Patent Grant
8945274
This is a §371 of International Application No. PCT/JP2010/063797, with an international filing date of Aug. 10, 2010 (WO 2011/019086 A1, published Feb. 17, 2011), which is based on Japanese Patent Application Nos. 2009-185412, filed Aug. 10, 2009, and 2010-175265, filed Aug. 4, 2010, the subject matter of which is incorporated by reference.
This disclosure relates to a method for operating a blast furnace using carbon iron composite (ferrocoke) produced by forming and carbonizing a mixture of coal and iron ore.
To decrease the reducing agent ratio of a blast furnace, there is an advantageous technique of using carbon iron composite as a material for the blast furnace to utilize the effect of decreasing the temperature of the thermal reserve zone of the blast furnace due to the use of carbon iron composite (for example, refer to Japanese Unexamined Patent Application Publication No. 2006-28594. Carbon iron composite produced by forming a mixture of coal and iron ore into a formed product and carbonizing the formed product has high reactivity and, hence, promotes reduction of sintered ore. Carbon iron composite also partially contains reduced iron ore and, hence, the temperature of the thermal reserve zone of a blast furnace can be decreased and the reducing agent ratio can be decreased.
A method for operating a blast furnace with carbon iron composite may be performed by mixing ore and carbon iron composite and charging the mixture into the blast furnace as disclosed in JP '594.
Carbon iron composite is characterized by having higher reactivity with CO2 gas as represented by a formula (a) below than conventional metallurgical coke produced by carbonizing coal with a coke oven or the like (hereafter, described as “conventional coke” to distinguish it from carbon iron composite). The reaction in the formula (a) below can be regarded as a reaction of returning CO2 generated through reduction of ore represented by a formula (b) below back to CO gas having reducing power:
CO2+C→2CO (a)
FeO+CO→Fe+CO2 (b).
Accordingly, when the reaction of the formula (a) above rapidly occurs in a region where the reaction of the formula (b) above occurs, both of the reactions successively occur to promote reduction of ore.
A region of a blast furnace where CO2 generated from the formula (b) above corresponds to a region where ore is not completely reduced by CO gas, that is, unreduced ore is present.
It is known that ore mainly containing sintered ore in an upper zone of a blast furnace is in the form of independent particles. As reduction proceeds, ore particles having softened and deformed cohere together to form the so-called cohesive zone (for example, refer to The Iron and Steel Institute of Japan, “Tetsu-to-Hagane,” 62, 1976, pages 559-569). Since ore particles having softened and deformed cohere together to form the cohesive zone, the cohesive zone has a small number of voids and has high gas-permeation resistance (for example, refer to The Iron and Steel Institute of Japan, “Tetsu-to-Hagane,” 64, 1978, page S548). This means that reducing gas is less likely to enter the cohesive zone. According to The Iron and Steel Institute of Japan, 62, 1976, reducibility of sintered ore in the cohesive zone is about 65% to 70% and reduction is not completed. Ore not completely reduced in the cohesive zone is, in the state of having a high FeO concentration, melted and dripped, resulting in reduction with solid carbon as represented by the following formula (c):
FeO+C→Fe+CO (c).
This reaction is an endothermic reaction. Thus, a decrease in the reaction rate of the formula (c) above contributes to a decrease in the reducing agent ratio and suppresses variation in furnace heat in a lower zone of a blast furnace, contributing to stable operation.
When carbon iron composite is used in operation of a blast furnace and carbon iron composite is used as a mixture with ore, carbon iron composite is present in the cohesive zone in a temperature range in which the cohesive zone is formed. When reduction of ore is not completed in the cohesive zone as described above, the gasification reaction of carbon iron composite in the cohesive zone becomes slow, which is problematic.
To exhibit the high-reactivity characteristic of carbon iron composite, that is, to achieve rapid transition from CO2 gas to CO gas in the cohesive zone, it is necessary that CO gas is introduced into the cohesive zone so that reduction of unreduced ore proceeds to generate CO2.
Accordingly, it could be helpful to overcome the problem of the existing techniques and provide a method for operating a blast furnace with carbon iron composite in which carbon iron composite is used as a mixture with ore in a blast furnace and slowing of the gasification reaction of carbon iron composite in the cohesive zone can be suppressed.
We thus provide:
In the cohesive zone, mixing conventional coke ensures the presence of voids in the ore layer to improve permeability, facilitating entry of CO gas into the cohesive zone. As a result, reduction of ore is promoted through the gasification reaction of carbon iron composite to thereby decrease the reducing agent ratio.
In a conventional operation of a blast furnace, ore and conventional coke are alternately charged into the blast furnace through a top portion of the furnace to alternately pile an ore layer and a conventional coke layer in the blast furnace. For the purpose of improving the operation of a blast furnace, there is a known technique of using a mixture of conventional coke and ore (for example, refer to The Iron and Steel Institute of Japan, “Tetsu-to-Hagane,” 92, 2006, pages 901-910). The Iron and Steel Institute of Japan, 92, 2006 describes the effect of improving the permeability of the cohesive zone due to mixing of conventional coke with an ore layer on the basis of a reduction test under load with which the cohesive behavior of ore can be evaluated. Note that, in our process, ore collectively denotes one or more iron-containing materials (mixture) charged into a blast furnace such as sintered ore produced from iron ore, lump iron ore, and pellets. Ore layers stacked in a blast furnace may contain, in addition to ore, an auxiliary material for adjusting the composition of slag, such as limestone.
We studied permeability in the case of mixing carbon iron composite and sintered ore with a reduction test under load apparatus of the same type as in The Iron and Steel Institute of Japan, 92, 2006 and compared this case with the case of mixing conventional coke and sintered ore. The test results are illustrated in
We found that mixing conventional coke, together with carbon iron composite, with ore promotes introduction of CO gas into the cohesive zone and the above-described successive reactions of reduction of unreduced ore and gasification of carbon iron composite are promoted to enhance reducibility of the ore.
Specifically, we provide a method for operating a blast furnace including charging carbon iron composite and conventional coke that are in a state of being mixed in the same ore layer, into a blast furnace. The state in which carbon iron composite and conventional coke are mixed in the same ore layer is a state in which carbon iron composite and conventional coke are dispersed in the entirety of the ore layer. This state excludes the following case: an ore layer is formed in a plurality of charging batches where carbon iron composite only is mixed with ore in some charging batches and conventional coke only is mixed with ore in other charging batches.
To charge carbon iron composite and conventional coke that are in a state of being mixed in the same ore layer into a blast furnace, for example, the following method may be used: a method of charging carbon iron composite, conventional coke, and ore having been mixed together in advance, into the furnace with a charging apparatus at the top of the furnace; or a method of charging carbon iron composite, conventional coke, and ore into the furnace while carbon iron composite, conventional coke, and ore are mixed together.
When materials are charged into a blast furnace, a coke layer composed of conventional coke and an ore layer mixed with carbon iron composite and conventional coke are preferably alternately stacked.
The percentage of conventional coke mixed with an ore layer is preferably 0.5 mass % or more with respect to the ore.
On the other hand, carbon iron composite may be mixed with ore under conditions similar to the above-described condition of mixing conventional coke. However, when the mixing amount of carbon iron composite is small, the number of positions where the effect of returning CO2 in an ore layer back to CO is exhibited through the reaction in the formula (a) above is limited. When the total amount of conventional coke and carbon iron composite mixed with ore is large, in an actual furnace, there may be cases where the cokes mixed in an ore layer after charging into the furnace are unevenly distributed and the reproduction effect of CO gas is not sufficiently exhibited. Specifically, the probability that conventional coke and carbon iron composite are present next to each other becomes high and carbon iron composite becomes separated from positions where CO2 is generated by reduction of ore.
The above-described mixing conditions are summarized in
As for a property of carbon iron composite, a carbon iron composite having a low iron content does not have high reactivity with CO2 gas and a carbon iron composite having a high iron content has low strength and is not suitable as a material to be charged into a blast furnace.
By mixing conventional coke with an ore layer, the permeability of the ore layer is improved. By making the particle size of conventional coke mixed with an ore layer be 5 mm or more, permeability is improved. However, when the particle size of conventional coke mixed with an ore layer becomes excessively large, in the case of making the mixing mass of conventional coke constant, the number of conventional coke particles mixed decreases with an increase in the particle size and conventional coke tends to be unevenly distributed in the ore layer. Accordingly, the particle size is preferably 100 mm or less. Thus, the particle size of conventional coke mixed with an ore layer is preferably 5 to 100 mm. To sufficiently improve permeability, conventional coke preferably has a particle size of more than 20 mm and 100 mm or less, more preferably a particle size of more than 36 mm and 100 mm or less.
A blast-furnace operation test to which our method was applied was performed. Carbon iron composite was produced by briquetting a mixture of coal and ore with a briquetting machine, charging the briquettes into a vertical shaft furnace, and carbonizing the briquettes. The carbon iron composite had the shape of an elliptic cylinder having dimensions of 30 mm×25 mm×18 mm. The iron content of the carbon iron composite was made 30 mass %.
Materials were charged into a blast furnace in the following manner. A coke layer composed of conventional coke only was first formed. An ore layer mixed with coke (carbon iron composite and/or conventional coke) was charged in two separate batches. The ore layer was charged in three different manners (Test Nos. 1 to 3).
Test No. 1 is our operation method and performed such that carbon iron composite and conventional coke were mixed in the same ore batch in each of the two batches for the ore layer. The state of charged materials stacked in this case is illustrated in
Test No. 2 is an operation method for comparison in which a mixture of conventional coke and ore was charged in the first batch and a mixture of carbon iron composite and ore was charged in the second batch. Although conventional coke and carbon iron composite appeared to be mixed as a whole of the ore layer, conventional coke and carbon iron composite were mixed in separate ore batches. The state of charged materials stacked in this case is illustrated in
Test No. 3 is also an operation method for comparison and is an operation serving as a base without using carbon iron composite. The ore layer was formed by charging a mixture of conventional coke and ore in both of the two batches. The state of charged materials stacked in this case is illustrated in
The test conditions, blast-furnace reducing agent ratios, and direct reducibility of the Tests are compared in Table 1. The particle size of conventional coke mixed with ore was changed in accordance with the following six conditions (A to F):
The layer composed of conventional coke only was constituted of coke having a particle size of 36 to 100 mm. Under each of the conditions A, B, and C, only coke having a smaller particle size than the coke forming the layer composed of conventional coke only was mixed. Under each of the conditions D and E, the coke forming the layer composed of conventional coke only and the coke having a smaller particle size than this coke were used. Under the condition F, coke that is equivalent to the coke forming the layer composed of conventional coke only was mixed.
In Table 1, the “Unmixed conventional coke” denotes conventional coke not mixed with ore and charged into a blast furnace (coke of coke layer). The “Mixed conventional coke” denotes conventional coke mixed with ore. In both of Test Nos. 1 and 2, the conventional coke ratio decreased, compared with Test No. 3 in which carbon iron composite was not used. The decrease in the conventional coke ratio was larger in Test No. 1 in which carbon iron composite and mixed conventional coke were mixed in the same ore batches than that in Test No. 2. This is because, as shown in the direct reducibility (the percentage of the reaction represented by the formula (c) above with respect to the total reduction amount, the percentage being calculated from the material balance of a blast furnace) in Table 1, the direct reducibility of Test No. 1 is lower than that of Test No. 2, that is, reduction of ore with the gas was promoted in Test No. 1.
In Test No. 1, which is our Example, the unit consumption of ore was 1562 kg/t-p; the unit consumption of mixed conventional coke was 33 kg/t-p; the mixing amount of conventional coke with respect to ore was 2.1 mass %; the unit consumption of carbon iron composite was 101 kg/t-p; the mixing amount of carbon iron composite with respect to ore was 6.5 mass %; and the total amount of conventional coke and carbon iron composite mixed with ore was 8.6 mass %. Herein, kg/t-p denotes kg per ton of pig iron.
Although the particle size of conventional coke mixed with the ore layers was changed in accordance with the six levels (conditions A to E), direct reducibility did not considerably vary among the conditions. This is probably because the effect of improving permeability of the cohesive zone is exhibited regardless of the particle size of conventional coke mixed with an ore layer. On the other hand, as for the conditions, the larger the particle size of conventional coke mixed in an ore layer, the smaller the variation in permeability became. This is probably because, as for the conditions, the larger the particle size of conventional coke mixed in the ore layer, the larger the particle size of coke in the dripping zone and the hearth, which are lower than the cohesive zone where the ore layer disappears; and gas flow and the flow of molten iron and slag in the lower portion of the furnace were stabilized.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-185412 | Aug 2009 | JP | national |
| 2010-175265 | Aug 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/063797 | 8/10/2010 | WO | 00 | 5/1/2012 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2011/019086 | 2/17/2011 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20120205839 | Sato et al. | Aug 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 63-210207 | Aug 1988 | JP |
| 2006-028594 | Feb 2006 | JP |
| 2008-106320 | May 2008 | JP |
| 2008189952 | Aug 2008 | JP |
| Entry |
|---|
| Machine translation of JP 2008-189952A, Aug. 2008. |
| Machine Translation of JP 2008-106320, Aug. 2008. |
| Machine Translation of JP 2006-028594, Feb. 2006. |
| Sasaki, M. et al., “Formation and Melt-Down of Softening-Melting Zone in Blast Furnace (Report on the Dissection of Blast Furnaces—3),” The Iron and Steel Institute of Japan, Tetsu-to-Hagane 62, 1976, pp. 559-569, Synopsis in English. |
| “Gas Permeability and Porosity of a Cohesive Zone Extracted fro Inside of a Blast Furnace,” The Iron and Steel Institute of Japan, Tetsu-to-Hagane 64, 1978, p. 94 and 2 pages of partial English translation. |
| Watakabe, S. et al., “Development of High Ratio Coke Mixed Charging Technique to the Blast Furnace,” The Iron and Steel Institute of Japan, Tetsu-to-Hagane 92, 2006, vol. 92, No. 12, pp. 209-218, Synopsis in English. |
| Number | Date | Country | |
|---|---|---|---|
| 20120205839 A1 | Aug 2012 | US |
