JP2017222902A - Lance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lance capable of preventing melt damage at a confluent part where a gas such as a combustion-supporting gas and a combustible gas collides with a transport pipe of a solid fuel such as a powdered coal.SOLUTION: An outside pipe 7 is disposed while being converged concentrically outside of an inside pipe 6 at a middle way of a pipe path, a part ahead in a blowing direction from the confluent part of the inside pipe 6 for blowing a solid fuel including at least the confluent part to the outside pipe 7 is formed like a straight pipe, the outside pipe 7 for blowing a combustion-supporting gas or a combustible gas is bent in one direction at the confluent part with the inside pipe 6, and an angle formed between a center axis of the outside pipe 7 at a bent part and a center axis of the inside pipe 6, that is a cross angle φ, is less than 90°, preferably greater than 0°and not greater than 60°, thereby the dynamic pressure when a gas blown from the outside pipe 7 collides with the inside pipe 6 is reduced to suppress melt damage.SELECTED DRAWING: Figure 2

Description

  In the present invention, solid fuel such as pulverized coal and granular synthetic resin, and flammable gas such as flammable gas such as oxygen or LNG (Liquefied Natural Gas) are individually blown into a blast furnace blow pipe. It relates to a lance to be burned.

  The pulverized coal injection into the blast furnace is adopted in many blast furnaces because it has a large cost merit based on the price difference with the coke, and greatly contributes to the improvement of economy. 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 increasingly injected. However, as the amount of pulverized coal injected into the blast furnace is increased, the combustion rate of pulverized coal decreases, and the pulverized coal cannot be burned in the raceway and is discharged into the furnace as unburned unburned char. . This unburned char is consumed in the furnace due to the solution loss reaction, but there is a limit value in the furnace consumption, so if unburned char is generated above the consumption limit value, it is discharged as dust from the top of the furnace. As a result, fuel costs increase. Furthermore, if unburned char accumulates in the furnace core or molten zone, the air permeability and liquid permeability are hindered, causing furnace instability and productivity reduction.

  As means for solving this problem, many methods have been proposed in which the pulverized coal blowing lance has a multi-tube structure, for example, the contact efficiency between pulverized coal and oxygen is improved, and the pulverized coal is actively combusted. However, by blowing separately powders (solid fuel) such as pulverized coal and granular synthetic resin and combustion-supporting gas such as oxygen, the lance tip and combustion-supporting gas transport pipes are not damaged. It often occurs and long-term stable blowing cannot be performed. For this reason, not only the repair cost increases due to the decrease in the lance life, but also the amount of low-powder pulverized coal decreases, which has been a factor in increasing costs. As a countermeasure against the lance melting, for example, in Patent Document 1 below, among the four tubes arranged concentrically, the third tube is made shorter than the second tube and the fourth tube, so that the second tube Between the first pipe and the third pipe, and between the third pipe and the fourth pipe as a cooling water return channel, and between the first pipe and the second pipe, a helical fin is provided. Provided. And by providing such a cooling water flow path, a large amount of cooling water can be made to flow uniformly in the pipe circumferential direction, and the cooling effect can be improved and the heat load of the lance can be greatly reduced. Yes.

JP 2000-160216 A

  However, melt damage caused by individually blowing powder (solid fuel) such as pulverized coal or granular synthetic resin and a combustion-supporting gas such as oxygen is not limited to the lance tip, but is also supported in the transport pipe. It has been found that the volatile gas also occurs at the junction where the solid gas collides with the solid fuel injection pipe. The temperature of the combustion-supporting gas may increase due to adiabatic compression and frictional heat. Adiabatic compression is a phenomenon in which high-pressure gas suddenly flows into a closed space such as a pressure regulator, a valve, and piping due to a sudden opening operation of the valve, and the gas pressure and the gas temperature rapidly increase. The frictional heat is heat generated by the fluid friction of the fluid when the high-pressure gas flows through a narrow gap, and the temperature of the gas and the temperature of the member that forms the gap rise due to this frictional heat. And the pipe | tube heated by these adiabatic compression and frictional heat generate | occur | produces further heat | fever by the self-oxidation heat accompanying contact with oxygen. In particular, high dynamic pressure is generated in the lance at the junction with the pulverized coal transport pipe where the flow direction of the combustion-supporting gas changes abruptly. For example, the oxide film generated on the outer surface of the pulverized coal transport pipe has high dynamic pressure. After that, the auto-oxidation and the removal of the oxide film may be repeated to cause melting damage. When flammable gas such as pulverized coal and LNG is blown individually, the self-oxidation of the pulverized coal transport pipe does not occur at the flammable gas confluence, but the temperature of the flammable gas rises due to adiabatic compression. In addition, since there is no change in that high dynamic pressure is generated in the joining portion, if such a state continues for a long time, there is a possibility that the pulverized coal transport pipe may also be melted in the joining portion.

  The present invention has been made paying attention to the above-described problems, and it is possible to prevent melting at a junction where a combustion-supporting gas or a flammable gas collides with a transport pipe of solid fuel such as pulverized coal. It aims at providing the lance which can be suppressed.

  The inventors of the present invention have made extensive studies to solve the above problems, and as a result, the merging angle of the outer tube is important at the merging portion between the outer tube and the inner tube, and this angle is set within an appropriate range. By doing so, it was found that the above-mentioned melting loss can be suppressed. That is, when the merging angle of the outer pipe is vertical or close to it, the temperature rise due to adiabatic compression is large, and high dynamic pressure is generated, so that melting damage is likely to occur. The flammable gas or the flammable gas flows from the oblique direction to the junction. As a result, the temperature rise due to adiabatic compression is reduced, and the dynamic pressure is also reduced, so that it is presumed that the lance can be prevented from being damaged.

The present invention is based on the above findings, and the outline thereof is as follows.
(1) A lance used by being inserted into a blower pipe for blowing hot air into a blast furnace through a tuyere, formed by concentrically joining an outer pipe to the outside of the inner pipe in the middle of the pipeline, The inner pipe into which the solid fuel is blown is formed in a straight tube shape in the blowing direction from the merging part including at least the merging part with the outer pipe, and the flammable gas or the flammable gas is blown into the inner pipe. The outer tube is at a junction with the inner tube and is bent in one direction, and an angle formed by the central axis of the outer tube and the central axis of the inner tube at the bent portion is less than 90 °. Lance to do.
(2) The lance according to (1), wherein an angle formed by a central axis of the outer tube and a central axis of the inner tube at the bent portion is set to 0 ° to 60 ° or less.

Examples of the solid fuel of the present invention include pulverized coal.
The combustion-supporting gas of the present invention is defined as a gas having an oxygen concentration of at least 50 vol%.
In addition, the flammable gas used in the present invention is literally a gas that is more flammable than pulverized coal. For example, in addition to hydrogen containing hydrogen as a main component, city gas, LNG, propane gas, in steelworks The generated converter gas, blast furnace gas, coke oven gas, etc. are applicable. Further, shale gas can be used as a gas similar to LNG. Shale gas is a natural gas extracted from the shale layer, and is produced from a place other than the conventional gas field, so it is called an unconventional natural gas resource. Combustible gases such as city gas ignite and burn very quickly, and those with a high hydrogen content have high combustion calories, and unlike pulverized coal, flammable gas does not contain ash. It is advantageous for air permeability and heat balance.

  In the lance of the present invention, since the dynamic pressure at which the combustion-supporting gas or the flammable gas blown from the outer tube collides with the inner tube is reduced, the inner tube can be prevented from being melted at the junction. .

It is a longitudinal cross-sectional view which shows one Embodiment of the blast furnace to which the blast furnace operating method of this invention was applied. It is a front view of the lance inserted in the air duct of FIG. It is the front view of the typical lance set in order to consider the dynamic pressure which arises in an inner side pipe | tube with the lance of FIG. FIG. 4 is a perspective view of the lance of FIG. 3. FIG. 4 is a plan view showing an outer surface of an inner tube and an inner surface of an outer tube in the lance of FIG. 3. It is a side view of the gas flow which collides with the outer surface of the inner side pipe | tube in the lance of FIG. It is explanatory drawing of the dynamic pressure evaluation parameter | index when the crossing angle of the outer side pipe | tube and an inner side pipe | tube in a junction part is changed variously by the lance of FIG.

  Next, an embodiment of the blast furnace operating method of the present invention will be described with reference to the drawings. FIG. 1 is an overall view of a blast furnace to which the blast furnace operating method of this embodiment is applied. As shown in the figure, a blast pipe 2 for blowing hot air is connected to the tuyere 3 of the blast furnace 1, and a lance 4 is installed through the blast pipe 2. For example, air is used as the hot air. A combustion space called a raceway 5 exists in the coke deposit layer ahead of the hot air blowing direction of the tuyere 3, and iron ore is reduced, that is, ironmaking is mainly performed in this combustion space. In the figure, the lance 4 is inserted only into the left blower pipe 2 shown in the figure, but as is well known, the lance is provided to both the blower pipe 2 and the tuyere 3 arranged circumferentially along the furnace wall. It is possible to insert and set 4. Further, the number of lances per tuyere is not limited to one, and two or more lances can be inserted. Moreover, the form of a lance can be applied to a single pipe lance, a double pipe lance, or a bundle of a plurality of lances. In this embodiment, a lance 4 serving as a double-pipe lance is used inside the blower pipe 2.

For example, when pulverized coal is blown from the lance 4 as a solid fuel, the pulverized coal is blown together with a carrier gas (carrier gas) such as N ₂ . When only pulverized coal is blown from the lance 4 as a solid fuel, the pulverized coal blown into the raceway 5 from the lance 4 through the tuyere 3 is burned with coke and its volatiles and fixed carbon. The aggregate of carbon and ash, generally called char, remaining without being exhausted is discharged from the raceway 5 as unburned char. Since unburned char is accumulated in the furnace and deteriorates the air permeability in the furnace, it is required to burn the pulverized coal as much as possible in the raceway 5, that is, to improve the flammability of the pulverized coal. The hot air velocity at the tip of the tuyere 3 in the direction of blowing hot air is about 200 m / sec, and the oxygen existing area in the raceway 5 from the tip of the lance 4 is about 0.3 to 0.5 m. In addition, it is necessary to raise the temperature of the pulverized coal particles and improve the contact efficiency with oxygen at a level of 1/1000 second.

  The pulverized coal blown into the raceway 5 from the tuyere 3 is first heated by convective heat transfer from the air blow, and then the particle temperature rapidly rises by radiant heat transfer and conduction heat transfer from the flame in the raceway 5. Then, thermal decomposition starts when the temperature rises to 300 ° C. or more, ignites volatile matter, forms a flame, and the combustion temperature reaches 1400 to 1700 ° C. When the volatile matter is released, it becomes the char described above. Since char is mainly fixed carbon, a reaction called a carbon dissolution reaction occurs along with a combustion reaction. At this time, the increase in the volatile content of the pulverized coal blown from the lance 4 into the blower pipe 2 promotes the ignition of the pulverized coal, and the increase in the combustion amount of the volatile component increases the heating rate and the maximum temperature of the pulverized coal. The rate of char reaction increases due to the dispersibility of pulverized coal and an increase in temperature. That is, it is considered that the pulverized coal is dispersed with the vaporization and expansion of the volatile matter, the volatile matter is combusted, and the pulverized coal is rapidly heated and heated by this combustion heat. On the other hand, when LNG is blown into the blow pipe 2 from the lance 4 together with pulverized coal, for example, as flammable gas, the LNG comes into contact with the oxygen being blown and the LNG burns, and the pulverized coal is rapidly heated by the combustion heat. It is considered that the temperature is raised, and this facilitates the ignition of pulverized coal.

  In this embodiment, the combustion-supporting gas is blown from the lance 4 together with the solid fuel. Pulverized coal was used as the solid fuel, and oxygen was used as the combustion-supporting gas. Note that the oxygen concentration of the combustion-supporting gas was 95 vol% or more. As described above, a double pipe lance is used for the lance 4, and pulverized coal is blown together with the carrier gas from the inner pipe 6 constituting the double pipe lance, and the outer pipe 7 (strictly speaking, the inner pipe 6 and the outer pipe 7). Oxygen is blown in through the gap. However, this double pipe lance is not a double pipe over the entire length, and is formed by concentrically joining the outer pipe 7 outside the inner pipe 6 in the middle of the pipe as shown in FIG. ing. In this double pipe lance, oxygen and pulverized coal are blown into the outer pipe 7 and the inner pipe 6 from the right to the left in the figure. Among these, the inner pipe 6 into which the pulverized coal is blown is formed in a straight tubular shape in the blowing direction ahead of the joining part including at least the joining part with the outer pipe 7. In addition, the outer tube 7 for blowing oxygen is at a junction with the inner tube 6 and is bent in one direction, and an angle formed by the central axis of the outer tube 7 and the central axis of the inner tube 6 at the bent portion is less than 90 °. It is said. In this embodiment, the angle between the central axis of the outer tube 7 and the central axis of the inner tube 6 at the bent portion (hereinafter, also simply referred to as the intersection angle between the outer tube 7 and the inner tube 6) exceeds 0 ° and 60 °. The following.

In order to set the crossing angle of the outer tube 7 and the inner tube 6 at the bent portion, that is, the junction of the outer tube 7 and the inner tube 6, the movement when oxygen blown from the outer tube 7 collides with the inner tube 6. Evaluate the pressure. When oxygen blown from the outer tube 7 collides with the inner tube 6, the dynamic pressure is considered to be the largest, as shown in FIGS. 3 and 4, because the merging angle between the outer tube 7 and the inner tube 6 is This is the case when it is vertical. Therefore, when the maximum value of the dynamic pressure when oxygen blown from the outer pipe 7 collides with the inner pipe 6 is defined as Pvmax, factors that affect the maximum dynamic pressure value Pvmax will be considered. Factors affecting the dynamic pressure maximum value Pvmax include, as shown in FIG. 4, the junction inlet Reynolds number Re, the inlet flow velocity Vin, the inlet dynamic pressure Pvin, the inlet area Sin (the outer pipe 7 joins the inner pipe 6). The inner area of the tube immediately before the merging), and the merging portion outlet flow velocity Vout. In addition, in this embodiment, the escape area Sesc from which oxygen blown from the outer tube 7 escapes from the collision with the inner tube 6 is considered. This escape area Sesc flows so that the oxygen blown from the outer pipe 7 does not collide with the inner pipe 6 at all and the oxygen blown from the outer pipe 7 flows along the outer surface of the inner pipe 6. Although it is in contact with the inner pipe 6, it is considered to be the sum of the flow area Sflow that is difficult to cause dynamic pressure. That is, the clearance area Sesc is expressed by the following equation (1).
Sesc = Sno + Sflow (1)
FIG. 5 is a plan view showing the outer surface of the inner tube 6 and the inner surface of the outer tube 7 at the junction of the lance shown in FIG. The symbol d in the drawing indicates the outer diameter of the inner tube 6, and the symbol D in the drawing indicates the inner diameter of the outer tube 7. The total area of hatched portions in FIG. 5 corresponds to the collision-free area Sno. From the figure, the collision-free area Sno is geometrically given by the following equation (2).

  6 is a side view of the gas flow that collides with the outer surface of the inner tube 6 at the merging portion of the lance of FIG. 3, and corresponds to the side view of FIG. Therefore, the circle in the figure indicates the outer surface of the inner tube 6, and the vertical arrow indicates the flow of oxygen blown from the outer tube 7. It is considered that oxygen colliding with each point of the upper semicircular arc drawn by the outer surface of the inner tube 6 flows mainly in the tangential direction of the point after the collision. An angle formed by a line segment connecting the collision point and the center point O of the inner tube 6 with respect to the horizontal axis in FIG. 6, for example, the horizontal direction is ψ, and the axial direction of the inner tube 6 in the plan view of FIG. Axis. In FIG. 5, the angle formed by the line connecting the intersection of the outer surface of the inner tube 6 and the inner surface of the outer tube 7 and the center point Q of the outer tube 7 with the horizontal axis of the drawing, that is, the axis of the inner tube 6 When the angle formed with the direction perpendicular to the direction z is θ0, the flow area Sflow is given by the following equation (3).

  Among these, the escape area Sesc given by the sum of the collision-free area Sno and the flow area Sflow varies depending on the inlet area Sin. Similarly, the outlet flow velocity Vout varies depending on the inlet flow velocity Vin (exactly, the square value of the outlet flow velocity Vout is proportional to the square value of the inlet flow velocity Vin). The dynamic pressure maximum value Pvmax varies according to the inlet dynamic pressure Pvin. In the case of this embodiment, oxygen flows throughout the pipe of the outer pipe 7, and therefore, the Reynolds number Re reflects the shape of the merging portion, particularly the layout of the inner pipe 6 in the outer pipe 7. Therefore, the evaluation index of the dynamic pressure accompanying the collision of oxygen blown from the outer tube 7 to the outer surface of the inner tube at the junction is assumed to be A given by the following equation (4). This dynamic pressure evaluation index A eliminates the influence of the inlet dynamic pressure, the Reynolds number, the diameter ratio between the inner pipe 6 and the outer pipe 7, and the flow velocity ratio before and after the gas merging by making it dimensionless. Can be evaluated.

  Therefore, in this embodiment, in order to reduce the dynamic pressure evaluation index A, the inner pipe 6 into which the pulverized coal is blown is blown more than the merging section including at least the merging section with the outer pipe 7 as described above. A front portion in the insertion direction is formed in a straight tube shape. Then, the outer tube 7 through which oxygen is blown is bent in one direction at the junction with the inner tube 6, and the intersection angle between the outer tube 7 and the inner tube 6 at the junction is less than 90 °. Here, in order to define the crossing angle of the outer tube 7 and the inner tube 6 at the bent portion, that is, the merge portion, a fluid analysis of the merge portion is performed by a computer using general-purpose fluid software, and the three cases shown in Table 1 below are performed. The dynamic pressure evaluation index A was determined while variously changing the crossing angle between the outer tube 7 and the inner tube 6.

  FIG. 7 is a graph of the calculated dimensionless dynamic pressure evaluation index A. In the figure, the dynamic pressure evaluation index A becomes the maximum at the intersection angle φ = 90 ° between the outer tube 7 and the inner tube 6 and rapidly decreases from φ = 90 ° to φ = 60 °. It becomes constant. Here, it was considered that the dynamic pressure evaluation index A is 40 or less and the maximum dynamic pressure value Pvmax is stable. This is because the crossing angle φ between the outer tube 7 and the inner tube 6 at the joining portion becomes small, so that the difference between the motion direction of oxygen flowing through the outer tube before joining and the motion direction of oxygen flow assumed after joining is small. Accordingly, the change in momentum is reduced accordingly, which is considered to be caused by a decrease in dynamic pressure when oxygen collides with the outer surface of the inner tube. Therefore, even if the temperature of the inner tube outer surface rises for some reason and auto-oxidation occurs, the dynamic pressure on the inner tube outer surface can be reduced by setting the crossing angle φ between the outer tube 7 and the inner tube 6 to 60 ° or less. It is considered that the inner pipe 6 can be prevented from being melted by this. Note that the minimum value of the crossing angle φ between the outer tube 7 and the inner tube 6 at the junction was over 0 °.

  In this embodiment, the case where pulverized coal is blown from the inner pipe 6 of the double pipe lance and oxygen is blown from the outer pipe 7 has been described. However, the double pipe lance in which the inner pipe 6 and the outer pipe 7 merge. Then, even when pulverized coal is blown from the inner pipe 6 and a flammable gas such as LNG is blown from the outer pipe 7, the same problem of melting damage may occur. The dynamic pressure evaluation index A when the crossing angle φ between the outer pipe 7 and the inner pipe 6 is changed is that the gas blown from the outer pipe 7 is oxygen, that is, a flammable gas such as LNG even if it is a combustion-supporting gas. However, since the same result is obtained, the lance of the present invention can be similarly applied even when solid fuel such as pulverized coal is blown from the inner pipe 6 and flammable gas is blown from the outer pipe 7. is there.

As described above, in the lance of this embodiment, the outer tube 7 is disposed outside the inner tube 6 in the middle of the pipe line when used by being inserted into the blower tube 2 that blows hot air into the blast furnace 1 through the tuyere 3. Are formed concentrically. Among these, the inner pipe 6 that blows the solid fuel includes at least a joining part with the outer pipe 7 and forms a portion in the blowing direction ahead of the joining part in a straight tube shape. In addition, the outer pipe 7 for blowing the combustion-supporting gas or the flammable gas is bent in one direction at the junction with the inner pipe 6. Then, the angle formed by the central axis of the outer tube 7 and the central axis of the inner tube 6 in the bent portion, that is, the crossing angle φ is set to less than 90 °. Thereby, the dynamic pressure at the time of the inner tube outer surface collision of the combustion-supporting gas or the flammable gas blown from the outer tube 7 can be reduced, and the melting damage of the inner tube 6 can be suppressed.
Further, by setting the angle between the central axis of the outer tube 7 and the central axis of the inner tube 6 at the bent portion, that is, the intersection angle φ to 0 ° to 60 °, the combustion-supporting gas blown from the outer tube 7 Alternatively, the dynamic pressure of the flammable gas when the inner pipe collides with the outer surface can be further reduced, and the inner pipe 6 can be reliably prevented from being melted.

DESCRIPTION OF SYMBOLS 1 Blast furnace 2 Fan pipe 3 Tuyere 4 Lance 5 Raceway 6 Inner pipe 7 Outer pipe

Claims (2)

  It is a lance used by being inserted into a blow pipe that blows hot air into the blast furnace through the tuyere, and is formed by concentrically joining the outer pipe to the outside of the inner pipe in the middle of the pipe. The inner pipe to be blown is formed in a straight tube shape at least in the blowing direction with respect to the merging part including at least the merging part with the outer pipe, and the outer pipe to which the combustion-supporting gas or the flammable gas is blown is A lance which is in a joining portion with the inner tube and is bent in one direction, and an angle formed by a central axis of the outer tube and a central axis of the inner tube in the bent portion is less than 90 °.   2. The lance according to claim 1, wherein an angle formed by a central axis of the outer tube and a central axis of the inner tube at the bent portion is set to be greater than 0 ° and equal to or less than 60 °.

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