Method for reducing nodulation in lime rotary kiln

Abstract

The invention relates to the technical field of rotary kiln processes, and provides a method for reducing nodulation in a lime rotary kiln, which comprises the following steps: S1, raw material pretreatment; s2, controlling the environment in the kiln; s3, optimizing the structural design of the kiln body; and S4, cleaning and maintaining in the kiln. According to the technical scheme, through the process steps of proportioning the raw materials, calculating the calcining temperature in a kiln, adjusting the stockline of a cooler to be 1.5 m, starting to discharge ash, and ending when the stockline of the cooler is 0.5 m, the CaO range of block ash is reduced by 11.44%, the SiO2 range is reduced by 1.52%, the activity range is reduced by 94.88 ml, the CaO range of surface ash is reduced by 6.95%, the SiO2 range is reduced by 0.54%, and the activity range is reduced by 100 ml; the data verifies that the quality of the finished product ash subjected to multi-fuel combustion in the rotary kiln is relatively stable after the new method is adopted.

Description

Technical Field

[0001] The invention relates to the technical field of rotary kiln technology, and in particular to a method for reducing nodules in a lime rotary kiln. Background Art

[0002] The Wuxingshi Mine, a limestone resource, has a high pulverization rate, with an average pulverization rate of approximately 60%. The average pulverization rate of externally mined, low-pulverization limestone is less than 15%. Due to this high pulverization rate, when using a rotary kiln to calcine metallurgical lime, dust floats in the kiln and the finished product is severely pulverized, with the finished product ash rate reaching 70% to 80%. This also easily causes process accidents such as nodules during production. This nodulated lime cannot be used properly in subsequent processes and must be treated as waste, resulting in no economic benefits and lost costs. Frequent nodulation accidents prevent the rotary kiln from achieving its designed production capacity, resulting in a high cost per ton of ash, far exceeding that of other metallurgical enterprises. Therefore, a lime rotary kiln that can improve production efficiency, product quality, and reduce the cost per ton of ash is urgently needed. Summary of the Invention

[0003] The present invention proposes a method for reducing nodules in a lime rotary kiln, which solves the problem in the related art that frequent nodule accidents cause the rotary kiln to be unable to achieve the designed production capacity, resulting in high cost per ton of ash. The method uses process optimization to improve production efficiency and product quality, thereby achieving the effect of reducing process energy consumption and production costs.

[0004] The technical solution of the present invention is as follows: A method for reducing nodules in a lime rotary kiln, comprising the following steps: S1, Raw material pretreatment: Before the raw materials enter the rotary kiln, the limestone is stored separately according to different qualities, the material composition is statistically analyzed to calculate the proportion in advance, and the batching software is developed to ensure the stability of the raw materials entering the kiln to reduce nodule formation; S2, kiln environment control: calculate the optimal calcination temperature after proportioning through the pulverization rate test report, calculate the parameters of gas flow into the kiln and ash output to ensure stable calcination and reduce the formation of nodules; S3, kiln structure design optimization: the kiln body is designed to change from continuous ash discharge to intermittent ash discharge, ensuring the stability of secondary air temperature and reducing the heat loss caused by continuous ash discharge; S4, kiln cleaning and maintenance: Under the premise of stable process operation in the kiln, reduce the frequency of kiln shutdown inspections, avoid unplanned shutdowns, and maintain a stable kiln environment.

[0005] Optionally, before the raw material proportioning pretreatment in S1, the following steps are further included: S11, Raw material selection and testing: Select limestone with high calcium (CaCO3 content ≥ 90%) and low impurities (such as MgO, SiO2), and evaluate the raw material quality through chemical analysis (such as XRF) and physical testing (hardness, particle size); S12, Crushing: Use a crusher to crush large limestone into a particle size suitable for calcination (usually 20-50 mm); S13, screening and impurity removal: Use a vibrating screener to screen out oversized or undersized particles, return them for crushing or discard, use a magnetic separator / iron remover to remove metal impurities, and use manual or mechanical sorting to remove visible impurities; S14, preheating: Use a preheater to utilize the exhaust gas from the kiln to preheat the raw materials and improve thermal efficiency.

[0006] Optionally, in S2, the calculation method for calcination is: the no-load current of the kiln is 30A, and the experiment is filled with 8t of material. At this time, the main current is 70A, then the calculation is 70-30=40A=8t, that is, every 1A=0.2t.

[0007] Optionally, in S3, the cooler feed line is adjusted to start ash discharge at 1.5 meters and end at 0.5 meters, ensuring that the ash discharge temperature is less than 150°C.

[0008] Optionally, in S2, the kiln environment control further comprises the following steps: S21, atmosphere and gas composition control: adjust the ratio of primary air to secondary air, or control the negative pressure through the kiln tail draft fan to maintain the O2 concentration, ensure the complete combustion of fuel, and avoid the formation of CO (which wastes fuel and pollutes the environment); S22, negative pressure control in the kiln: adjust the speed of the induced draft fan at the kiln tail to maintain a slightly positive pressure at the kiln head and a slightly negative pressure at the kiln tail. At the same time, pressure sensors are installed at key locations of the kiln head hood and the kiln tail smoke chamber to monitor the air pressure; S23, Material Residence Time and Movement Control: Adjust the rotary kiln speed and tilt angle to control the limestone residence time in the kiln to ensure full decomposition. At the same time, set a material retaining ring or lifting plate on the inner wall of the kiln to promote material tumbling and avoid "partial burning" or "caking"; S24, airflow distribution optimization: rationally arrange the kiln tail flue to reduce airflow short-circuiting or vortex, and ensure that the flame shape (length, rigidity) matches the kiln body through burner design (multi-channel burner) and refractory brick layout in the kiln to avoid local high temperature; S25, Monitoring and Automation: Use sensors to collect data in real time, integrate automated control systems, and dynamically adjust fuel, air volume, and speed parameters based on feedback data to achieve closed-loop control.

[0009] Optionally, in said S4, during the kiln shutdown inspection process, the following inspection steps are included: S41, burner cleaning: disassemble the burner nozzle, remove carbon deposits and blockages, check whether the fuel channel is unobstructed, and adjust the flame shape (to avoid biased burning); S42, dust removal system maintenance: clean the filter bags of the bag filter at the kiln tail, check for damage, remove dust accumulation in the cyclone dust collector, and maintain smooth airflow; S43, transmission device lubrication: Check the lubricating grease of the supporting rollers and gears, replenish or replace them (such as high-temperature grease), and remove material particles adhering to the surface of the transmission parts.

[0010] Optionally, the crusher selected in S12 is one of a jaw crusher, a hammer crusher, and an impact crusher; the metal impurities in S13 are iron blocks; the visible impurities are soil and debris; the preheater used in S14 is one of a vertical preheater and a cyclone preheater, and the preheating temperature is 600-900°C.

[0011] Optionally, the O2 concentration in S21 is 1% to 3%, and the pressure range of the slightly positive pressure at the kiln head and the slightly negative pressure at the kiln tail in S22 is -50 to -200 Pa.

[0012] Optionally, in S23, the rotation speed of the rotary kiln is 0.5-3 rpm, the inclination angle is 2-4°, and the limestone stays in the kiln for 4-8 hours.

[0013] Optionally, the sensors in S25 include infrared thermometer, O2 analyzer, CO analyzer, NO x Analyzers, pressure sensors.

[0014] The working principle and beneficial effects of the present invention are: In the present invention, by carrying out the process steps of raw material ratio, calculating the calcination temperature in the kiln, and adjusting the cooler material line to the 1.5-meter material line to start ash discharge and end at 0.5 meters, the CaO range of lump ash is reduced by 11.44%, the SiO2 range is reduced by 1.52%, and the activity range is reduced by 94.88 ml. The CaO range of surface ash is reduced by 6.95%, the SiO2 range is reduced by 0.54%, and the activity range is reduced by 100 ml. The above data verify that the quality of the finished ash after mixed firing in the rotary kiln is stable after adopting the new method, and the process accidents of nodules in the lime rotary kiln are greatly reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The preferred embodiments will be described below in a clear and understandable manner with reference to the accompanying drawings to further illustrate the above-mentioned characteristics, technical features, advantages and implementation methods of the present invention.

[0016] Figure 1 This is a broken line graph showing the quality improvement of the improved rotary kiln according to the present invention; Figure 2 This is a cost comparison line chart of the improved rotary kiln of the present invention; Figure 3 This is a schematic diagram of nodules in the kiln before the improvement of the present invention; Figure 4 This is a schematic diagram of the improved kiln of the present invention. DETAILED DESCRIPTION

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0018] To simplify the drawings, only portions relevant to the invention are schematically depicted in each figure; they do not represent the actual structure of the product. Furthermore, to simplify the drawings and facilitate understanding, in some figures, only one component with the same structure or function is schematically depicted or labeled. In this document, "one" not only means "only one" but also "more than one," and "several" includes "two" and "more than two."

[0019] It should be noted that, unless otherwise specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0020] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0021] A method for reducing nodules in a lime rotary kiln comprises the following steps: S1, Raw material pretreatment: Before the raw materials enter the rotary kiln, the limestone is stored separately according to different qualities, the material composition is statistically analyzed to calculate the proportion in advance, and the batching software is developed to ensure the stability of the raw materials entering the kiln to reduce nodule formation; S2, kiln environment control: calculate the optimal calcination temperature after proportioning through the pulverization rate test report, calculate the parameters of gas flow into the kiln and ash output to ensure stable calcination and reduce the formation of nodules;

[0022] S3, kiln structure design optimization: the kiln body is designed to change from continuous ash discharge to intermittent ash discharge, ensuring the stability of secondary air temperature and reducing the heat loss caused by continuous ash discharge; S4, kiln cleaning and maintenance: Under the premise of stable process operation in the kiln, reduce the frequency of kiln shutdown inspections, avoid unplanned shutdowns, and maintain a stable kiln environment.

[0023] See also Figure 1 After the above improved process, the quality of block ash and surface ash is improved as follows: (1) Lump ash: In 2022, the CaO content of the single-fired purchased low-pulverization rate limestone was as high as 90.24% and as low as 74.77%, with a quality deviation of 15.47%. The unstable quality will affect the production of the next process, so that the entire production line fluctuates; in 2023, the mixed ratio calcination, the mixed ratio of 8:1 (purchased: five stars) has the highest quality of 89.99%, and the mixed ratio of 2:1 (purchased: five stars) has the lowest quality of 85.96%, and the quality deviation is reduced to 4.03%, and the quality deviation decreases by 11.44% month-on-month.

[0024] (2) Surface ash: The highest monthly average CaO content in 2022 was 90.48% due to single-firing of purchased limestone, and the highest content in 2023 was 91.70% due to mixed firing with a ratio of 1:1 (purchased: five-star). According to the calculated ratio, the ash quality increased by 1.22%.

[0025] (3) Range: The range of CaO in lump ash decreased by 11.44%, the range of SiO2 decreased by 1.52%, and the range of activity decreased by 94.88 ml. The range of CaO in surface ash decreased by 6.95%, the range of SiO2 decreased by 0.54%, and the range of activity decreased by 100 ml. The above data verified that the quality of the finished ash after mixed firing in the rotary kiln was relatively stable after adopting the new method.

[0026] See also Figure 2 After the above improved process, the cost-effectiveness of the rotary kiln is as follows: (1) The rotary kiln is designed to produce 600 tons of metallurgical lime per day. Due to limestone, the current daily output is only 430 tons of metallurgical lime. Steelmaking requires 220 tons of nugget ash per day. After the rotary kiln meets the demand for nugget ash, the remaining metallurgical lime is all used for sintering. 1.8 tons of limestone can produce 1 ton of metallurgical lime.

[0027] (2) Starting from 2023, the rotary kiln will adopt a mixed calcination method of purchased limestone and five-star limestone. Gradually explore ways to increase the proportion of five-star limestone and reduce the amount of purchased limestone, thereby reducing the cost of raw materials for the finished ash of the rotary kiln. The first step is to adjust the position of the discharge pipe by exploring parameters such as the temperature at the kiln tail, the thickness of the material layer in the kiln, the distance between the push rods, and the ash discharge time. The purchased limestone ratio is 100%, and the manufacturing cost per ton of ash is 556.4 yuan / ton. Gradually adjust the manufacturing cost of 1:1 (purchased: five-star) to 443 yuan / ton, reducing the manufacturing cost of 113.4 yuan / ton of rotary kiln ash.

[0028] (3) The annual profit calculation is based on the period from January to June 2023. Since the unit price of Huadian limestone decreased in November 2023, the annual profit is calculated based on the profit generated in October to approximately RMB 18.22 million. This figure will fluctuate depending on factors such as seasonal raw material costs, ingredient ratios, and the impact of temperature on energy consumption.

[0029] Before the raw material proportioning pretreatment in S1, the following steps are also included: S11, Raw material selection and testing: Select limestone with high calcium (CaCO3 content ≥ 90%) and low impurities (such as MgO, SiO2), and evaluate the raw material quality through chemical analysis (such as XRF) and physical testing (hardness, particle size); S12, Crushing: Use a crusher to crush large limestone into a particle size suitable for calcination (usually 20-50 mm); S13, screening and impurity removal: Use a vibrating screener to screen out oversized or undersized particles, return them for crushing or discard, use a magnetic separator / iron remover to remove metal impurities, and use manual or mechanical sorting to remove visible impurities; S14, preheating: Use a preheater to utilize the exhaust gas from the kiln to preheat the raw materials and improve thermal efficiency.

[0030] In S2, the calculation method for calcination is: the no-load current of the kiln is 30A, and the experiment is filled with 8t of material. At this time, the main current is 70A, so the calculation is 70-30=40A=8t, that is, every 1A=0.2t.

[0031] In S3, the cooler starts discharging ash from the material level of 2 meters to 0.5 meters, which cannot ensure the ash discharge temperature required by the process. After calculation and consultation with relevant engineers from the technical center, the cooler material line was adjusted to start discharging ash from the material line of 1.5 meters to 0.5 meters, ensuring that the ash discharge temperature is less than 150℃.

[0032] In S2, the kiln environment control also includes the following steps: S21, atmosphere and gas composition control: adjust the ratio of primary air to secondary air, or control the negative pressure through the kiln tail draft fan to maintain the O2 concentration, ensure the complete combustion of fuel, and avoid the formation of CO (which wastes fuel and pollutes the environment); S22, negative pressure control in the kiln: adjust the speed of the induced draft fan at the kiln tail to maintain a slightly positive pressure at the kiln head and a slightly negative pressure at the kiln tail. At the same time, pressure sensors are installed at key locations of the kiln head hood and the kiln tail smoke chamber to monitor the air pressure; S23, Material Residence Time and Movement Control: Adjust the rotary kiln speed and tilt angle to control the limestone residence time in the kiln to ensure full decomposition. At the same time, set a material retaining ring or lifting plate on the inner wall of the kiln to promote material tumbling and avoid "partial burning" or "caking"; S24, airflow distribution optimization: rationally arrange the kiln tail flue to reduce airflow short-circuiting or vortex, and ensure that the flame shape (length, rigidity) matches the kiln body through burner design (multi-channel burner) and refractory brick layout in the kiln to avoid local high temperature; S25, Monitoring and Automation: Use sensors to collect data in real time, integrate automated control systems, and dynamically adjust fuel, air volume, and speed parameters based on feedback data to achieve closed-loop control.

[0033] In S4, during the kiln shutdown inspection process, the following inspection steps are included: S41, burner cleaning: disassemble the burner nozzle, remove carbon deposits and blockages, check whether the fuel channel is unobstructed, and adjust the flame shape (to avoid biased burning); S42, dust removal system maintenance: clean the filter bags of the bag filter at the kiln tail, check for damage, remove dust accumulation in the cyclone dust collector, and maintain smooth airflow; S43, transmission device lubrication: Check the lubricating grease of the supporting rollers and gears, replenish or replace them (such as high-temperature grease), and remove material particles adhering to the surface of the transmission parts.

[0034] The crusher selected in S12 is one of a jaw crusher, a hammer crusher, and an impact crusher; the metal impurities in S13 are iron blocks; the visible impurities are soil and debris; the preheater used in S14 is one of a vertical preheater and a cyclone preheater, and the preheating temperature is 600-900°C.

[0035] The O2 concentration in S21 is 1% to 3%, and the pressure range of the slightly positive pressure at the kiln head and the slightly negative pressure at the kiln tail in S22 is -50 to -200 Pa.

[0036] In S23, the rotary kiln speed is 0.5~3 rpm, the tilt angle is 2~4°, and the limestone stays in the kiln for 4~8 hours.

[0037] The sensors in S25 include infrared thermometer, O2 analyzer, CO analyzer, NO x Analyzers, pressure sensors.

[0038] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for reducing nodules in a lime rotary kiln, characterized in that: The following steps are involved: S1, Raw material pretreatment: Before the raw materials enter the rotary kiln, the limestone is stored separately according to different qualities, the material composition is statistically analyzed to calculate the proportion in advance, and the batching software is developed to ensure the stability of the raw materials entering the kiln to reduce nodule formation; S2, kiln environment control: calculate the optimal calcination temperature after proportioning through the pulverization rate test report, calculate the parameters of gas flow into the kiln and ash output to ensure stable calcination and reduce the formation of nodules; S3, kiln structure design optimization: the kiln body is designed to change from continuous ash discharge to intermittent ash discharge, ensuring the stability of secondary air temperature and reducing the heat loss caused by continuous ash discharge; S4, kiln cleaning and maintenance: Under the premise of stable process operation in the kiln, reduce the frequency of kiln shutdown inspections, avoid unplanned shutdowns, and maintain a stable kiln environment.

2. The method for reducing nodules in a lime rotary kiln according to claim 1, wherein: Before the raw material proportioning pretreatment in S1, the following steps are also included: S11, Raw material selection and testing: Select limestone with a calcium content ≥ 90%, and evaluate the raw material quality through chemical analysis and physical testing; S12, Crushing: Use a crusher to crush large limestone into a particle size suitable for calcination; S13, screening and impurity removal: Use a vibrating screener to screen out oversized or undersized particles, return them for crushing or discard, use a magnetic separator / iron remover to remove metal impurities, and use manual or mechanical sorting to remove visible impurities; S14, preheating: Use a preheater to utilize the exhaust gas from the kiln to preheat the raw materials and improve thermal efficiency.

3. A method for reducing nodules in a lime rotary kiln according to claim 2, characterized in that: In S2, the calculation method for calcination is: the no-load current of the kiln is 30A, and the experiment is filled with 8t of material. At this time, the main current is 70A, so the calculation is 70-30=40A=8t, that is, every 1A=0.2t.

4. The method for reducing nodules in a lime rotary kiln according to claim 3, wherein: In S3, the cooler feed line is adjusted to start ash discharge at 1.5 meters and end at 0.5 meters, ensuring that the ash discharge temperature is less than 150°C.

5. The method for reducing nodules in a lime rotary kiln according to claim 4, wherein: In said S2, the kiln environment control further comprises the following steps: S21, atmosphere and gas composition control: adjust the ratio of primary air to secondary air, or control the negative pressure through the kiln tail draft fan to maintain the O2 concentration, ensure the complete combustion of fuel and avoid the formation of CO; S22, negative pressure control in the kiln: adjust the speed of the induced draft fan at the kiln tail to maintain a slightly positive pressure at the kiln head and a slightly negative pressure at the kiln tail. At the same time, pressure sensors are installed at key locations of the kiln head hood and the kiln tail smoke chamber to monitor the air pressure; S23, Material Residence Time and Movement Control: Adjust the rotary kiln speed and tilt angle to control the limestone residence time in the kiln to ensure full decomposition. At the same time, set a material retaining ring or lifting plate on the inner wall of the kiln to promote material tumbling and avoid partial burning or agglomeration. S24, airflow distribution optimization: rationally arrange the kiln tail flue to reduce airflow short-circuiting or vortex, and ensure that the flame shape matches the kiln body through burner design and kiln refractory brick layout to avoid local high temperature; S25, Monitoring and Automation: Use sensors to collect data in real time, integrate automated control systems, and dynamically adjust fuel, air volume, and speed parameters based on feedback data to achieve closed-loop control.

6. The method for reducing nodules in a lime rotary kiln according to claim 5, wherein: In the above S4, during the kiln shutdown inspection process, the following inspection steps are included: S41, burner cleaning: disassemble the burner nozzle, remove carbon deposits and blockages, check whether the fuel channel is unobstructed, and adjust the flame shape; S42, dust removal system maintenance: clean the filter bags of the bag filter at the kiln tail, check for damage, remove dust accumulation in the cyclone dust collector, and maintain smooth airflow; S43, transmission device lubrication: Check the lubricating grease of the rollers and gears, and replenish or replace them, and remove material particles adhering to the surface of the transmission parts.

7. The method for reducing nodules in a lime rotary kiln according to claim 2, wherein: The crusher selected in S12 is one of a jaw crusher, a hammer crusher, and an impact crusher; the metal impurities in S13 are iron blocks; the visible impurities are soil and debris; the preheater used in S14 is one of a vertical preheater and a cyclone preheater, and the preheating temperature is 600-900°C.

8. The method for reducing nodules in a lime rotary kiln according to claim 5, wherein: The O2 concentration in the S21 is 1% to 3%, and the pressure range of the slightly positive pressure at the kiln head and the slightly negative pressure at the kiln tail in the S22 is -50 to -200 Pa.

9. The method for reducing nodules in a lime rotary kiln according to claim 5, wherein: In the step S23, the rotation speed of the rotary kiln is 0.5-3 rpm, the tilt angle is 2-4°, and the limestone stays in the kiln for 4-8 hours.

10. The method for reducing nodules in a lime rotary kiln according to claim 9, characterized in that: The sensors in S25 include infrared thermometer, O2 analyzer, CO analyzer, NO x Analyzers, pressure sensors.

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