Method for representing low-temperature reduction degradation performance of pellets

Abstract

The invention discloses a method for representing low-temperature reduction degradation performance of pellets. The method comprises the following steps: (1) carrying out low-temperature reduction degradation reaction on the pellets at 400-600 DEG C; (2) the reduction expansion rate of the pellets after the reaction is detected, and the crack morphology of the pellets after the reaction is analyzed; and (3) the detected reduction expansion rate and crack morphology are jointly used as characterization of the low-temperature reduction degradation performance of the pellets. According to the method, the reduction expansion rate of the pellets at 400-600 DEG C is adopted, so that the method is more suitable for representing the low-temperature reduction degradation performance of the pellets with regular shapes; meanwhile, the pulverization process and mechanism of the pellets after the reaction can be intuitively reflected by combining different section crack shapes of the pellets after the reaction; the pellet low-temperature reduction degradation performance can be accurately represented. The method has the characteristics of simplicity in operation, easiness in implementation and high accuracy, and can better replace the traditional low-temperature reduction degradation performance index.

Description

Technical Field

[0001] The invention relates to the field of metallurgical properties of pellets for blast furnaces, in particular to a method for characterizing the low-temperature reduction pulverization properties of pellets. Background Art

[0002] In recent years, the proportion of pellets in blast furnace ironmaking process has been increasing to achieve low-carbon and low-emission smelting. The role of pellets has become increasingly important. Among them, the low-temperature reduction pulverization performance as an important indicator of pellets has been continuously valued. The low-temperature reduction pulverization performance mainly reflects the degree of powder produced when the charge is reduced in the temperature range of 400-600℃ in the upper part of the blast furnace. The main reason for the low-temperature reduction pulverization is the volume expansion and lattice distortion caused by the crystal structure transformation when hematite is reduced to magnetite. Since the structure of blast furnace charge in my country has long been dominated by sintered ore, the low-temperature reduction pulverization performance is more used to characterize the metallurgical properties of sintered ore. However, sintered ore has irregular shape and uneven structure, which is not suitable for detection and analysis using volumetric method. Compared with sintered ore, pellets have regular shape, uniform and stable composition and structure. Therefore, it is easier and more accurate to determine the volume and expansion rate of pellets, and it can better reflect the reduction reaction mechanism of pellets.

[0003] At present, the test of pellet reduction expansion performance is mainly based on the national standard GB / T 13240-2018, which characterizes the medium-temperature reduction expansion performance of pellets at 900°C. However, the test of low-temperature reduction pulverization performance at 500°C is mainly based on the national standard GB / T 13242-2017. After the reduction reaction, the drum test is carried out to obtain the traditional index RDI that characterizes the low-temperature reduction pulverization performance of pellets. +6.3 、RDI +3.15 and RDI -0.5 Therefore, with the rapid development of domestic pelletizing technology and the continuous increase in the proportion of blast furnace pellets, it is of great significance to propose a new method to characterize the low-temperature reduction pulverization of pellets, which is still in a blank stage in China. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for characterizing the low-temperature reduction pulverization performance of pelletized ore, which can characterize the low-temperature reduction pulverization performance of pelletized ore and intuitively reflect the pulverization process and mechanism after the pelletizing reaction.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention includes the following steps: (1) performing a low-temperature reduction pulverization reaction on the pellets at 400-600°C; (2) Detect the reduction expansion rate of the pellets after the reaction and analyze the crack morphology of the pellets after the reaction; (3) The reduction expansion ratio and crack morphology detected are used together as the characterization of the low-temperature reduction pulverization performance of the pellets.

[0006] Furthermore, in step (1), the reaction time of the low-temperature reduction pulverization reaction is 0.1 to 2 hours, the total flow rate of the reaction gas is 1 to 50 L / min, and the volume fractions of the reaction gas components are: N2 0% to 90%, CO 5% to 50%, and CO2 5% to 50%.

[0007] Furthermore, in step (2), the volume of the pellets before and after the low-temperature reduction pulverization reaction is measured by a water immersion method, and the reduction expansion rate of the pellets is calculated.

[0008] Furthermore, the crack morphology includes surface crack morphology, morphology at 1 / 4 diameter and morphology at 1 / 2 diameter.

[0009] Furthermore, in step (3), the reduction expansion ratio and RDI are first +6.3 Indicators are compared to establish corresponding relationships.

[0010] The beneficial effect of adopting the above technical scheme is that: the present invention adopts the reduction expansion rate of the pellets, combined with the crack morphology of different cross sections of the pellets after the reaction, instead of the traditional drum method, based on the characteristics of the pellets with regular shape, uniform and stable composition and structure. It can not only characterize the low-temperature reduction pulverization performance of the pellets, but also intuitively reflect the pulverization process and mechanism of the pellets after the reaction, which has important guiding significance for the production of pellets and the smelting of high-proportion pellets in blast furnaces.

[0011] The present invention adopts the reduction expansion rate of pellets at 400-600°C to replace the traditional drum method, which is more suitable for characterizing the low-temperature reduction pulverization performance of pellets with regular shapes; at the same time, combined with the crack morphology of different cross-sections of the pellets after the reaction, the process and mechanism of the pulverization of the pellets after the reaction can be intuitively reflected; and the reduction expansion rate and crack morphology schematic diagram at 400-600°C are consistent with the RDI obtained by the traditional method. +6.3 The indicators have a good corresponding relationship and can accurately characterize the low-temperature reduction pulverization performance of pelletized ore. The invention has the characteristics of simple operation, easy implementation and high accuracy, and can better replace the traditional low-temperature reduction pulverization performance indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0013] Figure 1 Schematic diagram of crack morphology of the present invention; Figure 2 is a schematic diagram of the surface morphology of the pellets according to Example 1 of the present invention; Figure 3 This is a schematic diagram of the morphology of the pellet at 1 / 4 of Example 1 of the present invention; Figure 4This is a schematic diagram of the morphology of the pellet at 1 / 2 of Example 1 of the present invention; Figure 5 is a schematic diagram of the surface morphology of the pellets according to Example 2 of the present invention; Figure 6 This is a schematic diagram of the morphology of the pellet at 1 / 4 of Example 2 of the present invention; Figure 7 This is a schematic diagram of the morphology of the pellet at 1 / 2 of Example 2 of the present invention; Figure 8 is a schematic diagram of the surface morphology of the pellets according to Example 3 of the present invention; Fig. 9 This is a schematic diagram of the morphology of the pellet at 1 / 4 of Example 3 of the present invention; Fig.10 This is a schematic diagram of the morphology of the pellet at 1 / 2 of Example 3 of the present invention; Fig.11 is a schematic diagram of the surface morphology of the pellets according to Example 4 of the present invention; Fig.12 This is a schematic diagram of the morphology of the pellet at 1 / 4 of Example 4 of the present invention; Fig.13 This is a schematic diagram of the morphology of the pellet at 1 / 2 of Example 4 of the present invention; Fig.14 is a schematic diagram of the surface morphology of the pellets according to Example 5 of the present invention; Fig.15 This is a schematic diagram of the morphology of the pellet at 1 / 4 of Example 5 of the present invention; Fig.16 This is a schematic diagram of the morphology of the pellet at 1 / 2 of Example 5 of the present invention. DETAILED DESCRIPTION

[0014] The inventors found through experimental testing that the low-temperature reduction pulverization performance of pellets varies greatly, RDI +6.3 The fluctuation range is between 30% and 100%, but the mechanism of pulverization is not clear. By measuring the reduction expansion rate of pellets at 400-600℃, it is found that the reduction expansion rate of pellets at 400-600℃ fluctuates greatly, between 5% and 20%, and is consistent with RDI. +6.3 The indicators have a good correspondence; at the same time, the cross-sectional morphology of the pellets after the reaction was observed and analyzed, and the low-temperature reduction pulverization process and its mechanism of the pellets were further clarified. According to the GB / T 13242-2017 test standard, the low-temperature reduction pulverization performance of the pellets was tested, and the traditional indicator characterizing the low-temperature reduction pulverization performance of the pellets was RDI. +6.3 、RDI +3.15 and RDI -0.5 , it is difficult to characterize the causes and internal mechanisms of pellet pulverization.

[0015] Based on the low-temperature reduction pulverization process and its mechanism, the method for characterizing the low-temperature reduction pulverization performance of pellets adopts the following steps: (1) The pellets were subjected to low-temperature reduction pulverization reaction, with a reaction temperature of 400-600°C, a reaction time of 0.1-2 hours, a total reaction gas flow rate of 1-50 L / min, and the volume fractions of the reaction gas components: N2 0%-90%, CO 5%-50%, and CO2 5%-50%. Fixed parameters were selected within the above parameter range as unified reaction parameters for the detection of all pellet samples to ensure the comparability of the test results. Other reaction conditions were based on the low-temperature reduction pulverization test standard GB / T 13242-2017, but 500 g pellet samples were not used, and the drum test was not performed after the reaction. The optimal reaction parameters were: reaction temperature 500°C, reaction time 1 hour, total reaction gas flow rate 15 L / min, and the volume fractions of the reaction gas components were: N2 60%, CO 20%, and CO2 20%.

[0016] (2) Detection of the reduction expansion rate of the pellets after the reaction: Refer to the pellet reduction expansion index test standard GB / T 13240-2018, select a number of 10-12.5 mm regular pellets for testing, 10-30 pellets can be selected, preferably 18 pellets; use the water immersion method to measure the volume of the pellets before and after the reaction, and then use the following formula to calculate the reduction expansion rate of the pellets, the reduction expansion rate of the pellets = (V 反应后 -V 反应前 ) / V 反应前 × 100%, expressed as a percentage; the V 反应后 is the volume of pellets after low-temperature reduction pulverization reaction, V 反应前 It is the volume of the pellets before the low-temperature reduction pulverization reaction. Usually, the reduction expansion rate of the pellets at 400-600℃ is between 5% and 20%.

[0017] Figure 1 As shown, the crack morphology of the pellets after the reaction is analyzed: the surface crack morphology of the pellets after the reaction, the morphology at 1 / 4 diameter, and the morphology at 1 / 2 diameter are obtained respectively, so as to clarify the process and mechanism of the reduction and pulverization of the pellets. The crack morphology on the surface of the pellets is the crack caused by expansion after the low-temperature reduction and pulverization reaction, which can be directly observed. The morphology at 1 / 4 diameter and 1 / 2 diameter is obtained by polishing the pellets after the low-temperature reduction and pulverization reaction to the ratio of 1 / 4 diameter and 1 / 2 diameter, and then polishing to obtain a clear cross-sectional morphology of the pellets; sandpaper and polishing machine can be used for polishing.

[0018] (3) Based on the surface crack morphology, morphology at 1 / 4 diameter, and morphology at 1 / 2 diameter of the pellets after low-temperature reduction pulverization reaction, a schematic diagram was drawn to obtain the pellet reaction process and degradation process corresponding to different low-temperature reduction pulverization performances, which together with the reduction expansion rate detected at 400-600 °C were used as the characterization of the low-temperature reduction pulverization performance of the pellets.

[0019] The reduction expansion ratio and crack morphology of the pellets at 400-600℃ obtained by the new method are compared with the RDI obtained by the traditional method. +6.3 The indicators were compared and a better correspondence was obtained: ① In most cases, the smaller the reduction expansion rate detected, the fewer the number of cracks in the pellets after the reaction, the smaller the crack size, and the shorter the length, and the corresponding pellet RDI +6.3 The higher the index, the better the low-temperature reduction pulverization performance; the greater the reduction expansion rate detected, the more cracks there are in the pellets after the reaction, the coarser and longer the cracks are, and they extend inward, and the corresponding pellet RDI is +6.3 The lower the index, the worse the low-temperature reduction pulverization performance.

[0020] ② In a few cases, the reduction expansion rate of the pellets is low, but after the reaction, the number of cracks inside the pellets is large, the size is large, and they extend inward. The corresponding RDI of the pellets is +6.3 The indicators are low and the low-temperature reduction powderization performance is poor.

[0021] ③ In a few cases, the reduction expansion rate of the pellets is high, but the number of cracks inside the pellets after the reaction is small, the size is small, and the extension to the inside is not obvious. The corresponding pellet RDI is +6.3 The index is relatively high and the low-temperature reduction powdering performance is good. Example 1

[0022] Pellet traditional low temperature reduction powder performance RDI +6.3 The method shows that the reduction expansion rate of the pellets at 500℃ is 7%. The crack morphology of the pellets after the reaction is as follows: Figure 2-4 As shown in the figure, both the solid line and the dotted line represent cracks, and the thickness of the line represents the thickness of the crack. Figure 2-4 It can be seen that after low-temperature reduction and pulverization, the number of surface cracks and internal cracks of the pellets is small, the crack size is fine, and there is no crack in the core of the pellets. This shows that the low-temperature reduction and pulverization performance of the pellets described in this embodiment is good. Example 2

[0023] Pellet traditional low temperature reduction powder performance RDI +6.3 The method is used to obtain the pellet expansion rate of 14% at 500℃ reduction. The crack morphology of the pellet after the reaction is as follows: Figure 6-7It can be seen that there are many cracks on the surface and inside, the crack size becomes coarser and longer, and the cracks extend toward the core of the pellets. This shows that the low-temperature reduction pulverization performance of the pellets described in this example is average. Example 3

[0024] Pellet traditional low temperature reduction powder performance RDI +6.3 The method is used to obtain the pellet expansion rate of 17% at 500℃ reduction. The crack morphology of the pellet after the reaction is as follows: Figure 8-10 It can be seen that the number of surface and internal cracks increases significantly, the crack size becomes coarser and longer, and the cracks extend to the core of the pellet and penetrate through. This indicates that the low-temperature reduction pulverization performance of the pellet described in this example is poor. Example 4

[0025] Pellet traditional low temperature reduction powder performance RDI +6.3 The method is used to obtain the pellet expansion rate of 12% at 500℃ reduction. The crack morphology of the pellet after the reaction is as follows: Figure 11-13 It can be seen that there are many cracks on the surface and inside, the crack size is relatively coarse and long, and the cracks extend to the core of the pellets. This shows that the low-temperature reduction pulverization performance of the pellets described in this example is average. Example 5

[0026] Pellet traditional low temperature reduction powder performance RDI +6.3 The method is used to obtain the pellet expansion rate at 500℃, which is 13.5%. The crack morphology of the pellet after the reaction is as follows: Figure 14-16 It can be seen that there are fewer surface and internal cracks, the crack size is relatively small, and it does not extend to the core of the pellet, which shows that the low-temperature reduction pulverization performance of the pellet described in this example is good.

[0027] The traditional low temperature reduction powder performance RDI of the produced pellets +6.3 The new method is used to obtain a pellet expansion rate of more than 17% at 500°C, and a large number of cracks are generated in the pellet after the reaction, resulting in an unstable pellet structure, low strength, and fragility, making it difficult to observe the internal morphology. This shows that the low-temperature reduction pulverization performance of the pellet described in this example is poor.

Claims

1. A method for characterizing the low-temperature reduction pulverization performance of pellets, characterized in that: The steps include: (1) The pellets are subjected to low-temperature reduction and pulverization reaction at 400-600°C; (2) Detect the reduction expansion rate of the pellets after the reaction and analyze the crack morphology of the pellets after the reaction; (3) The reduction expansion ratio and crack morphology detected are used together as the characterization of the low-temperature reduction pulverization performance of the pellets.

2. A method for characterizing the low-temperature reduction pulverization performance of pellets according to claim 1, characterized in that: In the step (1), the reaction time of the low-temperature reduction pulverization reaction is 0.1 to 2 hours, the total flow rate of the reaction gas is 1 to 50 L / min, and the volume fractions of the reaction gas components are: N2 0% to 90%, CO 5% to 50%, and CO2 5% to 50%.

3. The method for characterizing the low-temperature reduction pulverization performance of pellets according to claim 1, characterized in that: In the step (2), the volume of the pellets before and after the low-temperature reduction pulverization reaction is measured by a water immersion method, and the reduction expansion rate of the pellets is calculated.

4. The method for characterizing the low-temperature reduction pulverization performance of pellets according to claim 1, characterized in that: The crack morphology includes the surface crack morphology, the morphology at 1 / 4 diameter and the morphology at 1 / 2 diameter.

5. A method for characterizing the low-temperature reduction pulverization performance of pellets according to any one of claims 1 to 4, characterized in that: In step (3), the reduction expansion ratio and RDI are firstly +6.3 Indicators are compared to establish corresponding relationships.

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