RU2490332C1 - Metal coating method of iron-ore raw material with obtainment of granulated cast iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: method involves dosing of iron-ore raw material, solid fuel, a binding agent and flux additives, mixing and pelletising of initial charge, drying and heat treatment of pellets in a furnace with a rotating bottom so that pelletised cast iron is obtained, cooling, crushing and separation of pelletised cast iron from slag. In dead rock of charge there provided are ratios of CaO/MgO, SiO₂/Al₂O₃ compounds within the limits of 2-5 and 4-6 respectively so that melting point of primary slag does not exceed 1400°C. The method's implementation allows improving production capacity of a unit owing to reducing iron losses and decreasing power consumption as to heat for heating of a furnace.

EFFECT: improving production efficiency of pelletised cast iron.

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Description

The invention relates to the field of ferrous and non-ferrous metallurgy and can be used in the production of granular cast iron.

A known method of metallization of ore-fuel pellets in a furnace with a rotating hearth at temperatures 1300-1350 ° C for 6-12 minutes [1].

The method allows to obtain a metallized product both from iron ores and from waste from metallurgical production with the removal of zinc, lead and alkalis from the latter. As a reducing agent, ordinary coal grades are used. The disadvantage of this method is the low quality of the metallized product, which limits its consumption as scrap in steelmaking. The low iron content (up to 70%) with an average degree of metallization of 92% is due to the fact that in the metallized product remains waste rock and coke ash.

Closest to the proposed solution in terms of technical nature and the achieved result is a method for producing granular cast iron, including dosing of iron-containing raw materials, solid fuel, binder and fluxing additives, mixing and pelletizing the resulting mixture, drying, heat treatment of oil-fuel pellets in a rotary hearth furnace for 9 -15 minutes at temperatures of 1250-1550 ° C, cooling, crushing and separation of granular iron from slag. In this case, the charge components are controlled with the formation of slag with a basicity (CaO + MgO) / SiO ₂ equal to 1.3 to 2.3 with an MgO content in the range of 5 to 13% [2].

The disadvantage of this solution is that the declared parameters of the slag in chemical composition do not take into account the influence of Al ₂ O ₃ on the most important characteristics of the slag: the melting temperature and fluidity of the slag. It is known that when producing cast iron, slag has the best mobility, in which the Al ₂ O ₃ content lies in the range from 10 to 15%. The gangue of iron ores of various mineralogical type contains Al ₂ O ₃ up to 10 percent or more. In order to avoid failure of the equipment of furnaces in the description of this method indicates the profile of operating temperatures in the range from 1250 to 1550 ° C. Calculations and data of slag state diagrams show [3] that, taking into account the declared parameters of the chemical composition of the slag when the content of Al ₂ O ₃ in the slag is from 5 to 10%, the melting point of the slag will be 1400-1500 ° C with a slag basicity of 1.3 and 1700– 1900 ° C with a basicity of 2.3. At such temperatures, operating conditions of equipment deteriorate, energy costs increase, and a pellet of refractory compounds forms in the pellets, which makes it difficult to separate cast iron from slag, leading to an increase in metal losses. This indicates that the declared parameters of the slag in chemical composition reflect the features of only one particular type of iron ore.

The objective of the invention is to increase the productivity of a furnace with a rotating hearth by reducing metal losses, reducing energy costs for heating the furnace by optimizing the composition of the charge from various mineralogical types of ores, providing a melting temperature of primary slag not higher than 1400 ° C.

The problem is solved in that in the method of metallization of iron ore raw materials with the production of granular cast iron, including dosing of iron ore, solid fuel, binder and fluxing additives, mixing and pelletizing of the original charge, drying and heat treatment of oil-fuel pellets in a rotary hearth furnace to produce granular cast iron , cooling, crushing and separation of granular pig iron from slag, in contrast to the closest analogue, the components of the initial charge are dosed with ensuring Wearing CaO / MgO compounds, SiO ₂ / Al ₂ O ₃ therein in the range 2-5 and 4-6, respectively.

A distinctive feature of the proposed method is that the component composition of the charge from any type of ore for the production of ore-fuel pellets is formed on the basis of obtaining the chemical composition of primary slag with a melting point of not higher than 1400 ° C. To do this, using slag state diagrams in the CaO-MgO-SiO ₂ -Al ₂ O _{3 system} , pyroxene regions were determined (Al ₂ O ₃ - 5-15%, SiO ₂ - 45-60%, CaO - 10-30%, MgO - 5-20%) and melilite (Al ₂ O ₃ - 5-15%, SiO ₂ - 35-50%, CaO - 30-50%, MgO - 5-20%) with melting points of slag within 1300- 1400 ° C. In the areas of pyroxene and melilite, the optimal ratios of the main slag-forming components CaO / MgO, SiO ₂ / Al ₂ O ₃ are in the range of 2-5 and 4-6, respectively. Knowing the consumption of ore and solid fuel for metallization, the weighted average chemical composition of the slag-forming components of waste rock ore and solid fuel ash is calculated. Solving the system of equations, they find the consumption of the necessary fluxing additive (limestone, lime, dolomitic limestone, bauxite or quartzite), which provides the indicated ratios of the main slag-forming components CaO / MgO, SiO ₂ / Al ₂ O ₃ in the initial charge for the formation of primary slag. The proposed ratios of the main slag-forming components in the initial charge for determining the chemical composition of primary slag with a melting point of no higher than 1400 ° C allow us to choose a fluxing additive and its consumption for all types of ores in order to reduce the slag yield (increase the capacity of the unit for producing granular cast iron), as well as take into account the cost of a particular additive in order to reduce the cost of production of granular cast iron. Thus, the high-temperature reduction of iron to a metallized state with the formation of cast iron granules due to carbonization of iron in combination with the low melting point of primary slag makes it easy to separate cast iron from slag, reducing iron loss.

The proposed method is as follows.

Control the chemical composition of the components of the mixture for the production of pellets. They are determined in a certain experimental way by the consumption of solid fuel and a binder material from the total mass of the charge. By calculation, using information on the melting point of slags from the state diagrams in the CaO-MgO-SiO ₂ -Al ₂ O _{3 system} , the fluxing agent consumption is determined in compliance with the requirements for the CaO / MgO, SiO ₂ / Al ₂ O ₃ ratios in the initial charge in limits 2-5 and 4-6, respectively. Further mixing, pelletizing the mixture, drying and heat treatment of the pellets, cooling, crushing and separation of granular iron from slag is carried out in a known manner.

The experiments on the production of granular cast iron from iron ore raw materials were carried out in a Nabertherm chamber heating furnace, which made it possible to control the set heating rate to 1800 ° C. The change in the ratios of CaO / MgO, SiO ₂ / Al ₂ O ₃ in the initial charge was controlled by the flow rate of quartzite and limestone, determined by calculation using slag state diagrams in the CaO-MgO-SiO ₂ -Al ₂ O _{3 system} .

The research results are shown in the table.

The analysis of the presented results shows not only the fundamental possibility of producing granular iron from iron ore according to the proposed solution (A), but also the improvement of technical and economic indicators of the process of producing granular iron in comparison with the prototype (B):

- reduce energy costs for heat to heat the furnace for the production of granular cast iron;

- increase the productivity of the unit for the production of granular cast iron by reducing iron loss.

Exceeding the declared limits worsens the technical and economic indicators of the process of producing granular iron

Information sources

1. J Jumbo, H. Tanaka, Y. Kuwata, New coal-based ironmaking Fastmet / Fastmelt. 4 ^th European Coke and Ironmaking Congress. June 19-22, 2000, Paris La Defanse, France / Proceedings, Volume II, p. 492-497.

2. RF patent №2301834, IPC СВВ 13/08.

3. The formation and properties of blast furnace slag. Zhilo N.L., M., Metallurgy, 1974, 120 p.

Claims (1)

The method of metallization of iron ore raw materials to produce granular cast iron, including dosing of iron ore, solid fuel, binder and fluxing additives, mixing and pelletizing of the initial charge, drying and heat treatment of oil-fuel pellets in a rotary hearth furnace to produce granular cast iron, cooling, crushing and separation of granular iron cast iron from slag, characterized in that the dosage of the components of the initial charge is provided with the ratios of the compounds CaO / MgO and SiO ₂ / Al ₂ O ₃ in it within 2-5 and 4-6, respectively.