RU2110589C1 - Method of producing fluxed agglomerates - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: crude mixture of fluxes in the form of carbonate minerals, taken in amount more than 50% the amount needed for caking solid fuel and quicklime taken in amount providing mixture moisture as high as ≤ 5%, is disintegrated to particle size less than < 0.10-0.16 mm with < 0.05-mm class content more than 85%. Mixture is then agglomerated to particle size below < 10 mm with < 1.25-mm and > 5-mm class contents 5-10 and 15-30%, respectively. The thus obtained mixture is added to charge, which is then agglomerated to particle size less than < 20 mm with < 2.5-mm and > 10-mm class contents 10-30 and 10- 20%, respectively. In this operation, fuel consumption satisfies condition to form agglomerate with FeO content within 6-10% range. Method provides for using disintegrated mixture in the form of powdered mass. Parameters of agglomerated charge and its requirements for temperature conditions for caking remain the same. EFFECT: facilitated agglomeration process. 3 tbl

Description

 The invention relates to methods for thermal sintering of iron ores and concentrates and can be used in the agglomeration of ores and concentrates of non-ferrous metals.

 A known method of preparing the sinter mixture for sintering, in which the fuel is mixed with flux, moisten and pelletize. The flux, for example, limestone, has a particle size of 0.2 - 0.5 mm. It is added to fuel in an amount of 5 - 20% of the total amount in the sinter mixture [1].

 The disadvantage of this method is the low efficiency in implementing the goal: an increase in the specific productivity of the sinter machine while reducing fuel consumption for sintering. This is because both flux (limestone) and fuel belong to the category of materials with low lumpiness. Therefore, granules from them when mixed with other components of the mixture under the influence of mechanical stresses are almost completely destroyed. As a result, the influence of only one factor remains - more than fine grinding of fluxes. This positively affects the yield and quality of the sinter, but does not justify the large capital costs of organizing an additional transport line with pelletizing fuel and fluxes.

где
m_т - количество топлива в смеси кг/(сух)/кг(сух) флюсов;
k - коэффициент, учитывающий активную поверхность частиц топлива, равный 0,30 - 0,50;
C_т - содержание углерода в топливе, %;

- количество CO₂ в 1 кг флюсов, кг.Closest to the proposed method is [2], the essence of which is as follows: 100% of fluxes in the form of carbonate rocks and part of the solid carbonaceous fuel are jointly crushed in active impact aggregates to a particle size of less than 3 mm with a fraction content of less than 0.10 mm - 20 - fifty%. The amount of fuel in the mixture is calculated by the formula:

Where
m _t - the amount of fuel in the mixture kg / (dry) / kg (dry) fluxes;
k is a coefficient taking into account the active surface of the fuel particles equal to 0.30 - 0.50;
C _t - carbon content in the fuel,%;

- the amount of CO ₂ in 1 kg of fluxes, kg

The humidity of the mixture is regulated by introducing quicklime into the unmilled mixture at the rate of 3.12 kg of CaO _sv per 1 kg of water in excess of 7%.

 The method provides two options for grinding the mixture: in one and two stages. In the first embodiment, grinding is carried out in one stage in units of active impact. In the second embodiment, in two stages: in the first, the mixture is crushed in hammer crushers, in the second, in a disintegrator or de-separator.

This method of sintering the mixture passed large-scale industrial testing and was introduced at the sinter plant of NLMK JSC as a new technology for the production of low-sinter agglomerate [3]. Its economic efficiency is expressed in a decrease in specific fuel consumption for sintering (1.1 kg / t of sinter) and in a decrease in specific consumption of coke for smelting cast iron (4 kg / t of cast iron). The latter is due to a significant increase in the hot strength of the agglomerate: when restored in the temperature range up to 800 ^o C, the experimental agglomerate is destroyed by 40-60% less than usual.

 The disadvantage of this method is that the mechanical strength of the sinter (GOST 151347-77) practically does not increase, and its recoverability even decreases by 9.1%. This limits the amount of implementation of the method [2] in production.

 The objective of the invention is to increase the technical and economic efficiency of sinter production by increasing the specific productivity of sinter machines, reducing specific fuel consumption, improving the quality of sinter and reducing environmental pollution.

The implementation of the proposed method provides:
1) increase in specific productivity of sinter machines by 25 - 45%;
2) decrease in specific fuel consumption by 5 - 7%;
3) increase the agglomerate reducibility by 10 - 12.5% (GOST 17212-84);
4) increasing the strength of the sinter during recovery by 50 - 74.0% (GOST 19575.84);
5) increasing the mechanical strength of the sinter by 10.0 - 25% (GOST 15137-77);
6) reduction of the amount of exhaust gases emitted into the atmosphere by 5 - 10%.

The essential features characterizing the invention:
1. Raw fluxes, solid fuels and quicklime are crushed to a particle size <(0.10 - 0.16) mm with a grade content <0.050 mm ≥ 85%.

 2. The amount of solid fuel in the co-milled mixture is ≥ 50% of the total consumption for sintering.

3. The amount of quicklime in the co-milling mixture satisfies the condition that the moisture content of the mixture does not exceed 5% (W _cm ≤ 5%).

4. The crushed fuel-flux mixture (TFS) is introduced into the mixture or in the form of a pelletized mass with the parameters:
Maximum size - 10 mm
Class content <1.25 mm - 5 - 10%
Class content> 5 mm - 15 - 30%,
or in the form of a powdery mass.

 5. The mixture after the introduction of TFS is mixed and pelletized to a particle size of <20 mm with a grade of <2.5 mm and> 10 mm, respectively, 10-30% and 10-20%.

 6. The fuel consumption for sintering satisfies the condition for the production of sinter with the content of FeO = 6 - 10%.

Features distinguishing from the prototype [2]:
1. A mixture of crude fluxes, fuel and quicklime is ground to a particle size <(0.10 - 0.16) mm with a grade content <0.050 mm ≥ 85%.

 2. The amount of solid fuel in the co-milled mixture is ≥ 50% of the total consumption for sintering.

3. The amount of quicklime in the co-milled flux and fuel mixture satisfies the condition that the moisture content of the mixture does not exceed 5% (W _cm ≤ 5%).

4. The ground fuel-flux mix (TFS) is used in two ways:
in pelletized form with parameters:
Maximum fineness - 10 mm
Class content 1.25 mm - 5 - 10%
Class content 5 mm - 15 - 30%
and unoccupied: in the form of a powdery mass.

 5. The entire charge is pelletized to a particle size of <20 mm with a grade of <2.5 mm and> 10 mm, respectively 10–30% and 10–20%.

 6. The fuel consumption for sintering satisfies the condition for producing an agglomerate with an FeO content in the range of 6-10%.

Signs sufficient in all cases to which the requested scope of legal protection applies:
1. A mixture of crude fluxes, fuel and quicklime is ground to a particle size <(0.10 - 0.16) mm with a grade content <0.050 mm ≥ 85%.

 2. The amount of solid fuel in the co-milled mixture is ≥ 50% of the total consumption for sintering.

3. The amount of quicklime in the co-milling mixture satisfies the condition that the moisture content of the mixture does not exceed 5% (W _cm ≤ 5%).

4. The crushed mixture is introduced into the mixture or in the form of a pelletized mass with parameters according to particle size distribution:
Maximum size - 10 mm
Class content <1.25 mm - 5 - 10%
Class content> 5 mm - 15 - 30%
or in the form of a powdery mass.

 5. The entire charge is pelletized to a particle size of <20 mm with a grade of <2.5 mm and> 10 mm, respectively 10–30% and 10–20%.

 6. The fuel consumption for sintering satisfies the condition for producing an agglomerate with an FeO content in the range of 6-10%.

 The basis of the proposed method for sintering an fluxed agglomerate is based on thermodynamic and kinetic sonicity of physicochemical processes at the stage of solid-phase transformations. The proposed technology for the preparation of the mixture by fine co-grinding of fluxes and fuels fundamentally changes their auto-adhesive properties. Particles of limestone, dolomite, coke, anthracite, etc. materials used as fluxes and fuels, when crushed to sizes <0.050 mm (85% or more) acquire high clumping properties [4, 5]. They become able to pelletize with the formation of rather strong granules, capable of retaining their structure when mixed with the charge, and when pelletizing, they play the role of granulation nuclei.

 If the crushed mixture is introduced into the mixture in the form of a powdery mass, then flux and fuel particles in the crushed mixture due to the change in shape and surface properties are evenly distributed between the classes of granules of the pelletized mixture and the thickness of the granules.

The thermophysical and physicochemical properties of particles of sizes <0.050 mm take such characteristics that the kinetic laws of chemical reactions of fuel combustion, dissociation of carbonates and the interaction of solid phases completely change. For example, processes such as the dissociation of carbonates (CaCO ₃ ----> CaO + CO ₂ ; MgCO ₃ ---> MgO + CO ₂ ) and carbon burning (C + O ₂ ---> CO ₂ ; C + 1 / 2 O ₂ ---> CO) go over the entire thickness of these particles. The role of heat and thermal diffusivity factors decreased so much that the incubation periods of these reactions did not take on any significant significance. As a result of this, the time for solid-phase reactions, as a result of which an agglomerate bunch is formed, has significantly increased. The fundamental difference in the mechanism of ligament formation in the agglomerate structure is that the primary liquid phase is iron silicates, in the melt of which CaO dissolves. With the inventive technology, the formation of calcium silicates at the stage of solid-phase reactions is minimized. Due to the fine grinding of the fuel and its close contact with the ore particles of the charge, the oxidation reactions of magnetite are minimized, but the reactions of reduction of ferric iron (Fe ³⁺ ) to ferrous (Fe ²⁺ ) are actively developing
Fe ₃ O ₄ + C (CO) ---> 3FeO + CO (CO ₂ ),
Fe ₂ O ₃ + C (CO) ---> 2FeO + CO (CO ₂ )
Iron oxide interacts with the SiO ₂ waste rock with the formation of fayalite - FeSiO ₄ , which dissolves calcium oxide. This sequence of binder formation in the structure of the agglomerate minimizes the formation of calcium silicates of the type larnite Ca ₂ SiO ₄ and wollastonite CaSiO ₃ . The latter have the most adverse effect on the metallurgical properties of the agglomerate due to modification transformations during cooling.

 The study of thin sections of sinter, sintered according to the inventive technology, showed that its structure is fundamentally different from the structure of ordinary sinter. This difference lies in the fact that the framework of the experimental agglomerate is composed of practically only magnetite crystals. The sizes of these crystals are many times smaller than the magnetite crystals forming the framework of a conventional agglomerate. The bundle of the experimental agglomerate has the form of thin interlayers enveloping almost all magnetite crystals. In a conventional agglomerate, an amorphous mass occupies large volumes and often takes part in the formation of a skeleton.

 A similar change in the structure of the agglomerate takes place during sintering according to the method [2]. However, this change is not as significant as it occurs with the claimed method.

Justification of regulated parameters
1. The regulated size of grinding (<0.10 - 0.16%) mm with a grade content of <0.050 mm ≥ 85% is dictated by the requirement of a radical change in the structural and texture characteristics of fluxes and fuels. When the particle size <0,050 mm, the reaction properties of these materials increase sharply. This occurs both as a result of a multiple increase in the specific surface (from 0.5 - 1.5 m ² / per 1 kg to 8 - 10 m ² / per 1 kg) and a change in the shape of the particles.

 With the indicated coarseness values, fluxes and fuel acquire the ability to pelletize with the formation of strong granules that can not break when overloaded, mixed with the charge and when pelletizing.

 2. The lower limit of the amount of co-crushed fuel ≥ 50% meets the condition when the effectiveness of the proposed method is most noticeable.

 The upper limit on the amount of co-milled fuel is not regulated. The greatest efficiency is achieved provided that all the fuel that is required for sintering the charge is sent to co-grinding. However, to implement such a technology is possible only with a high production culture, when the technological regimes are observed at all stages of the preparation of the charge. Especially important is the high quality averaging of raw materials. If this is not the case, then a certain amount of fuel is prepared according to the usual technology to a particle size <3 mm and loaded into the fuel bunkers of the charge compartment for the operational control of the thermal sintering mode.

 3. The regulated humidity of the mixture (≤ 5%) corresponds to its optimal rheological properties (for flowability and caking). Exceeding this value is undesirable due to increased caking in the hopper.

 The minimum value for humidity is not regulated. It is determined by the amount of lime used in the sinter charge. Excessive "dryness" is not recommended, as this enhances dust formation during overloads.

где
d $\genfrac{}{}{0ex}{}{\text{i}}{\text{max}}$ - максимальный размер ячейки сита класса i, мм;
d $\genfrac{}{}{0ex}{}{\text{i-1}}{\text{min}}$ - минимальный размер ячейки сита класса i-1, мм.4. The particle size distribution of the crushed mixture corresponds to the particle size distribution of the pelletized mixture, subject to the requirements of high pelletizing efficiency. From the point of view of the quality of the agglomerate, rolling large layers of the mixture (in thickness) onto the granules of the crushed mixture is impractical. The most favorable is the charge structure when the granules of the crushed mixture during pelletizing form the granules of the mixture one class higher, but not more. For example, granules of a ground mixture of a class 1.25 - 2.5 mm, when pelletizing, form granules of a charge of a class 2.5 - 5 mm. In this case, the maximum thickness of the rolled layers is equal to:

Where
d $\genfrac{}{}{0ex}{}{\text{i}}{\text{max}}$ - maximum mesh size of a sieve of class i, mm;
d $\genfrac{}{}{0ex}{}{\text{i-1}}{\text{min}}$ - the minimum mesh size of the sieve class i-1, mm

 5. Regulation of the content of FeO in the agglomerate in the range of 6-10% due to the fact that with high fuel consumption, when FeO >> 10%, the influence of the proposed method on the quality of the agglomerate is sharply reduced. This is explained by the fact that at high values of fuel consumption, the agglomerate acquires a cast structure, where the nature of solid-phase reactions is not traced.

 The inventive method is as follows.

 Raw fluxes (100% of the total amount), ≥ 50% of the total fuel consumption (coke, anthracite, coal) and quicklime are sent to the grinding body.

The amount of quicklime is set so as to bind the hygroscopic moisture coming from the fuel and flux, leaving the amount of free water not more than 5% relative to the total weight of the mixture. To bind 1 kg of water, 3.12 kg of CaO _{St. are} required.

 Grinding is carried out in ball mills of dry grinding or in hammer rotary crushers with air classification.

 The crushed mixture is sent to pelletizing (according to method 1), and after pelletizing - to the bunkers of the charge compartment. From the bunkers, with the help of feeders, for example, of selective action, the pelletized mixture is dosed onto a prefabricated charge conveyor. Dosing is carried out using weighing devices. The flow rate of the pelletized ground mixture satisfies the requirements for producing an agglomerate with the given parameters in terms of basicity and FeO content.

 Given the high stability of the supply of raw materials and good averaging quality, it seems possible to send all the fuel that is required for sintering to be sent to co-grinding with fluxes. In this case, the greatest effect of the proposed method is achieved.

 If the technological mode is unstable and a frequent change in fuel consumption is required, then it is advisable not to send all the fuel to co-grinding, leaving part of it (5 - 15%) for the operational control of the thermal sintering mode. Pelletization of the crushed mixture is carried out either in drum pelletizing machines or in bowl granulators. The desired fineness is achieved by optimizing humidity.

 After entering the pelletized TFS, the mixture is mixed, pelletized and sent to the loading bunkers on the sinter machine. The mode of pelletizing the charge is controlled by a change in humidity, reaching a predetermined particle size distribution.

 When you enter the crushed TFS in the form of a powdered mass (method 2), the parameters of the pelletized charge do not change.

 Testing of the proposed method was carried out in the laboratory of LSTU, located on the territory of the sinter plant of JSC "NLMK". The raw material conditions and the gas-dynamic sintering regime were as close as possible to the industrial conditions of this sinter plant. The ore part of the charge consisted of: Stoilenskaya oxidized ore 18.1%, a mixture of concentrates (from magnetite ferruginous quartzites KMA - St. GOK, LEbGOK, KMA ore) 63.6% and iron-containing waste 18.3%.

 As fluxes, Studenovsky limestone and dolomitic limestone of Dankovsky deposits were used in a ratio of 1: 1 (by weight).

Coke and anthracite headquarters served as fuel: C _mountains = 80.5%, S = 0.73%, V = 1.5%.

The chemical composition of the agglomerate,%: Fe _total. 57.3 - 57.6; FeO 5-11; SiO ₂ 7.00-7.42; CaO 8.90 - 9.10; Al ₂ O ₃ 0.90-1.10; MgO 1.57-1.83; CaO / SiO ₂ 1.20 - 1.27.

 The main technological features of the experiments.

 1. TFS was milled in an industrial ball mill of 1500 • 1600 mm.

 2. The amount of quicklime in TFS was added based on the conditions for the binding of hygroscopic water in excess of 5%.

 Calculation example: amount of TFS 100 kg, humidity 6%.

где
M_CaO и

- молярные массы CaO и H₂O;

- содержание CaO_св в извести (доли).Excess moisture in excess of the regulated level is 1% or 1 kg. To bind this amount of water is required

Where
M _CaO and

- molar masses of CaO and H ₂ O;

- the content of CaO _St. in lime (fraction).

Эта величина отвечает условию максимально допустимой влажности измельченной смеси: 5%.When the content of lime CaO _cb = 87.3%, its consumption is

This value meets the condition for the maximum permissible moisture content of the crushed mixture: 5%.

 3. The crushed mixture was pelletized on a disk pelletizer (D = 1 m). The limits of change in the humidity of the mixture were 7.5 - 9.0%.

 4. Mixing and pelletizing of the charge was also carried out on a plate granulator. Regulated humidity and duration of pelletizing. Humidity was varied in the range of 8.5 - 10.5%, the duration of pelletizing was kept constant - 5 minutes.

 5. When loading the pelletized mixture into the sintering bowl, the segregation conditions that apply when a single-layer loading of the mixture onto an sintering machine were observed. To do this, the pelletized mixture was poured along an inclined trough into a cone, which was divided by height into 3 parts, corresponding in weight as 1: 2: 1. The mixture from the lower part of the cone was loaded with the lower layer, from the middle part with the second layer and the mixture from the upper part with the upper layer. With such a load, the layer structure in the sinter bowl rather closely reproduced the structure of the charge layer on sinter machine No. 1 of NLMK JSC, on which a single-layer load was carried out.

 The mass of the loaded charge was 49.5 - 51.5 kg. Layer height 500 mm. The charge was ignited with a mixture of blast furnace, coke and natural gases.

 The mechanical processing of the cake according to the conditions of destruction and the particle size distribution of the usable one imitated the industrial conditions of the sinter plant of NLMK JSC. The yield was determined at the stage of formation of the "bunker" and "skip" agglomerates. The latter was subjected to stabilization. The dynamics of the yield change according to the stages of the processing of cake served as an indicator of cake and agglomerate.

 Suitable - "skip" was tested for strength (GOST 15137-77), recoverability (GOST 17212-84) and strength during recovery (GOST 19575-84).

 In the table. 1 shows the technological parameters of laboratory sintering, covering the boundary values of the parameters of the proposed method. The sintering indices of these experiments are given in table. 2. Here experience N 1 corresponds to the technology parameters of the prototype [2]. Tests 2, 3, 4, and 5 illustrate the effect of the amount of fuel specified for co-milling with fluxes; experiments 6, 7 and 8 - the effect of fineness grinding; experiments 9 and 10 - the effect of the size of the pelletized TFS; experiments 11 and 12 - the effect of the size of the pelletized mixture; experiments 13 and 14 - the effect of total fuel consumption (criterion is the content of FeO in the agglomerate); experiments 16 and 17 - the effect of humidity of the crushed mixture. Experience 18 illustrates the effectiveness of the proposed method according to the option when the TFS is not pelletized (method 2).

 The effectiveness of the proposed method is determined by the results of experiments 5, 11 and 13, the parameters of which correspond to the regulated values of method 1. A quantitative assessment of the effectiveness is given below.

 Technological parameters and technical and economic indicators and the quality of the sinter in experimental sintering are given in table. 12.

 Analysis of the data presented allows us to conclude that the inventive method for the production of fluxed sinter has great advantages compared to the prototype. These advantages apply to all indicators reflecting the technical and economic efficiency of sinter production and the quality of sinter. The latter will ensure a decrease in the specific consumption of coke for smelting pig iron and an increase in the productivity of blast furnaces.

Claims (1)

 A method for the production of fluxed agglomerate, including preliminary grinding of a mixture consisting of 100% crude fluxes necessary for agglomeration and represented by carbonate rock, part of solid fuel and quicklime, introducing the components of the mixture into the sintering mixture, mixing, pelletizing and sintering, characterized in that the amount of quicklime in the crushed part of the mixture is determined from the condition of ensuring the humidity of the mixture ≤ 5%, and the amount of solid fuel is more than 50% of the total fuel consumption for baking, which is established from the conditions for producing an agglomerate with a FeO content of 6-10%, while the mixture is crushed to a particle size <0.10 - 0.16 mm with a grade content of <0.050 mm ≤ 85% and introduced into the sinter mixture or in powder form, either the mixture is pre-pelletized to a particle size <10 mm with a grade content of <1.25 mm and> 5 mm, respectively 5 to 10% and 15 to 30%, and the agglomeration charge is pelletized to a particle size of <20 mm with a grade content of <2.5 mm and> 10 mm, respectively 10 - 30% and 10 - 20%.

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