What is converter steelmaking? And optimizing converter steelmaking process

Converter steelmaking uses molten iron, scrap steel, and ferroalloys as the main raw materials. It does not rely on external energy sources, but relies on the physical heat of the molten iron itself and the heat generated by the chemical reaction between the components of the molten iron to complete the steelmaking process in the converter. Converters are divided into acidic and alkaline types according to refractory materials, and top-blown, bottom-blown, and side-blown according to the location where the gas is blown into the furnace; they are divided into air converters and oxygen converters according to the type of gas. Alkaline oxygen top-blown and top-bottom combined-blown converters are the most commonly used steelmaking equipment due to their fast production speed, large output, high single-furnace output, low cost, and low investment. Converters are mainly used for the production of carbon steel, alloy steel, and the smelting of copper and nickel.

Optimizing converter steelmaking process

The various indicators of the converter steelmaking process depend on the chemical composition of the molten iron, and the main requirements for the molten iron are low sulfur content (less than 0.03%), correspondingly high silicon content (0.7%-0.9%), and manganese content (0.8%-1.0%) required for optimized slag making.

Analysis of the physical and chemical laws and dynamic characteristics of the desulfurization process at various stages of iron and steelmaking shows that, in terms of power, it is easier to ensure desulfurization reaction in molten iron than in molten steel, because sulfur has higher activity under conditions of higher carbon content and lower oxidation degree. However, desulfurization is difficult in blast furnace ironmaking, because in a series of complex oxidation-reduction reactions in the blast furnace, the energy of various thermodynamic conditions of deep desulfurization will inevitably increase the silicon content and thus lead to increased consumption of lime and coke and reduced production. Therefore, the production of low-sulfur iron requires careful planning of the process, the use of furnace materials with the least sulfur content and the preparation of high-basicity mixed slag.

Desulfurization is also ineffective in converter blowing, because the steel slag system cannot reach an equilibrium state, and the sulfur distribution coefficient between slag and steel is only 2-7 due to the high oxidation degree and low carbon content of the molten pool. Such a low sulfur distribution coefficient makes it difficult to achieve deep desulfurization in converter smelting, and leads to huge technical and economic consumption of steelmaking production. Neither in blast furnace ironmaking nor in converter steelmaking can the thermodynamic conditions required for effective desulfurization of metals be guaranteed. Therefore, it is technically and economically undesirable to conduct deep desulfurization research in blast furnace ironmaking and converter steelmaking. The reasonable approach is to separate the desulfurization process from the blast furnace and converter. This can simplify the sintering-blast furnace-converter production process and reduce production costs. Separating desulfurization from the blast furnace and converter makes desulfurization outside the blast furnace an important process link in the design of large-scale integrated steel plants. While smelting low-silicon iron, it is no longer necessary to carry out expensive desiliconization outside the blast furnace to ensure refining in the converter. The low original silicon content of molten iron can also reduce the manganese content. The role of manganese in oxygen converter steelmaking is very important. It determines the conditions required for early slag formation and regulates the oxidation degree of molten steel before tapping. Long-term practice has shown that it is necessary to try to keep the manganese in the molten iron at a level of 0.8%-1.0%, so manganese must be added to the sintering mixture, which increases the cost. The manganese balance analysis of the sintering-blast furnace-converter process shows that the reduction of manganese in the blast furnace and then oxidation in the converter leads to irreparable huge losses of manganese raw materials and manganese itself, and also adds a lot of trouble to the operation of each production process.

When the blowing is stopped under the condition of very low carbon content (0.05%-0.07%), the influence of oxidation degree is so great that the final manganese content will be set within a very narrow range, which is actually rarely related to the original manganese content of the molten iron. Under such conditions, although the original manganese content of the molten iron is 0.5%-1.2%, the final manganese content of the steel is actually the same (0.07%-0.11%). Therefore, under the conditions of contemporary converter steelmaking technology (each furnace has a blowing operation), it is unnecessary to use manganese-containing raw materials in the sintering mixture to increase the original manganese content of the molten iron. It is more reasonable to smelt low-manganese iron. At the same time, in order to save the amount of low-manganese iron used for deoxidation in converter steelmaking, it is of great significance to study the effect of directly using manganese ore. Comparison of process indicators obtained by industrial balance calculation of many furnaces shows that, compared with steelmaking with molten iron containing 1.13% manganese, the former can save 15.3kg of manganese ore per ton of pig iron. In addition, it can reduce the consumption of ferromanganese by 1.3kg/t steel, lime by 5kg/t, and oxygen by 2.17m3/t, and can greatly shorten the blowing time.

Low silicon and manganese content in molten iron and no need for desulfurization will change the slag-making mechanism and dynamic characteristics, because lime consumption decreases, slag volume decreases, and slag basicity and oxidation degree increase. Under such conditions, the refining function of slag is limited to dephosphorization of molten iron. In this way, slag can be used multiple times in the converter smelting itself, making the slag have a high refining capacity.

Based on this principle, a new converter steelmaking process has been developed, that is, the late slag is used multiple times (3-5 times) in the converter steelmaking itself (circular slag making). This process can reduce lime consumption and iron loss in slag. Early creation of high-basicity oxide slag and low silicon and manganese content can provide strong power required for deep dephosphorization of molten steel.

Converter steelmaking new technology: Intelligent one-click converter steelmaking >>