JP7697494B2 - Blast furnace operating method and pulverized coal for injection into blast furnace - Google Patents

Description

The present invention relates to a method of operating a blast furnace that uses pulverized coal with improved transportability when injecting pulverized coal into a blast furnace from the tuyere, and to pulverized coal for injection into a blast furnace.

In recent years, global warming due to an increase in carbon dioxide emissions has become a problem, and suppressing CO ₂ emissions has become an important issue in the steel industry as well. For this reason, in recent blast furnace operations, low reducing agent ratio (low RAR) operation, that is, operation in which the total amount of reducing agent (pulverized coal) injected from the tuyere and coke charged from the furnace top when producing 1 ton of pig iron, is small, is recommended.

Generally, blast furnaces use coke, which is charged from the top of the furnace, and pulverized coal, which is blown into the tuyere, as reducing agents. In order to achieve low reducing agent ratio operation and suppression of carbon dioxide emissions in the operation of blast furnaces, it is believed that one effective method is to reduce the coke ratio by blowing pulverized coal into the tuyere under conditions where there are as few operational problems as possible.

Generally, pulverized coal is transported by airflow through piping and finally injected into the blast furnace through the tuyere. However, the transportability of the pulverized coal varies greatly depending on the brand and particle size of the pulverized coal. As a result, the pulverized coal adheres to the inside of the piping during airflow transport, causing the piping to become clogged, leading to a decrease in the air permeability and temperature drop inside the blast furnace, and an increase in the coke ratio. Various methods have been proposed to solve these problems with the transportability of pulverized coal.

For example, Patent Document 1 discloses a method for injecting pulverized coal into a blast furnace, which includes a particle size distribution measurement step in which pulverized coal produced by a pulverized coal production apparatus is removed from a conveying path and periodically measured by a particle size distribution measurement device, and a grinding force adjustment step in which the coal grinding force in the pulverized coal production apparatus is adjusted using the deviation between the measured value measured in the particle size distribution measurement step and a target value, and the particle size distribution measurement step uses a particle size distribution measurement device with a standard deviation of the measured value of a standard sample within 1%. The particle size distribution of the pulverized coal is measured based on the mass proportion of particle sizes of -44 μm and -74 μm in the pulverized coal, and the pulverized coal is injected so that the particle size distribution of the pulverized coal is "45%≦-44 μm proportion (%)≦50%, 60%≦-74 μm proportion (%)".

Furthermore, Patent Document 2, with regard to a method for pneumatically transporting pulverized coal, focuses on the interparticle adhesive force of pulverized coal as an index other than particle size, and proposes a method in which pulverized coal having an interparticle adhesive force value of 3.26 × 10 ^-7 N or less, calculated based on the Rumpf formula, is injected into a blast furnace.

Patent Document 3 also proposes a method in which pulverized coal is charged into a cell consisting of an upper cell and a lower cell, the cell is compressed for 60 seconds at a pressure of 4.0 MPa to produce a pulverized coal powder layer, and then, while keeping the lower cell fixed, the upper cell and the pulverized coal powder layer are pulled upward at a speed of 0.1 mm/sec to separate them, and the pulverized coal required at this time to have a tensile breaking strength of 50 kPa or less is injected into the blast furnace.

Furthermore, Patent Document 4 proposes a method for measuring the nuclear magnetic resonance spectrum of ^27Al or ^29Si present in coal, classifying the chemical forms of inorganic minerals present in the coal and containing Al and Si as main components based on the measurement results, and evaluating the transportability of the above-mentioned coal (pulverized coal) based on the classification.

Patent Document 5 also proposes a method of adding a pulverized coal transportability improver made of a water-soluble inorganic salt to pulverized coal in order to improve the transportability of the pulverized coal injected through the injection port of a metallurgical furnace or sintering furnace.

JP 2013-43998 A JP 2016-113664 A JP 2019-59985 A JP 2005-207817 A Japanese Patent Application Publication No. 09-256015

The method disclosed in Patent Document 1 attempts to prevent blockages in the pipes leading to the blast furnace by adjusting the particle size distribution of pulverized coal to be "45%≦-44 μm ratio (%)≦50%, 60%≦-74 μm ratio (%)" regardless of the brand of coal. However, in actual operation, as shown in Figure 6, even if the particle size distribution is adjusted, there is a problem that some brands of coal have a high frequency of pipe blockages, and the number of blockages actually increases.

In addition, in the method disclosed in Patent Document 2, the brand of coal to be used is selected based on the interparticle adhesive force value based on the Rumpf formula, but when the pipe is clogged, the pulverized coal forms a powder layer and adheres to the pipe, so if the particle size of the pulverized coal changes or the porosity of the powder layer of the pulverized coal changes, there is a problem that the tensile breaking strength of the powder layer of the pulverized coal changes and the pipe is clogged. Furthermore, in actual operation, even if a brand with low interparticle adhesive force is selected, there are some that frequently clog the pipe, as shown in Figure 7.

In addition, in the method disclosed in Patent Document 3, a powder layer of pulverized coal created by compressing it at a pressure of 40 MPa for 60 seconds is pulled and broken, and the brand of coal to be used is selected based on the tensile breaking strength value required at that time. However, in actual operation, the pulverized coal flows through the pipes, so there was a problem with evaluating the transportability of the pulverized coal from the tensile breaking strength of a stationary powder layer as described above.

In addition, in the method disclosed in Patent Document 4, the nuclear magnetic resonance spectrum of ^27Al or ^29Si present in pulverized coal is measured, and the transportability of pulverized coal is evaluated from the measurement results, but since the nuclear magnetic resonance spectrometer is a very expensive and delicate equipment, it is difficult to use it in the operation of an actual machine in which the brand used and the injection amount are changed depending on the condition inside the blast furnace. In addition, in this method, although the chemical form of inorganic minerals mainly composed of aluminum and silicon is quantitatively measured, the final evaluation of transportability is made qualitatively depending on the abundance ratio, so it is difficult to say that it is a highly general method.

In addition, the method disclosed in Patent Document 5 is expected to improve the transportability by reducing the amount of triboelectric charge of pulverized coal, but the added inorganic salts may act as an obstruction factor to the stable operation of the blast furnace due to the deterioration of permeability caused by the increase in the fineness rate in the lower part of the blast furnace. In addition, the melting of these inorganic salts increases the total amount of molten slag remaining in the furnace, and there is a concern that the permeability will deteriorate due to the narrowing of the gas path in the lower part of the furnace. These problems can be addressed by increasing the amount of coke used, which acts as a gas path in the furnace, but this leads to an increase in the cost of molten pig iron. In addition, it is necessary to increase the reducing agent ratio in the blast furnace by the amount of heat required to raise the temperature and melt the inorganic salts, and there is a concern that the amount of CO ₂ emissions from the blast furnace will increase. Therefore, this method has a problem that there are many disadvantages in the blast furnace body, more than the effect obtained by improving the transportability of pulverized coal.

The present invention was made in consideration of the problems associated with the above-mentioned conventional technologies, and its purpose is to propose a method of operating a blast furnace and pulverized coal for injection into a blast furnace that can prevent blockage of pipes and suppress an increase in the coke ratio by injecting pulverized coal whose transportability has been improved in advance into the blast furnace.

As a result of thorough research to solve these problems, the inventors noticed that the electrostatic force of the pulverized coal causes adhesion and clogging of the transport pipes during the process of transporting the pulverized coal to the blast furnace, and discovered that the transportability can be evaluated by the saturated charge of the pulverized coal, which led to the development of the present invention.

The present invention has been made based on the above findings, and the gist of the present invention is as follows.
That is, the present invention is a method for operating a blast furnace in which pulverized coal is injected into the furnace in conjunction with the air blown from the tuyere, characterized in that the pulverized coal to be injected into the furnace is first supplied to a cyclone forming an electric field inside, a voltage is applied to the cyclone, and the saturation charge of the pulverized coal is measured with a potential meter installed at the outlet of the cyclone to evaluate its transportability, before the pulverized coal is injected into the furnace from the tuyere of the blast furnace.

In addition, in the blast furnace operation method of the present invention,
(1) The pulverized coal exhibiting suitable transportability for injection has a saturated charge of 400 nC/g or less when measured by a potential meter installed at the outlet of the cyclone;
(2) The pulverized coal is dried;
(3) The drying treatment of the pulverized coal is carried out by heating it to a temperature of 100° C. or more;
is preferred.

The present invention also relates to pulverized coal for injection into a blast furnace, which is treated by applying a voltage inside a cyclone that forms an electric field inside, and is characterized in that the saturated charge, as measured by a potential meter installed at the outlet of the cyclone, is 400 nC/g or less.

In addition, in the pulverized coal for injection into a blast furnace according to the present invention,
(1) The pulverized coal is dried;
(2) The pulverized coal is dried at a temperature of 100° C. or higher;
is preferred.

According to the present invention, by injecting pulverized coal, the transportability of which has been evaluated in advance, into the blast furnace through the tuyere, it becomes possible to operate the blast furnace while suppressing blockage of the piping caused by the characteristics of the pulverized coal itself. This makes it possible to suppress deterioration of the air permeability and decrease in temperature inside the blast furnace, and effectively suppresses increases in the coke ratio, etc.

FIG. 1 is a schematic diagram showing a blast furnace and its auxiliary equipment for carrying out the blast furnace operation method of the present invention. FIG. 2 is a schematic diagram illustrating a method for measuring the saturated charge amount of pulverized coal. 1 is a graph showing the relationship between the voltage applied to an internal electrode of a cyclone and the charge amount of pulverized coal A. FIG. 1 is a schematic diagram showing an experimental method for estimating the critical conveying distance of pulverized coal in an actual pulverized coal conveying line. 1 is a graph showing the relationship between the saturated charge amount of pulverized coal and the number of blockages (daily average) of conveying pipes when the pulverized coal is used in an actual machine. Graph (a) shows the relationship between the particle size distribution of pulverized coal (up to 44 μm (mass%)) and the number of pipe blockages (daily average), and graph (b) shows the relationship between the particle size distribution of pulverized coal (up to 74 μm (mass%)) and the number of pipe blockages (daily average). 1 is a graph showing the relationship between the adhesive force between pulverized coal particles and the number of blockages in pipes (daily average).

Hereinafter, a method for operating a blast furnace according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing a blast furnace and its associated equipment used to carry out the blast furnace operation method according to the present invention. A method of injecting pulverized coal into a blast furnace from a tuyere will be described with reference to FIG. 1.

Coal 1 stocked in the yard is stored in a coal hopper 2 and then fed by a feeder 3 to a pulverized coal production device 4. In the pulverized coal production device 4, the coal 1 is crushed, dried, and then adjusted to pulverized coal 5 of a specified particle size.

The pulverized coal 5 thus adjusted is air-transported to the bag filter 7 through the main pipe 6. The pulverized coal 5 collected in the bag filter 7 is stored in a coal bin 8 and then transported to the injection tank 9. The pulverized coal 5 transported to the injection tank 9 is supplied to the distributor 10 by air-transportation, and is further distributed from the distributor 10 to each tuyere 14 arranged at the bottom of the blast furnace 13 via multiple branch pipes 11 and a blowpipe 12. The pulverized coal 5 is injected into the hot air supplied from the hot stove 15 to the blowpipe 12 connected to each tuyere 14, and is blown into the blast furnace 13 from the tuyere 14 together with the hot air. In this manner, the blast furnace 13 is operated.

As described above, the pulverized coal 5 is injected into the blast furnace 13 from the tuyere 14 through several piping systems, i.e., pipes, valves, holders, etc., and injection devices. When a large amount of pulverized coal 5 is injected into the blast furnace 13 in this way, some of the pulverized coal 5 may adhere to the inside of the piping system, etc., and the powder layer of the adhered pulverized coal 5 may grow and block the piping, making it impossible to continue normal blast furnace operation. Therefore, when injecting pulverized coal 5 into the blast furnace 13, it is strongly required that the pulverized coal 5 flow smoothly without adhering to the piping system or causing blockages (improving transportability).

For the pulverized coal 5 to adhere to the inside of each pipe, some kind of adhesive force must be acting between the pulverized coal 5 and the pipe. If this adhesive force is classified by type, it can be van der Waals forces, liquid bridge forces, or electrostatic forces.

First, the van der Waals force is an intermolecular force acting between atoms, ions, and molecules, and its origin is the dispersion force between electric dipoles resulting from the non-steady distribution of electrons within the molecules. This force is isotropic and inversely proportional to the seventh power of the interatomic distance, so the force is extremely small when the pulverized coal 5 is not in contact with the piping. However, although this van der Waals force may have a significant effect in the process of generating a powder layer by the pulverized coal 5 adhering to the piping system, it is not thought to be the fundamental cause of the adhesion of the pulverized coal 5 to the piping system, etc.

Next, the liquid bridge force is an attractive force that acts between particles when liquid exists in the gas phase and is held between the particles, and can be physically explained as the surface tension in the liquid bridge having an uneven curved surface. This liquid bridge force varies depending on the shape of the bridge, the surface roughness of the particles, the adsorbed water state, and the impurity concentration in the adsorbed water, but it is said that it acts significantly as an adhesive force in an environment with a relative humidity of 60% or more. In contrast, inside the blowpipe 12 connected to the tuyere 14 of the blast furnace 13, the transport environment for the pulverized coal 5 is a temperature of about 100°C, the transport air flow is about 20 m/s, and the relative humidity is extremely low. Therefore, it is thought that this liquid bridge force does not cause the pulverized coal 5 to adhere to the piping system, etc.

On the other hand, the electrostatic force is a force acting between charged particles, and its value is proportional to the product of the charges and inversely proportional to the square of the distance between the charges. While the van der Waals force is inversely proportional to the seventh power of the interparticle distance, the electrostatic force is inversely proportional to the square of the distance, so there is a high possibility that a significant force acts on the contact even if the pipe and the particles are not in contact. In addition, the blowpipe 12 connected to the tuyere 14 of the blast furnace 13 is usually earthed, so it is thought that no electrostatic force acts, but it is known that an electrostatic force called an electric image force actually acts between an uncharged object and a charged particle. This is an attractive force that occurs when free electrons in an uncharged object are attracted to the charge of the charged particle. Therefore, it is thought that there is a very high possibility that the electrostatic force is the cause of the adhesion of the pulverized coal 5 during the process of transporting the pulverized coal 5 to the blast furnace 13.

Based on the above, in this invention, we focus on the electrostatic force during the process of transporting pulverized coal 5 to the blast furnace 13, and have come to the conclusion that it is effective to evaluate transportability based on the saturated charge amount of the pulverized coal 5 injected into the blast furnace 13 from the tuyere 14.

Therefore, the saturated charge amount of the pulverized coal 5 injected into the blast furnace was examined.
2 is a schematic diagram showing a method for measuring the saturated charge of pulverized coal 5. In the present invention, the saturated charge of pulverized coal 5 is the maximum charge (nC/g) measured by an electrometer 24 connected to a Faraday gauge 23 after the pulverized coal 5 is caused to flow into a cyclone 19 to which a voltage is applied together with a transport airflow 18 and the pulverized coal 5 is collected by a Faraday gauge 23 installed at the discharge portion of the cyclone 19. The voltage applied to the cyclone 19 is a voltage at which the pulverized coal 5 has at least a saturated charge, and is preferably in the range of -1 to 1 kV.

As shown in FIG. 2, the cyclone 19 has an external electrode 20 and an internal electrode 21, and a voltage is applied to the internal electrode 21 by a high-voltage generator 22. This creates an electric field inside the cyclone 19, and the pulverized coal 5 becomes charged as it passes through the electric field.

In the embodiment described below, pulverized coals A, B, C, D, E, F, and G were prepared as pulverized coals for evaluation. The particle size of each of the pulverized coals A to G was adjusted so that the harmonic mean particle size was 15 to 20 μm. The harmonic mean particle size was calculated by measuring the particle size distribution of the pulverized coals A to G using a wet particle size distribution measuring device using a laser diffraction scattering method, and using the volume ratio (volume %) of each particle size and the following formula (1).
Dp=Σn/Σ(n/d)...(1)
In the above formula (1), Dp is the harmonic mean particle diameter (μm), d is the particle diameter of the pulverized coal (μm), and n is the volume fraction (volume %).

In carrying out the experiment, each of the pulverized coals A to G was introduced into the inside of the cyclone 19, charged by passing through the electric field formed in the cyclone 19, and the saturated charge amount was measured. The voltage applied to the internal electrode 21 of the cyclone 19 was changed in increments of 0.2 kV, and measurements were continued until the charge amount was saturated.

The relationship between the voltage applied to the cyclone 19 and the charge amount of the pulverized coal 5 will be described with reference to FIG. 3, taking pulverized coal A as an example. As shown in FIG. 3, it can be seen that the charge amount of the pulverized coal A has an odd function relationship with the applied voltage. In addition, since the charge amount when the applied voltage is 0 kV fluctuates slightly toward a positive value, it was also found that the pulverized coal A tends to be positively charged. The charge amount of the pulverized coal A converges to a constant value when the absolute value of the applied voltage becomes about 0.5 kV or more. From these results, it was found that the pulverized coal A was charged to a saturated charge amount inside the cyclone 19 to which a voltage of 0.5 kV or more was applied. Note that there is a slight difference in the saturated charge amount when the applied voltage is positive and negative, but the maximum absolute value was taken as the saturated charge amount. It was also found that the pulverized coals B to G were charged to a saturated charge amount inside the cyclone 19 if a voltage in the range of -1 to 1 kV was applied. Table 1 below shows the saturated charge of pulverized coal A to G.

Next, in order to estimate the amount of charge of each of the pulverized coals A to G in the conveying line of the actual machine, a measurement test of the amount of charge of each of the pulverized coals A to G was carried out in a test system simulating the conveying line of the actual machine.
FIG. 4 is a schematic diagram of a test system for estimating the amount of charge of pulverized coal A to G in an actual machine. First, each of the pulverized coals A to G used in the test was loaded into a Faraday gauge 25, and the initial amount of charge was measured by an electrometer 26. After the initial amount of charge was measured, the pulverized coals A to G were entrained in compressed air 29 (temperature 100° C., 20 m/s in accordance with the actual machine) and passed through a pipe 30 having a length of 1 m. A stainless steel pipe having a diameter of 34 mm was used as the pipe 30. It was confirmed that the pulverized coals A to G were charged due to friction between the particles and with the inner wall of the pipe 30 while passing through the pipe 30.

Next, the pulverized coal A to G were collected in a Faraday gauge 31 installed at the outlet of the pipe 30, and the charge amount was measured by an electrometer 32 connected to the Faraday gauge 31. The charge amount (nC/g·m) per unit transport distance of the pulverized coal A to G that had passed through the pipe 30 was calculated from the difference between the initial charge amount of the pulverized coal A to G measured by the electrometer 26 and the charge amount of the pulverized coal A to G after passing through the pipe 30 measured by the electrometer 32.

Next, the critical conveying distance (m) for pulverized coal A to G until the saturated charge amount is reached was estimated from the charge amount per unit conveying distance (nC/g·m) of pulverized coal A to G measured in the test system shown in Figure 4 and the saturated charge amount (nC/g) of pulverized coal A to G measured in Figure 2.

Table 2 shows the charge amount per unit conveying distance (nC/g·m) for pulverized coal A to G, the critical conveying distance (m) until the saturated charge amount is reached, along with the saturated charge amount (nC/g). From the results shown in Table 2, it was estimated that all of pulverized coal A to G reach the saturated charge amount at a conveying distance of 10 m or less.

Considering that the results in Table 2 show that the pulverized coal transport line in the actual equipment is several hundred meters long, it is estimated that the pulverized coal will reach a saturated charge at the initial position of the transport line (within 10 m) during operation of the actual equipment. Therefore, we decided to use the saturated charge of the pulverized coal as an indicator to study the effect of the electrostatic force of the pulverized coal on adhesion to piping systems, etc., in the transport line of the actual equipment.

Based on the above findings, the saturated charge of pulverized coal and its transportability were verified using an actual machine. To confirm the effect of the saturated charge of pulverized coal in an actual machine, pulverized coals A to G shown in Tables 1 and 2 were each injected into a blast furnace and operation was carried out, and the correlation between the blockage of the pipes and the saturated charge of pulverized coal was investigated.

The actual machine used was a blast furnace with an internal volume of 4300 ^m3 equipped with 34 tuyeres and 68 pulverized coal transport pipes. The operation was carried out for 5 days with a lump coke ratio of 280 kg/t, a small coke ratio of 70 kg/t, and a target pig iron production volume of 10,000 t/day, injecting pulverized coal at a unit cost of 200 kg/t. Even if the pulverized coal transport pipe was clogged, the blockage was not cleared, and more pulverized coal than usual was transported to the unclogged pipe, so that the pulverized coal ratio was kept constant. In addition, the pulverization conditions were adjusted as needed so that the particle size of the pulverized coal to be injected would be 15 to 20 μm in harmonic mean particle size.

Figure 5 shows the average number of transport pipes blocked per day due to adhesion of pulverized coal for each saturated charge of pulverized coal A to G. When pulverized coal C, D, and E, which had a saturated charge of 500 nC/g or more, were used, the average number of blocked transport pipes per day was 7 to 10. However, when pulverized coal A, B, F, and G, which had a saturated charge of 400 nC/g or less, were used, the average number of blocked transport pipes per day was significantly reduced to 1 or less.

These results confirmed that, in blast furnace operation, by using pulverized coal with a saturated charge of 400 nC/g or less as the pulverized coal to be injected into the furnace, it is possible to reliably prevent the adhesion of pulverized coal to piping systems, etc., and to reduce the number of pipes that become clogged due to the adhesion of pulverized coal during blast furnace operation.

Therefore, when operating a blast furnace, the saturated charge of the pulverized coal to be injected into the blast furnace is measured, and pulverized coal with a saturated charge of 400 nC/g or less, preferably 360 nC/g or less, is used. This prevents the pulverized coal from adhering to the transport pipes, and prevents deviations in the amount of gas around the periphery of the blast furnace, temperature, and deterioration of the gas permeability inside the furnace, which in turn prevents an increase in the coke ratio due to blockage of the pipes.

In addition, in the present invention, it is preferable to use pulverized coal that has been heated and dried. By carrying out the heating process, volatile matter is released from the pulverized coal, and even if the coal adheres to the inside of the pipe, its growth is suppressed (it is modified), so that clogging of the pipe can be effectively suppressed.

In addition, for drying the pulverized coal, the heating temperature is preferably 90°C or higher, and more preferably 100°C or higher. By drying the pulverized coal, it is expected that the liquid bridging force will decrease due to the evaporation of moisture adhering to the particle surface, and clogging of the pipes can be prevented.

Although an embodiment of the present invention has been described above, this embodiment constitutes a part of the disclosure of the present invention, and the present invention is not limited to these descriptions and drawings. In other words, other embodiments, examples, operational techniques, etc. made by those skilled in the art based on this embodiment are all included in the scope of the present invention.

In addition to being used as a method for injecting pulverized coal into a blast furnace, the present invention can also be applied as a technology for transporting piping for similar powders and granular materials other than pulverized coal.

Reference Signs List 1 Coal 2 Coal hopper 3 Feeder 4 Pulverized coal production equipment 5 Pulverized coal 6 Main pipe 7 Bag filter 8 Coal bin 9 Injection tank 10 Distributor 11 Branch pipe 12 Blow pipe 13 Blast furnace 14 Tuyere 15 Hot stove 18 Transport air flow 19 Cyclone 20 External electrode 21 Internal electrode 22 High voltage generator 23 Faraday gauge 24 Electrometer 25 Faraday gauge 26 Electrometer 29 Compressed air 30 Pipe 31 Faraday gauge 32 Electrometer

Claims (6)

In a method of operating a blast furnace, pulverized coal is injected into the furnace in conjunction with the air blown from the tuyere.
This method for operating a blast furnace is characterized in that pulverized coal having a harmonic mean particle size of 15 to 20 μm to be injected into the furnace is first supplied to a cyclone forming an electric field inside, and a voltage of -1 to 1 kV is applied by passing the pulverized coal through the electric field, and then the saturated charge of the pulverized coal is measured with a potential meter installed at the outlet of the cyclone to evaluate transportability , and then the pulverized coal having a saturated charge of 400 nC/g or less, which shows suitable transportability for injection, is injected into the furnace from the tuyere of the blast furnace. The method for operating a blast furnace according to claim 1 , characterized in that the pulverized coal is dried. The method for operating a blast furnace according to claim 2 , characterized in that the drying treatment of the pulverized coal is carried out by heating it to a temperature of 100°C or more. Pulverized coal is blown into the blast furnace together with the air blown from the tuyere,
The pulverized coal for injection into a blast furnace is characterized in that the pulverized coal has a harmonic mean particle size of 15 to 20 μm, and exhibits a saturated charge of 400 nC/g or less when a voltage of -1 to 1 kV is applied inside a cyclone forming an electric field therein, as measured by a potential meter installed at the outlet of the cyclone. The pulverized coal for injection into a blast furnace according to claim 4 , characterized in that the pulverized coal is dried. The pulverized coal for injection into a blast furnace according to claim 5 , characterized in that the pulverized coal is dried at a temperature of 100°C or higher.

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