METHOD FOR PRODUCING SLAG HAVING A DESIRED QUALITY

Abstract

A method is disclosed for generating slag having desired characteristics.

Claims

1. A method for generating slag of desired characteristics in the production of pig iron, with steps as follows: a) heating iron oxide in a direct reduction plant, so that with a reducing agent present a majority of the iron oxide is reduced to iron and an iron-containing intermediate is formed; b) heating the iron-containing intermediate in a reactor arrangement, to give pig iron and the slag; c) analyzing, via an analysis unit, the iron-containing intermediate and/or the slag which deposits during the further heating of the iron-containing intermediate; at least one of: d1) determining a property of an additive to be added to the iron-containing intermediate during the heating, depending on the analysis, in order to alter the composition of the slag, and adding the additive during the heating, to give the slag of the desired characteristics; and/or d2) recognizing that the slag requires a thermal treatment to give the slag having the desired characteristics, and initiating the thermal treatment.

2. The method as claimed in claim 1, wherein the direct reduction plant comprises a feed for hydrogen as reducing agent.

3. The method as claimed in claim 2, wherein the reactor arrangement comprises a smelter having a reducing atmosphere.

4. The method as claimed in claim 3, wherein the direct reduction plant is configured to heat the iron oxide up to a temperature of between 900 C. and 1100 C.

5. The method as claimed in claim 4, wherein an analysis unit is used which is configured during the analysis to determine an actual composition of the iron-containing intermediate and/or of the slag in the reactor unit and to compare it with a desired target composition of the slag and to adjust the properties of the additive depending on the difference between actual composition and target composition.

6. The method as claimed in claim 5, wherein a control unit is used which is configured to determine, as property of the additive, an amount of the additive and a composition of the additive.

7. The method as claimed in claim 6, wherein a control unit is used which is configured to take account, for the target characteristics of the slag, of any selection from the following features in order to alter the actual characteristics of the slag: a desired chemical composition of the granulated slag, a desired physical property of the granulated slag, a mineralogical property of the granulated slag.

8. The method as claimed in claim 7, wherein the smelter has an opening for introducing raw material into the smelter; wherein an analysis unit is used which is configured to analyze the slag after the introduction of the raw material.

9. The method as claimed in claim 8, wherein a control unit is used which is configured to select the amount of the additive such that the slag has a basicity of 1 to 5.5.

10. The method as claimed in claim 9, wherein the reactor arrangement has a first reactor which is configured to receive and to heat the iron-containing intermediate to give the iron and the slag, and wherein the reactor arrangement has a second reactor which is configured to receive the slag from the first reactor; where a control unit is used which is configured to introduce the additive into the second reactor and/or to initiate the thermal treatment of the slag in the second reactor, to give the slag having the desired characteristics.

11. The method as claimed in claim 10, wherein the second reactor is configured to atomize the slag to give atomized slag, the atomized slag having a particle size of 1 to 100 m.

12. The method as claimed in claim 11, wherein the second reactor is configured a mineral building material, more particularly a binder; wherein the control unit is configured to introduce cement, as part of the additive, into the second reactor; wherein the second reactor is configured to mix the atomized slag and the cement with one another, the atomized slag being mixed with cement in a ratio of 36:64 to 95:5, to give the mineral building material, whose 28-d standard strength is at least 30 N/mm.sup.2.

Description

[0045] Preferred exemplary embodiments of the present invention are elucidated below with reference to the attached drawings, in which:

[0046] FIG. 1: contrasts the conventional blast furnace (FIG. 1a) with an exemplary embodiment of the smelting furnace (FIG. 1b), in each case in a schematic sectional representation;

[0047] FIG. 2: shows an exemplary embodiment of the smelting furnace from FIG. 1b;

[0048] FIG. 3: shows a further exemplary embodiment of the smelting furnace from FIG. 1b, which can also be combined with the exemplary embodiment from FIG. 2;

[0049] FIG. 4: shows a schematic representation of a ternary diagram of the principal constituents of the slag for the cement industry.

[0050] Ahead of further elucidation below of exemplary embodiments of the present invention in detail, using the drawings, it is noted that identical, functionally alike or equivalent elements, objects and/or structures across the various figures have been provided with the same reference signs, and so the descriptions of these elements depicted in different exemplary embodiments can be interchanged with one another and/or applied to one another.

[0051] FIG. 1 contrasts a conventional blast furnace 20a (FIG. 1a) with a smelting furnace 20b (FIG. 1b) which comprises a direct reduction plant 21a and a reactor arrangement 21b, represented here as a smelter. Both plants each have a material feed 22a, 22b, through which components including the iron oxide to be smelted enter the blast furnace. In the case of the blast furnace, the coke may also be added via this route. The smelting process is divided into different zones. A preheating zone 24a, 24b is followed by a reduction zone 26a, 26b, in which the major part of the reduction of the iron oxide to iron takes place. In the carbonizing zone 28a, 28b, a portion of the iron becomes enriched with carbon. The zones described so far are located in the direct reduction plant 21a of the smelting furnace. Below the carbonizing zone in the blast furnace, and in the smelter in the smelting furnace, there is also the smelting zone, in which the temperature is high enough for the iron to liquefy and separate from the likewise liquid slag. The liquid iron and the liquid slag may be withdrawn through tapping holes 32a, 32b, 32b.

[0052] The blast furnace 20a additionally has a feed 34 for hot blasts, while the direct reduction plant 21a has a feed 36a, 36b for a reduction gas, hydrogen or carbon monoxide for example. The smelter 21b comprises a main opening 38, through which an iron-containing intermediate 39 passes from the direct reduction plant into the smelter 21b. The smelter 21b additionally comprises an opening 40, through which an additive can be introduced into the smelter. If the additive is to contain different substances, there may be one opening provided per substance. Alternatively, the substances may be mixed beforehand to give the additive, and then enter the smelter through an opening in the form of a mixed additive. On the bottom of the smelter, furthermore, there is a pool of slag 42 and iron 44. The openings, however, are advantageously designed such that the smelter 21b carries out the heating in the absence of air. This means that the direct reduction plant can be connected securely to the smelter so that the iron-containing intermediate enters the smelter without air contact.

[0053] Because the smelter is a separate assembly from the direct reduction plant, it is now possible, in contrast to the blast furnace, to withdraw a sample of the slag and/or of the iron-containing intermediate 39 directly in the smelter before the withdrawal of the slag. Alternatively, the sample may even be taken from the direct reduction plant itself. The sample can be analyzed for its characteristics in an analysis unit 43. Based on the result of analysis, a control unit 45 ascertains the quality of the additive. Via signal line 51a, the control unit is able to produce the additive and introduce it into the reactor arrangement, more particularly the smelter. Additionally or alternatively, the control unit 45 may also, via a further signal line 51a, set a temperature of the smelter. It is thus possible to carry out thermal treatment of the melt by operation of a predetermined temperature curve, for example.

[0054] The smelting furnace 20b has the advantage, in contrast to a direct reduction plant in combination with an electric arc furnace operating under an oxidizing atmosphere, for example, that the further processing operation of an iron works attached to the blast furnace can also be used for the smelting furnace. Hence the iron can be refined into steel in a converter. The liquid steel may be desulfurized in a ladle furnace and adjusted in its quality and then shaped by means of a continuous casting plant.

[0055] FIG. 2 shows the representation of the smelting furnace 20b from FIG. 1b in an exemplary embodiment. The exemplary embodiment additionally comprises a feed 52 for raw material into the smelter. The feed 52 may be configured as a return conduit 52a from the direct reduction furnace 21a, to pass the raw material from the direct reduction furnace into the smelter. If the raw material is not directly suitable for being introduced into the smelter, it is also possible for it to be subjected to an aftertreatment beforehand. The blown introduction of the reduction gas has the effect in particular of swirling up furnace dust. This dust can be captured and optionally preprocessed (e.g., pressed to form pellets or filtered) and passed into the smelter. Additionally or alternatively, the feed comprises an external feed 52b for raw material. There, for example, furnace dust collected on the iron works site, or else raw material from other industries, can be introduced into the smelter.

[0056] FIG. 3 shows an alternative exemplary embodiment of the smelting furnace 20b from FIG. 1b. Here, the reactor arrangement 21b has a two-stage construction. A first reactor 54a, presently the smelter, already shown in FIG. 1b and FIG. 2, is supplemented by a second reactor 54b. The second reactor 54b then receives the liquid slag from the first reactor, which can be processed further in the second reactor 54b. This makes it possible to carry out further processing of the slag with greater degrees of freedom, since there is no need to take account of the liquid iron.

[0057] Furthermore, it is also possible to combine the feed for the raw material from FIG. 2 with the division of the reactor arrangement from FIG. 3.

[0058] FIG. 4 shows a schematic ternary diagram, which provides only an outline of the concentrations of the principal fractions of the slag for the cement industry. On the bottom side of the triangle, the fraction of CaO (calcium oxide) and MgO (magnesium oxide) is plotted. On the left-hand side, the fraction of SiO.sub.2 (silicon oxide) is plotted. On the right-hand side, the fraction of Al.sub.2O.sub.3 (aluminum oxide) and Fe.sub.2O.sub.3 (iron oxide) is plotted. The gangue 46 contained in the iron oxide may have a broad spectrum of substance fractions. For instance, illustratively, the CaO+MgO fraction may vary between around 10% to around 30%, while the SiO.sub.2 fraction varies between around 30% and around 70% and also the Al.sub.2O.sub.3 and Fe.sub.2O.sub.3 fraction varies between around 5% and around 55%. The objective, then, is to analyze the actual composition of the gangue and which substances must be added to the gangue in order to obtain a defined slag. Illustratively, compositions for slag sand 48 and Portland cement 50 are shown. In other words, by admixing an additive, which may comprise a plurality of substances at different concentrations, a homogeneous slag is generated, fundamentally on the basis of the gangue, with this slag having the physical composition, for example, of slag sand or Portland cement. It must be borne in mind here, however, that other physical properties of the slag as well, such as viscosity or the formation of a sufficient glass phase on solidification, are retained.

[0059] An advantage of the smelting furnace disclosed and of the corresponding method is that the existing limitation on slag composition to a composition characterized by a particularly low melting temperature is removed. It is now possible to operate the smelting furnace in principle without confinement of its degrees of freedom, in particular, but not limited to chemical, physical and mineralogical characteristics of the slag, both in the fixed time profile and in the time profile. Accordingly, the arrows in FIG. 4 indicate that, starting from the gangue 46, any desired composition of the slag may be obtained.

[0060] Certain aspects have been described in connection with an apparatus. It should nevertheless be understood that these aspects also constitute a description of the corresponding method, and so a block or a component of an apparatus is also understood to be a corresponding method step or a feature of a method step. In analogy to this, aspects described in connection with one or as one method step also constitute a description of a corresponding block or detail or feature of a corresponding apparatus.

[0061] The exemplary embodiments described above represent merely an illustration of the principles of the present invention. It will be appreciated that modifications and variations of the details and arrangements described herein will be clear to others in the art. The intention is therefore that the invention should be restricted solely by the scope of protection of the subsequent claims and not by the specific details presented herein on the basis of the description and the elucidation of the exemplary embodiments.

LIST OF REFERENCE SIGNS

[0062] 20a blast furnace [0063] 20b smelting furnace [0064] 21a direct reduction plant [0065] 21b reactor arrangement [0066] 22 material feed [0067] 24 preheating zone [0068] 26 reduction zone [0069] 28 carbonizing zone [0070] 32 tapping holes [0071] 34 feed for blasts [0072] 36 feed for reaction gas [0073] 38 main opening of the reactor arrangement [0074] 39 iron-containing intermediate [0075] 40 opening for adding the additive [0076] 42 slag [0077] 43 analysis unit [0078] 44 iron [0079] 45 control unit [0080] 46 gangue [0081] 48 slag sand [0082] 50 Portland cement [0083] 51 signal line of the control unit [0084] 52 feed for raw material [0085] 54a first reactor [0086] 54b second reactor