduction process, ammonia gas is mixed with hydrogen-rich tail gas and heated in an electric heating furnace 06. The heated gas then enters through an annular tuyer located in the middle of the hydrogen-based vertical furnace 01. In the middle of the hydrogen-based vertical furnace 01, the gas comes into contact with high-temperature pellets from the charging system. The reducing gas cools the high-temperature pellets while undergoing a reduction reaction with them. The reduced gas is discharged from the flue gas outlet at the top of the hydrogen-based vertical furnace 01. After heat recovery by the waste heat recovery device 02, removal of water vapor and dust by the cooling scrubber 03, and separation of nitrogen by the nitrogen separation device 04, hydrogen-rich tail gas and nitrogen are formed. The hydrogen-rich tail gas can be recycled as a reducing gas.

[0050] After the reduced gas discharged from the top of the hydrogen-based vertical furnace 01 is subjected to heat recovery by the waste heat recovery device 02, water vapor and dust removal by the cooling scrubber 03, and nitrogen separation by the nitrogen separation device 04, the separated nitrogen can be introduced into the charging system to pre-cool the high-temperature pellets in the hopper and / or to control the pressure of the lower hopper 09. In addition, the separated nitrogen can also participate in the cooling and protection treatment of the pre-reduced furnace charge.

[0051] According to another embodiment of the present invention, a method for preparing pre-reduced furnace charge by ammonia cooling reduction can be carried out using the following apparatus. (See reference) Figure 1 The apparatus for preparing pre-reduced furnace charge using ammonia cooling reduction in this invention includes a hydrogen-based vertical shaft furnace 01, a charging system, a cooling reduction system, and a cooling system. The charging system is located above the hydrogen-based vertical shaft furnace 01 and is used to continuously supply high-temperature pellets into the hydrogen-based vertical shaft furnace 01; the cooling reduction system is connected to the gas inlet located in the middle of the hydrogen-based vertical shaft furnace 01 and is used to achieve cooling reduction of the high-temperature pellets using ammonia gas; the cooling system is located below the hydrogen-based vertical shaft furnace 01 and is used to perform cooling and protection treatment on the reduced pre-reduced furnace charge.

[0052] refer to Figure 1 The charging system is used to uniformly supply high-temperature pellets to the hydrogen-based vertical shaft furnace 01. The charging system includes a distribution funnel 07, an upper hopper 08, and a lower hopper 09. To ensure a closed environment within each hopper, the distribution funnel 07, upper hopper 08, and lower hopper 09 are all equipped with automatically controllable valves. In a specific embodiment, the produced high-temperature pellets undergo a cooling process and enter the upper hopper 08 through the distribution funnel 07. To ensure a low-oxygen environment in the upper hopper 08, a venting pipe is provided to facilitate the introduction of nitrogen to replace oxygen in the air and achieve initial cooling. To ensure that the pressure in the lower hopper 09 is consistent with that in the hydrogen-based vertical shaft furnace 01, a pressure equalization device is provided on the lower hopper 09, using pressurized nitrogen for pressure equalization. To facilitate the distribution of high-temperature pellets into the hydrogen-based vertical shaft furnace 01, a rotary feeder can be installed below the lower hopper 09.

[0053] Continue to refer to Figure 1The cooling reduction system provides the reducing gas required for the reduction reaction and achieves the cooling reduction of the high-temperature pellets. It includes a waste heat recovery device 02, a cooling scrubber 03, a nitrogen separator 04, an ammonia tank 05, and an electric heating device 06. The waste heat recovery device 02 is connected to the gas outlet at the top of the hydrogen-based vertical shaft furnace 01. One end of the cooling scrubber 03 is connected to the waste heat recovery device 02, and the other end is connected to the nitrogen separator 04. One end of the electric heating device 06 is connected to the nitrogen separator 04 and the ammonia tank 05, and the other end is connected to the gas inlet in the middle of the hydrogen-based vertical shaft furnace 01. During the cooling and reduction process, ammonia gas in ammonia tank 05 is mixed with hydrogen-rich tail gas through a conveying pipeline and then enters an electric heating device 06. In the electric heating device 06, it is heated to form a medium-temperature (600-700℃) reducing gas. The reducing gas enters from the annular tuyeres of the hydrogen-based vertical shaft furnace 01 and comes into contact with high-temperature pellets from the charging system in the middle of the hydrogen-based vertical shaft furnace 01. The reducing gas cools the high-temperature pellets while undergoing a reduction reaction with them. The reduced gas after the reaction is discharged from the flue gas outlet at the top of the hydrogen-based vertical shaft furnace 01. After heat recovery by the waste heat recovery device 02, washing by the cooling scrubber 03, and nitrogen separation by the nitrogen separation device 04, hydrogen-rich tail gas and nitrogen are formed. The hydrogen-rich tail gas is recycled in the device as a reducing gas.

[0054] Continue to refer to Figure 1 The cooling system is used to cool the pre-reduced furnace charge and prevent its oxidation during the cooling process. The reduced gas discharged from the top of the hydrogen-based vertical shaft furnace 01 undergoes heat recovery via the waste heat recovery device 02, washing via the cooling scrubber 03, and nitrogen separation via the nitrogen separation device 04. The separated nitrogen then participates in the cooling and protection treatment of the pre-reduced furnace charge through the lower inlet of the hydrogen-based vertical shaft furnace 01. Preferably, a gas pressurization device is provided at the lower inlet to facilitate the introduction of nitrogen into the hydrogen-based vertical shaft furnace 01.

[0055] Combination Figure 1 As shown, the method for preparing pre-reduced furnace charge using ammonia cooling reduction in this invention is carried out using the above-mentioned apparatus. The method involves: bypassing the cooling process of the high-temperature oxidizing pellets and directly feeding them into the hydrogen-based vertical shaft furnace 01 for cooling and reduction with ammonia gas to obtain the pre-reduced furnace charge. Specifically, it includes the following steps:

[0056] (1) Charging: High-temperature pellets enter the charging system through the high-temperature resistant distribution funnel 07, and then sequentially enter the distribution funnel 07, the upper hopper 08 and the lower hopper 09 in the charging system before being distributed into the hydrogen-based vertical furnace 01. During this process, after the high-temperature pellets are loaded into the upper hopper 08 through the distribution funnel 07, nitrogen gas is introduced to ensure that the upper hopper 08 is under nitrogen protection. At this time, the high-temperature pellets are partially cooled. Then, the valve below the upper hopper 08 is opened. After the high-temperature pellets have completely entered the lower hopper 09, the valve below the upper hopper 08 is closed, and high-pressure nitrogen gas is introduced to achieve the same pressure as inside the hydrogen-based vertical furnace. After the pressure is equalized, the valve below the lower hopper 09 is opened, and the high-temperature pellets are distributed into the hydrogen-based vertical furnace 01 through the rotating charging device.

[0057] (2) Cooling and Reduction: The high-temperature pellets undergo a reduction reaction in the middle of the hydrogen-based vertical shaft furnace 01, where the ammonia in the reducing gas is pure ammonia. After the ammonia and hydrogen-rich tail gas are mixed, a medium-temperature reducing gas is formed under the action of the electric heating device 06. The reducing gas enters from the annular tuyer in the middle of the hydrogen-based vertical shaft furnace 01. After contacting the high-temperature pellets, the reducing gas (ammonia + optional hydrogen-rich tail gas) cools the high-temperature pellets while undergoing a reduction reaction with them. As the reaction proceeds, the concentration of the reducing gas gradually decreases, but because the temperature of the high-temperature pellets gradually increases during the rising process of the reducing gas, the reduction reaction continues. After the flue gas after the reduction reaction is discharged from the flue gas outlet at the top of the hydrogen-based vertical shaft furnace 01, its temperature is heated to about 900°C. The flue gas recovers heat through the waste heat recovery device 02, and then the water vapor and dust in the flue gas are removed by the cooling scrubber 03. Alternatively, a small amount of ammonia water can be injected into the cooling scrubber 03 according to process requirements to remove small amounts of carbon dioxide, sulfur dioxide, and nitrogen oxides from the flue gas. After nitrogen is separated by nitrogen separator 04, the flue gas undergoes simple washing treatment, becoming hydrogen-rich tail gas (mainly hydrogen) and nitrogen. The hydrogen-rich tail gas can be further recycled, while the nitrogen can be used for pressure equalization in the charging system and as a cooling gas in the cooling system. During the reduction reaction, the consumption of reducing gas is 800-1000 m³ / h. 3 / t, the reduction reaction time is 60-90min, and the pressure in the hydrogen-based vertical furnace 01 is 200-250kPa.

[0058] (3) Cooling: After the high-temperature pellets undergo a reduction reaction, they form pre-reduced charge in the lower part of the hydrogen-based vertical shaft furnace 01. Further cooling is achieved using cooling gas. The cooling gas is nitrogen obtained from the flue gas discharged from the upper part of the hydrogen-based vertical shaft furnace 01 after treatment by the waste heat recovery device 02, cooling scrubber 03, and nitrogen separation device 04. The nitrogen then enters the air inlet at the lower part of the hydrogen-based vertical shaft furnace 01 to participate in the cooling process. During the cooling process, a small amount of natural gas can be added to the gas pipeline. Simultaneously, the pre-reduced charge contains sponge iron, which catalyzes the cracking of methane to complete the carburizing process of direct reduced iron, preventing the direct reduced iron from re-oxidizing. The final product obtained from the hydrogen-based vertical shaft furnace 01 is the pre-reduced charge, with an outlet temperature below 100℃.

[0059] The method for preparing pre-reduced furnace charge using ammonia cooling reduction according to the present invention will be further described below with specific examples.

[0060] Example 1

[0061] Uncooled high-temperature oxidizing pellets produced by Steel Plant A through a chain grate rotary kiln were measured to be 1280℃. These high-temperature pellets were then fed into a hydrogen-based vertical shaft furnace via a charging system. Ammonia gas was introduced into the reducing gas pipeline and heated to 700℃ by an electric heating device at a gas flow rate of 800m³ / h. 3 / t gas was supplied, and after reduction in a hydrogen-based vertical furnace for 60 minutes, the reduced pellets were cooled under nitrogen protection to obtain pre-reduced furnace charge and reduced gas with an outlet temperature of 80℃.

[0062] The obtained pre-reduced furnace charge was analyzed by chemical titration to determine the content of metallic iron and total iron, and the metallization rate reached 47%. Furthermore, the composition of the reduced gas was analyzed by gas chromatography, revealing an ammonia utilization rate of 51%.

[0063] Example 2

[0064] The operation process in this embodiment is similar to that in embodiment 1, except that the ammonia gas is heated to 600°C in the electric heating device and the reduction time is 80 minutes.

[0065] Composition analysis of the obtained pre-reduced furnace charge showed a metallization rate of 36%. In this embodiment, the utilization rate of ammonia was 45%.

[0066] Example 3

[0067] Uncooled high-temperature oxidizing pellets produced by Steel Plant B through a vertical shaft furnace were measured to be 1250℃. These high-temperature pellets were then charged into a hydrogen-based vertical shaft furnace via a charging system. Ammonia gas was introduced into the reducing gas pipeline and heated to 630℃ by an electric heating device, with a gas flow rate of 900m³ / h. 3 / t gas was supplied, and after reduction in a hydrogen-based vertical furnace for 70 minutes, the reduced pellets were cooled under nitrogen protection to obtain pre-reduced furnace feed with a discharge temperature of 90℃.

[0068] Composition analysis of the obtained pre-reduced furnace charge showed a metallization rate of 41%. In this embodiment, the utilization rate of ammonia was 48%.

[0069] Example 4

[0070] The operation process in this embodiment is similar to that in embodiment 3, except that the ammonia gas is heated to 680°C in the electric heating device, the reduction time is 90 minutes, and the gas flow rate is 1000 m³ / s. 3 / t.

[0071] Composition analysis of the obtained pre-reduced furnace charge showed a metallization rate of 49%. In this embodiment, the utilization rate of ammonia was 52%.

[0072] Example 5

[0073] The operation process of this embodiment is similar to that of embodiment 1, except that a mixture of ammonia and hydrogen-rich tail gas is used instead of ammonia, wherein ammonia and hydrogen-rich tail gas are mixed in a volume ratio of 3:1.

[0074] Composition analysis of the obtained pre-reduced furnace charge showed a metallization rate of 45%. In this embodiment, the ammonia utilization rate was 55%.

[0075] Example 6

[0076] The operation process of this embodiment is similar to that of embodiment 3, except that a mixture of ammonia and hydrogen-rich tail gas is used instead of ammonia, wherein ammonia and hydrogen-rich tail gas are mixed in a volume ratio of 4:1.

[0077] Composition analysis of the obtained pre-reduced furnace charge showed a metallization rate of 46%. In this embodiment, the utilization rate of ammonia was 53%.

[0078] Example 7

[0079] The operation process of this embodiment is similar to that of embodiment 1, except that the ammonia gas is heated to a temperature of 750°C in the electric heating device.

[0080] The obtained pre-reduced furnace charge was analyzed for composition, and its metallization rate was 56%. In this embodiment, the utilization rate of ammonia was 55%.

[0081] In this embodiment, the temperature of the ammonia gas is 750°C. As mentioned above, a higher temperature reducing gas is beneficial to the reduction reaction, thus resulting in a higher metallization rate of the pre-reduced furnace charge. However, ammonia gas will further decompose at higher temperatures, requiring more heat to be absorbed to maintain a stable temperature, which significantly increases the power consumption of the electric heating furnace.

[0082] Comparative Example 1

[0083] The operation process of this comparative example is similar to that of Example 1, except that hydrogen is used instead of ammonia.

[0084] Compositional analysis of the obtained pre-reduced furnace charge showed that its metallization rate was 42%.

[0085] In this comparative example, hydrogen was used as the reducing gas. At the same flow rate, ammonia contains more hydrogen, resulting in a higher reduction effect. Therefore, the metallization rate of the pre-reduced charge in Example 1 was higher. Hydrogen is a commonly used gas in the prior art for preparing pre-reduced charges, but it presents problems in terms of transportation and storage.

[0086] Comparative Example 2

[0087] The operation process of this comparative example is similar to that of Example 1, except that the ammonia gas is heated to a temperature of 540°C in an electric heating device.

[0088] Compositional analysis of the obtained pre-reduced furnace charge revealed a metallization rate of 21%. In this comparative example, the utilization rate of ammonia was 31%.

[0089] The reduction effect on high-temperature pellets is related to the temperature of the reducing gas used. In this comparative example, the temperature of the reducing gas was below 600℃, resulting in a lower metallization rate of the pre-reduced charge and a lower utilization rate of ammonia.

[0090] In the method for preparing pre-reduced furnace charge using ammonia cooling reduction of the present invention, the cooling process of the produced high-temperature pellets is first eliminated, and they are directly charged into the charging system of the hydrogen-based vertical shaft furnace. Then, ammonia gas, or a mixture of ammonia gas and hydrogen-rich tail gas, is heated in an electric furnace to form a medium-temperature reducing gas. This medium-temperature reducing gas comes into full contact with the high-temperature pellets in the hydrogen-based vertical shaft furnace, achieving pellet cooling and a redox reaction, resulting in temperature reduction and reduction of iron oxides. Finally, the reduced gaseous products are discharged from the top of the hydrogen-based vertical shaft furnace, and after waste heat recovery, cooling washing, and nitrogen separation, hydrogen-rich tail gas and nitrogen gas are formed. The hydrogen-rich tail gas can be further recycled in the above method. The separated nitrogen gas can be used for cooling the pre-reduced furnace charge and for equalizing the pressure in the silo. The present invention uses ammonia gas as the direct reducing gas to cool and reduce high-temperature pellets in a hydrogen-based vertical shaft furnace to produce pre-reduced furnace charge for use in the blast furnace, improving the utilization efficiency of the reducing gas, reducing fuel consumption, and achieving heat recovery.

[0091] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A method for preparing pre-reduced furnace charge, characterized in that, The method includes the following steps performed sequentially: 1) High-temperature pellets are directly fed into the hydrogen-based vertical shaft furnace through the charging system; 2) Heating ammonia or mixing and heating ammonia and hydrogen-rich tail gas to form reducing gas; 3) The reducing gas is introduced into the hydrogen-based vertical furnace to cool and reduce the high-temperature pellets, thereby obtaining pre-reduced furnace charge and reduced gas; The method further includes step 4), where the reduced gas is discharged from the top of the hydrogen-based vertical furnace, and after nitrogen separation, it forms hydrogen-rich tail gas and nitrogen gas, and the hydrogen-rich tail gas is used again in step 2); The method further includes step 5), cooling the pre-reduced furnace charge obtained in step 3), so that the discharge temperature of the pre-reduced furnace charge is below 100°C; In step 4), before nitrogen separation, the reduced gas is subjected to waste heat recovery and cooling washing; the nitrogen obtained in step 4) is introduced into the charging system of step 1) for preliminary cooling of the high-temperature pellets and pressure equalization control of the lower hopper in the charging system, so that the pressure of the lower hopper is equal to that of the hydrogen-based vertical furnace; the nitrogen obtained in step 4) is introduced into step 5) to cool the pre-reduced furnace charge.

2. The method according to claim 1, characterized in that, The temperature of the high-temperature pellets is 1200-1300℃; the high-temperature pellets are metal oxide high-temperature pellets; the temperature of the reducing gas is 600-700℃.

3. The method according to claim 1, characterized in that, In step 3), the flow rate of the reducing gas is 800-1000 m³ / h. 3 / t, the cooling and reduction time is 60-90min.

4. The method according to claim 1, characterized in that, The metallization rate of the pre-reduced furnace charge is above 30%.

5. The method according to any one of claims 1-4, characterized in that, In step 2), ammonia and hydrogen-rich tail gas are mixed in a volume ratio of 3:1 to 4:1; in step 3), the utilization rate of ammonia is 45% to 55%.

6. An apparatus for preparing pre-reduced furnace feed, characterized in that, The device includes a charging system, a hydrogen-based vertical furnace, and a cooling and reduction system; The charging system is located above the hydrogen-based vertical furnace and is used to feed high-temperature pellets into the hydrogen-based vertical furnace. The charging system includes a distribution funnel, an upper silo, and a lower silo. The high-temperature pellets are sequentially fed into the hydrogen-based vertical shaft furnace through the distribution funnel, the upper silo, and the lower silo. The upper silo is equipped with a gas vent pipe to introduce nitrogen gas, and the lower silo is equipped with a pressure equalization device to make the pressure of the lower silo equal to that of the hydrogen-based vertical shaft furnace. Valves are provided in the distribution funnel, the upper silo, and the lower silo. The cooling and reduction system is used to introduce reducing gas into the middle of the hydrogen-based vertical furnace, and to cool and reduce the high-temperature pellets through the reducing gas to obtain pre-reduced furnace charge and reduced gas; The cooling and reduction system includes an ammonia tank and an electric heating device connected in sequence. The ammonia tank provides ammonia, and the electric heating device heats the reducing gas containing ammonia to 600-700°C. The electric heating device is connected to the inlet located in the middle of the hydrogen-based vertical shaft furnace to introduce the reducing gas into the furnace. The cooling and reduction system also includes a waste heat recovery device, a cooling scrubber, and a nitrogen separation device connected in sequence. One end of the waste heat recovery device is connected to the outlet at the top of the hydrogen-based vertical shaft furnace, and one end of the nitrogen separation device is connected to the electric heating device. The reduced gas is discharged from the outlet of the hydrogen-based vertical shaft furnace to the waste heat recovery device. After passing through the cooling scrubber and nitrogen separation device, it forms hydrogen-rich tail gas and nitrogen. The ammonia and hydrogen-rich tail gas are mixed in a conveying pipeline and then enter the electric heating device for heating to form reducing gas at 600-700°C. The reducing gas enters the hydrogen-based vertical shaft furnace from the inlet in the middle of the furnace to cool and reduce the high-temperature pellets. The device also includes a cooling system located below the hydrogen-based vertical furnace, used to cool the pre-reduced furnace charge so that the discharge temperature of the pre-reduced furnace charge is below 100°C. The nitrogen separation device serves as a cooling system. One end of the device is connected to the hydrogen-based vertical furnace. Nitrogen gas is introduced into the lower part of the hydrogen-based vertical furnace through an air inlet located at the bottom of the furnace to cool the pre-reduced furnace charge, thereby reducing the discharge temperature of the pre-reduced furnace charge to below 100°C.

7. The apparatus as claimed in claim 6, characterized in that, The electric heating device includes an electric heating element and a temperature control element. The temperature control element is used to achieve real-time control of the reducing gas temperature. One end of the nitrogen separation device is connected to the upper silo and the lower silo. It is used to perform preliminary cooling of the high-temperature pellets in the upper silo and to equalize the pressure in the lower silo, so that the pressure in the lower silo is equal to that of the hydrogen-based vertical furnace.

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