Grate plate type pellet coating system and pellet coating method

Abstract

The invention discloses a grate plate type pellet coating system and a pellet coating method. The grate plate type pellet coating system comprises a grate plate type coating device. The grate plate type coating device comprises a closed compartment body, a chain grate machine and a spraying nozzle; a feed port is formed in the front end of the closed compartment body, a discharge port is formed in the rear end of the closed compartment body, and a coating section and a drying section are arranged in the closed compartment body from front to back; the chain grate machine is positioned in the closed compartment body and is communicated with the feed port and the discharge port; a spraying nozzle is arranged above the coating section in the closed compartment body, and the spraying direction of the spraying nozzle is downwards aligned with a grate plate of the chain grate machine; the spraying nozzle is communicated with a coating slurry supply device; the closed compartment body is provided with a dry gas inlet and a dry gas outlet at the drying section, the dry gas inlet is positioned at the rear part of the dry gas outlet, and the dry gas inlet is communicated with a dry gas pipeline. According to the system and the method, the material flow during coating can be stably controlled, and the hardening of the coating on the surface of the coated pellet can be better controlled; and the production of coating sludge can be reduced, and the coating quality can be better controlled.

Description

Technical Field

[0001] The invention relates to the technical field of non-blast furnace ironmaking in metallurgy, in particular to a grate plate type pellet coating system and a pellet coating method. Background Art

[0002] The traditional gas-based direct reduction process uses lump ore or pellets as raw materials. In order to avoid sticking in the vertical furnace, a coating process is added before entering the furnace. That is, a layer of cement or lime slurry is sprayed on the pellets to form a coating on their surface.

[0003] The most common coating method in the world is to set up a coating station and spray the coating slurry on the pellet conveyor belt before the pellets enter the reduction shaft furnace. This method has the following problems in actual use: 1. The belt sprayed with slurry and its downstream belt are prone to adhesion and solidification of the slurry, and need frequent cleaning; 2. The coated belt is prone to spilling material, resulting in increased material loss and increased labor intensity for on-site cleaning; 3. After the coating slurry adheres to the belt or splashes into the surrounding environment, it cannot be recycled, resulting in certain waste; 4. During coating, the pellet bed on the coating belt has a certain thickness. The pellets on the upper layer are often coated better, but it is not easy to achieve uniform coating on the pellets on the lower layer.

[0004] 5. When the coated pellets are directly supplied to the charging system of the reduction shaft furnace without buffering, the pellet feeding rate needs to be adjusted according to the needs of the reduction shaft furnace system. In this case, in order to ensure the coating effect, the coating amount per unit time needs to be adjusted; when the coating is increased, it often brings the disadvantage of increased sludge and material spreading.

[0005] Considering the low-carbon and green process characteristics of the direct reduction process, its share in the ironmaking process will inevitably increase in the future. Therefore, the industry is in urgent need of a clean and efficient pellet coating system and method. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a clean and efficient grate plate type pellet coating system; the present invention also provides a grate plate type pellet coating method.

[0007] In order to solve the above technical problems, the technical solution adopted by the system of the present invention is: it includes a grate plate coating device; the grate plate coating device includes a closed box, a chain grate machine, and a spray nozzle; the front end of the closed box is provided with a feed port, the rear end is provided with a discharge port, and the inside of the closed box is respectively a coating section and a drying section from front to back; the chain grate machine is located in the closed box and is connected to the feed port and the discharge port; a spray nozzle is provided above the coating section in the closed box, and the spray direction of the spray nozzle is downwardly aimed at the grate plate of the chain grate machine; the spray nozzle is connected to a coating slurry supply device; the closed box is provided with a dry gas inlet and a dry gas outlet in the drying section, the dry gas inlet is located at the rear of the dry gas outlet, and the dry gas inlet is connected to the dry gas pipeline.

[0008] Furthermore, a high-pressure water spray head is provided at the lower part of the rear end of the closed compartment, and the spray direction of the high-pressure water spray head is directed upward or obliquely upward toward the grate plate of the chain grate machine.

[0009] Furthermore, the grate-type coating device is also provided with a cleaning slurry collecting tank and a conveying pump; a cleaning slurry outlet is provided at the rear end of the closed compartment, and the cleaning slurry collecting tank is connected to the cleaning slurry outlet and is located below it; the cleaning slurry collecting tank is connected to the coating slurry supply device through the conveying pump.

[0010] Furthermore, the coating slurry supply device includes a coating agent storage tank, a coating agent weighing device and a coating slurry preparation tank; the coating slurry supply device is arranged at the upper end of the closed compartment; the discharge port at the lower part of the coating agent storage tank is downwardly connected to the coating slurry preparation tank through the coating agent weighing device; the discharge port at the lower part of the coating slurry preparation tank is connected to the spray nozzle.

[0011] Furthermore, the dry gas pipeline is a preheating tail gas pipeline in the preheating stage before pellet roasting.

[0012] Furthermore, it also includes a pellet cooling device, a vibrating screen, a buffer bin, a distribution chute, a material transfer chute and a conveying belt; the pellet cooling device is connected to the vibrating screen, the buffer bin and the distribution chute in sequence; the distribution chute is connected to the feed inlet of the grate plate coating device, and the discharge port of the grate plate coating device is connected to the conveying belt through the material transfer chute.

[0013] In order to solve the above technical problems, the method of the present invention adopts the above system, and the technical solution adopted includes the following steps: 1) the pellets to be coated enter the closed compartment of the grate plate coating device through the feed inlet and fall to the front end of the grate plate of the chain grate; the drying gas enters the closed compartment of the grate plate coating device through the drying gas inlet; 2) The pellets move backward along with the grate plate of the chain grate machine, and when passing through the spray nozzle, the coating slurry in the coating slurry supply device is sprayed onto the surface of the pellets through the spray nozzle, and the surface of the pellets is coated; 3) The coated pellets move backwards with the grate plate to the drying section, moving in the opposite direction of the drying gas, and the coating slurry on the surface of the pellets is dried and hardened; 4) After coating and drying, the pellets are sent out of the grate coating device from the discharge port.

[0014] Furthermore, the high-pressure water spray head of the grate plate type coating device sprays the grate plate on the return journey, and the cleaning slurry after spraying returns to the coating slurry supply device.

[0015] Furthermore, in step 3), the drying gas is the preheated tail gas used in the preheating stage before the pellet roasting.

[0016] Furthermore, in the step 1), the pellets are first cooled by a pellet cooling device, screened by a vibrating screen, and then enter a buffer bin, and then enter a grate coating device through a distribution chute; in the step 4), the pellets are sent to a conveyor belt through a material chute after exiting a material outlet, and then sent to the next unit by the conveyor belt.

[0017] The beneficial effects of adopting the above technical scheme are as follows: the advantages of the present invention are that during the coating process, firstly, the material flow during coating can be completely and stably controlled, coating can be performed at a constant feeding speed, and fluctuations can be reduced; secondly, the coated pellets are dried using the preheated exhaust gas (at a lower temperature) used in the preheating stage of the pellets before roasting, which can not only make full use of the waste heat, but also better control the hardening of the coating on the surface of the pellets after coating; thirdly, a structure similar to that of a chain grate, a closed coating environment, and a wider slurry coating moving bed can be used, which can not only avoid material scattering during the coating process, but also can be operated in a concentrated and larger scale, thereby reducing the generation of coating sludge and the workload of cleaning, and better controlling the coating quality; fourthly, a nozzle and a mud collection pool are arranged below the coating chain grate, and a submersible pump is provided to send the collected cement slurry back into the coating mud preparation tank, which can reduce the consumption of coating agents such as water and cement. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0019] Figure 1 It is a schematic diagram of the structure of the system of the present invention.

[0020] In the figure: pellet cooling device 1; vibrating screen 2; buffer bin 3; distribution chute 4; coating agent storage tank 5; coating agent weighing device 6; cleaning slurry collection pool 7; material chute 8; conveyor belt 9; grate plate coating device 10; dry gas inlet 11; dry gas outlet 12; coating slurry preparation tank 13; spray nozzle 14; high-pressure water spray head 15; delivery pump 16; a to j are all process lines. DETAILED DESCRIPTION

[0021] Figure 1 As shown, the grate plate type pellet coating system comprises a grate plate coating device 10, a coating slurry supply device, a pellet cooling device 1, a vibrating screen 2, a buffer bin 3, a material distribution chute 4, a material transfer chute 8 and a conveying belt 9. The grate plate coating device 10 comprises a closed box, a chain grate machine, and a spray nozzle 14. The front end of the closed box is provided with a feed inlet, and the rear end is provided with a discharge port, and the inside of the closed box is a coating section and a drying section from front to back; the chain grate machine is located in the closed box, and the front end of the grate plate of the chain grate machine is aligned with the feed inlet, and the rear end is aligned with the discharge port, so as to connect the feed inlet and the discharge port. A spray nozzle 14 is provided above the coating section in the closed compartment; the spray nozzle 14 is preferably arranged in two rows, one for use and one for standby; a number of spray nozzles 14 in each row are arranged from front to back in the coating section; the spraying direction of the spray nozzle 14 is downward and aimed at the grate plate of the chain grate machine; the spray nozzle 14 is connected to a coating slurry supply device; in this way, the spray nozzle 14 can spray the coating slurry provided by the coating slurry supply device downward onto the surface of the pellets moving backward with the grate plate, thereby achieving coating of the pellets. The closed compartment is provided with a dry gas inlet 11 and a dry gas outlet 12 in the drying section. The dry gas inlet 11 is located at the rear of the dry gas outlet 12. It is best that the dry gas inlet 11 is located at the rear end of the drying section and the dry gas outlet 12 is located at the front end of the drying section. The dry gas inlet 11 and the dry gas outlet 12 are preferably arranged on both sides of the closed compartment. The dry gas inlet 11 is connected to the dry gas pipeline, which is preferably a preheating tail gas pipeline in the preheating stage before the pellet roasting. The dry gas pipeline of the dry gas outlet 12 is provided with a fan to provide power for the flow of dry gas. In this way, the preheated tail gas, as dry gas, enters the closed compartment from the dry gas inlet 11 on one side of the rear end of the drying section and exits the closed compartment through the dry gas outlet 12 on the other side of the front end of the drying section. In this process, it moves in the opposite direction to the pellets moving backward with the grate plate, so as to achieve the drying and hardening of the coating slurry on the surface of the pellets.

[0022] Figure 1As shown, a grate plate type pellet coating system, the coating slurry supply device includes a coating agent storage tank 5, a coating agent weighing device 6 and a coating slurry preparation tank 13. The coating slurry supply device is arranged at the upper end of the closed compartment, and the coating agent storage tank 5, the coating agent weighing device 6 and the coating slurry preparation tank 13 are arranged from top to bottom. The discharge port at the lower part of the coating agent storage tank 5 is connected to the feed port at the upper part of the coating agent weighing device 6 through the process line i, the discharge port at the lower part of the coating agent weighing device 6 is connected to the feed port at the upper part of the coating slurry preparation tank 13 through the process line h, and the discharge port at the lower part of the coating slurry preparation tank 13 is connected to the inlet of the spray nozzle 14. A stirrer is arranged in the coating slurry preparation tank 13, which is driven by a motor for stirring. The water inlet of the coating slurry preparation tank 13 is connected to the water supply pipeline through the process line f. It is best to set two coating agent weighing devices 6, one for use and one for standby. It is best to set three coating slurry preparation tanks 13, two for use and one for standby. In this way, the coating agent in the coating agent storage tank 5 is weighed by the coating agent weighing device 6 and then enters the coating slurry preparation tank 13, where it is mixed with water to prepare a coating slurry.

[0023] Figure 1 As shown, the grate plate coating device 10 of the grate plate pellet coating system is also provided with a high-pressure water spray head 15, a cleaning slurry collection tank 7 and a delivery pump 16. The high-pressure water spray head 15 is arranged at the rear end of the closed compartment, and the spray direction of the high-pressure water spray head 15 is upward or obliquely upward to the return grate plate of the chain grate machine; the high-pressure water spray head 15 is preferably arranged in two rows; the inlet of the high-pressure water spray head 15 is connected to the high-pressure water pipeline. A cleaning slurry outlet is provided at the bottom of the rear end of the closed compartment, and the cleaning slurry outlet is designed with an inclination around it, and the cleaning slurry outlet is located at the lowest end; the cleaning slurry collection tank 7 is connected to the cleaning slurry outlet and is located below it; the cleaning slurry collection tank 7 is connected to the coating slurry supply device through the delivery pump 16 and the process line g, and it is best that the cleaning slurry collection tank 7 is connected to one of the coating slurry preparation tanks 13 through the delivery pump 16. A sewage outlet is provided at the bottom of the collection tank 7, and the sewage outlet is connected to the sedimentation disposal unit through the process line j for disposal. After adopting such a structure, the high-pressure water spray head 15 sprays high-pressure water to the returning grate plate, and uses the high-pressure water to rinse the coating slurry remaining on the returning grate plate. The generated cleaning slurry flows into the cleaning slurry collection tank 7 through the cleaning slurry outlet, and is then sent to the coating slurry preparation tank 13 through the delivery pump 16 and the process line g, and is repeatedly used for coating; the sediment settled at the bottom of the collection tank 7 is discharged through the sewage outlet and the process line j and sent to the sedimentation disposal unit for disposal.

[0024] Figure 1As shown, in this grate plate type pellet coating system, the pellet cooling device 1 is connected to the feed port of the vibrating screen 2 through the process line a, the qualified material outlet of the vibrating screen 2 is connected to the feed port of the buffer bin 3 through the process line c, the discharge port of the buffer bin 3 is connected to the feed port of the material distribution chute 4 through the process line e, the discharge port of the material distribution chute 4 is connected to the feed port of the grate plate type coating device 10, and the discharge port of the grate plate type coating device 10 is connected to the conveying belt 9 through the material chute 8. The unqualified material outlet of the vibrating screen 2 is connected to the unqualified pellet processing and disposal unit through the process line b; the discharge port of the buffer bin 3 is connected to the storage warehouse through the process line d. In this way, the pellets are first cooled by the pellet cooling device 1, and then screened by the vibrating screen 2. The screened pellets with qualified particle size enter the buffer bin 3, and then enter the grate plate coating device 10 through the distribution chute 4 for coating; the coated pellets enter the material chute 8 through the discharge port, and then are sent to the conveyor belt 9, and are sent to the next unit by the conveyor belt 9. The pellets with unqualified particle size screened by the vibrating screen 2 are sent to the unqualified pellet disposal unit. When the pellet coating system needs to be repaired but the pellets continue to be produced, the pellets are stored in the storage warehouse through the process line d.

[0025] Figure 1 As shown, the grate plate type pellet coating system and pellet coating method adopt the above-mentioned pellet coating system, and the process steps are as follows: 1) the pellets for the direct reduction plant produced by the pellet production line are discharged from the cooling device 1 after cooling, and enter the vibrating screen 2 for screening through the process line a. After screening, the pellets with unqualified particle size are sent to the unqualified pellet disposal unit through the process line b; 2) The pellets with qualified particle size screened by the vibrating screen 2 enter the buffer bin 3 through the process line c, then go to the distribution chute 4 through the process line e, and then enter the grate plate coating device 10 through the feed port; when the pellet coating system needs to be repaired but the pellets continue to be produced, the pellets with qualified particle size go to the storage warehouse for storage through the process line d; 3) The pellets entering the grate plate coating device 10 fall to the front end of the grate plate of the chain grate in the closed compartment, and then the pellets move backward along with the grate plate of the chain grate; when the pellets pass through the spray nozzle 14 of the coating section, the coating slurry in the coating slurry supply device is sprayed onto the surface of the pellets through the spray nozzle 14, and the surface of the pellets is coated; 4) The coated pellets continue to move forward along the grate plate of the chain grate machine and enter the drying section. The preheated tail gas from the preheating stage before the pellet roasting in the pellet production line enters the closed compartment through the drying gas inlet 11, and as the drying gas, moves in the opposite direction to the coated pellet flow, and is sucked away by the flue gas fan through the drying gas outlet 12; in the drying section, the coating slurry on the surface of the pellets is dried and hardened by the drying gas; the drying gas temperature is controlled to ≤60°C, and can be adjusted according to the running speed of the chain grate machine and the drying and hardening of the coating slurry; 5) After coating and drying, the pellets are sent out of the grate plate coating device 10 from the discharge port, and then go to the conveyor belt 9 through the material chute 8, and finally transported to the material processing unit of the direct reduction plant through the conveyor belt 9 for use; 6) The high-pressure water spray head 15 sprays high-pressure water to the return grate plate, and uses the high-pressure water to wash the coating slurry remaining on the return grate plate; the generated cleaning slurry flows into the cleaning slurry collection tank 7 through the cleaning slurry outlet, 7) When the liquid level of the collection tank 7 reaches a set value, such as 80% of the volume, the delivery pump 16 is started to deliver the collected cleaning slurry to a selected coating slurry preparation tank 13 via process line g; the sediment precipitated at the bottom of the collection tank 7 is discharged via process line j and sent to the sedimentation disposal unit for disposal; 8) The coating agent stored in the coating agent storage tank 5 is sent to the weighing unit 6 via the process line i, and a certain amount of the weighed coating agent is loaded into the slurry preparation tank 13 in use. According to the control requirements of the slurry concentration and specific gravity, a certain amount of water is added via the process line f; the prepared coating slurry is sent to the row of spray heads 14 in use via the process line h; 9) The slurry preparation tank 13 can use the cleaning slurry from the collection tank 7. The amount of coating agent added to the tank can be appropriately reduced and can be flexibly adjusted on site according to the specific gravity of the actual coating slurry.

Claims

1. A grate plate type pellet coating system, characterized in that: The invention comprises a grate plate coating device (10); the grate plate coating device (10) comprises a closed box, a chain grate machine, and a spray nozzle (14); the closed box is provided with a material inlet at the front end and a material outlet at the rear end, and the inside of the closed box is respectively a coating section and a drying section from front to back; the chain grate machine is located in the closed box and is connected to the material inlet and the material outlet; a spray nozzle (14) is provided above the coating section in the closed box, and the spray direction of the spray nozzle (14) is downwardly directed to the grate plate of the chain grate machine; the spray nozzle (14) is connected to a coating slurry supply device; the closed box is provided with a dry gas inlet (11) and a dry gas outlet (12) in the drying section, the dry gas inlet (11) is located at the rear of the dry gas outlet (12), and the dry gas inlet (11) is connected to a dry gas pipeline.

2. A grate plate type pellet coating system according to claim 1, characterized in that: A high-pressure water spray head (15) is provided at the lower part of the rear end of the closed compartment, and the spray direction of the high-pressure water spray head (15) is directed upward or obliquely upward toward the grate plate of the chain grate machine.

3. A grate plate type pellet coating system according to claim 2, characterized in that: The grate plate coating device (10) is further provided with a cleaning slurry collecting tank (7) and a delivery pump (16); a cleaning slurry outlet is provided at the rear end of the closed compartment, and the cleaning slurry collecting tank (7) is connected to the cleaning slurry outlet and is located below the cleaning slurry outlet; the cleaning slurry collecting tank (7) is connected to the coating slurry supply device via the delivery pump (16).

4. The grate plate type pellet coating system according to claim 1, characterized in that: The coating slurry supply device comprises a coating agent storage tank (5), a coating agent weighing device (6) and a coating slurry preparation tank (13); the coating slurry supply device is arranged at the upper end of the closed compartment; the discharge port at the bottom of the coating agent storage tank (5) is downwardly connected to the coating slurry preparation tank (13) through the coating agent weighing device (6); the discharge port at the bottom of the coating slurry preparation tank (13) is connected to a spray nozzle (14).

5. A grate plate type pellet coating system according to any one of claims 1 to 4, characterized in that: The dry gas pipeline is a preheating tail gas pipeline in the preheating stage before pellet roasting.

6. A grate plate pellet coating method, using the pellet coating system according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: 1) the pellets to be coated enter the closed compartment of the grate plate coating device (10) through the feed inlet and fall to the front end of the grate plate of the chain grate machine; the drying gas enters the closed compartment of the grate plate coating device (10) through the drying gas inlet (11); 2) the pellets move backward along with the grate plate of the chain grate machine, and in the process of passing through the spray nozzle (14), the coating slurry in the coating slurry supply device is sprayed onto the surface of the pellets through the spray nozzle (14), thereby coating the surface of the pellets; 3) The coated pellets move backwards with the grate plate to the drying section, moving in the opposite direction of the drying gas, and the coating slurry on the surface of the pellets is dried and hardened; 4) After being coated and dried, the pellets are sent out of the grate plate coating device (10) from the discharge port.

7. A grate plate type pellet coating method according to claim 7, characterized in that: The high-pressure water spray head (15) of the grate plate type coating device (10) sprays the returning grate plate, and the cleaning slurry after spraying returns to the coating slurry supply device.

8. A grate plate type pellet coating method according to claim 6 or 7, characterized in that: In the step 3), the drying gas is the preheated tail gas used in the preheating stage before the pellet roasting.

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