RU2533239C2 - Blast-furnace fusion of alkaline materials - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy and may be used for fusion of alkali-containing charges in blast furnaces. Proposed process comprises charging the mix iron ore portion, coke and additives via mouth into furnace, heating, reducing and fusing of said mix, intermittent tap of iron and slag and control over iron composition and slag basicity. To remove alkalis from the furnace it is changed to operation for 16 to 24 hours at lower basicity of slags in CaO/SiO₂ by 0.1-0.2 unit than under normal furnace operating conditions. Periodicity is defined from relationship between the change in intensity of alkali yield from furnace at lower basicity operation and the change in yield intensity under normal operating conditions.

EFFECT: efficient removal of alkali from blast furnace.

9 dwg, 4 tbl, 2 ex

Description

The invention relates to the field of ferrous metallurgy and can be used in blast furnace production during the melting of alkali-containing blends.

A known method of blast-furnace smelting of alkali and zinc-containing blends [1], including loading a charge containing zinc and alkali, blowing, temperature control and outlet gas; form a buffer layer by loading fractioned slag crushed stone and coke into the blast furnace, lower the level of the mound to the horizon with a gas temperature of 750-800 ° C, and to prevent overheating of the metal structures of the top of the blast furnace and the alkali and zinc vapor to solidify on the top, the gas is cooled to temperature 480-500 ° C by supplying water to the top space.

The disadvantages of this method are:

- a significant deviation from the main technological regime;

- a significant decrease in the intensity of the blast furnace for a long time and, as a result, loss of production;

- increase in alkali supply due to loading fractional slag gravel with a high alkali content (up to 2.0%) into blast furnaces, since it is obtained from blast furnace slag;

- additional consumption of coke for the smelting of waste rock (fractionated slag crushed stone);

- the use of blown sludge and blast furnace dust with a high alkali content in the total flow and the lack of the possibility of their separation leads to re-involvement in the sintering production of alkali removed from the furnaces during the "blowing";

- increase in total costs for the production of pig iron.

As you know, the bulk of the alkali from the furnace leaves with slag (up to 97%), and with blast furnace dust and sludge the yield is only 4.4-2.4% of the total alkali output.

Blast furnace slag is the main carrier of alkalis removed from the blast furnace. The chemical composition and amount of slag determine its absorption capacity in relation to alkalis. An increase in the basicity of slag is accompanied by a decrease in the activity of silica in it, the amount of alkalis bound to it, and hence their content in the slag.

The closest technical solution to the proposed method is a method for blast-furnace smelting of alkali-containing mixtures [2], which includes loading into the furnace through the top of the iron-ore part of the charge, coke and additives, heating, recovery and melting of the mixture, periodic release of cast iron and slag, monitoring the composition of cast iron and slag, moreover, the basicity of the slag CaO / SiO _{2 is} maintained in the range of 0.7-0.9 units.

The disadvantage of this method is that a decrease in the basicity of the slag is accompanied by a decrease in its desulfurizing ability. A decrease in the CaO content in slags and a decrease in basicity lead to an increase in the sulfur content in pig iron and a decrease in its quality. The sulfur content in pig iron limits the lower limit of slag basicity to the requirements of the current technical specifications for the sulfur content in pig iron at each enterprise.

The work on acidic slag, considered as an effective way to solve the alkaline problem, with all its benefits due to high demands on the quality of cast iron, is complicated by the need for non-instantaneous desulphurization of cast iron, which is also an economic problem.

The basis of the invention is the task of increasing the efficiency of removal of alkalis from a furnace with slag in order to reduce the amount of circulating alkalis in the furnace, which have a destructive effect on the refractory lining of the furnace and adversely affect iron ore materials and coke in the blast furnace, leading to an increase in coke consumption and decrease in pig iron production , as well as the task of producing cast iron of the required quality.

In conditions when the alkali supply cannot be reduced, and the process of their accumulation in the column of materials is unremovable, the only real way to reduce the harmful effects on the condition of the blast furnace and its performance is to periodically remove the accumulated mass of alkali.

The technical problem to which the invention is directed is to increase the technical and economic indicators of the operation of furnaces by optimizing the physicochemical properties of slags by periodically changing its composition (changing the CaO content in slags and changing the basicity of slag).

The technical result is achieved by the fact that in the proposed method for blast-furnace smelting of alkali-containing materials, including loading into the furnace through the top of the iron ore part of the charge, coke and additives, heating, reducing and melting the mixture, periodically releasing cast iron and slag, monitoring the composition of cast iron and slag basicity, according to the invention , periodically translate the operation of the furnace for 16-24 hours with a reduced basicity of the slag CaO / SiO ₂ 0.1-0.2 units lower than in the normal operation of the furnace, and the frequency of alkali removal from the furnace is determined by the ratio of the change in the intensity of alkali output from the furnace during operation with a reduced basicity of slags to the change in the intensity of alkali output during operation on ordinary slags:

where PU is the frequency of alkali removal, days;

VS ^{↓ В} - slag yield on average per output during the period of operation on slag with reduced basicity, kg / t;

N _i ^{↓ B} - the number of releases during the period of work on slag with reduced basicity, pcs .;

VS ^{↑ В} - slag yield on average per output during the period of work on slags with usual basicity, kg / t;

N _gr - the number of issues on schedule on the blast furnace, pcs./day;

- изменение содержания щелочей в среднем за выпуск в период работы на шлаках с пониженной основностью, %, определяют по соотношению $${\overline{U}}^{\downarrow \mathrm{AT}}$$

- the change in alkali content on average for the output during the period of operation on slag with reduced basicity,%, is determined by the ratio

where Щ _i ^{↓ B} - alkali content on the i-th issue during the period of work on slag with reduced basicity,%;

Щ ₁ ^{↓ B} - alkali content on the 1st issue during the period of work on slag with reduced basicity,%;

- изменение содержания щелочей в среднем за выпуск в период работы на шлаках с обычной основностью, %, определяют по соотношению $${\overline{U}}^{\uparrow \mathrm{AT}}$$

- the change in alkali content on average over the release during the period of work on slags with the usual basicity,%, is determined by the ratio

where Щ ₁ ^{↑ B} is the alkali content on the 1st issue during the period of work on slags with the usual basicity,%;

Щ _i ^{↑ B} - alkali content on the i-th issue during the period of work on slags with the usual basicity,%;

N _i ^{↑ B} - the number of releases during the period of work on slags with the usual basicity, pcs.

The method includes loading alkali-containing materials (fluxed sinter, unfluxed pellets, additives, coke) through the top, heating, reducing and melting the mixture, periodically releasing pig iron and slag, monitoring the composition of pig iron and slag, periodically changing the basicity of the slag according to CaO / SiO ₂ with normal basicity 0.95-1.05 units lowered by 0.1-0.2 units. within 16-24 hours.

The normal operation of the furnace is a mode in which the basicity of the slag (slag mode) ensures a smooth running of the furnace, the normal condition of the hearth and the production of iron-conditioned pig iron in accordance with current regulatory documents, while the values of slag with a normal basicity depending on existing raw material conditions for each specific workshop or unit) is CaO / SiO ₂ = 0.95-1.05 units.

There are several technological methods for reducing the basicity of slag and CaO content in slag in blast furnaces: reducing the CaO supply by reducing the basicity of the sinter, replacing part of the agglomerate with non-fluxed pellets, diluting the slag by using raw ore or quartzite in the blast furnace charge. To go to work on slag with reduced basicity, the calculated basicity of slag is reduced by using one of these methods.

Experimental periods with alternating operating modes of the furnace on slag with reduced basicity (acidic slag) and slag with normal basicity are selected.

The frequency of alkali removal from the furnace is determined by the ratio of the change in the intensity of alkali output from the furnace during the period of operation with a reduced basicity of slags to the change in the intensity of alkali output during the period of operation on ordinary slags.

To do this, it is necessary to take slag samples at the outlets and determine its chemical composition (including alkali content) and basicity.

The alkali content is determined on the 1st and i-th issue (on the last issue in the experimental periods) when working with reduced basicity and when working on ordinary basicity. Determine the change in alkali content on average per release, then the additional alkali output on average per release for the experimental period with reduced basicity and the decrease in alkali yield on average per release for the experimental period with normal basicity. After that, the frequency of alkali removal from the furnace is determined from the ratio of the change in the intensity of alkali exit from the furnace during the period of operation with the reduced basicity of slags to the change in the intensity of alkali output during the period of operation on ordinary slags.

Typically, for 16-24 hours on blast furnaces, the number of issues is 10-15. The output of slag at the outlet depends on the composition of the charge and the iron content in the charge. Typically, the slag yield is 280-400 kg / t of pig iron.

The duration of operation of the furnace on slag of reduced basicity less than 16 hours will not make it possible to remove a sufficient amount of alkali from the furnace, and the duration of operation on slag of reduced basicity more than 24 hours will increase the sulfur content in cast iron and reduce its quality. Decrease in basicity of slag by less than 0.1 units. not enough for a more intense alkali output with slag, and a decrease in basicity of more than 0.2 units. will lead to a significant increase in the sulfur content in cast iron and a deterioration in its quality.

The method was carried out as follows.

Example 1. Blast furnace A (volume 1370 m ³ ).

The blast furnace operated on fluxed agglomerate (71%) and non-fluxed pellets of the Sokolovsko-Sarbaisky GOK (29%) with a calculated slag basicity of CaO / SiO ₂ = 1.02 units. The thermal regime and blast parameters of the furnace were maintained in accordance with the technological map (Si = 0.65-0.75%).

To increase the alkali yield, the furnace was switched to slag with a reduced basicity (to acidic slag). To this end, the calculated basicity of the slag for CaO / SiO _{2 was} reduced from 1.02 to 0.93 units. due to loading in the furnace ore of the Mikhailovsky GOK in the amount of 0.7 tons per feed. After 22 hours, the Mikhailovsky raw ore was removed from the charge, as a result of which the calculated basicity of CaO / SiO ₂ slag increased from 0.93 to 1.02 units, that is, they switched to normal basic slags.

The chemical composition of the slag during operation on acidic slag is presented in table 1 and during operation on conventional slag is presented in table 2. The frequency of production of melting products is in accordance with the schedule in 40-50 minutes after closing the previous release, the duration of releases is usually 50-60 min Sampling of slag in blast furnaces for determining the chemical composition is not carried out at each outlet. In accordance with the technological instruction, slag samples are sent twice a shift from the first and third releases to the laboratory for chemical analysis (in connection with this, the numbers of the releases where the chemical composition of the slag was not determined are not presented in the tables).

In the experimental period, the actual basicity of the slag for CaO / SiO ₂ varied from 0.94 to 0.89 units.

The alkali content in the experimental period at the first release is 1.858%, and after 14 releases the value is 2.266%. The change in alkali content on average per release is (2.266-1.858) / 14 = 0.029%. An additional estimated alkali output per output is (with an average actual slag output during the test period 347 kg / t of pig iron) 0.029 * 347/100 = 0.101 kg / t of cast iron.

Upon the transition of the furnace to normal operation, the actual slag basicity changed from 0.90 to 1.05 units.

The alkali content in the experimental period at the first release is 2.250%, and after 42 releases the value is 1.832%. The change in alkali content on average per release is (2.250-1.832) / 42 = 0.010%. The decrease in alkali output per output is 0.010 * 341/100 = 0.034 kg / t of pig iron (with an average slag output over a period of 341 kg / t of cast iron).

We determine the frequency of alkali removal from the furnace: 0.101 ∗ 14 / 0.034 / 14 = 3.0 days, where the second number 14 is the number of releases according to the schedule per day.

Thus, based on the results obtained under these conditions, it is suggested that at least once every 3 days on a blast furnace, it is possible to switch over to work with reduced CaO / SiO ₂ basicity by 0, within 16-24 hours (two or three shifts), 1-0.2 units lower than in normal oven operation.

Example 2. Blast furnace C (volume 2014 m ³ ).

The blast furnace operated on fluxed sinter (66.9%), unfluxed pellets of the Sokolovsko-Sarbaisky GOK (32.2%) and manganese ore (0.8%) with an estimated basic slag CaO / SiO ₂ = 1.01 units. The thermal regime and blast parameters of the furnace were maintained in accordance with the technological map (Si = 0.65-0.75%).

To increase the alkali yield, the furnace was switched to slag with a reduced basicity (to acidic slag). For this purpose, the calculated basicity of the slag for CaO / SiO _{2 was} reduced from 1.01 to 0.92 units. due to the loading in the furnace of quartzite in an amount of 0.4 tons per feed. After (approximately) 20 hours, quartzite was removed from the charge, as a result of which the calculated basicity of the slag for CaO / SiO ₂ increased from 0.92 to 1.01 units, that is, they switched to slags of the usual basicity. The actual change in slag basicity with a change in the calculated slag basicity is shown in Fig. 4. The chemical composition of slags during operation on acidic slags is presented in table 3 and during operation on ordinary slags is presented in table 4. The frequency of production of smelting products is in accordance with the schedule 40-50 minutes after closing the previous release, the duration of releases is usually 50-60 min Sampling of slags and determination of their chemical composition in the experimental periods was performed from each release.

In the experimental period, the actual basicity of the slag for CaO / SiO ₂ changed from 0.99 to 0.89 units.

The alkali content in the experimental period at the first release is 2.250%, and after 13 releases it is 3.420%. The change in alkali content on average per release is (3,420-2,250) / 13 = 0.090%. An additional alkali output per output is (with an average actual slag output for the test period of 340 kg / t of cast iron) 0.090 * 340/100 = 0.306 kg / t of cast iron.

When the furnace operation switched to normal mode, the actual slag basicity changed from 0.92 to 1.04 units.

The alkali content in the experimental period at the first release is 2.528%, and after 31 releases it is 2.040%. The change in alkali content on average per release is (2.528-2.040) / 31 = 0.016%. The decrease in alkali output per output is 0.016 * 335/100 = 0.054 kg / t of pig iron (with an average slag output over a period of 335 kg / t of cast iron).

We determine the frequency of alkali removal from the furnace: 0.306 * 13 / 0.054 / 14 = 5.3 days, where the number 14 is the number of releases according to the schedule per day.

Thus, based on the results obtained under these conditions, it is proposed that at least once every 5.5 days on a blast furnace, it is possible to switch over to work with reduced CaO / SiO ₂ basicity by 0, within 16-24 hours (two or three shifts), 1-0.2 units lower than in normal oven operation.

Literature

1. Patent RU 2237721 C1, cl. C21B 5/00 of February 25, 2003.

2. Koryakova O.F. and others. Improving the technology of blast furnace smelting in order to reduce the negative effects of alkalis and zinc. Bull. TSNIIICHM, 1980, No. 15, p.25.

Claims (1)

A method of blast-furnace smelting of alkali-containing iron ore materials, including loading into the furnace through the top of the iron ore part of the charge, coke and additives, heating, restoring and melting the charge, periodically releasing cast iron and slag, monitoring the composition of cast iron and slag basicity, characterized in that the furnace operation is periodically switched to 16-24 hours with a reduced basicity of slag in CaO / SiO ₂ 0.1-0.2 units lower than in the normal operation of the furnace, and the frequency of alkali removal from the furnace is determined by the ratio of the change in the intensity of alkali output from the furnace during operation with a reduced basicity of slags to the change in the intensity of alkali output during operation on ordinary slags:

where PU is the frequency of alkali removal, days;

- the average slag output for the output during the period of operation on slag with reduced basicity, kg / t;

- the number of releases during operation on slag with reduced basicity, pcs .;

- the average slag output for the output during the period of operation on slags with the usual basicity, kg / t;
N _gr - the number of issues on schedule on the blast furnace, pcs./day;

- the change in alkali content on average for the output during the period of operation on slag with reduced basicity,%, is determined by the ratio

Where

- alkali content on the i-th issue during the period of work on slag with reduced basicity,%;

- alkali content on the 1st issue during the period of work on slag with reduced basicity,%,

- the change in alkali content on average over the release during the period of work on slags with the usual basicity,%, is determined by the ratio

Where

- alkali content on the 1st issue during the period of work on slags with the usual basicity,%;

- alkali content on the i-th issue during the period of work on slags with the usual basicity,%,

- the number of releases during the period of work on slags with the usual basicity, pcs.

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