WO2014112521A1 - 溶銑の予備処理方法 - Google Patents
溶銑の予備処理方法 Download PDFInfo
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- WO2014112521A1 WO2014112521A1 PCT/JP2014/050561 JP2014050561W WO2014112521A1 WO 2014112521 A1 WO2014112521 A1 WO 2014112521A1 JP 2014050561 W JP2014050561 W JP 2014050561W WO 2014112521 A1 WO2014112521 A1 WO 2014112521A1
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- gas
- hot metal
- desiliconization
- slag
- concentration
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/02—Dephosphorising or desulfurising
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C1/00—Refining of pig-iron; Cast iron
- C21C1/04—Removing impurities other than carbon, phosphorus or sulfur
Definitions
- the present invention relates to a hot metal pretreatment method in which a single converter-type refining furnace is used to continuously perform desiliconization and dephosphorization of hot metal with an intermediate waste removal step in between.
- a refining method (“preliminary dephosphorization treatment” in which hot metal is preliminarily treated before decarburization refining in a converter and phosphorus in the molten iron is removed in advance.
- the dephosphorization treatment is performed by adding an oxidizing agent (oxygen source such as oxygen gas) and a dephosphorizing refining agent (CaO-based solvent) to hot metal, and oxidizing phosphorus in the hot metal with an oxidizing agent to form a phosphorus oxide.
- an oxidizing agent oxygen source such as oxygen gas
- a dephosphorizing refining agent CaO-based solvent
- this dephosphorization reaction is advantageous as the refining temperature is lower in terms of thermodynamics. That is, the dephosphorization reaction is more likely to proceed in the hot metal stage where the temperature is lower than that in the molten steel stage, and the dephosphorization treatment can be performed with less oxidizing agent and dephosphorizing agent. Therefore, by performing the preliminary dephosphorization treatment, the number of treatment steps increases, but the amount of slag generation in the entire steelmaking refining step can be reduced.
- the hot metal discharged from the blast furnace contains about 0.3 to 0.6 mass% of silicon.
- the silicon is first oxidized and removed. After the silicon concentration is reduced to a certain level, phosphorus in the hot metal is oxidized and removed. Oxidation of silicon produces slag containing SiO 2 as a main component, but this slag inhibits the dephosphorization reaction. This is because slag having a basicity ([CaO (mass%)] / [SiO 2 (mass%)]) of 1.2 or more is necessary for the dephosphorization reaction, whereas silicon oxidation is performed. This is because the SiO 2 produced by this has the effect of lowering the basicity of the slag.
- the heat source for melting cold iron sources such as iron scrap mainly consists of sensible heat of hot metal and combustion heat of carbon and silicon in hot metal. Cannot dissolve a large amount of cold iron source.
- the heat source for melting cold iron sources such as iron scrap mainly consists of sensible heat of hot metal and combustion heat of carbon and silicon in hot metal. Cannot dissolve a large amount of cold iron source.
- carbon and silicon in the hot metal as a combustion heat source are reduced. Since it is oxidized and reduced by the above desiliconization treatment and dephosphorization treatment, it is more disadvantageous for melting the cold iron source in the converter.
- Patent Document 1 discloses desiliconization and dephosphorization of hot metal using one converter-type refining furnace.
- a hot metal pretreatment method in which a slag produced in a furnace is tilted and discharged from a furnace port, and then a CaO-based solvent is newly added to perform dephosphorization.
- Patent Document 2 when performing desiliconization and dephosphorization of hot metal using one converter-type refining furnace, the dephosphorization process is completed, the hot metal is discharged, and the slag is not discharged.
- An intermediate waste removal process in which the hot metal of the next charge is charged into the smelting furnace while remaining in the furnace, oxygen is supplied to perform the desiliconization process, and after the desiliconization process, the blowing is temporarily interrupted and the slag is discharged.
- a hot metal pretreatment method that is provided and then subsequently dephosphorized.
- the temperature drop due to the transfer of hot metal can be prevented by performing the desiliconization process and the dephosphorization process in one converter-type refining furnace.
- the slag generated in the dephosphorization process (hereinafter also referred to as “dephosphorization slag”) is reused in the desiliconization process. It becomes possible to reduce. That is, by adopting the techniques of Patent Document 1 and Patent Document 2, the heat loss in the hot metal pretreatment process can be reduced, so that the blending ratio of the cold iron source is increased as compared with the conventional one, and the amount of greenhouse gas emissions Reduction and manufacturing cost can be reduced.
- JP-A-10-152714 Japanese Patent Laid-Open No. 11-323420
- Patent Document 1 shows that the slag is sufficiently fluid if the basicity of the slag at the end of the desiliconization process is controlled to 0.3 to 1.3. It is said that the desiliconization slag will be exhausted sufficiently.
- slag formation is insufficient, fluidity is poor, and slag can be discharged in a short time without causing molten iron to flow out. It may be difficult, or conversely, forming may be excessive, and slag may overflow from the furnace port during the desiliconization process, thereby hindering operation.
- Patent Document 2 is optimal to set the basicity of desiliconized slag to 1.0 to 3.0 and perform intermediate waste after the silicon concentration in the hot metal becomes 0.20 mass% or less.
- the reason for this is that when the silicon concentration in the hot metal at the end of the desiliconization process is higher than 0.20 mass%, the basicity of the slag at the next dephosphorization process is adjusted to 2.0. This is because the necessary CaO-containing material is excessively increased, which is disadvantageous in terms of cost, and no consideration is given to the elimination of the desiliconized slag.
- the present invention has been made in view of the above-mentioned problems in the prior art, and its purpose is to use a single converter-type refining furnace and to perform desiliconization treatment and dephosphorization of hot metal with an intermediate waste removal step in between.
- the hot metal preliminary treatment method in which the treatment is continuously performed, the dephosphorization property of the desiliconization slag generated by the desiliconization treatment is improved, and the dephosphorization treatment of the next step is performed while suppressing the temperature drop of the hot metal,
- the object is to propose a hot metal pretreatment method that can be performed at low cost.
- the first aspect of the present invention developed to solve the above problem is that the oxygen source is supplied to the hot metal in the converter type refining furnace and desiliconized, and then the hot metal remains in the furnace. Part of the slag present in the furnace is discharged from the converter-type refining furnace, and then the hot metal that has been dephosphorized by supplying a CaO-based solvent and an oxygen source into the converter-type refining furnace is discharged from the converter-type refining furnace.
- the exhaust gas treatment equipment of the converter type refining furnace is used during the desiliconization treatment.
- a hot metal pretreatment method characterized in that the concentration of a gas species containing at least one carbon atom in the sucked suction gas is analyzed, and the end point of the desiliconization treatment is determined based on the analysis value. .
- the suction rate of carbon in the exhaust gas discharged from the converter-type smelting furnace during the desiliconization process is set as the suction rate. Calculated based on the analytical value of the concentration of the gas species containing carbon atoms in the gas and the flow rate of the suction gas, and the calculated rate of carbon emission in the exhaust gas reaches a maximum value and then increases again after reaching a minimum value. An end point of the desiliconization process is determined based on a fluctuation pattern to be performed.
- the end point of the desiliconization treatment is determined by the CO gas concentration, the CO 2 gas concentration, and the CO gas in the suction gas.
- the analysis value of the concentration of any one of the total concentrations of CO 2 and CO 2 gas becomes a maximum value, and is determined based on a fluctuation pattern that increases again after reaching the minimum value.
- the end point of the desiliconization treatment is determined by the CO gas concentration, the CO 2 gas concentration and the CO gas in the suction gas.
- the CO gas flow rate in the suction gas, the CO 2 gas flow rate, and the CO gas and CO 2 calculated from the product of the analytical value of the concentration of any one of the total concentrations of CO 2 and CO 2 gas and the flow rate of the suction gas Any one of the total gas flow rates becomes a maximum value, and is determined based on a fluctuation pattern that increases again after reaching the minimum value.
- the end point of the desiliconization treatment becomes the maximum value and the minimum value.
- the increased value is within a predetermined elapsed time range with reference to a point in time when the increased value becomes equal to or greater than a predetermined ratio of 90% to 150% with respect to the maximum value.
- the maximum value in the fluctuation pattern that becomes the maximum value and increases again after reaching the minimum value is 10% or more of the maximum value.
- the end point of the desiliconization treatment is defined as a CO gas concentration, a CO 2 gas concentration, and a CO gas in the suction gas.
- the analysis value of any one of the total concentrations of CO 2 and CO 2 gas is set within a predetermined elapsed time range with reference to a time point when the analysis value of the concentration becomes equal to or higher than a predetermined threshold value.
- the exhaust gas treatment facility has a function of recovering the sucked exhaust gas from the converter refining furnace as fuel gas.
- the air is sucked together with the exhaust gas of the converter refining furnace to burn at least a part of the CO gas in the exhaust gas, and the end point of the desiliconization treatment is determined after the combustion. It is characterized in that the CO gas concentration in the suction gas is within a predetermined elapsed time range with reference to a time point when the CO gas concentration becomes 2.0 vol% or more and 18.0 vol% or less.
- the end point of the desiliconization treatment is defined as a CO gas concentration, a CO 2 gas concentration, and a CO gas in the suction gas.
- the CO gas flow rate in the suction gas, the CO 2 gas flow rate, and the CO gas and CO 2 calculated from the product of the analytical value of the concentration of any one of the total concentrations of CO 2 and CO 2 gas and the flow rate of the suction gas It is characterized in that any one of the total gas flow rates is within a predetermined elapsed time range with reference to a point in time when the flow rate becomes equal to or higher than a predetermined threshold value.
- the end point of the desiliconization treatment is determined as an analytical value of the concentration of a gas species containing carbon atoms in the suction gas. Based on the flow rate of the suction gas, the carbon discharge rate in the exhaust gas discharged from the converter-type refining furnace during the desiliconization process is calculated, and the time point when the discharge rate exceeds a predetermined threshold is used as a reference. And within a predetermined elapsed time range.
- the hot metal pretreatment method in the hot metal pretreatment method according to any one of the first to tenth aspects of the present invention, at least 30 mass% of the slag produced by the pre-charge dephosphorization treatment is left in the furnace. In this state, the hot metal of the next charge is charged into a converter type refining furnace and desiliconized.
- a hot metal pretreatment method according to any one of the first to eleventh aspects of the present invention, wherein a base of slag present in the converter type refining furnace at the end of the desiliconization process.
- the degree ([CaO (mass%)] / [SiO 2 (mass%)]) is controlled in the range of 0.80 to 1.50.
- the end point of the desiliconization process is determined as the converter. Because it is determined based on the analysis value of the gas species containing carbon atoms in the suction gas sucked into the exhaust gas treatment facility of the smelting furnace, the variation in the desiliconization process completion judgment is greatly reduced, and intermediate waste is always removed. Silica slag can be sufficiently formed and fluidized, and the desiliconized slag can be discharged sufficiently in a short time without causing molten iron to flow out. Thus, it is possible to reduce the cost in the dephosphorization process and to reduce the variation of the phosphorus concentration in the hot metal after the process.
- the inventors use one converter-type refining furnace to sandwich the desiliconized slag discharge after desiliconization (hereinafter also referred to as “intermediate waste”), and then desiliconize and dephosphorize the hot metal.
- intermediate waste the desiliconized slag discharge after desiliconization
- the various factors affecting the exhaustability of the desiliconized slag were repeatedly studied.
- the removal performance of desiliconized slag in intermediate waste is greatly influenced by the forming condition of the desiliconized slag in addition to the fluidity of the desiliconized slag itself. In order to do so, it is important that the desiliconized slag is sufficiently hatched and exhibits good fluidity at the time of discharge, and that the slag is sufficiently formed and the bulk specific gravity is reduced. Became clear.
- the desiliconization slag produced by the desiliconization process is formed by the hatching of SiO 2 produced by the combustion of silicon in the molten iron and the ironmaking material added or left in the furnace.
- the desiliconization reaction preferentially proceeds and the amount of SiO 2 in the furnace gradually increases, but the fluidity at the time of discharge is ensured.
- it is important to add or pre-load a slag-forming material containing CaO such as quicklime or steelmaking slag to adjust the composition of the slag to an appropriate range.
- the CO gas generation rate is low at the initial stage of the desiliconization process, but the silicon concentration in the hot metal decreases to less than 0.20 mass% as the desiliconization reaction proceeds, and the hot metal temperature rises.
- the decarburization reaction becomes active and gradually increases.
- the iron oxide concentration in the slag is relatively low at less than 10 mass% at the beginning of the desiliconization process, where the silicon concentration in the hot metal is high, but the desiliconization reaction proceeds and the silicon concentration in the hot metal decreases. As the amount of slag increases, it gradually increases.
- the concentration of iron oxide in the slag increases and exceeds 10 mass%, the melting point of the slag is lowered or the liquid phase ratio is significantly increased. Improves. Furthermore, the generation of CO gas due to the reaction between the iron oxide in the slag and the molten iron bath or the molten iron droplets entrained in the slag becomes active, and a large amount of CO gas bubbles are included in the slag. "Forming" state. Once the slag begins to form, the amount of oxygen supplied to the slag layer by the acid sent from the top blow lance also increases and promotes oxidation of iron, etc. In some cases, the forming height increases, leading to so-called “sloping”.
- the bulk specific gravity of the slag can be made very small, and even the same slag mass can be about 10 times larger in volume.
- the slag can be discharged quickly without causing the hot metal to flow out.
- slag forming is excessive during the desiliconization process, slag overflows from the furnace port, which may impede operation.
- the inventors have made extensive studies on a method of appropriately evaluating the forming state of the slag during the desiliconization process and determining the timing for finishing the desiliconization process and starting the intermediate evacuation.
- the emission rate of carbon in the exhaust gas shows a specific fluctuation pattern, and the forming state is optimal for exhaustion within a specific range of the fluctuation pattern.
- the timing at which the desiliconization process is completed and the intermediate waste is started is the suction gas (hereinafter simply referred to as “suction gas”) sucked into the exhaust gas treatment facility attached to the converter refining furnace.
- suction gas hereinafter simply referred to as “suction gas”
- FIG. 1 shows a converter-type smelting furnace when desiliconization treatment is performed to reduce hot metal having a silicon concentration of 0.35 mass% in hot metal to 0.10 mass% or less under conditions where desiliconization slag is easy to form.
- the discharge rate of carbon contained in the exhaust gas (per unit time) calculated based on the CO gas concentration, CO 2 gas concentration and suction gas flow rate (standard state) in the suction gas sucked into the exhaust gas treatment facility attached to This shows the transition (change over time) of the amount of carbon contained in the exhaust gas discharged together with the transition of the suction gas flow rate, the acid feed rate, and the sum of the CO gas concentration and CO 2 gas concentration in the suction gas. .
- the discharge rate of carbon contained in the exhaust gas gradually increases with the progress of the desiliconization reaction after the start of the desiliconization process (stage I), and once shows the maximum value. After that, it can be seen that it shows a unique fluctuation pattern of decreasing to show a minimum value (stage II) and then increasing again (stage III). Strictly speaking, the discharge rate of carbon in the exhaust gas includes CO 2 contained in the air sucked into the exhaust gas treatment facility. However, since the amount of CO 2 in the air is very small, the influence of this is not affected. Can be ignored.
- stage I is a stage in which the generation amount of CO gas gradually increases as the hot metal temperature rises and the silicon concentration in the hot metal decreases with the progress of desiliconization treatment. Since the amount of generation is small, the temperature is low, and no forming is performed. Therefore, as shown in FIG. 2A, the CO gas can easily pass through the desiliconized slag layer and be discharged out of the furnace. However, when the desiliconization reaction proceeds and stage II is reached, the amount of CO gas generated increases, and the temperature of the desiliconization slag rises and the viscosity decreases, as shown in FIG.
- the generated CO gas is taken into the desiliconized slag, and the slag begins to form, and the discharge rate of carbon in the exhaust gas apparently decreases temporarily. Further, when the desiliconization reaction proceeds and stage III is reached, CO gas cannot be further taken into the desiliconization slag, and the forming reaches a saturated state. Therefore, as shown in FIG. Gas begins to be discharged outside the furnace, and the discharge rate of carbon in the exhaust gas begins to increase again.
- stage I of the desiliconization process oxygen supplied from the top blowing lance is mainly consumed in the desiliconization reaction and decarburization reaction.
- stage II the amount of generated slag is increased and the thickness of the slag layer is reduced.
- the concentration of iron oxide in the slag increases and the oxygen supplied is also consumed in the oxidation reaction of iron, so the oxygen used for decarburization decreases accordingly, The carbon emission rate decreases.
- the amount of oxygen supplied to the slag layer by the acid sent from the top blowing lance increases at an accelerated rate, and the iron oxide concentration increases.
- CO gas is generated by the reaction between iron oxide in the slag and molten iron, and the iron oxide in the slag is reduced by that amount, and the balance of the iron oxide in the slag is balanced. Therefore, the generation rate of CO gas increases again, and the discharge rate of carbon in the exhaust gas begins to increase.
- the desiliconization process is completed at the stage III in which the discharge rate of carbon in the exhaust gas is changed from the maximum value to the minimum value and increases again from the minimum value and the desiliconization slag is in the forming state. It was found that if the intermediate waste was started, the waste rate of desiliconized slag could be reliably increased. In addition, the silicon concentration in the hot metal at this stage is stably reduced to 0.10 mass% or less, which enables efficient dephosphorization by reducing the amount of dephosphorizing agent used in the subsequent dephosphorization treatment. Confirmed that.
- the inventors have completed the desiliconization process within a specific region of the stage III, specifically, within a range of 90% to 150% with respect to the maximum value of the discharge rate of carbon in the exhaust gas.
- the removal rate of desiliconized slag can be further improved.
- the reason for this is that, as explained above, the temperature of the desiliconization slag rises due to the progress of the decarburization reaction, the viscosity decreases, and the fluidity is improved. It seems to be due to the fact that the height (thickness) of the slag layer on the hot metal bath increases and it tends to flow out of the furnace port because it apparently becomes smaller.
- the present invention has been developed on the basis of the above-described novel knowledge, and its features are present in the furnace after supplying an oxygen source to the hot metal in the converter type refining furnace and desiliconizing. At least a part of the slag is discharged from the converter-type refining furnace (intermediate waste), and then the hot metal in the converter-type refining furnace is supplied with a CaO-based solvent and an oxygen source for dephosphorization and discharged
- the concentration of the gas species containing carbon atoms in the suction gas sucked by the exhaust gas treatment facility of the converter type refining furnace during the desiliconization treatment is analyzed, and the desiliconization treatment is performed based on the analysis value. It is to determine the end point.
- a converter-type refining furnace 1 capable of top bottom blowing as shown in FIG. 3 is used.
- the upper blowing is performed by supplying an oxygen-containing gas 9 as an oxygen source from the tip of the upper blowing lance 2 through an upper blowing lance 2 that can move up and down in the converter type refining furnace 1.
- oxygen gas oxygen gas (industrial pure oxygen), oxygen-enriched air, air, a mixed gas of oxygen gas and inert gas, or the like can be used.
- bottom blowing is performed by blowing a bottom blowing gas 10 into the hot metal through a bottom blowing tuyere 3 provided at the bottom of the converter type refining furnace 1.
- the bottom blowing gas 10 may be a gas containing oxygen gas or only an inert gas such as Ar gas or nitrogen gas.
- the bottom blowing gas 10 has a function of accelerating the stirring of the hot metal 5 by blowing it into the hot metal and accelerating the melting of the cold iron source, but the conveying gas for blowing the iron making agent into the hot metal from the bottom blowing tuyere 3 You may give the function as.
- a skirt 11 that moves up and down to cover the furnace port of the converter type refining furnace 1 and a flue 12 connected to the skirt 11 are installed.
- the exhaust gas discharged from the converter type refining furnace 1 is sucked through an exhaust gas treatment facility (not shown) through a flue 12, and after sprinkling water to remove dust, the suction speed is measured.
- the exhaust gas treatment facility has a function of collecting the suction gas sucked as fuel gas, the suction gas is recovered or released as fuel gas depending on the composition and flow rate. Since the generation rate of CO gas is low, it is generally not recovered as fuel gas.
- the suction gas sucked in the exhaust gas treatment facility includes the differential pressure from the atmospheric pressure in the skirt 11 and the converter refining furnace 1. Also included is air (atmosphere) sucked according to the size of the gap between the skirt 11 and the skirt 11 (hereinafter also referred to as “skirt height”).
- the oxygen in the air sucked into the skirt together with the high-temperature exhaust gas reacts to produce CO 2 until the CO in the exhaust gas and either oxygen or CO are substantially consumed.
- the flue 12 is provided with a gas sampling probe 13 for collecting an exhaust gas for analysis.
- the gas sampling probe 13 is connected to the gas sampling probe 13 to collect CO, CO 2 , O in the suction gas collected by the gas sampling probe 13.
- a gas analyzer 14 for analyzing a gas composition such as 2 is provided. That is, the gas composition of the suction gas sampled by the gas sampling probe 13 is configured to be measured continuously or intermittently by the gas analyzer 14.
- a steam boiler may be installed in a portion through which a high-temperature gas such as the flue 12 passes.
- the operation of the exhaust gas treatment facility is usually performed by making the skirt height as small as possible so that the sucked air is minimized.
- the skirt height can be arbitrarily set. Therefore, for example, when the flue 12 has the function of a steam boiler, the skirt 11 is raised to actively suck air to burn the CO gas in the exhaust gas, and its combustion heat (thermal energy) Is preferably recovered as high-pressure steam.
- the exhaust gas treatment facility may be operated by lowering the position of the skirt 11 in order to suppress the suction of air. Can reduce the heat load.
- the component composition of the suction gas sucked by the exhaust gas treatment facility is completely different depending on the characteristics of the exhaust gas treatment facility and the operating conditions. That is, when the position of the skirt 11 is lowered to suppress the amount of air sucked, the CO and CO 2 concentrations are relatively high, but when the skirt 11 is raised and air is actively sucked. If the generation rate of the CO gas from the converter-type refining furnace 1 is not a certain ratio or more (specifically, about 30 vol% or more) with respect to the gas suction speed of the exhaust gas treatment facility, CO is determined in the analysis of the suction gas. Only 2 is detected, CO is not detected. This is because CO in the exhaust gas is burned with O 2 in the sucked air.
- FIG. 1 shows that the exhaust gas treatment facility which has a gas recovery function but does not have a steam boiler in the flue uses an exhaust gas treatment facility to confirm the ignition of the exhaust gas after the desiliconization process is started, and then lowers the skirt 11 to reduce the air flow.
- the example which is performing the operation which suppressed suction is shown.
- the discharge rate of carbon in the exhaust gas shown in FIG. 1 is the CO gas in the suction gas measured by the gas sampling probe 13 disposed in the flue leading to the converter exhaust gas treatment facility shown in FIG. This is calculated based on the concentration, the CO 2 gas concentration, and the gas suction speed of the exhaust gas treatment facility (the suction gas flow rate in the standard state).
- an infrared absorption analyzer is used to measure the gas composition of CO and CO 2.
- this measurement method has a slow response speed compared with the measurement of the gas flow rate, and it is 10 to several tens. Since a delay time of about seconds occurs, each measurement time is corrected.
- the gas suction amount in the exhaust gas treatment facility is larger than the amount of gas generated from the converter type refining furnace by desiliconization treatment or decarburization treatment in order to prevent the leakage of exhaust gas. Air is sucked in from between and at least a part of the generated CO is oxidized and converted to CO 2 .
- the carbon discharge rate in the exhaust gas, the CO concentration and CO 2 concentration in the suction gas, and the suction rate (standard state flow rate) of the exhaust gas treatment facility are measured.
- the method to find out by this is effective.
- the operating conditions (skirt height, furnace port pressure, etc.) of the converter exhaust gas treatment facility are constant, instead of the discharge rate of carbon in the exhaust gas, From the fluctuation pattern in which any one of the CO gas concentration, the CO 2 gas concentration, and the total concentration of CO gas and CO 2 gas becomes a maximum value and increases again after reaching the minimum value. It is possible to determine the end point of processing.
- the operating conditions in which the amount of air sucked is relatively small and CO remains in the suction gas can be determined based on the fluctuation pattern of the total concentration of CO gas and CO 2 gas.
- the amount of air to be produced does not vary so much and the CO 2 gas concentration is stable, it can be determined based on a variation pattern of only the CO gas concentration.
- the amount of air to be sucked is sufficiently large and CO in exhaust gas is completely burned, it can be determined based on a variation pattern of only the CO 2 gas concentration.
- the CO gas flow rate in the suction gas calculated from the product of the analysis value of the CO gas concentration and / or the CO 2 gas concentration in the suction gas and the flow rate of the suction gas, From the fluctuation pattern of any one of the CO 2 gas flow rate and the total flow rate of the CO gas and the CO 2 gas, which becomes a maximum value and increases again after reaching the minimum value, the end point of the desiliconization process is determined. It is also possible to decide. At this time, the operating conditions in which the amount of air sucked is relatively small and CO remains in the suction gas can be determined based on the fluctuation pattern of the total flow rate of CO gas and CO 2 gas.
- the amount of air to be produced does not vary much and the CO 2 gas flow rate is stable, it can also be determined based on a variation pattern of only the CO gas flow rate. Further, under an operating condition where the amount of air sucked is sufficiently large and CO in exhaust gas is completely burned, it may be determined based on a fluctuation pattern of only the CO 2 gas flow rate.
- the suction gas flow rate varies greatly by adjusting the skirt height before and after the silicon removal treatment (see FIG. 1), but as described above, the response speed is measured in the suction gas flow rate measurement and the gas composition analysis. Therefore, if the suction gas flow rate varies greatly, it may cause an error when measuring the change in the discharge rate of carbon in the exhaust gas. Therefore, in determining the maximum value and the minimum value, it is desirable to operate so as not to cause a significant fluctuation in the suction gas flow rate before and after the maximum value and the minimum value are generated.
- the skirt height is generally controlled so as to keep the gas suction pressure constant, or controlled so as to keep the skirt height constant. The fluctuation is at a level at which there is no problem in determining the maximum value and the minimum value.
- the end point of the desiliconization process is determined based on a fluctuation pattern in which any one of the measured values of the total flow rate of CO gas and CO 2 gas becomes a maximum value and increases again after reaching the minimum value.
- the difference between the maximum value and the minimum value is 10% or more of the maximum value, it is desirable to determine the maximum value and the minimum value in the above variation pattern.
- the end point of the desiliconization process is a time point when the fluctuation value increased again after reaching the above-mentioned minimum value becomes equal to or more than a predetermined ratio of 90% to 150% with respect to the above-mentioned maximum value.
- a predetermined ratio of 90% to 150% with respect to the above-mentioned maximum value As a reference, it is desirable to be within a predetermined elapsed time range.
- the reason why the value of the predetermined ratio in the above range with respect to the maximum value is set as the threshold value is that the region that increases again after reaching the minimum value in the above variation pattern is formed by the desiliconization slag forming,
- the area where the slag height of the slag rapidly increases is less than 90% of the maximum value, but the slag forming is insufficient and the removal rate of the desiliconized slag may be insufficient. This is because the area exceeding 150% may hinder the operation by overflowing slag from the furnace port before the desiliconization process is finished.
- the end point of the silicon removal treatment may be any time as long as the above fluctuation value is equal to or greater than the threshold value.
- the elapsed time is preferably in the range of 0 to 50 seconds, and more preferably in the range of 0 to 30 seconds. If it is within the range of the above time, it is possible to complete the desiliconization process and perform the intermediate evacuation sufficiently without excessively forming and inhibiting the operation.
- the end point of the desiliconization process determined as described above may be a point in time when any of the above measured values is equal to or greater than a predetermined ratio with respect to the maximum value, and from this point in time, It may be the time when the processing time of elapses. However, in the latter case, it is desirable to set the desiliconization process to end when any of the above measured values does not exceed 150% of the maximum value.
- the method for determining the end point of the desiliconization process is not limited to the method of determining based on the fluctuation pattern as described above, but also the discharge rate of carbon in the exhaust gas, the CO gas concentration in the suction gas, CO 2.
- the measured value of any one of the gas concentration, the total concentration of CO gas and CO 2 gas, the CO gas flow rate, the CO 2 gas flow rate, and the total flow rate of CO gas and CO 2 gas is greater than or equal to a predetermined threshold value It is also effective to set the time point within the predetermined elapsed time range as a reference.
- the elapsed time from the time when the measured value is equal to or greater than the threshold value to the end of the desiliconization process is in the range of 0 to 50 seconds, as described above, and is 0 to 30 seconds. It is more desirable to be within the range.
- the above measured value is equal to or greater than the threshold at the maximum value portion as seen in the variation pattern of the carbon discharge rate shown in FIG. It is necessary not to do so.
- 1.2 times the stoichiometrically required oxygen amount calculated from the Si concentration in the hot metal before the desiliconization treatment and the Si concentration in the hot metal after the target desiliconization treatment preferably 1 It is desirable to set the time when the above measured value is equal to or higher than a predetermined threshold after the time when the supply of .5 times oxygen is completed.
- the above threshold value may be a numerical value obtained empirically or may be a value calculated using variables such as the hot metal temperature and the Si concentration in the hot metal, but the waste state at the time of intermediate waste, It is preferable to determine in consideration of the results of the subsequent dephosphorization treatment.
- the exhaust gas treatment facility has a function of recovering the exhaust gas of the converter type refining furnace as fuel gas and a flue with a steam boiler, and the exhaust gas treatment facility is actively used during desiliconization treatment.
- the operation is performed so that at least a part of the CO gas in the exhaust gas is burned by sucking the atmosphere into the exhaust gas, when the end point of the desiliconization process is determined based on the threshold described above, specifically, An example of investigating the exhaustability of the desiliconization slag when the end point of the desiliconization process is determined based on the CO gas concentration in the suction gas will be described below.
- the decontamination performance of desiliconization slag is defined as the concentration of silicon in the hot metal before desiliconization and the mass of desiliconization slag that is generated, and the tilt angle of the converter-type refining furnace at the time of decontamination. Evaluation was made based on the amount of desiliconized slag discharged from the converter-type refining furnace under constant conditions.
- the case where the mass of desiliconized slag discharged to the receiving vessel directly under the converter type refining furnace is 50% or more of the mass of desiliconized slag present in the furnace is “Excellent”, the case where the above value was 30% or more and less than 50% was evaluated as “excellent”, and the case where the above value was less than 30% was evaluated as “exclusion”.
- Figure 4 shows the results of the above survey. From this figure, the higher the CO gas concentration in the suction gas at the end of the desiliconization process, the better the exhaustability of the desiliconization slag, and the CO gas concentration in the suction gas at the end of the desiliconization process is 6 It can be seen that “exclusion defect” does not occur when the value is 0.0 vol% or more. That is, the end of the desiliconization process can be determined based on the CO gas concentration in the suction gas during the desiliconization process, and in that case, the CO gas concentration in the suction gas is 6.0 vol% or more. It can be seen that the value is preferably used as a threshold value for determining the end point of the desiliconization process.
- the hot metal and molten steel in the furnace are refined batchwise, and this single unit of refining is called “charge”.
- the number of charges indicates the number of times.
- the CO gas concentration in the suction gas changes depending on the air sucked from between the furnace port and the skirt of the converter type refining furnace.
- the threshold value of “CO gas concentration of 6.0 vol% or more” in the gas is obtained under operating conditions in which the operating conditions (the amount of acid fed, the skirt height, the furnace port pressure, etc.) are constant. Therefore, if it is the condition, it can fully be used as a threshold value.
- an appropriate value as the above-mentioned threshold varies depending on equipment conditions such as the suction capacity of the exhaust gas treatment equipment and operating conditions such as the oxygen supply rate.
- the CO gas concentration in the suction gas is in the range of 2.0 vol% to 18.0 vol% It is preferable to select and use appropriate values.
- the CO gas concentration threshold is 2.0 vol% or more, slag forming is sufficiently accelerated even if only the measured value of the CO gas concentration is used instead of the variation pattern of the discharge rate of carbon in the exhaust gas. Misrecognition at the time of determining that the gas is discharged can be reduced. On the other hand, if the CO gas concentration threshold is 18.0 vol% or less, it is efficient while preventing an operation hindrance due to excessive slag forming. Therefore, it is possible to accurately determine the forming state for rejecting.
- the slag forming status during the desiliconization process and the timing suitable for ending the desiliconization process and starting the intermediate evacuation can be determined only from the information obtained from the suction gas, Necessary amount of oxygen in desiliconization blowing calculated from operating conditions obtained in advance, exhaust gas temperature, slag discharge status from the furnace port, slag outflow status from the steel outlet, changes in lance or sub lance vibration, oxygen blowing
- the determination conditions may be made more accurate by combining information such as acoustic changes during smelting, or a slag level estimation technique using a known method.
- the hot metal pretreatment method of the present invention will be specifically described with reference to an example in which the converter type refining furnace shown in FIG. 3 is used.
- the converter type refining furnace 1 in which the cold iron source 8 such as iron scrap is charged is subjected to desiliconization treatment and dephosphorization treatment. , That is, the hot metal 5 before the pretreatment is charged through the charging pan 15 (hot metal charging step).
- the hot metal 5 in the converter-type refining furnace 1 is supplied with oxygen-containing gas or oxygen-containing gas and iron oxide as an oxygen source and subjected to desiliconization treatment (desiliconization). Processing step).
- the silicon contained in the hot metal 5 reacts with the supplied oxygen to proceed a desiliconization reaction (Si + O 2 ⁇ SiO 2 ).
- the hot metal temperature is increased by the combustion heat of silicon due to this desiliconization reaction, and the melting of the cold iron source 8 in the hot metal is promoted.
- the silicon concentration in the hot metal gradually decreases and CO gas is generated.
- the desiliconization process further proceeds and the generation amount of desiliconization slag increases.
- the hot metal temperature rises the composition and physical properties of the slag also change, and the generated CO gas causes the slag to form.
- the desiliconized slag 6 produced by the above desiliconization treatment is obtained by decomposing phosphorus oxide (P 2 O 5 ) derived from the dephosphorization slag 7 described later during the desiliconization treatment.
- the basicity ([CaO (mass%)] / [SiO 2 (mass%)]) after the desiliconization treatment is set to 0. 80 or more is preferable.
- high basicity means that the ratio of CaO to the generated SiO 2 is high, and the amount of desiliconized slag 6 increases, so the upper limit is preferably about 1.50. More preferably, it is less than 1.30, More preferably, it is less than 1.20.
- the basicity of the desiliconized slag 6 can be adjusted to the above range by adding a medium solvent such as a CaO-based medium solvent into the furnace before and during the desiliconization process.
- a medium solvent such as a CaO-based medium solvent
- the basicity of the desiliconization slag 6 is lowest because the desiliconization process ends when the amount of generated SiO 2 is the largest. If the basicity at the end of the desiliconization treatment is 0.80 or more, the basicity during the previous desiliconization treatment inevitably becomes 0.80 or more.
- a medium solvent such as a CaO-based medium solvent is used.
- the addition method of the CaO-based medium solvent may be a method in which granular and lump-shaped ones are introduced from a hopper on the furnace, or a powdery one is introduced through the blowing lance 2, and there is no particular limitation. .
- the basicity of the desiliconized slag 6 is expressed by the following formula (1):
- Basicity [(Residual amount of CaO in furnace (kg / molten metal-t)) + (Amount of added CaO in desiliconization treatment (kg / molten metal-t))] / [(Remained amount of SiO 2 in furnace (kg / molten metal) -T)) + (amount of SiO 2 produced by desiliconization treatment (kg / molten metal-t))]
- Can be calculated based on The amount of SiO 2 produced by the desiliconization treatment in the above formula is calculated from the change in the silicon concentration in the hot metal before and after the desiliconization treatment.
- an oxygen source for the silicon removal treatment only the oxygen gas 9 supplied from the top blowing lance 2 may be used, or iron oxide (not shown) may be used in combination with the oxygen gas 9. .
- iron oxide it is not preferable to use iron oxide that absorbs heat during temperature rise and decomposition. Therefore, it is preferable to avoid using iron oxide as an oxygen source as much as possible.
- the end point of the desiliconization process is obtained when the discharge rate of carbon contained in the exhaust gas discharged from the converter type refining furnace during the desiliconization process is measured. Since it is determined based on a fluctuation pattern in which the maximum value is reached and then increases again after reaching the minimum value, the supply rate of the oxygen source is kept as constant as possible during the period in which the carbon emission rate reaches the maximum value and the minimum value. It is desirable to operate. In normal operation, since the desiliconization process is completed in a short time, the operation of increasing the acid feed rate or introducing iron oxide is performed at the initial stage of the desiliconization process. By making the speed constant, the maximum value and the minimum value of the carbon discharge rate can be stably measured.
- the top blow lance 2 is immediately raised to end the desiliconization process. In general, it is after about several tens of seconds required for operations such as necessary operations and operation of the apparatus from the determination time.
- the converter-type refining furnace 1 is tilted to the side opposite to the side where the outlet 4 is provided, and contains a large amount of SiO 2 generated by the desiliconization process.
- the low basicity desiliconized slag 6 is discharged from the furnace port of the converter-type refining furnace 1 (intermediate waste discharging process).
- the hot metal after the desiliconization treatment is indicated as 5a in order to distinguish it from the hot metal 5 before the desiliconization treatment.
- the removal rate of the desiliconized slag 6 in the intermediate removal step is set to 30 mass% or more in order to advance the dephosphorization reaction efficiently with a small amount of CaO-based solvent used in the dephosphorization treatment step described later. preferable. Furthermore, in order to reduce the total amount of the CaO-based solvent used between the hot metal pretreatment and the next decarburization and refining process, compared to the conventional method in which the intermediate waste process is not performed, the waste rate above 50 mass% is reduced. It is more preferable to ensure stably.
- Waste rate (mass%) (discharge slag mass) ⁇ 100 / [(slag mass generated in the desiliconization process) + (residual slag mass of the previous charge)] (2)
- a CaO-based medium solvent or an oxygen source is supplied to the hot metal 5a after the desiliconization treatment left in the converter type refining furnace to remove the phosphorus.
- Process (dephosphorization process).
- the basicity of the dephosphorization slag 7 generated in the furnace is preferably adjusted to a range of 1.2 to 3.0. If the basicity is 1.2 or more, the dephosphorization ability of the slag is in an appropriate range, and the phosphorus concentration in the hot metal can be reduced with a small amount of slag. On the other hand, if it is 3.0 or less, the dephosphorization reaction proceeds with the fluidity of the slag within an appropriate range without impairing the hatching of the CaO-based solvent.
- the oxygen source used in the dephosphorization process is mainly composed of the oxygen gas 9 from the top blowing lance 2 as in the desiliconization process, but iron oxide may be used in part.
- the present invention is intended to expand the use of the cold iron source 8, it is preferable to use as little iron oxide as possible to absorb heat during temperature rise and decomposition.
- the T. of dephosphorization slag 7 is controlled by appropriately controlling the acid feeding conditions and the lance height. It is preferable to adjust the Fe concentration and promote the hatching of the CaO-based solvent without depending on the use of iron oxide.
- quick lime (CaO), limestone (CaCO 3 ), slaked lime (Ca (OH) 2 ) and the like can be used as the CaO-based solvent used in the dephosphorization treatment.
- CaO-based solvent used in the dephosphorization treatment.
- group solvent can also be used as a CaO type
- group solvent is the same as when adding a CaO type
- the method may be a method of throwing it in through the like.
- phosphorus in the molten iron is oxidized by oxygen in an oxygen source to be converted into phosphorus oxide (P 2 O 5 ), and a dephosphorizing agent formed by the incubation of a CaO-based solvent.
- phosphorus oxide P 2 O 5
- a dephosphorizing agent formed by the incubation of a CaO-based solvent.
- the dephosphorization process may be terminated when the dephosphorization process time has elapsed or when the dephosphorization reaction has progressed and the phosphorus concentration in the hot metal 5a has fallen below a predetermined value.
- the converter-type refining furnace 1 is tilted in the direction opposite to the intermediate waste, and the hot metal 5b in the converter-type refining furnace 1 is discharged into the outlet 4 Then, the hot water is poured into a hot metal holding container (not shown).
- the hot metal after the dephosphorization process is indicated as 5b in order to distinguish it from the hot metal 5a after the desiliconization process.
- the converter type refining furnace 1 is inverted so that the furnace port faces upward, and the hot water is finished.
- the dephosphorization slag 7 may flow out mixed with the molten iron 5b flowing out from the hot water outlet 4, but the flow of the dephosphorization slag 7 is inevitable, but the amount is small. This is clearly distinguished from the later-described dephosphorization slag discharge. Therefore, a small amount of hot metal 5b (not shown) that has not been discharged and almost the entire amount of dephosphorization slag 7 remain in the converter-type refining furnace 1 after the end of the pouring.
- this dephosphorization slag 7 has a high phosphoric acid concentration, if it is used as it is as a desiliconization slag for the next charge as it is, there is a risk that the phosphorus concentration in the hot metal will rise due to recovery. For this reason, conventionally, the entire amount of dephosphorization slag has been discharged after the completion of the above-mentioned hot water discharge step. However, if the entire amount of dephosphorization slag is exhausted, the amount of ironmaking material used to generate the desiliconization slag necessary for the desiliconization process of the next charge increases, leading to an increase in the cost of auxiliary materials. .
- the dephosphorization treatment is performed after the intermediate waste, the hot metal is discharged, and then the converter type It is preferable that 30 mass% or more of the dephosphorization slag remaining in the refining furnace is left in the furnace and used as a part of the raw material of the desiliconization slag for the next charge.
- the dephosphorization slag to remain is more preferably 50 mass% or more.
- the furnace body after pouring is tilted to the opposite side from the pouring gate and discharged from the furnace port, as in the usual slag draining method.
- a method of adjusting the tilt angle and discharging the slag so as to partially remain in the furnace may be used.
- the basicity of the slag after the dephosphorization treatment is in the range of 1.2 to 1.8, and the concentration of iron oxide is 10 mass%. It is preferable to adjust so as to be above.
- This dephosphorization slag solidifying step is a step for preventing the bottom blowing tuyere 3 from being blocked by the dephosphorizing slag 7 and the molten iron 5b remaining in the furnace flowing into the bottom blowing tuyere 3. It is preferable that the bottom blowing gas 10 be ejected from the bottom blowing tuyere 3 at least until the dephosphorization slag 7 and the molten iron 5b are solidified and solidified. However, this step may be omitted when the bottom blowing gas is continuously supplied.
- the desiliconization process and the dephosphorization process can be continuously performed using the single converter-type refining furnace with the intermediate waste interposed therebetween. It is possible to utilize the heat loss as a heat source for melting the cold iron source. Further, according to the present invention, the end point of the desiliconization process is determined based on the concentration of the gas species including carbon atoms in the suction gas (exhaust gas) sucked into the exhaust gas treatment facility of the converter type refining furnace. Since the intermediate waste can be always performed in a state where the bulk specific gravity of the desiliconized slag is small and the fluidity is high, the waste rate of the desiliconized slag can be stably improved.
- a single converter-type refining furnace is used to sandwich the discharge of desiliconized slag after desiliconization (hereinafter, also referred to as “intermediate waste”), and then desiliconize the hot metal.
- two or more converter-type refining furnaces are used for refining the hot metal 5 and at least one of these converter-type refining furnaces is used.
- the refining furnace 1 is used for the hot metal pretreatment according to the present invention, and the remaining at least one converter type refining furnace 1 ′ is used for decarburization refining of the hot metal subjected to the hot metal pretreatment according to the present invention. Is preferred.
- the hot metal subjected to the hot metal pretreatment was one having a temperature of 1250 to 1320 ° C., a silicon concentration of 0.20 to 0.55 mass%, and a phosphorus concentration of about 0.12 mass%.
- the target silicon concentration in the hot metal after the above desiliconization treatment was set to 0.03 mass%, and the target basicity of the desiliconization slag after the desiliconization treatment was set in the range of 0.6 to 0.9.
- the target hot metal temperature at the end of the desiliconization process is set to 1300 to 1340 ° C., and the control is performed by keeping the scrap charge constant at 80 kg / t, and depending on the hot metal temperature to be charged.
- a cold iron source and / or iron ore or a carbon material and / or ferrosilicon as a heat source were added at the initial stage of the desiliconization treatment, and the amount of addition and the amount of acid sent were adjusted.
- the basicity of the dephosphorized slag is adjusted so that the basicity of the dephosphorized slag is in the range of 1.6 to 2.0. The amount used was adjusted.
- Method 1 Oxygen necessary for the silicon concentration in the molten iron to be 0.03 mass%, calculated from the silicon concentration in the molten iron before pretreatment and the desiliconization oxygen efficiency (experience value) corresponding to the concentration.
- the acid feed rate from the top blowing lance was constant at 30000 Nm 3 / hr, and nitrogen gas was blown at the bottom at a rate of 1200 Nm 3 / hr.
- the hot metal preliminary treatment for determining the end point of the desiliconization treatment by the two methods, Method 1 and Method 2 is carried out by several tens of charges for each method, and the desiliconization slag in the intermediate waste of each method is reduced. The rejection rate was compared. At this time, the removal of the desiliconization slag after the desiliconization treatment (intermediate waste) starts immediately after raising the upper blow lance after the desiliconization treatment and tilting the furnace body.
- Waste rate (mass%) (discharge slag mass) ⁇ 100 / [(slag mass generated in the desiliconization process) + (residual slag mass of the previous charge)] (2)
- the rejection rate of the desiliconization slag after the desiliconization process varies in the range of 20 to 70 mass%, and the average rejection Whereas the rate is 37 mass%
- the rejection rate of the desiliconized slag after the desiliconization process is 50 to 80 mass%.
- the range and the average rejection rate are 67 mass%, and it can be seen that the rejection rate of 50 mass% or more can be stably achieved.
- FIG. 6 shows the relationship between the time required for intermediate waste and the Si concentration in the hot metal before preliminary treatment.
- the work time required for intermediate waste is 10 minutes or less. It can be seen that it has been greatly shortened.
- the treatment pitch of the hot metal preliminary treatment it is possible to reduce the treatment pitch of the hot metal preliminary treatment to a level substantially equal to the treatment pitch of the decarburization treatment of the next step, so that the hot metal pretreatment can be carried out on almost the entire amount of hot metal. Became.
- the dephosphorization slag after the dephosphorization treatment is charged with molten iron of the next charge while leaving the entire amount in the furnace without being discharged, and the basicity of the slag in the desiliconization treatment is determined by the dephosphorization slag.
- the hot metal preliminary treatment is carried out under the same conditions as those of the invention example in which the end point of the desiliconization treatment is determined by the method 2 of Example 1 except that the range of 0.9 to 1.2 is controlled to prevent dephosphorization from The experiment which applied was carried out for 10 charges continuously.
- the amount of CaO-based solvent (quick lime) used in the desiliconization treatment is changed from 6.0 kg / molten iron t (see Table 1) in the case of the inventive example of Example 1 to 2.0 kg / molten iron t. It was possible to greatly reduce.
- the pre-charge dephosphorization slag was left in the furnace, there was almost no adverse effect on the amount of quicklime used in the dephosphorization process and the phosphorus concentration in the hot metal after the process. We were able to enjoy the benefits of reducing lime usage.
- the exhaust gas treatment facility of the converter type refining furnace 1 has a function of collecting suction gas as fuel gas, and suction of about 90000 to 100,000 Nm 3 / hr with the skirt 11 raised during blowing. Has the ability.
- the flue 12 is provided with a steam boiler (exhaust heat boiler), and during the desiliconization process, the suction gas is not collected. Therefore, the skirt 11 is raised to suck the atmosphere and remove the CO gas in the exhaust gas. The energy was recovered as high-pressure steam by aggressive combustion.
- a steam boiler exhaust heat boiler
- the hot metal pretreatment is carried out for 100 charges in each of the two methods 1 and 3, and the average waste rate of desiliconized slag in the intermediate waste after the desiliconization treatment and the phosphorus in the hot metal after the hot metal pretreatment
- the concentration was investigated and the results are shown in Table 2. From this result, the average removal rate of the desiliconization slag in Method 1 for determining the end point of the desiliconization process by the same method as the conventional method was 47 mass%, whereas the desiliconization process was completed by the method suitable for the present invention.
- the average removal rate of desiliconized slag in Method 3 for determining the time point is greatly improved to 62 mass%, and accordingly, the phosphorus concentration in the hot metal after hot metal pretreatment is greatly reduced. It can be seen that the variation (standard deviation) can be greatly reduced.
- Converter refining furnace 2 Top blowing lance 3: Bottom blowing tuyere 4: Outlet 5: Hot metal 5a: Hot metal after desiliconization 5b: Hot metal after dephosphorization 6: Desiliconization slag 7: Dephosphorization Slag 8: Cold iron source 9: Oxygen gas 10: Bottom blowing gas 11: Skirt 12: Flue 13: Gas sampling probe 14: Gas analyzer 15: Charging pan
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Abstract
Description
すなわち、特許文献1や特許文献2の技術の採用により、溶銑の予備処理工程における熱ロスを低減できるので、冷鉄源の配合比率を、従来に比べて増大するとともに、温室効果ガスの排出量の削減や製造コストの低減を図ることができる。
特許文献1や特許文献2に開示の技術のように、脱珪処理、中間排滓、脱燐処理を1つの転炉型精錬炉で連続して行う場合に、スラグの塩基度を脱燐に必要な所定の値以上とし、かつ、脱燐処理で使用するCaO系媒溶剤を低減するためには、脱珪処理で生成した、SiO2を大量に含有するスラグ(以降、「脱珪スラグ」ともいう)を転炉型精錬炉から所定量以上排出することが必須となる。
また、特許文献2の技術は、脱珪スラグの塩基度を1.0~3.0とし、溶銑中の珪素濃度が0.20mass%以下になった以降に、中間排滓を行うことが最適であることを提案している。しかし、その理由は、脱珪処理終了時の溶銑中の珪素濃度が0.20mass%よりも高い場合には、次工程の脱燐処理時のスラグの塩基度を2.0に調整するために必要なCaO含有物質が多くなり過ぎ、コスト的に不利になるからとしており、脱珪スラグの排滓性については何ら考慮していない。
つまり、上記の特許文献1および特許文献2の開示の技術では、脱珪スラグを十分に排滓することができず、次工程の脱燐処理でのCaO系媒溶剤の使用量を増加せざるを得なかったり、あるいは、脱燐処理後の溶銑中の燐濃度が高くなるおそれがあったりするという問題点を抱えている。
発明者らは、1つの転炉型精錬炉を用いて、脱珪処理後の脱珪スラグの排出(以降、「中間排滓」ともいう)を挟んで、溶銑に脱珪処理および脱燐処理を連続して行う場合において、上記脱珪スラグの排滓性を改善することを目的とし、脱珪スラグの排滓性に及ぼす各種要因について鋭意検討を重ねた。
まず、ステージIは、脱珪処理の進行よる溶銑温度の上昇および溶銑中の珪素濃度の低下に従ってCOガスの発生量は次第に上昇する段階であり、脱炭反応開始初期の脱珪スラグは、まだ生成量が少ない上に、温度が低く、フォーミングしていないため、図2(a)に示したように、COガスは容易に脱珪スラグ層を通過して炉外に排出することができる。しかし、脱珪反応が進行して、ステージIIになると、COガスの発生量が多くなるとともに、脱珪スラグの温度が上昇して粘性が小さくなるため、図2(b)に示したように、発生したCOガスは脱珪スラグ中に取り込まれ、スラグがフォーミングを起こすようになり、排ガス中の炭素の排出速度は、見掛け上、一次的に減少する。さらに脱珪反応が進行して、ステージIIIになると、脱珪スラグ中にCOガスをそれ以上取り込むことができなくなり、フォーミングが飽和状態に達するため、図2(c)に示したように、COガスが炉外に排出されるようになり、再び、排ガス中の炭素の排出速度が上昇し始める。
脱珪処理のステージIにおいては、上吹きランスから供給する酸素は、主に脱珪反応および脱炭反応に費やされるが、ステージIIになると、生成スラグ量が増大してスラグ層の厚さが増大するとともに、スラグ中の酸化鉄濃度が上昇し、供給する酸素が鉄の酸化反応にも消費されるようになるため、脱炭に使われる酸素がその分だけ減少することになり、排ガス中の炭素の排出速度が低下する。特に、スラグがフォーミングし始めてスラグ層の厚さが大きくなると、上吹きランスからの送酸によるスラグ層への酸素供給量が加速度的に増加して、酸化鉄濃度が上昇する。次に、ステージIIIになると、スラグ中の酸化鉄と溶銑との反応によって、COガスが発生するとともに、スラグ中の酸化鉄がその分だけ減少し、スラグ中の酸化鉄は収支が平衡した状態になるため、COガスの発生速度は再び増大して、排ガス中の炭素の排出速度が上昇し始める。
この理由は、上記に説明したように、脱炭反応の進行によって脱珪スラグの温度が上昇して粘性が低下し、流動性が向上することに加えて、フォーミングによって、脱珪スラグの比重が見掛け上小さくなるため、溶銑浴上のスラグ層の高さ(厚さ)が増大して炉口から流出し易くなることによるものと考えられる。排ガス中の炭素の排出速度が、上記極大値に対して90%未満で脱珪処理を終了した場合には、スラグのフォーミングが不十分で、脱珪スラグの排滓率も不十分となることがある。一方、上記極大値に対して150%超で脱珪処理を終了した場合には、脱珪処理を終了する前に炉口からスラグが溢れ出し、操業を阻害するおそれがあるからである。
まず、本発明の溶銑の予備処理方法では、図5(a)に示すように、鉄スクラップなどの冷鉄源8が装入された転炉型精錬炉1に、脱珪処理および脱燐処理の施されていない、すなわち、予備処理前の溶銑5を、装入鍋15を介して装入する(溶銑装入工程)。
なお、上記CaO系媒溶剤の添加方法は、粒状および塊状のものを炉上のホッパーから投入したり、粉状のものを吹きランス2を介して投入したりする方法でもよく、特に制限はない。
塩基度=[(炉内残留CaO量(kg/溶銑-t))+(脱珪処理での添加CaO量(kg/溶銑-t))]/[(炉内残留SiO2量(kg/溶銑-t))+(脱珪処理で生成したSiO2量(kg/溶銑-t))] ・・・(1)
に基づいて計算することができる。なお、上記式中の脱珪処理で生成したSiO2量は、脱珪処理前後の溶銑中の珪素濃度の変化から算出する。
しかし、脱珪スラグ6を80mass%超え排滓してしまうと、次工程の脱燐処理工程において新たに添加するCaO系媒溶剤の滓化が損なわれ、脱燐反応が阻害されるおそれがある。従って、本発明においては、脱珪スラグ6の排滓率を50~80mass%の範囲に制御することが好ましい。
なお、上記排滓率は、下記(2)式で定義される。
排滓率(mass%)=(排出スラグ質量)×100/[(脱珪処理工程で生成したスラグ質量)+(前チャージの残留スラグ質量)] ・・・(2)
なお、上記の溶銑予備処理を施す溶銑には、温度が1250~1320℃で、珪素濃度が0.20~0.55mass%、燐濃度が約0.12mass%のものを用いた。また、上記の脱珪処理後の溶銑中の目標珪素濃度は0.03mass%とし、脱珪処理終了後の脱珪スラグの目標塩基度は0.6~0.9の範囲に設定した。また、上記脱珪処理終了時の目標溶銑温度の目標溶銑温度は1300~1340℃とし、その制御は、スクラップ装入量を80kg/tで一定とし、装入する溶銑温度に応じて、冷却材となる冷鉄源および/または鉄鉱石あるいは熱源となる炭材および/またはフェロシリコンを脱珪処理の初期に添加し、これらの添加量と送酸量を調整することにより行った。
また、引続き行う脱燐処理では、炉内に残留する脱珪スラグ量とその組成の推定値に基いて、脱燐スラグの塩基度が1.6~2.0の範囲となるように生石灰の使用量を調整した。
・方法1:予備処理前の溶銑中の珪素濃度とその濃度に応じた脱珪酸素効率(経験値)とから計算される、溶銑中の珪素濃度が0.03mass%となるのに必要な酸素量を供給し終えた時点とする従来の方法(比較例)
・方法2:図1に示したように、排ガス中の炭素の排出速度の変動パターンにおいて、極大値、極小値を示した後、再び上昇した炭素の排出速度が、上記極大値以上となった時点を基準として脱珪処理の終了を決定し、上記時点から約20秒経過後に炭素の排出速度が上記極大値に対して100%以上150%以下の範囲において脱珪処理を終了する方法(発明例)
なお、いずれの方法も、上吹きランスからの送酸速度は30000Nm3/hrで一定とし、窒素ガスを吹き込み速度1200Nm3/hrで底吹きした。
この際、上記脱珪処理終了後の脱珪スラグの排滓(中間排滓)は、脱珪処理終了後、直ちに上吹きランスを上昇してから炉体を傾動して開始し、炉下の移動台車上に設置したスラグ用鍋に受滓するのに支障がなく、かつ、溶銑が流出しない範囲内で、転炉型精錬炉の傾動角度を可能な限り大きくして行い、中間排滓の終了は、秤量値で十分な排滓量が確認できたとき、溶銑を流出させることなくスラグのみを流出させることが困難となったとき、および、排滓時間が操業上許容できる最長時間となったときのうちのいずれかの時点とした。また、上記中間排滓における脱珪スラグの排滓率は、上記スラグ用鍋に受滓した脱珪スラグの質量を、炉下の移動台車に設置した秤量装置で測定し、下記(2)式から求めた。
排滓率(mass%)=(排出スラグ質量)×100/[(脱珪処理工程で生成したスラグ質量)+(前チャージの残留スラグ質量)] ・・・(2)
また、図6は、中間排滓に要した時間と予備処理前の溶銑中のSi濃度との関係を示したものであるが、本発明例では、中間排滓に要する作業時間を10分以下と、大幅に短縮できていることがわかる。この排滓時間の短縮によって、溶銑予備処理の処理ピッチを、次工程の脱炭処理の処理ピッチとほぼ同等レベルまで短縮することができるので、溶銑予備処理をほほ溶銑全量に対して実施できるようになった。
その結果、脱珪処理におけるCaO系媒溶剤(生石灰)の使用量を、実施例1の本発明例の場合の6.0kg/溶銑t(表1参照)から、2.0kg/溶銑tに、大幅に低減することができた。また、前チャージの脱燐スラグを炉内に残留させたことによる、脱燐処理での生石灰使用量や処理後の溶銑中の燐濃度への悪影響はほとんど無かったので、上記の脱珪処理における生石灰使用量削減メリットをそのまま享受することができた。
具体的には、図5に示したように、前チャージの溶銑予備処理で生成した脱燐スラグ7を排滓せずに全量を残留させた転炉型精錬炉1に鉄スクラップ8を装入し、次いで、上記転炉型精錬炉1に溶銑5を装入し、さらに必要に応じて生石灰を添加し、上吹きランス2から酸素ガス9を供給して脱珪処理を行った後、脱珪スラグ6の一部を排滓し、その後、生石灰を添加し、引き続き上吹きランス2から酸素ガス9を供給して脱燐処理を行う溶銑予備処理を繰り返した。なお、この転炉型精錬炉1の排ガス処理設備は、吸引ガスを燃料ガスとして回収する機能を有するものであり、吹錬時にスカート11を上昇させた状態で90000~100000Nm3/hr程度の吸引能力を有している。また煙道12には蒸気ボイラー(排熱ボイラー)を備えており、脱珪処理中は、吸引ガスの回収は行わないため、スカート11を上昇して大気を吸引し、排ガス中のCOガスを積極的に燃焼させて高圧の蒸気としてエネルギーの回収を行った。
・方法3;脱珪処理前の溶銑中のSi濃度と目標とする脱珪処理後の溶銑中のSi濃度とから計算される化学量論的に必要な酸素量の1.2倍の酸素を供給し終えた時点以降において、排ガス中のCOガス濃度が6.0vol%以上となった時点を基準として脱珪処理の終了を決定し、上記時点から約20秒経過後にCOガス濃度が6.0vol%以上18.0vol%以下の範囲内で脱珪処理を終了する方法(発明例)
この結果から、脱珪処理終了時点を従来と同様の方法で決定する方法1における脱珪スラグの平均排滓率は47mass%であったのに対し、本発明に適合する方法で脱珪処理終了時点を決定する方法3における脱珪スラグの平均排滓率は62mass%と大幅に向上していること、また、それに伴い、溶銑予備処理後の溶銑中の燐濃度が大幅に低減されているとともに、そのばらつき(標準偏差)も大幅に小さくできていることがわかる。
2:上吹きランス
3:底吹き羽口
4:出湯口
5:溶銑
5a:脱珪処理後の溶銑
5b:脱燐処理後の溶銑
6:脱珪スラグ
7:脱燐スラグ
8:冷鉄源
9:酸素ガス
10:底吹きガス
11:スカート
12:煙道
13:ガス採取プローブ
14:ガス分析装置
15:装入鍋
Claims (12)
- 転炉型精錬炉内の溶銑に酸素源を供給して脱珪処理した後、炉内に溶銑を残留させたまま炉内に存在するスラグの一部を転炉型精錬炉から排出し、その後、転炉型精錬炉内にCaO系媒溶剤および酸素源を供給して脱燐処理した溶銑を転炉型精錬炉から出湯することで、1つの転炉型精錬炉を用いて溶銑に対して脱珪処理および脱燐処理を行う溶銑の予備処理方法において、
前記脱珪処理中、転炉型精錬炉の排ガス処理設備で吸引した吸引ガス中の少なくとも1種以上の炭素原子を含むガス種の濃度を分析し、その分析値に基づいて脱珪処理の終了時点を決定することを特徴とする溶銑の予備処理方法。 - 前記脱珪処理中の転炉型精錬炉から排出される排ガス中の炭素の排出速度を前記吸引ガス中の炭素原子を含むガス種の濃度の分析値および前記吸引ガスの流量に基づいて算出し、前記算出した排ガス中の炭素の排出速度が、極大値となり、極小値となった後に再び増大する変動パターンに基いて前記脱珪処理の終了時点を決定することを特徴とする請求項1に記載の溶銑の予備処理方法。
- 前記脱珪処理の終了時点を、前記吸引ガス中のCOガス濃度、CO2ガス濃度およびCOガスとCO2ガスの合計濃度のうちのいずれか1の濃度の分析値が、極大値となり、極小値となった後に再び増大する変動パターンに基いて決定することを特徴とする請求項1に記載の溶銑の予備処理方法。
- 前記脱珪処理の終了時点を、前記吸引ガス中のCOガス濃度、CO2ガス濃度およびCOガスとCO2ガスの合計濃度のうちのいずれか1の濃度の分析値と前記吸引ガスの流量との積から算出した、前記吸引ガス中のCOガス流量、CO2ガス流量およびCOガスとCO2ガスの合計流量のうちのいずれか1つの流量が、極大値となり、極小値となった後に再び増大する変動パターンに基いて決定することを特徴とする請求項1に記載の溶銑の予備処理方法。
- 前記脱珪処理の終了時点を、前記極大値となり、極小値となった後に再び増大する変動パターンにおいて、再び増大した値が、極大値に対して90%以上150%以下の所定の比率の値以上となった時点を基準として所定の経過時間範囲内とすることを特徴とする請求項2~4のいずれか1項に記載の溶銑の予備処理方法。
- 前記極大値となり、極小値となった後に再び増大する変動パターンにおける極大値と極小値の差が、極大値の10%以上であることを特徴とする請求項2~5のいずれか1項に記載の溶銑の予備処理方法。
- 前記脱珪処理の終了時点を、前記吸引ガス中のCOガス濃度、CO2ガス濃度およびCOガスとCO2ガスの合計濃度のうちのいずれか1の濃度の分析値が所定の閾値以上となった時点を基準として所定の経過時間範囲内とすることを特徴とする請求項1に記載の溶銑の予備処理方法。
- 前記排ガス処理設備は、吸引した前記転炉型精錬炉の排ガスを燃料ガスとして回収する機能を有するものであり、前記排ガス処理設備で転炉型精錬炉の排ガスとともに大気を吸引して前記排ガス中のCOガスの少なくとも一部を燃焼させさせるとともに、
前記脱珪処理の終了時点を、前記燃焼後の吸引ガス中のCOガス濃度が2.0vol%以上、18.0vol%以下の所定の閾値以上となった時点を基準として所定の経過時間範囲内とすることを特徴とする請求項7に記載の溶銑の予備処理方法。 - 前記脱珪処理の終了時点を、前記吸引ガス中のCOガス濃度、CO2ガス濃度およびCOガスとCO2ガスの合計濃度のうちのいずれか1の濃度の分析値と前記吸引ガスの流量との積から算出した、前記吸引ガス中のCOガス流量、CO2ガス流量およびCOガスとCO2ガスの合計流量のうちのいずれか1つの流量が、所定の閾値以上となった時点を基準として所定の経過時間範囲内とすることを特徴とする請求項1に記載の溶銑の予備処理方法。
- 前記脱珪処理の終了時点を、前記吸引ガス中の炭素原子を含むガス種の濃度の分析値および前記吸引ガスの流量に基づいて、前記脱珪処理中の転炉型精錬炉から排出される排ガス中の炭素の排出速度を算出し、該排出速度が所定の閾値以上となった時点を基準として所定の経過時間範囲内とすることを特徴とする請求項1に記載の溶銑の予備処理方法。
- 前チャージの脱燐処理で生成したスラグを30mass%以上炉内に残留させた状態で、次チャージの溶銑を転炉型精錬炉に装入し、脱珪処理することを特徴とする請求項1~10のいずれか1項に記載の溶銑の予備処理方法。
- 前記脱珪処理終了時に、前記転炉型精錬炉に存在するスラグの塩基度([CaO(mass%)]/[SiO2(mass%)])を0.80~1.50の範囲に制御することを特徴とする請求項1~11のいずれか1項に記載の溶銑の予備処理方法。
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JP2017025379A (ja) * | 2015-07-22 | 2017-02-02 | 新日鐵住金株式会社 | 溶銑予備処理方法及び溶銑予備処理制御装置 |
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BR112015016931B1 (pt) | 2020-04-07 |
BR112015016931A2 (pt) | 2017-07-11 |
JP5950133B2 (ja) | 2016-07-13 |
CN104884641A (zh) | 2015-09-02 |
KR101701658B1 (ko) | 2017-02-01 |
CN104884641B (zh) | 2017-09-22 |
JPWO2014112521A1 (ja) | 2017-01-19 |
JP5790964B2 (ja) | 2015-10-07 |
TWI570244B (zh) | 2017-02-11 |
KR20150092298A (ko) | 2015-08-12 |
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