JPH10251715A - How to blow pulverized coal into the blast furnace - Google Patents

Abstract

(57) [Problem] To provide a method of injecting pulverized coal that maintains the flammability after pulverized coal is injected over the entire space and obtains a high combustion rate. SOLUTION: In a method of blowing pulverized coal from an inner pipe of a lance 1 having a double pipe structure provided by penetrating a wall of a blow pipe 2 connected to a tuyere tuyere and oxygen or oxygen-enriched air from an outer pipe. Two such lances are inserted for each tuyere, and the fine powder for the blast furnace is installed asymmetrically so that the extensions of the central axes do not intersect each other and do not intersect the central axis of the blow pipe. Charcoal injection method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injecting pulverized coal from tuyeres of a blast furnace.

[0002]

2. Description of the Related Art Pulverized coal injection is used in many blast furnaces because of its great cost advantage based on the price difference with coke, and it greatly contributes to improvement of economic efficiency. In recent years, the importance of coke ovens has been re-recognized from the viewpoint of extending the life of coke ovens, and more and more pulverized coal has been injected.

[0003] As the amount of pulverized coal injected into the blast furnace increases, various problems become apparent. One of them is a problem caused by discharge of unburned char into the furnace. In other words, as the amount of pulverized coal injected increases, the excess oxygen coefficient decreases, so the amount of combustion (burning rate) of pulverized coal decreases, and a large amount of unburned char that cannot be burned in the raceway is discharged into the furnace. You.
This unburned char may be preferentially consumed by the solution loss reaction in the lower part of the furnace, but there is naturally a limit value in the consumption amount in the furnace. For this reason, if chars are generated beyond the consumption limit value, they may be discharged from the furnace top as dust, which may cause a reduction in the replacement rate or an increase in the fuel ratio. in addition,
If this accumulates in the furnace core or the cohesive zone root, it causes a furnace condition instability and a decrease in productivity due to impaired ventilation and liquid permeability.

Therefore, in order to realize a stable pulverized coal injection operation, it is indispensable to suppress the amount of unburned char below the consumption limit in the furnace. It is necessary to further improve the combustion rate of pulverized coal.

In a normal pulverized coal injection operation, a single pipe lance tip for pulverized coal injection is projected into a blow pipe,
A method of blowing from the opening at the tip of the lance is generally used. In this method, since the entire amount of pulverized coal is ejected from one lance, the solid concentration immediately after ejection from the lance is high, and the inertia of hot air is large, so that it cannot be diffused much in the radial direction. Therefore, the mixing efficiency of the pulverized coal and hot air and the contact efficiency with oxygen are low, and the temperature rise of the solid is delayed. In addition, the oxygen around the pulverized coal is rapidly consumed with the progress of combustion, and the area around the pulverized coal is in a state of lack of oxygen.However, since the hot air basically flows in one direction, diffusion of oxygen is not easy. There was a drawback that a rise in combustion rate could not be expected.

As means for solving the above problems, a method has been developed in which the lance has a double-pipe structure to improve the contact efficiency between oxygen and pulverized coal. For example, JP-A-2-213
In Japanese Patent Publication No. 406 and Japanese Patent Laid-Open No. 6-100912, pulverized coal is flowed inside a concentric double tube lance, and oxygen or a mixture of oxygen and air (oxygen-enriched air) is flown outside the lance to reduce the oxygen concentration around the pulverized coal. By increasing the value, the combustion speed is improved and the problem of oxygen deficiency is solved. Also, JP-A-1-92
In Japanese Patent No. 304, in order to improve the oxygen introduction efficiency, the lance has a triple pipe structure, the outermost pipe is water-cooled, pulverized coal flows into the innermost pipe, and oxygen is supplied from a plurality of nozzles arranged so as to surround the inner circumference. For injecting pulverized coal toward pulverized coal. On the other hand, two lances are installed for each tuyere.
Attempts have also been made to improve the flammability by using a so-called double lance. Iron and steel vol. 80 (1994),
According to p288, an experiment is conducted in which two single-lance lances are inserted into a blowpipe, and half of the amount of pulverized coal to be blown from each lance. In this method, since the pulverized coal can have a plurality of injection starting points, the pulverized coal can be distributed over a wider space immediately after the injection, and relatively uniform dispersibility can be achieved. For this reason, it is said that the contact efficiency between the pulverized coal and oxygen in the hot air is increased, the temperature rise and the thermal decomposition of volatile components are accelerated, and as a result, the combustion proceeds rapidly to achieve a high combustion rate.

[0007]

However, in JP-A-2-213406 and JP-A-6-100912, all of pulverized coal and gas (oxygen or a mixture of oxygen and air) are blown from one lance. In this method, the introduced gas is mixed rapidly with the surrounding hot air before mixing with the pulverized coal, reducing the effect of increasing the oxygen concentration near the pulverized coal by half. May be lost. Even if it can be mixed with pulverized coal, the initial flammability up to consumption of the introduced high-concentration oxygen is improved, but after that, iron and steel vol. 80 (1994), p
Unlike the method of 288, since the dispersibility of pulverized coal cannot be essentially improved, oxygen in hot air cannot be effectively used for combustion, and the combustibility is suppressed. In Japanese Patent Application Laid-Open No. 1-92304, oxygen can be relatively efficiently introduced into pulverized coal because oxygen is ejected toward pulverized coal. However, since oxygen is water-cooled by the outermost tube, the introduced oxygen itself is There is a problem that the cooling effect causes a delay in temperature rise of the pulverized coal. In addition, iron and steel vol. 80
(1994), p. 288, is excellent in the utilization of oxygen in hot air by improving the dispersibility of pulverized coal, but from the viewpoint of burning rate, the oxygen concentration in hot air (generally, 2%).
(Approximately 1 to 25%) is the limit, so even if the ideal dispersion condition is satisfied, there is a limit value in the combustion rate.

Accordingly, an object of the present invention is to provide a method of injecting pulverized coal which maintains the flammability after pulverized coal is injected over the entire space and obtains a high combustion rate.

[0009]

The present invention achieves the above object by the following method.

In the first method, pulverized coal is blown from an inner pipe of a lance having a double pipe structure provided through a wall of a blow pipe connected to a tuyere tuyere, and oxygen or oxygen-enriched air is blown from an outer pipe. In this method, two such lances are inserted for each tuyere and the blast furnace is installed asymmetrically so that the extension lines of the respective central axes do not cross each other and do not cross the central axis of the blow pipe. This is a method of injecting pulverized coal into the furnace.

The second method is the same as the first method, wherein the angle between the direction of gas ejection from the outer tube of the double tube lance and the center axis of the lance is 30 ° or more, and the linear velocity of the gas is 30 m / s.
This is a method of injecting pulverized coal into a blast furnace to be blown out at a speed of 60 m / s or less.

[Operation] When only one double lance is used, the initial burning rate is once improved by the local enrichment of oxygen as described above, but thereafter, the dispersibility of the pulverized coal is reduced. Is low, the oxygen in the surrounding hot air cannot be used effectively, and the combustibility deteriorates rapidly. In contrast, 2
When two heavy pipe lances are used, the spatial dispersion is improved by using a plurality of dispersion starting points, and the lances are arranged asymmetrically as described above, so that mutual interference between the two main streams of pulverized coal is prevented. A high degree of dispersion can be achieved not only immediately after pulverized coal injection but also on the downstream side. Therefore, the initial combustion rate is improved in the same manner as in the case of the single double-tube lance described above, and thereafter, the contact with the surrounding gas can be maintained by the dispersion strengthening, and the combustion rate is high without deteriorating the combustibility. Flammability can be achieved. Therefore, compared to the case of blowing from one double lance or two single lances, the method of the present invention can promote combustion in the entire axial direction, and as a result, greatly improves the combustion rate. be able to.

[0013] Further, as a result of examining the conditions for jetting oxygen or oxygen-enriched air to be introduced from the outer tube of the double tube lance, the angle θ between the jet direction of oxygen or oxygen-enriched air and the center axis of the lance was determined. It has been found that it is necessary to jet the gas so that it is 30 ° or more and the linear velocity of the gas is 30 m / s or more and 60 m / s or less. The reason for setting θ to 30 ° or more is that if θ is 30 ° or less, it mixes with the surrounding hot air before reaching the main streamline of pulverized coal, and the oxygen concentration in the vicinity of pulverized coal cannot be locally increased. is there. However, if the angle exceeds 60 °, the ignition point approaches the lance, and the problem of erosion at the tip of the lance tends to occur. Therefore, the angle is preferably 60 ° or less.

The linear velocity of the gas is 30 m / s or more and 60 m / s or more.
The reason for setting it to m / s or less is that when it is 30 m / s or less, oxygen cannot be sufficiently supplied to the vicinity of the pulverized coal by overcoming the inertia force of the pulverized coal. This is because blow-off occurs and stable combustion cannot be maintained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

[0016]

EXAMPLES Examples of the present invention will be described below together with comparative examples. Example 1 A pulverized coal combustion experiment was performed using a pulverized coal combustion furnace shown in FIG. 3 is a packed bed of coke of the pulverized coal combustion furnace. The pulverized coal combustion furnace is a blow pipe 2 with an inner diameter of 90φ.
It has one tuyere and one tuyere with an inner diameter of 65φ. At the rear of the blow pipe 2, a lance guide tube 5 provided diagonally up and down is provided.
The lances 1a, 1b are protruded from
Is inserted inside. And as shown in FIG.
The lances 1a and 1b were mounted such that the central axes of the lances 1a and 1b did not intersect with the central axis of the blow pipe 2, and the tip positions were asymmetric with respect to the central axis of the blow pipe 2. The distance from the tip position of the lances 1a and 1b to the tuyere tip is 12
00 mm. FIG. 3 shows a longitudinal sectional view of the lance used. As shown in FIG. 3, the lance 1 has a double pipe structure including an inner pipe 10 and an outer pipe 11. A gas ejection hole 12 is formed at the tip of the lance 1 at an angle from the outer tube 11 to the tip of the inner tube 10. The angle θ between the direction of gas ejection from the gas ejection holes 12 and the center axis of the lance was 45 °.
FIG. 4 is a view taken in the direction of arrows AA in FIG. 3 and shows eight gas ejection holes 1.
2 is opened at an equal angle around the circumference of the inner tube 10 at the tip of the lance 1.

As shown in FIG. 1, 7 is a pulverized coal cutting hopper, 8 is a pulverized coal supply pipe, and the pulverized coal is blown into the blow pipe 2 from the lances 1a and 1b using nitrogen gas as a carrier gas.

Table 1 shows an industrial analysis of the pulverized coal used in the combustion experiment. The particle size of the pulverized coal is 80% at −74 μm.

[0019]

[Table 1]

In the experiment, first, 350 Nm ³ / h of pseudo air adjusted to have an oxygen concentration of 21% by mixing oxygen into the combustion gas of LPG was blown into the blow pipe 2 and the tuyere temperature was set to 1200 ° C. The temperature rose. Tuyere temperature is 1200 ℃
When stabilized, the pulverized coal was cut out from the pulverized coal cutting hopper 7 at 65 kg / h, and nitrogen gas of 12 Nm ³ / h was supplied as a carrier gas through the pulverized coal supply pipe 8.
After branching into two before the lance, two lances 1a,
1b was supplied into the blow pipe 2 from the inner pipe 10. At the same time, the outer tubes 11 of the two lances 1a and 1b have oxygen 14Nm.
³ / h. The oxygen enrichment rate in this experiment was 3.
0%, oxygen excess coefficient is 0.78.

The amount of pulverized coal injected is equivalent to 200 kg / t in terms of the amount of pulverized coal injected in an actual blast furnace. The flow rate of the pulverized coal / carrier gas ejected from the tip of the inner pipe is 16 m / s calculated from the cross-sectional area of the flow path, and the flow rate of oxygen gas at the tip of the gas ejection hole via one outer pipe is 40 m. (All converted at 25 ° C.).

During the combustion of the pulverized coal, a sampling probe is inserted from the sampling probe insertion guide tube 6 shown in FIG.
The pulverized coal dust was sampled at each position. The resulting dust was chemically analyzed to determine the combustion rate. FIG. 5 shows the change in the combustion rate at each distance from the lance tip.
At the 300 mm position, the burn rate has already increased to 60%, and at the 900 mm position, it has increased to 80%. This indicates that the combustion speed of the pulverized coal is high.

"Comparative Example 1" An experiment equivalent to 200 kg / t in terms of the pulverized coal blowing amount was performed in the same manner as in Example 1 using one double-tube lance used in Example 1. The inner diameter and outer diameter of the lance were adjusted so that the carrier gas flow rate at the tip of the lance and the gas flow rate at the tip of the gas ejection hole were the same as in Example 1. The results of the combustion rate measurement are also shown in FIG. The combustion rate at a position 300 mm from the tip of the lance is 50
%, But the combustion rate at 900 mm is 6%.
It improved only up to about 0%. This is thought to be due to the effect of enriching oxygen introduced from the lance immediately after pulverized coal injection and improving the combustion rate.However, since the dispersibility of the particles is low, efficient contact with hot air is considered. This is considered to be because the lack of oxygen in the pulverized coal stream could not be eliminated.

Comparative Example 2 The same experiment as in Example 1 was performed using two single-tube lances having no outer tube. The lance diameter was adjusted so that the carrier gas flow rate at the tip of the lance was the same as in Example 1. Further, the same amount of oxygen as in Example 1 was used as L
It was enriched in hot air, which is the combustion gas of PG. The results of the combustion rate measurement are also shown in FIG. The combustion rate at a position 300 mm from the tip of the lance is lower than that of Comparative Example 1, but 600%.
It was found that the rotation was reversed at the mm position, and it could be improved to about 75% at the 900 mm position. However, it did not reach Example 1. This indicates that the use of a plurality of injection points improves the dispersibility of the pulverized coal in the space and can maintain the combustibility over the entire space, but the ignition is delayed more than in the case of the first embodiment. In addition, the low combustion temperature is considered to be the reason that the combustion rate was not improved as in the first embodiment.

Example 2 An experiment similar to that of Example 1 was carried out by changing variously the oxygen gas jetting angle θ from the outer tube of the double tube lance shown in FIG. 3 and the cross-sectional area of the gas jetting hole. is changed every 15 ° from 30 ° to 75 °, and the gas flow velocity at the tip of the gas ejection hole is 20m from 20m / s to 80m / s.
Four lances having different cross-sectional areas of the gas ejection holes were manufactured for each θ so that the lances could be changed every. FIG. 6 is a graph showing the relationship between the gas ejection angle and the combustion rate at the 300 mm position for each gas flow velocity. From the figure, it can be seen that when θ is in the range of 30 ° to 60 °, the combustion rate increases as θ increases. Also, the combustion rate increases with an increase in the gas flow velocity. However, when the gas flow velocity is 20 m / s, even if θ is increased, the combustion rate is at most about 50%, and the effect is low. It is considered that the gas flow rate needs to be 30 m / s or more in order to obtain a clear effect as compared with the case of Comparative Example 2 in which oxygen is enriched in hot air. On the other hand, in a region where both the θ and the gas flow rate are large, erosion at the tip of the lance and blow-out of the flame began to be observed, and the combustion rate did not change or tended to decrease. . Therefore, θ is 30 ° or more, preferably 6
0 ° or less, and the gas flow velocity is 30 m / s or more and 60 m / s or more.
If s or less can be satisfied simultaneously, the combustion rate will be higher than in Comparative Example 1 or Comparative Example 2, and the method of the present invention will be effectively carried out.

[0026]

According to the present invention, at the beginning of combustion,
The ability to locally increase the oxygen concentration in the vicinity of pulverized coal and the improved dispersibility of pulverized coal can improve the flammability of pulverized coal. A high combustion rate can be obtained because mixing with oxygen can be maintained. That is, according to the method of the present invention, after the pulverized coal is injected, the flammability can be advanced without stagnating over the entire space, so that the final combustion rate of the pulverized coal can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a pulverized coal combustion furnace used in a pulverized coal combustion experiment according to the present invention.

FIG. 2 is an explanatory view of an arrangement of a lance according to the present invention.

FIG. 3 is a longitudinal sectional view of a lance used in a pulverized coal combustion experiment.

FIG. 4 is a view as viewed in the direction of arrows AA in FIG. 3;

FIG. 5 is a graph showing a relationship between a distance from a lance tip and a combustion rate of pulverized coal.

FIG. 6 is a graph showing a relationship between a gas ejection angle and a combustion rate at a position of 300 mm for each gas flow velocity.

[Explanation of symbols]

 1, 1a, 1b Lance 2 Blow pipe 3 Coke filling layer 4 Tuyere 5 Lance guide tube 6 Sampling probe insertion guide tube 7 Pulverized coal cutout hopper 8 Pulverized coal supply tube 10 Inner tube 11 Outer tube 12 Gas ejection hole

Claims (2)

[Claims] 1. A method of blowing pulverized coal from an inner pipe of a lance having a double pipe structure provided through a wall of a blow pipe connected to a tuyere of a blast furnace, and oxygen or oxygen-enriched air from an outer pipe. Insert two such lances per tuyere,
A method of injecting pulverized coal into a blast furnace, wherein the pulverized coal is installed asymmetrically so that extensions of respective central axes do not intersect with each other and do not intersect with the central axis of the blow pipe. 2. The gas is ejected such that the angle between the gas ejection direction of the outer tube of the double tube lance and the central axis of the lance is 30 ° or more and the linear velocity of the gas is 30 m / s or more and 60 m / s or less. The method for injecting pulverized coal into a blast furnace according to claim 1, wherein