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: 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. In US-A-3423080 is disclosed a blast furnace with inlets which are lances projecting into the furnace stack. Oxidising gases injected through the lances preheats the furnace burden. In FR-A-869065 is disclosed a blast furnace with inlets in the upper part of the stack through which recycled heated furnace gas is blown to preheat the burden. 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 accelerate 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. 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. This method, however, is too severe to permit a stable blast furnace operation with a low fuel ratio throughout a long period. It is an object of the present invention to provide stable operation of a blast furnace, with a low fuel ratio, throughout a long period. To attain the object, in accordance with the present invention, a method is provided in accordance with claim 1 hereinbelow. 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. With specific reference to Fig. 1 of the drawing, an embodiment of a blast furnace according to the present invention will now be described. 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 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 from 0.33 to 0.55 from the stock line. The reason for limiting the range of the position will now be described. 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. 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. 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. When position of the blow-in inlets for preheating gas ranges is in a range of from 0.33 to 0.55 downward from the stock line, however, this reduces further not only the fuel ratio but also the Si content in molten iron. 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 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. 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. 8 to 18 of blow-in inlets are specified 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 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. In fact, the downward slope of the blow-in inlets into the in-furnace with regard to the horizontal level is 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 There are two methods of preparing preheating gas to be considered. 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. 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. 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: A method of making iron in a blast furnace which comprises the steps of: feeding the furnace through tuyeres (12) in a lower part of the blast furnace body with a gas of 40 vol % or more oxygen, pulverised coal and a flame temperature control agent; charging the furnace with ore to a stock line (14) of the blast furnace body; providing inlet means to introduce gases into the furnace above the level of the tuyeres; setting the inlet means into the furnace wall, in the form of a peripheral arc of from 8 to 18 blow-inlets, the circle being located at a level downward from the stock line in a range of from 0.33 to 0.55 where the distance between the stock line and the level (15) of the tuyeres is 1.0; angling the blow-in inlets downwardly at an angle to the horizontal in a range of from 20° to 50°; and delivering to the blast furnace charge, through the blow-in inlets, a preheating gas which is the product of a combustion process which occurs either at the blow-in inlets or in a combustion furnace located in the neighbourhood of the blast furnace. A method according to claim 1 characterized by providing the blow-in inlets with gas burners equipped with fuel gas supply pipes, oxygen supply pipes and gas leading pipes for controlling gas temperature.

Inventors: HOTTA, HIROHISA, KAWADA, HITOSHI, OONO, YOTARO, TSUJIMOTO, KAZUHIKO, WAKIMOTO, KAZUMASA, Hotta, Hirohisa, c/o Nippon Kokan KK, Kawada, Hitoshi, c/o Nippon Kokan KK, Oono, Yotaro, c/o Nippon Kokan KK, Tsujimoto, Kazuhiko, c/o Nippon Kokan KK, Wakimoto, Kazumasa, c/o Nippon Kokan KK
Applicants: NIPPON KOKAN KABUSHIKI KAISHA
Application year: 1987
Main classification: C21B5
IPC codes: C21B5