Method and system for preparing direct reduced iron by coupling CO-rich gas and ammonia gas

Abstract

The invention discloses a method and system for preparing direct reduction iron by coupling CO-rich gas and ammonia gas, and the method comprises the following steps: pre-reducing an iron-containing raw material in a reduction reactor by CO-rich gas at the temperature of 500-800 DEG C; and carrying out high-temperature reduction by using ammonia gas, wherein the temperature of the ammonia gas is 900-1000 DEG C. According to the method, the raw materials are pre-reduced by utilizing the advantages of high low-temperature reduction rate of CO and heat release of reduction reaction, and then the furnace charge is finally reduced by utilizing the advantage of good high-temperature reduction effect of NH3 gas; the carbon emission in the reduction process is reduced, and the heat consumption in the process is reduced; the coupling reduction of CO and NH3 combines the advantages of the reduction processes of CO and NH3, and meanwhile, the problems of large carbon emission in the CO reduction process and high heat consumption in the NH3 reduction process are avoided; comprehensive utilization of the blast furnace gas and efficient production of the reduced iron can be achieved, and the metallization ratio of the reduced iron is 95% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of direct reduced iron, in particular to a method and a system for coupling rich CO gas and ammonia gas to prepare direct reduced iron. Background Art

[0002] Energy conservation and emission reduction in the iron and steel production process have become the main direction of the future development of the industry. The current low-carbon ironmaking technology is gradually developing towards the direct reduction process, and the traditional blast furnace ironmaking process has gradually lost its advantage in the low-carbon competition due to its small carbon reduction potential. In the direct reduction process, the hydrogen-based direct reduction process using hydrogen as a reducing agent has become the focus of development in various countries. However, the hydrogen resources required for hydrogen-based direct reduction are huge, and the transportation and storage costs of hydrogen are too high, which limits the development of hydrogen direct reduction technology.

[0003] The Chinese invention patent with the publication number CN113930568B discloses "a method for preparing direct reduced iron by introducing hydrogen into a reduction shaft furnace", which reduces iron-containing raw materials by introducing hot hydrogen-rich reducing gas into the shaft furnace. According to the temperature of the iron-containing burden in the reduction section of the shaft furnace, a combustion injection device injects oxygen into the reduction section of the shaft furnace to burn the reducing gas to provide heat for the reduction process. The reducing gas used in this method is a hydrogen-rich gas with a hydrogen content of more than 80%. For enterprises, the long-term stable supply of a large amount of hydrogen-rich gas resources will bring a large amount of costs such as pure hydrogen storage and transportation.

[0004] The Chinese patent application with the publication number CN107299176A discloses "a system and a method for producing direct reduced iron in a shaft furnace", which directly reduces iron-containing raw materials with reducing gas prepared from low-rank coal; however, the gas contains CO, CO2 and CH4, and the preheating temperature of the reducing gas is relatively high, and carbon deposition is likely to occur in the reducing gas, thus blocking the pipeline, which limits the development of the technology.

[0005] The Chinese patent with the publication number CN112813219B discloses "a system and a process for realizing near-zero emission by directly reducing iron with ammonia", which uses ammonia as a hydrogen-rich carrier to provide a reducing agent and heat for the reduction of iron-containing raw materials, and avoids the high cost of hydrogen storage and transportation. The reduction process of this method requires the temperature of the reducing gas to be above 900°C, consuming a large amount of heat. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for coupling rich CO gas and ammonia gas to prepare direct reduced iron with good reduction effect; the present invention also provides a system for coupling rich CO gas and ammonia gas to prepare direct reduced iron.

[0007] To solve the above technical problems, the technical solution adopted by the present invention includes the following steps: the iron-containing raw material is first pre-reduced by a CO-rich gas in a reduction reactor, and the temperature of the CO-rich gas is 500-800 °C; then it is subjected to high-temperature reduction by ammonia gas, and the temperature of the ammonia gas is 900-1000 °C.

[0008] Further, the reduction time for the pre-reduction is 10-20 min, and the reduction time for the high-temperature reduction is 20-40 min.

[0009] Further, the CO gas content in the CO-rich gas is greater than 80 vol%.

[0010] To solve the above technical problems, the technical solution adopted by the system of the present invention is: it includes a reduction reactor; inside the reduction reactor, the reduction zone from top to bottom is sequentially a low-temperature reduction zone and a high-temperature reduction zone; the low-temperature reduction zone is connected to a CO-rich gas pipeline, and the high-temperature reduction zone is connected to an ammonia gas pipeline.

[0011] Further, it also includes a blast furnace gas purification and upgrading device, a CO-rich gas heater, an ammonia gas heater and a gasification device; the inlet of the blast furnace gas purification and upgrading device is connected to a blast furnace gas pipeline, and the CO-rich gas outlet passes through the CO-rich gas heater and is connected to the low-temperature reduction zone of the reduction reactor through the CO-rich gas pipeline; the inlet of the gasification device is connected to a liquid ammonia pipeline, and the outlet passes through the ammonia gas heater and is connected to the high-temperature reduction zone of the reduction reactor through the ammonia gas pipeline.

[0012] Further, a #1 heat exchange device and a #2 heat exchange device are also provided; the #1 heat exchange device and the #2 heat exchange device are sequentially connected to the reduced iron outlet of the reduction reactor; the lean CO gas outlet of the blast furnace gas purification and upgrading device is connected to the cooling gas inlet of the #2 heat exchange device; the outlet of the gasification device is also connected to the cooling gas inlet of the #1 heat exchange device, and the cooling gas outlet of the #1 heat exchange device is connected to the inlet of the ammonia gas heater.

[0013] The beneficial effects produced by adopting the above technical solution are as follows: the method of the present invention combines CO reduction and NH3 gas reduction. Utilizing the advantages of high low-temperature reduction rate of CO and heat release from the reduction reaction, the raw material is first pre-reduced. After the pre-reduction, the final reduction of the furnace charge is carried out by utilizing the advantage of good high-temperature reduction effect of NH3 gas; in the whole process, compared with single CO reduction, the carbon emission in the reduction process is reduced; compared with pure NH3 reduction, the heat consumption in the process is reduced; the coupled reduction of CO and NH3 combines the advantages of the two reduction processes, and at the same time avoids the problems of a large amount of carbon emissions in the CO reduction process and high heat consumption in the NH3 reduction process. The present invention uses ammonia gas and the CO-rich gas after purification of blast furnace gas as the reducing agent for the iron-containing raw material. The process can realize the comprehensive utilization of blast furnace gas and the efficient production of reduced iron. At the same time, it can also avoid the problem of insufficient hydrogen source in direct hydrogen-based reduction. The metallization rate of the obtained reduced iron is above 95%.

[0014] In the system of the present invention, a rich CO gas pipeline is connected to the low-temperature reduction zone, an ammonia gas pipeline is connected to the high-temperature reduction zone, and the high-temperature reduction zone is connected; the low-temperature reduction zone is mainly used for reducing iron-containing raw materials with rich CO gas. Utilizing the characteristic that CO has a good reduction effect at low temperatures, the iron-containing raw materials are preliminarily reduced, and at the same time, the furnace charge is heated to a certain temperature; the high-temperature reduction zone is mainly used for directly reducing iron-containing furnace charge with ammonia gas. Utilizing the excellent high-temperature reduction characteristics of ammonia gas, the final direct reduction of the iron-containing raw materials is completed. The system of the present invention generates hot reduced iron by coupling the indirect reduction of CO and the direct reduction of ammonia gas, and can realize the comprehensive utilization of blast furnace gas and the efficient production of reduced iron.

[0015] In the method and system of the present invention, ammonia gas is used as a hydrogen carrier to reduce iron-containing raw materials, greatly reducing the costs of hydrogen transportation and storage; the rich CO gas purified from blast furnace gas is used as a reducing agent for iron-containing raw materials, making full use of the tail gas resources inside the steel plant; the method of coupling CO and ammonia gas to reduce iron-containing furnace charge gives full play to the advantages of low-temperature reduction of CO and high-temperature reduction of ammonia gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

[0017] Figure 1 It is a schematic structural diagram of the system of the present invention.

[0018] In the figure: blast furnace gas purification and purification device 1; rich CO gas heater 2; ammonia gas heater 3; gasification device 4; reduction reactor 5; 1# heat exchange device 6; 2# heat exchange device 7; low-temperature reduction zone I; high-temperature reduction zone II. SPECIFIC EMBODIMENTS

[0019] The method for coupling rich CO gas and ammonia gas to prepare direct reduced iron includes the following steps: 1) The blast furnace gas is purified to obtain rich CO gas and lean CO gas. The purification of the blast furnace gas mainly includes dust removal, compression, hydrolysis, deoxidation, CO adsorption, CO desorption, and tail gas recovery processes. The content of CO gas in the rich CO gas is greater than 80 vol%, and the main components of the lean CO gas are CO2 and nitrogen.

[0020] 2) The rich CO gas is heated to 500 - 800 °C and sent into the reduction reactor to pre-reduce the iron-containing raw materials. The pre-reduction time is 10 - 20 min to obtain pre-reduced furnace charge. The iron-containing raw materials use natural lump ore and / or pellet ore.

[0021] 3) The liquid ammonia is vaporized to obtain cold ammonia gas, which is heated to 900-1000 °C and fed into the reduction reactor for high-temperature reduction of the pre-reduced furnace charge. The high-temperature reduction time is 20-40 min. The heating method of the cold ammonia gas can be separate heating, heat exchange with the hot reduced iron in step 4) below, or a combined heating method of the above two.

[0022] 4) The temperature of the hot reduced iron generated by high-temperature reduction is 900 °C - 1000 °C. After being discharged from the reduction reactor, it exchanges heat with the cold ammonia gas described in step 3) for the first time to achieve the first cooling of the reduced iron, and the temperature of the reduced iron is reduced to 400-500 °C; then it exchanges heat with the lean CO gas described in step 1) as the cooling gas for the second time to achieve the second cooling and passivation of the reduced iron, and the temperature of the reduced iron is reduced to 50-100 °C; thus, cold reduced iron can be obtained.

[0023] Figure 1 As shown, the system for coupling rich CO gas and ammonia gas to prepare direct reduced iron includes a reduction reactor 5. In the internal reduction area of the reduction reactor 5, from top to bottom, there are a low-temperature reduction area I and a high-temperature reduction area II. The low-temperature reduction area I is connected to the rich CO gas pipeline, and the high-temperature reduction area II is connected to the ammonia gas pipeline. It also includes a blast furnace gas purification and upgrading device 1, a rich CO gas heater 2, an ammonia gas heater 3, and a gasification device 4. The inlet of the blast furnace gas purification and upgrading device 1 is connected to the blast furnace gas pipeline, and the rich CO gas outlet is connected to the low-temperature reduction area I of the reduction reactor 5 through the rich CO gas heater 2 and the rich CO gas pipeline. The inlet of the gasification device 4 is connected to the liquid ammonia pipeline, and the outlet is connected to the high-temperature reduction area II of the reduction reactor 5 through the ammonia gas heater 3 and the ammonia gas pipeline. The blast furnace gas purification and upgrading device 1 is equipped with dust removal, compression, hydrolysis, deoxidation, CO adsorption, and CO desorption units.

[0024] Figure 1 As shown, the system for coupling rich CO gas and ammonia gas to prepare direct reduced iron is also provided with a 1# heat exchange device 6 and a 2# heat exchange device 7. The 1# heat exchange device 6 and the 2# heat exchange device 7 are sequentially connected to the reduced iron outlet of the reduction reactor 5; the lean CO gas outlet of the blast furnace gas purification and upgrading device 1 is connected to the cooling gas inlet of the 2# heat exchange device 7; the outlet of the gasification device 4 is also connected to the cooling gas inlet of the 1# heat exchange device 6, and the cooling gas outlet of the 1# heat exchange device 6 is connected to the inlet of the ammonia gas heater 3.

[0025] Example 1: The method and system for coupling rich CO gas and ammonia gas to prepare direct reduced iron are specifically described as follows.

[0026] 1) Figure 1As shown in the figure, the blast furnace gas is purified by the blast furnace gas purification and purification device 1 to produce rich CO gas and lean CO gas. The purification and purification include treatment processes such as dust removal, compression, hydrolysis, deoxidation, CO adsorption, and CO desorption. The contents of CO, CO2, H2, and N2 in the blast furnace gas are 22.75 vol%, 21.25 vol%, 6.52 vol%, and 49.98 vol% respectively. The contents of CO, CO2, H2, and N2 in the obtained rich CO gas are 86% vol, 0.8 vol%, 0.4 vol%, and 12.03 vol% respectively.

[0027] 2) The rich CO gas is heated to 500 °C by the rich CO gas heater 2, and the heated rich CO gas is introduced into the low-temperature reduction zone I of the reduction reactor 5. The reduction time at this stage is 20 min. The hot rich CO gas contacts the iron-containing raw material for low-temperature reduction reaction and heat exchange to realize the pre-reduction of the iron-containing raw material and obtain the pre-reduced burden.

[0028] 3) At the beginning of the reaction, ammonia is heated to 900 °C by the ammonia heater 3; in subsequent production, ammonia is heated to 500 °C by heat exchange with the hot reduced iron in the following step 4), and then heated to 900 °C by the gas heater. The heated ammonia is introduced into the high-temperature reduction zone II of the reduction reactor 5, and the reduction time is 40 min. The hot ammonia contacts the pre-reduced burden for rapid reduction to produce hot reduced iron.

[0029] 4) The hot reduced iron is cooled to 500 °C after heat exchange with the reducing gas in the 1# heat exchange device 6 to complete the first cooling; the reduced iron after the first cooling is purged and cooled to 60 °C by the lean CO gas as the cooling gas in the 2# heat exchange device 7 to obtain cold reduced iron.

[0030] 5) The metallization rate of the cold reduced iron obtained in this example is 95%.

[0031] Example 2: The method and system for coupling rich CO gas and ammonia to prepare direct reduced iron are specifically described as follows.

[0032] 1) Figure 1 As shown in the figure, the blast furnace gas is purified by the blast furnace gas purification and purification device 1 to produce rich CO gas and lean CO gas. The purification and purification include treatment processes such as dust removal, compression, hydrolysis, deoxidation, CO adsorption, and CO desorption. The contents of CO, CO2, H2, and N2 in the blast furnace gas are 22.75 vol%, 21.25 vol%, 6.52 vol%, and 49.98 vol% respectively. The contents of CO, CO2, H2, and N2 in the obtained rich CO gas are 86% vol, 0.8 vol%, 0.4 vol%, and 12.03 vol% respectively.

[0033] 2) Heat the CO-rich gas to 700 °C with the CO-rich gas heater 2, and introduce the heated CO-rich gas into the low-temperature reduction zone I of the reduction reactor 5. The reduction time at this stage is 15 min. The hot CO-rich gas contacts the iron-containing raw material for low-temperature reduction reaction and heat exchange to realize the pre-reduction of the iron-containing raw material and obtain the pre-reduced burden.

[0034] 3) At the initial stage of the reaction, heat the ammonia gas to 950 °C with the ammonia gas heater 3; in subsequent production, the ammonia gas is heated by the following step 4) The hot reduced iron is heat-exchanged to 500 °C and then heated to 950 °C by the gas heater. Introduce the heated ammonia gas into the high-temperature reduction zone II of the reduction reactor 5. The reduction time is 30 min. The hot ammonia gas contacts the pre-reduced burden for rapid reduction to produce hot reduced iron.

[0035] 4) The hot reduced iron is cooled to 500 °C after heat exchange with the reducing gas in the No. 1 heat exchange device 6 to complete the first cooling; the reduced iron after the first cooling is purged and cooled to 60 °C by the CO-lean gas as the cooling gas in the No. 2 heat exchange device 7 to obtain the cold reduced iron.

[0036] 5) The metallization rate of the cold reduced iron obtained in this example is 95.8%.

[0037] Example 3: The method and system for coupling CO-rich gas and ammonia gas to prepare direct reduced iron are specifically described as follows.

[0038] 1) Figure 1 As shown in the figure, the blast furnace gas is purified and refined by the blast furnace gas purification and refining device 1 to produce CO-rich gas and CO-lean gas. The purification and refining include dust removal, compression, hydrolysis, deoxidation, CO adsorption, CO desorption and other treatment processes. The contents of CO, CO2, H2, and N2 in the blast furnace gas are: 22.75 vol%, 21.25 vol%, 6.52 vol%, and 49.98 vol% respectively. The contents of CO, CO2, H2, and N2 in the obtained CO-rich gas are: 86% vol, 0.8 vol%, 0.4 vol%, and 12.03 vol% respectively.

[0039] 2) Heat the CO-rich gas to 800 °C with the CO-rich gas heater 2, and introduce the heated CO-rich gas into the low-temperature reduction zone I of the reduction reactor 5. The reduction time at this stage is 10 min. The hot CO-rich gas contacts the iron-containing raw material for low-temperature reduction reaction and heat exchange to realize the pre-reduction of the iron-containing raw material and obtain the pre-reduced burden.

[0040] 3) At the initial stage of the reaction, ammonia is heated to 1000 °C by the ammonia heater 3; in subsequent production, ammonia is heated to 600 °C by heat exchange with the hot reduced iron in step 4) below, and then heated to 1000 °C by the gas heater. The heated ammonia is introduced into the high-temperature reduction zone II of the reduction reactor 5, and the reduction time is 20 min. The hot ammonia contacts the pre-reduced furnace charge for rapid reduction to produce hot reduced iron.

[0041] 4) The hot reduced iron is cooled to 500 °C for the first time after heat exchange with the reducing gas in the #1 heat exchange device 6; the reduced iron after the first cooling is purged and cooled to 60 °C by the lean CO gas as the cooling gas in the #2 heat exchange device 7 to obtain cold reduced iron.

[0042] 5) The metallization rate of the cold reduced iron obtained in this example is 98%.

Claims

1. A method for preparing direct reduced iron by coupling CO-rich gas and ammonia, characterized in that: The method comprises the following steps: the iron-containing raw material is pre-reduced in a reduction reactor by using rich CO gas, the temperature of the rich CO gas is 500-800°C; and then the iron-containing raw material is pre-reduced by using ammonia gas, the temperature of the ammonia gas is 900-1000°C.

2. The method for preparing direct reduced iron by coupling CO-rich gas and ammonia according to claim 1, characterized in that: The reduction time of the pre-reduction is 10 to 20 minutes, and the reduction time of the high-temperature reduction is 20 to 40 minutes.

3. The method for preparing direct reduced iron by coupling CO-rich gas and ammonia according to claim 1 or 2, characterized in that: The CO gas content in the CO-rich gas is greater than 80 vol%.

4. A system for preparing direct reduced iron by coupling CO-rich gas and ammonia, characterized in that: It comprises a reduction reactor (5); the reduction zone inside the reduction reactor (5) is composed of a low-temperature reduction zone (I) and a high-temperature reduction zone (II) from top to bottom; the low-temperature reduction zone (I) is connected to a CO-rich gas pipeline, and the high-temperature reduction zone (II) is connected to an ammonia gas pipeline.

5. The system for preparing direct reduced iron by coupling CO-rich gas and ammonia gas according to claim 4, characterized in that: It also comprises a blast furnace gas purification and refining device (1), a CO-rich gas heater (2), an ammonia heater (3) and a gasification device (4); the inlet of the blast furnace gas purification and refining device (1) is connected to a blast furnace gas pipeline, and the CO-rich gas outlet is connected to a low-temperature reduction zone (I) of a reduction reactor (5) via a CO-rich gas pipeline through the CO-rich gas heater (2); the inlet of the gasification device (4) is connected to a liquid ammonia pipeline, and the outlet is connected to a high-temperature reduction zone (II) of a reduction reactor (5) via an ammonia gas heater (3) and an ammonia gas pipeline.

6. A system for preparing direct reduced iron by coupling CO-rich gas and ammonia according to claim 4 or 5, characterized in that: A 1# heat exchange device (6) and a 2# heat exchange device (7) are also provided; the 1# heat exchange device (6) and the 2# heat exchange device (7) are sequentially connected to the reduced iron outlet of the reduction reactor (5); the lean CO gas outlet of the blast furnace gas purification and refining device (1) is connected to the cooling gas inlet of the 2# heat exchange device (7); the outlet of the gasification device (4) is also connected to the cooling gas inlet of the 1# heat exchange device (6), and the cooling gas outlet of the 1# heat exchange device (6) is connected to the inlet of the ammonia heater (3).

Images