Dry coating system and process for raw materials of gas-based shaft furnace

Abstract

The gas-based shaft furnace raw material dry coating system comprises a cement storage bin, a weightlessness feeder, a dry powder feeder, a humidity control spray head, a dry coating spray head, a material turning device, a belt conveying device and a spiral chute, and the belt conveying device is provided with a conveying belt; a bottom discharging port of the cement storage bin is communicated with a feeding port of the weightlessness feeder, a discharging port of the weightlessness feeder is communicated with a feeding port of the dry powder feeder, and a discharging port of the dry powder feeder is located above the conveying belt and right faces the conveying belt. The humidity control spray head and the dry coating spray head are both communicated with a water supply pipeline; the humidity control nozzle is located above the front end of the conveying belt, and the water spraying direction corresponds to the conveying belt; the dry coating nozzle is located above the conveying belt, and the water spraying direction corresponds to the conveying belt; the turning device is arranged above the conveying belt and used for turning the pellets on the conveying belt. According to the system and the process, the surface of the iron-containing raw material can be uniformly coated with a coating which is inactive under the reduction condition.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a system and process for dry coating raw materials of a gas-based shaft furnace. Background Art

[0002] During the direct reduction process of the gas-based shaft furnace, the iron-containing raw materials will stick together in the initial stage of metallization. The large pieces that stick together will block various valve bodies and discharge ports, seriously affecting the production rhythm of the shaft furnace. In the existing anti-sticking process, wet coating is used, which is to mix an inactive coating material with water to form a suspension and evenly coat it on the iron-containing raw materials to prevent the iron-containing raw materials from sticking and blocking various valve bodies and discharge ports, ensuring the smooth operation of the shaft furnace system.

[0003] The wet coating method has the following disadvantages: 1. It takes a long time to prepare cement slurry before coating (roughly about 90 minutes); 2. The mixing tank of the core equipment is prone to malfunction; 3. The ash conveying pipe above the mixing tank is easily blocked due to moisture from the water vapor below; 4. The overflow valves on both sides of the mixing tank are prone to hardening of cement slurry due to long-term coating and are difficult to handle; 5. When switching to the backup line for coating, the cement slurry of the current line needs to be emptied and the mixing tank needs to be cleaned, resulting in material waste and increased workload. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a gas-based shaft furnace raw material dry coating system and a gas-based shaft furnace raw material dry coating process.

[0005] In order to solve the above technical problems, the technical solution adopted by the system of the present invention is: it includes a cement storage bin, a loss-in-weight feeder, a dry powder feeder, a humidity control nozzle, a dry coating nozzle, a turner, a belt conveyor and a spiral chute, and the belt conveyor is provided with a conveyor belt; the bottom discharge port of the cement storage bin is connected to the feed port of the loss-in-weight feeder, the discharge port of the loss-in-weight feeder is connected to the feed port of the dry powder feeder, and the discharge port of the dry powder feeder is located above the conveyor belt and directly faces the conveyor belt; the humidity control nozzle and the dry coating nozzle are both connected to the water supply pipeline; the humidity control nozzle is located above the front end of the conveyor belt, and the water spraying direction corresponds to the conveyor belt; the dry coating nozzle is located above the conveyor belt, and the water spraying direction corresponds to the conveyor belt; the turner is arranged above the conveyor belt for turning over the pellets on the conveyor belt; the spiral chute is located below the conveyor belt, and the feed port directly faces the rear end of the conveyor belt.

[0006] Furthermore, two sets of the loss-in-weight feeder, dry powder feeder and dry coating nozzle are provided respectively; the bottom discharge port of the cement storage bin is connected to the feed ports of the two loss-in-weight feeders through a three-way distributor.

[0007] Furthermore, a humidity sensor is provided at the front end of the humidity control nozzle, and the humidity sensor detects the moisture content of the pellets on the conveyor belt and controls the water replenishment amount of the humidity control nozzle.

[0008] Furthermore, the humidity control nozzles and humidity sensors are provided in two sets correspondingly.

[0009] Furthermore, the front end and the rear end of the dry powder feeder are both provided with dry coating nozzles.

[0010] In order to solve the above technical problems, the process of the present invention adopts the above dry coating system, and the technical solution adopted includes the following steps: 1) the pellets to be coated are conveyed from the input end to the output end on the conveyor belt of the belt conveyor device; 2) The water supply pipeline supplies water to the humidity control nozzle, and the humidity control nozzle sprays water to the pellets passing thereunder to replenish the water to the pellets; 3) The dry powder cement in the cement storage bin enters the loss-in-weight feeder, and then the loss-in-weight feeder controls the feeding speed to enter the dry powder feeder, and finally the dry powder feeder covers the pellets passing below the dry powder feeder with the dry powder cement; 4) When the pellets on the conveyor belt pass through the material turner, the material turner turns the pellets; 5) After being transported to the output end by the conveyor belt, the pellets fall into the spiral chute, where they roll and adhere to each other.

[0011] Furthermore, in the step 2), the humidity sensor detects the moisture content of the pellets on the conveyor belt and controls the water replenishment amount of the humidity control nozzle.

[0012] The beneficial effects of adopting the above technical scheme are: the present invention adopts dry coating, which has the following characteristics: the preparation time before coating is short; water and cement are separated into dry and wet parts, and the ash conveying pipe is not easily blocked by moisture; in case of emergency, when it is necessary to switch to the backup line, it can be switched directly without affecting the coating and causing no waste of materials; the dry coating uses less equipment, which effectively reduces the links where problems may occur.

[0013] The present invention can evenly coat a layer of coating which is inactive under reducing conditions on the surface of the iron-containing raw material, and the coating can reduce the crystallization rate in the initial stage of pellet metallization, prevent the growth of fibrous iron precipitates, and prevent the pellets from sticking to each other during the reduction process to block the valve body and the discharge port, thereby ensuring the smooth operation of the vertical furnace system. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0015] Figure 1 It is a schematic diagram of the structure of the system of the present invention.

[0016] The numbers in the figure are: 1. dust collector; 2. cement storage bin; 3. loosener; 4. rotary discharge valve; 5. three-way distributor; 6. first loss-in-weight feeder; 7. second loss-in-weight feeder; 8. first dry powder feeder; 9. second dry powder feeder; 10. first humidity sensor; 11. second humidity sensor; 12. first humidity control nozzle; 13. second humidity control nozzle; 14. first dry coating nozzle; 15. second dry coating nozzle; 16. third dry coating nozzle; 17. fourth dry coating nozzle; 18. first turner; 19. second turner; 20. belt conveyor; 21. spiral chute; 22. sludge box; 23. third turner. DETAILED DESCRIPTION

[0017] Figure 1 As shown, the present gas-based vertical furnace raw material dry coating system includes a cement storage bin 2, a weightless feeder, a dry powder feeder, a humidity control nozzle, a dry coating nozzle, a material turner, a belt conveyor 20 and a spiral chute 21. The belt conveyor 20 is provided with a conveying belt, and the input end of the belt conveyor 20 is the front end and the output end is the rear end. The cement storage bin 2 is a silo with a cylindrical upper part and a conical lower part. Its top is closed and is provided with a pneumatic powder collection pipeline and an exhaust explosion-proof facility. The cement storage bin 2 is used to store cement purchased from the cement plant. The dry powder cement transported by the cement tank truck is pneumatically conveyed into the cement storage bin 2 for storage. A dust collector 1 is provided on the top of the cement storage bin 2 to intercept the cement powder scattered during pneumatic ash conveying and blow it back into the cement storage bin 2 to ensure that there is no dust overflow when the cement storage bin 2 is filled and maintain a good on-site environment. The bottom of the cement storage bin 2 is provided with a weighing sensor and the top is provided with a radar level sensor for monitoring the material quantity and level so that cement can be replenished in time according to the usage. A loosener 3 is provided at the lower cone bucket position of the cement storage bin 2, which is used to start when the weightless feeder is replenished to assist in unloading. The discharge port at the bottom of the cement storage bin 2 is provided with a rotary discharge valve 4, which can evenly transfer the dry powder cement in the cement storage bin 2 to the three-way distributor 5 of the cement storage bin below.

[0018] Figure 1As shown, the bottom discharge port of the cement storage bin 2 of the gas-based vertical furnace raw material dry coating system is connected to the three-way distributor 5. Two loss-in-weight feeders are provided, one for backup and one for use, namely the first loss-in-weight feeder 6 and the second loss-in-weight feeder 7; the loss-in-weight feeder is located below the three-way distributor 5, and the two discharge ports of the three-way distributor 5 are connected to the feed ports of the first loss-in-weight feeder 6 and the second loss-in-weight feeder 7 respectively; in this way, the three-way distributor 5 can gradually transfer cement to the two parallel loss-in-weight feeders. There are two dry powder feeders, one for backup and the other for use, namely the first dry powder feeder 8 and the second dry powder feeder 9; the first loss-in-weight feeder 6 is located below the first loss-in-weight feeder 6, and the discharge port of the first loss-in-weight feeder 6 is connected to the feed port of the first loss-in-weight feeder 6; the second dry powder feeder 9 is located below the second loss-in-weight feeder 7, and the discharge port of the second loss-in-weight feeder 7 is connected to the feed port of the second dry powder feeder 9; the loss-in-weight feeder uses a speed sensorless weightless control inverter to adjust the feeder speed, and the speed adjustment is linked to the raw material feeding set value. By adjusting the conveying amount, the distribution speed and weighing can be adjusted according to the pellet incoming material situation, and the dry powder cement can be evenly and quantitatively delivered to the dry powder feeder. The discharge port of the dry powder feeder is located above the conveyor belt and directly opposite to the conveyor belt, and the second dry powder feeder 9 is located at the front end of the first dry powder feeder 8; a vibration motor is arranged outside the dry powder feeder, and the dry powder feeder receives the dry powder cement transported by the loss-in-weight feeder above, and can evenly coat the cement onto the raw material pellets on the coating belt.

[0019] Figure 1 As shown, the humidity control nozzle and dry coating nozzle of the gas-based vertical furnace raw material dry coating system are connected to the water supply pipeline. The dry coating nozzle replenishes water for the raw material pellets, and is set according to the water-cement ratio of dry powder cement and water, so that the raw material pellets meet the water-cement ratio requirements for coating. The dry coating nozzle is located above the conveyor belt and is set at the front and rear ends of the dry powder feeder, and the water spraying direction corresponds to the conveyor belt; the front end of the first dry powder feeder 8 is provided with a third dry coating nozzle 16, and the rear end is provided with a fourth dry coating nozzle 17, and the front end of the second dry powder feeder 9 is provided with a first dry coating nozzle 14; the rear end is provided with a second dry coating nozzle 15.

[0020] Figure 1As shown, the humidity control nozzle of the gas-based vertical furnace raw material dry coating system replenishes water for the raw material pellets so that the humidity of the raw material pellets reaches the required pellet humidity; the humidity control nozzle is located above the front end of the conveyor belt, and the water spraying direction corresponds to the conveyor belt; a humidity sensor is provided at the front end of the humidity control nozzle, and the humidity sensor detects the moisture content of the pellets on the conveyor belt and controls the water replenishment amount of the humidity control nozzle. The humidity control nozzles and humidity sensors are provided in two sets correspondingly, namely, a first humidity control nozzle 12 and a first humidity sensor 10 at its front end, and a second humidity control nozzle 13 and a second humidity sensor 11 at its front end; the first humidity sensor 10 is used to detect the humidity of the incoming material, and according to the humidity detection of the incoming material, the first humidity control nozzle 12 replenishes water for the incoming material, and the second humidity sensor 11 is used to detect the humidity of the material after the first humidity control nozzle 12 replenishes water, and according to the humidity detection of the incoming material, the second humidity control nozzle 13 and the dry coating nozzle are set to replenish water for the incoming material according to the ash-to-ball ratio of the pellet ore and the dry powder cement, and the water-to-cement ratio of the dry powder cement and water; the ash-to-ball ratio is generally 3kg to 1t, and the water-to-cement ratio is generally 3L to 1kg.

[0021] Figure 1 As shown, the material turner of the gas-based vertical furnace raw material dry coating system is arranged above the conveyor belt, and is used to turn over the pellets on the conveyor belt. It is best to use a plow-type material turner. It is best to set a material turner below the material turner dry powder feeder, and set a material turner at the rear end of the conveyor belt; as shown in the figure, a second material turner 19 is set below the first dry powder feeder 8, a first material turner 18 is set below the second dry powder feeder 9, and a third material turner 23 is set at the rear end of the conveyor belt. The material turner turns over the pellets on the conveyor belt, so that the pellets are fully in contact with cement.

[0022] Figure 1 As shown, the spiral chute 21 of the gas-based vertical furnace raw material dry coating system is located below the conveyor belt, and the feed port is directly opposite to the output end of the belt conveyor 20. A wear-resistant lining is installed inside the spiral chute 21, which can bond the coated raw material pellets and the residual cement slurry to each other again, achieving a better coating effect and avoiding the waste of cement slurry.

[0023] Figure 1 As shown, a sludge box 22 is provided below the belt conveyor 20 of the gas-based vertical furnace raw material dry coating system. The sludge box 22 is used to collect residual waste materials on the coating belt working surface. Example

[0024] Compared with the description of the annual production capacity of 500,000 to 600,000 tons of DRI, the iron-containing raw material is high-grade pellets, cement is used as the coating material, and ordinary Portland cement with a strength of 32.5R is used for cement. This dry coating system adopts the above structure. The effective volume of the cement storage bin 2 used is 65m³, which can store about 100 tons of cement. It is estimated that 2,200 tons of high-grade pellets will be coated daily. Coating one ton of pellets requires 3KG of cement, which can meet the demand for fifteen days. The conveying capacity of the adopted loss-in-weight feeder can be adjusted between 0 and 1,800 kg / h. The belt conveyor device has a conveying belt width of 650mm, a horizontal machine length of 20m, a lifting height of 0.4m, an inclination of 3°, and a maximum transport capacity of 200t / h; its transmission motor adopts stepless frequency conversion speed regulation, which can be adjusted between 0 and 1.5m / s to control the coating time. The number of plow blades of the adopted plow-type turner is 12, made of polyurethane, with a spacing of 50mm and a height of 200mm. The sludge tank uses a cubic box with a volume of 1m³.

[0025] The gas-based vertical furnace raw material dry coating process adopts the following process: The vertical furnace is in continuous production, and the coating system also needs to work continuously and spray continuously to provide the vertical furnace with raw material pellets with coating. Therefore, the two branches can be used separately and can be operated alternately, and they can serve as backup for each other; when one branch is used separately, the other branch can be used for offline maintenance. By adjusting the three-way distributor passage, a single spray branch can be operated or two branches can work together.

[0026] Before coating: 1) The cement tank truck pumps cement into the cement storage silo 2 through pneumatic conveying for storage, and keeps the silo full.

[0027] 2) When adding or replenishing cement, first start the dust collector 1 on the top of the silo. After the cement tanker arrives, connect the pneumatic conveying pipeline and use the airflow provided by the pneumatic conveying blower to convey the cement to the cement storage silo 2. The selected blower has an airflow speed of 8-12m / s, an average ash conveying speed of 3-5m / s, and can convey 3 tons of cement per minute. The dust collector 1 intercepts the cement powder scattered during pneumatic ash conveying, so that there is no dust overflow when the cement storage silo 2 is filled, maintaining a good on-site environment. After the filling is completed, the dust collector 1 is backblown and shut down.

[0028] 3) After the cement storage silo 2 is filled for the first time, the weighing sensor and radar level sensor can be used to detect the cement storage weight and level. If the level drops to a low level, cement needs to be replenished in time.

[0029] When coating: The following description will be made by taking the left path connecting the first loss-in-weight feeder 6 and the first dry powder feeder 8 as an example.

[0030] 1) Parameters: Set the ratio of dry cement powder to pellets to 3kg / t, set the water replenishment ratio of the dry coating water nozzle, the water replenishment ratio is set within 0% to 100% according to the coating effect, and set the required pellet humidity to 3.1%.

[0031] 2) Then the three-way distributor 5 of the cement storage bin 2 is moved to the left, and then the rotary discharge valve 4 and the loosener 3 are started; the cement in the cement storage bin 2 is transported to the first loss-in-weight feeder 6 through the rotary discharge valve 4 and the three-way distributor 5. When the first loss-in-weight feeder 6 reaches the required amount of cement, the loosener 3 and the rotary discharge valve 4 are stopped in sequence, and the three-way distributor 5 is closed.

[0032] 3) According to the set ratio of dry powder cement to pellets 3kg / t and the setting of the material speed of the raw material belt pellets, the first loss-in-weight feeder 6 is adjusted in speed, and the first loss-in-weight feeder 6 adjusts the speed and quantity and then falls into the first dry powder feeder 8, so that the cement supply speed matches the pellet feed amount. During the process, if the weighing value of the first loss-in-weight feeder 6 is less than the set value, the three-way distributor 5 is turned to the left, and then the rotary discharge valve 4 and the loosening device 3 are started; the cement in the cement storage bin 2 is transported to the first loss-in-weight feeder 6 through the rotary discharge valve 4 and the three-way distributor 5, and the first loss-in-weight feeder 6 stops discharging when the weighing reaches the set value.

[0033] 4) In the first dry coating route, the amount of cement is controlled by the first loss-in-weight feeder 6, and the amount of water is controlled by the flow valve of the industrial water pipeline. The pellets are transported to the first humidity sensor 10, and the current pellet humidity is detected. The first humidity control nozzle 12 replenishes water for the incoming pellets, and the amount of water replenishment is 3.1% of the required pellet humidity minus the humidity detected by the first humidity sensor 10; the pellets are transported to the second humidity sensor 11, and the current pellet humidity is detected. The second humidity control nozzle 13 replenishes water for the incoming pellets, and the amount of water replenishment is 3.1% of the required pellet humidity minus the humidity detected by the second humidity sensor 11; if the incoming pellets fail to reach the required humidity after the second humidity control nozzle 13 replenishes water, the third dry coating nozzle 16, the fourth dry coating nozzle 17, the first dry coating nozzle 14 and the second dry coating nozzle 15 are set to replenish water for the incoming pellets at the respective water replenishment ratios to reach the required humidity set by the water-cement ratio; the cement-to-ball ratio is controlled at 3kg to 1t and the water-to-cement ratio is controlled at 3L to 1kg.

[0034] 5) When the coating conditions are met and the pellet head enters the coating belt monitoring point, the sequential control program detects the humidity sensor and performs normal coating.

[0035] 6) The conveyor belt of the belt conveyor device 20 can be set according to the incoming pellet material, and its running speed can be adjusted between 0 and 1.5 m / s, so that the pellets run slowly and pass under the first dry powder feeder 8.

[0036] 7) The pellets are rolled and spread on the upper part of the conveyor belt, and are continuously turned by the first plow-type turner 18, so that the coating surface is increased, the pellets are fully in contact with cement and water, and the raw material pellets are evenly coated.

[0037] 8) The coating raw material pellets and the remaining cement slurry on the coating belt enter the spiral chute 21 at the output end through the conveyor belt. The coating raw material pellets and the remaining cement slurry roll and adhere to each other in the spiral chute 21, which better ensures the coating effect.

[0038] 9) When coating is completed, first stop the first loss-in-weight feeder 6, then stop the first dry powder feeder, and then close the first humidity control nozzle 12, the second humidity control nozzle 13, the first dry coating nozzle 14, and the second dry coating nozzle 15 in an interlocked manner.

[0039] 9) After coating, the residual waste on the working surface of the coated belt is collected in the sludge box 22 through the pipeline.

[0040] After coating: Cement and water are evenly sprayed on the pellets to form a coating. Sampling and analysis show that the average coating thickness can reach 60 to 80 μm, and the coating coverage can reach more than 95%.

[0041] The coated pellet surface has an inactive cement coating, which can reduce the crystallization rate of the pellets in the initial stage of metallization in the initial stage of the reduction reaction in the vertical furnace, prevent the growth of fibrous iron precipitates, and effectively reduce the adhesion of the pellets during the reduction process of the vertical furnace, ensuring high productivity of the vertical furnace.

Claims

1. A gas-based vertical furnace raw material dry coating system, characterized in that: The invention comprises a cement storage bin (2), a weightless feeder, a dry powder feeder, a humidity control nozzle, a dry coating nozzle, a material turner, a belt conveyor (20) and a spiral chute (21), wherein the belt conveyor (20) is provided with a conveyor belt; the bottom discharge port of the cement storage bin (2) is connected to the feed port of the weightless feeder, the discharge port of the weightless feeder is connected to the feed port of the dry powder feeder, and the discharge port of the dry powder feeder is located above the conveyor belt and directly faces the conveyor belt; the humidity control nozzle and the dry coating nozzle are both connected to a water supply pipeline; the humidity control nozzle is located above the front end of the conveyor belt, and the water spraying direction corresponds to the conveyor belt; the dry coating nozzle is located above the conveyor belt, and the water spraying direction corresponds to the conveyor belt; the material turner is arranged above the conveyor belt and is used to turn over the pellets on the conveyor belt; the spiral chute (21) is located below the conveyor belt, and the feed port directly faces the rear end of the conveyor belt.

2. A gas-based vertical furnace raw material dry coating system according to claim 1, characterized in that: The loss-in-weight feeder, dry powder feeder and dry coating nozzle are provided in two sets respectively; the bottom discharge port of the cement storage bin (2) is connected to the feed ports of the two loss-in-weight feeders respectively through a three-way distributor (5).

3. The gas-based shaft furnace raw material dry coating system according to claim 1, characterized in that: A humidity sensor is provided at the front end of the humidity control nozzle. The humidity sensor detects the moisture content of the pellets on the conveyor belt and controls the water replenishment amount of the humidity control nozzle.

4. A gas-based vertical furnace raw material dry coating system according to claim 3, characterized in that: The humidity control nozzles and humidity sensors are correspondingly provided in two sets.

5. A gas-based shaft furnace raw material dry coating system according to any one of claims 1 to 4, characterized in that: The front end and the rear end of the dry powder feeder are both provided with dry coating spray heads.

6. A gas-based shaft furnace raw material dry coating process, using the dry coating system according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: 1) the pellets to be coated are transported from the input end to the output end on the conveying belt of the belt conveying device (20); 2) The water supply pipeline supplies water to the humidity control nozzle, and the humidity control nozzle sprays water to the pellets passing thereunder to replenish the water to the pellets; 3) The dry powder cement in the cement storage bin (2) enters the loss-in-weight feeder, and then the loss-in-weight feeder controls the feeding speed to enter the dry powder feeder, and finally the dry powder cement is covered on the pellets passing below the dry powder feeder; 4) When the pellets on the conveyor belt pass through the material turner, the material turner turns the pellets; 5) After being transported to the output end by the conveyor belt, the pellets fall into the spiral chute (21) and roll and adhere to each other in the spiral chute (21).

7. A gas-based shaft furnace raw material dry coating process according to claim 6, characterized in that: In the step 2), the humidity sensor detects the moisture content of the pellets on the conveyor belt and controls the water replenishment amount of the humidity control nozzle.

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