JP2011179092A - Roasting-reduction method for steel by-product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roasting-reduction method for steel by-product, in which occurrence of a blowing-up phenomenon is surely predicted without being accompanied with the time delay and the operational condition of a reducing furnace is changed before the blowing-up happens, to avoid the occurrence of the blowing-up. <P>SOLUTION: This invention relates to the roasting-reduction method for steel by-product, in which the raw material consisting of the steel by-product is supplied into the reducing furnace together with a carbonaceous material, and reduced, wherein in the process where melting of the raw material is started by supplying a prescribed electric power, and the raw material is melted and reduced with the carbonaceous material, to start formation of molten metal and molten slag, the temperature of the raw material charged in the reducing furnace, is measured with a radiation thermometer, and the reduced electric power for preventing the crushing and the blowing-up phenomena, calculated based on the prescribed electric power and the temperature variation, is supplied into the reducing furnace or the supply of electric power is suspended. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention efficiently and safely reduces steel by-products such as steelmaking dust containing valuable metals, pickling sludge, and scale materials during annealing, and enables reduction of valuable metals by recovery. Regarding the method.

  Steel by-products such as steelmaking dust, slag, pickling sludge, and scales during annealing contain valuable metals such as iron, nickel, chromium, and manganese, and many recovery methods have been proposed. It has been. As one of them, a method has been proposed in which these by-products are mixed with a carbon source such as coal or coke, formed into a briquette shape, and heated in an arc electric furnace for reduction treatment (for example, patent document). 1 and 2).

  Also, a by-product is mixed with a carbon source such as coal or coke, molded into a briquette shape, roasted once to remove volatile components such as moisture, and then reduced by heating in an arc electric furnace. Has been proposed (see, for example, Patent Documents 3 to 6).

  In these methods, depending on the components of the raw material, there may be a problem in operation such as hanging on a shelf or blowing up that is considered to be accompanied by an arc electric furnace. Moreover, the meltability and fluidity | liquidity of slag were not appropriate, and there also existed a problem that the recovery rate of valuable metals fell.

  In the above-described method of heating and reducing in an arc electric furnace after roasting, a method of adding aluminum ash is disclosed in order to effectively recover valuable metals (for example, see Patent Document 7). . However, since the reaction in the electric furnace is too intense, it is difficult to control the furnace, and there are cases where explosions and the like are involved.

  The explosion occurs by a mechanism as shown in FIG. That is, the raw material 2 charged into the submerged arc electric furnace 1 causes a shelf hanging phenomenon (symbol 7), and the cavity 6 is formed. This is a so-called steam explosion in which the water contained in the raw material 2 expands rapidly when it collapses. The shelf suspension 7 is a phenomenon that occurs when a large amount of powder is present in the raw material, because the raw materials are easily sintered. Naturally, if the moisture content of the raw material is high, the explosion scale is large and dangerous. This explosion phenomenon is called blowing up.

  With respect to such blowing-up problems, a technique for stabilizing the operation is disclosed by defining each raw material mixing ratio of steel by-products such as steelmaking dust, slag, pickling sludge, and annealing scale ( For example, see Patent Document 8). In addition, a technique for ensuring the strength of briquettes by defining the particle size distribution of the raw materials within a preferable range is disclosed (for example, see Patent Document 9). Alternatively, a method of operating stably by defining the amount of power input (see, for example, Patent Document 10) and a technique for dropping the briquette so that the briquette does not collapse are also disclosed (eg, Patent Literature). 11).

  Although it can be said that the operation has been stabilized by the above technical development, in rare cases, blowing-up has occurred. For this reason, there has been a strong demand for the development of so-called blow-up prediction technology that predicts blow-up and prevents accidents. For this purpose, a thermocouple is embedded in the refractory lined on the inner surface of the electric furnace required for reduction, and the shape of the raw material existing in the furnace is predicted from the temperature change, and the movement of the shape A technique for predicting the collapse of the raw material and preventing the blowing phenomenon is disclosed (for example, see Patent Documents 12 and 13).

JP-A-8-260014 JP 2003-247026 A JP-A 61-15929 JP-A 61-177331 JP 61-177332 A JP-A 61-177337 Japanese Patent Laid-Open No. 10-330822 JP 2008-31548 A JP 2008-31549 A JP 2008-240138 A JP 2009-7632 A JP 2008-116066 A JP 2008-115408 A

Heat transfer behavior of molten iron and nickel during the first 0.2 seconds of solidification, ISIJ international, 49 (2009), No.9, p.1347. (Hidekazu Todoroki and Natthapong Phinichka)

  As described above, it is possible to predict the shape of the raw material in the furnace from the temperature measurement by the thermocouple, but a time delay is inevitably caused. For example, detailed research results are disclosed in Non-Patent Document 1, for example. In other words, with thermocouples, even if a type with a small equivalent wire diameter and excellent responsiveness is used, temperature measurement is delayed as compared with optical temperature measurement. If the installation is performed so that the delay is shorter than 1 second, if it is an iron skin, a thermocouple must be made using the same wire material. That is, it is very difficult to measure the temperature on time and respond immediately.

  The present invention has been made in view of the above situation, and the present invention reliably predicts the occurrence of the blowing-up phenomenon without a time delay, and changes the operating conditions of the reducing furnace before reaching the blowing-up. An object of the present invention is to provide a method for reducing steel by-products that can avoid the occurrence of blow-up.

  The method for reducing steel by-product according to the present invention is to supply a predetermined power to start melting of the raw material, and in the process where the raw material is melted and reduced by the carbonaceous material and molten metal and molten slag begin to form, The temperature of the raw material existing in the inside is measured with a radiation thermometer, and the reduced power to prevent the collapse and the blow-up phenomenon calculated based on the predetermined power and temperature change is supplied to the reduction furnace or the power It is characterized by stopping the supply.

In the present invention, the reduced electric power Q ₂ (kW) for preventing the collapse and the blowing-up phenomenon is operated with the temperature change of the raw material per time measured by the radiation thermometer as dT / dt (° C./second). When the predetermined electric power is Q ₁ (kW), it is a preferable aspect that it is calculated by the following equation (1).
Q ₂ ≦ (4 dT / dt + 1.3) × Q ₁ dT / dt ≦ −0.1 (1)
In addition, a predetermined number of moving average processes are performed every second for the temperature change of the raw material measured by the radiation thermometer, and the average temperature in the _Nth section is defined as T _N, and the temperature difference ΔT _N = T _{When N−} T _N−1 is calculated, and the value obtained by dividing the temperature difference ΔT _N by the N−1 and Nth time intervals is −0.1 (° C./sec) or less three times continuously In a preferred embodiment, the reduced power for preventing the collapse and the blowing-up phenomenon is supplied to the reduction furnace or the supply of power is stopped.

  According to the present invention, since the temperature of the raw material is measured by the radiation thermometer, the responsiveness of the temperature measurement is improved as compared with the case where a thermocouple is used, and the temperature change of the raw material is quickly detected. It is possible to accurately grasp the abnormal phenomenon occurring in the furnace without delay. Further, by reducing or stopping the power supply due to this temperature change, it is possible to prevent the material from collapsing and blowing up.

It is a figure which shows typically the blowing up phenomenon in the conventional reduction furnace. It is a figure which shows typically the blowing up phenomenon in the reduction furnace of this invention. It is a graph which calculates | requires the electric power input amount for preventing a collapse and a blowing-up phenomenon. It is a graph which shows the relationship between the elapsed time and temperature in the normal operation where collapse / blow-up did not occur. It is a graph which shows the relationship between the elapsed time and temperature in the operation of the comparative example in which collapse / blowing occurred. It is a graph which shows the relationship of the elapsed time and temperature in the reduction operation of an Example. It is a graph which shows the relationship of the elapsed time and temperature in the reduction operation of an Example. It is a graph which shows the relationship of the elapsed time and temperature in the reduction operation of an Example. It is a graph which shows the relationship of the elapsed time and temperature in the reduction operation of an Example. It is a graph which shows the relationship of the elapsed time and temperature in the reduction operation of an Example. It is a graph which shows the relationship of the elapsed time and temperature in the reduction operation of an Example. It is explanatory drawing of the principle of blowing-up detection at the time of the start of collapse of a raw material.

Hereinafter, the present invention will be described in detail.
FIG. 1 shows the generation mechanism of the blow-up phenomenon to be solved by the present invention. First, the raw material raises the shelf (a), and as a result, a cavity is formed (b). After that, the dome-shaped raw material, which is a sintered body suspended from the shelf, collapses, and the cold raw material existing in the upper part suddenly comes into contact with the high-temperature raw material to cause a certain type of steam explosion (c). .

  The phenomenon from the shelf suspension to the collapse varies from several seconds to several minutes, and the elapsed time varies depending on the case. However, when it occurs immediately, it has been found that a response in seconds from the shelf suspension state is required. The present inventors detect the phenomenon leading to (a) to (b) in advance and reduce the power amount of the electrode before turning to (c) or turn off the power. We thought that once the heat supply was reduced, troubles due to blowing up could be avoided.

  First of all, I tried to install a thermocouple on the furnace wall to see if it could be detected by a thermocouple, but the temperature change detected by the thermocouple was not rapid, and there was a clear problem that the action to be taken was delayed. became. Furthermore, it was found that the problem is that the place where the collapse occurs is not constant, and the place that can be detected by the thermocouple does not include the entire interior of the furnace. Therefore, when the temperature was measured using a radiation thermometer and monitored for about 50 charges, it was found that there was no problem with the thermocouple as described above, and it was possible to monitor with good responsiveness, leading to the present invention.

  In the method of roasting and reducing steel by-products according to the embodiment of the present invention, a predetermined power is supplied to start melting of the raw material, the raw material is melted and reduced by the carbon material, and molten metal and molten slag are formed. In the process of starting, the temperature of the raw material existing in the reduction furnace is measured with a radiation thermometer, and the electric power for preventing the collapse and the blowing-up phenomenon calculated based on the predetermined electric power and temperature change is supplied to the reduction furnace. Alternatively, the reduction furnace can be controlled by stopping the supply of electric power.

In addition, the calculation method of the input electric energy Q ₂ for preventing the collapse / blowing phenomenon is that the temperature change is dT / dt (° C./second) from the raw material temperature measured by the radiation thermometer, and the electric power during operation is Q _{When 1} (kW) is set, the control amount of electric power is obtained so as to satisfy the following equation (1) according to the temperature change.
Q ₂ ≦ (4 dT / dt + 1.3) × Q ₁ , dT / dt ≦ −0.1 (1)

  FIG. 3 is a measurement result in a preliminary experiment of 11 charges in which the amount of input electric power is variously changed to prevent a collapse / blow-up phenomenon. Equation (1) is a boundary of presence / absence of blow-up in the measurement result of FIG. Obtained from the line.

Formula for calculating the input power amount Q ₂ to prevent the collapse-blown phenomenon was then determined as will be described. As shown in FIG. 2, a radiation thermometer was installed and monitored where the raw material charged in the furnace could be seen. When the thermometer was installed in this way and repeatedly monitored for about 50 charges, in most cases, the collapse phenomenon did not occur and good operation could be performed. A typical temperature transition at that time is shown in FIG. Here, the installed thermometer is a general radiation thermometer. Of course, any device that optically measures temperature, such as a two-color thermometer, may be used. This temperature measurement example is an example using what is detected when the raw material surface temperature in the furnace exceeds 700 ° C. The operation itself takes 1 charge in about 4 hours, and the timing of the collapse and blow-up phenomenon that must be monitored is about 2.5 hours after the raw material is reduced by the carbonaceous material, Fe-Ni-Cr-Mn. This is because the molten metal of the system and the molten slag of the CaO—SiO ₂ —Al ₂ O ₃ —MgO—FeO—Cr ₂ O ₃ —F system begin to form. By the way, the elapsed time shown in the graph is obtained by taking the temperature change after that with the time point of 2.5 hours as 0.

  During this series of temperature measurement tests, there was a charge that had collapsed and blown up. The temperature transition at that time is shown in FIG. In FIG. 4, which is a temperature transition in a normal operation where neither collapse nor blow-up has occurred, it is apparent that the temperature rises uniformly while repeating the fine vertical movement, but the figure that caused the blow-up has occurred. 5, it can be seen that the temperature starts to drop sharply, continues for about 10 minutes, and then suddenly starts to rise in temperature. When this is compared with the operation status at that time, the correspondence relationship is organized. As shown in the annotation in the graph of FIG. 5, the point at which the temperature suddenly started to fall is the start point of collapse, and then suddenly The point at which the temperature starts to rise is the point at which the blow-up occurs. Since the blow-up phenomenon causes smoke to rise outside the furnace, the phenomenon can be confirmed from outside the furnace, so the abnormal temperature drop that occurs just before that is the start point of the collapse, and flows to the electrode at that point. What is necessary is just to take measures, such as reducing the amount of electric power to be turned off or turning it off.

Here, it is necessary to smooth the temperature transition so as not to confuse the abnormal phenomenon with the normal temperature fluctuation. For this purpose, the following arithmetic treatment was performed.
(1) For example, 10 moving average processes are performed on the temperature every second. The average temperature of the _Nth section where this processing is performed is defined as _TN .
(2) Calculate the temperature difference ΔT _N = T _N −T _N−1 on the moving average line.
(3) If the value obtained by dividing ΔT in (2) by the time interval is −0.1 (° C./second) or less with respect to the N−1 and Nth time intervals (here 1 second), Proceed to (4) below.
(4) If the state satisfying the above (3) continues three times, it is determined that a collapse phenomenon has occurred. If it is less than 2 times, return to (1) again.
(5) If it is judged that the phenomenon of collapse, the alarm is activated and the worker who heard it will take appropriate measures.

  The graph when the actual measurement value indicated by the broken line in the graph of FIG. 4 is smoothed by the above process (1) is also shown in FIG. By performing smoothing in this way, it is possible to obtain a curve indicating a tendency of temperature increase / decrease in the reduction furnace without erroneously determining that a local minute temperature change in the actually measured value is a collapse phenomenon.

  Moreover, the schematic diagram of process (2)-(5) is shown in FIG. FIG. 12 is an enlarged view of the temperature decrease portion A of the material collapse start portion in FIG. As shown in FIG. 12, a numerical value obtained by dividing the temperature change of each section by the time interval, that is, a slope when the temperature curve of each section is approximated by a straight line is continuously calculated, and this slope is −0.1 or less. If a certain case continues three times, it is determined that blowing has been detected. By performing such a process, it is possible to accurately capture the material collapsed portion described in FIG.

  In addition, said process is an example and a numerical value can be changed with each furnace. The point is that a moving average of a certain number of data is taken in seconds (N-1 and the Nth time interval), and an alarm sounds when the temperature decrease rate at that time becomes higher than a certain critical value. Of course, instead of an alarm, it may be a facility that can automatically control the power amount to be reduced or turned off.

  The temperature sampling speed in the moving average process is 0.05 to 1 second / 1 point, that is, although not limited, 1 to 20 Hz is preferable. Although not particularly limited, the moving average may be about 5 to 30 pieces of data. The time unit for taking the moving average may be 0.1 to 10 seconds.

  A determination condition (the above state) for a state where a value obtained by dividing a temperature difference ΔT of one section of the moving average by a time interval is −0.1 (° C./second) or less and a collapse is determined to occur and an alarm is transmitted The number of repetitions of (2) may be set to about 2 to 10 times and a numerical value suitable for the equipment. However, if it is too smooth by moving average, it becomes too insensitive to the change and the phenomenon cannot be captured instantaneously, so it is necessary to optimize each facility.

  According to the present invention, it is possible to accurately grasp the abnormal phenomenon occurring in the reduction furnace without delay, and it is possible to take measures such as reducing the amount of supplied power based on the phenomenon. Thus, it is possible to prevent a blow-up accident.

Next, the effects of the present invention will be described with reference to examples and comparative examples.
Steelmaking dust, pickling sludge, scale material, SiC, slag generated by smelting of ferronickel (MgO-SiO ₂ system), and finishing slag in stainless steel refining AOD (CaO-SiO ₂ -MgO-F system) Mixing, mixing carbonaceous materials, moisture and fats and oils in the proportions shown in Table 1 (unit: mass%), and using a twin roll type machine, this was molded into briquettes of the shape shown in Table 1. .

  In addition, the carbon material was mix | blended with the weight of 100-200 kg with respect to the mix | blended raw material 1t as a part required for a reductive reaction, and a heat source in a roasting process.

  Next, the briquette molded as described above is charged into a roasting box, and then the upper part of the roasting box is sealed with a duct and the lower part is heated with a burner for 20 to 30 minutes while being sucked using a blower. Then, the mixture was ignited and roasting was performed for 120 to 180 minutes. Thereby, while volatilizing a water | moisture content, the raw material particle | grains inside each briquette were sintered.

Thereafter, in order to adjust the amount of slag and the basicity (CaO / SiO ₂ ), limestone and / or silica sand having the composition shown in Table 2 was mixed into the above briquette, and these were charged into a submerged arc electric furnace. . And this was heated and isolate | separated into the reduced metal part and the slag part, and valuable metals, such as Fe, Ni, Cr, and Mn, were collect | recovered. The recovered metal was approximately 5 to 6 t, and the remainder was slag. The size of the electric furnace was 13 t, and the electric power consumption was about 1800 kWh / metal t.

<Examples 1-4>
The temperature change when the raw material put into the reduction furnace is operated by changing the composition of Examples 1 to 4 in Table 1 above is shown in the graphs of FIGS. Examples 1 to 4 could be operated without any particular problem.

<Example 5>
The above treatment was carried out with the formulation shown in Example 5 of Table 1. In the graph of FIG. 10, at a time point of 60 minutes, the temperature decrease rate was −0.3 ° C./second, and the operation was stopped because an alarm sounded. As a result, production stopped, but it was possible to take safe measures without blowing up.

<Example 6>
The said process was performed by the same mixing | blending as Example 3 of Table 1. In the graph of FIG. 11, at the time of the arrow, the temperature decrease rate was −0.15 ° C./second and an alarm sounded. Therefore, the power that had been applied over 2700 kW was turned off and the raw material was dropped on the molten slag. After confirming, the power was reduced again to 2000 kW and continued. As a result, we were able to operate while avoiding sudden collapses and blowing problems. The meaning indicated by the dotted line indicates the expectation when the avoidance operation is not performed even though the alarm device is activated.

<Comparative example>
The said process was performed by the same mixing | blending as Example 2 of Table 1. At the time of the collapse of the raw material, a temperature decrease rate of −0.2 ° C./second was shown, but no action was taken. As a result, it was blown up, and the fumes rose outside the furnace, making it dangerous. After blowing up, he continued to operate and started steel production. In addition, the graph of the temperature change of this comparative example is shown in FIG.

  ADVANTAGE OF THE INVENTION According to this invention, a dangerous blowing up accident can be prevented and it can contribute to the safe operation of the reduction furnace of a steel byproduct.

  DESCRIPTION OF SYMBOLS 1 ... Submerged arc electric furnace, 2 ... Raw material (raw material briquette for reduction | restoration recycling), 3 ... Electrode, 4 ... Slag part, 5 ... Reduction metal part, 6 ... Cavity, 7 ... Shelf hanging, 8 ... Radiation thermometer, 9 ... Temperature measuring section.

Claims (4)

A method for roasting and reducing steel by-products, in which a raw material made of steel by-products is supplied to a reduction furnace together with carbonaceous material and reduced.
Supply predetermined power to start melting the raw material,
In the process where the raw material is melted and reduced by the carbonaceous material and molten metal and molten slag begin to form, the temperature of the raw material present in the reduction furnace is measured with a radiation thermometer,
Supplying reduced power to prevent the collapse and blowing-up phenomenon calculated based on the predetermined power and the temperature change to the reduction furnace or stopping the power supply Roasting reduction method. The reduced electric power Q ₂ (kW) for preventing the collapse and the blow-up phenomenon is the above-mentioned during operation while the temperature change of the raw material per time measured by the radiation thermometer is dT / dt (° C./second). The method for roasting and reducing steel by-products according to claim 1, wherein the predetermined power is Q ₁ (kW) and is calculated by the following formula (1).
Q ₂ ≦ (4 dT / dt + 1.3) × Q ₁ dT / dt ≦ −0.1 (1) A predetermined number of moving average processes are performed every second for the temperature change of the raw material measured by the radiation thermometer,
The average temperature of the _Nth section is defined as _TN ,
Calculate the temperature difference ΔT _N = T _N −T _N−1 ,
If the value of the temperature difference [Delta] T _N divided by N-1 th and N-th time interval is -0.1 (° C. / sec) or less continuous three times, to prevent the collapse and blow phenomenon The method of roasting and reducing steel by-products according to claim 1, wherein the reduced electric power is supplied to the reduction furnace or the supply of electric power is stopped.   The method for roasting and reducing steel by-products according to any one of claims 1 to 3, wherein the steel by-products are steelmaking dust, pickling sludge, scale material, and ferronickel slag.

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