JPH0192304A - Nozzle for blowing finely powdered coal in blast furnace - Google Patents

Abstract

PURPOSE:To improve combustibility and to prevent sticking of ash to a tuyere by intersecting axial lines of tip parts of plural oxygen gas blowing holes surrounding fine powdered coal blowing hole of a nozzle with axial line of the finely powdered coal blowing hole at front of the nozzle. CONSTITUTION:The nozzle 1 for blowing the finely powdered coal is constituted by arranging plural pipes 3 for blowing the oxygen at circumference of the pipe 2 for blowing the finely powdered coal. The blowing tip parts of the pipes 3 for blowing the oxygen are bent to nozzle part direction, and the center lines of the parts are intersected with the center line of the pipe 2 for blowing the finely powdered coal at one point P at front of the nozzle 1 for blowing the finely powdered coal. By this method, at the time of smelting in the blast furnace, a large quantity of the finely powdered coals can be used as auxiliary fuel without bringing about unstability in the operation, and the using quantity of the coke as main fuel can be reduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is directed to a method for injecting pulverized coal into a blast furnace in order to effectively burn a large amount of pulverized coal and significantly reduce coke consumption. It concerns the nozzle.

BACKGROUND TECHNOLOGY As is well known, the main fuel in blast furnace smelting of iron is coke. However, coke for blast furnaces is about 20% of coal reserves.
The price is high because the raw material is expensive coking coal, which accounts for only about 5% of coke.Therefore, in order to meet the increasingly strict cost reduction requirements for steel materials, the consumption of coke must be minimized. It has become necessary. Therefore, in recent years, tuyere injection of various auxiliary fuels has been carried out during blast furnace smelting.

Looking back, heavy oil injection first began in the 1950s, and the injection amount was 100k per ton of pig iron.
It has contributed to the reduction of coke consumption by reaching a point where it exceeds the average of However, since the late 1970s, as the price of heavy oil soared, the number of blast furnaces that injected heavy oil decreased worldwide, and instead injection of pulverized coal, which is made by pulverizing non-coking coal, became more and more common in blast furnace operations in various countries. It has become mainstream. Incidentally, such blowing of pulverized coal is carried out by a pulverized coal blowing nozzle 8 installed in a blowing branch pipe 6 connected to the tuyere 5, for example, as shown in FIG.

However, since pulverized coal is a powder (solid), it has poor combustibility compared to liquid fuels such as heavy oil, and in order to use it in large quantities, it is necessary to increase the oxygen concentration in the tuyere ventilation to improve combustibility. Countermeasures have been taken such as: ○ Raising the temperature of the blast; ○ Installing the burner as far away from the tuyere as possible to promote the combustion of pulverized coal from the tuyere to the time it flows into the furnace.

However, when the combustibility of pulverized coal is improved by such a method, the following problems tend to occur. In other words, pulverized coal contains minerals, and the ash in the pulverized coal that is blown from the blast pipe and burned before reaching the tip of the tuyere adheres to the inner surface of the tuyere, reducing the diameter of the tuyere. This tends to cause a phenomenon that obstructs ventilation, and since the adhesion state is not uniform at each tuyere, it also causes a significant imbalance in the distribution of air flow between each tuyere, hindering stable operation. The problem is that.

FIG. 5 shows the above-mentioned ash adhesion situation, and when a heat insulating ring is installed on the inner surface of the tuyere 5 to prevent heat loss, as shown by "A", When the insulation ring is not used, it tends to stick as shown by the "mouth".

Therefore, ``a phenomenon in which unburned pulverized coal accumulates in the furnace due to poor combustibility, inhibiting stable operation,'' and the phenomenon that tends to occur when measures to improve combustibility such as those described above are taken to deal with this phenomenon. ``A phenomenon in which combustion ash, which becomes molten due to the increase in combustion heat within the tuyere, adheres to the inner surface of the tuyere, causing ``wall blockage'' and ``unbalanced distribution of air flow between the tuyeres,'' which impedes stable operation.'' In order to use pulverized coal without causing such problems, the limits of its use are naturally limited.

Incidentally, at present, the amount of pulverized coal used in Japan's blast furnaces remains at a maximum of 100 kg per ton of pig iron, and this can be easily achieved in blast furnaces overseas under conditions of heavy oil operation or all-coke operation. Fuel ratio is 500k
g/l-pig (pig iron) 200kg/l or less
There are no examples of pulverized coal being used in excess of this amount.

Means for Solving the Problems> From the above-mentioned viewpoint, the present inventors injected a large amount of pulverized coal during blast furnace smelting to efficiently burn it, and
As a result of various studies in order to make it possible to significantly reduce the amount of coke used while sufficiently suppressing problems such as "ash content adhesion to the tuyeres," we found that pulverized coal can be used at a rate of, for example, 200 kg/l-pig.
We came to the conclusion that in order to stably achieve a high fuel ratio by using large quantities as described above, it was absolutely necessary to find a way to simultaneously achieve both ``improvement of combustibility'' and ``prevention of adhesion to the inner surface of the tuyere.'' In order to satisfy this requirement, a plurality of oxygen gas blowing holes are provided surrounding a central pulverized coal blowing hole, and the axis of at least the tip of each oxygen gas blowing hole is aligned with the axis of the pulverized coal blowing hole in front of the nozzle. characterized by intersecting
We have developed a pulverized coal injection nozzle for blast furnaces.

FIG. 1 is a schematic view showing an example of a pulverized coal injection nozzle according to the present invention, and FIG.
Figure (bl) shows a front view of the nozzle blowing surface, and FIG. 1(C) shows a cross-sectional view corresponding to the A-A' section in FIG. 1(a).

In FIG. 1, a pulverized coal injection nozzle 1 has a pulverized coal injection pipe 2 at its center, and a plurality of oxygen gas injection pipes 3 around it. The blowing tip part of the oxygen gas blowing pipe 3 is bent toward the center of the nozzle, and the center line of this part is the center line of the pulverized coal blowing pipe 2 and a point p in front of the pulverized coal blowing nozzle 1. are configured to intersect.

Here, if the distance from the nozzle tip to the point p is too short, there is a strong possibility that the nozzle tip will be damaged by melting. Preferably 50 to 500
It is best to set it to mm.

The pulverized coal injection nozzle shown in FIG. 1 is an example of a water-cooled structure in which a cooling water flow path 4 is provided.

The pulverized coal injection nozzle 1 is used, for example, by being attached to a blowing branch pipe 6 connected to a tuyere 5 of a blast furnace, as shown in FIG.

In the present invention, a plurality of oxygen gas blowing holes are installed around the pulverized coal blowing hole, and the axis of at least the tip of each of these oxygen gas blowing holes is set to intersect with the axis of the pulverized coal blowing hole in front of the nozzle. The reasons are: ■ Stipulating the combustion start position of injected pulverized coal, ■ Improving the combustibility of pulverized coal.

■ There are three points to prevent wear and tear on the pulverized coal injection nozzle. This point will be explained in more detail below.

That is, one of the reasons why the pulverized coal blow-off hole and the oxygen gas blow-off hole are made as separate bodies and their axes intersect for the first time in front of the nozzle is to define the combustion start position of the blown pulverized coal. , With such a nozzle configuration, the pulverized coal flowing out from the pulverized coal blowing hole is directed to the intersection of the blowing hole axes (
Until reaching point p in FIG. 1), it hardly mixes with the combustion improver, hot air or oxygen gas. Therefore, the pulverized coal does not burn until the point P is reached.

On the other hand, the pulverized coal flowing out from the pulverized coal outlet is at the intersection point p.
When the pulverized coal reaches this point, the pulverized coal mixes with the oxygen gas blown in from the oxygen gas blow-off hole, and combustion starts only at this point.

In addition, after the mixing point of oxygen gas and pulverized coal (point p above), pulverized coal mainly mixes with the oxygen gas blown in from the oxygen gas outlet, so the area around the pulverized coal has a very high oxygen concentration. situation. Therefore, since an atmosphere similar to that of high-concentration oxygen-enriched air is formed here, the combustibility of the pulverized coal is sufficiently improved.

Generally, it is a well-known fact that the combustibility of pulverized coal can be improved by increasing the oxygen concentration in the combustion improver, but according to experiments conducted by the present inventors, when the oxygen concentration in the blast is 21% (
For pulverized coal (fixed carbon 53%, volatile content 35%, ash content 10%, 9% of particles
When attempting to burn more than about 0.3 kg of 0% (44μ or less), the combustibility was extremely low.
When the oxygen concentration in the blast is 31%, the amount of pulverized coal is 0.6 kg for oxygen INrrr, when the oxygen concentration in the blast is 41%, the amount of pulverized coal is 0.9 kg, and when the oxygen concentration in the blast is increased to 60%, the amount of pulverized coal is 0.6 kg. It was possible to burn up to 1.4 kg of pulverized coal with high combustibility. However, the amount of oxygen in the blast furnace required to produce one ton of pig iron in a blast furnace is about 27 ONrrr/l under conditions where the fuel ratio is about 500 kg/l. Therefore, 200k
When trying to inject pulverized coal at a ratio of g/l-pig, the amount of pulverized coal used relative to the oxygen IN% during blowing is approximately 0.75.
kg, and in order to burn this at a high combustion rate, the oxygen concentration in the blast must be approximately 36%. Therefore, the oxygen concentration that must be enriched to ensure a high combustion rate is approximately 14ONn? /l-pig, which is a high value.

However, if this oxygen is injected through the oxygen blowing hole using the pulverized coal injection nozzle according to the present invention, the oxygen concentration in the atmosphere will be 100% after the mixing point of oxygen gas and pulverized coal (the above-mentioned point p). It becomes possible to burn pulverized coal under conditions close to Therefore, when the oxygen concentration is 60% as in the above experimental results, 1.
Considering that it is possible to use 4 kg of pulverized coal, it is possible to use 200 kg/l-pig of pulverized coal without increasing the amount of oxygen, which clearly leads to a reduction in the amount of oxygen used.

By the way, conventionally, as a nozzle for blowing heavy oil into a blast furnace,
A nozzle with a double pipe structure, in which heavy oil is blown into the center hole and oxygen gas is blown into the surrounding annular slit.
There are examples where it was used. However, in this case, the combustion start point of the fuel is not determined, and because of the double tube structure, the partition wall between the fuel port of the inner tube and the surrounding annular oxygen port is insufficiently cooled, so the flame is not stable. There have been problems such as the partition wall being damaged by melting when approaching the nozzle, or the partition wall being rapidly oxidized and worn out by the blown oxygen gas.

On the other hand, the pulverized coal injection nozzle according to the present invention has a plurality of pipe-shaped blowing holes for injecting oxygen gas, and has a pulverized coal flow path and an oxygen gas flow path. are completely separated, the mixing and combustion point of pulverized coal and oxygen gas can be reliably regulated at a position far from the nozzle tip, and cooling can also be strengthened, so there is minimal risk of nozzle wear. .

As described above, since the pulverized coal injection nozzle according to the present invention has the above-described configuration, the combustion start position of pulverized coal is defined, and the combustibility of pulverized coal can be improved, so that the combustion flame of pulverized coal can be improved. Not only can it be stabilized, but it can also significantly reduce consumables costs by extending the life of the nozzle. In other words, with the pulverized coal injection nozzle according to the present invention, the combustion start position is inevitably determined irrespective of the blowing conditions or the situation inside the furnace, and the pulverized coal combustibility is improved. If set, pulverized coal can be used with a stable flame even if the air blowing conditions are slightly changed, and as a result, a large amount of pulverized coal can be used.

On the other hand, when conventional nozzles are used, the combustion start position of the pulverized coal is not stabilized, and the pulverized coal nozzle tip must be pulled in from the tuyere tip as much as possible to improve combustibility. I can't. Of course, in this case, there is an appropriate position of the nozzle for various air blowing conditions, but because the combustion start temperature is not stable, the flame gets too close to the nozzle and comes into contact with the inner surface of the tuyere and the blower branch pipe. This tends to cause problems such as adhesion and pulverized coal entering the furnace unburned. In particular, when changing the air blowing conditions, the problem of "unburned pulverized coal" or "ash adhesion to the tuyere" will inevitably occur unless appropriate changes are made to the nozzle position. Therefore, it is very difficult to use large amounts of pulverized coal.

Next, the present invention will be specifically explained with reference to Examples.

<Example> First, a combustion model of the lower part of a blast furnace having a fan-shaped structure in which the lower part including the slats of a 1000 r/class blast furnace was modeled was prepared, and a combustion test when pulverized coal was injected was conducted using this model.

This blast furnace lower combustion model has one tuyere, and coke is charged from the top to form a coke packed bed, and fuel combustion tests are carried out in the coke packed bed just like in a blast furnace. It is structured so that you can get it.

For the tuyere, use one with a tip diameter of 135flφ and an inner diameter of 200flφ.
It was installed in a branch pipe of mφ.

The coke used is one that is applicable to commercial blast furnaces (carbon content is 88%, ash content is approximately 11%, average diameter is 20 mm, D
I=93.5%), and the fixed carbon is 53% as pulverized coal.
44% non-coking coal with 35% volatile content, 10% natural content, and 2% moisture content
It was used after being ground so that the ratio of μ or less was 90% or more.

The air blowing conditions were: air amount: 3000 Nnf/h, air blowing temperature: 1000°C, and the oxygen concentration in the air at this time was 32.3%. Further, the flow velocity in the blower branch pipe at this time was 123 m/see.

First, as a comparison, we installed a water-cooled single-hole nozzle for pulverized coal injection with a pulverized coal injection diameter of 15 mm. position.

Angle between the nozzle and the center axis of the blower branch pipe: 20°.

The pulverized coal was transported and blown in with nitrogen at 6ONrd/h while air and enriched oxygen were blown into the tuyere through a hot blast furnace, and the blowing amount, pulverized coal combustion rate, and natural properties on the inner surface of the tuyere were measured. The adhesion status was investigated. The pulverized coal blowing speed at this time was 94 m/sec. In addition, the pulverized coal combustion rate is
Dust was collected 800 m before entering the furnace, and the residual combustible component ratio was determined from the relationship with the combustible component ratio in the pulverized coal.

As a result, when the amount of pulverized coal injected exceeded about 600 kg/h, the combustibility decreased significantly.

Subsequently, a test was conducted by retracting the nozzle position to a position 1 m from the tip of the tuyere, and in this case, good combustibility was obtained until the amount of pulverized coal injected exceeded about 850 kg/h. However, at this time, a large amount of ash adhered to the inner surface of the tuyere, and after about 10 hours, the diameter at the tip of the tuyere was reduced to about 50 mm, making ventilation impossible. In this case, even if the amount of pulverized coal was reduced, the adhesion of ash to the inner surface of the tuyere did not disappear.

Further tests were carried out to find the nozzle position where the maximum amount of pulverized coal could be used without causing ash adhesion to the tuyere, and the result was that this position was 700 m from the tip of the tuyere, and the pulverized coal injection at this time The maximum amount was 700 kg/h.

Next, the situation when the pulverized coal injection nozzle according to the present invention was used was investigated.

The pulverized coal injection nozzle (outer diameter: 265 mm) used at this time surrounds the pulverized coal injection pipe 2 (inner diameter: 15++n) and connects to the oxygen gas injection pipe 3 (as shown in Fig. 3). Six pipes (inner diameter: 8 fl) were provided (the center distance between the pulverized coal injection pipe 2 and the oxygen gas injection pipe 3 was 18.
5 m), and the distance from the nozzle tip to the mixing point p of oxygen gas and pulverized coal was set to 100 m, and the test was conducted by blowing the entire amount of oxygen gas into the oxygen gas from the oxygen gas blowing pipe 3.

At this time, the pulverized coal blowing speed was 94 m/min, which is the same as the comparative condition.
sec, and the oxygen gas blowing speed is 312 m/sec.
Met.

The results were as follows.

First, when the distance between the nozzle tip and the tuyere tip was set to 0.6 m, ash content did not adhere to the tuyere, and pulverized coal was
It was possible to burn up to 0 kg/h.

Next, when the distance between the nozzle tip and the tuyere tip was set to 1 m, pulverized coal could be burned at up to 1000 kg/h, and no ash adhered to the inner surface of the tuyere.

Subsequently, when the nozzle tip was moved back to a position 1.2 m from the tuyere tip, the combustibility was further improved and the weight was reduced to 1200 kg.
Although it was possible to use pulverized coal up to 1/h, there was a tendency for ash to adhere to the inner surface of the tuyere.

As mentioned above, as a result of comparing the pulverized coal injection operations using two nozzles, the conventional one and the one according to the present invention, it was found that the conventional single-hole nozzle could only stably use pulverized coal up to 700 kg/h. On the other hand, in the case of the nozzle according to the present invention, stable use of pulverized coal was ensured up to a high value of 1000 kg/h.

Comparing these results in terms of pulverized coal ratio, the conventional nozzle has approximately 1
70 kg, whereas the nozzle according to the present invention has a weight of 2.
It becomes 40kg of pulverized coal. In other words, the amount of pulverized coal used can be increased by 40% or more under the same blowing temperature and oxygen usage conditions.

Summary of Effects> As described above, according to the present invention, it is possible to use a large amount of pulverized coal as auxiliary fuel during blast furnace smelting without causing operational instability, and the use of coke, which is the main fuel, can be reduced. This brings about industrially useful effects, such as the ability to significantly reduce the amount of iron smelting and reduce the cost of iron smelting.

[Brief explanation of the drawing]

FIG. 1 is a schematic view showing an example of a pulverized coal injection nozzle according to the present invention, and FIG.
FIG. 1(b) shows a front view of the nozzle blowing surface, and FIG. 1(C) shows a sectional view corresponding to the A-A section in FIG. 1(a). FIG. 2 is a conceptual diagram showing an example of how the pulverized coal injection nozzle according to the present invention is attached to a blower branch pipe. FIG. 3 is a schematic diagram of a pulverized coal injection nozzle according to the present invention used in Examples, and FIG. 3(a) is a longitudinal cross-sectional view thereof, and FIG. Figures are shown respectively. FIG. 4 is a conceptual diagram showing a conventional pulverized coal injection state in blast furnace operation. FIG. 5 is a conceptual diagram showing how ash adheres to the vicinity of the inner surface of the tuyere. In the drawings, 1.8... Nozzle for blowing pulverized coal, 2... Pipe for blowing pulverized coal, 3... Pipe for blowing oxygen gas, 4... Cooling water passage, 5... Tuyere, 6...
・Blower branch pipe, 7... Blast furnace wall, 42 ports...
・Adhesive ash content.

Claims (1)

[Claims] It has a plurality of oxygen gas blowing holes surrounding a central pulverized coal blowing hole, and the axis of at least the tip of each of these oxygen gas blowing holes intersects with the axis of the pulverized coal blowing hole in front of the nozzle. A nozzle for blowing pulverized coal into a blast furnace.