Method for quasi-in-situ observation of thermal state structure of coke

Abstract

The invention provides a method for quasi-in-situ observation of a coke thermal state structure, and belongs to the technical field of carbon-based material surface topography determination. The method comprises the following steps: S1, drying coal, and grinding the dried coal into powder to obtain pulverized coal; s2, mixing the pulverized coal and water, fully stirring in a stirrer, and carrying out compression molding through a mold, so as to obtain molded formed coke; s3, carrying out heat treatment on the formed coke in a protective gas atmosphere, and cooling to obtain coke; s4, heating the coke to a test temperature, taking out the coke at the test temperature, rapidly placing the coke in liquid nitrogen, and obtaining a sample after the liquid nitrogen is completely evaporated; and S5, levigating the obtained sample, and putting the levigated sample into an SEM instrument and a BET instrument for measurement. According to the method, SEM equipment does not need to be transformed or a complex high-temperature in-situ system does not need to be configured, and the apparent morphology data close to high temperature and real time can be obtained on a conventional instrument only by optimizing the sample preparation and cooling process.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon-based material surface morphology measurement, in particular to a method for quasi-in-situ observation of coke thermal structure. Background Art

[0002] As a key material in the metallurgical industry, coke plays an irreplaceable role in the blast furnace ironmaking process. It is both a reducing agent and a fuel, and its quality directly affects the operating efficiency of the blast furnace and the quality of pig iron. The thermal strength of coke is particularly important. It characterizes the mechanical stability of coke in a high-temperature environment and determines its ability to resist breakage when subjected to high temperature and mechanical stress in the blast furnace. If the thermal strength is insufficient, the coke will easily break in the blast furnace, resulting in increased air flow resistance, increased energy consumption, and even affecting production continuity. However, the existing technology for observing the high-temperature surface morphology of coke mainly relies on morphological analysis after natural cooling, and is unable to capture dynamic structural changes at high temperatures in real time, resulting in distortion of key information such as pore closure, which seriously restricts the research and process optimization of the high-temperature behavior of coke. Therefore, the development of a characterization method that can retain the instantaneous morphology of coke at high temperature quasi-in situ has become a core demand for solving this technical bottleneck.

[0003] Bouala, Galy & Clavier, Nicolas & Lechelle, Jacques & Mesbah, Adel & Dacheux, Nicolas. (2015). In situ HT-ESEM study of crystallites growth within CeO2 microspheres. Ceramics International. 41.14703.10.1016 / j.ceramint.2015.07.194. Bouala et al. used ex-situ and in situ scanning electron microscopy to heat treat samples in the range of 1000-1200℃, and deeply studied the law of microcrystal growth changing with temperature, providing new ideas for a deeper understanding of the formation mechanism of nanomaterials. Tang, Liang&Cheng, Xiaopeng&Wu, Rui&Cao, Tianci&Lu, Junxia&Zhang, Yuefei&Zhang, Ze.(2021).Monitoring the morphology evolution ofLiNi0.8Mn0.1Co0.1O2 during high-temperature solid state synthesis via in situSEM.Journal of Energy Chemistry.66.10.1016 / j.jechem.2021.07.021. etc. introduced a heater into the vacuum chamber of a scanning electron microscope, and combined with the independently developed high-temperature secondary electron probe lead, the temperature can be raised to 1100℃ for real-time observation, and its morphology changes can be observed under temperature changes of 300-1080℃.

[0004] However, achieving high-temperature in-situ SEM imaging requires significant modifications to traditional SEM equipment, such as installing specialized high-temperature heating devices and heat-resistant electron optical system components, which significantly increases equipment acquisition costs. Furthermore, equipment maintenance and calibration are more complex and expensive, requiring specialized technicians and specialized maintenance equipment, further increasing overall cost of ownership. Furthermore, to ensure sample stability and uniform heating at high temperatures, strict requirements are placed on sample shape, size, and mounting method, adding to the difficulty and complexity of sample preparation.

[0005] There is an urgent need to develop a new characterization method. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for quasi-in-situ observation of the thermal structure of coke, so as to solve the above technical problems.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for quasi-in-situ observation of the hot structure of coke, comprising the following steps:

[0009] S1, grinding the coal into powder after drying to obtain coal powder;

[0010] S2, mixing pulverized coal and water, placing the mixture in a blender and stirring thoroughly, and pressing the mixture into a mold to obtain formed coke;

[0011] S3, heat treating the molded coke under a protective gas atmosphere, and obtaining coke after cooling;

[0012] S4. Heating the coke to the test temperature, taking it out at the test temperature and quickly placing it in liquid nitrogen, and obtaining a sample after the liquid nitrogen is completely evaporated;

[0013] S5. Grind the obtained sample into powder and place it into SEM and BET instruments for measurement.

[0014] Furthermore, in step S1, the drying temperature is 70-80° C., and the drying time is 2-4 hours.

[0015] Furthermore, the protective gas is nitrogen, and the heat treatment is to first heat the tubular furnace to 800-900° C., add the molded coke after the temperature stabilizes, and then heat it to 1000-1100° C. and keep it warm for 1 hour.

[0016] Furthermore, the test temperature is 200-1100°C.

[0017] Furthermore, the flow rate of the protective gas is 90-110 ml / min.

[0018] Furthermore, the particle size of the sample after grinding is 200-300 mesh.

[0019] Beneficial effects of the present invention:

[0020] The present invention fixes the high-temperature instantaneous structure through the rapid cooling technology of liquid nitrogen, and combines it with conventional SEM and BET instruments for observation. It can avoid the morphological distortion caused by natural cooling without the need for complex equipment modification, and has the advantages of low cost and easy operation. The core idea of the invention is to "freeze" the instantaneous morphology of coke at high temperature through the rapid cooling technology of liquid nitrogen, and combine it with conventional SEM and BET characterization methods to achieve quasi-in-situ observation. Specifically, after the high-temperature treatment stage, the sample is quickly immersed in liquid nitrogen, and its high-temperature structure is fixed instantaneously at ultra-low temperature to avoid morphological distortion caused by natural cooling. This method does not require the modification of SEM equipment or the configuration of complex high-temperature in-situ systems. By simply optimizing the sample preparation and cooling process, near-real-time surface morphological data at high temperature can be obtained on conventional instruments. This idea not only reduces the equipment cost and operational difficulty, but also solves the pain point that traditional methods cannot retain dynamic high-temperature structures, providing an economical and efficient solution for the study of high-temperature behavior of coke and other carbon materials.

[0021] Compared with the prior art, the present invention also has the following advantages:

[0022] (1) The present invention provides a method for testing and characterizing the surface morphology of coke materials at high temperatures, which is a rapid detection method that can ensure rapid sample preparation.

[0023] (2) The test characterization method of the present invention does not require the preparation of an in-situ SEM instrument, and the required cost is relatively low.

[0024] (3) The test characterization method for observing the surface morphology of coke materials at high temperature of the present invention uses simple equipment and is easy to operate. The test method is easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are the SEM images of coke without freezing treatment: (a) SEM image of coke at 200℃; (b) SEM image of coke at 500℃; (c) SEM image of coke at 800℃; (d) SEM image of coke at 1100℃;

[0026] Figure 2 SEM images of coke after freezing treatment: (a) SEM image of coke at 200°C; (b) SEM image of coke at 500°C; (c) SEM image of coke at 800°C; (d) SEM image of coke at 1100°C;

[0027] Figure 3 The pore size distribution diagram of coke at different temperatures: (a) pore size distribution diagram of coke at 200℃; (b) pore size distribution diagram of coke at 500℃; (c) pore size distribution diagram of coke at 800℃; (d) pore size distribution diagram of coke at 1100℃. DETAILED DESCRIPTION

[0028] The present invention provides a method for quasi-in-situ observation of the hot structure of coke, comprising the following steps:

[0029] S1, grinding the coal into powder after drying to obtain coal powder;

[0030] S2, mixing pulverized coal and water, placing the mixture in a blender and stirring thoroughly, and pressing the mixture into a mold to obtain formed coke;

[0031] S3, heat treating the molded coke under a protective gas atmosphere, and obtaining coke after cooling;

[0032] S4. Heating the coke to the test temperature, taking it out at the test temperature and quickly placing it in liquid nitrogen, and obtaining a sample after the liquid nitrogen is completely evaporated;

[0033] S5. Grind the obtained sample into powder and place it into SEM and BET instruments for measurement.

[0034] In the present invention, the ratio of the coal powder to water is 20-50 g: 3-5 ml, preferably 20 g: 3 ml.

[0035] In the present invention, in step S1, the drying temperature is 70-80° C., preferably 75° C., and the drying time is 2-4 hours, preferably 3 hours.

[0036] In the present invention, the protective gas is nitrogen, and the heat treatment is to first heat the tubular furnace to 800-900°C, load the molded coke after the temperature stabilizes, and then heat it to 1000-1100°C and keep it warm for 1 hour; preferably, the heat treatment is to first heat the tubular furnace to 850°C, load the molded coke after the temperature stabilizes, and then heat it to 1050°C and keep it warm for 1 hour.

[0037] In the present invention, the test temperature is 200-1100°C, preferably 200°C, 500°C, 800°C, or 1100°C.

[0038] In the present invention, the flow rate of the protective gas is 90-110 ml / min, preferably 100 ml / min.

[0039] In the present invention, the particle size of the sample after grinding is 200-300 mesh, preferably 200 mesh.

[0040] In the present invention, the heated coke is quickly taken out and placed in liquid nitrogen. Note that the liquid nitrogen boils because the temperature is not stable. Liquid nitrogen should be added continuously to prevent insufficient liquid nitrogen from causing the temperature to not drop. Wait until the liquid nitrogen surface calms down and stop adding. After the liquid nitrogen is consumed, take out the sample for storage.

[0041] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] S1. Bake the coal in an oven at 75°C for 3 hours, then grind it into powder using a grinder.

[0044] S2. Add 3 ml of water to 20 g of coal powder, place the mixture in a blender and mix thoroughly, then form the mixture into a self-made mold to obtain formed coke.

[0045] S3. Place the molded coke in a tubular furnace at 850° C. and raise the temperature to 1050° C. in a nitrogen atmosphere over 30 minutes, then maintain the temperature at 1050° C. for 1 hour for coking, and obtain coke after cooling.

[0046] S4. Continue to raise the temperature of the tube furnace to 200°C, place the coke sample into the furnace, and maintain the constant temperature for 30 minutes. Take out the sample at this temperature and quickly place it in a container containing liquid nitrogen. When the nitrogen is completely evaporated, collect the sample for subsequent morphology testing.

[0047] S5. Grind the obtained sample to 200 mesh and then place it into SEM and BET instruments for measurement.

[0048] Example 2

[0049] S1. Bake the coal in an oven at 75°C for 3 hours, then grind it into powder using a grinder.

[0050] S2. Add 3 ml of water to 20 g of coal powder, place the mixture in a blender and mix thoroughly, then form the mixture into a self-made mold to obtain formed coke.

[0051] S3. Place the molded coke in a tubular furnace at 850° C. and raise the temperature to 1050° C. in a nitrogen atmosphere over 30 minutes, then maintain the temperature at 1050° C. for 1 hour for coking, and obtain coke after cooling.

[0052] S4. Continue to raise the temperature of the tube furnace to 500°C, place the coke sample into the furnace, and maintain the constant temperature for 30 minutes. Take out the sample at this temperature and quickly place it in a container containing liquid nitrogen. When the nitrogen is completely evaporated, collect the sample for subsequent morphology testing.

[0053] S5. Grind the obtained sample to 200 mesh and then place it into SEM and BET instruments for measurement.

[0054] Example 3

[0055] S1. Bake the coal in an oven at 75°C for 3 hours, then grind it into powder using a grinder.

[0056] S2. Add 3 ml of water to 20 g of coal powder, place the mixture in a blender and mix thoroughly, then form the mixture into a self-made mold to obtain formed coke.

[0057] S3. Place the molded coke in a tubular furnace at 850° C. and raise the temperature to 1050° C. in a nitrogen atmosphere over 30 minutes, then maintain the temperature at 1050° C. for 1 hour for coking, and obtain coke after cooling.

[0058] S4. Continue to raise the temperature of the tube furnace to 800°C, place the coke sample into the furnace, and maintain the constant temperature for 30 minutes. Take out the sample at this temperature and quickly place it in a container containing liquid nitrogen. When the nitrogen is completely evaporated, collect the sample for subsequent morphology testing.

[0059] S5. Grind the obtained sample to 200 mesh and then place it into SEM and BET instruments for measurement.

[0060] Example 4

[0061] S1. Bake the coal in an oven at 75°C for 3 hours, then grind it into powder using a grinder.

[0062] S2. Add 3 ml of water to 20 g of coal powder, place the mixture in a blender and mix thoroughly, then form the mixture into a self-made mold to obtain formed coke.

[0063] S3. Place the molded coke in a tubular furnace at 850° C. and raise the temperature to 1050° C. in a nitrogen atmosphere over 30 minutes, then maintain the temperature at 1050° C. for 1 hour for coking, and obtain coke after cooling.

[0064] S4. Continue to raise the temperature of the tube furnace to 1100°C, place the coke sample into the furnace, and maintain the constant temperature for 30 minutes. Take out the sample at this temperature and quickly place it in a container containing liquid nitrogen. When the nitrogen is completely evaporated, collect the sample for subsequent morphology testing.

[0065] S5. Grind the obtained sample to 200 mesh and then place it into SEM and BET instruments for measurement.

[0066] Comparative Example 1

[0067] The same as Example 1, except that the tube furnace is heated to 200°C, the coke sample is loaded into the furnace and kept at a constant temperature for 30 minutes, the furnace body is naturally cooled to room temperature, and the sample is taken out to obtain a naturally cooled sample.

[0068] Comparative Example 2

[0069] The method is the same as Example 1, except that the tube furnace is heated to 500°C, the coke sample is loaded into the furnace and kept at a constant temperature for 30 minutes, the furnace body is naturally cooled to room temperature, and the sample is taken out to obtain a naturally cooled sample.

[0070] Comparative Example 3

[0071] The method is the same as Example 1, except that the tube furnace is heated to 800°C, the coke sample is loaded into the furnace and kept at a constant temperature for 30 minutes, the furnace body is naturally cooled to room temperature, and the sample is taken out to obtain a naturally cooled sample.

[0072] Comparative Example 4

[0073] The method is the same as Example 1, except that the tube furnace is heated to 1100°C, the coke sample is loaded into the furnace and kept at a constant temperature for 30 minutes, the furnace body is naturally cooled to room temperature, and the sample is taken out to obtain a naturally cooled sample.

[0074] BET analysis shows that the volume of micropores with a characteristic pore size of 2-5 nm in coke shows a continuous growth trend at high temperature. Combined with SEM analysis, it can be seen from the examples and comparative examples that at 200°C, 500°C, 800°C and 1100°C, the volume of micropores with a characteristic pore size of 2-5 nm in coke shows a continuous growth trend. Figure 1 As shown in the figure, under natural cooling conditions, the pore structure of coke is difficult to be observed, which may be due to the pore closure caused by natural cooling. Figure 2 It can be seen that under liquid nitrogen treatment, the pore structure of coke can be observed at 200°C, 500°C, 800°C, and 1100°C, and the coke clearly shows the evolution of the pore structure. This method effectively solves the problem of morphological changes of high-temperature samples at room temperature, proving that the effect can be achieved at different temperatures, not just a single temperature point, providing reliable technical support for the surface morphology analysis of coke.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for quasi-in-situ observation of coke thermal structure, characterized in that: The following steps are involved: S1, grinding the coal into powder after drying to obtain coal powder; S2, mixing pulverized coal and water, placing the mixture in a blender and stirring thoroughly, and pressing the mixture into a mold to obtain formed coke; S3, heat treating the molded coke under a protective gas atmosphere, and obtaining coke after cooling; S4. Heating the coke to the test temperature, taking it out at the test temperature and quickly placing it in liquid nitrogen, and obtaining a sample after the liquid nitrogen is completely evaporated; S5. Grind the obtained sample into powder and place it into SEM and BET instruments for measurement.

2. The method for quasi-in-situ observation of coke thermal structure according to claim 1, characterized in that: In step S1, the drying temperature is 70-80° C., and the drying time is 2-4 hours.

3. The method for quasi-in-situ observation of coke thermal structure according to claim 1 or 2, characterized in that: The protective gas is nitrogen, and the heat treatment is to first heat the tubular furnace to 800-900°C, add the molded coke after the temperature stabilizes, and then heat it to 1000-1100°C and keep it warm for 1 hour.

4. The method for quasi-in-situ observation of coke thermal structure according to claim 3, characterized in that: The test temperature is 200-1100°C.

5. The method for quasi-in-situ observation of coke thermal structure according to claim 3, characterized in that: The flow rate of the protective gas is 90-110 ml / min.

6. The method for quasi-in-situ observation of coke thermal structure according to claim 1, 2 or 5, characterized in that: The particle size of the sample after grinding is 200-300 mesh.

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