Method for calcining low-ash lime in a lime rotary kiln

Abstract

The present application belongs to the technical field of rotary kiln roasting, and particularly relates to a method for calcining low-carbon ash in a lime rotary kiln, and the specific steps are as follows: S1: preparing raw materials and fuel; S2: adjusting the kiln condition; S3: preheating: the preheating inlet temperature of the raw materials is 200-250 DEG C, the discharge temperature is higher than 140 DEG C, and the limestone burst rate is reduced to below 2%; S4: calcining: (1) quality adjustment stage: the coal injection amount, yield and secondary air are finely adjusted according to the kiln head temperature; (2) quality stable stage: after the cylinder temperature, the riding wheel temperature and the support pipe temperature tend to be stable, the process is adjusted. The method effectively reduces the powder rate in the calcining process, improves the coal powder combustion efficiency, reduces the residual carbon in the lime by relying on sufficient oxygen and long residence time, stably produces high-quality low-carbon ash, prolongs the calcining zone length by combining long flame calcining, avoids the concentrated release of heat, simultaneously improves the outer air pressure, strengthens the entrainment effect of the axial flow air on the high-temperature secondary air, and improves the coal powder burnout rate.

Description

Technical Field

[0001] This invention belongs to the field of rotary kiln calcination technology, and particularly relates to a method for calcining low-carbon ash in a lime rotary kiln. Background Technology

[0002] Taiyuan Iron & Steel Group Xinlei's current mining sources are mainly outcrop K6 and K7 ores, whose roasting powder rate is 2.2 percentage points higher than that of the K3 and K4 ores under preparation. This increases the uncertainty of calcining low-carbon ash. The traditional method of calcining low-carbon ash results in a high limestone roasting powder rate, poor air permeability of the preheater during rotary kiln calcination, low coal combustion efficiency, material segregation in the kiln, local underburning, high residual carbon content in lime, and poor quality of low-carbon ash produced. Summary of the Invention

[0003] The purpose of this invention is to provide a method for calcining low-carbon ash in a rotary kiln, which solves the problems of high limestone calcination powder rate, poor preheater permeability, low coal combustion efficiency, large residual carbon content in lime, and poor quality of low-carbon ash produced by traditional methods for calcining low-carbon ash.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A method for calcining low-carbon lime in a rotary kiln, the specific steps of which are as follows: S1: Prepare raw materials and fuel (1) Limestone CaO > 52%, MgO < 2.5%, SiO2 < 2.0%, S < 0.020%, bursting rate ≤ 2%, drum powder rate ≤ 25%. Select raw materials with low bursting rate and low calcined powder rate to reduce the kiln head powder rate to below 8%. (2) Particle size of coal powder - 200 mesh > 95%, moisture ≤ 3.0%, ash content ≤ 8%, volatile matter 30-35%, net calorific value of coal powder received > 6700 KCal / Kg, sulfur ≤ 0.25%. By reasonably controlling the fineness, moisture and calorific value of coal powder, the combustion efficiency of coal powder is guaranteed.

[0005] S2: Adjust kiln conditions (1) Use high-quality ore to adjust the kiln condition and reduce the roasting powder rate in the kiln; (2) Control the burner flame: long flame 3000-6000mm, axial flow 100%, swirl flow 20-40%; high pulverized coal kiln condition calcination, increase the proportion of axial flow, strengthen the entrainment of primary air on high temperature secondary air, and improve the pulverized coal combustion rate. (3) Thoroughly clean the preheater to ensure its permeability and to ensure negative pressure production during the calcination of low-carbon ash, effectively reducing residual carbon. The cleaning operation of the preheater shall be suspended during the calcination of low-carbon ash.

[0006] S3: Preheating The raw material preheating inlet temperature is 200℃~250℃, and the outlet temperature is >140℃ to ensure the preheating effect, reduce the ore bursting rate, and reduce the limestone bursting rate to below 2%.

[0007] S4: Calcination (1) Quality adjustment stage: Fine-tune the coal injection rate, output and secondary air according to the kiln head temperature; (2) Quality stabilization stage: After the temperature of the cylinder, the temperature of the support roller and the temperature of the support pipe tend to be stable, process adjustment is carried out: the principle of "frequent adjustment and fine adjustment" is implemented to solidify the low carbon ash process parameters.

[0008] Preferably, step S3 further includes: The opening degrees of the upper, middle and lower valves of the preheating chamber are 20-40%, 60-80% and 100% respectively, and the preheating mode is set to feed and discharge at the same time.

[0009] Preferably, the specific content of the quality adjustment stage (1) in step S4 is as follows: If the kiln head temperature is <950℃, reduce production or increase the amount of coal injected appropriately; if the kiln head temperature is >1000℃, increase production or reduce the amount of coal injected appropriately. Secondary air / excess air coefficient: 1.20-1.25.

[0010] Preferably, the parameters in step S4 (2) of the quality stabilization stage are adjusted as follows: The kiln head temperature is controlled at 1000-1050℃, the output is adjusted to 5-10t / cycle, and the pulverized coal injection rate is adjusted to 50-100kg / cycle.

[0011] Preferably, the parameter adjustment in step S4 (2) of the quality stabilization stage further includes: a. Kiln speed: 1.0-1.2 r / min, extending the calcination time in the kiln for more thorough decomposition; b. Heat consumption: 1200-1250 Kcal / kg; increasing the calcination temperature accelerates lime decomposition. c. Kiln pressure: Slight negative pressure -5 to -10 Pa, ensuring smooth flue gas flow, guaranteeing pulverized coal combustion efficiency, and improving decomposition efficiency.

[0012] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: (1) By selecting raw materials and controlling preheating, the pulverization rate in the calcination process can be effectively reduced, the pulverized coal combustion efficiency can be improved, and the CO at the kiln tail can be reduced to below 10,000 ppm (daily > 20,000 ppm). (2) Change from high temperature and fast burning to high temperature, low speed and high excess air, rely on sufficient oxygen and long residence time to reduce the residual carbon in lime, avoid material segregation and local underburning in the kiln, and stably produce high quality low carbon ash. (3) By extending the length of the calcination zone through long flame calcination, heat is not concentrated and released. At the same time, the external air pressure is increased, the axial flow wind is strengthened to enhance the entrainment effect of high temperature secondary air, the pulverized coal combustion rate is improved, and the pulverized coal is prevented from burning after combustion, which would cause ring formation in the middle and rear part of the kiln shell. (4) Stabilize the kiln condition by frequent and fine adjustments to prevent large fluctuations in the temperature at the kiln tail and kiln head, which could cause the lime to be overburned or underburned. Detailed Implementation

[0013] The technical solution of the present invention will be described in detail below with reference to the embodiments.

[0014] From October 28th to October 30th, 2025, our company will conduct 3... # The rotary kiln, using a method for calcining low-carbon ash in a lime rotary kiln provided by this invention, was used to produce low-carbon ash for two days. The specific steps are as follows: S1: Raw Material Preparation The raw ore reserves are approximately 9,000 tons. The mining site took samples of limestone K7 from the ore source for testing in advance. The ore source was subjected to bursting and high-temperature tests according to the standards, as shown in Table 1. At the same time, no less than 3 batches of uninsulated bursting tests were conducted. The ore entry point was confirmed based on the test results.

[0015] Table 1 Sampling and Testing Standards and Results of Limestone K7 from Mineral Source

[0016] S2: Fuel Preparation The raw coal reserves are approximately 1,100 tons. We contacted the raw coal supplier in advance to ensure the supply of low-sulfur coal. The raw coal samples were tested as shown in Table 2, with a focus on sulfur content testing. If the samples meet the requirements, they will be stored separately.

[0017] Table 2. Standards and Results of Raw Coal Sampling and Testing

[0018] S3: Enable device protection (1) High-temperature protection of cooling grate support pipes: Compressed air is used to force-cool the cooling grate support tubes. (2) High-temperature protection of kiln head cylinder and support roller system: Axial flow fans are installed on both sides of the kiln body and on the trolley at kiln head points 3#, 4#, 5#, and 6# for cooling.

[0019] S4: Adjust kiln conditions (1) Starting at 8:00 on October 27, the kiln condition of pure K7 ore (high-quality ore) in warehouse 8 of kiln No. 3 was adjusted; (2) Control the burner flame: long flame 6000mm, axial flow 100%, swirl flow 20-40%; (3) Clean the preheater of kiln No. 3 in advance. During the calcination of low carbon ash, the cleaning operation of the preheater shall be suspended.

[0020] S5: Preheating Preheating method: The exhaust gas from the kiln tail of kiln No. 3 is used for heating. The inlet temperature is >200℃. The opening of the upper, middle and lower valves of the preheating chamber is 20%, 80% and 100% respectively. The preheating mode is set to feed and discharge at the same time.

[0021] S6: Calcination (1) Quality adjustment phase (October 28, 7:30-20:00) On October 28th at 7:30, production was reduced and adjusted to produce low-carbon ash. At 8:30, the kiln head sample was tested and found to have TC% and S% of 0.017%. At 10:30, the low-carbon ash was put into the turnover ash shed. The process parameters are controlled as shown in Table 3.

[0022] Table 3 Process Parameter Control during Quality Adjustment Stage

[0023] Process adjustments: 1) Adjust the amount of coal injection and output according to the kiln head temperature. If the kiln head temperature is <950℃, reduce the output or increase the amount of coal injection. If the kiln head temperature is >1000℃, increase the output or decrease the amount of coal injection. 2) Blackening of dust from the kiln head dust collector: Secondary air volume reduced from 43000 Nm 3 / h increased to 50000 Nm 3 / h, the secondary air-to-coal ratio increased from 7.2 to 8.3; 3) At 16:30, the TC% of the kiln head ash was tested and found to be 0.34%. If the quality does not meet the standard, the ash will be stopped at the primary ash shed and transferred to the general ash silo. Production: 850t / d to 810t / d; pulverized coal injection rate: 5900t / h to 6200t / h; kiln head temperature gradually increased to 1000-1050℃; quality was adjusted; at 18:30, the TC% of the kiln head ash was tested and found to be 0.18%; at 20:00, the ash was transferred to the primary ash silo.

[0024] During the quality stabilization phase (October 28, 20:00 - October 30, 8:00), the process parameters are controlled as shown in Table 4.

[0025] Table 4 Process Parameter Control During Quality Stabilization Stage

[0026] Process adjustments: The central control system adjusts the calcination quality based on the kiln head temperature, keeping the kiln head temperature between 1000-1050℃ and the output between 5-10t / cycle; the coal injection rate is adjusted to 50-100kg / cycle, with frequent fine adjustments to avoid large fluctuations in the kiln's operating conditions.

[0027] Operating discipline: (1) It is strictly forbidden to reduce coal consumption significantly, frequently adjust kiln speed, or significantly increase air volume (adjust the speed of high-temperature blowers). Small adjustments should be made frequently. (2) The central control unit records temperature, negative pressure, CO, and air-coal parameters every hour to stabilize the operating conditions; (3) The preceding and following processes are linked, and the material, coal, air, temperature and speed are matched and operated in an integrated manner.

[0028] S7: Effect Verification The low-carbon ash obtained from the embodiments of this invention was tested at AOD #0 from November 11th to 24th, and the results are as follows: (1) The data of 55 heats of ultra-low carbon steel are shown in Table 5. The desulfurization effect is normal. The average sulfur content of 316 series and duplex steel is <0.003%. (2) The carbon composition of the reduced C and the tapped C of the 55 heats of ultra-low carbon steel, the low carbon lime showed no obvious carbon increase, and the carbon content met the requirements of ultra-low carbon stainless steel in the North District.

[0029] Table 5. Heat data for 55 heats of ultra-low carbon steel.

Claims

1. A method for calcining low-carbon ash in a lime rotary kiln, characterized in that, The specific steps are as follows: S1: Prepare raw materials and fuel (1) Limestone CaO > 52%, MgO < 2.5%, SiO2 < 2.0%, S < 0.020%, bursting rate ≤ 2%, drum powder rate ≤ 25%, kiln head powder rate reduced to below 8%; (2) Particle size of coal powder - 200 mesh > 95%, moisture ≤ 3.0%, ash content ≤ 8%, volatile matter 30-35%, net calorific value of coal powder received > 6700 KCal / Kg, sulfur ≤ 0.25%. By reasonably controlling the fineness, moisture and calorific value of coal powder, the combustion efficiency of coal powder is guaranteed. S2: Adjust kiln conditions (1) Use high-quality ore to adjust the kiln condition and reduce the roasting powder rate in the kiln; (2) Control the burner flame: long flame 3000-6000mm, axial flow 100%, swirl flow 20-40%; high pulverized coal kiln condition calcination, increase the proportion of axial flow, strengthen the entrainment of primary air on high temperature secondary air, and improve the pulverized coal combustion rate. (3) Thoroughly clean the preheater to ensure its permeability and to ensure negative pressure production during the calcination of low-carbon ash, effectively reducing residual carbon. The cleaning operation of the preheater shall be suspended during the calcination of low-carbon ash. S3: Preheating The raw material preheating inlet temperature is 200℃~250℃, and the outlet temperature is >140℃ to ensure the preheating effect, reduce the ore bursting rate, and reduce the limestone bursting rate to below 2%. S4: Calcination (1) Quality adjustment stage: Fine-tune the coal injection rate, output and secondary air according to the kiln head temperature; (2) Quality stabilization stage: After the temperature of the cylinder, the temperature of the support roller and the temperature of the support pipe tend to be stable, process adjustment is carried out: the principle of "frequent adjustment and fine adjustment" is implemented to solidify the low carbon ash process parameters.

2. The method for calcining low-carbon ash in a rotary kiln according to claim 1, characterized in that, Step S3 further includes: The opening degrees of the upper, middle and lower valves of the preheating chamber are 20-40%, 60-80% and 100% respectively, and the preheating mode is set to feed and discharge at the same time.

3. The method for calcining low-carbon ash in a rotary kiln according to claim 1, characterized in that, The specific content of the quality adjustment stage (1) in step S4 is as follows: If the kiln head temperature is <950℃, reduce production or increase the amount of coal injected appropriately; if the kiln head temperature is >1000℃, increase production or reduce the amount of coal injected appropriately. Secondary air / excess air coefficient: 1.20-1.

25.

4. The method for calcining low-carbon ash in a lime rotary kiln according to claim 1, characterized in that, The parameters for the quality stabilization stage in step S4 (2) are adjusted as follows: The kiln head temperature is controlled at 1000-1050℃, the output is adjusted to 5-10t / cycle, and the pulverized coal injection rate is adjusted to 50-100kg / cycle.

5. The method for calcining low-carbon ash in a rotary kiln according to claim 1, characterized in that, The parameter adjustment in step S4 (2) of the quality stabilization stage also includes: a. Kiln speed: 1.0-1.2 r / min; b. Heat consumption: 1200-1250 kcal / kg; c. Kiln pressure: slightly negative pressure -5 to -10 Pa.

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