JP2017102040A - Operation method for steelmaking furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operation method for a steelmaking furnace capable of adjusting an operation condition in accordance with an amount of ferrous particles in exhaust gas.SOLUTION: An operation method for a steelmaking furnace which produces dust comprises: a Doppler frequency measuring process S1 which includes the steps to irradiate exhaust gas flowing in a gas duct with microwaves, detect reflective waves reflected on the dust in the exhaust gas and calculate frequency distribution of intensity of the reflective waves; a step S2 to extract, from the frequency distribution, the intensity of the reflective waves having frequency corresponding to ferrous particles in the dust; and a step S3 to adjust an operation condition of a furnace in accordance with the intensity of the reflective waves having the frequency corresponding to the ferrous particles. Given that a propagation angle of the microwaves is expressed as θ, the frequency corresponding to the ferrous particles can be estimated by sinθ components of speeds of the ferrous particles predicted from diameters and density of the ferrous particles which can be generated in the furnace and a flow rate of the exhaust gas.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for operating a steelmaking furnace.

  In order to manufacture steel materials, for example, a blast furnace that takes pig iron (molten iron) from iron ore, a converter that blows oxygen to convert pig iron to steel (molten steel), an electric furnace that melts iron scrap to obtain molten steel, and components of molten steel A variety of steelmaking furnaces such as smelting furnaces for adjusting the temperature are used. In the narrow sense, the process of converting pig iron to steel is called steelmaking, and may be distinguished from smelting to obtain pig iron and smelting to adjust the composition of the molten steel. In the present invention, the term “steel making furnace” Is used as a concept that includes furnaces used in the ironmaking and smelting processes.

  As a method for operating such a steelmaking furnace, that is, a control method for optimizing the operation state, the amount of dust in the exhaust gas discharged to the flue is monitored, and from the correlation between the amount of dust and the operation state, oxygen A method of optimizing various parameters such as supply amount has been proposed (see, for example, Japanese Patent Application Laid-Open No. 2007-0771820).

  Specifically, in the above publication, the exhaust gas discharged from the furnace to the flue is irradiated with microwaves to detect the reflected wave, and the frequency of the reflected wave reflected by the dust in the exhaust gas is shifted by the Doppler effect. In particular, a method for calculating the dust concentration by integrating the areas of the Doppler frequency distribution of the reflected wave intensity is described. In addition, the above publication discloses that the upper blowing lance height and the amount of oxygen supply gas (oxygen blowing amount) are controlled in accordance with the dust concentration measured by this dust concentration measuring method.

  The dust in the exhaust gas of a general combustion furnace is mainly composed of fine particles of an ash compound (so-called ash) such as CaO. However, the exhaust gas of the steelmaking furnace contains a relatively large amount of fine particles containing iron (iron-based particles), and the ratio changes. In the operation of a steelmaking furnace, the increase in iron-based particles in the exhaust gas leads to a decrease in the yield of the steel to be produced and the adhesion of metal to the furnace mouth, so the iron-based particles in the dust, not the entire dust in the exhaust gas. It is considered that productivity can be further improved by adjusting the operating parameters according to the amount of water.

  However, the dust concentration measurement method described in the above publication can grasp the total amount of dust, but cannot grasp the type of dust. For this reason, even if the dust density | concentration measuring method described in the said gazette is applied, an operating condition cannot be adjusted according to the quantity of iron-type particle | grains.

JP 2007-071820 A

  In view of the above inconveniences, an object of the present invention is to provide a method for operating a steelmaking furnace in which operating conditions can be adjusted according to the amount of iron-based particles in exhaust gas.

  The invention made to solve the above problems is a method of operating a steelmaking furnace that generates dust, the step of irradiating the exhaust gas flowing through the flue with microwaves, the step of detecting reflected waves due to dust in the exhaust gas And a Doppler frequency measurement step having a step of calculating a frequency distribution of the intensity of the reflected wave, a step of extracting the intensity of the reflected wave having a frequency corresponding to the iron-based particles in the dust, and the iron Adjusting the operating conditions of the furnace according to the intensity of the reflected wave of the frequency corresponding to the system particles, and the frequency corresponding to the iron-based particles is generated in the furnace with the propagation angle of the microwave as θ A method for operating a steelmaking furnace, characterized by the frequency of the reflected wave estimated from the sin θ component of the iron-based particle velocity predicted from the particle size and density of the iron-based particles and the flow rate of the exhaust gas The

  The method for operating the steelmaking furnace is the reflection estimated from the sin θ component of the velocity of iron-based particles in the intensity distribution of the Doppler frequency obtained by irradiating the exhaust gas flowing through the flue with microwaves and detecting the reflected waves. By deriving the intensity of the wave frequency, a value highly correlated with the amount of iron-based particles in the exhaust gas can be obtained. In addition, the operation method of the steelmaking furnace adjusts the operating conditions of the furnace based on a value highly correlated with the amount of iron-based particles in the exhaust gas, so it is possible to improve yield and suppress adhesion of metal to the furnace mouth Therefore, productivity can be improved. The “propagation angle” means a microwave irradiation angle with respect to a direction perpendicular to the flow direction of the exhaust gas.

  The estimation of the frequency corresponding to the iron-based particles includes the Doppler frequency measurement step, the step of investigating the particle size distribution of the dust by sampling the dust contained in the exhaust gas, the flow rate and temperature measurements of the exhaust gas, and the flue Calculating the flow velocity of the exhaust gas from the cross-sectional area of the above, the step of converting the peak value of the frequency distribution obtained in the Doppler frequency measurement step into the sin θ component of the absolute velocity of the particles contained in the dust, and the particle size distribution of the dust And a step of calculating an absolute velocity for each type of particles that can be included in the dust based on the flow velocity of the exhaust gas, and a velocity component that contributes to the Doppler effect for each particle type from the absolute velocity for each particle type, and The step of deriving the relationship with the propagation angle, and the propagation angle that matches the sin θ component of the absolute velocity converted from the peak value of the frequency distribution using the above relationship. The method may include a step of estimating the degree and a step of determining the frequency of the reflected wave by the iron-based particles in the frequency distribution based on the estimated propagation angle.

  Thus, the estimation of the frequency corresponding to the iron-based particles is performed by the Doppler frequency measurement step, the particle size distribution investigation step, the exhaust gas flow velocity calculation step, the sin θ component conversion step, the absolute velocity calculation step, the relationship derivation step, and the propagation angle estimation step. And the frequency determining step, the absolute velocity for each particle type is calculated from the combination of each peak of the particle size distribution and the density for each assumed dust type. For this reason, the kind (material and particle size) of the dust corresponding to the peak value of the frequency distribution obtained in the Doppler frequency measurement process can be estimated. Therefore, the productivity can be more reliably improved by adjusting the operating conditions of the furnace based on the intensity of the frequency corresponding to the iron-based particles estimated in this way.

  Thus, the operation method of the steelmaking furnace of this invention can adjust an operating condition according to the quantity of the iron-type particle | grains in waste gas.

It is a flowchart which shows the procedure of the operating method of the steelmaking furnace of one Embodiment of this invention. It is a schematic diagram which shows the structure of the measuring apparatus used for the operating method of the steelmaking furnace of FIG. It is a flowchart which shows the procedure of the preliminary investigation in the operating method of the steelmaking furnace of FIG. It is Doppler frequency distribution measured by the preliminary | backup investigation in the Example of the operating method of the steelmaking furnace of this invention. It is the frequency distribution of the particle size of the dust measured by the same preliminary survey as FIG. 6 is an integrated distribution of the particle size of dust in FIG. 5. It is a figure which shows the relationship between the sin (theta) component of the speed | rate of the coarse-grained dust derived | led-out by the same prior survey as FIG. 4, and a propagation angle. It is a figure which shows the relationship between the sin (theta) component of the speed | velocity | rate of the fine-particle dust derived | led-out by the same preliminary investigation as FIG. 4, and a propagation angle. It is a graph which shows the change over time of the intensity | strength of the reflected wave of the frequency corresponding to the iron-type particle | grains in the Example of the operating method of the steelmaking furnace of this invention, and oxygen blowing amount. It is a graph which shows the change over time of the intensity | strength of the reflected wave of the frequency corresponding to the iron-type particle | grains, and the oxygen blowing amount in the comparative example of the operating method of the steelmaking furnace of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[Operation method of steelmaking furnace]
In FIG. 1, the procedure of the operating method of the steelmaking furnace which concerns on one Embodiment of this invention is shown. The operation method of the steelmaking furnace is an operation method that can optimize the operating conditions of the steelmaking furnace that generates dust (fine particles).

  The method for operating the steelmaking furnace can be applied to various steelmaking furnaces such as blast furnaces, converters, electric furnaces, smelting furnaces, etc., but typically impurities in hot metal are removed by blowing oxygen from a lance. Applicable to converters. In the converter, dust (dust) containing non-ferrous particles such as iron-based particles and oxides is generated due to the generation of CO gas and fumes during the reaction, and flows out into the flue together with the exhaust gas.

As shown in FIG. 2, the operation method of the steelmaking furnace is arranged in a nozzle 2 provided in a flue 1 for discharging exhaust gas from a steelmaking furnace (not shown), and a microwave having a constant frequency is applied to the flue. A Doppler measuring device 3 is used that detects the intensity of the reflected wave due to dust in the exhaust gas that irradiates and flows through the flue. In such a configuration, the propagation angle θ of the microwave that can reach the dust in the flue 1 from the Doppler measurement device 3 substantially depends on the length and the inner diameter of the nozzle 2. However, since the propagation angle θ may be observed by the Doppler measuring apparatus 3 after being reflected a plurality of times, strictly speaking, the propagation angle θ is wider than the viewing angle determined by the geometric shape of the nozzle 2. In the drawing, the component (v _s · sin θ) contributing to the Doppler effect of the absolute velocity vs of dust, which will be described in detail later, is indicated by arrows.

  In the operation method of the steelmaking furnace, the intensity distribution of the Doppler frequency (difference between the frequency of the irradiated microwave and the frequency of the reflected wave) in the reflected wave due to dust when the exhaust gas flowing through the flue 1 is irradiated with the microwave. Measuring step <Step S1: Doppler frequency measurement step> and extracting the intensity of the reflected wave having a frequency corresponding to the iron-based particles in the dust from the Doppler frequency distribution <Step S2: intensity extraction step> A step of adjusting the operating conditions of the furnace in accordance with the intensity of the reflected wave having a frequency corresponding to the extracted iron-based particles (step S3: operating condition adjusting step).

<Doppler frequency measurement process>
The Doppler frequency measurement step of step S1 includes a step of irradiating the exhaust gas flowing through the flue with a microwave, a step of detecting a reflected wave due to dust in the exhaust gas, and a step of calculating a frequency distribution of the intensity of the reflected wave. .

<Strength extraction process>
In the intensity extraction step of step S2, the intensity of the reflected wave in a preset frequency range is extracted as a reflected wave corresponding to the iron-based particle (a reflected wave observed when the iron-based particle reflects the microwave). The frequency at which this intensity is extracted is defined as the sin θ component (v of the iron-based particle velocity v _s predicted from the particle size and density of the iron-based particles that can be generated in the furnace and the exhaust gas flow velocity, where θ is the propagation angle of the microwave. The frequency of the reflected wave estimated from ( _s · sin θ).

  The exhaust gas flow rate may be a representative value of the flow rate under normal operating conditions of the furnace, instead of the actual measurement value. Thereby, since the frequency corresponding to iron-type particle | grains can be predetermined, the calculation load at the time of operation can be reduced.

  The estimation of the frequency of the reflected wave corresponding to the iron-based particles whose strength is extracted in this intensity extraction step corresponds to the iron-based particles discharged in the steel-making furnace by operating the steel-making furnace in advance, as will be described later. Preferably, this is done through a preliminary survey that estimates the Doppler frequency.

In addition, the intensity extraction of the reflected wave preferably extracts a certain frequency range including the frequency of the reflected wave estimated from the sin θ component (v _s · sin θ) of the iron-based particle velocity v _{s in} the intensity distribution. However, peak intensity (intensity at the maximum point of the graph) within a certain frequency range may be extracted as representative intensity.

<Operation condition adjustment process>
In the operation condition adjustment step of step S3, the operation conditions of the steelmaking furnace, such as the amount of oxygen blown during oxygen blowing, are adjusted according to the intensity of the reflected wave having a frequency corresponding to the iron-based particles. Specifically, when the intensity of the reflected wave having a frequency corresponding to the iron-based particles is excessively increased, for example, adjustment of reduction of the oxygen blowing amount or the like may be performed so as to suppress generation of the iron-based particles.

<Preliminary survey>
As shown in FIG. 3, the preliminary survey is performed in the preliminary operation of the steelmaking furnace, and the same Doppler frequency measurement process (Step S11: Doppler frequency measurement process) as in Step S1 and sampling of dust contained in the exhaust gas. A step of investigating the particle size distribution of the dust (step S12: particle size distribution examining step), a step of calculating the flow rate of the exhaust gas from the measured values of the flow rate and temperature of the exhaust gas and the cross-sectional area of the flue (step S13: flow rate calculating step); The step of converting the peak value of the frequency distribution obtained in the Doppler frequency measurement step of Step S11 into the sin θ component of the absolute velocity of the particles contained in the dust (Step S14: sin θ component conversion step), the particle size distribution of the dust, and the exhaust gas The step of calculating the absolute velocity for each type of particles that can be contained in the dust (step S15: Absolute velocity calculation step) and a step of deriving the relationship between the velocity component contributing to the Doppler effect for each particle type and the propagation angle θ from the absolute velocity for each particle type (step S16: relationship derivation step) ) And the relationship derived in the relationship deriving step in step S16, and estimating the propagation angle that matches the sin θ component of the absolute velocity obtained by converting the peak value of the frequency distribution in the sin θ component converting step in step S14 (step S17: A propagation angle estimation step) and a step of determining the frequency of the reflected wave by the iron-based particles in the frequency distribution obtained in the Doppler frequency measurement step of Step S11 based on the estimated propagation angle θ (Step S18: frequency determination step). It is good to have. The “preliminary operation” means an operation that is performed prior to an operation in which the operation conditions are adjusted by the operation method of the steelmaking furnace, and it does not matter whether or not the steel obtained in this preliminary operation is commercialized.

(Doppler frequency measurement process)
In the Doppler frequency measurement process of Step S11, similarly to the Doppler frequency measurement process of Step S1 of FIG. 1, a process of irradiating the exhaust gas flowing through the flue with microwaves, a process of detecting a reflected wave due to dust in the exhaust gas, The intensity distribution of the Doppler frequency due to the dust in the exhaust gas is obtained by performing the step of calculating the frequency distribution of the intensity of the reflected wave.

(Particle size distribution survey process)
In the particle size distribution investigation step in step S12, dust in the exhaust gas is collected and the particle size distribution is measured. Examples of the dust collection method include a method of sampling the collected water of a wet dust collector provided in the exhaust gas flow path. As a method for measuring the particle size distribution of dust, for example, a laser diffraction method can be applied. The particle size distribution of dust may be obtained as a frequency distribution based on volume, for example.

(Flow velocity calculation process)
In the flow velocity calculation step in step S13, the exhaust gas flow rate and the exhaust gas temperature are measured, and the exhaust gas velocity in the flue is calculated from these measured values and the flue cross-sectional area. The exhaust gas flow rate can be calculated, for example, by detecting a differential pressure of a throttling mechanism of the exhaust gas flow path or by installing a flue venturi flow meter. The exhaust gas velocity V [m / s] is V = Q × (T + 273) / 273, where the exhaust gas flow rate is Q [Nm ³ / s], the exhaust gas temperature T [° C.], and the cross-sectional area in the flue is S [m ² ]. / S. As the exhaust gas temperature used for calculating the exhaust gas velocity V, a detection value of a thermometer arranged in the vicinity of the Doppler frequency measurement position is used, or is estimated from detection values of a plurality of thermometers arranged before and after the Doppler frequency measurement position. The temperature at the Doppler frequency measurement position can be used.

(Sin θ component conversion step)
In the sin θ component conversion step of step S14, a component (sin θ component) in a direction perpendicular to the Doppler measurement device of the absolute velocity of the particle corresponding to the peak frequency of the intensity distribution of the Doppler frequency obtained in the Doppler frequency measurement step is calculated. .

Here, the Doppler frequency f [Hz] is f = (2v _s · sin θ) / λ where the absolute velocity of the particles is v _s [m / s] and the wavelength of the microwave to be irradiated is λ [m]. A relationship is established. Therefore, the sin θ component of the absolute velocity of the particle corresponding to the Doppler frequency f can be expressed by v _s sin θ = f · λ / 2.

(Absolute speed calculation process)
The absolute velocity calculation process in step S15, the absolute velocity v _s of the particles corresponding to the peak of the particle size distribution measured with a particle size distribution survey process, is likely to be discharged the material of the particles from the steelmaking furnace, and comparison The calculation is performed on the assumption that the iron-based particles having a large target density and non-ferrous particles (for example, CaO, SiO _2, etc.) having a relatively low density.

Specifically, the terminal velocity when particles having a particle size (diameter) corresponding to the peak of the particle size distribution and made of an assumed material drop by gravity in a stationary exhaust gas is calculated, and the exhaust gas velocity is calculated. By subtracting from, the expected absolute velocity of the particles _vs is calculated.

The termination velocity of the particles in the exhaust gas is calculated using the particle size of the particles corresponding to the peak of the particle size distribution and the density of the material assumed as the particles. More specifically, the particle termination velocity u _s [m / s] includes the particle diameter d [m], the particle density ρ _s [kg / m ³ ], and the exhaust gas density ρ _f [kg / m ^3]. ], The viscosity coefficient of exhaust gas is μ _f [Pa · s], the gravitational acceleration is g [m / s ² ], and the Reynolds number is Re [dimensionless number].

Examples of the iron-based particles include metallic iron (Fe) and iron oxide (FeO). The particle density is assumed to be 7000 kg / m ³ .

On the other hand, examples of the non-ferrous particles include calcium oxide (CaO) and silicon oxide (SiO ₂ ), and the density is assumed to be 3000 kg / m ³ .

(Relationship derivation process)
In the relationship deriving step in step S16, the relationship between the propagation angle θ of each particle and the velocity component contributing to the Doppler effect is calculated from the absolute velocity for each particle type (diameter and material) calculated in the absolute velocity calculating step. It specifies by showing in figure.

(Propagation angle estimation process)
In the propagation angle estimation step of step S17, in the relationship between the propagation angle θ of each particle specified in the relationship derivation step and the velocity component contributing to the Doppler effect, the peak frequency of the intensity distribution of the Doppler frequency calculated in the sin θ component conversion step is used. Estimate the propagation angle θ that matches the sin θ component of the absolute velocity of the corresponding particle. Specifically, on the graph created in the relationship derivation step, the value of the sin θ component of the absolute velocity calculated for each peak frequency of the intensity distribution in the sin θ component conversion step is shown by a straight line, and an intersection with each graph is obtained. The propagation angle θ is specified.

(Frequency determination process)
In the frequency determination step of step S18, the one obtained by reflection of iron-based particles in the peak frequency of the intensity distribution obtained in the Doppler frequency measurement step based on the propagation angle θ estimated in the propagation angle estimation step. Identify peaks that are considered.

  Thus, as shown in FIG. 3, the estimation of the frequency corresponding to the iron-based particles is performed using the Doppler frequency measurement step, the particle size distribution investigation step, the flow velocity calculation step, the sin θ component conversion step, and the absolute By performing the preliminary calculation including the velocity calculation step, the relationship derivation step, the propagation angle estimation step, and the frequency determination step, the frequency corresponding to the iron-based particles can be estimated more accurately.

<Advantages>
As described above, in the method of operating a steelmaking furnace, in the intensity extraction process of step S2, the estimated speed of the iron-based particles is estimated from the intensity distribution of the Doppler frequency measured in the Doppler frequency measurement process of Step S1. Since the intensity corresponding to the sin θ component is extracted, a value highly correlated with the amount of iron-based particles in the exhaust gas can be obtained. Moreover, since the operation method of the said steelmaking furnace adjusts the operating condition of a furnace based on the intensity | strength extracted at the intensity | strength extraction process of step S2 in the operating condition adjustment process of step S3, it is desirable of the iron-type particle | grains in waste gas. The rise can be suppressed, and the productivity can be improved by improving the yield and suppressing the adhesion of the metal to the furnace opening.

[Other Embodiments]
The said embodiment does not limit the structure of this invention. Therefore, in the above-described embodiment, the components of each part of the above-described embodiment can be omitted, replaced, or added based on the description and common general knowledge of the present specification, and they are all interpreted as belonging to the scope of the present invention. Should.

  As long as each process of the operation method of the said steelmaking furnace is performed prior to the process using the result obtained by the process, those orders can be arbitrarily changed.

  In the operation method of the steelmaking furnace, the estimation of the frequency corresponding to the iron-based particles may be performed by a method different from the above-described preliminary survey, for example, empirically, based on data of other steelmaking furnaces. Also good.

  EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.

  The operation method of the steelmaking furnace was applied to an oxygen blowing process for decarburization and phosphorus removal treatment in a converter, and the effect was confirmed.

<Preliminary survey>
First, the above-mentioned pre-adjustment was performed at the time of actual oxygen blowing in the converter. As the converter, a converter having a furnace wall mainly made of a refractory made of MgO-C and having a standard capacity of 250 tons was used.

  Specifically, the hot metal charging amount was 250 t or more and 270 t or less. As hot metal before blowing, a C concentration of about 4% by mass, a P concentration of 0.01% to 0.1% by mass, and a Si concentration of 0.01% to 0.6% by mass are used. Using. The amount of scrap blended in the hot metal was 40 t or less.

  In this decarburization and dephosphorization treatment, a dephosphorizing agent (CaO source), a heating agent, a basicity adjusting agent, a refractory protective material, and a temperature adjusting agent / iron source are added to the hot metal, and oxygen is introduced from the top of the converter. Was blown to remove carbon and phosphorus in the hot metal.

  Burnt lime was used as a dephosphorizing agent. An Fe—Si alloy was used as the heat raising agent. Meteorite was used as the basicity adjuster. Light fired dolomite was used as a refractory protective agent. Mill scale and iron ore were used as the temperature regulator and iron source.

As an upper blowing lance for blowing oxygen into the converter, a nozzle having a nozzle diameter of 55 mm, a nozzle inclination angle of 15 °, and six nozzles was used. As the top blowing conditions by this top blowing lance, the lance height is set to 3.0 m or more and 3.2 m or less, and the blowing oxygen flow rate per unit mass of the molten iron is set to 2.2 Nm ³ / min / t or more and 2.8 Nm ³ / min. / T or less.

Further, N ² , Ar or CO is used as a stirring gas from the bottom of the converter to stir the hot metal at a flow rate of 6 Nm ³ / min to 15 Nm ³ / min (0.02 Nm in terms of unit mass of hot metal). ³ / min / t to 0.06 Nm ³ / min / t).

  The C concentration of the hot metal after blowing was set to more than 0% and 1% by mass or less. Moreover, as P concentration of the hot metal after blowing, it was set as 0.004 mass% or more and 0.025 mass% or less.

(Doppler frequency measurement process)
In the Doppler frequency measurement step, a Doppler measurement device for measuring the Doppler frequency distribution of the reflected wave due to dust in the exhaust gas was used with a microwave frequency of 24.5 GHz applied to the exhaust gas. The Doppler measuring device was attached to the tip of a nozzle made of a steel pipe for piping having a nominal pressure of 10K and a nominal diameter of 40A of JIS-B2220 (2012) disposed in the flue using a pipe flange.

  The Doppler frequency distribution of the reflected wave is a frequency distribution of integrated values for each frequency of 50 Hz by using a microwave dust concentration meter of Ace Giken as a Doppler measurement device, taking the detection signal into a personal computer, and processing the software. Got.

  FIG. 4 shows the distribution of the intensity of the obtained reflected wave for each Doppler frequency. As shown in the figure, the obtained Doppler frequency distribution had peaks of reflected wave intensity at 200 Hz, 500 Hz, 700 Hz, and 1050 Hz.

(Flow velocity calculation process)
At the time of oxygen blowing in the converter, the exhaust gas flow rate was measured, the exhaust gas temperature at the position where the Doppler measuring device was installed was estimated, and the exhaust gas flow velocity was calculated. Specifically, the measured exhaust gas flow rate was 20 Nm ³ / s, and the temperature at the installation position of the Doppler measuring apparatus was estimated to be 1000 ° C. As a result, the flow rate of the exhaust gas at the position where the Doppler measuring device was installed was calculated to be 10.4 m / s.

(Particle size distribution survey process)
After completion of oxygen blowing, sampling the dust collection water thickener that is in contact with the exhaust gas discharged by the above oxygen blowing and concentrating the collected dust that has taken in the dust in the exhaust gas, and investigating the particle size distribution of the dust contained in the exhaust gas did. That is, the collected sample is an average of the entire dust discharged from the start to the end of oxygen blowing.

  In the converter used, the exhaust gas comes into contact with the dust collection water in two stages to remove the dust, and the dust collection water of the first stage dust collection equipment contains particles with a relatively large particle size. The dust collection water in the second stage dust collection facility takes in particles with a relatively small particle size. Here, the dust captured by the dust collection water of the first stage dust collection equipment is called coarse dust, and the dust captured by the dust collection water of the second stage dust collection equipment is called fine dust.

  The particle size distribution of the coarse dust and fine dust was measured by a laser diffraction particle size distribution measuring device “SALD-3000S” manufactured by Shimadzu Corporation. 5 and 6 show the frequency distribution and cumulative distribution of the particle size on the volume basis of coarse dust and fine dust.

  From the cumulative distribution of the particle sizes, the coarse dust was estimated to have a 10% by volume particle size of 80 μm, a 50% by volume particle size of 200 μm, and a 90% volume particle size of 350 μm. On the other hand, the fine dust was estimated to have a 10 volume% particle diameter of 1.5 μm, a 50 volume% particle diameter of 3 μm, and a 90 volume% particle diameter of 10 μm.

(Absolute speed calculation process)
First, for each particle having a particle size estimated in the particle size distribution investigation step, a case of iron particles (density 7000 kg / m ³ ) as a kind of iron-based particles and a case of calcium oxide particles (density) as a kind of non-ferrous particles It was divided into the case of 3000 kg / m ³ ), and the terminal velocity due to free fall in the stationary exhaust gas was calculated.

  As a result, when it is assumed that the terminal speed of coarse dust is iron-based particles, 0.48 m / s at a particle diameter of 80 μm, 2.01 m / s at a particle diameter of 200 μm, and 3.52 m at a particle diameter of 350 μm. / S. On the other hand, when it is assumed that the terminal speed of coarse dust is non-ferrous particles, the particle size is 0.21 m / s at a particle size of 80 μm, 1.14 m / s at a particle size of 200 μm, and 2.00 m / s at a particle size of 350 μm. s. The terminal speed of fine dust was 0.00 m / s in both cases of iron-based particles and non-ferrous particles. Further, the terminal velocity of the coarse iron-based dust having a particle diameter of 750 μm was calculated to be 7.55 m / s.

  The absolute velocity of each particle was calculated by subtracting these terminal velocities from the exhaust gas flow velocity calculated in the flow velocity calculation step. As a result, the absolute velocity of each particle of the iron-based coarse dust is 9.88 m / s at a particle size of 80 μm, 8.35 m / s at a particle size of 200 μm, 6.84 m / s at a particle size of 350 μm, and a particle size of 0.8. It was calculated to be 2.81 m / s at 75 mm. The absolute velocity of each particle of non-ferrous coarse dust is 10.15 m / s at a particle size of 80 μm, 9.22 m / s at a particle size of 200 μm, 8.36 m / s at a particle size of 350 μm, and a particle size of 0.75 mm. And calculated to be 6.07 m / s. On the other hand, the absolute velocity of each particle of ferrous and non-ferrous fine dust was calculated to be 10.36 m / s.

(Relationship derivation process)
The component (sin θ component) contributing to the Doppler effect of the velocity of each particle calculated in the absolute velocity calculation step was calculated for each case where the microwave propagation angle θ was changed from 0 ° to 90 °. FIG. 7 shows the relationship between the velocity component contributing to the Doppler effect of iron-based coarse dust and the propagation angle for each particle diameter, and FIG. 8 shows the velocity component and propagation angle contributing to the Doppler effect of non-ferrous coarse dust. In addition, the relationship between the velocity component contributing to the Doppler effect and the propagation angle of non-ferrous coarse dust, and ferrous and non-ferrous fine dust having almost the same absolute velocity is shown. Indicates.

(Sin θ component conversion step)
The peak frequencies of the reflected waves obtained in the Doppler frequency measurement step, 200 Hz, 500 Hz, 700 Hz, and 1050 Hz, are converted into sin θ components of the absolute velocity of the particles, and lines indicating these converted values are shown in FIGS. 7 and 8. I added.

(Propagation angle estimation process)
7 and 8, a point where the line indicating the velocity component of each particle graphed in the relationship deriving step intersects with the line indicating the converted value added in the sin θ component converting step is confirmed, and the propagation angle θ is shown in FIG. It is estimated that it is a shaded area in. In this device configuration, there are particles approaching the Doppler measurement device and particles moving away, that is, since the Doppler effect differs depending on the position of the particles, two peak frequencies are observed with particles of the same type and the same diameter.

  Specifically, in FIG. 7, coarse dust (80 to 350 μm) corresponds to a Doppler frequency of 500 Hz or 700 Hz when the propagation angle is about 30 °, and a Doppler frequency of 700 Hz or 1050 Hz when the propagation angle is about 40 °. It is judged that it corresponds. That is, the value of the propagation angle θ in this embodiment is estimated to be 30 ° and 40 °. The distribution of Doppler frequency further has a peak of 200 Hz, but relatively large iron-based particles are confirmed in the flue upstream of the dust collection facility from which the collected water was collected. Is considered to correspond to iron-based particles having a particle diameter of 750 μm. Further, in FIG. 8, it is determined that the propagation angle of 30 ° corresponds to the Doppler frequency of 700 Hz, and the propagation angle of 40 ° corresponds to the Doppler frequency of 1050 Hz. Therefore, it can be considered that the reflected waves with the Doppler frequencies of 200 Hz and 500 Hz are due to only the iron-based particles and are not affected by the non-ferrous particles.

(Frequency determination process)
Based on the Doppler propagation angle θ estimated in the propagation angle estimation step, the frequency range to be referred to in order to adjust the operating condition of the furnace was determined in the Doppler frequency distribution of the reflected wave. Specifically, oxygen blowing was performed by adjusting the operating conditions of the furnace, assuming that reflected waves with a Doppler frequency of 50 Hz to 600 Hz correspond to iron-based particles. The reflected wave having a Doppler frequency of 50 Hz was excluded because it was confirmed by actual measurement that it was detected by vibration of the apparatus even when particles were not discharged. That is, since the equipment vibration was 50 Hz or less, it was determined that the reflected wave having a Doppler frequency of 50 Hz or less does not depend on the dust in the exhaust gas.

<Operation>
As an example of the method for operating a steelmaking furnace of the present invention, while performing oxygen blowing using the converter, the integrated value of the intensity of reflected waves in the frequency range corresponding to the iron-based particles (the graph area of the frequency distribution) ) To change the oxygen blowing amount. On the other hand, as a comparative example of the operation method of the steelmaking furnace, the oxygen blowing amount was changed based on the integrated value of the intensity of the reflected wave in the entire frequency range of the Doppler frequency distribution while performing oxygen blowing under the same conditions as in the above example. The operation to do. Since the operation method for reducing the oxygen blowing amount when dust is generated has been conventionally performed, a detailed description of the action by adjusting the oxygen blowing amount is omitted.

  In FIG. 9, the change of the integrated value of reflected wave intensity | strength corresponding to the iron-type dust in the said Example and oxygen blowing amount is shown. Further, in FIG. 10, in addition to the change in the integrated value of the reflected wave intensity at all frequencies and the oxygen blowing amount in the comparative example, the integrated value of the reflected wave intensity corresponding to the iron-based dust similar to the example for reference. Shows changes.

  As a general theory, for example, as shown in FIG. 10, even if the operating condition (oxygen blowing amount) is kept constant, the total discharge amount of dust shows a high value immediately after the start of oxygen blowing, It gradually decreases until just before the end of the refining process. On the other hand, the discharge amount of iron-based dust increases immediately after the start of oxygen blowing and then gradually decreases, but shows a tendency to increase again between 400 seconds and 500 seconds after the start of oxygen blowing. On the other hand, in the embodiment of the operation method shown in FIG. 9, the increase in iron-based particles could be suppressed by detecting the increasing tendency of the iron-based particles and reducing the oxygen blowing amount. In the comparative example of the operation method shown in FIG. 10, this increase in iron-based particles could not be suppressed.

  As described above, the method for operating a steelmaking furnace according to the present invention can effectively suppress iron-based particles in exhaust gas, and can improve steelmaking efficiency by improving yield and suppressing adhesion of metal to the furnace mouth. It could be confirmed.

  The method for operating a steelmaking furnace of the present invention can be applied to all steelmaking furnaces that generate dust, but can be suitably applied particularly to the operation of a converter.

1 Flue 2 Nozzle 3 Doppler Measuring Device

Claims (2)

A method of operating a steelmaking furnace that generates dust,
A step of irradiating the flue gas flowing through the flue with microwaves, a step of detecting a reflected wave due to dust in the flue gas, and a step of calculating the frequency distribution of the intensity of the reflected wave; and
Extracting the intensity of the reflected wave at a frequency corresponding to the iron-based particles in the dust from the frequency distribution;
Adjusting the operating conditions of the furnace according to the intensity of the reflected wave of the frequency corresponding to the iron-based particles,
The frequency corresponding to the iron-based particles is the sin θ component of the velocity of the iron-based particles predicted from the particle size and density of the iron-based particles that can be generated in the furnace and the flow rate of the exhaust gas, where the propagation angle of the microwave is θ. A method for operating a steelmaking furnace, characterized in that the frequency of the reflected wave is estimated from the above. The estimation of the frequency corresponding to the iron-based particles is
The Doppler frequency measurement step,
Investigating the particle size distribution of the dust by sampling the dust contained in the exhaust gas,
Calculating the flow rate of the exhaust gas from the measured values of the flow rate and temperature of the exhaust gas and the cross-sectional area of the flue;
Converting the peak value of the frequency distribution obtained in the Doppler frequency measurement step into a sin θ component of the absolute velocity of particles contained in dust,
Calculating an absolute velocity for each type of particles that can be contained in the dust based on the particle size distribution of the dust and the flow rate of the exhaust gas;
Deriving the relationship between the velocity component contributing to the Doppler effect for each particle type and the propagation angle from the absolute velocity for each particle type,
Using the above relationship, estimating a propagation angle that matches the sin θ component of the absolute velocity converted from the peak value of the frequency distribution;
The method for operating a steelmaking furnace according to claim 1, wherein the method comprises: determining a frequency of a reflected wave by the iron-based particles in the frequency distribution based on the estimated propagation angle.