SPECIFICATION
TITLE OF INVENTION
PRODUCING METHOD OF SINTER
Field of the Invention
[0001]
The present invention relates to a producing method of sinter (iron ore sinter) used as a blast furnace raw material in an iron-making process.
Priority is claimed on Japanese Patent Application No. 2009-063466, filed March 16,2009, the content of which is incorporated herein by reference.
Description of Related Art [0002] FIG 1 shows a schematic process of a producing method of sinter in which a
Dwight-Lloyd sintering machine is used. As shown in FIG. 1, sinter is manufactured by sintering a sintering feed 6 in a sintering machine 30. The sintering feed 6 is prepared by granulating a mixture of the main raw material of iron ore la and an auxiliary raw material of limestone 2a, coke 3 a which is a solid fuel, and return fines 4a. The iron ore la, the limestone 2a, the coke 3a, and the return fines 4a are fed from an iron ore hopper 1, a limestone hopper 2, a coke hopper 3, and a return fine hopper 4 in predetermined amounts, respectively. The fed raw materials are granulated using a granulating machine 5, such as a drum mixer, while the moisture is controlled so that the amount of moisture becomes about 5.5 mass% to 8.5 mass%. The granules are composed mainly of pseudoparticles in which adhering fines having a particle diameter of 0.5 mm or smaller are adhered to the circumferences of nuclei (nuclei particles) having a particle
diameter of 1 mm or larger. Permeability in the sintering machine can be maintained
using the granules as the sintering feed 6.
[0003]
The sintering feed 6 of the granules is charged into a surge hopper 7. The sintering feed 6 is cut out by a drum feeder 8 and is fed onto the palette in the sintering machine 30 through a chute 8a, thereby forming a feed bed (raw material bed) 9. The coke 3a on the surface layer portion of the feed bed 9 is ignited by an igniter 10, and the coke 3 a is combusted with the air suction to the bottom of the feed bed 9 using an exhaust fan 20, thereby sequentially sintering the sintering feed 6 from the top layer toward the bottom layer by the combustion heat of the coke 3 a. A sinter cake 11 obtained by sintering the sintering feed 6 is discharged at a discharge end 12 and is crushed and sieved. Sieved agglomerates of 5 mm or larger are supplied to a blast furnace as product sinter. Meanwhile, the sinter of 5 mm or smaller is recycled as the return fines 4a. In addition, some of the product sinter is recycled as a sinter for hearth layer 46.
[0004]
Due to an increase in global steel demand in recent years, there is a demand for further improvement in the production efficiency of sinter as an iron-making raw material. At the same time, from the aspect of the environment, there is a strong demand for reduction of the air pollutant emissions, such as a NOx exhaust gas generated by combustion of a solid fuel during sintering.
[0005]
For example, Patent Citation 1 and Patent Citation 2 suggest the following methods of manufacturing sinter as conventional techniques which improve the productivity of sinter and reduce air pollutants.
[0006]
In order to improve the combustibility of a solid fuel and the productivity of sinter, Patent Citation 1 discloses a method of inducing a hydrogen-generating reaction by supplying water vapor generated by sprinkling water on the surface of the sinter during sintering to the combustion reaction of the solid fuel in a sintering bed.
[0007]
In order to improve the combustibility of a solid fuel, improve the productivity of sinter, and, furthermore, reduce NOx, Patent Citation 2 discloses a method of maximizing the supplying effect of water vapor by optimizing the allocation of the amount of moisture in the sinter mix and the amount of sprinkled water and supplying water vapor.
[0008] Patent Citation
[Patent Citation 1] Japanese Examined Patent Application, Second Publication No. S51-6002
[Patent Citation 2] Japanese Examined Patent Application, Second Publication No. H7-78257
SUMMARY OF THE INVENTION Problems to be Solved by the Invention
[0009]
However, there are two problems described below in the sintering technologies of Patent Citation 1 and Patent Citation 2. The first problem is that it is necessary to secure the heat necessary for the evaporation of moisture. When considering the macroscopic heat balance, it is necessary to supply the latent heat of vaporization
corresponding to the amount of sprinkled water to the sintering bed in the method of
sprinkling water on the surface of the feed bed. Since sintering is performed with a
solid fuel whose blending fraction is reduced to near the lower limit of the necessary
amount in recent energy-saving operations, the margin in regard to the amount of heat in
the sintering bed is extremely small. Therefore, when water is sprinkled to the sintering
bed, it is necessary to increase the solid fuel separately to obtain the heat corresponding
to the amount of sprinkled water.
[0010]
Since the latent heat of vaporization is consumed in a plant for manufacturing vapor in the method of mixing vapor with air supplied to the sintering bed and supplying moisture, when considering the macroscopic heat balance, it is necessary to input the heat corresponding to the amount of supplied moisture.
[0011]
The second problem is that a large-scale water sprinkling facility should be installed on sintering strands in order to supply moisture to the sintering bed. The sintering area in an ordinary sintering machine is 200 m to 600 m , and it is necessary to evenly sprinkle water across the majority of the sintering area in order to improve the combustion reaction of a solid fuel throughout the entire sintering bed. For that, it is necessary to install a plurality of pipes and nozzles for water sprinkling regularly in the top portion of the sintering machine.
[0012]
Generally, a replacement operation, in which a used sintering palette is raised and carried out of the sintering machine by an overhead crane, and a repaired sintering palette is carried into the sintering machine in reverse order, is routinely performed in the periodic repairs of the sintering machine. When a large-scale water sprinkling grid and
a water sprinkling apparatus are installed on the strands in the sintering machine, since
the replacement operation of the sintering palettes needs to be performed without hitting
the water sprinkling grid and the water sprinkling apparatus, adverse effects, such as the
extension of repairing time, are created.
[0013]
The present invention has been made in consideration of the above circumferences, and an object of the present invention is to substantially improve the combustibility of a solid fuel and improve the productivity by supplying a sintering feed which supplies water vapor to the combustion reaction of the solid fuel without using the water sprinkling and water vapor addition of the conventional techniques in the manufacture of sinter which is a raw material charged into a blast furnace in an iron-making process. In addition, an object of the present invention is to provide a new sintering technology in which the power consumption by an exhaust fan can be reduced by reducing the specific consumption of the gas flow rate per a sinter product, and the load of emitting controlled substances for air environment can be reduced by reducing the total amount of the exhaust gas and the amount of NOx discharged. Methods for Solving the Problem
[0014]
The inventors have carried out progressive research and development to improve the combustibility of a solid fuel in a sintering bed. Particularly, the inventors have carried out a variety of studies to bring about dehydrating combined water in an iron ore occurring in the sintering bed and combusting the solid fuel at the same time. As a result, the inventors confirmed the effectiveness of a sintering method in which both high-combined water iron ore and a solid fuel combusted at a relatively low temperature are used.
[0015]
FIG. 2 is a schematic diagram of the vertical cross section of the sintering bed (feed bed after ignition). The sintering bed is classified into a plurality of zones according to each stage of sintering. The sintering bed has a temperature distribution shown in FIG 2, and the combustion reaction of the solid fuel progresses sequentially from the top layer toward the bottom layer. In addition, the sintering bed at an arbitrary time is configured to sequentially form a raw material zone 9a, a drying zone 9b, a calcination zone 9c, a coke combustion zone 9d, and a cooling zone 9e from the bottom. The characteristics of each zone are as follows.
[0016]
The raw material zone 9a is a zone corresponding to a temperature range of less than 100°C. The blended raw material (sintering feed) charged into the sintering machine is in a wet state in the raw material zone 9a.
[0017]
The drying zone 9b is a zone corresponding to a temperature range of from 100°C to less than 300°C. Drying of the blended raw material actively progresses in the drying zone 9b.
[0018]
The calcination zone 9c is a zone corresponding to a temperature range of from 300°C to less than 700°C. Reactions, such as dehydration of the combined water in the iron ore or decarbonation of limestone, occur in the calcination zone 9c.
[0019]
The coke combustion zone 9d is a zone corresponding to a temperature range of from 700°C to less than 1300°C. The solid fuel reacts with oxygen in the air flow so as to be combusted, and the melting and the liquid-phase sintering of the iron ore and the
auxiliary raw material progress at the same time in the coke combustion zone 9d.
[0020]
The cooling zone 9e is a zone corresponding to a temperature range of from 1300°C to room temperature. A series of sintering stages are completed, and generated sintered lump (sinter cake) are cooled in the cooling zone 9e.
[0021]
Coke breeze and anthracite, which are broadly used as the ordinary solid fuels for sintering, start the combustion reaction in the coke combustion zone 9d that reaches a temperature of 700°C or higher. On the other hand, the combined water included in the iron ore emits water vapor by dehydration in the calcination zone 9c whose temperature is lower than that of the coke combustion zone 9d.
[0022]
The inventors found that it is possible to effectively use water vapor generated by the dehydration of the combined water in the iron ore for improvement in the combustibility of the solid fuel using the combustion solid fuel having a low combustion initiation temperature which is combusted in the calcination zone 9c.
[0023]
More specifically, as a result of sintering tests performed using a raw material (sintering feed) in which the combustion solid fuel having a low combustion initiation temperature and the high-combined water iron ore are mixed, the inventors found that the dehydration of the combined water and combustion of the low temperature combustion solid fuel occur at the same time in the calcination zone 9c, and water vapor can be effectively supplied to the combustion atmosphere of the solid fuel. Furthermore, the inventors confirmed that a reaction between H2O and C is accelerated, the productivity is improved, and NOx in the exhaust gas by the combustion is reduced by using the
combustion solid fuel (low temperature combustion solid fuel) having a low combustion
initiation temperature.
[0024]
The invention has been made based on the above findings and thus employs the following methods.
(1) A producing method of sinter according to the present invention includes: blending an iron ore which includes a high-combined water iron ore containing 4.0 mass% or more of combined water, an auxiliary raw material, and a solid fuel which includes 10 mass% or more of a low temperature combustion solid fuel having a combustion initiation temperature of less than 450°C in order to prepare a sintering feed so that the sintering feed includes 30 mass% or more of the high-combined water iron ore; charging the sintering feed into a Dwight-Lloyd sintering machine; igniting the surface layer portion of the sintering feed; and suctioning air from the top toward the bottom of the sintering feed.
(2) In the producing method of sinter according to (1), the low temperature combustion solid fuel may be char obtained by carbonizing subbituminous coal, brown coal, or a mixed coal of subbituminous coal and brown coal.
Effects of the Invention
[0025]
According to the present invention, it is possible to provide a sintering feed which supplies water vapor to the combustion reaction of a solid fuel without using the water sprinkling and water vapor addition of the conventional techniques in the production of sinter which is a raw material charged into a blast furnace in an iron-making process. In addition, it is possible to improve the productivity of sinter and reduce NOx in the exhaust gas using the sintering feed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026]
FIG. 1 is a process view showing the schematic process of a producing method of sinter.
FIG. 2 is a schematic diagram of the cross section in the vertical direction of the sintering bed.
DETAILED DESCRIPTION OF THE INVENTION
[0027]
The specific method of the present invention will be described below. In the producing method of sinter using the above Dwight-Lloyd sintering machine, a low temperature combustion solid fuel having a combustion initiation temperature of less than 450°C is used as the solid fuel mixed into the sintering feed.
[0028]
Char (carbonaceous material) obtained by carbonizing subbituminous coal, brown coal, or a mixed coal of subbituminous coal and brown coal at a relatively low temperature of about 800°C can be used as the low temperature combustion solid fuel. The char starts combustion in a low temperature range of 330°C to 450°C and reaches the maximum combustion (maximum weight-reducing temperature) in a temperature range of 530°C to 550°C. The char having a low combustion temperature can be sufficiently combusted in the calcination zone 9c. At the same time, the supplying effect of water vapor generated from the combined water in iron ore can be used in the calcination zone 9c.
[0029]
On the other hand, when ordinary coke breeze and anthracite are used as the
solid fuel, since the maximum weight reducing temperature of coke breeze and anthracite
is high, 700°C to 800°C, the amount of the solid fuel combusted in the calcination zone
9c is far from the total amount of fuel. Therefore, the combustion reaction occurs
mainly in the coke combustion zone 9d in which water vapor is not supplied. In such a
combustion condition, the expected supplying effect of water vapor cannot be obtained
regardless of how much the high combined water iron ore is blended. Here, the
ordinary coke breeze refers to fine coke generated in the manufacturing process of blast
furnace coke and the conveyor line to the blast furnace, or fine coke obtained by crushing
coke. In addition, caking coal and non-coking or slightly-caking coal are used as the
coal for coke making.
[0030]
Here, the combustion performances of the low temperature combustion solid fuel and the solid fuel in the conventional techniques are shown in Table 1. The combustion initiation temperatures and the maximum weight reducing temperatures in Table 1 were measured using a differential thermal analyzer.
[0031]
[Table 1]
(Table Removed)
[0032]
The solid fuel used in the producing method of sinter of the present invention
may include only the low temperature combustion solid fuel. In addition, the solid fuel
may include the low temperature combustion solid fuel and a solid fuel other than the
low temperature combustion solid fuel (for example, coke breeze, anthracite,
carbon-containing dust, and the like). The low temperature combustion solid fuel may
be char obtained by carbonizing subbituminous coal, brown coal, or a mixed coal of
subbituminous coal and brown coal (low temperature combustion char). When only the
low temperature combustion char is used as the solid fuel, the combustion effect of the
solid fuel can be increased to the maximum extent. Preferably, char obtained by
carbonizing subbituminous coal at 800°C accounts for the full amount of the solid fuel.
The combustion initiation temperature of the char obtained by carbonizing
subbituminous coal at 800°C (char prepared by carbonization of subbituminous coal) is
330°C, and the maximum weight reducing temperature is 530°C. Therefore, the char
obtained from subbituminous coal can be combusted at a lower temperature among the
low temperature combustion solid fuels. However, even when subbituminous coal is
used, the texture of char carbonized at a high temperature higher than 1000°C (char
prepared by high temperature carbonization of subbituminous coal) becomes dense, and
therefore the combustion initiation temperature increases. For example, as shown in
Table 1, the combustion initiation temperature of char prepared by the high temperature
carbonization of subbituminous coal at 1100°C is 540°C. Therefore, when char
prepared by the high temperature carbonization of subbituminous coal is used, the
combustibility of the solid fuel cannot be improved. Therefore, even when
subbituminous coal is used, it is preferable to use char carbonized at 1000°C or lower.
[0033]
In addition, carbon-containing fines generated in the coke process or inside and
outside ironworks can be used as the solid fuel by using the solid fuel obtained by mixing
the low temperature combustion solid fuel with a solid fuel other than the low
temperature solid fuel. However, the blending ratio of the low temperature combustion
solid fuel to the total of the solid fuel should be 10 mass% or more. The combustibility
of the solid fuel can be sufficiently improved by including 10 mass% or more of the low
temperature combustion solid fuel.
[0034]
Next, the blending conditions of the high-combined water iron ore will be described. Iron ores containing 4.0 mass% or more of combined water are used as the high combined water iron ore. Since the dehydration is completed in the initial phase of the calcination zone 9c in iron ores containing less than 4.0 mass% of combined water, water vapor is not sufficiently supplied to the combustion reaction of the solid fuel. It is necessary to use a high combined water iron ore containing 4.0 mass% or more of combined water in order to continuously supply water vapor through a temperature range in which combustion of the solid fuel occurs. For the high combined water iron ore used for the sintering feed, it is not necessary to perform a preliminary treatment for removing moisture before blending.
[0035]
Examples of the high combined water iron ore containing 4.0 mass% or more of combined water that is preferably used include pisolite ore containing 7 mass% to 9 mass% of combined water, Marra Mamba ore containing 4 mass% to 8 mass% of combined water, and Brockman ore containing 4 mass% to 6 mass% of combined water. All of the high combined water iron ores include the mineral phases of iron hydroxide. In addition, for example, carbonized iron and scales containing goethite, which contain
4.0 mass% or more of combined water, can also be used as the raw material of sinter.
Meanwhile, as shown in Table 2, a mixture of a plurality of high combined water iron
ores may be used.
[0036]
Furthermore, it is more preferable that pisolite ore containing 8.0 mass% or more of combined water (for example, Yandicoogina in Table 2) be used. The pisolite ore (Yandicoogina) has the largest amount of combined water in the iron ores distributed in the current market. The upper limit of the amount of combined water of the high combined water iron ore is not particularly limited. However, since combined water is water combined with compounds in iron ore, the amount of combined water of the high combined water iron ore does not include 100 mass%.
[0037]
The blending ratio of the high combined water iron ore needs to be 30 mass% or more of the entire sintering feed. When the blending ratio of the high combined water iron ore in the sintering feed is less than 30 mass%, a sufficient amount of water vapor cannot be supplied to the calcination zone 9c. That is, water vapor generated by the dehydration of combined water is sequentially accompanied by suction gas and is discharged as an exhaust gas. Therefore, when the amount of generated water vapor is small, the water vapor concentration in the calcination zone 9c is lowered.
[0038]
On the other hand, since the reaction rate of carbon and water vapor on the solid fuel surface is significantly dependent on the water vapor concentration in an atmosphere, it is necessary to increase the water vapor concentration in order to develop a sufficient effect of water vapor. According to the inventors' studies, the blending ratio of the high combined water iron ore in the sintering feed needs to be 30 mass% or more in order to
obtain a sufficient reaction rate of carbon and water vapor. Meanwhile, when
considering the combination of the auxiliary raw material and the solid fuel, the blending
ratio of the high combined water iron ore in the sintering feed is preferably 80 mass% or
less.
[0039]
It is preferable that the sintering feed include 35 mass% to 45 mass% of pisolite ore having 8.0 mass% or more of a combined water. In this case, a sufficient amount of water vapor in the calcination zone 9c of the sintering bed can be secured. Using the above method, water vapor is continuously supplied from the high combined water iron ore by heat supplied from the low temperature combustion solid fuel in the calcination zone 9c. The supply of water vapor accelerates the water gas reaction (a reaction between water vapor and carbon) and the water gas shift reaction (a reaction between water vapor and carbon monoxide), and thereby hydrogen is supplied. Therefore, the heat transfer rate in the calcination zone 9c is improved, and the productivity of sinter increases. Furthermore, hydrogen reduces NOx, and the amount of NOx can be suppressed. Additionally, the combustion efficiency of the solid fuel is also improved by the water gas shift reaction. In addition, it is not necessary to consider generation of excessive melt because the heat transfer rate in the calcination zone 9c is improved, and thus the productivity (sintering rate) of sinter increases. The inventors confirm that sinter can be manufactured using the low temperature combustion solid fuel and the high combined water iron ore without generating excessive melt.
[0040]
Specifically, for example, in the sintering process shown in FIG 1, iron ore including the high combined water iron ore containing 4.0 mass% or more of combined water, auxiliary raw materials, solid fuel including 10 mass% or more of the low
temperature combustion solid fuel having a combustion initiation temperature of lower
than 450°C are blended so that 30 mass% or more of the high combined water iron ore is
included, and the resulting mixture is used as a sintering feed. The sintering feed is
charged into a Dwight-Lloyd sintering machine, and the surface layer portion of the
sintering feed is ignited. Air is suctioned from the top (the cooling zone 9e) toward the
bottom (the raw material zone 9a) of the sintering bed (sintering feed) in the sintering
machine. Sintering is continuously progressed by the air flow, and sinter is
manufactured.
[0041]
According to the above method, the combustibility of the solid fuel can be significantly improved, and the productivity of sinter can be improved. In addition, the NOx concentration in the exhaust gas as well can be significantly reduced.
[Examples]
[0042]
Hereinafter, the examples of the present invention will be described in detail.
[0043]
Sinter was manufactured experimentally from a predetermined sinter mix (sintering feed) using a sintering test apparatus having a diameter of 30 cm and a bed height of 60 cm. After the sinter mix was charged into the sintering test apparatus up to a height of 60 cm, the solid fuel on the surface layer of the feed bed was ignited by operating a propane gas burner for 90 seconds. After that, sintering was performed while air was suctioned downward at a constant negative pressure of 15 kPa. After sintered lump done with a series of sintering stages was sufficiently cooled, the sintered lump was dropped 4 times from a height of 2 m so as to be crushed, and sinter having a particle size of 5 mm or larger was sampled. The sinter productivity and sinter yield
were calculated from the material balance of the sinter and the sinter mix. Similarly, the
flame front speed (FFS) showing the sintering rate was also calculated. In addition, the
oxygen concentration and the NOx concentration in the exhaust gas were also measured.
The blending conditions of the sintering feed and the test results of the sintering feed are shown in Tables 2 and 3, respectively. Here, each of the solid fuels in Table 2 corresponds to each of the solid fuels in Table 1.
[0044]
[Table 2]
(Table Removed)
[0045]
[Table 3]
(Table Removed)
* 1 FFS Is Flame Front Speed (Speed of Combustion Front Face for Sintering).
*2 Concentration of NOx Is Concentration (ppm) of Nitrogen Oxides Converted at 15% of Oxygen Concentration.
[0046]
As shown in Table 2, iron ore including the high combined water iron ore containing 4.0 mass% or more of combined water and solid fuel including 10 mass% or more of the low temperature combustion solid fuel having a combustion initiation temperature of lower than 450°C (for example, the char in Table 2) were used as the sinter mix of Examples 1 to 5. In addition, the iron ore was blended so as to include 30 mass% or more of the high combined water iron ore in the sinter mix (sintering feed) of Examples 1 to 5. Therefore, as shown in Table 3, the sintering rate (FFS) was improved without lowering the sinter yield, and the productivity could be significantly increased. In addition, the combustibility of the solid fuel was also significantly improved, and the oxygen concentration (excess air ratio) and the amount of NOx in the exhaust gas were lowered in Examples 1 to 5.
[0047]
On the other hand, the low temperature combustion solid fuel was not used in the sinter mix of Comparative Examples 1,2, and 6. The high combined water iron ore was not used in the sinter mix of Comparative Example 3. In addition, the sinter mix (sintering feed) of Comparative Example 4 did not include 30 mass% or more of the high combined water iron ore. The solid fuel in the sinter mix of Comparative Example 5 did not include 10 mass% or more of the low temperature combustion solid fuel. Meanwhile, char prepared by high temperature carbonization of subbituminous coal and having a high combustion initiation temperature is blended as the solid fuel in the sinter mix of Comparative Example 6. The productivity and the FFS were reduced, the combustibility of the solid fuel was degraded, and the oxygen concentration (excess air rate) and the amount of NOx in the exhaust gas increased in Comparative Examples 1 to 6.
Industrial Applicability
[0048]
It is possible to provide a producing method of sinter that significantly improves the combustibility of solid fuel, improves the sinter productivity, and significantly reduces the NOx concentration in the exhaust gas. Reference Symbol List [0049]
1 IRON ORE HOPPER la IRON ORE
2 LIMESTONE HOPPER 2a LIMESTONE
3 COKE HOPPER 3a COKE
4 RETURN FINE HOPPER 4a RETURN FINES
5 GRANULATING MACHINE
6 SINTERING FEED
7 SURGE HOPPER
8 DRUM FEEDER 8a CHUTE
9 FEED BED (SINTERING BED) 9a RAW MATERIAL ZONE
9b DRYING ZONE
9c CALCINATION ZONE
9d COKE COMBUSTION ZONE
9e COOLING ZONE
10 IGNITER
11 SINTER CAKE
12 DISCHARGE END
20 EXHAUST FAN
30 SINTERING MACHINE
46 SINTER FOR HEARTH LAYER

What is claimed is:
1. A producing method of a sinter, the method comprising:
blending an iron ore which includes a high combined water iron ore containing 4.0 mass% or more of a combined water, an auxiliary raw material, and a solid fuel which includes 10 mass% or more of a low temperature combustion solid fuel having a combustion initiation temperature of less than 450°C in order to prepare a sintering feed so that the sintering feed includes 30 mass% or more of the high combined water iron ore; charging the sintering feed into a Dwight-Lloyd sintering machine;
igniting a surface layer portion of the sintering feed; and suctioning an air from a top toward a bottom of the sintering feed.
2. The producing method of the sinter according to claim 1,
wherein the low temperature combustion solid fuel is a char obtained by
carbonizing a subbituminous coal, a brown coal, or a mixed coal of the subbituminous coal and the brown coal.