Patent Application
20220177985
The present invention relates to a method for operation of a blast furnace.
Conventionally, in a blast furnace, molten iron is produced by: alternately charging coke and iron ore raw materials (iron ore, sintered iron ore, pellets, and the like) in layers from a furnace top; and injecting pulverized coal together with hot air (air, oxygen) from a tuyere, to reduce and melt the iron ore raw materials. To conduct stable operations in such a blast furnace having a solid/gas countercurrent transfer layer, it is important to maintain favorable gas permeability inside the furnace because lowering the gas permeability hinders stable operations.
For example, coke has a role as a spacer which secures gas permeability inside the furnace; thus, a certain amount of coke must be used. However, if the use of coke can be reduced and the gas permeability inside the furnace can be lowered, expensive coke can be substituted with inexpensive pulverized coal, whereby a coke usage amount (coke rate) can be decreased.
In recent years, it has become common to conduct blast furnace operations in which pulverized coal is injected from a tuyere of the blast furnace, the pulverized coal being used as a fuel to replace a part of the coke (reducing agent). Recently, high pulverized coal injection operations, in which a usage amount of pulverized coal is as high as 150 kg/tp or more, have come to be stably carried out.
Herein, the pulverized coal to be injected into the blast furnace contains ash in a content of about 10% by mass (hereinafter, simply denoted as “%”), the ash consisting of 50% to 60% SiO2, 20% to 30% Al2O3, and also Fe2O3, CaO, and the like, being mainly constituted from acidic components.
Thus, when the injection rate of the pulverized coal rises, acidic slag derived from the ash in the pulverized coal increases, thereby increasing viscosity and/or a melting point of a slag layer (commonly referred to as “bird's nest slag”) which accumulates in a bird's nest region in an interior of a raceway. Accordingly, an accumulation amount of the bird's nest slag (hold-up) increases, whereby gas permeability in a lower portion of the blast furnace lowers (see
With respect to the above-mentioned lowering of gas permeability in the lower portion of the blast furnace, Patent Document 1 discloses a technique in which productivity of the blast furnace is increased and the coke rate is decreased by using iron ore having a combined-water content of greater than or equal to 2.0% by weight as a raw material for a blast furnace smelting method. Specifically, the technique according to Patent Document 1 includes: reducing the iron ore having a combined-water content of greater than or equal to 2.0% by weight to have a reduction percentage of greater than or equal to 30%, followed by charging and/or injecting the iron ore, as a raw material for the blast furnace smelting method, into the blast furnace. The reduction of the iron ore is conducted in a reducing atmosphere containing CO and/or H2 at a high temperature of greater than or equal to 400° C.
Furthermore, Patent Document 2 discloses a technique relating to a method for operation of a blast furnace, the technique particularly relating to inhibiting a rise in Si in molten iron that has been tapped. Specifically, the technique of Patent Document 2 involves: simultaneously injecting pulverized ore and pulverized coal from each tuyere, and making a rate of the pulverized ore and the pulverized coal upon injection equivalent to a rate of ore and coke charged from an upper portion of the blast furnace. In the technique of Patent Document 2, it is held that due to injecting the pulverized ore in addition to the pulverized coal, a rise in Si is inhibited, and furthermore, due to making the rate of the pulverized ore and the pulverized coal upon injection equivalent to the rate of ore and coke charged from the upper portion of the blast furnace, a distribution of charged matter in the furnace does not change, thereby making it easy to control the distribution of the charged matter. Moreover, it is reported that due to injecting by division into separate tuyeres, the amount injected from each tuyere is low, and an effect of making equipment trouble unlikely to occur can be achieved.
Patent Document 1: Japanese Unexamined Patent Application, Application No. H09-165607
Patent Document 2: Japanese Unexamined Patent Application, Application No. H04-002708
In the method according to Patent Document 1, the injection rate of the non-dehydrated iron ore is as high as 100 kg/tp, and there is significant temperature loss; thus, the accumulation amount of the bird's nest slag (hold-up) cannot be reduced.
Furthermore, with regard to the method disclosed in Patent Document 2, the injection rate of the pulverized coal is as low as 0 to 40 kg/tp, whereby the accumulation amount of the bird's nest slag (hold-up) cannot be reduced. Moreover, characteristic features of the ore are not disclosed in Patent Document 2; thus, at the time of injection, there is a possibility that the molten iron temperature in the blast furnace will decrease due to insufficient reduction of the ore, whereby a further increase in the coke rate will be necessitated. In addition, the technique of Cited Publication 2 is a technique relating to reducing Si in molten iron; thus, unlike the present invention, Patent Document 2 does not have an object of improving gas permeability in a lower portion of the blast furnace.
The present invention was made in view of the foregoing problems, and an object of the present invention is to provide a method for operation of a blast furnace that enables gas permeability in a lower portion of a blast furnace by injection of pulverized iron ore from a tuyere to be improved.
In order to solve the aforementioned problems, the method for operation of a blast furnace of the present invention involves the following technical measures.
Specifically, the method for operation of a blast furnace of the present invention includes: pulverizing coal to make pulverized coal, and pulverizing iron ore to make pulverized iron ore; and injecting the pulverized coal and the pulverized iron ore from a tuyere, characterized in that a loss on ignition of the iron ore is greater than or equal to 9% by mass and less than or equal to 12% by mass, an injection rate of the pulverized coal is greater than or equal to 150 kg/tp, and an injection rate of the pulverized iron ore is greater than or equal to 2.5 kg/tp and less than or equal to 50.0 kg/tp.
It is to be noted that the iron ore and the coal are preferably pulverized together.
According to the method for operation of a blast furnace of the present invention, improvement of gas permeability in a lower portion of a blast furnace by injecting the pulverized iron ore from a tuyere is enabled.
Hereinafter, embodiments of a method for operation of a blast furnace 1 according to the present invention are described in detail based on the drawings.
As shown in
Specifically, with regard to the blast furnace 1 for which the method for operation of the present invention is conducted, coke and iron ore raw material (iron ore, sintered iron ore, pellets, and the like) are alternately charged in layers from a furnace top, pulverized coal is injected together with hot air (air, oxygen) from the tuyere 2, and molten iron is produced by reducing and melting the iron ore raw material. To conduct stable operations using the blast furnace 1, having a solid/gas countercurrent transfer layer, it is important to favorably maintain gas permeability inside the furnace because lowering of gas permeability hinders stable operations. Coke has a role of a spacer, which secures gas permeability inside the furnace; however, if gas permeability inside the furnace can be made favorable, expensive coke can be substituted with inexpensive pulverized coal, whereby a coke usage amount (coke rate) can be reduced.
In the method for operation of the present invention, as described above, the pulverized coal, being the coal which has been pulverized, and the pulverized iron ore, being the iron ore which has been pulverized, are injected from the tuyere 2.
For example, the pulverized coal has a maximum grain size of less than or equal to 1,000 μm and an average grain size of 50 μm, and is injected into the blast furnace 1 at a rate of greater than or equal to 150 kg/tp. In other words, the method for operation of the present invention is directed toward operations with a high pulverized coal rate, and is a technique which has an object of improving gas permeability inside a furnace in operations with a high pulverized coal rate, and decreasing the coke rate in operations of the blast furnace 1 (the mass (kg) of coke needed in producing 1 ton of molten iron).
Furthermore, the pulverized coal contains ash in a content of about 10% by mass (hereinafter, simply denoted as “%”), the ash consisting of 50% to 60% SiO2, 20% to 30% Al2O3, and also Fe2O3, CaO, and the like, being mainly constituted from acidic components.
Thus, when the injection rate of the pulverized coal becomes high, acidic slag derived from the pulverized coal increases, thereby increasing viscosity and/or a melting point of a slag layer (commonly referred to as “bird's nest slag 4”) which accumulates in an interior of a raceway (being a bird's nest region 3), as shown in
Incidentally, the method for operation of the present invention involves injecting iron ore from the tuyere 2 in addition to the pulverized coal. There is already knowledge of such iron ore injection in Japanese Unexamined Patent Application, Application No. 05-214414 and the like. For example, as shown in
In other words, as is seen from the aforementioned
However, in a case in which iron oxide contained in the pulverized iron ore reacts with coke in the furnace, it will result in a direct reducing reaction (for example, FeO+C Fe+CO). Due to this reaction being accompanied by significant heat absorption, there is a possibility of a molten iron temperature being decreased, thereby becoming a cause of cooling of the molten iron. In other words, the pulverized iron ore cannot be immoderately injected with simply the intention of making the gas permeability favorable.
Thus, in the method for operation of the blast furnace 1 of the present invention, iron ore characteristics and the injection rate are regulated to appropriate conditions so as to enable achieving both improvement in gas permeability and prevention of cooling.
Next, iron ore characteristics of the iron ore, being a raw material for pulverized iron ore in the method for operation of the present invention, and the injection rate of the pulverized iron ore are described.
The pulverized iron ore is obtained by pulverizing the iron ore. The iron ore, being the raw material for the pulverized iron ore, has a loss on ignition of greater than or equal to 9% by mass and less than or equal to 12% by mass. Loss on ignition (LOI) in the iron ore is an index measured in accordance with JIS M8850; in the case of the iron ore, LOI indicates mainly a content of combined water.
Thus regulating the loss on ignition (LOI) of the iron ore has the purpose of making a pulverizing property of the pulverized iron ore equivalent to that of the coal for the pulverized coal, thereby making the iron ore easily pulverizable (easily made fine), whereby the grain size of each of the iron ore and the coal in the case of being pulverized is matched. The HGI (Hardgrove Index) is an index expressing the pulverizing property, indicated by a coal HGI strength test (JIS M8801). The pulverizing properties of multiple types of iron ore are measured in accordance with a coal HGI strength test procedure; determining a relationship between the pulverizing property and the loss on ignition (LOI) results in a relationship such as that shown in
As shown in
Herein, the HGI of the coal used as the pulverized coal for the burst furnace 1 is typically 40 to 90. The HGI of the coal is set to greater than or equal to 40 because when the HGI falls below 40, the pulverizing property deteriorates and the grain size increases, whereby equipment wear and the like may occur. Furthermore, the HGI of the coal is set to less than or equal to 90 because when the HGI exceeds 90, coal being pulverized too finely may be a cause of pipe occlusion.
In the case in which the loss on ignition is greater than or equal to 9% by mass and less than or equal to 12% by mass, the HGI of the iron ore becomes 40 to 90, similar to that of the coal for the pulverized coal, and the grain size of the pulverized iron ore when the iron ore has been pulverized becomes similar to that of the pulverized coal (maximum grain size of less than or equal to 1,000 μm, average grain size of 50 μm), thereby enabling preventing equipment wear and rupturing of transportation pipes.
Furthermore, as shown in
Due to the above, at the time when the pulverized iron ore is trapped in the bird's nest slag 4 in the interior of the raceway, accumulation of the bird's nest slag 4 can be decreased by lowering the viscosity of the bird's nest slag 4. As a result, the pressure loss of the blast furnace 1 is reduced, whereby gas permeability in the lower portion of the blast furnace 1 can be made favorable.
It is to be noted that in the case in which the loss on ignition (LOI) of the iron ore is less than 9% by mass, pulverizing is difficult due to using iron ore having a low HGI as the raw material. As a result, the grain size of the pulverized iron ore increases and significant equipment wear may occur, possibly leading to operation trouble such as the rupturing of the transportation pipes, thereby disabling usage. Moreover, iron ore in which the loss on ignition (LOI) is low has a low specific surface area, whereby the reduction percentage in the raceway decreases during injection from the tuyere 2. Thus, there is increased heat absorption due to a direct reducing reaction with furnace core coke in the interior of the raceway, facilitating a decrease in the molten iron temperature (a decrease in furnace heat). As a result, the pressure loss conversely increases, whereby it may be impossible to obtain the effect due to the injection of the pulverized iron ore.
Furthermore, with regard to a case in which the loss on ignition (LOI) of the iron ore is greater than 12% by mass, iron ore having such a loss on ignition does not exist; thus, the case in which the LOI is greater than 12% by mass is excluded.
Next, the injection rate of the pulverized iron ore is described.
Using the calculation procedure of
It is to be noted that the results in
As shown in
Furthermore, in a case in which the injection rate of the pulverized iron ore is greater than 50 kg/tp, sensible heat of the injection (a heat absorption amount) increases, whereby the temperature of the bird's nest slag (T) decreases. Furthermore, an inflowing slag amount (W) also increases, whereby the pressure loss increases in excess of the base before the injection.
It is to be noted that the pulverized iron ore as described above means iron ore having been subjected to pulverizing treatment by a roller mill, ball mill, or the like, and means iron ore having been pulverized to less than or equal to 1,000 μm. Moreover, the pulverized coal means coal having been subjected to pulverizing treatment by the same roller miller, ball mill, or the like, and means coal having been pulverized to less than or equal to 1,000 μm.
Hereinafter, the effects of the method for operation of the blast furnace 1 of the present invention are described in detail by way of Comparative Examples and Examples.
First, changes in the pressure loss reduction amount with respect to the injection rate of the pulverized iron ore were determined in accordance with the calculation procedure disclosed in
Furthermore, hereinafter, the results of the method for operation of the present invention are described using symbols defined as shown in Table 1.
P
First, the upper limit of the injection rate (upper limit of injection) of the pulverized iron ore from the tuyere 2 will be described. First, changes of the reduction ratio and melting percentage in the raceway, and of a raceway border temperature (temperature of the bird's nest slag 4) are calculated in relation to the injection rate of the pulverized iron ore. This calculation method was carried out based on a mathematical model disclosed in “Iron and Steel, Xiao et al., Vol. 78, 1992, page 1,230.” The calculation results are shown in
At this time, based on the premise that only the molten iron ore contributes to the decrease in the viscosity of the bird's nest slag 4, the relationship between the molten iron ore (flux) and the unmelted iron ore was determined from the injection rate and melting percentage of the pulverized iron ore. The thus determined relationship between the molten iron ore and the unmelted iron ore is shown in
Furthermore, based on the premise that an entire amount of the injected pulverized iron ore should be added to a slag ratio of the bird's nest slag 4, a relationship between the injection rate of the pulverized iron ore and the amount of the bird's nest slag 4 (w) was determined. The thus determined relationship is shown in
Moreover, based on the premise that the injected pulverized iron ore directly reduced with an entire amount of the coke, the heat absorption amount (heat absorption portion) of the reduction reaction was subtracted from the raceway border temperature (temperature of the bird's nest 3), and a relationship between the injection rate of the pulverized iron ore and the temperature of the bird's nest slag 4 was determined. The thus determined relationship is shown in
Next, the viscosity of the bird's nest slag 4 (μ) was determined. The temperature dependency of the viscosity of the bird's nest slag 4 in each flux rate was determined by way of experiments.
Using the change in the temperature of the bird's nest 3 (the temperature of the bird's nest slag 4) in
The relationship between the injection rate of the pulverized iron ore and the viscosity (μ) of the bird's nest slag 4, determined by the above-described procedure, is shown in
Furthermore, with regard to the linear velocity of the dripping of the slag (μ), based on a relational expression described in “Materials and Processes, Kato et al., Vol. 28, 2015, S25,” a relationship between the injection rate of the pulverized iron ore and the linear velocity of the dripping was determined. The thus determined relationship is shown in
Further, with regard to the hold-up (h), based on a relational expression described in “Materials and Processes, Kato et al., Vol. 28, 2015, S25,” a relationship between the injection rate of the pulverized iron ore and the hold-up (h) was determined. The thus determined relationship is shown in
At this time, based on the premise that a packed bed cross-sectional area S is 6.67 m2 (constant), the values in
Lastly, a relationship between the injection rate of the pulverized iron ore and the pressure loss reduction amount (pressure loss change amount) was determined. The pressure loss was calculated based on a calculation formula described in “Iron and Steel, Fukutake et al., Vol. 66, 1980, page 1,974.” It is to be noted that the calculation factors are as shown in Table 3. The thus determined relationship between the injection rate of the pulverized iron ore and the pressure loss change amount is shown in
It is to be noted that the “bosh gas volume” in Table 3 is a calculated value of a total gas volume generated in front of the tuyere due to, e.g., combustion of coke in front of the tuyere due to blasts of: air blown from the tuyere, oxygen for oxygen enrichment, blasted moisture content, and the like; and combustion of supplemental fuel such as pulverized coal, and is indicated by Nm3/min. A calculation method of this bosh gas volume is, for example, described in Iron and Steel, Vol. 48 (1962), No. 12, page 1,606.
As shown in
Incidentally, in order to derive the viscosity of the bird's nest slag 4 from the temperature of the bird's nest 3, described above, it is preferable to conduct a preliminary experiment to grasp how a mixture ratio of the molten iron ore (flux), the slag temperature, and/or the like affect the viscosity of the slag.
With regard to the preliminary experiment described above, as preliminary preparation, a rotating torque meter 5 such as that shown in
rotor coefficient: K0=[standard viscosity (mPa·s)]/[regression coefficient b].
When the rotor coefficient is thus obtained, a reagent (a slag containing flux) mixed in a predetermined formulation (a formulation shown in the following Table 4) is charged into the pure iron crucible 7. The reagent-containing pure iron crucible 7 is then heated to a predetermined temperature using an electronic furnace to melt the reagent. A temperature for the heating is 1,300° C., 1,350° C., 1,400° C., 1,450° C., and 1,500° C. The rotor (the pure iron rotor 6) attached to the rotating torque meter 5 is inserted into a center of the molten slag, and rotation of the rotor is commenced. When a change in measured torque becomes 0.1%/min, it is considered that the viscosity has stabilized, measurement is continued for 1 minute after the viscosity has stabilized, and the values measured in the 1-minute interval are considered to be torque measurement values. Following the measurement, the rotation is stopped, and the experiment is terminated. It is to be noted that the cases in which the viscosity did not stabilize were excluded from the data.
The 1-minute measurement values in which the torque was stabilized, as described above, are adopted as torque measurement values (torque (%)). The obtained torque (%) is substituted into the following equation:
viscosity η (mPa·s)=torque (%)×K0÷rotation speed (rpm), and
the slug viscosities η (mPa·s) for which the flux rates differ are determined. The thus determined slug viscosities η (mPa·s) are shown in Table 4.
The change in the viscosity of the bird's nest slag 4 (μ) with respect to the injection rate of the pulverized iron ore was thus determined in the case in which the slag basicity C/S was 0.6 and the case in which the basicity C/S was 1.0, in a temperature-dependent manner. Taken together, the obtained results of the temperature dependence of each of the thus obtained slag viscosities (μ) are as shown in
Each viscosity was determined from the relational expression in
In accordance with the above-described viscosity calculation method, when the relationship between the injection rate and the viscosity of the pulverized iron ore is organized, the relationship shown in
According to the relationship shown in
It is to be noted that details of the above-described calculation procedure can be summarized as in Table 5.
On the other hand, the lower limit of the injection rate of the pulverized iron ore can be derived from an experiment using an actual blast furnace (actual apparatus test).
The blast furnace 1 used in the actual apparatus test was an actual furnace of 2,112 m3, having productivity of 1.8 t/m3/day. The test operation was conducted over a span of five days while changing the iron ore amount of the pulverized iron ore injected into the blast furnace 1 in the following order: 0.0 kg/tp to 1.3 kg/tp to 2.5 kg/tp to 5.0 kg/tp.
It is to be noted that the pulverized iron ore injected into the actual furnace has a composition as shown in Table 6.
It is to be noted that the above-described pulverized iron ore was pulverized by conducting treatment such as that shown in
The results of the actual apparatus test are shown in Table 7 below.
Looking at Table 7, the pulverized coal rate (the injection rate of the pulverized coal) in both of the Examples and the Comparative Examples is 208 kg/tp (satisfying the condition of greater than or equal to 150 kg/tp), and the loss on ignition (LOI) of the coal, being the raw material of the pulverized coal, is 11.1% by mass (satisfying the condition of 9.0% to 12.0% by mass). Furthermore, the reducing agent rate (sum of the pulverized coal rate and the coke rate) is 524 kg/tp for both the Examples and the Comparative Examples.
Operations were conducted while carrying out injection of the pulverized iron ore under such conditions for the pulverized coal rate, the loss on ignition, and the reducing agent rate, and measurement was carried out regarding the manner in which the pressure loss changed with respect to that before the injection. The measurement results are shown in Table 7.
As shown in Table 7, the injection rates of the pulverized iron ore in the Examples are 2.5 kg/tp and 5.0 kg/tp, and the injection rates of the pulverized coal in the Comparative Examples were 0.0 kg/tp and 1.3 kg/tp.
Concerning the above-described Examples and Comparative Examples, with regard to the Examples, the pressure loss change amounts were −1.72 kPa and −3.33 kPa; thus, it can be understood that the pressure loss was lower compared to that before the injection, and the gas permeability was favorable. In contrast, with regard to the Comparative Examples, the pressure loss change amounts were 0.00 kPa and 0.73 kPa; thus, the pressure loss was the same as that before the injection, or was greater than that before the injection, and the gas permeability was not improved.
From the above, it can be inferred that the effect of improving the gas permeability can be obtained in the case in which the injection rate of the pulverized iron ore is greater than or equal to 2.5 kg/tp.
Comprehensively inferring from the results of the above-described Examples and Comparative Examples, it is inferred that by pulverizing the coal to make the pulverized coal, and pulverizing the iron ore to make the pulverized iron ore; and injecting the pulverized coal and the pulverized iron ore from the tuyere 2, wherein the loss on ignition of the iron ore is greater than or equal to 9% by mass and less than or equal to 12% by mass, the injection rate of the pulverized coal is greater than or equal to 150 kg/tp, and the injection rate of the pulverized iron ore is greater than or equal to 2.5 kg/tp and less than or equal to 50.0 kg/tp, improving the gas permeability in the lower portion of the blast furnace 1 by injection of the pulverized iron ore from the tuyere 2 is enabled.
It is to be noted that the embodiments disclosed herein should be considered exemplary in all respects and should not be construed as limited. In particular, in the embodiments disclosed herein, items which are not clearly disclosed, e g, running conditions, operating conditions, various parameters, and dimensions, weights, and volumes of structures, do not depart from ranges pertaining to general execution by a person of average skill in the art, and values which can be easily estimated by a person of average skill in the art have been employed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-063381 | Mar 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/013733 | 3/26/2020 | WO | 00 |
