A method for evaluating the combustion state of cement kilns based on sulfur element detection

Abstract

This invention relates to the field of cement production technology and discloses a method for evaluating the combustion state of a cement kiln based on sulfur detection. The method includes the following steps: S1, within a set time period, obtaining a fixed amount of hot raw meal from the feed pipe of the final preheater and a fixed amount of clinker from the clinker hopper; S2, detecting the mass percentage of sulfur in the obtained hot raw meal and clinker, and determining the sulfur circulation ratio M within the cement kiln based on the ratio of the mass percentage of sulfur in the hot raw meal to the mass percentage of sulfur in the clinker; S3, evaluating the combustion state at a set process location within the cement kiln based on the sulfur circulation ratio, and identifying process locations with unreasonable combustion states. This method overcomes the limitations of traditional methods that rely solely on CO detection at the kiln tail and smoke chamber, which cannot accurately reflect the fuel combustion state. Therefore, it can more accurately and promptly evaluate the fuel combustion state within the kiln system and quickly determine process locations that need adjustment.

Description

Technical Field

[0001] This invention relates to the field of cement clinker production technology, and in particular to a method for evaluating the combustion status of cement kilns based on sulfur detection. Background Technology

[0002] In existing cement clinker calcination process control, the evaluation method for fuel combustion status mainly involves obtaining carbon monoxide (CO) content at corresponding locations using online gas analyzers installed in the kiln tail, flue, and precalciner. This information is then used to evaluate the fuel combustion status and adjust various system operating parameters accordingly. This evaluation method has the following drawbacks:

[0003] 1. For example Figure 1 As shown, during the long-distance movement of CO gas generated by incomplete combustion in the firing zone towards the kiln tail, due to the presence of excess oxygen in the kiln, some of the CO undergoes secondary combustion in areas outside the firing zone, forming CO2. This reduces the true CO content detected from the decomposition furnace and smoke chamber in the firing zone, thus failing to accurately characterize the fuel combustion state. This leads to misjudgments in fuel quantity adjustments by cement kiln operators, easily resulting in excessive adjustments to fuel consumption.

[0004] 2. For example Figure 1 As shown, unreasonable modifications to the flue gas chamber's narrowing size, such as increasing it excessively (even exceeding the original design by 40%), or adding all tailings coal from the decomposer cone, reduce the upward thrust of the secondary air at the bottom of the decomposer, weakening its ability to lift pulverized coal and raw materials. In severe cases, this can even cause coal collapse. Some unburned fixed carbon falls directly into the flue gas chamber's feed ramp and into the rotary kiln. During the kiln's horizontal movement and tumbling from the kiln tail towards the kiln head, some CO is produced. This results in an increased CO content reading in the flue gas chamber, potentially misleading operators into believing that the fuel combustion at the kiln head is poor, thus missing the optimal adjustment opportunity. Furthermore, the large amount of pulverized coal falling directly from the decomposer into the kiln has a more serious negative impact on clinker quality, causing rapid ring formation within the kiln, sometimes requiring manual cleaning and kiln shutdown, and increasing safety hazards for personnel during construction.

[0005] 3. Due to incomplete combustion in the decomposition furnace, a large amount of unburned fixed carbon is carried along with the material to the final preheater, and then fed into the kiln tail through the feed pipe, which will also add some CO. As a result, the CO detection result in the smoke chamber is increased, which may lead the operator to mistakenly believe that the fuel combustion at the kiln head is not good (traditional evaluation methods use the CO content in the smoke chamber or kiln tail to evaluate the combustion status at the kiln head), thus missing the best time for adjustment; the consequences of this part of unburned fixed carbon entering the kiln are the same as those in 2 above.

[0006] 4. The reduction in CO in point 1 above will partially offset the increase in CO in points 2 and 3, making it impossible for enterprises to distinguish the correct process location and quantity of CO generation, which will mislead the operation of process parameters.

[0007] The aforementioned situation makes it impossible for operators to determine the exact location and amount of CO generated within the cement kiln, thus misleading the setting of process parameters. Furthermore, the CO flue gas analyzer probe, operating in a high-temperature, high-dust, alkaline environment for extended periods, is prone to clogging and cracking, resulting in a high failure rate and complicating the monitoring of fuel combustion by operators.

[0008] Due to inaccurate CO content detection at kiln tail and smoke chamber, and the inability to quickly determine the process location of poor combustion, operators can only rely on visual observation and work experience to judge the fuel combustion status. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] The purpose of this invention is to address the shortcomings of the prior art by providing a method for evaluating the combustion state of cement kilns based on sulfur element detection, which can quickly and accurately determine the combustion state of cement kilns.

[0011] (II) Technical Solution

[0012] To address the above problems, this invention provides a method for evaluating the combustion state of cement kilns based on sulfur element detection, comprising the following steps:

[0013] S1. Within a set time period, a certain amount of hot raw material is obtained from the feed pipe of the final stage preheater and a certain amount of clinker is obtained from the clinker hopper.

[0014] S2. Detect the mass percentage of sulfur in the hot raw material and the clinker, and determine the sulfur circulation ratio M in the cement kiln based on the ratio of the mass percentage of sulfur in the hot raw material to the mass percentage of sulfur in the clinker.

[0015] S3. Based on the sulfur element circulation ratio, evaluate the combustion state at the set process position in the cement kiln, and determine the process position where the combustion state is unreasonable.

[0016] Optionally, the set process location includes the kiln head burner and the decomposition furnace.

[0017] Optionally, in step S3,

[0018] When M = 1.2-2.5, the combustion status of the kiln head burner and the decomposition furnace is determined to be good;

[0019] When M < 1.2, the combustion state of the decomposition furnace is determined to be poor or extremely poor.

[0020] When M > 2.5 and remains constant, the combustion state of the kiln head burner is determined to be poor.

[0021] When the value of M fluctuates within the set time period, and the absolute value of the fluctuation is between 0.1 and 10, the combustion state in the decomposition furnace is determined to be poor or extremely poor. The magnitude of the absolute value of the fluctuation is inversely proportional to the quality of the combustion state.

[0022] Optionally, the set time period is 2-4 hours.

[0023] Optionally, a manual or automatic material handling device or an online detection device containing an automatic sampling device is provided on the wall of the feed pipe of the final preheater to obtain the sulfur content of the material before entering the kiln, for obtaining and detecting the sulfur content of the hot raw material from the feed pipe of the final preheater.

[0024] Optionally, in step S1, the set time length is 30 minutes.

[0025] (III) Beneficial Effects

[0026] This invention provides a method for evaluating the combustion status of cement kilns based on sulfur element detection. By detecting sulfur levels in the hot raw materials in the feed pipe of the final preheater and in the clinker hopper, the sulfur circulation ratio within the cement kiln is obtained, and the combustion status is evaluated based on this ratio. This method overcomes the limitations of traditional methods that rely solely on CO detection in the kiln tail flue, which cannot accurately reflect the fuel combustion state. It allows operators to more accurately and promptly evaluate the fuel status within the kiln system and quickly pinpoint necessary process adjustments. Therefore, it not only saves fuel but also mitigates the negative impact of poor fuel combustion on clinker quality and yield in the cement kiln clinker calcination system. The method is simple to operate, requires no investment in large-scale equipment modifications, is highly reliable, and can be implemented by all cement companies. There are nearly 1700 cement clinker raw material production lines nationwide, with a clinker production capacity exceeding 2 billion tons. If this technology can be widely adopted, it could save the industry 6 million tons of standard coal per year. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced 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.

[0028] Figure 1 This is a schematic diagram of the cement kiln structure in an embodiment of the present invention;

[0029] Figure 2 This is a flowchart of the cement kiln combustion status evaluation method in an embodiment of the present invention.

[0030] The reference numerals in the attached figures are as follows:

[0031] 1. Final stage preheater feed pipe; 2. Clinker hopper; 3. Kiln head burner; 4. Decomposition furnace; 5. Feeding device; 6. Final stage preheater; 7. Rotary kiln; 8. Smoke chamber; 9. Sulfur element circulation path; 10. Material direction; 11. Air direction; 12. Sulfur dioxide; 13. Unburned fixed carbon; 14. Carbon monoxide. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Here, the following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0033] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a method for evaluating the combustion state of a cement kiln based on sulfur detection, comprising the following steps:

[0034] S1. Within a set time period, a certain amount of hot raw material is obtained from the feed pipe 1 of the final preheater and a certain amount of clinker is obtained from the clinker hopper 2.

[0035] The set time length can be 30 minutes. A certain amount of hot raw material can be obtained from the final stage preheater feed pipe 1 and a certain amount of clinker can be obtained from the clinker hopper 2 at the same time; or a certain amount of hot raw material can be obtained from the final stage preheater feed pipe 1 and a certain amount of clinker can be obtained from the clinker hopper 2 within 30 minutes.

[0036] To facilitate the extraction of hot raw material from the final preheater feed pipe 1, a manual or automatic material extraction device 5 is installed on the pipe wall of the final preheater feed pipe 1. Alternatively, an online detection device containing an automatic sampling device can be used to obtain the sulfur content of the material before it enters the kiln. This device is used to extract and detect the sulfur content of the hot raw material from the final preheater feed pipe 1. The position of the material extraction device 5 or the online detection device on the final preheater feed pipe 1 can be set as needed; this embodiment of the invention does not impose specific limitations on this.

[0037] S2. Detect the mass percentage of sulfur in the obtained hot raw materials and clinker, and determine the sulfur circulation ratio M in the cement kiln based on the ratio of the mass percentage of sulfur in the raw materials to the mass percentage of sulfur in the clinker.

[0038] The obtained hot raw materials and clinker are prepared into sample patterns for testing. Then, the mass percentage of sulfur in the hot raw material sample and the clinker sample are tested separately. The ratio of the mass percentage of sulfur in the hot raw material obtained from the final preheater feed pipe 1 to the mass percentage of sulfur in the clinker obtained from the clinker hopper 2 is the sulfur circulation ratio M in the cement kiln.

[0039] S3. Evaluate the combustion status at the designated process locations within the cement kiln based on the sulfur element circulation ratio M. This can also help determine which process location has a problem.

[0040] The process locations are defined as the kiln head burner 3 and the preheater 4. The vast majority of fuel in the cement kiln system is burned at these two process locations. The fuel for the kiln head burner 3 includes coal and other alternative fuels; the fuel for the preheater 4 includes coal, hazardous waste (combustible), municipal sludge, combustible general solid waste, and other alternative fuels.

[0041] In the cement kiln clinker production process, the internal circulation path of sulfur element 9 (closed dashed line) is as follows:

[0042] The internal circulation path I generated by fuel combustion in the kiln head burner 3 is: rotary kiln 7 → smoke chamber 8 → decomposition furnace 4 → final stage preheater 6 → rotary kiln 7.

[0043] Internal circulation path II generated by fuel combustion in the decomposition furnace 3: Decomposition furnace 4 → final stage preheater 6 → previous stage or multiple stage preheaters → decomposition furnace 4 → final stage preheater 6 → rotary kiln 7 → smoke chamber 8 → decomposition furnace 4.

[0044] During the circulation of sulfur in a cement kiln system, decomposition and capture reactions mainly occur:

[0045] The decomposition reaction refers to the reaction that occurs in the high-temperature rotary kiln 7 when unburned fixed carbon brought in by the initial coal falls into the material and reacts with sulfate compounds in the material under anaerobic conditions, as follows:

[0046] R2SO4+C==R2O+SO2↑+CO↑ (1)

[0047] The capture reaction refers to the following reaction that occurs in sulfur dioxide gas within decomposition furnace 4:

[0048] 2R2O+2SO2↑+O2↑==2R2SO4 (2)

[0049] In the above chemical formula, "R" refers to alkali metals such as Ca, K, Na, and Mg.

[0050] During the reciprocating circulation of sulfur-containing compounds within the cement kiln, the sulfur concentration reaches its highest point in the feed pipe 1 of the final preheater. When the combustion conditions of the fuel in the rotary kiln 7 and the decomposition furnace 4 change, the corresponding decomposition and capture reactions will also change accordingly. Real-time monitoring of the sulfur content of the material in the feed pipe 1 of the final preheater can reveal fluctuations in the circulation ratio. Different calcination process control levels will produce significantly different sulfur circulation ratios. Conversely, timely monitoring of the sulfur circulation ratio can optimize and improve the calcination process control level of cement clinker. The flow path of the material in the cement kiln is as follows: Figure 1 The material flow path in the cement kiln is shown in Figure 10 (solid arrow). The airflow path in the cement kiln is as follows: Figure 1 The wind direction in the cement kiln is shown in 11 (dashed arrow). Sulfur dioxide (SO2) in the cement kiln is represented by a triangle 12; unburned fixed carbon 13 is represented by a solid ellipse; carbon monoxide (CO) 14 is represented by a ring.

[0051] The correspondence between the changes in combustion state at kiln head burner 3 and decomposition furnace 4 and the changes in sulfate content ratio in hot raw materials and clinker is as follows:

[0052] In the kiln head burner 3, if the fuel combustion is poor, some fixed carbon will inevitably fall into the material without complete combustion. This carbon then reacts with sulfates in the material under the high temperature environment of the kiln, producing gaseous SO2 which moves with the secondary air to the decomposition furnace 4. In the decomposition furnace 4, SO2 reacts fully with a large amount of suspended, boiling CaO, producing CaSO4 (sulfate). This CaSO4 enters the final preheater 6 and then re-enters the rotary kiln 7 through the final preheater feed pipe 1. When a significant change in the sulfate content of the material (hot raw material) in the final preheater feed pipe 1 is detected, the ratio of sulfate content in the raw material to that in the clinker in the clinker hopper 2 will inevitably change (the difference between the sulfate content in the hot raw material and the sulfate content in the clinker is the amount of sulfur circulating in the kiln system). Therefore, the change in the ratio of sulfate content in the hot raw material and the clinker can be used to evaluate the change in the combustion state of the fuel at the kiln head.

[0053] In the decomposition furnace 4, if the combustion state of the fuel is not good, according to chemical formula (2), since there is a lack of O2 in the decomposition furnace for SO2 to be captured and generated into sulfate, a large amount of SO2 will still enter the final stage preheater in gaseous form and then enter the next stage (fourth stage) preheater with the rising hot air. Therefore, at this time, SO2 in the decomposition furnace cannot be efficiently captured by CaO to generate sulfate, thereby greatly reducing the sulfate content in the feed pipe of the final stage preheater, that is, the circulation ratio M is greatly reduced (even less than 1). At the same time, since there is still some O2 and R2O in the fourth stage and above preheaters, according to chemical formula (2), this large amount of SO2 will continue to generate sulfate and return to the decomposition furnace 4 with the material. This part of the returned sulfate is superimposed with the sulfate normally generated in the decomposition furnace, which makes the sulfate content of the material in the feed pipe of the final stage preheater 6 greatly increase, that is, the sulfur element circulation ratio M is greatly increased. The alternation of these two situations will inevitably cause repeated fluctuations in the sulfur cycle ratio M. Conversely, if repeated fluctuations in the sulfur cycle ratio M occur, it can be determined that the fuel combustion state in the decomposition furnace is not good.

[0054] Based on the sulfur cycle ratio M, the combustion status of a set process location (e.g., kiln head burner 3 and decomposition furnace 4) in a cement kiln can be evaluated.

[0055] When M = 1.2-2.5, it can be determined that the combustion status of the kiln head burner 3 and the decomposition furnace 4 is good; the amount of raw material, air and fuel in the system is matched, and the existing process parameters are maintained.

[0056] When M < 1.2, the combustion state of the fuel in the decomposition furnace 4 is judged to be poor or extremely poor. When the sulfate circulation ratio in the final preheater 6 is low or even lower than the sulfate content in the clinker exiting the kiln, it indicates that the SO2 transmitted from the kiln or generated in the decomposition furnace 4 has not been captured by CaO. According to chemical formula (2), it can be known that there must be a lack of O2 in the decomposition furnace 4 at this time, which leads to the fuel being in an incomplete combustion state. The cause of oxygen deficiency may be that when the coal weight fluctuates, the calorific value of pulverized coal increases, or the calorific value of the added waste increases, the amount of tail coal is not reduced, and the uncaptured SO2 still enters the upper stage preheater in gaseous form with the rising hot air. In the upper stage preheater, it may be captured by CaO, or it may escape directly from the preheater outlet, which may lead to excessive sulfur emissions in the plant in severe cases.

[0057] When M > 2.5 and remains constant, it can be determined that the combustion state of the kiln head burner 3 is poor. According to chemical reaction formula (1), it indicates that there is a constant amount of fixed carbon mixed into the material in the kiln near the kiln head burner 3, and the magnitude of the change in the value of M corresponds to the amount of fixed carbon mixed in.

[0058] When the value of M is unstable within a set time period, fluctuating up and down, with the absolute value of the fluctuation ranging from 0.1 to 10, the combustion state in the decomposition furnace 4 is determined to be poor or extremely poor. The magnitude of the fluctuation is inversely proportional to the quality of the combustion state. At this time, it is necessary to focus on adjusting the matching relationship between materials, fuel, and air volume in the decomposition furnace 4.

[0059] Therefore, regardless of whether it is in the kiln head firing zone or the decomposition furnace, whenever incomplete combustion occurs, that is, if fuel is mixed into the material in the rotary kiln 7 or the final stage preheater 6, this method can detect and pinpoint the process location and corresponding quantity of fuel mixing.

[0060] The above sampling, testing, and evaluation steps can be performed as needed according to the set testing frequency. For example, step S1 sampling can be performed approximately every 0.5 to 2 hours.

[0061] In the description of this invention, it should be noted that "clinker hopper" includes not only clinker hoppers on the production line, but also related equipment or containers for transporting and storing clinker.

[0062] Regardless of the frequency of sulfur detection or the use of other M-value ranges to determine the combustion state within the kiln system, all methods fall within the protection scope of this invention.

[0063] The cement kiln combustion status evaluation method provided by this invention detects the sulfur content in the hot raw material in the feed pipe of the final preheater and the clinker in the clinker hopper to obtain the sulfur circulation ratio within the cement kiln, and evaluates the cement kiln combustion status based on the sulfur circulation ratio. This method overcomes the limitations of traditional methods that rely solely on CO content detection in the kiln tail flue, which cannot accurately reflect the fuel combustion state. It allows operators to more accurately and promptly evaluate the fuel status within the kiln system and quickly pinpoint the process adjustments that need to be made. Therefore, it not only saves fuel but also mitigates the negative impact of poor fuel combustion on clinker quality and yield within the cement kiln clinker calcination system. The method is simple to operate, requires no investment in large-scale equipment modifications, has high reliability, and can be implemented by all cement companies. There are nearly 1700 cement clinker raw material production lines nationwide, with a clinker production capacity exceeding 2 billion tons. If this technology can be widely adopted, it could save the industry 6 million tons of standard coal per year.

[0064] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0065] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances, and they should not be construed as limitations on this invention.

[0066] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0067] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the invention do not depart from the spirit and scope of the invention and should be covered within the scope of the claims of the invention.

Claims

1. A method for evaluating the combustion state of a cement kiln based on sulfur element detection, characterized in that, Includes the following steps: S1. Within a set time period, a certain amount of hot raw material is obtained from the feed pipe (1) of the final stage preheater and a certain amount of clinker is obtained from the clinker hopper (2); S2. Detect the mass percentage of sulfur in the hot raw material and the clinker, and determine the sulfur circulation ratio M in the cement kiln based on the ratio of the mass percentage of sulfur in the hot raw material to the mass percentage of sulfur in the clinker. S3. Based on the sulfur element circulation ratio, evaluate the combustion state at the set process position in the cement kiln, and determine the process position where the combustion state is unreasonable. The set process location includes the kiln head burner (3) and the decomposition furnace (4); In step S3, When M = 1.2-2.5, the combustion state of the kiln head burner (3) and the decomposition furnace (4) is determined to be good; When M < 1.2, the combustion state of the decomposition furnace (4) is determined to be poor or extremely poor. When M>2.5 and remains constant, the combustion state of the kiln head burner (3) is determined to be poor; When the value of M fluctuates within a set time period and the absolute value of the fluctuation is between 0.1 and 10, the combustion state in the decomposition furnace (4) is determined to be poor or extremely poor. The magnitude of the absolute value of the fluctuation is inversely proportional to the quality of the combustion state.

2. The evaluation method according to claim 1, characterized in that, The set time period is 2-4 hours.

3. The evaluation method according to claim 1, characterized in that, A manual material handling device or an automatic material handling device (5) or an online detection device containing an automatic sampling device is provided on the pipe wall of the feed pipe (1) of the final preheater to obtain the sulfur content of the material before entering the kiln. This device is used to obtain and detect the sulfur content of the hot raw material from the feed pipe (1) of the final preheater.

4. The evaluation method according to claim 1, characterized in that, In step S1, the set length is 30 minutes.

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