PROCESS FOR PREPARING CEMENT CLINKER UNDER OXYGEN-RICH COMBUSTION CONDITIONS AND CEMENTITIOUS MATERIAL

Abstract

PROCESS FOR PREPARING CEMENT CLINKER UNDER OXYGEN-RICH COMBUSTION CONDITIONS AND CEMENTITIOUS MATERIAL This application falls within the technical field of cementitious materials, and relates in particular to a process for preparing cement clinker and a cementitious material. The process for preparing cement clinker provided by this application comprises the following steps: 1) preparation of raw cement flour; 2) calcination of the raw cement flour under an oxygen-rich atmosphere, the oxygen-rich atmosphere being a mixture of oxygen and carbon dioxide gases in a volume ratio of (0.21-0.61): (0.39-0.79).The cement clinker preparation process provided by this application does not readily generate NOx pollutants; the main component in the combustion gases is CO2, which is conducive to carbon capture and sequestration; and the cement clinker obtained has a high C3S content and good performance (hydration effects and stability). (Fig 1).

Description

Title of the invention: PROCESS FOR PREPARING CEMENT CLINKER UNDER OXYGEN-RICH COMBUSTION CONDITIONS AND CEMENT MATERIAL. SCOPE OF THE INVENTION

[0001] The present application falls within the technical field of cementitious materials, and relates in particular to a process for preparing cement clinker under oxygen-rich combustion conditions and a cementitious material. PREVIOUS ART

[0002] Cement clinker, as a semi-finished cement product, is a key step in cement production. Cement clinker is made from raw materials containing limestone, clay, and iron as the main raw materials in an appropriate ratio to prepare raw cement meal, which is calcined to become cement clinker.

[0003] In the traditional cement clinker calcination process, air is used as the calcination atmosphere, the internal temperature of the kiln is low, and consequently, the decomposition rate of carbonate salts in the raw materials is low. This results in a low rate of transformation of 2CaOSiO2 (C2S) to 3CaOSiO2 (C3S) during the clinker formation process, and the clinker formed has a low C3S content, which is not conducive to improving clinker quality. Furthermore, the air is not conducive to the complete combustion of the fuel, and the N2 and inert gases, which constitute approximately 79% of the air, not only fail to act as combustion aids but also lead to an increase in the amount of NOx pollutant generated, while the relatively low volume fraction of CO2 in the combustion chamber increases the difficulty of carbon capture and sequestration. Summary of the invention

[0004] Accordingly, the present application provides a process for preparing cement clinker under oxygen-rich combustion conditions, aimed at solving to some extent the problems of generating high amounts of NOX pollutant, difficulty in capturing and sequestration carbon, low C3S content of cement clinker, and poor clinker performance of existing cement clinker production processes.

[0005] This application also provides the cement clinker produced using the above-mentioned process and the cementitious material which contains it.

[0006] This application provides a process for preparing cement clinker, comprising the following steps:

[0007] 1) preparation of raw cement flour; and

[0008] 2) calcination of raw cement flour under an oxygen-rich atmosphere, the oxygen-rich atmosphere being a mixture of oxygen gas and carbon dioxide in a volume ratio of (0.21-0.61) : (0.39-0.79).

[0009] Preferably the percentage by volume of oxygen in the oxygen-rich atmosphere of step 2) is in a range of 21% to 50%.

[0010] Preferably the percentage by volume of oxygen in the oxygen-rich atmosphere of step 2) is 31% or 41%.

[0011] Preferably, step 2) of calcination is carried out in a temperature range of 1430 °C to 1470 °C for a period of 45 minutes to 75 minutes.

[0012] Preferably, the composition of the raw material of the raw cement flour of step 1) comprises the following elements by weight: 75-85 parts of limestone, 5-15 parts of coal slag, 1-5 parts of iron residues and 5-10 parts of gas ash.

[0013] Preferably, the composition of the raw material of the raw cement meal of step 1) further comprises fly ash; and

[0014] fly ash is added in an amount of 0.8% to 4% of the total mass of the raw materials of the raw cement flour.

[0015] Optionally, the fly ash of the present application is obtained by combustion at 815°C of pulverized coal.

[0016] Optionally, the raw cement material powder for preparing the raw cement flour of step 1) has a particle size of 4%-6% of 80 pm sieve residue.

[0017] The present application provides a cement clinker prepared using the above cement clinker preparation process.

[0018] Preferably, the cement clinker comprises the following mineral phases by mass percentages: from 58% to 70% of C3S, from 10% to 17% of C2S, from 2.0% to 2.7% of C3A, from 17% to 23% of C4AF, and various mineral phases for balancing.

[0019] Preferably, the cement clinker comprises the following mineral phases in the following mass percentages: 69.1% C3S, 11.4% C2S, 2.0% C3A, 17.4% C4AF, and various mineral phases for balancing; or,

[0020] The cement clinker comprises the following mineral phases by mass percentages: 63.3% C3S, 14.2% C2S, 2.0% C3A, 20.4% C4AF and various mineral phases for balancing.

[0021] The present application also provides a cement material comprising the cement clinker described above.

[0022] The technical solution of this application has the following advantages.

[0023] 1. This application provides a process for preparing cement clinker, comprising the steps 1) preparation of raw cement meal; and 2) calcination of the raw cement meal under an oxygen-rich atmosphere, the oxygen-rich atmosphere being a mixture of oxygen and carbon dioxide gases in a volume ratio of (0.21-0.61): (0.39-0.79). The process of this application changes the equilibrium partial pressure of CO2 in the system and the fuel combustion mechanisms by calcining under an oxygen-rich atmosphere with a specific oxygen-to-carbon-dioxide ratio without changing the composition and ratio of the raw cement meal.With the addition of CO2, the activation energy and the pre-exponential reaction factor of fuel combustion are both lowered, and the reaction rate constant is decreased, which increases the peak combustion period, effectively reduces coal consumption in clinker calcination, increases cement clinker yield, while increasing the decomposition rate of carbonate salts in raw materials, and promoting the transformation of C2S to C3S, which is conducive to the generation of more C3S in cement clinker, and the prepared clinker has a better submicroscopic morphology, in which the crystal size of Alite (its main ingredient is C3S) becomes larger, the boundaries are clearer, the crystal morphology is excellent, and more CSH gel needle crystals appear on the surface of the hydrated product.Calcining under an oxygen-rich atmosphere with a specific oxygen-to-carbon dioxide ratio significantly reduces NOx pollutant generation. Since CO2 is the main component of the combustion gases after calcination, separation becomes more difficult, and carbon capture and sequestration are facilitated. The cement clinker preparation process described in this application does not readily generate NOx pollutants. The main component of the combustion gases is CO2, which is more conducive to carbon capture and sequestration. The prepared cement clinker has a higher C3S content and exhibits good performance (hydration effect and stability).

[0024] 2. In the process for preparing cement clinker provided herein preferably requires that the oxygen volume percentage in the oxygen-rich atmosphere of step 2) be in the range of 21% to 50%. By controlling the oxygen volume percentage of the oxygen-rich atmosphere to remain within this range, the compressive strength of the resulting cement clinker is significantly improved. Furthermore, preferably, the oxygen volume percentage in the oxygen-rich atmosphere of step 2) is 31% or 41%. Thanks to the selection of an oxygen-rich atmosphere with a specific ratio of oxygen and carbon dioxide for calcination, the cement clinker obtained has good properties (hydration effect and stability), while the compressive strength of the cement clinker and the quality of the cement clinker are better.

[0025] 3. The process for preparing cement clinker provided by this application can reduce the clinker coefficient when the prepared cement clinker produces cement of the same strength level, thereby reducing carbon emissions from the cement production process, which is conducive to the low-carbon transformation of the cement industry.

[0026] 4. The process for preparing cement clinker provided by this application is highly efficient, low carbon and environmentally friendly, and the process is simple and easy to implement, providing great environmental and economic benefits. BRIEF DESCRIPTION OF THE FIGURES

[0027] In order to illustrate more clearly the technical solutions of specific embodiments of the present application or of the prior art, the accompanying figures which are to be used in the description of specific embodiments or of the prior art will be presented briefly below; of course the accompanying figures in the description which follow constitute certain embodiments of the present application, and a person skilled in the art can obtain other figures based on these figures without creative effort.

[0028] Fig. 1 represents a comparison of the XRD profiles of cement clinker from Examples 1-5 and Comparative Example 1 of the present application;

[0029] Fig. 2 represents a comparison of the mass contents of free calcium oxide (f-CaO) in the cement clinker of Examples 1-5 and Comparative Example 1 of this application;

[0030] Fig. 3 represents a comparison of the compressive strength on days 3 and 28 of the cement of the present application containing the cement clinker of Examples 1-5 and Comparative Example 1;

[0031] Fig. 4 represents a comparison of the cement clinker of Example 1 (A1), Example 2 (A2) and Comparative Example 1 (A0) of the present application under a polarizing microscope (in which Alite means Alite crystals, and Belite means Belite crystals);

[0032] Figure 5 shows a comparison of the cement clinker of Example 3 (A3), Example 4 (A4) and Example 5 (A5) of this application under a microscope polarizing (in which Alite means Alite crystals, and Bélite means Bélite crystals);

[0033] Figure 6 shows a hydrated cement clinker comparison of Example 1 (A1), Example 2 (A2), and Comparative Example 1 (AO) of this application under a scanning electron microscope; and

[0034] Fig. 7 represents a hydrated cement clinker comparison of Example 3 (A3), Example 4 (A4) and Example 5 (A5) of this application under a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0035] The following examples are provided to offer a better and more thorough understanding of this application, and are not limited to the preferred embodiments described, they do not constitute a limit to the content and scope of protection of this application, and any product identical or similar to this application which is derived therefrom and which is obtained by any person inspired by this application or by combining the features of this application with those of the prior art is covered by the scope of protection of this application.

[0036] When specific experimental steps or conditions are not indicated in the examples, the operations or conditions of conventional experimental steps described in the relevant documentation may be applied. When no manufacturer is mentioned for the reagents or instruments used, the reagents or instruments used are conventional reagents and products that can be obtained on the market.

[0037] The composition of the limestone used in the examples and comparative examples of this application comprises: 48.24% CaO, 5.76% SiO2, 1.46% Al2O3, 0.70% Fe2O3, 1.78% MgO, 0.30% SO3, 0.43% K2O, 0.08% Na2O, and 41.25% loss by calcination.

[0038] The composition of coal ash includes: 5.17% CaO, 62.01% SiO2, 21.87% Al2O3, 4.13% Fe2O3, 0.26% MgO, 0.03% SO3, 2.56% K2O, 1.07% Na2O, and 2.90% loss by calcination.

[0039] The composition of the iron residues comprises: 2.02% CaO, 79.41% SiO2, 3.20% Al2O3, 9.77% Fe2O3, 2.04% MgO, 0.28% SO3, 0.59% K2O, 0.23% Na2O, and 2.46% loss by calcination; and is sourced from Anshan Jinhe Mining Co., Ltd.

[0040] The composition of the gas ash includes: 5.43% CaO, 10.37% SiO2, 5.75% Al2O3, 34.96% Fe2O3, 1.59% MgO, 0.13% SO3, 0.91% K2O, 0.39% Na2O, and 40.48% loss by calcination. Example 1

[0041] The example provides a process for preparing cement clinker, comprising the following steps:

[0042] 1) preparation of raw cement flour by mixing 81.34% limestone, 7.94% of coal ash, 1.98% iron residue, 7.93% gas ash and 0.81% fly ash depending on the composition of the raw material of the raw cement meal, in which the fly ash obtained by combustion of pulverized coal from bituminous coal at 815°C, and limestone powder, coal ash, iron residue, gas ash and fly ash have 80 µm sieve residues of 5%; and

[0043] 2) calcination of raw cement flour under an oxygen-rich atmosphere, The oxygen-rich atmosphere being a mixture of oxygen gas and carbon dioxide in a volume ratio of 0.61:0.39, calcination was carried out at a temperature of 1450°C for a period of 75 minutes. Example 2

[0044] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2) was a mixture of oxygen gas and carbon dioxide in a volume ratio of 0.51:0.49. Example 3

[0045] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2) was a mixture of oxygen gas and carbon dioxide in a volume ratio of 0.41:0.59. Example 4

[0046] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2) was a mixture of oxygen gas and carbon dioxide in a volume ratio of 0.31:0.69. Example 5

[0047] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2) was a mixture of oxygen gas and carbon dioxide in a volume ratio of 0.21:0.79. Example 6

[0048] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of the step 2) was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.41:0.59, and calcination was carried out at 1430°C for 75 minutes. Example 7

[0049] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.31:0.69, and calcination was carried out at 1430°C for 60 minutes. Example 8

[0050] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.21:0.79, and calcination was carried out at 1430°C for 75 minutes. Example 9

[0051] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.41:0.59, and calcination was carried out at 1450°C for 45 minutes. Example 10

[0052] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.21:0.79, and calcination was carried out at 1450°C for 45 minutes. Example 11

[0053] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.61:0.39, and calcination was carried out at 1450°C for 60 minutes. Example 12

[0054] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.51:0.49, and calcination was carried out at 1450°C for 60 minutes. Example 13

[0055] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2) was a mixture of oxygen gas and carbon dioxide in a volume ratio of 0.31:0.69, and calcination was carried out at 1470°C for 45 minutes. Example 14

[0056] This example provides a process for preparing cement clinker, which differs from Example 1 only in that the oxygen-rich atmosphere of step 2 was a mixture of oxygen and carbon dioxide gases in a volume ratio of 0.41:0.59, and calcination was carried out at 1470°C for 60 minutes. Comparative Example 1

[0057] This comparative example provides a process for preparing cement clinker, which differs from Example 1 only in that in step 2), the raw cement flour was placed in a silicon molybdenum kiln in which the atmosphere can be adjusted, and calcination was carried out under an air atmosphere at 1450°C for 75 minutes to obtain the cement clinker. Example of a test 1

[0058] The advanced D8 X-ray diffractometer from the German company Brucker was used to scan the cement clinker of Examples 1-5 and Comparative Example 1, under the following test conditions: accelerating voltage of 40 kV, accelerating current of 40 mA, step size of 0.02°, scan time of 1 second per step, and scan angle of 10-70°. At the end of the scan, the MAUD software was used to refine the scan results of the clinker samples using the Rietveld total spectrum fitting analysis method, and the XRD patterns and refinement results were obtained to determine the mineral phase content. The results of the analyses of the various mineral phase contents for different samples are shown in Table 1, and the XRD patterns are shown in [Fig. 1].

[0059] 3CaO SiO2 (C3S), 2CaO SiO2 (C2S), 3CaOAl2O3 (C3A), and 4CaO Al2O3 Fe2O3 (C4AF) were the four principal mineral phases of the cement clinker, and the remainder consisted of a small amount of various other mineral phases. Under different calcination regimes, the crystal structure and mineral composition of the cement clinker can vary significantly. The sample numbers corresponding to Examples 1-5 and Comparative Example 1 are shown in Table 1, which are the same as the sample numbers in the test examples that follow.

[0060] [Tables 1] Sample No. on Main mineral content in the linker (wt.%) C3S C2S C3A c4af Example 1 Al 61.9 13.5 2.5 21.9 Example 2 A2 64.7 12.4 2.7 20.1 Example 3 A3 69.1 11.4 2.0 17.4 Example 4 A4 63.3 14.2 2.0 20.4 Example 5 A5 66.9 11.1 2.3 19.4 Comparative Example 1 A0 52.2 21.2 2.9 23.5

[0061] As shown in Table 1, compared to sample AO, which was calcined in an air atmosphere in Comparative Example 1, the samples in Examples 1-5, which were calcined in an oxygen-rich CO2 / O2 mixture atmosphere, show a more significant increase in C3S content, but a more significant reduction in C2S, C3A, and C4AF content. The C3S and C4AF contents change significantly with changes in CO2 concentration. It can be observed that calcination under an oxygen-rich CO2 / O2 mixture atmosphere in the present application can significantly increase the C3S content of the cement clinker.

[0062] Furthermore, when the CO2 content was relatively low, the C3S content of the calcined samples gradually increased with increasing CO2 / O2 ratio. In Example 3, the C3S content of sample A3, which was calcined under atmospheric conditions with a CO2 / O2 ratio reaching 0.59 / 0.41, was highest (69.1%). The C3S content then began to decrease with increasing CO2 / O2 ratio, and the C3S content began to increase again when the CO2 / O2 ratio reached 0.79 / 0.21. Clearly, the effect of the CO2 / O2 atmosphere on the mineral phase composition of the calcined samples was relatively complex, primarily due to the temperature changes in mineral and liquid phase formation caused by the CO2 / O2 atmosphere during the combustion process.In particular, the content and properties of the liquid phase were crucial for C3S generation. The optimal calcination atmosphere was most favorable for the conversion of C2S to C3S, resulting in the highest C3S clinker content. As we can see from the aforementioned results, sample A3 from Example 3 has the highest C3S content (69.1%), indicating that the CO2 / O2 ratio of 0.59 / 0.41 is the most favorable calcination atmosphere for C3S growth in clinker. Example of a test 2

[0063] A rapid free calcium oxide tester of cement FC-6 was used to determine the mass content of free calcium oxide of the cement clinker of Examples 1-5 and Comparative Example 1. The results are shown in [Fig.2].

[0064] The cement clinker of Examples 1-5 and Comparative Example 1 was ground until all the cement clinker passed through a 5 mm square-hole sieve, and then pulverized with natural gypsum dihydrate conforming to the provisions of GB / T5483 in a standard test mill to form PI-type Portland cement, in which the mass content of natural gypsum dihydrate was 5%. The compressive strength at 3 and 28 days of the PI-type Portland cement was measured in accordance with GB / T 17671-2021 (Test Method for Strength of Cementitious Mortar (ISO Method)), and the results are shown in [Fig. 3].

[0065] As can be seen in [Fig. 2], the free calcium oxide (f-CaO) content of the samples calcined in an air atmosphere was 0.88 wt%, and the f-CaO content of all samples calcined in a CO2 / O2 atmosphere decreased. This was due to the fact that adding a certain concentration of CO2 to the atmosphere changed the equilibrium partial pressure of CO2 in the system and slowed the decomposition process of the carbonate salts. On the other hand, the f-CaO content of the clinker showed a clear upward trend as the CO2 / O2 ratio increased from 0.39 / 0.61 to 0.79 / 0.21. Furthermore, the f-CaO content of all the experimental samples was always below 1.0 wt%, meeting the f-CaO control requirements for clinker.Increasing the free calcium oxide (f-CaO) content in cement clinker directly affects cement stability; therefore, we find that the examples in this application, in which calcination was carried out under a CO2 / O2 atmosphere, guarantee cement stability and improve cement quality.

[0066] As shown in [Fig. 3], the compressive strength of samples A1 to A3 in the examples increased, and the compressive strength of samples A4 and A5 decreased, indicating that a moderate increase in the CO2 / O2 concentration ratio was conducive to improving the compressive strength of the cement, e.g., this may also reflect the fact that the compressive strength of the cement clinker increased, and that the compressive strength of the cement clinker was highest when the CO2 / O2 ratio reached 0.59 / 0.41 (sample A3); when the CO2 / O2 ratio increased further, the compressive strength, on the contrary, began to decrease, however, even with a CO2 / O2 ratio of 0.79 / 0.21, the compressive strength of the cement clinker was still comparable to that of sample A0 which was calcined under a conventional air atmosphere.That is to say, the cement clinker obtained by calcination under a CO2 / O2 atmosphere with concentration ratios of 0.59 / 0.41, 0.69 / 0.31, and 0.79 / 0.21. in Examples 3-5 has a higher compressive strength, and the quality of the cement clinker has been further improved.

[0067] Furthermore, it can be observed that sample A4 showed the highest strength growth rate (79.10%) in the 3-28 day range, and that sample A3 also showed a relatively high strength growth rate (77.32%). Samples AO, Al, and A2 showed similar strength growth rates, all at 75.10%, while sample A5 showed a relatively low strength growth rate. These results indicate that the CO2-containing calcination atmosphere has an effect on the strength growth rate of the clinker, and the highest strength growth rate of cement clinker was observed when the CO2 / O2 ratios were 0.59 / 0.41 and 0.69 / 0.31.

[0068] In summary, it can be observed that a calcination atmosphere containing CO2 has an effect on the strength growth rate of the clinker. When the CO2 / O2 concentration ratio was in the range of 0.39 / 0.61 to 0.79 / 0.21, a moderate increase in the CO2 / O2 concentration ratio was conducive to improving the compressive strength of the cement clinker. When the CO2 / O2 ratio was 0.59 / 0.41 and 0.69 / 0.31, the strength of the cement clinker was highest, and the strength growth rate was highest in the range of 3-28 days. Example of a test 3

[0069] The cement clinker of Examples 1-5 and Comparative Example 1 was fixed with phenolic resin, then ground flat and polished. The flat surface of the samples was corroded with ammonium chloride solution (wt% = 1%). Observations, measurements, and microstructural analyses of the cement clinker of Examples 1-5 and Comparative Example 1 were then carried out using an Olympus BX-51 polarizing microscope. The images obtained using the polarizing microscope are shown in Figures 4 and 5, with two different positions selected for each sample. The observations were performed under a polarizing microscope. In this case, free calcium oxide was stained. Alite crystals (with the main ingredient C3S) were mainly blue or dark brown, hexagonal or square in shape, and Belite crystals (with the main ingredient C2S) were light brown and round in shape.

[0070] The submicrostructures of clinker minerals obtained under different calcination atmospheres are shown in FIGS. 4 and 5. Comparison of the morphologies of the six sample groups under a reflected light microscope shows that when the calcination atmosphere changed from air to CO2 / O2, the number of Alite crystals in the clinker increased, as did their size, and the boundaries became clearer. With the change in the CO2 / O2 ratio in In the calcination atmosphere, the alite crystals in the clinker became larger and had clearer, more complete outlines, while the belite crystals became smaller and had more blurred outlines. Of all the samples, sample A3 exhibited the best crystal morphology. Most of the alite crystals in sample A3 were relatively regular and complete in shape; most were flat, short, hexagonal columns of uniform size, more abundant (approximately 60-70%), and with more inclusions. The belite crystals were less abundant, moderately sized, mostly ellipsoidal and ovoid in shape, with smooth edges, and a small proportion had grain lines and transverse bands.On the other hand, the AO sample of the comparative example has fewer Alite crystals, the shapes are irregular, the sizes are not homogeneous, the edges are blurred, and there is more adhesion among the minerals; the Belite crystals can be observed in the field of view in higher content, they are basically round shapes, with smooth edges, and with scattered C3S. Example of a test 4

[0071] The cement clinkers of Examples 1-5 and Comparative Example 1 were hydrated for 3 days respectively, and the specific hydration steps included: in accordance with a water-cement ratio of 0.4:1, the cement clinker samples were molded into 20 mm x 20 mm x 20 mm cement paste test blocks, then demolded after 1 day of holding under standard constant temperature and constant humidity conditions (temperature of 20 ± 1°C, humidity of 95 ± 1%), then placed in deionized water at 20 ± 1°C for 2 days of immersion, then the test blocks were removed and broken, and anhydrous ethanol was used to complete the hydration and for subsequent testing and analysis.The hydrated cement clinker samples from Examples 1-5 and Comparative Example 1 were characterized by field emission reading electron microscopy (UltraPlus, Zeiss) to observe the size and morphology of the crystals formed after hydration of the cement clinker; the electron scanning micrographs obtained are shown in FIGS. 6 and 7, with two different positions selected for each sample.

[0072] Figures 6 and 7 show the microscopic surface morphology of the clinker after hydration (for 3 days) obtained from different calcination atmospheres. From the images, we see that the hydrated products on the surface of the samples with different calcination atmospheres were essentially the same; e.g., the early hydration products, hydrated calcium silicate type I (CSH), were an elongated substance growing radially outwards from the cement particles. However, the distribution of the hydrated products on the surface of Al₂O and Al was more dispersed, and the difference in mineral sizes was greater. important; Sample A2 showed CSH similar to laths and tubular; the mineral distribution of A3 and A4 was homogeneous and denser, and the cogwheel and fibrous CSH gels were distributed in staggered agglomerates, in the form of an interlacing mesh, which suggests that the degree of hydration of the cement clinker of Samples A3 and A4 was high, and that the rate of hydration was rapid, also indirectly indicating that the compressive strength of the cements of A3 and A4 was excellent under the CO2 / O2 atmosphere ratios of Examples 3 and 4.The distribution of hydrated minerals on the surface of A5 was sparse, with a clearly visible increase in the number of inter-mineral cracks and fissures. The minerals were small and essentially fully hydrated, with elongated bands of particles forming on the spherical granular minerals that had already been hydrated, scattered, and distributed within them. On the other hand, sample AO, corresponding to Comparative Example 1, has a low degree of hydration, and there were still more flat, short hexagonal columns. Example of a test 5

[0073] The free calcium oxide content of the cement clinker in Examples 6-14 was determined by a rapid free calcium oxide cement analyzer FC-6. The test results are shown in Table 4.

[0074] The cement clinker of Examples 6-14 was scanned using a Brucker D8 advanced X-ray diffractometer, Germany, under the following test conditions: accelerating voltage of 40 kV, accelerating current of 40 mA, step size of 0.02°, scan time of 1 second per step, and scan angle of 10-70°. At the end of the scan, the MAUD software was used to refine the scan results of the clinker samples using the Rietveld total spectrum fitting analysis method to determine the mineral phase content. The test results are shown in Table 4.

[0075] The cement clinker of Examples 6-14 was ground until all the cement clinker passed through a 5 mm square-hole sieve, and then pulverized with natural gypsum dihydrate conforming to the provisions of GB / T5483 in a standard test mill to form PI type Portland cement, in which the mass content of natural gypsum dihydrate was 5%. The 3- and 28-day compressive strength of the PI type Portland cement was measured in accordance with GB / T 17671-2021 (Test Method for Strength of Cementitious Mortar (ISO Method)), and the results are shown in [Fig. 4].

[0076] A lithofacies rating was performed on the cement clinker obtained in Example 4 and Examples 6-14, and the lithofacies score was determined using a An Olympus BX-51c polarizing microscope was used to observe the clinker's microstructure. Scores were determined based on: porosity, hole size and dimensions; mineral content, degree of erosion and uniformity of distribution; and crystal shapes, sizes, etc. The lithofacies scoring criteria are shown in Table 3, and the test results in Table 4.

[0077] [Tables3] Appearance Score (Total 9) Pores Small porosity, dense structure, no obvious holes 3 Small porosity, holes observed, hole diameters being essentially less than 50 µm 2 Relatively large porosity, more holes observed, hole diameters being essentially greater than 50 µm but less than 100 µm 1 Large porosity, many holes observed, hole diameters being essentially greater than 100 µm 0 Mineral Content High C3S content, homogeneous distribution, sporadic f-CaO may be observed 3 Relatively high C3S content, relatively homogeneous distribution, scattered f-CaO may be observed 2 Relatively low C3S content with relatively homogeneous distribution, high C2S content with relatively homogeneous distribution, scattered f-CaO may be observed 1 Low C3S content, high C2S content, non-homogeneous distributionA significant number of agglomerated f-CaO can be observed. 0 Crystal: Alite crystals are large in size, with clear and complete outlines; Belite crystals are small in size, with blurred outlines. 3 Alite crystals are relatively large in size, with clear and relatively complete outlines; Belite crystals are relatively small in size, with relatively blurred outlines. 2, Alite crystals are relatively small in size, with relatively indistinct outlines; belite crystals are relatively small in size, with clear outlines.

[0078] [Tables4] C3S content (wt%) f-CaO (wt%) Lithofacies Score Example 4 60.4 0.66 8 Example 6 58.2 0.71 6 Example 7 59.3 0.77 5 Example 8 60.5 0.65 8 Example 9 60.3 0.71 6 Example 10 61.9 0.8 6 Example 11 61.8 0.57 5 Example 12 63.9 0.55 6 Example 13 61.4 0.54 7 Example 14 63.7 0.62 8 Comparative example f 52.2 0.88 4

[0079] Obviously, the above examples are merely illustrative and do not limit the embodiments. For a person skilled in the art, other variations or changes in different forms can be made based on the above description. It is neither necessary nor possible to mention all embodiments here. Variations or changes that are clearly derived from them are covered by the scope of protection of this application.

Claims

Demands

1. A process for preparing cement clinker, comprising the following steps: 1) preparation of raw cement meal; and 2) calcination of the raw cement meal under an oxygen-rich atmosphere, the oxygen-rich atmosphere being a mixture of oxygen gas and carbon dioxide in a volume ratio of (0.21-0.61): (0.39-0.79).

2. A method according to claim 1, wherein the volume percentage of oxygen in the oxygen-rich atmosphere of step 2) is in a range of 21% to 50%.

3. A method according to claim 2, wherein the volume percentage of oxygen in the oxygen-rich atmosphere of step 2) is 31% or 41%.

4. A method according to claim 1, wherein step 2) of calcination is carried out in a temperature range of 1430 °C to 1470 °C for a period of 45 minutes to 75 minutes.

5. A process according to claim 1, wherein the composition of the raw material of the raw cement meal of step 1) comprises the following elements by weight: 75-85 parts of limestone, 5-15 parts of coal slag, 1-5 parts of iron residues and 5-10 parts of gas ash.

6. A process according to claim 5, wherein the composition of the raw cement meal raw material of step 1) further comprises fly ash; and the fly ash is added in an amount of 0.8% to 4% of the total mass of the raw cement meal raw material.

7. Cement clinker prepared using the cement clinker preparation process according to any one of claims 1-6.

8. Cement clinker according to claim 7, wherein the cement clinker comprises the following mineral phases by mass percentages: from 58% to 70% C3S, from 10% to 17% C2S, from 2.0% to 2.7% C3A, from 17% to 23% C4AF, and various mineral phases for balancing.

9. Cement clinker according to claim 8, wherein the cement clinker comprises the mineral phases by mass percentages

10. the following: 69.1% C3S, 11.4% C2S, 2.0% C3A, 17.4% C4AF, and various mineral phases for balancing; or, the cement clinker comprises the following mineral phases by mass percentages: 63.3% C3S, 14.2% C2S, 2.0% C3A, 20.4% C4AF and various mineral phases for balancing. Cement material comprising cement clinker according to any one of claims 7-9.

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