AU2010269436B2

AU2010269436B2 - Method for producing material for use in sintering

Info

Publication number: AU2010269436B2
Application number: AU2010269436A
Authority: AU
Inventors: Takahide Higuchi; Nobuyuki Oyama
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2009-07-10
Filing date: 2010-07-07
Publication date: 2014-06-26
Anticipated expiration: 2030-07-07
Also published as: ZA201109441B; BR112012000638B1; CN102482729B; CN102482729A; JP2011032577A; BR112012000638A2; WO2011004907A1; JP4840524B2; AU2010269436A1

Abstract

Disclosed is a method for producing a starting material for sintering that allows for the efficient production of an excellent starting material even when using a disk pelletizer for pelletization. Sintering starting materials, other than the limestone-based and the solid fuel-based powder starting materials, are load into a drum mixer (1) for mixing and stirring, where said powder starting materials are mixed, and the resulting mixture is supplied to a disk pelletizer (2) and pelletized. The pellets obtained by pelletization are supplied along with the limestone-based powder starting material to a drum mixer (3) for outer layer formation. Then, the solid fuel-based powder starting material is added so that by the time that the pellets reach the discharge port of the drum mixer (3) for outer layer formation, a limestone-based powder starting material layer and a solid fuel-based powder starting material layer have formed by adhesion to the outer layer of the pellets. In this manner, in the adhering of the solid fuel-based powder starting material to the outermost layer of the pellets for sintering, which have been pelletized by the disc pelletizer (2), making it possible to reliably avoid uneven burning during sintering.

Description

DESCRIPTION Title of Invention METHOD FOR PRODUCING MATERIAL FOR USE IN SINTERING Field of the Invention [0001) The present invention relates to a producing method of a material for use in sintering used to produce sintered ore for blast furnaces using a downdraft Dwight-Lloyd sintering machine. Description of the Related Arts [0002] In general, sintered ore used as blast furnace feed is produced through a method for processing sintering material as described below. Iron ore with a particle size of 10 mm or less; a SiO 2 -containing material such as silica stone, serpentine, or nickel slag; a limestone base powdery material containing CaO such as limestone; and a solid fuel type powdery material, such as coke breeze or anthracite, acting as a heat source are mixed in a drum mixer together with an appropriate amount of watgr, followed by granulation, whereby a granulated material called granulated particles is formed. Blended raw materials including the granulated material are provided on a pallet of a Dwight-Lloyd sintering machine so as to form a layer with a thickness of, -2 for example, 500 mm to 700 mm; a solid fuel present in a surface portion thereof is ignited; the ignited solid fuel is burned in such a manner that air is pulled downward; and the blended raw materials are sintered into a sintered cake by the heat of combustion thereof. The sintered cake is crushed, followed by screening, whereby sintered ore with a predetermined particle size is obtained. Return fines with a less particle size are recycled into sintering material. [0003] The reducibility of sintered ore produced as described above is a factor greatly affecting the operation of blast furnaces as already pointed out. The reducibility of sintered ore negatively correlates with the fuel ratio through the gas utilization efficiency in blast furnaces. The enhancement in reducibility of sintered ore reduces the fuel ratio in blast furnaces. The cold strength of sintered ore as described above is a factor important in ensuring the permeability of blast furnaces. Each blast furnace is operated in such a manner that the lower limit of the cold strength thereof is preset. Therefore, sintered ore suitable for blast furnaces is one having excellent reducibility and high cold strength. [0004] Therefore, techniques disclosed in Patent Documents 1 to 3 have been completed. The techniques are methods, -3 capable of enhancing the cold strength and reducibility of sintered ore, for producing sinter mixtures. The methods do not require any large pretreatment facility for a process for producing iron ore. In the methods, iron ore and a SiO 2 containing material are formed into granulated particles step by step separately from a limestone material and a solid fuel material, whereby sintbred ore having the following structure is produced: *a structure in which calcium ferrite (CF), which has high strength, is formed on the surface of each sintered ore and hematite (He), which has high reducibility, is selectively formed in the inside of the sintered ore. [0005] Furthermore, a producing method of a material for use in sintering has been proposed (see, for example, Patent Document 4) . This method is referred to as a so-called HPS (hybrid pelletized sinter) process. In this method, powdery iron ore which is a mixture of fine iron ore and coarse iron ore, limestone, and burnt lime are mixed in a mixer; the mixture and water added thereto are granulated with a first pelletizer; granulated particles are sieved through a screen; and oversize particles are charged into a second pelletizer; whereby the oversize p articles are coated with coke breeze.

-4 Prior art Document Patent Documents [0006] PATENT DOCUMENT 1: Japanese Patent No. 3755452 PATENT DOCUMENT 2: Japanese Patent No. 3794332 PATENT DOCUMENT 3: Japanese Patent No. 3656632 PATENT DOCUMENT 4: Japanese Examined Patent Application Publication No. 2-4658 Summary of the Invention Problems to be solved [0007] In the producing method of the material for use in sintering disclosed in Patent Document 4, a disk pelletizer is used to granulate sintering material. The use of the disk pelletizer allows iron ore containing pellet feed, which is fine powder, to be granulated. Iron ore containing fine powder such as pellet feed can be granulated by a combination of the HPS process and the producing methods of the material for use in sintering disclosed in Patent Documents 1 to 3. [0008] However, in recent years, iron ore and raw material prices have greatly varied from the development thereof and the blending of raw materials has been significantly varied. The processes disclosed in Patent Documents 1 to 3 have been - 5 developed for the purpose of increasing the usage of pellet feed made of iron ore fines (an average particle size of 150 pm or less), which were inexpensive in those days, and for the purpose of enhancing the quality of 5 sintered ore. However, the usage of the iron ore fines is currently reduced because of the increase in price of the iron ore fines and granules produced with pelletizers have reduced strength. Therefore, in the case of directly using the producing methods disclosed in Patent Documents 10 1 to 3, granulated particles with a small size are used for operation. This causes bad permeability and uneven burning. Therefore, improvements are necessary. The present invention has been made to solve the above problems and it would be advantageous if at least 15 preferred embodiments of the present invention were to provide a producing method of a material for use in sintering, the method being capable of efficiently producing good raw materials even if a disk pelletizer is used for granulation. 20 Means to solve the Problem [0009] According to a first aspect, the present invention provides a method of producing a material for use in sintering comprising: 25 providing sintering material including iron ore having a particle size of 8 mm or less, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; 50337201 (GHMatters) P89120.AU 5/06/14 - 6 the iron ore excluding a pellet feed containing 70% or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; 5 mixing the iron ore, the SiO 2 -containing material, and the limestone base powdery material in a drum mixer for stirring to produce a raw sinter mix; granulating the raw sinter mix with a disk pelletizer to produce granulated particles; 10 supplying the granulated particles to an outer layer forming drum mixer; and adding the solid fuel type powdery material to the granulated particles, supplied to the outer layer-forming drum mixer, from the outlet side of the outer layer 15 forming drum mixer, and forming a layer of the solid fuel type powdery material on the granulated particles during a coating time of 10 seconds to 40 seconds from addition of the solid fuel type powdery material to the outer layer forming drum mixture to discharge of the added solid fuel 20 type powdery material from the outer layer-forming drum mixer. In the method of producing the material for use in sintering according to the first aspect of the invention, it is preferable that the coating time is set to the range 25 of 20 seconds to 40 seconds. In the method of producing the material for use in sintering according to the first aspect of the invention, it is more preferable that the coating time is set to the range of 20 seconds to 30 seconds. 30 50337201 (GHMatters) P89120.AU 5/06/14 -7 [0010] According to a second aspect, the present invention provides a method of producing a material for use in sintering comprising; 5 providing sintering material including iron ore having a particle size of 8 mm or less, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; the iron ore excluding a pellet feed containing 70% 10 or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; mixing the iron ore and the SiO 2 -containing material in a drum mixer for stirring to produce a raw sinter mix; 15 granulating the raw sinter mix with a disk pelletizer to produce granulated particles; supplying the granulated particles to an outer layer forming drum mixer; and supplying the limestone base powdery material to the 20 outer layer-forming drum mixer and forming a layer of the limestone base powdery material on the granulated particles, and adding the solid fuel type powdery material from the outlet side of the outer layer-forming drum mixer, after supplying the limestone base powdery 25 material, to form a layer of the solid fuel type powdery material on the layer of the limestone base powdery material during a coating time of 10 seconds to 40 seconds 50337201 (GHMatters) P89120.AU 5/06/14 - 8 from addition of the solid fuel type powdery material to the outer layer-forming drum mixer to discharge of the granulated particles from the outer layer-forming drum mixer, thereby forming the layer of the limestone base 5 powdery material and the layer of the solid fuel type powdery material on the granulated particles. [0011] In the method of producing the material for use in sintering according to the second aspect of the invention, 10 it is preferred that the limestone base powdery material is supplied to the outer layer-forming drum mixer from the inlet side of the outer layer-forming drum mixer. In the method of producing the material for use in sintering according to the second aspect of the invention, 15 the limestone base powdery material is preferably supplied to the outer layer-forming drum mixer together with the granulated particles produced with the disk pelletizer. [0012] In the method of producing the material for use in 20 sintering according to the second aspect of the invention, it is preferable that the coating time is 20 to 40 seconds, and more preferably 20 to 30 seconds. In the method of producing the material for use in sintering according to the second aspect of the invention, 25 the limestone base powdery material is preferably supplied to the outer layer-forming drum mixer such that the addition of the limestone base powdery material takes a coating time of 90 seconds or less until the supplied limestone base powdery material is discharged from the 30 50337201 (GHMatters) P89120.AU 5/06/14 - 9 outer layer-forming drum mixer and also takes a coating time not less than the time from the addition of the solid fuel type powdery material to the outer layer-forming drum mixer to the discharge of the solid fuel type powdery 5 material from the outer layer-forming drum mixer. [0013] A method of producing a material for use in sintering according to a third aspect of the present invention comprises: 10 providing sintering material including iron ore having a particle size of 8 mm or less, an ultra-fine iron ore having an average particle size of 1 pm to 10 pm, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; 15 the iron ore excluding a pellet feed containing 70% or more of particles having an average size of -75 pm and also excluding an ultra-fine ore having an average particle size of 1 pm to 10 pm; mixing the iron ore, the ultra-fine iron ore, the 20 SiO 2 -containing material, and the limestone base powdery material in a drum mixer for stirring to produce a raw sinter mix; granulating the raw sinter mix with a disk pelletizer to produce granulated particles; 25 supplying the granulated particles to an outer-layer forming drum mixer; 50337201 (GHMatters) P89120.AU 5/06/14 - 10 adding the solid fuel type powdery material to the granulated particles, supplied to outer layer-forming drum mixer, from the outlet side of the outer layer-forming drum mixer and forming a layer of the solid fuel type 5 powdery material on the granulated particles during a coating time of 30 seconds to 70 seconds from addition of the solid fuel type powdery material to the outer layer forming drum mixer to discharge of the granulated particles from the outer layer-forming drum mixer. 10 [0014] In the method of producing the material for use in sintering according to the third aspect of the invention, it is preferred that the ultra-fine iron ore has an average particle size of 1 pm to 10 pm and the amount 15 thereof is 10% to 60% by mass of the total iron ore amount. [0015] A method of producing a material for use in sintering according to a fourth aspect of the present invention 20 comprises: providing sintering material including iron ore having a particle size of 8 mm or less, a pellet feed, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; 25 the iron ore excluding a pellet feed containing 70% or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; 50337201 (GHMatters) P89120.AU 5/06/14 - 11 mixing the iron ore, the pellet feed, the SiO 2 containing material, and the limestone base powdery material in a drum mixer for stirring to produce a raw sinter mix; 5 granulating the raw sinter mix with a disk pelletizer to produce granulated particles; supplying the granulated particles to an outer layer forming drum mixer; and adding the solid fuel type powdery material to the 10 granulated particles, supplied to outer layer-forming drum mixer, from the outlet side of the outer layer-forming drum mixer, and forming a layer of the solid fuel type powdery material on the granulated particles during a coating time of 30 seconds to 90 seconds from addition of 15 the solid fuel type powdery material to the outer layer forming drum mixer to discharge of the granulated particles from the outer layer-forming drum mixer. [0016] In the method of producing the material for use in 20 sintering according to the fourth aspect of the invention, it is preferred that the pellet feed contains 70% or more particles with an average size of -75 pm and the amount thereof is 10% to 60% by mass of the total iron ore amount. 50337201 (GHMatters) P89120.AU 5/06/14 - 12 In this sinter mixture-producing method, it is preferred that the outer layer-forming drum mixer has a residence time of 120 seconds or less and the residence time thereof is 90- seconds to 120 seconds. Advantageous Effects of Invention [0017] According to a producing method of a material for use in sintering according to the present invention, a limestone base powdery material is attached to or formed on granulated particles produced with a disk pelletizer and a solid fuel type powdery material such as coke breeze is then attached thereto or formed thereon, whereby the solid fuel type powdery material is attached to the outermost layers of the granulated particles produced with the disk pelletizer. This allows uneven burning to be securely prevented from occurring during sintering. The average size of the granulated particles can be appropriately adjusted and the reducibility thereof can be enhanced. Furthermore, yield is reduced and therefore productivity can be increased. Optimum granulation can be performed depending on the blend of iron ore raw materials such as a combination of coarse iron ores, a combination of coarse iron ore and ultra-fine ore, a combination of coarse iron ore and pellet feed in such a manner that the solid fuel type powdery - 13 material is added to a outer layer-forming drum mixer from the outlet side thereof and the coating time from the addition of the solid fuel type powdery material to the outer layer-forming drum mixer to the discharge of the solid fuel type powdery material from the outer layer-forming drum mixer is set to be short with any one of a reduction in size, a reduction in crushing strength, and a reduction in strength of the granulated particles. Brief Description of the Drawings [0018) Fig. 1 is an illustration of a production process to which a producing method of a material for use in sintering according to an embodiment of the present invention is applied and which uses a disk pelletizer. Fig. 2 is an illustration of an example of a production process to which a conventional method for producing a material for use in sintering is applied and which uses a disk pelletizer. Fig. 3 is an illustration of a test method used in a producing method of a material for use in sintering according to the present invention. Fig. 4 is a graph showing test results of Fig. 3. Fig. 5 is an illustration of a test method used in a producing method of a material for use in sintering according to the present invention.

- 14 Fig. 6 is a graph showing test results of Fig. 5. Fig. 7 is an illustration of an example of a conventional process for producing granulated particles using no disk pelletizer. Fig. 8 is a graph showing test results of another embodiment of the present invention, wherein Fig. 8(a) is a graph showing the relationship between the coating time of coke breeze and the average size of granulated particles, Fig. 8(b) is a graph showing the relationship between the coating time of coke breeze and productivity, and Fig. 8(c) is a graph showing the relationship between crushing strength and appropriate coating time. Fig. 9 is an illustration showing granulated particles, wherein Fig. 9(a) is a schematic view of a granulated particle that is produced in such a manner that pellet feed is used and the coating time of coke breeze is 90 seconds and Fig. 9(b) is a schematic view of a granulated particle that is produced in such a manner that pisolite ore, which is coarse iron ore, is used and the coating time of coke breeze is 90 seconds. Fig. 10 is an illustration of a wettability evaluation test. Fig. 11 is a characteristic chart showing the relationship between the time used to evaluate wettability and the elevation of water level.' - 15 Embodiments for carrying out the invention [0019] A producing method of a material for use in sintering according to an embodiment of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is an illustration of a production process to which the producing method of the material for use in sintering according to this embodiment is applied and which uses a disk pelletizer. Examples of the producing process of the material for use in sintering (HPS process) using the disk pelletizer include those disclosed in Japanese Patent Nos. 2748782 and 2755036. With reference to Fig. 1, sintering material including iron ore, a SiO 2 -containing material, a limestone base powdery material, and coke breeze, which is a solid fuel type powdery material, are prepared. P feed is pellet feed and B powder is blending fine. The sintering material other than the coke breeze, which is the solid fuel type powdery material, or the sintering material other than the coke breeze and limestone, which is the limestone base powdery material, are supplied to a drum mixer 1 for stirring and are mixed with added water, whereby a raw sinter mix is produced. [0020] - 16 The raw sinter mix is supplied to a disk pelletizer 2 and is granulated with the disk pelletizer 2, whereby granulated particles are produced. The granulated particles are supplied to an outer layer-forming drum mixer 3. In the outer layer-forming drum mixer 3, outer layers of limestone and outer layers of coke breeze are formed on the granulated particles. The sintering having has the outer layers formed with the outer layer-forming drum mixer 3, is charged into a Dwight-Lloyd sintering machine 4 which is of a downdraft type. In the Dwight-Lloyd sintering machine 4, coke breeze in the sinter material is ignited with an ignition furnace 5 and is then burned. The outer layer-forming drum mixer 3 includes a coke breeze feeder 6 for feeding coke breeze, which is the solid fuel type powdery material, from, for example, the outlet side and a limestone feeder 7 for feeding limestone, which is the limestone base powdery material, from, for example, the inlet side. Each feeder includes, for example, a conveyer and a spray nozzle. [0021] In the Dwight-Lloyd sintering machine 4, after coke breeze is ignited with the ignition furnace 5, coke breeze is burned in such a manner that the air is pulled downward with a blower and the sintering material is conveyed on a conveyer. The sintering material is sintered into a sintered cake. The sintered cake is crushed, followed by

I

- 17 screening. Sintered ore with a particle size of, for example, 4 mm or more is supplied to a blast furnace. Return fines other than sintered ore are recycled into a sintering raw material corresponding to iron ore. Therefore, iron ore included in the sintering material includes the return fines as described herein. Fig. 2, as well as Fig. 1, shows a conventional production method in which coke breeze, which is the solid fuel type powdery material, is fed from the inlet side of the outer layer-forming drum mixer 3 in a process of producing the material for use in sintering using the disk pelletizer 2. In this case, limestone, which is the limestone base powdery material, is charged from the drum mixer 1 for stirring. [0022] The inventors have performed.a test to find an optimum point for adding coke breeze, which is the solid fuel type powdery material. Fig. 3 shows a test method. In the outer layer-forming drum mixer 3 (also referred to as a coating mixer), the time taken to form layers of coke breeze on surface layers of granulated particles was determined. The length of the outer layer-forming drum mixer 3 was set such that the residence time of raw materials which were charged and then discharged was 120 seconds or less. That is, the drum mixer is a granulator in which although granulation 'is - 18 performed by rotation, breakage and granulation are substantially repeated. When the residence time thereof is long, the granulated particles are broken. Therefore, the limit thereof is 120 seconds or less and preferably 90 seconds or less. In the test, for example, Australian coarse iron ore A (-8 mm), South American coarse iron ore B (-8 mm), iron ore B (-1 mm), a silica stone powder, burnt lime, return fines, limestone, coke breeze were used as sintering material and were blended at a weight ratio shown in Table 1. [0023] Table 1 Weight percentage of each material (weight percent) Raw materials Blend Ore A (-8 mm) 33.2 Ore B (-8 mm) 26.6 Ore B (-1 mm) 6.6 Silica stone powder -1.6 Burnt lime 2.0 Return fines 20 Limestone 10 Coke breeze (not included) 5.0 [0024] In the test, the following relationship was evaluated: the relationship between the residence time of coke breeze in the outer layer-forming drum mixer, productivity, granulation performance, and the quality of sintered ore. A test level was as follows: a conventional example was tested using a method in which the outer layer-forming drum - 19 mixer 3, which had a preferable residence time of 90 seconds, was used and raw materials of granulated particles and coke breeze were charged into the outer layer-forming drum mixer 3 from the inlet side thereof. The relationship between the residence time of coke breeze in the drum mixer and productivity was tested in such a manner that the adding position of coke breeze was changed. The residence time (coating time) of coke breeze and the times taken in other granulation steps are as shown in Table 2. The productivity obtained in each test, the average size of granulated particles, and results of reducibility are shown in Fig. 4. [0025] Table 2 Mixing time Granulation Outer layer-forming drum mixer of mixer for time of disk Coke breeze Raw material stirring (s) pelletizer (s) coating time (s) Granulation time (s) Conventional 120 120 90 90 example Comparative 120 120 60 90 Example 1 Example 1 120 120 40 90 Example 2 120 120 30 90 Example 3 120 120 20 90 Example 4 120 120 10 90 [00261 These results show that a reduction in residence time of coke breeze improves productivity and a condition for improving productivity is that the residence time of coke breeze, that is, the coating time thereof is within the - 20 range of 10 seconds to 40 seconds. The coating time is preferably within the range of 20 seconds to 40 seconds and more preferably 20 seconds to 30 seconds because productivity peaks substantially. This is probably because when the residence time of coke breeze is more than 40 seconds, broken portions and coke.breeze-containing portions are present in surface layers of granulated particles and the deterioration in burning performance of coke breeze inhibits productivity. Alternatively, this is probably because coke breeze is hydrophobic and is inferior in granulation performance to other sintering material and therefore while coke breeze is retained in the outer layer forming drum mixer together with the granulated particles, coke breeze is trapped between the granulated particles during granulation and disruption ,in the outer layer-forming drum mixer to cause the disruption of the granulated particles and the granulated particles are likely to have a reduced size. [0027] When the residence time of coke breeze, that is, the coating time thereof is less than 20 seconds, coke breeze is not uniformly coated on the granulated particles and is unevenly burned and productivity is slightly reduced although the disruption of the granulated particles is suppressed. When the coating time is less than 10 seconds, - 21 coke breeze is nonuniformly coated on the granulated particles and productivity is significantly reduced. For reducibility, the reduction of the coating time of coke breeze allows the granulated particles to have an increased size to improve permeability and therefore a large amount of a calcium ferrite microstructure with high reducibility is produced by high-temperature sintering. [0028] Next, productivity was investigated in such a manner that the optimum time to coat the outermost layers with coke breeze was used and limestone, which was a limestone base powdery material, was added to the outer layer-forming drum mixer 3 with a test apparatus shown in Fig. 5. Tests were performed in such a manner that the residence time of coke breeze, that is, the coating time thereof was constant, 30 seconds, and the residence time of limestone, that is, the coating time thereof was varied. The residence time in each of a conventional example, examples, and comparative examples is as shown in Table 3. Fig. 6 shows the results of sintering time, yield, and productivity in each test. [0029] -22 E o c0, o o a) L- "aO~ -a)C) 'C')M 0 00 0 m0 o0 o0m o 00 0 0 0 L- C~oco) C) C) C) LL. I I I I III a) U) wn U/, (1), _a d) cu a) m a) N N N N~ N I WUUaa) W-C 0 aa) ) M CUo "m 0 cu o0 MC) 0) a) .C- CD3 )-) Q 0 0U 0 C0 C0 C o) C~4 C\J N\ 04 C\J M a) C) ) ) ) a)) U) U)C U)0 UC' C/) a)C. C u C : C : C : C a) a) 0 ) 0 a) 0 ) 0 >- - C1 0- U) UD 0 U 0 0 E C a) E ) E E~ E o a) a) ~ a) H _ _ _ _ _ _ _ _ _ _ _ _ - 23 [0030] Patent Documents 1 to 3 cited above describe that the coating time of coke breeze or limestone does not affect productivity. This embodiment, in which the disk pelletizer is used for granulation, has revealed the coating time of limestone needs to be set to be not less than the coating time of coke breeze. That is, in Example 5 in which limestone is charged into the outer layer-forming drum mixer 3 together with.granulated particles produced with the disk pelletizer 2, the sintering time is longer than that in the conventional example and the yield and the productivity are significantly increased as shown in Fig. 6. In Example 6 in which the coating time of limestone is 60 seconds, the yield is further increased and the productivity peaks. In the case of, for example, Example 7 in which limestone and coke breeze are added together and this embodiment in which the disk pelletizer is used for granulation, the yield is increased with the coating of limestone and the productivity can be ensured as well as that in Example 5 in which the coating time is 90 seconds although the yield is reduced because the coating state of coke breeze is slightly deteriorated by the influence of limestone. [0031] In the case of setting the coating time of limestone to 10 seconds, that is, in the case of setting the coating time - 24 of limestone to be less than the coating time of coke breeze that is 30 seconds like Comparative Example 2, burning is uneven, the yield tends to reduce with an increase in sintering time, and the productivity is reduced close to that in the conventional example; hence, the coating effect of limestone cannot be achieved. Therefore, the coating time of limestone is preferably within the range of 30 seconds, which is equal to the coating time of coke breeze, to 90 seconds. [0032] As described above, in the sinter mixture-producing method according to this embodiment, as a pretreatment for a process for producing sintered ore for blast furnaces using the Dwight-Lloyd sintering machine 4, which is of a downdraft type, the sintering material, which include iron ore, the SiO 2 -containing material, the limestone base powdery material, and the solid fuel type powdery material, are prepared;. the raw sinter mix is produced by mixing iron ore and the SiO 2 -containing material in the drum mixer 1 for stirring except the solid fuel type powdery material; the produced raw sinter mix is formed into granulated particles with the disk pelletizer 2; the granulated particles are supplied to the outer layer-forming drum mixer 3; the coating time taken for the solid fuel type powdery material, which is added to the outer layer-forming drum mixer 3 from - 25 the outlet side thereof, to reach an outlet of the outer layer-forming drum mixer 3 is set to the range of 10 seconds to 40 seconds; and layers of the solid fuel type powdery material are attached to or formed on outer portions of the granulated particles within the coating time. Alternatively, the sintering material other than the limestone base powdery material and the solid fuel type powdery material are charged into the drum mixer 1 for stirring and are mixed therein; the raw sinter mix is supplied to the disk pelletizer 2 and is granulated; the obtained granulated particles are supplied to the outer layer-forming drum mixer 3; the limestone base powdery material is added to the outer layer-forming drum mixer 3; the limestone base powdery material is applied to the surfaces of the granulated particles formed with the disk pelletizer 2 in such a manner that layers of the limestone base powdery material and the solid fuel type powdery material layers are attached to or formed on the outer portions of the granulated particles before the added solid fuel type powdery material reaches the outlet of the outer layer-forming drum mixer 3; and the solid fuel type powdery material, such as coke breeze, is applied thereto, whereby the solid fuel type powdery material is attached to the outermost layers of the granulated particles for sintering with the disk pelletizer 2. Therefore, uneven burning can be securely prevented from - 26 occurring during sintering. [0033] Furthermore, the limestone base powdery material is added to the outer layer-forming drum mixer 3 from the inlet side thereof and the solid fuel type powdery material is added to the outer layer-forming drum mixer 3 from the outlet side thereof, whereby the solid fuel type powdery material is securely applied to the outermost layers of the granulated particles for sintering. The limestone base powdery material is charged into the outer layer-forming drum mixer 3 together with the granulated particles produced with the disk pelletizer 2, whereby uneven burning is prevented and productivity is increased. [0034] Furthermore, the length of the outer layer-forming drum mixer 3, which is placed downstream of the disk pelletizer 2, is adjusted such that the residence time of charged raw materials therein is 120 seconds or less. The solid fuel type powdery material is added to the outer layer-forming drum mixer 3, which is placed downstream of the disk pelletizer 2, in such a manner that the residence time is adjusted to 40 seconds or less. These allow the average size of the granulated particles to be appropriately adjusted to enhance the reducibility thereof and also allow - 27 yield to be reduced to increase productivity. [0035] In the above embodiment, only coarse iron ore is granulated with the disk pelletizer 2 as described above. The present invention is not limited thereto. The following cases were tested in substantially the same manner as that described above: the case where ultra-fine ore with an average particle size of 1 pm to 10 jam was added to two types of coarse iron ores A and B within the range of 10% to 60% by mass, preferably 10% to 30% by mass, of the total iron ore amount and the case where pellet feed containing 70% by mass or more ore with an average particle size of -75 jam was added to two types of coarse iron ores A and B within the range of 10% to 60% by mass, preferably at 60% by mass, of the total iron ore amount. In this test, materials were blended at a weight ratio shown in Table 4 and test conditions were as shown in Table 5. [0036] - 28 Table 4 Weight percentage of each material (weight percent) Raw materials No. 1 No. 2 No. 3 No. 4 Ore A (-8 mm) 33.2 33.2 29.9 13.3 Ore B (-8 mm) 26.6 26.6 24 10.6 Ore B (-1 mm) 6.6 6.6 5.9 2.6 Pellet feed 0 0 0 39.8 Ultra-fine ore (average particle size of 10 pm) 0 0 6.6 0 Silica stone powder 1.6 1.6 1.6 1.6 Burnt lime 2.0 2.0 2.0 2.0 Return fines 20 20 20 20 Limestone 10 10 10 10 Coke breeze (not included) 5.0 5.0 5.0 5.0 -29 a) *~E U) (M : 0 0 C0 0 .xE c) 0) 0) a) E 3 r EE 0 0 0 0 L-= 0) 0m 0) 0) 10 &m 6 0 0 L. CT-N- -N 0U 0 0D 0D 0o 01_ Co CT CT CT aU) 000 CDW N N N 0 C0 1 o ) 0 0/0 75o N N N C C

CU

0 D 4- 0 a)LU 0)0 0 0 0 a) c N N N% U) Ut) U) U) U) UD C _ ) U) a) CO)a U, CLU JU, CLU U) + + + + _ Q) C: 00 00C ) 0 U , 0 l )0 U,) C))) U-) UN C)UU 0U CUE QE (1 LEI C: E CU-C m m mC Ln )= ) )o = 0 <_ ___ __O <_ _ 0 O <0 ,o M H N ce) 6 6 6 6i E z Z lZ Z - 30 [0038] Herein, Test Condition No. 1 is an example in which 50% Australian coarse iron ore and 50% South American coarse iron ore were blended as described in the above example and an HPS process shown in Fig. 3 was used as a granulation process. Test Condition No. 2 is a conventional example in which the same iron ores as those used in Test Condition No. 1 were used and a DL process shown in Fig. 7 was used as a granulation process. [0039] Test Condition No. 3 is an example in which 45% Australian coarse iron ore, 45% South American coarse iron ore, and 10% ultra-fine ore with an average particle size of 10 jim were blended and the HPS process shown in Fig. 3 was used as a granulation process. Test Condition No. 4 is an example in which 20% Australian coarse iron ore, 20% South American coarse iron ore, and 60% pellet feed containing 70% or more ore with an average particle size of -75 jm were blended and the HPS process shown in Fig. 3 was used as a granulation process. [0040] Test results obtained from Test Condition Nos. 1 to 4 are shown in Figs. 8 (a) to 8(c). Fig. 8(a) is a graph showing the relationship between the coating time of coke breeze and the size of granulated particles, wherein the granulated particle size shown in the left side is applied - 31 to Test Condition Nos. 1 to 3 and the granulated particle size shown in the right side is applied to Test Condition No. 4. Fig. 8(b) is a graph showing the relationship between the coke breeze coating time and productivity. Fig. 8(c) is a graph showing the relationship between the crushing strength (kg/P) and the appropriate coating time (s). [0041] As shown in Fig. 8(a), the test results indicate that the size of granulated particles produced under Test Condition No. 2, which is the conventional example, is the least, followed by Test Condition No. 1, No. 3, and No. 4 in that order. In Test Condition Nos. 1 and 3, the size of granulated particles increases with a reduction in coating time of coke breeze when the coating time of coke breeze is less than 90 seconds. For Test Condition No. 4, the size of granulated particles is about two to three times greater than those obtained under other test conditions, does not increase when the coating time of coke breeze is less than 90 seconds, and is substantially constant, about 4.5 mm. [0042] As is clear from Fig. 8(b), which shows the relationship between the coke breeze coating time and productivity, the productivity of Test Condition No. 4, in which the size of granulated particles is the largest, peaks when the coating time of coke breeze is within the - 32 range of 30 seconds to 90 seconds and the productivity thereof falls when the coating time of coke breeze is more than 90 seconds or less than 30 seconds. As shown in Fig. 8(b), the productivity of Test Condition No. 3, in which the size of granulated particles is the second largest, peaks when the coating time of coke breeze is within the range of 30 seconds to 70 seconds and the productivity thereof falls when the coating time of coke breeze is more than 70 seconds or less than 30 seconds. [00431 As shown in Fig. 8(b), the productivity of Test Condition No. 4, in which the size of granulated particles is the third largest, peaks when the coating time of coke breeze is within the range of 20 seconds to 40 seconds and the productivity thereof falls when the coating time of coke breeze is more than 40 seconds or less than 20 seconds. The above results show that the maximum of the coating time of coke breeze needs to be reduced with a reduction in size of granulated particles. (0044] For the relationship between the crushing strength (kg/P) and the appropriate coating time (s), as shown in Fig. 8(c), in Test Condition No. 4, the crushing strength is the highest and the appropriate coating time is 90 seconds. In Test Condition No. 3, the crushing strength is the second highest and the appropriate coating time is 70 - 33 seconds. In Test Condition No. 1, the crushing strength is the third highest and the appropriate coating time is 30 seconds. These test results show that the coating time of coke breeze needs to be reduced with a reduction in crushing strength. [0045] Granulated particles of iron ore are mixed with coke breeze in a mixer and are grown with repeated adhesion and disruption as described above. Australian iron ore such as pisolite ore is coarser than pellet feed and granulated particles thereof have reduced strength. When coke breeze is present inside granulated particles, the granulated particles have reduced strength because coke breeze is hydrophobic. Therefore, in order to prevent the entrance of coke breeze into the granulated particles and the disruption of the granulated particles, the coating time of coke breeze needs to be reduced. [0046] The strength o (N) of granulated particles can be given by the following equation (1): a = 6-p-S { (1 - s) / s))- (ycosO/d) (1) wherein p is the fullness (-) of a liquid, S is the surface area (m 2) of powder, s is the porosity (-) of a granulated substance, y is the surface tension (N/m) of water, 0 is the contact angle (0), and d is the equivalent specific surface - 34 diameter (m). In the case where pellet feed is used and the coating time of coke breeze is 90 seconds, the following structure is formed: a particle structure in which centered nucleus iron ore 21 is coated with a mixture 22 of pellet feed and limestone as schematically shown in Fig. 9(a) and hydrophobic coke breeze 23 is attached to an outer layer of the mixture 22. In this case, the granulated particle strength a is as follows: a = 6.8 x 10-3 N. [0047] On the other hand, in the case where only pisolite ore, which is coarse iron ore, is used and the coating time of coke breeze is 90 seconds, pisolite ore 24 and hydrophobic coke breeze 23 are present around nucleus iron ore 21. In this case, the granulated particle strength a is an order of magnitude less than that obtained using pellet feed and is as follows: a = 8.4 x 10~4 N. Iron ore, limestone, and coke breeze were evaluated for wettability from the rising rate of water in a powder packed column by capillary action. In this evaluation test, the elevation of water level was measured in such a manner that pieces of gauze were attached to the lower ends of glass tubes 31 with a diameter of 25 p; each of coke breeze, limestone (lime stone), and iron ore was packed into a corresponding one of the glass tubes 31; and the gauze pieces were placed in a vessel 32 filled with water.

- 35 [0048] The result of measurement, that is, the relationship between the time qt (S112) and the elevation (mm) of water level is as follows: the elevation of water level determined using each of iron ore (a contact angle 0 of 450) and limestone (a contact angle 0 of 550) increases in approximate proportion to the time 1t and the elevation of water level determined using coke breeze (a contact angle 0 of 840) is about half of that determined using each of iron ore and limestone. This shows that coke breeze is inferior in wettability to iron ore and limestone. Therefore, the entrance of coke breeze into pseudo-particles causes a reduction in strength of the pseudo-particles, resulting in a reduction in size of granulated particles. [0049] The Hagen-Poiseuille equation is used to evaluate wettability and is as follows: H = {(pdycos0 / 21j)t} (2) wherein H is the elevation (m) of water level, t is the time (s), 0 is the contact angle (0), rj is the viscosity (N-s/m 2 ) of water, y is the surface tension (N/m), d is the particle size (m), p is the shape factor (-) [0050] Thus, in order to increase the size of granulated particles to ensure the strength of the granulated particles, coke breeze needs to be prevented from entering - 36 the granulated particles. When the strength of granulated particles made of only coarse iron ore is less than the strength of granulated particles that is increased by mixing coarse iron ore with ultra-fine powder or pellet 5 feed, the coating time of coke breeze needs to be reduced. The coating time of coke breeze is set to be short with a reduction in strength of the granulated particles. Reference Numerals [0051] 10 Reference numeral 1 is a drum mixer for stirring, reference numeral 2 is a disk pelletizer, reference numeral 3 is an outer layer-forming drum mixer, reference numeral 4 is a Dwight-Lloyd sintering machine, reference numeral 5 is an ignition furnace, reference numeral 6 is a 15 coke breeze feeder, and reference numeral 7 is a limestone feeder. [0052] It is to be understood that, if any prior art publication is referred to herein, such reference does not 20 constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. [0053] In the claims which follow and in the preceding 25 description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but 30 not to preclude the presence or addition of further features in various embodiments of the invention. 50337201 (GHMatters) P89120.AU 5/06/14

Claims

1. A method of producing a material for use in 5 sintering, comprising: providing sintering material including iron ore having a particle size of 8 mm or less, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; 10 the iron ore excluding a pellet feed containing 70% or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; mixing the iron ore, the SiO 2 -containing material, and 15 the limestone base powdery material in a drum mixer for stirring to produce a raw sinter mix; granulating the raw sinter mix with a disk pelletizer to produce granulated particles; supplying the granulated particles to an outer layer 20 forming drum mixer; and adding the solid fuel type powdery material to the granulated particles, supplied to the outer layer-forming drum mixer, from the outlet side of the outer layer forming drum mixer, and forming a layer of the solid fuel 25 type powdery material on the granulated particles during a coating time of 10 seconds to 40 seconds from addition of the solid fuel type powdery material to the outer layer forming drum mixer to discharge of the added solid fuel type powdery material from the outer layer-forming drum 30 mixer.

2. The method according to claim 1, wherein the coating time is 20 seconds to 40 seconds. 50337201 (GHMatters) P89120.AU 5/06/14 - 38

3. The method according to claim 1, wherein the coating time is 20 seconds to 30 seconds. 5

4. A method of producing a material for use in sintering, comprising: providing sintering material including iron ore having a particle size of 8 mm or less, a SiO 2 -containing material, a limestone base powdery material, and a solid 10 fuel type powdery material; the iron ore excluding a pellet feed containing 70% or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; 15 mixing the iron ore and the SiO 2 -containing material in a drum mixer for stirring to produce a raw sinter mix; granulating the raw sinter mix with a disk pelletizer to produce granulated particles; supplying the granulated particles to an outer layer 20 forming drum mixer; and supplying the limestone base powdery material to the outer layer-forming drum mixer and forming a layer of the limestone base powdery material on the granulated particles, and adding the solid fuel type powdery material 25 from the outlet side of the outer layer-forming drum mixer, after supplying the limestone base powdery material, to form a layer of the solid fuel type powder material on the layer of the limestone base powdery material during a coating time of 10 seconds to 40 seconds 30 from addition of the solid fuel type powdery material to the outer layer-forming drum mixer to discharge of the granulated particles from the outer layer-forming drum mixer, thereby forming the layer of the limestone base 50337201 (GHMatters) P89120.AU 5/06/14 - 39 powdery material and the layer of the solid fuel type powdery material on the granulated particles.

5. The method according to claim 4, wherein 5 the supplying of the limestone base powdery material comprises supplying the limestone base powdery material to the outer layer-forming drum mixer from the inlet side of the outer layer-forming drum mixer. 10

6. The method according to claim 4, wherein the supplying of the limestone base powdery material comprises supplying the limestone base powdery material to the outer layer-forming drum mixer together with the granulated particles produced with the disk pelletizer. 15

7. The method according to claim 4, wherein the coating time is 20 to 40 seconds.

8. The method according to claim 4, wherein the coating 20 time is 20 seconds to 30 seconds.

9. The method according to claim 4, wherein the supplying of the limestone base powdery material comprises supplying the limestone base powdery material to 25 the outer layer-forming drum mixer such that the addition of the limestone base powdery material takes a coating time of 90 seconds or less until the supplied limestone base powdery material is discharged from the outer layer forming drum mixer and also takes a coating time not less 30 than the time from the addition of the solid fuel type powdery material to the outer layer-forming drum mixer to the discharge of the solid fuel type powdery material from the outer layer-forming drum mixer. 50337201 (GHMatters) P89120.AU 5/06/14 - 40

10. A method of producing a material for use in sintering, comprising: providing sintering material including iron ore 5 having a particle size of 8 mm or less, an ultra-fine iron ore having an average particle size of 1 pm to 10 pm, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; the iron ore excluding a pellet feed containing 70% 10 or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; mixing the iron ore, the ultra-fine iron ore, the SiO 2 -containing material, and the limestone base powdery 15 material in a drum mixer for stirring to produce a raw sinter mix; granulating the raw sinter mix with a disk pelletizer to produce granulated particles; supplying the granulated particles to an outer layer 20 forming drum mixer; adding the solid fuel type powdery material to the granulated particles, supplied to outer layer-forming drum mixer, from the outlet side of the outer layer-forming drum mixer, and forming a layer of the solid fuel type 25 powdery material on the granulated particles during a coating time of 30 seconds to 70 seconds from addition of the solid fuel type powdery material to the outer layer forming drum mixer to discharge of the granulated particles from the outer layer-forming drum mixer. 30

11. The method according to claim 10, wherein the ultra fine iron ore has an average particle size of 1 pm to 10 50337201 (GHMatters) P89120.AU 5/06/14 - 41 pm and the amount thereof is 10% to 60% by mass of the total iron ore amount.

12. A method of producing a material for use in 5 sintering, comprising: providing sintering material including iron ore having a particle size of 8 mm or less, a pellet feed, a SiO 2 -containing material, a limestone base powdery material, and a solid fuel type powdery material; 10 the iron ore excluding a pellet containing 70% or more of particles having an average size of -75 pm and also excluding an ultra-fine iron ore having an average particle size of 1 pm to 10 pm; mixing the iron ore, the pellet feed, the SiO 2 15 containing material, and the limestone base powdery material in a drum mixer for stirring to produce a raw sinter mix; granulating the raw sinter mix with a disk pelletizer to produce granulated particles; 20 supplying the granulated particles to an outer layer forming drum mixer; and adding the solid fuel type powdery material to the granulated particles, supplied to outer layer-forming drum mixer, from the outlet side of the outer layer-forming 25 drum mixer, and forming a layer of the solid fuel type powdery material on the granulated particles during a coating time of 30 seconds to 90 seconds from addition of the solid fuel type powdery material to the outer layer forming drum mixer to discharge of the granulated 30 particles from the outer layer-forming drum mixer.

13. The method according to claim 12, wherein the pellet feed contains 70% or more particles with an average size 50337201 (GHMatters) P89120.AU 5/06/14 - 42 of -75 pm and the amount thereof is 10% to 60% by mass of the total iron ore amount.

14. The method according to any one of claims 1 to 13, 5 wherein the outer layer-forming drum mixer has a residence time of 120 seconds or less.

15. The method according to claim 14, wherein the residence time thereof is 90 seconds to 120 seconds. 10

16. The method according to claim 1, claim 4, claim 10 or claim 12, substantially as herein described with reference to any one of the invention Examples. 15 50337201 (GHMatters) P89120.AU 5/06/14