Matching method of blast furnace ore reducibility and coke reactivity

Abstract

A method for matching the reducibility of blast furnace ore with the reactivity of coke. The method uses a variety of iron ores of different qualities as raw materials and conducts a reduction degree measurement experiment using a programmed reduction furnace. A relationship between the iron ore reducibility and the activation energy in the FeO reaction rate constant is established. An unreacted core model of the FeO reduction process in the thermal reserve zone is established, and a relationship between the thermal reserve zone gas utilization rate and the ore reduction rate constant and temperature is established. Thus, a matching relationship between the ore reducibility and coke reactivity is obtained. By establishing a relationship between the ore reducibility and the reaction rate constant, and studying the effects of different quality ores and cokes on the thermal reserve zone gas utilization rate, the present invention establishes a matching system for ore reducibility and coke reactivity, which can be used to improve blast furnace gas utilization and reduce fuel ratios.

Description

Technical Field

[0001] The present invention relates to the technical field of blast furnace smelting, and in particular to a method for matching the reducibility of blast furnace ore and the reactivity of coke. Background Art

[0002] Iron-containing charge is the basis of blast furnace smelting. In recent years, the price of iron ore has fluctuated greatly, resulting in a wide variety of iron-containing charge required for smelting, with large differences in composition and performance, causing significant fluctuations in blast furnace smelting and difficulty in reducing the fuel ratio.

[0003] Coke, an indispensable raw material in the blast furnace smelting process, acts as a reducing agent, exothermic agent, carburizing agent, and skeleton in the blast furnace. The friction and collision of the coke entering the furnace in the block belt slightly reduce its strength and slightly deteriorate its permeability. When the coke falls to the middle of the blast furnace, it is exposed to high temperatures and undergoes a carbon-dissolving reaction, which increases the coke's porosity and reduces its strength. The carbon-dissolving reaction of the coke in the dripping zone weakens, but its strength continues to decrease due to the scouring and erosion of molten iron and slag. Blast furnace process modifications, such as the use of large fans to increase the kinetic energy of the blast, have intensified the erosion of the coke, making the role of the coke as a skeleton and gas channel in the blast furnace even more important, which also places higher requirements on the strength of the coke.

[0004] How to match iron-containing furnace charge and coke? A document published in the Journal of Materials and Metallurgy, 2020, 19(04), pp. 253-258, points out that the use of highly reactive coke in blast furnaces to reduce the temperature of the heat reserve zone and thus improve the gas utilization coefficient requires that the ore has high reducibility. When the ore has low reducibility, the use of highly reactive coke will lead to a decrease in the gas utilization coefficient. The document points out the problem of ore-coke matching but does not provide specific guidance.

[0005] In the Chinese patent literature, a patent with application number 201410027145.0 and titled "Highly Reactive Coke and Its Production Method" proposes to use blended coal as raw material for coking, wherein steel slag is added to the raw material. The method of the present invention improves the reactivity of the obtained coke and reduces the starting temperature of the gasification reaction between coke and carbon dioxide. The coke has a lower starting temperature for the gasification reaction, which can reduce the temperature of the blast furnace heat reserve zone. When used with ore with high reducibility, it can reduce blast furnace fuel consumption. At the same time, it can also ensure that the post-reaction strength of the coke meets the requirements of blast furnace ironmaking. In addition, steel slag as an additive is cheap and widely available. This invention uses steel slag as an additive to blended coal for coking, but does not study the matching relationship between ore reducibility and coke, nor does it study how to improve the utilization rate of coal gas. Summary of the Invention

[0006] In view of the problems existing in the above-mentioned prior art, the present invention proposes a method for matching the reducibility of blast furnace ore with the reactivity of coke, which can improve the gas utilization rate and reduce the blast furnace fuel ratio.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A method for matching the reducibility of blast furnace ore with the reactivity of coke is carried out in the following steps:

[0009] (1) Take a variety of iron ores of different qualities as raw materials and use a program reduction furnace to conduct a reduction degree determination experiment. The iron ore reduction degree satisfies formula a,

[0010]

[0011] Where: m0 is the mass of the sample, in g; m1 is the mass of the sample before reduction, in g; m t -The mass of the sample after reduction tmin, in g, W1(%) is the FeO content in the sample before the test, and W2(%) is the total iron content of the sample before the test;

[0012] (2) Take the same batch of iron ore as raw material, use a program reduction furnace to reduce it to FeO sample, then use the prepared FeO as raw material to reduce it at 850℃, 900℃, 950℃ and 1000℃ respectively in a program reduction furnace, calculate the reaction rate of FeO at different temperatures, fit the data, and the reaction rate constant of FeO in the range of 850℃-1000℃ satisfies formula b; the relationship between the reduction degree of iron ore and the activation energy in the FeO reaction rate constant satisfies formula ③;

[0013]

[0014]

[0015] In formula (b), k is the reaction rate constant in mm / s, A is the pre-exponential factor, and E a is the activation energy, in kg / mol, and R is the ideal gas constant, in J / (mol -1 ·K -1 ), T is temperature, unit is K;

[0016] In formula ③, B and C are constants;

[0017] (3) Establish an unreacted core model of the FeO reduction process in the thermal reserve area. The relationship between the gas utilization rate in the thermal reserve area and the ore reduction rate constant and temperature satisfies formula ④;

[0018]

[0019] Where Q, N oxy , t, f are respectively the reduction rate of the ore ball, the molar amount of reducible oxygen, time and reduction degree; r0, P, R, T are respectively the diameter of the ore ball, the total pressure of the system, the ideal gas constant and the temperature; Y A,b and Y A,e are the mole fraction of gas phase reactant component A in the gas phase and the mole fraction in the reaction equilibrium state respectively; K, k, D eff are the gas-solid reaction equilibrium constant, rate constant, and effective diffusion coefficient of the mixed gas through the porous product layer; τ and ρ are oxy are the reduction time experienced by the ore ball and the molar density of reducible oxygen therein; f end Y is the reduction degree of the ore ball corresponding to the time τ; B,b and Y B,e are the mole fraction of gas phase product component B in the gas phase and the mole fraction in the reaction equilibrium state, respectively; the unreacted core model ignores the effects of external diffusion and H2;

[0020] (4) As the reactivity of coke increases, the temperature of the heat reserve area decreases, and the strength after reaction decreases. The strength of coke after reaction is required to reach more than 65% to ensure its skeleton effect;

[0021] (5) The matching relationship between the reduction degree of the ore entering the furnace and the reactivity of the coke satisfies formula ⑤;

[0022] CRI=DR t -E…………⑤;

[0023] Where D and E are constants;

[0024] In the above-mentioned method for matching the reducibility of blast furnace ore with the reactivity of coke, the experimental temperature for determining the reduction degree of iron ore is 900° C., the atmosphere composition is 70% N 2 + 30% CO, and the reaction time is 3 hours.

[0025] In the above-mentioned method for matching the reducibility of blast furnace ore with the reactivity of coke, the FeO preparation experiment temperature is 900°C, the atmosphere is 50% CO2+50% CO, and the reduction time is 3 hours.

[0026] In the above-mentioned method for matching the reducibility of blast furnace ore with the reactivity of coke, the experimental temperatures for determining the FeO reduction rate constant are 850°C, 900°C, 950°C and 1000°C, the atmosphere composition is 70% N2 + 30% CO, and the reaction time is 3 hours.

[0027] The matching method of blast furnace ore reducibility and coke reactivity is as follows: In formula ④, temperature and reaction rate constant are variables, and the values ​​of other parameters are as follows: r0 is 20 mm, ρ oxy Take 3×10 4 mol·m -3 , ε / ζ is taken as 0.11, find Take 0.55, R take 8.314, Y A,b +Y B,b Take 0.45, and τ take 3×10 3 s, P is 2×10 5 Pa.

[0028] In the above-mentioned method for matching the reducibility of blast furnace ore with the reactivity of coke, the isotropy content in the optical structure of the coke is less than 5%.

[0029] The above-mentioned method for matching the reducibility of blast furnace ore with the reactivity of coke is such that the degree of ore reduction is not less than 74% and not more than 86%.

[0030] Beneficial effects

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention uses the unreacted core model of the thermal reserve area, and the formula for determining the gas utilization rate of the thermal reserve area is:

[0033] Combined blast furnace

[0034] Under the smelting conditions of high pressure, high air temperature and large air volume, ignoring the effect of external diffusion on the reduction reaction, the gas utilization rate of the heat reserve area is converted into:

[0035] Sure

[0036] By understanding the relationship between gas utilization and ore reduction, we can determine how gas utilization varies with temperature in the thermal reserve zone for ores with varying reduction degrees. This allows us to combine simulations with actual smelting conditions and select coke with varying reactivity based on the degree of reduction of the ores. This effectively guides improving gas utilization and reducing the blast furnace fuel ratio. It also provides a solution for complex raw material fluctuations faced by blast furnaces, making the use of blast furnace coke more rational. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is the relationship curve between the gas utilization rate in the thermal reserve area and the ore reduction rate constant and temperature. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to specific embodiments.

[0039] In the present invention, formula ④ represents the limiting link of the iron ore reduction process, CO reduces FeO and is subject to the common limitation of thermodynamics and kinetics, resulting in incomplete reduction. Thermodynamic conditions represent the limit of CO reducing FeO, and in actual conditions, the reduction reaction is affected by factors such as reaction temperature, time, and the properties of the ore itself, resulting in incomplete reduction, that is, the reduction of FeO will show a change different from the thermodynamic function as the reduction conditions change. In this formula, under the condition that other conditions such as reduction time remain unchanged, the variation of the reduction degree of FeO (gas utilization rate in the thermal reserve area) as a function of ore reduction rate (properties of the ore itself) and reduction temperature (which can be changed by changing the coke reducibility) is investigated. With the goal of improving gas utilization, a matching relationship between ores of different reduction degrees and cokes of different reactivity is established, ultimately achieving the effect of improving gas utilization and reducing blast furnace fuel ratio.

[0040] Example 1

[0041] (1) Taking the blast furnace of a steel plant in Hebei as an example, the iron ore commonly used in the blast furnace was used as raw material and the reduction degree was measured using a program reduction furnace. The ore reduction degree ranged from 74% to 86%.

[0042] (2) The same batch of iron ore was used as raw material and reduced to FeO samples using a programmed reduction furnace. The prepared FeO was then reduced at 850°C, 900°C, 950°C, and 1000°C using a programmed reduction furnace. The reaction rates of FeO at different temperatures were calculated and fitted. The reaction rate constant of FeO in the range of 850°C-1000°C satisfies Equation 6. The relationship between the iron ore reduction degree and the FeO reaction rate constant satisfies Equation 7.

[0043]

[0044]

[0045] (3) The relationship between the gas utilization rate in the thermal reserve area and the ore reduction rate constant and temperature is as follows Figure 1 The curve of gas utilization versus temperature resembles a downward-opening quadratic curve. When the ore reaction rate constant is low, the gas utilization rate is low. As the temperature decreases, the gas utilization rate first increases and then decreases. This indicates that as the temperature decreases, the ore reduction is first dominated by thermodynamic factors and then by kinetic factors. Furthermore, the kinetic gap between the actual gas utilization coefficient and the thermodynamic equilibrium coefficient increases more significantly with decreasing temperature. As the ore reaction rate constant increases, the function shifts to the upper left, the gas utilization rate in the thermal reserve zone increases, and the vertex shifts to the left. The gap between the temperature corresponding to the maximum gas utilization rate and the lower edge temperature of the thermal reserve zone (1000°C) increases, and the reactivity of the thermal reserve zone to accept coke increases.

[0046] (4) When the coke reactivity is 22%, the temperature of the heat reserve zone is 1000°C. When the coke reactivity increases by 1%, the temperature of the heat reserve zone decreases by 10°C. Taking the gas utilization rate of the heat reserve zone as a reference, the temperature of the heat reserve zone is adjusted so that the ore added thereto reaches the maximum gas utilization rate in the heat reserve zone. The matching relationship between the ore reduction degree and the coke reactivity satisfies formula ⑧.

[0047] CRI=0.5R t -15…………⑧;

[0048] (5) The isotropy content in the optical structure of coke should be less than 5%, and a certain post-reaction strength should be maintained to maintain the skeleton effect of coke. In this example, the coke meets this condition.

[0049] (6) Based on the ore-coke matching relationship in this example, the matching relationship between the ore and coke fed into the blast furnace is adjusted. The results are as follows: for the same type of ore, adjusting the reactivity of the coke fed into the furnace can increase the gas utilization rate by 0.41% and reduce the fuel ratio by 2.15 kg / t. For different types of ores, adjusting the reactivity of the coke fed into the furnace can increase the gas utilization rate by 1.67% and reduce the fuel ratio by 7.46 kg / t.

[0050] Comparative Example 1

[0051] The difference between Comparative Example 1 and Example 1 is that the reduction degree of the iron ore entering the furnace is lower than 74%. Through small-scale comparative tests, it was found that appropriately increasing the coke reactivity in this comparative example actually reduced the gas utilization rate by 1.57% and increased the fuel ratio by 6.21 kg / t, while this situation did not occur in Example 1. This is because the reduction degree of the iron ore is too low, and the reduction in the thermal reserve area is controlled by kinetic factors. Increasing the coke reactivity actually inhibits the indirect reduction of FeO, resulting in a significant decrease in the gas utilization rate.

[0052] Comparative Example 2

[0053] The difference between this comparative example 2 and example 1 is that the reduction degree of the iron ore entering the furnace is higher than 86%. Through small-scale comparative tests, the use of high-reactivity coke in this comparative example 2 reduces the gas utilization rate by 1.08% and increases the fuel ratio by 4.15 kg / t, while this situation does not occur in example 1. This is because although increasing the reactivity of coke promotes the increase in gas utilization in the heat reserve area, the excessive reactivity of coke produces more broken coke and coke powder, which affects the permeability of the blast furnace and reduces the gas utilization rate.

[0054] Comparative Example 3

[0055] The difference between this comparative example 3 and Example 1 is that the matching coke is selected according to the reduction degree of the ore entering the furnace. Through small-scale comparative tests, the gas utilization rate in this comparative example 3 has been below 43% for a long time and fluctuates significantly. This is because the fluctuation of the coke reactivity causes the temperature fluctuation of the heat reserve area, which has different effects on the indirect reduction of FeO.

Claims

1. A method for matching blast furnace ore reducibility with coke reactivity, characterized in that: It proceeds as follows: (1) Take a variety of iron ores of different qualities as raw materials and use a program reduction furnace to conduct a reduction degree determination experiment. The iron ore reduction degree satisfies formula ①, Where: m0 is the mass of the sample, in g; m1 is the mass of the sample before reduction, in g; m t The mass of the sample after reduction tmin, in g; W1% is the FeO content in the sample before the test, and W2% is the total iron content of the sample before the test; (2) Take the same batch of iron ore as raw material, use a program reduction furnace to reduce it to FeO sample, then use the prepared FeO as raw material to reduce it at 850℃, 900℃, 950℃ and 1000℃ respectively in a program reduction furnace, calculate the reaction rate of FeO at different temperatures, fit the data, and the reaction rate constant of FeO in the range of 850℃-1000℃ satisfies formula b; the relationship between the reduction degree of iron ore and the activation energy in the FeO reaction rate constant satisfies formula ③: In formula ②, k is the reaction rate constant, in mm / s; A is the pre-exponential factor, E a is the activation energy, in kg / mol; R is the ideal gas constant, in J / (mol -1 ·K -1 ); T is temperature, unit is K; In formula ③, B and C are constants; (3) Establish an unreacted core model of the FeO reduction process in the thermal reserve area. The relationship between the gas utilization rate in the thermal reserve area and the ore reduction rate constant and temperature satisfies formula ④. Where Q, N oxy , t, f are respectively the reduction rate of the ore ball, the molar amount of reducible oxygen, time and reduction degree; r0, P, R, T are respectively the diameter of the ore ball, the total pressure of the system, the ideal gas constant and the temperature; Y A,b and Y A,e are the mole fraction of gas phase reactant component A in the gas phase and the mole fraction in the reaction equilibrium state respectively; K, k, D eff are the gas-solid reaction equilibrium constant, rate constant, and effective diffusion coefficient of the mixed gas through the porous product layer; τ and ρ are oxy are the reduction time experienced by the ore ball and the molar density of reducible oxygen therein; f end Y is the reduction degree of the ore ball corresponding to the time τ; B,b and Y B,e are the mole fraction of gas phase product component B in the gas phase and the mole fraction in the reaction equilibrium state, respectively; the unreacted core model ignores the effects of external diffusion and H2; (4) As the reactivity of coke increases, the temperature of the heat reserve area decreases, and the strength after reaction decreases. The strength of coke after reaction is required to reach more than 65% to ensure its skeleton effect; (5) The matching relationship between the reduction degree of the ore entering the furnace and the reactivity of the coke satisfies formula ⑤; CRI=DR t -E…………⑤; Where D and E are constants.

2. The method for matching blast furnace ore reducibility and coke reactivity according to claim 1, characterized in that: The experimental temperature for determining the reduction degree of iron ore is 900°C, the atmosphere composition is 70% N2+30% CO, and the reaction time is 3 hours.

3. The method for matching blast furnace ore reducibility and coke reactivity according to claim 1, characterized in that: The experimental temperature for FeO preparation was 900°C, the atmosphere was 50% CO2 + 50% CO, and the reduction time was 3 hours.

4. The method for matching blast furnace ore reducibility and coke reactivity according to claim 1, characterized in that: The experimental temperatures for determining the FeO reduction rate constant were 850°C, 900°C, 950°C and 1000°C, the atmosphere composition was 70% N2 + 30% CO, and the reaction time was 3 hours.

5. The method for matching blast furnace ore reducibility and coke reactivity according to claim 1, characterized in that: In formula ④, temperature and reaction rate constant are variables, and the values ​​of other parameters are as follows: r0 is 20 mm, ρ oxy Take 3×10 4 mol·m -3 ;ε / ζ is taken as 0.11; f ind Take 0.55; R take 8.314; Y A,b +Y B,b Take 0.45; τ take 3×10 3 s; P is 2×10 5 Pa.

6. The method for matching blast furnace ore reducibility and coke reactivity according to claim 1, characterized in that: The isotropy content in the coke optical structure is less than 5%.

7. The method for matching blast furnace ore reducibility and coke reactivity according to claim 1, characterized in that: The degree of ore reduction shall not be lower than 74% and not higher than 86%.

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