ABSTRACKT

RELEVANCE OF THE TOPIC

The degree of desulphurization of steel at a given composition of slag and its quantity is not determined by consumption of gas and power mixing. Mixing of argon intensifies mass transfer of sulfur from metal to slag. Dependence of the mass transfer of sulfur from power Ks mixing (according to IRSID) is shown in Fig. 1a. The value of Ks is also dependent on the initial content of sulfur in the metal (Fig. 1b). According to laboratory experiments, under certain hydrodynamic conditions, with high sulfur content in the metal to about 0,030% the value of Ks increases, reaches a maximum and then decreases again. Ceteris paribus a decisive influence on the degree of desulphurisation and the final sulfur content in steel has a number of refining slag. To obtain the specified content of sulfur in the metal required amount of slag {qshl, kg/100 kg (%)}, can be calculated by the equation:

qsl = {100 ([S] n - [S] a)} / {LS [S] to - (S) n}
where [S] n and [S] k - initial and final sulfur content in the metal; LS - coefficient of sulfur distribution between slag and metal; (S) n - initial content of sulfur in the slag are induced.

Fig. 1 - Dependence of the mass transfer coefficient of sulfur (Ks) on the power of stirring the metal in the ladle (a) and the sulfur content in steel (b).

The sulfur content in the metal <0,005% (degree of desulphurization> = 80%) is achieved when you hover the slag with a high desulfurizing ability (Ls> = 100) in an amount not less than 4%. To receive no more than 0,010-0,015% S (for the degree of desulfurization of about 50%) is sufficient guidance slag in an amount of 1-2%. When Ls> = 150 Number of slag in the ladle in order to achieve very low sulfur content in steel is comparable to the respective costs and expenses in processing the metal expensive synthetic shlakom.Odnako on PPC, as a result of metal heating by electric arcs, somewhat changed the role of slag, which should be in addition to removing sulfur, ensure steady burning electric arcs for the normal mode of heating the metal to reduce heat loss and heat and cover the bucket with the exhaust gases. The presence of silicon in the steel reduces the activity of oxygen in the metal, helping to enlarge Ls, and thus a more complete transition of sulfur from metal to slag. When processing low carbon steel content (FeO + MnO) in slag is usually higher, which reduces the value of Ls, and attained a degree of desulfurization.

Modern steel production requires the responsible use of high purity metal content of harmful impurities, particularly sulfur (<0,001 - 0,003%). Currently, very low sulfur content in the metal most often achieved by desulphurization unit furnace - ladle (AIC). The high degree of desulfurization have on agriculture is achieved only under conditions of intensive mixing of metal and slag with argon. Argon with blowing does not dissolve, so the volume of liquid steel produced a large number of bubbles that rapidly stirred metal and carried to the surface of nonmetallic inclusions. Mixing of argon intensity sified mass transfer of sulfur from metal to slag. The equations of the kinetics of desulfurization at time t:

Form of the equation reflects the speed limit, due mainly to the transfer of sulfur in the liquid metal phase, and is unfair to all the usual low concentrations of sulfur in the metal ([S] <0,05%); liquid slag, for the same throughout the volume of metal values [S]. Thus, it is necessary that the duration of homogenization was less than the rate of mass transfer to the interface. For installations of various sizes and volumes of liquid phases obtained a satisfactory description of the reactions of the metal-slag during desulfurization in the ladle with the stirring with inert gas, expressed in the following form:

Mixing energy is proportional to the gas flow rate. The figure shows the influence of specific gas mixing or gas flow rate on the kinetic coefficient is given for a hypothetical desulfurization ladle - furnace capacity of 220t with a diameter of 3.8 m. The shaded area defined for bucket-furnace capacity of 60 tons, BAD installation capacity of 50 tons, bucket 150 and 250 tons.

The figure also shows the data of refining steel in an electric furnace with argon gas refining. These results show that the kinetic coefficient of desulfurization is a function of specific energy of mixing surface. There was no dependence of its value on the size of the bucket or the mass melting.

Optimization of the technology to install desulfurization ladle furnace, taking into account the existing characteristics of each plant allows for the normal processing cycle time for PPC (<40 - 50 min) to the production of steel with any regulated low sulfur content, including the production of very low sulfur (not more than 0,001 - 0,003 % S) steels respective destination. Normal mixing does not provide such energy of mixing as a gas, for normal operating conditions. For the typical energy of mixing, the value is 1 * 10-3 m s-1 * - 3 * 3.10 m * s-1. With such a low value of the kinetic coefficient of the intensity of mixing is not sufficient for high-speed de-sulfuratsii. Industry studies indicate a need for a gas mixing for obtaining satisfactory rates of desulfurization.

1. Производство стали на агрегате ковш-печь / Д.А. Дюдкин, С.Ю. Бать, С.Е. Гринберг, С.Н. Маринцев // Донецк: ООО «Юго-Восток. Лтд». – 2003.– 300 с.
2. Григорян В.А. Физико-химические расчеты электросталеплавильных процессов / В.А. Григорян, А.Я. Стомахин, А.Г. Пономаренко. – М.: Металлургия. – 1989. – 288 с.
3. Внепечная десульфурация стали / Г. Грунер, Ф. Барденхойер, Х. Роммерсвинкер и др. // Черные металлы. – 1976. – № 20. – С. 23 – 27.
4. Смирнов Н.А. Оптимизация технологии десульфурации стали на установке ковш-печь / Н.А. Смирнов // Электрометаллургия. – 2004. – № 1. – С. 20 – 28.