TWI837828B - Sinter manufacturing method - Google Patents

Abstract

The present invention provides a method for producing a sintered ore, which is to use microwaves to agglomerate a sintered raw material, wherein the sintered raw material includes an iron ore with hematite as a main component and a flux, and the method produces the sintered ore by efficiently heating in a shorter time. The method for producing a sintered ore of the present invention is to agglomerate a sintered raw material, wherein the sintered raw material includes a powdered iron ore with hematite as a main component and a flux, wherein the sintered raw material includes magnetite with a FeO conversion of 3.0 mass % or more, and irradiate the sintered raw material with microwaves to heat the sintered raw material to 1000°C or more.

Description

Sintered ore production method

The present invention relates to a method for producing sintered ore by heating sintered raw materials using microwaves.

In recent years, in order to reduce environmental load, especially to reduce _CO2 emissions, in the production process of sintered ore in the steel industry, the development of a method for heating the sintered raw materials without the combustion of coke has been continuously promoted. As one of the methods for heating the sintered raw materials without the combustion, there is a method of irradiating microwaves. Microwaves are a type of electromagnetic wave, and are electromagnetic waves with a frequency range of 300MHz to 300GHz. It is known that microwaves have the effect of heating dielectrics by giving energy, and in particular, materials with a high dielectric constant tend to absorb the energy of the irradiated microwaves.

Recently, the development of technology for producing sintered ore from iron ore mainly composed of hematite using microwaves is expected.

Patent document 1 discloses a method of irradiating microwaves with a frequency of 20 GHz to 30 GHz for the purpose of reducing iron ore and heating hematite and goethite, which are components of iron ore. It discloses that if high-frequency (short-wavelength) microwaves of 20 GHz to 30 GHz are used, even iron ore raw materials containing hematite or goethite as the main component can be heated or sintered.

Patent document 2 discloses a method for improving the quality and recovery rate of sintered ore by irradiating microwaves to the surface layer after the ignition furnace in an existing sintering machine using a combustion reaction, thereby supplying heat to the surface layer.

Patent document 3 discloses that in the production of sintered ore using microwave irradiation, a sintering raw material of unspecified iron oxide is used and irradiated with 2.45 GHz microwaves. The sintering rate increases in proportion to the irradiation time, and sintering is completed within 20 minutes.

[Prior art literature]

[Patent Literature]

Patent document 1: Japanese Patent Publication No. 2011-184718

Patent document 2: Japanese Patent Publication No. 2018-505965

Patent document 3: Japanese Patent Publication No. 07-268494

However, in Patent Document 1, since high-frequency microwaves of 20 GHz to 30 GHz are used for heating, a specialized large-scale gyrotron device is required, and the equipment investment becomes too large during the manufacturing process.

In Patent Document 2, microwaves are used to compensate for the heat on the surface of the ignited sintering raw material. Since the heat energy source during sintering is the combustion of carbon, there is a problem of generating CO ₂ .

In Patent Document 3, since iron ore without distinguishing the type of iron oxide is used as the sintering raw material, there is a problem that heating by microwave irradiation requires a long irradiation time and has low efficiency.

As described above, in the sintering step, as an alternative to heating using coke combustion, some technical developments using microwave heating have been studied. However, on the other hand, the prior art has the following problem, that is, when using iron ore containing hematite as the main component, a large-scale microwave generating device or long-term microwave irradiation is required.

The present invention is completed in view of the above situation. The purpose of the present invention is to provide a method for producing sintered ore, which can efficiently heat the sintering raw material with hematite as the main component in a shorter time to produce sintered ore even when using microwaves with a frequency of 2.4GHz~2.5GHz.

The inventors of the present invention have repeatedly conducted diligent research to solve the above-mentioned problem, and as a result, have discovered a method for producing sintered ore, in which a sintering raw material containing a certain amount of raw material including magnetite as a dielectric is mixed with a powdered iron ore containing hematite as a main component, and is heated by irradiating microwaves to thereby sinter. The present invention is completed by further research based on these insights, and the present invention is structured as follows.

[1] A method for producing sintered ore, comprising agglomerating a sintered raw material, the sintered raw material comprising powdered iron ore containing hematite as a main component and a flux, the sintered raw material comprising 3.0 mass % or more of magnetite in terms of FeO, and irradiating the sintered raw material with microwaves to heat the sintered raw material to a temperature of 1000°C or more.

[2] A method for producing a sintered ore as described in [1], wherein the sintered raw material contains a mixture of one or more of iron ore including magnetite, sintered ore and dust generated in an iron smelter.

[3] A method for producing sintered ore as described in [1], wherein the flux is one or more of limestone, quicklime, slaked lime and slag produced in an iron smelter.

[4] The method for producing sintered ore as described in [2], wherein the flux is one or more of limestone, quicklime, slaked lime and slag produced in an iron smelter.

[5] A method for producing sintered ore as described in any one of [1] to [4], wherein the frequency of the microwave is 2.4 GHz to 2.5 GHz.

According to the present invention, a sintered raw material containing a magnetite having a FeO content of 3.0 mass % or more can obtain high dielectric heating performance, so that the sintered raw material can be efficiently heated by microwaves in a shorter time, thereby being able to produce sintered ore.

1: Sintering raw material supply device

2: Pallet

3: Microwave irradiation device

4: Pallet width

5: Pallet loading layer height

6: Length of microwave irradiation device

7: Microwave oven

8: Alumina crucible

9: Thermocouple

10: Inner diameter of the upper surface of the crucible

11: Crucible height

12: Thermocouple insertion height

FIG1 is a schematic diagram showing an example of a sintering machine that can implement the sintered ore manufacturing method of the present invention.

FIG2(a) is a schematic diagram showing the production of sintered ore in an experimental example of the present invention. FIG2(b) is a schematic diagram showing the shape of an alumina crucible and the configuration of a thermocouple.

Figure 3 is a photo of the upper surface of the crucible after heating (upper photo) and a photo of the sintered structure observation (lower photo). (a) is Comparative Example 1, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

Figure 4 is a graph showing the relationship between the microwave irradiation time and the temperature change of the sintered raw material in Experiment 2.

Hereinafter, the implementation of the method for producing sintered ore of the present invention will be described in detail with reference to the drawings. Furthermore, the implementation shown below is an example of the implementation of the present invention, and the present invention is not limited to these implementations.

[Sintered ore production equipment]

FIG1 is a schematic diagram showing an example of a sintered ore manufacturing device that can implement the sintered ore manufacturing method of the present embodiment. Sintered raw materials are loaded into a sintered raw material supply device 1. Sintered raw materials are continuously loaded from the sintered raw material supply device 1 into a ring-shaped movable pallet 2 to form a loading layer of sintered raw materials. Microwaves are irradiated from a microwave irradiation device 3 to heat the loading layer of sintered raw materials, and the sintered raw materials are agglomerated by liquid phase sintering to manufacture sintered ore.

[Sintering raw materials]

Sintering raw materials include iron ore as an iron source and flux acting as a flux. Sintering raw materials may also include dust or sintered ore and silica generated in an iron smelter.

In order to further contain magnetite in an appropriate proportion, the sintering raw materials may be mixed with one or more of iron ore containing magnetite, sintered ore containing magnetite and dust generated in the iron smelting plant. The so-called appropriate proportion is an amount of magnetite of 3.0 mass % or more calculated as FeO. When the amount of magnetite is less than 3.0 mass % calculated as FeO, if microwaves with a frequency of 2.4 GHz to 2.5 GHz are used, it takes a long time of irradiation to heat to the specified temperature, which is not preferred. In addition, it is preferred that the amount of magnetite is less than 10.0 mass % calculated as FeO. When the blending ratio exceeds 10.0 mass % in terms of FeO, the blending amount of raw materials other than iron ore with hematite as the main component is increased, so the sintering raw material cost becomes higher. The more preferable range is 4.0 mass % or more and 8.0 mass % or less. In addition, it is preferable that the sintering raw material is not agglomerated by granulation or pressure molding in advance. This is because when the agglomerated object is heated, the microwave will attenuate with the penetration distance, and the heating efficiency inside the agglomerated object may be reduced. In addition, when the agglomerates are not formed, unlike the general sintering method using coke, there is an advantage that air supply is not required. When water is used to form agglomerates during granulation or molding, there is a disadvantage that excess heat is required due to the evaporation heat of the water.

[Iron Ore]

The main component of iron ore is iron oxide, and includes hematite (Fe ₂ O ₃ ) and magnetite (Fe ₃ O ₄ ). In the present embodiment, powdered iron ore with a particle size of 8 mm or less is used as the iron ore.

[Hematite]

Hematite (Fe ₂ O ₃ ) is an iron oxide commonly used as the main raw material in the blast furnace process. Hematite is reddish brown or black in color and is widely distributed in rocks or soil. In the modern blast furnace process, hematite is mixed with a flux or coke and sintered to be used as a sintered ore. However, hematite has a low dielectric constant, and it is difficult to heat hematite alone using microwaves of 2.4 GHz to 2.5 GHz. In this embodiment, a raw material containing 75% to 99% by mass of hematite in a powdered iron ore with hematite as the main component is used.

[Magnetite]

Magnetite (Fe ₃ O ₄ ) is a type of iron oxide. Basically, most of the available materials in the world are of low quality. It has high dielectric heating properties and can be easily heated using microwaves.

The sintered ore in this embodiment is produced by sintering a sintered raw material containing iron ore and flux. The sintered ore contains magnetite. In addition, the return ore is a sintered ore smaller than the product particle size obtained in the process of manufacturing the sintered ore, which can be added to the sintered raw material again. In addition, the dust is the dust containing Fe generated in the iron smelting plant, for example, rusty scraps, converter dust, blast furnace dust can be used. In addition, silica can also be blended to adjust the alkalinity.

[Flux]

The flux in this embodiment is a material containing a substance that becomes CaO by heating, such as limestone, quicklime, slaked lime, or a raw material containing CaO produced in an iron smelting plant, and plays a role in melting and consolidating the iron oxides in the sintered raw materials. The amount of flux is preferably prepared in such a way that the CaO/ _SiO2 of the sintered raw materials becomes 1.7 to 2.3. The so-called slag containing CaO produced in an iron smelting plant refers to, for example, blast furnace slag produced in a blast furnace or steelmaking slag produced in a steelmaking step.

[Sintering]

The magnetite dispersed in the sintering raw material has a high dielectric heating performance, so the heated magnetite becomes a heat source to heat the entire sintering raw material by heating it with microwaves. The CaO and iron oxide in the flux are heated and melted, turning the powdered iron oxide into a lump.

[Heating temperature]

The heating temperature of the raw material for sintering using microwaves is set to be above 1000°C. As the upper limit of the heating temperature, it is preferably set to be below 1350°C. This is because if the heating temperature is higher than 1350°C, the hematite will turn into magnetite, and when the temperature drops and it becomes hematite again, it will become secondary hematite with extremely poor reduction disintegration index (RDI). Furthermore, the heating temperature is more preferably set to be above 1200°C and below 1300°C.

[Microwave irradiation device]

Microwaves are a type of electromagnetic wave. According to the International Safety Management (ISM) or the Radio Law, the frequency band that can be used in devices that do not have large-scale leakage prevention devices for electromagnetic waves is limited.

Magnetrons are small and general-purpose microwave generating devices used in microwave furnaces, etc. The frequency of the magnetrons includes the range of 2.4GHz~2.5GHz, which is considered to be the ISM basic frequency. Within the range specified by the ISM basic frequency, the restrictions for preventing interference with electromagnetic waves of other frequencies are not strict, so as long as microwaves in the range of 2.4GHz~2.5GHz can be used, magnetrons that are cheaper than gyrotrons can be used to produce sintered ore, so the production equipment of sintered ore becomes cheaper. Furthermore, if it is a microwave of 2.4GHz~2.5GHz, there is no need to use large-scale radio wave leakage prevention equipment, so sintered ore can be produced using small and inexpensive equipment.

As the form of the microwave irradiation device in this embodiment, the tunnel type shown in Figure 1 can be cited. However, as long as the shape and configuration can irradiate the loading layer of the sintering raw material with microwaves, it is not limited to the shape exemplified in this embodiment.

In the method for producing sintered ore of the present embodiment, even when using microwaves of 2.4 GHz to 2.5 GHz, the sintered raw material can be heated to 1000°C or above in a short time of about 135 seconds by irradiating the microwaves, and the sintered raw material can be agglomerated by liquid phase sintering to produce sintered ore. If a microwave irradiation device having a length 6 of 40 to 50 m is used, the pallet speed can be 20 m/min, so if the pallet width 4 is set to 4 to 5 m and the pallet loading layer height 5 is set to 100 mm, a production of 3 million tons of sintered ore per year can be obtained. In this way, if sintered ore can be produced by heating sintered raw materials using microwaves, sintered ore can be produced without using pulverized coke or the like, thereby also being able to reduce the amount of CO ₂ generated in the production of sintered ore.

[Implementation example]

[Experiment 1]

First, an experiment using a magnetite test agent was conducted. The formulation is shown in Table 1. The magnetite test agent was adjusted to 3 to 10 mass % in terms of FeO. The amount of magnetite in the raw material was measured by chemical analysis as the amount of FeO in the raw material. The measured values are shown in Table 1.

CaO and _SiO2 in the raw materials are prepared using test materials to simulate the actual operation. _SiO2 is prepared to adjust the slag composition in the next step of the blast furnace and control the alkalinity.

The mass of each sample is set to a total of 36g~38g, and a mortar and pestle are used for mixing, and the sample is mixed thoroughly until the color becomes uniform visually. Each sample is filled to a height of about 2mm from the upper end of the alumina crucible 8 while being gently vibrated. The device is shown in Figure 2. The following device is used, that is, an alumina crucible 8 is placed in a microwave furnace 7, and a thermocouple 9 is installed at a position where the thermocouple insertion height 12 is 18mm. The inner diameter 10 of the upper surface side of the crucible is set to φ30mm, and the crucible height 11 is set to 27mm.

The microwave frequency was set to 2.45 GHz, and the microwave output (wattage) was controlled by a program at a heating rate of 1000°C/min. After reaching 1300°C, the microwave heating was stopped and the alumina crucible 8 was air-cooled.

The experimental results are shown in Table 2. The presence or absence of sintering is determined based on the compressive strength and the presence or absence of rearrangement of pores. In addition, the compressive strength is measured using a precision electronic universal material testing machine (Autograph) (speed: 1mm/min). Since the compressive strength of the sintered ore used as a blast furnace raw material is 2MPa~4MPa, if it has a strength of 2MPa or more, it is judged to be qualified for practical application.

In Examples 1 to 3, the sintering raw materials are heated to above 1000°C. The samples of Examples 1 to 3 are in a molten state immediately after the test. Figures 3 (b) to 3 (d) show the upper surface photographs of the crucibles after heating (upper figure) and the sintered structure observation photographs (lower figure) of Examples 1 to 3. As shown in Figure 3, it can be seen that Examples 1 (b), 2 (c), and 3 (d) are melted, and the pores are rearranged, indicating that a sintering reaction has taken place. In Examples 1 to 3, the magnetite contains 3.3% by mass, 6.4% by mass, and 9.4% by mass, respectively, calculated as FeO. Therefore, these raw materials are heated by microwaves with a frequency of 2.45 GHz, and the sintered raw materials as a whole reach a temperature of more than 1000°C, undergoing a sintering reaction to form agglomerates, thereby producing sintered ore with a specified strength.

In Comparative Example 1, the temperature rise stopped midway and no microwave absorption was observed, so the test was terminated. As shown in Figure 3 (a), it can be seen that the test body of Comparative Example 1 remained in a powder state after the test. When observing the structure, the pores in Comparative Example 1 were not rearranged, and the original ore particles remained directly without sintering reaction. It can be considered that since magnetite was not added in Comparative Example 1, magnetite only contained 0.2 mass% in terms of FeO, so it could not be heated if it was a microwave with a frequency of 2.45GHz, so no sintering reaction occurred.

[Experiment 2]

Next, a total of 36g~38g of samples were used as raw materials using magnetite concentrate and rusty iron chips used in industry. Examples 4 to 6 were based on the formulation confirmed to be sintered in Example 1, and the formulation ratio was set to 3% by mass in terms of FeO. In addition, the same raw materials as those in Example 5 were used in Reference Example 1, and the raw materials were granulated and dried in advance. Table 3 shows the formulation of Comparative Example 2, Examples 4 to 6, and Reference Example 1. Table 4 shows the proportion of the Fe element in each raw material. These samples were heated with 3kW of microwave irradiation frequency of 2.45GHz.

FIG4 shows the measured temperature curve. In Comparative Example 2, which does not mix magnetite concentrate and rusty scraps, magnetite contains only 0.7 mass % in terms of FeO, so it takes about 180 seconds (3 minutes) to reach 1000°C at the start of sintering. On the other hand, in Examples 4 to 6, which mix magnetite concentrate or rusty scraps, magnetite contains more than 3.0 mass % and therefore has a fast heating rate, reaching 1000°C and sintering in less than 135 seconds (2 minutes 15 seconds). In addition, in Reference Example 1, the heating rate is higher than that of Comparative Example 2, but compared with Example 5 using the same raw materials, the heating rate is very low.

1: Sintering raw material supply device

2: Pallet

3: Microwave irradiation device

4: Pallet width

5: Pallet loading layer height

6: Length of microwave irradiation device

Claims (5)

A method for producing sintered ore, wherein a sintered raw material is agglomerated, wherein the sintered raw material comprises a powdered iron ore with hematite as a main component and a flux, wherein the flux is a raw material comprising limestone, quicklime, slaked lime, or slag produced in an iron smelter containing CaO which is converted into CaO by heating, wherein the sintered raw material comprises a magnetite with a FeO content of 3.0 mass % or more, and the sintered raw material is heated to 1000°C or more by irradiating with microwaves. A method for producing sintered ore as described in claim 1, wherein the sintered raw material is mixed with one or more of iron ore including magnetite, sintered ore and dust generated in an iron smelter. The method for producing sintered ore as described in claim 1, wherein the flux is one or more of limestone, quicklime, slaked lime and slag produced in an iron smelter. The method for producing sintered ore as described in claim 2, wherein the flux is one or more of limestone, quicklime, slaked lime and slag produced in an iron smelter. A method for producing sintered ore as described in any one of claim 1 to claim 4, wherein the frequency of the microwave is 2.4 GHz to 2.5 GHz.