EP2851434A1

EP2851434A1 - Method for loading raw material into blast furnace

Info

Publication number: EP2851434A1
Application number: EP13790282.1A
Authority: EP
Inventors: Kazuhira ICHIKAWA; Shiro Watakabe; Jun Ishii; Toshiyuki HIROSAWA; Akinori Murao
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2012-05-18
Filing date: 2013-05-17
Publication date: 2015-03-25
Anticipated expiration: 2033-05-17
Also published as: KR101630279B1; EP2851434B1; TR201903647T4; CN104302788A; CN104302788B; EP2851434A4; JPWO2013172046A1; JP5601426B2; KR20150004840A; WO2013172046A1

Abstract

A method for charging blast furnace raw material into a blast furnace, includes, when charging blast furnace raw material including coke and ore material such as sintered ore, pellet, or lump ore into the blast furnace using a rotating chute: mixing the ore material with the coke to produce mixed material; and charging the mixed material into the blast furnace to form a mixed layer in a predetermined region in the blast furnace, in which the mixed material is discharged into the blast furnace at a discharge rate of 1.5 t/s or more to thereby improve homogeneity of the mixed layer.

Description

TECHNICAL FIELD

The present invention relates to a method for loading (charging) blast furnace raw material into a blast furnace by charging blast furnace raw material into the furnace with a rotating chute, and in particular, to homogenization of a mixed layer of ore material and coke.

BACKGROUND ART

Generally, ore material such as sintered ore, pellet, lump ore, and the like and coke are charged into a blast furnace from the furnace top in a layer state, and combustion gas is injected through a tuyere to yield pig iron. The coke and ore material that constitute the blast furnace raw material charged into the blast furnace descend from the furnace top to the furnace bottom, the ore reduces, and the temperature of the raw material rises. The ore material layer gradually deforms due to the temperature rise and the load from above while filling the voids between ore materials, and at the bottom of the shaft of the blast furnace, gas permeability resistance grows extremely large, forming a cohesive layer where nearly no gas flows.
Conventionally, blast furnace raw material is charged into a blast furnace by alternately charging ore material and coke. In the furnace, ore material layers and coke layers form alternately. At the bottom of the blast furnace, in the so-called cohesive zone, ore material layers with a large gas permeability resistance, where ore has softened and cohered, exist along with a coke slit, derived from coke, with a relatively small gas permeability resistance.
The gas permeability of the cohesive zone greatly affects the gas permeability of the blast furnace as a whole and limits the rate of productivity in the blast furnace. When performing a low coke operation, the amount of coke that is used is reduced, which is considered to cause unlimited thinning of the coke slit.
In order to improve the gas permeability resistance of the cohesive zone, mixing coke into the ore material layer is known to be effective, and much research has been reported for achieving an appropriate mixing state. For example, JP H3-211210 A (PTL 1) discloses charging, in a bell-less blast furnace, coke into an ore hopper that is downstream among the ore hoppers, layering coke onto the ore on a conveyor, and charging the ore and coke into the furnace top bunker and then into the blast furnace via a rotating chute. In PTL 1, however, ore material and coke are mixed in a furnace top bunker and segregation occurs therein, leading to the problem of the mixing ratio of iron ore and coke being unable to maintain precisely.
JP 2004-107794 A (PTL 2) discloses separately storing ore and coke in furnace top bunkers and mixing the coke and ore while charging them simultaneously.
PTL 2, however, does not give proper consideration to potential separation of coke and ore after blast furnace raw material has been charged into the furnace and, accordingly, separation of coke and ore could result from the segregation of coarse and fine particles that would occur after the charging of the raw material.
Furthermore, in order to prevent the cohesive zone shape from becoming unstable during blast furnace operation, to prevent a reduction in the gas utilization rate near the central region, and to improve operation safety and thermal efficiency, JP S59-10402 B2 (PTL 3) discloses a method for charging blast furnace raw material into a blast furnace whereby all of the ore and all of the coke are charged into the furnace after being completely mixed. Regarding the technique disclosed in PTL 3, however, PTL 3 refers to a blast furnace without a coke slit, yet fails to give any particulars of a raw material charging method in the blast furnace, and is silent on how to control the mixing ratio of materials charged.
On the other hand, the inventors of the present invention have already proposed an invention in JP 2012-97301 A (PTL 4) directed to a method for charging blast furnace raw material into a blast furnace that improves gas permeability resistance without a coke slit:

"A method for charging blast furnace raw material into a blast furnace, comprising, when charging blast furnace raw material including coke and ore material such as sintered ore, pellet, or lump ore into the blast furnace using a rotating chute:
forming a central coke layer at a shaft central portion; and
forming a mixed layer of the coke and the ore material on the outside of the central coke layer so as not to form a coke slit."

CITATION LIST

Patent Literature

PTL 1: JP H3-211210 A
PTL 2: JP 2004-107794 A
PTL 3: JP S59-10402 B2
PTL 4: JP 2012-97301 A

SUMMARY OF INVENTION

(Technical Problem)

The development of the technique proposed in PTL 4 significantly improved the gas permeability in the blast furnace and allowed for stable blast furnace operation.
The present invention relates to an improvement of the aforementioned technique disclosed in PTL 4, and an object thereof is to achieve further homogenization of a mixed layer, and consequently, allow for more stable blast furnace operation.

(Solution to Problem)

The inventors intensely investigated how to achieve further homogenization of a mixed layer in a blast furnace.
As a result, the inventors made a new finding that by increasing the discharge rate at which blast furnace raw material is charged into the blast furnace, the resulting mixed layer becomes greatly homogenized.
The present invention was completed based on this finding.
Specifically, main features of the present invention are as follows.

[1] A method for charging blast furnace raw material into a blast furnace, comprising, when charging blast furnace raw material including coke and ore material such as sintered ore, pellet, or lump ore into the blast furnace using a rotating chute:
- mixing the ore material with the coke to produce mixed material; and
- charging the mixed material into the blast furnace to form a mixed layer in a predetermined region in the blast furnace,
- wherein the mixed material is discharged into the blast furnace at a discharge rate of 1.5 t/s or more.
[2] The method for charging blast furnace raw material into a blast furnace according to the aspect [1] above, further comprising:
- disposing at least two furnace top bunkers at a top of the blast furnace, and a collecting hopper at an outlet of the furnace top bunkers to mix the raw material discharged from the furnace top bunkers and feed the raw material to the rotating chute;
- storing, in either one or two of the furnace top bunkers, either one or both of the ore material and mixed material obtained by mixing the ore material with the coke;
- storing only coke in one of the remaining furnace top bunkers;
- simultaneously discharging the coke and the ore material and/or the mixed material from the furnace top bunkers;
- mixing the discharged coke with the discharged ore material and/or mixed material in the collecting hopper to form a mixture; and
- feeding the mixture to the rotating chute to form the mixed layer.
[3] The method for charging blast furnace raw material into a blast furnace according to the aspect [1] or [2] above, further comprising: forming a central coke layer at a shaft central portion of the blast furnace during charging of the blast furnace raw material into the blast furnace.

(Advantageous Effect of Invention)

The present invention allows for more stable blast furnace operation through further homogenization of a mixed layer formed in a blast furnace by charging mixed material obtained by mixing ore material with coke into the blast furnace.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be further described below with reference to the accompanying drawings, wherein:

FIG. 1 schematically illustrates the raw material charging condition including furnace top bunkers;
FIG. 2 is a schematic configuration diagram of an experimental device for measuring high temperature properties of the ore material;
FIG. 3 is a graph showing the relationship between the mixing ratio of coke with ore material and the maximum pressure drop ratio, plotting parameters of the particle diameter of coke;
FIG. 4 is a graph showing the changes in coke mixing ratio in charged raw material over time, for in-bunker mixture and simultaneous discharge mixture;
FIG. 5 is a graph showing the changes in coke mixing ratio in the furnace radial direction with varying discharge rates under simultaneous discharge condition; and
FIG. 6 is a graph showing the changes in mixing ratio with varying discharge rates for simultaneous discharge.

DESCRIPTION OF EMBODIMENTS

The following describes an embodiment of the present invention with reference to the drawings.
The specific way of charging ore material and coke into a blast furnace according to PTL 4 is described based on FIG. 1.
In this example, it is assumed that the furnace top bunker 12b stores mixed material of ore material and coke, the furnace top bunker 12a stores coke alone, and the furnace top bunker 12c stores ore material alone.
In this case, for the mixed material stored in the furnace top bunker 12b, the mixing amount of coke is preferably adjusted to be 30 mass% or less of the total amount of coke. The reason is that if the amount of coke mixed with ore material is 30 mass% or less of the total amount of coke, coke and ore material are not significantly segregated when stored in the furnace top bunker 12b, and consequently, the mixing ratio of the mixed layer of ore material and coke formed by the rotating chute 16 may become substantially even.
In contrast, if the mixing amount of coke is more than 30 mass% of the total amount of coke, coke and ore material are more prone to segregation due to the differences in specific gravity and particle size and are largely segregated when stored in the furnace top bunker 12b, which causes regions where either one of ore material or coke alone is present.
In charging blast furnace raw material from the furnace top bunkers, coke, mixed material, and ore material that have been discharged from the furnace top bunkers 12a to 12c at a predetermined flow rate regulated by a flow regulating gate 13 are mixed in a collecting hopper 14, fed to a bell-less charging device 15 immediately below the collecting hopper 14, and charged through a rotating chute 16 of the bell-less charging device 15 into the blast furnace 10.
The following describes raw material charging using a so-called reverse tilting control scheme, where the rotating chute 16 is controlled by reverse tilting control to be tilted from the shaft central portion of the blast furnace 10 towards the furnace wall, while simultaneously rotating about the shaft center of the blast furnace 10.
Also described is a central coke layer formed at a shaft central portion of the blast furnace.
In this case, raw material charging is performed using a so-called reverse tilting control scheme, where the rotating chute 16 is controlled to be tilted from the shaft central portion of the blast furnace 10 in the furnace central region towards the furnace wall, while simultaneously rotating about the shaft center of the blast furnace 10, and the blast furnace raw material discharged from the furnace top bunker 12 is charged in the direction from the furnace central region towards the furnace wall.
At this time, in an initial charging state where the rotating chute 16 is set to tilt in substantially vertical direction, the flow regulating gates 13 of the furnace top bunkers 12b and 12c are closed, the flow regulating gate 13 of only the furnace top bunker 12a is opened, and only the coke stored in the furnace top bunker 12a is fed to the rotating chute 16. In this way, a central coke layer 12d is formed in the shaft central portion of the blast furnace, as shown in FIG. 1.
Then, upon completion of the formation of the central coke layer 12d while gradually tilting the rotating chute 16 towards the horizontal direction, the flow regulating gates 13 of the remaining two furnace top bunkers 12b and 12c are opened at a predetermined rate, and coke discharged from the furnace top bunker 12a, mixed material discharged from the furnace top bunker 12b, and/or ore material discharged from the furnace top bunker 12c are simultaneously fed to the collecting hopper 14. Then, the coke and ore material are completely mixed in the collecting hopper 14 before being fed to the rotating chute 16 and, as shown in FIG. 1, the mixing ratio of coke and ore material becomes substantially even on the outside of the central coke layer 12d in the blast furnace 10. As a result, a mixed layer 12e is formed without a coke slit.
In this case, the amount of coke in the central coke layer 12d is set to be approximately 5 mass% to 30 mass% of the total amount of coke charged per charge, while the amount of coke in the mixed layer 12e approximately 70 mass% to 95 mass% of the total amount of coke.
It is desirable that the region where the central coke layer is formed has a dimensionless radius of the blast furnace of 0 or more to 0.3 or less, when 0 is the shaft central portion of the blast furnace and 1 is the furnace wall. The reason is that collecting some of coke in the shaft central portion of the furnace may be effective for improving the gas permeability at the shaft central portion, and thus the gas permeability of the blast furnace as a whole. Note that the amount of coke charged to form a central coke layer is preferably approximately 5 mass% to 30 mass% of the amount of coke charged per charge. This is because if the amount of coke charged into the shaft central portion is less than 5 mass%, the gas permeability around the shaft central portion improves insufficiently, and if coke is collected in the shaft central portion by more than 30 mass%, not only does the amount of coke used to form a mixed layer decrease, but also too much gas passes through the shaft central portion, leading to increased heat removal from the furnace body. Preferably, the amount of coke charged into the shaft central portion is 10 mass% to 20 mass%.
The above-described central coke layer 12d and mixed layer 12e are formed sequentially inside the blast furnace 10 from the bottom to the top. In this way, by sequentially layering central coke layers 12d and mixed layers 12e, the central coke layers 12d with small gas permeability resistance are formed from the bottom of the blast furnace towards the top of the blast furnace at the shaft central portion inside the blast furnace 10, and the mixed layers 12e in which coke and ore material are mixed are formed on the periphery thereof.
In order to prove the effects of the present invention, the inventors simulated the raw material reduction and elevated temperature process in a blast furnace and tested the change in gas permeability resistance, using the laboratory device illustrated in FIG. 2.
In the laboratory device, a furnace core tube 32 is disposed on the inner peripheral surface of a cylindrical furnace body 31, and a cylindrical heater 33 is disposed on the outside of the furnace core tube 32. On the inside of the furnace core tube 32, a graphite crucible 35 is disposed at the upper edge of a cylindrical body 34 constituted by refractory material, and charged raw material 36 is charged inside the crucible 35. A load is applied to the charged raw material 36 from above by a load application device 38 connected via a punch rod 37, so that the charged raw material 36 adopts approximately the same state as the cohesive layer at the bottom of the blast furnace. A device 39 for sampling drops is provided at the bottom of the cylindrical body 34.
The gas adjusted by a gas mixing device 40 is fed to the crucible 35 through the cylindrical body 34 provided on its underside, and the gas passing through the charged raw material 36 in the crucible 35 is analyzed by a gas analysis device 41. A thermocouple 42 for controlling the heating temperature is provided in the heater 33, and by having a control device (not illustrated) control the heater 33 while measuring the temperature with the thermocouple 42, the crucible 35 is heated to 1200 °C to 1500 °C.
In this case, as the ore in the charged raw material 36 charged into the crucible 35, a mixture of 50 mass% to 100 mass% of sintered ore and 0 mass% to 50 mass% of lump iron ore was used.
FIG. 3 is a graph showing the results of examining the relationship between the maximum pressure drop ratio and the mixing amount for coke of different sizes, with varying coke mixing ratios in relation to ore.
As FIG. 3 shows, it can be seen that pressure drop was most pronounced where no coke was mixed, while gas permeability resistance remarkably decreased where coke was added, and above all, this effect became more pronounced with increasing amount of coke. The reason seems to be that mixing with coke suppressed deformation of ore, preserved voids near the mixed coke, and accordingly prevented the occurrence of a phenomenon that would otherwise cause a decrease in the amount of voids among particles and an increase in gas permeability resistance due to deformation of ore.
As FIG. 3 also shows, it was found that lump coke and small-and-middle lump coke showed a different gas permeability resistance in the cohesive layer, leading to a different pressure drop, i.e., the use of small-and-middle lump coke resulted in a smaller pressure drop than when using lump coke for a same mixing amount.
As used herein, the term "lump coke" refers to coke having a particle size of approximately 30 mm to 60 mm, and "small-and-middle lump coke" refers to coke having a particle size of approximately 10 mm to 30 mm. On the other hand, ore material usually has a particle size of approximately 5 mm to 25 mm.
In this case, for avoiding deterioration in in-furnace gas permeability due to the particle sizes of ore material and coke, it is preferable that ore material has a particle size of 10 mm to 30 mm and coke has a particle size of 30 mm to 55 mm, and that the ratio of these particle sizes (particle size of coke / particle size of ore material) is approximately 1.0 to 5.5.
The inventors investigated a coke ratio in the mixed layer (amount of coke / amount of ore material) that would be preferable for reducing pressure drop, i.e., for improving gas permeability, and, as a result, found that the coke ratio is preferably approximately 7 % to 25 % in terms of mass ratio. The coke ratio is more preferably within a range of 10 % to 15 %. Note that the proportion of coke in the mixed layer is preferably about 20 % to 95 % in terms of a percentage of the total amount of coke.
Meanwhile, in a simulation test conducted under the aforementioned preferable conditions, an increase in gas permeability resistance was also observed, which could result from unevenness of the mixed layer.
Then, the inventors conducted evaluation tests of coke mixing ratios in ore material, using a charging model device (1/18 scale of the actual blast furnace), simulating the blast furnace top as shown in FIG 1.
In this model device, for simulating the falling trajectory and deposition behavior of blast furnace raw material conform to the actual furnace, the particle diameter of raw material was set to be 1/18 of the actual blast furnace, the charging amount of raw material was set to be 1/18, and the rotating speed of the charging chute was set to be 1/18.
FIG. 4 is a graph showing the results of investigating the changes in coke mixing ratio in charged raw material over time, for in-bunker mixing of ore and coke and for simultaneous discharging of ore and coke from two bunkers. In either case, the amount of ore and the amount of coke were constant and the target mixing ratio was set to be 0.05.
As FIG. 4 shows, for in-bunker mixing of ore and coke, the mixing ratio increased in the early and late stages of the discharging period, while the mixing ratio turned to be lower than the target value (0.05) in the middle stage of the discharging period. In contrast, for simultaneously discharging of ore and coke from two bunkers, the coke mixing ratio in ore was substantially constant in relation to the target value. Therefore, it can be seen that simultaneous discharge mixing allows for more precise control of coke mixing ratios than in-bunker mixing.
Reference is now made to FIG. 5, which shows the results of investigating the changes in coke mixing ratio in the furnace radial direction with different discharge rates of 0.85 t/s and 1.27 t/s (both in terms of actual machine) under simultaneous discharge condition.
As FIG. 5 shows, it can be seen that the discharge rate of 1.27 t/s in terms of actual machine measurements showed a smaller difference between the maximum and minimum coke mixing ratios and yielded more even mixing than the discharge rate of 0.85 t/s in terms of actual machine measurements.
Then, the inventors examined the changes in mixing ratio during simultaneous discharging with different discharge rates. The quality of the mixing ratio was determined by the difference between the maximum and minimum mixing ratios in the furnace radial direction. The obtained results are shown in FIG. 6. It can be concluded that a smaller difference represents more even mixing.
As FIG. 6 shows, the difference between the maximum mixing ratio and the minimum mixing ratio becomes smaller with increasing discharge rate of raw material. In other words, it will be appreciated that ore and coke may be mixed in a more even manner by increasing the discharge rate of raw material. In particular, by setting the discharge rate to be 1.5 t/s or more, the difference between the maximum and minimum mixing ratios becomes significantly smaller and turns out to be substantially constant at 1.8 t/s or more.
Note that a conventional and typical discharge rate for charging raw material is approximately 0.8 t/s to 1.3 t/s, and there has not been a particular focus on such discharge rate in the conventional art.
Although the mechanism by which the difference between the maximum and minimum mixing ratios becomes smaller with increasing discharge rate of charged raw material, or by which homogenization of the resulting mixed layer is achieved has not yet been elucidated fully, but can be inferred as follows.
The inventors believe that segregation of charged raw material occurs, because the movement of ore of small particle size tends to be stopped under the influence of unevenness of the raw material deposition surface when the charged raw material flows over the stationary raw material deposition surface.
In this regard, as the charge rate increases, the charged raw material has larger transfer energy when traveling over the deposition surface, resulting in less stoppage of transfer of ore of small particle diameter. In addition, as the discharge rate of raw material increases, the layer formed by the flow of charged raw material becomes thicker. Moreover, as the thickness of the layer formed by the flow of charged raw material increases, the ratio of particles that come in contact with the underlying surface becomes relatively lower, and consequently, the influence of unevenness of the underlying surface becomes less pronounced.
In view of the above, it is inferred that segregation of charged raw material is suppressed with increasing charge rate, with the result that homogenization of the resulting mixed layer is achieved.
Note that an advantageous operation is as follows: when a shaft pressure anomaly is detected while monitoring shaft pressure during blast furnace operation, in the course of continuous blast furnace charging according to the present invention, the raw material charging should be switched to a normal mode in which ore material layers and a coke slit are separately formed and, when the shaft pressure anomaly is resolved later, switched back to the charging scheme according to the present invention.

REFERENCE SIGNS LIST

10: Blast furnace
12a to 12c: Furnace top bunker
12d: Central coke layer
12e: Mixed layer
13: Flow regulating gate
14: Collecting hopper
15: Bell-less charging device
16: Rotating chute
31: Cylindrical furnace body
32: Furnace core tube
33: Cylindrical heater
34: Cylindrical body
35: Graphite crucible
36: Charged raw material
37: Punch rod
38: Load application device
40: Mixing device
41: Gas analysis device
42: Thermocouple

Claims

A method for charging blast furnace raw material into a blast furnace, comprising, when charging blast furnace raw material including coke and ore material such as sintered ore, pellet, or lump ore into the blast furnace using a rotating chute:
mixing the ore material with the coke to produce mixed material; and

charging the mixed material into the blast furnace to form a mixed layer in a predetermined region in the blast furnace,

wherein the mixed material is discharged into the blast furnace at a discharge rate of 1.5 t/s or more.
The method for charging blast furnace raw material into a blast furnace according to claim 1, further comprising:
disposing at least two furnace top bunkers at a top of the blast furnace, and a collecting hopper at an outlet of the furnace top bunkers to mix the raw material discharged from the furnace top bunkers and feed the raw material to the rotating chute;

storing, in either one or two of the furnace top bunkers, either one or both of the ore material and mixed material obtained by mixing the ore material with the coke;

storing only coke in one of the remaining furnace top bunkers;

simultaneously discharging the coke and the ore material and/or the mixed material from the furnace top bunkers;

mixing the discharged coke with the discharged ore material and/or mixed material in the collecting hopper to form a mixture; and

feeding the mixture to the rotating chute to form the mixed layer.
The method for charging blast furnace raw material into a blast furnace according to claim 1 or 2, further comprising: forming a central coke layer at a shaft central portion of the blast furnace during charging of the blast furnace raw material into the blast furnace.