A blast furnace method

Abstract

 A blast furnace comprising: a blast furnace body (11); tuyeres (12) set in a lower part of the blast furnace body through which tuyeres gas or 40 vol.% or more oxygen is blown in; and blow-in inlets (13) for preheating gas set in a range of 0.15 to 0.60 downward from a stock line (14) of the blast furnace body where the distance between the stock line and a tuyere nose level (15) equals 1. The blow-in inlets are set in one or multiple levels of the blast furnace body, and slope downward with an angle of 20 to 50° with regard to the horizontal level for introducing preheating gas. The blow-in inlets are equipped with burners having fuel gas supply pipes, oxygen supply pipes and gas control pipes for temperature control gas.

Description

[0001] The present invention relates to a blast furnace for iron-making, and more particularly, to blowing-in of preheating gas to preheat burdens introduced into a blast furnace.

[0002] In the conventional blast furnace operation for producing pig iron from iron ores, a hot air blast has been dependent mainly on blowing-in through tuyeres almost without exception. Nitrogen, occupying 79% of blast air content, takes no part in reduction, but contributes to the transfer of considerable heat energy to burdens piled between a level of and the stock line of the blast furnace to accelate the gas reduction. In other words, nitrogen provides additional heat energy to cokes which work as a reduction agent and as a heat source. Therefore, it is particularly effective in preheating burdens existing in the upper portion of furnace shaft, and so there has been no need to supply heat for preheating the burdens.

[0003] Recently, in order to raise productivity in blast furnace operation, or make use of furnace top gas material for synthetic chemical products, various methods for blast furnace operation wherein blast gas blown in through the tuyeres is mainly composed of oxygen have been proposed. For example, a method is disclosed in a Japanese Patent Application Laid Open (KOKAI) No. 159104/85 wherein:

(1) Through a furnace top, burdens composed mainly of iron ores and cokes are charged into a blast furnace;

(2) Through furnace tuyeres, pure oxygen, pulverized coal and temperature control gas which prevents flame temperature at the tuyere nose from rising are blown in;

(3) Through an intermediate level of the blast furnace, preheating gas which is substantially free from nitrogen is blown in to preheat the burdens; and

(4) By means of the pure oxygen blown in, the cokes included in the burdens are burned to melt and reduce the iron ores charged as well as to generate a blast gas which is substantially free from nitrogen from the furnace top.

[0004] This method, however, is too hard to last a stable blast furnace operation with a low fuel ratio throughout a long period.

[0005] It is an object of the present invention to provide a blast furnace which allows a stable operation with a low fuel ratio throughout a long period.

[0006] To attain the object, in accordance with the present invention, a blast furnace is provided, which comprises:
    a blast furnace body;
    tuyeres set in a lower part of the blast furnace body through which tuyeres gas of 40 vol.% or more oxygen is blown in; and
    blow-in inlets for preheating gas set in a range of 0.15 to 0.60 downward from a stock line where a distance between the stock line and a level of a tuyere nose is equal to 1.0.

[0007] The object and other objects and advantages of the present invention will become more apparent from the detailed description to follow, taken in conjunction with the appended drawings.

Fig. 1 is a sectional vertical view of a blast furnace of the present invention;

Fig. 2 is a horizontal end view of the blast furnace, taken on line II-II in Fig. 1, according to the present invention;

Fig. 3 is a graphic representation showing relation of relative position of blow-in inlets to fuel ratio of the blast furnace according to the present invention;

Fig. 4 is a graphic representation showing relation of relative position of blow-in inlets to Si content in molten iron; and

Fig. 5 is a schematic sectional view of a burner of the present invention.

[0008] With specific reference to Fig. 1 of the drawing, an embodiment of a blast furnace according to the present invention will now be described.

[0009] Fig. 1 shows a vertical sectional view illustrating a blast furnace of the present invention. Burdens composed of iron ores, cokes and fluxes are charged into blast furnace until they pile up to a predetermined level of stock line 14. Tuyeres 12 are set in blast furnace body 11. Through tuyeres 12, gas of 40 vol.% or more oxygen, pulverized coal and flame temperature control agent are blown in into the blast furnace. Blow-in inlets 13 for introducing preheat gas are set in a level at 0.50 apart from the stock line where a distance from the stock line through the level of the tuyeres is equal to 1.0. The blow-in inlets constitute a set consisting of sixteen inlets set in a single level, and have a downward slope with an angle of 25° with respect to the horizontal level. Through these blow-in inlets 13, preheating gas is introduced into the blast furnace to preheat the burdens. Thus the gas of 40 vol.% or more oxygen blown in allows cokes and pulverized coal to combust perfectly and thanks to the generated high temperature reduction gas, iron ores are melted and reduced to pig iron and slag. Fig. 2 is a horizontal end view taken on line II-II in Fig. 1. 16 blow-in inlets 13 are set, in an equal interval, one another on the peripheral circle.

Position of Blown-in Inlets

[0010] In the embodiment, the position of blow-in inlets is set at the level of 0.50 downward from a stock line where a distance between the stock line and a level of the tuyere nose equals 1.0. The position, however, can be set at any point of a range of 0.15 to 0.60 downward from the stock line. The position range is preferably 0.30 to 0.55 from the stock line.

[0011] The reason for limiting the range of the position will now be described.

[0012] Fig. 3 graphically represent relation of a relative position of blow-in inlets 13, to a fuel ratio in blast furnace operation. In the abscissa, a ratio of a distance from a stock line to a position of the blow-­in inlets is shown where a distance between the stock line and the level of the tuyere nose equals 1.0. Fig. 4 graphically shows relation of a relative position of blow-in inlets 13, for introducing preheating gas to Si content in molten pig iron. In the abscissa, similarly to Fig. 3, a ratio of a distance between a stock line and a position of the blow-in inlets is shown where a distance from the stock line and the level of the blow-in inlets equals 1.0.

[0013] As seen from Fig. 3, in the range of 0.15 to 0.60 downward from the stock line where a distance between the stock line and the level of the tuyere nose equals 1, fuel ratio is low enough to be in the range 500 to 600 kg/ton., molten pig iron, and, in addition, trouble occurrence is also infrequent. If the blow-in inlets are set in a position of less than 0.15 downward from the stock line, decrease of molten iron temperature or damage of wearing plates occurs in the case that a blast furnace is operated at a fuel ratio of 650 kg/ton., molten pig iron or less. If the blow-in inlets are set in a position of over 0.60 from the stock line, decrease of molten iron temperature or hanging occurs. When the blow-in inlets are set in a position of less than 0.15 or more than 0.60 from the stock line, it is impossible to maintain a stable blast furnace operation throughout a long period unless the blast furnace is operated at a fuel ratio of more than 700 kg/ton., molten pig iron.

[0014] As recognized from Fig. 4, when the position of the blow-in inlets is set at 0.15 to 0.60 downward from the stock line, Si content in molten iron is reduced to almost 0.30 wt.% or less. This is quite advantageous to the blast furnace operation, since desiliconization after tapping of molten iron becomes unnecessary.

[0015] The position of the blow-in inlets for preheating gas ranges is preferably 0.33 to 0.55 downward from the stock line. This range reduces further not only the fuel ratio but also the Si content in molten iron.

[0016] Thanks to limiting the position range of blowing in preheating gas as described in the foregoing, reduction of the fuel ratio, prevention of operation trouble and production of low Si molten iron can be attained.

Levels of Blow-in Inlets and Number thereof in Each Level

[0017] Preheating gas is blown-in, based on the results of measuring burden temperature or gas temperature by means of probes provided within the intermediate portion of the furnace shaft. The blow-in of the preheating gas is blown in through a single level or multiple levels of the blown-in inlets. In the case of the blowing through the multiple levels of the blow-in inlets, blow-in inlets of each level set in peripheral circle of the furnace wall are divided into some zone groups, and then, if gas amount and gas temperature is varied simultaneously between an upper group and a lower zone group which are vertically positioned in the same zone, the effect in preheating comes out by far quicker than in the case of the blowing control through the single-level of the blow-in inlets. In the case of the multiple levels of the blow-in inlets, it is preferable to design the arrangement of the blow-in inlets so as to allow gas amount or gas temperature to be changed every level or between blown-in inlets adjacent to each other on the same level. In this arrangement, various optional controls can be carried out. In addition, in the case of blowing in through the multiple levels of the blow-in inlets, it is preferable that each of the blow-in inlets is positioned so that they are staggered parallel to one another in relation to up and down levels in view of allowing gas to flow up uniformly along the periphery of the furnace wall.

[0018] When the same amount gas is blown in without change of temperature, it is desirable to blow in preheating gas of high temperature through branch pipes deriving from a ring-shaped pipe. These blow-in inlets of every level are not specifically limited in number. 8 to 18 of blow-in inlets are preferable so as to allow gas constituent and temperature prevailing near the furnace wall to become almost homogeneous in the vicinity of the stock line level. Furthermore, it is preferable if the different levels of the blow-in inlets are 1 to 4 levels in number.

Angle of Blow-in Inlets

[0019] It is preferable that an angle of downward slope of the blow-in inlets to be set in the blast furnace body is larger than a repose angle of burdens. This is because powdery particles of burdens block openings of the blow-in inlets. The downward slope of the blow-in inlets into the in-furnace with regard to the horizontal level is preferably in the range 20 to 50°. If the downward slope is less than 20°, the powdery particles of burdens block the openings of the blow-in inlets. On the other hand, it is useless to let the downward slope be more than 50°, considering that the repose angle of the burdens is 45 to 50° at the most. In addition, more than 50° downward slope is undesirable in view of protecting a furnace body, since, due to this obtuse angle, blow-in holes become large.

Preparation of Preheating Gas

[0020] There are two methods of preparing preheating gas to be considered.

[0021] One is a method wherein preheating gas is generated, by means of furnace top gas generated from a blast furnace and oxygen, in a combustion furnace built in the neighbourhood of the blast furnace. In carrying out this method, it is recommendable that in order to blow-in preheating gas uniformly into a blast furnace, hot blast leading pipe is allowed to go up to the furnace shaft level and still to connect to a fireproofed heavy ring-shaped pipe, which are further connected, by means of a manifold to every blow-in inlet.

[0022] In another method, gas burners having a fuel gas supply pipe, an oxygen supply pipe and a gas temperature control gas supply pipe are set at the blow-in inlets to introduce preheating gas into the blast furnace. Every burner independently controls temperature and amount of preheating gas by controlling fuel gas amount and oxygen gas amount. Those transfer pipes leading to the burners are not required to be fireproofed. In this method different from the first method wherein hot blast is transfered from a large-scaled combustion furnace, a burner is set at every blow-in inlet and gas temperature and amount can be freely and simply controlled at every of the blow-in inlets. Furthermore, there is no need for laying a heavy ring-shaped hot blast pipe on the furnace shaft. In operation, quick response to movement of furnace conditions can be practiced.

[0023] Fig. 5 schematically illustrates a sectional view of a burner to be used for the present invention. Either of fuel gas supply pipe 21 and oxygen supply pipe 22 is connected to burner body 28 in such a manner as gas flow amount can be freely controlled. Pilot burner 29 is set at a portion where oxygen jets out. The outer side of the burner body is covered with sheet iron shell. Gas supply pipe 25 is also jointed to burner body 28 for controlling freely temperature of gas generated in the burner. Pipes for cooling water are composed of water feed pipe 23 and water drain pipe 24.

Claims

1. A blast furnace comprising:
      a blast furnace body (11); and
      tuyeres (12) set in a lower part of the blast furance body through which tuyeres gas of 40 vol.% or more oxygen is blown in;
      characterized by blow-in inlets (13) for preheating gas set in a range of 0.15 to 0.60 downward from a stock line (14) of the blast furnace body where the distance between the stock line and the level (15) of a tuyere nose equals 1.

2. A blast furnace according to claim 1, characterized in that the blow-in inlets include being set in a range of 0.30 to 0.55 of said distance.

3. A blast furnace according to claim 1 or 2, characterized in that the blow-in inlets include being set in a single level of the blast furnace body.

4. A blast furnace according to claim 1 or 2, characterized in that the blow-in inlets include being set in two or more different levels of the blast furnace body.

5. A blast furnace according to any one of claims 1 to 4, characterized in that the blow-in inlets include being set in with a sloping angle of 20 to 50° with regard to the horizontal level line on the vertical plane.

6. A blast furnace according to any one of claims 1 to 5, characterized in that the blow-in inlets include having gas burners equipped with fuel gas supply pipes, oxygen supply pipes and gas leading pipes for controlling gas temperature.

Drawing