KR100356156B1 - A method for promoting combustibility in balst furnace - Google Patents

Abstract

PURPOSE: A method for improving combustion efficiency of blast furnace by maintaining furnace circumstances stably during blast furnace operation and increasing the limit injection quantity of pulverized coal, thereby enabling a large quantity of pulverized coal to be injected. CONSTITUTION: In a blast furnace operation method comprising the process of injecting 100 to 170 kg of pulverized coal per ton of molten iron as blowing oxygen and air through tuyere, the method for improving combustion efficiency of blast furnace is characterized in that flow rate of the tuyere is maintained to 215 to 240 m/s, wherein the flow rate is maintained to the range of 218 to 237 m/s when pulverized coal injection quantity is less than 110 kg or exceeds 150 kg per ton of molten iron, wherein the flow rate is maintained to the range of 225 to 235 m/s, and wherein flow rate of the tuyere is controlled by adjusting diameter of the tip of the tuyere.

Description

A method for promoting combustibility in balst furnace

The present invention relates to a blast furnace operation, and more particularly to a method for improving the combustion efficiency of the blast furnace by not only maintaining the stable yellowing in the blast furnace operation, but also increasing the marginal injection amount of pulverized coal. will be.

Recently, in the blast furnace operation, a part of the coke used as a heat source and a reducing agent in the blast furnace has been replaced by pulverized coal. The pulverized coal injection condition is directly related to the reduction of the environmental pollution and the cost reduction of the blast furnace charter due to the decrease in the operation rate of the coke oven. However, the pulverized coal injection can only be carried out below a certain limit due to the limitation of the amount of fine coal that can be consumed in the furnace by the direct reduction of combustion and molten oxide and the reduction of carbon dioxide in the blast furnace.

1 is a schematic diagram showing the blast furnace behavior of the pulverized coal blown during blast furnace operation.

As shown in FIG. 1, the pulverized coal blown into the furnace through the tuyere 1 at the bottom of the blast furnace passes through the furnace upper sediment layer 8 in the state of unburned pulverized coal and exits the furnace. At this time, the pulverized coal blown into the tuyere 1 is preferentially burned in the form of Scheme 1 in the combustion zone 2 which is the cavity of the front face of the tuyere, and the unburned pulverized coal that is not burned due to the combustion zone is the coke stagnant layer. Passing through the dropping zone (5) between the core (3) and the fusion zone (4) to meet the molten iron oxide in the slag to participate in the reduction reaction as shown in Scheme 2, or to meet the carbon dioxide to lose the reaction by gasification reaction as shown in Scheme 3 do. In addition, the unburned pulverized coal which does not lose the reaction in the dropping zone 5 is further lost by the gasification reaction as in Scheme 3 in the 1000-1200 ° C. temperature section 6 directly above the fusion zone 4, and the reaction here also occurs. Unburned pulverized coal which has not been lost escapes out of the furnace as the mass 7 and the upper sediment rise with gas.

C (S) + 1 / 2O ₂ (g) = CO (g)

FeO (ℓ) + C (s) = Fe (ℓ) + CO (g)

CO ₂ (g) + C (s) = 2CO (g)

Therefore, the limit of the amount of pulverized coal in the combustion zone represented by Equation 1, and the reaction loss amount in the dropping zone given by Equations 2 and 3 in the constant state without increasing the oxygen injection amount or the equipment fluctuations to increase the hot air temperature. And, it is determined by the amount of reaction loss in a high temperature region of 1000 ° C. or higher on the upper portion of the fusion zone according to the reaction formula (3). That is, when the amount of fine coal blown into the tuyere is larger than the furnace loss according to the reaction formulas 1 to 3, it is discharged out of the furnace in the form of unburned pulverized coal. Pulverized coal injection is possible only below the threshold. In fact, when the amount of pulverized coal injection increases, as shown in FIG. 2, the change in theoretical temperature of the combustion zone decreases and the change in carbon concentration in dust discharged to the outside of the furnace due to the decrease in the combustion rate in the combustion zone is mainly derived from the coal dust. It can be confirmed from dust type observation.

On the other hand, Japanese Patent Laid-Open Publication Nos. 94-212218 and 94-100911 as a method of increasing the limited amount of pulverized coal is disclosed to increase the oxygen enrichment rate and blowing temperature to improve the combustion rate of pulverized coal in the combustion zone. However, this method has a disadvantage in that it is difficult to stably increase oxygen supply due to fluctuations in oxygen supply and demand in steel mills, and an oxygen plant must be established in order to supply stable oxygen increase. In addition, since most of the blast furnaces operate hot blast furnaces near the upper limit of equipment stability, a significant increase in the blower temperature has to be difficult, requiring a major replacement of the hot blast furnace equipment.

As another example, Japanese Laid-Open Patent Publication No. 94-240319 discloses a method of calculating the coke substitution rate attributable to a difference in calorific value of each coal type when using a plurality of pulverized coals, and increasing the amount of pulverized coal blown based on this. However, when the pulverized coal is mixed as in the above method, the combustion efficiency is not determined solely by the calorific value, but the volatile matter content, the form of the structure, the porosity, etc. of each type of carbon are considered in consideration of the influence on the combustion efficiency. In order to use the mixed pulverized coal, it is required to establish a pulverized coal mixing facility, and there are problems in the facilities such as the change of operating conditions of the pulverized coal crushing facility.

As another example, Japanese Laid-Open Patent Publication No. 95-278624 uses 1.5 times more reactivity than general coke and replaces a part of general coke with a small particle size, and mixes it with iron ore so that a certain amount is charged in the periphery of the furnace to suppress the generation of the lower part. There is provided a method capable of blowing a large amount of pulverized coal. However, this method also has a problem in the practical blast furnace application, such as the need to introduce a separate facility for producing high-reactive coke.

Therefore, the present invention is stable operation state while increasing the critical injection amount of pulverized coal by using the correlation between the time when the unburned pulverized coal generation discharged from the blast furnace blast furnace rises and the length of the combustion table instead of the operation factor like the conventional one or the conventional operation factor. To provide a method for improving the combustion efficiency of the blast furnace combustion zone.

1 is a schematic diagram of a blast furnace showing the behavior of pulverized coal blown into the tuyere.

Figure 2 is a graph showing the relationship between the amount of carbon discharged to the top and the theoretical combustion temperature of the combustion zone according to the amount of pulverized coal blown in general blast furnace operation

Figure 3 is a cross-sectional view of the tuyere in accordance with the present invention

Figure 4 is a graph showing the relationship between the wind speed and the depth of combustion during blast furnace operation according to the present invention

Figure 5 is a graph showing the relationship between the flow rate and the wind pressure in the wind tunnel during blast furnace operation according to the present invention

6 is a graph showing the relationship between the wind pressure and the combustion zone depth during blast furnace operation according to the present invention

Figure 7 is a graph showing the behavior of the carbon content discharged to the top of the blast furnace operation according to the present invention during blast furnace operation

8 is a graph showing the behavior of carbon content directly lost in the furnace according to the wind flow velocity during blast furnace operation according to the present invention

9 is a graph showing the relationship between the amount of carbon discharged to the top and the theoretical combustion temperature of the combustion zone according to the amount of pulverized coal blown during blast furnace operation according to the present invention

In the present invention for achieving the above object in the operating method of the blast furnace, including blowing the pulverized coal while blowing oxygen and air through the tuyere,

It relates to a method for improving the combustion efficiency of the blast furnace to maintain the flow velocity of the tuyere at 215 m / s or more.

Hereinafter, the present invention will be described in detail.

The present invention increases the combustion efficiency of the blast furnace combustion zone by increasing the limit of the amount of pulverized coal, which is increased when the amount of unburned pulverized coal discharged to the outside of the blast furnace increases sharply, thereby increasing the combustion efficiency of the blast furnace combustion zone, and maintaining the sulfur stability stably. have. To this end, the present invention is a windball as the most important operating factor affecting the combustion rate in the combustion zone (2) and the reaction loss in the dropping zone (5) to determine the unburned pulverized coal discharged to the outside of the furnace, which is the standard of the fine coal injection. (1) Select the flow rate of the tip. Specifically, the present invention is to change the flow velocity of the tuyere as a means of raising the threshold of pulverized coal.

In addition, in the case of the present invention, the flow rate change of the tuyere is adjusted to the diameter of the wind instead of the wind pressure adjustment or blowing control. For example, as shown in FIG. 3, a means for reducing the diameter of the tuyere may be used by inserting the metal ring 9 inside the tip of the tuyere 1, and may directly vary the diameter of the tuyere.

The flow opening velocity according to the diameter of the opening may be a general relational expression, but an example of the relation is as follows.

By controlling the diameter of the tip of the tuyere by this means, if the flow velocity of the tuyere is maintained at 215 m / s or more, the unburned pulverized coal discharged to the outside of the blast furnace can be maintained substantially constant. As can be seen from FIG. 7, the flow velocity of the tuyere is more preferably 215 ~ 240m / s.

Preferably, the flow rate is maintained in the range of 218 to 237 m / s when the amount of fine coal blown (PCR) is less than 110 Kg or more than 150 Kg per molten ton. That is, when the amount of pulverized coal blown (PCR) is less than 110Kg per molten ton or more than 150Kg, the unburned pulverized coal discharged to the top is rapidly increased when operating in the same manner as the conventional method, but the flow rate of the tuyere is controlled according to the conditions of the present invention. In this case, the unburned pulverized coal sudden increase may disappear, and the combustion rate and the amount of reaction loss of the pulverized coal may be increased. More preferably, the flow velocity is maintained in the range of 225 to 235 m / s.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

In a blast furnace with an internal volume of 3800 m3, it is composed of weight%, C: 4.56%, Si: 0.39%, Mn: 0.34%, P: 0.02%, S: 0.025%, Ti: 0.06%, balance Fe and other unavoidable impurities. When manufacturing molten iron, air is blown under the condition of 6000 ~ 6200Nm3 / min, wind temperature: 1120 ℃, oxygen enrichment rate: 2.78%, humidity level: 26.57g / Nm3, and 100% of tonnes of pulverized coal with a carbon content of about 82.2% Blown in the range of ~ 170kg. At this time, the flow velocity of the tuyere was adjusted by changing the average cross-sectional area of the tip of the tuyere of the blast furnace in the range of 0.488 ~ 0.558㎡.

In this blast furnace operation, the depth (depth) of the blast furnace raceway (estimation) was estimated, and the correlation between the wind pressure and the wind speed was shown in Figs.

FIG. 4 is a diagram illustrating a combustion zone depth estimation equation such as Equation 1 in which the depth of the combustion zone is changed by changing the diameter of the balloon, and 5 is a flow rate and blowing pressure at the tip of the balloon. 6 shows the relationship between the combustion zone depth and the blowing pressure in FIG.

Dr / Dt ~ = ~ 2.0818 ~ * 10 SUP {-2} RF ~ + ~ 0.9645

Where RF = [ρ (go) Vg ² Tt 1.033] / [273 g S ² Pb d (st) ρ (st)]

Dr: combustion depth (m)

Dt: Fenggu diameter (m)

RF: Raceway Factor

ρ (go): Air density at standard condition (kg / m ³ )

Vg: Bosch gas volume (Nm ³ / sec)

Tt: theoretical combustion temperature (K)

g: acceleration of gravity (m / sec ² )

S: Wind ball cross section (m ² )

Pb: Blowing pressure (kg / cm ² )

d (st): Coke particle size in front of the air vent (m)

ρ (st): apparent density of front coke coke (kg / m ³ )

4 to 6, as the flow velocity of the tuyere increases and the wind pressure lowers, the depth of the combustion zone is increased, and as the flow velocity of the tuyere increases, the blowing pressure decreases to stably blow hot air into the blast furnace. It can be seen that.

On the other hand, the carbon content in the dust discharged from the hearth of the blast furnace was measured according to the flow velocity of the blast furnace, and the result is shown in FIG.

In addition, the solution loss consumed by the direct reduction reaction in the blast furnace was measured for each flow velocity of the tuyere, and the results are shown in FIG.

In addition, the theoretical combustion temperature according to the powdered coal injection amount (PCR) and the carbon content in the dust are shown in FIG.

As shown in FIG. 7, it can be seen that the amount of carbon in the dust discharged to the outside of the furnace is kept substantially constant at the flow velocity of the tuyere more than about 215 m / s. This means that the amount of unburned pulverized coal discharged to the top of the blast furnace is maintained substantially constant when the flow velocity of the tuyere according to the present invention is adjusted to 215 m / s or more. Preferably, it can be seen that when the flow velocity is maintained in the range of 218 to 237 m / s, the blowing amount of pulverized coal can be taken widely. This fact is disproved in FIG. 8 which shows the amount of pulverized coal, that is, the solution amount, required for the direct reduction in the blast furnace according to the flow rate of the tuyere.

In addition, when the combustion temperature and the amount of fines generated according to the flow rate of the tuyere, as shown in Fig. 9, when the injection rate of the pulverized coal is less than 110Kg per molten iron or exceeds 150Kg to maintain the flow rate in the range of 218 ~ 237m / s It can be seen that the theoretical combustion temperature is kept very stable even at low temperatures.

As described above, according to the present invention, by controlling the discharge of unburned pulverized coal generated in the blast furnace, through the flow rate of the tuyere, the limit of the pulverized coal that can be actually blown is raised to enable stable blast furnace operation without blowing resistance, but also combustion efficiency. This greatly increases the effect.

Claims (4)

In the operation method of the blast furnace, including blowing 100 ~ 170kg of pulverized coal per ton of molten air while blowing oxygen and air through the tuyere, Method for improving the combustion efficiency of the blast furnace, characterized in that to maintain the flow rate of the tuyere at 215 ~ 240m / s The method according to claim 1, wherein the flow rate is maintained in the range of 218 to 237 m / s when the amount of powdered coal (PCR) is less than 110 Kg per tonne or more than 150 Kg. The method of claim 2, wherein the flow rate is maintained in the range of 225 to 235 m / s. The method according to any one of claims 1 to 3, wherein the flow velocity of the tuyere is controlled by adjusting the diameter of the tuyere tip.

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