JP4992407B2 - Hot metal production method using vertical scrap melting furnace - Google Patents

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) 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.
(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.

  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 appropriately dried the materials charged in the furnace (iron-based scrap, coke), preferably by optimizing the conditions to appropriately solve the above-mentioned problems. It was found that it can be solved.
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:
The furnace top temperature is increased to 130 ° C. or more by enriching the hot air with oxygen and drying and / or preheating the iron-based scrap and / or coke charged in the furnace in advance to reduce the moisture content. A hot metal production method using a vertical scrap melting furnace, characterized in that it is maintained .
[2] In the manufacturing method of [1] above, a vertical scrap melting furnace characterized in that iron scrap and / or coke is dried and / or preheated so as 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

[3] 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] or [2].

  According to the present invention, even if the amount of exhaust gas is increased in order to increase productivity, the oxygen supply in the furnace is adequate by performing blast oxygen enrichment and pre-drying and preheating the furnace charging raw material. As a result, the combustion of coke and the melting of iron-based scrap occur appropriately in the entire furnace, and the decrease in the top temperature of the furnace is suppressed, so that condensation of corrosive gas in the exhaust gas pipe and accumulation of dust in the furnace occur. It can be suppressed. For this reason, hot metal can be manufactured with high productivity and low cost without causing operational troubles due to a decrease in furnace top temperature. 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.

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 portion 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 6 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.

Enrichment of blown oxygen is effective for increasing the production amount. However, when blown oxygen enrichment is performed, the ratio of N _{2 in} the hot air is reduced, so that the heat receiving efficiency is increased and the furnace top temperature is lowered. When the furnace top temperature falls, as mentioned above, the corrosive gas is condensed to cause corrosion of the exhaust pipe, or dust is not discharged but accumulates in the furnace, resulting in a decrease in gas permeability. Produce. In order to solve such a problem, in the present invention, oxygen-enriched hot air and iron-based scrap and / or coke charged in the furnace are dried and / or preheated in advance. At that time, the iron-based scrap and / or coke is preferably 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

In this way, oxygen is enriched in hot air and the raw materials charged in the furnace are dried and preheated in advance, so that the supply of oxygen in the furnace is optimized, so that the combustion of coke and the melting of iron-based scrap are performed in the furnace. Appropriately occurring as a whole, and by suppressing the decrease in furnace top temperature, condensation of corrosive gas in the exhaust gas pipe and accumulation of dust in the furnace can be suppressed.
Examples of forms of oxygen enrichment include, for example, (a) a method of adding oxygen to hot air in advance and supplying this to the tuyere, (b) a method of supplying oxygen into the tuyere and mixing with hot air in the tuyere, (C) Arbitrary methods such as a method in which an oxygen injection nozzle is disposed in the tuyere, oxygen is injected from the oxygen injection nozzle into the furnace, and hot air is injected from the outside thereof can be employed.

  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.

  In the present invention, in order to secure the furnace top temperature, the iron-based scrap and / or coke is dried and / or preheated in advance. The furnace top temperature is the exhaust gas temperature at the furnace top outlet. The lower the moisture content of the raw material (iron scrap and / or coke) at the time of furnace charging, the higher the raw material temperature, Can be high. When 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. Therefore, in the present invention, 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.

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. As the temperature rises by 1 ° C, the exhaust gas temperature is expected to rise by 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 rise by 1 ° C as the exhaust gas temperature rises by 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.

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. 3 shows an example of the gas composition distribution in the furnace height direction when the operation is performed using cokes having 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).

  For the problem associated with such a reduction in the diameter of coke, it is effective to enrich the hot air with oxygen as in the present invention. An increase in solution loss (endothermic reaction) is unavoidable due to a reduction in the diameter of coke, and in order to cope with a decrease in the amount of output due to such an increase in endotherm, it is necessary to increase combustion in order to compensate for the endotherm. At this time, if the amount of blast is simply increased, the amount of exhaust gas increases and exceeds the allowable amount of the exhaust gas treatment system. On the other hand, if the blast oxygen enrichment is performed without increasing the blast amount itself, the combustion can be increased while suppressing the exhaust gas amount. Therefore, the shortage of heat accompanying the reduction in the diameter of coke can be compensated.

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. 4 shows the operating conditions and results (blast pressure, furnace top temperature, amount of tapping) in operation using a melting furnace with a furnace inner diameter D of 2.1 m at the tuyere height (coke ratio: 130 kg / t). , Oxygen enrichment rate, scrap charging temperature). In the present example, the furnace interior of iron-based scrap (preheated scrap) preheated from the stage during operation was performed.
In this example, during operation under the base operating conditions, there was a demand for an increase in the amount of output at time A, and the amount of output was increased by increasing the oxygen enrichment rate. However, as the oxygen enrichment rate increased, the furnace top temperature decreased, the blast pressure gradually increased, and the fluctuation amount increased. The increase in the blowing pressure and the increase in pressure fluctuation are thought to be due to the inhibition of the discharge of dust to the outside of the furnace (discharge accompanying the exhaust gas). Therefore, the furnace charging scrap was switched from the normal temperature scrap (nominal temperature 25 ° C.) to the preheated scrap (nominal temperature 65 ° C.). The scrap was preheated by putting the scrap into a container having an effective internal volume of 3 m ³ , blowing hot air (300 ° C.) from a hot air inlet provided on the side wall of the container, and charging the furnace immediately after preheating. The preheating temperature of the scrap was calculated and adjusted according to the above equation (1) by setting a target furnace top temperature 40 ° C. higher than the current furnace top temperature. As a result, the furnace top temperature gradually increased to reach the target furnace top temperature, and accordingly, the blowing pressure gradually decreased and the fluctuation amount became small.

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 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. The graph which shows transition of the operation conditions in the operation of an Example, and the operation result (Blasting pressure, furnace top temperature, amount of tapping, oxygen enrichment rate, scrap charging temperature).

Explanation of symbols

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

Claims (3)

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:
The furnace top temperature is increased to 130 ° C. or more by enriching the hot air with oxygen and drying and / or preheating the iron-based scrap and / or coke charged in the furnace in advance to reduce the moisture content. A hot metal production method using a vertical scrap melting furnace, characterized in that it is maintained . The hot metal production method using a vertical scrap melting furnace according to claim 1, 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   Coke having an arithmetic average particle size of 120 mm or less is used. The hot metal production method using the vertical scrap melting furnace according to claim 1 or 2.

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