Patent Application
20150247212
The present invention relates to a blow-pipe structure for use in a blast furnace facility, and, in particular, to a blow-pipe structure that can be advantageously used for injecting pulverized coal obtained by pulverizing low-grade coal into a furnace as an auxiliary fuel together with hot air.
A blast furnace facility has been configured so as to be capable of producing pig iron from iron ore by introducing a starting material such as iron ore, limestone, and coal from the top into the interior of a blast furnace main body and injecting hot air and pulverized coal (pulverized coal injection: PCI coal) as an auxiliary fuel from a tuyere disposed at a lower portion on the side of the blast furnace main body.
In such a blast furnace facility, if low-grade coal generally having a low ash melting point of from 1,100 to 1,300° C., such as sub-bituminous coal or lignite, is used as the pulverized coal during the operation of injecting pulverized coal, the oxygen contained in the hot air having roughly 1,200° C., the hot air being used to inject the pulverized coal into the furnace, and a portion of the pulverized coal engages in a combustion reaction. The combustion heat generated thereby causes ash (hereafter, called “slag”) having a low-melting point to melt within the injection lance or tuyere.
The melted slag is rapidly cooled through contact with the tuyere, which is constantly cooled in order to be protected from the temperature of the blast furnace. As a result, solid slag adheres to the tuyere, leading to the problem of blockage of the flowpath of the blow pipe.
In order to solve this problem, the softening point (temperature) of the slag within the pulverized coal is adjusted to a melting point that is equal to or greater than the temperature within the blast furnace if the slag has a low softening point, preventing slag from adhering to tuyeres, as, for example, in the conventional art disclosed in Patent Document 1 listed below.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H05-156330A
However, attention has been called to the following two problems in the method according to the conventional art described above.
The first problem is that it is difficult to completely (homogeneously) mix pulverized coal and additives, with the result that slag formation cannot be prevented at a portion where the proportion of additive in the mixture is less than a predetermined value.
The second problem is that a new source of calcium oxide (CaO), such as limestone or serpentinite, is necessary, creating excessive costs.
In view of these circumstances, there is a demand for a blow-pipe structure for use in a blast furnace facility that allows for suppression of slag adhesion using a simple structure without the need for softening point adjustment.
The present invention has been conceived in order to solve the problems described above, and an object thereof is to provide a blow-pipe structure for a blast furnace facility that allows slag adhesion to be suppressed using a simple structure even if pulverized coal of an unadjusted softening point is used.
In order to solve the problems described above, the present invention employs the following means.
A blow-pipe structure according to an aspect of the present invention is a blow-pipe structure attached to a tuyere of a blast furnace main body for producing pig iron from iron ore. The blow-pipe structure injects pulverized coal as an auxiliary fuel together with hot air, and slag from the pulverized coal contains a component that is melted by the hot air and/or heat from combustion of the pulverized coal. The blow-pipe structure is provided with a resisting element on a downstream side of an injection lance for introducing the pulverized coal into a blow pipe. The resisting element increases flowpath resistance on a side of a pipe inner wall and concentrates a flow of the hot air and pulverized coal to a flowpath axis center.
With this blow-pipe structure, the resisting element for increasing flowpath resistance on the side of the pipe inner wall and concentrating the flow of the hot air and pulverized coal to the flowpath axis center is provided on the downstream side of the injection lance for introducing the pulverized coal into the blow pipe, thereby concentrating the flow of the pulverized coal being injected into the blast furnace main body to the center of the flowpath, and impeding the adhesion of slag to the surface of the tuyere or the inner wall of the blow pipe. In other words, a distribution in pulverized coal concentration is formed on the downstream side of the resisting element, creating a flow of hot air containing a high concentration of pulverized coal in the center of the flowpath, and reducing the pulverized coal concentration along the surface of the tuyere and on the inner wall side of the blow pipe, thereby suppressing slag adhesion.
In the invention described above, it is preferable that the resisting element be a plurality of block elements projecting from the inner wall, the block elements projecting further toward the flowpath axis center than an outlet port of the tuyere and being disposed so as to collectively cover the entire circumference of the pipe inner wall as viewed from the outlet port. In this case, the block elements may be arranged in such a manner that a plurality of units, each constituted by a plurality of block elements disposed at intervals along the circumferential direction, are disposed at different positions with respect to the circumferential direction (i.e., rotating around the circumferential direction) along the direction of the flowpath axis so as to cover the entire circumference, or one or a plurality of unit rows may be disposed on the same circumference so as to cover the entirety thereof.
In the invention described above, it is preferable that the resisting element be one or a plurality of ring forming block elements projecting from around the entire circumference of the inner wall, the ring forming block element(s) projecting from the outlet port of the tuyere toward the center of the flowpath.
In the invention described above, it is preferable that the block element and the ring forming block elements be provided on an upstream side thereof with a slanted surface that gradually decreases the cross-sectional area of the flowpath. This allows abrupt decreases in the cross-sectional area of the flowpath to be prevented. Examples of cross-sectional shapes capable of forming a slanted surface that gradually decreases the cross-sectional area of the flowpath on the upstream side include triangles and wedges.
In the invention described above, it is preferable that the block element and the ring forming block elements be provided with a mechanism for varying the level of projection toward the flowpath axis center. This allows for easy adjustment and optimization of the level of projection according to slag adhesion state.
In accordance with the blow-pipe structure of the present invention described above, the flow of pulverized coal being injected into the blast furnace main body is concentrated to the center of the flowpath, impeding the adhesion of slag to the surface of the tuyere or the inner wall of the blow pipe, thereby allowing slag adhesion to be suppressed using the simple structure of providing a resisting element, such as a block element or ring forming block elements, without the need to adjust softening point.
As a result, even low-grade coals having low ash melting points of 1,100 to 1,300° C., such as sub-bituminous coal or lignite, can be used as the pulverized coal constituting the auxiliary fuel by being modified or the like for use as feedstock coal.
An embodiment of the blow-pipe structure according to the present invention will now be described with reference to the drawings.
The blow-pipe structure according to the embodiment is used in a blast furnace facility in which pulverized low-grade coal constituting the feedstock coal is injected from a tuyere into a blast furnace together with hot air.
For example, in a blast furnace facility as illustrated in
A pulverized-coal-producing device 50 that performs a pretreatment (modification) such as evaporating moisture in the coal out of the feedstock coal (sub-bituminous coal, lignite, or other low-grade coal), followed by pulverizing the low-grade coal to produce pulverized coal, is provided near the blast furnace main body 20.
Modified pulverized coal (modified coal) 3 produced by the pulverized-coal-producing device 50 is conveyed by a carrier gas 4, such as nitrogen gas, to a cyclone separator 60. The pulverized coal 3 conveyed by the gas is separated from the carrier gas 4 by the cyclone separator 60, after which the coal falls into and is stored in a storage tank 70. This modified pulverized coal 3 is used as blast furnace injection coal (PCI coal) for the blast furnace main body 20.
The pulverized coal 3 within the storage tank 70 is fed into an injection lance (hereafter, called “lance”) 31 of the blow pipe 30 described above. The pulverized coal 3 combusts upon being fed into the hot air flowing through the blow pipe 30, producing a flame at the end of the blow pipe 30 and forming a raceway. This causes the coal and the like contained in the starting material 1 being introduced into the blast furnace main body 20 to combust. As a result, the iron ore contained in the starting material 1 is reduced to result in pig iron (molten iron) 5, which is drawn out from a taphole 23.
Preferred properties of the pulverized coal 3 fed from the lance 31 into the blow pipe 30 as blast furnace injection coal, that is, of the modified pulverized coal (auxiliary fuel) formed by modifying and pulverizing low-grade coal, are that an oxygen atom content (dry basis) is from 10 to 18 wt %, and an average pore size is from 10 to 50 nm (nanometers). A more preferable average pore size for the modified pulverized coal is from 20 to 50 nm (nanometers).
In pulverized coal 3 having such properties, there is a large release of and reduction in tar-forming groups of oxygen-containing functional groups (carboxyl groups, aldehyde groups, ester groups, hydroxyl groups, etc.) but breakdown (reduction) of the main skeleton (the combustible component primarily formed from carbon, hydrogen, and oxygen) is greatly suppressed. Thus, when the coal is injected from the tuyeres 22 into the blast furnace main body 20 together with the hot air 2, the high oxygen atom content of the main skeleton and the large diameter of the pores not only facilitates dispersion of the oxygen in the hot air 2 into the coal, but also greatly impedes the generation of tar, allowing for complete combustion with almost no uncombusted carbon (soot) being produced.
In order to produce (modify) this pulverized coal 3, a drying step of heating (at from 110 to 200° C. for from 0.5 to 1 hours) and drying the sub-bituminous coal, lignite, or other low-grade coal (dry-basis oxygen atom content: greater than 18 wt %; average pore size: from 3 to 4 nm) constituting the feedstock coal in a low-oxygen atmosphere having an oxygen concentration of 5 vol % or less is performed in the pulverized-coal-producing device 50 described above.
After moisture is removed in the drying step described above, a dry distillation step in which the feedstock coal is reheated (at from 460 to 590° C., preferably from 500 to 550° C., for from 0.5 to 1 hours) in a low-oxygen atmosphere (oxygen concentration: 2 vol % or less) is performed. Dry distilling the feedstock coal in this dry distillation step removes generated water, carbon dioxide, and tar in the form of dry distillation gas or dry distillation oil.
The feedstock coal then proceeds to a cooling step in which the coal is cooled (to 50° C. or less) in a low-oxygen atmosphere having an oxygen concentration of 2 vol % or less, then pulverized (particle diameter: 77 μm or less (80% pass)) in a pulverization step.
In the embodiment, as illustrated, for example, in
The resisting element 80 illustrated in the drawing is constituted by a plurality of block elements 81 projecting from the inner wall of the blow pipe 30.
Each of the block elements 81 is provided so as to project further toward the flowpath axis center than an outlet port of the tuyere 22. As illustrated, for example, in
Each of the block elements 81 is a substantially rectangularly cross-sectioned member having a circumferential direction width that covers, for example, roughly from ¼ to ⅛ of the inner circumference of the blow pipe 30, and a height h of projection from the inner wall of the pipe toward the flowpath axis. In this case, the projection height h is a value yielding greater projection toward the flowpath axis center than the height H to which the outlet end of the tuyere 22 is narrowed; i.e., the projection height h is greater than the narrowing height H (h>H). As a result, as illustrated, for example, in
Around four to sixteen of these block elements 81 are disposed at an equal pitch around the circumferential direction at different positions along the direction of the flowpath axis, thus serving as a resisting element 80 that forms flowpath resistance and impedes flow outside the flowpath (on the inner wall side).
Specifically, a ring forming member, for example, that has a rectangular cross section and is divided into a plurality of sections (eight in the example illustrated in the drawing) along the circumferential direction is used as the block elements 81. The block elements 81 form a resisting component, one unit of which is constituted by a plurality of block elements (such as four at a pitch of 90°) disposed at intervals around the same circumferential direction. One or multiple resisting component units shifted, for example, 45° with respect to the circumferential direction are disposed at intervals along the direction of the flowpath axis so as to cover the entire circumference of the inner wall of the blow pipe 30.
In other words, the block elements 81 of the resisting components, are rotated, as appropriate, around the circumferential direction so that the positions of the units are displaced from each other around the circumferential direction; thus, disposing a plurality of such resisting component units at intervals along the direction of the flowpath axis causes the entire circumference of the pipe inner wall to be covered as viewed from within the blast furnace main body 20.
The block elements 81 of the resisting element 80 are not limited to an arrangement in which a plurality of units, each unit constituted by a plurality of block elements disposed at intervals around the circumferential direction, are disposed at different positions with respect to the circumferential direction along the direction of the flowpath axis so as to cover the entire circumference. For example, one or a plurality of unit rows, each unit constituted by a plurality of block elements 81 disposed on the same circumference so as to cover the entire circumference, may be disposed along the direction of the flowpath axis. That is, a unit in which a plurality of adjacent block elements 81 is disposed in contact with one another around the same circumference so as to cover the entire circumference without any gaps may also be used.
The resisting element 80 described above may be constituted by one or a plurality of ring forming block elements projecting from around the entire circumference of the inner wall of the blow pipe 30, the projection height h of these ring forming block elements being such that the block elements project further toward the flowpath axis center than the outlet port of the tuyere 22, as in the case of the block elements 81 described above.
The blow pipe 30 described above is provided with a resisting element positioned on a downstream side of the lance 31 for injecting pulverized coal 3 into the blow pipe 30. The resisting element increases flowpath resistance on the side of the pipe inner wall and concentrates the flow of the hot air 2 and pulverized coal 3 to the flowpath axis center, thereby allowing the flow of the pulverized coal 3 being injected into the blast furnace main body 20 to be concentrated to the center of the flowpath, where flowpath resistance is low. As a result, the flow of pulverized coal 3 passes through a position away from the surface of the tuyere 22 and the inner wall of the blow pipe 30, thereby impeding the adhesion of slag upon the tuyere 22 and the blow pipe 30. In other words, a distribution in pulverized coal concentration is formed on the downstream side of the resisting element 80, creating a flow of hot air containing a high concentration of pulverized coal in the center of the flowpath, and reducing the pulverized coal concentration along the surface of the tuyere and on the inner wall side of the blow pipe, thereby suppressing slag adhesion on the tuyere 22 and the blow pipe 30.
In the embodiment described above, the block elements 81 and the ring forming block elements have rectangular cross-sections, but it is also possible to provide slanted surfaces 82, 83 that gradually reduce the cross-sectional area of the flowpath on the upstream side, as, for example, in the case of the block elements 81A, 81B illustrated in
The block element 81A according to a first modified example illustrated in
Similarly, the block element 81B according to a second modified example illustrated in
The slanted surfaces 82, 83 described above are not limited to linear inclinations, and may instead be concavely or convexly curved surfaces.
In the embodiment and modified examples described above, each of the block elements 81 and ring forming block elements is preferably provided with a mechanism 90 for varying the level of projection toward the flowpath axis center.
The projection-level-varying mechanism 90 allows for variations in the projection height h of the block elements 81, and is a drive mechanism that moves the block elements 81 up or down to a desired projection height h, examples of which include a hydraulic or air pressure-actuated cylinder or a linking mechanism linked to an electric motor; suitable mechanisms may be selected for various conditions.
Enabling the projection height h to be adjusted by the projection-level-varying mechanism 90 in this way allows for easy adjustment of the projection level according to slag adhesion state. Specifically, the actual slag adhesion state can be confirmed during maintenance or the like after operating at an initial setting for the projection height h; if the slag adhesion level is greater than expected, the projection height h is increased to concentrate the flow of the pulverized coal 3 toward the center of the flowpath, and if, conversely, the slag adhesion level is low, the projection height h can be reduced to reduce the flowpath resistance within the blow pipe 30, allowing for operation at an optimal balance between slag adhesion and flowpath resistance.
As described above, using the blow-pipe structure according to the embodiment allows the flow of the pulverized coal 3 being injected into the blast furnace main body 20 to be concentrated to the center of the flowpath. As a result, the reduction in the concentration of pulverized coal in areas near the surface of the tuyere 22 and the inner wall of the blow pipe 30 impedes slag adhesion.
It is therefore possible to perform the operation with suppressed slag adhesion by virtue of the simple structure of providing the resisting element 80, such as block elements 81 or ring forming block elements, without the need to adjust the softening point of the slag contained in the pulverized coal 3, or the need for special technology or techniques. As a result, the maintenance interval of the blow pipe 30 can be extended, for example, to the wear lifespan of the tuyere 22.
The component that is contained in the slag from the pulverized coal 3 described above and is melted by the hot air 2, the heat from combustion of the pulverized coal 3, or the like, i.e., the low-melting-point slag component, has an ash melting point of roughly 1,100 to 1,300° C. when the hot air 2 of roughly 1,200° C. is used. Such a low-melting-point slag component is also contained in modified coal produced by modifying low-grade coal, such as sub-bituminous coal or lignite, used as the feedstock coal for the pulverized coal 3 via drying, dry distillation, or the like, but, by using the blow-pipe structure of the embodiment, the pulverized coal 3 produced by modifying low-grade coal as feedstock coal can be used as an auxiliary fuel.
The present invention is not limited to the embodiment described above, and various modifications may be made thereto, as appropriate, within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-207272 | Sep 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/074412 | 9/10/2013 | WO | 00 |
