Improved method for controlling the reducing atmosphere in a rotary kiln

Abstract

The application relates to the technical field of cement production, and provides an improved rotary kiln inner reducing atmosphere control method. The first spark observation port is used to check the five-stage downcomer spark, so as to eliminate the spark in the first spark observation port; after confirming that the five-stage downcomer is free of spark through the first spark observation port, the kiln tail smoke chamber is used to check the kiln tail spark state; the Fe2+ content in the clinker discharged from the rotary kiln is detected to determine the rotary kiln inner reducing atmosphere state; according to the determined rotary kiln inner reducing atmosphere state, the outer shaft flow wind and / or the inner rotary flow wind are adjusted, so that the coal powder burnout rate is improved by means of the length reduction of the flame black head, and the rotary kiln inner reducing atmosphere improvement purpose is achieved. The application provides an efficient reducing atmosphere detection mode, so that the reducing atmosphere control in the whole cement production process can be repeatedly operated, and the state can be accurately verified.

Description

Technical Field

[0001] This invention relates to the field of cement production technology, and in particular to an improved method for controlling the reducing atmosphere inside a rotary kiln. Background Technology

[0002] As a crucial component in the cement-making process, the rotary kiln has always been a focus of research in cement processing plants, with its performance parameters being a primary concern. For cement production, the most critical factor—the yellow core of the clinker—originates precisely during the heating stage of the rotary kiln.

[0003] In existing technologies, a crucial aspect of controlling rotary kilns is the control of the reducing atmosphere within the kiln. However, in actual operation, due to the objective nature of the high-temperature environment inside the rotary kiln, the determination of the atmosphere is always delayed, and the presence or absence of a yellow core is often used as a criterion.

[0004] The drawbacks of this approach are also quite obvious, because the presence of a yellow core during clinker production is not necessarily caused by the single factor of the reducing atmosphere in the kiln. The number of influencing factors that work together in the existing technology will vary with the iteration of related products and the evolution of the technology.

[0005] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this field. Summary of the Invention

[0006] The technical problem this invention aims to solve is how to provide a solution that effectively improves the yellow core of cement in the cement firing system currently used by the company, and further, can quickly complete the control process iteration by adjusting the firing amount during the firing process.

[0007] Once the material in the fifth-stage feed pipe enters the kiln tail, the air blowing direction inside the rotary kiln is from the burner end towards the kiln tail. Furthermore, the temperature inside the rotary kiln is sufficient to maintain the sparks present in the material introduced from the fifth-stage feed pipe. This not only leads to excessively high temperatures at the kiln tail, but more seriously, it can cause operational deviations in the rotary kiln control process (because at this time, checking the kiln tail smoke chamber at the narrowing point may reveal that the sparks at the kiln tail originate from the fifth-stage feed pipe). Currently, there is no effective theory or solution proposed to address this issue in existing technology.

[0008] The present invention adopts the following technical solution:

[0009] An improved method for controlling the reducing atmosphere in a rotary kiln includes setting a first spark observation port in the fifth-stage feed pipe. The method includes:

[0010] The sparks in the fifth-stage feed pipe are checked through the first spark observation port. If sparks are present, the sparks in the first spark observation port are eliminated by adjusting the temperature control of the decomposition furnace outlet and / or the amount of coal used in the decomposition furnace.

[0011] After confirming that there are no sparks in the fifth-stage feed pipe through the first spark observation port, check the spark status at the kiln tail through the narrowing of the kiln tail smoke chamber. If there are sparks, it indicates that there is incomplete combustion of coal in the rotary kiln. Adjust the amount of first coal conveyed or adjust the air force of the coal air nozzle in the burner to ensure complete combustion of the first coal.

[0012] The Fe2+ content in the clinker coming out of the rotary kiln is detected to determine the reducing atmosphere state inside the rotary kiln.

[0013] Based on the determined reducing atmosphere state inside the rotary kiln, the outer axial airflow and / or inner swirl airflow are adjusted in order to improve the pulverized coal combustion rate by reducing the length of the black flame head, thereby achieving the purpose of improving the reducing atmosphere inside the rotary kiln.

[0014] Preferably, detecting the Fe2+ content in the clinker exiting the rotary kiln can effectively provide insight into the atmosphere inside the rotary kiln, specifically including:

[0015] Take the yellow core or abnormally colored part of the broken clinker from the rotary kiln as a sample and place it in a white ceramic container.

[0016] Add two drops of 2,2'-bipyridine acidic aqueous solution to the sample. If the solution does not turn red within 2 minutes, add two more drops of trisodium citrate aqueous solution and wait 5 minutes. If the solution turns clearly red, it indicates that there is a high level of Fe2+ in the sample and a severe reducing atmosphere in the rotary kiln. If adding the 2,2'-bipyridine acidic aqueous solution does not produce a color change, but adding the trisodium citrate aqueous solution results in a light pink color, it indicates that there is a slight reducing atmosphere in the clinker. If neither the 2,2'-bipyridine acidic aqueous solution nor the trisodium citrate aqueous solution produces a pink color, it indicates that the clinker is normal and there is no reducing atmosphere.

[0017] Preferably, adjusting the outer axial airflow and / or inner vortex airflow based on the determined reducing atmosphere state within the rotary kiln specifically includes:

[0018] When the reducing atmosphere in the rotary kiln is severe, the system analyzes whether the current feed rate of the preheater system has changed. If there is no change in the total feed rate, the corresponding coal supplied to the burner is adjusted first, and the tertiary air volume is adjusted as an auxiliary measure to increase the air volume in the kiln to improve the reducing atmosphere in the kiln. If there is a change in the total feed rate, the system returns to the first spark observation port to check and adjust the sparks in the fifth-stage feed pipe.

[0019] When the reducing atmosphere in the rotary kiln is slight, the system analyzes whether the adjusted flame black head length is still within the critical value. If so, the outer axial flow and / or inner vortex flow are further adjusted to improve the pulverized coal combustion rate by further reducing the flame black head length, thereby achieving the required reducing atmosphere.

[0020] Preferably, adjusting the coal supply to the burner specifically includes:

[0021] Choose one or more of the following: a coal type with a higher combustion rate, further reduce the fineness of the original coal powder, or a coal type with a higher oxygen content than hydrogen content.

[0022] Preferably, the particle size of the yellow core or abnormal cross-sectional color portion of the crushed clinker removed from the rotary kiln is less than or equal to 4 mm, and the corresponding weight is 10 mg + 2 mg.

[0023] Preferably, when confirming the presence of a reducing atmosphere within the kiln, the method further includes:

[0024] The content of M3-type C3S in clinker was tested. A calcination temperature that was too high was not conducive to the formation of M1-type C3S. Therefore, the calcination temperature was mainly controlled by cooling down, and the calcination was still mainly carried out by short flame and rapid burning to create conditions for the formation of M1-type C3S.

[0025] Preferably, the calcination temperature is controlled primarily by cooling, and the calcination process still mainly involves short-flame rapid firing, specifically including:

[0026] By adopting a higher opening degree of the tertiary air damper valve, and adjusting the height of the bottom of the tertiary air damper valve from the inner lining of the tertiary air duct from 1050mm to approximately 1100mm, a larger tertiary air volume is used to reduce the air volume and velocity inside the kiln, thereby enabling flame recovery and shortening the flame length; and / or,

[0027] Regarding the adjustment of the pulverized coal injection pipe at the kiln head, the high outer shaft air pressure was increased from 56,000 Pa to 60,000 Pa, the middle and outer cyclone air pressure remained unchanged at 50,000 Pa, and the inner cyclone air pressure was reduced from 8,000 Pa to 5,000 Pa to ensure that the flame length is short and powerful (less than 17m), creating conditions for the rapid burning of clinker with short flame.

[0028] Preferably, the method reduces the formation of M3-type C3S by lowering the calcination temperature in the kiln, and the method further includes...

[0029] Controlling the secondary and tertiary air temperatures is crucial. When clinker granulation remains relatively stable, these temperatures indirectly reflect kiln temperature changes. Higher secondary and tertiary air temperatures result in higher calcination temperatures, and vice versa. To prevent over-burning of the clinker, the secondary air temperature is lowered from 1200℃ to 1000-1150℃, and the tertiary air temperature is generally controlled at 950-1000℃ to control the M3 type C3S content; and / or...

[0030] Controlling free calcium oxide in the clinker is crucial, as it's an important indicator of kiln temperature. Under normal clinker composition control, lower free calcium oxide levels reflect a higher degree of C2S-CaO bonding, indicating a higher absolute kiln temperature. The ideal free calcium oxide level is between 0.6 and 1.5. If it falls below 0.6, the amount of initial coal used needs to be reduced to lower the kiln calcination temperature.

[0031] Preferably, the burner of the rotary kiln includes a burner head 12, an outer axial flow air transmission pipe 13, an outer swirling flow air transmission pipe 14, an inner swirling flow air transmission pipe 15, a central oil pipe 16, a coal and air duct pipe 17, an outer axial flow air regulating valve 18, an outer swirling flow air regulating valve 19, an inner swirling flow air regulating valve 20, and a clean air duct pipe 21. Specifically:

[0032] The outer axial flow air transmission pipe 13 is sleeved outside the outer swirling flow air transmission pipe 14, and the gap in the pipe wall between the two forms the outer axial flow air transmission channel 23.

[0033] The outer swirling air transmission pipe 14 is sleeved outside the inner swirling air transmission pipe 15, and the gap in the pipe wall between the two forms the outer swirling air transmission channel 24.

[0034] The inner swirling air transmission pipe 15 is sleeved outside the central oil pipe 16, and the gap in the pipe wall between the two forms the inner swirling air transmission channel 25.

[0035] The coal air duct 17 is installed between the outer axial flow air transmission channel 23 and the outer vortex flow air transmission channel 24, thereby constructing a coal air duct 26 between the coal air duct 17 and the outer vortex flow air transmission channel 24. Furthermore, the external interface of the coal air duct 17 is located on one side of the outer vortex flow air transmission pipe 14.

[0036] The clean air duct 21 is connected to the side wall of the outer axial flow air transmission pipe 13, the outer swirling flow air transmission pipe 14, and the inner swirling flow air transmission pipe 15 respectively through at least three branch pipes; and the wind speed of the corresponding outer axial flow air, outer swirling flow air, and inner swirling flow air is controlled by valves installed on the branch pipes respectively; the coal air speed is individually controlled by valves installed on the coal air duct 17;

[0037] The burner head 12 is connected to the outlet of the outer axial flow air transmission channel, the coal air duct outlet, the outer swirling flow air transmission channel outlet, the inner swirling flow air transmission channel outlet, and the central oil pipe outlet, respectively.

[0038] Preferably, the burner head 12 specifically includes:

[0039] 126. Center oil gun nozzle, 127. Inner swirling air nozzle, 128. Outer swirling air nozzle, 129. Coal air nozzle, 1210. Outer shaft air nozzle, 1211. Flame hood;

[0040] Among them, the inner swirling air nozzle 127, the outer swirling air nozzle 128, the coal air nozzle 129, the outer axial air nozzle 1210, and the flame hood 1211 are sequentially installed at the end output ports of each transmission pipe that connects to the central oil pipe 16, the inner swirling air transmission pipe 15, the outer swirling air transmission pipe 14, the coal air duct pipe 17, and the outer axial air transmission pipe 13.

[0041] This invention addresses the issue that the presence of sparks at the kiln tail flue constriction of a rotary kiln can lead to excessively high kiln tail temperatures, causing premature material dissolution and resulting in burn-in problems. Furthermore, it extends the observation point to the spark condition in the fifth-stage feed pipe. This is because once material enters the kiln tail through the fifth-stage feed pipe, the airflow direction inside the rotary kiln is from the burner end towards the kiln tail, and the temperature inside the rotary kiln is sufficient to maintain the spark state present in the material introduced from the fifth-stage feed pipe. The proposed method begins by eliminating the possibility of sparks in the fifth-stage feed pipe. After eliminating sparks in the fifth-stage feed pipe, it then delves into the kiln tail flue constriction to inspect for sparks at the kiln tail. Finally, it proposes an efficient method for detecting reducing atmosphere, enabling repeatable and accurately verifiable control of the reducing atmosphere throughout the cement production process. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0043] Figure 1 This is a schematic diagram of an improved method for controlling the reducing atmosphere inside a rotary kiln, provided by an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram of the reduction atmosphere calibration method in an improved rotary kiln reduction atmosphere control method provided in an embodiment of the present invention;

[0045] Figure 3 This is a flowchart detailing the adjustment of the reducing atmosphere inside the rotary kiln in an improved method for controlling the reducing atmosphere inside the kiln, provided in an embodiment of the present invention.

[0046] Figure 4 This is a schematic diagram of the burner structure in an improved method for controlling the reducing atmosphere inside a rotary kiln provided in an embodiment of the present invention;

[0047] Figure 5This is a schematic diagram of the burner structure from another perspective in an improved method for controlling the reducing atmosphere inside a rotary kiln provided in an embodiment of the present invention.

[0048] Figure 6 This is a schematic diagram of the burner head structure in an improved method for controlling the reducing atmosphere in a rotary kiln provided in an embodiment of the present invention;

[0049] Figure 7 This is a schematic diagram of the rotary kiln structure in an improved rotary kiln reducing atmosphere control method provided in an embodiment of the present invention;

[0050] Figure 8 This is a schematic diagram of the five-stage preheating system in an improved rotary kiln reducing atmosphere control method provided in an embodiment of the present invention;

[0051] Figure 9 This is an enlarged view of a crystal phase structure provided in an embodiment of the present invention;

[0052] Figure 10 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0053] Figure 11 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0054] Figure 12 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0055] Figure 13 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0056] Figure 14 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0057] Figure 15 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0058] Figure 16 This is an enlarged view of another crystal phase structure provided in an embodiment of the present invention;

[0059] Figure 17 This is a raw data diagram of clinker XRD mineral content provided in an embodiment of the present invention;

[0060] Figure 18 This is a raw data diagram of clinker XRD mineral content provided in an embodiment of the present invention;

[0061] Figure 19 This is a raw data diagram of clinker XRD mineral content provided in an embodiment of the present invention. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0063] In the description of this invention, the terms "inner", "outer", "longitudinal", "lateral", "upper", "lower", "top", "bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and do not require that this invention must be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0064] Example 1:

[0065] An improved method for controlling the reducing atmosphere in a rotary kiln involves installing a first spark observation port on the fifth-stage feed pipe, as referenced. Figures 4-8 The structural diagram can be referenced, and the description of the corresponding structural features in Embodiment 2 can be used as a reference, such as... Figure 1 As shown, the method includes:

[0066] In step 201, the sparks in the fifth-stage feed tube are checked through the first spark observation port.

[0067] like Figure 8 As shown, the corresponding first spark observation port 52 is located near the discharge end of the fifth-stage feeding pipe. Considering the extension length and diameter of the fifth-stage feeding pipe, it has a certain blocking effect on the light entering the fifth-stage feeding pipe cavity. Therefore, the first spark observation port here can be made into a camera for automatic shooting and monitoring by image recognition, thereby improving the efficiency of automated control.

[0068] In step 202, if sparks are present, the sparks appearing in the first spark observation port are eliminated by adjusting the outlet temperature control of the decomposition furnace and / or the amount of coal used in the decomposition furnace.

[0069] Research has revealed that checking for sparks in the fifth-stage feed pipe can lead to high temperatures in the kiln tail flue, premature appearance of the liquid phase, resulting in a blistering phenomenon and causing the clinker to have a yellow core.

[0070] In step 203, after confirming that there are no sparks in the fifth-stage feed pipe through the first spark observation port, the spark status at the kiln tail is checked through the narrowing of the kiln tail flue.

[0071] In step 204, if sparks are present, it indicates that there is incomplete combustion of coal in the rotary kiln. Adjust the amount of first coal fed or adjust the air force of the coal tuyeres in the burner to ensure complete combustion of the first coal.

[0072] In step 205, the Fe2+ content in the clinker exiting the rotary kiln is detected to determine the reducing atmosphere state inside the rotary kiln. If a reducing atmosphere exists inside the rotary kiln, it will reduce Fe3+ in the clinker to Fe2+.

[0073] In step 206, the outer axial airflow and / or inner swirl airflow are adjusted according to the determined reducing atmosphere state inside the rotary kiln, so as to improve the pulverized coal combustion rate by reducing the length of the black flame head, thereby achieving the purpose of improving the reducing atmosphere inside the rotary kiln.

[0074] This invention, in addressing the issue that the presence of sparks at the kiln tail flue constriction of a rotary kiln could lead to excessively high kiln tail temperatures, causing premature material dissolution and resulting in burn-in problems, further extends the observation point to the spark condition in the fifth-stage feed pipe. This is because once material enters the kiln tail through the fifth-stage feed pipe, the air blowing direction inside the rotary kiln is from the burner end towards the kiln tail, and the temperature inside the rotary kiln is sufficient to maintain the spark state present in the material introduced from the fifth-stage feed pipe. The method proposed in this invention begins by eliminating the possibility of sparks in the fifth-stage feed pipe. After eliminating sparks in the fifth-stage feed pipe, the process then delves into the kiln tail flue constriction of the rotary kiln to check for sparks at the kiln tail. Finally, an efficient reducing atmosphere detection method is proposed, enabling repeatable and accurately verifiable control of the reducing atmosphere throughout the cement production process.

[0075] The solutions proposed in the embodiments of the present invention are more often applied to the calibration process when the kiln is first opened; or when certain changes occur during the production process, the steps 201-206 of the embodiments of the present invention are introduced; or when the stability and consistency of the entire system are verified after a long period of production, the above steps 201-206 are executed.

[0076] In conjunction with the embodiments of the present invention, the detection of the Fe2+ content in the clinker exiting the rotary kiln in step 205 can effectively provide insight into the atmosphere inside the rotary kiln. In this embodiment, a specific preferred implementation is also provided, such as... Figure 2 As shown, it includes:

[0077] In step 2051, the yellow core or abnormally colored part of the broken clinker from the rotary kiln is taken as a sample and placed in a white ceramic vessel.

[0078] In this embodiment of the invention, the particle size of the yellow core or abnormal cross-sectional color portion of the crushed clinker from the rotary kiln is less than or equal to 4 mm, and the corresponding weight is less than 10 mg. + 2mg. Furthermore, the smaller the particle size, the easier it is to distinguish the detection results.

[0079] In step 2052, two drops of 2,2'-bipyridine acidic aqueous solution are added to the sample. If the solution does not turn red within 2 minutes, two more drops of trisodium citrate aqueous solution are added. After waiting for 5 minutes, if the solution turns red, it indicates that there is a high level of Fe2+ in the sample and the reducing atmosphere in the rotary kiln is severe.

[0080] In step 2053, if no color is developed after adding an acidic aqueous solution of 2,2'-bipyridine, but a light pink color is developed after adding an aqueous solution of trisodium citrate, it indicates that there is a slight reducing atmosphere in the clinker.

[0081] In step 2054, if the addition of acidic aqueous solution of 2,2'-bipyridine and aqueous solution of trisodium citrate does not produce a pink color, it indicates that the clinker is normal and there is no reducing atmosphere.

[0082] In conjunction with the embodiments of the present invention, regarding step 206, which involves adjusting the outer axial flow and / or inner vortex flow based on the determined reducing atmosphere state within the rotary kiln, a specific preferred implementation method is also provided in the embodiments of the present invention, such as... Figure 3 As shown, it includes:

[0083] In step 2061, when the reducing atmosphere inside the rotary kiln is severe, the system analyzes whether the current feed rate of the preheater system has changed.

[0084] In step 2062, if there is no change in the total amount of feed, the coal supplied to the burner is adjusted first, and the tertiary air volume is adjusted as an auxiliary measure to increase the air volume in the kiln to improve the reducing atmosphere in the kiln.

[0085] The adjustment of the coal supplied to the burner includes one or more of the following: selecting a coal variety with a higher combustion rate, further reducing the fineness of the original coal powder, and selecting a coal variety with a higher oxygen content than a higher hydrogen content.

[0086] In step 2063, if a change occurs in the total feed amount, the process returns to the first spark observation port to check and adjust the sparks on the fifth-stage feed pipe.

[0087] In step 2064, when the reducing atmosphere in the rotary kiln is slight, the system analyzes whether the adjusted flame blackhead length is still within the critical value. If so, the outer axial flow and / or inner swirl flow are further adjusted to improve the pulverized coal combustion rate by further reducing the flame blackhead length, thereby achieving the reducing atmosphere standard.

[0088] In this embodiment of the invention, when confirming the presence of a reducing atmosphere within the kiln, the method further includes:

[0089] The content of M3 type in clinker was tested. A calcination temperature that was too high was not conducive to the formation of M1 type C3S. Therefore, the calcination temperature was mainly controlled by cooling down. Then, the calcination was still mainly carried out by short flame and rapid burning to create conditions for the formation of M1 type C3S.

[0090] The calcination temperature is mainly controlled by cooling, and the calcination process still primarily uses short-flame rapid firing, specifically including:

[0091] By adopting a higher opening degree of the tertiary air damper valve, and adjusting the height of the bottom of the tertiary air damper valve from the inner lining of the tertiary air duct from approximately 1050mm to 1100mm, a larger tertiary air volume is used to reduce the air volume and velocity inside the kiln, thereby enabling flame recovery and shortening the flame length; and / or,

[0092] Regarding the adjustment of the pulverized coal injection pipe at the kiln head, the high outer shaft air pressure was increased from 56000Pa to 60000Pa, the middle and outer cyclone air pressure remained unchanged at 50000Pa, and the inner cyclone air pressure was reduced from 8000Pa to 5000Pa to ensure that the flame length is short and powerful (less than or equal to 17m), thus creating conditions for the rapid burning of clinker with short flame.

[0093] The method of reducing the formation of M3-type C3S by lowering the calcination temperature in the kiln also includes...

[0094] Controlling the secondary and tertiary air temperatures is crucial. When clinker granulation remains relatively stable, these temperatures indirectly reflect kiln temperature changes. Higher secondary and tertiary air temperatures result in higher calcination temperatures, and vice versa. To prevent over-burning of the clinker, the secondary air temperature is lowered from 1200℃ to 1000-1150℃, and the tertiary air temperature is generally controlled at 950-1000℃ to control the M3 type C3S content; and / or...

[0095] Controlling free calcium oxide in the clinker is crucial, as it's an important indicator of kiln temperature. Under normal clinker composition control, lower free calcium oxide levels reflect a higher degree of C2S-CaO bonding, indicating a higher absolute kiln temperature. The ideal free calcium oxide level is between 0.6 and 1.5. If it falls below 0.6, the amount of initial coal used needs to be reduced to lower the kiln calcination temperature.

[0096] Example 2:

[0097] To better understand the product structure related to the equipment described in Embodiment 1 of the present invention, the present invention describes the objective product structure on which the solution of Embodiment 1 of the present invention is based from three structural levels: rotary kiln, burner installed on rotary kiln, and five-stage preheating system that establishes a material feeding relationship with rotary kiln.

[0098] like Figure 4 and Figure 5The burner structure of the rotary kiln shown includes a burner head 12, an outer axial flow air transmission pipe 13, an outer swirling flow air transmission pipe 14, an inner swirling flow air transmission pipe 15, a central oil pipe 16, a coal and air duct pipe 17, an outer axial flow air regulating valve 18, an outer swirling flow air regulating valve 19, an inner swirling flow air regulating valve 20, and a clean air duct pipe 21. It should be noted that... Figure 5 Compared Figure 4 Structural diagram, a view of the structure after rotating 90° around the axis. Specifically:

[0099] The outer axial air transmission pipe 13 is sleeved outside the outer swirling air transmission pipe 14, and the gap in the pipe wall between the two forms the outer axial air transmission channel 23; the outer swirling air transmission pipe 14 is sleeved outside the inner swirling air transmission pipe 15, and the gap in the pipe wall between the two forms the outer swirling air transmission channel 24; the inner swirling air transmission pipe 15 is sleeved outside the central oil pipe 16, and the gap in the pipe wall between the two forms the inner swirling air transmission channel 25; the coal air duct pipe 17 is arranged between the outer axial air transmission channel 23 and the outer swirling air transmission channel 24, thereby constructing a coal air duct 26 between the coal air duct pipe 17 and the outer swirling air transmission channel 24, and the external interface of the coal air duct pipe 17 is arranged on one side of the outer swirling air transmission pipe 14.

[0100] The clean air duct 21 is connected to at least three branch ducts (see reference). Figure 4 The three branch pipes (each connected to the horizontal clean air duct 21 and equipped with an outer axial flow regulating valve 18, an outer vortex flow regulating valve 19, and an inner vortex flow regulating valve 20) are respectively connected to the side wall of the outer axial flow transmission pipe 13, the outer vortex flow transmission pipe 14, and the inner vortex flow transmission pipe 15; and the wind speeds of the corresponding outer axial flow, outer vortex flow, and inner vortex flow are controlled by the valves set on the branch pipes; the coal air speed is individually controlled by the valves set on the coal air duct 17.

[0101] The burner head 12 is connected to the outlet of the outer axial flow air transmission channel, the coal air duct outlet, the outer swirling flow air transmission channel outlet, the inner swirling flow air transmission channel outlet, and the central oil pipe outlet, respectively.

[0102] like Figure 6 As shown, the burner head 12 specifically includes:

[0103] 126. Center oil gun nozzle, 127. Inner swirling air nozzle, 128. Outer swirling air nozzle, 129. Coal air nozzle, 1210. Outer shaft air nozzle, 1211. Flame hood;

[0104] Among them, the inner swirling air nozzle 127, the outer swirling air nozzle 128, the coal air nozzle 129, the outer axial air nozzle 1210, and the flame hood 1211 are sequentially installed at the end output ports of each transmission pipe that connects to the central oil pipe 16, the inner swirling air transmission pipe 15, the outer swirling air transmission pipe 14, the coal air duct pipe 17, and the outer axial air transmission pipe 13.

[0105] For reference Figure 5 and Figure 6 The correspondence, where, Figure 5 The structure located at the left burner head 12 end face is... Figure 6 The structure consists of a central oil gun nozzle 121, an inner swirling air nozzle 122, an outer swirling air nozzle 123, a coal air nozzle 124, an outer shaft air nozzle 125, and a flame shroud 126, located on its right end face.

[0106] like Figure 7 As shown, this is the corresponding adaptation. Figure 4 The rotary kiln 7 shown is a commercially available product, and will not be described in detail here. Instead, the structural relationship between the rotary kiln 7 and the aforementioned burner will be explained, along with its connection to the kiln tail flue gas chamber narrowing 74 described in Example 1. The above-mentioned connection with... Figure 4 The burner head 12-phase compatible port 71 of the burner shown is located at Figure 7 The rotary kiln 7 shown has a discharge port 72 for the heated clinker at its head position.

[0107] like Figure 8 As shown, the five-stage preheating system includes a primary preheater 1, a secondary preheater 2, a tertiary preheater 3, a quaternary preheater 4, a quinary preheater 5, and a decomposition furnace 6. The quinary preheater is an existing product technology purchased by the patentee company; therefore, its working principle will not be elaborated upon. However, in the implementation scheme of Embodiment 1 of this invention, for Figure 8 The fifth-stage feed pipe 51 shown is equipped with a first spark observation port 52, and the corresponding fifth-stage feed pipe 51 is finally connected to the adapter port 75 through the conduit 61 to finally feed the material into the... Figure 7 In the kiln tail smoke chamber 73 shown, while Figure 7 The one that is directly connected to the catheter 61 is Figure 7 The adapter port is 75.

[0108] Example 3:

[0109] The harmful alkali in cement can easily cause alkali-aggregate reaction, leading to expansion and cracking. GB175-2007 stipulates that the alkali content of low-alkali cement (R2O=0.658K2O+Na2O, expressed as the total equivalent of Na2O, i.e., the content of alkaline substances in cement) should be less than 0.6%. In strict application scenarios, the R2O of low-alkali 425 cement should be less than 0.57%. However, the alkali content of limestone in mines is relatively high, reaching 0.34%, and the R2O content of the clinker produced reaches 0.85%. The R2O content of PC425 cement exceeds 0.7%, which fails to meet the requirements for low-alkali cement.

[0110] This invention, in one aspect, applies the application scenario provided in Basic Embodiment 2, and combines the rotary kiln reducing atmosphere control method proposed in Embodiment 1. It further reduces the R2O content of clinker to 0.68% and the R2O content of PC425 cement to 0.61% by replacing the high-alkali shale feedstock with low-alkali wet fly ash. XDR (X-ray diffraction) is used to detect clinker minerals, adjust the batching scheme, optimize process parameters, improve clinker strength, and reduce the amount of clinker admixture in cement, thereby reducing the alkali content in cement to meet internal control requirements. The clinker is made from limestone, silica correcting materials, alumina correcting materials, and ferrous correcting materials through grinding, mixing, high-temperature calcination, and cooling. The cement is made from clinker, converter slag, gravel, and gypsum ground to a certain fineness.

[0111] Chemical composition of clinker and cement raw materials studied in the embodiments of this invention:

[0112]

[0113] Existing solutions use shale as a component of aluminum correction materials:

[0114]

[0115] The present invention proposes using wet fly ash as an ingredient in aluminum correction materials:

[0116]

[0117] The average 28-day strength of clinker using shale as a raw material is 57.8 MPa. The average composition of P.C425 cement is 78% clinker + 11.5% converter slag + 5% gravel + 5.5% gypsum. The cement's various properties are as follows:

[0118]

[0119] The average 28-day strength of clinker using wet fly ash as a raw material was 59.2 MPa. The average composition of P.C425 cement was 76.0% clinker + 13.5% converter slag + 5% gravel + 5.5% gypsum. The cement's various properties are as follows:

[0120]

[0121] Next, we will further improve the quality of clinker, reduce the clinker content, and increase the converter slag content so that the cement alkali content can meet the internal control target of 0.57.

[0122] Silicate cement clinker is mainly composed of silicate minerals (C3S and C2S) and flux minerals (C3A and C4AF). Different minerals and crystal forms correspond to different hydraulic properties. Their content and form determine the clinker performance. C3S exists in two crystal forms in cement clinker minerals: M1 and M3. M3 type C3S is mainly produced under high temperature and long calcination time, while M1 type C3S is mainly produced under short calcination time and relatively low temperature.

[0123] Example 4:

[0124] Furthermore, based on the above-mentioned Example 3, which uses wet fly ash to replace shale to produce a better R2O low-alkali cement alkali content solution, this embodiment of the invention further studies and elaborates on its optimizable aspects.

[0125] Aspect 1: Ingredient Optimization

[0126] Wet fly ash was used as feedstock for four consecutive months, and XRD mineral content analysis of the clinker was performed daily. The results were statistically combined according to the different contents of M3 type, and the following results were obtained:

[0127]

[0128] As can be seen from the table above, when the C3S content of M3 type gradually decreases, the KH of clinker shows a decreasing trend, while the clinker strength shows an increasing trend.

[0129] The effects of KH variation on clinker strength and C3S crystal form were analyzed separately, and the results are shown in the table below:

[0130]

[0131] As can be seen from the table above, as KH decreases, the content of M3-type C3S decreases. When KH decreases to between 0.890 and 0.900, the clinker strength reaches its highest value. However, when KH decreases to below 0.890, the content of M1-type C3S decreases, while the content of M3-type C3S remains unchanged. The total C3S content decreases, thus the 28-day strength declines.

[0132] The data in the table above shows that to improve clinker quality, it is necessary to increase the proportion of M1 type C3S, while also taking into account the change in the total amount of C3S; otherwise, the strength will also decline to some extent.

[0133] The ingredient ratio has been adjusted, with KH controlled at 0.895±0.01, while SM and IM remain unchanged. The specific details after the ingredient ratio adjustment are as follows:

[0134]

[0135] Part Two: Calcination Adjustment (The control of the reducing atmosphere here can be referred to the content of Example 1, and some of it will be excerpted below in the following description)

[0136] 1. Control of reducing atmosphere

[0137] For details, see the petrographic images of clinker with a 28-day strength below 60 MPa. Figure 9 The area enclosed by the elliptical frame exhibits the intergrowth of A-type ore and uneven crystal size. Additionally, in... Figure 10 In the diagram, the dark circle represents the decomposition of ore A into secondary ore B at higher temperatures; the light-colored ellipse represents the intermediate phase enclosed by ore A (i.e.,...). Figure 10 The light-colored oval portion shown in the image has a brighter middle phase.

[0138] Lithofacies characteristics:

[0139] 1) The clinker has a yellow core, the reducing atmosphere inside the rotary kiln is relatively strong, and through-cracks are visible on the surface of the A-ore crystals in the lithofacies (such as...). Figure 11 and Figure 12 (Taking the crystal surface marked by a medium ellipse as an example) and the encapsulation of intermediate phases is quite common, with some A-ore boundaries showing dissolution phenomena;

[0140] 2) The mineral crystals are uneven in size, and the overall size is relatively small;

[0141] 3) The clinker granules are uneven, and secondary B ore can be seen around some A ore, which reflects the high calcination temperature and indicates that the rotary kiln conditions are unstable.

[0142] The images above show that when the clinker strength is poor, the reducing atmosphere inside the rotary kiln is relatively strong, mainly due to excessive use of head coal. The following measures can be taken to improve this situation.

[0143] First, check for sparks in the fifth-stage feed pipe. If sparks are present, it will cause high temperature in the kiln tail smoke chamber, premature appearance of the liquid phase, resulting in burnt-out phenomenon and yellow core of clinker. The spark situation can be resolved by adjusting the temperature control of the decomposition furnace outlet.

[0144] Secondly, check for sparks at the constriction of the kiln tail smoke chamber. If sparks are present, it indicates that there is incomplete combustion of coal in the rotary kiln. Adjust the first coal or adjust the opening of the tertiary gate valve to ensure complete combustion of the first coal.

[0145] Third, a clinker reducing atmosphere titration is performed to quickly determine the reducing atmosphere inside the rotary kiln; the specific method is as follows:

[0146] If a reducing atmosphere exists inside the rotary kiln, it will reduce Fe3+ in the clinker to Fe2+. By simply monitoring the Fe2+ content in the rotary kiln clinker, the atmosphere inside the rotary kiln can be effectively understood.

[0147] Take approximately 10 mg of the yellow core or abnormally colored cross-section portion of the crushed clinker from the rotary kiln (particle size should be less than 4 mm, and the smaller the particle size, the easier it is to distinguish the test results). Place it in a white ceramic container. Add two drops of solution A (acidic aqueous solution of 2,2'-bipyridine) to the sample. If the solution does not turn red within 2 minutes, add two drops of solution B (aqueous trisodium citrate solution). Wait 5 minutes. If the solution turns distinctly red, it indicates that there is a high level of Fe2+ in the sample, and the reducing atmosphere in the rotary kiln is severe. If adding solution A does not produce a color change, but adding solution B results in a light pink color, it indicates that there is a slight reducing atmosphere in the clinker. If neither solution A nor solution B produces a pink color, it indicates that the clinker is normal and there is no reducing atmosphere.

[0148] 2. Calcination control (This has been elaborated in Example 1; here, we will describe the content in a real-world scenario).

[0149] Considering the low M3 content in clinker of poor quality, excessively high calcination temperatures are detrimental to the formation of M1-type C3S. Therefore, calcination temperature should be controlled at a lower level, and short-flame rapid calcination should still be the primary method to create conditions for the formation of M1-type C3S. The specific procedures are as follows:

[0150] First, a higher opening degree of the tertiary air damper valve is adopted. The height of the bottom of the tertiary damper valve from the inner lining of the tertiary air duct is adjusted from approximately 1050mm to 1100mm. By using a larger tertiary air volume, the air volume and velocity inside the rotary kiln are reduced, allowing the flame to be recovered and its length shortened.

[0151] Secondly, regarding the adjustment of the pulverized coal injection pipe at the rotary kiln head, the high outer shaft air pressure was increased from 56,000 Pa to 60,000 Pa, while the middle and outer cyclone air pressure remained unchanged at 50,000 Pa. The inner cyclone air pressure was reduced from 8,000 Pa to 5,000 Pa to ensure a short and powerful flame, thus creating conditions for the rapid burning of clinker with a short flame.

[0152] 3. Precisely control the calcination temperature

[0153] Based on the formation mechanism of M3-type C3S, the formation of M3-type C3S is reduced by lowering the calcination temperature in the rotary kiln. The main methods employed are as follows:

[0154] First, the secondary and tertiary air temperatures are strictly controlled. When the clinker granulation does not change significantly, the secondary and tertiary air temperatures can indirectly reflect the temperature changes inside the rotary kiln. Higher secondary and tertiary air temperatures result in higher calcination temperatures, and lower secondary and tertiary air temperatures result in lower calcination temperatures. To ensure that the clinker is not overburned, based on the company's situation, the secondary air temperature is reduced from 1200℃ to 1000-1150℃, and the tertiary air temperature is generally controlled at 950-1000℃ to control the M3 type C3S content.

[0155] Secondly, strict control of free calcium oxide in the clinker is crucial. Free calcium oxide is also an important indicator of temperature within the rotary kiln. Under normal clinker composition control, lower free calcium oxide levels reflect a higher degree of bonding between C2S and CaO, indicating a higher absolute temperature within the rotary kiln. Generally, free calcium oxide is controlled between 0.6% and 1.5%. If the free calcium oxide level falls below 0.6%, the amount of head coal used needs to be reduced to lower the calcination temperature within the rotary kiln.

[0156] Third, the temperature inside the rotary kiln can be determined by examining the clinker facies. The calcination temperature inside the rotary kiln can be determined by the mineral state within the clinker facies. Figure 13 and Figure 14 The two images show that the A mineral is large in size and exhibits intergrowth, and secondary B minerals can be seen around some A minerals, indicating that the calcination temperature was high.

[0157] See the image of the petrographic facies at normal calcination temperature. Figure 15 and Figure 16 The two images show that the A mineral is well-developed, with regular crystal shapes and uniform sizes, indicating that the calcination temperature was appropriate.

[0158] 4. Grate control

[0159] In the operation of the grate cooler, the material layer of the grate cooler is mainly controlled by combining the current of the fixed grate fan. The current of the two fans of the fixed grate is kept above 190A. This is because the cooling of clinker in the high-temperature section is directly related to the activity of the clinker.

[0160] The original data of clinker XRD mineral content after adjustment.

[0161] like Figure 17 As shown, the content of C3S of type M3 is 36.44%, and the content of C3S of type M1 is 27.45%.

[0162] like Figure 18 As shown, the C3S content of type M3 is 36.04%, and the C3S content of type M1 is 26.15%.

[0163] like Figure 19 As shown, the C3S content of type M3 was 36.33%, and the C3S content of type M1 was 28.53%.

[0164] The average values ​​of various clinker indicators over the past three months after statistical adjustments are shown below:

[0165]

[0166] Through adjustments to the batching scheme and optimization of the calcination process, the average 28-day strength of the clinker was 64.8 MPa. The average batching scheme for P.C425 cement was 68.0% clinker + 21.5% converter slag + 5% gravel + 5.5% gypsum. The various indicators of the cement are as follows:

[0167]

[0168] It should be noted that without the control of the reducing atmosphere within the rotary kiln as described in Example 1, the production of low-alkali-content, high-strength cement as described in this embodiment of the invention cannot be achieved. The strength of the cement is closely related to the reducing atmosphere environment within the rotary kiln.

[0169] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An improved method for controlling the reducing atmosphere in a rotary kiln, characterized in that, The method for setting a first spark observation port in the fifth-stage feed pipe includes: The sparks in the fifth-stage feed pipe are checked through the first spark observation port. If sparks are present, the sparks in the first spark observation port are eliminated by adjusting the temperature control of the decomposition furnace outlet and / or the amount of coal used in the decomposition furnace. After confirming that there are no sparks in the fifth-stage feed pipe through the first spark observation port, check the spark status at the kiln tail through the narrowing of the kiln tail smoke chamber. If there are sparks, it indicates that there is incomplete combustion of coal in the rotary kiln. Adjust the amount of first coal conveyed or adjust the air force of the coal air nozzle in the burner to ensure complete combustion of the first coal. The Fe2+ content in the clinker coming out of the rotary kiln is detected to determine the reducing atmosphere state inside the rotary kiln. Based on the determined reducing atmosphere state inside the rotary kiln, the outer axial airflow and / or inner swirl airflow are adjusted in order to improve the pulverized coal combustion rate by reducing the length of the black flame head, thereby achieving the purpose of improving the reducing atmosphere inside the rotary kiln.

2. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 1, characterized in that, The detection of Fe2+ content in the clinker exiting the rotary kiln can effectively provide insight into the atmosphere inside the rotary kiln, specifically including: Take the yellow core or abnormally colored part of the broken clinker from the rotary kiln as a sample and place it in a white ceramic container. Add two drops of 2,2'-bipyridine acidic aqueous solution to the sample. If the solution does not turn red within 2 minutes, add two more drops of trisodium citrate aqueous solution and wait 5 minutes. If the solution turns clearly red, it indicates that there is a high level of Fe2+ in the sample and a severe reducing atmosphere in the rotary kiln. If adding the 2,2'-bipyridine acidic aqueous solution does not produce a color change, but adding the trisodium citrate aqueous solution results in a light pink color, it indicates that there is a slight reducing atmosphere in the clinker. If neither the 2,2'-bipyridine acidic aqueous solution nor the trisodium citrate aqueous solution produces a pink color, it indicates that the clinker is normal and there is no reducing atmosphere.

3. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 2, characterized in that, The adjustment of the outer axial airflow and / or inner vortex airflow based on the determined reducing atmosphere state inside the rotary kiln specifically includes: When the reducing atmosphere in the rotary kiln is severe, the system analyzes whether the current feed rate of the preheater system has changed. If there is no change in the total feed rate, the corresponding coal supplied to the burner is adjusted first, and the tertiary air volume is adjusted as an auxiliary measure to increase the air volume in the kiln to improve the reducing atmosphere in the kiln. If there is a change in the total feed rate, the system returns to the first spark observation port to check and adjust the sparks in the fifth-stage feed pipe. When the reducing atmosphere in the rotary kiln is slight, the system analyzes whether the adjusted flame black head length is still within the critical value. If so, the outer axial flow and / or inner vortex flow are further adjusted to improve the pulverized coal combustion rate by further reducing the flame black head length, thereby achieving the required reducing atmosphere.

4. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 3, characterized in that, The adjustment of the coal supply to the burner specifically includes: Choose one or more of the following: a coal type with a higher combustion rate, further reduce the fineness of the original coal powder, or a coal type with a higher oxygen content than hydrogen content.

5. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 2, characterized in that, The particle size of the yellow core or abnormally colored portion of the crushed clinker removed from the rotary kiln is less than or equal to 4 mm, and the corresponding weight is less than 10 mg. + 2mg.

6. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 2, characterized in that, When confirming the presence of a reducing atmosphere within the kiln, the method also includes: The content of M3-type C3S in clinker was tested. A calcination temperature that was too high was not conducive to the formation of M1-type C3S. Therefore, the calcination temperature was mainly controlled by cooling down, and the calcination was still mainly carried out by short flame and rapid burning to create conditions for the formation of M1-type C3S.

7. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 6, characterized in that, The calcination temperature is mainly controlled by cooling, and the calcination process still primarily uses short-flame rapid firing, specifically including: By adopting a higher opening degree of the tertiary air damper valve, and adjusting the height of the bottom of the tertiary air damper valve from the inner lining of the tertiary air duct from 1050mm to approximately 1100mm, a larger tertiary air volume is used to reduce the air volume and velocity inside the kiln, thereby enabling flame recovery and shortening the flame length; and / or, Regarding the adjustment of the pulverized coal injection pipe at the kiln head, the high outer shaft air pressure was increased from 56,000 Pa to 60,000 Pa, while the middle and outer cyclone air pressure remained unchanged at 50,000 Pa. The inner cyclone air pressure was reduced from 8,000 Pa to 5,000 Pa to ensure a short and powerful flame, thus creating conditions for the rapid burning of clinker with a short flame.

8. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 6, characterized in that, The method of reducing the formation of M3-type C3S by lowering the calcination temperature in the kiln also includes... Controlling the secondary and tertiary air temperatures is crucial. When clinker granulation remains relatively stable, these temperatures indirectly reflect kiln temperature changes. Higher secondary and tertiary air temperatures result in higher calcination temperatures, and vice versa. To prevent over-burning of the clinker, the secondary air temperature is lowered from 1200℃ to 1000-1150℃, and the tertiary air temperature is generally controlled at 950-1000℃ to control the M3 type C3S content; and / or... Controlling free calcium oxide in clinker is crucial, as it is an important indicator of kiln temperature. Under the premise of normal clinker composition control, the lower the free calcium oxide level, the higher the degree of combination between C2S and CaO, indicating a higher absolute temperature inside the kiln. The free calcium oxide level should be controlled between 0.6 and 1.

5.

9. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 1, characterized in that, The burner of the rotary kiln includes a burner head (12), an outer axial flow air transmission pipe (13), an outer swirling flow air transmission pipe (14), an inner swirling flow air transmission pipe (15), a central oil pipe (16), a coal air duct pipe (17), an outer axial flow air regulating valve (18), an outer swirling flow air regulating valve (19), an inner swirling flow air regulating valve (20), and a clean air duct pipe (21). Specifically: The outer axial flow air transmission pipe (13) is sleeved outside the outer swirling flow air transmission pipe (14), and the gap between the pipe walls of the two forms the outer axial flow air transmission channel (23). The outer swirling air transmission pipe (14) is sleeved outside the inner swirling air transmission pipe (15), and the gap between the pipe walls of the two forms the outer swirling air transmission channel (24). The inner swirling air transmission pipe (15) is sleeved outside the central oil pipe (16), and the gap in the pipe wall between the two forms the inner swirling air transmission channel (25). The coal air duct pipe (17) is set between the outer axial flow air transmission channel (23) and the outer vortex flow air transmission channel (24), thereby constructing a coal air duct (26) between the coal air duct pipe (17) and the outer vortex flow air transmission channel (24). Furthermore, the external interface of the coal air duct pipe (17) is set on one side of the outer vortex flow air transmission pipe (14). The clean air duct (21) is connected to the side wall of the outer axial flow air transmission pipe (13), the outer swirling flow air transmission pipe (14), and the inner swirling flow air transmission pipe (15) respectively through at least three branch pipes; and the wind speed of the corresponding outer axial flow air, outer swirling flow air and inner swirling flow air is controlled by the valves set on the branch pipes respectively; the coal air speed is controlled separately by the valves set on the coal air duct (17); The burner head (12) is connected to the outlet of the outer axial flow air transmission channel, the outlet of the coal air duct, the outlet of the outer swirling flow air transmission channel, the outlet of the inner swirling flow air transmission channel, and the outlet of the central oil pipe, respectively.

10. The improved method for controlling the reducing atmosphere in a rotary kiln according to claim 9, characterized in that, The burner head (12) specifically includes: The center oil gun nozzle (126), the inner swirling air nozzle (127), the outer swirling air nozzle (128), the coal air nozzle (129), the outer shaft air nozzle (1210), and the flame hood (1211). Among them, the inner swirling air nozzle (127), the outer swirling air nozzle (128), the coal air nozzle (129), the outer axial air nozzle (1210), and the flame hood (1211) are sequentially installed at the end output ports of each transmission pipe that connects to the central oil pipe (16), the inner swirling air transmission pipe (15), the outer swirling air transmission pipe (14), the coal air duct pipe (17), and the outer axial air transmission pipe (13).

Images