Blast furnace operation method

Abstract

A method of operating a blast furnace by blowing a pulverized coal at an amount of not less than 150 kg/tp from tuyeres through a lance into a blast furnace, wherein when the operation is performed under a condition that lump coke charged from a furnace top has a strength defined in JIS K2151 (DI.sup.150.sub.15) of not more than 87%, the pulverized coal blown through the tuyere contains not more than 60 mass % as a weight ratio of coal having a particle size of not more than 74 m and has an average volatile matter of not more than 25 mass %, and a blast temperature blown through the tuyere is not higher than 1100 C., oxygen is simultaneously blown into the furnace with the blowing of the pulverized coals through the lance and a gas having an oxygen concentration of 60 vol %-97 vol % is used as a carrier gas for the blowing of the pulverized coal.

Claims

1. A method of operating a blast furnace by blowing a pulverized coal at an amount of not less than 150 kg/tp from tuyeres through a lance into a blast furnace, wherein when the operation is performed under two or more of the following three conditions a, b and c: a. employing lump coke having a strength defined in JIS K2151 (DI.sup.150.sub.15) of not more than 87%, the lump coke being charged from a furnace top; b. the pulverized coal blown through the tuyere containing not more than 60%, by mass, as a weight ratio of coal having a particle size of not more than 74 m, the pulverized coal having an average volatile matter of not more than 25%, by mass; and c. a blast temperature blown through the tuyere is not higher than 1100 C.; oxygen is simultaneously blown into the furnace with the blowing of the pulverized coals through the lance and a gas having an oxygen concentration of 60%-97%, by volume, is used as a carrier gas for the blowing of the pulverized coal.

2. The method of operating a blast furnace according to claim 1, wherein when the strength (DI.sup.150.sub.15) of the lump coke is not more than 85%, a gas having an oxygen concentration of 70%-97%, by volume, is used as a carrier gas.

3. The method of operating a blast furnace according to claim 1, wherein when the strength (DI.sup.150.sub.15) of the lump coke is not more than 83%, a gas having an oxygen concentration of 80%-97%, by volume, is used as a carrier gas.

4. The method of operating a blast furnace according to claim 1, wherein the strength (DI.sup.150.sub.15) of the lump coke is not less than 78%.

5. The method of operating a blast furnace according to claim 1, wherein a weight ratio of a pulverized coal having a particle size of not more than 74 m is not less than 30%, by mass.

6. The method of operating a blast furnace according to claim 1, wherein the blast temperature is not less than 900 C.

7. The method of operating a blast furnace according to claim 1, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

8. The method of operating a blast furnace according to claim 2, wherein a weight ratio of a pulverized coal having a particle size of not more than 74 m is not less than 30%, by mass.

9. The method of operating a blast furnace according to claim 3, wherein a weight ratio of a pulverized coal having a particle size of not more than 74 m is not less than 30%, by mass.

10. The method of operating a blast furnace according to claim 4, wherein a weight ratio of a pulverized coal having a particle size of not more than 74 m is not less than 30%, by mass.

11. The method of operating a blast furnace according to claim 2, wherein the blast temperature is not less than 900 C.

12. The method of operating a blast furnace according to claim 3, wherein the blast temperature is not less than 900 C.

13. The method of operating a blast furnace according to claim 4, wherein the blast temperature is not less than 900 C.

14. The method of operating a blast furnace according to claim 5, wherein the blast temperature is not less than 900 C.

15. The method of operating a blast furnace according to claim 2, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

16. The method of operating a blast furnace according to claim 3, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

17. The method of operating a blast furnace according to claim 4, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

18. The method of operating a blast furnace according to claim 5, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

19. The method of operating a blast furnace according to claim 6, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

20. The method of operating a blast furnace according to claim 14, wherein the amount of the pulverized coal blown is not more than 300 kg/tp.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic view of a blast furnace adapted to an example of the invention method.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(2) FIG. 1 is a view illustrating an outline of a blast furnace applied to the blast furnace operation method according to an example of the invention. As shown in this FIGURE, a blowpipe (blast pipe) 2 for blowing hot air is connected to a tuyere 3 at the rear part thereof in a blast furnace 1, and a lance 4 is inserted into the blowpipe 2 in a direction of directing toward the inside of the furnace. A combustion space being a coke deposited layer and called as a raceway 5 is considered to be existent ahead the tuyere 3 in a direction of blowing hot air. The reduction of iron ore is mainly performed in this combustion space. Although only one lance 4 is inserted into the blowpipe 2 in this FIGURE, it is common that the lance 4 is inserted into each of the plural blowpipes 2 arranged along the periphery of the furnace. Also, the number of lances per one blowpipe is not limited to one, and hence two or more lances may be arranged. As a structure of the lance may be used a single tube lance, a multiple-tube type lance and a tube bundling type lance prepared by bundling plural blowing tubes.

(3) In general, a pulverized coal blown through the lance 4 inserted into the blowpipe 2 arrives at the raceway 5 through the tuyere 3 in the blast furnace, where volatile matter and fixed carbon included in the pulverized coal and lump coke charged from a furnace top are combusted to raise the temperature. An aggregate of unburned carbon and ash called as a char is discharged out of the raceway 5 as an unburned char. This char is composed mainly of the fixed carbon and generates a reaction called as a carbon dissolution reaction in addition to the combustion reaction.

(4) When the pulverized coal blown through the lance 4 into the blowpipe 2 and tuyere 3 contains a greater amount of volatile matter, ignition combustion is promoted to increase combustion volume, whereby a heating rate and a maximum temperature of the pulverized coal are raised and a reaction rate of the char is increased associated with the increase of dispersibility and temperature of the pulverized coal. That is, the pulverized coal is widely dispersed associated with the vaporization expansion of the volatile matter to promote the combustion of the volatile matter, and further the pulverized coal is rapidly heated by combustion heat to raise the temperature. Thus, for example, the pulverized coal is combusted at a place near to the furnace wall efficiently. As to the lump coke strength defined in JIS K2151 (DI.sup.150.sub.15)[%], it is considered that as the lump coke strength (DI.sup.150.sub.15)[%] becomes larger, the rate of coke breeze in the furnace becomes less and the amount of coke breeze deposited into a central portion of the furnace becomes small.

(5) An operation test evaluating air permeability is performed in a blast furnace of 5000 m.sup.3 in volume by changing a strength of lump coke charged from a furnace top (DI.sup.150.sub.15)[%], an amount of pulverized coal, characteristics of the pulverized coal (granularity, volatile matter) and a blast temperature to examine blast furnace operation conditions adapted to aspects of the invention. The results are explained below.

(6) In this operation test, a blast volume is controlled so as to make a tapping amount of 10000 t/d constant, and the air permeability is compared every each condition. Moreover, the value of the air permeability is obtained from a pressure difference between pressure at a furnace top portion and blast pressure and the blast volume.

(7) Also, the operation test is performed so that the temperature at the tip of the tuyere is controlled to a certain range by adjusting a humidity content in the blast, whereby a temperature of pig iron is set to a range of 1500 C.10 C. in each level. As shown in Table 1, the operation is performed under a condition as a test condition 1 that a coke ratio is 340 kg/tp, a pulverized coal ratio is 150 kg/tp, a blast temperature is 1100 C., a coke strength (DI.sup.150.sub.15) is 87%, a volatile matter of the pulverized coal is 25 mass % and a granularity of pulverized coal having a particle size of not more than 74 m is 60 mass %. The air permeability in this operation is 1.0, to which an air permeability obtained by changing the each operation condition is relatively compared. As the numerical value of the air permeability becomes larger, the air permeability is deteriorated, but an index of air permeability up to 1.05 is an acceptable range in the stable operation. Moreover, the one single tube lance per tuyere is used in all of the operation tests.

(8) In these operation tests, the blast temperature, volatile matter in the pulverized coal and granularity of the pulverized coal are relatively compared based on the test condition 1. In case of a test condition 2, both the coke ratio and air permeability are improved by changing all items (the blast temperature and the like) in a direction of increasing combustion efficiency as compared to the test condition 1. Moreover, the direction of increasing the combustion efficiency means that the blast temperature is made high and the volatile matter in the pulverized coal is made large and the granularity of the pulverized coal is made large. In case of a test condition 3, only the pulverized coal ratio is set to +10 kg/tp as compared to the test condition 1, so that the air permeability is somewhat deteriorated but is within the acceptable range of the stable operation. In case of test conditions 4-6, only one of the volatile matter in the pulverized coal, the granularity of the pulverized coal and the blast temperature is operated in a direction of decreasing the combustion efficiency as compared to the test condition 3, that is, the blast temperature is decreased or the volatile matter in the pulverized coal is made low or the granularity of the pulverized coal is made small. In the test conditions 4-6, the air permeability is somewhat deteriorated but is within the acceptable range of the stable operation.

(9) In case of test conditions 7-9, two items of the volatile matter in the pulverized coal, the granularity of the pulverized coal and the blast temperature are adjusted in a direction of decreasing the combustion efficiency as compared to the test condition 3 under a condition that the lump coke strength (DI.sup.150.sub.15) is 88%. In the test conditions 7-9, the air permeability is somewhat deteriorated but is within the acceptable range of the stable operation. This is considered due considered that the lump coke strength (DI.sup.150.sub.15) is increased to suppress deposition of coke breeze in the furnace and hence the air permeability is not so damaged. In case of test conditions 10-12, the coke strength (DI.sup.150.sub.15) is decreased to 85.5% and further two items of the volatile matter in the pulverized coal, the granularity of the pulverized coal and the blast temperature are adjusted in a direction of decreasing the combustion efficiency as compared to the test condition 3. As a result, the air permeability is significantly deteriorated and the stable operation is difficult regardless of increasing the coke ratio. This is considered due to the fact that the deposition of coke breeze in the furnace is deteriorated due to the lowering of the coke strength (DI.sup.150.sub.15).

(10) TABLE-US-00001 TABLE 1 Test conditions 1 2 3 4 5 6 7 Tapping amount T/d/m.sup.3 10000 10000 10000 10000 10000 10000 10000 Coke ratio Kg/t 340 333 334 335 335 337 343 Pulverized Kg/t 150 150 160 160 160 160 160 coal ratio Reducing Kg/t 490 483 494 495 495 497 503 material ratio Blast temperature C. 1100 1200 1100 1100 1100 1050 1100 Coke strength % 87 87 87 87 87 87 88 Volatile matter in % 25 30 25 15 25 25 15 pulverized coal Granularity of % 60 70 60 60 50 60 50 pulverized coal** Oxygen % concentration* Index of air 1.00 0.98 1.03 1.04 1.02 1.01 1.03 permeability Test conditions 8 9 10 11 12 Tapping amount T/d/m.sup.3 10000 10000 10000 10000 10000 Coke ratio Kg/t 345 345 350 348 351 Pulverized Kg/t 160 160 160 160 160 coal ratio Reducing Kg/t 505 505 510 508 511 material ratio Blast temperature C. 1050 1050 1050 1100 1050 Coke strength % 88 88 85.5 85.5 85.5 Volatile matter in % 15 25 15 15 25 pulverized coal Granularity of % 60 50 60 50 50 pulverized coal** Oxygen % concentration* Index of air 1.04 1.05 1.12 1.11 1.14 permeability **74 mass % *Oxygen concentration of carrier gas

(11) A double-tube type lance is used in each operation test shown in the following Tables 2 and 3, in which pulverized coal is blown through an inner tube of the double-tube type lance and oxygen is blown from between an inner tube and an outer tube. In this case, the pulverized coal is blown through the inner tube of the double-tube type lance together with a carrier gas such as nitrogen or the like. Moreover, the blowing pattern in the double-tube type lance may be opposite to the said blowing pattern. Also, a tube bundling type lance prepared by bundling single tubes can be used instead of the double-tube type lance, in which the pulverized coal is blown through either one of the two single tubes and oxygen is blown through the other tube. In any cases, it is preferable to blow oxygen close to the pulverized coal blown. When the single tube lance is used instead of the double-tube type lance, the pulverized coal and oxygen (and carrier gas) may be transferred in admixture.

(12) As shown in Tables 2 and 3, the test 13 is a blast furnace operation method of simultaneously blowing pulverized coal and oxygen (carrier gas) through the lance based on the test condition 10 of Table 1. That is, the pulverized coal is blown through the inner tube of the double-tube type lance together with the carrier gas, and an oxygen-containing carrier gas (N.sub.2+O.sub.2) is blown from between the inner tube and the outer tube of the double-tube type lance. As a result, when the oxygen concentration of the carrier gas for blowing oxygen and pulverized coal through the double-tube type lance is merely set to 50 vol %, the effect of improving the air permeability is insufficient. In the test conditions 14-16, the oxygen concentration in the carrier gas through the double-tube type lance is set to 60 vol % as compared to the test conditions 10-12 of Table 1, so that the effect of improving the air permeability is confirmed and it is possible to perform the stable operation. In the test conditions 17-19, the oxygen concentration in the carrier gas for carrying the pulverized coal through the double-tube type lance is set to 70 vol % as compared to the test conditions 10-12, so that the effect of further improving the air permeability is confirmed as compared to the test conditions 14-16 and the improvement of the air permeability is confirmed as compared to the test condition 1. In the test 20, the blast furnace operation of blowing the pulverized coal and oxygen through the lance is applied to the test condition 1, in which the pulverized coal is blown through the inner tube of the double-tube type lance together with the carrier gas and oxygen (carrier gas) is blown from between the inner tube and the outer tube. As seen from the results of Table 2, the pulverized coal ratio can be improved by increasing the combustion efficiency of the pulverized coal and it is possible to largely decrease the coke ratio under good air permeating condition. In the test conditions 21-23, the coke strength (DI.sup.150.sub.15) is decreased from 85.5% to 84.5% as compared to the test conditions 14-16. As a result, the air permeability is deteriorated because the oxygen concentration in the carrier gas is set to 60 vol % like the test conditions 14-16.

(13) As shown in Table 3, the air permeability is improved in the test conditions 24-26, because the oxygen concentration in the carrier gas is set to 70 vol % as compared to the test conditions 21-23. That is, the combustibility of the pulverized coal can be improved by increasing the oxygen concentration in the carrier gas even under the condition that the coke strength (DI.sup.150.sub.15) is decreased to 84.5%, which means that the stable operation is made possible.

(14) In the test conditions 27-29, the coke strength (DI.sup.150.sub.15) is decreased from 84.5% to 82.5% as compared to the test conditions 24-26. In this case (test conditions 27-29), the oxygen concentration in the carrier gas for carrying the pulverized coal through the double-tube type lance is set to 70 vol % like the test conditions 24-26, so that the air permeability is significantly deteriorated. In the test conditions 30-32, the oxygen concentration in the carrier gas is increased to 80 vol % as compared to the test conditions 27-29, whereby the air permeability is improved. Thus, even when the coke strength (DI.sup.150.sub.15) is decreased to 82.5%, the combustibility of the pulverized coal is improved by increasing the oxygen concentration in the carried gas for the pulverized coal in the lance, whereby it is made possible to perform the stable operation.

(15) TABLE-US-00002 TABLE 2 Test conditions 13 14 15 16 17 18 Tapping amount T/d/m.sup.3 10000 10000 10000 10000 10000 10000 Coke ratio Kg/t 339 335 333 336 335 333 Pulverized Kg/t 160 160 160 160 160 160 coal ratio Reducing Kg/t 499 495 493 496 495 493 material ratio Blast temperature C. 1050 1050 1100 1050 1050 1100 Coke strength % 85.5 85.5 85.5 85.5 85.5 85.5 Volatile matter in % 15 15 15 25 15 15 pulverized coal Granularity of % 60 60 50 50 60 50 pulverized coal** Oxygen % 50 60 60 60 70 70 concentration* Index of air 1.07 1.03 1.01 1.02 0.97 0.96 permeability Test conditions 19 20 21 22 23 Tapping amount T/d/m.sup.3 10000 10000 10000 10000 10000 Coke ratio Kg/t 336 290 335 333 336 Pulverized Kg/t 160 210 160 160 160 coal ratio Reducing Kg/t 496 500 495 493 496 material ratio Blast temperature C. 1050 1100 1050 1100 1050 Coke strength % 85.5 87 84.5 84.5 84.5 Volatile matter in % 25 25 15 15 25 pulverized coal Granularity of % 50 60 60 50 50 pulverized coal** Oxygen % 70 60 60 60 60 concentration* Index of air 0.98 0.97 1.07 10.5 10.6 permeability **74 mass % *Oxygen concentration of carrier gas

(16) TABLE-US-00003 TABLE 3 Test conditions 24 25 26 27 28 29 30 31 32 Tapping amount T/d/m.sup.3 10000 10000 10000 10000 10000 10000 10000 10000 10000 Coke ratio Kg/t 335 333 336 335 333 336 335 333 336 Pulverized Kg/t 160 160 160 160 160 160 160 160 160 coal ratio Reducing Kg/t 495 493 496 495 493 496 495 493 496 material ratio Blast temperature C. 1050 1100 1050 1050 1100 1050 1050 1100 1100 Coke strength % 84.5 84.5 84.5 82.5 82.5 82.5 82.5 82.5 82.5 Volatile matter in % 15 15 25 15 15 25 15 15 25 pulverized coal Granularity of % 60 50 50 60 50 50 60 50 50 pulverized coal** Oxygen % 70 70 70 70 70 70 80 80 80 concentration of lance* Index of air 1.02 1.00 1.01 1.08 1.06 1.07 1.03 1.01 1.02 permeability **74 mass % *Oxygen concentration of carrier gas

(17) As mentioned above, according to an example of the blast furnace operation method of the invention, the coke strength (DI.sup.150.sub.15) of the lump coke charged from the furnace top is low (87%) and the granularity and volatile matter of the pulverized coal blown through the lance (74 M60 mass %, volatile matter 25 mass %) are low and the blast temperature (1100 C.) is low, so that when the method is applied even in the operation condition of decreasing the combustion efficiency, it is possible to improve the combustion efficiency of the pulverized coal and hence it is possible to increase the productivity and reduce CO.sub.2 emission. Also, it is confirmed that if the operating conditions of the blast furnace are constant, the degree of freedom of the operation is increased by performing the above blast furnace operation.

(18) In the invention, the following conditions are preferable. At first, it is preferable to use a pulverized coal having an average volatile matter of not less than 5 mass %. When the average volatile matter of the pulverized coal is less than 5 mass %, the coal is hard and the pulverization thereof becomes difficult to increase the cost.

(19) The strength (DI.sup.150.sub.15) of the lump coke charged from the furnace top is preferable to be not less than 78%. When the strength (DI.sup.150.sub.15) of the lump coke is less than 78%, the coal is not shrunk sufficiently and hence non-carbonized coke is formed, resulting in the damage of the coke oven.

(20) The weight ratio of the pulverized coal having a particle size of not more than 74 m is preferable to be not less than 30%. When the weight ratio of the pulverized coal having a particle size of not more than 74 m is less than 30%, the temperature rise of the pulverized coal is slow and the ignition becomes difficult to deteriorate the combustibility violently.

(21) The blast temperature is preferable to be not lower than 900 C. Since bricks in a hot blowing furnace are designed so as to entangle them at 900-1200 C., when the blast temperature is lower than 900 C., the damage of bricks in the hot air furnace is caused.

(22) The blowing amount of the pulverized coal per 1 ton of pig iron is not more than 300 kg/tp. When the blowing amount of the pulverized coal exceeds 300 kg/tp, the combustibility is significantly deteriorated to bring about the decrease of coke replacement rate, while the oxygen concentration or blast temperature is largely increased or the humidity of air blown is largely decreased for maintaining the temperature at the tip of the tuyere (theoretical combustion temperature), the adjustment of which becomes difficult in view of not only the operation but also the equipment capacity. A more preferable upper limit of the pulverized coal blowing amount is not more than 250 kg/tp.

DESCRIPTION OF REFERENCE SYMBOLS

(23) 1 blast furnace, 2 blowpipe, 3 tuyere, 4 lance, 5 raceway