JP6560868B2 - Slag treatment method - Google Patents

Description

  The present invention relates to a slag treatment method and a slag treatment apparatus in which molten slag generated in a steelmaking process is temporarily held in a molten state in a slag holding furnace and then injected and reduced into an electric furnace.

  Slag (steel slag) produced by desulfurization, dephosphorization, or decarburization refining using a converter or the like in a steelmaking process contains a large amount of CaO. For this reason, since steelmaking slag has high expansibility and poor volume stability, conventionally, reuse to cement raw materials, aggregates, and the like has been limited. However, in recent years, there has been a demand for separation and recovery of valuable materials such as Fe and P from steelmaking slag, while reforming steelmaking slag to high-quality slag and reusing it, while the demand for resource recycling is increasing. Various slag treatment methods have been proposed so far.

  For example, in Patent Document 1, steel slag is added to the molten steel in the melting furnace, heat and reducing material are added to transform the steel slag, and Fe, Mn, and P in the slag are transferred to the molten metal. A slag treatment method is disclosed, which includes a first step of obtaining Mn and P, and second and third steps of oxidizing Mn and P in the molten metal and sequentially transferring them to a metamorphic slag and sequentially taking out high Mn slag and high P slag. Yes.

  In Patent Document 2, steel slag with an iron oxide content of more than 5 wt% is introduced into a steel bath with a carbon content of less than 1.5 wt%, and then the steel bath is carbonized by introducing carbon or a carbon carrier to contain the carbon. A method is disclosed in which a steel bath with a rate of greater than 2.0 wt% is obtained and thereafter the oxide in the steel slag is reduced. In this method, in order to suppress slag foaming (slag forming) and eruption from the furnace (overflow) due to a violent reaction with the steel bath when slag is charged, the carbon content of the steel bath is reduced before slag is charged. The reaction rate at the time of slag injection is eased by setting, and the carbon content is then increased to reduce the slag.

  Non-Patent Document 1 discloses a result of a steel slag powder, a carbon material powder, and a slag modifier powder charged in an electric furnace and subjected to a slag reduction test. Furthermore, Patent Document 3 discloses a method of recovering valuable metals by reducing molten slag generated by non-ferrous refining with a carbonaceous reducing material in an open DC electric furnace, separating it into a metal layer and a slag layer. Has been.

  In addition, in Patent Document 4, in order to melt and reform steelmaking slag having low fluidity at low temperatures, the slag surface layer is added before and after the modifier is added or sprayed to the low fluidity steelmaking slag contained in the container. A method is disclosed in which after stirring mechanically, a mixed layer of slag and modifier is heated and melted using a heating burner, and the resulting molten slag is discharged from a container and solidified.

Japanese Patent Laid-Open No. 52-033897 Special table 2003-520899 gazette Australian Patent AU-B-20553 / 95 Specification JP 2005-146357 A

Scandinavian Journal of Metallurgy 2003; 32: p. 7-14

  However, in the slag treatment method described in Patent Document 1, since the reduction treatment is performed using a converter, the molten metal and slag are strongly stirred. For this reason, if the carbon concentration of the molten metal is high when the slag is charged, the reaction is promoted by the slag coming into contact with the molten metal and forming occurs. In order to avoid this, it is necessary to repeat the batch process in order to increase the carbon concentration of the molten metal by introducing carbon in order to promote the reduction reaction after the slag is introduced into the molten metal having a low carbon concentration. That is, in order to obtain a slag having a required component composition, it is necessary to repeatedly perform a plurality of batch processes (multiple slag reduction processes and Mn and P oxidation and removal processes), so that work efficiency and productivity are improved. descend.

  Similarly, in the slag reduction method described in Patent Document 2, since the reduction treatment is performed using a converter, in order to reduce or increase the carbon concentration in the molten iron and perform the slag reduction treatment, decarburization heating and heating are performed. The batch process of charcoal reduction is repeated, and the work efficiency and productivity are reduced.

  On the other hand, in the reduction test described in Non-Patent Document 1, a solidified cold steelmaking slag pulverized product is treated, and in the method described in Patent Document 3, the solidified cold slag is treated. In this case, in order to perform the reduction treatment of slag, it is necessary to heat and melt the cold slag, and the energy intensity increases accordingly.

  As described above, the conventional methods (Patent Documents 1 and 2) in which hot steelmaking slag is recycled by batch processing have a problem that work efficiency and productivity of slag processing are low. On the other hand, in the conventional methods (Non-patent Document 1 and Patent Document 3) in which cold steelmaking slag is heated and melted for recycling, there is a problem that the energy intensity required for the slag treatment increases.

  Therefore, the inventors of the present application can treat the molten steelmaking slag (hereinafter referred to as molten slag) generated in the steelmaking process in the molten state without solidifying in order to reduce the energy intensity. In order to improve the working efficiency and productivity, the inventors have intensively studied a method that can continuously perform the reduction treatment of the molten slag.

  If molten slag is put in a molten state on molten iron in an electric furnace, the energy intensity can be suppressed as compared with the case where cold slag is heated and melted. However, when molten slag is put on the molten iron in the electric furnace, the slag suddenly reacts with the molten iron to cause bumping (slag forming), and when this becomes severe, the slag overflows from the electric furnace (overflow) May occur. Therefore, it is necessary to take measures to suppress such slag forming and prevent overflow.

  In a reduction furnace (converter, etc.), the reduction reaction is promoted by the reaction between slag and molten iron, and C in the molten iron reduces FeO in the slag. Need to be repeated, resulting in lower work efficiency. In contrast, it was found that the reduction reaction in the electric furnace is dominated by the reaction between iron (FeO) and carbon (C) in the slag rather than between the slag and molten iron. Therefore, when an electric furnace is used, even if the C concentration in the molten iron is as low as about 1.5% by mass, it is possible to perform slag reduction without carburizing, and work efficiency can be improved. It turns out that it can improve. Therefore, using an electric furnace instead of a reducing furnace can be one of the measures for suppressing slag forming when molten slag is charged.

  However, the C concentration in the molten iron in the electric furnace may be high. Therefore, even in such a case, the inventors of the present application can suppress slag forming and the like at the time of slag injection, and appropriately perform molten slag with high work efficiency without performing decarburization / carburization processing. We studied earnestly about the method of reduction treatment and repeated experiments.

  As a result, (a) the high-temperature molten slag having fluidity is not directly charged into the electric furnace, but once held in the slag holding furnace disposed adjacent to the electric furnace, the overflow does not occur. The molten slag is gradually injected into the electric furnace from the slag holding furnace while adjusting the injection amount, and (b) a molten slag layer (preferably an inert reduced slag layer on the molten iron layer in the electric furnace) ) As a buffer zone and injecting molten slag into the molten slag layer from a slag holding furnace proved to be preferable from the viewpoint of suppressing slag forming during slag charging and avoiding overflow did.

  In this way, by using the slag holding furnace and injecting the molten slag into the molten slag layer in the electric furnace while adjusting the injection amount of the molten slag, it is possible to suppress the occurrence of rapid slag forming during the slag injection and to decarburize. -It is possible to continuously perform slag reduction treatment in an electric furnace without carburizing.

By the way, in said electric furnace, the exhaust gas containing CO gas is generated with the reduction process of slag. Since CO gas is toxic, it must be removed on the exhaust path from the electric furnace. For example, if oxygen is supplied into the slag holding furnace after introducing the exhaust gas from the electric furnace into the slag holding furnace, CO can be removed by detoxifying the CO gas as CO ₂ by combustion. Thereby, the removal equipment installed in the exhaust path after the slag holding furnace can be simplified. Furthermore, in this case, the atmospheric temperature in the slag holding furnace can be maintained at a high temperature by using heat generated by the combustion of the CO gas. Since the molten slag is likely to solidify when the atmospheric temperature in the slag holding furnace decreases, it is important to maintain the atmospheric temperature at a high temperature.

  In this way, when CO gas is burned in the slag holding furnace, maintaining an appropriate oxygen supply amount into the slag holding furnace is sufficient for removing CO gas and maintaining the atmospheric temperature in the slag holding furnace. is important. That is, if the amount of oxygen supplied into the slag holding furnace is too small compared to the amount of CO gas in the exhaust gas, the CO gas cannot be completely burned, and the unburned gas is not combusted in the exhaust path after the slag holding furnace. In addition to the outflow of CO gas, the effect of maintaining the atmospheric temperature is reduced. Also, if the amount of oxygen supplied into the slag holding furnace is too large compared to the amount of CO gas in the exhaust gas, the CO gas will be completely burned, but excess oxygen gas (in many cases, normal temperature at the time of supply) Is left in the slag holding furnace, the ambient temperature is lowered.

  Considering the above points, it is conceivable to introduce feedback control in order to appropriately maintain the oxygen supply amount into the slag holding furnace. For example, the concentration of oxygen and CO contained in the exhaust gas exiting the slag holding furnace is measured, and when CO is detected, it is judged that oxygen is insufficient, the oxygen supply amount is increased, and oxygen is detected. In such a case, it can be considered that the oxygen supply amount is decreased by judging that oxygen is excessive. For example, if the molten slag is continuously injected from the slag holding furnace into the electric furnace, the feedback control is effective.

  However, in actual operation, if there is a small amount of molten slag injected per hour, there is a concern that the molten slag will easily solidify at the spout of the slag holding furnace, etc. Often injected into. In this case, the amount of CO gas generated in the electric furnace changes abruptly as the molten slag is injected. More specifically, the amount of CO gas that has been reduced due to the convergence of the reduction reaction before the injection of the molten slag rapidly increases as the reduction reaction becomes active again immediately after the injection of the molten slag.

  In the above case, the feedback control based on the amount of CO gas generated before the injection of the molten slag has been performed, and the oxygen supply amount is greatly increased in the amount of CO gas generated after the injection of the molten slag. It takes time to follow, and a large amount of CO gas flows out to the exhaust path after the slag holding furnace before reaching an appropriate oxygen supply amount. Therefore, it is conceivable to separately set the oxygen supply amount at the time of pouring molten slag, but as described above, if the oxygen supply amount is too large, the ambient temperature in the slag holding furnace will decrease, so there is no excess or shortage of oxygen supply. There is a need for a method to properly determine the amount. Such a method has not yet been proposed.

  Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to appropriately determine the amount of oxygen supplied to the slag holding furnace immediately after the injection of molten slag, It is an object of the present invention to provide a new and improved slag processing method and slag processing apparatus.

ここで、
ＦＯ _２ ：溶融スラグの注入直後の酸素含有ガスの流量
ＦＯ _２ ’：注入前の酸素含有ガスの流量
ΔＷ：溶融スラグの注入量
Ｓｗ：注入前に溶融スラグ層に含まれる溶融スラグの量
Ｔ：注入前に溶融スラグ層に含まれる溶融スラグの温度
α，β：定数 In order to solve the above problems, according to one aspect of the present invention, molten slag generated in a steelmaking process is charged into a slag holding furnace in a molten state, and formed on the molten iron layer and the molten iron layer from the slag holding furnace. The molten slag is intermittently injected into the electric furnace containing the molten slag layer, and the molten slag is continuously reduced in the electric furnace to recover valuable materials in the molten slag into the molten iron layer. A slag treatment method that introduces exhaust gas generated in an electric furnace into a slag holding furnace and burns combustible components in the exhaust gas by supplying an oxygen-containing gas at a predetermined flow rate into the slag holding furnace. At this time, the flow rate of the oxygen-containing gas immediately after the injection of the molten slag is changed to the injection amount ΔW of the molten slag, the amount Sw of the molten slag contained in the molten slag layer before the injection, and the molten slag contained in the molten slag layer before the injection. temperature T After setting the flow rate calculated by the following equation on the basis of and the performance-based value constant α during operation beta, the flow rate of the oxygen-containing gas, CO concentration and the oxygen in the exhaust gas in the vicinity of the gas outlet of the slag holding furnace Provided is a slag processing method for feedback control based on concentration .

here,
FO ₂ : Flow rate of oxygen-containing gas immediately after injection of molten slag
FO ₂ ': Flow rate of oxygen-containing gas before injection
ΔW: Injection amount of molten slag
Sw: Amount of molten slag contained in molten slag layer before injection
T: temperature of the molten slag contained in the molten slag layer before injection
α, β: Constant

  As described above, according to the present invention, the oxygen supply amount to the slag holding furnace immediately after the injection of the molten slag can be appropriately determined.

It is process drawing which shows the slag processing process which concerns on the 1st Embodiment of this invention. It is a mimetic diagram showing the whole slag processing equipment composition concerning the embodiment. It is a longitudinal cross-sectional view which shows the slag holding furnace (holding attitude | position) and electric furnace which concern on the embodiment. It is a longitudinal cross-sectional view which shows the slag holding furnace (injection attitude | position) and electric furnace which concern on the embodiment. It is a graph which shows the determination process of the constant used for the calculation formula of oxygen gas flow volume in the Example of this invention. It is a graph which shows progress of the operation in the example of the present invention. It is a graph which shows progress of the operation in the comparative example with respect to the Example of FIG.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

(1. Outline of slag treatment process)
First, the outline of the slag processing process according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a process diagram showing a slag treatment process according to this embodiment.

  As shown in FIG. 1, hot metal is produced using a blast furnace in the iron making process (S1), and pig iron is refined into steel using a converter or the like in the steel making process (S2). This steel making process (S2) is a desulfurization, dephosphorization, and decarburization process that removes sulfur, phosphorus, carbon, etc. in the hot metal, and gas, sulfur, etc., remaining in the molten steel, and component adjustment. The secondary refining process (S6) which performs, and the casting process (S7) which casts molten steel with a continuous casting machine.

  In the steelmaking step (S2), the hot metal is refined in the converter using a flux mainly composed of calcium oxide. At this time, oxygen, blown into the converter, oxidizes C, Si, P, Mn and the like in the hot metal, and the oxide is combined with calcium oxide and generated as slag. Moreover, in each process (S3, S4, S5) of desulfurization, dephosphorization, and decarburization, slag (desulfurization slag, dephosphorization slag, decarburization slag) having different components is generated.

  In this specification, the slag produced | generated at the said steelmaking process is named generically as steelmaking slag, and the said steelmaking slag is the concept containing desulfurization slag, dephosphorization slag, and decarburization slag. Steelmaking slag in a molten state at high temperature is referred to as molten slag, and similarly, desulfurized slag, decarburized slag, and dephosphorized slag in molten state are respectively melted desulfurized slag, molten dephosphorized slag, and molten decarburized slag. Called.

  In the slag treatment step (S10), the molten slag generated in the steel making step (S2) is transported from the converter to the electric furnace in a molten state, and continuously reduced and melt-modified in the electric furnace. Then, valuable materials (feature elements such as Fe and P) in the molten slag are recovered in the molten iron layer, which is the lower layer of the molten slag layer. At this time, in the electric furnace, a reduction process of oxides such as Fe and P in the molten slag, a process of separating granular iron (iron) from the slag, a process of adjusting the basicity of the slag, and the like are performed.

  As a result, high-phosphorus molten iron containing phosphorus and the like separated from the molten slag is recovered, and molten slag, which is steelmaking slag, is reduced and reformed, and high-quality reduced slag equivalent to blast furnace slag is recovered. . Since this reduced slag is less expansible than steelmaking slag, it can be effectively recycled into cement raw materials, fine aggregates, ceramic products and the like.

  Further, the recovered high-phosphorus molten iron is subjected to dephosphorization treatment (S11) to oxidize P in the molten iron and transfer it to the slag, so that the high-phosphorus molten iron is separated into high phosphate slag and molten iron. Is done. High phosphoric acid slag can be recycled as phosphoric acid fertilizer or phosphoric acid raw material. Further, the molten iron is recycled to the steel making process (S2) and is put into a converter or the like.

  In addition, when the molten iron which is discharged from the blast furnace is used as the molten iron to be accommodated in the electric furnace, a low silicon molten iron is obtained by performing a dephosphorizing process (S11) on the high phosphorus molten iron. Therefore, it can be recycled to the converter as it is.

  The outline of the slag processing process according to the present embodiment has been described above. In the present process, it is preferable to treat the molten dephosphorization slag among the various molten slags generated in the steel making step (S2). The molten dephosphorized slag is at a lower temperature than the molten decarburized slag, but contains a large amount of granular iron and phosphoric acid. For this reason, recovery efficiency of valuable elements (Fe, P, etc.) by this process becomes high by melt-modifying molten dephosphorization slag not by oxidation treatment but by reduction treatment. Therefore, in the following description, an example in which molten dephosphorization slag is mainly used as the molten slag to be processed will be described. However, the molten slag of the present invention is not limited to molten dephosphorization slag, and any steelmaking slag generated in the steelmaking process such as molten desulfurization slag and molten decarburization slag can be used.

(2. Configuration of slag treatment equipment)
Next, slag processing equipment for realizing the slag processing process will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating the overall configuration of the slag treatment facility according to the present embodiment.

  As shown in FIG. 2, the slag treatment facility includes an electric furnace 1 and a slag holding furnace 2 that is connected and disposed above the electric furnace 1. In addition, a slag pan 3 is used to introduce the molten slag 4 into the slag holding furnace 2, and this slag pan 3 is a converter (not shown) used in the steel making process and the slag holding furnace 2. Reciprocate between them. The molten slag 4 discharged from the converter is put into the slag pan 3. The slag pan 3 is charged into the slag holding furnace 2 after conveying the molten slag 4 from the converter to the slag holding furnace 2. The slag holding furnace 2 can store and hold the molten slag 4 and intermittently injects the held molten slag 4 into the electric furnace 1. Details of the slag holding furnace 2 will be described later.

  Note that the molten slag 4 held in the slag holding furnace 2 does not need to be completely melted, and may have fluidity that can be injected from the slag holding furnace 2 into the electric furnace 1. That is, even if a part of the molten slag 4 is melted and the remaining part is solidified, it is only necessary to have fluidity as a whole.

  The electric furnace 1 reduces and reforms the molten slag 4 using a reducing material such as a carbonaceous material and a secondary material such as a modifying material. The electric furnace 1 is a reduction-type electric furnace for melting and reducing the molten slag 4 as described above, and is composed of, for example, a fixed DC electric furnace. The outer shell of the electric furnace 1 includes a furnace bottom 11, a furnace wall 12, and a furnace lid 13, and a slag inlet 14 is formed on one side of the furnace lid 13. Thus, the electric furnace 1 has a sealed structure except for the slag inlet 14 so that the furnace space can be kept warm.

  In the center of the electric furnace 1, an upper electrode 15 and a furnace bottom electrode 16 are disposed so as to face each other in the vertical direction. A DC power supply is applied to the upper electrode 15 and the furnace bottom electrode 16 to generate an arc discharge between the electrodes 15 and 16, thereby heating the molten slag 4 and promoting a reduction reaction. If the upper electrode 15 is a hollow electrode as shown in the figure, the auxiliary material can be charged into the arc spot through the hollow electrode without installing a separate material charging device.

  A furnace wall 12 of the electric furnace 1 is provided with a tap outlet 17 for discharging reduced slag and a tap outlet 18 for discharging molten iron. The pouring gate 17 is arranged at a height position corresponding to the molten slag layer 5 on the molten iron layer 6, and the pouring gate 18 is arranged at a height position corresponding to the molten iron layer 6 on the furnace bottom side.

In addition, FIG. 2 illustrates a case where the raw material supply devices 31, 32, and 33 are all provided in the electric furnace 1. The raw material supply device 31 is provided when iron-containing materials such as iron scrap and direct reduced iron (DRI) are supplied into the electric furnace 1. Moreover, the raw material supply apparatus 33 is provided when supplying fine powdery iron-containing material (for example, FeO powder), such as dust powder containing iron, into the electric furnace 1 through the hollow electrode (upper electrode 15). Thereby, these iron-containing materials can be melted and recycled in the electric furnace 1. Further, the raw material supply device 32 is necessary for supplying auxiliary raw materials such as a reducing material and a reforming material necessary for the reduction treatment of the molten slag 4, and here, in the electric furnace 1 through the hollow electrode (upper electrode 15). The case where it supplies to is illustrated. As the reducing material, for example, fine powdery carbon materials such as coke powder, smokeless coal powder, and graphite powder are used. Further, the modifier is mainly for adjusting the concentration of SiO ₂ , Al ₂ O ₃ or MgO in the slag, and for example, silica sand, fly ash, MgO powder, waste refractory powder and the like can be used.

  With reference to FIG. 2, the reduction process of the molten slag 4 using the electric furnace 1 having the above configuration will be described.

  First, a considerable amount of molten iron (for example, molten iron transported from a blast furnace) is stored in advance in the electric furnace 1 as a molten iron layer 6 as seed hot water. The C concentration of molten iron is usually 1.5 to 4.5% by mass. In the electric furnace 1, the present inventors correlate the C concentration (mass%) of the molten iron with the total Fe concentration (T.Fe) (mass%) of the molten slag 4 (reduced slag) after the reduction treatment. It has been confirmed by experiments. For example, when the C concentration of the molten iron exceeds 3% by mass, the reduction of the oxide in the molten slag 4 is promoted, and (T.Fe) of the reduced slag can be reduced to 1% by mass or less. Therefore, it is preferable to adjust the C concentration of the molten iron in the molten iron layer 6 in accordance with the desired (T.Fe) of the reduced slag.

  Next, after supplying electric power to the electric furnace 1 and operating it continuously, an amount of molten slag 4 corresponding to the reduction processing capacity of the electric furnace 1 (for example, the amount of electric power supplied to the electric furnace 1 per unit time) Injection into the electric furnace 1 from the holding furnace 2. The molten slag 4 injected into the electric furnace 1 forms a molten slag layer 5 on the molten iron layer 6. Further, the auxiliary materials such as the reducing material (carbon material) and the reforming material are continuously fed into the molten slag layer 5 in the electric furnace 1 through the upper electrode 15, for example. In the electric furnace 1, the temperature of the molten iron layer 6 is controlled to be, for example, 1400 to 1550 ° C., and the temperature of the molten slag layer 5 is, for example, 1500 to 1650 ° C. This temperature control can be performed by adjusting the supply amount of the molten slag 4 or adjusting the power supply amount within a range where the power supply amount per unit time is constant.

As a result, the reduction reaction of the molten slag 4 in the molten slag layer 5 proceeds in the electric furnace 1 by the arc heat between the upper electrode 15 and the furnace bottom electrode 16. In this reduction treatment, oxides (FeO, P ₂ O _{5 and the} like) contained in the molten slag 4 are reduced by carbon of the carbonaceous material in the molten slag layer 5 to produce Fe and P, and the Fe, P Moves from the molten slag layer 5 to the molten iron layer 6 (molten iron) on the furnace bottom side. On the other hand, the surplus carbon material C does not move to the molten iron layer 6 but is suspended in the molten slag layer 5. In the reduction treatment, the slag component in the molten slag 4 is reformed by the modifying material.

  In the above reduction treatment, FeO contained in the injected molten slag 4 preferentially reacts with C of the carbonaceous material in the molten slag layer 5 rather than C contained in the molten iron in the molten iron layer 6 (FeO + C → Fe + CO ↑). That is, since carbon C of the input carbon material does not move to the molten iron layer 6 but is suspended in the molten slag layer 5, a reduction reaction of FeO + C → Fe + CO ↑ hardly occurs at the interface between the molten iron layer 6 and the molten slag layer 5. . For this reason, the reduction reaction proceeds preferentially in the molten slag layer 5, and the generated reduced iron (Fe) moves to the molten iron layer 6.

  Thus, in the reduction treatment by the electric furnace 1, the reaction between FeO and C in the molten slag layer 5 is more dominant than the reaction between FeO in the molten slag layer 5 and C in the molten iron layer 6. is there. Therefore, when the molten slag 4 is injected into the electric furnace 1, the molten slag layer 5 on the molten iron layer 6 becomes a buffer zone for the reaction between the injected molten slag 4 and the molten iron in the molten iron layer 6. Rapid reaction between the slag 4 and molten iron can be suppressed.

  That is, by injecting the molten slag 4 into the molten slag layer 5 having a low FeO concentration, the FeO concentration of the injected molten slag 4 can be reduced, and the injected molten slag 4 and the molten iron of the molten iron layer 6 can be reduced. Direct contact can be suppressed. Therefore, when the molten slag 4 is injected from the slag holding furnace 2 into the electric furnace 1, bumping phenomenon (slag forming) due to a rapid reaction between the molten slag 4 and the molten iron can be suppressed, and the molten slag 4 is outside the electric furnace 1. The phenomenon of overflowing (overflow) can be avoided.

  As described above, the oxide contained in the molten slag 4 injected into the molten slag layer 5 in the electric furnace 1 is reduced, and Fe and P are recovered from the molten slag 4 to the molten iron layer 6. The slag component of the molten slag 4 is modified. Therefore, if the reduction process proceeds after the injection of the molten slag 4, the components of the molten slag layer 5 are gradually reformed from the molten slag 4 (steel slag) to reduced slag (high quality slag equivalent to blast furnace slag). Go. The molten slag layer 5 modified to reduced slag becomes a buffer zone having a lower FeO concentration. Therefore, when newly injecting the molten slag 4 from the slag holding furnace 2 into the molten slag layer 5, more slag forming is performed. It becomes possible to suppress it reliably.

Further, as the reduction treatment proceeds, Fe moves into the molten iron, and the layer thickness of the molten iron layer 6 gradually increases.
In addition, the layer thickness of the molten slag layer 5 is preferably 100 to 600 mm, and more preferably 100 to 800 mm, from the viewpoint of expressing a function as a buffer zone. For this reason, when the molten slag 4 is injected and the thickness of the molten slag layer 5 reaches a predetermined layer thickness, the spout 17 is opened and the reduced slag of the molten slag layer 5 is discharged. Moreover, when the interface of the molten iron layer 6 approaches the hot metal outlet 17, the hot water outlet 18 is opened, and the molten iron (for example, high P hot metal) of the molten iron layer 6 is discharged. In this manner, reducing slag is intermittently discharged and recovered from the hot water outlet 18 and the molten iron is intermittently discharged and recovered. Thereby, in the electric furnace 1, the reduction process of the molten slag 4 can be continued without interruption.

Further, during the operation of the electric furnace 1 (that is, during the reduction process), high temperature exhaust gas containing CO and H ₂ or the like is produced by reducing the oxide of the molten slag 4 using C in the carbonaceous material. Occur. For example, when reducing iron oxide, CO gas is generated by the reaction of FeO + C → Fe + CO ↑. The exhaust gas flows into the slag holding furnace 2 through the slag inlet 14 of the electric furnace 1 and is discharged outside through the slag holding furnace 2 as an exhaust path. Thus, by making the electric furnace 1 into a closed type and using the slag holding furnace 2 as an exhaust path, the atmosphere in the electric furnace 1 is generated from the thermal decomposition of the CO gas generated by the reduction reaction and the carbonaceous material (reducing material). A reducing atmosphere containing H ₂ as a main component is maintained. Therefore, the oxidation reaction on the surface of the molten slag layer 5 can be prevented.

(3. Configuration of slag holding furnace)
Next, the configuration of the slag holding furnace 2 used in the slag treatment process according to the present embodiment will be described in detail with reference to FIGS. 3 and 4. FIG. 3 is a longitudinal sectional view showing the slag holding furnace 2 (holding posture) according to the present embodiment, and FIG. 4 is a longitudinal sectional view showing the slag holding furnace 2 (injecting posture) according to the present embodiment. 3 and FIG. 4 (including oxygen gas supply nozzle 51, control device 52, summing box 53, radiation thermometer 54, gas sampler 55, and exhaust gas analyzer 56). The configuration will be described in detail later.

  As shown in FIG. 3, the slag holding furnace 2 is a heat-resistant container and has a function of holding a high-temperature molten slag 4 and injecting it into the electric furnace 1. The slag holding furnace 2 has a structure capable of holding the molten slag 4 and adjusting the injection amount of the molten slag 4 into the electric furnace 1, and also functions as an exhaust path for the exhaust gas generated in the electric furnace 1. To do. The slag holding furnace 2 injects the slag holding furnace body 20 (hereinafter referred to as “furnace body 20”) for storing and holding the molten slag 4 and the molten slag 4 in the furnace body 20 into the electric furnace 1. And a spout portion 21 for the purpose.

  The furnace body 20 is a sealed container including a lower wall 22, a side wall 23, and an upper wall 24, and has an internal space for storing the molten slag 4. The lower wall 22 is composed of an iron skin 22a and a heat insulating material 22b outside the iron skin 22a, and an inner refractory 22c inside the iron skin 22a, and is excellent in strength and heat resistance. A lining refractory is also applied to the inner surfaces of the side wall 23 and the upper wall 24.

  A gas discharge port 25 and a slag input port 26 are provided on the upper portion of the furnace body 20 on the furnace lid 27 side. The gas discharge port 25 is an exhaust port for discharging the exhaust gas of the electric furnace 1 and is connected to an intake device such as a dust collector (not shown). By this intake device, the atmosphere in the slag holding furnace 2 is maintained in a negative pressure state. The slag inlet 26 is an opening for introducing the molten slag 4 from the upper slag pot 3 into the furnace body 20. An openable / closable furnace lid 27 is installed at the slag inlet 26, and the furnace lid 27 is opened when the molten slag 4 is charged. On the other hand, when the molten slag 4 is not charged, the furnace and the furnace lid 27 are closed and the slag charging port 26 is closed, so that outside air can be prevented from entering the furnace body 20 and the inside of the furnace body 20 can be kept warm.

  The spout portion 21 is a cylindrical portion provided on the electric furnace 1 side of the furnace body 20. The internal space of the spout 21 is a slag injection path 28 for injecting the molten slag 4 from the furnace body 20 into the electric furnace 1, and the opening formed at the tip of the spout 21 is the spout 29. The slag injection path 28 is narrower in the vertical direction and the furnace width direction (perpendicular to the paper surface of FIG. 3) than the internal space of the furnace body 20, and is curved downward as it goes forward in the injection direction. Further, the internal space of the furnace body 20 is gradually narrowed toward the spout portion 21 side. The shape of the furnace body 20 and the spout portion 21 is suitable for adjusting the injection amount when the molten slag 4 in the furnace body 20 is injected into the electric furnace 1.

  The spout 21 of the slag holding furnace 2 is connected to the slag inlet 14 of the electric furnace 1. In the illustrated example, the slag inlet 14 of the electric furnace 1 is made thicker than the spout 21 and the tip of the spout 21 is inserted into the slag inlet 14. There is a gap. In addition, the connection structure of the spout part 21 and the slag injection port 14 is not limited to such an example, and variously, such as connecting both together airtightly using a bellows or the like, or connecting a filler filled in a gap between the two. Can be changed.

Due to the structure of the slag holding furnace 2, when the dust collector (not shown) is operated with the furnace lid 27 closed, and the atmosphere in the slag holding furnace 2 is brought into a negative pressure state, the slag holding furnace 2 is It functions as an exhaust path for exhaust gas generated in the electric furnace 1. That is, the exhaust gas containing CO and H ₂ generated by the reduction treatment in the electric furnace 1 passes through the slag inlet 14 of the electric furnace 1 and the spout part 21 of the slag holding furnace 2 as shown by arrows in FIG. Then, it flows into the furnace body 20 of the slag holding furnace 2 in a negative pressure state. At this time, since the inside of the slag holding furnace 2 is maintained at a negative pressure, the exhaust gas in the electric furnace 1 is not affected even though outside air may enter through the gap between the connecting portions of the electric furnace 1 and the slag holding furnace 2. There is no leakage from the gap to the outside. Further, the exhaust gas flowing into the slag holding furnace 2 advances into the furnace body 20 and is discharged from the gas discharge port 25, reaches a dust collector (not shown), and is processed.

  Further, a tilting device 40 is provided on the lower side of the furnace body 20 of the slag holding furnace 2. The tilting device 40 has a function of tilting the slag holding furnace 2 toward the pouring part 21 and injecting the molten slag 4 in the furnace body 20 into the electric furnace 1 from the pouring part 21. The tilting device 40 includes a cylinder 41, support members 42 and 43, a tilting shaft 44, a carriage 45, and a load cell 46.

  The cylinder 41 is composed of, for example, a hydraulic cylinder, and generates power for tilting the slag holding furnace 2. The upper end of the cylinder 41 is connected to the lower wall 22 of the furnace body 20 at a position where the slag holding furnace 2 is tiltably spaced toward the electric furnace 1, and the lower end of the cylinder 41 is connected to the upper surface of the carriage 45. The tilting shaft 44 is provided below the spout portion 21 of the slag holding furnace 2 and serves as the central axis of the tilting operation of the slag holding furnace 2. The support members 42 and 43 are coupled to each other by a tilting shaft 44 so as to be rotatable. The upper end of the support member 42 is connected to the lower side of the spout portion 21, and the lower end of the support member 43 is connected to the upper surface of the carriage 45. The slag holding furnace 2 is tiltably supported by the cylinder 41, the support members 42 and 43, and the tilt shaft 44.

  With the tilting device 40 having such a configuration, the slag holding furnace 2 can be tilted between the holding posture (FIG. 3) and the pouring posture (FIG. 4) around the tilting shaft 44. Here, as shown in FIG. 3, the holding posture is a posture when the slag holding furnace 2 holds the molten slag 4 in the furnace body 20 without injecting the molten slag 4 into the electric furnace 1. On the other hand, as shown in FIG. 4, the pouring posture is a posture when the slag holding furnace 2 is tilted toward the spout 21 and the molten slag 4 in the furnace body 20 is poured into the electric furnace 1. .

  When changing the slag holding furnace 2 from the holding position to the pouring position, the cylinder 41 is extended, the rear part of the furnace body 20 is lifted, and the slag holding furnace 2 is tilted toward the electric furnace 1 with the tilting shaft 44 as the center. As a result, as shown in FIG. 4, the position of the spout portion 21 is relatively low with respect to the furnace body 20, so that the molten slag 4 held in the furnace body 20 is moved to the spout portion 21 side. Then, it flows from the spout 29 through the slag injection path 28 and is poured into the electric furnace 1. At this time, the amount of molten slag 4 injected can be adjusted by controlling the extension length of the cylinder 41 and adjusting the tilt angle of the slag holding furnace 2.

  On the other hand, when changing the slag holding furnace 2 from the pouring posture to the holding posture, the cylinder 41 is contracted to return the furnace body 20 to the holding posture. As a result, as shown in FIG. 3, the position of the spout portion 21 is relatively high with respect to the furnace body 20, and the liquid level of the molten slag 4 in the furnace body 20 is lower than the slag injection path 28. The molten slag 4 is held in the furnace body 20 without being injected into the electric furnace 1.

  Moreover, the trolley | bogie 45 supports the tilting apparatus 40 so that a movement is possible. By using the carriage 45 to move the slag holding furnace 2 backward or forward, the slag holding furnace 2 can be easily inspected, replaced, or repaired. The load cell 46 is installed, for example, between the carriage 45, the cylinder 41, and the support member 43, and measures the load applied by the furnace body 20 including the molten slag 4 that is held.

  As described above, by tilting the slag holding furnace 2 using the tilting device 40, it is possible to inject the molten slag 4 into the electric furnace 1 intermittently or to adjust the injection amount. When injecting the molten slag 4 into the electric furnace 1, an appropriate amount of injection is used using the tilting device 40 so that the injected molten slag 4 does not rapidly react with the molten iron in the electric furnace 1 and overflow from the electric furnace 1. It is preferable to inject the molten slag 4 intermittently while adjusting (i.e., adjusting the tilt angle of the slag holding furnace 2). If the injection speed is too high during the injection of the molten slag 4, the molten slag 4 may be in a forming state in the electric furnace 1, and overflow may occur. In this case, the tilt angle of the slag holding furnace 2 is reduced by the tilting device 40 and the injection of the molten slag 4 is temporarily stopped, or the injection amount is reduced to calm the reaction in the electric furnace 1. It is preferable to do.

  The amount of molten slag 4 injected per unit time by the slag holding furnace 2 is determined according to the reduction capacity of the electric furnace 1. The reduction processing capacity depends on the amount of power supplied to the electric furnace 1 per unit time, for example, the amount of power applied to the electrodes 15 and 16 of the electric furnace 1. Therefore, the injection amount of the molten slag 4 per unit time may be determined based on the power consumption necessary for the reduction treatment of the molten slag 4 and the actual power applied to the electrodes 15 and 16.

  Further, as a method of intermittently injecting the molten slag 4 from the slag holding furnace 2 into the electric furnace 1, a method of injecting the molten slag 4 while repeating injection and interruption of the molten slag 4 or in the slag holding furnace 2 at a predetermined time interval. There is a method of injecting a predetermined amount of molten slag 4 held in a batch, and any method may be employed in the embodiment of the present invention. When intermittently injecting the molten slag 4, it is desirable to confirm beforehand by experiments or the like that the total amount of molten slag 4 to be injected all at once is an amount that does not cause overflow due to slag forming. .

(4. Configuration of oxygen gas supply equipment)
Next, an oxygen gas supply facility incidental to the slag treatment facility will be described with reference to FIGS. 3 and 4. As shown in FIGS. 3 and 4, the oxygen gas supply facility 50 includes an oxygen gas supply nozzle 51 installed in the slag holding furnace 2 and a control for controlling the flow rate of the oxygen gas supplied to the oxygen gas supply nozzle 51. A summing box 53 connected to the device 52, the load cell 46, adding the measured values and outputting the result to the control device 52, a radiation thermometer 54 for measuring the surface temperature of the molten slag layer 5 in the electric furnace 1, A gas sampler 55 installed in the vicinity of the gas outlet 25 of the slag holding furnace 2 and an exhaust gas analyzer 56 for analyzing components of the exhaust gas sampled by the gas sampler 55 are included. In the present embodiment, the exhaust gas analyzer 56 measures at least the concentrations of oxygen and CO in the exhaust gas.

  In the oxygen gas supply facility 50 as described above, the control device 52 configures the molten slag layer 5 in the electric furnace 1 before the injection, the oxygen gas flow rate immediately after the injection of the molten slag 4 and the injection amount of the molten slag 4. Of molten slag (hereinafter also simply referred to as molten slag amount before injection) and the temperature of molten slag forming molten slag layer 5 in the electric furnace 1 before injection (hereinafter simply referred to as molten slag before injection). (Also called temperature). As described in detail below, this makes it possible to determine an appropriate oxygen gas flow rate corresponding to the generation amount of CO gas that increases rapidly immediately after the injection of the molten slag 4.

  Here, the injection amount of the molten slag 4 is calculated from a change in load by the furnace body 20 including the molten slag 4. More specifically, the control device 52 calculates the difference in load before and after the injection of the molten slag 4 based on the measurement value of the load cell 46 output via the summing box 53. The load difference calculated in this way corresponds to the amount of molten slag 4 injected. The molten slag temperature before injection is estimated from the surface temperature measured by the radiation thermometer 54. The amount of molten slag before pouring is specified based on the components and cumulative amount of the molten slag 4 injected into the electric furnace 1, and the discharge history of the reduced slag and molten iron from the tap outlet 17 and the hot water outlet 18. The More specifically, immediately after the molten iron is discharged from the hot water outlet 18, the interface height of the molten iron layer 6 substantially coincides with the hot water outlet 18. The subsequent change in the interface height of the molten iron layer 6 occurs when FeO contained in the molten slag layer 5 is reduced to Fe and moves into the molten iron. Therefore, if the amount of the molten slag 4 injected into the electric furnace 1 after the discharge of the molten iron and the FeO concentration in the molten slag 4 are known, the interface height of the molten iron layer 6 at an arbitrary time can be calculated. it can. Immediately after the reduced slag is discharged from the tap outlet 17, the molten metal surface level of the molten slag layer 5 substantially matches the tap outlet 17. Therefore, the amount of molten slag 4 injected into the electric furnace 1 after discharge of the reduced slag and the interface height of the molten iron layer 6 (corresponding to the amount of Fe transferred from the molten slag layer 5) are identified. For example, the amount of molten slag contained in the molten slag layer 5 can be calculated at an arbitrary time.

  On the other hand, in the oxygen gas supply facility 50, the control device 52 switches the control of the oxygen gas flow rate to feedback control after determining the oxygen gas flow rate immediately after the injection of the molten slag 4 as described above. More specifically, the control device 52 increases the oxygen gas flow rate by a predetermined amount when the CO concentration measured by the exhaust gas analyzer 56 exceeds a threshold value (for example, 1%). In addition, the control device 52 decreases the oxygen gas flow rate by a predetermined amount when the oxygen concentration measured by the exhaust gas analyzer 56 exceeds a threshold value. When the molten slag 4 is injected again, the control device 52 interrupts the feedback control of the oxygen gas flow rate, and immediately after the injection of the molten slag 4, the injection amount of the molten slag 4 and the molten slag before the injection as described above. The oxygen gas flow rate determined based on the amount and the molten slag temperature before injection is set.

  Note that the control device 52 in the oxygen gas supply facility 50 as described above is realized as, for example, a control circuit or a computer in which a CPU (Central Processing Unit) executes a program stored in a memory. The control device 52 may include an output device such as a monitor for presenting information to the operator, and an input device such as a button for acquiring an operation input of the operator.

  In the oxygen gas supply equipment 50 as described above, the problem in the feedback control of the oxygen gas flow rate that it is difficult to follow the rapid increase in the amount of CO gas generated immediately after the injection of the molten slag 4 is that immediately after the injection of the molten slag 4. This can be solved by separately setting an appropriate oxygen gas flow rate and starting feedback control. However, in order to obtain such an effect, the oxygen gas flow rate immediately after injection determined based on the injection amount of the molten slag 4, the amount of molten slag before injection, and the temperature of the molten slag before injection is determined as follows: The amount should be appropriate for the gas generation state. Below, the point which can calculate such an oxygen gas flow volume in this embodiment is further demonstrated.

As already explained, the main reaction in the reduction reaction of the molten slag 4 in the electric furnace 1 is a reaction of FeO + C → Fe + CO ↑. Therefore, the CO gas generation rate FCO can be expressed by the following Equation 1. Incidentally, k is the reaction rate constant, the surface area of the carbonaceous material in contact with the (FeO) is the FeO concentration in the reaction site (the melt surface near the molten slag layer 5), S _C molten slag 4 was injected Show.

Here, the reaction rate constant k can be expressed by the following equation 2 using the reaction site temperature T, gas constant R, reaction activation energy Ea, and constant A ₁ (Arrhenius equation).

Here, the reaction site temperature T in Equation 2 above is the temperature of the molten slag forming the molten slag layer 5 in the electric furnace 1 before injection, and the molten slag layer 5 measured by the radiation thermometer 54. It has been experimentally confirmed that it can be treated as equivalent to the hot water surface temperature. For this reason, as the temperature T of the reaction site, the surface temperature of the molten slag layer 5 measured by the radiation thermometer 54 can be used. Further, the FeO concentration (FeO) at the reaction site is expressed by the following formula 3 using the molten slag amount Sw before injection, the injected amount ΔW of the molten slag 4 and the FeO concentration (FeO) _P of the molten slag 4. be able to.

  As described above, in the present embodiment, the amount of molten slag Sw before injection includes the components and accumulated amount of the molten slag 4 injected into the electric furnace 1, the reduced slag and molten iron from the tap 17 and the tap 18 Based on the discharge history. Further, the injection amount ΔW of the molten slag 4 is calculated by the control device 52 from the change in load caused by the furnace body 20 including the molten slag 4 measured by the load cell 46.

In Formula 3, since the FeO concentration in the molten slag layer 5 before injection of the molten slag 4 is reduced to a negligible level due to the progress of the reduction reaction, the FeO contained in the injected molten slag 4 is melted. This is based on the assumption that the molten slag contained in the slag layer 5 can be regarded as diluted. In actual operation, the FeO concentration (FeO) _P of the molten slag 4 is substantially constant throughout the operation. Therefore, hereinafter, the FeO concentration (FeO) _P of the molten slag 4 is treated as a specific constant for each operation.

On the other hand, the surface area S _C of the carbonaceous material in contact with the injected molten slag 4 is influenced by the amount of carbonaceous material contained in the molten slag layer 5, a stirring state of the electric furnace 1. Stirring stronger becomes carbonaceous material is easily caught up in the interior of the molten slag layer 5, thus the surface area S _C of the carbonaceous material in contact with the molten slag 4 is increased. However, in an actual operation, a sufficient amount (in some cases, an excessive amount) of carbonaceous material is introduced in advance, particularly when the molten slag 4 is injected, and the stirring state is substantially constant throughout the operation. Therefore, in the following, for the surface area S _C of the carbonaceous material is treated as constants specific for each operation.

Based on the above, Equation 1 representing the CO gas generation rate FCO can be rewritten as Equation 4 below. Incidentally, the constant _{A 2} is multiplied by the FeO concentration of formula 2 constants _{A 1} to the surface area of the carbonaceous material _{S C} and molten slag 4 _{(FeO) P} (As described above, both of which are treated as constants specific for each operation) It is a thing.

Next, an appropriate oxygen gas flow rate FO ₂ immediately after the injection of the molten slag 4 is calculated based on the above formula 4. Here, since the combustion reaction of CO gas is 2CO + O ₂ → CO ₂ , the oxygen gas flow rate FO ₂ necessary for burning the CO gas generated by the injection of the molten slag 4 without excess or shortage is the generation of CO gas. Half of the speed FCO (1/2 FCO).

Further, in the case of the second and subsequent injections of the molten slag 4 or the like, when the oxygen gas is already supplied from the oxygen gas supply nozzle 51 before the injection, the flow rate FO ₂ ′ is generated in the state before the injection. This is considered to be the oxygen gas flow rate required to burn the CO gas without excess or deficiency (when sufficient time has passed since the previous injection, the oxygen gas flow rate set by feedback control converges to an appropriate value. For). Accordingly, assuming that the CO gas generated before the injection of the molten slag 4 continues to be generated after the injection, the oxygen gas flow rate FO ₂ burns the CO gas generated by the newly injected molten slag 4. This is obtained by adding the oxygen gas flow rate (FO ₂ ′) before injection to the oxygen gas flow rate (½ FCO).

From the above, the appropriate oxygen gas flow rate FO ₂ immediately after the injection of the molten slag 4 is calculated by the following equation 5.

In order to simplify the mathematical expression, ½A ₂ is set as a new constant α in the following. Further, the gas constant R and the activation energy Ea are combined to form a new constant β (β = Ea / R). When Expression 5 is expressed using constants α and β, the following Expression 6 is obtained.

In the above formula 6, the constant α is a constant specific to each operation, as is the case with the constant A ₂ in formula 4. In addition, the constant β is theoretically a constant that does not depend on the operating conditions, but in the oxygen gas supply facility 50, the hot water surface temperature of the molten slag layer 5 measured by the radiation thermometer 54 and the actual reaction site temperature. There is a possibility that a difference may occur between T and it is considered appropriate to evaluate this difference as a specific constant for each operation. Therefore, in the present embodiment, in order to calculate an appropriate oxygen gas flow rate FO ₂ based on the above-described formula 6, it is necessary to specify the constants α and β based on the actual values at the time of operation under the same conditions. become. The method will be further described below.

When the above equation 4 representing the CO gas generation rate FCO is expressed by using constants α and β, the following equation 7 is obtained (α = 1 / 2A ₂ , β = Ea / R).

  If the logarithm of both sides of Equation 7 is taken and arranged, the following Equation 8 is obtained.

From Equation 8, if the relationship between 1 / T and ln (1 / 2FCO · Sw / ΔW) in the actual data is plotted, the constants α and β can be specified as the intercept (lnα) and the slope (−β). it can. The CO gas generation rate FCO is obtained by multiplying the exhaust gas flow rate by the sum of the concentration of CO gas detected by the exhaust gas analyzer 56 and the concentration of CO ₂ gas (generated when the CO gas burns). Calculated. As described above, the other amounts included in Equation 8, namely, the injection amount ΔW of the molten slag 4, the molten slag amount Sw before injection, and the molten slag temperature T before injection are all in the oxygen gas supply facility 50. It can be measured.

As described above, in the present embodiment, the oxygen immediately after the injection of the molten slag 4 is based on the injection amount ΔW of the molten slag 4, the molten slag amount Sw before the injection, and the molten slag temperature T before the injection. The gas flow rate FO ₂ can be calculated. The oxygen gas flow rate FO ₂ calculated in this way is an appropriate amount adapted to the generation state of the CO gas immediately after the injection of the molten slag 4, as shown by the embodiment of the present invention described below. It is.

FIG. 5 is a graph showing a process of determining constants used in the formula for calculating the oxygen gas flow rate in the embodiment of the present invention. In this example, first, in order to determine the constants α and β using Equation 8 above, an operation for collecting actual values in the slag treatment facility was performed. In operation, the injection amount ΔW (kg) of the molten slag 4, the molten slag temperature T (K) before injection, the molten slag amount Sw (ton) before injection, and the CO gas generation rate FCO (Nm ³ / h) was measured. As main operating conditions, the electric furnace 1 was a 4 MW closed DC arc furnace, and had a furnace inner diameter of 3.0 m. Further, as the molten slag 4, a converter slag is used. Fe = 24% to 26%. The amount of charcoal charged into the molten slag layer 5 was 1.3 times the FeO content of the injected molten slag 4. The carbon content of the molten iron layer 6 was 4% to 4.5%.

A total of 24 injections of molten slag 4 were performed and the above measured values were collected. As a result, the relationship between 1 / T and ln (1/2 FCO · Sw / ΔW) was as shown in the graph of FIG. . From this, as shown in the graph, an approximate straight line y = −41135x + 22.718 is obtained. Note that y = ln (1 / 2FCO · Sw / ΔW) and x = 1 / T. Accordingly, the values of the constants α and β are determined to be α = e ^22.718 = 7.7 × 10 ⁹ and β = 41135 = 4.1 × 10 ⁴ .

By substituting the values of the determined constants α and β into Equation 6 above, melting based on the injection amount ΔW of the molten slag 4, the molten slag amount Sw before injection, and the molten slag temperature T before injection An appropriate oxygen gas flow rate FO ₂ immediately after the injection of the slag 4 can be calculated. Hereinafter, this manner the oxygen gas flow rate FO ₂ that is calculated will be described the results of operations of applying the oxygen gas flow rate immediately after the injection of the molten slag 4.

Note that, as described above, the injection amount ΔW of the molten slag 4 is calculated from the change in the load by the furnace body 20, and thus is not calculated until the injection is actually performed. However, other numerical values, that is, the molten slag amount Sw before injection and the molten slag temperature T before injection can be calculated or measured before the injection is performed. In addition, since the calculation process for the injection amount ΔW is simple, it is possible to obtain a result immediately after the injection. Therefore, in this embodiment, the oxygen gas flow rate FO ₂ is determined almost simultaneously with the injection of the molten slag 4.

Moreover, as already explained, the oxygen gas supply equipment 50, the control device 52, after determining the oxygen gas flow rate immediately after the injection of the molten slag 4 as described above, feedback control of the control of the oxygen gas flow rate FO ₂ Switch to. In the present embodiment, the control device 52 that is executing the feedback control increases the oxygen gas flow rate FO ₂ by 40 Nm ³ / h when the CO concentration in the exhaust gas exceeds 1%. In addition, when the oxygen concentration in the exhaust gas exceeds 1%, the control device 52 decreases the oxygen gas supply amount FO ₂ according to the amount at that time. Decrease in this ^{case, 60Nm 3 / h, 150Nm 3} / h or more 250 Nm ³ / is less than ^{h 50Nm 3 / h, 150Nm 3} / under h if the oxygen gas supply amount FO ₂ is 250 Nm ³ / h or more If so, it is 40 Nm ³ / h.

FIG. 6 is a graph showing the progress of operation in this example. In this example, from time 0, the supply power to the electric furnace 1 was set to 2.5 MW, and the molten slag reduction process was started. At the start of treatment, a molten iron layer 6 made of about 10 ton pig iron and a molten slag layer 5 made of reduced 2 ton molten slag were formed in the electric furnace 1. Therefore, the molten slag amount Sw before the first injection is 2 ton. The molten slag temperature T before injection was 1490 ° C. (1763 K). Since it is before the start of the reduction treatment, no exhaust gas containing CO gas is generated, and therefore oxygen gas is not supplied from the oxygen gas supply nozzle 51 before injection (FO ₂ ′ = 0).

  Under such conditions, the first injection of molten slag 4 was performed. More specifically, the cylinder 41 was extended to tilt the slag holding furnace 2 so that the pouring posture as shown in FIG. Thereby, the molten slag 4 in the slag holding furnace 2 is injected into the electric furnace 1 through the spout portion 21. After maintaining this state for a predetermined time, the cylinder 41 was contracted, and the slag holding furnace 2 was returned to the holding posture as shown in FIG. In this embodiment, since the time during which the pouring posture of the slag holding furnace 2 is maintained during the pouring of the molten slag 4 is short, the graph of FIG. 5 shows that the pouring is performed instantaneously. In the first injection, the injection amount ΔW of the molten slag 4 calculated from the change in the load by the furnace body 20 including the molten slag 4 was 1100 kg.

Immediately after the first injection as described above, the controller 52 calculates the oxygen gas flow rate FO ₂ based on the molten slag amount Sw before injection, the molten slag temperature T before injection, and the injection amount ΔW of the molten slag 4. , FO ₂ = 340 Nm ³ / h. According to this result, the controller 52 started supplying oxygen gas to the oxygen gas supply nozzle 51 at a flow rate of 340 Nm ³ / h. On the other hand, in the electric furnace 1 into which the molten slag 4 was injected, a reduction reaction was started, and exhaust gas containing CO gas was generated. Thereby, the flow rate of the exhaust gas discharged from the gas outlet 25 of the slag holding furnace 2 increased to 800 Nm ³ / h. However, since the CO gas was completely burned in the slag holding furnace 2 by the oxygen gas supplied from the oxygen gas supply nozzle 51, the exhaust gas analyzer 56 did not detect CO.

After setting the oxygen gas flow rate FO ₂ = 340 Nm ³ / h calculated as described above, the control device 52 switches the control of the oxygen gas flow rate FO ₂ to feedback control. Thereafter, since the oxygen concentration detected by the exhaust gas analyzer 56 exceeded 1%, the controller 52 lowered the oxygen gas flow rate FO ₂ to 280 Nm ³ / h. Thereafter, the controller 52 decreases the oxygen gas flow rate FO ₂ every time the oxygen concentration exceeds 1%, and when about 20 minutes have elapsed from the start of processing, the oxygen gas flow rate FO ₂ is kept constant at 40 Nm ³ / h. became. At this point, the reduction reaction of the molten slag in the electric furnace 1 has almost converged.

Therefore, the second injection of the molten slag 4 was performed when 33 minutes had elapsed since the start of the treatment. Prior to the injection, the controller 52 interrupts the feedback control of the oxygen gas flow rate FO ₂ , maintains the flow rate at that time (FO ₂ ′ = 40 Nm ³ / h), and immediately after the injection of the molten slag 4 Preparation for calculating the gas flow rate FO ₂ was made. In the second injection, the molten slag amount Sw before injection was 3.1 ton, and the molten slag temperature T before injection was 1495 ° C. (1768 K).

In the second injection, the molten slag 4 was injected from the slag holding furnace 2 to the electric furnace 1 by the operation of the slag holding furnace 2 as in the first time. The injection amount ΔW of the molten slag 4 calculated from the change in the load by the furnace body 20 including the molten slag 4 was 1500 kg. Immediately after the second injection, before injection of the molten slag amount Sw, molten slag temperature T prior to injection, and the control unit 52 based on the injection quantity ΔW of molten slag 4 was calculated oxygen gas flow rate FO ₂ results, FO2 = 360 Nm ³ / h. According to this result, the controller 52 changed the flow rate of the oxygen gas supplied to the oxygen gas nozzle to 360 Nm ³ / h. Thereafter, the control device 52 switched the control of the oxygen gas flow rate FO ₂ to feedback control.

Immediately after the second injection, the amount of CO gas generated by the reduction reaction of the molten slag 4 in the electric furnace 1 is slightly larger than the assumed value according to the present invention, and therefore the CO concentration detected by the exhaust gas analyzer 56 is It exceeded 1%. In response to this, the controller 52 raised the oxygen gas flow rate FO ₂ to 400 Nm ³ / h. As a result, the CO gas completely combusted in the slag holding furnace 2, and after a while, the oxygen concentration detected by the exhaust gas analyzer 56 exceeded 1%. Thereafter, as in the case of the first injection, the control device 52 gradually decreases the oxygen gas flow rate FO ₂ by feedback control, and about 55 minutes have elapsed from the start of the process, and about 22 minutes have elapsed since the second injection. At that time, the oxygen gas flow rate FO ₂ became constant at 80 Nm ³ / h.

Thereafter, when 78 minutes and 93 minutes passed from the start of the treatment, the third and fourth injections of the molten slag 4 were performed, respectively. The injection amount ΔW of the molten slag 4 was 500 kg at the third time and 1000 kg at the fourth time. Also at this time, the control device 52 interrupts the feedback control of the oxygen gas flow rate FO ₂ prior to the injection, and the oxygen gas calculated based on the molten slag amount Sw, the molten metal surface temperature T, and the injection amount ΔW immediately after the injection. It was resumed feedback control on setting the flow rate FO _2. As a result, CO is not detected by the exhaust gas analyzer 56 in both the third injection and the fourth injection, and the operation is stably continued while the oxygen gas flow rate FO ₂ is gradually reduced by feedback control. We were able to.

FIG. 7 is a graph showing the progress of operation in a comparative example with respect to the above embodiment. In the comparative example, the molten slag was reduced using the same slag processing equipment as in the above example, but the oxygen gas flow rate FO ₂ immediately after the injection of the molten slag 4 was changed to the average processing speed of the reduction treatment in the electric furnace 1. The fixed value estimated on the basis (100 Nm ³ / h) was set. The point that the control of the oxygen gas flow rate FO ₂ is switched to the feedback control after setting the fixed value and the condition of the feedback control are the same as in the embodiment.

When the treatment was started under the above conditions and 1300 kg of molten slag 4 was injected from the slag holding furnace 2 to the electric furnace 1, the CO concentration detected by the exhaust gas analyzer 56 increased rapidly and exceeded the measurable range. . Although the oxygen gas flow rate FO ₂ was increased by feedback control, the CO concentration did not decrease, and the oxygen gas flow rate FO ₂ finally increased to 360 Nm ³ / h. Since the analysis of the exhaust gas component by the exhaust gas analyzer 56 was repeated (6 times) for feedback control, it took about 2 minutes for the oxygen gas flow rate FO ₂ to be set to the above value. During this time, unburned CO gas continued to flow into the exhaust path after the slag holding furnace 2, and a large amount of CO gas had to be removed by equipment on the exhaust path.

In the above comparative example, a somewhat high value was set as the oxygen gas flow rate FO ₂ immediately after injection of the molten slag 4 (the flow rate FO ₂ ′ before injection was 0, whereas 100 Nm ³ / h was set). Nevertheless, it has not been possible to prevent a large amount of CO gas from flowing into the exhaust passage without being burned. Thus, for example, when also conducted normal feedback control (oxygen gas flow rate FO ₂ stepwise increases from 0) immediately after the injection of the molten slag 4 further leave the exhaust passage of a large amount of CO gas is unburned It is assumed that the result was an outflow.

On the other hand, in the embodiment of the present invention, even when the amount of generated CO gas is larger than expected, for example, at the time of the second injection, the oxygen gas flow rate FO ₂ immediately after the injection is set to a sufficiently high value. Thus, the oxygen gas flow rate FO ₂ can be increased to an appropriate amount by one-step feedback control, and the outflow of CO gas can be minimized. Also, when the amount of generated CO gas is within the expected range as in the first injection, the third injection, and the fourth injection, oxygen is detected excessively (for example, greatly exceeding 1%) in the exhaust gas. However, an appropriate amount of the oxygen gas flow rate FO ₂ is maintained by feedback control.

  According to the embodiment described above, the present invention appropriately determines the oxygen supply amount to the slag holding furnace 2 immediately after the injection of the molten slag 4, and sufficiently burns the CO gas contained in the exhaust gas. It can be said that this is effective for maintaining the atmospheric temperature in 2 at a high temperature.

  In the above description of the embodiments and examples of the present invention, the oxygen gas flow rate for burning the CO gas in the exhaust gas generated in the electric furnace immediately after the injection of the molten slag has been calculated. The form is not limited to such an example. For example, the oxygen gas flow rate for burning combustible components (for example, hydrogen etc.) other than CO gas in exhaust gas may be calculated by the same method. In this case, the flow rate of oxygen gas supplied to the slag holding furnace may be calculated as the sum of the flow rate for burning CO gas and the flow rate for burning other combustible gases. Further, the combustible component to be burned may not necessarily be a toxic component such as CO gas. As described above, the combustion of combustible components in the slag holding furnace is also effective for maintaining the atmospheric temperature, so even if it is not a toxic component and a component that does not need to be removed in the exhaust path, If it is a combustible component, it may be burned by oxygen supplied into the slag holding furnace. In the above description, oxygen gas is supplied into the slag holding furnace. However, pure oxygen gas is not necessarily supplied, and oxygen-containing gas such as air may be supplied.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Electric furnace 2 Slag holding furnace 3 Slag pan 4 Molten slag 5 Molten slag layer 6 Molten iron layer 14 Slag inlet 15 Upper electrode 16 Furnace electrode 17 Outlet 18 Outlet 40 Tilting device 46 Load cell 50 Oxygen gas supply equipment 51 Oxygen Gas nozzle 52 Control device 53 Summing box 54 Radiation thermometer 55 Gas sampler 56 Exhaust gas analyzer

Claims (1)

The molten slag generated in the steel making process is charged into a slag holding furnace in a molten state, and intermittently from the slag holding furnace into an electric furnace that accommodates the molten iron layer and the molten slag layer formed on the molten iron layer. Injecting the molten slag in an automatic manner, continuously reducing the molten slag in the electric furnace, and recovering valuable materials in the molten slag in the molten iron layer,
When introducing the exhaust gas generated in the electric furnace into the slag holding furnace and burning the combustible component in the exhaust gas by supplying an oxygen-containing gas at a predetermined flow rate into the slag holding furnace,
The flow rate of the oxygen-containing gas immediately after the injection of the molten slag is included in the molten slag injection amount ΔW , the amount Sw of the molten slag contained in the molten slag layer before the injection, and the molten slag layer before the injection. After setting the flow rate calculated by the following formula based on the temperature T of the molten slag and constants α and β based on the actual values at the time of operation ,
A slag treatment method in which the flow rate of the oxygen-containing gas is feedback-controlled based on the CO concentration and oxygen concentration in the exhaust gas in the vicinity of the gas discharge port of the slag holding furnace .

here,
FO ₂ : Flow rate of the oxygen-containing gas immediately after injection of the molten slag
FO ₂ ': Flow rate of the oxygen-containing gas before injection
ΔW: injection amount of the molten slag
Sw: The amount of the molten slag contained in the molten slag layer before injection
T: temperature of the molten slag contained in the molten slag layer before injection
α, β: Constant

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