Method for producing low-carbon cement

Abstract

The embodiment of the present application discloses a low-carbon cement production method, which comprises the following steps: preheating cement raw materials; heating and decomposing the preheated raw materials to decompose calcium carbonate in the cement raw materials into semi-clinker and carbon dioxide gas; sintering the semi-clinker into clinker and cooling the clinker; capturing the carbon dioxide gas; recycling part of the carbon dioxide gas into a decomposition furnace to form a carbon dioxide circulation loop; and supplementing external carbon dioxide into the carbon dioxide circulation loop when the circulation gas amount in the carbon dioxide circulation loop is insufficient. The low-carbon cement production method of the embodiment of the present application avoids the dilution of nitrogen to process emission CO2 in the traditional process by introducing controllable pure CO2 protective gas into the decomposition furnace and maintaining micro-negative pressure.

Description

Technical Field

[0001] This invention relates to the field of cement production technology, and more specifically to a method for producing low-carbon cement. Background Technology

[0002] Cement production is a major source of global carbon emissions, primarily from "process emissions" of limestone decomposition and "energy emissions" of fuel combustion. Current mainstream dry-process cement production tightly couples raw material decomposition and fuel combustion within a precalciner, resulting in a high degree of mixing between process-emitted CO2 and combustion flue gas. This leads to low CO2 concentrations (typically below 30%) and complex composition in the flue gas. This necessitates the processing of massive amounts of mixed gas for subsequent carbon capture, utilization, and storage (CCUS), presenting challenges such as high energy consumption, large equipment size, and high costs.

[0003] While various precalciner designs exist in related technologies, such as swirling and jet-type furnaces, these are all internally heated reactors and cannot solve the fundamental problem of CO2 dilution. Existing jacketed external heating equipment is mostly used in low- and medium-temperature processes in chemical and food industries. Applying jacketed heating structures to cement production provides a new path for the cement industry's decarbonization, but applying jacketed externally heated rotary decalciners to the high-temperature decomposition processes in cement production faces many challenges. For example, how to set key parameters such as rotation speed, zoned heating, and the atmosphere within the decomposition furnace to achieve uniform material decomposition while ensuring that the CO2 gas flow is not diluted and maintaining the safe and stable operation of the decomposition furnace remains a challenge. Currently, there is a lack of a mature process method to achieve high-concentration CO2 enrichment while efficiently pre-decomposing cement. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a method for producing low-carbon cement. This method avoids the dilution of CO2 emitted during the process by nitrogen gas in traditional processes by introducing controllable pure CO2 protective gas into the decomposition furnace and maintaining a slight negative pressure.

[0006] The low-carbon cement production method of this invention includes preheating cement raw materials; heating and decomposing the preheated raw materials to decompose calcium carbonate in the cement raw materials into semi-clinker and carbon dioxide gas; sintering the semi-clinker obtained after decomposition into clinker and cooling the clinker, and capturing the carbon dioxide gas obtained after decomposition; circulating a portion of the carbon dioxide gas obtained after decomposition into a decomposition furnace to form a carbon dioxide circulation loop, and supplementing the carbon dioxide circulation loop with external carbon dioxide when the amount of circulating gas in the carbon dioxide circulation loop is insufficient.

[0007] Compared to related technologies, when the circulating gas volume in the carbon dioxide circulation loop is insufficient, external carbon dioxide can be added to the loop. Employing an externally heated pre-decomposition method, by introducing controllable pure CO2 protective gas into the decomposition furnace and maintaining a slight negative pressure, avoids the dilution of CO2 emitted during the process by nitrogen in traditional processes. This increases the CO2 concentration in the raw material decomposition tail gas from less than 30% in traditional mixed flue gas to over 90%, reducing CO2 capture energy consumption and costs compared to traditional internally heated processes.

[0008] In some embodiments, the low-carbon cement production method of the present invention controls the ratio of the carbon dioxide gas flow rate circulating to the decomposition furnace to the raw material processing volume to be between 1:2 and 3:2.

[0009] In some embodiments of the present invention, before decomposing the raw materials, carbon dioxide gas may be introduced into the decomposition furnace to purge the air inside the decomposition furnace.

[0010] In some embodiments of the present invention, when the raw materials are heated and decomposed in the low-carbon cement production method, the rotation speed of the rotary zone can be adjusted to control the residence time of the raw materials in the decomposition furnace so as to fully decompose the calcium carbonate in the raw materials.

[0011] In some embodiments, the low-carbon cement production method of the present invention sets the rotation speed of the decomposition furnace to 0.8-2.2 rpm and controls the cement raw materials to rise at a constant speed from 830°C-870°C at the inlet to 930°C-970°C at the outlet.

[0012] In some embodiments of the present invention, the preheating temperature of the low-carbon cement production method is controlled at 780°C-870°C when preheating the cement raw materials.

[0013] In some embodiments of the present invention, when sintering semi-clinker in the low-carbon cement production method, the slab clinker is sintered into clinker at 1450℃-1550℃.

[0014] In some embodiments, the low-carbon cement production method of the present invention involves collecting the carbon dioxide gas obtained after decomposition after cooling, dehydration, and dust removal.

[0015] In some embodiments, the high-temperature gas flow after cooling clinker in the low-carbon cement production method of the present invention can be circulated to the decomposition furnace to assist the combustion of fuel in the decomposition furnace.

[0016] In some embodiments, the high-temperature gas from the decomposition furnace after combustion in the low-carbon cement production method of this invention can be sent to the raw material preheating zone for countercurrent heat exchange with the cement raw materials. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the low-carbon cement production method according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the structure of the second discharge port in the low-carbon cement production method of this invention.

[0019] Figure label:

[0020] 1. Preheater; 101. First feed inlet; 102. First discharge outlet; 2. Decomposer; 201. Second discharge outlet; 202. Third discharge outlet; 3. Sintering unit; 301. Rotary kiln; 302. Grate cooler; 4. Carbon collector. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] Reference Figures 1-2 As shown, the low-carbon cement production method of this invention includes preheating cement raw materials; heating and decomposing the preheated raw materials to decompose calcium carbonate in the cement raw materials into semi-clinker and carbon dioxide gas; sintering the semi-clinker obtained after decomposition into clinker, and cooling the clinker; capturing the carbon dioxide gas obtained after decomposition; and circulating a portion of the carbon dioxide gas obtained after decomposition back into the decomposition furnace to form a carbon dioxide circulation loop. Compared to related technologies, when the circulating gas volume in the carbon dioxide circulation loop is insufficient, external carbon dioxide can be added to the loop. Employing an externally heated pre-decomposition method, by introducing controllable pure CO2 protective gas into the decomposition furnace and maintaining a slight negative pressure, avoids the dilution of CO2 emitted during the process by nitrogen in traditional processes. This increases the CO2 concentration in the raw material decomposition tail gas from less than 30% in traditional mixed flue gas to over 90%, reducing CO2 capture energy consumption and costs compared to traditional internally heated processes.

[0023] Optionally, the low-carbon cement production method of this embodiment of the invention produces cement using a cement production system. This system includes a preheater 1, a decomposer 2, a calciner 3, and a carbon trap 4. The preheater 1 has a first inlet 101 and a first outlet 102. The first inlet 101 receives cement raw meal, and the first outlet 102 discharges the cement raw meal preheated by the preheater 1. The decomposer 2 is connected to the first outlet 102 to receive the preheated cement raw meal discharged from the preheater 1. It is used to heat and decompose the calcium carbonate in the cement raw meal entering the decomposer 2 into semi-clinker and carbon dioxide gas. The decomposer 2 has a second outlet 201 for discharging the semi-clinker and a third outlet 202 for discharging the carbon dioxide gas. A portion of the calciner 3 is connected to the second outlet 201 to receive the semi-clinker discharged from the decomposer 2 and sinter it into clinker. The carbon trap 4 is connected to the third outlet 202 to receive and collect the carbon dioxide gas discharged from the decomposer 2.

[0024] In the cement production system, raw cement meal first enters preheater 1 for preheating to improve the energy efficiency of subsequent decomposition processes. The preheated meal then enters decomposer 2, where it is heated by a device located on the outer wall of the cylinder. The key to this design is the placement of the device on the outer wall of decomposer 2, which separates the flue gas generated from combustion from the carbon dioxide gas produced by the decomposition of calcium carbonate. Decomposer 2 has two outlets: a second outlet 201 discharges the semi-cooked meal, and a third outlet 202 specifically discharges the carbon dioxide gas produced by the decomposition of calcium carbonate. The semi-cooked meal enters calciner 3 through the second outlet 201, where it is finally sintered into clinker. The high concentration of carbon dioxide gas directly enters carbon trap 4 through the third outlet 202 for collection and recovery. Air inside decomposer 2 is purged by introducing carbon dioxide gas into the decomposer 2.

[0025] In some embodiments, such as Figures 1-2 As shown, the low-carbon cement production method of this invention controls the ratio of carbon dioxide gas flow rate to raw meal processing volume in the decomposition furnace to be between 1:2 and 3:2. Maintaining the CO2 circulating gas volume to raw meal processing volume within this range ensures a sufficiently high CO2 concentration environment within the decomposition furnace. This ratio effectively vents air from the decomposition furnace, preventing nitrogen dilution of the emitted CO2 and maintaining a CO2 concentration above 90% within the furnace, significantly improving subsequent carbon capture efficiency.

[0026] Optionally, the ratio of the carbon dioxide gas flow rate to the raw material processing volume circulated into the decomposition furnace is 1.5 to 2, which can ensure that a sufficiently high CO2 concentration environment is maintained in the decomposition furnace.

[0027] In some embodiments, such as Figures 1-2As shown, in the low-carbon cement production method of this embodiment of the invention, carbon dioxide gas can be introduced into the decomposition furnace to vent the air inside the furnace before the raw materials are decomposed. In traditional cement production, nitrogen (78%) in the air mixes with the CO2 produced during decomposition, resulting in a CO2 concentration in the flue gas of less than 30%. By pre-introducing CO2 to vent the air, the dilution of CO2 emitted during the process by nitrogen can be fundamentally eliminated.

[0028] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this embodiment of the invention, when heating and decomposing raw materials, the rotation speed of the rotary zone can be adjusted to control the residence time of the raw materials in the decomposition furnace, so as to fully decompose the calcium carbonate in the raw materials.

[0029] By precisely controlling the residence time of raw materials in the decomposition furnace, sufficient time can be ensured for calcium carbonate to complete the decomposition reaction, avoiding incomplete decomposition due to insufficient residence time. A suitable residence time allows the calcium carbonate decomposition rate in the raw materials to reach its maximum level, improving the quality of the semi-clinker and laying a solid foundation for the subsequent sintering process.

[0030] In some embodiments, such as Figures 1-2 As shown, the low-carbon cement production method of this embodiment of the invention sets the rotation speed of the decomposition furnace to 0.8-2.2 rpm and controls the cement raw meal to rise uniformly from 830℃-870℃ at the inlet to 930℃-970℃ at the outlet. By optimizing the decomposition furnace rotation speed, the raw meal movement speed is matched with the temperature inside the decomposition furnace, ensuring uniform heating of the raw meal inside the decomposition furnace and improving the decomposition conversion rate.

[0031] A rotation speed range of 0.8-2.2 rpm provides suitable residence time for the raw materials, ensuring that calcium carbonate has sufficient time to complete the decomposition reaction. A temperature control method that rapidly increases the temperature from 830℃-870℃ to 930℃-970℃ avoids thermal shock to the materials and equipment from sudden temperature changes.

[0032] The rotation speed of the rotary zone is adjusted to 1.5 rpm, and the residence time of the material in the decomposition furnace is controlled to be about 20 minutes, so that the decomposition rate of calcium carbonate in the raw material reaches 97%. In the combustion zone of decomposer 2, the power of the burners arranged in sections along the axis of decomposer 2 is controlled to establish and maintain a temperature gradient from the tail of the decomposition furnace to the head of the decomposition furnace, and the raw material is controlled to rise uniformly from 850°C at the inlet to 950°C at the outlet.

[0033] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this embodiment, the preheating temperature of the cement raw meal is controlled at 780℃-870℃. Preheating to 780℃-870℃ can significantly reduce the external energy input required for the subsequent decomposition process, because the raw meal has already absorbed a large amount of heat.

[0034] Optionally, 100t / h of cement raw meal is preheated to 800℃ by countercurrent heat exchange with high-temperature hot air in raw meal preheater 1.

[0035] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this invention, the semi-clinker is sintered at 1450℃-1550℃. This temperature range of 1450℃-1550℃ ensures complete reaction while avoiding excessive energy consumption, achieving an optimal balance between reaction rate and energy consumption.

[0036] Optionally, the sintering unit 3 includes a rotary kiln 301, which is connected to a second discharge port 201 to receive the semi-clinker discharged from the decomposer 2 and sinter it into clinker. The sintering unit 3 also includes a grate cooler 302, which is connected to the rotary kiln 301 to receive and cool the clinker discharged from the rotary kiln 301.

[0037] The semi-clinker is fed into rotary kiln 301 and sintered into clinker at 1450-1550℃, and then cooled to produce sintered cement clinker.

[0038] In some embodiments, such as Figures 1-2 As shown, the low-carbon cement production method of this invention involves cooling, dehydrating, and removing dust from the carbon dioxide gas obtained after decomposition before capturing it. This cooling, dehydration, and dust removal pretreatment removes impurities from the CO2 gas, providing a clean gas environment for subsequent carbon capture and improving capture efficiency.

[0039] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this invention, the high-temperature airflow after cooling clinker can be circulated to the decomposition furnace to assist in the combustion of fuel in the decomposition furnace. Recycling the high-temperature airflow generated from cooling clinker achieves efficient recovery of waste heat during the production process, significantly improving energy utilization efficiency.

[0040] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this invention, the high-temperature gas from the decomposition furnace combustion can be sent to the raw material preheating zone for countercurrent heat exchange with the cement raw materials. Sending the high-temperature gas (typically at a high temperature) from the decomposition furnace combustion into the raw material preheater 1 achieves efficient recovery and reuse of waste heat during the production process, significantly improving overall energy efficiency.

[0041] In some embodiments, such as Figures 1-2As shown, the low-carbon cement production method of this embodiment of the invention extracts 50 t / h of CO2-rich tail gas from the CO2 circulation loop and reintroduces it into the decomposition furnace as protective gas. The calcium carbonate decomposition rate in the raw materials in the decomposition furnace reaches 97%, and the CO2 concentration in the tail gas sent to the carbon trap 4 is approximately 90%.

[0042] The reduced flow rate of CO2 protective gas allows a small amount of air to infiltrate, resulting in a decrease in the CO2 concentration in the exhaust gas.

[0043] In some embodiments, such as Figures 1-2 As shown, the low-carbon cement production method of this embodiment extracts 150 t / h of CO2-rich tail gas from the CO2 circulation loop and reintroduces it into the decomposition furnace as protective gas. The calcium carbonate decomposition rate in the raw material in the rotary kiln 301 reaches 97%, and the CO2 concentration in the tail gas sent to the carbon trap 4 is approximately 98%.

[0044] The increased flow rate of CO2 protective gas improves the sealing effect on the atmosphere inside the decomposition furnace, resulting in a higher CO2 concentration in the exhaust gas.

[0045] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this embodiment, the rotation speed of the decomposition furnace is adjusted to 1.0 rpm, and the residence time of the material in the decomposition furnace is controlled to be about 30 minutes. The decomposition rate of calcium carbonate in the raw material in the decomposition furnace reaches 98%, and the CO2 concentration in the tail gas sent to the carbon capture device 4 is about 96%.

[0046] Low rotation speed results in a longer residence time for raw materials, leading to a more complete and thorough reaction and a higher decomposition rate.

[0047] In some embodiments, such as Figures 1-2 As shown, in the low-carbon cement production method of this embodiment, the rotation speed of the decomposition furnace is adjusted to 2.0 rpm, and the residence time of the material in the decomposer 2 is controlled to be about 15 minutes. The decomposition rate of calcium carbonate in the raw material in the decomposer 2 reaches 93%, and the CO2 concentration in the tail gas sent to the carbon capture device 4 is about 96%.

[0048] High rotation speed results in short raw material residence time and low raw material decomposition rate.

[0049] In some embodiments, such as Figures 1-2 As shown, the low-carbon cement production method of this embodiment does not extract CO2-rich tail gas into the decomposition furnace, has no protective gas, and does not constitute a CO2 circulation loop. The calcium carbonate decomposition rate in the raw materials in the decomposition furnace is 78%, and the CO2 concentration in the tail gas sent to the carbon capture device 4 is approximately 20%.

[0050] The CO2 protective gas not only maintains the CO2 concentration in the decomposer 2 and the tail gas, but also helps to improve the heat transfer efficiency in the rotary decomposer. Without the CO2 protective gas, the intake of external air into the decomposer causes the raw material reaction temperature in the decomposer to drop and the decomposition rate to decrease.

[0051] Comparative Example The CO2-rich tail gas is not extracted and fed into the decomposition furnace. There is no protective gas, and no CO2 circulation loop is formed. The calcium carbonate in the raw material in the decomposition furnace is decomposed at a rate of 78%, and the CO2 concentration in the tail gas sent to carbon collector 4 is approximately 20%.

[0052] The CO2 protective gas not only maintains the CO2 concentration in the decomposition furnace and the tail gas, but also helps to improve the heat transfer efficiency in the rotary decomposition furnace. Without the CO2 protective gas, the intake of external air into the rotary kiln 301 causes the raw material reaction temperature in the decomposition furnace to drop and the decomposition rate to decrease.

[0053] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0054] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0055] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0057] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0058] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for producing low-carbon cement, characterized in that, include: Preheating of cement raw materials; The preheated raw materials are decomposed by external heating, which decomposes the calcium carbonate in the cement raw materials into semi-clinker and carbon dioxide gas. The semi-clinker obtained after decomposition is sintered into clinker, and the clinker is cooled. The carbon dioxide gas obtained after decomposition is captured. Part of the carbon dioxide gas obtained after decomposition is recycled back into the decomposition furnace to form a carbon dioxide recycling loop. When the amount of recycled gas in the carbon dioxide recycling loop is insufficient, external carbon dioxide can be added to the carbon dioxide recycling loop.

2. The method for producing low-carbon cement according to claim 1, characterized in that, The ratio of the carbon dioxide gas flow rate circulating into the decomposition furnace to the raw material processing volume is controlled between 1:2 and 3:

2.

3. The method for producing low-carbon cement according to claim 1, characterized in that, Before the raw materials are decomposed, carbon dioxide gas can be introduced into the decomposition furnace to purge the air inside.

4. The method for producing low-carbon cement according to claim 1, characterized in that, When heating and decomposing raw materials, the rotation speed of the rotary zone can be adjusted to control the residence time of the raw materials in the decomposition furnace, so as to fully decompose the calcium carbonate in the raw materials.

5. The method for producing low-carbon cement according to claim 4, characterized in that, The rotation speed of the decomposition furnace is set to 0.8-2.2 rpm, and the temperature of the cement raw meal is controlled to rise at a constant speed from 830℃-870℃ at the inlet to 930℃-970℃ at the outlet.

6. The method for producing low-carbon cement according to claim 1, characterized in that, When preheating cement raw materials, the preheating temperature should be controlled between 780℃ and 870℃.

7. The method for producing low-carbon cement according to claim 1, characterized in that, When sintering semi-clinker, the slab clinker is sintered into clinker at 1450℃-1550℃.

8. The method for producing low-carbon cement according to claim 1, characterized in that, The carbon dioxide gas obtained after decomposition is collected after cooling, dehydration, and dust removal.

9. The method for producing low-carbon cement according to claim 1, characterized in that, The high-temperature airflow after cooling the clinker can be circulated to the decomposition furnace to assist in the combustion of fuel in the decomposition furnace.

10. The method for producing low-carbon cement according to claim 1, characterized in that, The high-temperature gas from the decomposition furnace combustion can be sent to the raw material preheating zone for countercurrent heat exchange with the cement raw materials.

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