JP5823368B2 - Dust recycling method - Google Patents

Description

  The present invention relates to a method for recycling zinc-containing dust.

  In recent steelmaking processes, the dephosphorization process and the decarburization process are separated, and the dephosphorization process is often performed on the hot metal before the decarburization process in the converter vessel. By separating the dephosphorization process and the decarburization process in this way, the total amount of discharged slag can be reduced. Previously, the dephosphorization process was often carried out in a transport container such as a kneading vehicle. However, the transport container has a small freeboard, so the oxygen supply rate cannot be increased, and the process takes time. It was. For this reason, dephosphorization using a converter vessel that is large in free board and capable of increasing the oxygen supply rate is now widespread.

  Since the dust generated by the dephosphorization treatment or the decarburization treatment contains a large amount of iron, it is preferably reused as much as possible. As a method for recycling these dusts, there is a method in which the dust is used as a sintered ore raw material or a pellet raw material and is charged into the blast furnace as a sintered ore or pellet. However, in this case, since the amount of deposits on the blast furnace refractory increases when the zinc concentration in the dust is high, there is a quantitative limit in recycling these dusts to the blast furnace raw material (see JP 2007-9240 A). . For the same reason, galvanized scraps cannot be recycled in large quantities as blast furnace raw materials.

  Under such circumstances, a method of recycling zinc-containing dust as an auxiliary material in the dephosphorization process has been proposed (see JP-A-6-264126, JP-A-7-26317, and JP-A-8-333612). ). When dust containing zinc is used in the dephosphorization process, zinc volatilizes in the dephosphorization furnace. Therefore, by using a secondary raw material that does not substantially contain zinc in the decarburization process in the subsequent step, the zinc concentration of dust generated during the decarburization process is reduced, and this dust can be recycled as a blast furnace raw material. ing.

  However, in the conventional method of recycling the dust to the dephosphorization process in this way, (1) a large amount of dust may be thrown into the dephosphorization furnace due to equipment restrictions such as heat margin and cutting out the auxiliary material hopper. It may be difficult in actual operation. In addition, (2) not all zinc volatilizes during the dephosphorization process, so when a raw material containing a large amount of zinc is used in the dephosphorization process, the zinc remaining in the molten metal is transferred to the decarburization furnace. Since it is contained in the decarburized dust, the above inconvenience cannot be solved. Further, (3) since lead is also concentrated in the dust in addition to zinc, there is an inconvenience that the elution concentration of lead in the slag generated during the dephosphorization treatment is increased and it is difficult to recycle the slag.

  On the other hand, as a technique for suppressing the elution of lead in the slag, a method of insolubilizing lead in the slag by adjusting the slag composition has been proposed (see Japanese Patent Application Laid-Open No. 2002-20815). However, although this technology contributes to the effective use of slag, it is not a reference for effective dust recycling.

Japanese Patent Laid-Open No. 2007-9240 JP-A-6-264126 Japanese Unexamined Patent Publication No. 7-26317 JP-A-8-333612 Japanese Patent Laid-Open No. 2002-20815

  The present invention has been made based on the above-described circumstances, and the lead elution concentration from the slag produced by the decarburization treatment and the amount of deposits when the fine dust produced by the decarburization treatment is introduced into the blast furnace can be tolerated. It is an object of the present invention to provide a dust recycling method capable of reusing the dust generated in the iron making process as much as possible.

In order to solve the above-mentioned problems, the present inventors studied to introduce fine dust into not only a dephosphorization furnace but also a decarburization furnace. As a result, if the prescribed conditions are satisfied, the fine particle dust is within the allowable range of the lead elution concentration from the slag generated by the decarburization process and the amount of deposits when the fine dust generated by the decarburization process is charged into the blast furnace. It was found that it could be put into a decarburization furnace.
The resulting dust recycling method according to the present invention is
A step of dephosphorizing the hot metal, and a step of decarburizing the hot metal after the dephosphorization treatment,
In the dephosphorization treatment and decarburization treatment, when recycling at least one of dephosphorization dust and decarburization fine dust as an iron source, the amount of zinc X (kg / t) in the iron source recycled for the decarburization treatment And lead amount Y (kg / t) is a dust recycling method that satisfies the following formulas (1) and (2).
X ≦ 0.166−0.122 × HMR × A (1)
Y ≦ 0.0290−0.182 × HMR × a + 0.000390 × W _s −0.00514 × C _s (2)
(In the above formulas (1) and (2), HMR is the hot metal ratio in the decarburization furnace and is (molten metal mass / decarburization furnace main raw material input mass). A is in the iron source recycled for dephosphorization treatment Z is the amount of zinc (kg / t), a is the amount of lead (kg / t) in the iron source recycled for dephosphorization, and W _s is the amount of slag (kg / t) generated by decarburization. there .C _s is basicity of slag generated in the decarburization process.)

  Here, [kg / t] is the mass with respect to the main raw material 1t, and the amount of the main raw material means the total amount of hot metal, cold iron and scrap (including galvanized scraps) to be processed. The auxiliary raw material refers to raw materials other than the main raw materials (hot metal, cold iron, and scrap).

  According to the dust recycling method of the present invention, the zinc concentration in the decarburized fine dust generated in the decarburization process can be controlled by satisfying the formula (1) when the zinc amount X in the iron source recycled for the decarburization process is satisfied. For this reason, the decarburized fine particle dust in which the zinc concentration is controlled can be effectively reused as a blast furnace raw material such as sintered ore and pellets. Moreover, the lead elution density | concentration from the slag which arises in the case of a decarburization process can be suppressed to a predetermined density | concentration because the lead amount Y in the iron source recycled to a decarburization process satisfy | fills Formula (2). Therefore, according to the dust recycling method, the lead elution concentration from the slag generated by the decarburization process and the amount of deposits when the fine dust generated by the decarburization process is input to the blast furnace are acceptable in the iron making process. Dust can be reused as much as possible.

A graph showing the relationship between the decarburized fine dust zinc concentration and the amount of zinc input in the decarburization process Graph showing the relationship between the decarburized slag lead elution concentration and the amount of lead introduced in the decarburization process The schematic diagram which shows the dust collection | recovery separation system used for one Embodiment of the dust recycling method of this invention Graph showing the relationship between the dephosphorization slag lead elution concentration and the amount of lead input in the dephosphorization process The graph which shows the result of an Example

  Hereinafter, embodiments of the dust recycling method of the present invention will be described in detail with reference to the drawings.

The dust recycling method is
(1) a step of dephosphorizing the hot metal, and (2) a step of decarburizing the hot metal after the dephosphorization treatment. Hereinafter, each step will be described.

(1) Dephosphorization process In this process, a dephosphorization process is implemented using a converter vessel prior to a decarburization process. Note that desiliconization may be performed prior to dephosphorization for the purpose of preventing slopping in the dephosphorization.

  It does not specifically limit as said converter vessel, A well-known thing can be used. Moreover, the same converter vessel as the converter vessel used in the decarburization process of a post process may be used, and another converter vessel may be used. Specifically, an upper bottom blowing converter, a bottom blowing converter, an upper blowing converter, or the like can be used, but an upper bottom blowing furnace is preferable from the viewpoint of processing efficiency. The size of the converter vessel is not particularly limited, and, for example, one having a steel output amount of 50 to 400 t can be used.

  Examples of the treatment target of the dephosphorization treatment include main raw materials (hot metal and, if necessary, cold iron and scrap) and auxiliary raw materials (sintered ore, lime, dust, etc.) put into the converter vessel. In the dust recycling method, at least one of dephosphorization dust and decarburization fine dust β containing zinc and lead is used as an auxiliary material. Moreover, plating scraps such as galvanized scraps are used as the main raw material scrap. Therefore, typical examples of the zinc source in the raw material include dephosphorization dust, decarburization fine dust β, and zinc plating waste.

  The dephosphorization dust and the decarburization dust mean dust generated during the dephosphorization treatment or the decarburization treatment. In addition, the dephosphorization treatment and the decarburization treatment are each carried out by a batch treatment (batch type), and the dephosphorization treatment dust and the decarburization treatment fine dust β used in this (1) dephosphorization treatment step are treated in this step. It is dust generated during the treatment of hot metal other than hot metal. For convenience, in the dust recycling method of the present invention, (2) decarburized fine dust generated in the decarburizing process is decarburized fine dust α, and (1) the decarburized fine dust used in the dephosphorizing process is removed. Distinguish as charcoal-treated fine dust β.

  Further, the decarburized fine dust refers to particles having a particle size of less than 50 μm of 80% by volume or more. This particle size is a value measured by a laser diffraction / scattering particle size analyzer.

  As will be described later, the amount of zinc and the amount of lead in the iron source recycled by the decarburization process needs to be within a range satisfying formulas (1) and (2) described later. The source is preferably adjusted so as to maximize the amount of iron source to be recycled in the entire dust recycling method in relation to the amount of iron source that can be recycled by the subsequent decarburization treatment.

  In the dephosphorization process, the generated dust is recovered. The collection means is not particularly limited, and a known dust collector or the like can be used. However, it is necessary to separate and collect the dust from the decarburization process described in detail later. The method of separating and collecting in this way is not particularly limited. For example, a method of performing dephosphorization treatment and decarburization treatment in a converter having different exhaust gas dust collection systems, or using the same exhaust gas dust collection system. And a method of distributing dust for each treatment. In addition, unlike the decarburization processing dust mentioned later, this dephosphorization processing dust does not need to be divided into a fine particle and a coarse particle.

(2) Decarburizing treatment step In this step, the dephosphorized hot metal is decarburized using a converter vessel. As described above, the converter vessel used in the decarburization process may be the same as or different from the converter vessel used in the dephosphorization process. Alternatively, a so-called intermediate waste method may be employed in which only the dephosphorization slag is discharged and the decarburization process is performed after the dephosphorization process.

  This decarburization process includes the main raw materials (the hot metal subjected to the above dephosphorization treatment and the cold iron and scrap if necessary) and the auxiliary raw materials (sintered ore, lime, dust, etc.) And so on. In the decarburization process, as in the dephosphorization process, at least one of dephosphorization dust and decarburization fine dust containing zinc and lead as auxiliary materials is used. Moreover, as scrap, plating scraps such as galvanized scraps can be used. Therefore, typical examples of the zinc source in the raw material include dephosphorization dust, decarburization fine dust β, and zinc plating waste.

The zinc amount X (kg / t) in the iron source recycled by this decarburization treatment satisfies the following formula (1), and the lead amount Y (kg / t) satisfies the following formula (2).
X ≦ 0.166−0.122 × HMR × A (1)
Y ≦ 0.0290−0.182 × HMR × a + 0.000390 × W _s −0.00514 × C _s (2)
(In the above formulas (1) and (2), HMR is the hot metal ratio in the decarburization furnace and is (molten metal mass / decarburization furnace main raw material input mass). A is in the iron source recycled for dephosphorization treatment. Z is the amount of zinc (kg / t), a is the amount of lead (kg / t) in the iron source recycled for dephosphorization, and W _s is the amount of slag (kg / t) generated in the decarburization process. .C _s is the basicity of the slag generated in the decarburization process.)

  Here, the grounds for deriving the above formulas (1) and (2) are shown.

(About formula (1))
The detrimental effect when decarburized fine dust α generated in the decarburization process is thrown into the blast furnace as a recycled raw material such as sintered ore, pellets, etc., is adhering to the blast furnace refractory when the zinc concentration in the dust increases as described above This is an increase in quantity. At this time, if the zinc concentration in the dust is 0.7% by mass or more, the amount of deposits is said to increase (see JP 2007-9240 A). Therefore, the zinc concentration threshold value of the decarburized fine dust α to be recycled to the blast furnace was set to 0.7 mass%.

The zinc concentration of decarburized fine dust α is positively correlated with the product of the hot metal ratio in the decarburization furnace and the amount of zinc in the iron source recycled for dephosphorization (hereinafter also referred to as dephosphorization input zinc amount). In addition, it is considered that there is a positive correlation with the amount of zinc in the iron source to be recycled for decarburization treatment (hereinafter also referred to as decarburization treatment input zinc amount). Therefore, the zinc concentration of the decarburized fine dust α as the actual value is V _Zn (mass%), the hot metal ratio in the decarburization furnace is HMR, the dephosphorization treatment input zinc amount is A (kg / t), and the decarburization treatment. The amount of zinc input is defined as X (kg / t), V _Zn is defined as a dependent variable, the product of HMR and A, and X is defined as an independent variable. i) was obtained (see FIG. 1). For the multiple regression analysis, data shown in Tables 3 and 4 described later were used. Note that R ^{2 in} FIG. 1 is a determination coefficient.
V _Zn = 0.512 × HMR × A + 4.20 × X (1-i)

Further, as described above, the zinc concentration V _Zn of the decarburized fine dust α needs to be 0.7% by mass or less. Therefore, the above formula (1) is obtained by substituting V _Zn ≦ 0.7 into the above formula (1-i) for deformation.

(Regarding formula (2))
The adverse effect of lead in dust recycling is that, as described above, lead that has not volatilized during the decarburization treatment remains in the decarburized slag and causes lead elution from the decarburized slag. Generally, this decarburized slag is used for roadbed materials, backfill materials for civil engineering work, and the like. At this time, this slag needs to satisfy the standard of lead elution concentration of 0.01 mass ppm or less in the soil elution test described in Ministry of the Environment Notification No. 46. Therefore, the formula (2) was derived as an index satisfying this lead elution concentration standard.

Here, the lead elution concentration from the decarburization slag is the product of the hot metal ratio in the decarburization furnace and the amount of lead in the iron source recycled to the dephosphorization process (hereinafter also referred to as the dephosphorization input lead amount). It is considered to have a positive correlation and to have a positive correlation with the amount of lead in the iron source recycled to the decarburization process (hereinafter also referred to as the amount of lead input to the decarburization process). Further, when the amount of generated slag (kg / t) is large, the lead concentration in the slag decreases. Therefore, as the amount of generated slag increases, the lead elution concentration tends to decrease. Furthermore, if the basicity (CaO / SiO ₂ ) of the generated decarburized slag is high, the reaction amount of CaO + H ₂ O = Ca (OH) ₂ increases, so the pH of the water in contact with the decarburized slag is high. Therefore, the lead elution concentration tends to increase. Based on these points, as the actual values, the lead elution concentration from decarburization slag is V _Pb (mass ppm), the hot metal ratio in the decarburization furnace is HMR, the dephosphorization input lead amount is a (kg / t), The amount of charcoal slag is defined as W _s (kg / t), the basicity of the decarburized slag is defined as C _s , the amount of lead decarburized as Y (kg / t), V _Pb is defined as a dependent variable, and HMR and a The following equation (2-i) was obtained by performing multiple regression with the product of, W _s , C _s, and Y as independent variables and an intercept 0 (see FIG. 2). For the multiple regression analysis, data shown in Tables 2 to 4 described later were used. Note that R ² in FIG. ² is a determination coefficient.
V _Pb = 0.063 × HMR × a−1.34 × 10 ⁻⁴ × W _s + 1.77 × 10 ⁻³ × C _s + 0.345Y (2-i)

On the other hand, since the lead elution concentration V _Pb needs to be 0.01 mass ppm or less as described above, the above formula (2) can be obtained by substituting V _Pb ≦ 0.01 into the above formula (2-i). ) Is obtained.

  In addition, the quantity of zinc and lead contained in each raw material can be calculated | required by the product of the mass of each raw material seed | species, and zinc or lead density | concentration. The method for measuring the zinc or lead concentration is not particularly limited, and a known method can be used.

  In the decarburization process, the generated dust is collected, and the collected dust is separated into fine dust and coarse dust. The collection means is not particularly limited, and a known dust collector or the like can be used. The separation means is not particularly limited, and a known classifier or the like can be used. For example, a dust collection / separation system 1 shown in FIG. 3 is preferably used.

  3 includes a decarburization furnace 2 (converter), three types of dust collection hoods 3a, 3b, and 3c, a sprinkler 4, a classifier 5, a thickener 6, and a ventilation dust collector 7. The dust collection hood 3a is provided immediately above the decarburization furnace 2, and the dust collection hoods 3b and 3c are provided around the dust collection hood 3a.

  In the dust recovery and separation system 1, during blowing, the exhaust gas G including the dust D from the decarburization furnace 2 is sent to the sprinkler 4 through the dust collection hood 3 a, and the exhaust gas G in the sprinkler 4. And dust D. The separated dust D is sent to the classifier 5 together with water. In the classifier 5, coarse dust γ having a large mass is recovered. On the other hand, the fine dust α having a small mass is sent to the thickener 6 together with the supernatant, and then collected by precipitation.

  On the other hand, the exhaust gas G is processed by the ventilation dust collector 7 when the hot metal is charged and when steel is discharged. That is, when hot metal is charged and when steel is discharged, the decarburization furnace 2 is tilted so that the work is performed, so that the ventilation dust collector 7 is provided via the dust collection hoods 3b and 3c arranged around the dust collection hood 3a. Exhaust gas G is sent.

  In the recovery / separation system 1, the dust D generated during blowing can be recovered and separated into coarse dust γ and fine dust α. The coarse dust refers to particles having a particle size of 50 μm or more and 80 vol% or more, and the fine dust refers to particles having a particle diameter of less than 50 μm of 80 vol% or more.

(3) Recycling step (step of putting decarburized fine dust α generated in the above decarburizing step into the blast furnace as a recycled material)
The decarburized fine particle α generated, recovered and separated in the decarburization process is controlled to have a zinc concentration of 0.7% by mass or less with little adhesion to the blast furnace refractory. Therefore, the decarburized fine dust α can be input to the blast furnace as a recycled raw material without considering quantitative restrictions. At this time, the decarburized fine dust α is normally used as a sintered ore raw material or a pellet raw material and charged into the blast furnace as a sintered ore or pellet. The decarburized fine dust α generated in the decarburizing process does not have to be recycled as a blast furnace raw material, and can be used for dephosphorization or decarburization. The blast furnace is supplied with iron ore and coke as main raw materials to obtain hot metal (pig iron). In addition, when the zinc concentration is extremely low, the decarburized coarse dust γ can be recycled as scrap for dephosphorization and decarburization without considering the zinc content.

  According to the dust recycling method of the present invention, the zinc concentration in the decarburized fine dust generated in the decarburization process can be controlled by satisfying the formula (1) when the zinc amount X in the iron source recycled for the decarburization process is satisfied. For this reason, the decarburized fine particle dust in which the zinc concentration is controlled can be effectively reused as a blast furnace raw material such as sintered ore and pellets. Moreover, the lead elution density | concentration from the slag which arises in the case of a decarburization process can be suppressed to a predetermined density | concentration because the lead amount Y in the iron source recycled to a decarburization process satisfy | fills Formula (2). Therefore, according to the dust recycling method, the lead elution concentration from the slag generated by the decarburization process and the amount of deposits when the fine dust generated by the decarburization process is input to the blast furnace are acceptable in the iron making process. Dust can be reused as much as possible.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

For example, if the slag in the dephosphorization process is used for a roadbed material, a backfill material for civil engineering work, etc. as in the slag in the decarburization process, the lead elution concentration from the dephosphorization slag is 0. It is possible to adopt a method of dust recycling by limiting the amount of lead in the iron source recycled for the dephosphorization treatment so that it becomes 01 mass ppm or less. In this case, the iron source amount H (kg / t) recycled for the dephosphorization treatment preferably satisfies the following formula (3).
_{H ≦ (4.78-100e + 0.0384W p -1.297C} SP) / d ··· (3)
In (the above formula (3), e is the amount of lead contained in the dephosphorization other than iron source to be recycled to the raw material (main raw material) (kg / t) .W _p is generated in the dephosphorization (C _SP is the basicity of the slag, d is the lead concentration (mass%) in the iron source recycled for the dephosphorization process.)

The grounds for deriving the above equation (3) will be shown. It is considered that the lead elution concentration V _{Pb / P} (mass ppm) of the dephosphorization slag has a positive correlation with the lead amount a (kg / t) in the iron source recycled in the dephosphorization process. The amount of lead a is considered to have a positive correlation with the amount of hot metal and the lead concentration in the hot metal, and the amount of dust to be recycled and the lead concentration in the dust. In addition, when the amount of slag W _p (kg / t) generated by the dephosphorization process is large, the lead concentration in the slag decreases, and therefore the lead elution concentration tends to decrease as the amount of generated slag increases. Furthermore, when the basicity C _SP (CaO / SiO ₂ ) of the generated slag is high, the reaction amount of CaO + H ₂ O = Ca (OH) ₂ increases, so the pH of the water in contact with the slag increases. Lead elution concentration tends to increase. Based on these points, as the actual values, the lead elution concentration from dephosphorization slag is V _{Pb / P} (mass ppm), the dephosphorization treatment input lead amount is a (kg / t), and the slag amount generated by dephosphorization treatment is By defining W _p (kg / t) and the basicity of this slag as C _SP , V _{Pb / P} as a dependent variable, a, W _p and C _SP as independent variables, and performing multiple regression analysis with intercept 0 The following formula (3-i) was obtained (see FIG. 4). Table 1 shows the test data used in the multiple regression analysis.
V _{Pb / P} = 0.209a−8.00 × 10 ⁻⁵ W _p + 2.76 × 10 ⁻³ C _SP (3-i)

Here, the dephosphorization treatment input lead amount a (kg / t) is the amount H (kg / t) of the iron source recycled to the dephosphorization treatment, the lead concentration d (mass%) in the iron source, and the dephosphorization amount. It can be expressed by the following formula (3-ii) using the amount of lead e (kg / t) contained in the raw material other than the iron source recycled by the phosphorus treatment.
a = H × d / 100 + e (3-ii)

By substituting a in the above formula (3-ii) into the formula (3-i), the following formula (3-iii) is obtained.
V _{Pb / P} = 0.209 (H × d / 100 + e) −8.00 × 10 ⁻⁵ W _p + 2.76 × 10 ⁻³ C _SP (3-iii)

On the other hand, since the lead elution concentration V _{Pb / P} needs to be 0.01 mass ppm or less as described above, by substituting V _{Pb / P} ≦ 0.01 into the above formula (3-iii), The above formula (3) can be derived.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples. The measuring method, the converter vessel (dephosphorization furnace / decarburization furnace) and the raw materials used in the examples are as follows. In this example, the amount of iron source recycled for dephosphorization treatment is determined without considering the lead elution concentration from the dephosphorization slag, but the lead elution concentration of each dephosphorization slag in the example is 0.01 mass. It was below ppm.

[Measuring method]
(1) Concentrations of zinc and lead in dust (dephosphorized dust, decarburized fine dust α, and decarburized fine dust β) and galvanized scraps Used for dephosphorization as one of the iron sources to be recycled Decarburized fine dust (decarburized fine dust for dephosphorization recycling) was decarburized fine dust β, decarburized fine dust generated by decarburization in the examples (decarburized fine dust for blast furnace recycling) Is decarburized fine dust α.
Each concentration was measured by ICP emission spectrometry. The lower limit of analysis is 0.01% by mass.

(2) Dephosphorization treatment input zinc amount and dephosphorization treatment input lead amount In this example, it is assumed that raw materials other than the iron source to be recycled (including hot metal) do not contain zinc and lead for simplification. The dephosphorization treatment input zinc amount A and the dephosphorization treatment lead amount a are the decarburization treatment fine dust β, dephosphorization dust, zinc content and lead content contained in the dephosphorization treatment. It was calculated by the following formula.

here,
Wi: Input amount [kg / t] of iron source i (decarburized fine dust β, dephosphorized dust and galvanized scrap) recycled for dephosphorization treatment
[% Zn] i: Zinc concentration in the iron source i [mass%]
[% Pb] i: Lead concentration in the iron source i [mass%]

(3) Decarburization treatment input zinc amount and decarburization treatment input lead amount In this example, it is assumed that raw materials other than the iron source to be recycled (including hot metal) do not contain zinc and lead for simplification. Decarburization treatment input zinc amount X and decarburization treatment input lead amount Y are decarburization treatment fine dust β, dephosphorization treatment dust, zinc content contained in galvanized scrap, and lead content. It was calculated by the following formula.

here,
Wi: Input amount of iron source i (decarburized fine dust β, dephosphorized dust and galvanized scrap) to be recycled for decarburization [kg / t]
[% Zn] i: Zinc concentration in the iron source i [mass%]
[% Pb] i: Lead concentration in the iron source i [mass%]

(4) Decarburization furnace slag amount The decarburization furnace slag amount W _s is the mass of slag generated during the decarburization process, and was derived from the following equation.

here,
W _i : Input amount of auxiliary material i [kg]
W _j : Input amount of main raw material j (hot metal, cold iron and scrap) [kg]
(% CaO) _i : CaO concentration of auxiliary material i [mass%]
(% SiO ₂ ) _i : SiO ₂ concentration [mass%] of the auxiliary material i
[% Si] _j : Si concentration [mass%] in the main raw material j
M _SiO2 : Formula amount of SiO ₂ [kg / mol]
M _Si : Atomic weight of Si [kg / mol]
(% SiO ₂ +% CaO) max: Maximum values of CaO concentration and SiO ₂ concentration in slag. The (% SiO ₂ +% CaO) max was 63% by mass based on the analysis value of dephosphorization slag by a person skilled in the art. Thereby, since the amount of slag becomes the minimum value in the actual operation range, the dust recyclable amount is estimated on the safe side.

(5) decarburization slag basicity decarburization furnace slag basicity C _s is derived by the following equation.

here,
W _i : Input amount of auxiliary material i [kg]
W _j : Input amount of main raw material j (hot metal, cold iron and scrap) [kg]
(% CaO) _i : CaO concentration of auxiliary material i [mass%]
(% SiO ₂ ) _i : SiO ₂ concentration [mass%] of the auxiliary material i
[% Si] _j : Si concentration [mass%] in the main raw material j
M _SiO2 : Formula amount of SiO ₂ [kg / mol]
M _Si : Atomic weight of Si [kg / mol]
It is.

(6) Lead elution concentration from slag Measured according to the soil elution test defined by Ministry of the Environment Notification No. 46.

[Dephosphorization furnace and decarburization furnace]
As the dephosphorization furnace and decarburization furnace (converter), an upper bottom blowing converter (upper blowing nozzle: 6 holes, throat diameter: 42 mm, hole angle: 15 °) having a capacity of 250 t (crude steel ton) was used. Further, N ₂ and CO gas were used as the bottom blowing gas. The bottom-blown tuyere type is a single-layer annular tube, the number of which is four.

[material]
(1) Dephosphorization furnace charged hot metal [C]: 4.2 to 4.6% by mass
[Si]: 0.3 to 0.5% by mass
[Mn]: 0.1 to 0.4% by mass
[P]: 0.10 to 0.130 mass%
HMR = 0.94-0.98

(2) Decarburization furnace charged hot metal [C]: 3.4 to 3.8% by mass
[Si]: 0.01 mass% or less [Mn]: 0.1-0.2 mass%
[P]: 0.015-0.025 mass%
HMR = 0.88-1 (HMR for each example is shown in Table 2)

(3) Hot metal, dephosphorized dust, decarburized fine dust β, and zinc source other than galvanized scrap and Pb source Scrap as one of the main raw materials is generated in the factory substantially free of Zn and Pb. Was used.

(4) Dephosphorization dust and decarburization fine dust β put into the dephosphorization furnace and decarburization furnace
The dephosphorization dust used was a briquette (40 mm × 40 mm × 25 mm) made of 5% by mass starch as a binder without classifying the recovered dephosphorization dust.
The decarburized fine dust β is a decarburized fine dust (80% by volume or more of particles having a particle size of less than 50 μm) obtained by collecting and separating from the decarburization furnace with the apparatus shown in FIG. % Starch was used as a binder to form a briquette (40 mm × 40 mm × 25 mm).

[Examples 1-15, Comparative Examples I-1 to I-6 and Comparative Examples II-1 to II-6]
Hot metal and scrap as main raw materials were charged into the dephosphorization furnace. As with other scraps, galvanized scraps were charged with a scrap shooter before hot metal was charged. Next, the dephosphorized dust and decarburized fine dust β made into briquette together with auxiliary materials such as coal and sintered ore were introduced from the furnace hopper, and blown (dephosphorized). Next, the hot metal and scrap that had undergone the dephosphorization treatment as the main raw material were put into the decarburization furnace. Next, the dephosphorized dust and decarburized fine dust β made into briquette together with auxiliary materials such as coal and sintered ore were introduced from the furnace hopper, and blown (decarburized). The dust generated during the decarburization process was recovered and separated from the decarburization furnace with the apparatus shown in FIG. 3 to obtain a decarburized fine dust α. In addition, slag generated during the dephosphorization treatment was recovered.

  The amount of main raw materials (hot metal and scrap) input in the dephosphorization treatment of each Example and Comparative Example, the amount of hot metal, and the iron source (dephosphorization dust, decarburization treatment) recycled in the dephosphorization step and decarburization step Table 2 shows the input amount of fine dust β and galvanized scrap), the Zn concentration and the Pb concentration, and the HMR in the decarburization furnace. Other conditions are the same in each example and comparative example. All concentrations (%) in Table 2 are based on mass.

Further, with respect to the formula (1) which is the control condition of the input zinc amount in the decarburization treatment, the dephosphorization treatment input zinc amount (implementation amount) A and the upper limit amount of the decarburization treatment input zinc amount derived from the equation (1) Table 3 shows X _Max and the decarburization treatment input zinc amount (implementation amount) X. Also relates formula (2) is a control condition of the input lead content in the decarburization, and dephosphorization charged amount of lead (carried amount) a, a decarburization furnace slag weight W _s, and slag basicity C _s, Table 3 shows the upper limit amount Y _Max of the decarburization treatment input lead amount derived from the equation (2) and the decarburization treatment input lead amount (implementation amount) Y.

  In addition, in the column of suitability in Table 3, “◯” satisfies the formula (1) or (2), and “L” satisfies the formula (1) or (2) but is close to the upper limit (with respect to zinc) Is 0.03 kg / t or less, and regarding lead is 0.005 kg / t or less), “↑” indicates that Formula (1) or (2) is not satisfied.

  The zinc concentration in the fine dust α generated by the decarburization treatment and the lead elution concentration from the slag generated during the decarburization treatment were measured by the above method. The measurement results are shown in Table 4 and FIG. In the evaluation column in Table 4, “◯” indicates that the zinc concentration in molten steel or the lead elution concentration from the slag is not more than the upper limit value, and “×” indicates that the upper limit value is exceeded. The concentrations (ppm and%) in Table 4 are based on mass.

  As Table 4 and FIG. 5 show, since Examples 1-15 are recycling the iron source of the quantity which satisfy | fills Formula (1) and (2), the zinc concentration of the fine dust alpha which arises by a decarburization process Can be suppressed to 0.7 mass% or less, and the lead elution concentration from the slag generated in the decarburization treatment can be suppressed to 0.01 mass ppm or less. In addition, since the zinc density | concentration of the said fine dust is 0.7 mass% or less, this fine dust alpha can be used for a blast furnace as a recycle raw material. On the other hand, in Comparative Example I (I-1 to I-6), the zinc content in the fine dust α exceeds the upper limit, and in Comparative Example II (II-1 to II-6), the lead elution concentration from the slag has an upper limit. Over.

  As described above, in the dust recycling method of the present invention, the lead elution concentration from the slag produced by the decarburization treatment and the amount of deposits when the fine dust produced by the decarburization treatment is introduced into the blast furnace are within an allowable range. Thus, dust generated in the iron making process can be reused to the maximum. Therefore, the dust recycling method is suitably used for iron making.

DESCRIPTION OF SYMBOLS 1 Dust collection separation system 2 Decarburization furnace 3a, 3b, 3c Dust collection hood 4 Sprinkler 5 Classifier 6 Thickener 7 Ventilation dust collector G Exhaust gas D Dust α Fine dust γ Coarse dust

Claims (1)

A step of dephosphorizing the hot metal, and a step of decarburizing the hot metal after the dephosphorization treatment,
In the dephosphorization process and the decarburization process, when the dephosphorization process dust and particles having a particle size of less than 50 μm are recycled as iron sources, at least one of the decarburization process fine dust having 80% by volume or more is recycled to the decarburization process. A dust recycling method in which the amount of zinc X (kg / t) and the amount of lead Y (kg / t) in the iron source satisfy the following formulas (1) and (2).
X ≦ 0.166−0.122 × HMR × A (1)
Y ≦ 0.0290−0.182 × HMR × a + 0.000390 × Ws−0.00514 × Cs (2)
(In the above formulas (1) and (2), HMR is the hot metal ratio in the decarburization furnace and is (molten metal mass / decarburization furnace main raw material input mass). A is in the iron source recycled for dephosphorization treatment Z is the amount of zinc (kg / t), a is the amount of lead (kg / t) in the iron source recycled for dephosphorization, and Ws is the amount of slag (kg / t) generated in the decarburization process. Cs is the basicity of slag generated in the decarburization process.)

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