Powder detection method and blast furnace operation method using the same

Abstract

To stably operate a blast furnace by detecting the deterioration of air permeability in the furnace caused by an increase in an accumulated amount of powder.SOLUTION: Provided are: a powder detection method for detecting an increase in an accumulated amount of powder in a furnace by detecting a pulse-like pressure fluctuation that is a phenomenon in which a furnace pressure increases by 100 hPa or more and then decreases by 100 hPa or more within a predetermined time set at a value of less than 20 minutes by a pressure gauge for measuring the furnace pressure in blast furnace operation; and a blast furnace operation method using the same.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for detecting powder in a blast furnace and a method for operating a blast furnace using the same. In particular, the present invention relates to a method for detecting powder derived from carbonaceous materials in the belly or morning glory part of a blast furnace and a method for operating a blast furnace using the same.

Background Art

[0002] A blast furnace is a furnace for extracting pig iron by subjecting iron ore (mainly Fe2O3), which is a kind of iron oxide, and coke as a carbonaceous material to a chemical reaction at a high temperature to reduce the iron ore. In the furnace, usually, iron ore and coke are charged alternately in layers. Further, hot air (oxygen-enriched air) and pulverized coal, which is a supplementary reducing agent, are blown into the furnace from the tuyeres at the lower part of the blast furnace, and the pulverized coal and coke are burned by this hot air to generate reducing gas (carbon monoxide, hydrogen, etc.). The generated reducing gas rises in the furnace while reducing the iron ore in the furnace to produce pig iron. Then, the pig iron accumulated in the molten iron sump at the bottom of the furnace is taken out from the tapping hole.

[0003] The reducing gas reacts with the iron ore while passing through the voids in the packed bed of the iron ore and coke in the furnace and rising in the furnace. Therefore, in order to perform stable blast furnace operation, it is preferable to maintain the air permeability in the furnace at a desired level so that the reducing gas can rise in the furnace at a desired flow rate or speed and the reducing gas can sufficiently react with the iron ore in the furnace. The air permeability in the furnace can be monitored by measuring the furnace pressure. If the air permeability in the furnace deteriorates, there is a risk of blow-through, and also, if the reducing gas flows partially in the shaft cross-section (even if the air permeability seems good), the reduction efficiency of the iron ore may decrease. Therefore, maintaining the air permeability in the furnace at a desired level, and thus suppressing fluctuations in the furnace pressure, are important matters in stable operation of the blast furnace.

[0004] The furnace pressure, an indicator of the permeability within the furnace, is normally measured continuously by multiple pressure gauges installed vertically and circumferentially along the furnace body (furnace wall). Therefore, monitoring the changes in furnace pressure measured by these multiple pressure gauges and taking appropriate measures (operational actions) to suppress fluctuations when they are detected is crucial for stable blast furnace operation.

[0005] For example, Patent Document 1 describes a blast furnace control method in which the differential pressure between a pressure detection end installed on the furnace side and the tuyere pressure is constantly measured, the amount of water injected during blowing is calculated from the ratio of the theoretical pressure loss to the actual pressure loss calculated in advance, the amount of water injected during blowing, the temperature conditions of the tuyere, and the blowing conditions, so that the amount of water in the furnace core becomes the required amount, and the water during blowing is controlled. Furthermore, Patent Document 1 teaches that by implementing this blast furnace control method, blast furnace operation can be carried out normally. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-28807 [Overview of the project] [Problems that the invention aims to solve]

[0007] Patent Document 1 describes a method for controlling a blast furnace based on pressure and other factors measured inside the furnace, specifically controlling the amount of moisture blown into the tuyeres during airflow (airflow moisture). While it is generally known that controlling airflow moisture is an effective means of improving airflow inside the furnace, it is also known that an increase in airflow moisture can increase the reducing agent ratio (total mass of reducing agent used to produce 1 ton of molten iron; kg / t), which can affect productivity.

[0008] Generally, there are various causes of fluctuations in furnace pressure. Therefore, depending on the cause of these fluctuations, controlling the moisture content of the air blown in from the tuyeres is not always the optimal means of improving airflow within the furnace and thus suppressing fluctuations in furnace pressure. In such cases, there is a risk that the period during which the reducing agent ratio increases due to the increase in moisture content of the air blown in may be unnecessarily prolonged. For this reason, technology to identify the cause of fluctuations in furnace pressure is desired in order to take appropriate measures to suppress fluctuations in furnace pressure.

[0009] For example, the main causes of fluctuations in furnace pressure include changes in the temperature and composition of the reducing gas, changes in the reduction status of the iron ore, changes in the distribution of the charge, changes in the amount of stored slag, and changes in the amount of accumulated powder. By identifying which of these causes is responsible for the fluctuations in furnace pressure and taking prompt and appropriate measures (operational actions) to address that cause, it becomes possible to operate the blast furnace stably while minimizing the cost and time required to suppress fluctuations in furnace pressure.

[0010] One of the main causes of fluctuations in furnace pressure is "changes in the amount of powder accumulated" inside the furnace. The powder present in the furnace can be generated, for example, by detaching particles attached to the iron ore or coke being charged, or by abrasion caused by the physical contact between the iron ore or coke. Such powder can be a factor that hinders stable blast furnace operation, as it can blow up inside the furnace, clog the voids in the packed bed of iron ore or coke, worsen the air permeability of the furnace, and reduce productivity.

[0011] Therefore, the present invention has been made in view of these circumstances, and aims to provide a method for detecting an increase in the amount of accumulated powder, and a method for operating a blast furnace using the same, in order to detect deterioration of the air permeability inside the furnace caused by an increase in the amount of accumulated powder and to operate the blast furnace stably. [Means for solving the problem]

[0012] The inventors, through analysis of the changes in furnace pressure, which is constantly measured during blast furnace operation, discovered that a special type of pressure fluctuation occurs in the changes in furnace pressure. Specifically, a pressure fluctuation in which the furnace pressure increases relatively large within a short period of time and then decreases, i.e., a pulse-like pressure fluctuation of the furnace pressure. Furthermore, the inventors, through detailed analysis of the periods when these pulse-like pressure fluctuations occur frequently, found that among the various possible causes of furnace pressure fluctuations, these pulse-like pressure fluctuations are caused by an increase in the amount of powder accumulated, particularly an increase in the amount of powder derived from carbon material. In other words, they found that by detecting pulse-like pressure fluctuations, it is possible to determine that the amount of powder accumulated in the blast furnace has increased.

[0013] This invention is based on the above findings, and its main points are as follows. (1) In blast furnace operation, a powder detection method (method for detecting the amount of powder accumulated in a furnace) detects an increase in the amount of powder accumulated in the furnace by detecting pulse-like pressure fluctuations, which are phenomena in which the internal pressure of the furnace increases by 100 hPa or more and then decreases by 100 hPa or more within a predetermined time period set to a value of less than 20 minutes, using a pressure gauge that measures the internal pressure of the furnace. (2) The powder detection method according to (1), which detects an increase in the amount of powder accumulated in the furnace by detecting a phenomenon in which the furnace pressure increases by 200 hPa or more and then decreases by 200 hPa or more among the pulse-like pressure fluctuations. (3) The powder detection method according to (1) or (2), wherein the furnace pressure is the furnace pressure in the furnace body or the bell-shaped section. (4) In a blast furnace operation method using any one of the powder detection methods described in (1) to (3), when the powder detection method detects an increase in the amount of powder accumulated in the furnace, (a) Increase the amount of moisture in the oxygen-enriched air blown into the furnace from the tuyeres. (b) To increase the strength of the coke charged from the top of the furnace, (c) Reduce the rate of accumulation (d) Reducing the velocity of oxygen-enriched air blown from the tuyere into the furnace, and (e) Increasing the hydrogen content in the pulverized coal blown from the tuyere into the furnace A blast furnace operation method including performing at least one of the above.

Advantages of the Invention

[0014] According to the present invention, by detecting the pulsed pressure fluctuations of the furnace pressure, it is possible to detect an increase in the accumulation amount of powder in the furnace. Therefore, appropriate measures (operation actions) can be promptly taken with respect to the pressure fluctuations, and as a result, while minimizing the cost and time required to suppress the fluctuations of the furnace pressure, it is possible to promptly eliminate the deterioration of the air permeability in the furnace and operate the blast furnace stably. In particular, according to the present invention, it is possible to detect the deterioration of the air permeability in the furnace caused by an increase in the accumulation amount of powder derived from carbonaceous materials present in the belly or bellows part of the blast furnace, and operate the blast furnace stably.

Brief Description of the Drawings

[0015] [Figure 1] It is a graph showing the transition of the furnace pressure of the blast furnace used in the examples.

Modes for Carrying Out the Invention

[0016] <Powder Detection Method> As described above, as a result of the present inventor's detailed analysis of the transition of the furnace internal pressure measured by a plurality of pressure gauges installed in the furnace body (furnace wall), it was discovered that there may be a pulsed pressure fluctuation in which the furnace internal pressure increases relatively largely (100 hPa or more) within a short period of time and then decreases. Further, as a result of the present inventor's more detailed analysis of this pulsed pressure fluctuation of the furnace internal pressure, it was discovered that the timing when such pressure fluctuations occur overlaps with the timing when there is a large amount of powder derived from carbon materials such as coke and pulverized coal charged into the furnace. Therefore, the present inventor succeeded in detecting an increase in the accumulation amount of powder (particularly powder derived from carbon materials), which could not be specified from the transition of the furnace internal pressure in the past, by monitoring the transition of the furnace internal pressure (particularly the furnace internal pressure in the belly part or morning glory part of the furnace).

[0017] Therefore, the present invention relates to a method for detecting an increase in the accumulation amount of powder in blast furnace operation, and particularly relates to a method for detecting an increase in the accumulation amount of powder derived from carbon materials. More specifically, the present invention relates to a powder detection method (a method for detecting the accumulation amount of powder in the furnace) in which, in blast furnace operation, when a pulsed pressure fluctuation, which is a phenomenon in which the furnace internal pressure increases by 100 hPa or more within a predetermined time set with a value of less than 20 minutes and then decreases by 100 hPa or more, is detected by a pressure gauge that measures the furnace internal pressure, it is determined that the accumulation amount of powder in the furnace has increased, and an increase in the accumulation amount of powder in the furnace is detected. Therefore, the powder detection method according to the present invention is characterized by associating a so-called pulsed pressure fluctuation in which the furnace internal pressure increases by 100 hPa or more within a short period of time and then decreases by 100 hPa or more with an increase in the accumulation amount of powder in the furnace. Thus, according to the present invention, it becomes possible to detect an increase in the accumulation amount of powder in the furnace by monitoring the transition of the furnace internal pressure and detecting the pulsed pressure fluctuation of the furnace internal pressure. In particular, by monitoring the transition of the furnace internal pressure in the belly part or morning glory part of the furnace and detecting the pulsed pressure fluctuation of the furnace internal pressure, it becomes possible to detect an increase in the accumulation amount of powder derived from carbon materials in the furnace.

[0018] There are various possible causes for fluctuations in furnace pressure, particularly in the furnace body or bellows of a blast furnace. Besides the increase in powder accumulation, which is the subject of this invention, the main causes of such fluctuations include changes in the temperature and composition of the reducing gas, changes in the reduction status of the iron ore, changes in the distribution of charges, and changes in the amount of stored slag. In other words, fluctuations in furnace pressure are influenced by factors other than an increase in powder accumulation, so the cause of a fluctuation in furnace pressure is not necessarily an increase in powder accumulation. However, when fluctuations in furnace pressure occur due to causes other than an increase in powder accumulation, unlike when the fluctuation is caused by an increase in powder accumulation, the fluctuation is thought to occur over a relatively long period (at least 20 minutes), as will be explained in detail below. Therefore, pressure fluctuations such as a 100 hPa increase followed by a 100 hPa decrease in furnace pressure over a short period of time, such as a value set to less than 20 minutes—that is, pulse-like pressure fluctuations in furnace pressure—are considered to be caused by an increase in powder accumulation.

[0019] (Temperature change of reducing gas) Reducing gas is generated when coke or pulverized coal burns in oxygen-enriched air blown in through the tuyeres. It passes through the voids in the packed bed of iron ore and coke charged into the furnace, reducing the iron ore to produce pig iron. In blast furnace operation, the airflow conditions are set so that a certain amount (a predetermined normal cubic meter, i.e., a predetermined weight) of reducing gas circulates in the furnace for a certain period. When the temperature of the reducing gas rises when trying to circulate the same weight in the furnace, the volume of the reducing gas increases, worsening the airflow into the furnace. Therefore, the furnace pressure rises with increasing temperature of the reducing gas. However, the temperature of the reducing gas does not increase or decrease instantaneously, but rather fluctuates over a relatively long period, for example, 30 minutes or more to several hours. Therefore, fluctuations in furnace pressure due to changes in the temperature of the reducing gas occur over at least 30 minutes.

[0020] (Changes in the composition of reducing gases) The composition of the reducing gas changes, for example, when the amount and / or composition of pulverized coal blown in from the tuyeres changes. For example, if the concentration of hydrogen gas (H2), which has a low specific gravity (molecular weight), increases in the reducing gas, the density and viscosity of the reducing gas decrease, making it easier for the reducing gas to pass through the voids in the packed bed of iron ore and coke. Conversely, if the hydrogen gas concentration in the reducing gas decreases, the density and viscosity of the reducing gas increase, worsening its permeability. Thus, when the composition of the reducing gas changes, such as the hydrogen gas concentration, the furnace pressure fluctuates. This composition of the reducing gas is usually changed as needed during blast furnace operation, but this change in the composition of the reducing gas is done once a day or every few days, or at most once every few months. Therefore, fluctuations in furnace pressure due to changes in the composition of the reducing gas occur over at least several hours. It should be noted that the composition of the reducing gas may change naturally due to changes in the conditions inside the furnace, but since the composition does not change instantaneously, even in such cases, fluctuations in the furnace pressure due to changes in the composition of the reducing gas will occur over at least several hours.

[0021] (Changes in the reduction status of iron ore) Inside the furnace, between the furnace top and the core, there is a fusion zone where iron ore is in a semi-molten state (syrup-like). Reducing gas has difficulty passing through this fusion zone, and it rises inside the furnace by passing through the voids in the remaining coke layer. When the reduction state of the iron ore inside the furnace changes, such as when the amount of unreduced FeO increases, the volume of the fusion zone changes, affecting the permeability of the reducing gas. However, this change in permeability due to the reduction state of the iron ore continues to affect at least until the semi-molten iron ore drips from the top surface of the fusion zone to the furnace core. Here, assuming that the temperature of the top surface of the fusion zone is about 1200°C and the temperature of the dripping part is about 1400°C, and assuming, for example, that there is only one layer of iron ore with poor reduction status, it is thought that the permeability will deteriorate for at least 20 minutes or more until the iron ore drips from the top surface of the fusion zone to the furnace core. In reality, it is unlikely that such a situation would affect only one layer; it is more likely to affect multiple layers. Therefore, fluctuations in furnace pressure due to changes in the reduction state usually take several hours. Consequently, fluctuations in furnace pressure due to changes in the reduction state of the iron ore in the furnace usually occur over several hours or more, and at the very least, over 20 minutes.

[0022] (Changes in the distribution of loaded materials) In blast furnace operation, the method of charging materials such as iron ore and coke is sometimes changed to adjust the distribution of these materials in order to alter the conditions inside the furnace. When the distribution of these materials changes, the permeability inside the furnace changes, which in turn changes the pressure inside the furnace. However, since such adjustments to the distribution of these materials are made only two or three times a day at most, the fluctuations in the pressure inside the furnace resulting from changes in the distribution of these materials occur over at least several hours.

[0023] (Changes in the amount of stored pig iron slag) Normally, if the amount of oxygen-enriched air blown in from the tuyeres remains constant, the amount of molten iron produced will remain relatively constant. On the other hand, the amount of iron tapped may decrease due to factors such as tapping operations, or it may increase as the diameter of the tapping port increases due to wear and tear during use. Therefore, the amount of iron tapped is not always constant in blast furnace operation. For example, if the amount of iron tapped decreases, slag may accumulate on the hearth, causing buoyancy to act on the core and reducing the porosity of the fusion zone or the zone between the core and the fusion zone (active coke zone). This decrease in porosity leads to poor air permeability within the furnace, which in turn increases the furnace pressure. In such cases, if slag removal is improved, the poor air permeability within the furnace will be resolved. However, one tapping operation usually takes about 1 to 3 hours, and the furnace pressure rises and falls within that time. Therefore, fluctuations in furnace pressure due to changes in the amount of stored slag occur over a period of 30 minutes or more.

[0024] As described above, fluctuations in furnace pressure due to changes in the temperature and / or composition of the reducing gas, changes in the reduction status of the iron ore, changes in the distribution of the charge, and changes in the amount of stored slag occur over a period of at least 20 minutes, and usually over several hours.

[0025] In contrast, if the amount of powder accumulated in the furnace increases, pulse-like pressure fluctuations in the furnace pressure may occur, which are a phenomenon in which the furnace pressure increases by 100 hPa or more and then decreases by 100 hPa or more within a predetermined time set to a value of less than 20 minutes. In this specification, powder refers to solid particles with a diameter of 3 mm or less. The powder can clog the voids in the packed bed of iron ore and coke, and as a result, the permeability of the reducing gas rising in the furnace through the voids in the packed bed deteriorates, which can increase the furnace pressure. On the other hand, this packed bed of iron ore and coke gradually descends in the furnace during blast furnace operation, but because the blast furnace has a structure in which the furnace diameter changes in the direction of furnace height, the coke and / or iron ore move as the packed bed descends, causing rearrangement of the iron ore and coke (rearrangement of coke after the fusion zone where most of the iron ore has melted). Typically, a blast furnace consists of four sections from top to bottom: the furnace mouth, the furnace chest (shaft), the furnace belly (belly), the bellows (Bosch), and the hearth. The furnace chest is a frustoconical shape, with the diameter increasing downwards, while the bellows is a frustoconical shape, with the diameter decreasing downwards. During this rearrangement, clogging of the voids with powder may be resolved, restoring permeability. This clogging and resolution can occur in less than 20 minutes. Therefore, fluctuations in furnace pressure due to increased powder accumulation can occur in less than 20 minutes, resulting in furnace pressure fluctuations on a timescale not possible with the other causes of furnace pressure fluctuations mentioned above. While the clogging and resolution may sometimes take more than 20 minutes, if pulse-like pressure fluctuations occur, where the furnace pressure increases and then decreases within less than 20 minutes, the cause is not due to an increase in powder accumulation.

[0026] Of the powder inside the furnace, the powder that accumulates in the furnace body and bellows is thought to be powder derived from carbon materials such as coke charged from the top of the furnace and pulverized coal blown in from the tuyeres. This is because a fusion zone exists above the furnace body and bellows, so powder derived from iron ore is thought to have become liquid by the time it reaches the furnace body and bellows, and therefore does not exist as powder in those areas. Thus, if pulse-like pressure fluctuations occur in the furnace body or bellows of a blast furnace, where the internal pressure increases and then decreases within 20 minutes, it can be considered that clogging and subsequent release of carbon material-derived powder have occurred.

[0027] [Detection of pulsed pressure fluctuations in the furnace pressure] In the powder detection method according to the present invention, a pressure gauge that measures the pressure inside the furnace detects pulse-like pressure fluctuations, which are a phenomenon in which the pressure inside the furnace increases by 100 hPa or more and then decreases by 100 hPa or more within a predetermined time period set to a value of less than 20 minutes.

[0028] (Pressure gauge) The type of pressure gauge used in this invention is not particularly limited as long as it can be used in a blast furnace, and any pressure gauge known to those skilled in the art may be used. Generally, in blast furnace operation, multiple pressure gauges (for example, 30 to 40) can be installed in the furnace walls of the furnace mouth, shaft, body, and bellows in both the vertical and circumferential directions to measure the pressure at various locations in the blast furnace. Preferably, pressure gauges are installed at least in the body and bellows of the blast furnace. The pressure measurement interval should be 1 / 5 or less of a predetermined time for detecting pulse-like pressure fluctuations, preferably 1 / 6 or less, 1 / 8 or less, 1 / 10 or less, or 1 / 20 or less, in order to detect pulse-like pressure fluctuations. For example, measurements may be taken every 3 minutes, preferably every 2 minutes, or every 1 minute. Alternatively, the pressure may be measured every few seconds, and the average value over a measurement interval of, for example, 3 minutes or 1 minute may be calculated to detect pulse-like pressure fluctuations.

[0029] In the powder detection method according to the present invention, it is preferable to determine that an increase in the amount of powder accumulated in the furnace has been detected if pulse-like pressure fluctuations in the furnace pressure are detected in at least one of a plurality of pressure gauges installed on the furnace body (furnace wall). Even under normal, stable operation, it is thought that some powder is present in the furnace, but it is extremely rare for small amounts of powder to clog the voids in the iron ore or coke, and it is thought that pulse-like pressure fluctuations are unlikely to occur with small amounts of powder. Therefore, if pulse-like pressure fluctuations are detected in even one pressure gauge once a day, it is thought that this suggests that a relatively large amount of powder is already present in the furnace, and it is preferable to promptly improve the conditions inside the furnace. However, the powder detection method according to the present invention is not limited to the above method, and the determination conditions for detecting an increase in the amount of powder accumulated can be set as appropriate. For example, an increase in the amount of powder accumulated may be detected only when pulse-like pressure fluctuations are detected in a predetermined number or more pressure gauges, or an increase in the amount of powder accumulated may be detected only when pulse-like pressure fluctuations are detected a predetermined number or more times within a predetermined time.

[0030] (Scheduled time) In the powder detection method according to the present invention, the "predetermined time" should be set to less than 20 minutes, preferably 19 minutes or less, 18 minutes or less, 17 minutes or less, 16 minutes or less, 15 minutes or less, or 14 minutes or less. Furthermore, the "predetermined time" should be sufficiently longer than the measurement interval by the pressure gauge (or the time interval for taking the average value of the pressure if the average value is taken), for example, it should be set to 2 minutes or more, 3 minutes or more, 4 minutes or more, 5 minutes or more, or 6 minutes or more. As described above, by setting the "predetermined time" for detecting pulse-like pressure fluctuations to less than 20 minutes, it becomes possible to clearly distinguish between pressure fluctuations due to an increase in the amount of accumulated powder, which is the target of the present invention, and pressure fluctuations due to factors other than an increase in the amount of accumulated powder, which require at least 20 minutes or more.

[0031] (Pulsifying pressure fluctuations) A "pulsed pressure fluctuation" refers to a phenomenon in which the furnace pressure increases by 100 hPa or more within a predetermined time period and then decreases by 100 hPa or more. Therefore, for example, cases where the furnace pressure increases by 100 hPa or more and is maintained at around the increased pressure for 20 minutes or more before decreasing, or cases where the furnace pressure increases by 100 hPa or more over 20 minutes or more before decreasing, are not included in the "pulsed pressure fluctuation" of this invention. Furthermore, the thresholds (pressure increase and pressure decrease) for determining a pulsed pressure fluctuation may be set to be larger as needed. For example, the threshold may be set to "150 hPa or more" or "200 hPa or more" instead of "100 hPa or more". Therefore, alternatively, a "pulsed pressure fluctuation" may be a phenomenon in which the furnace pressure increases by 150 hPa or more or 200 hPa or more within a predetermined time period and then decreases by 150 hPa or more or 200 hPa or more. It is preferable that the threshold for the pressure increase and the threshold for the pressure decrease are the same, but they may be different. When a blast furnace is operating stably, it is rare for the furnace pressure to increase by 100 hPa and decrease by 100 hPa within a given time. Therefore, setting the threshold for detecting pulsed pressure fluctuations to 100 hPa or higher is considered sufficient to detect an increase in powder accumulation. However, if the pressure fluctuations during steady-state operation of the blast furnace are relatively large, an insufficient threshold for detecting pulsed pressure fluctuations is undesirable because it increases noise including pressure fluctuations due to other factors. In such cases, it is advisable to set the threshold for detecting pulsed pressure fluctuations higher. On the other hand, setting the threshold for detecting pulsed pressure fluctuations too high may increase the chances of overlooking an increase in powder accumulation, so this threshold should be set appropriately.

[0032] (furnace pressure) The powder detection method according to the present invention, and therefore the measurement of furnace pressure, can be performed at any location in the furnace body. However, as described above, it is preferable to perform the measurement at a location deeper than the fusion zone, such as the furnace body or the bell-shaped section, where the accumulation of powder derived from materials other than carbon, such as iron ore, is extremely small or nonexistent. Therefore, in the present invention, it is preferable that the furnace pressure is the furnace pressure in the furnace body or the bell-shaped section. In the furnace body or the bell-shaped section, the proportion of powder derived from carbon is extremely high among the existing powder, making it possible to detect only the increase in the accumulation of powder derived from carbon.

[0033] [Detection of increased powder accumulation] In the powder detection method according to the present invention, an increase in the amount of powder accumulated in the furnace is detected by detecting pulse-like pressure fluctuations in the furnace pressure. More specifically, in the powder detection method according to the present invention, when pulse-like pressure fluctuations in the furnace pressure are detected as a result of monitoring the changes in the furnace pressure, it can be considered that the amount of powder accumulated in the furnace has increased. In other words, an increase in the amount of powder accumulated in the furnace, which is difficult to detect directly, can be indirectly detected by measuring the changes in the furnace pressure, which is easy to measure. In particular, when detecting an increase in the amount of powder derived from carbon material accumulated in the furnace by detecting pulse-like pressure fluctuations in the furnace body or bellows, it is possible to identify that the powder is derived from carbon material and then indirectly detect an increase in the amount of powder derived from carbon material accumulated in the furnace, which is difficult to detect directly, by measuring the changes in the furnace pressure, which is easy to measure.

[0034] (powder) In the powder detection method according to the present invention, "powder" refers to solid particles with a diameter of 3 mm or less. The diameter of the powder can be calculated using a known method, but for example, it can be calculated from the equivalent diameter of a circle based on an image observed with an optical microscope. The diameter of the powder can also be expressed, for example, as the sieve size when classified with a sieve. "Powder derived from carbon material" refers to powder mainly composed of carbon, produced from, for example, coke charged from the top of the furnace, or pulverized coal blown in with oxygen-enriched air from the tuyeres. Generally, not only powder derived from carbon material but also powder from iron ore, etc., is present in the furnace, and for example, both powder derived from carbon material and iron ore are present in the furnace mouth and shaft. On the other hand, since carbon material (coke, pulverized coal, etc.) has a higher melting point than other blast furnace raw materials (for example, iron ore), powder derived from carbon material exists as a solid even in positions below the fusion zone where the iron ore has already melted and is in liquid form. Therefore, the powder detection method according to the present invention is preferably carried out in a location where the majority of the powder is derived from charcoal material, or where all of the powder present is derived from charcoal material, such as the furnace chamber or the bell-shaped section.

[0035] <Blast Furnace Operation Method> As described above, the powder detection method according to the present invention makes it possible to detect an increase in the amount of powder, particularly powder derived from carbon, accumulated in the furnace by detecting pulse-like pressure fluctuations in the furnace pressure. In connection with this, the present invention also relates to a blast furnace operation method that includes taking predetermined measures (operational actions) to reduce the amount of powder derived from carbon when an increase in the amount of powder accumulated in the furnace is detected using the powder detection method according to the present invention. The predetermined measures in the blast furnace operation method are at least one selected from (a) increasing the amount of humidified air blown into the furnace from the tuyeres, (b) increasing the strength of the coke charged from the top of the furnace, (c) reducing the amount of debris, (d) reducing the velocity of the oxygen-enriched air blown into the furnace from the tuyeres, and (e) increasing the hydrogen content in the pulverized coal blown into the furnace from the tuyeres. Therefore, in the blast furnace operation method according to the present invention, the measures (a) to (e) above can be taken individually or in combination.

[0036] When an increase in the accumulation of carbon-derived powder in the furnace is detected, one or more of the measures (a) to (e) listed above can be taken to reduce the accumulation of carbon-derived powder in the furnace body or bellows, thereby suppressing pressure fluctuations in the furnace and enabling stable blast furnace operation. The choice of which of the above measures to take should be appropriately selected considering the conditions in the furnace at the time (e.g., the frequency of pulse-like pressure fluctuations), the cost and time required for the measure, etc. Therefore, by implementing the blast furnace operation method according to the present invention, it is possible to efficiently and quickly eliminate fluctuations in furnace pressure caused by the occurrence and elimination of clogging with carbon-derived powder, thereby enabling stable blast furnace operation.

[0037] Conventionally, when fluctuations in furnace pressure were detected, such as an increase in furnace pressure, it was often impossible to fully determine whether the cause of the fluctuation was due to an increase in powder accumulation or some other reason. However, even in such cases, it was necessary to suppress the fluctuations in furnace pressure in order to improve the furnace conditions, and one of the above measures was sometimes taken. However, as mentioned above, since fluctuations in furnace pressure can have various causes, the optimal measure was not always implemented. Furthermore, as will be explained in detail below, from the perspective of stable blast furnace operation, it is sometimes undesirable to continue the above measures for a long period of time. Therefore, taking any measure without identifying the cause of the fluctuations in furnace pressure is thought to require more cost and time than necessary to suppress the fluctuations in furnace pressure, and may even hinder stable blast furnace operation.

[0038] In contrast, the present invention makes it possible to detect an increase in the amount of carbon-derived powder accumulated in the furnace from the changes in furnace pressure. Therefore, appropriate measures can be taken promptly in response to a specific cause of pressure fluctuation, such as an increase in the amount of carbon-derived powder accumulated, minimizing the cost and time required to suppress fluctuations in furnace pressure and enabling stable blast furnace operation.

[0039] (Increase in moisture content from airflow) One effective method for reducing the accumulation of carbon-derived powder in the furnace is to increase the amount of moisture in the oxygen-enriched air blown into the furnace from the tuyeres. "Moisture in the air" refers to the amount of oxygen-enriched air (hot air) blown into the furnace from the tuyeres (1 Nm³). 3 This refers to the mass of water (total moisture) contained per normal cubic meter. Blowing moisture can be increased, for example, by adding water vapor to oxygen-enriched air. The reason why increasing blowing moisture can reduce the accumulation of carbon-derived powder is due to the difference in the reaction rates of oxygen (O2) and water (H2O) with carbon. Carbon-derived powder usually accumulates in greater quantities in the core (furnace core) than in the surface layer of the furnace core where the flow rate of reducing gas is slower. Since O2 reacts with carbon faster than H2O, most of the O2 is consumed by reacting with carbon in the raceway near the tuyeres outlet. On the other hand, H2O can pass through the raceway and remain unreacted until it reaches the area where a large amount of carbon-derived powder has accumulated (powder accumulation area), thus reaching that area. Although lump coke is also present as carbon material in the powder accumulation area, H2O can preferentially react with powder with a high specific surface area. Therefore, by increasing the amount of humidified air, H2O can be reacted with the carbon-derived powder in the powder accumulation area, reducing the amount of carbon-derived powder accumulated in the furnace and thus reducing fluctuations in furnace pressure associated with an increase in powder accumulation. However, since increasing the amount of humidified air may increase the reducing agent ratio, it is preferable to keep the period of increasing the amount of humidified air as short as possible. In the blast furnace operation method according to the present invention, fluctuations in furnace pressure associated with an increase in the amount of carbon-derived powder are addressed by increasing the amount of humidified air, thus efficiently suppressing fluctuations in furnace pressure without requiring unnecessary time and cost.

[0040] (Improvement of coke strength) By increasing the strength of the coke charged into the furnace, the amount of carbon-derived powder accumulated in the furnace can be reduced. Carbon-derived powder can be generated when the surface of the coke deteriorates due to reaction with CO2 at high temperatures, and that area is subjected to shear stress. Therefore, increasing the strength of the coke suppresses the generation of coke-derived powder that occurs during charging into the blast furnace or during descent within the furnace, and as a result, it becomes possible to suppress fluctuations in furnace pressure associated with an increase in the accumulation of carbon-derived powder in the furnace. High-strength coke can be obtained, for example, by changing the type or blend of coal used during coke production. The strength of the coke can be controlled, for example, by CSR (Post-Reaction Strength Index) and DI (Cold Strength Index). CSR is the weight ratio of +9.5 mm after 600 rotations (20 rpm) of a Type I drum after a CRI (Reactivity Index) test (CRI is the weight loss rate after 2 hours of reaction of coke (particle size 20 ± 1 mm, 200 g) at 1100°C with CO2; 5 Nl / min). DI is the weight ratio of +15mm after 150 rotations (15 rpm) of a 10±0.2 kg lump coke (particle size +25mm) according to the particle size distribution. Although improving coke strength is somewhat costly and time-consuming, the blast furnace operation method according to the present invention addresses fluctuations in furnace pressure due to the increase in the accumulation of coal-derived powder by improving coke strength, thereby efficiently suppressing fluctuations in furnace pressure without requiring excessive time and cost.

[0041] (Reduction of the accumulation rate) In some cases, coke used in furnaces is yard coke, which has been exposed to the outside air for a long period of time. Such yard coke contains a lot of moisture and may have powder adhering to it, and the use of yard coke can increase the amount of powder accumulated in the furnace. Therefore, by reducing the debris rate shown in the following formula, the amount of carbon-derived powder from the charged coke can be reduced, and as a result, the amount of carbon-derived powder accumulated in the furnace can be reduced, and fluctuations in furnace pressure caused by an increase in powder accumulation can be suppressed. Scraps storage rate (%) = [(Yard coke cost per unit) / (Coke ratio)] × 100 Here, "yard coke cost" and "coke ratio" refer to the mass of yard coke and the total mass of coke charged from the top of the furnace to produce one ton of molten iron, respectively. Note that yard coke can be more expensive than domestically produced coke, but by reducing the amount of spent coke, it is possible to efficiently suppress fluctuations in furnace pressure without incurring unnecessary costs. Note that yard coke may be purchased and used out of necessity when domestically produced coke is insufficient, and in such cases, it is preferable to reduce the amount of spent coke for a short period of time.

[0042] (Decrease in the rate of oxygen-enriched air) The oxygen-enriched air blown in from the tuyeres causes the coke to swirl near the raceway. Therefore, as the velocity of the oxygen-enriched air blown in from the tuyeres increases, the impact from the swirl energy of the air increases the generation of powder from the surface of the coke swirling in the raceway. Thus, by reducing the velocity of the oxygen-enriched air blown in from the tuyeres, the generation of powder from the coke can be reduced, and fluctuations in furnace pressure associated with the increase in the accumulation of carbon-derived powder can be suppressed. The velocity of the oxygen-enriched air is the airflow velocity (wind speed, linear flow velocity) at the tip of the tuyeres, and the amount of oxygen-enriched air blown in (m³) 3 / s) tuyere cross-sectional area (m 2 It is calculated by dividing by ). For example, reducing the amount of air blown in (without increasing the cross-sectional area of ​​the tuyeres) and thereby reducing the velocity of oxygen-enriched air may reduce productivity to some extent. However, in the blast furnace operation method according to the present invention, the response to fluctuations in furnace pressure due to the increase in the accumulation of powder derived from coal material is to reduce the velocity of oxygen-enriched air, so fluctuations in furnace pressure can be efficiently suppressed without requiring more time and cost than necessary.

[0043] (Increase in hydrogen content in pulverized coal) By increasing the hydrogen content of the pulverized coal blown into the furnace from the tuyeres, the amount of coal-derived powder in the furnace can be reduced. The hydrogen contained in the pulverized coal is converted to H2O at the tip of the tuyeres. As described above, H2O, which has a slower reaction rate with carbon than O2, is transported to the powder accumulation area deeper than the furnace core surface where the reducing gas flow rate is slower, and the H2O can react with the coal-derived powder. As a result, the amount of coal-derived powder in the furnace can be reduced, and fluctuations in furnace pressure associated with an increase in powder accumulation can be suppressed. The hydrogen content of the pulverized coal can be adjusted by changing the brand and blend of pulverized coal. Note that increasing the hydrogen content of the pulverized coal may decrease the replacement rate of the pulverized coal and may increase the reducing agent ratio somewhat. However, in the blast furnace operation method according to the present invention, fluctuations in furnace pressure associated with an increase in the amount of coal-derived powder are addressed by increasing the hydrogen content of the pulverized coal, so fluctuations in furnace pressure can be suppressed efficiently without requiring unnecessary time and cost.

[0044] As described above, when an increase in the accumulation of coal-derived powder in the furnace is detected using the powder detection method according to the present invention, the accumulation of coal-derived powder in the furnace can be reduced by implementing at least one of the following: (a) increasing the amount of humid air blown into the furnace from the tuyeres, (b) increasing the strength of the coke charged from the top of the furnace, (c) reducing the amount of debris, (d) decreasing the velocity of the oxygen-enriched air blown into the furnace from the tuyeres, and (e) increasing the hydrogen content in the pulverized coal blown into the furnace from the tuyeres. This allows for a rapid and efficient improvement of the deterioration of the air permeability inside the furnace and enables stable blast furnace operation.

[0045] The powder detection method and blast furnace operation method according to the present invention can be implemented in any blast furnace. Although the absolute value of the furnace pressure measured by the pressure gauge may vary depending on the size and operating conditions of the blast furnace, pulse-like pressure fluctuations occur as the amount of accumulated powder increases. Therefore, the powder detection method and blast furnace operation method according to the present invention can be applied to blast furnaces of any volume and shape, and their effects can be demonstrated in blast furnaces of any volume and shape. [Examples]

[0046] The powder detection method and blast furnace operation method according to the present invention will be described in more detail below with reference to examples. However, the scope of the present invention as described in the claims is not intended to be limited by the specific examples described below.

[0047] The blast furnace was operated under the following operating conditions: Tapping ratio=2.0t / day / m 3 (Furnace volume 1m 3 (Daily pig iron production in [location]) Coke ratio = 340 kg / t (the mass of coke charged to produce 1 ton of molten iron) pulverized coal ratio = 155 kg / t (mass of pulverized coal blown in from the tuyeres to produce 1 ton of molten iron) Hydrogen content in pulverized coal = 4.1% Reducing agent ratio = 495 kg / t (mass of reducing agent used to produce 1 ton of molten iron) Blowing moisture = 25g / Nm 3 Coke's CSR (Post-Reaction Strength Index) = 61.0 Coke's DI (Cold Strength Index) = 85.2 Storage rate = 40% Velocity of oxygen-enriched air = 260 m / s In this example, since only coke and pulverized coal were used as reducing agents, the reducing agent ratio is the sum of the coke ratio and the pulverized coal ratio.

[0048] Figure 1 is a graph plotting the pressure fluctuations inside the furnace every minute, measured by two pressure gauges installed on the furnace hull (located at the same height but circumferentially 180° apart). For pulse-like pressure fluctuations inside the furnace, instances where the internal pressure increased by 100 hPa or more followed by a decrease of 100 hPa or more over a 19-minute period were counted, and corresponding locations are marked with dotted circles.

[0049] The detection of these pulse-like pressure fluctuations led to the determination that the amount of charcoal-derived powder had increased in the furnace wall, and the amount of moisture in the blown air was increased to 25 g / Nm³. 3From 30g / Nm 3 The amount was increased. Figure 1 shows the pressure fluctuations over three days, and the time t=0 on the horizontal axis of the figure indicates the point in time when the amount of humidified air was increased. Table 1 shows the change in the number of pulse-like pressure fluctuations during the measurement period of the furnace pressure after the amount of humidified air was increased.

[0050] [Table 1]

[0051] Table 1 and Figure 1 show that the number of pulse-like pressure fluctuations gradually decreased as the amount of humidified air blown into the furnace increased, and the furnace pressure stabilized. This indicates that by detecting pulse-like pressure fluctuations according to the powder detection method of the present invention, it was possible to detect an increase in the amount of powder (in this example, powder derived from carbon material) accumulated in the furnace. Furthermore, it is thought that the furnace pressure was quickly stabilized by increasing the amount of humidified air blown into the furnace from the tuyeres as a measure to reduce the amount of powder derived from carbon material. Therefore, the increase in the reducing agent ratio associated with the increase in humidified air was minimized, the cost and time required to suppress fluctuations in furnace pressure were reduced, and blast furnace operation was stabilized.

[0052] Similarly, when pulsed pressure fluctuations were detected in the furnace pressure transition, increasing the coke strength CSR from 61% to 65%, reducing the lumps ratio from 40% to 15%, reducing the oxygen-enriched air velocity from 260 m / s to 240 m / s, or increasing the hydrogen content in pulverized coal from 4.1% to 4.6% also gradually reduced the number of pulsed pressure fluctuations and stabilized the furnace pressure. [Industrial applicability]

[0053] According to the present invention, by detecting pulse-like pressure fluctuations in the furnace pressure, it is possible to detect an increase in the accumulation of powder (particularly powder derived from carbon material) in the furnace. As a result, appropriate measures (operational actions) can be taken in response to such pressure fluctuations, and the permeability of the furnace is properly maintained, enabling stable operation of the blast furnace. Therefore, the present invention can be said to be an invention of extremely high industrial value.

Claims

1. A powder detection method for blast furnace operation, which detects an increase in the amount of powder accumulated in the furnace by detecting pulse-like pressure fluctuations, which are phenomena in which the internal pressure of the furnace increases by 100 hPa or more and then decreases by 100 hPa or more within a predetermined time period set to a value of less than 20 minutes, using a pressure gauge that measures the internal pressure of the furnace.

2. The powder detection method according to claim 1, wherein an increase in the amount of powder accumulated in the furnace is detected by detecting a phenomenon in which the furnace pressure increases by 200 hPa or more and then decreases by 200 hPa or more among the pulse-like pressure fluctuations.

3. The powder detection method according to claim 1 or 2, wherein the furnace pressure is the furnace pressure in the furnace body or the bell-shaped section.

4. A blast furnace operation method using the powder detection method described in claim 1 or 2, wherein when the powder detection method detects an increase in the amount of powder accumulated in the furnace, (a) Increase the amount of moisture in the oxygen-enriched air blown into the furnace from the tuyeres. (b) To increase the strength of the coke charged from the top of the furnace, (c) Reduce the rate of accumulation of rubble, (d) Reducing the velocity of oxygen-enriched air blown into the furnace from the tuyeres, (e) Increasing the hydrogen content in the pulverized coal blown into the furnace from the tuyeres. A blast furnace operating method comprising performing at least one of the following.

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