Abstract:
A method for the continuous production of steel using metal charge material that is preheated in an upper part of a melting vessel, is then melted in a lower part of the melting vessel with fossil fuels and the molten material is continuously discharged into a treatment vessel in which the desired steel quality is adjusted while gases are introduced into the melting vessel from the exterior to afterburn the melting exhaust gases. The process gases are step-wise afterburned when ascending in the melting vessel by introducing the afterburn gases into the interior of the charge material column by way of an interior shaft that projects into the material column and in whose walls inlet openings for the gases are disposed and form afterburn planes arranged one on top of the other.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Divisional application of U.S. patent application Ser. No. 10/498,632, filed Mar. 17, 2005, now U.S. Pat. No. 7,897,100, which is a 371 of International application PCT/EP03/00123 filed Jan. 9, 2003, which claims priority of DE 102 05 660.9, filed Feb. 12, 2002, the priority of these applications is hereby claimed and these applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns a process for the continuous production of steel with the use of metal charge materials, such as scrap, sponge iron, or the like, wherein the charge materials are preheated in an upper part of a melting vessel and then melted in a lower part of the melting vessel using fossil fuels, wherein the molten metal is continuously discharged into a treatment vessel, in which the desired grade of steel is adjusted, and wherein gases are introduced into the melting vessel from the outside for post combustion of the process gases. 
     2. Description of the Related Art 
     The invention also concerns equipment for the continuous production of steel with the use of metal charge materials, which comprises a melting vessel with at least one fossil fuel burner that acts on the metal charge materials in a lower part of the melting vessel, and a treatment vessel, which is connected with the lower part of the melting vessel by a taphole, such that the molten metal is continuously discharged into the treatment vessel, in which the desired grade of steel is adjusted, such that the charge materials are preheated in an upper part of the melting vessel by the process gases, and such that gases are introduced into the melting vessel from the outside for post combustion of the process gases. In the treatment vessel, the molten iron is subjected especially to superheating and an alloying treatment to produce steel. 
     A method of this type and equipment of this type are described in DT 2 325 593. A method is described for the continuous production of steel with the use of charge materials, such as scrap, sponge iron, or the like, which are continuously melted from below by a burner lance in a shaft furnace, which serves as the melting vessel, wherein the molten metal is discharged into a heated continuous vessel, in which slag separation is carried out continuously, and wherein the material present in the vessel is superheated, and the desired steel analysis is adjusted by the addition of suitable alloying additives and deoxidation additives. The superheating and slag reduction are accomplished electrically. The continuous vessel is heated for this purpose by induction or by an electric arc. A lance-like oil/oxygen burner is inserted in the shaft furnace by means of a lance guide in such a way that it can be moved vertically into the interior of the melting vessel, and the flame produced by the burner acts on the charge material from below and continuously melts it. Air for post-combustion of the exhaust gases from the melting process, which are used to preheat the material to be melted, can be introduced through an annular gap in the casing of the shaft furnace. The interior of the melting vessel is essentially cylindrical and can have a diameter that increases slightly towards the bottom. 
     This continuous process of melting scrap by the countercurrent principle is also described in  Stahl und Eisen,  92 (1972), No. 11, p. 501. In this mode of operation, a column of scrap is melted from below with an oil/oxygen burner. The molten metal runs continuously out of the melting vessel together with the iron oxide slag that forms. At the same time, the column of scrap is replenished by continuous recharging. A problem associated with this process is that, although the sensible heat is used, the share of chemically bound exhaust gas heat remains unutilized for preheating. Moreover, the process has the problem of high iron oxidation due to the use of fossil fuels in combination with oxygen. 
     A different direction of development is described in  Stahl und Eisen  115 (1995), No. 5, p. 75. In this case, scrap is preheated in a preheating column and melted down in an iron bath reactor. Either the preheating can occur in the iron bath reactor itself before the melting, or the scrap is preheated in a basket located above the melting reactor and then allowed to fall into the reactor. During the melting, coal and oxygen are blown into the iron bath, and the exhaust gases can be post-combusted above the melt in the reactor. To minimize oxidation of the scrap during the preheating, the fuel gas is burned in stages during the preheating. 
     SUMMARY OF THE INVENTION 
     The objective of the present invention is to optimize a process of this general type and equipment of this general type with the introduction of melting energy by fossil fuels and with utilization of the chemical exhaust gas heat to preheat the charging material. 
     In accordance with the process of the invention, as the process gases ascend in the melting vessel, they are post-combusted in stages in post-combustion planes (E 1 -E 4 ) arranged one above the other, such that, to accomplish this, in addition to the post-combustion gases introduced into the column of charge materials from the outside, post-combustion gases, i.e., oxidizers, such as oxygen, air, or a mixture thereof, are also introduced or injected into the interior of the column of charge materials through an interior shaft that projects into the column of charge material. 
     Optimum post combustion with a low level of oxidation of the charge material and thus a high degree of efficiency of the utilization of the chemical heat of the exhaust gases are achieved by the combination of post combustion in stages and the introduction of post-combustion gases into the column of charge materials both from the outside and from the inside. Due to the interior shaft, fossil energy can be effectively introduced into the column of charge material, so that favorable heat transfer and lower iron oxidation are achieved. The post-combustion gas must move only short distances to achieve mixing and thus post combustion of the process gases. 
     Advantageously, the amount, type, and/or composition of the post-combustion gases is adjusted as a function of the properties of the process gases along the height of the melting vessel, preferably in each post-combustion plane or in most of the post-combustion planes, and as a function of the desired degrees of post combustion at a certain height, for example, by suitable metering of mixtures of air and oxygen. It is also proposed that the post combustion be influenced by, among other means, adjustment of the amount, type, and/or composition of the oxidizers and fossil fuels and by the position of the burner in relation to the interior shaft. 
     In particular, it is proposed that the post-combustion planes be adjusted in height by varying the arrangement of the interior shaft relative to the melting vessel and/or that they be adjusted by rotation of the interior shaft about its longitudinal axis. In this way, the post-combustion planes, which are formed by the admission of post-combustion gases from the outside and the inside, can be variably adjusted relative to one another. In accordance with an especially preferred refinement of the invention, at least a portion of the process gases to be post-combusted is removed from the column of charge materials, and these process gases are post-combusted outside the column of charge materials, especially outside the melting vessel. The post-combusted process gases are then returned to the column of charge materials in a plane above the plane from which they were removed. 
     The post combustion occurs in corresponding combustion spaces, which are separate from the column of material and into which the post-combustion gases are introduced. To this end, feed lines for the post-combustion gases open into the combustion spaces, and the post-combustion gas comes into contact with the process gases circulating through the combustion gases. Introduction of the post-combustion gases with an injector effect is especially advantageous due to an entrainment effect. 
     With respect to the equipment of the invention, the melting vessel has a centrally arranged hollow interior shaft, which extends into the melting vessel from above along the longitudinal axis of the melting vessel. This results in the formation of an annular shaft furnace. The wall of the interior shaft has inlets for post-combustion gases, which are arranged one above the other along the casing of the interior shaft and form the post-combustion planes that are arranged one above the other. The inlets are connected especially with separate feed gas lines. This makes it possible to introduce the post-combustion gases or oxidizers into the scrap column containing the charge material from the inside according to the desired post-combustion distribution. 
     Preferably, measuring instruments are provided for determining the properties of the process gases along the given height of the melting vessel, preferably in each post-combustion plane or in selected post-combustion planes, and means are provided for making corresponding adjustments of the type, amount, and/or composition of the gases being admitted for the post combustion. 
     It is proposed that the inlets arranged in a given plane in the melting vessel have a staggered arrangement in relation to two planes of inlets of the interior shaft that are arranged one below the other, i.e., post-combustion planes arranged one above the other are alternately formed by the interior shaft inlets and the inlets in the vessel wall, which can be varied by adjusting the interior shaft relative to the melting vessel. This makes it possible to adjust not only the type, amount, and composition of the post-combustion gases, but also the post-combustion planes. 
     In accordance with an especially preferred embodiment, not only the process gases formed during the melting are post-combusted to utilize the chemical energy, but also the process gases formed during the treatment of the molten metal in the treatment vessel. For this purpose, the gas spaces of the two vessels are connected with each other in a gastight manner. 
     Energy is supplied primarily by fossil fuels in combination with oxidizers, for example, a natural gas/oxygen mixture or oil/oxygen mixture without conversion to an electric form. In this regard, the treatment vessel should also be operated at least partly by means of fossil energy, while the remaining energy is supplied in the form of electric energy. 
     To achieve further reduction of undesired oxidation of the iron-bearing charge materials during a post combustion, at least part of the post combustion of the gases, preferably a large part, should be carried out in a place that is spatially separated from the column of charge material, specifically, in the post-combustion spaces or channels, which are integrated in the wall of the melting vessel or outside the melting vessel and/or in the interior shaft, and into which the feed lines for post-combustion gases open, and in which the gas emerging from the inlets, which supports the post combustion, comes into contact with the exhaust gases circulating in the channel. Preferably, these channels can also be provided in the region in which the inlets open in the wall of the interior shaft. Post combustion of the exhaust gases in the combustion spaces that are separated from the scrap column has the additional advantage that the scrap is not overheated. In accordance with an especially preferred embodiment, a combustion space extends annularly around the melting vessel. Alternatively, it is possible to provide several independent spaces, which are arranged especially side by side at the same height. In accordance with another embodiment, the combustion spaces are formed as lines, into which the process gas on a (lower) plane is drawn in, and which convey the post-combusted process gas back into the shaft on a plane situated at a higher level. The suction effect is based on the fact that the flow resistance for the process gases through the column of material is higher than the flow resistance through the lines. 
     Additional details and advantages of the invention are apparent from the dependent claims and from the following description, in which the embodiments of the invention illustrated in the drawings are explained in detail. In this connection, besides the combinations of features specified above, features alone or in other combinations are an integral part of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the drawing: 
         FIG. 1  shows a partial sectional side view of equipment in accordance with the invention for producing steel with a melting vessel and a treatment vessel. 
         FIG. 2  shows a partial section of  FIG. 1  showing the measurement and control engineering for carrying out the post combustion in stages. 
         FIG. 3  shows a cross section through the melting vessel with an interior shaft. 
         FIG. 4  shows a sectional view of a preferred embodiment of the melting vessel with an annular combustion space. 
         FIG. 5  shows a detail view of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows equipment  1  for the continuous production of steel with the use of metal charge materials, especially scrap. It consists of a melting vessel  2  and a superheating and treatment vessel  3  installed next to it, i.e., a furnace in which superheating of the melt produced in the melting vessel  2  and alloying adjustments of the steel are carried out. The melting vessel  3  comprises a shaft  4 , into which an interior shaft  5  extends gastight from above, not quite to the lower part  6 , here the base, of the shaft  4  and substantially up to a level of a taphole  10 . An annular shaft furnace is formed in this way. Hereinafter, the melting vessel  3  will be referred to as the shaft furnace. In the embodiment shown in the drawing, the vessel wall  7  of the shaft furnace has the shape of a cone whose diameter increases towards the bottom, while the interior shaft  5  has the shape of a cone with decreasing diameter towards the bottom. As a result of this expanding structure of the shaft furnace, the scrap column  8 , which is charged from above, is more mobile from top to bottom, and the free space that forms towards the bottom allows sufficient scrap to advance from top to bottom. In the meltdown zone  9 , i.e., in the lower third of the shaft furnace, the shaft furnace can become cylindrical or can even be designed with the opposite conical shape, i.e., with decreasing diameter towards the bottom. The opposite conical shape of the interior shaft  5  increases this free space towards the bottom; however, the interior shaft may also be cylindrically shaped. 
     The shaft furnace is connected with the treatment vessel  3  via a taphole  10  arranged in the lower part and a refractory seal. In the embodiment shown here, the treatment vessel  3  consists essentially of a lower molten bath vessel part  11  and an upper vessel part  12 . The process is carried out by charging scrap  8  into the shaft furnace from above. The scrap column is preheated by the hot exhaust gases  13  from the treatment vessel  3  and the shaft furnace, which flow in the opposite direction from the scrap, and is melted down in the lower part  9  of the shaft furnace by a burner  14 , which is integrated in the tip  15  of the interior shaft  5 . The molten metal  16  flows continuously into the lower molten bath vessel part  11  of the treatment vessel  3  through the taphole  10 . In the opposite direction, exhaust gases from the treatment vessel  3  can flow through the taphole  10  or through a separate gas line into the melting vessel. 
     The interior shaft  5 , which extends centrally into the scrap column  8 , has feed lines  18 ,  19  in its hollow interior space  17  and inlets  21  in its wall  20  for systematically conveying post-combustion gases or oxidizers  22  brought in through the feed lines  18  from the interior shaft  5  to the scrap column  8 . The inlets  21  are located in planes E 1 , E 2  arranged one above the other. They are arranged radially in the wall  20  of the interior shaft  5  and transversely with respect to the longitudinal axis of the interior shaft. In this way, they form post-combustion planes E 1 , E 2 , which can expand into sectors as a result of the flow of the exhaust gas. It is also possible for several inlets to be arranged directly one above the other to form a sector. The hot exhaust gases  13  flowing through the scrap  8  are post-combusted according to the given post-combustion plane E 1 , E 2  and according to the mixture of post-combustion gases  22  adjusted for the given post-combustion plane. 
     In addition, the tip  15  of the interior shaft  5  facing the bottom  6  of the shaft furnace  4  has a burner  14 , which is supplied with fossil fuels  23  by a separate feed line  19 . The fossil energy sources  23  are preferably gas/oil, which, together with oxidizers (for example, oxygen, air, or mixtures thereof) introduced through a separate line, are mixed and burned in the burner. The combustion of the fossil fuels to melt the scrap  8  is preferably carried out with less than the stoichiometric amount of oxygen, so that less oxygen is available for oxidation of the iron. 
     By feeding the gases  22  that support the post combustion and the fuels  23  necessary for melting the scrap through the interior shaft  5 , they are already preheated. To increase the degree of preheating, a heat-exchange unit  24  may be installed outside the interior shaft  5 . The gases and fuels  22 ,  23  are then heated by countercurrent heat exchange with hot exhaust gases  13 . 
     After preheating and melting of the scrap  8 , the melt  16  is continuously discharged into the treatment vessel  3 . The treatment vessel  3  is rotatably supported. After the steel treatment has been completed, the vessel is rotated about an axis of rotation  26  that is parallel to the horizontal foundation  25  to tap first the slag and then the molten steel through a taphole  27  in the lower part  11  of the vessel. To this end, the lower part  11  of the vessel is supported in a swivel mechanism  28 . It can be moved up to the melting vessel  2  by means of a movable bottom plate  25 . In the illustrated embodiment, the treatment vessel  3  is designed as an arc furnace with two electrodes  29 ,  30 , which are positioned in the furnace by a holding device  31 . However, the power may also be supplied with three-phase current through three electrodes. The energy necessary for treatment of the melt can also be introduced by fossil fuels. The treatment vessel  3  is closed by an upper vessel part  12  or a cover. A lance  32  for supplying carbon sources and/or oxygen or air is provided in the cover for carrying out the superheating and slag foaming. In addition, the vessel  3  has a charging device  34  for supplying additives for the metallurgical treatment of the melt. 
     The positioning of the post-combustion planes E 1 , E 2  in relation to the melting vessel and thus in relation to the post-combustion planes E 2 , E 4  and the properties of the emerging gases  22  are controlled or automatically regulated in the given post-combustion planes as a function of the properties of the process gases along the height of the melting vessel. This is shown in  FIG. 2 . In each post-combustion plane or in selected post-combustion planes, means  35  are provided for determining the given process gas properties at a given height of the melting vessel. These means  35  take and further convey gas samples or determine the composition and measure the temperature of the hot process gases. The process gas samples taken in the post-combustion planes can be analyzed in an analyzer  36   a . Depending on these results, which are transmitted to a computer unit  37  over instrument leads  36 , the properties of the gases  22  for the post combustion are calculated, and suitable adjustment means  39  are activated over control lines  38 . These adjustment means  39  comprise, for example, metering and mixing devices for air and oxygen, i.e., a distributor of the oxidizing agents for the individual post-combustion planes. The post combustion is controlled not only by adjustment of the parameters of the gases  22 , but also by variation of the arrangement of the interior shaft  5  relative to the shaft furnace or by variation of the position of the burner  14  in the interior shaft  5 . The interior shaft  5  can be moved along the longitudinal axis of the shaft furnace by positioning mechanisms or a positioning device  40 . In addition, turning mechanisms  41  may be provided, which allow the interior shaft  5  to be rotated about its longitudinal axis. The interior shaft  5  preferably can be rotated up to an angle of at least 0.5φ relative to the shaft furnace (see  FIG. 3 ) to allow favorable positioning of the inlets  21  in the interior shaft  5  in relation to the inlets  42  in the vessel wall  7  of the outer shaft. The inlets  42  are further discussed below. Each of the one or more burners  14  can be moved within the interior shaft  5  by positioning mechanisms  43 . 
     At the same time, measuring devices  44  for determining the position of the interior shaft  5  in relation to the shaft furnace and measuring devices  45  for determining the position of the burner  14  in the interior shaft  5  are provided. These measurement results are also transmitted to the computer unit  37  and are used to control or automatically regulate the properties of the gases  22 ,  23  for the post combustion via appropriate actuation of the positioning and turning mechanisms  40 ,  41 ,  43 . This preferably occurs in such a way that local overheating of the surface of the scrap to greater than 90% of the melting point of iron oxide is not reached in any post-combustion plane or post-combustion sector, and that the degree of post combustion of the exhaust gas emerging from the melting vessel is approximately 100%. 
     In addition to the inlets  21  in the interior shaft  5 , inlets  42  are arranged in the wall  7  of the melting vessel  4  and are connected to feed lines for post-combustion gases  22 . In this regard, the planes E 1 , E 2  and E 3 , E 4  formed by the interior shaft inlets  21  and the vessel wall inlets  42 , respectively, are offset relative to each other, so that a post-combustion plane with inlets  42  from the outside of the vessel and a post-combustion plane with inlets  21  from the inside of the interior shaft  5  alternate from bottom to top. The amount by which they are offset is up to 50% of the distance between the planes of the inlets. This offset arrangement prevents it from becoming too hot in individual places in the scrap column  8 , while other regions remain too cold, so that post combustion does not occur. The external and internal injection ports or slots are arranged in such a way that the inlets do not interfere with one another, but rather create favorable gas distribution in the scrap column by their arrangement relative to one another. In addition,  FIG. 3  illustrates a preferred configuration of the angle of the inlets  21 ,  42  relative to each other. The inlets  42  in the wall  7  of the melting vessel  2  are arranged at an angular displacement of up to 0.5φ, preferably at an angular displacement of 0.5φ, relative to the inlets  21  in the interior shaft  5 , where φ is the angle between two adjacent inlets  42  in a post-combustion plane. 
     In accordance with an especially preferred embodiment, which is illustrated in  FIGS. 4 and 5 , the wall  107  of the shaft furnace is provided with an annular channel or combustion space  146  at the height of the inlets  142 . 
     In the design shown here, this combustion space  146  consists of a bulge  147  in the vessel wall  107 , such that the interior of the combustion space  146  is separated from the interior of the shaft furnace and thus from the scrap column  8  by a partition  149  that is formed as a continuation of the inside surface  148  of the vessel wall  7 . This partition  149  is positioned at the combustion space  146  in such a way that an inlet zone  150  for process gases  113  flowing past it is formed at the bottom, and an outlet zone  151  for post-combusted gases  113 ′ is formed at the top. This allows the process gases  113  to circulate through the combustion space or channel  146  and the post combustion to occur to a large extent in the combustion space or channel  146 .  FIG. 5  shows the arrangement of the inlets  142  in the vessel wall  107  of the shaft furnace in relation to the partition  149 . The angle α formed by the opening of the inlet ports  142  or slots between the linear extension of the opening and the partition  149  can take on values between 90° and −90°. The opening angle is preferably determined in such a way that an entrainment effect is produced for the process gas flowing in. The inlet  142  can also be designed as a de Laval nozzle, i.e., a nozzle that first converges and then diverges to produce acceleration of the gases. 
     All together, the proposed process and equipment offer an effective possibility for steel production with the use of fossil energy and are therefore also of interest for use in sites with poor electric energy supply.