Cement clinker prepared by completely replacing limestone with carbide slag and preparation method of cement clinker

Abstract

The invention provides a method for preparing cement clinker by using carbide slag to completely replace limestone, which comprises the following steps: respectively crushing calcium material carbide slag, siliceous material coal-fired slag, aluminum material muck and ferrous material sulfuric acid slag, uniformly mixing according to a ratio to form a mixture, preheating the mixture at a certain temperature before calcining to eliminate moisture, and calcining to obtain the cement clinker. The raw materials are calcined at 1300-1500 DEG C for a certain time, so that various components are subjected to chemical reaction to generate main components such as C3S and C2S of the cement, and the main components are rapidly cooled to prevent beta-C2S from being converted into gamma-C2S to finally form the cement clinker. According to the cement clinker and the carbide slag prepared by the method, limestone can be replaced by 100%, exploitation of natural limestone resources is saved, and emission of greenhouse gas CO2 is reduced. And a great deal of solid wastes such as coal-fired slag, muck and sulfuric-acid slag are also consumed to a certain extent. And meanwhile, the energy consumption in the cement clinker production process is reduced, and the industrial production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the fields of cement materials science and industrial solid waste utilization, specifically to a method for preparing cement clinker by completely replacing limestone with carbide slag. Background Technology

[0002] Calcium carbide slag, a major solid waste generated by the chlor-alkali industry (mainly composed of Ca(OH)2), is highly alkaline, and its large-scale stockpiling severely pollutes the environment, necessitating its resource utilization. Meanwhile, the cement industry, as a major source of CO2 emissions, faces severe pressure to reduce carbon emissions. Utilizing calcium carbide slag, rich in calcium, to replace limestone raw materials can significantly reduce process CO2 emissions generated by the decomposition of calcium carbonate.

[0003] However, existing technologies for producing cement clinker from carbide slag face fundamental bottlenecks. On the one hand, the Ca(OH)2 in carbide slag undergoes premature dehydration and heat absorption in the preheating system, significantly increasing heat consumption and generating a large amount of water vapor. This, combined with impurities such as alkali, sulfur, and chlorine in the raw meal, easily leads to severe scaling and blockage in the preheater system, threatening operational stability. On the other hand, its high moisture content, fine particle size, viscosity, and fluctuating impurities make raw meal preparation and transportation difficult. Furthermore, at high admixture levels (generally below 40%), the mineral composition (e.g., low C3S content, high f-CaO) and performance of the clinker are difficult to control stably. Existing new dry-process kiln systems and processes are mainly designed for limestone and are ill-suited to the unique physicochemical properties of high-admixture carbide slag raw meal, thus restricting the large-scale, high-value-added utilization of carbide slag and the deep carbon reduction in cement production. Therefore, there is an urgent need to develop a high-utilization, low-carbon cement clinker preparation method using carbide slag that can overcome admixture limitations, ensure stable system operation, and achieve high-quality clinker production. Summary of the Invention

[0004] Therefore, in view of the technical problems of high carbon emissions in traditional limestone cement preparation and low utilization rate of cement prepared by carbide slag, this invention provides a method for preparing cement clinker by completely replacing limestone with carbide slag.

[0005] The technical solution of the present invention is a cement clinker prepared by completely replacing limestone with carbide slag. The raw materials, by mass percentage, include: 65-75% calcareous carbide slag, 2-5% siliceous coal-fired furnace slag, 15-25% aluminous slag, and 1-5% ferrous sulfuric acid slag.

[0006] Calcium carbide slag is mainly a solid byproduct of the hydrolysis of calcium carbide to produce acetylene. It is easier to decompose during the calcination process, has higher reactivity than limestone, and releases less carbon dioxide. Coal-fired boiler slag is a mineral melting-cooling product after combustion in coal-fired power plants or industrial boilers, with SiO2-Al2O3 as its framework. Slag soil comes from the tailings after resource processing / mineral washing and washing, and the mixture of weathered aluminum-containing waste residue from industrial stockpiles with soil-like materials, as well as the fine powder recycled from building demolition. It is mainly composed of Al2O3+SiO2, often containing certain clay minerals (kaolinite / illite, etc.), with fine particles and strong plasticity, which is conducive to uniform batching. Sulfuric acid slag is the roasting slag / burning residue after sulfuric acid production from pyrite. Its main characteristic is high iron content. It is often used as a "correcting iron" raw material for cement clinker, which helps to form a liquid phase and reduce the calcination temperature.

[0007] The reason why this invention can completely replace limestone with carbide slag is that the effective source of CaO provided by carbide slag is more active, the decomposition path is better, and it is easier to synergistically generate clinker mineral phases with solid wastes such as Si / Al / Fe during the calcination process. Thus, under the premise of meeting the batching modulus (KH / SM / IM), calcium can be supplied by carbide slag.

[0008] Limestone provides calcium: CaCO3 → CaO + CO2↑ (This requires decomposition and release of CO2; the decomposition temperature is higher, and CO2 diffusion can affect the reaction). Calcium supply from carbide slag: Ca(OH)2 → CaO + H2O↑ (lower dehydration temperature, resulting in finer and more reactive CaO) Synergistic effects: Synergistic effect with siliceous materials (coal-fired furnace slag 2-5%) promotes the formation of silicate phase; synergistic effect with aluminous materials (slag soil 15-25%) stabilizes the modulus and generates aluminate phase; synergistic effect with ferrous materials (sulfuric acid slag 1-5%) forms liquid phase and reduces the difficulty of calcination.

[0009] The main substitution effects are: calcium source substitution; calcium carbide slag replaces limestone. Calcium carbide slag provides all the CaO required for clinker, eliminating the need for CaCO3 decomposition to supply calcium, thus achieving complete substitution.

[0010] Coal-fired furnace slag: Replacing part of the silica-based corrective raw materials (SiO2 contribution from sandstone / silica powder / part of clay). Slag: a substitute for traditional aluminosilicate raw materials (clay / shale / siltstone, etc.) Sulfuric acid slag: a substitute for iron-based corrective raw materials (iron ore powder / iron slag, etc.).

[0011] According to the present invention, a cement clinker prepared by completely replacing limestone with carbide slag is preferably prepared in the following manner: The carbide slag contains 40-80% CaO, 1-5% SiO2, 1-5% Al2O3, and 0.1-5% Fe2O3; the coal-fired slag contains 1-5% CaO, 50-80% SiO2, 1-10% Al2O3, and 1-5% Fe2O3; the slag soil contains 1-10% CaO, 40-60% SiO2, 5-20% Al2O3, and 1-15% Fe2O3; and the sulfuric acid slag contains 1-5% CaO, 20-40% SiO2, 1-10% Al2O3, and 30-60% Fe2O3. The above describes the composition of each material in the raw meal. During calcination, the CaO, SiO2, and Fe2O3 content... 2， Al2O 3， Fe2O3 has already been reacted during the calcination process. The main components of the clinker are dicalcium silicate, tricalcium silicate, dicalcium aluminate, and tetracalcium aluminoferrite.

[0012] This invention also provides a method for preparing cement clinker by completely replacing limestone with carbide slag, comprising the following steps: Step 1: Grind the carbide slag, coal slag, slag soil and sulfuric acid slag into powder to obtain raw meal; Step 2: Dry the mixture at 80-120℃ for 20-30 hours; Step 3: Add water to the mixture, the water mass being 3-12% of the raw material; after stirring evenly, press it into blocks under certain pressure, and dry the raw material blocks at 80-120℃ for 8-16 hours; Step 4: Calcine the dried raw material blocks at high temperatures of 900-1000℃ and 1300-1500℃ in sequence, and then rapidly cool them down to 60-120℃ after calcination.

[0013] In step 4, the first stage of heating and holding is to ensure that all the calcium oxide is decomposed, and the second stage of heating and holding is to ensure that the raw material reacts fully.

[0014] According to the present invention, a method for preparing cement clinker by completely replacing limestone with carbide slag is preferred, wherein the grinding in step 1 is carried out using a ball mill; and the ground material is then screened using a 100-300 mesh sieve.

[0015] According to the present invention, a method for preparing cement clinker by completely replacing limestone with carbide slag is preferably characterized by pre-drying before grinding, with a pre-drying temperature of 60-80℃ and a drying time of 6-12 hours. Pre-drying dehydrates and dries the carbide slag.

[0016] According to the present invention, a method for preparing cement clinker by completely replacing limestone with carbide slag is preferably wherein, in step 3, the mass of water added is 5-10% of the raw meal, and the pressure is 20-40 MPa.

[0017] Preferably, in step 3, the raw material blocks are dried at 90-110℃ for 9-14 hours.

[0018] According to the present invention, a method for preparing cement clinker by completely replacing limestone with carbide slag is preferably described in step 4, wherein the calcination process is as follows: heating to 900-1000℃ at a rate of 8-12℃ / min, holding for 20-40min, and then heating to 1300-1500℃ at a rate of 4-10℃ / min, holding for 30-80min.

[0019] Preferably, in step 4, the material is placed in a muffle furnace for calcination.

[0020] According to the present invention, in a method for preparing cement clinker by completely replacing limestone with carbide slag, preferably, in step 4, the rapid cooling refers to cooling to 60-120℃ within 2-5 minutes.

[0021] This invention provides a method for preparing cement clinker by completely replacing limestone with carbide slag. It has the following beneficial effects: The core advantage of this method lies in its first-ever complete replacement of limestone with calcium carbide slag, achieving 100% substitution. Simultaneously, it utilizes various solid wastes to produce cement clinker, enabling industrial application. Cement meeting national standards can be obtained from waste materials, saving on cement raw materials. This achieves a win-win situation for resources, the environment, and the economy. At the resource and environmental level, this technology significantly reduces reliance on the extraction of non-renewable natural limestone resources and directly and substantially reduces process carbon dioxide emissions from calcium carbonate decomposition during cement production, representing an effective practice in addressing the "dual carbon" challenge. Furthermore, it successfully solves the problem of large-scale, high-value disposal of calcium carbide slag, a major alkaline solid waste, and synergistically utilizes various industrial solid wastes such as coal-fired slag, waste soil, and sulfuric acid slag, turning waste into treasure and fundamentally mitigating the potential environmental risks of solid waste stockpiling.

[0022] At the technical level, this invention successfully overcomes the core bottleneck caused by high-volume calcium carbide slag—the industry problem of severe scaling and blockage in the preheater system due to its high moisture content, fine particle size, and impurities—through innovative "raw material block pretreatment" (including pressing and pre-drying) and a carefully optimized "preheating-decomposition-calcination" process. This ensures the long-term safe and stable operation of the production line. At the product performance level, thanks to scientific raw material proportioning and precise process control, it can stably produce high-quality cement clinker with a reasonable mineral composition, low free calcium oxide (f-CaO) content, and excellent mechanical properties. Its product quality is comparable to clinker prepared from traditional limestone raw materials, completely breaking the traditional limitation that high-volume utilization of industrial solid waste often sacrifices product performance. Finally, in terms of economics, this method, by replacing high-priced raw materials and reducing solid waste disposal costs, opens up a new green path for cement companies to reduce costs and increase efficiency, creating considerable economic benefits. In summary, this invention is not only a technological breakthrough, but also a sustainable cement production solution that can simultaneously achieve environmental protection, resource conservation, carbon emission reduction, and improved economic benefits. Attached Figure Description

[0023] Figure 1 A schematic diagram of a process for preparing cement clinker by completely replacing limestone with carbide slag. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The chemical composition of all raw materials in the examples is shown in Appendix 1; Table 1. Chemical composition of raw materials (dry basis)

[0026] Example 1: In this embodiment, the chemical composition of each raw material is shown in Table 1; By mass percentage, the composition includes: 73% calcium carbide slag, 4.87% siliceous coal-fired furnace slag, 19.63% aluminous slag, and 2.5% ferrous sulfuric acid slag. Step 1: Thoroughly pre-dry the calcium carbide slag, coal-fired furnace slag, slag soil and sulfuric acid slag at a temperature of 60℃ for 12 hours. Grind them thoroughly using a ball mill, and then screen and mix them evenly with a 300-mesh sieve to obtain raw materials. Step 2: Dry at 80℃ for 24 hours; Step 3: Add water at 10% of the raw material weight to the raw material, stir well, press into blocks under 20MPa pressure, and put the raw material blocks into an oven at 100℃ for 8 hours to dehydrate; Step 4: Place the dried raw material into a muffle furnace for high-temperature calcination for a certain period of time. After calcination, rapidly cool down. The calcination process is as follows: heat to 900℃ at a rate of 10℃ / min, hold for 20min, then heat to 1400℃ at a rate of 5℃ / min, hold for 60min, and after calcination, rapidly cool down within 3min to bring the temperature to 60℃.

[0027] Example 2

[0028] In this embodiment, the chemical composition of each raw material is shown in Table 1; By mass percentage, the composition includes: 73.91% calcium carbide slag, 3.98% siliceous coal-fired furnace slag, 19.11% aluminous slag, and 3% ferrous sulfuric acid slag. Step 1: Thoroughly pre-dry the carbide slag, coal slag, slag soil and sulfuric acid slag at a temperature of 70℃ for 10 hours. Grind them thoroughly using a ball mill, and then screen and mix them evenly with a 300-mesh sieve to obtain raw materials. Step 2: Dry at 90℃ for 30 hours; Step 3: Add 5% water by weight of the raw material to the raw material, stir well, press into blocks under 30MPa pressure, and put the raw material blocks into a 90℃ oven for 10 hours to dehydrate. Step 4: Place the dried raw material into a muffle furnace for high-temperature calcination for a certain period of time, and then rapidly cool it down after calcination. The calcination process is as follows: heat to 900℃ at a rate of 10℃ / min, hold for 30min, then heat to 1450℃ at a rate of 5℃ / min, hold for 60min, and then rapidly cool down for 5min after calcination to bring the temperature down to 120℃.

[0029] Example 3

[0030] In this embodiment, the chemical composition of each raw material is shown in Table 1; By mass percentage, the composition includes: 72.04% calcium carbide slag, 4.06% siliceous coal-fired furnace slag, 22.8% aluminous slag, and 1.1% ferrous sulfuric acid slag. Step 1: Thoroughly pre-dry the carbide slag, coal-fired furnace slag, slag soil and sulfuric acid slag at a temperature of 80℃ for 6 hours. Grind them thoroughly using a ball mill, and then screen and mix them evenly with a 300-mesh sieve to obtain raw materials. Step 2: Drying temperature is 110℃, drying time is 24 hours; Step 3: Add water at 12% of the raw material mass to the raw material, stir well, press into blocks under 20MPa pressure, and put the raw material blocks into an oven at 110℃ for 16 hours to dehydrate. Step 4: Place the dried raw material into a muffle furnace for high-temperature calcination for a certain period of time, and then rapidly cool it down after calcination. The calcination process is as follows: heat to 900°C at a rate of 10°C / min, hold for 20 minutes, then heat to 1350°C at a rate of 5°C / min, hold for 80 minutes, and then rapidly cool down for 2 minutes after calcination to bring the temperature down to 80°C. Example 4

[0031] In this embodiment, the chemical composition of each raw material is shown in Table 1; By mass percentage, the composition includes: 73.09% calcium carbide slag, 4.36% siliceous coal-fired furnace slag, 19.3% aluminous slag, and 3.25% ferrous sulfuric acid slag. Step 1: Thoroughly pre-dry the carbide slag, coal-fired furnace slag, slag soil and sulfuric acid slag at a temperature of 80℃ for 8 hours. Grind them thoroughly using a ball mill, and then screen and mix them evenly with a 200-mesh sieve to obtain raw materials. Step 2: Drying temperature is 120℃, drying time is 20 hours; Step 3: Add water equal to 10% of the raw material weight to the raw material, stir well, press into blocks under 40MPa pressure, and put the raw material blocks into an oven at 100℃ for 9 hours to dehydrate; Step 4: Place the dried raw material into a muffle furnace for high-temperature calcination for a certain period of time, and then rapidly cool it down after calcination. The calcination process is as follows: heat to 1000℃ at a rate of 8℃ / min, hold for 40min, then heat to 1500℃ at a rate of 10℃ / min, hold for 30min, and then rapidly cool down for 2min after calcination to bring the temperature down to 80℃. Example 5

[0032] This invention provides a method for preparing cement clinker by completely replacing limestone with carbide slag, comprising the following steps: In this embodiment, the chemical composition of each raw material is shown in Table 1; By mass percentage, the composition includes: 67% calcium carbide slag, 4.51% siliceous coal-fired furnace slag, 25% aluminous slag, and 3.49% ferrous sulfuric acid slag. Step 1: Thoroughly pre-dry the calcium carbide slag, coal-fired furnace slag, slag soil and sulfuric acid slag at a temperature of 80℃ for 9 hours. Grind them thoroughly using a ball mill, sieve them through a 100-mesh screen and mix them evenly to obtain raw materials. Step 2: Dry at 105℃ for 24 hours; Step 3: Add water equal to 10% of the raw material weight to the raw material, stir well, press into blocks under 20MPa pressure, and put the raw material blocks into an 80℃ oven for 13 hours to dehydrate. Step 4: Place the dried raw material into a muffle furnace for high-temperature calcination for a certain period of time, and then rapidly cool it down after calcination. The calcination process is as follows: heat to 900°C at a rate of 12°C / min, hold for 20 minutes, then heat to 1300°C at a rate of 8°C / min, hold for 60 minutes, and then rapidly cool down for 3 minutes after calcination to bring the temperature down to 90°C.

[0033] This invention utilizes calcareous carbide slag, siliceous coal-fired furnace slag, aluminous slag, and ferrous sulfuric acid slag. These are separately pulverized and then mixed uniformly in a specific ratio to form a mixture. Before calcination, the mixture is preheated at a certain temperature to remove moisture. Calcination at 1300-1500℃ for a certain time allows the various components to undergo chemical reactions, generating the main cement components C3S and C2S. The mixture is then rapidly cooled to prevent the transformation of β-C2S to γ-C2S, ultimately forming cement clinker. The cement clinker prepared using this method can completely replace limestone with carbide slag, saving on the mining of natural limestone resources and reducing CO2 emissions. It also consumes a number of solid wastes, including coal-fired furnace slag, slag, and sulfuric acid slag. Furthermore, it saves energy in the cement clinker production process and improves industrial production efficiency, among other advantages.

[0034] This invention employs a preheating and calcination process, which can completely replace limestone with carbide slag in the preparation of cement clinker. This greatly saves on the mining of natural limestone, reduces carbon emissions, and saves energy consumption in the cement production process. At the same time, it can effectively eliminate industrial solid waste carbide slag, achieving high-value utilization of industrial solid waste.

Claims

1. A type of cement clinker prepared by completely replacing limestone with carbide slag, characterized in that: The raw materials, by weight percentage, include: 65-75% calcium carbide slag, 2-5% siliceous coal-fired furnace slag, 15-25% aluminous slag, and 1-5% ferrous sulfuric acid slag.

2. The cement clinker prepared by completely replacing limestone with carbide slag according to claim 1, characterized in that: The carbide slag contains 40-80% CaO, 1-5% SiO2, 1-5% Al2O3, and 0.1-5% Fe2O3; the coal-fired slag contains 1-5% CaO, 50-80% SiO2, 1-10% Al2O3, and 1-5% Fe2O3; the slag soil contains 1-10% CaO, 40-60% SiO2, 5-20% Al2O3, and 1-15% Fe2O3; and the sulfuric acid slag contains 1-5% CaO, 20-40% SiO2, 1-10% Al2O3, and 30-60% Fe2O3.

3. The method for preparing cement clinker by completely replacing limestone with carbide slag as described in claim 1, characterized in that: Includes the following steps: Step 1: Grind the carbide slag, coal slag, slag soil and sulfuric acid slag into powder to obtain raw meal; Step 2: Dry the mixture at 80-120℃ for 20-30 hours; Step 3: Add water to the mixture, the water mass being 3-12% of the raw material; after stirring evenly, press it into blocks under certain pressure, and dry the raw material blocks at 80-120℃ for 8-16 hours; Step 4: Calcine the dried raw material blocks at high temperatures of 900-1000℃ and 1300-1500℃ in sequence, and then rapidly cool them down to 60-120℃ after calcination.

4. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: The grinding described in step 1 is carried out using a ball mill; after grinding, the material is screened using a 100-300 mesh sieve.

5. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: In step 1, pre-drying is performed before grinding. The pre-drying temperature is 60-80℃ and the drying time is 6-12 hours.

6. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: In step 3, the mass of water added is 5-10% of the raw material; the pressure is 20-40 MPa.

7. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: In step 3, the raw material blocks are dried at 90-110℃ for 9-14 hours.

8. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: In step 4, the calcination process involves heating to 900-1000℃ at a rate of 8-12℃ / min and holding for 20-40min, then heating to 1300-1500℃ at a rate of 4-10℃ / min and holding for 30-80min.

9. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: In step 4, the material is placed in a muffle furnace for calcination.

10. The method for preparing cement clinker by completely replacing limestone with carbide slag according to claim 3, characterized in that: In step 4, rapid cooling refers to cooling down to 60-120°C within 2-5 minutes.

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