Apparatus and method for sintering, grinding and pelletizing limonite and removing crystal water

Abstract

This invention discloses an apparatus and method for grinding sintered limonite powder into pellet concentrate and removing crystal water. The apparatus includes a vertical mill, with a ring of air nozzles around the mill's grinding disc, a classifier above the grinding disc, a hopper below the classifier, and a discharge pipe at the center of the hopper. The vertical mill has a coarse powder outlet and a return material inlet. The hopper is connected to a coarse powder conveying device via the coarse powder outlet, which is connected to the air inlet of a roasting furnace. The air outlet of the roasting furnace is connected to a flue gas inlet, and the discharge outlet of the roasting furnace is connected to a return material inlet via a roasting return material device. The return material inlet is connected to the discharge pipe. This invention grinds coarse-grained limonite sintered powder into pellet concentrate using a vertical mill. While grinding the pellet concentrate, in addition to removing free water from the limonite sintered powder, it can remove some or even all of the crystal water from the limonite with high heat utilization, reducing the adverse effects of crystal water release during the pellet roasting process.

Description

Technical Field

[0001] This invention relates to pellet preparation processes and equipment, particularly to an apparatus and method for grinding sintered limonite powder into pellet concentrate and removing water of crystallization. Background Technology

[0002] Limonite pellet concentrate is one of the raw materials for pelletizing. ≥80% of the raw material has a particle size of 20 mesh, and in addition to free water, it also contains a certain proportion of water of crystallization. During pellet roasting, the release of this water of crystallization not only requires a large amount of high-quality heat but also increases the risk of pellet bursting. Limonite sintered powder typically has a particle size of 0–10 mm and is generally used as a sintering raw material. If sintered limonite powder is ground to the particle size of pellet concentrate, and some of its water of crystallization is removed, not only can the price difference between pellet concentrate and sintered powder be obtained, but the grade of limonite is also improved due to the reduction of water of crystallization. This also reduces the adverse effects on the pellets caused by the release of water of crystallization during roasting.

[0003] Limonite sintered powder generally contains a certain amount of free water and crystal water. During the process of grinding limonite sintered powder into limonite pellet concentrate using a vertical mill, to prevent the material layer from caking and affecting normal grinding, hot air is usually needed to remove its free water, resulting in a moisture content of approximately 1% in the finished pellet concentrate. After being ground by the grinding rollers, the material is thrown to the tuyeres around the grinding disc. The finer pieces are then blown by hot air ejected from the tuyeres to a classifier for separation. Because the inlet flue gas temperature of a vertical mill is typically 200–300°C, which is relatively low, and because the moisture in the material evaporates rapidly at the outlet of the tuyeres, causing the flue gas temperature to drop rapidly to 80°C, the contact time between the material and the relatively high-temperature flue gas (200–300°C) is very short, making it difficult to remove the crystal water from the material. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide an apparatus and method for grinding sintered limonite powder into pellet concentrate and removing crystal water. A vertical mill is used to grind coarse-grained limonite sintered powder into pellet concentrate. During the grinding process, in addition to removing free water from the sintered limonite powder, some or all of the crystal water in the limonite can be removed with high heat utilization, thereby improving the iron grade of the limonite pellet concentrate, reducing the adverse effects on the pellets caused by the release of crystal water during pellet roasting, and increasing the amount of limonite used in the pellets.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An apparatus for grinding sintered limonite powder into pellet concentrate and removing crystal water includes a vertical mill. The vertical mill includes a grinding disc, a vent ring around the grinding disc, a flue gas inlet on the vent ring, a classifier above the grinding disc, a flue gas outlet on the upper side of the classifier, the flue gas outlet connected to the inlet of a bag filter, the outlet of the bag filter connected to an exhaust pipe, the exhaust pipe equipped with a main exhaust fan, a hopper below the classifier, a discharge pipe at the center of the hopper, a return outlet below the vent ring, the vertical mill having a coarse powder outlet and a return inlet, the hopper connected to a coarse powder conveying device through the coarse powder outlet, the coarse powder conveying device connected to the inlet of a roasting furnace, the outlet of the roasting furnace connected to the flue gas inlet, the discharge port of the roasting furnace connected to the return inlet through a roasting return device, and the return inlet connected to the discharge pipe.

[0007] Furthermore, the bottom of the hopper has a buffer trough, the inner side wall of the buffer trough is provided with a discharge port, and the outer side wall of the buffer trough is connected to the coarse powder outlet.

[0008] Furthermore, the coarse powder conveying device includes a mixer, the feed inlet of which is connected to the coarse powder outlet, the air inlet of which is connected to the discharge pipe of the main exhaust fan outlet, and the discharge outlet of which is connected to the air inlet of the roasting furnace.

[0009] Furthermore, the roasting furnace includes a vertical cylindrical furnace body, a burner is provided at the center of the top of the furnace body, an air inlet is provided on the upper part of the side wall of the furnace body along the tangential direction, an air outlet is provided on the lower part of the side wall of the furnace body along the tangential direction, a spiral blade is provided inside the side wall of the furnace body between the air inlet and the air outlet, and a discharge port is provided at the center of the bottom of the furnace body.

[0010] Furthermore, a fluidizer is provided around the discharge port, and the air inlet of the fluidizer is connected to the air outlet of the roasting furnace through a fluidizing blower; the pipeline between the air outlet of the roasting furnace and the flue gas inlet is connected to the discharge pipeline through a flue gas regulating valve.

[0011] Furthermore, the roasting return device includes a return conveyor, the feeding end of which is connected to the discharge port of the roasting furnace through a high-temperature airlock valve, and the unloading end of which is connected to the return inlet.

[0012] Furthermore, the return material outlet is connected to the return material inlet via a mill return material device; the mill return material device includes an external circulation belt conveyor, an external circulation bucket elevator, and a three-way valve. The feeding end of the external circulation belt conveyor is connected to the return material outlet, the unloading end of the external circulation belt conveyor is connected to the feeding end of the external circulation bucket elevator, and the unloading end of the external circulation bucket elevator is connected to the waste residue buffer bin and the return material inlet via the three-way valve. The external circulation belt conveyor is equipped with an iron remover.

[0013] A method for grinding sintered limonite powder into pellet concentrate and removing crystal water: The sintered limonite powder is fed into a grinding disc through a feed pipe. The grinding disc grinds the sintered limonite powder into powder. Small particles of the powder overflowing from the edge of the grinding disc are conveyed upwards by a high-temperature airflow from a nozzle ring and pass through an air classifier. The air classifier separates the small particles of the powder into coarse powder that does not meet the particle size requirement and fine powder that meets the particle size requirement. The fine powder is discharged from the vertical mill through the flue gas outlet and then collected by a bag filter dust collector. The coarse powder enters the dust collection chamber. The hopper, through a coarse powder conveying device, sends all or part of the coarse powder in the hopper into the roasting furnace for roasting to remove the crystal water in the coarse powder. Part of the roasted coarse powder is discharged through the discharge port of the roasting furnace and then sent to the return inlet of the vertical mill through the return material device. It is then fed back onto the grinding disc for grinding through the feeding pipe. The other part of the roasted coarse powder is discharged through the air outlet of the roasting furnace with the high-temperature flue gas and then introduced into the flue gas inlet of the air nozzle ring. It is then mixed with the newly ground powder material overflowing from the edge of the grinding disc and dried.

[0014] Furthermore, the large particles of powdery material overflowing from the edge of the grinding disc are discharged through the return outlet below the air nozzle ring, and then sent to the return inlet of the vertical mill through the mill return device, and then fed back to the grinding disc for grinding through the feed pipe.

[0015] Furthermore, the coarse powder roasting temperature is 900~1000℃; the high-temperature flue gas temperature introduced into the air nozzle ring is not lower than 400℃.

[0016] Compared with existing pellet preparation processes, the present invention has the following advantages:

[0017] 1) In traditional vertical mill grinding systems for producing limonite pellets, the mill inlet temperature is typically ≤300℃. Due to the low flue gas temperature and short residence time of the material in the high-temperature zone, it is difficult to remove the water of crystallization. This invention can remove some or even all of the water of crystallization during the preparation of pellets, thereby improving the iron grade of the limonite pellets, reducing the adverse effects on the pellets caused by the release of water of crystallization during pellet roasting, and increasing the amount of limonite used in the pellets.

[0018] 2) The process of removing water of crystallization in this invention has a high thermal utilization rate:

[0019] Typically, sintered limonite powder is dehydrated using methods such as rotary kilns. The resulting roasted material and exhaust gas are usually at high temperatures, carrying away a significant amount of heat and resulting in low thermal efficiency. This invention addresses this by roasting the sintered limonite powder during the grinding process into finely pelletized pellets. Because the particles are smaller, their specific surface area is larger, resulting in a larger contact area with the hot roasting flue gas and higher heat transfer efficiency.

[0020] The high-temperature material after roasting is reintroduced into the mill and mixed with the raw material. Through solid-solid and solid-gas heat transfer, the heat carried by the high-temperature material itself is used as part of the heat source required for grinding and drying the raw material. Ultimately, the temperature of the high-temperature material is reduced to a lower temperature, saving roasting heat consumption and improving heat utilization.

[0021] The high-temperature flue gas after roasting enters the mill and is used as a heat source for grinding, ventilation and drying, thus saving roasting heat consumption and improving heat utilization rate.

[0022] 3) Compared with independent rotary kiln roasting and independent grinding, this scheme organically combines the powder making and roasting processes, saving investment and land area. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the device structure of the present invention.

[0024] Figure 2 This is a schematic diagram of a vertical mill.

[0025] Figure 3 This is a schematic diagram of the roasting furnace structure.

[0026] Figure 4 This is a schematic diagram of the air inlet structure of the roasting furnace.

[0027] Figure 5 This is a schematic diagram of the air outlet structure of the roasting furnace.

[0028] In the diagram: 1-Vertical mill; 2-Bag collector; 3-Main exhaust fan; 4-Exhaust pipe; 5-Roasting furnace; 6-Mixer; 7-High-temperature airlock valve; 8-Fluidizing fan; 9-Return conveyor; 10-Flue gas inlet; 11-Coarse powder outlet; 12-Flue gas regulating valve; 13-External circulation belt conveyor; 14-External circulation bucket elevator; 15-Three-way valve; 16-Waste residue silo buffer; 17-Iron separator; 18-Grinding disc; 19-Air nozzle ring; 20-Air classifier; 21-Flue gas outlet; 22-Feed hopper; 23-Feeding pipe; 24-Raw material inlet; 25-Return material outlet; 26-Return material inlet; 27-Furnace body; 28-Burner; 29-Air inlet; 30-Air outlet; 31-Spiral blade; 32-Discharge port; 33-Fluidizer; 34-Reversible conveyor; 35-Buffer tank. Detailed Implementation

[0029] The invention will now be further explained with reference to the accompanying drawings.

[0030] like Figures 1 to 3As shown, the apparatus for grinding limonite sintered powder into pellets and removing crystal water according to the present invention includes a vertical mill 1. The vertical mill 1 includes a grinding disc 18, a nozzle ring 19 is arranged around the grinding disc 18, and the nozzle ring 19 is provided with a flue gas inlet 10. A classifier 20 is arranged above the grinding disc 18, and a flue gas outlet 21 is arranged on the upper side of the classifier 20. The flue gas outlet 21 is connected to the air inlet of a bag filter 2, and the air outlet of the bag filter 2 is connected to an exhaust pipe 4. The exhaust pipe 4 is provided with a main exhaust fan 3 and the classifier 20. A hopper 22 is provided on the lower side, and a discharge pipe 23 is provided in the center of the hopper 22. A return outlet 25 is provided below the air nozzle ring 19. The vertical mill 1 is provided with a coarse powder outlet 11 and a return inlet 26. The hopper 22 is connected to a coarse powder conveying device through the coarse powder outlet 11. The coarse powder conveying device is connected to the air inlet 29 of the roasting furnace 5. The air outlet 30 of the roasting furnace 5 is connected to the flue gas inlet 10. The discharge port 32 of the roasting furnace 5 is connected to the return inlet 26 through the roasting return device. The return inlet 26 is connected to the discharge pipe 23.

[0031] In this invention, the bottom of the hopper 22 has a buffer trough 35, the inner side wall of the buffer trough 35 is provided with a discharge port, and the outer side wall of the buffer trough 35 is connected to the coarse powder outlet 11. The coarse powder that does not meet the particle size requirements separated by the classifier accumulates along the hopper into the inner buffer trough 35. The coarse powder in the buffer trough 35 can be discharged from the vertical mill 1 through the coarse powder outlet 11, and then sent to the calcining furnace 5 through the coarse powder conveying device. A regulating valve is set at the coarse powder outlet 11 to adjust the discharge amount of coarse powder. Alternatively, the coarse powder in the buffer trough 35 can be discharged through the discharge port and directly returned to the grinding disc for further grinding.

[0032] When the vertical mill is working, the sintered limonite powder to be ground is fed into the feed pipe through the raw material inlet and then fed into the grinding disc. The grinding disc grinds the limonite powder into powder. The large particles of powder overflowing from the edge of the grinding disc are discharged through the return outlet below the air nozzle ring. The small particles of powder overflowing from the edge of the grinding disc are conveyed upward by the high-temperature airflow from the air nozzle ring and pass through the air classifier. The air classifier separates the small particles of powder into coarse powder that does not meet the particle size requirement and fine powder that meets the particle size requirement. The fine powder is discharged from the vertical mill through the flue gas outlet and then collected by the bag dust collector. The coarse powder is returned to the grinding disc through the hopper and ground again. The above process is repeated so that the particle size of the powder changes from coarse to fine until it meets the particle size requirement set by the air classifier. The coarse powder from the hopper is fed into the roasting furnace via a coarse powder conveying device. The high-temperature flue gas generated in the roasting furnace can remove some or even all of the crystal water from the coarse powder, thereby improving the iron grade of the limonite pellet concentrate. The roasted coarse powder can be fed back into the return inlet through the roasting return device and then fed back into the grinding disc for grinding through the feed pipe. The high-temperature flue gas generated during roasting can be introduced into the flue gas inlet of the tuyeres ring to dry the freshly ground powder that overflows from the edge of the grinding disc.

[0033] Furthermore, during the above process, since the inside of the feeding pipe and the hopper are isolated from each other, the roasted coarse powder will only come into contact with the newly added limonite sintered powder in the feeding pipe, and will not come into contact with the coarse powder in the hopper.

[0034] In this invention, the coarse powder conveying device feeds the coarse powder into the calcining furnace via pneumatic conveying, such as... Figure 1 As shown, the coarse powder conveying device includes a mixer 6. The feed inlet of the mixer 6 is connected to the coarse powder outlet 11, the air inlet of the mixer 6 is connected to the exhaust pipe of the main exhaust fan 3, and the discharge outlet of the mixer 6 is connected to the air inlet of the roasting furnace 5. The main exhaust fan 3 provides the required air volume and air pressure to the nozzle ring 19. The coarse powder in the hopper 22, through the mixer 6, forms a gas-solid two-phase flow with a stream of flue gas from the outlet of the main exhaust fan 3 and enters the air inlet of the roasting furnace 5 tangentially.

[0035] Dewatering of materials requires sufficient flue gas temperature and sufficient time. For example... Figures 3 to 5 As shown, the roasting furnace 5 includes a vertical cylindrical furnace body 27. A burner 28 is provided at the center of the top of the furnace body 27. An air inlet 29 is provided on the upper part of the side wall of the furnace body 27 in the tangential direction. An air outlet 30 is provided on the lower part of the side wall of the furnace body 27 in the tangential direction. A spiral blade 31 is provided inside the side wall of the furnace body 27 between the air inlet 29 and the air outlet 30. A discharge port 32 is provided at the center of the bottom of the furnace body 27.

[0036] The burners in the roasting furnace produce sufficiently high-temperature flue gas, and the furnace temperature can reach 900~1000℃. By setting spiral blades, the material moves in a spiral motion inside the furnace, thereby extending the residence time of the material in the roasting furnace. By controlling the height and diameter of the roasting furnace, the pitch of the spiral blades, and the length of the pipeline between the roasting furnace and the vertical mill, the sum of the material's movement time inside the roasting furnace and the time the material moves with the flue gas from the roasting furnace to the mill's air nozzle ring can be controlled to reach a certain time, thereby achieving the removal of 10%~100% of the water of crystallization.

[0037] Furthermore, particle size is a major factor affecting dehydration time and heat and mass transfer. Reducing particle size increases the dehydration rate and shortens the dehydration time. Smaller particles have a larger specific surface area, resulting in more thorough contact with flue gas and faster heat conduction. In this invention, during the pulverization process, as the particle size decreases from coarse to fine, this portion of the material is allowed to contact the high-temperature flue gas at a higher specific surface area before reaching the acceptable particle size. Each time the material is ground, the particle diameter decreases, and generally, several grinding cycles are sufficient to reach the acceptable particle size. Each time the particle size decreases, it is first roasted in a roasting furnace before re-grinding, thus doubling the contact time between the particles and the high-temperature flue gas. Due to heat conduction and moisture migration, particle dehydration is a process from the outside in, with the particle surface being more susceptible to dehydration. If there are incompletely dehydrated portions inside large particles, they will be easily exposed during the particle size reduction process before reaching the acceptable particle size, facilitating moisture removal during subsequent roasting.

[0038] like Figure 1 and 3 As shown, the coarse powder moves along a spiral trajectory from the air inlet 29 at the top of the furnace body 27 to the air outlet 30 at the bottom of the furnace body 27 with the two-phase flow. Part of it settles at the bottom of the furnace body 27 and is sent into the roasting furnace 5 through the discharge port 32 via the roasting return device. The other part is suspended in the flue gas and is discharged from the air outlet 30 of the roasting furnace 5 with the flue gas, and then conveyed to the air nozzle ring 19 of the vertical mill 1 through the flue gas inlet 10. This part of the flue gas serves as a heat source and ventilation airflow to dry and transport the freshly ground powdery material overflowing from the edge of the grinding disc. At the same time, the heat carried by the roasted coarse powder material entering the vertical mill with the flue gas is transferred to the freshly ground material and flue gas through collision and contact inside the vertical mill, also serving as part of the drying heat source.

[0039] In this invention, a fluidizer 33 is provided around the discharge port 32, and the air inlet of the fluidizer 33 is connected to the air outlet 30 of the calcining furnace 5 through a fluidizing blower 8. The coarse powder settling at the bottom of the calcining furnace 5 is buffered inside the calcining furnace. Through the fluidizer 33, the flue gas discharged from the calcining furnace 5 is drawn out by the fluidizing blower 8, and fluidizing air is blown into the fluidizer 33, so that the material at the bottom of the calcining furnace 5 is in a fluidized state. At this time, the coarse powder is still in a temperature environment in which crystal water can be removed, which is conducive to the removal of crystal water from the material.

[0040] like Figure 1 As shown, in order to facilitate the adjustment of the flue gas flow rate entering the vertical mill 1, the pipeline between the air outlet 30 of the calcining furnace 5 and the flue gas inlet 10 is connected to the discharge pipeline 4 through the flue gas regulating valve 12. Through the flue gas regulating valve 12, a portion of the gas in the discharge pipeline 4 can be directly sent into the flue gas inlet 10.

[0041] like Figure 1 and 2 As shown, the roasting return material device includes a return material conveyor 9. The feeding end of the return material conveyor 9 is connected to the discharge port 32 of the roasting furnace 5 through a high-temperature airlock valve 8, and the unloading end of the return material conveyor 9 is connected to the return material inlet 26. The return material inlet 26 is connected to the discharge pipe 23. Coarse powder is discharged from the discharge port at the bottom of the roasting furnace through the high-temperature airlock valve and transported to the return material inlet of the mill by the roasting return material conveyor. Then, it is ground together with the new limonite sintered powder raw material on the surface of the grinding disc. The heat carried by this coarse powder material itself is transferred to the newly ground material and flue gas as part of the drying heat source through collision and contact with the newly ground material inside the mill.

[0042] like Figure 1 As shown, the return outlet 25 is connected to the return inlet 26 via the mill return device. When the vertical mill is working, the large particles of powdery material overflowing from the edge of the grinding disc are discharged through the return outlet below the air nozzle ring. This part of the material can also be sent back to the return inlet through the mill return device and fed back to the grinding disc for re-grinding. The mill return device includes an external circulation belt conveyor 13, an external circulation bucket elevator 14, and a three-way valve 15. The feeding end of the external circulation belt conveyor 13 is connected to the return outlet 25, and the unloading end of the external circulation belt conveyor 13 is connected to the feeding end of the external circulation bucket elevator 14. The unloading end of the external circulation bucket elevator 14 is connected to the waste slag silo buffer 16 and the return inlet 26 via the three-way valve 15. The external circulation belt conveyor 13 is equipped with an iron separator 17.

[0043] Large particles of the powdery material overflowing from the edge of the grinding disc cannot be conveyed upwards by the high-temperature airflow provided by the nozzle ring. Instead, they flow downwards through the return outlet, and then through the external circulation belt conveyor, external circulation bucket elevator, and three-way valve to the feed pipe of the vertical mill. There, they are mixed with new limonite sintered powder raw material and continue grinding on the grinding disc surface. A magnetic separator installed on the external circulation belt conveyor removes large iron impurities (bolts, iron blocks, etc.). Under different operating conditions, the powdery material discharged through the return outlet can enter the waste slag silo buffer via the three-way valve. A reversible conveyor can be installed below the waste slag silo buffer, allowing the material in the silo buffer to either return to the mill for further grinding via the external circulation bucket elevator or be discharged externally.

[0044] The present invention relates to a method for grinding sintered limonite powder into pellets and removing crystal water: Sintered limonite powder is fed into a grinding disc through a feed pipe. The grinding disc grinds the sintered limonite powder into powder. Small particles of the powder overflowing from the edge of the grinding disc are conveyed upwards by a high-temperature airflow from a duct ring and pass through a classifier. The classifier separates the small particles of the powder into coarse powder (not meeting the particle size requirement) and fine powder (meeting the particle size requirement). The fine powder is discharged from the vertical mill through the flue gas outlet and collected by a bag filter. The coarse powder enters a hopper, and a coarse powder conveying device sends all or part of the coarse powder in the hopper into a roasting furnace for roasting. The roasting temperature of the coarse powder is 900~1000℃. The temperature is ℃ to remove the water of crystallization from the coarse powder. Part of the coarse powder after roasting is discharged through the discharge port of the roasting furnace and then sent to the return inlet of the vertical mill through the return material device. It is then fed back to the grinding disc for grinding through the feeding pipe. The other part of the coarse powder after roasting is discharged through the air outlet of the roasting furnace with the high-temperature flue gas and then introduced into the flue gas inlet of the air nozzle ring. The temperature of the high-temperature flue gas introduced into the air nozzle ring is not lower than 400℃. It is then mixed with the newly ground powder material overflowing from the edge of the grinding disc and dried. The large particles of the powder material overflowing from the edge of the grinding disc are discharged through the return outlet below the air nozzle ring and then sent back to the feeding pipe of the vertical mill through the mill return material device, and then fed back to the grinding disc for grinding.

[0045] The effect of this method

[0046] For example, a type of limonite powder from Indonesia, with a particle size of 0-10mm, contains 21% free water and 12% water of crystallization. Its composition is as follows:

[0047]

[0048] The pellet powder produced by the apparatus and method of the present invention has a particle size of ≥80% 20 mesh, 1% free water, and 9.6% crystal water, which can meet the requirements for pellet production.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An apparatus for grinding sintered limonite powder into pellet concentrate and removing crystal water, comprising a vertical mill, the vertical mill including a grinding disc, a duct ring arranged around the grinding disc, a flue gas inlet arranged on the duct ring, an air classifier arranged above the grinding disc, a flue gas outlet arranged on the upper side of the air classifier, the flue gas outlet connected to the air inlet of a bag filter, the air outlet of the bag filter connected to an exhaust pipe, the exhaust pipe equipped with a main exhaust fan, a hopper arranged below the air classifier, a discharge pipe arranged in the center of the hopper, and a return outlet arranged below the duct ring, characterized in that: The vertical mill is equipped with a coarse powder outlet and a return material inlet. The discharge hopper is connected to a coarse powder conveying device through the coarse powder outlet. The coarse powder conveying device is connected to the air inlet of the roasting furnace. The air outlet of the roasting furnace is connected to the flue gas inlet. The discharge port of the roasting furnace is connected to the return material inlet through the roasting return material device. The return material inlet is connected to the discharge pipe.

2. The apparatus for grinding limonite sintered powder into pellets and removing crystal water according to claim 1, wherein the bottom of the hopper has a buffer trough, the inner side wall of the buffer trough is provided with a discharge port, and the outer side wall of the buffer trough is connected to the coarse powder outlet.

3. The apparatus for grinding sintered limonite powder into pellets and removing water of crystallization according to claim 1, characterized in that: The coarse powder conveying device includes a mixer, the feed inlet of which is connected to the coarse powder outlet, the air inlet of which is connected to the discharge pipe of the main exhaust fan outlet, and the discharge outlet of which is connected to the air inlet of the roasting furnace.

4. The apparatus for grinding sintered limonite powder into pellets and removing water of crystallization according to claim 1, characterized in that: The roasting furnace includes a vertical cylindrical furnace body, a burner at the center of the top of the furnace body, an air inlet at the upper part of the side wall of the furnace body along the tangential direction, an air outlet at the lower part of the side wall of the furnace body along the tangential direction, spiral blades inside the side wall of the furnace body between the air inlet and the air outlet, and a discharge port at the center of the bottom of the furnace body.

5. The apparatus for grinding sintered limonite powder into pellets and removing water of crystallization according to claim 4, characterized in that: A fluidizer is provided around the discharge port, and the air inlet of the fluidizer is connected to the air outlet of the roasting furnace through a fluidizing blower; the pipeline between the air outlet of the roasting furnace and the flue gas inlet is connected to the discharge pipeline through a flue gas regulating valve.

6. The apparatus for grinding sintered limonite powder into pellets and removing water of crystallization according to claim 1, characterized in that: The roasting return device includes a return conveyor, the feeding end of which is connected to the discharge port of the roasting furnace through a high-temperature airlock valve, and the unloading end of which is connected to the return inlet.

7. The apparatus for grinding sintered limonite powder into pellets and removing water of crystallization according to claim 1, characterized in that: The return material outlet is connected to the return material inlet through the mill return material device; the mill return material device includes an external circulation belt conveyor, an external circulation bucket elevator, and a three-way valve. The feeding end of the external circulation belt conveyor is connected to the return material outlet, and the unloading end of the external circulation belt conveyor is connected to the feeding end of the external circulation bucket elevator. The unloading end of the external circulation bucket elevator is connected to the waste residue buffer bin and the return material inlet through the three-way valve. The external circulation belt conveyor is equipped with an iron remover.

8. A method for grinding sintered limonite powder into pellets and removing water of crystallization using the apparatus according to claim 1, characterized in that: Limonite sintered powder is fed into the grinding disc through a feed pipe. The grinding disc grinds the limonite sintered powder into powder. Small particles of the powder overflowing from the edge of the grinding disc are conveyed upwards by a high-temperature airflow from the tuyer ring and pass through a classifier. The classifier separates the small particles of the powder into coarse powder that does not meet the particle size requirements and fine powder that meets the particle size requirements. The fine powder is discharged from the vertical mill through the flue gas outlet and then collected by a bag filter. The coarse powder enters the hopper and is sent to a roasting furnace for roasting by a coarse powder conveying device to remove the crystal water from the coarse powder. Part of the roasted coarse powder is discharged through the discharge port of the roasting furnace and then sent to the return inlet of the vertical mill through a return material device. It is then fed back into the grinding disc through the feed pipe for grinding. The other part of the roasted coarse powder is discharged through the vent of the roasting furnace with the high-temperature flue gas and then introduced into the flue gas inlet of the tuyer ring. It is then mixed with the newly ground powder overflowing from the edge of the grinding disc and dried.

9. The method for grinding sintered limonite powder into pellets and removing crystal water according to claim 8, characterized in that: Large particles of powdery material overflowing from the edge of the grinding disc are discharged through the return outlet below the air nozzle ring, then fed into the return inlet of the vertical mill through the mill return device, and then fed back onto the grinding disc for grinding through the feed pipe.

10. A method for grinding sintered limonite powder into pellets and removing water of crystallization according to claim 8, characterized in that: The coarse powder roasting temperature is 900~1000℃; the high-temperature flue gas temperature introduced into the air nozzle ring is not lower than 400℃.

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