JP6730684B2 - Sintered ore manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a high-strength sinter that is used as a raw material for a blast furnace and has a good reduction powdering property.

The blast furnace, as an iron source raw material, while mainly charging the iron source raw material such as lump iron ore and sinter ore together with the auxiliary raw material into the furnace from the top of the blast furnace, by blowing a reducing gas from the bottom of the furnace, It is a refining furnace for producing hot metal by melting and reducing the iron source material. In this case, in order to promote the reaction between the reducing gas and the iron source material, for example, sinter, in the blast furnace, make sure that the gas in the furnace sufficiently flows in the blast furnace, that is, the gas permeability in the furnace. It is effective to improve the hot metal productivity and the cost reduction. Further, in order to improve the air permeability in the blast furnace, it is effective to suppress the powder ratio of the charging raw material, and for that purpose, it is required to use a sintered ore having high strength. Against this background, various methods for improving the strength of the sinter, which is the main raw material of the blast furnace, have been mainly studied so far.

For example, using a Dwightroid (DL) sintering machine, a gaseous fuel is supplied into a sintering raw material charging layer on the sintering machine (on a pallet), and this is burned to produce a high-strength sintered ore. A method of doing so has been proposed (Patent Documents 1 and 2). According to the methods according to these proposals, since the combustion region of the sintering raw material charging layer is widened during sintering, the heat is supplemented to the portion where the strength is originally reduced, so that the strength of the sintered ore is improved. It is believed that it will be possible to improve. In addition, a method of producing high-strength sinter by creating a temperature condition suitable for sintering in the sintering machine (charge layer) by simultaneously blowing oxygen and gaseous fuel during sintering has also been studied. There is.

JP, 2008-95170, A JP, 2014-31580, A

In the method for producing a sintered ore disclosed in the above-mentioned Patent Documents 1 and 2, it is essential to use a fuel gas (gaseous fuel) in order to improve the strength, and there is a problem that the cost becomes high. Moreover, these methods do not take into consideration the reduction powdering property, and there is no guarantee that this value will improve. Further, in these known methods, there is a problem that the gas permeability is deteriorated because the combustion region during combustion and the melt generation region are expanded by using the fuel gas.

Therefore, an object of the present invention is to improve both the strength and the reduction powderability of the sinter by utilizing nitrogen gas or oxygen-enriched gas without relying on the increase in air volume or the use of gaseous fuel. To propose effective technology.

As a result of extensive studies aimed at achieving the above-mentioned object, the inventors have found that it is effective to optimize the temperature distribution in the sintering raw material charging layer during sintering. It is effective to optimize the amount and concentration of combustion control gas, such as nitrogen gas and blown oxygen, to be introduced into the raw material charging layer, and this reduces not only the strength of the sinter but also the reduction powderability. The present invention has been developed to identify improvements that can be made.

That is, if the concentration of the blown oxygen introduced into the sintering raw material charging layer during sintering is made higher (increased) than before, the strength of the sintered ore can be greatly improved, and after sintering, By newly supplying nitrogen gas to a certain sinter, it has been newly found that the reduction powdering property of the sinter can be improved.

The present invention is exactly a method developed on the basis of the above findings, in which the fuel is removed from the sintering raw material charging layer on the sintering machine pallet and/or the sintered ore deposit layer on the moving carriage of the sintering cooling device. In the method for producing a sintered ore in which a gas is blown, nitrogen gas is used as the gas from the position where the exhaust gas temperature in the sintering machine wind box becomes maximum to 2/3 of the total length from the inlet side of the sintering cooling device. The nitrogen gas concentration used is higher than that in the atmosphere, and the volume of nitrogen gas used is 21 vol. % Of oxygen-rich gas is blown into the sintered ore.

In addition, regarding the present invention according to the above-mentioned configuration,
(1) blowing the pre Symbol nitrogen gas, since the position where the exhaust gas temperature in the sintering machine wind box is maximized, and those performed between the entrance side of the sintered cooling device to 1/3 of the total length, use Use a nitrogen gas concentration higher than that in the atmosphere .
(2 ) The oxygen-enriched gas has a concentration of 30 to 50 vol. %,
( 3 ) When the total length of the sintering machine is 1, the oxygen-enriched gas is blown from above the sintering raw material charging layer at a position within a range of more than 0 to 0.5 from the raw material charging side. thing,
Is considered to be the more preferred embodiment.

According to the present invention having the above-mentioned configuration, the required nitrogen gas is blown into the combustion control gas peculiar to the present invention, that is, the required nitrogen gas is blown into the proper place (timely). As a result, not only a high-strength sinter can be obtained, but also a sinter having a good reduction pulverization property and an excellent reduction pulverization property can be produced without increasing the cost.

FIG. ₃ is a state diagram of Fe ₂ O ₃ concentration-temperature showing the grounds for secondary matite formation. It is a schematic diagram which shows the mode of temperature distribution in a sintering raw material charging layer. It is explanatory drawing (a) which shows distribution of the exhaust gas temperature in each wind box position in the machine length direction of a sintering machine, and explanatory drawing (b) of the nitrogen gas blowing position to a sintering cooling device. It is explanatory drawing which shows the relationship between oxygen concentration and a production rate. It is a figure which shows the influence which oxygen concentration and wind pressure give to a production rate and intensity. It is a figure which shows the influence which the presence or absence of nitrogen blowing has on oxygen concentration and RDI.

Generally, in the operation of a sintering machine, coke, which is a coagulant, is blown by blowing oxygen (oxygen gas as a gas) into a sintering raw material charging layer (hereinafter also simply referred to as “charging layer”) on a pallet. Is known to burn easily. Moreover, in the Dwightroid type sintering machine, it is also known that the moving speed of the pallet becomes faster when the concentration of the blown oxygen is increased (enriched). By the way, in order to increase the strength of the sinter, it is advantageous to keep the holding time in the high temperature range (1200° C.) for a long time. In this respect, an increase in the moving speed associated with the movement of the pallet in the high-temperature combustion zone shortens the holding time in the high-temperature region, that is, the transit time in the combustion zone, which in turn leads to a decrease in strength. Therefore, conventionally, a method of increasing the air flow rate to increase the supply of oxygen and increase the burning rate has been adopted. However, in this case, it is known that the strength of the sintered ore rather decreases. On the other hand, if the oxygen concentration is increased (oxygen-enriched gas is used) instead of increasing the air volume, the cooling speed of the upper part of the combustion zone can be suppressed. In other words, in this case (using oxygen-enriched gas), the moving speed of the combustion zone increases, but the cooling speed remains constant, so the range of the high temperature part expands and the strength of the sinter is increased. It means that you can.

It is generally known that the upper layer portion of the charging layer on the sinter machine pallet has lower strength than the lower layer portion of the charging layer. It is the significance of introducing the oxygen-enriched gas to increase the strength of the upper portion of the charging layer, and it is desirable to increase the strength of the sinter. The oxygen-enriched gas is blown in at a place other than a place where at least nitrogen gas, which will be described later, is blown in.

By the way, it is known that when secondary hematite is generated in the sinter, the reduction powderability of the sinter is deteriorated. Therefore, in the present invention, a study aimed at stabilizing magnetite generated from high temperatures was conducted. As is clear from the state diagram showing the relationship between the Fe ₂ O ₃ concentration and temperature in FIG. 1, a phase transition from hematite to magnetite occurs at a high temperature of 1350° C. or higher. Then, a part of this magnetite becomes a liquid phase, and returns to hematite again when the temperature drops. This is the cause of the formation of secondary hematite and is the background to the development of the present invention.

According to the studies by the inventors, the introduction of enriched oxygen into the charging layer once promotes the formation of the secondary hematite. However, if the blowing of oxygen, especially the blowing of oxygen-enriched gas, can be stopped during firing, the production of secondary hematite can be suppressed, and after that, the same firing-cooling rate as normal firing will be achieved. Therefore, the high temperature portion that has been expanded up to that point will continue to be fired while being expanded. As a result, in this case, even if the oxygen enrichment (introduction of the oxygen-enriched gas) is stopped, the high temperature part does not narrow at once, so the high temperature part remains expanded and magnetite The environment is easy to generate.

As described above, according to the present invention, not only can the production of secondary hematite be suppressed by maintaining the above-mentioned high temperature portion and the increase of magnetite can be expected, but also the reoxidation of the red hot sinter can be prevented by supplying nitrogen gas. This is a method that suppresses the formation of secondary hematite, and therefore, it is possible to improve the reduction powdering property.

Next, in the present invention, when oxygen is blown from above the sintering machine during firing of the sintering compound material, as described above, when introducing an oxygen-enriched gas with an increased blown oxygen concentration, It is preferable to blow the sintered ore during the setting process when the strength of the sintered ore is still low, that is, at the initial stage of firing. The preferable blowing position is a position that is less than half the sintering time, specifically, a position that exceeds 0 (immediately after the ignition furnace) to 0.5 (half the pallet moving distance) when the total length of the sintering machine is 1. It is preferable to blow a high concentration of oxygen from above the raw material charging layer.

In the present invention, as an oxygen-enriched gas having a high oxygen concentration, which is used in place of the conventional increase in air volume for improving strength, 21 vol. % Concentration, preferably 30 to 50 vol. It is preferred to blow in an oxygen-enriched gas with a concentration of %. The concentration is 30 vol. % Oxygen, the formation of hematite by oxygen is 30 vol. %, the effect of nitrogen blowing is small compared with the case of 50% by volume. If it exceeds %, the firing rate becomes too fast, the melting time becomes short, oxygen is not effectively used, and the effect of improving the strength of the sinter cannot be obtained.

Regarding the position where the oxygen-enriched gas is blown in, when the total length of the sintering machine is set to 1, the reason for setting the position from more than 0 to 0.5 is that sintering at a portion of 0.5 or more is performed. This is because ore has a long firing time and is originally high in strength, so that the effect of improving strength is relatively small.

Next, what is particularly characteristic of the method of the present invention is that the nitrogen gas is blown into a proper place and at a proper time in order to suppress the excessive firing as described above. The blowing of the nitrogen gas is performed at least at the position after the firing is completed, that is, at the position after the firing reaches the lowermost layer of the raw material charging layer. For example, after the firing of all the charged sintering raw materials on the sinter machine pallet is completed and the exhaust gas temperature in the wind box reaches the maximum, and further to the first half of the sintering cooling device (total length is T). It is preferable to blow at 1/3 to 2/3).

Specifically, as shown in FIG. 3( b ), the nitrogen gas is blown into the sintering cooler from the inlet side of the sintering cooling device to the entire length T from the position where the exhaust gas temperature in the sintering machine windbox becomes maximum. The nitrogen gas concentration used is up to 2/3, and the nitrogen gas concentration used is preferably higher than the atmospheric concentration.

The blowing of the nitrogen gas also causes a red-hot state at a position up to 1/3 of the entire length T of the sinter cooling device, that is, in the cooled sinter deposit layer on the moving carriage of the sinter cooling device. It is preferable that the nitrogen gas is blown in from the time when the cooled sinter is received until the moving distance of the moving carriage reaches 1/3 of the total length (T). The reason is that by setting the moving distance of the moving carriage of the cooling device to be within 2/3 (T), preferably within 1/3 (T), it becomes possible to reliably prevent the production of secondary hematite. Because.

FIG. 2 shows an example of the temperature distribution in the height direction of the sintering raw material charging layer. When the total charging layer thickness is 600 mm, the sintering zone/melting zone is at a position of about 300 to 400 mm. It is an example when it is in. Usually, in the sintering raw material charging layer, the combustion zone moves from the upper layer to the lower layer, but when this combustion zone reaches the lowermost layer, that is, when the coke combustion ends, nitrogen gas is discharged. This is because the combustion will not be hindered even if it is blown in. Further, when the combustion zone is in the lowermost layer, the exhaust gas temperature becomes the highest, so it is preferable to blow nitrogen gas after the exhaust gas temperature becomes the highest.

FIG. 3 is an example of a profile of exhaust gas concentration measured in the wind box 2 of the sintering machine 1. Generally, in the sintering machine 1, air is sucked through a wind box 2, and a thermometer is installed in the wind box 2 in the present invention. In this figure, the wind boxes are numbered (No. 1 to No. 23) in order from the raw material charging side, and the exhaust gas temperature at that point is shown. Then, the blowing of nitrogen described above is performed at a point including the wind box 2 in which the exhaust gas temperature is maximum, that is, in the illustrated example, No. It is a preferred embodiment to start blowing nitrogen gas from above the raw material charging layer (sintering layer) 3 of the sinter machine pallet at a position corresponding to the 21 air box.

As described above, in the present invention, the blowing of the nitrogen gas is performed on the moving carriage (cooling machine in the illustrated example) of the cooling device (cooler) 5 after the sintered product is crushed by the crusher 4. When charged and cooled, as described above, the range from the inlet side of the cooling device 5 to 2/3 (T) of the total length (T), preferably 1/3 (T). It is preferable to blow nitrogen gas inside.

(Test 1)
FIG. 4 shows the results of a pot test in which oxygen was enriched from the initial stage of firing until the combustion zone was located at a half position in the thickness direction of the raw material charging layer. The oxygen concentration is the oxygen concentration just above the charging layer. In this example, the sintering compound material was granulated with a drum mixer, and the test was conducted in a transparent quartz baking pot in which the position of the combustion zone was known. According to the result of the test at this time, the oxygen concentration was 50 vol. It has been found that the production rate increase is small when the percentage exceeds %.

(Test 2)
Next, FIG. 5 shows the results of a test conducted to examine the effects on the production rate and strength when the oxygen concentration was increased during firing and when the air pressure was increased to increase the air volume. It is shown. Here, the strength was evaluated by rotational strength (tumbler strength) according to JIS M 8712-2009. In this test, the sintering raw material was granulated with a drum mixer, and oxygen enrichment was carried out until it reached the half position of the raw material charging layer, as in Example 1. In the usual case where the wind pressure was increased to improve the production rate, the tumbler strength (TI) of the sinter decreased as the production rate increased. However, it has been clarified that the strength is greatly improved when oxygen is enriched at a predetermined position. As shown in Table 1, this strength has an oxygen concentration of 50 vol. %, the oxygen concentration is 50 vol. % Is considered to be the upper limit.

(Example 1)
Next, FIG. 6 shows that after the initial firing, the combustion zone was enriched with oxygen until the combustion zone reached half the position of the raw material charging layer, then nitrogen was blown in after the exhaust gas temperature reached the maximum, and the oxygen concentration 10 vol. ． The results of the test when ventilation and cooling are performed under the condition of% are shown. The oxygen concentration is the oxygen concentration just above the charging layer in the inlet gas.

In this example, a sintering compound material adjusted to have a basicity of 2.0 was granulated with a drum mixer, and then the obtained sintering compound material was made of quartz so that the position of the combustion zone was known. Sintering test was performed using the transparent baking pot of. Firing at this time was performed at a constant wind pressure (7 kPa). As shown in Table 2, from the test results of Comparative Example 1-4 (without blowing nitrogen gas), the time at which the exhaust gas temperature reached the maximum at each oxygen concentration was measured, and Example 1-4 (nitrogen gas) conforming to the present invention was measured. (With blowing), nitrogen was enriched from the time when the maximum temperature of exhaust gas was reached at each oxygen concentration.

As a result, it became clear that nitrogen gas was blown into the sinter when it entered the cooling process, and that it was possible to improve the reduction dustability (RDI) with an increase in oxygen enrichment. It is considered that this is because the re-oxidation of magnetite generated at high temperature into secondary hematite was suppressed by the decrease in oxygen concentration due to the blowing of nitrogen.

(Example 2)
In this example, when the exhaust gas temperature in the windbox reaches the maximum after oxygen enrichment (oxygen concentration 30 vol.%) from the initial stage of firing until the combustion zone reaches half the position of the sintering raw material charging layer. Then, a test was conducted in which nitrogen gas was blown into each starting time for a certain period of time.
In this test, a sintering compound material adjusted to have a basicity of 2.0 was granulated with a drum mixer, and then the test was performed with a transparent baking pot made of quartz that made the position of the combustion zone visible. It was The firing was performed at a constant wind pressure (7 kPa). Regarding the cooling start time of the nitrogen gas, the difference between the maximum temperature of the exhaust gas and the temperature of 50° C., which is considered to be the end of cooling, was divided into 3 sections, and nitrogen was blown into each temperature section. In this test, the maximum temperature of the exhaust gas is known only after the temperature has dropped, so the maximum temperature is considered to be the time when the exhaust gas temperature rises and drops by 3°C. Specifically, since it was 430° C. in Example 5, 300° C. in Example 6, 179° C. in Example 7, and 420° C. in Example 8, nitrogen was blown in the following exhaust gas temperature range. When the nitrogen gas was blown in, the oxygen concentration on the inlet side was 10 vol. It was set to be %.
-Example 5: (430-303°C)
-Example 6: (300-175°C)
-Example 7: (179-50°C)
-Example 8: (420-173°C)

The results are shown in Table 3. As shown in this table, the RDI after each test is shown as the blowing temperature range when the temperature range between the maximum temperature and 50° C. is T. From this result, it was found that the effect of the nitrogen gas injection is significantly exhibited when the exhaust gas temperature is high, that is, when the temperature of the sinter is high. It is considered that this is because the higher the sinter temperature is, the more the magnetite remains, and the change to the secondary hematite can be suppressed.
In addition, T-2/3T in the table corresponds to the blowing position in the sinter cooler for cooling the sinter, and in the case of the circular sinter cooler, it is 1/3 of the total length of the sinter cooler. It is considered desirable to blow nitrogen gas to a part.

INDUSTRIAL APPLICABILITY The technique of the present invention is applied not only to a method for producing a sintered ore aiming at improvement of the strength of the sintered ore and improvement of reduction powderability, but also improvement of other various properties and development of a desired operating technology of a sintering machine Is possible.

1. Sintering machine 2. Wind box 3. Sintering raw material charging layer 4. Crusher 5. Cooling system

Claims (4)

In a method for producing a sintered ore in which a gas other than a fuel is blown into a sintering raw material charging layer on a sintering machine pallet and/or a sintered ore deposition layer on a moving carriage of a sintering cooling device, nitrogen gas is used as the gas. After the position where the exhaust gas temperature in the sintering machine windbox reaches the maximum, blowing shall be performed from the inlet side of the sintering cooling device to 2/3 of the total length, and the nitrogen gas concentration used shall be the atmospheric concentration. In addition to using a higher concentration than the above, 21 vol. % Of oxygen-rich gas is blown into the sintered ore. The nitrogen gas should be blown in from the position where the exhaust gas temperature in the sintering machine wind box is maximum to a third of the total length from the inlet side of the sintering cooling device. The method for producing a sinter according to claim 1, wherein the sinter has a concentration higher than the atmospheric concentration. The oxygen-enriched gas has a concentration of 30 to 50 vol. %, The method for producing a sintered ore according to claim 1 or 2 , wherein When the total length of the sintering machine is 1, the oxygen-enriched gas is blown from above the sintering raw material charging layer at a position within a range of more than 0 to 0.5 from the raw material charging side. The method for producing a sinter according to any one of claims 1 to 3 .

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