JP2002003917A - Oxygen supply method for vertical melting furnace - Google Patents

Abstract

(57) [Summary] [Problem] To provide an oxygen supply method capable of improving the secondary combustion rate and effectively utilizing thermal energy when melting iron scrap in a vertical melting furnace. SOLUTION: Primary combustion oxygen is supplied from a primary blowing tuyere provided at a lower part of a vertical melting furnace, and secondary oxygen is supplied from a secondary blowing tuyere provided above the primary blowing tuyere. The combustion oxygen is supplied to maintain the supply rate of the secondary combustion oxygen in an appropriate range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen supply method for burning carbon material charged in a vertical melting furnace to generate heat energy required for melting iron scrap.

[0002]

2. Description of the Related Art As an iron source for steelmaking, hot metal discharged from a blast furnace, cold iron obtained by cooling and solidifying hot metal or iron scrap is used. In recent years, the amount of generated iron scrap has been increasing, and the need to reuse iron scrap has been increasing from the viewpoint of environmental protection, energy saving, and reduction of steelmaking costs.

When hot metal or cold iron is used in the steel making process, a great deal of energy is consumed for pretreatment of raw materials such as iron ore and coke and melting and reduction of iron ore in a blast furnace. It is economically disadvantageous because large-scale equipment such as a blast furnace is required. On the other hand, when iron scrap is used, the reduction treatment by the blast furnace is not necessary, and the pretreatment of the raw material can be simplified, so that there are merits such as reduction of energy consumption and simplification of equipment.

[0004] In melting iron scrap, a method of melting iron scrap using equipment utilizing electric energy such as an electric arc furnace or induction melting furnace is generally known. However, the method of melting iron scrap using electric energy has an energy conversion efficiency of about 35 during power generation.
%, So that a significant improvement in energy efficiency cannot be achieved.

[0005] Accordingly, it has been studied to melt iron scrap using a vertical melting furnace such as a cupola. When melting iron scrap using a vertical melting furnace, an inexpensive carbon material such as coke can be used as a heat source, and thermal energy can be recovered when gas generated by burning the carbon material passes through the raw material layer. Therefore, advantages can be obtained from both the raw material cost and the energy efficiency.

Generally, combustion of carbonaceous materials such as coke in a vertical melting furnace is represented by the following equation (2). Hereinafter, the combustion represented by the equation (2) is referred to as primary combustion. If iron scrap is melted only by heat energy obtained by primary combustion, a large amount of carbon material is required, which is economically disadvantageous. C + 1 / 2O ₂ → CO (2) Then, CO gas generated by the primary combustion is further converted to CO ₂
It is necessary to develop a technology to burn more heat and generate more heat energy. This combustion is represented by the following equation (3). Hereinafter, the combustion represented by the equation (3) is referred to as secondary combustion. By utilizing the thermal energy obtained not only in the primary combustion but also in the secondary combustion, it is possible to obtain several times the thermal energy even with the same unit carbon material as compared with the case of only the primary combustion. .

CO + ／ O ₂ → CO ₂ (3) The secondary combustion rate (%) is used as an index indicating the efficiency of secondary combustion. The secondary combustion rate (%) is expressed by the following equation (4) using the CO gas concentration and the CO ₂ gas concentration in the gas generated by burning the carbonaceous material. Secondary combustion rate (%) = 100 × (% CO ₂ ) / [(% CO) + (% CO ₂ )] (4) (% CO ₂ ): CO ₂ gas concentration (vol%) (% CO): CO gas concentration (vol%) In the conventional method of disposing a tuyere at the lower part of a vertical melting furnace such as a cupola and supplying oxygen from the tuyere to melt iron scrap, The secondary combustion rate calculated from the CO gas concentration and the CO ₂ gas concentration in the exhaust gas collected at the furnace top is about 40%, and the thermal energy generated by the combustion of the carbonaceous material is not sufficiently utilized. Therefore, in order to effectively use heat energy, it is necessary to improve the secondary combustion rate.

[0008] Therefore, two stages of blowing tuyeres are arranged in the lower part of the vertical melting furnace in the height direction, and primary combustion is caused by oxygen supplied from the lower blowing tuyeres and supplied from the upper blowing tuyeres. A method has been devised in which secondary combustion is caused by oxygen to improve the secondary combustion rate. However, only by using this method, the secondary combustion rate is improved only up to about 50%.
This is because when oxygen is excessively supplied and the temperature of the carbon material in the vertical melting furnace rises to 700 ° C or more, the CO ₂ gas generated by the secondary combustion passes through the carbon material packed bed and becomes This is due to reacting and causing solution loss. The solution loss is expressed by the following equation (5).

CO ₂ + C → 2CO (5) Since this solution loss is an endothermic reaction, it hinders the heating and melting of the iron scrap and hinders the improvement of the thermal energy efficiency in the vertical melting furnace. ing.
In order to further improve the secondary combustion rate, various methods have been proposed for controlling the distribution of the raw materials charged into the vertical melting furnace.

For example, Japanese Patent Application Laid-Open No. 7-70625 discloses a method for charging raw materials into a moving bed type scrap melting furnace. In this method, tuyeres are arranged in two stages in the height direction below the moving bed type scrap melting furnace, coke is charged around the furnace wall, and scrap is charged from the center to the middle. Thus, thermal efficiency is improved, and productivity and economic efficiency of pig iron are enhanced. But with this method,
If the supply amount of oxygen is increased for the purpose of improving the secondary combustion rate, the scrap is locally heated and oxidized and fused, causing a shelving phenomenon. There was a problem that it was not possible.

[0011]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and, when melting iron scrap in a vertical melting furnace, improves the secondary combustion rate and makes it possible to effectively use thermal energy. It is intended to provide a supply method.

[0012]

Means for Solving the Problems The present inventors have arranged a plurality of blowing tuyeres in the lower part of a vertical melting furnace in the height direction to melt secondary scrap when melting iron scrap. As a result of examining the cause of the inability to achieve a significant improvement in the rate, the setting of the supply speed of oxygen for secondary combustion is due to the number of stages of the tuyere and the height of the tuyere for supplying oxygen for secondary combustion. It has been found that the secondary combustion rate can be greatly improved by adjusting the supply rate of the secondary combustion oxygen in accordance with the interval in the direction and the furnace inner diameter of the vertical melting furnace.

The present invention relates to an oxygen supply method for burning carbonaceous material in a vertical melting furnace to generate heat energy required for melting iron scrap, and is provided in a lower stage of the vertical melting furnace. Supply the primary combustion oxygen from the primary blast tuyeres,
One or two or more stages above the primary air tuyere
The secondary combustion oxygen is supplied from the next blowing tuyere, and the furnace inner diameter D (m) of the vertical melting furnace, the secondary combustion space height H (m) in the vertical melting furnace, and the secondary combustion oxygen are supplied. Supply speed Q ₂ (Nm ³
/ Hr) is an oxygen supply method for a vertical melting furnace for supplying oxygen in a range satisfying the expression (1).

55π × H × D ² ≦ Q ₂ ≦ 80π × H × D ² (1) H: height of secondary combustion space in vertical melting furnace (m) D: furnace of vertical melting furnace Inner diameter (m) Q ₂ : Supply rate of oxygen for secondary combustion (Nm ³ / hr) π: Pi

[0015]

1 is a sectional view showing an example of an apparatus to which the present invention is applied, (a) is a longitudinal sectional view, and (b) is an AA
FIG. At the upper part of the vertical melting furnace 1, a carbon material charging pipe 2 for charging the carbon material 6 is provided. Through the carbon material charging pipe 2, the carbon material 6 such as coke is placed at the center of the vertical melting furnace 1. Be charged. Iron scrap 7 as a raw material is supplied to the vertical melting furnace 1
From the upper part of the furnace through the raw material charging chute 3 into the furnace wall of the vertical melting furnace 1.

At the lower part of the vertical melting furnace 1, a primary blowing tuyere 4 is arranged, and a gas 8 containing oxygen for primary combustion is blown from the primary blowing tuyere 4. The carbon material 6 is burned by oxygen contained in the gas 8 containing oxygen for primary combustion.
This combustion is primary combustion represented by the equation (2), and CO gas is generated. A secondary blowing tuyere 5 is disposed above the primary blowing tuyere 4, and a gas 9 containing oxygen for secondary combustion is blown from the secondary blowing tuyere 5. The oxygen contained in the gas 9 containing oxygen for secondary combustion burns CO gas,
Secondary combustion represented by equation (3) proceeds.

FIG. 1 shows an example in which the primary blowing tuyere 4 is arranged in one stage and the secondary blowing tuyere 5 is arranged in one stage. However, in the present invention, the number of stages of the secondary blowing tuyere 5 is limited. It is not limited to one stage.
That is, two or more secondary blowing tuyeres 5 may be arranged above the primary blowing tuyeres 4 in the height direction. Further, the gas 8 containing the primary combustion oxygen and the gas 9 containing the secondary combustion oxygen are not limited to specific types, and a gas containing oxygen such as air or oxygen-enriched air may be used.

Using the vertical melting furnace shown in FIG. 1, the supply rate Q ₁ (Nm ³ / hr) of the primary combustion oxygen is kept constant.
The relationship between the supply rate Q ₂ (Nm ³ / hr) of the secondary combustion oxygen and the secondary combustion rate was investigated. In addition, oxygen-enriched air (oxygen content 40 vol%) is used as the primary combustion oxygen-containing gas 8, air is used as the secondary combustion oxygen-containing gas 9, and coke is used as the carbonaceous material 6. used.

The supply amount of oxygen-enriched air blown from the primary tuyere 4 was constant at 900 Nm ³ / hr in terms of the amount of oxygen contained in the oxygen-enriched air. That is,
The supply rate Q _{1 of} oxygen for primary combustion is constant at 900 Nm ³ / hr. The amount of air supplied from the secondary tuyere tuyere 5 is converted into the amount of oxygen contained in the air to 450 to 70
It was changed in the range of 0 Nm ³ / hr. That is, the feed rate Q ₂ of the secondary combustion oxygen is in the range of 450~700 Nm ³ / hr.

Thus, the iron scrap 7 is melted by using the vertical melting furnace 1, and the amount of CO ₂ gas in the generated exhaust gas 11 and C
The O gas amount was measured, and the secondary combustion rate was calculated using equation (4). The result is shown in FIG. As apparent from FIG. 2, the feed rate Q ₂ of the secondary combustion oxygen is more than 600 Nm ³ / hr, the secondary combustion rate decreases. This means that if the supply rate Q ₂ of the secondary combustion oxygen is excessive, CO ₂ gas generated by the secondary combustion flows into the coke layer
Causing a solution loss represented by equation (5),
And coke reacting with oxygen for secondary combustion to cause primary combustion as shown in equation (2).

Therefore, in order to determine the range of the supply rate Q ₂ of the oxygen for secondary combustion required to maintain the secondary combustion rate at a high level, the space in which the secondary combustion proceeds in the vertical melting furnace 1 is determined. Various studies were made on the relationship between the density of oxygen for secondary combustion in a secondary combustion space (hereinafter referred to as secondary combustion space) and the progress of secondary combustion. As a result, the density q of oxygen for secondary combustion in the secondary combustion space q
₂ (hereinafter referred to as secondary combustion oxygen density q ₂ ) was found to be an important factor.

That is, using the vertical melting furnace 1 shown in FIG. 1, oxygen-enriched air (oxygen content 40 vol%) as the gas 8 containing oxygen for primary combustion blown from the primary blowing tuyere 4
Use, 900 Nm feed rate to Q ₁ primary combustion oxygen
³ / to be constant at hr, and using air as the gas 9 containing secondary combustion oxygen blown from the secondary air blowing tuyere 5, changing the feed rate Q ₂ of the secondary combustion oxygen, secondary combustion The relationship between the service oxygen density q ₂ (Nm ³ / hr / m ³ ) and the secondary combustion oxygen efficiency (%) was investigated. The result is shown in FIG.

The oxygen density q ₂ for secondary combustion is the supply rate Q ₂ (Nm ³ / hr) of oxygen for secondary combustion per 1 m ³ of the volume of the secondary combustion space. Is a value calculated by Secondary combustion oxygen density ^{_{q 2 (Nm 3 / hr /}} m 3) = Q 2 / V = Q 2 / (π × H × D 2/4) ··· (6) Q 2: 2 post combustion oxygen speed of supply (Nm ³ / hr) V: volume of the secondary combustion space (m ³⁾ H: 2 afterburning space height (m) D: furnace internal diameter of the vertical furnace (m) π: circular constant the The secondary combustion oxygen efficiency is the ratio of the amount of oxygen Q _CO (Nm ³ / hr) consumed in the combustion of CO gas (ie, secondary combustion) to the supply rate Q ₂ (Nm ³ / hr) of oxygen for secondary combustion. It is a ratio and is a value calculated by the following equation (7).

Secondary combustion oxygen efficiency (%) = 100 × Q _CO / Q ₂ (7) Q _CO : amount of oxygen consumed for secondary combustion (Nm ³ / hr) Q ₂ : for secondary combustion Oxygen supply rate (Nm ³ / hr) The secondary combustion oxygen efficiency is different from the secondary combustion rate represented by equation (4) as shown in equation (7). That is, when the secondary combustion oxygen efficiency is 100%, it means that all the secondary combustion oxygen supplied from the secondary blowing tuyere 5 is consumed for the secondary combustion. On the other hand, CO gas concentration varies depending on the feed rate to Q ₁ primary combustion oxygen supplied from the primary blast tuyere 4. Therefore, even if the secondary combustion oxygen efficiency is 100%,
The secondary combustion rate is not always 100%. However, in order to improve the secondary combustion rate, it is necessary to operate while maintaining the secondary combustion oxygen efficiency at a high level (for example, 100%).

As is apparent from FIG. 3, the secondary combustion oxygen efficiency decreases as the secondary combustion oxygen density q ₂ increases.
In order to make the secondary combustion oxygen efficiency 100%, the secondary combustion oxygen density q ₂ is in the range of 220 to 320 Nm ³ / hr / m ³ , that is, 220 ≦ q ₂ ≦ 320 (8) There is a need to. As shown in equation (6), q ₂ = Q ₂ /
Because it is ^{(π × H × D 2/} 4), (8) Equation _{220 ≦ Q 2 / (π ×} H × D 2/4) ≦ 320 55π × H × D 2 ≦ Q 2 ≦ 80π × H × D ² ... (1) That is, in the present invention, if the oxygen for secondary combustion is supplied within the range satisfying the expression (1), the secondary combustion rate can be greatly improved.

The height H of the secondary combustion space was determined by quenching the contents of the furnace after quenching the vertical melting furnace operating under various conditions with an inert gas and disassembling the furnace contents as shown in FIG. When using the vertical melting furnace 1 in which the next blowing tuyere 5 is arranged in one stage, 0.75
m. When the vertical melting furnace 1 in which the secondary blowing tuyere 5 is arranged in two or more stages in the height direction is used, the uppermost secondary blowing tuyere 5 and the lowermost secondary blowing tuyere 5 are connected. The value obtained by adding 0.75 m to the distance (m) can be used as the secondary combustion space height H.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a primary blast tuyere 4 is arranged in one stage, and a secondary blast tuyere 5 is arranged above the primary blast tuyere 4 in a height direction. The iron scrap was dissolved using a cupola having a dissolving capacity of 12 to 15 t / hr. The distance between the secondary wing tuyere 5 and the primary wing tuyere 4 was 0.75 m, and the inner diameter D of the cupola furnace was 1.74 m. Iron scrap is 25-150m
The shredder waste cut into pieces having a particle size of 30 to 60 mm was used as the carbonaceous material 6.

In operating the cupola, first, coke as a carbonaceous material 6 is introduced into the furnace bottom of the cupola, and
It was charged to a height of 1.5 m above the next tuyere 4. Next, after the iron scrap 7 was charged into the furnace wall via the raw material charging chute 3, coke as a carbon material 6 and limestone as a slag-making agent were charged into the center through the carbon material charging pipe 2.
The amount of iron scrap 7 charged was 2 tons, and the amount of coke charged was 226 kg. The charging amount of coke is an amount sufficient for the C concentration in the hot metal 10 to reach the target value of 3.5 mass%.

Thereafter, the operation of charging the iron scrap 7 into the furnace wall and charging the coke and limestone into the center was repeated, and the iron scrap 7 was charged to a height of 6 m above the primary blowing tuyere 4. Next, oxygen-enriched air (oxygen content 40 vol%) is converted from the primary blowing tuyere 4 as a gas 8 containing oxygen for primary combustion.
Was infused. The supply amount of the oxygen-enriched air depends on the supply amount of the contained oxygen (that is, the supply rate Q of the primary combustion oxygen).
It was 900 Nm ³ / hr in terms of ₁ ).

Further, air was blown from the secondary blowing tuyere 5 as a gas 9 containing oxygen for secondary combustion. The supply amount of the air is converted into the supply amount of the contained oxygen (that is, the supply speed Q _{2 of the} oxygen for the secondary combustion) to obtain a total of 550 Nm ^3.
/ Hr. The supply rate of the oxygen for secondary combustion Q ₂ = 5
50 Nm ³ / hr is a value that satisfies the range of Expression (1). In this way, iron scrap 7 while supplying oxygen into the cupola
Was dissolved. After the melting of the iron scrap 7 is started, the height of the raw material in the cupola is increased by 6 m ± 6 m above the primary blowing tuyere 4.
Hot metal 10 was produced continuously while charging the raw material so as to maintain 0.3 m. This is an invention example.

Next, as a comparative example, the cupola shown in FIG. 4 was operated with the supply rate Q _{2 of} oxygen for secondary combustion set to 700 Nm ³ / hr. This secondary combustion oxygen supply rate Q ₂ = 7
00Nm ³ / hr is a value exceeding the upper limit of the range of the expression (1). Other operating conditions are the same as those of the invention example, and the description is omitted. The dissolution rate of iron scrap (t / hr), the basic unit of coke (kg / t), and the secondary combustion rate (%) were investigated for the invention examples and comparative examples. The results are as shown in Table 1. In addition, the melting rate (t / hr) of iron scrap is the input amount (t) of iron scrap per 1 hour of operation time, and the basic unit of coke (kg / t) is the charging amount of coke (kg) per ton of hot metal. Yes, the secondary combustion rate (%) is calculated using the measured values of CO ₂ gas concentration and CO gas concentration in exhaust gas. (4)
This is a value calculated from the equation.

[0032]

[Table 1]

Comparing the invention example with the comparative example, the dissolution rate of the iron scrap is lower in the invention example because the sum of the oxygen for primary combustion and the oxygen for secondary combustion is smaller in the invention example.
The unit of coke was lower in the invention example, and the secondary combustion rate was higher in the invention example. That is, in the example of the invention, the thermal energy could be used efficiently.

[0034]

According to the present invention, when melting iron scrap using a vertical melting furnace, the secondary combustion rate is improved, and heat energy can be used efficiently.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of an apparatus to which the present invention is applied, in which (a) is a vertical cross-sectional view, and (b) is a cross-sectional view as viewed from AA.

FIG. 2 is a graph showing the relationship between the supply rate of secondary combustion oxygen and the secondary combustion rate.

FIG. 3 is a graph showing a relationship between secondary combustion oxygen density and secondary combustion oxygen efficiency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical melting furnace 2 Carbon material charging pipe 3 Raw material charging chute 4 Primary blast tuyere 5 Secondary blast tuyere 6 Carbon material 7 Iron scrap 8 Gas containing primary combustion oxygen 9 Containing oxygen for secondary combustion Gas 10 Hot metal 11 Exhaust gas

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K012 CB00 4K045 AA02 BA02 DA02 DA06 GA17 GB10 GB12 4K056 AA01 CA02 FA02

Claims (1)

[Claims] 1. An oxygen supply method for burning carbonaceous material in a vertical melting furnace to generate heat energy required for melting iron scrap, wherein the oxygen supplying method is provided in a lower stage of the vertical melting furnace. The primary combustion tuyere supplies oxygen for primary combustion, and one or two or more stages are provided above the primary ventilation tuyere.
Secondary combustion oxygen is supplied from the next blow tuyere, and the furnace inner diameter D (m) of the vertical melting furnace, the secondary combustion space height H (m) in the vertical melting furnace, and the secondary combustion An oxygen supply method for a vertical melting furnace, characterized in that oxygen is supplied within a range where a supply rate Q ₂ (Nm ³ / hr) of oxygen for use satisfies the following expression (1). 55π × H × D ² ≦ Q ₂ ≦ 80π × H × D ² (1) H: Height of secondary combustion space in vertical melting furnace (m) D: Inner diameter of vertical melting furnace (m ) Q ₂ : supply rate of oxygen for secondary combustion (Nm ³ / hr) π: pi