JPH11279611A - Method for rapidly reducing iron oxide in rotary hearth heating furnace and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for rapidly and efficiently reducing iron oxide in a rotary hearth heating furnace (RHF) and an apparatus therefor. SOLUTION: Compacts 32 are supplied on the furnace hearth of the RHF 34 in the depth at no more than two layers and exposed at about 1315 - about 1430 deg.C with a radiation heat source for about 1-3 min in a first period to remove all volatile matter. Then, the compacts are charged in the oxidizing atmosphere, in which sufficient quantity of free oxygen exists, and a large part of combustible gas generated from the compact 32 is burnt and also, combustion gas is generated. Successively, the compact is exposed at about 1310 - about 1430 deg.C with the radiation heat source in the atmosphere, in which the free oxygen does not exist, for about 3-9 min in a second period and metallized. The metallized iron product is producted and discharged so that the gas and the compact 32 is fluidized as the parallel current during the first period and as the counter current during the second period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for rapidly and efficiently reducing iron oxide in a rotary hearth heating furnace.

[0002]

2. Description of the Related Art Conventionally, all patents and documents covering technologies for directly reducing iron oxide in a rotary hearth (Heat Fast, Inmetco and Zia) are disclosed in a rotary hearth heating furnace (hereinafter, referred to as "heat furnace").
Also called RHF. ) Low to medium temperature (about 1
(Less than 315 ° C.) and dry and devolatilize the pellets to avoid exfoliation of the pellets. This method has the disadvantage that productivity is reduced because the pellets require a long time to reach the minimum reduction temperature.

[0003] Table 1 shows U.S. patents which the applicant has known about a rotary hearth heating furnace used for direct reduction of iron ore.

[0004]

[Table 1]

US Patent No. 3,443,9 to Beggs
No. 31 discloses a method for metallizing iron oxide compacts containing carbonaceous materials. The compact is molded, dried and pre-cured to a temperature between 1600 and 1800 ° F. (° C.). The pellet is then rapidly heated by exposure to a radiant heat source. The radiant heat source is 230
An environment is created for a sufficient time such that a liquid phase forms within the compact at a temperature between 0 and 2600 ° F. (° C.).
As the liquid phase forms, the compact tends to shrink and is then immediately exposed to a cooling environment and cooled.

US Pat. No. 3,452,9 to Beggs
No. 72 discloses an apparatus for a refractory hearth containing wustite (FeO) as a composition and a production method thereof. The hearth, the subject of which is used in particular for the treatment of iron oxide containing raw materials, can support the raw materials during the reduction process so that the raw materials are not destroyed.

US Pat. No. 3,836,35 to Holly
No. 3 discloses a method for recovering iron and impure oxides from steel mill dust, where the dust is first mixed with finely ground coke and then the mixture is pelletized. The uncured pellets thus formed are placed on a burnt pellet layer on a rotary hearth. The rotary hearth transports the pellets sequentially, the pellets first passing through a drying zone, and then in the initial heating zone, the temperature of the pellets is gradually raised to the coke ignition point. Then, the temperature of the pellet in the impurity removal region is rapidly increased to a temperature at which impurities of zinc, lead, and sulfur evaporate, and these impurities are carried away and recovered as an oxide. And
Eventually, the temperature of the pellet is further raised to a sufficient temperature in the re-oxidation and hardening region, and the pellet is held for a sufficiently long time. To form a bonded pellet.

[0008] Heinwald et al., US Patent No. 4,5
No. 97,564 discloses a rotary hearth in which a horizontal plane having an upper surface formed of coarse granular refractory material, preferably hardened dolomite grains, is rotated.

US Pat. No. 4,62, McDagol et al.
No. 2,905 shows an improvement in a direct flame type rotary hearth heating furnace using a fuel burning with a bright flame such as coal, in which a refractory is disposed on the upper surface of an impermeable rotary hearth. .

US Patent No. 4,636,1 to Orano et al.
No. 27 shows a countercurrent liquid-cooled conveying screw. The screw is suitable for furnace applications and has an outer shaft that circumscribes and circumscribes the inner cylinder. A plurality of hollow liquid cooling blades are attached to the outer shaft, and circulate as a refrigerant and a liquid flowing in the screw. The coolant flows first through the blades and then through the outer shaft, and is then discharged through the inner cylinder.

U.S. Pat. No. 4,676,674 to Purgeter
No. 741 discloses a moving hearth heating furnace heated by radiation with an auxiliary supply means. This auxiliary supply means is arranged between the initial supply point and the final unloading point,
Increasing the volume of processed material supplied to the furnace. If the processed material is iron oxide pellets and a carbonaceous reducing agent, the reduced iron is exposed to a fossil fuel combustion type atmosphere by providing an auxiliary supply means at almost the middle point along the moving path of the hearth. To prevent re-oxidation and increase the uniformity of the product.

Kaneko et al., US Pat.
No. 14 discloses a method for producing iron from finely pulverized iron oxide, and includes the following steps (1) to (7). (1) Mixing iron oxide or iron ore with finely ground coal and binder to form a mixture. (2) The mixture is formed into a lump by compression and pelletization, or the mixture is briquetted into a lump or pellet. (3) The pellets are introduced into a rotary hearth heating furnace to preliminarily reduce iron in the pellets. (4) The pre-reduced pellets are introduced as a metal injection component into a smelting reduction vessel. (5) The atomized carbonaceous fuel and oxygen are introduced from the bottom of the smelting reduction vessel and reacted with the melt and the bath in the vessel to reduce iron to iron element and to remove exhaust gas containing CO and H _2. Generate. (6) The exhaust gas is introduced as a processing gas into a rotary hearth heating furnace, and the pellets inside are preliminarily reduced. (7) Withdraw high-temperature metal from the smelting reduction vessel.

[0013] The pre-reduced compact is preferably discharged at least 1000 ° C from a rotary hearth furnace into a smelting reduction vessel to form a molten iron product.

No. 5,186, Kotoraba et al.
No. 741 discloses a process for regenerating pellets, which includes lignit furnace dust, coal, charcoal, lignite and other low quality coal (lignit).
e) to form uncured pellets, which are a mixture of carbonaceous raw materials such as petroleum coke or coke and organic binders.
The uncured pellets are supplied on a burned pellet layer on a rotary hearth heating furnace, and the hearth sequentially transports the pellets through a drying and coking area to dry the pellets and to remove the pellets from the carbonaceous material. Eliminate volatiles. Thereafter, the pellets are exposed to a higher temperature while moving through the reduction zone, and the contained iron oxide is reduced, and the remaining substances and zinc, lead, and cadmium oxide in the pellets are reduced, volatilized, and reoxidized, and the exhaust gas Exhausted as oxides in. The reduced pellets are finally conveyed to the discharge area and discharged from the rotary hearth heating furnace. Kotoraba et al. Also discloses an apparatus for performing such processing.

[0015]

SUMMARY OF THE INVENTION It is a primary object of the present invention to provide an improved method for rapidly and efficiently reducing iron oxide in a rotary hearth furnace.

Another object of the present invention is to provide a means for dividing the rotary hearth gas stream into two parts, rather than accumulating and projecting the gas in a supply area where dust is most likely to be introduced.

Another object of the present invention is to reduce the ceiling height in the initial heating area of the rotary hearth heating furnace to increase the radiant heat transfer to the compact layer on the hearth.

Another object of the present invention is to provide a rotary hearth heating furnace apparatus in which volatile substances emitted from a compact stay for a longer time and can be more easily burned.

Another object of the present invention is to provide a rotary hearth heating furnace that achieves more efficient combustion than previously available, thereby reducing the volume of gas that needs to be cleaned. As much as possible.

Another object of the present invention is to provide a rotary hearth heating furnace in which the direction of gas at the outlet of the heating furnace is separated from the hearth, not from the direction crossing the hearth toward the side wall. That is.

Another object of the present invention is to provide a rotary furnace provided with an in-furnace gas outlet having a size sufficient to reduce the gas flow rate, so that the captured fine particles fall back onto the hearth by gravity and fall. It is to provide a floor heating furnace.

Still another object of the present invention is to provide a rotary hearth heating furnace which improves atmosphere control at the hearth level and prevents oxidation of metallic iron.

Another object of the present invention is to provide a rotary hearth furnace apparatus which produces highly metallized iron with a lower carbon content.

Another object of the present invention is to realize an improvement in a rotary hearth heating furnace which improves energy efficiency by preheating part of the fuel in the rotary hearth heating furnace using the sensible heat of the metallized compact. It is to be.

Another object of the present invention is to provide a rotary hearth heating furnace which can operate with a very short residence time of 4 to 10 minutes.

It is another object of the present invention to provide a rotary hearth furnace which prevents any disturbances in the carbon monoxide protective blanket generated from the compact in the final stage of reduction.

It is another object of the present invention to provide a rotary hearth heating furnace wherein at least one percent of the excess carbon component remains in the metallized compact.

[0028]

SUMMARY OF THE INVENTION To achieve the above and other objects, a method of producing iron by direct reduction from a dry compact comprising iron oxide, a carbonaceous material, and a volatile material according to the present invention. Providing said compact at a depth not exceeding two layers above the hearth, and said compact being radiated from about 1315 ° C. to about 1430 ° C.
Exposure to a temperature of ゜ C for a first period of 1 to 3 minutes to remove any volatiles and place the compact in an oxidizing atmosphere in which there is sufficient free oxygen to remove any flammable emissions from the compact. Burning most of the reactive gas and producing a combustion gas, and combining the compact with a radiant heat source in an atmosphere free of free oxygen.
Exposing the compact to a temperature of 5 ° C. to about 1430 ° C. for a second period of 3 to 9 minutes, wherein the gas and the compact are co-current during the first period; Flow as countercurrent during said second period,
Forming a metallized iron product; and discharging the metallized iron product from the hearth.

Preferably, said compact is metallized by reducing, sintering or partially melting said dried compact.

Preferably, the method further comprises the step of partially cooling the compacts while discharging them from the hearth.

[0031] The metallized iron product is exposed to an atmosphere that is oxidized during the last three minutes of the second period, wherein the metallized iron product is converted to excess carbon or carbon monoxide. It may be protected by a thin blanket with and / or with hydrogen.

Preferably, just before discharging the metallized iron product, a coolant is injected above or near said iron product,
Thereby, the method may further comprise a step of partially cooling the metallized iron product before discharging it.

The coolant may be selected from the group consisting of natural gas, coal powder, fuel oil, and by-product gas. The iron oxide can be selected from the group consisting of finely ground iron ore, iron oxide concentrate, by-product iron oxide, and waste from steel mills. Further, the carbonaceous material may be selected from the group consisting of coal, coke powder, petroleum coke, char, and charcoal powder.

Preferably, the iron oxide and the carbonaceous material in the compact are bound by an organic binder.

[0035] The radiant heat source may be configured to obtain energy at least partially by the combustible volatiles and carbon monoxide generated from the compact. Further, the radiant heat source may obtain energy at least partially by burning a fuel selected from the group consisting of natural gas, coal powder, fuel oil, and by-product gas.

The oxygen source can be selected from the group consisting of preheated air, oxygen, and oxygen-rich air, and the oxygen can be introduced into the furnace to promote combustion.

It is preferable that the ratio between the iron oxide and the carbonaceous substance in the compact is controlled so as to be always maintained at a constant ratio.

The method may further include discharging the partially cooled iron metal product from the hearth into a high-temperature transfer vessel, and supplying the iron metal product at a high temperature into the melting furnace. Good. Alternatively, the method may further include discharging the partially cooled iron metal product from the hearth into a briquetting press to produce hot briquette iron.

The apparatus according to the present invention removes iron from a dry compact containing iron oxide and powdered carbonaceous material in a rotary hearth heating furnace, and produces metal by directly reducing the iron. The present invention is characterized by having the following requirements (a) to (f).

(A) A means for mixing iron oxide powder and carbonaceous material powder to form a dry compact. (B) A rotary hearth heating furnace having a substantially flat hearth surface and receiving the dry compact. (C) means for supplying said dry compact such that no more than two layers are on the hearth surface. (D) heating and reducing the dried compact on the hearth;
And means for sintering or partially melting to produce reduction products. (E) means for discharging the reduced compact from the rotary hearth heating furnace. (F) interposed between the supply means and the discharge means,
Means for removing gas in the furnace from the rotary hearth heating furnace.

The compacts may further comprise means for partially cooling the compacts while discharging them from the hearth.

Also, the means for supplying the compact to the hearth to a depth of one or two layers may include at least one adjustable gate or leveler having a lower edge for controlling the thickness of the layer. Preferably, there are two adjustable vertical supply pipes.

Preferably, the means for discharging the compact from the hearth comprises at least one helical screw or at least one plow.

Further, a means for injecting a coolant onto or near the compact immediately before discharging the compact from the hearth may be further provided.

Still further, a water-cooled probe is provided for taking a gas sample less than one inch above the surface of the compact immediately prior to discharging the compact from the hearth, whereby the level of carbon monoxide and oxygen in the gas sample is provided. Can be monitored to control product quality and / or optimize productivity.

[0046]

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, and more particularly to FIG. 1, the method and apparatus of the present invention provides for rapid and efficient reduction of iron oxide in a rotary hearth furnace. Supply bins 10, 12 and 1 containing raw materials used for the treatment of
4 is provided. The feed bin 10 contains iron oxide 16.
The iron oxides referred to here include finely ground iron ore, concentrate, iron oxide by-products, and steel mill waste,
Not limited to these. The feed bin 12 contains a carbonaceous material 18. The carbonaceous material here includes, but is not limited to, pulverized coal, fine coke, char, anthracite, charcoal, and petroleum coke. The supply bin 14
The binder 20 is stored. The binder herein includes, but is not limited to, an organic binder, bentonite, and slaked lime.

The raw materials supplied from the supply bins 10, 12, and 14 are mixed in the mixing unit 22 at an appropriate ratio. The mixture 24 is transferred to the aggregation unit 26,
Pelletization, briquetting,
Extruded or compacted, solid mass 2
It becomes 8. The solid mass 28 is transferred to a drying unit 30 and dried at about 120 ° C. to 180 ° C. to remove moisture and form a dry compact 32.

The drying compact 32 is supplied to a rotary hearth heating furnace (RHF) 34 through a supply port 102,
As shown in FIG. 5, the solid hearth 36 is arranged in a single or double layer (reference numeral 38). The supply port 102 is provided with a leveler gate 104 that is vertically movable and adjustable. The hearth 36 of FIG. 1 rotates clockwise. The compact 32 passes under the radiation barrier 100 and is burned by the radiant heat source 40 at approximately 1315 to 1430 ° C. for 4 to 10 minutes. During this time, volatiles and carbon monoxide are released from the compact 32 and burned in the heating furnace, while iron oxides are mostly reduced to metallic iron and iron carbide. That is, metallic iron is obtained by reducing, sintering, or partially melting the dried compact 32.

As shown in FIG. 4, the compacts 38 are arranged in a single layer or double layer on the hearth 36 through at least one vertical supply port 102. A leveler gate 104 or leveler is adjustably provided, the lower end of which provides a compact 38.
Can be adjusted in thickness. On the other hand, as shown in FIG. 4, an independently provided leveling machine 112, such as a water-cooled leveling roll, is provided at a suitable height above the hearth 36 immediately downstream of the feed port 102 and above the hearth 36. 36 is provided.

The effect of rapid heating and reduction at elevated temperatures on the reduction rate of a dry compact 32 containing a mixture of iron oxide and carbonaceous material is shown in Table 2. The experiments were performed in an electrically heated tubular furnace equipped with a nitrogen atmosphere. Dry compacts formed from a mixture of purified magnetite, low-volatility bituminous coal, and a binder are placed in a preheated tubular furnace, removed every 2 minutes, and analyzed for total iron and metallic iron Then, a degree of metallization (percentage of metallic iron to the total amount of iron) -time curve was created.

[0051]

[Table 2]

Looking at a given feedstock and supply to the hearth, the productivity of the rotary hearth heating furnace 34 (lb / hf
t ² ) is inversely proportional to the holding time in the furnace. For example, when comparing the holding time of 5.8 minutes with the holding time of 7.6 minutes, the productivity of the former exceeds the latter by 31%.

The effect of the rapid heating of a dry compact containing a mixture of iron oxide 16 and carbonaceous material 18 in an oxygen-rich atmosphere on the reduction rate depends on the experimental results in a nitrogen atmosphere and the first 2 The determination was made by comparing the results of experiments performed in an air atmosphere for a minute and then the remaining time in a nitrogen atmosphere. The experimental procedure was the same as described above. In each experiment, the radiant heat source was kept constant at 1343 ° C. Approximately similar results were obtained when using a dry compact containing a mixture of refined hematite, low volatility bituminous coal, and a binder.

Since all the heating zones in the heating furnace are kept at a uniform temperature, the heat of the products produced by the combustion can be utilized without providing a combustion exhaust duct at the end of the supply port. Also, no matter where the gas exhaust port 42 is provided in the RHF 34, the temperature of the combustion exhaust gas is almost the same. That is, when a carbonaceous substance containing a volatile substance is used, the gas exhaust port 42 is provided in the middle part of the rotary hearth heating furnace 34, that is, between the supply port and the discharge port, so that the fuel efficiency can be improved. As a result, in the first part 44 of the RHF, the products of compaction and combustion flow in a co-current direction and in the second part 46 of the RHF in a counter-current direction.

The gas flow passing through the RHF 34 is divided into two flows 47 and 48, and the gas is accumulated and grown in the RHF supply region 102 where dust is most likely to be taken in, so that the gas does not protrude upward. This gives R
Since the volume of gas passing through the initial heating area of the HF 34 is reduced, the height of the ceiling in that area can be reduced, thereby increasing radiant heat transfer to the compact layer. Volatiles released from the compact become more persistent inside the RHF and can be more easily burned. The increased combustion efficiency inside the RHF reduces the final volume of gas that needs to be cleaned.

Since the in-furnace gas outlet 42 is arranged on the ceiling of the RHF 34, the following advantages can be obtained. For example, the direction of the furnace gas at the outlet is pulled away from the hearth rather than flowing across the hearth and blowing away toward the sidewalls. The diameter of the in-furnace gas outlet 42 is formed sufficiently large so as to reduce the gas flow rate, so that the captured fine particles fall back onto the hearth by gravity.

The hot radiant heat source 40 is initially generated by burning fuel. The burner fuel is supplied from a supply source 50, such as, but not limited to, natural gas, fuel oil, by-product gas, and pulverized coal. This fuel is distributed to a ceiling or wall mounted burner 52. Oxygen used for combustion is supplemented by preheated air or oxygen-rich air 54. Further preheated air or oxygen-rich air is supplied to burn the volatiles and CO emitted from the compact. The high operating temperature results in efficient combustion, and the in-furnace gas outlet 42 is located at the center of the RHF 34 rather than at the RHF feed end, thus providing a furnace for volatiles and carbon monoxide. Residence time inside

During the initial stages of heating and reduction, operating in an oxidizing atmosphere and at high temperatures, the volatiles ignite on or near the surface of the dry compact to form a radiant flame and promote heat transfer to the compact. .

In the final stage of the reduction, the atmosphere maintained inside the heating furnace oxidizes metallic iron as a whole. This allows the burner to operate more efficiently, reduces fuel consumption, and provides flexibility in using fuel such as pulverized coal or fuel oil. The reduced iron is protected from oxidation as follows. That is,
With a very short residence time of 4 to 10 minutes,
It prevents the carbon monoxide protective blanket generated in the final stage of the reduction from being disturbed and keeps one percent extra carbon in the metallized compact.

One way to partially cool the metallized compact is to use an injector 116 on or near the compact just prior to discharge from the rotary hearth furnace.
Inject coolant from As this coolant, natural gas,
Those containing pulverized coal, fuel oil, or by-product gas can be used. The coolant may dissociate into carbon and hydrogen. Some or all of the carbon may react with carbon dioxide and water vapor to form carbon monoxide. Free carbon attached to the surface of the compact will further protect it from oxidation. The regenerated gas, carbon monoxide, and hydrogen further form a blanket that protects against oxidation products from combustion above the compact. By dissociating and / or regenerating the coolant, the hot compact is partially cooled and heat is transferred to the regenerated gas for combustion in the rotary hearth furnace 34.

The advantages of this method are as follows. That is, by improving the atmosphere control at the hearth level, it is possible to prevent the oxidation of metallized iron, to produce highly metallized iron with a lower carbon content, and Since the fuel of the rotary hearth heating furnace is preheated using the compact sensible heat, energy efficiency is improved.

[0062] A second radiation barrier 100A is provided immediately before the cooling and discharging area.

A water-cooled gas sampling probe 118 is provided inside the rotary hearth furnace to maximize productivity and help monitor product quality. This takes a sample of the gas within one inch above its surface just before the compact is ejected. As the metallization level of the compact reaches 90 to 95 percent, the rate of reduction begins to decrease and the amount of carbon monoxide generated also begins to decrease. By monitoring the carbon monoxide and oxygen contained in the gas at this point, the quality of the product can be predicted before obtaining a chemical analysis of the product.
High levels of carbon monoxide indicate that the rate of reduction is still high and the degree of metallization of the product may be low. If the level of carbon monoxide is moderate,
It can be seen that the reduction rate has already been reduced and the product is highly metallized. Low levels of carbon monoxide, or the presence of oxygen, or both, indicate that the reduction rate has been stopped and that the product may be oxidized. By adjusting the speed of the hearth, the supply of the raw material, the temperature, and / or the atmosphere based on such knowledge, optimum productivity and quality can be maintained. The carbon monoxide and oxygen levels for the above three conditions must be calibrated according to the respective furnace conditions and the mixture supplied.

The metallized compact is discharged from the hearth 36 via one or more helical water-cooled screws 56. The discharge device also has a function of leveling the hearth. The hearth 36 is solid and consists of a raw material being processed, approximately 4 inches thick, the main constituent being wustite. At this point, the hearth is self-healing. Whatever cracks or pits occur, they are automatically filled with new fines and there is no need to consider the protection of the refractory below.

An alternative means of discharging the compact from the hearth comprises at least one plow 120, as shown in FIGS. The plow may be straight or curved. Similar to the case of discharging with a screw, the plow-type discharging device also has a function of leveling the hearth.

The temperature of the discharged product is about 900 to 1210 ° C. The product 58 is charged into the melting furnace 60 while being hot, or is heated and compacted (reference numeral 6).
2) or cooled and stored (reference numeral 64). When the discharged product is sent to the melting furnace 60, the product may be stored in the transfer can 66 as high-temperature directly reduced iron. The discharged product 58 is pressed into a compacting press 68.
To form hot iron briquettes.
Alternatively, the discharged product 58 can be sent to the rotary drum type cooling device 70 to generate low-temperature reduced iron.

The reducing gas 72 that has exited the RHF 34 enters a furnace gas conditioner 74. The conditioned gas 76 is transferred to a heat exchanger 78. The heat exchanger 78 is also supplied with combustion air 80 through a fan 82. With the heat exchanger 78,
The combustion air 80 is heated and becomes the preheated air 54. The conditioned furnace gas 76 exits the heat exchanger and is sent to an appropriate pollution control device 84. The pollution control device includes a scrubber (gas washer), an electrostatic precipitator, a cyclone, and a bag house. The treated gas 86 is extracted from the pollution control device 84 by the fan 88, sent to the chimney 90, and released to the atmosphere 92. The hearth is conventionally sealed to the hearth containment by a water seal 108, as described in Beggs U.S. Pat. No. 3,452,972. The annular hearth is supported on wheel members 108 and may be driven by any conventional drive means. This is described in Beggs's U.S. Pat.
No. 2,972, or U.S. Pat. No. 4,597,564 to Heinwald et al.

As described in detail above, the present invention provides an improved method and apparatus for rapidly and efficiently reducing iron oxide in a rotary hearth furnace. Test results for this process (which may be known by the trade name or trademark FASTMET ^™ ) show that properly formed pellets (dry compacts) can be reduced to 1%.
Immediate exposure to a radiant heat source at temperatures of 315 to 1430 ° C., without exfoliation.
By eliminating the low to medium temperature preheating zone and reducing at high temperature, hearth productivity is reduced by 3% compared to other processes.
0-100% improvement. Further, most of the volatiles released from the compacts in the rotary hearth furnace are burned, and the compacts and combustion products are co-current in the first part of the furnace and the second part of the furnace. By flowing in the countercurrent direction, the energy efficiency can be improved.

The foregoing description and specific embodiments are merely illustrative of the best mode of the present invention and its principles. In addition, those skilled in the art of the present invention can make various changes and additions without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be limited only by the scope set forth in the appended claims.

[0070]

As is apparent from the above description, the present invention provides an improved method and apparatus for rapidly and efficiently reducing iron oxide in a rotary hearth heating furnace. is there. The advantages of this method are as follows. (1) The oxidation of metallic iron is prevented by improving the atmosphere control at the hearth level. (2) Highly metallized iron with lower carbon content can be produced. (3) Energy efficiency is improved by preheating part of the fuel in the rotary hearth heating furnace using the sensible heat of the metallized compact.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing steps of an improved method for realizing rapid and efficient iron oxide reduction in a rotary hearth heating furnace.

FIG. 2 is a sectional view of an improved rotary hearth heating furnace.

FIG. 3 is a top view of an improved rotary hearth heating furnace.

FIG. 4 is a schematic side view of a feeder showing a feedstock or pellet leveler.

FIG. 5 is a schematic side view of the discharge portion of the device showing the cooling device.

FIG. 6 is a schematic side view of the discharge portion of the device showing the pellet discharge plow.

FIG. 7 is a schematic top view showing a discharge portion of the apparatus of FIG. 6;

[Explanation of symbols]

16 Iron oxide 18 Carbonaceous substance 20 Binder 22 Mixing unit 26 Agglomeration unit 30 Drying unit 32, 38 Compact 34 Rotating bed heating furnace (RHF) 36 Hearth (of RHF34) 42 Gas exhaust port (furnace gas) Removal means) 56 helical screw (discharge means) 58 reduction product 102 supply line (means for supplying compact 32 to RHF 34)

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[Procedure amendment]

[Submission date] July 19, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

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[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

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[0028]

SUMMARY OF THE INVENTION To achieve the above and other objects, a method of producing iron by direct reduction from a dry compact comprising iron oxide, a carbonaceous material, and a volatile material according to the present invention. Providing the compact at a depth not exceeding two layers on the hearth, exposing the compact to a temperature of 1315 ° C. to 1430 ° C. by a radiant heat source for a first period of 1 to 3 minutes, and Removing volatiles and placing the compact in an oxidizing atmosphere in which there is sufficient free oxygen to burn most of the flammable gas generated from the compact and generate combustion gas; At a temperature of 1315 ° C. to 1
Exposing the compact to a temperature of 430 ° C. for a second period of 3 to 9 minutes to metallize the compact; and wherein the gas and the compact are co-current during the first period; Inside flows countercurrent, metallized compact
And forming the metallized compact
Cool on or near the compact just before discharging
The metallized compact.
And a step of partially cooling the metallized compact prior to its discharge, and discharging the metallized compact from the hearth.

[Procedure amendment 3]

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[0031] While the metallized compact is exposed to the atmosphere to be oxidized at the end of the second period, the oxidation
The metallized compact may be protected by a thin blanket of excess carbon and / or carbon monoxide and / or hydrogen in order to prevent the occurrence.

[Procedure amendment 6]

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The coolant may be selected from the group consisting of natural gas, coal powder, fuel oil, and by-product gas.

[Procedure amendment 8]

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[0035] The radiant heat source may be configured to obtain energy at least partially by the combustible volatiles and carbon monoxide generated from the compact.

[Procedure amendment 9]

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[Procedure amendment 10]

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[Correction contents]

Further, the partially cooled metallized con
Pact is discharged from the hearth into a high-temperature transfer vessel and metallized.
The method may further include a step of supplying the compact at a high temperature into the melting furnace. Alternatively, the partially cooled metallization
The method may further include discharging the compact from the hearth into a briquetting press to produce hot briquetted iron.

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction contents]

The apparatus according to the present invention removes iron from a dry compact containing iron oxide and powdered carbonaceous material in a rotary hearth heating furnace, and produces metal by directly reducing the iron. Then, from the next (a)
(G) .

[Procedure amendment 12]

[Document name to be amended] Statement

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[Correction method] Change

[Correction contents]

(A) A means for mixing iron oxide powder and carbonaceous material powder to form a dry compact. (B) A rotary hearth heating furnace having a substantially flat hearth surface and receiving the dry compact. (C) means for supplying said dry compact such that no more than two layers are on the hearth surface. (D) heating and reducing the dried compact on the hearth;
And means for sintering or partially melting to produce reduction products. (E) means for discharging the reduced compact from the rotary hearth heating furnace. (F) interposed between the supply means and the discharge means,
Means for removing gas in the furnace from the rotary hearth heating furnace. (G) immediately before discharging the compact from the hearth;
Means for injecting coolant on or near the compact.

[Procedure amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Deleted

[Procedure amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Deleted

[Procedure amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0045

[Correction method] Change

[Correction contents]

Further, just before discharging the compact from the hearth, one inch above the surface of the compact.
(2.54 cm) may be provided with a water-cooled probe for taking gas samples.

[Procedure amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction contents]

Looking at a given feedstock and supply to the hearth, the productivity of the rotary hearth heating furnace 34 (lb / hf
t ² (kg / hm ² )) is inversely proportional to the holding time in the furnace. For example, when comparing the holding time of 5.8 minutes with the holding time of 7.6 minutes, the productivity of the former exceeds the latter by 31%.

[Procedure amendment 17]

[Document name to be amended] Statement

[Correction target item name] 0063

[Correction method] Change

[Correction contents]

A water-cooled gas sampling probe 118 is provided inside the rotary hearth furnace to maximize productivity and help monitor product quality. This is one inch above the surface of the compact just before ejection.
Collect a gas sample within (2.54 cm) . As the metallization level of the compact reaches 90 to 95 percent, the rate of reduction begins to decrease and the amount of carbon monoxide generated also begins to decrease. By monitoring the carbon monoxide and oxygen contained in the gas at this point, the quality of the product can be predicted before obtaining a chemical analysis of the product. High levels of carbon monoxide indicate that the rate of reduction is still high and the degree of metallization of the product may be low. At moderate levels of carbon monoxide, the rate of reduction has already been reduced, indicating that the product is highly metallized. Low levels of carbon monoxide, or the presence of oxygen, or both, indicate that the reduction rate has been stopped and that the product may be oxidized. By adjusting the speed of the hearth, the supply of the raw material, the temperature, and / or the atmosphere based on such knowledge, optimum productivity and quality can be maintained. The carbon monoxide and oxygen levels for the above three conditions must be calibrated according to the respective furnace conditions and the mixture supplied.

[Procedure amendment 18]

[Document name to be amended] Statement

[Correction target item name] 0064

[Correction method] Change

[Correction contents]

The metallized compact is discharged from the hearth 36 via one or more helical water-cooled screws 56. The discharge device also has a function of leveling the hearth. The hearth 36 is solid and consists of a raw material being processed having a thickness of about 4 inches (about 10.2 cm) , the main constituent of which is wustite. At this point, the hearth is self-healing. Whatever cracks or pits occur, they are automatically filled with new fines and there is no need to consider the protection of the refractory below.

[Procedure amendment 19]

[Document name to be amended] Statement

[Correction target item name] 0067

[Correction method] Change

[Correction contents]

The reducing gas 72 that has exited the RHF 34 enters a furnace gas conditioner 74. The conditioned gas 76 is transferred to a heat exchanger 78. The heat exchanger 78 is also supplied with combustion air 80 through a fan 82. With the heat exchanger 78,
The combustion air 80 is heated and becomes the preheated air 54. The conditioned furnace gas 76 exits the heat exchanger and is sent to an appropriate pollution control device 84. The pollution control device includes a scrubber (gas washer), an electrostatic precipitator, a cyclone, and a bag house. The treated gas 86 is extracted from the pollution control device 84 by the fan 88, sent to the chimney 90, and released to the atmosphere 92. The hearth is conventionally sealed to the hearth containment by a water seal 106 as described in Beggs U.S. Pat. No. 3,452,972. The annular hearth is supported on wheel members 108 and may be driven by any conventional drive means. This is described in Beggs's U.S. Pat.
No. 2,972, or U.S. Pat. No. 4,597,564 to Heinwald et al.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Thomas H. Inventor. Boyd 28115 Mooresville Box, North Carolina, United States of America 200-H Route 4 (72) Inventor James A. Lipinski, North Carolina, USA 28215 Charlotte Lakeside Drive 7124 (72) Inventor Jimmy Dee. Sloop, North Carolina, USA 28134 Charlotte # 708-236 Pinville-Matthews Road 8318

Claims (22)

[Claims] 1. A method for producing iron by direct reduction from a dry compact comprising iron oxide, a carbonaceous substance and a volatile substance, said compact being supplied on the hearth with a depth not exceeding two layers. Exposing the compact to a temperature of about 1315 ° C. to about 1430 ° C. by a radiant heat source for a first period of 1 to 3 minutes to remove any volatiles and to allow the compact to be sufficiently free Placing the compact in an oxidizing atmosphere in the presence of oxygen to burn most of the combustible gas generated from the compact and generating a combustion gas; and placing the compact in an atmosphere free of free oxygen by a radiant heat source. Metallizing the compact by exposing to a temperature of 1315 ° C. to about 1430 ° C. for a second period of 3 to 9 minutes; Flowing in a co-current during the first period and countercurrent during the second period to form a metallized iron product; and converting the metallized iron product into a furnace. Discharging from the floor. 2. The method of claim 1, wherein the compact is metallized by reducing, sintering, or partially melting the dried compact. 3. The method of claim 1 further comprising the step of partially cooling the compacts while discharging them from the hearth. 4. The iron metallized product is exposed to an atmosphere that is oxidized during the last three minutes of the second period, wherein the iron metallized product is free of excess carbon or The method of claim 1, wherein the method is protected by a thin blanket of carbon oxide and / or hydrogen. 5. Injecting a coolant over or near the iron product immediately prior to discharging the iron metallized product, thereby partially cooling the metallized iron product prior to its discharge. The method of claim 1, further comprising: 6. The method of claim 5, wherein the coolant is selected from the group consisting of natural gas, coal powder, fuel oil, and by-product gas. 7. The method of claim 1, wherein the iron oxide is selected from the group consisting of finely ground iron ore, iron oxide concentrate, by-product iron oxide, and steel mill waste. 8. The carbonaceous substance may be coal, coke powder,
The method of claim 1, wherein the method is selected from the group consisting of petroleum coke, char, and charcoal powder. 9. The method of claim 1, wherein the iron oxide and carbonaceous material in the compact are bound by an organic binder. 10. The method of claim 1, wherein the radiant heat source is at least partially energized by combustible volatiles and carbon monoxide generated from the compact. 11. The method of claim 1, wherein the radiant heat source is at least partially energized by burning a fuel selected from the group consisting of natural gas, coal powder, fuel oil, and by-product gas. the method of. 12. The method of claim 1, wherein the oxygen source is selected from the group consisting of preheated air, oxygen, and oxygen-rich air, and the oxygen is introduced into the furnace to promote combustion. 13. The method according to claim 1, wherein the ratio between the iron oxide and the carbonaceous material in the compact is controlled so as to be always maintained at a constant ratio. 14. The method according to claim 1, further comprising the step of discharging the partially cooled iron metal product from the hearth into a high temperature transfer vessel and supplying the metal iron product at a high temperature into the melting furnace. Item 1. The method according to Item 1. 15. The method of claim 1, further comprising the step of discharging the partially cooled iron metallized product from the hearth into a briquetting press to produce hot briquetted iron. the method of. 16. Iron is removed from a dry compact containing iron oxide and powdered carbonaceous material in a rotary hearth heating furnace having the following requirements (a) to (f), and the iron is directly reduced: A device that produces metal by doing (A) A means for mixing iron oxide powder and carbonaceous material powder to form a dry compact. (B) A rotary hearth heating furnace having a substantially flat hearth surface and receiving the dry compact. (C) means for supplying said dry compact such that no more than two layers are on the hearth surface. (D) heating and reducing the dried compact on the hearth;
And means for sintering or partially melting to produce reduction products. (E) means for discharging the reduced compact from the rotary hearth heating furnace. (F) means for interposed between the supply means and the discharge means for removing gas in the furnace from the rotary hearth heating furnace. 17. The apparatus of claim 16, further comprising means for partially cooling the compacts while discharging them from the hearth. 18. The compact is placed on the hearth for 1 to 2
17. The method according to claim 16, wherein the means for feeding to the depth of the layer comprises at least one adjustable vertical feed pipe with an adjustable gate or leveler having a lower edge for controlling the thickness of the layer. The described device. 19. The apparatus according to claim 16, wherein the means for discharging the compact from the hearth comprises at least one helical screw. 20. The means for discharging the compact from the hearth comprises at least one plow.
An apparatus according to claim 1. 21. The apparatus of claim 16, further comprising means for injecting a coolant onto or near the compact just before discharging the compact from the hearth. 22. A water-cooled probe for taking a gas sample less than one inch above the surface of the compact immediately prior to discharging the compact from the hearth, thereby reducing the levels of carbon monoxide and oxygen in the gas sample. 17. The apparatus of claim 16, wherein the monitoring is performed to control product quality and / or optimize productivity.