Method and system for directly reducing iron and preparing hydrogen-rich reducing gas by ammonia cooling

Abstract

The invention discloses a method and a system for directly reducing iron and preparing hydrogen-rich reducing gas by using ammonia gas cooling, and the method comprises the following steps: cooling hot-state DRI reduced by a hydrogen shaft furnace by using ammonia gas, so that the hot-state DRI is cooled and passivated; and the cooled tail gas is discharged from the middle part of the hydrogen-based shaft furnace, and then is subjected to nitrogen separation to form hydrogen-rich tail gas and nitrogen. According to the invention, ammonia gas is used for cooling and directly reducing iron, so that the efficient cooling of hot-state DRI can be realized, the heat exchange efficiency is improved, the DRI is passivated, the subsequent storage and transportation of the DRI are facilitated, the formed hydrogen-rich reducing gas can further enter a reducing gas system, the consumption of the reducing gas is reduced, and the low-carbon emission is realized.

Description

Technical Field

[0001] This invention relates to the field of direct reduced iron technology, and more specifically, to a method and system for cooling direct reduced iron with ammonia and preparing hydrogen-rich reducing gas. Background Technology

[0002] Direct reduced iron (DRI) is a product obtained by gas-solid reduction of iron ore or pellets using pure H2 or a H2+CO mixture at 950℃. The iron ore is reduced during the gas contact process, and the resulting DRI, due to its high porosity, is also known as sponge iron. The reducing gas is obtained by reforming and heating natural gas, coke oven gas, and hydrogen in a reformer or tubular furnace.

[0003] Because DRI possesses high purity and low levels of harmful impurities, it can be used in the subsequent production of high-quality steel. If pure hydrogen smelting is employed, zero CO2 emissions can be achieved. Studies have shown that the apparent density of sponge iron is approximately 2 g / cm³. 3 It has a very high specific surface area and is very easy to react with water or oxygen in the air. The heat generated can easily cause explosions in stockpiles and storage tanks. Therefore, sponge iron needs to be stabilized during the cooling process.

[0004] The existing technologies related to direct reduced iron cooling are as follows:

[0005] Chinese Patent Publication No. CN 117344075 A discloses a method for direct reduction iron (DRI) using CO2 cooling protection. The method is characterized by purifying the CO2 gas extracted from the top gas of the blast furnace and exchanging heat with the hot DRI to achieve the function of cooling the DRI, saving the cost of production cooling gas, and further utilizing the CO2 in the process itself to improve the heat utilization efficiency.

[0006] Chinese Patent Publication No. CN 115652012 A discloses a method, system, and application for carburizing cooling and gas utilization in the production of sponge iron from a hydrogen-based vertical shaft furnace. The method involves using carburizing gas to carburize and heat exchange the hot sponge iron produced in the furnace, resulting in carburized sponge iron. Nitrogen gas is then used to cool the carburized sponge iron, yielding cold sponge iron. The cooling gas flow rate is 70,000–80,000 Nm³ / h when the annual production capacity is 1 million tons of sponge iron. The process involves a significant amount of nitrogen, and further treatment of the cooling gas, including dust removal, waste heat recovery, cooling, and pressurization, is required.

[0007] Chinese patent CN 108504814 B discloses a gas-based vertical shaft furnace direct reduction iron cooling system, which includes a CO2 storage tank, a dry ice machine, a silo pump, a high-pressure N2 storage tank, a cooling lock hopper, and a DRI storage hopper. The system uses high-pressure N2 to spray dry ice into the cooling lock hopper to cool the DRI and then store it. Although this technology achieves the recycling of CO2 in the gas-based vertical shaft furnace purification process, the production of dry ice from CO2 further increases energy consumption and does not achieve CO2 emission reduction.

[0008] In summary, DRI requires protection with cooling gas during the cooling process, and must be cooled to room temperature before transportation and storage. Currently used cooling gases include coke oven gas, natural gas, nitrogen, and carbon dioxide. Coke oven gas needs to be purified before entering the vertical shaft furnace cone section for cooling; otherwise, it will increase the sulfur and impurity content in the DRI. Natural gas is only used to crack the DRI into reducing gas during the cooling process, which is then further cooled with nitrogen. The resulting DRI poses certain safety risks during transportation. Nitrogen and carbon dioxide have large gas flow rates during use, low heat exchange efficiency, and the resulting exhaust gas still requires further purification.

[0009] Therefore, it is necessary to find a new cooling gas that can solve the problems of DRI product quality, subsequent safe storage and transportation, and low heat exchange efficiency faced by the aforementioned cooling gas. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a method and system for cooling direct reduced iron (DRI) with ammonia and preparing hydrogen-rich reducing gas. Cooling DRI with ammonia not only achieves efficient cooling of hot DRI and improves heat exchange efficiency, but also passivates the DRI, facilitating its subsequent storage and transportation. Furthermore, the resulting hydrogen-rich reducing gas can be further introduced into the reducing gas system, reducing reducing gas consumption and achieving low carbon emissions.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] The first aspect of the present invention provides a method for cooling direct reduction of iron and preparing hydrogen-rich reducing gas using ammonia gas. The hot DRI after reduction in a hydrogen shaft furnace is cooled by ammonia gas, thereby cooling and passivating the hot DRI. The cooled tail gas exits from the middle of the hydrogen-based shaft furnace and is then separated by nitrogen gas to form hydrogen-rich tail gas and nitrogen gas.

[0013] Preferably, it includes the following steps:

[0014] S1, liquid ammonia is purified by an ammonia purification device to form ammonia gas, which is then introduced into the furnace from the bottom of the hydrogen-based vertical furnace;

[0015] S2, in the hydrogen-based vertical furnace, ammonia gas exchanges heat with the hot DRI, so that the DRI is fully cooled and passivated;

[0016] S3, the cooled tail gas comes out from the middle of the hydrogen-based vertical furnace, and after nitrogen separation, it forms hydrogen-rich tail gas and nitrogen.

[0017] Preferably, in step S1,

[0018] The liquid ammonia is selected from gray ammonia, blue ammonia, or green ammonia; and / or

[0019] The ammonia gas has a dew point below -60°C, total hydrocarbon content less than 1 μmol / mol, and a flow rate of 800–1200 m³ / min. 3 / t; and / or

[0020] The conveying pipeline between the ammonia purification device and the hydrogen-based vertical furnace is equipped with an electric heating device, and the ammonia gas vaporized by the ammonia purification device enters from the bottom of the conical section of the hydrogen-based vertical furnace.

[0021] Preferably, in step S2, after the ammonia gas enters the hydrogen-based vertical furnace, it undergoes physical heat exchange with the descending hot DRI during the upward process, while simultaneously decomposing and absorbing heat under the catalytic action of the DRI to achieve chemical heat exchange; during the heat exchange process, when the DRI cools down to 500-700°C, the ammonia gas generates an iron nitride film on the surface of the DRI.

[0022] Preferably, the residence time of the DRI in the cone section of the hydrogen-based vertical furnace is 60–90 min; and / or

[0023] The cooled DRI has a temperature of 150–250°C and a nitrogen content of 0.1–0.15 wt.%.

[0024] Preferably, in step S3:

[0025] Before nitrogen separation, the exhaust gas undergoes dust removal, waste heat recovery, cooling and washing; and / or

[0026] The hydrogen-rich tail gas contains 50–65 vol.% H2 and 10–25 vol.% N2.

[0027] Preferably, it also includes S4, where the hydrogen-rich tail gas enters the reducing gas system as a reducing gas, and after being mixed and heated with the reducing gas, it enters the hydrogen-based vertical shaft furnace to participate in the reduction of iron.

[0028] A second aspect of the present invention provides a system for directly reducing iron by cooling with ammonia and preparing hydrogen-rich reducing gas, comprising:

[0029] Hydrogen-based vertical shaft furnace;

[0030] An ammonia injection system is used to convert liquid ammonia into ammonia gas for supplying a hydrogen-based vertical furnace. The ammonia injection system includes a liquid ammonia tank and an ammonia purification device connected in sequence, wherein the ammonia purification device is connected to the bottom of the conical section of the hydrogen-based vertical furnace.

[0031] The hydrogen-rich tail gas system is used to purify the tail gas from the hydrogen vertical furnace to obtain hydrogen-rich tail gas and nitrogen; the hydrogen-rich tail gas system is connected to the middle of the hydrogen-based vertical furnace.

[0032] The system for cooling direct reduced iron with ammonia and preparing hydrogen-rich reducing gas is used to perform the method for cooling direct reduced iron with ammonia and preparing hydrogen-rich reducing gas as described in the first aspect of the present invention.

[0033] Preferably, the bottom of the hydrogen-based vertical shaft furnace cone section is provided with multiple annular ammonia tuyeres; the middle part of the hydrogen-based vertical shaft furnace is provided with a tail gas outlet connected to the hydrogen-rich tail gas system.

[0034] Preferably, the conveying pipeline between the ammonia purification device and the hydrogen-based vertical furnace is equipped with an electric heating device.

[0035] Preferably, the hydrogen-rich tail gas system includes a dust removal device, a waste heat recovery device, a cooling and washing device, and a nitrogen separation device connected in sequence; the dust removal device is connected to the flue gas outlet in the middle of the hydrogen-based vertical furnace.

[0036] Preferably, the hydrogen-rich tail gas outlet of the nitrogen separation device is connected to the reducing gas system of the hydrogen-based vertical furnace.

[0037] The method and system for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia provided by this invention have the following beneficial effects:

[0038] 1. This invention uses ammonia to directly cool the hot DRI. While the cold ammonia and the hot DRI are undergoing physical heat exchange, the heat absorbed by the decomposition of ammonia is also undergoing chemical heat exchange, which improves the heat exchange efficiency and reduces the cooling time of the hot DRI.

[0039] 2. The hot DRI of the present invention will react chemically with ammonia when cooled to form an iron nitride (Fe4N) film on the surface of the DRI, which passivates the DRI. There is no need to protect the DRI with nitrogen gas afterward, which makes the DRI easy to store and transport.

[0040] 3. When the present invention uses ammonia to cool the hot DRI, the catalytic effect of the hot DRI will decompose the ammonia into hydrogen and nitrogen. After purification, the hydrogen-rich tail gas can be further participated in the hydrogen-based vertical furnace reduction, which reduces the consumption of reducing gas, saves energy, and achieves low carbon emissions. Attached Figure Description

[0041] Figure 1This is a schematic diagram of the system of the present invention that utilizes ammonia gas to cool and directly reduce iron and prepare hydrogen-rich reducing gas;

[0042] In the diagram, 1 is a hydrogen-based vertical shaft furnace; 2 is a liquid ammonia tank; 3 is an ammonia purification device; 4 is a dust removal device; 5 is a waste heat recovery device; 6 is a cooling and washing device; and 7 is a nitrogen separation device. Detailed Implementation

[0043] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0044] Combination Figure 1 As shown, this invention provides a method for cooling direct reduction of iron (DRI) and preparing hydrogen-rich reducing gas using ammonia gas. Ammonia gas is used to cool the hot DRI after reduction in a hydrogen shaft furnace 1, thereby cooling and passivating the hot DRI. The cooled tail gas exits from the middle of the hydrogen-based shaft furnace 1, and after nitrogen separation, forms hydrogen-rich tail gas and nitrogen gas. Specifically, the method includes the following steps:

[0045] S1, liquid ammonia is purified by ammonia purification device 3 to form ammonia gas, which is then introduced into the furnace from the bottom of hydrogen-based vertical furnace 1;

[0046] Cooling gas preparation: Liquid ammonia enters the ammonia purification unit 3 from the liquid ammonia tank 2 through a pipeline. After being heated and purified in the ammonia purification unit 3, stable high-purity ammonia gas is obtained. The pressure-stabilized ammonia gas is then supplied to the hydrogen-based vertical furnace 1 from the bottom of the conical section. Electric heating devices are installed on the pipelines between the ammonia purification unit 3 and the hydrogen-based vertical furnace 1 to ensure a constant ammonia gas temperature and prevent re-liquefaction. The ammonia gas vaporized in the ammonia purification unit 3 enters from the bottom of the conical section of the hydrogen-based vertical furnace 1.

[0047] The ammonia gas produced after vaporization of the liquid ammonia has a dew point below -60℃, total hydrocarbon content less than 1 μmol / mol, and a gas flow rate of 800–1200 m³ / mol. 3 / t;

[0048] S2, in the hydrogen-based vertical furnace 1, ammonia gas exchanges heat with the hot DRI, so that the DRI is fully cooled and passivated;

[0049] In the cooling process of the hot DRI, ammonia gas, after passing through the conical section of the hydrogen-based vertical shaft furnace 1, comes into contact with the hot DRI. As the cold ammonia gas rises, it undergoes both physical heat exchange with the descending hot DRI and chemical heat exchange through decomposition under the catalytic action of the DRI. The gas after heat exchange is discharged from the flue gas outlet in the middle of the hydrogen-based vertical shaft furnace 1, forming tail gas. During this heat exchange process, the temperature of the ammonia gas gradually increases as it rises. Physical heat exchange is used to lower the temperature of the DRI. When the ammonia gas temperature reaches 500–700°C, it decomposes under the catalytic action of the DRI, absorbing heat and effectively absorbing the heat from the hot DRI, thus improving heat utilization efficiency. When the DRI cools down to 500–700°C, it is passivated by the ammonia gas, which forms iron nitride on the surface of the DRI. This iron nitride acts as an air barrier during subsequent transportation, effectively protecting the DRI and ensuring safe storage and transport. During the cooling process, the residence time of DRI in the first cone section of the hydrogen-based vertical furnace is 60–90 min, and the temperature of the cooled DRI is 150–250 °C with a nitrogen content of 0.1–0.15 wt.%.

[0050] Traditional cooling methods rely on physical heat exchange between the cooling gas and the DRI, resulting in low cooling efficiency and requiring further nitrogen protection. In this invention, however, the DRI is cooled using ammonia gas, which passivates the DRI during the cooling process, forming iron nitride on its surface. The DRI is then cooled to room temperature before transportation and storage.

[0051] S3, the cooled exhaust gas exits from the middle of the hydrogen-based vertical furnace 1, and after nitrogen separation, forms hydrogen-rich exhaust gas and nitrogen gas. Before nitrogen separation, the exhaust gas undergoes dust removal, waste heat recovery, and cooling and washing.

[0052] Hydrogen-rich gas separation: After ammonia gas exchanges heat with the hot DRI, the tail gas is discharged from the flue gas port in the middle of the hydrogen-based vertical furnace 1. After passing through the dust removal device 4 to remove dust from the gas, the waste heat recovery device 5 to recover heat, the cooling and washing device 6 to remove water vapor and residual ammonia gas, and the nitrogen separation device pressure swing adsorption to separate nitrogen gas, hydrogen-rich tail gas and nitrogen gas are formed. In the cooling and washing device 6, after the ammonia gas dissolved in water reaches a certain concentration, the ammonia water is extracted, heated and evaporated to remove water, and the ammonia gas is recycled.

[0053] The hydrogen-rich tail gas can be recycled as a reducing gas. It can be piped into the reducing gas system of the hydrogen-based shaft furnace 1, thereby reducing the consumption of reducing gas in the hydrogen-based shaft furnace 1 and achieving low carbon emissions. Nitrogen can be further used as a cooling gas (such as in a DRI storage tank) to cool the DRI to below 50°C, or it can be used to participate in the pressure equalization of the silo in the hydrogen-based shaft furnace 1.

[0054] In the aforementioned hydrogen-rich tail gas, the H2 content is 50–65 vol.% and the N2 content is 10–25 vol.%.

[0055] The present invention provides a method for directly reducing iron by cooling with ammonia and preparing hydrogen-rich reducing gas, which further includes S4, in which hydrogen-rich tail gas enters the reducing gas system as reducing gas, and after being mixed with reducing gas and heated, enters the hydrogen-based vertical furnace 1 to participate in the reduction of iron.

[0056] Combination Figure 1 As shown, the present invention also provides a system for cooling direct reduction of iron and preparing hydrogen-rich reducing gas using ammonia gas, comprising a hydrogen-based vertical shaft furnace 1, an ammonia gas injection system, and a hydrogen-rich tail gas system. The ammonia gas injection system is located at the bottom of the hydrogen-based vertical shaft furnace 1 to continuously supply a stable supply of ammonia gas to the furnace 1, and the hydrogen-rich tail gas system is located in the middle of the furnace 1 to purify the cooled tail gas.

[0057] Combination Figure 1 As shown, to ensure uniform ammonia supply to the conical section of the hydrogen-based vertical shaft furnace 1, multiple annular ammonia tuyeres are provided at the bottom of the conical section. The middle section of the hydrogen-based vertical shaft furnace 1 has a tail gas outlet connected to the hydrogen-rich tail gas system. Cooling of the hot DRI (Dihydrogen-Rich Integrated Gas) is carried out in the conical section of the hydrogen-based vertical shaft furnace 1. Ammonia enters the furnace from the bottom of the conical section and undergoes physical and chemical heat exchange with the slowly descending hot DRI during its ascent. The tail gas after heat exchange is discharged from the middle of the hydrogen-based vertical shaft furnace 1, while the cooled hot DRI is discharged from the discharge port of the hydrogen-based vertical shaft furnace 1 for subsequent storage and transportation.

[0058] Combination Figure 1 As shown, the ammonia injection system is used to vaporize liquid ammonia into ammonia gas for supplying the hydrogen-based vertical furnace 1. The ammonia injection system includes a liquid ammonia tank 2 and an ammonia purification device 3 connected in sequence. The ammonia purification device 3 is connected to the bottom of the conical section of the hydrogen-based vertical furnace 1. In a specific embodiment, the liquid ammonia in the liquid ammonia tank 2 is transported to the ammonia purification device 3 through a pipeline. The liquid ammonia undergoes liquefaction, heating, and purification in the ammonia purification device 3 to obtain stable, high-purity ammonia gas, which is then injected into the hydrogen-based vertical furnace 1 from the bottom of the conical section. The pipeline between the ammonia purification device 3 and the hydrogen-based vertical furnace 1 is equipped with an electric heating device to ensure a constant ammonia gas temperature and prevent re-liquefaction of the ammonia gas.

[0059] Combination Figure 1As shown, the hydrogen-rich tail gas system is used to purify the tail gas from the hydrogen shaft furnace to obtain hydrogen-rich tail gas and nitrogen. This system is connected to the flue gas outlet in the middle of the hydrogen-based shaft furnace 1. In a specific embodiment, the hydrogen-rich tail gas system includes a dust removal device 4, a waste heat recovery device 5, a cooling and scrubbing device 6, and a nitrogen separation device connected in sequence. The dust removal device 4 is connected to the flue gas outlet in the middle of the hydrogen-based shaft furnace 1. One end of the preheating and recovery device is connected to the dust removal device 4, and the other end is connected to the cooling and scrubbing device 6. One end of the nitrogen separation device is connected to the cooling and scrubbing device 6, and the other end's hydrogen-rich tail gas outlet is connected to the reducing gas system of the hydrogen-based shaft furnace 1. This hydrogen-rich tail gas outlet is connected to the reducing gas pipeline of the reducing gas system. During the exhaust gas purification process, the exhaust gas discharged from the flue gas outlet in the middle of the hydrogen-based vertical furnace 1 passes through the dust removal device 4 to remove dust from the gas, the waste heat recovery device 5 to recover heat, the cooling and washing device 6 to remove water vapor and residual ammonia, and the nitrogen separation device to separate nitrogen, resulting in hydrogen-rich exhaust gas and nitrogen. The hydrogen-rich exhaust gas can be recycled as a reducing gas into the reduction pipeline of the reducing gas system.

[0060] The following section provides a further description of the method and system for directly reducing iron by cooling it with ammonia and preparing hydrogen-rich reducing gas, using specific examples.

[0061] Example 1

[0062] This embodiment adopts Figure 1 The system shown utilizes ammonia gas to cool and directly reduce iron and prepare hydrogen-rich reducing gas. It employs a large hydrogen-based vertical shaft furnace 1, and the specific process is as follows:

[0063] (1) Cooling gas preparation: Liquid ammonia enters the ammonia purification unit 3 from the liquid ammonia tank 2 through a pipeline. After being heated and purified by the ammonia purification unit 3, stable high-purity ammonia gas is obtained. The pressure-stabilized ammonia gas is further supplied to the hydrogen-based vertical furnace 1 from the bottom of the conical section. The vaporized ammonia gas enters from the bottom of the conical section of the hydrogen-based vertical furnace 1. The conveying pipeline between the ammonia purification unit 3 and the hydrogen-based vertical furnace 1 is equipped with an electric heating device. The dew point of the ammonia gas is below -60℃, the total hydrocarbon content is less than 1 μmol / mol, and the ammonia gas flow rate is 800 m³ / mol. 3 / t;

[0064] (2) Hot DRI cooling: Ammonia gas comes into contact with hot DRI after the conical section of hydrogen-based vertical furnace 1. As the cold ammonia gas rises, it undergoes physical heat exchange with the descending hot DRI while simultaneously decomposing and absorbing heat under the catalytic action of the DRI to achieve chemical heat exchange. The gas after heat exchange is discharged from the flue gas outlet in the middle of hydrogen-based vertical furnace 1 to form tail gas. During the above heat exchange process, when the DRI cools down to 500-700°C, the DRI is passivated by ammonia gas, and iron nitride is generated on the surface of the DRI. After staying in the conical section of hydrogen-based vertical furnace 1 for 65 minutes, the DRI is discharged from the outlet.

[0065] (3) Hydrogen-rich gas separation: After the ammonia gas exchanges heat with the hot DRI, the tail gas is discharged from the flue gas port in the middle of the hydrogen-based vertical furnace 1. After passing through the dust removal device 4 to remove dust from the gas, the waste heat recovery device 5 to recover heat, the cooling and washing device 6 to remove water vapor and residual ammonia, and the nitrogen separation device to separate nitrogen, hydrogen-rich tail gas and nitrogen are formed. The hydrogen-rich tail gas enters the reducing gas system as a reducing gas, and after being mixed and heated with the reducing gas, it enters the hydrogen-based vertical furnace 1 to participate in the reduction of iron.

[0066] After sampling, the temperature and chemical composition of the DRI were measured, and the content of hydrogen-rich tail gas was obtained using an infrared component analyzer. Subsequently, 10 kg of cooled DRI was subjected to a 30-day continuous weighing experiment in air.

[0067] Analysis showed that the temperature of the DRI at the outlet was 220℃, the nitrogen content of the DRI was 0.11 wt.%, the hydrogen content in the hydrogen-rich tail gas was 56.6 vol.%, the nitrogen content was 19.5 vol.%, and the mass of the DRI increased by 1.8% after continuous weighing experiments.

[0068] Example 2

[0069] This embodiment adopts Figure 1 The system shown utilizes ammonia gas to cool and directly reduce iron and prepare hydrogen-rich reducing gas. It employs a large hydrogen-based vertical shaft furnace 1, and the specific process is as follows:

[0070] (1) Cooling gas preparation: Liquid ammonia enters the ammonia purification unit 3 from the liquid ammonia tank 2 through a pipeline. After being heated and purified by the ammonia purification unit 3, stable high-purity ammonia gas is obtained. The pressure-stabilized ammonia gas is further supplied to the hydrogen-based vertical furnace 1 from the bottom of the conical section. The vaporized ammonia gas enters from the bottom of the conical section of the hydrogen-based vertical furnace 1. The conveying pipeline between the ammonia purification unit 3 and the hydrogen-based vertical furnace 1 is equipped with an electric heating device. The dew point of the ammonia gas is below -60℃, the total hydrocarbon content is less than 1 μmol / mol, and the ammonia gas flow rate is 1200 m³ / min. 3 / t;

[0071] (2) Hot DRI cooling: Ammonia gas comes into contact with hot DRI after the conical section of hydrogen-based vertical furnace 1. As the cold ammonia gas rises, it undergoes physical heat exchange with the descending hot DRI while simultaneously decomposing and absorbing heat under the catalytic action of the DRI to achieve chemical heat exchange. The gas after heat exchange is discharged from the flue gas outlet in the middle of hydrogen-based vertical furnace 1 to form tail gas. During the above heat exchange process, when the DRI cools down to 500-700°C, the DRI is passivated by ammonia gas, and iron nitride is generated on the surface of the DRI. After the DRI stays in the conical section of hydrogen-based vertical furnace 1 for 90 minutes, it is discharged from the outlet.

[0072] (3) Hydrogen-rich gas separation: After the ammonia gas exchanges heat with the hot DRI, the tail gas is discharged from the flue gas port in the middle of the hydrogen-based vertical furnace 1. After passing through the dust removal device 4 to remove dust from the gas, the waste heat recovery device 5 to recover heat, the cooling and washing device 6 to remove water vapor and residual ammonia, and the nitrogen separation device to separate nitrogen, hydrogen-rich tail gas and nitrogen are formed. The hydrogen-rich tail gas enters the reducing gas system as a reducing gas, and after being mixed and heated with the reducing gas, it enters the hydrogen-based vertical furnace 1 to participate in the reduction of iron.

[0073] After sampling, the temperature and chemical composition of the DRI were measured, and the content of hydrogen-rich tail gas was obtained using an infrared component analyzer. Subsequently, 10 kg of cooled DRI was subjected to a 30-day continuous weighing experiment in air.

[0074] Analysis showed that the temperature of the DRI at the outlet was 150℃, the nitrogen content of the DRI was 0.15 wt.%, the hydrogen content in the hydrogen-rich tail gas was 62.6 vol.%, the nitrogen content was 13.5 vol.%, and the mass of the DRI increased by 1.1% after continuous weighing experiments.

[0075] Example 3

[0076] This embodiment adopts Figure 1 The system shown utilizes ammonia gas to cool and directly reduce iron and prepare hydrogen-rich reducing gas. It employs a large hydrogen-based vertical shaft furnace 1, and the specific process is as follows:

[0077] (1) Cooling gas preparation: Liquid ammonia enters the ammonia purification unit 3 from the liquid ammonia tank 2 through a pipeline. After being heated and purified by the ammonia purification unit 3, stable high-purity ammonia gas is obtained. The pressure-stabilized ammonia gas is then supplied to the hydrogen-based vertical furnace 1 from the bottom of the conical section. The vaporized ammonia gas enters from the bottom of the conical section of the hydrogen-based vertical furnace 1. Electric heating devices are installed on the conveying pipelines between the ammonia purification unit 3 and the hydrogen-based vertical furnace 1. The dew point of the ammonia gas is below -60℃, the total hydrocarbon content is less than 1 μmol / mol, and the ammonia gas flow rate is 960 m³ / mol. 3 / t;

[0078] (2) Hot DRI cooling: Ammonia gas comes into contact with hot DRI after the conical section of hydrogen-based vertical furnace 1. As the cold ammonia gas rises, it undergoes physical heat exchange with the descending hot DRI while simultaneously decomposing and absorbing heat under the catalytic action of the DRI to achieve chemical heat exchange. The gas after heat exchange is discharged from the flue gas outlet in the middle of hydrogen-based vertical furnace 1 to form tail gas. During the above heat exchange process, when the DRI cools down to 500-700°C, the DRI is passivated by ammonia gas, and iron nitride is generated on the surface of the DRI. After the DRI stays in the conical section of hydrogen-based vertical furnace 1 for 80 minutes, it is discharged from the outlet.

[0079] (3) Hydrogen-rich gas separation: After the ammonia gas exchanges heat with the hot DRI, the tail gas is discharged from the flue gas port in the middle of the hydrogen-based vertical furnace 1. After passing through the dust removal device 4 to remove dust from the gas, the waste heat recovery device 5 to recover heat, the cooling and washing device 6 to remove water vapor and residual ammonia, and the nitrogen separation device to separate nitrogen, hydrogen-rich tail gas and nitrogen are formed. The hydrogen-rich tail gas enters the reducing gas system as a reducing gas, and after being mixed and heated with the reducing gas, it enters the hydrogen-based vertical furnace 1 to participate in the reduction of iron.

[0080] After sampling, the temperature and chemical composition of the DRI were measured, and the content of hydrogen-rich tail gas was obtained using an infrared component analyzer. Subsequently, 10 kg of cooled DRI was subjected to a 30-day continuous weighing experiment in air.

[0081] Analysis showed that the temperature of the DRI at the outlet was 180℃, the nitrogen content of the DRI was 0.13 wt.%, the hydrogen content in the hydrogen-rich tail gas was 59.2 vol.%, the nitrogen content was 17.9 vol.%, and the mass of the DRI increased by 1.1% after continuous weighing experiments.

[0082] Comparative Example

[0083] A flow rate of 1600 m³ / h was introduced into the bottom of the conical section of a large hydrogen-based vertical shaft furnace. 3 The DRI was cooled with nitrogen gas for 150 minutes and then discharged from the outlet. After sampling, the temperature and chemical composition of the DRI were measured and analyzed. The content of the exhaust gas was obtained using an infrared component analyzer. Subsequently, 10 kg of the cooled DRI was subjected to a 30-day continuous weighing experiment in air.

[0084] Analysis revealed that the temperature of the DRI at the discharge port was 268℃, and the nitrogen content in the DRI was undetectable. The N2 content in the exhaust gas was measured at 100 vol.%, and after continuous weighing experiments, the mass of the DRI increased by 13.7%.

[0085] As can be seen from Examples 1-3 and the comparative examples, using ammonia to directly cool the hot DRI involves both physical heat exchange between the cold ammonia and the hot DRI, and chemical heat exchange due to the heat absorbed by the decomposition of ammonia. Compared with nitrogen cooling of the DRI in the comparative example, the required cooling gas flow rate is smaller, reducing the cooling time. Therefore, the method of the present invention can improve the utilization efficiency of the cooling gas and the heat exchange efficiency. In addition, the temperature of the DRI is lower after cooling, and the resulting exhaust gas has a higher hydrogen content, which can be further recycled as a reducing gas. Moreover, after 30 days of continuous weighing tests in air, the increase in mass in Examples 1-3 was much smaller than that in the comparative example. This shows that the method of the present invention facilitates the subsequent storage and transportation of the DRI.

[0086] In summary, in the method of using ammonia to cool direct reduction of iron and prepare hydrogen-rich reducing gas according to the present invention, liquid ammonia is purified by an ammonia purification device to form ammonia gas, which is then introduced into the hydrogen-based vertical shaft furnace from the bottom of the conical section. In the hydrogen-based vertical shaft furnace, the cold ammonia gas undergoes physical heat exchange with the hot DRI, and the ammonia gas decomposes using the catalytic effect of the DRI. The heat absorbed during decomposition achieves chemical heat exchange, thereby fully cooling and passivating the DRI. The tail gas formed by the ammonia decomposition exits from the flue gas outlet in the middle of the hydrogen-based vertical shaft furnace, and after dust removal, waste heat recovery, cooling washing, and nitrogen separation, forms hydrogen-rich tail gas and nitrogen gas. The hydrogen-rich tail gas can be recycled as reducing gas, and the nitrogen gas can be further used as cooling gas to cool the DRI to below 50°C, or participate in the pressure equalization of the hydrogen-based vertical shaft furnace hopper. The method of this invention utilizes ammonia gas to cool direct reduced iron, achieving efficient cooling of hot DRI, improving heat exchange efficiency, and passivating DRI for easier subsequent storage and transportation. Furthermore, the resulting hydrogen-rich reducing gas can be further introduced into the reducing gas system, reducing reducing gas consumption and achieving low carbon emissions.

[0087] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for directly reducing iron by cooling with ammonia and preparing hydrogen-rich reducing gas, characterized in that, Ammonia is used to cool the hot DRI after reduction in the hydrogen shaft furnace, thereby cooling and passivating the hot DRI; the cooled tail gas comes out from the middle of the hydrogen-based shaft furnace, and then is separated by nitrogen to form hydrogen-rich tail gas and nitrogen.

2. The method for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia gas according to claim 1, characterized in that, Includes the following steps: S1, liquid ammonia is purified by an ammonia purification device to form ammonia gas, which is then introduced into the furnace from the bottom of the hydrogen-based vertical furnace; S2, in the hydrogen-based vertical furnace, ammonia gas exchanges heat with the hot DRI, so that the DRI is fully cooled and passivated; S3, the cooled tail gas comes out from the middle of the hydrogen-based vertical furnace, and after nitrogen separation, it forms hydrogen-rich tail gas and nitrogen.

3. The method for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia gas according to claim 2, characterized in that, In step S1 The liquid ammonia is selected from gray ammonia, blue ammonia, or green ammonia; and / or The ammonia gas has a dew point below -60°C, total hydrocarbon content less than 1 μmol / mol, and a flow rate of 800–1200 m³ / min. 3 / t; and / or The conveying pipeline between the ammonia purification device and the hydrogen-based vertical furnace is equipped with an electric heating device, and the ammonia gas vaporized by the ammonia purification device enters from the bottom of the conical section of the hydrogen-based vertical furnace.

4. The method for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia gas according to claim 2, characterized in that, In step S2, after ammonia enters the hydrogen-based vertical furnace, it undergoes physical heat exchange with the descending hot DRI during the upward process, while simultaneously decomposing and absorbing heat under the catalytic action of the DRI to achieve chemical heat exchange. During the heat exchange process, when the DRI cools down to 500-700°C, ammonia forms an iron nitride film on the surface of the DRI.

5. The method for directly reducing iron by cooling with ammonia and preparing hydrogen-rich reducing gas according to claim 4, characterized in that: The residence time of the DRI in the cone section of the hydrogen-based vertical shaft furnace is 60–90 min; and / or The cooled DRI has a temperature of 150–250°C and a nitrogen content of 0.1–0.15 wt.%.

6. The method for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia gas according to claim 2, characterized in that, In step S3: Before nitrogen separation, the exhaust gas undergoes dust removal, waste heat recovery, cooling and washing; and / or The hydrogen-rich tail gas contains 50–65 vol.% H2 and 10–25 vol.% N2.

7. The method for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia gas according to claim 2, characterized in that, It also includes S4, where hydrogen-rich tail gas enters the reducing gas system as a reducing gas, mixes and heats with the reducing gas, and then enters the hydrogen-based vertical furnace to participate in the reduction of iron.

8. A system for directly reducing iron and preparing hydrogen-rich reducing gas by cooling with ammonia gas, characterized in that, include: Hydrogen-based vertical shaft furnace; An ammonia injection system is used to convert liquid ammonia into ammonia gas for supplying a hydrogen-based vertical furnace. The ammonia injection system includes a liquid ammonia tank and an ammonia purification device connected in sequence, wherein the ammonia purification device is connected to the bottom of the conical section of the hydrogen-based vertical furnace. The hydrogen-rich tail gas system is used to purify the tail gas from the hydrogen vertical furnace to obtain hydrogen-rich tail gas and nitrogen; the hydrogen-rich tail gas system is connected to the middle of the hydrogen-based vertical furnace.

9. The system for cooling direct reduction of iron and preparing hydrogen-rich reducing gas using ammonia gas according to claim 8, characterized in that, The bottom of the hydrogen-based vertical shaft furnace cone section is provided with multiple annular ammonia tuyeres; the middle part of the hydrogen-based vertical shaft furnace is provided with a tail gas outlet connected to the hydrogen-rich tail gas system.

10. The system for cooling direct reduction of iron and preparing hydrogen-rich reducing gas using ammonia gas according to claim 8, characterized in that, The conveying pipeline between the ammonia purification unit and the hydrogen-based vertical furnace is equipped with an electric heat tracing device.

11. The system for cooling direct reduction of iron and preparing hydrogen-rich reducing gas using ammonia gas according to claim 8, characterized in that, The hydrogen-rich tail gas system includes a dust removal device, a waste heat recovery device, a cooling and washing device, and a nitrogen separation device connected in sequence; the dust removal device is connected to the flue gas outlet in the middle of the hydrogen-based vertical furnace.

12. The system for cooling direct reduction of iron and preparing hydrogen-rich reducing gas using ammonia gas according to claim 11, characterized in that, The hydrogen-rich tail gas outlet of the nitrogen separation device is connected to the reducing gas system of the hydrogen-based vertical furnace.

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