JP5721009B2 - Melting furnace operation method - Google Patents

Description

  The present invention relates to a method for operating a melting furnace such as a cupola or a blast furnace, and more particularly to a method for determining a coke ratio necessary for operation of a melting furnace using coke as a fuel.

  Conventionally, in order to produce castings, melting furnaces such as cupolas for producing molten iron (molten metal) have been widely used.

  For example, in the case of a cupola (melting furnace) 1 as shown in FIG. 1, a coke fuel C as a fuel is charged into the furnace together with an iron source S such as pig iron and steel scrap, and a bed coke layer is formed. 10 is formed. The coke fuel C in the bed coke layer 10 is burned by blowing hot air from the tuyere 4 passing through the side wall of the cupola 1 and opening into the furnace, and the iron source S is melted out by the combustion heat.

  Since the coke fuel C in the furnace is reduced by the combustion, the coke fuel C is supplied (supplemented) into the furnace together with the iron source S in order to perform continuous melting. The replenished coke fuel C is indicated by reference numeral 11 in FIG. 1 and is called a drive-up coke 11 charged from the furnace top together with the iron source S.

  Here, the charging ratio between the driving coke 11 and the iron source S is called a coke ratio, and this coke ratio is one of the operating conditions determined for each melting furnace. By determining and managing the optimum coke ratio, the temperature and components (carbon content, etc.) of the molten iron produced by the melting furnace can be maintained within an appropriate range.

  Since the optimum coke ratio varies depending on the properties and quality of the coke fuel C, even if the coke fuel C itself is operated under the same conditions under the same cupola, the coke ratio to be set may have to be changed.

By the way, conventionally, coke for casting has been used as the main fuel of cupola. However, in recent years, the market distribution volume of casting coke has decreased. For this reason, for the purpose of achieving stable operation of the cupola, it has been desired to use coke for blast furnaces with a large amount of circulation as a substitute for coke for casting.
However, since the blast furnace coke is significantly different in properties from the casting coke, when used as it is, the temperature and components (carbon content, etc.) of the molten iron change, and the numerical values cannot be kept within an appropriate range.

  Therefore, as a countermeasure technique, a technique of using graphite electrode scraps together with blast furnace coke is disclosed. In this technology, blast furnace coke and graphite electrode scraps are used together as fuel for cupola, so that the difference in properties between blast furnace coke and foundry coke does not affect the temperature and composition of molten iron, Blast furnace coke can be used in a cupola as an alternative to casting coke (see, for example, Patent Document 1).

JP 2009-007618 A

  However, there are various types of blast furnace coke, and the properties and quality of the blast furnace coke vary greatly depending on the type of blast furnace coke (production area, etc.). For this reason, every time the type of coke for blast furnace changes, there is a high possibility that the appropriate coke ratio will also change. Therefore, when trying to use a type of coke fuel C that has never been used (hereinafter referred to as “new coke”) as a fuel, it is necessary to first obtain an appropriate coke ratio of the new coke.

  As a method of finding the appropriate coke ratio of new coke, the method of finding the proper coke ratio while gradually increasing the composition of the new coke into the current coke and confirming fluctuations in the composition of the molten iron, etc. It has been adopted from the past.

  However, since this method takes time and effort, the time required to determine the coke ratio increases as the number of opportunities to try various new cokes increases. For this reason, there is a risk of hindering the operation of the melting furnace. Further, since a large quantity of coke cannot be purchased until an appropriate coke ratio is found, there is a problem that the purchase price of the new coke becomes high as a result.

  Accordingly, an object of the present invention is to make it possible to determine an appropriate coke ratio in a short time.

  In order to overcome the above-mentioned problems, the present invention relates to a method of operating a melting furnace in which an iron source is melted by combustion of a charged coke fuel, and at least two types of coke fuel are used in the melting furnace. The correlation between the bulk specific gravity of the coke fuel in the furnace and the appropriate coke ratio was obtained, and when using a new type of coke fuel, the bulk specific gravity of the newly used coke fuel was measured, and based on the measured bulk specific gravity An appropriate coke ratio of the newly used coke fuel is determined from the correlation, and the operation method of the melting furnace is characterized by operating with the newly used coke fuel according to the determined appropriate coke ratio. Adopted.

  In other words, the operation method of the melting furnace of the present invention is a conventional coke ratio determination method (increase the blend of new coke into the current coke little by little and confirm the fluctuations in the composition of the molten iron, etc. By determining the correlation (regression equation) between the coke ratio derived by coke ratio and the coke bulk density (regression equation), the proper coke ratio of the new coke fuel to be used is measured. Then, it was determined from the measured bulk specific gravity and the correlation (regression equation), and was configured to operate at an appropriate coke ratio.

  In this way, when melting a certain iron source in a certain melting furnace, there is a certain correlation between the bulk specific gravity of the coke fuel used and the appropriate coke ratio of the coke fuel. The inventors have discovered. However, the correlation differs depending on the melting furnace and iron source used.

  This correlation is obtained by, for example, obtaining an appropriate coke ratio in each coke fuel by using at least two different types of coke fuel for a specific iron source in a specific melting furnace, and determining the volume of each coke fuel. A specific gravity value and an appropriate coke ratio value are plotted on a graph, and on the graph, the correlation between the two can be obtained by a regression equation based on the plotted information of at least two points. The regression equation can be obtained if there are at least two points to be plotted, but it is desirable that the number of points to be plotted is as small as possible. As the regression equation, for example, regression analysis such as a least square method may be used.

  As described above, by determining the correlation between the bulk specific gravity of the coke fuel and the appropriate coke ratio, the bulk specific gravity of the coke fuel to be newly used (the new coke) is determined for the specific iron source in the melting furnace. It is possible to easily obtain an appropriate coke ratio to be set only by obtaining. For this reason, even if the opportunity to try new coke increases, the time required to determine the coke ratio does not take long. In addition, since an appropriate coke ratio can be obtained in a short time, the degree of freedom in various conditions when purchasing a large amount of coke is increased, and as a result, a situation where expensive coke is used can be avoided.

  In the present invention, an appropriate coke ratio to be easily set can be obtained simply by measuring the bulk specific gravity of a newly used coke fuel. Therefore, when various coke fuels are used in a melting furnace such as a cupola or a blast furnace. In addition, it is possible to greatly reduce the labor for determining the proper coke ratio and to determine the proper coke ratio in a short time.

Overall view of melting furnace (cupola) The graph figure which shows an example of the regression equation defined with the determination method of the appropriate coke ratio which concerns on this invention

  An embodiment of the present invention will be described. FIG. 1 is an example of a cupola (melting furnace) 1 in which the operation method of the melting furnace of the present invention is adopted as described above. Reference numeral 2 in the figure denotes an inlet for charging the coke fuel C and the iron source S, reference numeral 3 denotes a molten iron outlet, reference numeral 4 denotes a tuyere, and reference numeral 5 denotes a cooling device.

  In the cupola 1, coke fuel C is charged from an inlet 2 together with an iron source S such as pig iron, steel scrap, and return material. As shown in the figure, on the bed coke layer 10 composed of the lowermost coke fuel C, additional coke fuel C (catch-up coke 11) is sequentially supplied (supplemented) together with the iron source S. The hot air blown from the tuyere 4 burns the coke C, melts the iron source S by the combustion heat, and takes out the molten iron from the hot water outlet 3.

  In addition, as a component change of the molten metal in the cupola 1, for example, if the iron source S has a small material C value such as iron scrap, the iron source S absorbs carbon from the coke fuel C. In this case, generally, as the amount of the coke fuel C is increased, the inside of the cupola 1 becomes higher and the amount of absorbed carbon tends to increase. Further, for example, if the iron source S has a high material C value, it may be slightly decarburized.

  In this melting furnace, when a new type of coke fuel C (new coke) is used, how to obtain an appropriate coke ratio of the new coke will be described based on experimental examples.

  First, by using a plurality of different types of coke in the same cupola 1, the correlation between the bulk specific gravity of the coke fuel C in the cupola 1 and an appropriate coke ratio is obtained. At this time, the iron source S is the same material for each coke. Further, all other conditions relating to the operation of the cupola 1 such as conditions of hot air blown from the tuyere 4 are the same.

  Example 1 (setting of correlation between coke ratio and bulk specific gravity) is shown below. In Experiments A, B, and C shown in Table 1, graphite electrode scrap, blast furnace coke A (Australia, blast furnace coke A), and blast furnace coke B (China a company, blast furnace coke B) were used as coke fuel C. .

  In Experiments A, B, and C, the target output C% was set to 3.60%, and the experiment was performed using the conventional coke ratio determination method. Table 2 shows the output C% in the actual experiment.

  As shown in Table 1, experiment A used coke fuel C in which the experimental coke ratio (%) was 1.5 for graphite electrode scrap, 14.0 for coke A for blast furnace, and 15.5 as a whole. Is. Experiment B uses coke fuel C in which blast furnace coke A is 7.3, blast furnace coke B is 7.5, and 14.8 as a whole. Experiment C uses a coke fuel C in which the graphite electrode scrap is not used, the blast furnace coke B is 13.5, and the total is 13.5.

  “Electrode waste” in the table indicates graphite electrode waste. The specific component ratio of the graphite electrode scrap used in this example is 98.0% by weight of fixed carbon, 1.2% by weight of ash, 0.6% by weight of volatiles, and 0.5% by weight of total sulfur. is there.

  As shown in Table 2, in Experiment B, the target output C% value of 3.60% can be obtained. However, in Experiments A and C, the C value is higher or lower than the target output of 3.60%.

  From here, the carbon absorption per 1% was calculated by the following formula (1). The iron source material C% supplied from the iron source S material was 1.258%.

[Formula (1)]
Carbon absorption per 1% = (Average C% value minus 1.258) / Experimental coke ratio

  The amount of carbon absorption per 1% of each coke fuel C determined by the equation (1) is shown in the rightmost column of Table 2. Using the obtained amount of carbon absorption per 1%, a coke ratio for achieving the target output C% value of 3.60% was obtained as a corrected coke ratio from the following formula (2).

[Formula (2)]
Corrected coke ratio = (3.60-1.258) ÷ Carburization per 1%

  The calculated corrected coke ratio is shown in the middle column of Table 2. In addition, the reference values in Reference 1 and Reference 2 in Table 2 were obtained from the results of experiments conducted separately, and the carbon absorption per 1% of graphite electrode scrap and blast furnace coke A was obtained. In the case of operation, the corrected coke ratio is calculated. Here, the amount of absorbed carbon per 1% is set to 0.254 and 0.149, respectively.

  The bulk specific gravity was calculated by filling a coke in a container capable of grasping an arbitrary volume (here, 1500 mm × 1820 mm × 760 mm) and measuring the weight.

The experimental values and reference values shown in Tables 1 and 2 are plotted on a graph. FIG. 2 shows a graph plotting information of the experimental value and the reference value. The horizontal axis in the figure indicates the bulk specific gravity (kg / m ³ ), and the vertical axis indicates the corrected coke ratio (%).

On the graph, based on the plotted information, the correlation between the two, that is, the correlation between the measured bulk specific gravity and the corrected coke ratio obtained from the experimental results (regression formula) was obtained. The regression equation was obtained by regression analysis using the least square method.
Based on the correlation between the bulk specific gravity and the corrected coke ratio, in the subsequent experiments, it is possible to derive a roughly appropriate coke ratio simply by measuring the bulk specific gravity of the newly used coke.

That is, by using the regression equation of this graph, when using the new coke with the cupola 1, if the new coke bulk specific gravity (kg / m ³ ) is measured, the regression is based on the measured bulk specific gravity. An appropriate modified coke ratio can be easily determined from the equation. If operation is performed using new coke with the determined appropriate corrected coke ratio, molten iron having desired specifications and components can be obtained.

  The commonly used index coke ratio is a ratio (%) obtained by dividing the weight of the coke fuel C introduced into the melting furnace 1 such as the cupola 1 by the weight of the iron source S. That is, it is an index indicating the weight ratio of the iron source S and the amount of coke necessary for producing hot metal. On the other hand, the experimental coke ratio is the coke ratio actually employed in the experiment.

  Further, as described above, the carbon absorption amount per 1% is the carbon absorption amount (carbon absorption rate) given to the iron source S per 1% of the experimental coke ratio of each coke fuel C.

  The corrected coke ratio is obtained by dividing the difference between the target C value (3.6%) and the material C value of iron source S (1.258%) by the amount of carbon absorbed per 1%. That is, the coke ratio corrected from the amount of carbon absorption (carbon absorption rate), in other words, the value of the ratio (%) of the iron source S and the amount of coke necessary for producing hot metal on the basis of the amount of carbon absorption. .

  As Example 2, Experiment D is shown below. In Experiment D, blast furnace coke A and blast furnace coke C (China b) were used as new coke. The coke fuel C used in Experiment D is a mixture of blast furnace coke A and blast furnace coke C in a ratio (weight ratio) of 48:52 shown in the bottom row of Table 3. The bulk specific gravity of this mixed coke was measured, and the coke ratio was calculated from the measured bulk specific gravity using the correlation shown in the graph of FIG. The results are shown in Table 3.

As shown in the lowermost row and the rightmost column of Table 3, an appropriate coke ratio calculated based on the measured bulk specific gravity is 14.7%. In general, regarding the coke ratio, it is considered that when a low coke ratio is set compared to the appropriate coke ratio, the risk to operations such as in-furnace troubles is greater than when a high coke ratio is set. It has been.
Therefore, in this experiment, as described in the column of experimental coke ratio in the table, 14.8%, which is slightly higher than the coke ratio obtained from the bulk specific gravity, Adopted as a ratio.

The average yield C% value in Experiment D with an experimental coke ratio of 14.8% is shown in the Average Output C% Value column in Table 3. The average output C% value in Experiment D is 3.59%, and the target output C% value of 3.60% is almost achieved. The carbon absorption per 1% calculated from the above formula (1) was 0.158%, and the corrected coke ratio calculated from the above formula (2) was 14.8%.
The coke ratio obtained from the bulk specific gravity shown in Table 3 is 14.7% with respect to the corrected coke ratio of 14.8% obtained from the result of Experiment D, and the correlation between the coke ratio of the approximate value and the bulk specific gravity is obtained. It was possible to calculate. When the coke ratio is calculated at 14.7%, the output C% value is 3.58%.

In this way, by obtaining the correlation between the bulk specific gravity of the coke fuel C to be used and the appropriate coke ratio (corrected coke ratio), it is possible to newly apply the same iron source S to the same cupola 1. An appropriate coke ratio to be set can be easily obtained simply by obtaining the bulk specific gravity of the new coke to be used.
For this reason, even if the opportunity to try new coke increases, the time required to determine the coke ratio does not take long. In addition, since an appropriate coke ratio can be obtained in a short time, the degree of freedom in various conditions when purchasing a large amount of coke is increased, and as a result, a situation where expensive coke is used can be avoided.

1 Cupola (melting furnace)
2 Inlet 3 Outlet 4 Tuyere 5 Cooling device 10 Bed coke layer 11 Drive-in coke C Coke fuel S Iron source

Claims (1)

In the operation method of the melting furnace that melts the iron source by burning the charged coke fuel, before using the new type of coke fuel , at least two types of coke fuel are separately used in the melting furnace and dissolved. The difference between the bulk specific gravity of the coke fuel in the furnace and the target C value of the tapping and the material C value of the iron source is the amount of carbon absorbed by the iron source per 1% of the experimental coke ratio, which is the coke ratio of the coke fuel used. When a new type of coke fuel is used, the bulk specific gravity of the newly used coke fuel is measured, and the correlation is calculated based on the measured bulk specific gravity. determining a correction coke ratio corresponding to coke fuel the newly used from the relationship, and set the determined modified coke ratio coke ratio, the coke combustion to be newly used Melting furnace method operation, characterized in that to operate without changing the operation conditions other than coke ratio by the melting furnace in.

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