Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-02-04
2002-05-28
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S384000, C075S561000, C075S540000, C065S020000
Reexamination Certificate
active
06395054
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for producing pozzolanes, synthetic blast furnace slags, belite or alite clinkers as well as pig iron alloys from oxidic slags by reducing the oxidized liquid slags above an iron bath. The invention also relates to an arrangement for carrying out said process.
2. Related Art
German Auslegeschrift No. 26 48 290 describes a process for treating iron-containing metallurgical slags, which essentially resides in mixing blast furnace slag with steel works slag in order to obtain an end product having a suitable composition. In doing so, it is particularly advantageous to carry out the mixing process through an oxygen feed lance designed as an agitator for oxidizing the iron granules and producing a homogenous mixture. The synthetic slag produced exhibits physical properties superior to those of the blast furnace slag, thus being excellently apt for granulation. The free lime residues approximately correspond to those of the blast furnace slag.
German Patent No. 26 11 889 mentions a process for producing hydraulic binders from metallurgical wastes and lime. In an integrated steel making plant about 400 kg of metallurgical wastes are formed per ton of pig iron on the production route from ore to steel, 48% being blast furnace slag and 35% being steel works slag. The balance is comprised of metallurgical debris, sludges and dusts. The idea underlying that invention resides in mixing such metallurgical wastes with lime at appropriate weight ratios in the liquid state and quenching the ready melt to form granulates in order to produce a cement clinker. Basically, all of the converters known in a steel making plant are suitable for mixing and melting while supplying fuel and oxygen. The bottom-blowing OBM converter is, however, particularly advantageous, its bottom tuyeres being suitable for introducing fuel and fine lime. The melting procedure is effected in an oxidizing manner, the oxides being present in the finished melt in the dissolved state.
A process for producing cement from metallurgical slags is known from South-African Patent Specification 94/0521. According to that process, the acidic blast furnace slags are mixed with the basic steel works slags in the liquid state at high temperatures exceeding 1700° C. In order to produce an advantageous cement clinker, the mixing ratio may range between 30% and 80% blast furnace slag and between 20% and 70% converter slag. According to that invention, the mixed slag melt is slowly cooled down to a temperature of 1000° C. in a first step and, after this, more rapidly in a second step, the solidified end product being ground afterwards.
South-African Patent Specification 94/05222 shows and describes a process for producing pig iron and cement clinker. There is provided a melter gasifier comprising a fluidized bed of coal, in which the necessary energy is generated by supplying oxygen, an iron bath comprising a slag layer being present therebelow. At first, limestone and iron ore are charged into a preheating shaft. There, they are dried and calcined and finally sintered together to calcium ferrite to the major extent before getting into the melter gasifier. The heat for that preheating shaft is generated by burning the offgas from the melter gasifier by means of preheated air. The iron melt from the reduced iron ore collecting within the melter gasifier and the liquid slag in cement clinker composition are removed from the melter gasifier in the liquid state. It is in the sense of that invention to introduce into the melter gasifier toxic waste substances containing, for instance, dioxin, furan, PCB and chlorides. Liquid steel works converter slag may likewise be added in an amount acceptable for the production of cement clinker.
Another process for producing steel and hydraulically active binders, i.e., cement is described in Austrian Patent No. 400 037. The idea of that invention resides in refining pig iron by adding steel slag and utilizing the high content of iron oxide of the steel slag in order to thereby eliminate carbon and silicon from the pig iron. The steel slag was, for instance, united with 0.5 weight portions of liquid pig iron and that mixture was maintained at 1660° C. for six hours, thereby having been able to reduce the FeO and MnO contents of the steel slag from 30.5% to 10.5%. The final slag obtained may be used as a cement clinker.
When processing oxidic slags, chromium-oxide-containing slags, in particular, constitute problems in the production of cement grinding admixtures since the chromium content of such slags would have to lie substantially below 500 ppm. In connection with the parameters required from a slag-metallurgical point of view for working up oxidic slags, it has been recognized that the iron oxide content of an iron bath used for reduction may be of importance. With different charging materials, reduction above an iron bath results in end products incapable of being precisely controlled and, in particular, when using chromium-oxide-containing slags the necessary dechroming cannot be readily ensured with an iron bath. It is known to blow carbon into the iron bath, wherein it has, however, been proved that too high a carbon content will result in local overheatings and negative reactions in the course of reduction. Precise process control has not yet been readily feasible because of the parameters hitherto observed in the reduction of oxidic slags.
SUMMARY OF THE INVENTION
The invention aims at providing a simple and economical procedure using conventional reactors, such as, for instance, bottom-blowing converters without applying non-proven blowing technologies and nozzling technologies, which enables the values required for effective dechroming to be precisely observed, it being primarily aimed at carrying out the process rapidly and in a simple manner. The economy is to be enhanced, in particular, by avoiding regional overheatings as well as excessive foaming. Furthermore, the blowing in of carbon and oxygen is to be ensured in a manner that refining of the pig iron during coal blowing is avoided with conventional nozzling and blowing technologies while simultaneously reducing the respective quantities, thereby preventing coal from being blown through and iron from being discharged as well as overfoaming during the running process.
To accomplish this object, the process according to the invention essentially resides in the blowing of carbon into the iron bath through submerged tuyeres in order to maintain a carbon content of between 2.5 and 4.6% by weight. By the fact that the carbon content is kept within narrow limits ranging between 2.5 and 4.6% by weight, oversaturation and hence floating of carbon involving the risk of subsequent burning are avoided on the boundary layer, on the one hand. In addition, dechroming is observed to proceed in a surprisingly rapid manner by keeping the carbon content within the indicated limits. While dechroming reactions so far have taken 15 to 30 minutes, it has surprisingly been shown that dechroming can be completed within few minutes when observing the concrete limit values indicated for the carbon content. In an advantageous manner, the process is carried out by adjusting the carbon content to between 2.5 and 3.5% by weight.
In a particularly advantageous manner, the height of the iron bath is adjusted to between 300 and 1200 mm, wherein, upon exceeding of an iron bath height of 1200 mm, pig iron is tapped and the amount of carbon blown in is controlled as a function of a measuring probe. By adjusting the height of the iron bath to between 300 and 1200 mm, operation may be effected at normal pressure by means of conventional tuyeres without involving the risk of blowing through. By using conventional tuyere technologies, well-tested pressure controls may be applied to ensure that the amounts of oxygen and carbon can actually be controlled with a view to safely maintaining the desired carbon values within the iron bath.
The process of the invention a allows for the simple cont
"Holderbank" Financiere Glarus AG
King Roy
McGuthy-Banks Tima
Pillsbury & Winthrop LLP
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