A rotary kiln mixing calcination method for limestone with high calcination pulverization rate

Abstract

The present application belongs to the technical field of rotary kiln calcination, and particularly relates to a rotary kiln mixing and calcination method for high-pulverization-rate limestone, characterized by that, in a rotary kiln system composed of a preheater, a rotary kiln and a cooler, raw materials are processed in two ways, one way is that the raw materials pass through a main limestone bin, a first downpipe and a preheater bin body to enter the rotary kiln, and the other way is that the raw materials pass through an adjusted limestone bin, a second downpipe and an intermediate storage bin to enter the rotary kiln, the weight ratio of the main limestone and the adjusted limestone is 8-12:1; the adjusted limestone route does not pass through the preheater, and the addition amount of the adjusted limestone is adjusted according to the decomposition reaction state in the rotary kiln. The present application has the following beneficial effects: 1) the mixing method is innovated, the mixing amount is dynamically controlled, the operation state of the rotary kiln is stabilized, the use amount of the high-pulverization-rate limestone is increased, and the waste of resources is greatly avoided; 2) the use amount of domestic limestone is increased; 3) the structure is simple, compact and convenient to operate.

Description

Technical Field

[0001] This invention belongs to the field of rotary kiln calcination technology, and particularly relates to a rotary kiln mixing and calcination method for limestone with high calcination pulverization rate. Background Technology

[0002] A lime rotary kiln (also known as a drum rotary kiln) is a calcination device that uses a combined scale seal at both ends of a rotary kiln for limestone processing. See [link / reference] Figure 2 In the traditional rotary kiln process for limestone, limestone is fed into a limestone silo via a conveyor belt. The silo has over a dozen feed chutes at its lower part, which guide the limestone into the preheater chamber below. The material inside the preheater chamber is static, and the hot flue gas preheats and partially decomposes the limestone within the chamber. A hydraulic pusher then pushes the limestone into a feed cone, which in turn enters a transfer chute. From there, the limestone is fed into the rotary kiln via a feeding mechanism. Inside the kiln, the limestone undergoes further reaction. After the reaction is complete, the limestone enters a cooler, where it is cooled to a suitable temperature by cooling air before being discharged and finally stored in a lime storage unit. Due to varying mineralization processes, limestone in many areas undergoes significant pulverization during calcination, causing numerous adverse effects on traditional rotary kiln production. These adverse effects are briefly described below: 1) Impact on vertical preheaters: Uneven material pulverization leads to inconsistent air resistance, frequently resulting in localized overheating. This results in poor heat exchange efficiency. Furthermore, caking of the pulverized material can cause material buildup in some compartments, preventing the pusher from discharging material. Additionally, clumps of powder can accumulate in dead zones between compartments, causing unstable material buildup on individual pushers and a decrease in overall pushing capacity. 2) Impact on rotary kilns: Rotary kilns calcining limestone with high pulverization rates often experience ring formation. This leads to unstable thermal regimes, increased heat consumption, rapid increase in drive motor current, and decreased product quality, among other adverse effects. 3) Impact on vertical coolers: A high powder content drastically reduces the air passages in the cooler's material layer, leading to a sharp increase in air resistance. Insufficient contact between cooling air and material results in frequent instances of excessively high temperatures at individual cooler outlets, leading to poor overall cooling performance. Furthermore, the excessive air resistance necessitates lowering the material layer height and increasing the cooling airflow for adjustment. This results in a relatively large difference in air resistance between the four material feeding zones of the cooler, while also causing excessive secondary airflow into the kiln, increasing heat consumption and resulting in unnecessary fuel waste.

[0003] Cause Analysis: The fundamental reason for the instability of the entire rotary kiln system caused by limestone pulverization is the shortened chemical reaction time and the uncertainty of the reaction time. The reaction time of lime is directly proportional to the square of the material's diameter. Therefore, much of the pulverized limestone has already decomposed in the high-temperature firing zone. This lime will rapidly heat up in the high-temperature zone to reach melting, and then form rings. The normal operation of the lime rotary kiln involves large pieces of material wrapping around smaller pieces and tumbling forward. The large pieces of material that have not fully reacted continue to absorb a large amount of heat to ensure that the overall temperature of the material in the high-temperature zone is relatively low, preventing over-burning. According to field experimental experience, increasing the particle size of the material at the feed end has little effect, because no matter how large the particle size is, after the material is preheated and broken up by the preheater, the size of the material entering the kiln is very small, which cannot achieve the purpose of extending the reaction time. According to field experimental experience, only when the proportion of limestone with a low pulverization rate is very high will the reaction state be corrected. This is because in the rotary kiln, when the amount added is insufficient, the pulverized small pieces of material wrap around the large pieces of limestone that are not easy to pulverize and move forward, while the pulverized material is exposed and still heats up rapidly.

[0004] There are large quantities of limestone mines with high powder content in Northeast and Northwest my country. However, due to the lack of corresponding technology, these resources cannot be utilized, or the finished products have high costs and low prices, putting them at a disadvantage in market competition. This situation urgently needs to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a rotary kiln mixing and calcination method for limestone with a high pulverization rate, which overcomes the shortcomings of the prior art. Through innovative mixing methods, the mixing amount is dynamically controlled, the operating state of the rotary kiln is stabilized, product quality is improved, the amount of admixture is reduced, and the amount of limestone with a high pulverization rate is increased.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A rotary kiln mixed calcination method for limestone with high calcination pulverization rate involves a rotary kiln system consisting of a preheater, a rotary kiln, and a cooler. The raw materials are processed in two streams: one stream enters the rotary kiln via a main limestone silo, a first discharge chute, and the preheater silo; the other stream enters the rotary kiln via a regulating limestone silo, a second discharge chute, and an intermediate storage silo. The weight ratio of the main limestone to the regulating limestone is 8-12:1. The main limestone is grade II, and the regulating limestone is grade I, meaning it is not easily pulverized. The regulating limestone does not enter the preheater, and its addition amount is adjusted according to the decomposition reaction state within the rotary kiln.

[0007] Furthermore, in the decomposition reaction process inside the rotary kiln, the limestone is adjusted to play a temperature control role. From the time the limestone enters the kiln to the calcination section, the limestone is adjusted so that it cannot react completely. The temperature inside the limestone cross section of the rotary kiln is controlled below 1250 degrees Celsius.

[0008] Furthermore, the particle size of the adjusted limestone is 8-20 mm, and the volume percentage of particles smaller than 8 mm is less than 5%.

[0009] Furthermore, the limestone silo, the second discharge chute, and the intermediate storage silo are independent. The inlet and outlet of the intermediate storage silo are each equipped with a hemispherical valve, which controls the amount of limestone added.

[0010] Furthermore, the intermediate storage silo is a weighing silo.

[0011] Furthermore, the ball valve is an electric or pneumatic side-mounted eccentric ball valve.

[0012] Furthermore, the outlet of the intermediate storage silo is connected to a third discharge chute with an inclination angle of ≥55°.

[0013] Furthermore, the two raw materials converge in the feeding cone hopper, enter the rotary kiln via a transfer chute, and then enter the lime storage device through a cooler from the rotary kiln outlet.

[0014] Furthermore, the main limestone silo and the regulating limestone silo share a material distribution device and a feeding conveyor belt, which are respectively connected to the main limestone stockpile and the regulating limestone stockpile.

[0015] Furthermore, the preferred weight ratio of the main limestone and the regulating limestone is 10:1.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1) This invention innovates the mixing method, dynamically controls the mixing amount, stabilizes the operating state of the rotary kiln, improves product quality, reduces the amount of admixture, and increases the amount of limestone with high pulverization rate. It can make use of limestone ore with high pulverization rate and greatly avoids the waste of resources. 2) Since the adjusting limestone does not participate in preheating, the present invention greatly reduces the amount of adjusting limestone used and increases the amount of domestically produced easily pulverized limestone used. 3) This invention has the characteristics of simple and compact structure and easy operation. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of an embodiment of the present invention; Figure 2 This is a flow chart of a traditional rotary kiln lime production process; Figure 3 This is a schematic diagram of the process equipment distribution according to an embodiment of the present invention; In the diagram: 3-Main limestone silo, 4-First discharge chute, 5-Preheater silo, 6-Hydraulic pusher, 7-Discharge cone, 8-Transfer chute, 9-Rotary kiln, 10-Cooler, 11-Lime storage device, 13-Regulating limestone silo, 14-Second discharge chute, 15-Spherical valve, 16-Intermediate storage silo, 17-Spherical valve, 18-Third discharge chute. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] The components of the embodiments of the invention described and shown in the accompanying drawings can typically be arranged and designed in a variety of different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0021] See Figure 1-3 This is a schematic diagram of the process flow of a rotary kiln mixing and calcining method for limestone with a high calcination pulverization rate according to an embodiment of the present invention. In the rotary kiln system consisting of a preheater silo 5, a rotary kiln 9, and a cooler, the raw materials are processed in two routes. One route enters the rotary kiln 9 through the main limestone silo 3, the first discharge chute 4, and the preheater silo 5. The other route enters the rotary kiln 9 through the regulating limestone silo 13, the second discharge chute 14, and the intermediate storage silo 16. The weight ratio of the main limestone and the regulating limestone is 8-12:1, with a preferred value of 10:1. The grade of the main limestone is grade II, and the grade of the regulating limestone is grade I (grade II limestone is limestone with a breakage rate greater than 15% after a drop strength test after calcination in the laboratory; grade I limestone has a breakage rate less than or equal to 15%). The regulating limestone route does not enter the preheater silo 5, and the amount of regulating limestone added is adjusted according to the decomposition reaction state inside the rotary kiln 9. In this embodiment of the invention, the main limestone is preheated in the preheater chamber, while the regulating limestone is not preheated in the preheater chamber and only interferes with the decomposition reaction in the rotary kiln.

[0022] The optimal decomposition reaction state within the rotary kiln is such that the adjusted limestone does not react completely from the kiln inlet to the calcination section. The temperature within the limestone cross-section of the rotary kiln is controlled below 1250 degrees Celsius. To ensure the adjusted limestone can better intervene in the decomposition process within the rotary kiln and to maintain a low bed temperature, the particle size of the adjusted limestone is smaller than that of the standard limestone. To ensure proper coating of the powder, a slightly larger proportion of small-sized particles in the adjusted limestone is used. The particle size of the adjusted limestone is 8-20 mm, with a particle size distribution where particles smaller than 8 mm account for less than 5% of the volume.

[0023] The regulating limestone silo 13, the second discharge chute 14, and the intermediate storage silo 16 are independent. To ensure effective regulation of the decomposition process within the rotary kiln 9, the limestone feeding process is independent. The intermediate storage silo 16 is equipped with a hemispherical valve 15 at the inlet and a hemispherical valve 17 at the outlet. Hemispherical valves 15 and 17 control the amount of limestone added, and the hemispherical valves act as a seal to cut off material flow and prevent hot flue gas from rising from the lower part of the kiln. The intermediate storage silo 16 is a weighing silo, serving as a buffer and metering unit, enabling precise control of the amount of regulating limestone entering the kiln. The hemispherical valve 15 is an electrically or pneumatically operated side-mounted eccentric hemispherical valve. The main limestone is powered by a hydraulic pusher 6 and pushed into the feeding cone 7. The two raw materials converge in the feeding cone 7 and enter the rotary kiln 9 via the transfer chute 8. The two types of limestone undergo the next reaction together in the rotary kiln 9. After the reaction is complete, the limestone enters the cooler 10, is cooled to a suitable temperature by cooling air, and is then discharged from the cooler 10, finally entering the limestone storage device 11. The main limestone silo 3 and the regulating limestone silo 13 share a material distribution device and a feeding belt conveyor (not shown in the figure). The feeding belt conveyor is connected to the main limestone stockpile and the regulating limestone stockpile, respectively.

[0024] The outlet of the intermediate storage silo 16 is connected to the third discharge chute 18, with an inclination angle of ≥55°, to ensure that the regulating limestone does not remain in the preheater silo and directly enters the discharge cone 7.

[0025] In this embodiment, the temperature inside the preheater chamber is 900-1000℃, and the temperature in the calcination zone inside the rotary kiln 9 is 1200℃. During the process of moving from the preheater chamber to the transfer chute and then tumbling forward inside the rotary kiln, a large amount of fragments smaller than 10mm are generated. There is insufficient large, unreacted material to completely encapsulate the fully reacted small pieces, causing the small pieces to heat up rapidly, liquefy on the surface, and form rings in the rotary kiln. Therefore, adding unreacted limestone of similar particle size allows these limestone fragments to react within the rotary kiln, absorbing a large amount of heat and helping to control the temperature. Simultaneously, calculations show that to ensure the limestone is not fully reacted before reaching the high-temperature zone, a particle size of 13mm or larger is required. Therefore, the limestone particle size is controlled between 8-20mm, with the volume ratio of fragments smaller than 8mm being less than 5%, thus achieving the goal of temperature-controlled calcination.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A rotary kiln mixing and calcination method for limestone with high calcination pulverization rate, characterized in that, In a rotary kiln system consisting of a preheater, a rotary kiln, and a cooler, the raw materials are processed in two streams. One stream enters the rotary kiln via the main limestone silo, the first discharge chute, and the preheater silo. The other stream enters the rotary kiln via the regulating limestone silo, the second discharge chute, and the intermediate storage silo. The weight ratio of the main limestone and regulating limestone is 8-12:

1. The main limestone is grade II, and the regulating limestone is grade I, meaning it is not easily pulverized. The regulating limestone does not enter the preheater, and the amount of regulating limestone added is adjusted according to the decomposition reaction state within the rotary kiln. The decomposition reaction process inside the rotary kiln involves adjusting the limestone to control the temperature. From the time the limestone enters the kiln to the calcination section, the limestone is adjusted so that it cannot react completely. The temperature inside the limestone cross section of the rotary kiln is controlled below 1250 degrees Celsius. The adjusted limestone has a particle size of 8-20 mm, and the volume percentage of particles smaller than 8 mm is less than 5%.

2. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 1, characterized in that, The regulating limestone silo, the second discharge chute, and the intermediate storage silo are independent. The inlet and outlet of the intermediate storage silo are each equipped with a hemispherical valve, which controls the amount of limestone added.

3. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 1, characterized in that, The intermediate storage silo is a weighing silo.

4. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 2, characterized in that, The ball valve is an electric or pneumatic side-mounted eccentric ball valve.

5. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 1, characterized in that, The outlet of the intermediate storage silo is connected to a third discharge chute with an inclination angle of ≥55°.

6. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 1, characterized in that, The two raw materials converge in the feeding cone and enter the rotary kiln via a transfer chute. The discharge port of the rotary kiln then enters the lime storage device via a cooler.

7. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 1, characterized in that, The main limestone silo and the regulating limestone silo share a material distribution device and a feeding conveyor belt, which are respectively connected to the main limestone stockpile and the regulating limestone stockpile.

8. The rotary kiln mixing and calcination method for limestone with high calcination pulverization rate according to claim 1, characterized in that, The preferred weight ratio of the main limestone and regulating limestone is 10:1.

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