EA033747B1 - Method of pig iron production using romelt liquid phase reduction process - Google Patents

Abstract

The present invention relates to the pig iron production in the Romelt furnaces. Simultaneous loading of iron containing materials, fluxes and more than 5 mm sized coal fractions into the liquid slag bath of the Romelt furnace through the top loading port. Bubbling of the liquid slag bath and initiation of incomplete coal combustion are achieved by supplying air/oxygen blowing gas to the bottom tuyeres of the Romelt furnace. Oxidation of released CO and Hin the combustion zone is carried out by supplying oxygen to the top tuyeres of the Romelt furnace. The combustion rate of the gases released from the liquid slag bath is maintained at 60-85% of the maximum possible combustion rate by dividing coal into more than 5 and less than 5 mm sized fractions. The less than 5 mm sized coal fraction is crushed to less than 1 mm size and supplied to the liquid slag bath through the bottom tuyeres of the Romelt furnace together with the air/oxygen blowing gas at a rate of 400-1000 m/mof furnace area at the bottom tuyere level. A heat flow from the combustion zone to the liquid slag bath is maintained at 3-6 MW/mof liquid slag bath area. The invention provides reduction of iron loss with the slag and exclusion of uncontrolled boiling of a slag bath.

Description

The invention relates to ferrous metallurgy, namely to the production of liquid carbon intermediate and cast iron, but may find application in other industries, such as non-ferrous metallurgy, the production of building materials, etc.

A known method of producing pig iron by the Romelt liquid-phase reduction process, comprising continuously loading iron-containing materials of various mineralogical composition, all coal, lime, supplying oxygen and an oxygen-containing blast into zones above and below the slag level into one slag bath, withdrawing the formed metal, slag and gases (Romelt process / V. A. Romenets [et al.] - M.: MISiS, Publishing House Ore and Metals, 2005. p. 8).

The disadvantage of this method is the process control only on the basis of calculating the consumption of coal and oxygen according to the equations of material balance; while smelting is carried out regardless of the particle size distribution of the coals. In this case, all the coal is fed through loading holes on top of the furnace to the slag bath. As practical experiments show, during the operation of the Romelt furnace using this technology, the degree of afterburning, calculated by the composition of the carbon-containing gases leaving the furnace, СО ₂ / (СО ₂ + СО) does not exceed 0.3-0.5 at a theoretically possible value close to unity. The operation of the Romelt furnace at low levels of afterburning significantly increases energy costs and reduces productivity. At the same time, the amount of heat transferred to the slag bath and the intensity of the blast supplied to the lower tuyeres are not controlled either.

Closest to the proposed invention is the Method of controlling the Romelt process (RU 2182603, published. 05/20/2000), according to which during the smelting, the content of iron oxides in the slag is maintained and regulated at a predetermined level depending on the temperature of the slag and the gas composition by increasing / reduce the amount of coal loaded and increase / decrease the amount of oxygen supplied above the level of molten slag.

According to this method, the process control and production of pig iron is also carried out regardless of the particle size distribution of coal, and all coal is loaded on top of the furnace. At the same time, high degrees of afterburning of gas in the furnace are also not ensured.

The disadvantage of these methods is that when loading coal from above onto the slag bath, fractions of less than 3-5 mm do not reach the slag bath or are removed from it without interacting with iron oxides, soar in the afterburning zone and interact with the resulting CO ₂ and H afterburning ₂ O, reducing the degree of afterburning, the amount of heat released from the afterburning, and the transfer of heat to the bath. Moreover, the degree of afterburning does not exceed 0.3-0.5, and there is an overspending of oxygen and coal.

According to the technologies mentioned above, the heat flow from the afterburning zone to the slag bath is not taken into account and is not controlled, which should be optimized and within certain limits. Underestimation of this factor is especially dangerous when performing design calculations of Romelt furnaces, since unreliable results can be obtained without taking these factors into account.

The invention achieves the technical result, which consists in the possibility of operation of the Romelt furnace at high degrees of afterburning and the efficient use of coals containing small fractions of coal, without reducing the melting rate;

the possibility of efficient utilization of small fractions of coal due to their injection into a slag bath in the area of the lower tuyeres;

reduction of iron and slag loss to less than 5% in comparison with the melting of highly oxidized materials by the classic Romelt technology by increasing the rate of reduction of iron oxides;

eliminating the possibility of uncontrolled boiling of a slag bath;

monitoring and maintaining at an optimal level the heat flux transferred from the afterburning zone to the slag bath;

monitoring and maintaining at the required level the specific consumption of blast on the lower tuyeres.

The technical result is achieved as follows.

In the Romelt liquid-phase reduction process production method of iron, iron-containing materials, fluxes and coal fractions of more than 5 mm are simultaneously loaded into the liquid slag bath of the Romelt furnace through the upper feed opening. The bubbling of a liquid slag bath and the initiation of incomplete combustion of coal is achieved by supplying air-oxygen blast to the lower tuyeres of the Romelt furnace. The oxidation in the afterburning zone of CO and H ₂ released from the liquid slag bath of gases is carried out by supplying oxygen to the upper tuyeres of the Romelt furnace. The degree of afterburning of gases leaving the liquid slag bath is maintained at the level of 60-85% of the maximum possible degree of afterburning by separating coal into fractions of more than 5 mm and less than 5 mm.

A coal fraction of less than 5 mm is subjected to grinding to a particle size of less than 1 mm and fed into a liquid slag bath through the lower tuyeres of the Romelt furnace together with air-oxygen blast with an intensity of 400-1000 m ³ / m ^{2 the} area of the furnace at the level of the lower tuyeres. The heat flow from the afterburning zone to the liquid slag bath is provided within 3-6 MW / m ^{2 of the} surface of the liquid slag bath.

In this case, metallurgical waste in the form of sludge, dust, scale and iron ores is used as iron-containing materials.

Also, lime or calcined dolomite or silica sand or

- 1,033,747 mixtures thereof.

The degree of afterburning of gases leaving the liquid slag bath is determined by the ratio of carbon-containing components α = С0 ₂ / (С0 ₂ + С0) -100%, where CO ₂ and СО are the content in volume percent of the corresponding gases after afterburning.

In this case, additional lower tuyeres can be installed in the end and side walls of the Romelt furnace.

The amount of coal fraction of less than 1 mm supplied to additional lower tuyeres is at least 20% of the total amount of coal loaded.

The invention is illustrated in the drawing, which shows a diagram of the implementation of the method. The drawing shows a transition gate 1, a single-screen screen 2, loading chutes 3 and 4 for coal, a first vertical conveyor 5, a plant 6 for grinding coal of a particle size less than 1 mm, a second vertical conveyor 7, a feed hopper 8 coal fractions more than 5 mm, a charge hopper 9 fractions of coal less than 5 mm, liquid slag bath 10, upper tuyeres 11, lower tuyeres 12, upper feed opening 13.

In the well-known Romelt technology, part of the fine particles of coal loaded through the upper feed opening, due to the small relative density of coal, is in the afterburning area above the slag bath, and part is taken out of the furnace as dust. This is facilitated by significant gas flows both of the gases released from the bath and those generated from the blast supplied to the upper tuyeres. An example is the calculation of the gas velocity above the slag bath of an experimental Romelt furnace. With the area of the furnace at the level of the lower tuyeres of 20 m ^{2, the} emission of gases from the slag bath reached 40-60 thousand m ³ / h. Thus, given the high temperature of the gases, the linear velocity of the upward flows can be estimated at 5.4 m / s.

Coal dust interacts with the gas phase, which leads to a decrease in the degree of afterburning. This is reflected in the release of heat from afterburning, as Under conditions of incomplete afterburning and a lack of oxygen, coal burns only to CO, and the thermal effect of this reaction, which is 117 kJ / mol, is more than two times less than the thermal effect of the combustion reaction of CO and H _2, respectively, 279 kJ / mol and 251 kJ / mol.

Dustiness of gas by carbon will lead not only to an increase in the fraction of CO, but also to a redistribution of oxygen between the carbon- and hydrogen-containing components of the gas phase.

In the proposed method, these disadvantages are eliminated.

The method is as follows.

Iron-containing materials, fluxes and coal fractions of more than 5 mm are simultaneously loaded into the liquid slag bath 10 of the Romelt furnace through the upper feed opening 13. At the same time, metallurgical waste in the form of sludges, dust, scale and iron ore are used as iron-containing materials. Also used as fluxes are lime or calcined dolomite or quartz sand or a mixture thereof.

Simultaneously with the loading of iron-containing materials, fluxes and coal, air-oxygen blast is fed to the lower tuyeres 12, which initiates incomplete combustion of coal and sparging of the liquid slag bath 10.

For oxidation in the afterburning zone of CO and H ₂ released from the liquid slag bath 10, oxygen is supplied to the upper tuyeres 11 of the Romelt furnace with a purity of at least 80%.

In the Romelt process, all the main endothermic reactions of the reduction of iron and other metal oxides occur in a slag bath:

The only exothermic reaction of incomplete carbon burning

С + 1 / 2О ₂ = СО does not compensate for the heat deficit, which leads to a negative heat balance of the bath. Complete combustion of coal in a slag bath to CO ₂ by reaction

C + o ₂ = co _{2 is} impossible, because in this case, the thermodynamic conditions necessary for the reduction of iron oxide will not be provided.

In the production of pig iron from wet iron-containing material with a total Fe content of _total 50% using steam coal 65% Sf _x , the average heat consumption will be about 12.3 MJ / kg of pig iron, taking into account heat losses to the environment, while from the combustion reaction no more than 3 MJ / kg of pig iron will be released, which is insufficient to compensate for the lack of heat.

Therefore, the main heat source in the Romelt furnace is the afterburning of the released reducing gases above the slag bath and the transfer of the resulting heat to the bath. The volume of CO and H ₂ gases released from the bath is more than is necessary to eliminate the heat deficit in the slag bath, therefore, even partial afterburning of these gases allows to obtain a sufficient amount of heat. With the proper organization of the afterburning zone, enough combustion of 60-85% of the volume of gases released from the bath. An increase in heat from afterburning can be achieved by removing the floating particles of coal and, accordingly, the redistribution of all oxygen supplied above the level of slag to the combustion reaction of gases, which

- 2,033,747 is provided in the alleged patent.

Coal is fed through a gate 1 to a single-screen screen 2, where coal is divided into fractions of more than 5 mm and less than 5 mm. A large fraction of coal more than 5 mm through the second vertical container 7 is fed into the bunker 8, and from the bunker 8 into the liquid slag bath 10 through the upper loading hole 13.

Coal fractions of less than 5 mm are fed through a loading chute 3 to the first vertical conveyor 5, from where it enters the charge hopper 9. After this, a fraction of coal less than 5 mm from the charge hopper 9 enters the coal grinding unit 6, where coal fractions of less than 1 mm are obtained.

This fraction is blown into the liquid slag bath 10 through the lower tuyeres 12 or through additional tuyeres made in the end and side walls of the Romelt furnace at a height of 0.8-1.8 m from the hearth of the furnace.

Coal fractions of less than 1 mm are fed to the lower tuyeres 12 of the Romelt furnace at a blast intensity of 400-1000 m ³ / m ^{2 of} the furnace area.

When the intensity of the blast is less than 400 m ³ / m ^{2 the} area of the furnace, bubbling in a liquid slag bath is carried out in the bubble mode, which leads to insufficient intensity of mixing.

When the intensity of the blast is more than 1000 m ³ / m ^{2 the} area of the furnace, breakdowns of the jet through a liquid slag bath and a decrease in the intensity of mixing appear.

Iron oxides, falling into the layer of bubbling slag containing coal, dissolve in the slag and are reduced on coal particles mixed in the slag. The iron obtained by reduction is carbonized and, in the form of droplets of metal, is deposited on the hearth of the furnace under the influence of its own weight. Thus, three layers of melts are formed in the furnace: metal on the bottom of the furnace, a layer of calm slag between the metal and the lower tuyeres, and a layer of bubbling slag (reaction zone). The injection of finely dispersed fractions of coal significantly increases the number of centers of reduction of iron, which leads to an increase in the amount of metal obtained and increase the productivity of the unit.

When coal is divided into fractions of more than 5 mm and less than 5 mm, the degree of afterburning of the exhaust gases from the liquid slag bath 10 is maintained at a level of 60-85% of the maximum possible degree of afterburning.

The separation into fractions of ± 5 mm is due to the fact that when loading coal from above through a loading hole, a fraction of more than 5 mm falls into the slag bath, and a fraction of less than 5 mm, due to the relatively low density of coal and high gas flow velocities, soar in the afterburning zone and interact with blast oxygen upper tuyeres.

When the degree of afterburning of gases leaving the liquid slag bath, calculated by the ratio of СО ₂ / (СО ₂ + СО) -100%, less than 60%, the performance of the Romelt furnace deteriorates and the energy consumption increases.

When the degree of afterburning of gases leaving the liquid slag bath is more than 85%, the processes of dissociation of the resulting CO ₂ and H ₂ O can occur due to high temperature, which reduces the amount of heat received from afterburning, and also increases the heat loss through the walls of the furnace.

With an insufficient degree of afterburning of gases, the coal fraction of less than 5 mm is fed through the slide gate 1 through the loading chute 4 to the vertical conveyor 5 and to the installation 6 for grinding coal fractions of less than 1 mm.

The supply of coal fractions of less than 1 mm is due to the following. In the case of supplying coal with a particle size of more than 1 mm to the lower tuyeres 12 on the inner surfaces of the coal preparation and supply system, mechanical wear processes occur intensively due to the interaction of the system material with sharp edges of coal particles, and there is also a reduction in the reduction rate in the slag layer.

The amount of coal fractions less than 1 mm supplied to the additional and lower tuyeres 12 is at least 20% of the total amount of coal. With a smaller amount, an increase in the degree of afterburning is not enough to obtain a value of more than 60%, and the number of centers of nucleation of the metal phase on coal does not increase enough.

Under these conditions, a heat flow is generated from the afterburning zone to the liquid slag bath within 3-6 MW / m ^{2 of the} surface of the liquid slag bath. When the heat flux is less than 3 MW / m ^{2 of the} surface of the liquid slag bath, there is insufficient heat transfer to the slag bath from the afterburning zone and an excess of coal and oxygen is observed on the lower row of tuyeres. At a heat flux of more than 6 MW / m ^{2 of the} surface of the liquid slag bath, an increased degree of afterburning, dissociation of CO ₂ and H ₂ O, and an increase in heat loads on the furnace walls are observed.

In this case, the oxygen consumption for the upper tuyeres decreases by 10 m ³ with a decrease in the amount of coal fraction of less than 5 mm in the afterburning zone by 1 kg of fixed carbon in coal. At the same time, the increase in productivity of the Romelt furnace for cast iron will be 1.2 kg per 1 kg of blown coal, due to an increase in the number of centers of reduction of iron oxides on coal particles.

- 3 033747

Examples of the method

Example 1

The liquid slag bath Romelt furnace simultaneously charged with a mixture of iron-containing metallurgical waste (sludge, dust, scale) with an average Fe content of 50.4% and _commonly grade coal TSSH Kuznetsk coal basin with a fixed carbon content of 67.5%. In this case, a coal fraction of more than 5 mm is fed into the liquid slag bath of the Romelt furnace through the upper feed opening, and a coal fraction of less than 5 mm is subjected to grinding to a particle size of less than 1 mm. After that, a fraction of coal of less than 1 mm is blown into the liquid slag bath through the lower tuyeres and through the additional tuyeres installed in the end and side walls of the Romelt furnace together with air-oxygen blast with an intensity of 1000 m ³ / m ^{2 of} the furnace area at the level of the lower tuyeres. The degree of afterburning of gases leaving the slag bath is 60% of the maximum possible. In this way, a heat flow from the afterburning zone to the liquid slag bath of 3 MW / m ^{2 of the} surface of the liquid slag bath is provided. The amount of coal fraction of less than 1 mm supplied to the lower tuyeres is 20% of the total coal consumption. In this case, the specific consumption of coal and oxygen is 820 kg / t of pig iron and 940 m ³ / t of pig iron, respectively. Compared to loading all of the coal through the top loading port, the furnace capacity has increased by 15%.

Example 2

At the same time, iron ore with an average Fe content of _total 38.5% and grade T coal from the Kuznetsk coal basin with a fixed carbon content of 76.5% are simultaneously loaded into the liquid slag bath of the Romelt furnace. In this case, a coal fraction of more than 5 mm is fed into the liquid slag bath of the Romelt furnace through the upper feed opening, and a coal fraction of less than 5 mm is subjected to grinding to a particle size of less than 1 mm. After that, a fraction of coal of less than 1 mm is blown into the liquid slag bath through the lower tuyeres and through the additional tuyeres installed in the end and side walls of the Romelt furnace together with air-oxygen blast with an intensity of 400 m ³ / m ^{2 of} the furnace area at the level of the lower tuyeres. The degree of afterburning of gases leaving the slag bath is 85% of the maximum possible. Thus, a heat flow from the afterburning zone to the liquid slag bath of 6 MW / m ^{2 of the} surface of the liquid slag bath is provided. The amount of coal fraction less than 1 mm supplied to the lower tuyeres is 40% of the total coal consumption. The specific consumption of coal and oxygen is 980 kg / t of pig iron and 1030 m ³ / t of cast iron, respectively. Compared to loading all of the coal through the top loading port, the furnace capacity has increased by 30%.

Thus, the proposed method increases the productivity of the technology and provides savings in the consumption of coal and oxygen in comparison with the loading of coal only on top of the liquid slag bath.

Claims (6)

CLAIM 1. A method of producing pig iron by the Romelt liquid-phase reduction process, comprising simultaneously loading iron-containing materials, fluxes, and coal fractions of more than 5 mm into the liquid slag bath of the Romelt furnace through the top loading hole, sparging the liquid slag bath and initiating incomplete combustion of coal by supplying air-oxygen blast to Romelt bottom tuyeres of the furnace, the oxidation zone in the afterburning of CO and H _2, released from the liquid slag bath, by supplying oxygen to the upper tuyeres and the furnace Romelt removal of iron and slag from the oven Romelt, while the degree of afterburning of gases leaving the liquid slag bath is maintained at the level of 60-85% of the maximum possible degree of afterburning by separating coal into fractions of more than 5 mm and less than 5 mm, and the coal fraction of less than 5 mm is subjected to grinding to a particle size of less than 1 mm and fed into the liquid slag bath through the lower tuyeres of the Romelt furnace together with air-oxygen blast with an intensity of 400-1000 m ³ / m ^{2 the} area of the furnace at the level of the lower tuyeres and provide a heat flow from the afterburning zone to the liquid slag bath within 3-6 MW / m ² surface awn of a liquid slag bath. 2. The method according to claim 1, in which the iron-containing materials used waste metallurgical production in the form of sludge, dust, scale and ore. 3. The method according to claim 1, in which lime, or calcined dolomite, or quartz sand, or a mixture thereof is used as fluxes. 4. The method according to claim 1, in which the degree of afterburning of the gases leaving the liquid slag bath is determined by the ratio α = СО ₂ / (СО ₂ + СО) -100%. 5. The method according to claim 1, in which coal fractions of less than 1 mm are fed through additional lower tuyeres made in the end and side walls of the Romelt furnace. 6. The method according to claim 1, in which the amount of coal fraction of less than 1 mm supplied through additional and lower tuyeres is at least 20% of the total amount of coal.