Direct reduction ironmaking method with liquid ammonia as medium

Abstract

The invention provides a method for direct reduction ironmaking by taking liquid ammonia as a medium, which comprises the following steps of: cracking the liquid ammonia to obtain mixed gas of N2 and H2, and pressurizing the mixed gas to be used as reducing gas; the iron ore is heated and reduced under the action of the reducing gas, and metallized pellets are obtained; and the metallized pellets react with a C reducing agent, and molten iron and melt separation slag are obtained. According to the method provided by the invention, the ammonia gas is firstly cracked, H2 is substantially utilized for reduction, compared with the ammonia gas directly serving as a reducing agent, the cracked reducing gas can avoid the problem of furnace body heat shortage caused by endothermic reduction reaction, and the tail gas does not contain NH3, so that the additional NH3 recovery process is avoided, and the whole process flow is relatively compact.

Description

Technical Field

[0001] This invention belongs to the field of low-carbon metallurgical technology, and in particular relates to a direct reduction ironmaking method using liquid ammonia as a medium. Background Technology

[0002] With increasingly stringent global carbon emission policies, technological innovation in low-carbon metallurgical processes has become imperative. The industry consensus is that clean energy sources such as hydrogen-rich gas should partially or completely replace traditional fossil fuels to achieve carbon reduction targets, and related technologies have become a research hotspot. Currently, blast furnace ironmaking remains the mainstream process globally, but its energy efficiency and carbon emission control are nearing their theoretical limits. Although new technologies such as hydrogen-rich injection, top gas recirculation, oxygen-enriched blast furnaces, and biomass injection have shown some carbon reduction potential, the rigid demand for coke (carbonaceous raw material) as aggregate in blast furnace smelting makes it impossible to completely break free from fossil fuel dependence, hindering large-scale emission reductions. Therefore, non-blast furnace smelting processes, represented by direct reduction, are receiving increasing attention. Among them, hydrogen-based vertical shaft furnace technology, due to its significant carbon reduction potential and high process maturity, is considered a promising next-generation mainstream technology to replace blast furnaces.

[0003] Existing gas-based vertical shaft furnace processes primarily rely on natural gas as the reducing medium, generating reducing gases containing CO and H2 through in-furnace or external reforming. The differences in process mainly lie in parameters such as the reforming method, the CO / H2 ratio in the reducing gas, temperature, and pressure, but the core principle remains the same: utilizing CO and H2, two competing yet synergistic reducing agents, to reduce iron ore. Increasing the proportion of H2 in the reducing gas can effectively reduce carbon emissions, which has given rise to the concept of pure hydrogen vertical shaft furnaces pursuing extreme carbon reduction. However, H2 reduction is an endothermic reaction, while CO reduction is exothermic. Furthermore, H2 itself has a low heat capacity per unit mass, making vertical shaft furnaces in a pure hydrogen environment prone to insufficient heat, leading to decreased reduction and affecting subsequent slag-iron separation. Therefore, high-H2 smelting often requires supplementary measures such as furnace pressurization and increasing the gas-solid ratio. In addition, the current high cost of hydrogen production through water electrolysis makes pure hydrogen vertical shaft furnaces economically uncompetitive. Against this backdrop, exploring the feasibility of ammonia (NH3) as a clean ironmaking reducing medium is of considerable value. Compared to carbon-containing CH4, ammonia is a completely carbon-free clean energy source. Compared to pure H2, ammonia has significant advantages in terms of volumetric hydrogen storage density, transportation safety, the ability to utilize the sensible heat of N2 for heating the reduction process, and a mature and well-established industrial production chain. However, there are currently no reported processes using ammonia as the main reducing agent in iron smelting, and technological breakthroughs are urgently needed. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a direct reduction ironmaking method using liquid ammonia as a medium, which has a stable and safe gas source and low carbon emission intensity.

[0005] This invention provides a method for direct reduction ironmaking using liquid ammonia as a medium, comprising the following steps:

[0006] Liquid ammonia is cracked to obtain a mixture of N2 and H2, which is then pressurized and used as a reducing gas.

[0007] Iron ore is heated and reduced under the action of the reducing gas to obtain metallized pellets;

[0008] The metallized pellets are reacted with a C-type reducing agent to obtain molten iron and slag.

[0009] Preferably, the pyrolysis is carried out in a heated pyrolysis furnace;

[0010] The working temperature of the heating pyrolysis furnace is 1100~1200℃, and the working pressure is 1~3 bar.

[0011] Preferably, the ratio of hydrogen to nitrogen in the cracked gas is 3:1 to 9:1;

[0012] The temperature of the pyrolysis gas is 900~1050℃.

[0013] Preferably, the heating and reduction are carried out in a vertical furnace;

[0014] The working pressure of the vertical shaft furnace is 1.5~3MPa, and the temperature of the reducing gas entering the vertical shaft furnace is 850~950℃;

[0015] The gas-solid ratio is 1500~2200 Nm 3 / t iron ore.

[0016] Preferably, the utilization rate of H2 in the heating reduction is 15-25%.

[0017] Preferably, the metallization rate of the iron ore is 85-95%.

[0018] Preferably, the exhaust gas discharged from the vertical furnace after heating and reduction is first dusted, then condensed, and finally N2 and H2 are separated.

[0019] Preferably, membrane separation or molecular sieve separation is used to separate N2 and H2.

[0020] Preferably, the liquid ammonia is preheated to fully vaporize and initially heated to 150~250°C before being cracked.

[0021] Preferably, the reducing agent C is coke;

[0022] The amount added is 30~50kg / t of iron ore.

[0023] The method provided by this invention first cracks ammonia, which is essentially reduced by H2. Compared with ammonia as a reducing agent, the reducing gas after cracking can avoid the furnace heat shortage problem caused by the endothermic reduction reaction. In addition, the tail gas does not contain NH3, avoiding the need to add an NH3 recovery process. The whole process is relatively more compact. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the direct reduction ironmaking process using liquid ammonia as a medium, as used in an embodiment of the present invention. Detailed Implementation

[0025] This invention provides a method for direct reduction ironmaking using liquid ammonia as a medium, comprising the following steps:

[0026] Liquid ammonia is cracked to obtain a mixture of N2 and H2, which is then pressurized and used as a reducing gas.

[0027] Iron ore is heated and reduced under the action of the reducing gas to obtain metallized pellets;

[0028] The metallized pellets are reacted with a C-type reducing agent to obtain molten iron and slag.

[0029] This invention involves cracking liquid ammonia to obtain a mixture of N2 and H2, which is then pressurized and used as a reducing gas. The synthesized ammonia is fed into a storage tank via pipeline or tanker truck, first undergoing thorough vaporization and preliminary heating in a preheating furnace, and then pumped into a heated cracking furnace via pipeline. Preferably, the preliminary heating is carried out at 150-250°C before cracking; specifically, the temperatures can be 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C.

[0030] In this invention, pyrolysis is carried out in a heating pyrolysis furnace, which has two functions: first, to pyrolyze NH3, and second, to heat the circulating H2. The heating pyrolysis furnace can be configured as an AB furnace, with furnace A heating furnace B for heat storage.

[0031] The operating temperature of the heating pyrolysis furnace described in this invention is 1100~1200℃, specifically 1100℃, 1150℃ or 1200℃; the operating pressure is 1~3 bar, specifically 1 bar, 2 bar or 3 bar.

[0032] The resulting N2 and H2 mixture is then fed into a pressurizing device and pressurized to a preset pressure before being fed into the bottom of the vertical shaft furnace. The hydrogen to nitrogen ratio in the pyrolysis gas is 3:1 to 9:1; specifically, it can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, or 9:1; the temperature of the pyrolysis gas is 900 to 1050℃; specifically, it can be 900℃, 950℃, 1000℃, or 1050℃.

[0033] This invention involves heating and reducing iron ore under the action of a reducing gas to obtain metallized pellets. One form of iron ore processing is pelletizing, whose main components are Fe2O3 and gangue. Under the action of a high-temperature reducing gas, the pellets are gradually heated and reduced, and the oxygen in the iron ore is gradually stripped away by H2 in the reducing gas, producing high-temperature steam. The reduced iron ore exists in the form of metallic iron and gangue, and is called metallized pellets. In this invention, the heating and reduction are carried out in a vertical shaft furnace; the operating pressure of the vertical shaft furnace is 1.5~3 MPa, specifically 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2.0 MPa, 2.1 MPa, 2.2 MPa, 2.3 MPa, 2.4 MPa, 2.5 MPa, 2.6 MPa, 2.7 MPa, 2.8 MPa, 2.9 MPa, or 3 MPa; the temperature of the reducing gas entering the vertical shaft furnace is 850~950℃, specifically 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃; the gas-solid ratio is 1500~2200 Nm³. 3 / t iron ore, specifically 1500 Nm 3 / t iron ore, 1600 Nm 3 / t iron ore, 1700 Nm 3 / t iron ore, 1800 Nm 3 / t iron ore, 1900 Nm 3 / t iron ore, 2000 Nm 3 / t iron ore, 2100 Nm 3 / t iron ore or 2200 Nm 3 / t iron ore.

[0034] In the heating and reduction process described in this invention, the utilization rate of H2 is 15-25%, specifically 15%, 20%, or 25%. The metallization rate of iron ore is 85-95%, specifically 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95%.

[0035] This invention reacts the metallized pellets with a carbon-based reducing agent to obtain molten iron and slag. The metallized pellets are then fed into an electric furnace, where the carbon-based reducing agent is added, and the mixture is melted into slag and carbon-containing molten iron. The slag and carbon-containing molten iron are then fed into the subsequent processes of an existing steel plant. In this invention, the carbon-based reducing agent is coke; the addition amount is 30-50 kg / t iron ore, specifically 30 kg / t, 35 kg / t, 40 kg / t, 45 kg / t, or 50 kg / t iron ore. The amount of carbon-based reducing agent used in this invention is much smaller than that used in conventional processes, resulting in low carbon emission intensity.

[0036] In this invention, the utilization rate of gas in the vertical furnace is very low, and the tail gas of the vertical furnace contains a large amount of unused H2, which needs to be recycled.

[0037] In this invention, the exhaust gas discharged from the vertical furnace after heating and reduction is first dedusted, then condensed, and finally N2 and H2 are separated. Preferably, this invention uses membrane separation or molecular sieve separation of N2 and H2, with a separation efficiency of over 95%.

[0038] The exhaust gas from the vertical shaft furnace first passes through a dust removal device to filter out dust, then enters a condenser where water vapor is condensed and separated from the exhaust gas. The remaining N2 and H2 are separated by membrane separation or pressure swing adsorption. The initially separated N2 can be used as a byproduct or directly vented, while most of the H2 is reused after being heated in a cracking furnace, with the remainder entering the subsequent purification stage as a byproduct. Theoretically, H2 can be completely recycled, but considering the strong endothermic reduction and low heat capacity of H2, a certain proportion of N2 needs to be retained in the reducing gas to ensure the heat supply to the vertical shaft furnace, thus a path for H2 to be vented is reserved. High-purity N2 and H2 are produced as byproducts. N2 does not participate in the recycling; 20-30% is used for high-purity N2 preparation, and the remainder is vented. Most of the H2 participates in the recycling, with 10-25% used for purification.

[0039] Calculations show that the proportion of H2 entering the vertical furnace using the method described in this invention is between 75% and 90%, a proportion that has been proven to be entirely feasible by current hydrogen-rich vertical furnace processes.

[0040] Unlike existing processes that use natural gas or pure H2 as the main reducing medium, the method described in this invention uses liquid ammonia as the reducing medium. NH3 is pre-decomposed in a heating furnace to generate high-temperature reducing gases of H2 and N2 to reduce iron ore. This method has several advantages over existing processes: 1. Stable gas source. my country's natural gas resources are relatively scarce and exhibit a strong regional distribution trend, while NH3, as a basic chemical raw material, has a large production volume and a mature process; 2. NH3 storage and transportation are relatively safe. Compared with H2 storage and transportation, there are no material performance limitations such as hydrogen embrittlement; 3. Compared with natural gas, NH3 decomposes into H2 and N2, resulting in extremely low carbon emission intensity. Compared with pure H2, the additional N2 can serve as a heat source, avoiding problems such as insufficient heat in vertical furnaces under high H2 content.

[0041] To further illustrate the present invention, the following detailed description of a direct reduction ironmaking method using liquid ammonia as a medium, in conjunction with embodiments, is provided by the present invention, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0042] Figure 1 This is a schematic diagram of the direct reduction ironmaking process using liquid ammonia as a medium, as used in an embodiment of the present invention.

[0043] Example 1

[0044] Taking a 600,000-ton iron production capacity demonstration line as an example, the main workflow described in this invention is as follows:

[0045] (1) Purchased synthetic ammonia was transported to storage tanks via tank trucks;

[0046] (2) The synthesized ammonia enters the preheating furnace for vaporization and is initially heated to about 150~250℃.

[0047] (3) The vaporized NH3 and circulating H2 (approximately 25°C) enter the regenerative heater together. An AB regenerative heater is used for heating. First, the furnace is heated to 1100~1200°C. Then, NH3 undergoes endothermic decomposition in contact with the furnace packing agent. The N2 content of the decomposed gas is between 10~25%, while the H2 content is between 75%~90%. The reducing gas exits the furnace at approximately 900~1000°C.

[0048] (4) The reducing gas is pressurized to 1.5~2.4MPa by a pressurizing device;

[0049] (5) N2 and H2 are piped into the vertical shaft furnace. Due to heat loss, their temperature is between 850 and 950°C. The total reducing gas volume is 15,000 to 22,000 Nm³. 3 / h, gas-solid ratio approximately 1800 Nm 3 / t of ore. H2 utilization coefficient is between 15% and 25%, and pellet metallization rate can reach 85% to 95%;

[0050] (6) The reduced ore pellets are then fed into an electric arc furnace for smelting. The furnace operates at 1600-1800℃, and 30-50 kg / t of coke is added as a reducing agent to further reduce the pellets. The iron slag and carbon-containing molten iron obtained from the smelting process are then fed into the subsequent stages of the existing ironworks.

[0051] (7) The top gas of the vertical furnace first passes through a dust removal device to remove dust, then enters a condenser to cool to below the dew point temperature, and enters the gas separation unit after gas-liquid separation.

[0052] (8) A molecular sieve separation device is used to coarsely separate the tail gas. 20% of the separated N2 is used as raw material to be sent to the purification section to produce high-purity N2, and the remaining 80% is directly discharged into the air. H2 is distributed in a manner of 75% recycling and 25% by-product.

[0053] The above process can achieve an annual production of 600,000 tons of carbon-containing molten iron, with an NH3 consumption of 500-800 Nm³ per ton of iron. 3 Byproduct high-purity N2: 300,000 to 480,000 Nm³ 3 High-purity H2 produced as a byproduct: 50,000 to 150,000 Nm³ 3 .

[0054] As can be seen from the above embodiments, the present invention provides a method for direct reduction ironmaking using liquid ammonia as a medium, comprising the following steps: cracking liquid ammonia to obtain a mixture of N2 and H2 gas, which is then pressurized and used as a reducing gas; heating and reducing iron ore under the action of the reducing gas to obtain metallized pellets; reacting the metallized pellets with a C-type reducing agent to obtain molten iron and slag. The method provided by the present invention first cracks ammonia gas, essentially utilizing H2 for reduction. Compared with directly using ammonia gas as a reducing agent, the cracked reducing gas avoids the furnace heat shortage problem caused by the endothermic reduction reaction, and the tail gas does not contain NH3, avoiding the need for an additional NH3 recovery process, making the entire process relatively more compact.

[0055] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for direct reduction ironmaking using liquid ammonia as a medium, comprising the following steps: Liquid ammonia is cracked to obtain a mixture of N2 and H2, which is then pressurized and used as a reducing gas. Iron ore is heated and reduced under the action of the reducing gas to obtain metallized pellets; The metallized pellets are reacted with a C-type reducing agent to obtain molten iron and slag.

2. The method according to claim 1, characterized in that, The pyrolysis is carried out in a heated pyrolysis furnace; The working temperature of the heating pyrolysis furnace is 1100~1200℃, and the working pressure is 1~3 bar.

3. The method according to claim 1, characterized in that, The ratio of hydrogen to nitrogen in the cracked gas is 3:1 to 9:1; The temperature of the pyrolysis gas is 900~1050℃.

4. The method according to claim 1, characterized in that, The heating and reduction are carried out in a vertical furnace; The working pressure of the vertical shaft furnace is 1.5~3MPa, and the temperature of the reducing gas entering the vertical shaft furnace is 850~950℃; The gas-solid ratio is 1500~2200 Nm 3 / t iron ore.

5. The method according to claim 1, characterized in that, The utilization rate of H2 in the heating reduction process is 15-25%.

6. The method according to claim 1, characterized in that, The metallization rate of iron ore is 85-95%.

7. The method according to claim 4, characterized in that, After heating and reduction, the exhaust gas discharged from the vertical furnace is first dusted, then condensed, and finally N2 and H2 are separated.

8. The method according to claim 7, characterized in that, N2 and H2 are separated by membrane separation or molecular sieve separation.

9. The method according to claim 7, characterized in that, Liquid ammonia is first preheated to fully vaporize and then initially heated to 150~250℃ before being cracked.

10. The method according to claim 1, characterized in that, The reducing agent for C is coke; The amount added is 30~50kg / t of iron ore.

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