MXPA00004699A - Method for reprocessing steel slags and ferriferous materials - Google Patents

Abstract

The invention relates to a method for reprocessing steel slags and ferriferous materials, e.g. electric furnace slags, converter slags, fine ores, dusts from steel manufacturing, millscale for obtaining pig iron and environmentally safe slags, wherein a molten slag and an iron bath are used at a volume ratio ranging between 0.5:1 and 1.5:1, wherein carboniferous material is introduced in the bath and hot air is blown. A mixed slag is obtained from the initial slags and the ferriferous materials having alkalinity CaO/SiO2 ranging between 1.2 and 2.5 and placed in a hearth type furnace or a ladle, wherein hot air for post-combustion of CO formed from the carbon in the bath is blown with a post-combustion degree of PC=(a) (CO2 + H2O)/(CO + CO2 + H2 + H2O) between 0.70 and 0.85. The hot exhaust gases of the furnace or the ladle are evacuated tangentially to the axis of the mouth of the hot air feeding lance.

Description

PROCEDURE FOR THE RECONDITIONING OF STEEL SCRAPS AND IRON CARRIERS The invention demonstrates the procedure for the reconditioning, that is, the further treatment of steel slags and iron carriers, such as slag from electric ovens, converters, also fine minerals and powders from steelmaking, such as scale from rolling mills in order to obtain crude iron and ecologically favorable slag. From WO 96/24696 a process for the production of crude iron or steel and cement clinker from slag is known, in which liquid slags containing iron oxide have been mixed, such as, for example, slag from steel mills, with carriers of iron oxide and lime after which a ferrite slag was formed. This ferrite slag was then reduced in a reducing reactor under the formation of an iron bath and a sintering phase under carbon combustion after which the sintering phase in the form of a clinker was expelled. The slags have a relatively low heat conducting capacity and a thermal capacity of 1.5 to 2 times higher compared to iron. Essential for the economy of such a procedure is the achievable transfer of heat, that is, the so-called degree of post-combustion. This degree of post-combustion is defined here as follows: Degree of post-combustion = C02 + H20 gas phase • CO + C02 + H2 + H20 In the known procedures, until the date has only been able to ensure a degree of post - insufficient combustion. Nor is it enough in known systems to achieve an economical method, Heat transfer = 1- Ha Hb He In which H, is the enthalpy of the gas (at the temperature of the gas) Hb is the enthalpy of the gas (at the temperature of the melt) Hpc is the enthalpy of combustion (at the temperature of the melt). Degrees of thermal effectiveness well above 70% have not been achieved neither in the case of conventional technologies applied in the blast furnaces nor in other systems such as for example in the processes with swirl beds. Thus, it is already known to inject prereduced and at least partially preheated loads together with the coal in a swirl bed, in which case, under reduction of the load, the coal is gasified in a swirling layer and the sponge iron is melted and removed. Such gasification reactions in a single melt are further optimized up to the level of extraction of the desired crude iron so that no ecologically favorable slag is formed. In the previous proposals of the present successor, procedures of the kind mentioned at the beginning have already been described, aimed at obtaining crude iron and ecologically tolerable slags, in which a slag bath and an iron bath in molten condition are used, in a volume ratio between 0.5: 1 and 1.5: 1, introducing a carbon carrier in the bath and blowing a stream of hot air over it. With the known method, the initial purpose has not only been a reconditioning of steel slags, such as slags from electric furnaces, but also and in the first instance the reconditioning of slags from converters and thus only with optional quality oxygen has also been blown into the bath. Slag from converters and especially slag from LD systems (Linz-Donawitz) stand out, compared to slag from electric ovens, for a fundamentally higher basicity of CaO / SiO2 of more than 3, in most cases, whereas the slag from electric ovens has a slightly lower basicity. Considering the different possibilities, as they were marked in the previous proposals, we focused specifically on the execution of the system in a converter and used a more or less complicated blowing technology. However, fundamentally this previous procedure, by its nature, also served for use in ovens or bowls. Now the present invention is directed to improve the known procedures for the use of, above all, the slags from the electric ovens, and achieve the extraction according to the previous proposals, but with a lower expense for equipment concept. In order to solve this task, the procedure of the class indicated at the beginning fundamentally consists in that from the slag of exit and the carriers of iron a slag of mixed or slag is established mixed with a basicity of CaO / Si02 located between 1.2 and 2.5, By introducing this slag in a crucible furnace or a bowl, then a stream of hot air is blown over the material for the subsequent combustion of the CO formed from the bath carbon, with a post-combustion degree PC = \ F (C02 + H20; CO + C02 + H2 = H20) between 0.70 and 0.85 and because the hot residual gases are removed from the furnace or the bowl, in a direction tangential to the axis of the mouth of the feeder nozzle of the hot air stream. For the use of kilns or cups, equipment that has a fundamentally more favorable cost is used, and the portion of the expenses corresponding to the determination of the fire is also basically lower. Considering the circumstance that in this case it may be necessary to accept a greater degree of wear in the refractory materials without having to go to excessive investments, a fundamentally higher basicity up to 2.5 is observed as acceptable in this method according to the invention so that The slag from electric furnaces can be used immediately, specifically without any salt load or any appreciable reduction in basicity. But at the same time and within the framework of a steel factory by the electric route can be ensured a complete mastery of the output currents that are produced in these factories. In addition to the slag from electric ovens, cup slags, powders, sheeter slags and kilns are generated as waste, which can be removed or economically used immediately in combination with the process according to the invention, while at the same time achieving a liquid crude iron of the favorable cost price and that is fundamentally free of trace elements. Since in the process according to the present invention the post-combustion or post-combustion is increased to values between 0.7 and 0.85 and especially to values of the order of 0.8, the embodiment or execution of the method according to the invention is also configured in a fundamentally more simple, since it is only necessary to provide the carbon feed corresponding to the bath and ensure a corresponding mixture of slag and bath, to subsequently burn the dissolved CO in the slag then with the current of hot air that impinges on the material with a high speed. A blowing inside the material or through the oxygen or hot air material, through the bath, can be eliminated here in its entirety so that the expense for equipment can be substantially reduced. The carbon can be introduced basically through simple spears or nozzles on the floor so that the costs for the bowl or the oven are not increased fundamentally. On the other hand, carbon can also be blown in the bath, through immersion lances. In a particularly advantageous manner, the carbon can also be loaded in coarse grains directly on the melt bath, from above, whereby a bowl can be used which is stirred from its bottom or. floor. Fundamental to the efficiency of the subsequent combustion and consequently to the high degree of heat transfer and the omission of an additional heating system from the furnace or the bowl by external heating measures, is also the deviation of the hot waste gases from the furnace, according to The present invention proposes a deviation which, according to the present invention, must be carried out tangentially with respect to the axis of the nozzle or opening of the lance that feeds the hot air stream. With such a gas guidance system not only can the desired degree of subsequent combustion be ensured, but also the desired heat transition is ensured so that a whole series of waste from the electric power factories can be disposed of or exploited economically. steel, as already described initially. With advantageous effects, the process according to the present invention is carried out in such a way that the removed waste gases are mixed in another external section of subsequent combustion, with additives from the group of fine minerals., powders, sheeters of rolling mills and possibly another additional fuel, blowing the solids heated on the slag, together with the current of hot air. In this section of the post-combustion by its nature can also be fused those streams of waste that are generated in the steel electric factories, fusion that is achieved at least partially, in which case, by virtue of the adjustment of this degree of post-combustion within of the furnace or, if necessary, in the bowl located between 0.7 and 0.85, in this case a sufficient chemical energy is also contained within the waste gases in order to guarantee an effective subsequent combustion, of the class indicated, outside the furnace or outside the furnace. the bowl. In another sequence or as an alternative form, it is also possible to proceed in such a way that the residual combustion gases, which are produced in the subsequent combustion stage, are led through a heating cyclone in order to separate the solids eventually liquefied and also a heat exchanger for heating the hot air stream, whereby a particularly high energy efficiency is achieved. The waste streams, which are in a partially cold state, can be advantageously melted before loading, in which case and preferably such additives are carried out. they melt in a melting cyclone and mix in a liquid form with the basic slags, such as steel slags or those from an electric furnace, after which the mixed slag is brought to the furnace or pan and they are blowing the hot driving gases containing 02, from the melting cyclone, like a stream of hot air over the slags. An effective demarcation of the said subsequent combustion inside the furnace or in the bowl, and a corresponding convection with a greater heat transfer to the interior of the gas enclosure inside the furnace of the bowl, can be further improved because in the line for the Hot residual gases from the furnace or the bowl maintain a reduced pressure compared to that gaseous pressure prevailing in the space for the gas inside the furnace or in the bowl. As a whole, this system results in this system according to the invention, in the first line, certain advantages related to the operation of a steel manufacturing plant by the electric way, in which case materials such as the metal can be improved or passed directly to the metallurgical processors. zinc concentrate or products that contain zinc oxide, which are generated from the powders produced, making this operation in the same place. The strongly basic mining waste as well as the kiln release materials, such as those materials that are separated from the walls of the kilns, can become a very valuable clinker material and very valuable raw iron, thanks to the addition of fine acid minerals, which have a favorable price. In order to lower the basicity of the slag from an electric furnace or from a converter, slag from the blast furnaces can advantageously also be used. The invention is illustrated in the following, in greater detail, with the help of an exemplary embodiment. Electric furnace slag, pan slag, furnace dusts as well as fine minerals were used with the following compositions: Filter powder Component Portion (%) Fe, FexOy 19.2 CaO 14.3 MgO 0.0 MnO 2.4 Si02 3.9 A1203 2.6 ZnO 29.0 Ti02 0.0 Cr203 0.5 Na20 1.0 In a steel factory with electric furnaces, these use materials are generated as mentioned above, the electric furnace slag usually being generated in an amount of 10 to 12 times greater than the cup slag or filter dust. In order to lower the basicity, a fine mineral quality having the following composition was used as the acid component: For technological reasons related to the cement, a basicity of CaO with respect to Si02 and 1.5 was adjusted for the slag that was wanted to be produced and a content of A1203 located between 10 and 15% by weight. The mixing balance is calculated here as follows: (Excipient) = X • CaO (fine mineral) + CaO (mixed slag) (X) • Si02 (fine mineral) + Si02 (mixed slag) This results, regardless of the basicity of the contemplated slag (excipient) of the fine mineral portion that had to be added (X) in the following equation: X = CaO (mixed slag) - (excipient) • Si02 (mixed slag) (excipient) • Si02 (fine mineral) - CaO (fine mineral) In the case of an annual production of the steel mill of 60,000 tons per year for electric furnace slag, 5,000 tons per year of slag and 4,500 tons per year of filter powder, a mixed slag results with the following analysis: Mixed slag Component Portion (%) CaO 36 Si02 15 MgO 3.9 MnO 4.6 FeO 29 A1203 6 ZnO 2 UNCLE 0.3 Cr203 0.9 Na20 0.1 P205 0.9 CaF2 0.6 Total 99.3 C / S ( excipient) 2.4 To adjust the basicity contemplated of 1.5, 1 ton of mixed slag was blown with 1.06 tons of fine ore, resulting in an analysis of the previous slag as follows: After an optimum reduction of this slag, for example in a reductive bowl, similar to a secondary metallurgical bowl, which is rinsed by the bottom, the following slag composition was achieved with the following composition of the iron bath: Slag Component Portion (%) Mn - 3.8 Cr 0.6 P 0.4 C 4 Fe 91 In total, therefore, starting from 1 ton of previous slag, an amount of 0.386 tons of slag, as well as 0.442 tons of iron bath, highlighting the iron obtained because it contains neither copper nor zinc. By means of an intermediate refining and the formation of small quantities of highly concentrated special slags, the elements of manganese, chromium and phosphorus can be removed without any problem in a conventional manner from the aforementioned bath composition.

The separation of selective P can advantageously be carried out under reducing conditions: 2 [P] Fe + 3CaC2 - > Ca3P2 + 6 [C] Fe _ so that a crude iron with a "high chromium content" can be produced for electric furnaces. From this execution example it turns out that currents of the waste materials generated in a steel factory with an electric furnace can be mastered without any problem. In addition to the additions and powders, mentioned at the beginning, it is also possible to successfully use the melts of filter powders from those facilities that burn garbage, but in this case we must take care that they are melts of filter powders, which in a high degree are free of heavy metals. A typical composition of such filter ashes or fly ash from thermal generating plants is mentioned in the following: Ash Component Portion (%) "L.o. I." 7 Si02 24.4 A1203 11.8 Fe203 2.3 CaO 12.7 When using these volatile ashes or ashes of garbage combustion filters to lower the basicity to values between 1.5 and 1.2, it is valid, according to the calculation methods initially indicated that for each ton of slag of electric furnace should be used around 0.35 tons of the slag melt obtained from the waste combustion equipment. The slag melt, as it is made from the garbage burning equipment, had the following composition: The mixed slag obtained had the following composition: After reducing this mixed slag, the following final slag was formed, in addition to the metal bath: From 1 ton of mixed slag, 0.68 tons of slag were obtained as well as 0.23 tons of an iron bath whose orientation analysis was established as follows: Iron bath Component Portion (%) Mn 10 Cr 4.4 Cu 0.15 P 4.3 C 4 As a result of the use of the ashes obtained by the incineration or combustion of garbage, an iron bath with residual copper was now established, being able to categorize as acceptable the value of copper for a whole series of products. Also in this case it is advisable to tune the iron bath constituted in an interim manner in order to achieve at least the conversion of manganese, chromium and phosphorus into special slags, for which conventional procedures can be applied. The special slag constituted in this class of refining procedures contains relatively high portions of harmful substances, which on the other hand can be exploited separately. - In the pan or in the furnace, therefore, slags and dusts from other combustion equipment can also be discarded, such as, for example, garbage incineration plants or thermal generating plants, all without major problems, as we have already pointed out at the beginning, the system for carrying out the process according to the invention, its particularly high economic importance, in the first line, in those steel mills that work with electric ovens. The process according to the present invention can be carried out with the help of the equipment represented schematically in the drawing. Here Figure 1 ^ represents a first embodiment of an installation that serves to carry out the method according to the invention while Figure 2 is a second variant of the equipment. In Figure 1, with number 1, a crucible furnace in which the slag 2 is floating above the iron load 3 has been identified. Through the feed lance 4 a stream of hot air is blown to achieve the Subsequent combustion of the CO formed from the carbon of the bath, the hot residual gases from the furnace being removed tangentially to the axis 5 of the opening of the hot air feeder nozzle 4, through a hole 6. In the section of the post -combustión 7 the waste gases withdrawn are mixed with additives from the group of fine minerals, powders, sheeters of mills and possibly other fuels, and this material is conducted through a hot cyclone 8 to the point of separation of the solids eventually liquefied, and with the help of a heat exchanger, gane regenerator 9. In the heat exchanger, which regenerates gases, 9, cold air is heated, after which the hot air stream to the introduction lance 4 through a line identified with the number 10, so that this material is blown together with the liquified solids separated in the thermal cyclone 8, on the slag bath 2. Between the feeder lance of hot air 4 and the post-combustion section 7, in addition a powder regeneration heat exchanger 11 can also be mounted. In Figure 2 a different embodiment of the equipment according to Figure 1 is illustrated, keeping for the same parts the same reference numbers. In this configuration, the waste gases withdrawn through the orifice 6 of the furnace 1 are fed directly to a heat exchanger for the regeneration of gases, in order to heat the hot air stream. The stream of hot air is fed through a line 12 to a melt cyclone 13 in which the additives introduced through the line 17 leading to the line 12 melt. The liquefied additives are mixed in a bowl 14 with the steel slag fed through the line 15 after which the mixed slag formed inside the furnace 1 is brought, as indicated schematically with the number 16. The driving gases of the melting cyclone 13 containing 02, and they are in hot condition, they are blown through the introducer lance 4 in the form of a stream of hot air over the slag 2.

Claims (1)

1. CLAIMS A process for the reconditioning of steel slag and iron carriers, such as, for example, slag from an electric furnace or converter, fine minerals, powders from steelmaking and mill scale to obtain raw iron. and ecologically favorable slags, in which the slag bath and the iron bath, of molten condition, are used in a proportion in volumes between 0.5: 1 and 1.5: 1, and the carbon carrier is introduced into the bath and a stream of hot air is blown on it, characterized in that a mixed slag having a basicity of CaO / SiO2 between 1.2 and 2.5 is formed from the starting slags and the iron carriers, this slag being taken to an oven of crucible or a bowl, because then a stream of hot air is blown in order to achieve the subsequent combustion of the CO formed from the carbon of the bath with a degree of post-combustion PC = C02 + H20 _____ CO + C02 + H2 + H20 Located between 0.70 and 0.85 and because the hot residual gases are removed from the furnace or the bowl in a tangential direction to the axis of the mouth of the current feeder hot air. The method according to claim 1, characterized in that the removed waste gases are mixed in a subsequent combustion section with additives consisting of the group of fine minerals, powders, sheeter husks and possibly other fuels and the heated solids are blown together with the stream of hot air over the slag. The method according to claim 1 or 2, characterized in that the combustion waste gases from the post-combustion section are conducted through a thermal cyclone in order to separate the liquified solids and a heat exchanger to heat the flow hot air. The process according to claim 1, 2 or 3, characterized in that the additives are melted in the melting cyclone and mixed in liquid form with the basic slags such as, for example, steel slag or electric slag, after which the mixed slag is taken to the furnace or to the bowl and the hot driving gases, containing 02, coming from the melting cyclone, are blown as a stream of hot air over the slags. The method according to any of claims 1 to 4, characterized in that a pressure lower than that prevailing in the gas chamber of the oven or the bowl is maintained in the line designed to conduct the hot residual gases from the oven or the bowl. The process according to claims 1 to 5, characterized in that the carbon carrier is loaded in the form of coarse granules from above on the melt bath. The process according to claims 1 to 6, characterized in that blast furnace slag is added for the purpose of reducing the basicity. The process according to claims 1 to 7, characterized in that the phosphorus is separated from the metal bath under reducing conditions, with calcium carbide.