JPH11222617A - Rotary hearth furnace for producing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the flow rate of exhaust gas exhausted into the atmo sphere, to improve the thermal efficiency by efficiently recovering this sensible heat and to reduce the cost of an equipment and the cost of operation, mainte nance and checking, in a rotary hearth furnace for producing reduced iron. SOLUTION: In the rotary hearth type furnace for producing the reduced iron by reducing iron oxide-containing raw material, several pairs of regenerative heat exchangers which communicate with several pairs of supplying and exhausting gas meansare arranged in the oxidizing atmospheric zone and/or the reducing atmospheric zone in the furnace. The operation for exhausting the high temp. exhaust gas in the furnace through one side of the regenerative heat exchanger in non-heat reserving state and on the other hand, the operation for supplying the air for burning combustion component in the furnace through the other side of the regenerative heat exchanger in heat reserving state, are alternately changed over in each prescribed time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary hearth furnace for the production of reduced iron, and more particularly, to a fine iron ore or an iron furnace containing iron oxide recovered from a blast furnace, a converter or an electric furnace used in an iron making process. The present invention relates to a rotary hearth furnace for producing reduced iron from iron oxide-containing raw materials such as dust.

[0002]

2. Description of the Related Art Conventionally, as a method for reducing iron oxide-containing dust recovered from an iron making process, a method of directly reducing the dust with a rotary kiln and a method of melting and reducing with a shaft furnace have been adopted. However, in the case of a rotary kiln, the material charged in the form of pellets may be powdered during processing,
It is often the case that the operation during the reduction is accumulated in a ring shape inside the kiln and the operation becomes inoperable. In the case of a shaft furnace, a method of kneading dust and coal powder to form pellets and melt-reduce in the furnace, a method similar to what is called a blast furnace, is a method of reducing iron oxide in dust, but once the furnace is started up If it raises, the problem that the furnace cannot be stopped easily like the blast furnace, the treatment of the molten slag generated in the furnace,
There is a problem that the pretreatment process of the input material is complicated, and as a result, the processing cost is increased. For this reason, there is a demand for the development of a method for producing reduced iron by reducing the iron oxide-containing dust at low cost.

[0003] On the other hand, the demand for iron sources has increased with the extension of electric steelmaking, and various methods for producing reduced iron from fine iron ore have been developed to meet the demand. Among them, a reduced iron production process using coal has attracted attention as a method capable of producing reduced iron at low cost. The reduced iron production process using this coal is a method of reducing the iron oxide by pelletizing a mixed powder of fine iron ore and coal and heating it at 1200 to 1450 ° C. in a rotary hearth furnace.

As shown in FIG. 4, the rotary hearth type furnace includes a rotary hearth type furnace main body 1 and a raw material supply system for supplying fine iron ore and coal powder as raw materials into pellets.
An exhaust gas treatment system for treating exhaust gas generated in the furnace main body 1 is provided. Inside the furnace body 1, an oxidizing atmosphere region (heating region) 1a, a reducing atmosphere region (reducing region)
1b and the cooling region 1c are sequentially formed in the direction of rotation of the hearth (counterclockwise as indicated by the arrow in the figure). A burner 2a and a secondary combustion air supply port 3a are provided in the oxidizing atmosphere area 1a, and a burner 2b and a secondary combustion air supply port 3b are provided in the subsequent reducing atmosphere area 1b. A fuel supply line 4 and a combustion air supply line 5 are connected to each of the burners 2a and 2b.
Is supplied. The secondary combustion air supply ports 3a and 3b are supplied with secondary combustion air at 600 to 650C.

In the production of reduced iron, the raw material fine iron ore, coal powder and binder are supplied from a hopper 6a, 6b, 6c of a raw material supply system to a mixer 7 at a predetermined ratio, where they are mixed and homogenized. After pelletizing with a pelletizer 8 and drying the resulting pellets with a drier 9, the pellets are supplied into the furnace body 1. The pellets supplied into the furnace body 1 are generated by the combustion heat of the burners 2a and 2b and the secondary combustion heat of the combustible gas (mainly CO gas) generated from the pellets.
By radiant heating under the atmosphere of 00 to 1450 ° C,
A reduction reaction is performed in the pellets to reduce the iron oxide to metallic iron, and the generated reduced iron is cooled to 1000 to 1200 ° C. and discharged to the outside of the furnace, or the reduced iron is semi-molten to be half-melted. Removed as molten pig iron.

On the other hand, the exhaust gas in the furnace is exhausted out of the furnace through a flue 11 arranged in the oxidizing atmosphere region 1a or the reducing atmosphere region 1b by the action of the suction fan 10 of the exhaust gas treatment system. This exhaust gas is passed from the extraction side to the flue 11
Since the exhaust gas is a mixed exhaust gas of the exhaust gas flowing to the exhaust gas and the exhaust gas flowing from the charging side to the flue 11, the unburned gas in the exhaust gas is burned by air and then discharged from the flue 11. This exhaust gas is cooled to 900 to 1000 ° C. by water spray and then enters the heat exchanger 12 to preheat air to 600 to 650 ° C. The exhaust gas itself is cooled to around 400 ° C. and then sent to the exhaust gas treatment equipment 13. The gas is then desulfurized, dusted and released from the chimney 14 into the atmosphere.

[0007]

However, in the conventional rotary hearth furnace, the exhaust gas is extremely high at 1400 ° C. or more, and cannot be directly supplied to the heat exchanger 12 as it is due to the problem of heat resistance of the heat exchanger 12. Therefore, it is necessary to spray water into the flue 11 with a separately provided water spray device to lower the temperature of the exhaust gas to the heat-resistant temperature of the heat exchanger, for example, 900 to 1000 ° C. Also, there is a problem that water must be sprayed and cooled to about 200 ° C. which is suitable for desulfurization and dust removal in the exhaust gas treatment equipment 13.

For this reason, in the conventional rotary hearth furnace, the heat loss of the exhaust gas is large, and the total heating value of the entire furnace is about 5%.
There is a problem that only about 0% of the heat can be recovered, and the thermal efficiency is extremely low. In addition, the high temperature of the exhaust gas increases the size of exhaust gas cooling equipment such as water spray equipment, and further increases the amount of exhaust gas, which inevitably increases the size of auxiliary equipment such as heat exchangers and exhaust gas treatment equipment. As a result, various costs such as equipment costs, operation costs, and maintenance and inspection costs increase significantly.

Accordingly, the present invention efficiently reduces the sensible heat of the exhaust gas discharged into the atmosphere when producing reduced iron from iron oxide-containing raw materials such as iron oxide-containing dust and fine iron ore using a rotary hearth furnace. The purpose is to improve the thermal efficiency by recovering well, and to reduce equipment costs, operation, maintenance and inspection costs.

[0010]

According to the present invention, there is provided a rotary hearth type furnace for producing reduced iron by reducing an iron oxide-containing raw material, as an means for solving the above-mentioned problems. And / or a plurality of pairs of supply / exhaust means and a plurality of pairs of regenerative heat exchangers communicating with the supply / exhaust means are provided in the reducing atmosphere region, and high-temperature exhaust gas in the furnace is passed through each pair of non-thermal storage heat exchangers. The operation of supplying air for burning the combustible components in the furnace into the furnace through the pair of heat storage heat exchangers in the heat storage state is alternately switched at predetermined time intervals.

The air supply / exhaust means is constituted by a regenerative burner provided in the tuyere or the oxidizing atmosphere area and / or the reducing atmosphere area. When the regenerative burner is used as the air supply / exhaust means, the regenerative burner functioning as the secondary combustion air supply means of the pair of regenerative burners has a necessary amount of air and oxidizing atmosphere region for fuel combustion and The regenerative burner, which is supplied with an amount of air that is combined with the amount of air necessary to combust the combustible gas generated in the reducing atmosphere region, and functions as the other exhaust means, comprises an oxidizing atmosphere region and High temperature exhaust gas is sucked from the reducing atmosphere region and supplied to the non-thermal storage type heat storage heat exchanger. In the case where a plurality of pairs of regenerative heat exchangers are provided in the reducing atmosphere region, the in-furnace high-temperature exhaust gas from the reducing atmosphere region contains a flammable component. It is preferable to burn the oxidized exhaust gas and supply it to the regenerative heat exchanger.

In order to improve the thermal efficiency of the furnace,
It is preferable that exhaust gas in the furnace is exhausted from the oxidizing atmosphere region or the reducing atmosphere region of the furnace, and the exhaust gas is diluted with air, cooled and then supplied to a dryer.

Further, in order not to increase the total amount of exhaust gas from the furnace, the temperature of the furnace exhaust gas discharged from the oxidizing atmosphere region or the reducing atmosphere region of the furnace is diluted with low-temperature exhaust gas having passed through a regenerative heat exchanger and cooled. It is desirable to supply the heat to the heat exchanger for preheating combustion air.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings showing a rotary hearth furnace for producing reduced iron according to the present invention. In the drawings, the same or equivalent members are denoted by the same reference numerals.

FIG. 1 shows a rotary hearth furnace for producing reduced iron according to the present invention.
And a raw material supply system for supplying an iron oxide-containing raw material thereto, and an exhaust gas treatment system for treating exhaust gas from the furnace. An oxidizing atmosphere region (heating region) 1 is provided in the furnace body 1.
a, reducing atmosphere region (reducing region) 1b and cooling region 1
c are formed, and a plurality of burners 2a are provided in the heating region 1a and the reduction region 1b at predetermined intervals in the circumferential direction.
2b are provided respectively. A fuel supply line 4a and a combustion air supply line 5 for room temperature air are connected to each burner 2a in the heating area 1a, and each burner 2a in the reduction area 1b.
A fuel supply line 4b and a combustion air supply line 35 for preheating air are connected to b. The reason why a burner is also provided in the reduction region 1b is that the reduction region 1b is maintained in a reducing atmosphere by incomplete combustion of the combustible gas generated during the heat treatment, but is reduced only by the secondary combustion of the generated gas. This is because a sufficient amount of heat for maintaining the reaction cannot be obtained, which is compensated for.

In the heating area 1a, a plurality of pairs of regenerative heat exchangers (20a) are arranged at predetermined intervals in the circumferential direction of the furnace body 1.
1, 20b1), (20a2, 20b2),... (2
0an, 20bn) are provided in communication with the tuyeres, and a pair of supply / exhaust ducts (21a1, 2a1) are connected to each other via a heat storage medium made of ceramics or other heat-resistant material stored in each heat storage type heat exchanger.
1b1), (21a2, 21b2),... (21an,
21bn). Each pair of supply and exhaust ducts (21a
n, 21bn) are connected to an exhaust gas discharge line 17 via on-off valves V1, V2, respectively, and to an air supply line 18 via on-off valves V3, V4, respectively. The air supply line 18 is provided with a blower 19.

The exhaust gas discharge line 17 is branched into an exhaust system main exhaust line 23 and an exhaust gas dilution system exhaust line 24 via a suction fan 22. The exhaust system main exhaust line 23 is connected to an exhaust system through an exhaust gas flow control valve V5. It is connected to processing equipment 13. The exhaust gas dilution system exhaust line 24 is connected to an air preheating exhaust gas line 25 via an exhaust gas temperature control valve V6. The low-temperature exhaust gas in the exhaust gas dilution system exhaust line 24 is diluted and cooled in the high-temperature exhaust gas in the air preheating exhaust gas line 25 and supplied to the heat exchanger 26, where the air is preheated and then exhausted through the furnace pressure control valve 29. It is mixed with the low-temperature exhaust gas from the system main exhaust line 23, diluted to a predetermined temperature and heated, and supplied to the exhaust gas treatment equipment 13.

The drying air supply line 31 includes flow control valves V8 and V15, a mixer 32 and a suction fan 33,
An exhaust line 30 is connected to the mixer 32, and a high-temperature exhaust gas of 1200 to 1450 ° C. flows from the flue 11 to the temperature control valve V 1.
0. What is the high temperature exhaust gas from the flue 11? The air is supplied to the mixer 32 by the action of the suction fan 33, and the air that flows in through the flow control valve V <b> 8
The temperature is diluted to ℃, and supplied to the dryer 9 as drying air. Although the exhaust line 30 is branched to supply a part of the high-temperature exhaust gas to the heat exchanger 26 via the air preheating exhaust gas line 25, the exhaust lines 25 and 30 may be independent lines. .

In the air preheating heat exchanger 26, the blower 2
7 from 600 to 700 by heat exchange with exhaust gas
° C, and the preheated air is supplied from the combustion air supply line 35 via the flow control valve V9 to the reduction zone 1
b is supplied to each burner 2b and the secondary combustion air supply port 3b. Other configurations such as a raw material supply system and an exhaust gas treatment system are the same as those in FIG. 4 and therefore are omitted in FIG.

In the production of reduced iron from fine iron ore and lime, fine iron ore, coal powder and binder are supplied from a hopper 6a, 6b, 6c to a mixer 7 at a predetermined ratio, and mixed there. Then, the pellets are supplied to a pelletizer 8 to be pelletized, and the pellets are dried by a dryer 9 and supplied into the furnace body 1. Furnace body 1
The pellets supplied into the inside are conveyed counterclockwise by the rotation of the hearth, and 1200 heat is generated by the combustion heat of the burners 2a and 2b and the secondary combustion heat of the combustible gas generated from the pellets themselves.
By being radiantly heated at an ambient temperature of ~ 1450 ° C,
A reduction reaction is performed in the pellets to reduce iron oxide to metal iron, and the generated reduced iron is cooled to 1000 to 12 in the cooling region 2c.
It is cooled down to a predetermined temperature of 00 ° C., and is discharged out of the furnace when the rotary hearth has rotated substantially once.

In the rotary hearth furnace, a plurality of pairs of regenerative heat exchangers (20a1, 20b1), (20a2,
20b2),... (20an, 20bn) are supply / exhaust ducts (21a1, 21b1), (21a2, 21b2) of each pair,
..... (21an, 21bn) and on-off valves V1, V
2, V3, and V4 are used by switching every predetermined time, and the operation at that time is performed by a pair of regenerative heat exchangers (20a1, 20a1).
20b1) will be described as an example.

Now, the on-off valves V1 and V4 are opened, V2 and V
Assuming that 3 is in the closed state, the high-temperature oxidizing exhaust gas in the heating area 1a is discharged to the outside of the furnace through the pair of regenerative heat exchangers 20a1 and the exhaust duct 21a1 by the action of the suction fan 22. The high-temperature oxidizing exhaust gas is absorbed by the heat storage medium in the heat storage heat exchanger 20a1 while passing through the heat storage heat exchanger 20a1, and is cooled to a predetermined temperature (for example, 160 to 180 ° C.). The exhaust gas is exhausted to the exhaust gas discharge line 17 via the on-off valve V 1, and is sent directly to the exhaust gas treatment equipment 13 by the action of the suction fan 10. A part of the low-temperature exhaust gas is mixed with a high-temperature exhaust gas of 1200 to 1450 ° C. in an air preheating exhaust gas line 25 via an exhaust gas dilution system exhaust line 24 and a flow control valve V6,
This is diluted to 900-1000 ° C. medium-temperature exhaust gas, cooled and then supplied to the heat exchanger 26. In the heat exchanger 26, the temperature of the air from the blower 27 is raised to 600 to 650 ° C., and the temperature of the exhaust gas itself is reduced to 400 to 500 ° C., mixed with the low-temperature exhaust gas in the main exhaust line 23 of the exhaust system. Supplied.

At this time, the other regenerative heat exchanger 20 of the pair
b1 is a process in which the air supplied from the blower 19 passes through the regenerative heat exchanger 20b1 because the internal heat storage medium is in a heat storage state, and the on-off valve V4 is open and the on-off valve V2 is closed. Heat from the heat storage medium at a temperature of 1100
The temperature is raised to １２1250 ° C. and supplied directly to the heating area 1a. For this reason, in the initial rising stage, the fuel such as natural gas or heavy oil is burned by the burner 2a and heated in the heating region 1a.
It is necessary to maintain the temperature of the heating area 1a only by the secondary combustion of the combustible gas component generated from the pellets after the entire facility has established a predetermined temperature pattern and entered the steady state. May be possible, so in that case,
It is not necessary to keep burning the burner 2a in the heating area 1a.
Accordingly, during the steady operation, the flow control valve V12 of the fuel supply line 4a and the flow control valve V7 of the combustion air supply line 5 may be closed to stop the combustion of the burner 2a, so that the fuel consumption can be significantly reduced.

The heat storage medium inside the heat storage type heat exchanger 20a1 is in a non-heat storage state, absorbs heat from the high-temperature exhaust gas, rises in temperature over time, and has the other heat storage type heat exchanger 2a.
The heat storage medium inside Ob1 is in a heat storage state and is deprived of heat by air, so that the temperature falls with the passage of time. After a lapse of a predetermined time (for example, 30 to 60 seconds) from the start of heat absorption of the regenerative heat exchanger 20a1 (the start of heat release in the regenerative heat exchanger 20b1), the on-off valves V1 and V4 are closed from open to closed by control means (not shown). V2 and V3 are switched from closed to open.
As a result, one regenerative heat exchanger 20a1 is switched from the non-thermal storage state to the thermal storage state, and the other regenerative heat exchanger 20b1 is switched from the thermal storage state to the non-thermal storage state, and the operation opposite to the above case is repeated. Further, the above operation is performed in parallel with another pair of regenerative heat exchangers or with a certain time difference.

Therefore, the sensible heat of the high-temperature oxidizing exhaust gas from the heating area 1a in the furnace body 1 is temporarily absorbed by the heat storage medium of the heat storage type heat exchanger, and the heat absorbed by the heat storage medium is fresh. As a result of being recovered by the air and being returned to the furnace, the heat loss can be reduced by lowering the outlet temperature of the regenerative heat exchanger of the exhaust gas. The temperature of the exhaust gas at the outlet of the heat storage type heat exchanger can be arbitrarily set depending on the heat capacity of the heat storage medium and the set time of switching from the non-heat storage state to the heat storage state or vice versa, but corresponds to the SO3 content in the exhaust gas. It is preferable to secure the acid dew point or higher.

On the other hand, the exhaust gas in the furnace body 1 joins in the flue 11 part, and the unburned gas in the exhaust gas is burned by the excess oxygen in the heating area 1a, while the flue gas is operated by the suction fan 10 of the exhaust gas treatment system. The gas is exhausted out of the furnace through 11.

1200 to 1450 ° C. after leaving the flue 11
Is mixed with the low temperature exhaust gas of the exhaust gas dilution system exhaust line 24 as described above,
After the temperature of the exhaust gas is reduced to 0 ° C., the exhaust gas is sent to the heat exchanger 26 where the air from the blower 27 is preheated to 600 to 650 ° C., and the exhaust gas itself cools to around 400 ° C. After being cooled to a temperature required by the exhaust gas treatment facility 13, the mixture is sent to the exhaust gas treatment facility 13.

Therefore, in the furnace according to the present invention, most of the sensible heat of the high-temperature exhaust gas is recovered, and is effectively used as heat for heating the primary combustion air, the secondary combustion air, and the pellet drying air. . Incidentally, a rotary hearth furnace for producing reduced iron having the above-described configuration according to the present invention, and about 600 to 650
FIG. 2 shows the results of measuring the temperature change when the pellets were heated using a conventional rotary hearth furnace for producing reduced iron, in which preheated air of ° C. was supplied as primary air and secondary air. In the figure, a curve A represents a change in gas temperature in a heating area in the furnace according to the present invention, a curve B represents a change in the temperature of the pellet in the heating area, and a curve C represents the temperature of the pellet in the heating area in the conventional furnace. The changes are shown respectively.

As is apparent from the figure, in the present invention, since the secondary combustion air is supplied to the heating area by heating to about 1200 ° C. by the regenerative heat exchanger, the pellets at normal temperature are 1200
The heating time until the temperature rises to about 1.15 minutes is about 15% shorter than the conventional 1.5 minutes. Therefore, in the conventional furnace, from the start of heating until the complete reduction is completed, 8 to
Although 10 minutes were required, the heating time is shortened, so that the required time can be shortened by 3.5 to 4.4%.

In the above embodiment, an example in which a plurality of regenerative heat exchangers are provided in the heating area has been described. However, a plurality of pairs of regenerative heat exchangers may be provided in the reducing area. In this case, it is desirable to provide a post-combustion chamber between each regenerative heat exchanger and the furnace main body, supply air to the post-combustion chamber, perform afterburning, and then supply high-temperature exhaust gas to the regenerative heat exchanger. In this way, even if the exhaust gas from the reduction region contains iron dust, it is possible to prevent the unburned components in the exhaust gas from burning in the post-combustion chamber, and at the same time, prevent the iron dust from being oxidized and fused to the heat storage medium. In addition, there is no possibility that the heat storage medium is blocked. In addition, flue 1
A portion of the hot exhaust gas from 1 is drawn into the mixer 32 by the action of the suction fan 33, where drying air is added directly and at a temperature suitable for drying the pellets, for example,
After the temperature is reduced to 380 ° C., the pellets are supplied to the dryer 8 to dry the pellets. The outlet gas of the dryer 8 is preferably supplied to the cooling area as cooling air.

FIG. 3 shows another embodiment of the rotary hearth type furnace for producing reduced iron according to the present invention, in which a regenerative burner integrally provided with a regenerative heat exchanger instead of a tuyere as a supply / exhaust means. It is what it was.

In the heating area 1A and the reduction area 1b,
A plurality of pairs of regenerative burners (40A ₁ , 40B ₁ ) on the inner and outer side walls of the furnace body 1 at predetermined intervals in the circumferential direction thereof,
(40A ₂ , 40B ₂ ), ... (40A _n , 40B _n )
Are arranged. Each regenerative burner (40A _n , 40B _n )
Are regenerative heat exchangers (41
A ₁ , 41B ₁ ), (41A ₂ , 41B ₂ ) (41)
A _n , 41B _n ) and a pair of supply and exhaust ducts (42A ₁ , 42A
B ₁ ), (42A ₂ , 42B ₂ ),... (42A _n , 4
2B _n ). Each pair of supply / exhaust ducts has an on-off valve (VA ₁ ... VA _n , VC _1.
C _n ) and an on-off valve (VB _1.
· · · · · VB _n, are connected to _{VD 1, VD 2 ······ VD n} ) air supply line 18 via the. Moreover, each regenerative burner (40A ₁ ... 40A _n , 40
B ₁ ······ 40Bn) is off valve (VEA ₁ · · · · · ·
VEB _n , VEB ₁ ... VEB _n ). The other configuration is the same as that of FIG. 1, and the description is omitted.

In use, while one regenerative burner of each pair is burning with the high-temperature air heat-exchanged in the regenerative heat exchanger, the other regenerative burner is an exhaust port for discharging high-temperature exhaust gas in the furnace. The sensible heat of the high-temperature exhaust gas is stored in the heat storage medium inside the heat storage heat exchanger of the heat storage burner. That is, the burners 40A ₁ , 40A ₂ ,...
· 40A _n is in the combustion, the burner 40B ₁ of the B series, 40B ₂ ·
· · · · · 40B _n is assumed to be in the exhaust, will be described with a pair of regenerative burners 40A _1, 40B ₁ as an example, on-off valve in the fuel supply line 4 VEA ₁ is opened, VEB ₁ is closed in-off valve of the air supply line 17 VB ₁ is opened, VD ₁ is in the closed-off valve of the exhaust gas discharge line 17 VA ₁ is closed, VC ₁ is in the open state. Accordingly, the fuel gas is supplied via an on-off valve VEA ₁ in regenerative burners 40A _1, air is supplied via an on-off valve VB ₁ and regenerative heat exchangers 41A _1. The air supplied to the regenerative heat exchanger 41A _1, the inside of the heat storage state is the heat storage medium and exchanging heat supplied is heated to a temperature close to the furnace temperature, where the fuel gas is burned in the furnace Heat. At this time, the amount of air supplied to the regenerative burner 40A ₁ is the sum of the amount of air necessary for burning a combustible gas component generated in the stoichiometric amount and the furnace required for combustion.

[0034] At this time, the other regenerative burner 40B ₁ of the regenerative burner 40A ₁ and pair hot exhaust gas sucked from the furnace by the action of the suction fan 22, the high-temperature exhaust gas regenerative heat exchanger 41B ₁ deprived of heat in the heat storage medium in a non-heat storage state in the process of passing through the, is exhausted to the exhaust gas discharge line 17 via an on-off valve VC ₁ becomes 200 ° C. or less of the low temperature exhaust gas.

When the set time has elapsed, the fuel supply line 4
The on / off valve of the air supply line 18 and the on / off valve of the exhaust gas discharge line 17 are switched to switch between combustion and exhaust, and the above operation is performed. Therefore, in the present embodiment, as in the embodiment of FIG. 1, the sensible heat of the high-temperature oxidizing exhaust gas from the heating area 1a in the furnace main body 1 is temporarily absorbed by the heat storage medium of the heat storage type heat exchanger. After that, the heat absorbed by the heat storage medium is recovered by fresh air and returned to the furnace, so that heat loss can be significantly reduced.

[0036]

As described above, the present invention relates to a rotary hearth type furnace for producing reduced iron from iron oxide-containing raw materials such as fine iron ore and ironmaking dust. A plurality of pairs of regenerative heat exchangers are provided in the region through a plurality of pairs of supply / exhaust means, and high-temperature exhaust gas in the furnace is exhausted through each pair of regenerative heat exchangers in a non-thermal storage state, while the heat storage of the pair is performed. Since the air for burning the flammable atmosphere through the regenerative heat exchanger in the state is supplied to the furnace alternately at predetermined time intervals,
The following excellent effects can be obtained.

(1) The sensible heat of the high-temperature exhaust gas in the oxidizing atmosphere region or the reducing atmosphere region is mostly absorbed by the heat storage medium when passing through the heat storage type heat exchanger, and the heat is supplied to the heat storage medium. Absorbed by air, 1100-1250
℃ high-temperature air is supplied into the furnace, so that more than 90% of the sensible heat of the high-temperature exhaust gas in the oxidizing atmosphere region or the reducing atmosphere region can be recovered, and the residual sensible heat of the exhaust gas in the discharge line Can also be effectively used in the exhaust gas treatment equipment, so that heat loss can be significantly reduced.

(2) Since the air supplied to the heating area is almost the same as the furnace temperature, the amount of heat required to maintain the furnace temperature at the set temperature is the combustion heat of the combustible gas component generated during heating. The cost of supplementary fuel can be significantly reduced.

(3) Since the secondary combustion air is supplied by heating to about 1200 ° C. in the regenerative heat exchanger, the heating time can be shortened.

(4) As in the case of the heating zone, by providing a regenerative heat exchanger in the reduction zone and using it by switching every predetermined time, the heat loss from the heating zone can be reduced.

(5) A part of the exhaust gas discharged from the heating area or the reduction area is diluted and cooled with low-temperature exhaust gas from the exhaust duct to be used as a heat source for a heat exchanger for preheating combustion air, while the remaining exhaust gas is reduced. Since the air is directly mixed and used as drying air for the pellet dryer, almost 100% of the sensible heat of the exhaust gas from the flue can be used.

(6) For cooling the exhaust gas from the flue, a water spraying device, which was conventionally required, becomes unnecessary, and the equipment exposed to a high temperature requires a dry air supply line blower (400 ° C.).
(Before and after), the risk due to equipment damage can be significantly reduced.

(7) The only equipment requiring power is a blower or suction fan, and the running cost of the equipment can be significantly reduced.

(8) The heat exchanger for preheating air can appropriately set the temperature of the exhaust gas from the stack by adjusting the mixing ratio with the low-temperature exhaust gas from the regenerative heat exchanger. Since it is not required and does not require a water spray device for cooling the exhaust gas, it is possible to simplify the entire equipment without reducing the total amount of the exhaust gas, and to reduce the equipment cost and the maintenance and inspection cost.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a rotary hearth furnace for producing reduced iron showing one embodiment of the present invention.

FIG. 2 is a diagram showing a temperature change of a pellet in a furnace heating area according to the present invention and a conventional example.

FIG. 3 is an explanatory view of a rotary hearth furnace for producing reduced iron according to another embodiment of the present invention.

FIG. 4 is an explanatory view of a conventional rotary hearth furnace for producing reduced iron.

[Explanation of symbols]

1: Furnace body 1a: Oxidizing atmosphere area (heating area) 1b: Reducing atmosphere area (reducing area) 1c: Cooling area 11: Flue 9: Dryer 20a1, 20a2, 20an: Regenerative heat exchanger 20b1, 20b2, 20bn: regenerative heat exchanger 21a1, 21b1: exhaust duct 23: exhaust system main exhaust line 24: exhaust gas dilution system exhaust line 25: exhaust gas line for preheating air 26: heat exchanger V1, V2, V3, V4: open / close valve 30 : Exhaust duct 31: Drying air supply line 32: Mixer 40A ₁ ,... 40A _n : Regenerative burner 40B ₁ ,... 40B _n : Regenerative burner 41A ₁ ,. ... 41A _n : regenerative heat exchanger 41B ₁ , ... 41B _n : regenerative heat exchanger

Claims (4)

[Claims] 1. A rotary hearth furnace for producing reduced iron by reducing an iron oxide-containing raw material, wherein a plurality of pairs of supply / exhaust means and said supply / exhaust means are provided in an oxidizing atmosphere region and / or a reducing atmosphere region of the furnace. A plurality of pairs of regenerative heat exchangers communicating with each other, and exhausting the high-temperature exhaust gas in the furnace through each pair of regenerative heat exchangers in a non-thermal storage state, while the furnace passes through the pair of regenerative heat exchangers in a thermal storage state. A rotary hearth furnace for producing reduced iron, wherein an operation of supplying air for burning combustible components in the furnace is alternately switched at predetermined intervals. 2. The method according to claim 1, wherein a combustible component contained in the in-furnace high-temperature exhaust gas discharged from the supply / exhaust means is burned with air to form an oxidizing exhaust gas and then supplied to a regenerative heat exchanger. The rotary hearth furnace according to claim 1 for producing reduced iron. 3. The furnace according to claim 1, wherein exhaust gas in the furnace is exhausted from an oxidizing atmosphere region or a reducing atmosphere region of the furnace, and the exhaust gas is diluted with air and cooled, and then supplied to a dryer. 2. The rotary hearth furnace for producing reduced iron according to 2. 4. The furnace exhaust gas discharged from the oxidizing atmosphere region or the reducing atmosphere region of the furnace is diluted and cooled by low-temperature exhaust gas passing through a regenerative heat exchanger, and is supplied to a heat exchanger for preheating combustion air. The rotary hearth furnace for producing reduced iron according to claim 3, characterized in that: