JP2012246514A - Method for producing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing reduced iron which can improve the heat-retaining property of a rotary hearth furnace at a low cost.SOLUTION: In the method for producing the reduced iron, combustible powder K is introduced into a rotary hearth type heating and reducing furnace A and burnt, and a raw material mixture including a carboneceous reducing agent and an oxidized iron-containing material is heated and reduced to produce the reduced iron. The content of ash in the combustible powder is preferably ≤1.3 wt.%, and as the example of the combustible powder, a biomass or brown coal, etc., is cited.

Description

  The present invention relates to a method for producing reduced iron.

  In recent years, coal is used as a reducing agent instead of natural gas and agglomerates with iron oxide and put into a rotary hearth furnace (RHF) to produce reduced iron (DRI). Many methods have been adopted.

  In order to improve the heat retention of the rotary hearth furnace, a method for improving the emissivity and emissivity of the flame in the rotary hearth furnace has been proposed. For example, there is a method of improving the flame radiation rate of the burner by blowing metal powder into the burner (see, for example, Patent Document 1).

  Moreover, in a glass melting furnace, a method for improving the emissivity by supplying powder made of glass raw material to a burner has been proposed (see, for example, Patent Document 2). Furthermore, in an ash melting furnace, a method for improving the emissivity by blowing ash into a burner has been proposed (see, for example, Patent Document 3).

JP 51-75231 A JP-A-11-11953 JP 2000-88234 A

  Heat transfer from the atmosphere in the rotary hearth furnace heated to high temperature to the object to be heated is performed by convection heat transfer and radiation heat transfer, but the heat flux in the furnace is not so high and the heat transfer area is limited. Therefore, radiant heat transfer is mainly used.

Radiation heat transfer is classified into solid radiation by the furnace wall and gas radiation by gas. Although gas radiation is mainly due to CO ₂ and H ₂ O, the wall radiation rate is about 0.7 to 0.9, whereas the gas radiation rate is as small as about 0.3. Is lower than the solid radiation from the furnace wall.

  On the other hand, in a burner (heavy oil burner, pulverized coal burner, etc.) that uses a liquid or solid other than gaseous fuel as fuel, carbon fine particles (so-called soot) are generated from the fuel, and the soot is heated to a high temperature. The solid radiation from soot is superimposed on the gas radiation from the gas, and the emissivity of the flame is high.

  However, when heavy oil is used as the fuel, there is a concern about the negative effects on the product due to sulfur contained in the fuel, and when pulverized coal is used as the fuel, the pulverized coal has a high ash content, so it melts in the furnace. There is a drawback that the operation becomes difficult due to ash sticking. Moreover, the said fuel is not necessarily usable for the purpose of cost reduction or the like.

  Moreover, in the above-mentioned patent documents 1 to 3, as a method for improving the flame emissivity, incombustibles (metal, glass, ash, etc.) are introduced into the furnace, but these substances are introduced into the rotary hearth furnace. In such a case, there is a high possibility that these substances melt and adhere in a high temperature atmosphere in the furnace, resulting in operational troubles.

  This invention is made | formed in view of this situation, The objective of this invention is providing the manufacturing method of reduced iron which can improve the heat retention of a rotary hearth furnace at low cost.

  The method for producing reduced iron according to the present invention is achieved by introducing combustible powder into a mobile heating reduction furnace and burning it, and heating and reducing a raw material mixture containing a carbonaceous reducing agent and an iron oxide-containing substance. The gist is to produce iron.

  In the method for producing reduced iron according to the present invention, the combustible powder that is substantially free of ash is introduced into the furnace, so that the combustible powder is completely burned out in the furnace without generating dust. The amount of heat input to the object to be heated can be increased. Therefore, the heat retention in the furnace can be improved.

  In addition, by using the combustible powder in the present invention, the use of fossil fuels such as heavy oil can be reduced and the cost is low.

  If the ash content of the combustible powder is 1.3% by weight or less, the amount of ash accumulated on the inner wall surface of the furnace can be suppressed.

  If the combustible powder contains biomass or lignite, the ash content can be remarkably suppressed.

  If the combustible powder is introduced into the mobile heating reduction furnace from the combustible material introduction part provided in the burner, the flame from the burner and the combustible powder are easily mixed, and the combustible powder is burned. Is easily performed.

  If combustible powder is introduced into the mobile heat reduction furnace from the combustible material introduction section provided in the secondary combustion air introduction section, the combustible powder is moved inside the furnace by the secondary combustion air introduced into the furnace. Since it becomes easy to flow and contacts the flame of a burner, the combustion efficiency of combustible powder can be improved.

  According to the present invention, by introducing combustible powder that is substantially free of ash into the furnace, the combustible powder is completely burned out in the furnace, and no dust is generated. The amount of heat input can be increased. Therefore, the heat retention in the furnace can be improved.

It is a schematic process explanatory drawing which shows the structure of a moving hearth type heating reduction furnace. (A)-(c) is a figure for demonstrating the example of the method of introduce | transducing combustible powder in a reduction furnace. It is a graph which shows the calculation result of the heat input amount to a to-be-heated material when sawdust is blown in into a furnace from the burner central axis.

  The method for producing reduced iron according to the present embodiment can be applied to a moving hearth type heating reduction furnace described below, for example, a rotary hearth type reduction furnace, but is not limited thereto, and is a fixed type. It can also be applied to a heating reduction furnace. Hereinafter, a rotary hearth type reduction furnace will be described as an example.

  In the production of reduced iron, a powder mixture of a carbonaceous reducing agent and an iron oxide-containing substance is agglomerated as a raw material mixture by directly mixing powder of a carbonaceous reducing agent and an iron oxide-containing substance or by agglomeration means. The agglomerated material is used. As the agglomeration means, in addition to using a press machine such as a briquetting press machine (cylinder press, roll press, ring roller press, etc.), an extrusion molding machine, a rolling granulator (pan pelletizer, Various known devices such as a drum pelletizer can be used.

  The shape of the agglomerated material is not particularly limited, and various shapes such as a lump shape, a granular shape, a briquette shape, a pellet shape, and a rod shape can be employed. Although the agglomerate is reduced to produce reduced iron, the specific reduction method is not particularly limited, and a known reduction furnace may be used.

  FIG. 1 is a schematic process explanatory diagram showing the configuration of a moving hearth-type heat reduction furnace, showing a rotary hearth type.

  As shown in FIG. 1, the agglomerate 1 is continuously charged into the rotary hearth 4 through the raw material charging hopper 3 in the rotary hearth type heating reduction furnace A.

  The rotary hearth 4 of the rotary hearth type heating and reducing furnace A is rotated counterclockwise and, depending on the operating conditions, makes one round in about 10 to 20 minutes, and is included in the agglomerate 1 during that time. Iron oxide is solid reduced.

  A plurality of combustion burners 5 are provided on the upper side wall and / or ceiling of the rotary hearth 4 in the reduction furnace A, and heat is supplied to the hearth by the combustion heat of the combustion burner 5 or its radiant heat.

  The agglomerate 1 charged on the rotary hearth 4 made of refractory material moves in the reduction furnace A on the hearth 4 in the circumferential direction, and the combustion heat and radiant heat from the combustion burner 5 The iron oxide in the agglomerate 1 is solid-reduced while passing through the heating zone in the reduction furnace A, becomes reduced iron, and is cooled in the downstream zone of the rotary hearth 4. It is discharged from the hearth via a hopper 8 by a discharge device 6 such as a screw. The exhaust gas in the rotary hearth 4 is discharged outside from the exhaust gas duct 7.

  FIG. 2 is a view for explaining an example of a method for introducing the combustible powder K into the reducing furnace A.

  As shown in FIG. 2A, the reduction furnace A is provided with the above-described combustion burner 5 and a secondary combustion air introduction section 10 for introducing secondary combustion air. In the example of FIG. 2A, a combustible material introducing portion 15 is provided in the combustion burner 5. The combustible powder K is introduced into the reduction furnace A together with the flame from the combustion burner 5.

  In the present embodiment, the combustible powder K is biomass or lignite. Biomass includes wood chips, paper, sawdust, flour, herbaceous material, mowing lawn, algae, food ingredient mixture, cotton, hemp, flax, UBC (modified brown coal) and hypercoal.

  Further, as shown in FIG. 2 (b), a combustible material introducing portion 15 may be provided in the secondary combustion air introducing portion 10. The combustible powder K is introduced into the reduction furnace A together with the air from the secondary combustion air introduction unit 10.

  In addition, as shown in FIG. 2 (c), the combustible material introduction part 15 may be provided separately and the combustible material powder K may be introduced into the reduction furnace A from the combustible material introduction part 15.

  As described above, in this embodiment, by introducing the combustible powder K substantially free of ash into the furnace, the combustible powder K is completely burned out in the furnace and is heated without generating dust. The amount of heat input to the object can be increased. Therefore, the heat retention in the furnace can be improved.

  In addition, by using the combustible powder K in the present embodiment, the use of fossil fuel such as heavy oil can be reduced and the cost is low.

  The combustible powder K introduced into the furnace may be either biomass or lignite, or may be combined and introduced into the furnace.

  Further, the combustible material introduction part 15 may be provided in both the combustion burner 5 and the secondary combustion air introduction part 10, or may be additionally provided separately and in addition to this.

  The present invention is not limited by the above-described embodiments, and can be implemented with appropriate modifications within a range that can be adapted to the gist of the present invention, all of which are within the technical scope of the present invention. Is included.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the following examples, and can of course be implemented with appropriate modifications within a range that can be adapted to the above-described gist. Included in the range.

  As an example, for a 2 m × 2 m × 7 m square furnace equipped with a combustion burner having a burner combustion amount of 2.9 MW, in which natural gas is used as fuel and combustion air can be injected at a ratio of 1.0. FIG. 3 shows the calculation results of the heat input to the object to be heated when sawdust is blown into the furnace from the burner central axis.

  The composition of the sawdust is as shown in Table 1, and there was almost no ash, and the one that burned out in the furnace was adopted. The average furnace temperature was 1525 ° C.

  The amount of heat input increased by 2% or more by blowing 0.6% of sawdust into the furnace with respect to the amount of burner combustion gas, and combustible powder such as sawdust that completely burns out was introduced. Even in this case, it was confirmed that the heat input greatly increased. Even when all the ash is attached to the inner wall of the furnace, it is desirable that the ash concentration is 1.3% by weight or less so that the accumulated amount of ash is less than 20 mm.

5 Combustion burner 10 Secondary combustion air introduction part 15 Combustible substance introduction part A Rotary hearth type heating reduction furnace K Combustible substance powder

Claims (6)

  Reduced iron characterized in that reduced iron is produced by introducing and burning combustible powder into a mobile heating and reducing furnace and heating and reducing a raw material mixture containing a carbonaceous reducing agent and an iron oxide-containing substance. Manufacturing method.   The method for producing reduced iron according to claim 1, wherein the ash content of the combustible powder is 1.3 wt% or less.   The method for producing reduced iron according to claim 1, wherein the combustible powder contains biomass.   The said combustible powder is a manufacturing method of the reduced iron of any one of Claims 1-3 containing lignite.   The manufacturing method of reduced iron of any one of Claims 1-4 which introduce | transduce the said combustible powder into the said mobile heating reduction furnace from the combustible material introduction part provided in the burner. The method for producing reduced iron according to any one of claims 1 to 5, wherein the combustible powder is introduced into the mobile heating reduction furnace from a combustible material introduction section provided in a secondary combustion air introduction section.

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