JPH07207328A - Treatment of exhaust gas produced at the time of melting scrap - Google Patents

Abstract

PURPOSE:To efficiently utilize the heat of combustion of a carbonaceous material and to prevent waste gas from bad influence upon the environment by specifying the operational condition and treating the waste gas by a specific method, at the time of molten scrap in a metallurgical furnace enabling top- bottom blowing. CONSTITUTION:High concn. of oxygen-containing gas is used in the melting furnace 2 and the scrap is melted with the heat generated at the time of burning the carbonaceous material to obtain molten iron alloy 5. At this time, the scrap is melted under the condition of existence of the slag of >=300kg/t to metal and of the carbonaceous material having >=80% fixed carbon of 50-400kg/t to slag, and secondary combustion ratio is made to be 80-96%. Then, the exhaust gas produced at the time of burning the carbonaceous material, is blown so that the waste gas temp. exhausted from the upper part of the melting furnace 2 through an exhaust tube 9 becomes 1450-1630 deg.C to execute the temp. adjustment. Together with this, carbon dust in the waste gas is made to be >=30g/Nm<3>, and coal powder 12 is blown into the exhaust gas to execute desulfurizing and the absorption of chlorine-based organic gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas generated when scrap is melted by using a metallurgical furnace such as a converter capable of blowing a bottom.

[0002]

2. Description of the Related Art In recent years, it has become a technical subject to efficiently produce molten metal by recycling solid metal raw materials such as scrap due to resource and environmental problems. There are various kinds of metal scraps, but as a method for obtaining molten iron by using steel scrap, which has a large amount of generation, conventionally, most has been carried out in an electric furnace. However, the electric furnace consumes a large amount of electric power for melting and refining scrap, which is not preferable in a country with a significantly high electric power price, such as cost increase. Therefore, as a method for economically melting and refining scrap without using an electric furnace, a method for melting and refining scrap using inexpensive carbonaceous materials by utilizing the surplus production capacity of a converter with a high acid transfer capacity is available. It has come to be considered.

Under such circumstances, general scrap is adhering to chlorine-containing organic substances such as cutting oil and plastics. In addition, organic waste produced in the shredder process called fluff exists as a substance that is difficult to process. It is said that when this is used in a normal converter, the duct is severely worn. However, generally, the existing top-bottom blown composite blowing converter is used to prevent the increase in equipment, and at the same time, the carbonaceous material is charged into the furnace together with the scrap, and oxygen is blown up to dissolve it. A method of refining is proposed.

[0004]

However, in the above-described upper-bottom blowing composite blowing, there is a large loss of carbonaceous material scattered outside the furnace due to the blowing gas flow, and therefore the heat source for melting scrap is inexpensive and inexpensive. There is a problem that the benefits required for timber are not fully utilized. This problem is remarkable when using coal as a carbonaceous material, and the amount of dust generated increases as the amount of top-blown O ₂ increases. Further, especially when the secondary combustion rate becomes high, NO _{X is} generated in a large amount, and there is a concern that corrosion by nitric acid and sulfuric acid corrosion by SO _X may occur. There remains a problem that the countermeasures against these NO _x and SO _x are not sufficient, and the operation method that reduces the NO _x is not established.

[0005]

[Means for Solving the Problems] It is possible to solve the above-mentioned problems, prevent corrosion, etc., and positively process fluff. In addition, scrap produces combustion of carbonaceous materials such as coke. Providing an exhaust gas treatment method in the melting process of scrap that improves melting productivity by operating conditions and exhaust gas treatment that efficiently use heat to melt at low cost and at the same time make exhaust gas have no adverse effect on the environment To do. The gist of the invention is (1) a metallurgical furnace capable of blowing gas from above and below, using a high-concentration oxygen-containing gas,
When the scrap is melted by the heat generated when the carbonaceous material is burned to obtain a molten iron alloy, the slag is added to the metal t in an amount of 3
Slag t with carbonaceous material of 00kg or more and fixed carbon content of 80% or more
The scrap is melted in a state of 50 to 400 kg per second, the secondary combustion rate is 80 to 96%, and the exhaust gas temperature is 1450.
The temperature is adjusted by blowing the exhaust gas generated when the carbonaceous material is burned to ~ 1630 ° C, and the carbon dust in the exhaust gas is set to 30 g / Nm ³ or more, and lime powder is blown into the exhaust gas to be desulfurized. And a chlorine-based organic gas are adsorbed, a method for treating exhaust gas generated during scrap melting, (2) (1),
It is a method for treating exhaust gas generated during scrap melting, which is characterized in that dust in the generated exhaust gas is recovered and charged into a metallurgical furnace.

The present invention will be described in detail below with reference to the drawings.
explain. FIG. 1 shows a scrap melting and blowing method according to the present invention.
It is a conceptual diagram of the reaction container used. As shown in Figure 1,
The reaction vessel 1 is lined with refractory material 2, for example a converter,
An oxygen top blowing lance 3 is provided. From oxygen top blowing lance 3
Spraying oxygen gas onto the molten slag 4 on the molten iron alloy 5
It Coal 6 such as coal and coke and scrap 7
It is charged from one side and charged on the molten slag 4 in the furnace. This
Effectively transfer the combustion gas generated from these carbon materials to the molten slag
Therefore, from the bottom of the furnace, for example, N ₂, C
Stir the molten iron alloy with stirring gas 8 such as O and carbon dioxide gas.
The purpose is to perform good heat transfer by stirring.

[0007]

The oxygen gas is blown from above the converter through the oxygen top blowing lance. This oxygen gas is a high-concentration oxygen-containing gas, and is pure oxygen gas or 70
A relatively low-purity oxygen gas containing at least 50% oxygen, or a mixture of pure oxygen gas and air, or a diluting gas such as nitrogen,
An oxygen concentration of 70% or more. Such oxygen gas may be supplied from above the molten slag 4 or may be blown obliquely from above. When supplying oxygen from a plurality of holes, it is possible to use a pulverized coal burner as a part. Carbon material, slag material and scrap are mainly input from above. In this case, the scrap is charged by not dividing it into preheated ones or preheated ones by continuous charging or intermittent charging and appropriately dividing them.

Then, the oxygen gas burns the combustible gas components such as carbonaceous material and generated CO to generate heat, and supplies heat for melting scrap. On the other hand, the bottom-blown gas has the effect of stirring the melt and is necessary for the progress of heat transfer. As the bottom blowing gas, as described above, one kind or a mixed gas of two or more kinds of N ₂ , CO, CO ₂ , argon and the like is used. In this step, to increase the secondary combustion rate is intended to increase the dissolution of the scrap, while likely secondary combustion rate increases the NO _X and SO _X increases.

That is, the secondary combustion rate is (CO ₂ +
H ₂ O) / (CO + CO ₂ + H ₂ O + H ₂ ) × 100%
The higher the value is, the more the amount of heat generated per oxygen supply rate or the amount of exhaust gas increases, which is advantageous because the productivity of the facility increases. On the other hand, as a result of increasing the secondary combustion rate, the exhaust gas temperature becomes high, and NO _X and SO _X become high, which is not preferable. Therefore, the secondary combustion rate is 80 to 96
It is intended to reduce the NO _X by suppressing it to%. If the secondary combustion rate is less than 80%, the heat of melting the scrap is insufficient, and the productivity of scrap melting deteriorates. In addition, when it exceeds 96%, the amount of NO _X generated sharply increases and exceeds the NO _X agreed value, which is a fixed regulation.
It is necessary to remove NO _x .

The proper secondary combustion rate depends on the fixed carbon content of the carbonaceous material used, and in order to raise the secondary combustion rate as much as possible, it is necessary to use carbonaceous material having a fixed carbon content of 80% or more. That is, FIG. 2 is a diagram showing the relationship between the fixed carbon content of the used carbonaceous material and the secondary combustion rate of the gas in the furnace. As shown in FIG. 2, it is clearly shown that the secondary combustion rate is high when the fixed carbon is 80% or more. The secondary combustion rate can be adjusted by combining the oxygen supply condition and the amount of carbonaceous material.

Therefore, in the present invention, the amount of slag is 300 kg or more per metal t. FIG. 3 is a diagram showing the relationship between the amount of slag and the amount of iron oxide-based dust generated.
As shown in this figure, when the amount of slag is less than 300 kg per t, it indicates that the amount of iron oxide-based dust generated sharply increases. Therefore, the amount of slag is t
When the amount is 300 kg or more, generation of dust can be suppressed. Further, as the charging of the carbonaceous material in the present invention, lump coke or coal is charged and the scrap is melted in a state where 50 to 400 kg of slag is present. For that purpose, it can be understood by excluding gasification and scattering as powder from the fixed carbon amount of the charged coal material. If this value is less than 50 kg, slag foams and stable operation cannot be performed. On the other hand, if it exceeds 400 kg, the secondary combustion rate will be low.

FIG. 4 is a graph showing the influence of the secondary combustion rate on the exhaust gas NO _x content. As shown in FIG. 4, as the secondary combustion rate increases, the NO content increases accordingly. From this, the content of NO is 1
This shows that the exhaust gas temperature needs to be 1450 ° C to 1630 ° C in order to suppress the secondary combustion rate to 00 ppm or less and to maintain the high secondary combustion rate of 80 to 96% as described above. Figure 5 shows CO ₂ / CO in the hood and average S
It is a figure which shows the relationship with _Ox content. C in this hood
Assuming that O ₂ / CO is the secondary combustion rate, as shown in FIG. 5, the SO _X in the exhaust gas is as high as 300 to 500 ppm in order to maintain the secondary combustion rate of 80 to 96%, and therefore is below the regulation value. In order to achieve this, it is necessary to perform desulfurization treatment. For this reason, SO _x is desulfurized with limestone in the exhaust gas process so that it falls below the SO _x regulation value.

FIG. 6 shows the carbon dust concentration in the exhaust gas and the gas
It is a figure which shows the relationship of the organic chlorine compound concentration of. Shown in Figure 6
So that the concentration of carbon dust in the exhaust gas is 30 g / Nm³Since
By setting it above, the concentration of organic chlorine in the gas is reduced.
Rukoto can. Conversely, the carbon dust concentration is 30 g / Nm³
If it is less than the range, the concentration of organic chlorine in the gas may increase sharply.
Is shown. That is, the organic chlorine compound gas is
30g / Nm ³Adsorbed by the above
To maintain environmental regulations by lowering the gas concentration.
You can Moreover, when this dust is returned to the furnace, it is absorbed
It is capable of decomposing organic chlorine compounds
It In addition, organic chlorine compound gas is
The gas temperature in the furnace to 1
Suppressing the amount generated by setting it to 450 ° C or higher
Can be done. On the contrary, add scrap when not blowing oxygen
And organic chlorine compounds are not fully decomposed
It is not preferable because it will increase.

FIG. 7 is a process diagram showing the exhaust gas treatment according to the present invention. As shown in FIG. 7, the exhaust gas discharged from the upper part of the melting furnace 2 is discharged from the discharge pipe 9. However, if the temperature of the exhaust gas at this time exceeds 1630 ° C., the refractory materials and NO _{x of the} melting furnace will rapidly increase. Therefore, it is necessary to keep the temperature below 1630 ° C. For that purpose, it is necessary to adjust the temperature. The lower flue gas 10 of nitrogen concentration to lower the blowing temperature suppressing NO _X generation amount for the temperature adjustment. That is, exhaust gas super seat = exhaust gas amount x
It is determined by (gas temperature-melt temperature), and by adjusting this gas temperature, it is possible to prevent the supersheet of exhaust gas. Subsequently, the temperature of the gas discharged from the exhaust gas pipe 9 is lowered by the boiler heat exchanger 11, and powdered limestone 12 is charged in the exhaust gas pipe 9 to perform desulfurization and adsorption of chlorine-based organic gas, and then the hot cyclone 1
The lime separated over 3 and the duct together with the transfer conveyor 1
It is charged into the melting furnace 1 via 4 and reused.

FIG. 8 is a graph showing the relationship between the amount of lime powder blown into the flue and the SO _X removal rate in the exhaust gas. As shown in FIG. 8, in order to efficiently remove SO _X in the exhaust gas, in order to efficiently remove it, 5 g / Nm ³ or more of CaO should be blown to remove 50% or more of SO _X. Indicates that you can. Further, FIG. 9 is a diagram showing the relationship between the gas temperature in the furnace and the concentration of the organic chlorine compound in the gas. As shown in FIG. 9, when the temperature is 1450 ° C. or higher, the amount of organic chlorine compounds in the exhaust gas is extremely reduced. Conversely, 1450
It shows that the amount of organic chlorine compounds in the exhaust gas increases when the temperature exceeds ℃. . Therefore, in order to operate with a reduced amount of organic chlorine compounds in the exhaust gas, it is necessary to set the temperature to 1450 ° C or higher.

[0016]

【Example】

Example 1 Internal volume 180 lined with magnesia-carbon brick
Using a m ³ converter, the bottom of the furnace is provided with four bottom blowing tuyeres,
Using a furnace in which nitrogen gas is blown into the hot metal at 1400 Nm ³ / h, molten metal (hot metal) is first produced by burner melting of scrap, or it is charged in a molten metal 50t converter melted in another furnace. . We made slag and started operation. While blowing acid at 25,000 Nm ³ / h from the top blowing lance, steel scrap internal oil that does not contain plastics (55% of the total charging amount) is charged by tilting the furnace, while oil and plastic The rest containing soot was continuously charged while blowing oxygen, and a total of 70 tons of steel scrap was charged. And while blowing acid coke (solid carbon: 82%,
S: 0.04%, SiO ₂ : 8%) was added. At the same time, CaO is added to make the slag CaO / SiO ₂ = 1.2. Emission of molten iron produced is 80% of the maximum amount of molten iron present
With 95% of the slag left in the furnace, the amount of slag was 350 to 450 kg per t, and the slag was repeatedly used again. In the next heat, these steps are repeated. The carbonaceous material in the furnace is 100 to 250 kg per slag t, the secondary combustion rate at this time is in the range of 85 to 90%, and the exhaust gas temperature is 1470 to
The temperature could be adjusted to 1590 ° C. The components of the molten iron alloy were C: 4.0% and S: 0.03%. The carbon content in the dust was 40 to 60 g / Nm ³ . As a result, NO _X can be suppressed to 90 ppm or less, and 400 ppm of SO _X is 80 ppm or less by desulfurization treatment by injecting 15 g / Nm ^{3 of} powdered limestone from the discharge pipe to perform desulfurization treatment, and total organic chlorine compounds 2 ppm or less. It was possible to reduce NO _X and SO _X.

EXAMPLE 2 Inner volume 180 lined with magnesia-carbon brick
Using a m ³ converter, the bottom of the furnace is provided with four bottom blowing tuyeres,
Using a furnace in which nitrogen gas is blown into the hot metal at 1400 Nm ³ / h, molten metal (hot metal) is first produced by burner melting of scrap, or it is charged in a molten metal 50t converter melted in another furnace. . We made slag and started operation. While blowing acid at 25,000 Nm ³ / h from the top blowing lance, steel scrap internal oil that does not contain plastics (55% of the total charging amount) is charged by tilting the furnace, while oil and plastic The rest containing soot was continuously charged while blowing oxygen, and a total of 70 tons of steel scrap was charged. And while blowing acid coke (solid carbon: 82%,
S: 0.04%, SiO ₂ : 8%) was added. At the same time, CaO is added to make the slag CaO / SiO ₂ = 1.2. Emission of molten iron produced is 80% of the maximum amount of molten iron present
With 95% of the slag left in the furnace, the amount of slag was 350 to 450 kg per t, and the slag was repeatedly used again. In the next heat, these steps are repeated. The carbonaceous material in the furnace is 100 to 250 kg per slag t, the secondary combustion rate at this time is in the range of 85 to 90%, and the exhaust gas temperature is 1470 to
The temperature could be adjusted to 1590 ° C. The components of the molten iron alloy were C: 4.0% and S: 0.03%. The carbon content in the dust was 40 to 60 g / Nm ³ . As a result, NO _X can be suppressed to 90 ppm or less, and 400 ppm of SO _X is 80 ppm or less by desulfurization treatment by injecting 15 g / Nm ^{3 of} powdered limestone from the discharge pipe to perform desulfurization treatment, and total organic chlorine compounds 2 ppm or less. After the desulfurization treatment, the dust content is total Fe: 36%, total C: 35%, total Zn: 15%, total organic chlorine content 15 ppm.
And this dust could be reused. Also,
We were also able to improve the yield of iron.

[0018]

As described above, by carrying out the present invention, the secondary combustion rate of 80 to 96% can be achieved while effectively utilizing scrap and organic waste.
Further, NO _X, SO _X, etc. in the exhaust gas can be reduced, the amount of dust generated can be reduced, and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a reaction vessel using the scrap melting and blowing method according to the present invention,

FIG. 2 is a diagram showing a relationship between a fixed carbon content rate of a used carbon material and a secondary combustion rate of gas in a furnace,

FIG. 3 is a diagram showing the relationship between the amount of slag and the amount of iron oxide-based dust generated,

FIG. 4 is a diagram showing the influence of the secondary combustion rate on the exhaust gas NO _x content,

FIG. 5 is a diagram showing the relationship between CO ₂ / CO in the hood and the average SO _X content,

FIG. 6 is a diagram showing a relationship between carbon dust concentration in exhaust gas and organic chlorine compound concentration in gas,

FIG. 7 is a process diagram showing an exhaust gas treatment according to the present invention,

FIG. 8 is a diagram showing the relationship between the amount of lime powder blown into a flue and the removal rate of SO _X in exhaust gas;

FIG. 9 is a diagram showing a relationship between a furnace gas temperature and an organic chlorine compound concentration in the gas.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction vessel 2 Refractory 3 Oxygen top blowing lance 4 Molten slag 5 Molten iron alloy 6 Carbon material 7 Scrap 8 Stirring gas 9 Exhaust pipe 10 Combustion exhaust gas 11 Boiler heat exchanger 12 Powder limestone 13 Hot cyclone 14 Transfer conveyor

Claims (2)

[Claims] 1. A metallurgical furnace capable of blowing gas from the top and bottom, using a high-concentration oxygen-containing gas, and melting the scrap by the heat generated when the carbonaceous material is burned to obtain a molten iron alloy, the slag is metal. 300 kg or more per t, fixed carbon content 80
% Of carbonaceous material is present in the amount of 50 to 400 kg per slag t, scrap is melted, and the secondary combustion rate is 80 to 96.
%, While adjusting the temperature by blowing the exhaust gas generated when the carbonaceous material is burned so that the exhaust gas temperature becomes 1450 to 1630 ° C., the carbon dust in the exhaust gas is set to 30 g / Nm ³ or more, and the discharged exhaust gas is lime. A method for treating exhaust gas generated during scrap melting, which comprises blowing powder to desulfurize and adsorb chlorine-based organic gas. 2. The method according to claim 1, wherein the dust in the generated exhaust gas is recovered and charged in a metallurgical furnace to treat the exhaust gas generated during scrap melting.