JP2008150668A - Method for producing molten pig iron with the use of vertical scrap-melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively producing molten pig iron with high productivity, while using a vertical scrap-melting furnace and using ferrous scrap as a raw material. <P>SOLUTION: This production method is directed at melting the ferrous scrap with a combustion heat of cokes by charging the ferrous scrap and the cokes into the furnace from the furnace top, and blowing hot blast into the furnace from a plurality of tuyeres in a lower part of the furnace, and comprises the steps of: arranging an oxygen-spouting nozzle which spouts oxygen at a supersonic speed, in at least one part of the tuyeres; and spouting the oxygen so that the flow speed of oxygen spouted from the oxygen-spouting nozzle can be 20 to 70 Nm/sec at the center of the furnace, while blowing the hot blast from the tuyere. The production method optimizes a gas flow in the whole diametric direction of the furnace including the center part of the furnace; burns the cokes and melts the ferrous scrap adequately in the whole furnace; and accordingly can inexpensively produce the molten pig iron with high productivity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing hot metal by melting iron scrap with combustion heat of coke using a vertical scrap melting furnace.

Conventionally, a process for melting iron-based scrap using a vertical melting furnace is known (for example, Patent Document 1). In this process, iron-based scrap and coke are charged from the top of the vertical melting furnace. Hot metal is blown from a plurality of tuyere (blower tuyere) provided at the lower part of the furnace, and iron scrap is melted by the combustion heat of coke to obtain hot metal.
JP-A-56-156709

When iron-based scrap is melted in the above process to produce hot metal, there are the following problems.
(1) To increase the production volume, it is necessary to increase the furnace diameter. However, if the furnace diameter is increased, the hot air blown from the tuyere will not reach the center of the furnace sufficiently. The flow is reduced, so that coke combustion and iron-based scrap melting in the same area become insufficient, and in some cases, the operation itself may be hindered.
(2) If the particle size of the coke used is small, the coke burns quickly, so the so-called solution loss reaction (endothermic reaction) in which CO ₂ generated by combustion reacts with coke in the process of rising in the furnace. This is likely to occur, and there is a problem that the amount of heat generation decreases and the amount of output decreases. In order to prevent this, it is necessary to increase the use ratio of expensive casting coke, which leads to an increase in manufacturing cost.
(3) Blowing oxygen enrichment is effective for increasing the production volume. However, when this oxygen enrichment is performed, the furnace top temperature decreases, and corrosive gas is condensed to cause corrosion of the exhaust pipe, and dust is generated. There is a problem that gas is not discharged but accumulates in the furnace and gas permeability is lowered.

  Accordingly, the object of the present invention is to solve the above-described problems and to melt iron scrap using a vertical scrap melting furnace to produce hot metal, while maintaining stable operation and high productivity of hot metal. It is another object of the present invention to provide a method that can be manufactured at low cost.

As a result of repeated studies to solve the above-mentioned problems, the present inventors perform blast oxygen enrichment by injecting supersonic oxygen from an oxygen injection nozzle disposed in the tuyere and optimize the injection conditions. Furthermore, it has been found that the above-mentioned problems can be appropriately solved by drying and preheating the furnace charging raw materials (iron-based scrap, coke), and preferably by optimizing the conditions.
The present invention has been made on the basis of such knowledge and has the following gist.

[1] In a vertical scrap melting furnace, iron-based scrap and coke are charged from the top of the furnace, hot air is blown from a plurality of tuyere at the bottom of the furnace, and iron-based scrap is melted by the combustion heat of the coke. A method for producing hot metal by:
An oxygen injection nozzle for injecting oxygen at a supersonic speed is disposed in at least some tuyere, and the oxygen flow rate from the oxygen injection nozzle to the furnace center position is 20 to 70 Nm / sec while blowing hot air from the tuyere. Thus, the hot metal manufacturing method using the vertical scrap melting furnace characterized by injecting oxygen.
[2] A hot metal production method using a vertical scrap melting furnace, wherein coke having an arithmetic average particle size of 120 mm or less is used in the production method of [1].

[3] A vertical scrap melting furnace characterized in that in the manufacturing method of [1] or [2] above, iron-based scrap and / or coke charged in the furnace is dried and / or preheated in advance. The hot metal manufacturing method used.
[4] In the manufacturing method of [3] above, a vertical scrap melting furnace characterized in that iron scrap and / or coke is dried and / or preheated to satisfy the following formula (1): Hot metal manufacturing method.
ΔTs + (2 × ΔTc × Co) / 1000 + 50 × ΔWs + (50 × Co × ΔWc) / 1000
≧ GTt−GTm… (1)
However,
ΔTs (° C.): Increase width of iron-based scrap temperature due to preheating ΔTc (° C.): Increase width of coke temperature due to preheating ΔWs (mass%): Reduction width of iron-based scrap moisture content due to drying treatment and / or preheating ΔWc ( mass%): Decrease in coke moisture content due to drying and / or preheating Co (kg / molten iron): Coke ratio
GTt (℃): Target exhaust gas temperature at the top of the furnace
GTm (° C): Actual exhaust gas temperature at the top of the furnace

According to the present invention, even if the furnace diameter is sufficiently large to ensure the production amount of hot metal, the blast oxygen enrichment is performed and the oxygen injection nozzle arranged in the tuyere as a form of this oxygen enrichment is supersonic. By injecting oxygen and optimizing the injection conditions, the gas flow and oxygen supply in the furnace are optimized, so that coke combustion and iron scrap melting occur properly throughout the furnace . For this reason, hot metal can be manufactured with high productivity and low cost. The same effect can be obtained even when coke having a small particle size with an arithmetic average particle size of 120 mm or less is used.
Further, according to the inventions according to claims 3 and 4, the furnace top temperature is prevented from lowering by drying and preheating the raw materials charged in the furnace in advance. For this reason, condensation of corrosive gas and dust Accumulation in the furnace is suppressed, and stable operation can be performed without causing corrosion of the exhaust gas pipe or trouble in operation.

FIG. 1 schematically shows a vertical scrap melting furnace (hereinafter simply referred to as “melting furnace”) used in the present invention and its basic operation mode. In the figure, 1 is a raw material charging section provided at the top of the furnace, 2 is a plurality of tuyere (blower tuyere) provided at appropriate intervals in the circumferential direction of the lower part of the furnace, and 3 is supplying hot air to the tuyere 2 A hot air pipe, 4 is an exhaust gas outlet, and 5 is an outlet. Although there is no essential limitation on the size of the melting furnace or the like, the furnace inner diameter at the tuyere position is usually about 2 to 4 m and the furnace height is 6 to 6 as a size that is substantially operable or advantageous in operation. It is about 10m.
FIG. 2 is an enlarged view of the tuyere 2, and in this example, the tip of the tuyere tube 20 constituting the tuyere 2 protrudes from the furnace inner wall 7 into the furnace. The number of tuyere is not limited, but it is usually about 4 to 10.

In such a melting furnace, iron-based scrap and coke are charged from the raw material charging section 1 at the top of the furnace, and hot air is blown from a plurality of tuyere 2 to melt the iron-based scrap by the heat of coke combustion gas. Let's use hot metal. The produced hot metal is taken out of the furnace through the outlet 5 at the bottom of the furnace.
The raw iron scrap and coke may be charged into the furnace at the same time or alternately. The main furnace charge materials are iron scrap and coke, but other than this, for example, pig iron, reduced iron, agglomerates of dust and sludge, iron sources such as iron ore, charcoal such as charcoal and anthracite Materials may be charged.

  In order to ensure a sufficient amount of hot metal production and perform economical operation by charging large-size iron scrap without cutting, the furnace diameter of the melting furnace is preferably as large as possible. Specifically, it is desirable that the furnace inner diameter at the tuyere height position is 3 m or more. However, if the furnace diameter is increased, the hot air blown from the tuyere will not reach the center of the furnace sufficiently, resulting in less gas flow in the area on the center of the furnace, and insufficient coke combustion in that area. As a result, the iron-based scrap cannot be sufficiently melted and not only the output amount is lowered, but also the operation itself may be hindered. FIG. 3 shows the difference in gas flow between a melting furnace with a small furnace diameter and a melting furnace with a large furnace diameter. FIG. 4 shows melting furnaces with different furnace diameters (furnace inner diameter at the tuyere height position). According to these, the gas flow rate ratio at the radial position is shown. According to these, when the furnace diameter increases, the hot air blown from the tuyere cannot reach the furnace center, so the gas flow at the furnace center side It turns out that becomes small.

  In order to solve such a problem, in the present invention, an oxygen injection nozzle for injecting oxygen at supersonic speed is disposed in at least some tuyere, and hot air is blown from the tuyere, and the oxygen injection nozzle is positioned at the center of the furnace. Oxygen is injected so that the oxygen flow rate of 20 to 70 Nm / sec. The gas flow in the entire furnace radial direction including the furnace center is achieved by enriching the blown oxygen by injecting supersonic oxygen from the oxygen injection nozzle arranged in the tuyere and optimizing the injection conditions. As a result, coke combustion and iron scrap dissolution will occur properly throughout the furnace.

5 and 6 show an embodiment of the oxygen injection nozzle disposed in the tuyere. FIG. 5 shows the arrangement structure of the oxygen injection nozzle 6 in the tuyere 2. FIG. 6 shows the oxygen injection nozzle. 6 shows a cross section.
The oxygen injection nozzle 6 is a so-called rubber nozzle having a throat portion 60, usually, the throat diameter _d t: 4 to 20 mm, an outlet diameter _d e: 4 to 20 mm approximately, back pressure: 0.2 to 1.0 MPa approximately In this condition, the oxygen jet can be injected at an outlet flow velocity (initial flow velocity) of over sonic speed to about 500 Nm / sec. Such an oxygen injection nozzle 6 is disposed concentrically at substantially the center in the tuyere tube 20. The oxygen injection nozzle 6 may be disposed on all of the plurality of tuyere 2 or may be disposed on only some tuyere 2.

In the tuyere 2 where the oxygen jet nozzle 6 is arranged, an oxygen jet is jetted from the oxygen jet nozzle 6 located substantially in the center of the tuyere 2 at supersonic speed, and hot air is blown from the tip of the tuyere outside. Blowing oxygen enrichment is performed by such supersonic oxygen jet injection by the oxygen injection nozzle 6.
Although there is no restriction | limiting in particular in oxygen enrichment rate (= increase part of the oxygen concentration in ventilation), In order to acquire the effect of ventilation oxygen enrichment, it is preferable to set it as an oxygen enrichment rate of 2 vol% or more generally. On the other hand, if the oxygen enrichment rate is excessive, the amount of heat extracted from the tuyere increases easily due to the increase in the temperature before the tuyere, and the frequency of melting of the tuyere refractory may increase. In addition, the temperature distribution in the furnace radial direction becomes large, and problems such as difficulty in controlling the gas flow tend to occur. For this reason, the oxygen enrichment rate is preferably about 50 vol% as the upper limit.

FIG. 7 shows the flow rate and coke at the furnace center position of oxygen (jet) injected from the oxygen injection nozzle 6 in the operation using each melting furnace with furnace inner diameter D of 2.5 m, 3.0 m, and 3.5 m. It shows the relationship with the basic unit. Each melting furnace used had 8 tuyere, of which oxygen jet nozzles were installed at 4 tuyere (every other tuyere in the furnace circumferential direction). Coke having an arithmetic average particle diameter of 160 mm was used. Here, the oxygen flow velocity V at the furnace center position is a calculated value in a free process in which coke is not charged before the tuyere, and is obtained by the following equation.

According to FIG. 7, regardless of the furnace inner diameter D of the melting furnace, the oxygen flow velocity V at the furnace center position.
However, the coke basic unit is remarkably reduced at 20 to 70 Nm / sec. Here, the low coke basic unit means that the gas flow in the entire furnace radial direction including the area on the furnace center side is optimized, so that the combustion of coke and the melting of iron-based scrap are properly performed throughout the furnace. It means that it has occurred. When the oxygen flow velocity V at the furnace center position is less than 20 Nm / sec, the oxygen supplied from the oxygen injection nozzle 6 does not reach the furnace center part sufficiently, so the gas flow at the furnace center side is small and heat is insufficient. The coke basic unit increases. On the other hand, when the oxygen flow velocity V at the furnace center position exceeds 70 Nm / sec, the oxygen jets injected from the plurality of tuyere oxygen injection nozzles 6 interfere with each other, and the gas flow becomes unstable. It is thought that the combustion and melting of iron scrap are insufficient.

In order to melt iron scrap at a low cost, it is necessary to increase the use ratio of inexpensive coke having a small particle diameter such as iron-making coke. From such a viewpoint, it is preferable to use coke having an arithmetic average particle size of 120 mm or less in the present invention. However, if the diameter of the coke used is small, the coke burns quickly, so that the CO ₂ generated by the combustion of the coke reacts with the coke (C) in the process of rising in the furnace, so-called solution loss reaction (CO ₂ + C → 2CO: endothermic reaction) is likely to occur, and this solution loss reaction causes a problem that the calorific value is reduced and the amount of output is reduced. FIG. 8 shows an example of the gas composition distribution in the furnace height direction when operation is performed using coke with arithmetic average particle sizes of 160 mm and 65 mm, respectively. When coke is used, since the combustion speed of coke is slow, the O ₂ concentration gradually decreases from the tuyere to the middle stage of the furnace, while the CO ₂ concentration increases. A solution loss reaction may occur above the middle furnace stage where the O ₂ concentration has dropped considerably, but the reaction rate is slow due to the large coke particle size, so the CO ₂ concentration maintains a peak above the middle furnace stage, and the CO concentration Maintains a low level. On the other hand, when small-diameter coke is used, the CO ₂ concentration peaks at the lower part of the furnace, and from there to the middle stage of the furnace, the CO2 concentration rapidly decreases due to the solution loss reaction (therefore, the CO concentration rapidly increases).

  It is effective to enrich the blown oxygen by supersonic oxygen injection from the oxygen injection nozzle as in the present invention for the problem associated with such a reduction in the diameter of the coke. By performing such blast oxygen enrichment, the calorific value per unit time can be increased, and the decrease in the calorific value accompanying the reduction in coke diameter can be compensated, and the oxygen supply conditions can be optimized to The gas flow and oxygen supply in the interior will be optimized, so that coke combustion and iron scrap melting will occur properly throughout the furnace.

When using an inexpensive coke having an arithmetic average particle size of 120 mm or less in the present invention, if the particle size of the coke is too small, a reduction in the amount of brewing is unavoidable due to blast oxygen enrichment. The average particle size is preferably 40 mm or more. As the coke having an arithmetic average particle size of 120 mm or less, usually, iron coke (usually arithmetic average particle size: about 25 to 80 mm) and casting coke (usually arithmetic average particle size: about 150 to 250 mm) are appropriately mixed. And use.
The arithmetic average particle size is a particle size obtained by the average particle size = (Σai × Xi) / (Σai) (where Xi: representative particle size, ai: ratio).

  FIG. 9 shows an injection from the oxygen injection nozzle 6 in an operation performed using each melting furnace having a furnace inner diameter D of 2.5 m, 3.0 m, and 3.5 m and using a coke having an arithmetic average particle diameter of 120 mm or less. It shows the relationship between the flow velocity of the oxygen (jet) produced at the furnace center position and the coke unit. Each melting furnace used had 8 tuyere, of which oxygen jet nozzles were installed at 4 tuyere (every other tuyere in the furnace circumferential direction). Coke having an arithmetic average particle diameter of 100 mm was used. Here, the oxygen flow velocity V at the furnace center position is obtained by the above-mentioned formula.

  According to FIG. 9, even when coke having an arithmetic average particle size of 120 mm or less is used, the coke basic unit is obtained when the oxygen flow rate V at the furnace center position is 20 to 70 Nm / sec regardless of the furnace inner diameter D of the melting furnace. Remarkably reduced. As mentioned earlier, the low coke unit consumption means that the gas flow in the entire furnace radial direction including the area on the furnace center side is optimized, which allows the combustion of coke and the melting of iron scrap to occur in the furnace. Means that it has occurred properly overall. The reason why the coke basic unit is significantly reduced when the oxygen flow rate V is 20 to 70 Nm / sec is as described above with reference to FIG.

When the blown oxygen enrichment is performed, the ratio of N _{2 in} the hot air decreases, so that the heat receiving efficiency increases and the furnace top temperature decreases. When the furnace top temperature is lowered, the corrosive gas is condensed to cause corrosion of the exhaust pipe, or dust is not discharged but accumulated in the furnace to cause problems such as deterioration of gas permeability. Here, if the furnace top temperature is lower than 130 ° C., condensation of corrosive gases (NOx, SOx) and the like are likely to occur. Therefore, the furnace top temperature is preferably maintained at 130 ° C. or higher. Here, the furnace top temperature is the exhaust gas temperature at the furnace top outlet.

  In the present invention, when a decrease in the furnace top temperature becomes a problem due to the blast oxygen enrichment, the iron-based scrap and / or coke may be dried and / or preheated in advance in order to ensure the furnace top temperature. Preferably, in that case, for example, iron-based scrap and / or coke is dried and / or preheated so that the furnace top temperature is maintained at 130 ° C. or higher. The furnace top temperature can be increased as the moisture content of the raw material (iron-based scrap and / or coke) at the time of furnace charging is lower and the raw material temperature is higher.

Further, when the iron-based scrap and / or coke is dried and / or preheated in advance, it is preferable to dry or preheat so as to satisfy the following formula (1).
ΔTs + (2 × ΔTc × Co) / 1000 + 50 × ΔWs + (50 × Co × ΔWc) / 1000
≧ GTt−GTm… (1)
However,
ΔTs (° C.): Increase width of iron-based scrap temperature due to preheating ΔTc (° C.): Increase width of coke temperature due to preheating ΔWs (mass%): Reduction width of iron-based scrap moisture content due to drying treatment and / or preheating ΔWc ( mass%): Decrease in coke moisture content due to drying and / or preheating Co (kg / molten iron): Coke ratio
GTt (℃): Target exhaust gas temperature at the top of the furnace
GTm (° C): Actual exhaust gas temperature at the top of the furnace (measured exhaust gas temperature)

When iron-based scrap and / or coke is dried and / or preheated in advance, the furnace top temperature is measured, and then dried and / or preheated according to the above equation (1) based on this actual furnace top temperature. The furnace top temperature can be set to a target temperature, that is, a temperature at which corrosive gas does not condense or a temperature at which dust is smoothly discharged.
Here, the above equation (1) relates that the difference in latent sensible heat of the furnace charge (furnace charge temperature, moisture evaporation heat) appears as a difference in exhaust gas temperature. In the above equation (1), the first term on the left side is the increase in sensible heat of iron-based scrap due to preheating, and the exhaust gas temperature is expected to rise by 1 ° C with a rise of 1 ° C. The second term on the left side is the increase in sensible heat of coke due to preheating, which is also expected to increase 1 ° C as the exhaust gas temperature increases 1 ° C. However, since this sensible heat rise of coke changes depending on the coke ratio, the coke ratio is taken into consideration and the coefficient is multiplied in consideration of the influence on the exhaust gas temperature. The third term on the left side is the heat of water evaporation of iron-based scrap due to drying or preheating, and is multiplied by a coefficient in consideration of the effect on the exhaust gas temperature. The fourth term on the left side is the moisture evaporation heat of coke due to drying treatment or preheating. Since it changes depending on the coke ratio, the coke ratio is taken into consideration, and the coefficient is multiplied taking into consideration the effect on the exhaust gas temperature.

  There is no particular restriction on the method of pre-drying or preheating iron-based scrap or coke. For example, the drying treatment may be performed using an appropriate heat source, or may be stored for a long time in a covered yard for natural use. Drying may be performed. Moreover, you may perform preheating using heating equipment, such as a rotary kiln.

Explanatory drawing schematically showing a vertical scrap melting furnace used in the present invention and its basic operation mode Enlarged view of the tuyere of the vertical scrap melting furnace of Fig. 1 Explanatory drawing showing the difference in gas flow between vertical scrap melting furnace with small furnace diameter and vertical scrap melting furnace with large furnace diameter Explanatory drawing which shows the gas flow rate ratio in the radial direction position of the vertical scrap melting furnace with different furnace inner diameter Explanatory drawing which shows one Embodiment of the arrangement structure of the oxygen injection nozzle in a tuyere Explanatory drawing which shows the cross section of the oxygen injection nozzle of FIG. In an operation carried out using a vertical scrap melting furnace with different furnace inner diameters and coke with an arithmetic average particle size of 160 mm, the flow velocity at the center position of the oxygen jet injected from the oxygen injection nozzle and the basic unit of coke Graph showing the relationship Explanatory drawing showing an example of gas composition distribution in the furnace height direction when operation is performed using coke with arithmetic average particle sizes of 160 mm and 65 mm, respectively. In an operation performed using a vertical scrap melting furnace with different furnace inner diameters and coke with an arithmetic average particle diameter of 100 mm, the flow velocity at the center of the oxygen jet injected from the oxygen injection nozzle and the basic unit of coke Graph showing the relationship

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw material charging part 2 Tuyere 3 Hot air pipe 4 Exhaust gas outlet 5 Outlet 6 Oxygen injection nozzle 7 Furnace wall 20 Tuyere pipe 60 Throat part

Claims (4)

In a vertical scrap melting furnace, iron scrap and coke are charged from the top of the furnace, hot air is blown from a plurality of tuyere at the bottom of the furnace, and iron scrap is melted by the combustion heat of the coke. A method of manufacturing comprising:
An oxygen injection nozzle for injecting oxygen at a supersonic speed is disposed in at least some tuyere, and the oxygen flow rate from the oxygen injection nozzle to the furnace center position is 20 to 70 Nm / sec while blowing hot air from the tuyere. Thus, the hot metal manufacturing method using the vertical scrap melting furnace characterized by injecting oxygen.   Coke having an arithmetic average particle size of 120 mm or less is used, The hot metal manufacturing method using the vertical scrap melting furnace according to claim 1.   The hot metal production method using the vertical scrap melting furnace according to claim 1 or 2, wherein iron-based scrap and / or coke charged in the furnace is dried and / or preheated in advance. The hot metal production method using the vertical scrap melting furnace according to claim 3, wherein the iron-based scrap and / or coke is dried and / or preheated so as to satisfy the following formula (1).
ΔTs + (2 × ΔTc × Co) / 1000 + 50 × ΔWs + (50 × Co × ΔWc) / 1000
≧ GTt−GTm… (1)
However,
ΔTs (° C.): Increase width of iron-based scrap temperature due to preheating ΔTc (° C.): Increase width of coke temperature due to preheating ΔWs (mass%): Reduction width of iron-based scrap moisture content due to drying treatment and / or preheating ΔWc ( mass%): Decrease in coke moisture content due to drying and / or preheating Co (kg / molten iron): Coke ratio
GTt (℃): Target exhaust gas temperature at the top of the furnace
GTm (° C): Actual exhaust gas temperature at the top of the furnace

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