阅读说明：本技术 转炉的操作方法 (Method for operating converter ) 是由 天野胜太 高桥幸雄 菊池直树 三木祐司 于 2018-05-07 设计创作，主要内容包括：每当从顶吹枪顶吹氧气而实施铁液的脱碳精炼时,抑制铁液的摆动,并抑制气泡破裂及与气泡破裂相伴的喷溅物。在使用下端设置有拉瓦尔喷嘴的顶吹枪,并从拉瓦尔喷嘴向转炉内的铁水浴面喷吹氧气而对转炉内的铁液进行脱碳的转炉的精炼方法中,以蓄积氧指标S(F)成为40以下的方式调整来自顶吹枪的送氧速度及枪高度LH中的任一方或双方。(When decarburization refining of molten iron is performed by blowing oxygen gas from the top of a top-blowing lance, the swinging of the molten iron is suppressed, and the bubble collapse and the splashes accompanying the bubble collapse are suppressed. In a method for refining a converter in which a top-blowing lance having a laval nozzle at its lower end is used and oxygen is blown from the laval nozzle to the molten iron surface in the converter to decarburize molten iron in the converter, either or both of the oxygen feed rate from the top-blowing lance and the lance height LH are adjusted so that the accumulated oxygen index S (F) becomes 40 or less.)

1. A method for operating a converter, which is a method for refining a converter, wherein a top-blown lance having a laval nozzle at a lower end thereof is used, oxygen is blown from the laval nozzle to a bath surface of molten iron in the converter to decarburize the molten iron in the converter,

adjusting the oxygen feeding rate Q from the top-blowing lance so that the oxygen accumulation index S (F) in the furnace satisfies the following expression (3)_gAnd a lance height LH, wherein the oxygen accumulation index S (F) in the furnace is determined based on an oxygen flow rate F (Nm) per unit area of a fire point determined by the following formula (1)³/(m²Xs)), the oxygen gas flow rate F, and the following formula (2),

[ mathematical formula 1]

S(F)≤40…(3)

In the formula (1), the compound (I),

n is the number (-) of laval nozzles provided at the lower end of the top-blowing lance,

d_cis the throat diameter (mm) of the laval nozzle,

Q_gis the oxygen delivery rate (Nm) from the top-blowing lance³/s)，

P₀Is a supply pressure (Pa) of the oxygen gas to the Laval nozzle,

v_gcis the molten iron bath surface calculated according to the gun height LH (m)Is the flow velocity (m/s) of the oxygen on the central axis of the laval nozzle,

r is a radius (mm) of a pit formed by collision of the oxygen gas against the molten iron bath surface,

l is the depth (mm) of the pit,

in the formula (2), the compound represented by the formula (I),

α is a constant ((m)²×s)/Nm³)，

F₀Is a constant (Nm)³/(m²×s))，

Δ t is the data collection interval(s).

2. The method of operating a converter according to claim 1,

the constant alpha is determined by monitoring the actual value of the accumulated oxygen index S (F) calculated by the expression (2) and an unknown oxygen amount which is the difference between an input oxygen amount, which is the sum of the oxygen supply amount from the top-blowing lance and the oxygen amount in the sub-raw material charged into the converter, and an output oxygen amount, which is the sum of the CO gas and CO present in the converter exhaust gas, during the blowing₂Gas, oxygen and consumed as SiO in the desilication reaction₂The sum of the oxygen amounts present in the furnace.

Technical Field

The present invention relates to a method for operating a converter that melts molten steel from molten iron by blowing oxygen gas into molten iron from a plurality of laval nozzles provided in a top-blowing lance to suppress discharge of molten iron to the outside of the converter. Here, "molten iron" refers to molten iron or molten steel, and when the two can be clearly distinguished, they are described as "molten iron" or "molten steel".

Background

In the decarburization refining of the converter, an operation of increasing the amount of oxygen supplied per unit time (also referred to as "oxygen feed rate") is employed from the viewpoint of improving the productivity of the converter. However, when the oxygen supply amount per unit time is increased, the amount of iron that is scattered to the outside of the furnace as dust or the like and the amount of iron that adheres and accumulates in the furnace wall or the vicinity of the furnace opening increases. The loss of iron is finally recovered and reused as an iron source, but if the amount of iron increases, the cost required for dust recovery and removal of iron adhering to the vicinity of the furnace opening increases and the operating rate of the converter decreases, and therefore, this is one of the important problems to be solved.

Therefore, much research and study has been made on the generation and suppression of dust in the decarburization refining of the converter. As a result, it is known that the mechanism of generation of dust is roughly classified into 2 mechanisms described below, and the amount of dust generated and the generation ratio of dust generated by each generation mechanism change as the blowing progresses.

[1] Dust is generated by the collapse of bubbles (splashed matter (pig iron nuggets are scattered) or the scattering of granular iron accompanying the detachment of the melt surface of bubbles).

[2] Dust is generated due to smoke (evaporation of iron atoms).

On the other hand, it is known that the decarburization reaction rate by the top-blown oxygen from the top-blowing lance is an oxygen supply rate limit during a period until the carbon concentration in the molten iron reaches the critical carbon concentration, and that the decarburization reaction rate by the top-blown oxygen from the top-blowing lance is a movement (diffusion) rate limit of carbon in the molten iron at a carbon concentration equal to or lower than the critical carbon concentration. However, non-patent document 1 describes that the decarburization rate based on the continuous analysis of the exhaust gas is not constant and varies even during the oxygen supply rate limiting period. As a result of direct observation of the bath surface in the decarburization refining using a small melting furnace, it is considered that, during the oxygen supply rate limiting period, if the decarburization rate fluctuates, large bubbles are generated from the bath surface, and therefore, the fluctuation in the decarburization rate is generated by the enlargement of the reaction area due to the shift from the surface reaction to the reaction in the bath.

It is known that decarburization reaction by top-blown oxygen mainly progresses at a collision interface between an oxygen jet and molten iron, a so-called "pit" called "fire point". Non-patent document 2 describes the following cases: the area of the fire point is defined as shown in the following formula (4) except that the surface area A of the pits geometrically_pEquivalent interface area A considering the influence of liquid droplets generated on the bath surface^*As shown in the following formula (5), the flow rate F is accompanied by top-blown oxygen_O2And equivalent interface area A^*Ratio of (1) to (B) oxygen load F_gThe decarburizing oxygen efficiency is decreased.

[ mathematical formula 1]

In the formula (4), d_cThe throat diameter of a Laval nozzle, I the momentum of the top-blown oxygen jet, kappa the correction coefficient of the momentum I, and sigma the surface tension of the molten iron.

However, in a refining reactor such as a converter, molten iron in the reactor oscillates with the supply of refining and stirring gas by top-blowing or bottom-blowing and the generation of CO gas by decarburization reaction. The amplitude of oscillation is maximized at so-called resonance in which the oscillation frequency of oscillation matches the natural frequency determined by the shape of the reaction vessel. Such a phenomenon is called "sloshing". When the sloshing occurs, the amount of iron adhering to and accumulating in the top-blowing lance, the furnace wall, and further the vicinity of the furnace opening increases.

Non-patent document 3 describes shaking, and describes that the natural frequency f of the cylindrical container is thereby obtained_calcAnalytically, the inside diameter D of the cylindrical vessel and the bath depth H can be calculated by the following equation (6). In equation (6), g is the acceleration of gravity, and k is a constant (═ 1.84).

[ mathematical formula 2]

Non-patent document 4, in which the vibration of a converter during decarburization refining is actually measured, describes that the vibration frequency due to the oscillation of molten iron in a commercial-scale converter is about 0.3 to 0.4 Hz. The measured value substantially coincides with the natural frequency of the converter calculated by the expression (6).

Therefore, it is known that the sloshing phenomenon occurs also in a commercial-scale converter. When the sloshing phenomenon occurs, the splashing (slag spouting) is likely to occur, and hence the amount of iron adhering to and accumulating in the top-blowing lance, the furnace wall, and further the vicinity of the furnace opening increases.

Patent document 1 describes the following refining method: in order to suppress the occurrence of splashes and spills in the operation of a converter by increasing the amount of oxygen supplied per unit time, the concentration of residual oxygen in the converter is calculated based on the amount of oxygen supplied into the converter, the flow rate of exhaust gas from the converter, the composition of the exhaust gas, the amount of molten iron components, and the amount of used secondary raw materials, and at least one of the amount of oxygen supplied, the lance height, and the flow rate of bottom-blown gas is adjusted based on the calculated concentration of residual oxygen in the converter, thereby suppressing the occurrence of splashes and spills.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2013-108153

Non-patent document

Non-patent document 1: production study, vol.22(1970) No.11.p.488

Non-patent document 2: iron and steel, vol.57(1971) No.12.p.1764

Non-patent document 3: production study, vol.26(1974) No.3.p.119

Non-patent document 4: kawasaki iron report, vol.19(1987) No.1.p.1

Disclosure of Invention

Problems to be solved by the invention

However, in the refining method of patent document 1, since the sign of spilling (slag spouting) is monitored and then the action is performed, although spilling can be detected, it is not possible to suppress bubble collapse and splashes (pig iron nugget scattering) associated with bubble collapse.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method of operating a converter, which can suppress the swing of molten iron, suppress the bubble collapse and the splashes associated with the bubble collapse, and suppress the decrease in the iron yield, every time decarburization refining of molten iron is performed by blowing oxygen gas from the top of a top-blowing lance.

Means for solving the problems

The features of the present invention for solving such problems are as follows.

[1] A method for operating a converter, which is a method for refining a converter, wherein a top-blown lance having a laval nozzle at a lower end thereof is used, oxygen is blown from the laval nozzle to a bath surface of molten iron in the converter to decarburize the molten iron in the converter,

adjusting the oxygen feeding rate Q from the top-blowing lance so that the oxygen accumulation index S (F) in the furnace satisfies the following expression (3)_gAnd a lance height LH, wherein the oxygen accumulation index S (F) in the furnace is determined based on an oxygen flow rate F (Nm) per unit area of a fire point determined by the following formula (1)³/(m²Xs)), the oxygen flow rate F, and the following formula (2).

[ mathematical formula 3]

S(F)≤40…(3)

In the formula (1), the compound (I),

n is the number (-) of laval nozzles provided at the lower end of the top-blowing lance,

d_cis the throat diameter (mm) of the laval nozzle,

Q_gis the oxygen delivery rate (Nm) from the top-blowing lance³/s)，

P₀Is a supply pressure (Pa) of the oxygen gas to the Laval nozzle,

v_gcis the flow velocity of the oxygen gas at the collision surface of the molten iron bath surface calculated from the gun height LH (m) and is the flow velocity (m/s) of the oxygen gas on the central axis of the Laval nozzle,

r is a radius (mm) of a pit formed by collision of the oxygen gas against the molten iron bath surface,

l is the depth (mm) of the pit.

In the formula (2), the compound represented by the formula (I),

α is a constant ((m)²×s)/Nm³)，

F₀Is a constant (Nm)³/(m²×s))，

Δ t is the data collection interval(s).

[2] The method for operating a converter according to [1], wherein,

the constant alpha is determined by monitoring the actual value of the accumulated oxygen index S (F) calculated by the expression (2) and an unknown oxygen amount which is the difference between an input oxygen amount, which is the sum of the oxygen supply amount from the top-blowing lance and the oxygen amount in the sub-raw material charged into the converter, and an output oxygen amount, which is the sum of the CO gas and CO present in the converter exhaust gas, during the blowing₂Gas, oxygen and consumed as SiO in the desilication reaction₂The sum of the oxygen amounts present in the furnace.

Effects of the invention

According to the invention, the oxygen supply rate Q from the top-blowing lance is defined as_gAnd an index of accumulated oxygen defined by the formula (2) as a function of the gun height LHS (F) is controlled within a predetermined range, so that not only the swing of the molten iron in the converter can be suppressed, but also the amount of iron deposited and accumulated on the top-blowing lance, the converter wall, and the vicinity of the converter mouth of the converter can be reduced.

Drawings

Fig. 1 is a graph showing a relationship between the average decarbonization oxygen efficiency η and the oxygen flow rate F per unit area of the ignition point calculated from the formula (1).

FIG. 2 is a graph showing the maximum value S (F) of the index W of falling pig iron and the oxygen accumulation index S (F) calculated according to the formula (2)_maxA graph of the relationship between.

FIG. 3 is a graph showing the maximum acceleration a of the vibration of the furnace body_maxMaximum value S (F) of oxygen accumulation index S (F) calculated according to formula (2)_maxA graph of the relationship between.

Detailed Description

The present invention will be described below with reference to embodiments of the invention. First, the original commission to achieve the present invention will be described.

The present inventors have confirmed the influence of the lance height LH of the top-blowing lance on the amount of the deposited pig iron nuggets on the furnace wall or the top-blowing lance when decarburization refining is performed by top-blowing oxygen (industrial pure oxygen) into molten iron in the converter using a 300 ton-sized converter capable of blowing stirring gas from the bottom blade port of the bottom of the converter while blowing oxygen from the top-blowing lance. Argon gas was used as the stirring gas for bottom blowing. The "lance height LH" is a distance (m) from the tip of the top-blowing lance to the molten iron bath surface when the molten iron in the converter is in a stationary state.

In the experiment, as shown in Table 1, 3 kinds of top-blowing guns (top-blowing guns A, B, C) were used, and the oxygen feed rate (oxygen supply flow rate) from the top-blowing guns was set to 750 to 1000Nm³The gun height LH was changed within the range of 2.2 to 2.8m, and the pig iron nuggets falling down into the furnace during the blowing were collected and weighed after the blowing, and the influence of the gun height LH and the blowing conditions on the amount of the pig iron nuggets adhered was confirmed.

[ Table 1]

In the test, an accelerometer is attached to a tilting axis of a converter, and the acceleration in the tilting axis direction during blowing is measured. The obtained acceleration signal is recorded in an analysis device and subjected to high-speed fourier transform processing, and the frequency of the furnace body vibration is analyzed.

In the test, the supply of oxygen from the top-blowing lance was started when the carbon concentration in the molten iron was 4.0 mass%, and the supply of oxygen was terminated when the carbon concentration in the molten steel was 0.05 mass%.

In decarburization refining of molten iron by top-blowing oxygen, the oxygen flow rate per unit area of fire F (Nm)³/(m²Xs)) is represented by the following formula (1). The oxygen flow rate per unit area of the fire F is an average flow rate during decarburization refining of oxygen which collides with each unit area of the fire at a plurality of fires which are collision portions with top-blown oxygen on the molten iron bath surface in the furnace.

[ mathematical formula 4]

In the formula (1), n is the number (-) of laval nozzles provided at the lower end of the top-blowing lance. d_cThe throat diameter (mm) of the laval nozzle. Q_gIs the oxygen delivery rate (Nm) from a top-blowing lance³/s)。P₀The pressure (Pa) of oxygen gas supplied to the Laval nozzle of the top-blowing lance. v. of_gcThe flow velocity of the oxygen gas at the collision surface of the molten iron surface calculated from the lance height LH is the flow velocity (m/s) of the oxygen gas on the central axis of the laval nozzle. r is the radius (mm) of a pit formed by the collision of oxygen against the molten iron surface. L is the depth (mm) of the aforementioned pit.

Illustrating the flow velocity v of oxygen_gc(m/s), the radius r (mm) of the pit, and the depth L (mm) of the pit.

When the gas flow in the laval nozzle is assumed to be adiabatically changingDischarge flow velocity v of gas discharged from a Laval nozzle_g0(m/s) is represented by the following formula (7). In the formula (7), g is the acceleration of gravity (m/s)²)。p_cIs the pressure at the throat of the laval nozzle (static pressure) (Pa). p is a radical of_eIs the pressure (static pressure) (Pa) at the nozzle outlet of the laval nozzle. v. of_cIs the specific volume (m) at the throat of the Laval nozzle³/kg)。v_eSpecific volume (m) at the outlet of the Laval nozzle³In kg). K is the isentropic coefficient of expansion.

[ math figure 5]

On the other hand, it is found that the flow velocity v of oxygen on the central axis of the laval nozzle after the injection from the laval nozzle_gcAs a function of the distance from the nozzle to the bath surface. Therefore, the length x of the region called potential nucleus formed just below the outlet of the laval nozzle is considered_c(m) flow velocity v of oxygen_gcIs represented by the following formula (8). In the formula (8), β and γ are constants. Therefore, if v_g0、LH、x_cIt is understood that the flow velocity v of oxygen can be calculated by using the following expression (8)_gc。

[ mathematical formula 6]

The depth L (mm) of the dimple formed on the iron bath collision surface of the jet is represented by the following expression (9). In the formula (9), ε is a constant having a dimension of 1 and is a value in the range of 0.5 to 1.0. In the present embodiment, the pit depth L is calculated with ∈ being 1.0.

[ math figure 7]

The radius r (mm) of the pit formed on the iron bath collision surface of the jet is represented by the following expression (10). In the formula (10), the compound represented by the formula (I),θ_sis the spread angle (°) of the jet.

[ mathematical formula 8]

r＝LH×tan(θ_s)…(10)

FIG. 1 is a graph showing the average decarburization oxygen efficiency eta (%) in a blow during which the carbon concentration in the blow is from 3 mass% to 1 mass% and the oxygen flow rate F (Nm) per unit area of ignition point calculated according to the formula (1)³/(m²Xs)) of the same. Average decarbonization oxygen efficiency η uses the exhaust gas flow Q_offgas(Nm³S), CO concentration in exhaust gas (C)_CO(ii) a Vol.%), CO in the exhaust gas₂Concentration (C)_CO2(ii) a Vol%) is defined by the following formula (11).

[ mathematical formula 9]

As is clear from fig. 1, the average decarbonization oxygen efficiency η decreases as the oxygen flow rate F per unit area of the ignition point increases. In other words, the oxygen flow rate F per unit area of the fire point increases, the more oxygen accumulates in the furnace.

FIG. 2 is a graph showing the maximum value S (F) of the index W of falling pig iron and the index S (F) of oxygen accumulation in the furnace during blowing_maxA graph of the relationship between. Here, the oxygen accumulation index s (f) in the furnace is defined by the following formula (2). (2) The F in the formula is the oxygen flow rate F per unit area of the ignition point calculated by the formula (1). α is a constant ((m)²×s)/Nm³)。F₀Is a constant (Nm)³/(m²Xs)). In the present embodiment, the constant α is set to 0.07 (m)²×s)/Nm³Constant F₀Set to 0.60Nm³/(m²Xs). The constant alpha is 0.05 to 0.10 (m) in accordance with the flow rate of bottom-blowing gas per unit mass of molten steel²×s)/Nm³The value of (c). Δ t is a data collection time interval (second), and in the present embodiment, for example, 1 second. (1/F) was calculated every 1 second when Δ t was 1 second and the blowing time was 20 minutes₀-1/F) and multiplying the integrated value of about 1200 times by α to calculate the oxygen storage index s (F).

[ mathematical formula 10]

The furnace dropping pig iron block index W is defined by the following formula (12). (12) The "average furnace falling pig iron mass" indicated by the denominator on the right side of the formula is an average value of the falling amount of the pig iron after completion of blowing in the test with multiple challenges.

[ mathematical formula 11]

As is clear from FIG. 2, the maximum value S (F) of the oxygen accumulation index S (F) in the furnace_maxWhen the value exceeds 40, the index W of the falling pig iron block of the furnace sharply increases.

FIG. 3 shows the maximum acceleration a of 0.35Hz, which is the natural frequency calculated from the equation (6), in the furnace vibration during blowing_maxMaximum value S (F) of oxygen accumulation index S (F) in furnace_maxA graph of the relationship between.

As can be seen from FIG. 3, the maximum acceleration a_maxMaximum value S (F) of oxygen accumulation index S (F) in furnace during converting_maxIncrease when the maximum value S (F)_maxAt an acceleration of 40, the maximum acceleration a_maxThe amount of increase of (c) becomes large. In other words, the maximum value S (F)_maxIf the amount exceeds 40, the swing of molten iron may increase.

Here, it should be noted that, regardless of the difference in the Laval nozzle of the top-blowing lance, the oxygen flow rate F per unit area of the ignition point and the average decarburization oxygen efficiency eta are inversely related to each other, and the maximum value S (F) of the oxygen accumulation index S (F) in the furnace during the blowing is concerned_maxWith the index W of the falling pig iron mass of the furnace and the vibration acceleration a of the furnace body_maxShows a positive correlation with a maximum value of S (F)_maxAn index W of a falling pig iron mass of the furnace and a vibration acceleration a of the furnace body at a point of 40_maxBoth of these are rapidly increasing.

That is, isThe maximum value S (F) of the oxygen accumulation index S (F) in the converter is found by suppressing the swing of the molten iron, reducing the pig iron nuggets adhered to the converter mouth or the shield, and preventing the decrease of the iron yield_maxIt is important to control the amount to 40 or less, that is, to satisfy the following expression (3).

S(F)≤40…(3)

The constant α varies slightly depending on the operating conditions of the furnace and the like. Therefore, in the operation, the actual value of the accumulated oxygen index s (f) calculated by the above expression (2) and the unknown oxygen amount which is the difference between the input oxygen amount, which is the total of the oxygen supply amount from the top-blowing lance and the oxygen amount in the sub-raw material charged into the converter, and the output oxygen amount, which is the CO gas and CO in the converter exhaust gas, are monitored during the blowing₂Gas, oxygen, consumed in the desilication reaction and as SiO₂The sum of the amounts of oxygen present in the furnace is preferably determined by the constant α based on the actual value of the accumulated oxygen index s (f) and the unknown oxygen amount.

Based on the above-described results of study, in a method for refining a converter in which a top-blowing lance having a laval nozzle at its lower end is used and oxygen is blown from the laval nozzle to a surface of a molten iron bath in the converter to perform oxidation refining such as decarburization refining on the molten iron in the converter, the oxygen feed rate Q from the top-blowing lance is adjusted so that the oxygen accumulation index s (f) in the converter satisfies the above-described formula (3)_gAnd a lance height LH, wherein the oxygen accumulation index S (F) in the furnace is determined by the oxygen flow rate F per unit area of the fire point determined by the above expression (1) and the expression (2).

Adjusting the oxygen supply rate Q from the top-blowing lance so that the accumulated oxygen index S (F) satisfies the formula (3)_gAnd a lance height LH, thereby suppressing excessive supply of oxygen to the surface of the molten iron bath and suppressing CO bubbles generated by the reaction of carbon and oxygen in the molten iron bath from becoming excessively large. This can suppress bubble collapse and splashes associated with bubble collapse.

Further, as shown in FIG. 3, the oxygen feeding rate Q from the top-blowing lance is adjusted so that the accumulated oxygen index S (F) satisfies the expression (3)_gAnd a gun height LH, wherebyThe increase in the swing of the molten iron can be suppressed.

As described above, by implementing the method of operating the converter according to the present embodiment, it is possible to suppress the swing of the molten iron and suppress the bubble collapse and the splashes associated with the bubble collapse. This reduces the escape of iron to the outside of the converter, thereby reducing the cost required for the recovery and reuse of the pig iron nuggets and suppressing the reduction in the operating rate of the converter associated with the removal of the pig iron nuggets adhered to and deposited on the converter mouth or the like.