JPH11337264A - Rotary hearth furnace - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To eliminate the increase in equipment cost and the difficulty of transporting pellets. SOLUTION: A rotatable hearth 2 is provided, and raw pellets P charged from a charging inlet 51 are supplied and mounted on the hearth 2 and sent to a pre-tropical zone 42. Hearth 2 in Pre-Tropical 42
The moisture and gasification components inside the raw pellet P are gently evaporated and vaporized under a low temperature caused by the residual heat, and the raw pellet P is dried without explosion or the like. The dried pellet P is heated 43
, And is sent to the reduction zone 45 via the intermediate zone 44 to be subjected to a reduction process. The pellets P subjected to the reduction treatment are discharged out of the furnace through the outlet 52 by the screw conveyor 53.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a rotary hearth furnace,
Particularly, the present invention relates to a rotary hearth furnace suitable for heat treatment of a material to be processed such as raw pellets.

[0002]

2. Description of the Related Art In order to reuse steelmaking dust and fine ore, a binder and a reducing agent are mixed into steelmaking dust and the like, kneaded, granulated into raw pellets, and supplied to a rotary hearth furnace. Then, heat treatment such as heating and reduction is performed.
In this case, when the raw pellets are directly supplied to the rotary hearth furnace and rapidly heated, the internal pressure of the raw pellets rises rapidly due to the vaporization and expansion of moisture and gasification components contained therein, which may cause explosion. Therefore, in order to avoid this, a drying device for drying the raw pellets at a relatively low temperature is often provided at the subsequent stage of the granulator.

[0003]

However, the provision of a drying apparatus causes an increase in equipment cost, and the pellets after drying become brittle, so that the pellets may be broken during transportation to a rotary hearth furnace. In order to prevent this, there is a problem that attention must be paid to handling during transportation.

Accordingly, an object of the present invention is to solve such a problem, and an object of the present invention is to provide a rotary hearth furnace which eliminates an increase in equipment cost and a difficulty in transporting a material to be processed.

[0005]

According to a first aspect of the present invention, there is provided a hearth that rotates and moves,
The material to be treated (P) charged and supplied from the charging port (51) is placed on the hearth (2) and moved to the heat treatment zone (43, 44, 45) for heat treatment. In a rotary hearth furnace in which the material to be processed is moved to the discharge port (52) and discharged, the undried material to be processed (P) immediately after charging is preheated by the residual heat of the hearth (2). The tropics (42) are provided before the heat treatment zones (43, 44, 45).

In the first aspect of the invention, the undried material supplied from the charging inlet to the pre-tropical zone of the rotary hearth furnace is preheated at a relatively low temperature by the residual heat of the hearth, and the internal moisture and gas are removed. After the vaporized components are slowly evaporated and vaporized and dried without explosion, they are sent to a high-temperature heat treatment zone. Therefore,
Since the hearth residual heat is effectively used, and there is no need to provide a separate drying furnace outside the rotary hearth furnace, the increase in equipment cost is suppressed, and materials that become brittle when dried are handled outside the furnace. The difficulty of doing so is also eliminated.

In the second invention, an auxiliary burner (64) is provided in the pre-tropical zone (42). According to this, when the temperature of the pre-tropical zone does not rise sufficiently only by the residual heat of the hearth, the insufficient amount of heat can be compensated for by the relatively small auxiliary burner.

[0008] In the third invention, in the pre-tropical zone (42),
An exhaust port (7) for discharging exhaust gas from the heat treatment zone (43, 44, 45) to the outside of the furnace is provided. According to this, while the high-temperature gas generated in the heat treatment zone goes to the exhaust port of the pre-tropical zone, the insufficient heat of the pre-tropical zone is supplemented by the high-temperature gas, and the temperature of the pre-tropical zone is raised to an appropriate temperature. When the amount of heat of the high-temperature gas is sufficient, it is not necessary to provide an auxiliary burner.

In the fourth aspect of the present invention, exhaust ports (7, 7 ') for discharging exhaust gas to the outside of the furnace are provided in the pre-tropical zone (42) and the heat treatment zones (43, 44, 45). Note that the exhaust port (7 ') of the heat treatment zone is preferably provided at a position near the pre-tropical zone (42), for example, in the heating zone (43) constituting the heat treatment zone. According to this, the temperature of the pre-tropical zone can be controlled by adjusting the amount of exhaust gas discharged from each exhaust port of the pre-tropical zone and the heating zone to the outside of the furnace, so that more effective heat treatment can be performed.

[0010] The reference numerals in parentheses indicate the correspondence with specific means described in the embodiment described later.

[0011]

(First Embodiment) FIG. 1 shows a horizontal section of a rotary hearth furnace according to a first embodiment of the present invention, and FIGS. 2 and 3 show vertical sections thereof. The rotary hearth furnace 1 has inner and outer peripheral walls 11 and 12 of concentric circular shape (FIG. 1), and inner and outer peripheral walls 11 and 12, a bottom wall 13 and a top wall 14 (FIGS. 2 and 3).
Thereby, the furnace space S having a rectangular closed cross section is formed in an annular shape. The hearth 2 is located on the bottom wall 13 with a small gap formed between the inner and outer peripheral walls 11, 12.
And is supported on the bottom wall 13 by wheels 21 provided at inner and outer positions on the bottom surface at intervals in the circumferential direction. The hearth 2 is rotated in the direction of the arrow in FIG. 1 by a drive mechanism (not shown). Hearth 2
The upper surface is concave except for both side edges (FIGS. 2 and 3),
Here, the pellets P as the material to be processed are stacked and mounted.

The rotary hearth furnace 1 is provided with curtain walls 31 to 35 (FIG. 1) at a plurality of positions in the circumferential direction. The curtain walls 31 to 35 have their peripheral edges fixed to the inner surface of the top wall 14 and the inner surfaces of the upper halves of the peripheral walls 11 and 12 (FIG. 3), and hang down to just above the hearth 2. As shown in FIG. 1, each region is divided into a plurality of regions in the circumferential direction by the walls 31 to 35, and each region is provided with a supply / discharge chamber 41 and a pre-tropical zone 42 in the rotation direction of the hearth 2, and a heating zone 43 as a heat treatment zone, respectively. , An intermediate zone 44 and a reduction zone 45.

In the supply / discharge chamber 41, a rectangular entrance 51 extending in the width direction of the top wall 14 close to the curtain wall 31 is opened. On the other hand, the outer peripheral wall 1 substantially at the center of the supply / discharge chamber 41
2, a discharge port 52 is opened, and a screw conveyor 53 penetrates the discharge port 52 and crosses directly above the hearth 2. The screw conveyor 53 is driven to rotate by a motor 54 provided outside the furnace. The heating zone 43, the intermediate zone 44, and the reduction zone 45 are provided with a required number of burners 61 to 63 on the inner and outer peripheral walls 11 and 12, respectively. The gas is burned to generate heat sufficiently, and its ambient temperature is about 1100 ° C.

Each burner 62 in the intermediate zone 44 has an air-fuel ratio of 0.1.
The fuel gas is burned at 98 to 1.0 to form a slightly reducing atmosphere, and the atmosphere temperature is about 1250 ° C. Further, in each burner 63 of the reduction zone 45, the fuel gas is burned at an air-fuel ratio of 0.85 to 1.0 and O2
While the unburned gas such as CO and H2 is generated, and a reducing atmosphere of about 1250 ° C. is obtained. In the present embodiment, as described above, since the intermediate zone 44 is located between the heating zone 43 and the heating zone 43, it is possible to reliably prevent the oxidizing gas in the heating zone 43 from entering the reduction zone 45. The heating zone 43 is provided with an exhaust port 7 on the top wall 14 near the curtain wall 32 (FIG. 2), and the oxidizing gas generated in the heating zone 43 is discharged from the exhaust port 7 as a matter of course.
The reducing gas generated in the intermediate zone 44 and the reduction zone 45 is also heated in the heating zone 4.
3, where it is burned and contributes to the temperature rise of the heating zone 43, and then discharged from the exhaust port 7.

Here, no burner is provided in the pre-tropical zone 42, but the residual heat of the hearth 2 heated while moving to the heating zone 43, the intermediate zone 44, and the reduction zone 45 causes the pre-tropical zone 4.
2 is an appropriate temperature of 600 ° C. or less (for example, 50 ° C.).
(About 0 ° C).

In the rotary hearth furnace 1 having such a structure,
The spherical raw pellets P made from steelmaking dust and the like charged into the furnace from the charging inlet 51 are dropped and supplied onto the hearth 2, and are leveled at the lower edge of the curtain wall 31 as the hearth 2 moves. Thus, they are stacked and placed almost uniformly on the entire upper surface of the hearth 2.
The raw pellets P are transported to the pre-tropical zone 42, where 600
Heated at a low temperature of not more than ℃, moisture and gasified components inside are slowly evaporated and vaporized, and dried without explosion or the like.

The dried pellets P are heated in the heating zone 43 and the temperature thereof is sufficiently raised, and reaches the reduction zone 45 through the intermediate zone 44. The pellets are reduced by the reducing atmosphere and the reducing material contained in the pellets P. The metal oxide in P is reduced to a metal. The pellets P after the reduction treatment are supplied to the supply / discharge chamber 4
1 and the outlet 52 by the screw conveyor 53.
From the furnace.

(Second Embodiment) When the temperature rise of the pre-tropical zone 42 is not sufficient only by the residual heat of the hearth 2, as shown in FIG. 4, an auxiliary burner 64 is provided to compensate for the insufficient heat quantity. It is good to

(Third Embodiment) When the temperature rise of the pre-tropical zone 42 is not sufficient only by the residual heat of the hearth 2, the exhaust port may be further provided in the pre-tropical zone 42 as shown in FIG. good. According to this, the high-temperature gas generated in the heating zone 43 passes through the curtain wall 32 and goes to the exhaust port 7 of the pre-tropical zone 42, during which the insufficient heat of the pre-tropical zone 42 is supplemented by the high-temperature gas. In this case, it is not necessary to provide the auxiliary burner 64.

(Fourth Embodiment) When the temperature rise of the pre-tropical zone 42 is insufficient only by the residual heat of the hearth 2, the exhaust ports 7, 7 'are connected to the pre-tropical zone 42 and the heating zone as shown in FIG. 43 respectively. If an exhaust gas flow control valve is provided at each exhaust port 7, 7 'to control the amount of exhaust gas from the pre-tropical zone 42 and the heating zone 43, the atmospheric temperature of the pre-tropical zone 42 can be controlled to a desired value. And more effective heat treatment can be performed.

In the above embodiments, raw pellets such as steelmaking dust are given as an example of the material to be treated, but the present invention is not limited to this. The configuration of the heat treatment zone including the heating zone, the intermediate zone, and the reduction zone in each of the above embodiments is merely an example.

[0022]

As described above, according to the rotary hearth furnace of the present invention, it is possible to eliminate the increase in equipment cost and the difficulty in transporting the material to be processed.

[Brief description of the drawings]

FIG. 1 is an overall horizontal sectional view of a rotary hearth furnace according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line II-II of FIG.

FIG. 3 is a sectional view taken along the line III-III in FIG. 1;

FIG. 4 is an overall horizontal sectional view of a rotary hearth furnace according to a second embodiment of the present invention.

FIG. 5 is an overall horizontal sectional view of a rotary hearth furnace according to a third embodiment of the present invention.

FIG. 6 is an overall horizontal sectional view of a rotary hearth furnace according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 ... rotary hearth furnace, 2 ... hearth, 31, 32, 33, 34,
35: curtain wall, 41: supply / discharge chamber, 42: pre-tropical zone, 43: heating zone, 44: middle zone, 45: reduction zone, 51
… Inlet, 52… outlet, 53… screw conveyor,
61, 62, 63 ... burner, 64 ... auxiliary burner, 7, 7
exhaust port.

Claims (4)

[Claims] An object having a rotatable hearth is placed on the hearth and transferred to a heat treatment zone for heat treatment, and a heat treatment is performed after the heat treatment. In a rotary hearth furnace in which the material is moved to the outlet and discharged, a pre-tropical zone for preheating the undried material to be processed immediately after charging by the residual heat of the hearth is placed before the heat treatment zone. A rotary hearth furnace provided. 2. The rotary hearth furnace according to claim 1, wherein an auxiliary burner is provided in the pre-tropical zone. 3. The rotary hearth furnace according to claim 1, wherein an exhaust port for discharging exhaust gas from the heat treatment zone to the outside of the furnace is provided in the pre-tropical zone. 4. The rotary hearth furnace according to claim 1, wherein an exhaust port for discharging exhaust gas to the outside of the furnace is provided in each of the pre-tropical zone and the heat treatment zone.