METHOD FOR PRODUCING SINTERED ORE

Abstract

A method produces a high-strength sintered ore while maintaining a high production rate by performing appropriate oxygen enrichment at a position closer to an ore discharging section than an ignition position without using gaseous fuel in the operation of a sintering machine. In a method for producing sintered ore including sequentially combusting carbonaceous material in a sinter bed (raw material charged layer) in a DL sintering machine to sinter the mixed raw material, in performing oxygen enrichment from above the raw material charging layer on the sintering machine, the oxygen enrichment is performed at a position closer to the ore discharging section than the position where 4 minutes have passed since the upper surface of the charging layer was ignited

Claims

1. A method for producing sintered ore comprising charging mixed raw material for sintering containing iron ore and carbonaceous material into a raw material ore charging section on a pallet that circulates in a sintering machine to thus form a raw material charged layer, igniting the carbonaceous material on an upper surface (upper layer part) of the raw material charged layer by an ignition furnace disposed downstream of the raw material ore charging section while sucking gas above the raw material charged layer through a wind box disposed below the pallet, introducing the gas into the raw material charged layer to sequentially ignite the carbonaceous material in the raw material charged layer and thus sinter the mixed material, wherein in performing oxygen enrichment from above the raw material charging layer on the sintering machine, the oxygen enrichment is performed at a position closer to an ore discharging section than the position where 4 minutes have passed since the upper surface of the charging layer was ignited.

2. The method for producing sintered ore according to claim 1, wherein the oxygen enrichment is completed within 13 minutes after the raw material charging layer is ignited.

3. The method for producing sintered ore according to claim 1, wherein the time of the oxygen enrichment to the raw material charged layer is from 1 to 7 minutes as a passage time of the mixed raw material for sintering.

4. The method for producing sintered ore according to claim 1, wherein the oxygen enrichment is not performed until 4 minutes have elapsed after the upper surface of the charging layer is ignited.

5. The method for producing sintered ore according to claim 1, wherein the method is not used in combination with an exhaust gas recirculation process.

6. The method for producing sintered ore according to claim 1, wherein the oxygen concentration of the oxygen-enriched air to be introduced onto the raw material charged layer is more than 25 vol. %.

7. The method for producing sintered ore according to claim 2, wherein the time of the oxygen enrichment to the raw material charged layer is from 1 to 7 minutes as a passage time of the mixed raw material for sintering.

8. The method for producing sintered ore according to claim 2, wherein the oxygen enrichment is not performed until 4 minutes have elapsed after the upper surface of the charging layer is ignited.

9. The method for producing sintered ore according to claim 3, wherein the oxygen enrichment is not performed until 4 minutes have elapsed after the upper surface of the charging layer is ignited.

10. The method for producing sintered ore according to claim 7, wherein the oxygen enrichment is not performed until 4 minutes have elapsed after the upper surface of the charging layer is ignited.

11. The method for producing sintered ore according to claim 2, wherein the method is not used in combination with an exhaust gas recirculation process.

12. The method for producing sintered ore according to claim 3, wherein the method is not used in combination with an exhaust gas recirculation process.

13. The method for producing sintered ore according to claim 7, wherein the method is not used in combination with an exhaust gas recirculation process.

14. The method for producing sintered ore according to claim 2, wherein the oxygen concentration of the oxygen-enriched air to be introduced onto the raw material charged layer is more than 25 vol. %.

15. The method for producing sintered ore according to claim 3, wherein the oxygen concentration of the oxygen-enriched air to be introduced onto the raw material charged layer is more than 25 vol. %.

16. The method for producing sintered ore according to claim 7, wherein the oxygen concentration of the oxygen-enriched air to be introduced onto the raw material charged layer is more than 25 vol. %.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0029] FIG. 1 is a schematic diagram showing the state of the cross-section of a raw material charged layer between an ore charging section and an ore discharge section thereof on the DL sintering machine pallet.

DESCRIPTION OF EMBODIMENTS

[0030] The present invention proposes a method for producing sintered ore by operating oxygen enrichment with a downward suction Dwight-Lloyd (DL) sintering machine, in which, basically, the effect of the oxygen enrichment appears at least when the middle layer part of a raw material charged layer is combusted. In the present invention, therefore, the upper surface of the raw material charged layer is first ignited, and after a certain period of time has elapsed, the blowing of oxygen-enriched gas, i.e., the oxygen enrichment to the middle layer part is started. In other words, the oxygen enrichment is started after the raw material charged layer on the pallet moves toward the ore discharging section for a certain period of time after ignition and completed after being conducted for a predetermined period of time.

[0031] As described above, the present invention is a method including oxygen enrichment by blowing oxygen-enriched gas from above the raw material charged layer on the pallet of the sintering machine after a lapse of a prescribed time after ignition. That is, the present invention is characterized by performing oxygen enrichment by feeding oxygen-enriched gas to a position closer to the ore discharging section than the position where 4 minutes have passed at the normal sintering machine pallet speed (1.5 to 3.5 m/min) since the upper surface of the charging layer was ignited, and continuing the feeding for a certain time toward the ore discharging side.

[0032] The time when the upper surface of the material charging layer is ignited can be determined by measuring with a thermometer or the like, but for simplicity, the time when the upper surface passes through the outlet of the ignition furnace can be considered as the ignition time.

[0033] When performing the oxygen enrichment to the middle layer part of the raw material charged layer by introducing oxygen-enriched gas at the above-described position, in both cases of using oxygen-enriched air that is obtained by enriching the air directly sucked from the outside air with oxygen of a specified concentration and of circulating the exhaust gas from the sintering machine, it is preferable to use a hood-shaped cover and feed oxygen into the cover for the purpose of preventing abnormal combustion in an unintended position due to leakage of oxygen for the enrichment and achieving reliable oxygen enrichment in a designated position.

[0034] In the present invention, in order to secure the prescribed sintering time and to proceed with the sintering reaction sufficiently, the oxygen concentration of the oxygen-enriched air to be introduced should be not less than 21 vol. % but not more than 50 vol. %. This is because, when the oxygen concentration after oxygen enrichment exceeds 50 vol. %, the coke combustion becomes faster to thus increase the moving speed of the combustion zone, so that the time for holding a high temperature at which the combustion zone remains in each layer is reduced, failing in sufficient sintering reaction. That is also because when the oxygen concentration after oxygen enrichment is less than 21 vol. %, the oxygen concentration is lower than that of normal air and lower rather than when the air outside is directly sucked, decreasing the sinterability. Preferably, the oxygen concentration is not less than 23 vol. % but not more than 50, more preferably not less than 25 vol. % but not more than 50 vol. %.

[0035] There is conducted a test on a preferable method of oxygen enrichment to the middle layer part conforming to the present invention, the result of which is described in the following.

[0036] (Test 1)

[0037] In this test, oxygen enrichment is performed in such a manner that a sinter bed (raw material charged layer) was divided into three equal parts (upper, middle, and lower layers) in the direction of height and oxygen-enriched air was introduced into each location. First, a sintering test (Comparative Example 1) without oxygen enrichment was conducted as the base case to determine the base (standard) sintering time (15.5 minutes). The oxygen enrichment time was determined by subtracting the time required for the ignition operation (1 minute) from the sintering time and dividing it into three equal parts was determined (formula below).

Oxygen enrichment time=(base sintering time−1)/3

[0038] In this test, mixed raw material for sintering as shown in Table 1 was used as the sintering raw material, which was adjusted to have a basicity (B2) of 2.0. The mixed raw material for sintering was granulated in a drum mixer while adding moisture to bring the moisture content to 7.5 mass %, and the resulting granulated material was sintered using a sintering pot. In this sintering test, the air pressure was kept constant (6 kPa) and the oxygen concentration of the oxygen-enriched air was kept at 30 vol. %.

TABLE-US-00001 TABLE 1 (mass %) Australian ore A 33.9 Brazilian ore A 23.8 Brazilian ore B 10.2 Return ore 20.0 Silica sand 0.1 Limestone 11.0 Quicklime 1.0 Total 100 Coke breeze 4.5

[0039] Table 2 shows the result. In this test, the base sintering time is 15.5 minutes, which means that the oxygen enrichment time for each position is 4.8 minutes. Thus, the oxygen enrichment of 4.8 minutes was performed in the upper layer (Comparative Example 2), middle layer (Inventive Example 1), and lower layer (Inventive Example 2) of the sintering raw material layer. The result shows that the strength of the sintered ore (TI strength) could be improved the most when the oxygen enrichment was applied to the middle layer. This means that it is the most preferable to perform oxygen enrichment for 5.8 minutes after the ignition was started, that is, for the next 4.8 minutes after 4.8 minutes have elapsed since the ignition was completed. In consideration of the oxygen enrichment effect on the upper layer part (Comparison Example 2) and the lower layer part (Invention Example 2), it is effective to perform oxygen enrichment to the sinter bed (sintering raw material layer) at a position closer to the ore discharging section than the position where 4 minutes has passed after the ignition.

[0040] The result shown in Table 2 indicates that the oxygen enrichment to the lower layer part following the middle layer part also improves the strength, although not as much as to the middle layers. This means that oxygen enrichment when conducted during the 4.8-minute period after 10.6 minutes from the start of ignition (after 9.6 minutes from the completion of ignition), does not reduce the effect of oxygen enrichment. In other words, the effect of increasing the strength by the oxygen enrichment to the lower layer part of the sintering raw material layer (63.5%−61.6%=1.9) was equivalent to 53% of the effect of increasing the strength by the oxygen enrichment to the middle layer part (65.2%−6.1.6%=3.6).

[0041] This is considered to result from excessive heat in the lower layer part, especially in the bottom part thereof, where the increase in strength due to the progress of sintering and the decrease in strength due to overheating cancel each other out. Therefore, when oxygen enrichment is performed on the lower layer part, it should be limited to within 2.5 minutes (4.8 minutes×53%) from 10.6 minutes after the start of ignition (9.6 minutes after completion of ignition), i.e., the oxygen enrichment should be performed within 13 minutes (10.6 minutes+2.5 minutes) after the ignition is started on the upper surface of the raw material charged layer.

TABLE-US-00002 TABLE 2 Comparative Comparative Inventive Inventive Example 1 Example 2 Example 1 Example 2 Position of oxygen — Upper Middle Lower enrichment layer part layer part layer part Yield (%) 70.4 72.0 68.8 66.7 Sintering time 15.5 15.2 14.7 14.6 (min) Production rate 1.43 1.49 1.48 1.44 (t/h/m.sup.2) TI strength (%) 61.6 62.0 65.2 63.5

EXAMPLE

[0042] The examples described below examined the influence of the oxygen enrichment time in the middle layer part of the sintered raw material layer. A mixed raw material for sintering adjusted to have SiO.sub.2: 4.9 mass % and a basicity: 2.0 (Table 1) was used. The mixed raw material for sintering was granulated in a drum mixer while adding water to bring the moisture content to 7.5 mass %, and the resulting granulated raw material for sintering was subjected to a sintering test in a sintering pot, where the air pressure is constant (6 kPa) and the oxygen concentration of the granulated raw material for sintering was adjusted to 30 vol. %. The sintering time of the base case without oxygen enrichment (Comparative Example 1) was 15.5 minutes. In this test, the timing of the oxygen enrichment was within the period of 5.8 to 10.6 minutes after the ignition (in the middle layer part), and the duration of the oxygen enrichment was changed to 0.3 to 4.8 min.

[0043] As shown in Table 3, the result shows that oxygen enrichment time to the middle layer of not shorter than 1.0 minutes caused, at least, a significant improvement in the production rate and sintered ore strength (TI strength). Although the oxygen enrichment time is not specified, as described above, 7 minutes, which corresponds to the total of 4.8 minutes for oxygen enrichment to the middle layer part and 2.5 minutes to be 53% of 4.8 minutes to the lower layer part, is thought to be effective.

TABLE-US-00003 TABLE 3 Comparative Example 1 Example 1 Example 2 Example 3 Oxygen enrichment 0 0.3 1 4.8 time (min) Yield (%) 70.4 69.7 69.7 68.8 Sintering time 15.5 15.3 15.1 14.7 (min) Production rate 1.43 1.46 1.46 1.48 (t/h/m.sup.2) TI strength (%) 61.6 62.0 63.7 65.2

[0044] The example described below verified the influence of oxygen concentration during oxygen enrichment treatment on the middle layer part of the sintered raw material layer. A mixed raw material for sintering adjusted to have SiO.sub.2: 4.9 mass % and a basicity: 2.0 (Table 1) was used. The mixed raw material for sintering was granulated in a drum mixer while adding water to bring the moisture content to 7.5 mass %. The resulting granulated raw material for sintering was subjected to a sintering test in a sintering pot by using oxygen-enriched air adjusted to have a constant air pressure (6 kPa) and the oxygen concentration of the granulated raw material for sintering of 30 vol. %. As in Example 3, oxygen enrichment was conducted for 5.8 minutes after the ignition was started, that is, for the next 4.8 minutes after 4.8 minutes have elapsed since the ignition was completed. The oxygen concentration during the oxygen enrichment was changed within the range of 30 to 40 vol. %. As shown in FIG. 4, the result shows that the strength continues increasing until the concentration of the oxygen-enriched air reaches 40 vol. %.

TABLE-US-00004 TABLE 4 Example 3 Example 6 Example 7 Oxygen enrichment 4.8 4.8 4.8 time (min) Yield (%) 68.8 71.7 72.1 Sintering time 14.7 14.6 13.9 (min) Production rate 1.48 1.56 1.64 (t/h/m.sup.2) Oxygen 30 35 40 concentration of oxygen-enriched air (vol. %) TI strength (%) 65.2 66.9 67.4

INDUSTRIAL APPLICABILITY

[0045] The invention has been described based primarily on the operation of sintering machines that do not use gaseous fuels, but the invention can also be applied to the operation of sintering machines that use gaseous fuels in combination.