JPH0723489B2 - Nozzle for blowing pulverized coal in blast furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention is for blowing pulverized coal into a blast furnace in order to effectively burn a large amount of pulverized coal and significantly reduce coke consumption. It concerns a nozzle.

<Background Art> As is well known, the main fuel in iron blast furnace smelting is coke. However, blast furnace coke has about 25
The cost is high because the raw material is expensive coking coal, which is only about%. Therefore, it is necessary to suppress the consumption of coke as much as possible in order to meet the demand for cost reduction of steel materials that has become more severe. Has become. Therefore, in recent years
The tuyere injection of various auxiliary fuels has come to be carried out in blast furnace smelting.

Looking back, first, heavy oil was blown in from the 1950s, and the amount of blown oil exceeded 100 kg per ton of pig iron, contributing to coke savings. However, since the late 1970s, the price of heavy oil has soared, so the number of blast furnaces that inject heavy oil has decreased worldwide. It has become the mainstream. It should be noted that such pulverized coal injection is performed by a pulverized coal injection nozzle 8 installed in a blower branch pipe 6 connected to a tuyere 5, as shown in FIG. 4, for example.

However, because pulverized coal is a powder (solid), it has poorer combustibility than liquid fuel such as heavy oil, and in order to use it in large quantities, it is necessary to improve combustibility. ○ Increase the oxygen concentration in the tuyere ventilation. , ○ Raise the air temperature, ○ Install the burner as far from the tuyere as possible,
Measures have been taken, such as promoting combustion of pulverized coal between the tuyere and the flow into the furnace.

However, when the combustibility of pulverized coal is improved by such a method, another problem as described below tends to occur. In other words, pulverized coal contains ash, so the ash contained in the pulverized coal burned between the blast branch pipe and the tip of the tuyere adheres to the inner surface of the tuyere to reduce the diameter of the tuyere. It is easy to cause a phenomenon that obstructs ventilation, and since the adhered state is not uniform in each tuyere, it also induces a significant imbalance in the distribution of air flow between each tuyere and hinders stable operation. That is the problem.

FIG. 5 shows the above-mentioned ash content adhesion state. As shown in "a" when the heat insulating ring for preventing heat loss is attached to the inner surface of the tuyere 5, When the heat insulating ring is not used, it easily adheres as shown by "b".

Therefore, "a phenomenon in which unburned pulverized coal is accumulated in the furnace due to unfavorable combustibility and hinders stable operation", and it tends to occur when the above-mentioned combustibility improvement measures are taken to address this. "Combustion ash, which has become molten due to the increase in combustion heat in the tuyere, adheres to the inner surface of the tuyere, causing" tuyle blockage "and" uneven distribution of air flow between the tuyere "and hinders stable operation. In order to use pulverized coal without causing "phenomenon" etc., its use limit is naturally limited.

At present, the amount of pulverized coal used in Japan's blast furnace is limited to the maximum 100 kg per ton of pig iron, and it can be easily achieved even in overseas blast furnaces under the conditions of heavy oil operation and all coke operation. Fuel ratio is 500kg / t ・ pig
There is no example of using pulverized coal in excess of 200 kg / t under the condition of (pig iron) or less ”.

<Means for Solving Problems> From the viewpoints described above, the present inventors blow a large amount of pulverized coal during blast furnace smelting and efficiently burn it, and
As a result of various studies to make it possible to significantly reduce the amount of coke used while sufficiently suppressing the problem of "ash tuyere adhesion", etc., pulverized coal was used in large amounts up to, for example, 200 kg / t ・ pig or more. In order to achieve a stable high fuel ratio, we came to the conclusion that it is absolutely necessary to take measures to simultaneously achieve both "combustibility improvement" and "ash content tuyere inner surface adhesion prevention." A plurality of oxygen gas blowing holes are provided so as to surround the pulverized coal blowing hole at the center, and the axis line of at least the tip of each oxygen gas blowing hole intersects with the axis line of the pulverized coal blowing hole in front of the nozzle. And
Developed a blast furnace pulverized coal injection nozzle.

FIG. 1 is a schematic view showing an example of a pulverized coal blowing nozzle according to the present invention, and FIG. 1 (a) is a vertical sectional view thereof.
Figure (b) is a front view of the nozzle blowing surface, and
FIG. 3C is a sectional view corresponding to the portion AA in FIG.

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 blowout tip of the oxygen gas blowing pipe 3 is bent in the direction of the center of the nozzle, and the centerline of the portion is at a point p in front of the centerline of the pulverized coal blowing pipe 2 and the pulverized coal blowing nozzle 1. It is configured to intersect.

Here, if the distance from the tip of the nozzle to the point p is too short, there is a strong possibility of causing meltdown of the nozzle tip, while if it is too long, the mixing property of the blown pulverized coal and oxygen gas tends to deteriorate. Therefore, it is preferable to set it to 50 to 500 mm.

The pulverized coal blowing nozzle shown in FIG. 1 is an example having a water cooling structure in which a cooling water passage 4 is provided.

The pulverized coal blowing nozzle 1 is used by being attached to a blower branch pipe 6 formed on a tuyere 5 of a blast furnace as shown in FIG. 2, for example.

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 oxygen gas blowing hole is set to intersect the axis of the pulverized coal blowing hole in front of the nozzle. There are three reasons: the regulation of the starting position of combustion of pulverized coal, improvement of combustibility of pulverized coal, and prevention of wear of the nozzle for blowing pulverized coal. Hereinafter, this point will be described in more detail.

That is, one of the reasons why the pulverized coal blowing hole and the oxygen gas blowing hole are formed as separate bodies and their axes intersect at the front of the nozzle for the first time is that the combustion starting position of the blowing pulverized coal is defined. With such a nozzle configuration, the pulverized coal flowing out from the pulverized coal blowing hole is almost mixed with hot air or oxygen gas which is a combustion improver until it reaches the intersection (point p in FIG. 1) of the blowing hole axis. do not do. Therefore, p
Pulverized coal does not burn up to the point.

On the other hand, the pulverized coal flowing out from the pulverized coal blowing hole is
When the temperature reaches, the pulverized coal mixes with the oxygen gas blown from the oxygen gas blow-out hole, so that the combustion starts for the first time.

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

In general, 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 the experiments by the present inventors, when the oxygen concentration in the blast is 21% ( when blowing air) is conventionally, using hot air at 1000 ° C., pulverized coal (fixed carbon 53 relative to blowing oxygen 1 Nm ³
%, Volatile content 35%, ash content 10%, 90% of particles 44μ or less)
However, when the oxygen concentration in the blast was set to 31%, the oxygen concentration in the blast was up to 0.6 kg per 1 Nm ^{3 of} oxygen when the oxygen concentration in the blast was set to 31%. It was possible to burn pulverized coal up to 0.9 kg, and pulverized coal up to 1.4 kg under high flammability by increasing the oxygen concentration in the blast to 60%. However, the amount of oxygen in the blast required to produce 1 ton of pig iron in the blast furnace is about 270 Nm ³ / t under the condition that the fuel ratio is about 500 kg / t. Therefore, when blowing pulverized coal at a rate of 200 kg / t ・ pig, the amount of pulverized coal used for blowing oxygen of 1 Nm ³ is approximately 0.75 kg. The concentration should be about 36%. Therefore, the oxygen concentration that must be enriched in order to secure a high burning rate is a high value of about 140 Nm ³ / t · pig.

However, if this oxygen is blown through the oxygen blowing hole using the pulverized coal blowing nozzle according to the present invention, the oxygen concentration in the atmosphere becomes 100% after the mixing point of oxygen gas and pulverized coal (point p above). It becomes possible to burn pulverized coal under conditions close to the above. Therefore, considering that it is possible to use 1.4 kg of pulverized coal for 1 Nm ³ of oxygen when the oxygen concentration is 60% as in the above experimental results, 200 k without increasing the oxygen amount.
It is clear that the use of pulverized coal of g / t · pig is possible, which leads to a reduction in oxygen consumption.

By the way, conventionally, as a nozzle for injecting heavy oil into a blast furnace, a "nozzle having a double pipe structure, in which heavy oil is injected through a central hole and oxygen gas is injected through a peripheral annular slit", has been used. There is an example. However, in this case, the combustion start point of the fuel is not determined, and due to the double pipe structure, the cooling of the partition wall between the fuel port of the inner tube and the surrounding annular oxygen port is insufficient, etc. There are problems that the partition wall is melted and damaged when approaching the nozzle, and that the partition wall is rapidly oxidized by the blown oxygen gas and worn.

On the other hand, in the pulverized coal blowing nozzle according to the present invention, the pulverized coal flow path and the oxygen gas flow path are completely formed by having a plurality of pipe-shaped blowout holes even for the injection of oxygen gas. In addition, since the mixing / burning point of pulverized coal and oxygen gas can be reliably regulated at a position away from the nozzle tip, and cooling can be enhanced, the risk of nozzle wear is minimized.

Thus, since the pulverized coal blowing nozzle according to the present invention is configured as described above, the combustion start position of the pulverized coal is defined, and the combustibility of the pulverized coal can be improved, so that the combustion flame of the pulverized coal is reduced. In addition to being stabilized, the effect of greatly reducing the cost of consumables by extending the life of the nozzle can be obtained. That is, in the pulverized coal blowing nozzle according to the present invention, the combustion start position is inevitably determined without depending on the blowing conditions or the in-furnace conditions,
In addition, since the pulverized coal combustibility is improved, once the nozzle is set at the proper position, it is possible to use pulverized coal with a stable flame even if the blowing conditions are changed to some extent.As a result, a large amount of pulverized coal can be used. It will be possible.

On the other hand, the combustion start position of pulverized coal is not stabilized when the conventional nozzle is used, and the combustibility is improved unless the nozzle end of the pulverized coal is pulled out from the tuyere tip as much as possible. I can't. Of course, in this case, there is a proper position of the nozzle for various blowing conditions, but since the combustion start temperature is not stable, the flame comes too close to the nozzle and comes into contact with the tuyere or the inner surface of the blower branch pipe, and the ash adheres to the inner surface of the tuyere. And the pulverized coal enters the furnace without being burned. In particular, when changing the blowing conditions, the problem of "non-burning of pulverized coal" or "adhesion of ash tuyere" will always occur unless the nozzle position is changed appropriately. Therefore, it is very difficult to use a large amount of pulverized coal.

Next, the present invention will be specifically described with reference to examples.

<Examples> First, a blast furnace lower combustion model having a fan-shaped structure simulating the lower part including the tuyere of a 1000 m ³ class blast furnace was prepared, and a combustion test was carried out when pulverized coal was injected. The lower combustion model of the blast furnace has one tuyere, and the coke is charged from the upper part to form a coke packed layer, and the structure is such that the fuel can be burnt in the coke packed layer as in the blast furnace. It has become.

The tuyere with a tip diameter of 135 mmφ was installed on a blower branch pipe with an inner diameter of 200 mmφ.

The coke used is for commercial blast furnaces (carbon content is 88%, ash content is about 11%, average diameter is 20mmφ, ▲ DI ³⁰ ₁₅
▼ = 93.5%), as pulverized coal 53% fixed carbon, volatile matter
Non-caking coal of 35%, ash content 10%, water content 2% is 90% for 44μ or less
It was crushed and used as described above.

The blowing conditions were air volume: 3000 Nm ³ / h and blowing temperature: 1000 ° C., but the oxygen concentration during blowing was 32.3%. The flow velocity in the blast branch pipe at this time was 123 m / sec.

As a comparison, first, a water-cooled pulverized coal injection single-hole nozzle with a pulverized coal injection diameter of 15 mmφ is installed: the nozzle tip and tuyere tip are 600 mm apart, and the nozzle tip is 30 mm above the center axis of the blower branch pipe. Position, the angle between the nozzle and the central axis of the blast branch pipe: 20 °, the air and the enriched oxygen are both blown from the tuyere through the hot air stove, and the pulverized coal is transported and blown with nitrogen of 60 Nm ³ / h. The amount of entrapment, pulverized coal burning rate, and ash deposition on the tuyere inner surface were investigated. The pulverized coal blowing rate at this time was 94 m / sec.
The combustion rate of pulverized coal was obtained by collecting dust at a position that entered the furnace 800 mm in front of the tuyere and the ratio of the residual combustible components in the pulverized coal.

As a result, the combustibility was remarkably reduced when the pulverized coal injection rate exceeded about 600 kg / h.

Subsequently, the nozzle position was retracted to a position 1 m from the tuyere tip and tested. 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 about 10
After a lapse of time, the diameter of the tuyere tip decreased to about 50 mmφ and ventilation was disabled. In this case, even if the amount of pulverized coal was reduced, the adhesion of ash to the tuyere inner surface was not eliminated.

The test was further continued, and as a result of investigating the nozzle position where the pulverized coal can be used to the maximum without causing the adhesion of tuyere to the ash, this position is 700 mm from the tip of the tuyere. The maximum value of loading was 700 kg / h.

Next, the situation when the pulverized coal blowing nozzle according to the present invention was used was examined.

Pulverized coal injection nozzle used at this time (outer diameter: 65 mm)
As shown in FIG. 3, 6 pieces of oxygen gas injection pipes 3 (inner diameter: 8 mm) are provided surrounding the pulverized coal injection pipe 2 (inner diameter: 15 mm) (powdered coal injection pipe 2 and oxygen The center distance from the gas injection pipe 3 is 18.5 mm), and the distance from the nozzle tip to the mixing point p of oxygen gas and pulverized coal is 10 mm.
The test was carried out by setting the length to 0 mm and blowing the entire amount of the blown oxygen gas from the oxygen gas blowing pipe 3. At this time, the pulverized coal blowing rate was 94 m / sec, which was the same as the comparison condition, and the oxygen gas blowing rate was 312 m / sec.

The results were as follows.

First, when the distance between the tip of the nozzle and the tip of the tuyere was set to 0.6 m, tuyere adhesion of ash did not occur and 800 kg / h of pulverized coal was used.
Could be burned up to.

Next, when the distance between the tip of the nozzle and the tip of the tuyere was set to 1 m, pulverized coal could be burned up to 1000 kg / h, and ash did not adhere to the tuyere inner surface.

Subsequently, when the nozzle tip was retracted to a position 1.2 m from the tuyere tip, the combustibility was further improved and pulverized coal up to 1200 kg / h could be used, but in this case ash content was found on the tuyere inner surface. A tendency to adhere has become visible.

As described above, as a result of comparing the pulverized coal injection operation with the two nozzles of the conventional one and the one according to the present invention, it was found that the conventional single-hole nozzle could stably use the pulverized coal up to 700 kg / h. On the other hand, in the case of the nozzle according to the present invention, 10
Stable use of pulverized coal was secured up to a high value of 00 kg / h.

Comparing this result with the pulverized coal ratio, about 17
While it is 0 kg / t, it is 240 kg / t in the nozzle according to the present invention.
It becomes pulverized coal. That is, the amount of pulverized coal used can be increased by 40% or more under the same blast temperature and oxygen use conditions.

<Summary of Effects> As described above, according to the present invention, it becomes possible to use a large amount of pulverized coal as an auxiliary fuel during blast furnace smelting without causing unstable operation, and use of coke as a main fuel. Industrially useful effects are brought about, such as a significant reduction in the amount and a reduction in iron smelting cost.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a pulverized coal blowing nozzle according to the present invention, and FIG. 1 (a) is a vertical sectional view thereof.
FIG. 1 (b) is a front view of the nozzle blowing surface, and FIG. 1 (c) is a sectional view corresponding to the portion AA in FIG. 1 (a). FIG. 2 is a conceptual diagram showing an example of attaching the pulverized coal blowing nozzle according to the present invention to the blower branch pipe. FIG. 3 is a schematic view of a pulverized coal blowing nozzle according to the present invention used in Examples. FIG. 3 (a) is a longitudinal sectional view thereof, and FIG. 3 (b) is a nozzle blowing surface. The front views are respectively shown. FIG. 4 is a conceptual diagram showing a conventional pulverized coal injection state in a blast furnace operation. FIG. 5 is a conceptual diagram showing the ash adhesion state near the inner surface of the tuyere. In the drawings, 1,8 ... Pulverized coal injection nozzle, 2 ... Pulverized coal injection pipe, 3 ... Oxygen gas injection pipe, 4 ... Cooling water passage, 5
... tuyere, 6 ... blast branch pipe, 7 ... blast furnace wall, a, b ... adhering ash.

Claims (1)

[Claims] 1. A plurality of oxygen gas blowing holes are provided so as to surround a central pulverized coal blowing hole, and an axis of at least the tip of each oxygen gas blowing hole intersects with the axis of the pulverized coal blowing hole in front of the nozzle. Nozzle for blowing pulverized coal in a blast furnace.