The subject of the invention is a method of steel smelting directly from iron ore in one metallurgical reactor.

Current technologies for producing steel from iron ores are p rocesses consisting of several stages: preparation of iron-bearing charge (sintering and/or pelletisation of iron ore), production of coke (coking plants), production of pig iron (blast furnaces), production of steel (oxygen converters).

The processes taking place in blast furnaces and oxygen converters are chemically opposite: a reducing atmosphere prevails in the blast furnace, resulting in the production of pig iron, while oxidising processes take place in steel furnaces, the main purpose of which is to reduce the excess amount of carbon contained in pig iron.

Due to the dwindling resources of coking coals over the next decades, alternative technologies for the production of liquid iron, apart from the blast furnace process, are being developed in recent years, referred to as coke-free metallurgy.

Polish patent description Pat.236288 discloses the method of producing steel directly from iron ore in one metallurgical reactor characterised in that the fine iron ore with a grain size of less than 3 mm, fluxes with a grain size of less than 3 mm in the amount ensuring the required basicity of the slags, and a gas reducer in the form of hydrogen or a mixture of hydrogen and carbon monoxide are blown into the reactor, and the reduction of iron oxides is carried out at a temperature of not less than 1300°C, while the desired final carbon content in the steel is controlled by introducing such an amount of carbon gas reducer in the reducing atmosphere or by introducing such amount of carbon directly for the metal bath which ensures the achievement of the assumed level of steel carburisation.

Despite the solution to the problem in the aforementioned invention, which was the reduction of CO2 emissions, there was a need to change the method of introducing the reducer, as well as change the supply of thermal energy necessary to carry out the process.

The purpose of the invention is to provide a method for the introduction of a hydrogen reducer and to provide thermal energy, which would be much more effective than the state of the art. The purpose of the invention is also to reduce the specific emission of CO2 to the atmosphere in the steelmaking process as well as to reduce the operating costs related to the production.

The essence of the invention is a method of smelting carbon steels directly from iron ore in one metallurgical reactor, consisting in introducing, by blowing, fine iron ore and fine fluxes into the reactor from the top of the reactor and a gas reducer in the form of hydrogen or hydrogen and carbon monoxide from the bottom of the reactor and reducing iron oxides in the liquid phase, while the desired final carbon content in the steel is controlled by introducing an amount of carbon directly into the metal bath which ensures that the desired level of carburisation of the steel is achieved, or by introducing a specific amount of carbon reducer in the form of coke breeze into the iron-bearing charge, characterised by the fact that the gas reducer introduced from the bottom of the reactor flows through the layer of liquid iron oxides and the thermal energy in the reactor is generated in the process of combustion of natural gas with oxygen in the upper part of the reactor, and the supplied excess of natural gas in relation to the amounts resulting from the stoichiometry of the combustion process is thermally decomposed into carbon and molecular hydrogen providing a reducing atmosphere at the bottom of the reactor.

Optionally, additional thermal energy is supplied to the metallurgical reactor via the thermal energy of the electric arc.

According to the invention, the method of producing steel directly from iron ore in one metallurgical reactor consists in introducing fine iron ore and fine fluxes into the reactor by blowing in an amount ensuring the required basicity of the slags and reducing iron oxides in the liquid phases. The reducer in the form of a mixture of hydrogen and carbon monoxide is blown in at the bottom of the reactor and flows through the liquid phases of iron oxides. The method according to the invention enables the smelting of high-carbon, medium-carbon and low-carbon steels. The desired final carbon content in the steel is adjusted by introducing such an amount of carbon directly into the metal bath which ensures that the assumed carburisation level of the steel is achieved or by introducing a specific amount of carbon reducer in the form of coke breeze into the iron-bearing charge, and any excess carbon in the smelted steel is removed using oxygen from the oxygen lance of the reactor (Fig. 1 a).

In the method according to the invention, the thermal energy necessary for melting the charge and the reduction process is supplied by blowing oxygen and natural gas into the reactor in an excess amount in relation to the amounts resulting from the stoichiometry of the combustion process; under the process temperature conditions, the excess amount of CH4 is thermally decomposed into carbon and molecular hydrogen, which provides a reducing atmosphere in the space above the metal-slag liquid phases. In the method according to the invention, thermal energy can also be generated by electric arc energy via an electrode mounted in the central part of the reactor.

In the process of the invention using a hydrogen gas reducer, a mixture of fine iron ore and fluxes is blown into the metallurgical reactor from above and iron oxides are reduced in the liquid phase. Hydrogen is the reducer, introduced from the bottom of the reactor, which flows through the melted iron oxides.

With the use of hydrogen as a reducing agent and the supply of heat using electricity, there is no carbon in the reaction reactor, which allows the smelting of ultra-low-carbon steels by introducing microalloying carbon at the final stage of the process.

The process temperature is determined by the requirements related to the kinetics of the reduction process and the liquefaction of iron.

The subject of the invention is illustrated in figures, where Fig. 1a shows a diagram of the method of smelting high-carbon, medium-carbon and low-carbon steels, while Fig. 1 b shows a diagram of the method of smelting ultra-low carbon steels.

The iron-bearing charge is blown into the closed metallurgical reactor in the form of a mixture of fine iron ore and limestone flux in an amount sufficient to ensure the required basicity of the slags together with the gas reducer, which in this example is hydrogen.

For melting 100 Mg of iron from the Lebedynski magnetite concentrate with the composition given in the table below, 143.3 Mg of the concentrate is needed, assuming iron losses amounting to 0.5 wt%. Assuming the basicity of the slag in the process at the level of CaO/SiO2 = 1.20, 7.5 Mg of CaCOs should be added to this amount of ore (the calculations do not take into account the amount of CaO needed to bind sulphur in the reduction process).

Table. Chemical composition of Lebedynski magnetite concentrate, wt%

Assuming that the Fe ₃ C>4 reduction process takes place at 1550°C with the use of hydrogen, the calculations show that in order to reduce 1 mole of Fe ₃ O4 to metallic iron according to reaction:

Fe ₃ O ₄ + 4H ₂ = 3Fe +4H ₂ O (1) a reducer excess defined by factor 2.37 is sufficient, i.e. as a result of the reaction of the components of the system defined by expression Fe3O4+9.48 H2=3Fe+9.48 H2O, one mole of magnetite is practically completely reduced to metallic iron (0.05% mole of Fe ₃ O4 is not reduced).

In relation to the assumed amount of 100 Mg of metallic iron (steel) from the Fe ₃ C>4 reduction process, 126,400 m ³ of H2 should be used in this process (temp. 1550°C) .

The equilibrium composition of the gas after reduction contains (vol%): 57.75 of H2; 42.20 of H2O. The thermal potential of these gases will be used to provide thermal energy to the reactor charge heating system.

The energy demand for the single-stage steel smelting process is covered from the methane combustion process in the upper part of the reactor, while an excess amount of methane is supplied in the lower part of the reactor, which undergoes thermal dissociation into carbon and molecular hydrogen, which ensures the reducing nature of the atmosphere directly above the surface of the metallic-oxide liquid phases.

The approximate heat balance for smelting 1 Mg of steel takes into account the following physicochemical processes: a) iron oxide reduction process, b) thermal energy of liquid iron, c) heat of slag, heat of gas and dust, heat losses and other), ad. a) thermochemical calculations show that the endothermic process of reducing FesO4 to metallic iron with hydrogen at the temperature of 1550°C consumes energy equal to 12.2 GJ/Mg of Fe, ad. b) the thermal energy necessary to heat 1 Mg of iron to 1550°C is 1 .3 GJ/Mg of Fe, ad. c) it was estimated that the energy expenditure related to the heat carried by slag, gases and dust, and thermal (and other) losses should be in the range of 20-25% of the sum of the energy of items a) and b), which is 2.7-3.4 GJ I Mg of Fe. In total, the energy expended in the process of reducing FesO4 to metallic iron at the temperature of 1550°C should not exceed 16.2-16.9 GJ/Mg (average value of 16.6 GJ/Mg).

This balance does not take into account the amount of methane fed to the system to ensure a reducing atmosphere in the reactor, due to the balancing of this energy expenditure in the further process of using the sensible and chemical heat of hydrogen and carbon (from the thermal decomposition of methane) contained in the post-reaction gases.