Direct reduction iron passivation treatment method and system

Abstract

The invention discloses a direct reduction iron passivation treatment method and system, and the method comprises the following steps: carrying out hydrogen group reduction on pellets in a gas-based shaft furnace to obtain direct reduction iron with Fe3C content of 2-4%; and spraying an organic passivating agent on the surface of the direct reduced iron to obtain the passivated direct reduced iron. According to the method, the in-furnace passivation is firstly carried out to enable iron and carbon to react to generate Fe3C, the Fe3C content of the direct reduced iron is reasonably controlled, and then the passivating agent is sprayed for passivation, so that the direct reduced iron can be effectively prevented from being re-oxidized, and a safe and effective passivation result is achieved; the obtained direct reduction iron is stable in component and convenient to store for a long time, reoxidation can be remarkably reduced, and the longest anti-rust period can reach 1-3 months when the direct reduction iron is stored at the room temperature.

Description

Technical Field

[0001] The invention relates to the technical field of direct reduction, in particular to a direct reduced iron passivation treatment method and system. Background Art

[0002] Direct reduction technology has the advantages of low carbon emissions, clean reduction products, and efficient reduction reactions. Vertical furnace production of direct reduced iron technology is widely used. The metallization rate of direct reduction produced by gas-based vertical furnaces is about 94%. When exposed to the atmosphere, it is very easy to be re-oxidized, so the direct reduced iron needs to be passivated.

[0003] Conventional passivation methods are: 1. hot-pressed iron blocks, 2. silo passivation. The first method is to use hot-pressed iron blocks to increase the density of direct reduced iron, reduce porosity, and reduce specific surface area, but hot-pressed iron blocks need to be reprocessed, which increases costs, and hot-pressed iron block passivation is often used for transportation to long-distance factories. The second method is to place the direct reduced iron in an environment with an oxygen atmosphere of 3% to 5% to oxidize its surface to form an oxide film, and then store it in a silo with a nitrogen atmosphere. This requires the construction of a large silo and the maintenance of a nitrogen atmosphere in the silo. Moreover, when downstream users cannot consume the direct reduced iron in time, the direct reduction plant is forced to shut down. Therefore, the direct reduced iron plant needs an economical and convenient method to achieve direct reduced iron passivation; after passivation, the direct reduced iron can be stored in a silo or directly stacked. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a fast and effective direct reduced iron passivation treatment method; the present invention also provides a direct reduced iron passivation treatment system.

[0005] In order to solve the above technical problems, the technical solution adopted by the method of the present invention includes the following steps: the pellets are subjected to hydrogen-based reduction in a gas-based vertical furnace to obtain direct reduced iron with a Fe3C content of 2% to 4%; an organic passivating agent is sprayed on the surface of the direct reduced iron to obtain the direct reduced iron after passivation treatment.

[0006] Furthermore, the hydrogen radical reduction temperature is 1020°C to 1050°C.

[0007] Furthermore, the direct reduced iron is sprayed with an organic passivating agent at 20-50°C.

[0008] Furthermore, the process gas for hydrogen-based reduction includes coke oven gas.

[0009] Furthermore, the direct reduced iron is sprayed with an organic passivating agent during the conveying process of the discharge belt.

[0010] In order to solve the above technical problems, the technical solution adopted by the system of the present invention is: it includes a gas-based vertical furnace, a discharge tank, a discharge belt and a passivation device; the discharge port of the gas-based vertical furnace is connected to the discharge tank, the discharge tank is located above the discharge belt and its discharge port is directly opposite to the discharge belt; the passivation device is used to spray an organic passivating agent onto the surface of the direct reduced iron transported by the discharge belt.

[0011] Furthermore, the passivation device includes a passivator storage tank; the passivator storage tank is located above the discharge belt and at the rear end of the discharge tank; the bottom of the passivator storage tank is connected to a nozzle, the nozzle is facing the discharge belt, and a passivation valve is provided on the nozzle.

[0012] Furthermore, a material flow sensor is provided above the discharge belt between the discharge tank and the passivating agent storage tank; the material flow sensor senses the direct reduced iron conveyed by the discharge belt and controls the passivating valve to open the nozzle.

[0013] Furthermore, an organic passivating agent collecting tank is provided at the lower part of the discharge belt.

[0014] Furthermore, a belt blowing device is provided at the lower part of the discharge belt.

[0015] The beneficial effects of the above technical solution are as follows: the present invention first performs in-furnace passivation to react iron with carbon to generate Fe3C, and then sprays a passivating agent for passivation by reasonably controlling the Fe3C content of the direct reduced iron, thereby effectively preventing the direct reduced iron from being reoxidized, thereby achieving a safe and effective passivation result; the direct reduced iron obtained by the present invention has a stable component and is convenient for long-term storage, and can significantly reduce reoxidation. When stored at room temperature, the longest anti-rust period can reach 1 to 3 months.

[0016] The characteristics and outstanding advantages of the method and system of the present invention are as follows: 1. Low investment cost. The required equipment investment cost is low, and no site investment is required. Hot pressed iron block passivation and silo passivation require high investment costs; 2. Low operating cost. Passivation of hot pressed iron requires a lot of water, electricity, etc. Silo passivation requires consumption of oxygen and nitrogen to maintain the gas composition in the silo; 3. Direct reduced iron sprayed with organic passivating agent can be piled up for storage. The storage capacity of direct reduced iron stored in the silo is limited. When the electric furnace fails or other situations occur, the direct reduced iron cannot be consumed in time. When the silo is full, the direct reduction plant will be forced to shut down; 4. Direct reduced iron has a high carbon content and is flammable. Ordinary dust removal processes cannot safely achieve dust removal effects. Wet dust removal is required. When spraying organic passivating agents, dry dust removal can be used, and dust removal ash can be recycled, reducing the sludge treatment cost caused by wet dust removal; 5. Silo passivation requires oxidation of the direct reduced iron to form an oxide film. This will reduce the metallization rate of the direct reduced iron. The method of spraying organic passivating agent can maintain the metallization rate of the direct reduced iron after reduction; 6. This method is different from the traditional method of spraying phosphating agent and other passivation agents. It uses organic passivation agents. When the direct reduced iron enters the electric furnace, the organic passivation agent evaporates at high temperature and is flammable. It will not cause molten steel pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] Figure 1 It is a structural schematic diagram of the system of the present invention; Figure 2 It is a structural schematic diagram of the gas-based vertical furnace of the present invention.

[0019] In the figure: No. 1 discharge tank 1; passivator replenishing valve 2; thermometer 3; pressure gauge 4; stamping valve 5; passivator storage tank 6; passivator level gauge 7; main passivation valve 8; spare passivation valve 9; material flow sensor 10; discharge belt 11; heater 12; No. 2 discharge tank 13; organic passivator collecting tank 14; nitrogen tank 15; belt purge nitrogen valve 16; nitrogen tank replenishing gas regulating valve 17; gas-based vertical furnace 18; preheating zone thermometer 19; reduction zone upper thermometer 20; reduction zone middle thermometer 21; reduction zone lower temperature 22; bottom gas outlet 23; supplementary coke oven gas inlet 24; process gas inlet 25. DETAILED DESCRIPTION

[0020] The direct reduced iron passivation treatment method comprises the following steps: 1) the pellets are subjected to hydrogen-based reduction in a gas-based vertical furnace, the pellets undergo carburization reaction in the reduction zone (high temperature zone) of the vertical furnace to generate Fe3C, and carbon deposition reaction occurs in the low temperature zone, thereby reducing the content of Fe3C in the direct reduced iron; direct reduced iron with a Fe3C content of 2% to 4wt% is obtained; the process gas temperature used in the hydrogen-based reduction is 1020°C to 1050°C, thereby controlling the hydrogen-based reduction temperature to be 1020°C to 1050°C; gas-based vertical furnace production requires consumption of coke oven gas, and the process gas needs to be supplemented with coke oven gas, and the gas temperature of the supplemented coke oven gas is 30 to 50°C.

[0021] 2) After the direct reduced iron is discharged, the direct reduced iron with a temperature of 20 to 50° C. is sprayed with an organic passivating agent on its surface during the conveying process of the discharge belt. The temperature of the passivating agent is 20 to 40° C., and the direct reduced iron after passivation treatment can be obtained.

[0022] Figure 1 , Figure 2As shown, the direct reduction iron passivation treatment system comprises a gas-based vertical furnace 18, a discharge tank, a discharge belt 11 and a passivation device. The gas-based vertical furnace is divided into a preheating zone, a reduction zone and a discharge zone from top to bottom; the preheating zone is provided with a preheating zone thermometer 19, the reduction zone is provided with an upper reduction zone thermometer 20, a middle reduction zone thermometer 21 and a lower reduction zone thermometer 22; the reduction zone is provided with a process gas inlet 25 and a bottom gas outlet 23, and the discharge zone is provided with a supplementary coke oven gas inlet 24.

[0023] Figure 1 , Figure 2 As shown, in the direct reduced iron passivation treatment system, the discharge port of the gas-based vertical furnace is connected to the discharge tank, the discharge tank is located above the discharge belt 11 and its discharge port is directly opposite to the discharge belt 11; the discharge tank is preferably provided with two, namely, No. 1 discharge tank 1 and No. 2 discharge tank 13, which are used alternately; the passivation device is used to spray an organic passivating agent onto the surface of the direct reduced iron transported by the discharge belt 11.

[0024] Figure 1 , Figure 2 As shown, the direct reduced iron passivation treatment system, the passivation device includes a passivation agent storage tank 6; the passivation agent storage tank 6 is located above the discharge belt 11 and at the rear end of the discharge tank; the bottom of the passivation agent storage tank 6 is connected to a nozzle, the nozzle is directly facing the discharge belt 11, and a passivation valve is arranged on the nozzle; the nozzle is preferably two, one for backup and one for use, and the passivation valves on the two nozzles are respectively the main passivation valve 8 and the backup passivation valve 9. The passivation agent storage tank 6 is provided with a thermometer 3, a pressure gauge 4, a passivation agent level gauge 7 and a heater 12; the passivation agent storage tank 6 is also connected to the passivation agent pipeline through a pipeline and a passivation agent replenishing valve 2, and is also connected to a high-pressure gas pipeline through a pipeline and a stamping valve 5. The passivation agent replenishing valve 2, when the passivation agent liquid level is low, opens the passivation agent replenishing valve to replenish the passivation agent to the passivation tank 6. The thermometer 3 monitors the passivation agent temperature and controls the heater 12 to heat. The pressure gauge 4 monitors the pressure in the passivation tank 6. The punch valve 5 is used to charge the passivation tank 6 when the pressure in the passivation tank is low. The passivation agent level gauge 7 is used to monitor the passivation agent level in the passivation tank 6 and control the opening and closing of the passivation agent replenishing valve 2. The main passivation valve 8 is used to spray the passivation agent onto the direct reduced iron; the standby passivation valve 9 is used to spray the passivation agent when the main passivation valve 8 fails. The heater 12 is preferably an electric heater. When the temperature of the passivation agent in the passivation tank 6 is low, the heater is turned on to maintain the normal working temperature of the organic passivation agent.

[0025] Figure 1 , Figure 2 As shown, in the direct reduced iron passivation treatment system, a material flow sensor 10 is provided above the discharge belt 11 between the discharge tank and the passivating agent storage tank 6; the material flow sensor 10 senses the direct reduced iron transported by the discharge belt 11 and controls the passivation valve to open the nozzle.

[0026] Figure 1 , Figure 2 As shown, in the direct reduced iron passivation treatment system, an organic passivating agent collecting tank 14 is provided at the lower part of the discharge belt 11, and a belt purge device is provided at the lower part of the discharge belt 11. The belt purge device includes a purge nozzle and a nitrogen tank 15; the purge nozzle is connected to the nitrogen tank 15, and is provided with a belt purge nitrogen valve 16; the nitrogen tank 15 is connected to the nitrogen pipeline through a pipeline and a nitrogen tank supplementary gas regulating valve 17. The purge nozzle purges the discharge belt 11 upward. The organic passivating agent is sticky. When the passivating agent attached to the discharge belt 11 is agglomerated, the passivating agent is blown off by opening the belt purge valve 16; the dropped passivating agent is collected in the organic passivating agent collecting tank 14.

[0027] Figure 1 , Figure 2 As shown, the use process of this direct reduced iron passivation treatment system is: 1) The pellets enter the gas-based vertical furnace 18 and pass through the preheating zone, where they are preheated by heat exchange with process exhaust gas. The discharge speed is controlled according to the temperature of the preheating zone thermometer 19.

[0028] According to the temperature feedback from the reduction zone upper thermometer 20 and the reduction zone middle thermometer 21, the process gas flow rate of the process gas inlet 25 is controlled. The process gas temperature is controlled at 1020°C to 1050°C. The high-temperature process gas can increase the temperature of the reduction zone.

[0029] According to the temperature feedback from the lower temperature 22 of the reduction zone, the flow rate of the bottom gas outlet 23 is controlled when the supplementary coke oven gas enters the system. The gas temperature of the supplementary coke oven gas is 30-50°C, part of which is discharged from the vertical furnace through the bottom gas outlet 23 and enters the circulation system. Part of it directly enters the reduction zone of the vertical furnace to reduce the temperature of the reduction zone.

[0030] Gas-based vertical furnace production requires consumption of coke oven gas; the system is continuously supplemented with coke oven gas through the supplementary coke oven gas inlet 24 .

[0031] 2) After being cooled by the cooler, the direct reduced iron is discharged into the No. 1 discharge tank 1 or the No. 2 discharge tank 13. When the No. 1 discharge tank 1 is full, the direct reduced iron is charged from the cooler to the No. 2 discharge tank 13; and the No. 1 discharge tank 1 starts to discharge onto the discharge belt 11. When the No. 1 discharge tank 1 is discharged, wait until the No. 2 discharge tank 13 is full before charging. When the No. 2 discharge tank 13 is full, the No. 1 discharge tank 1 is charged from the cooler. And so on.

[0032] When the passivating agent liquid level is low, the passivating agent replenishing valve 2 is opened to replenish the passivating agent to the passivating agent storage tank 6. The thermometer 3 is used to monitor the passivating agent temperature. The pressure gauge 4 monitors the pressure in the passivating agent storage tank 6. When the pressure in the passivating agent storage tank 6 is low, the punch valve 5 charges the passivating agent storage tank 6. The passivating agent liquid level gauge 7 is used to monitor the passivating agent liquid level in the passivating agent storage tank 6. The main passivating valve 8 is used to spray the passivating agent onto the direct reduced iron; the spare passivating valve 9 is used as a spare, and when the main passivating valve 8 fails, the spare passivating valve 9 is used to spray the passivating agent. When the No. 1 discharge tank 1 or the No. 2 discharge tank 13 is opened to discharge, the material flow sensor 10 monitors the direct reduced iron material flow on the discharge belt 11. The discharge belt 11 is used to transport direct reduced iron.

[0033] When the thermometer 3 detects that the temperature of the passivator in the passivator storage tank 6 is low, the heater 12 is turned on to maintain the normal working temperature of the organic passivator, and the passivator temperature is controlled at 20-40°C. The organic passivator is sticky. When the passivator attached to the discharge belt 11 is agglomerated, the belt purge nitrogen valve 16 is opened to purge regularly to blow the passivator off. The fallen passivator is collected in the organic passivator collection tank 14. The purge intensity is controlled by controlling the pressure of the nitrogen tank 15 and the opening of the belt purge nitrogen valve 16. When the pressure of the nitrogen tank 15 is low, the pressure of the nitrogen tank 15 is controlled to be maintained at 10-20Kpa by opening the nitrogen tank supplementary gas regulating valve 17.

[0034] The specific process is: 1. The No. 1 discharge tank 1 and the No. 2 discharge tank 13 discharge the direct reduced iron onto the discharge belt 11 by means of loading and discharging.

[0035] 2. After the material flow sensor 10 senses the presence of direct reduced iron on the discharge belt 11, it feeds back a material flow signal.

[0036] 3. After receiving the material flow feedback signal, the system opens the main passivation valve 8 to spray the passivating agent. When the system material flow feedback information shows that there is no material flow, close the main passivation valve 8. If the valve feedback signal is normal within 1 second after the main passivation valve 8 is opened, continue to use the main passivation valve 8 to spray until the material flow feedback signal disappears. If the opening feedback of the main passivation valve 8 is abnormal within 1 second, open the spare passivation valve 9 and close the main passivation valve 8; and alarm to prompt that the main passivation valve 8 is abnormal; when using the spare passivation valve 9, when the system material flow feedback information shows that there is no material flow, close the spare passivation valve 9.

[0037] 4. The liquid level of the passivator in the passivator storage tank 6 is displayed by the passivator liquid level gauge 7.

[0038] 5. When the passivator liquid level is lower than 30%, open the passivator replenishing valve 2, replenish the passivator liquid level to 90%, and close the passivator replenishing valve 2.

[0039] 6. The passivation agent storage tank 6 adopts a closed pressurized container, and the pressure is monitored by a pressure gauge 4; the pressure in the tank is maintained at 10Kpa±2Kpa; when the pressure in the tank is lower than 8Kpa, the stamping valve 5 is opened; when the pressure increases to 12Kpa, the stamping valve 5 is closed.

[0040] 7. Monitor the temperature of the passivating agent by thermometer 3 and control the temperature of the passivating agent at 20-40°C.

[0041] 8. When the temperature of the passivating agent is lower than 15°C, start the heater 12. When the temperature of the passivating agent is higher than 35°C, turn off the heater 12.

[0042] 9. The passivator nozzle adopts a spray foam device to make the passivator spray surface larger and adhere more evenly to the direct reduced iron.

[0043] 10. The passivator will adhere to a part of the discharge belt 11. When the discharge belt 11 turns to the lower side, part of the passivator will fall off and be collected. Check the passivator collection tank 14 regularly and recycle the passivator.

[0044] 11. If the passivating agent adheres to the discharge belt 11, open the belt purge nitrogen valve 16 and control the purge pressure to 8-15Kpa.

[0045] 12. The dropped passivating agent is collected in the passivating agent collecting tank 14 and recycled.

[0046] 13. Control the pressure of the nitrogen tank 15 and maintain it at 10-20Kpa. When the pressure of the nitrogen tank 15 is lower than 8Kpa, open the nitrogen tank supplementary gas regulating valve 17 to supplement nitrogen from the outside.

Claims

1. A direct reduced iron passivation treatment method, characterized in that: The method comprises the following steps: performing hydrogen-based reduction on pellets in a gas-based vertical furnace to obtain direct reduced iron with a Fe3C content of 2% to 4%; spraying an organic passivating agent on the surface of the direct reduced iron to obtain the direct reduced iron after passivation treatment.

2. A direct reduced iron passivation treatment method according to claim 1, characterized in that: The hydrogen radical reduction temperature is 1020°C to 1050°C.

3. A direct reduced iron passivation treatment method according to claim 1, characterized in that: The direct reduced iron is sprayed with an organic passivating agent at 20-50°C.

4. A direct reduced iron passivation treatment method according to claim 1, characterized in that: The process gas for the hydrogen-based reduction includes coke oven gas.

5. A direct reduced iron passivation treatment method according to any one of claims 1 to 4, characterized in that: The direct reduced iron is sprayed with an organic passivating agent during the conveying process of the discharge belt.

6. A direct reduced iron passivation treatment system, characterized in that: It comprises a gas-based vertical furnace, a discharge tank, a discharge belt (11) and a passivation device; the discharge port of the gas-based vertical furnace is connected to the discharge tank, the discharge tank is located above the discharge belt (11) and its discharge port faces the discharge belt (11); the passivation device is used to spray an organic passivating agent onto the surface of the direct reduced iron transported by the discharge belt (11).

7. A direct reduced iron passivation treatment system according to claim 6, characterized in that: The passivation device comprises a passivation agent storage tank (6); the passivation agent storage tank (6) is located above the discharge belt (11) and at the rear end of the discharge tank; the bottom of the passivation agent storage tank (6) is connected to a nozzle, the nozzle is directly facing the discharge belt (11), and a passivation valve is provided on the nozzle.

8. A direct reduced iron passivation treatment system according to claim 7, characterized in that: A material flow sensor (10) is provided above the discharge belt (11) between the discharge tank and the passivating agent storage tank (6); the material flow sensor (10) senses the direct reduced iron transported by the discharge belt (11) and controls the passivating valve to open the nozzle.

9. A direct reduced iron passivation treatment system according to claim 6, characterized in that: An organic passivating agent collecting tank (14) is provided at the lower part of the discharge belt (11).

10. A direct reduced iron passivation treatment system according to any one of claims 6 to 9, characterized in that: A belt blowing device is provided at the lower part of the discharge belt (11).

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