Method for efficiently calcining high-pulverization-rate limestone in a gas-fired shaft kiln

Abstract

The application provides a method for efficiently calcining high-pulverization-rate limestone in a gas-fired shaft kiln, and belongs to the field of calcination of gas-fired shaft kiln. In the production process, a part of air fuel is sent in through bottom air, and the air fuel is heated to high-temperature hot air by passing through a cooling section; the high-temperature hot air meets the gas fuel sent in through the lower side air in the calcination section, and the first combustion is completed in the calcination section; the high-temperature combustible flue gas generated by the first combustion moves upward, and the combustible flue gas meets another part of air fuel sent in through the upper side air, the second combustion occurs in the upper part of the calcination section, and the gas fuel is fully combusted. The new method for efficiently calcining high-pulverization-rate limestone in a gas-fired shaft kiln overcomes the problem that the existing gas-fired shaft kiln cannot calcine high-pulverization-rate limestone raw materials, and realizes efficient calcination of high-pulverization-rate limestone raw materials; limestone with a pulverization rate of less than or equal to 52% is used as raw material, which greatly widens the suitability of raw materials of the gas-fired shaft kiln, and improves the yield and quality of metallurgical lime.

Description

Technical Field

[0001] This invention relates to a method for efficiently calcining limestone with a high pulverization rate in a gas-fired vertical kiln, belonging to the field of gas-fired vertical kiln calcination. Background Technology

[0002] Lime is an important industrial raw material with wide applications in metallurgy, construction, and other fields. In 2020, China's lime production was approximately 300 million tons, indicating a large-scale industry. However, the lime industry is also highly resource-dependent. Metallurgical lime production primarily involves calcining and decomposing limestone (CaCO3)-containing ores to produce CaO lime. The reaction equation is as follows:

[0003]

[0004] In this process, theoretically, producing 1 kg of CaO metallurgical lime requires 1.8 kg of CaCO3, resulting in a huge consumption of raw limestone. Simultaneously, due to the high requirements of existing calcination technology and equipment on the performance of the raw materials (especially pulverization rate and particle size), a considerable portion of the raw ore mined from mines is discarded because it does not meet the requirements, further contributing to the large-scale consumption of raw materials. With the rapid development of the domestic lime industry at present (annual production growth rate exceeding 5%–10%), the consumption rate of limestone raw materials will further intensify. Therefore, developing metallurgical lime calcination technology with broader adaptability to raw materials and improving the utilization rate of high-pulverization limestone are problems that the metallurgical lime industry needs to solve as soon as possible.

[0005] Gas-fired vertical kilns are currently the most widely used equipment for calcining metallurgical lime. Due to their simple structure, low cost, and relatively stable product quality, gas-fired kilns were once the preferred choice for metallurgical lime production. Currently, gas-fired kilns account for approximately 10% of my country's total lime production. The main body of a gas-fired vertical kiln is a vertically arranged hollow kiln chamber. During production, limestone meeting the particle size requirements is loaded into the kiln chamber from the top and moves downwards, passing through different temperature zones within the chamber to achieve preheating, calcination, and cooling. The finished metallurgical lime is finally discharged from the bottom of the kiln chamber. Cooling air and gaseous fuel are fed into the kiln chamber from the bottom and sides, completing cooling, combustion, and preheating functions. The generated waste gas is finally discharged from the top of the kiln chamber and enters a dust collector to achieve ultra-low emissions. To obtain qualified metallurgical lime, it is necessary to ensure the uniformity of the flow field and temperature field within the furnace chamber. In existing technologies, the air required for the gas-fired vertical kiln production process (used for cooling finished products, fuel combustion, and furnace heat transfer, etc.) is mainly supplied from the calcination section (middle of the furnace) (accounting for 60%–70% of the total air volume), while the remaining portion is supplied from the cooling section (bottom of the furnace) (accounting for 30%–40% of the total air volume). This airflow arrangement has a good calcination effect when calcining limestone with a low pulverization rate, but it encounters difficulties when calcining limestone with a high pulverization rate. This is mainly because high pulverization rate limestone forms a large number of fine powdery products during calcination. These fine particles accumulate near the furnace wall, increasing the resistance at the wall and preventing the air supplied from the side from reaching the center of the furnace. Therefore, under existing calcination technology, gas-fired vertical kilns cannot effectively calcine high pulverization rate limestone, resulting in a significant waste of resources.

[0006] To address the problem that existing calcination technologies cannot calcine high-pulverization-rate limestone raw materials using gas-fired vertical kilns, this patent proposes a new method for calcining high-pulverization-rate limestone using gas-fired vertical kilns. This method enables efficient calcination of high-pulverization-rate limestone using gas-fired vertical kilns, effectively broadens the adaptability of gas-fired vertical kilns to raw material ores, improves the utilization rate of the furnace feed, and avoids resource waste during the production process. Summary of the Invention

[0007] The purpose of this invention is to solve the problems existing in the prior art and to provide a method for efficiently calcining limestone with a high pulverization rate in a gas-fired vertical kiln.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for efficiently calcining high-pulverization limestone in a gas-fired vertical kiln involves feeding limestone material (mainly CaCO3) from the top of the kiln chamber. After preheating, calcination, and cooling, the resulting finished lime (CaO) at a temperature below 100°C is discharged from the bottom of the kiln chamber. Gaseous fuel is supplied from the lower side air system located in the lower part of the calcination zone, while most of the combustion air is supplied from the bottom air system located at the bottom of the kiln chamber, with the remaining air supplied from the upper side air system located in the upper part of the calcination zone. The bottom air passes through a cooling zone, cooling the high-temperature limestone while simultaneously heating itself to approximately 400–900°C, forming high-temperature hot air. This high-temperature hot air encounters the fuel in the lower part of the calcination zone, causing the fuel to undergo its first combustion. Due to insufficient bottom air volume to ensure complete combustion, the combustion temperature is lower than in conventional combustion, resulting in a larger and more uniform combustion zone. The generated high-temperature flue gas containing combustible gases rises further and encounters the upper side air in the upper part of the calcination zone, undergoing secondary combustion and ensuring complete combustion of the fuel. The high-temperature flue gas is generated and passes through the preheating zone. After exchanging heat with the cold material in the preheating zone, the flue gas temperature drops to about 200°C and is discharged from the top of the kiln.

[0010] The inventors discovered in production practice that by independently feeding fuel and combustion air into the kiln chamber, the combustion temperature and temperature uniformity of the combustion zone can be effectively controlled. Furthermore, by dividing the combustion air into upper side air and bottom air, and controlling the ratio of the two air streams, the length of the calcination zone and the maximum flame temperature can be further adjusted, thereby controlling the degree of pulverization of high-pulverization limestone during the calcination process.

[0011] Furthermore, the inventors discovered in production practice that using low-calorific-value fuel for heating can reduce the combustion temperature and prevent excessively high flame temperatures from causing severe pulverization during the calcination process. For limestone with a high pulverization rate, the fuel calorific value should not exceed 1000 kcal, which is the opposite of the high fuel calorific value sought in calcining conventional lime. It should be noted that in this patented technology, by creating a two-stage combustion atmosphere for the fuel, the length of the calcination zone is widened. Therefore, the calcination rate and yield of conventional high-temperature calcination can be obtained at a lower calcination temperature. Based on production practice, the inventors proposed that the appropriate fuel quantity for calcining 1 ton of CaO product is positively correlated with the fuel calorific value, with a typical range of (1300~1800) Nm3 / t-CaO. Too high a value will lead to an increase in pulverization rate, while too low a value will reduce the CaO content of the product and affect the yield.

[0012] Furthermore, the inventors discovered in production practice that the combustion temperature can be further controlled by adjusting the fuel-to-air ratio. In this invention, the suitable fuel-to-air ratio is 1:1.1 to 1.2, meaning the required air volume is much greater than the equivalent air-fuel ratio of blast furnace gas (1:0.7). This is because at the equivalent air-fuel ratio, the highest combustion temperature of blast furnace gas is above 1200℃. At this temperature, the pulverization degree of high-pulverization limestone is too high during calcination, making normal production impossible. When the fuel-to-air ratio is controlled at approximately 1:1.1 to 1.2, the flame temperature is around 1050℃, at which point the pulverization degree during calcination can be minimized. Based on this, the inventors, drawing on both theory and practice, propose that the suitable total air volume for producing one unit of lime is approximately (1400–2000 Nm³ / t-CaO).

[0013] Furthermore, the inventors discovered in production practice that increasing the bottom air volume and decreasing the side air volume is beneficial for calcining limestone with a high pulverization rate. This is because ① the side air temperature is low, and its contact with the high-temperature finished lime causes rapid cooling of the lime, increasing the pulverization rate at the wall surface; ② the side air carries small pulverized particles from the wall surface to the center of the kiln, worsening the overall permeability of the kiln. Therefore, reducing the side air volume and increasing the bottom air volume is beneficial for calcining limestone with a high pulverization rate. However, at the same time, if the side air volume is too small, the temperature in the center of the furnace may be high, resulting in good calcination, while the temperature near the furnace wall may be low, resulting in poor calcination. The inventors found in production practice that the suitable bottom air volume ratio is 50% to 80%, preferably 60% to 70%.

[0014] Furthermore, the inventors conducted a series of industrial-scale experiments and found that the appropriate bottom air ratio is positively correlated with the pulverization rate of the lime raw materials entering the kiln. The appropriate bottom air ratios corresponding to different pulverization rates are shown in the table below.

[0015]

[0016]

[0017] Furthermore, the inventors discovered through practice that, unlike the traditional 1:1:1 three-zone ratio (preheating: calcining: cooling) of a gas-fired vertical kiln, in this design, the calcining zone, through secondary combustion and separate air and gas injection into the kiln, can be extended to 2 / 5 of the kiln body length. At this point, the suitable distance between the upper and lower side airflows is between 1 / 3 and 2 / 3 of the kiln length.

[0018] This invention provides a method for the efficient calcination of high-pulverization-rate limestone in a gas-fired vertical kiln. This method overcomes the problem that existing gas-fired vertical kilns (one of the main lime production equipment) cannot efficiently calcine high-pulverization-rate limestone (limestone with a pulverization rate > 20%), achieving efficient calcination of high-pulverization-rate limestone, significantly improving the raw material adaptability of the gas-fired vertical kiln, and increasing the yield and quality of metallurgical lime. In this invention, a small portion of the combustion air required for fuel combustion is fed into the furnace from the upper side (above the fuel), and the remaining portion is fed from the bottom of the furnace. This approach offers several advantages:

[0019] ①In the prior art, most of the air enters from the side, while in this patent, most of the air enters from the bottom, which greatly reduces the side air volume supplied from the side. This can effectively prevent the powdery material gathered on the side from spreading to the center of the kiln and avoid deteriorating the permeability of the material layer.

[0020] ② As the side air volume decreases, the pulverization of side materials caused by rapid cooling can be effectively reduced, thus reducing the pulverization of materials during the calcination process;

[0021] ③Most of the combustion air is supplied from the bottom, which can form a combustion zone from bottom to top in the center of the kiln calcination zone, so that the most difficult-to-burn central material can be fully calcined.

[0022] ④ The fuel undergoes staged combustion within the calcination zone, effectively controlling the combustion temperature and preventing excessively high combustion temperatures from increasing the pulverization rate. Simultaneously, it increases the length of the combustion zone, extending the calcination and decomposition area. This makes the decomposition reaction more moderate and reduces the pulverization rate. Attached Figure Description

[0023] Figure 1 This is a simplified structural diagram of the prior art gas-fired vertical kiln equipment in Embodiment 1 of the present invention.

[0024] Figure 2 This is a typical airflow distribution of the prior art gas-fired vertical kiln equipment in Embodiment 1 of the present invention.

[0025] Figure 3 The distribution of pulverized lime in the furnace is shown in the prior art gas-fired vertical kiln equipment of Embodiment 1 of the present invention without considering the side air and bottom air.

[0026] Figure 4 This invention relates to an air distribution method for a gas-fired vertical kiln method for efficiently calcining limestone with a high pulverization rate.

[0027] Figure 5 This is a schematic diagram of the furnace state of a gas-fired vertical kiln for efficient calcination of limestone with a high pulverization rate, according to the present invention.

[0028] Figure 1The attached diagram is labeled as follows: 1 is the vertical kiln body; 2 is the material distributor; 3 is the unloading tray; 4 is the primary air system; 5 is the secondary air system; and 6 is the exhaust gas outlet channel. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings: This embodiment is implemented under the premise of the technical solution of the present invention, and detailed implementation methods are given, but the protection scope of the present invention is not limited to the following embodiments.

[0030] Example 1: As Figure 1-3 As shown, in the existing gas-fired vertical kiln process involved in this embodiment, lime (CaCO3) material is fed from the top and passes through preheating, calcination, and cooling sections sequentially during its downward movement, ultimately forming finished CaO which is discharged from the bottom of the vertical kiln. Gas burners are installed in the calcination zone on the side of the vertical kiln, supplying gaseous fuel and combustion air into the kiln chamber from the side. The gas is burned in the center of the kiln chamber to provide heat, achieving the calcination and decomposition of the lime raw material. Cooling air is supplied from the bottom of the kiln chamber to cool the high-temperature CaO formed by calcination to approximately 100°C. The high-temperature flue gas formed by calcination (approximately 1100°C) and the high-temperature flue gas formed by cooling (approximately 900°C) mix and then pass upward through the preheating zone. The high-temperature flue gas exchanges heat with the room-temperature material in the preheating zone, transferring heat from the flue gas to the material. The material temperature rises, while the flue gas temperature decreases, achieving the goal of improving thermal energy utilization efficiency. The limestone raw material is low-pulverization limestone with a pulverization rate of less than 20%, and the fuel is a mixed gas with a calorific value of approximately 1500 kcal / Nm3. The lengths of the preheating, calcining, and cooling zones each account for 1 / 3.

[0031] Figure 1This is a simplified structural diagram of a commonly used gas-fired vertical kiln. It mainly consists of six parts: 01 the kiln body, 02 the kiln top distributor, 03 the kiln bottom conical ash discharger, 04 the bottom air (secondary air) system, 05 the side air (primary air) system, and 06 the kiln top exhaust outlet. During production, limestone material meeting the particle size requirements (40-90mm) is evenly loaded into the kiln body through the kiln top distributor located at the top of the kiln chamber. Under the combined effects of material volume shrinkage during calcination and bottom discharge, the material in the kiln chamber moves slowly from top to bottom, sequentially passing through three zones with different temperature atmospheres: the preheating zone, the calcination zone, and the cooling zone, completing the high-temperature calcination decomposition and cooling of the lime. Finally, the metallurgical lime is discharged from the kiln bottom by the bottom conical ash discharger. The gaseous fuel and combustion air used for combustion are supplied to the kiln chamber by the side air system located on the side of the kiln chamber. Cooling air is supplied to the kiln chamber from the bottom air system located at the bottom of the kiln chamber. The bottom air passes through the high-temperature metallurgical lime screw discharger at the bottom of the kiln, where it exchanges heat with the high-temperature metallurgical lime, cooling the lime to below 150°C to its discharge temperature. The air itself is heated to approximately 700°C. This heat mixes with fuel fed from the side of the furnace in the central calcination zone, where the fuel burns, releasing heat and forming high-temperature flue gas. This provides heat for the limestone decomposition reaction in the calcination zone. The high-temperature CO2 gas generated from calcination and the high-temperature flue gas from combustion continue to flow upwards, passing through the relatively cool material layer in the preheating section. There, it exchanges heat with the material, heating it from room temperature to approximately 600°C. After participating in the combustion of the coal gas, the material is discharged outside the kiln through the kiln top exhaust channel.

[0032] Figure 2 The typical airflow distribution under existing technology is presented. It can be seen that the amount of combustion air supplied from the side burners is approximately 3300 Nm³ / t-CaO, the amount of gaseous fuel is approximately 1100 Nm³ / t-CaO, and the amount of cooling air supplied from the bottom of the furnace is approximately 1030 Nm³ / t-CaO. The total amount of gas supplied from the side burners is approximately 4400 Nm³ / t-CaO, about four times the amount supplied from the bottom. This process technology is very effective when calcining materials with low pulverization rates. With all gaseous fuel and combustion air supplied from the side burners, a highly penetrating airflow from the wall to the center is formed circumferentially in the kiln chamber, allowing the calcining flame to penetrate deep into the center of the kiln chamber, achieving uniform calcination.

[0033] However, the aforementioned technology has significant drawbacks when calcining lime with a high pulverization rate. During calcination, limestone with a high pulverization rate is prone to fragmentation and pulverization. Particles originally 40–90 mm in diameter break into smaller particles of 10–40 mm, some even crumbling into powdery ash. This pulverization within the kiln severely deteriorates the kiln's permeability, impacting normal production. Limestone pulverization typically occurs in the middle to late stages of calcination, when CO2 in CaCO3 is rapidly released, leaving tiny pores inside the particles, while the particle volume shrinks to some extent. During this process, the larger grain structure of limestone with a high pulverization rate easily leads to significant internal shrinkage stress. When this stress exceeds the structural strength, the original structure of the particles is destroyed, resulting in fragmentation or pulverization. Rapid cooling and mechanical impact both exacerbate the pulverization of limestone with a high pulverization rate because they increase internal stress within the particles.

[0034] Figure 3 This describes the distribution of pulverized lime in the furnace without considering side and bottom airflow. Near the furnace wall of a gas-fired vertical kiln, a pulverized layer forms, starting from the top of the calcination zone and gradually thickening downwards. This pulverized layer mainly consists of small, broken or pulverized metallurgical lime particles. This is because: ① Pulverization occurs during the high-temperature calcination and cooling stages, not the preheating stage, thus the starting point of the pulverized layer is within the calcination zone; ② Collisions between particles, and the compression, friction, and impact between particles and the wall are more intense near the wall than in the center of the furnace, resulting in concentrated pulverization near the wall and faster material flow in the center; ③ Cold side airflow is introduced from near the wall, causing rapid cooling of the metallurgical lime at the wall, further exacerbating pulverization near the wall; ④ Due to the cumulative effect and the tendency of powder particles to aggregate towards the wall, the pulverized layer becomes thicker towards the bottom. In summary, this ultimately forms a layer like... Figure 3 The distribution of the powdery layer is shown.

[0035] Under the existing process, a large amount of side air (fuel and combustion air) is sent in from the side of the calcination zone, which carries the dust that accumulates near the wall into the center of the furnace. This causes the pulverized limestone to spread throughout the kiln space, occupying the gaps between large particles and the finished product. The permeability of the kiln increases sharply, which seriously affects the normal operation of limestone calcination. As a result, the existing calcination process cannot be operated normally when using limestone with a high pulverization rate as raw material.

[0036] The above-mentioned shortcomings of existing technologies:

[0037] First: The high-temperature material in the calcination zone was rapidly cooled by the side airflow, resulting in severe pulverization.

[0038] In current technology, fuel and combustion air are all supplied from the side. This side airflow is large in volume and low in temperature (reaching 200-300℃ after passing through the heat exchanger), directly contacting the high-temperature material (approximately 1100℃) in the calcination section. The material in the calcination section is rapidly cooled by the cold air, causing its volume to shrink quickly and creating significant shrinkage stress within the particles, inducing some material to burst and pulverize. Especially when calcining limestone with a high pulverization rate, the rapid cooling effect of the side air leads to severe pulverization of the material near the air inlet, affecting product quality, worsening kiln permeability, and creating safety risks due to air and air backflow.

[0039] Second: Powdered lime diffuses inside the furnace under the influence of crosswinds, severely deteriorating the furnace's permeability.

[0040] In existing technologies, when calcining limestone with a high pulverization rate, a pulverized layer gradually thickens from top to bottom near the furnace wall, starting from the top of the calcining chamber. A large amount of side air (fuel and combustion air) is introduced from the side of the calcining zone, carrying the dust accumulated near the wall into the center of the furnace. This causes the pulverized limestone to diffuse throughout the kiln space, occupying the gaps between large particles and the finished product. The kiln's permeability increases dramatically, severely affecting the normal operation of limestone calcination. Therefore, existing calcination processes are simply unusable when using limestone with a high pulverization rate as raw material.

[0041] Example 2: Figure 4 As shown in the figure, this embodiment involves a method for high-efficiency calcination of high-pulverization limestone in a gas-fired vertical kiln. Compared with the prior art, the raw material in this embodiment is a high-pulverization raw material with a pulverization rate of 40%, and the fuel is blast furnace gas with a calorific value of 900 kcal / Nm3. The fuel consumption is 1500 Nm3 / t-CaO, and the total air consumption is 1800 Nm3 / t-CaO. Among them, the air volume supplied from the bottom is 10480 Nm3 / t-CaO, accounting for 60% of the total air volume, and the air volume supplied from the upper side is 720 Nm3 / t-CaO, accounting for 40% of the total air volume. The fuel gas volume supplied from the lower side is 1500 Nm3 / t-CaO. The length ratios of the preheating zone, calcination zone, and cooling zone are 3 / 10, 2 / 5, and 3 / 10, respectively. The upper side air is set at a position 1 / 3L away from the starting point of the calcination zone, and the lower side air is set at a position 2 / 3L away from the starting point of the calcination zone, with a distance of 1 / 3L between the upper and lower side air. Where L is the total length of the calcination zone.

[0042] During calcination, the bottom air passes through the high-temperature metallurgical lime screw discharger at the bottom of the kiln, exchanging heat with the high-temperature metallurgical lime. This cools the limestone to below 150°C, reaching its discharge temperature, while the bottom air itself is heated to approximately 400-500°C. It then mixes and combusts with fuel (bottom air) supplied from the side of the furnace in the central calcination section. The hot flue gas produced (which, due to insufficient combustion air, accounts for only about 70-80% of the total combustion air volume and contains some unburned intermediate products such as CO) flows upward. Upon encountering the top air, the combustible gases in the flue gas undergo further complete combustion, releasing heat to heat the lime decomposition in the calcination section. The resulting high-temperature flue gas then moves further upward, exchanging heat with the materials in the preheating section before being discharged from the top of the furnace.

[0043] Example 3: In the method of high-efficiency calcination of high-pulverization limestone in a gas-fired vertical kiln involved in this example, the limestone material is limestone with a pulverization rate between 20-52%. When the limestone is ≥52%, high and low pulverization rate materials are mixed to make the average pulverization rate between 20-52% before calcination. The preferred method for calculating the average pulverization rate of the material is the blended average method.

[0044] After using this method, the quality of the finished metallurgical lime is ≥85%, as shown in the table below. The monthly average quality of the finished metallurgical lime in 2020 ranged from a minimum of 76.18% to a maximum of 84.23%, with an average of 80.88%. In 2021, the monthly average quality of the finished metallurgical lime ranged from a minimum of 77.76% to a maximum of 85.54%, with an average of 83.83%. In 2022, the monthly average quality of the finished metallurgical lime ranged from a minimum of 82.98% to a maximum of 87.53%, with an average of 85.31%. As of the end of July 2023, the monthly average quality of the finished metallurgical lime ranged from a minimum of 87.44% to a maximum of 84.23%. The output was 210,684 tons in 2020, 189,514 tons in 2021, 212,997 tons in 2022, and 132,536 tons as of the end of July 2023, with an estimated annual output of 227,200 tons. Since 2020, the method of this application has been improved, and the quality of the finished metallurgical lime has increased compared with the previous method. After using this method, the quality of the finished metallurgical lime is ≥85%.

[0045] Mass of lime from vertical kiln (unit: %)

[0046]

[0047]

[0048] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for efficiently calcining high-pulverizing-rate limestone in a gas-fired shaft kiln, characterized by, The method for high-efficiency calcination of high-pulverization-rate limestone in a gas-fired vertical kiln is as follows: Lime material, primarily composed of CaCO3, is fed into the kiln from the top, passing through the preheating section, calcination section, and cooling section in sequence. The resulting quicklime, at a temperature below 100°C, is discharged from the bottom of the kiln. During production, a portion of the fuel-air mixture is introduced through the bottom airflow at the bottom of the kiln. This fuel-air mixture passes through the material layer in the cooling section and is heated to a high-temperature hot air temperature. This hot air encounters the gaseous fuel supplied by the lower side airflow in the lower part of the calcination section, resulting in primary combustion in the lower part of the calcination section. The high-temperature combustible flue gas generated from the primary combustion and the high-temperature flue gas generated from complete combustion rise upwards. This combustible flue gas encounters another portion of the fuel-air mixture supplied by the upper side airflow in the upper part of the calcination section, resulting in secondary combustion in the upper part of the calcination section. The gaseous fuel is fully combusted, and the high-temperature flue gas generated from the primary and secondary complete combustion rises upwards, exchanging heat with the lime material in the preheating section. After the flue gas temperature drops to approximately 200°C, it is discharged from the top of the kiln. The gentle flame generated by the primary and secondary combustion, which runs throughout the entire calcination section, provides uniform heating to the material within the calcination section. The lengths of the preheating section and the cooling section each account for three-tenths of the kiln chamber length, and the length of the calcination section accounts for two-fifths of the kiln chamber length. The high pulverization rate limestone has a pulverization rate greater than 20%; The fuel flow rate of the lower side wind is 1300-1800 Nm3 / t-CaO 3 The total fuel flow rate of the air fuel, i.e., the total flow rate of the upper side wind and the bottom wind, is 1400-2000 Nm3 / t-CaO; The proportion of air fuel supplied by the bottom wind to the total air fuel is 50-80%.

2. The method for high-efficiency calcination of high-pulverization limestone in a gas-fired vertical kiln according to claim 1, characterized in that, The gaseous fuel for the lower side wind is a low-calorific-value gas with a calorific value of less than 1000 kcal.

3. The method for high-efficiency calcination of high-pulverization limestone in a gas-fired vertical kiln according to claim 1, characterized in that, The proportion of air fuel supplied by the bottom wind to the total air fuel is 60% to 70%.

4. The method for high-efficiency calcination of high-pulverization limestone in a gas-fired vertical kiln according to claim 1, characterized in that, The upper side wind is set within a height range of 1 / 6 to 1 / 3L from the starting point of the calcination section, and the lower side wind is set within a height range of 2 / 3 to 1L from the starting point of the calcination zone. The distance between the upper side wind and the lower side wind is within a range of 1 / 3 to 2 / 3L, where L is the total length of the calcination section.

5. The method for high-efficiency calcination of high-pulverization limestone in a gas-fired vertical kiln according to claim 1, characterized in that, The lime material used is limestone with a pulverization rate between 20-52%. When the limestone content is ≥52%, materials with high and low pulverization rates are mixed to bring the average pulverization rate to between 20-52% before calcination.

Images