JPH1112627A - Method for controlling rotating speed of rotary furnace hearth in reduced iron production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for suitably controlling rotating speed of a furnace hearth by judging the completing point of reduction reaction at high accuracy at the time of producing reduced iron. SOLUTION: At the time of producing the reduced iron by charging mixed material of powdery iron material and powdery solid reducing agent and burning, CO and CO2 concns. in the atmospheric gas near the discharging part of the burnt reduced iron are continuously measured, and the rotary speed of the furnace hearth is controlled so that CO/CO2 or CO/(CO+CO2 ) becomes a prefixed value, or CO and CO2 concns. are measured as the same way in plural positions along the shifting direction of the furnace hearth near the discharging part so that the difference of CO/CO2 or the difference of CO/(CO+CO2 between each measured position become prefixed value. Dust concn. contained in the same atmospheric gas is continuously measured and the rotating speed of the furnace hearth may be controlled so that the dust concn. becomes the prefixed value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for converting a raw material obtained by mixing a powdery iron raw material such as dust, sludge, scale or the like containing powdered iron ore or iron and a powdery solid reducing agent such as coal or coke. The present invention relates to a method for controlling a rotating speed of a hearth when the reduced iron is manufactured by being charged into a heating furnace in which a floor rotates horizontally.

[0002]

2. Description of the Related Art In recent years, a powdered iron ore and a powdery solid reducing agent are mixed and agglomerated, and the resulting agglomerate is heated in a hearth (hereinafter referred to as a "rotating hearth") in which a hearth rotates horizontally. Attention has been focused on a technique for producing reduced iron by charging a furnace having this hearth into a "rotary hearth furnace".

[0003] Unlike a rotary kiln furnace which has been used for a long time, this rotary hearth furnace is characterized in that the equipment cost is low. On the other hand, since the hearth rotates horizontally, it is necessary to charge raw materials and discharge products. Care must be taken. As a typical example of the technology, a powdered iron ore is mixed with a solid reducing agent to form an agglomerate (pellet), which is heated to a high temperature to reduce iron oxide in the iron ore. (See, for example, US Pat. No. 3,443,9).
31, specification, JP-A-7-238307).

FIG. 1 is a schematic view showing an example of a conventional reduced iron production process in which heating is performed using a rotary bed furnace. As shown in the figure, bentonite as a binder is added to fine iron ore and fine coal, and water and tar are further added and mixed by a kneader. This mixed raw material is agglomerated by a pelletizer or a double-roll compressor, transferred to a raw material charging section of a rotary hearth furnace, charged into the furnace, and rotated once along with the movement of the hearth while the iron ore in the iron ore is rotated. Iron oxide is reduced at high temperature to form solid metallic iron. The obtained metallic iron is taken out from the discharge part.

[0005] In the above-mentioned method for producing reduced iron, as the powdered iron raw material, in addition to powdered iron ore, various dusts, sludges, scales, etc. containing iron generated in ironworks can be used. As the powdery solid reducing agent, coal, coke, char, oil coke and the like can be used.
These iron raw materials and solid reducing agents may be subjected to drying treatment and crushing treatment in some cases.

The powdered iron raw material and the powdered solid reducing agent are then kneaded. At this time, if necessary, water as a binder, tar, molasses, organic resin, cement, slag, bentonite, quicklime, Light dolomite and slaked lime are added.

The kneaded raw material is compacted into spherical pellets by a desk pelletizer or briquettes by a double roll compressor. In this case, in order to form pellets, a raw material having a particle size of 0.1 mm or less is suitable, and a briquette having a particle size of 1 mm or less is suitable. . Further, in order to increase the strength of the agglomerate (refer to the above-mentioned pellets and briquettes), a drying treatment or a curing treatment may be performed after the agglomeration.

The agglomerates obtained are conveyed by belt conveyor to the upper part of a rotary hearth furnace, from where they are charged using a charging chute so as to be widely distributed on the rotary hearth and leveled by a leveler. Subsequently, it is reduced by heating while moving in the furnace and becomes metallic iron.

In the rotary bed furnace, a furnace temperature of 1100 ° C. to 1300 ° C. is secured by feeding and burning fuel gas and air into the furnace. The above-mentioned agglomerate was spread on the hearth of this rotary hearth furnace with a thin thickness of 10 to 20 mm, and the temperature was raised to 900 ° C. or more mainly by radiant heat from the furnace inner wall, and
During the rotation, reduction sintering is performed while adjusting the rotation speed of the hearth so as to reach a predetermined metallization ratio, and the mixture is discharged from a discharge portion by a screw feeder.

[0010] In the above-described reduced iron production process, setting of the heating reduction time in the rotary bed furnace, that is, the setting of the rotation speed of the rotary hearth, is an important issue from the viewpoint of improving productivity.

In this process, if the rotating speed of the rotary hearth is too high, the raw material is discharged as a product even though the reduction of the raw material is not sufficiently performed, so that reduced iron having a low metallization ratio is obtained. . Conversely, if the rotating speed of the rotary hearth is too slow, the reduction of the raw material proceeds sufficiently, but the firing time becomes longer, and the productivity is reduced. Also, if the generated reduced iron stays in the furnace for an unnecessarily long time, it is re-oxidized by H ₂ O or CO ₂ in the exhaust gas, or carbon (C) remaining in the reduced iron is gasified by CO ₂ . However, all of these are major operational losses. Therefore, it is important to quickly determine the metallization rate of the obtained reduced iron and control the rotation speed of the rotary hearth so as to achieve the target metallization rate.

Of course, if there are no fluctuations in the raw material conditions and the furnace temperature, there is no problem as long as the rotation speed is once set to an appropriate speed, but the raw material conditions and the furnace temperature do not fluctuate. It is always necessary to reset the hearth rotation speed to an optimum value each time it fluctuates.

Generally, the metallization ratio (m
-Fe / T. Fe) is obtained by sampling the product, shrinking the product, crushing the product, and performing analysis by wet chemical analysis and atomic absorption spectrometry. Therefore, it takes a lot of trouble and time, and it is difficult to quickly determine the metallization ratio.

On the other hand, in Japanese Patent Application Laid-Open No. Hei 7-238307, a gas sampler is installed just above a raw material (pellet) layer in the vicinity of a discharge part, and the C of sampled gas is measured.
There is a description that a point in time when the combined concentration of O and CO ₂ (concentration of CO + CO ₂ ) becomes 5% or less is a point in time when the reduction reaction is stopped.

[0015] However, this method of judging when to stop the reduction reaction has a significant drawback. Certainly, C (carbon) in the solid reducing agent reacts with O (oxygen) of iron oxide in the powdered iron raw material to generate CO and CO _2. Can be determined to be complete. However, C in the solid reducing agent also reacts with H ₂ O and CO ₂ in the combustion exhaust gas generated when heating the inside of the furnace to generate CO. Therefore, when the (CO + CO ₂ ) concentration of the sampled gas becomes 5% or less, which indicates that C in the solid reducing agent is disappearing, the O of iron oxide in the powdery iron raw material is reduced. It does not mean that all (oxygen) has been removed by reduction. For example, when the amount of C in the solid reducing agent is large, it is too late to judge that the reduction has been completed when the (CO + CO ₂ ) concentration of the sampled gas becomes 5% or less. When the amount of C in the solid reducing agent is small, (CO
When the concentration of (+ CO ₂ ) becomes 5% or less, it is too early to judge reduction completion.

[0016]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the production of reduced iron and, by appropriately controlling the rotating speed of the hearth, produces a product with a stable and high metallization rate at a high rate. It was made with the task of manufacturing at a high rate. A specific object of the present invention is to provide a method for determining the completion point of the reduction reaction with high accuracy in the production of reduced iron and appropriately controlling the rotation speed of the hearth.

[0017]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that the concentration of (CO + CO ₂ ) in the sampled gas is not CO / CO _2.
Alternatively, CO / (CO + CO ₂ ) was obtained, and it was found that when the ratio reached a predetermined value, it was determined that the reduction was completed. The determination at the time of the completion of the reduction can also be made by measuring the concentration of dust contained in the gas near the discharge portion of the calcined reduced iron. Therefore, if the rotation speed of the hearth is controlled so that these values become predetermined values, it is possible to obtain an appropriate rotation speed.

The present invention has been made based on the above findings, and the gist of the invention resides in the following method (1) to (3) for controlling the rotation speed of a rotary hearth in the production of reduced iron.

(1) A mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a rotary hearth and fired to produce reduced iron. C
The concentration of O ₂ is continuously measured and CO / CO ₂ or CO /
A method for controlling the rotation speed of a rotary hearth, wherein the rotation speed of the hearth is controlled so that (CO + CO ₂ ) becomes a predetermined value.

(2) A mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a heating hearth that is horizontally rotated and fired to produce reduced iron. The concentration of CO and CO ₂ in the atmosphere gas is continuously measured at a plurality of points along the moving direction of
/ CO ₂ or CO / (CO + CO ₂ ) is calculated, and the difference of CO / CO ₂ or CO / (CO + CO
₂ ) A method for controlling the rotation speed of a rotary hearth, wherein the rotation speed of the hearth is controlled so that the difference of the predetermined value becomes a predetermined value.

(3) A mixture of the powdered iron raw material and the powdered solid reducing agent is charged into a rotary hearth and fired to produce reduced iron, which is contained in the atmosphere gas near the reduced iron discharge section. A method for controlling the rotation speed of a rotary hearth, comprising continuously measuring the concentration of dust and controlling the rotation speed of the hearth so that the dust concentration becomes a predetermined value.

Here, the "pulverized iron raw material" is a powdered iron raw material containing iron oxide as a main component, and specifically includes the above-mentioned powdered iron ore and iron generated in an ironworks. Waste, sludge (eg, sintering machine generated dust, blast furnace generated dust, converter generated dust, rolling plant generated sludge), scale, and the like. In the present invention, these can be used alone or in a mixture of two or more.

The "pulverized solid reducing agent" is a powder of a solid substance mainly containing carbon, such as coal, coke, char, and oil coke. These can also be used alone or in combination of two or more.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention (the above (1) to
The invention (3) will be described in detail.

The invention of the above (1) is characterized in that a mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a rotary hearth and fired to produce reduced iron. Continuously measure the concentration of CO and CO ₂ in the surrounding atmosphere gas,
In this method, the rotational speed of the hearth is controlled so that O / CO ₂ or CO / (CO + CO ₂ ) becomes a predetermined value.

As described above, C in the gas sampled by the gas sampler installed immediately above the raw material layer (which is a reduced iron layer in a substantially reduced state) in the vicinity of the discharge section.
Although the concentrations of O and CO ₂ provide valuable information about the reduction reaction, determining the (CO + CO ₂ ) concentration does not determine the completion of the reduction reaction. However, CO / CO
According to the value of ₂ or CO / (CO + CO ₂ ), it was found that the completion of the reduction reaction can be almost determined as described below.

When volatilization of low-boiling components from the powdery solid reducing agent is completed and raw material (iron oxide) is reduced to the final stage, C, CO, CO ₂ , iron oxide (FeO) and metallic iron There are five components of (Fe), and the following reaction is performed.

Reduction reaction: FeO + C → Fe + CO Gasification reaction: C + CO ₂ → 2CO Here, paying attention to the ratio of CO / CO ₂ , only CO is generated in the reduction reaction. In the gasification reaction, CO ₂ is reduced and CO is doubled. Therefore, when the ratio at which the gasification reaction occurs is relatively higher than the reduction reaction, CO /
The value of CO ₂ increases and its change also increases.
That is, when iron oxide (FeO) is present and the raw material is being reduced, the change in the value of CO / CO ₂ is not large, but as the reduction is almost completed, the rate at which the gasification reaction occurs increases. Therefore, the value of CO / CO ₂ changes greatly.

Therefore, in the method of the invention (1),
CO and CO ₂ in the atmosphere gas near the reduced iron discharge section
Of CO / CO ₂ or CO / (CO + C
O ₂ ) is obtained, and the completion point of the reduction reaction is determined from the value.

The measurement of the concentrations of CO and CO ₂ is carried out continuously. This is because the ratio at which the above-described reduction reaction and gasification reaction occur changes every moment. Therefore, the “continuous measurement” may be any continuous measurement that can at least follow this change.

The sampling of the atmosphere gas in the vicinity of the reduced iron discharge section may be performed by attaching a gas sampler directly above the raw material layer (reduced iron layer) in the vicinity of the discharge section, for example, as in the method described in the above-mentioned publication. . In addition, at the time of sampling,
Alternatively, water vapor contained in the atmospheric gas is removed before the measurement after sampling. This is because, in a commonly used continuous gas analyzer, when water vapor is present in the sample gas, dew condensation occurs in the analyzer, and dust or the like adheres to the portion, which hinders measurement.

In the method of the present invention (1), the rotational speed of the hearth is controlled so that CO / CO ₂ or CO / (CO + CO ₂ ) obtained as described above becomes a predetermined value. Here, the “predetermined value” differs in absolute value depending on the heating conditions of the rotary bed furnace (for example, the amount of cooking of the heating burner, the amount of exhaust gas, etc.), and therefore, is determined in advance according to the heating conditions during the actual operation. The relationship between the value of CO / CO ₂ or CO / (CO + CO ₂ ) and the rotation speed of the hearth may be determined and determined based on the relationship. In addition,
CO / CO ₂ and CO / (CO + CO ₂ ) mean substantially the same, and any of them may be used.

In the invention of the above (2), the CO and CO ₂ concentrations are continuously measured at a plurality of places near the discharge portion of the reduced iron along the moving direction of the hearth, as in the case of the invention of (1). , CO / CO ₂ or CO / (C
O + CO ₂ ) is obtained, and the rotational speed of the hearth is controlled so that the difference in CO / CO ₂ or the difference in CO / (CO + CO ₂ ) between the measurement points becomes a predetermined value.

According to this method, since the gas analysis data at one place along the moving direction of the hearth in the case of the above (1) becomes data at a plurality of places, the completion of the reduction reaction is determined. Can be performed more accurately, and CO
By grasping the change in / CO ₂ or CO / (CO + CO ₂ ), it becomes easier to more strictly grasp the change in the progress of the reduction reaction. Note that the accuracy of CO and CO ₂ concentration increases as the number of measurement locations increases, but usually, the measurement may be performed at two locations.

The "predetermined value" is defined as (1)
As in the case of the method of the invention, the relationship between the difference in CO / CO ₂ or the difference in CO / (CO + CO ₂ ) between the measurement points and the rotation speed of the hearth during actual operation is determined based on the relationship. It should be left.

The invention of the above (3) is characterized in that the mixture of the powdered iron raw material and the powdered solid reducing agent is charged into a rotary hearth and fired to produce reduced iron, and the discharged portion of the fired reduced iron is used. This is a method of measuring the concentration of dust contained in a nearby atmosphere gas and controlling the rotation speed of the hearth so that the dust concentration becomes a predetermined value.

That is, in this method, completion of the reduction reaction is determined by measuring the concentration of dust contained in the gas near the reduced iron discharge portion.

The raw material is heated, and the iron oxide contained therein is reduced to metallic iron and sintered. Therefore, what is reduced is what is called sponge iron, which is strong. On the other hand, the portion where the unreduced material remains does not have a strong bond, and is pulverized and dusted by the impact at the time of discharge. That is, when the reduction is completely completed, the dust concentration is low, but when the unreduced portion is large, the dust concentration increases. Therefore, the completion point of the reduction reaction can be determined by measuring the dust concentration. .

The "predetermined value" is defined as (1)
As in the case of the method of the invention, the relationship between the dust concentration and the rotation speed of the hearth during the actual operation may be determined and determined based on the relationship.

There are various methods for measuring the dust concentration. Any method can be used as long as it can follow the change in the dusting state (that is, the change in the dust concentration) corresponding to the change in the reduction state of the iron raw material. It may be a method. Among them, the optical type and the electric type are preferable because the measurement of the absolute value of the dust concentration has a problem but continuous measurement is possible. The optical type has a light-emitting portion and a light-receiving portion across a measurement site, and continuously measures dust concentration by reducing the amount of light. On the other hand, the electric type has an electrode probe and utilizes the fact that the electric resistance changes according to the dust concentration.

The method of the invention of the above (1) and (2)
Regardless of the shape of the raw material charged into the rotary bed furnace,
It is a technique that can be applied to any case such as pellets, briquettes, tiles, plates, and sheets.

According to the method of the present invention, it is possible to appropriately control the rotational speed of the hearth based on the measured values of the concentrations of CO and CO ₂ or the dust in the atmosphere gas near the discharge portion of reduced iron. As a result, reduced iron having a stable and high metallization ratio can be efficiently produced.

[0043]

EXAMPLES Using fine iron ore shown in Table 1 and fine coal shown in Table 2 and blending at the blending ratio shown in Table 3, the fine powder was mixed with No. 1
-No. In each of the cases No. 8, reduced iron was produced, and the effect of the present invention was evaluated based on the metallization rate and production rate of the reduced iron at that time.

In the production of reduced iron, following the production process shown in FIG. 1, the blended raw materials are mixed, molded into briquettes by a double-roll compressor, and then charged into a rotary bed furnace and fired. It was done by doing. Table 4 shows the equipment specifications and operating conditions of the rotary hearth furnace used.

[0045]

[Table 1]

[0046]

[Table 2]

[0047]

[Table 3]

[0048]

[Table 4]

In the operation of the rotary bed furnace, a gas sampler is installed just above the raw material layer near the discharge section, and the CO and CO ₂ concentrations or dust concentrations are continuously measured, and CO / C
The rotation speed of the hearth was controlled so that O ₂ , CO / (CO + CO ₂ ), or dust concentration became a predetermined value. In addition, 8 points from the position where the gas sampler is installed
m, a gas sampler is further installed immediately above the raw material layer on the upstream side, and the CO and CO ₂ concentrations are continuously measured to obtain CO / CO ₂
Alternatively, CO / (CO + CO ₂ ) is obtained, and the difference from the value obtained on the downstream side (that is, CO / CO ₂ difference, CO / (CO +
The rotation speed of the hearth was controlled so that the CO ₂ ) difference) became a predetermined value.

The production of reduced iron was carried out according to No. 1 to N
o. 8 was carried out while controlling the rotation speed of the hearth by the method shown in each case. Table 5 also shows the metallization rate and the production rate.

[0051]

[Table 5]

FIG. 3-No. 8, dust concentration, CO / CO ₂ , CO / (CO + CO ₂ ), CO
/ CO ₂ difference (indicated as ΔCO / CO ₂ ) and CO / (C
The change with time of the O + CO ₂ difference (indicated as ΔCO / (CO + CO ₂ )) is shown in comparison with the case where the rotation speed control was not performed. “ON” in the figure indicates a case in which the rotation speed control is performed, and values of various control factors such as dust concentration and CO / CO ₂ are almost constant values (this value is a “predetermined value” in the present invention). Value "). That is,
This is a case where the rotation speed of the hearth is controlled so that the values of various control factors become the “predetermined values”. on the other hand,
“OFF” indicates that the rotation speed control was not performed, and the values of various control factors such as dust concentration and CO / CO ₂ showed remarkable fluctuation. In addition, No. in the figure. 3 to No. No. 8 in Table 5 are No. 3 to No. Corresponds to 8.

No. shown in Table 5 Case 1 is a conventional example in which the floor rotation speed control of the rotary hearth furnace was not performed, and the rotation speed was set so that the metallization rate of the product was approximately 92%. In this case, although not shown, various control factors are considered to be fluctuating by analogy with the other cases shown in FIG. 2, and as a result, the fluctuation of the metallization rate of reduced iron is seen in the standard deviation. It was so big. For this reason, even if the rotation speed needs to be adjusted (especially, the rotation speed is increased), it cannot be increased, resulting in a low production rate.

No. The case No. 2 is described in the above-mentioned JP-A-7-2.
No. 38307, based on a method of judging that the point at which (CO + CO ₂ concentration) becomes 5% or less is the point at which the reduction reaction is stopped, using (CO + CO ₂ ) concentration <5% as a guide In the case where numerical control is performed,
No. No significant improvement was observed compared to case 1.

No. 3-No. The case of No. 8 is an example of the present invention. 3 and No. 3 No. 4 indicates that when the rotation speed of the hearth was controlled so that the measured value of dust concentration became a predetermined value, No. 5-No. 8 is obtained from the measured values of CO and CO ₂ concentrations (gas analysis values), CO / CO ₂ and CO / (C
O + CO ₂ ), CO / CO ₂ difference and CO / (CO + C
O ₂ ) difference is obtained and the rotational speed control is performed based on the difference.

In the example of the present invention, the average was 92% as compared with the conventional example.
While maintaining the metallization rate of
Reduced iron could be produced at a high production rate.

[0057]

According to the method of the present invention, when a mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a rotary hearth and calcined to produce reduced iron, the reduced iron is discharged in the vicinity of the discharge section. The rotation speed of the hearth can be appropriately controlled based on the measured values of the CO and CO ₂ concentrations or the dust concentrations in the atmospheric gas. As a result, it is possible to efficiently produce reduced iron having a stable and high metallization ratio.

[Brief description of the drawings]

FIG. 1 is a schematic view of an example of a conventional reduced iron production process performed using a rotary hearth furnace.

FIG. 2 is an example of the results obtained in the examples, showing the dust concentration, CO / CO ₂ , CO
/ (CO + CO ₂ ), CO / CO ₂ difference and CO / (C
O + CO ₂₎ is a diagram showing changes with time of the difference.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Masahiko Hoshi 4-5-33 Kitahama, Chuo-ku, Osaka City, Osaka Inside Sumitomo Metal Industries, Ltd.

Claims (3)

[Claims] 1. A mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a heating furnace bed which is horizontally rotated and baked to produce reduced iron. C
Characterized by continuously measuring the concentrations of O and CO ₂ and controlling the rotation speed of the hearth so that CO / CO ₂ or CO / (CO + CO ₂ ) becomes a predetermined value. Control method. 2. A mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a heating hearth which is horizontally rotated and baked to produce reduced iron. CO and CO in the atmospheric gas at multiple points along the moving direction
₂ was measured continuously, and the CO / CO
₂ or CO / (CO + CO ₂ ), and controlling the rotation speed of the hearth so that the difference in CO / CO ₂ or the difference in CO / (CO + CO ₂ ) between the measurement points becomes a predetermined value. A method for controlling a rotating speed of a rotary hearth. 3. A mixture of a powdered iron raw material and a powdered solid reducing agent is charged into a heating furnace bed which is horizontally rotated and baked to produce reduced iron. A method for controlling the rotation speed of a rotary hearth, comprising: continuously measuring the concentration of dust contained in the furnace, and controlling the rotation speed of the hearth so that the dust concentration becomes a predetermined value.