Sealing mechanism of feeding device

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sealing mechanism of a vibrating feeder which is used for feeding material to a moving-hearth furnace such as a rotary hearth furnace or a straight grate. More specifically, the present invention relates to a sealing mechanism for preventing gas inside a furnace from leaking through a gap between the lower part of a vibrating feeder and the upper part of a feeding duct extending through the ceiling of the furnace.

[0003] 2. Description of the Related Art

[0004] A shaft furnace method represented by a Midrex process has been known as a direct iron making in which reduced iron (metallic iron) is obtained by directly reducing iron oxides such as iron ore or iron oxide by using a carbonaceous material and a reducing gas. In this type of direct iron making, a reducing gas produced from a natural gas or the like is blown into a shaft furnace through a tuyere in a lower portion of the shaft furnace and iron oxide is reduced by using the reducing force of the reducing gas so as to obtain metallic iron. Further, a reduced iron making process, using a carbonaceous material such as coal as a reducing agent instead of a natural gas, has drawn attention in recent years. Specifically, a so-called SL/RN method has been put to practical use.

[0005] In recent years, the following metallic iron making method using a carbonaceous material has been known. That is, in the method, a mixture containing iron oxide such as iron ore and a carbonaceous reducing agent such as coal is loaded onto the hearth of a moving-hearth heating furnace such as a rotary furnace or a straight grate. Then, the mixture is heated by a burner and a radiant heat while moving in the heating furnace so that the iron oxide is reduced by the carbonaceous reducing agent. The obtained reduced iron is carburized, melt, aggregated, and is separated from molten slag, and is cooled and solidified so that granular solid metallic iron is taken out of the furnace.

[0006] When the mixture containing iron oxide and a carbonaceous reducing agent is loaded into the moving-hearth heating furnace, a vibrating feeder is used as a feeding device so that the width in the width direction of the hearth and/or thickness of the mixture loaded onto the hearth is even.

[0007]
FIG. 4 is a schematic view showing a general feeding device using a vibrating feeder. Material to be fed such as mixture, which is reserved in a hopper 10, is fed through a quantity-adjusting mechanism 8, which is provided in the hopper 10, to a trough 11 of a vibrating feeder 12. The mixture on the trough 11 is sequentially moved toward a hole 13 provided in the trough 11 by the vibration generated by a vibrating device 7, while the thickness of a layer of the mixture on the trough 11 is adjusted to become even in the thickness. Then, the mixture is continuously fed from the hole 13 through a feeding nozzle 14 and a duct 15 onto a hearth 2.

[0008] In this type of feeding device, the trough vibrates, and thus the feeding nozzle 14 provided on the lower surface of the trough 11, the nozzle extending along the edge of the opening of the hole, and the duct 15 extending through the ceiling 3 of the furnace are in a non-contacting state (non-contacting portion) 19. However, if the non-contacting portion 19 is not closed, a high-temperature gas in the furnace may flow out through the non-contacting portion or dust may scatter outside the furnace in accordance with the exhaust gas. Further, the high-temperature gas flowing out through the non-contacting portion may deteriorate peripheral devices of the vibrating feeder. Also, the air outside the furnace may flow into the furnace so that turbulence of atmosphere may be caused in the furnace. Accordingly, in order to overcome these problems, the feeding nozzle 14 and the duct 15 are connected by using a rubber boot 20 so as to seal the non-contacting portion.

[0009] However, in a sealing mechanism using a rubber boot, the rubber boot is deteriorated due to the heat of the gas inside the furnace or rising powder is adhered to the rubber boot so that the elasticity of the rubber boot is decreased. Thus, the rubber boot must be frequently checked and changed. Further, since the rubber boot is provided in a relatively small space, a sufficient operation space cannot be obtained and thus a setting operation and a maintenance operation for the rubber boot are difficult to perform. Also, the feeder must be placed at a high position in order to obtain an operation space. However, when the feeder is set at a high position, material fed by the feeder may be broken at the hearth due to the shock of drop and the amount of rising dust increases.

[0010] The present invention has been made in view of the above-described problems, and the object of the present invention is to provide a sealing mechanism in which maintenance can be easily performed and a great sealing effect can be achieved.

SUMMARY OF THE INVENTION

[0011] The present invention provides a sealing mechanism of a feeding device for feeding lumps and/or powder to a moving-hearth heating furnace. The feeding device comprises a vibrating feeder including a trough in which a hole for feeding the lumps and/or powder to the furnace is formed; and a duct for guiding the lumps and/or powder dropped through the hole to a hearth of the heating furnace. The sealing mechanism comprises a water sealing mechanism including a skirt plate, a weir plate, a side surface of the duct, and liquid. The skirt plate is provided on the lower surface of the trough such that the skirt plate surrounds the periphery of the upper end of the duct and such that the lower end of the skirt plate is positioned below the upper end of the duct. The weir plate is provided above a ceiling of the heating furnace such that the weir plate surrounds the periphery of the lower end of the skirt plate and such that the upper end of the weir plate is positioned above the lower end of the skirt plate. The liquid is kept in a tank serving as a pool of liquid which is formed by the side surface of the duct and the weir plate such that the liquid surface is above the lower end of the skirt plate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]
FIG. 1 is a cross-sectional view of a moving-hearth heating furnace to which a feeding device provided with a sealing mechanism of the present invention is set;

[0013]
FIGS. 2A and 2B are plan views viewed from the top showing the critical portion of the moving-hearth heating furnace to which the feeding device provided with the sealing mechanism of the present invention is set;

[0014]
FIG. 3 is a cross-sectional view showing the critical portion of the moving-hearth heating furnace to which the feeding device provided with the sealing mechanism of the present invention is set;

[0015]
FIG. 4 is a cross-sectional view for illustrating a known feeding device and sealing mechanism; and

[0016]
FIG. 5 is a schematic view of a rotary hearth furnace used as the moving-hearth heating furnace.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention provides a sealing mechanism of a feeding device for feeding lumps and/or powder (hereinafter referred to as material to be fed) to a moving-hearth heating furnace. The feeding device comprises a vibrating feeder including a trough in which a hole for feeding the material to the furnace is formed; and a duct for guiding the material dropped through the hole to a hearth of the heating furnace. The sealing mechanism comprises a water sealing mechanism including a skirt plate, a weir plate, a side surface of the duct, and liquid. The skirt plate is provided on the lower surface of the trough such that the skirt plate surrounds the periphery of the upper end of the duct and such that the lower end of the skirt plate is positioned below the upper end of the duct. The weir plate is provided above a ceiling of the heating furnace such that the weir plate surrounds the periphery of the lower end of the skirt plate and such that the upper end of the weir plate is positioned above the lower end of the skirt plate. The liquid is kept in a tank serving as a pool of liquid which is formed by the side surface of the duct and the weir plate such that the liquid surface is above the lower end of the skirt plate.

[0018] This sealing mechanism can be easily maintained and has a great sealing effect.

[0019] Lumps and/or powder (material to be fed) which are to be fed by using the feeding device of the present invention include a powder or a mixed powder containing two or more types of powder, or lumps prepared by forming the powder into an arbitrary form, such as a pellet or a briquette. Also, material, sub material, and additives of any type can be used. For example, the following matter may be used as a material for reduced iron (metallic iron); a mixed powder prepared by mixing an iron-oxide-containing powder and a carbonaceous powder, which are used for producing reduced iron (metallic iron), (another component may be contained); various types of raw powder such as an iron-oxide-containing powder and a carbonaceous powder; lumps prepared by forming the mixed powder into an arbitrary form such as a pellet and a briquette; or various types of sub material and additive such as a carbonaceous powder laid on the hearth, a refractory powder, a slag powder, a basicity-adjusting agent (for example, lime), a hearth-maintaining material (for example, the same material as that of the hearth), and a melting point-adjusting agent (alumina, magnesia, or the like). Of course, the material to be fed is not limited to the above-described examples and any types of powder or lumps may be fed to the furnace. Therefore, the sealing mechanism of the present invention may be provided to a feeding device for each material to be fed.

[0020] As the moving-hearth heating furnace, a heating furnace including a moving hearth, such as a rotary hearth furnace or a straight grate may be used. Also, any types of furnace, for example, a reducing furnace, a heating furnace, and reducing and fusing furnace, may be used as the moving-hearth heating furnace. Among them, a reducing and fusing furnace using a rotary hearth furnace is desired and is particularly suitable for producing metallic iron, because a process from reduction to fusion can be efficiently performed inside the furnace.

[0021] Incidentally, a specific method of producing metallic iron by using a moving-hearth heating furnace is disclosed in Japanese Unexamined Patent Application Publication No. 2000-144224.

[0022] The above-described feeding device is used for feeding material to a heating furnace and includes at least a hopper for feeding material, a vibrating feeder, and a duct.

[0023] Hereinafter, the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and the design can be modified as long as the advantages of the present invention can be achieved.

[0024]
FIG. 5 is a schematic view of a dome-shaped rotary hearth furnace having a doughnut-shaped rotary moving hearth. FIGS. 1 and 3 are cross-sectional views taken along the line A-A of FIG. 5, and FIGS. 2A and 2B are plan views showing a feeding device-setting part of the moving-hearth heating furnace viewed from the top.

[0025] In the figures, the moving-hearth heating furnace 1 includes a hearth 2, to which material 9 (lumps in FIG. 1) is fed by a feeding device. The material 9 is loaded in a hopper 10. The material 9 is fed from the hopper 10 through a quantity-adjusting mechanism 8 to a trough 11 of a vibrating feeder or to an indirect conveying unit (not shown), such as a belt conveyer, which communicates with the trough 11 of the vibrating feeder. Although not shown, a frame is formed at the edges of the trough 11 in order to prevent the material from dropping due to the vibration of the trough 11.

[0026] In the vibrating feeder, a vibrating device 7 vibrates the trough 11 so that the material on the trough 11 is allowed to move toward a hole 13, which is provided in the trough 11.

[0027] As such a vibrating feeder, the following known feeders may be used: for example, a shaking feeder, an electromagnetic vibrating feeder, an electric-motor-driven vibrating feeder, and a stick-slip feeder. Among them, an electromagnetic vibrating feeder is recommended, in which the amount of material to be fed can be adjusted so that the material is fed to the furnace constantly (for example, with a constant width and uniform thickness).

[0028] The hole 13 through which the material is fed to the hearth 2 is formed in the trough 11. The shape, size, and position of the hole 13 is not specified and may be determined according to the application. For example, as shown in FIG. 2A, a plurality of slit-shaped holes 13 may be formed in a staggered arrangement over the width of the hearth 2. Alternatively, as shown in FIG. 2B, one slit-shaped hole may be formed over the width of the hearth 2. In order to evenly feed the material to the furnace over the width of the hearth 2 and to prevent the material from falling over the edges of the trough 11, it is preferable to form a plurality of slit-shaped holes in a staggered arrangement or one slit-shaped hole in a slanting direction over the width of the hearth 2, as shown in FIGS. 2A and 2B. In particular, as shown in FIG. 2B, it is desired that one slit-shaped hole 13 be formed in a slanting direction with respect to the longitudinal direction of the trough 11 (that is, ends 13a and 13b of the hole 13 are positioned at ends 11a and 11b in the longitudinal direction of the trough 11, respectively, so that the hole extends in a slanting direction with respect to the width direction of the hearth 2) so that the two ends 13a and 13b of the hole 13 are positioned at the two ends of the hearth 2. Of course, a plurality of partitions may be provided on the trough 11 as required so as to form paths for the material to be fed. Although not shown in FIGS. 2A and 2B, a cover 11a is desirably provided over the trough 11 so as to effectively shield and seal the trough 11.

[0029] Preferably, a feeding nozzle 14 having an arbitrary length is formed below the trough 11, the nozzle 14 extending downward along the edge of the opening of the hole 13. The feeding nozzle 14 prevents the material dropping through the hole 13 from scattering and functions as a guide for reliably guiding the material to a duct 15. Therefore, the feeding nozzle 14 extends so that a lower end 14a of the feeding nozzle 14 is positioned below an upper end 15a of the duct 15 and the upper end 15a of the duct 15 is placed so as to surround the periphery of the nozzle 14.

[0030] The duct 15 extends through a ceiling 3 of the heating furnace 1 and the upper end 15a of the duct 15 is positioned between the lower end 14a of the feeding nozzle 14 and the lower surface of the trough 11. Also, a lower end 15b of the duct 15 is positioned above the hearth 2 of the heating furnace 1 such that the duct 15 is open.

[0031] The feeding nozzle 14 provided in the trough 11 vibrates due to the vibration of the trough 11 (for example, it vibrates in the vertical and horizontal directions), and thus the vibrating feeder and the duct 15 must always be prevented from coming into contact so that the vibrating feeder (in particular, the feeding nozzle 14 and the trough 11) is not brought into contact with the duct 15. On the other hand, when the vibrating feeder is not in contact with the duct 15, high-temperature gas and dust in the furnace rise through the duct 15 and flow out through the non-contacting portions. Thus, the area of the non-contacting portions should be as small as possible. Specifically, the distance between the lower surface of the trough 11 and the upper end 15a of the duct 15 and the distance between the periphery of the feeding nozzle 14 and the duct 15 are preferably as short as possible, while maintaining the above-described non-contacting state.

[0032] In the present invention, when the feeding nozzle 14 of the vibrating feeder is not in contact with the duct 15, a water sealing mechanism is provided so that high-temperature gas and dust rising through the duct 15 do not flow out through the non-contacting portions.

[0033] The specific configuration of the water sealing mechanism is not limited as long as the flow of gas can be blocked at the non-contacting portions.

[0034] The water sealing mechanism shown in FIG. 1 includes a skirt plate 16, a weir plate 17, a side surface of the duct 15, and liquid 18.

[0035] The skirt plate 16 functions as a weir for blocking the flow of gas and is formed so as to surround the periphery of the upper end 15a of the duct 15. Also, the skirt plate 16 is provided on the lower surface of the trough 11 such that a lower end 16a of the skirt plate 16 is positioned below the upper end 15a of the duct 15.

[0036] Herein, the skirt plate 16 may be provided at an arbitrary position between the duct 15 and the weir plate 17. However, it is desired to place the skirt plate 16 as close as possible to the duct 15 in order to prevent a wide range of the trough 11 from being heated by high-temperature gas rising through the duct 15. Incidentally, the skirt plate 16 vibrates in accordance with the vibration of the trough 11, and thus the skirt plate 16 should also be placed so that it is not in contact with the duct 15 and the weir plate 17.

[0037] The weir plate 17 also functions as a weir for holding the liquid 18 and is formed so as to surround the periphery of the lower end 16a of the skirt plate 16. Also, the weir plate 17 is provided above the ceiling of the heating furnace 1 such that an upper end 17a of the weir plate 17 is positioned above the lower end 16a of the skirt plate 16.

[0038] A pool of liquid 18 for water sealing is held in a tank formed by the side surface of the duct 15 and the weir plate 17. At this time, in order to prevent leakage of high-temperature gas, the lower end 16a of the skirt plate 16 must always be under the liquid 18 even when the trough 11 vibrates. Therefore, the liquid surface must always be kept above the lower end 16a of the skirt plate 16 by adjusting the amount of the liquid 18. Incidentally, the liquid 18 is simply kept in the tank; the liquid 18 does not flow.

[0039] The liquid surface also vibrates due to the vibration of the trough 11. Thus, it is desired to adequately set the length of the duct 15, the skirt plate 16, and the weir plate 17 and the amount of the liquid 18 so that the liquid 18 does not leak out of the water sealing mechanism, for example, into the furnace, due to the vibration.

[0040] As the sealing liquid, water and so on may be used. But water is the best in terms of cost efficiency and safety. Of course, known additives such as a boiling point adjusting agent and a preservative may be added to the water.

[0041] The weir plate 17 should be placed near the periphery of the skirt plate 16 in order to obtain a sealing effect by using the above-described water sealing mechanism. By adopting such a water sealing mechanism, high-temperature gas and dust in the furnace do not leak through the non-contacting portions of the nozzle 14 and the duct 15 to the atmosphere. Further, the above-described water sealing mechanism can be maintained simply by changing the liquid. Also, it is easy to visually check the water sealing status (level of the liquid surface and condition of the liquid), and thus the mechanism can be easily checked.

[0042] Preferably, in the above-described water sealing mechanism, by forming the pool of liquid at an area including the feeding nozzle 14 of the trough 11, as shown in FIG. 1, the trough 11 positioned above the pool of liquid is not heated More preferably, the weir plate 17 is provided to surround the area including the trough 11 and the width of the hearth 2 below the trough 11 so as to form the pool of liquid, as shown in FIGS. 2A, 2B, and 3. Since the heating furnace 1 is operated at high-temperature, the external upper surface of the furnace 1 is heated to considerably high temperature. However, by increasing the area of the pool of liquid in the water sealing mechanism described above, a rise in temperature at the ceiling of the heating furnace (outer side) is suppressed and deterioration in the vibrating feeder including the trough 11 can be advantageously prevented.

[0043] For example, when the weir plate 17 is provided near the duct 15, as shown in FIG. 1, only the vicinity of the feeding nozzle 14 is cooled, and thus the distance between the external upper surface of the furnace 1 and the trough 11 cannot be reduced, as described later.

[0044] On the other hand, as shown in FIGS. 2A, 2B, and 3, by forming the pool of liquid over the whole area under the trough 11 corresponding to the width of the ceiling of the furnace, a rise in temperature at the trough 11 above the pool of liquid can be suppressed. In this way, by suppressing a rise in temperature at the trough 11, the distance between the ceiling of the furnace and the trough 11 can be set to be shorter than in the known art.

[0045] That is, when the material 9 on the trough 11 is heated by the heat from the ceiling of the furnace, the quality of the material declines or the trough 11 is deformed by the heat. Thus, in the known art, the trough 11 is placed at a considerable distance from the ceiling of the furnace in order to prevent this problem.

[0046] For example, when metallic iron is produced by using the above-described heating furnace, and when a mixed powder containing a carbonaceous reductant and iron oxide is heated on the trough, the carbonaceous material is vaporized and adheres to the inside of the trough 11. Otherwise, the trough 11 is deformed by heat and therefore the material cannot be fed evenly.

[0047] However, by forming the pool of liquid under the entire area of the trough 11 so as to prevent a rise in temperature at the trough 11, all of the above-described problems can be overcome. In addition, since the distance between the trough 11 and the hearth 2 can be shortened, breaking of lumps due to impact upon dropping and the amount of dust can be reduced.

[0048] The area of the pool of liquid which is formed below the trough 11 and the amount of the liquid may be determined in consideration of various factors such as heat resistance of the material to be fed and the operating conditions of the heating furnace. For example, a decline in quality of the material to be fed can be sufficiently suppressed, depending on the operating conditions, when the pool of liquid is formed below the trough 11, such that the distance between the pool of liquid and the trough 11 corresponds to about half of the width of the ceiling of the furnace.

[0049] More preferably, as described above, the weir plate 17 is formed to surround the area including the trough 11 and the width of the ceiling of the furnace which exists under the trough 11 so that this area is regarded as the pool of liquid. Also, by extending the area of the pool of liquid, the thickness of a fireproof wall of the ceiling of the furnace at the corresponding portion can be reduced. In order to further improve the increased temperature suppressing effect, the amount of liquid (volume) per unit area is preferably increased.

[0050] In order to suppress evaporation of the liquid due to a rise in temperature of the liquid, the liquid in the pool of liquid should be adequately changed. Therefore, as shown in FIGS. 2A and 2B, at least one inlet 21 through which the liquid is fed to the tank including the side surface of the duct 15 and the weir plate 17 and at least one outlet 22 for discharging the liquid are preferably provided, In this way, by providing the inlet 21 and the outlet 22, the liquid can be easily changed, and thus maintenance can be easily performed even in a relatively small space.

[0051] Preferably, the liquid is fed to or discharged from the tank continuously or intermittently in order to prevent a decrease in the cooling effect due to a rise in temperature and a decrease in fluidity of the liquid due to mixing of dust. Also, a flow path or a liquid conveyer may be provided so that the function of the liquid as a cooling medium can be evenly ensured over the whole area,

[0052] The feeding device according to the present invention is not limited to the above-described embodiment, and improvements and modifications are possible without deviating from the fundamental principle of the present invention.

Sealing mechanism of feeding device

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