JP3493937B2 - How to blow pulverized coal into the blast furnace - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for blowing pulverized coal from tuyere of a blast furnace.

[0002]

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

When the amount of pulverized coal blown into the blast furnace is increased, various problems become apparent, one of which is a problem caused by discharge of unburned char into the furnace. That is, as the amount of pulverized coal injected increases, the oxygen excess coefficient decreases, so the combustion amount (combustion rate) of pulverized coal decreases, and a large amount of unburned char that cannot be completely burned in the raceway is discharged into the furnace. It
There is a possibility that this unburned char will be preferentially consumed in the lower part of the furnace due to the solution loss reaction, but there is naturally a limit value for the amount consumed in the furnace. Therefore, if char is generated above the consumption limit value, it may be discharged from the furnace top as dust, resulting in a decrease in the replacement rate and an increase in the fuel ratio. in addition,
Accumulation of this in the core of the furnace or the root of the cohesive zone causes instability of the furnace and deterioration of productivity due to obstruction of ventilation and liquid permeability.

Therefore, in order to realize a stable operation of blowing a large amount of pulverized coal, it is indispensable to suppress the amount of unburned char generated within the furnace consumption limit. For this purpose, in the raceway section It is necessary to further improve the burning rate of pulverized coal.

In a normal pulverized coal blowing operation, the tip of a single pipe lance for blowing pulverized coal is projected into the blow pipe,
The method of blowing from the opening at the tip of the lance is common. In this method, since the entire amount of pulverized coal is ejected from one lance, the solid concentration immediately after being ejected from the lance is high, and the inertial force of hot air is large, so that it cannot be diffused so much in the radial direction. Therefore, the mixing efficiency of pulverized coal and hot air and the contact efficiency with oxygen are low, and the temperature rise of the solid is delayed. Also, as combustion progresses, oxygen around the pulverized coal is rapidly consumed, and the surroundings of the pulverized coal are in an oxygen-deficient state, but since hot air is basically one-way flow, diffusion of oxygen is not easy. There was a drawback that it could not be expected to raise the burning rate.

As a means for solving the above problems, a method of improving the contact efficiency between oxygen and pulverized coal by forming the lance with a double tube structure has been developed. For example, Japanese Patent Laid-Open No. 2-213
In Japanese Patent Application Laid-Open No. 406 and Japanese Patent Application Laid-Open No. 6-100912, pulverized coal is flown inside a concentric double tube lance, and oxygen or a mixture of oxygen and air (oxygen-enriched air) is flowed outside to adjust the oxygen concentration around the pulverized coal. By increasing it, the burning rate is improved and the problem of oxygen deficiency is solved. In addition, JP-A-1-92
In JP 304, in order to improve the efficiency of introducing oxygen, the lance has a triple tube structure, the outermost tube is water-cooled, the pulverized coal is flown to the innermost tube, and oxygen is supplied from a plurality of nozzles arranged so as to surround it. It discloses a method of ejecting the powder toward a pulverized coal. On the other hand, install two lances for each tuyere,
Attempts have been made to improve the combustibility by so-called double lance. Iron and steel vol. 80 (1994),
According to p288, two single lances are inserted into the blow pipe, and an experiment is performed in which half of the amount of pulverized coal blown is blown from each lance. In this method, since the pulverized coal can be ejected from a plurality of starting points, it is possible to distribute the pulverized coal in a wider space immediately after the injection, and a relatively uniform dispersibility is achieved. Therefore, 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 matter are accelerated, and as a result, the combustion proceeds rapidly and a high combustion rate can be achieved.

[0007]

However, in JP-A-2-213406 and JP-A-6-100912, the entire amount of pulverized coal and gas (oxygen or a mixture of oxygen and air) is blown from one lance. In this method, the gas is introduced so that it surrounds the pulverized coal, but the introduced gas is rapidly mixed with the hot air around it before mixing with the pulverized coal, and the effect of increasing the oxygen concentration near the pulverized coal is halved. There is a possibility that it will end up. Even if it could be mixed with pulverized coal, the initial combustibility before the high concentration oxygen introduced was improved, but after that, iron and steel vol. 80 (1994), p
Unlike the method of No. 288, since the dispersibility of pulverized coal cannot be essentially improved, oxygen in hot air cannot be effectively used for combustion, and combustibility is suppressed. In Japanese Patent Laid-Open No. 1-92304, oxygen is jetted toward pulverized coal, so that oxygen can be introduced into pulverized coal relatively efficiently. However, since oxygen is water-cooled by the outermost pipe, the amount of introduced oxygen itself is reduced. There is a problem that the temperature rise of the pulverized coal is delayed due to the cooling effect. In addition, iron and steel vol. 80
Although the method of (1994), p288 is excellent in the utilization factor of oxygen in hot air by improving the dispersibility of pulverized coal, from the viewpoint of the combustion rate, the oxygen concentration in hot air (generally, 2
Since the numerical value corresponding to (1 to 25%) is the limit, there is a limit value in the combustion rate even if the ideal dispersion condition is satisfied.

[0008] Therefore, it is an object of the present invention to provide a pulverized coal blowing method which maintains the combustibility after pulverized coal injection 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 the inner tube of a lance having a double tube structure provided through the wall of a blow pipe connected to the tuyere of the blast furnace, and oxygen or oxygen-enriched air is blown from the outer tube. In this method, two such lances are inserted per tuyere and installed asymmetrically so that the extension lines of the respective central axes do not intersect with each other and do not intersect with the central axis of the blow pipe. It is a method of blowing pulverized coal into.

The second method is the same as the first method, except that the angle formed between the jet direction of the gas 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.
It is a method for injecting pulverized coal into a blast furnace in which it is jetted at a rate 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 pulverized coal is increased. Since oxygen is low, the oxygen in the surrounding hot air cannot be effectively used, and the flammability rapidly deteriorates. On the other hand, 2
When two heavy pipe lances are used, spatial dispersion is improved due to the multiple dispersion starting points, and the lances are arranged asymmetrically as described above, so mutual interference between the two main streams of pulverized coal is prevented. It is possible to achieve a high degree of dispersion not only immediately after blowing pulverized coal but also on the downstream side. Therefore, the initial combustion speed is improved similarly to the case of the above-mentioned single double tube lance, and thereafter, the contact with the surrounding gas can be maintained by the dispersion strengthening, so that the combustibility is not deteriorated and is high. Flammability can be achieved. Therefore, the method of the present invention can promote combustion over the entire axial direction as compared with the case of injection from one double lance or the case of injection from two single tube lances, and as a result, the combustion rate is greatly improved. be able to.

Further, as a result of investigating the ejection conditions of oxygen or oxygen-enriched air introduced from the outer pipe of the double pipe lance, the angle θ formed by the ejection direction of oxygen or oxygen-enriched air and the central axis of the lance is determined. It has been found that it is necessary to eject gas at a temperature of 30 ° or more and a linear velocity of gas of 30 m / s or more and 60 m / s or less. The reason why θ is set to 30 ° or more is that if it is 30 ° or less, the oxygen concentration in the vicinity of the pulverized coal cannot be locally increased because it mixes with the hot air before reaching the main streamline of the pulverized coal. is there. However, if it exceeds 60 °, the ignition point approaches the lance and the problem of melting damage at the tip of the lance is likely to occur. Therefore, it is preferably 60 ° or less.

Further, the linear velocity of the gas is 30 m / s or more 60
The reason for setting m / s or less is that when it is 30 m / s or less, the inertial force of the pulverized coal cannot be overcome and oxygen cannot be sufficiently supplied in the vicinity of the pulverized coal. This is because blowout occurs and stable combustion cannot be maintained.

[0015]

DETAILED DESCRIPTION OF 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 conducted using the pulverized coal combustion furnace shown in Fig. 1. Reference numeral 3 is a coke packed bed of the pulverized coal combustion furnace. The pulverized coal combustion furnace has 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, there is provided a lance guide pipe 5 which is provided obliquely up and down.
Blow pipe 2 by protruding the ends of books lances 1a, 1b
Has been inserted inside. Then, as shown in FIG.
The lances 1a and 1b were attached so that the central axes of the lances 1a and 1b do not intersect with the central axis of the blow pipe 2 and the tip positions thereof are asymmetric with respect to the central axis of the blow pipe 2. The distance from the tip of the lances 1a and 1b to the tuyere is 12
It was set to 00 mm. A longitudinal sectional view of the lance used is shown in FIG. 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 obliquely formed at the tip of the lance 1 from the outer tube 11 to the tip of the inner tube 10. The angle θ formed by the gas ejection direction of the gas ejection hole 12 and the lance center axis was 45 °.
FIG. 4 is a view on arrow AA of FIG. 3, showing eight gas ejection holes 1
2 are opened at an equal angle on 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 and 8 is a pulverized coal supply pipe. The pulverized coal is blown into the blow pipe 2 from the lances 1a and 1b using nitrogen gas as a carrier gas.

An industrial analysis of the pulverized coal used in the combustion experiment is shown in Table 1. The particle size of pulverized coal is 80% at -74 μm.

[0019]

[Table 1]

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

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

During the combustion of pulverized coal, the sampling probe is inserted from the sampling probe insertion guide tube 6 shown in FIG. 1, and 300, 600, 900 mm from the tip of the lance.
Pulverized coal dust was sampled at each position. The obtained dust was chemically analyzed to determine the burning rate. FIG. 5 shows changes in the combustion rate at various distances from the tip of the lance.
The burning rate has already improved to 60% at the 300 mm position, and has risen to 80% at the 900 mm position. This indicates that the burning rate of pulverized coal is high.

"Comparative Example 1" Using one double tube lance used in Example 1, an experiment equivalent to 200 kg / t in terms of pulverized coal blowing rate was conducted in the same manner as 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 burning rate measurement results are also shown in FIG. The burning rate at the position of 300 mm from the tip of the lance is 50
%, But the burning rate at 900 mm is 6
It improved only to about 0%. It is considered that the effect of enriching the oxygen introduced from the lance appeared immediately after the injection of pulverized coal, and the combustion speed improved, but after that, since the dispersibility of particles was low, efficient contact with hot air was achieved. It is considered that this was not achieved and the lack of oxygen inside the pulverized coal flow could not be resolved.

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

[Example 2] The same experiment as in Example 1 was carried out by changing the ejection angle θ of oxygen gas from the outer tube of the double tube lance shown in Fig. 3 and the cross-sectional area of the gas ejection hole. θ is changed from 30 ° to 75 ° at intervals of 15 °, and the gas flow velocity at the tip of the gas ejection hole is 20 m from 80 m / s to 20 m / s.
For each θ, four lances with different cross-sectional areas of the gas ejection holes were manufactured so that they could be changed every / s. 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 in the range of θ from 30 ° to 60 °, the combustion rate increases as θ increases. Further, the combustion rate also rises as the gas flow velocity increases. 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 necessary to set the gas flow velocity to 30 m / s or more in order to obtain a clear effect as compared with the case of Comparative Example 2 in which hot air is enriched with oxygen. On the other hand, in the region where both θ and the gas flow velocity are large, melting loss at the tip of the lance and flame blowout phenomenon are observed, and the burning rate is unchanged or tends to decrease. . Therefore, θ is 30 ° or more, preferably 6
0 ° or less, gas flow velocity is 30 m / s or more, 60 m / s
If s or less is satisfied at the same time, the combustion rate becomes higher than that of Comparative Example 1 or Comparative Example 2, and the method of the present invention is effectively carried out.

[0026]

According to the present invention, in the early stage of combustion,
The oxygen concentration near the pulverized coal can be locally increased and the dispersibility of the pulverized coal can be improved to improve the combustibility of the pulverized coal, and thereafter, the dispersibility of the pulverized coal can be maintained in hot air. A high combustion rate can be obtained because the mixing with the oxygen of the above can be continued. That is, according to the method of the present invention, after the pulverized coal is blown, the combustibility can be advanced over the entire space without stagnation, so that the final combustion rate of the pulverized coal can be significantly improved.

[Brief description of drawings]

FIG. 1 is a vertical 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 lances according to the present invention.

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

FIG. 4 is a view on arrow AA of FIG.

FIG. 5 is a graph showing the relationship between the distance from the tip of the lance and the burning 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 packed bed 4 tuyere 5 Lance guide tube 6 Sampling probe insertion guide tube 7 Pulverized coal cutting hopper 8 Pulverized coal supply pipe 10 inner tube 11 outer tube 12 gas ejection holes

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C21B 7/00 309

Claims (2)

(57) [Claims] 1. A method of injecting pulverized coal from an inner tube of a lance having a double-tube structure provided by penetrating a wall of a blow pipe connected to a tuyere of a blast furnace, and oxygen or oxygen-enriched air from an outer tube, Insert two such lances for each tuyere,
A method for injecting pulverized coal into a blast furnace, characterized in that the extension lines of the respective central axes are installed asymmetrically so that they do not intersect with each other and also with the central axes of the blow pipes. 2. The double pipe lance is jetted so that the angle between the gas jetting direction of the outer pipe 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