Suspension preheater for calcining kaolin and preheating method thereof

Abstract

The invention relates to the technical field of kaolin processing, in particular to a suspension preheater for calcining kaolin and a preheating method thereof.The method comprises the following steps that S1, in the high-temperature airflow trapping and primary preheating stage, a flow guide mode is adopted in a flue opening formed in the tail of a rotary kiln; in the high-temperature airflow trapping and primary preheating stage, while kiln flue gas is recycled, solid particles are filtered, primary heating is conducted through the radiation preheating cavity, and it is ensured that the temperature of raw material particles is evenly distributed. In the infrared primary heating and centrifugal force preheating stage, the primary heating effect of the particles is improved by controlling the infrared irradiation temperature, and hot air flow generated by a rotary centrifugal fan is utilized, so that the particles are in full contact with high-temperature gas under the action of centrifugal force, and the heating efficiency is improved. In the infrared deep heating and material calcining stage, raw material particles rapidly reach the calcining temperature through deep heating on a heat-resistant conveying belt, and the stability and controllability of the calcining process are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of kaolin processing, in particular to a suspension preheater for calcining kaolin and a preheating method thereof. Background Art

[0002] The field of kaolin processing technology mainly involves the extraction, purification, modification and processing methods of kaolin in various industrial applications. As an important non-metallic mineral resource, kaolin is widely used in ceramics, papermaking, rubber, plastics, coatings and other industries. The research focus in this field is to improve the quality and performance of kaolin, and to achieve the excellent performance of kaolin in different applications by optimizing the processing technology, such as calcination, preheating, grinding, classification and other steps.

[0003] The existing technology lacks a high-temperature airflow recovery and filtration system. A large amount of heat energy is wasted during the preheating process, and the recovered kiln flue gas cannot be fully utilized. At the same time, the temperature distribution of the raw material particles is uneven during the preheating process, resulting in some particles failing to fully heat up, affecting the consistency and quality of the calcined product. In addition, the long preheating time leads to low overall production efficiency, increased energy consumption, and thus increased production costs. Summary of the invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a suspension preheater for calcining kaolin and a preheating method thereof.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme, a preheating method for calcining kaolin, comprising the following steps: S1: In the stage of high-temperature airflow capture and primary preheating, the flue gas outlet at the rear of the rotary kiln is diverted and the airflow collection hood is used to capture the kiln flue gas, and the solid particles in the gas are removed through the filter screen; the raw material particles are initially heated in the radiation preheating chamber; S2: Infrared primary heating and centrifugal preheating. Through the setting of infrared heating section, the raw material particles pass through the infrared irradiation area with controlled temperature on the conveyor belt. The heated particles are introduced into the centrifugal heating chamber. With the help of the hot air flow generated by the rotating centrifugal fan, the raw material particles diffuse outward under the action of centrifugal force, and the surface of the raw material particles is fully in contact with the high-temperature gas. S3: Infrared deep heating and material calcination. On the heat-resistant conveyor belt, the raw material particles are exposed to infrared radiation in the infrared heating chamber to reach the calcination temperature; then the raw material particles are transported to the rotary kiln for calcination to produce kaolin clinker.

[0006] Preferably, the step S1 includes: High-temperature airflow capture: by guiding the flue port extending out of the rear of the rotary kiln, the flue gas out of the kiln is captured by the airflow collection hood, the flue gas flow is controlled within the range of 500-800m³ / min, and the filter is used for purification to intercept solid particles with a particle size greater than 50μm in the gas; the airflow output is maintained at a speed of 230-500RPM by the axial flow fan, and the output end of the airflow is connected to the preheating inlet pipe to obtain high-temperature flue gas; In the primary preheating stage, the preheating inlet pipe is connected to the radiation preheating cavity, the raw material particles at room temperature are heated, and the raw material particles are added to the radiation preheating cavity. The cavity length of the radiation preheating cavity is controlled at 3-5m, and the temperature of the raw material particles is increased from 25°C to 200-300°C; and then the radiation preheating cavity is equipped with a stirring blade with a rotation speed of 230-500RPM for mixing to obtain primary radiation preheated raw material.

[0007] Preferably, the step S2 comprises: Infrared primary heating, the primary radiation preheated raw material is introduced into the conveyor belt of the infrared heating section, the surface temperature of the infrared emitting plate is controlled in the range of 800-1000°C, and the infrared band is between 2.5-3.5μm; the conveyor belt of the infrared heating section slowly passes through the infrared irradiation area, the primary radiation preheated raw material is irradiated by infrared radiation, so that the moisture and volatile components in the internal microporous structure are desorbed, and after the average temperature of the primary radiation preheated raw material reaches 300-400°C, the raw material that has been primarily heated by infrared is obtained; Centrifugal primary preheating: the raw material that has been primarily heated by infrared rays is introduced into a centrifugal heating chamber, and a centrifugal fan is used to rotate to generate an annular hot air flow, so that the raw material particles diffuse outward in a centrifugal manner; the speed of the centrifugal fan is controlled within the range of 800-1500RPM, and the high-speed airflow suspends the raw material particles in the centrifugal chamber, and the average gas flow rate is maintained within the range of 5-10m / s. After the raw material temperature is raised to 400-500℃, the raw material that has been primarily preheated by centrifugal force is obtained.

[0008] Preferably, the S3 step includes: Infrared deep heating, the raw meal preheated by centrifugal force is introduced into an infrared heating chamber, the emission surface temperature is controlled within the range of 900-1100°C, and the infrared wavelength is distributed within the range of 2.0-3.0 μm; the raw meal is spread on a heat-resistant conveyor belt in the infrared heating chamber, and the line speed of the heat-resistant conveyor belt is maintained at 0.1-0.3 m / s to obtain the raw meal deeply heated by infrared; Preheat the graded materials for calcination, and convey the raw materials deeply heated by infrared rays to a rotary kiln for calcination. The temperature in the rotary kiln is controlled in the range of 1200-1450°C, and the kiln rotation speed is maintained at 1-3RPM to obtain kaolin clinker.

[0009] Preferably, the raw material particles are mixed with limestone powder, clay powder and iron powder in a mass ratio of 1:0.3:0.1.

[0010] Preferably, the conveyor belt speed in the infrared heating section is 0.2-0.5 m / s.

[0011] Preferably, the calcination time is 1-5 hours.

[0012] The present invention provides a suspension preheater, comprising a U-shaped preheating inlet pipe for connecting an airflow collection hood and a radiation preheating cavity.

[0013] Compared with the prior art, the advantages and positive effects of the present invention are: In the present invention, the high-temperature airflow capture and primary preheating stage filters solid particles while recycling kiln flue gas and uses a radiation preheating cavity for initial heating to ensure that the temperature distribution of the raw material particles is uniform. In the infrared primary heating and centrifugal preheating stage, the initial heating effect of the particles is improved by controlling the infrared irradiation temperature, and the hot air flow generated by the rotating centrifugal fan is used to make the particles fully contact with the high-temperature gas under the action of centrifugal force, thereby improving the heating efficiency. In the infrared deep heating and material calcination stage, the raw material particles quickly reach the calcination temperature through deep heating on the heat-resistant conveyor belt, ensuring the stability and controllability of the calcination process. The entire preheating method shortens the preheating time, reduces energy consumption, and at the same time improves the particle recovery rate and fineness distribution, thereby improving the efficiency of the kaolin calcination process and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the steps of the present invention. DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0016] Example 1, please refer to Figure 1 The present invention provides a technical solution, a preheating method for calcining kaolin, comprising the following steps: S1: In the stage of high-temperature airflow capture and primary preheating, the flue gas outlet at the rear of the rotary kiln is diverted and the airflow collection hood is used to capture the kiln flue gas, and the solid particles in the gas are removed through the filter screen; the raw material particles are initially heated in the radiation preheating chamber; S2: Infrared primary heating and centrifugal preheating. Through the setting of infrared heating section, the raw material particles pass through the infrared irradiation area with controlled temperature on the conveyor belt. The heated particles are introduced into the centrifugal heating chamber. With the help of the hot air flow generated by the rotating centrifugal fan, the raw material particles diffuse outward under the action of centrifugal force, and the surface of the raw material particles is fully in contact with the high-temperature gas. S3: Infrared deep heating and material calcination. On the heat-resistant conveyor belt, the raw material particles are exposed to infrared radiation in the infrared heating chamber to reach the calcination temperature; then the raw material particles are transported to the rotary kiln for calcination to produce kaolin clinker.

[0017] In this embodiment, step S1 includes: High-temperature airflow capture: by guiding the flue outlet extending from the rear of the rotary kiln, the outgoing flue gas is captured by the airflow collection hood, the flue gas flow is controlled within the range of 800m³ / min, and the filter is used for purification to intercept solid particles with a particle size greater than 50μm in the gas; the airflow is output with the axial flow fan speed maintained at 500RPM, and the output end of the airflow is connected to the preheating inlet pipe to obtain high-temperature flue gas; In the primary preheating stage, the preheating inlet pipe is connected to the radiation preheating chamber to heat the raw material particles at room temperature, and the raw material particles are added to the radiation preheating chamber. The length of the radiation preheating chamber is controlled at 5m, and the temperature of the raw material particles is increased from 25°C to 300°C. Then, a stirring blade with a rotation speed of 500RPM is configured in the radiation preheating chamber to mix the raw material to obtain primary radiation preheated raw material.

[0018] In this embodiment, step S2 includes: Infrared primary heating: the primary radiation preheated raw material is introduced into the conveyor belt of the infrared heating section, and the surface temperature of the infrared emitting plate is controlled at 1000℃, and the infrared band is 3.5μm; the conveyor belt of the infrared heating section slowly passes through the infrared irradiation area, and the primary radiation preheated raw material is irradiated by infrared radiation, so that the moisture and volatile components in the internal microporous structure are desorbed. After the average temperature of the primary radiation preheated raw material reaches 400℃, the raw material that has been preheated by infrared primary heating is obtained; Centrifugal primary preheating: the raw meal that has been primarily heated by infrared rays is introduced into a centrifugal heating chamber, and a centrifugal fan is used to rotate to generate an annular hot air flow, so that the raw meal particles diffuse outward in a centrifugal manner; the speed of the centrifugal fan is controlled at 1500RPM, and the high-speed air flow suspends the raw meal particles in the centrifugal chamber, and the average gas flow rate is maintained at 5m / s; in this way, the raw meal is evenly dispersed in the chamber, the particles collide with each other and the heat transfer rate is accelerated, the particle surface is fully in contact with the high-temperature gas, and the raw meal temperature is raised to 500℃ to obtain the raw meal that has been primarily preheated by centrifugal force.

[0019] In this embodiment, step S3 includes: Infrared deep heating, the raw meal preheated by centrifugal force is introduced into the infrared heating chamber, the emission surface temperature is controlled at 1100℃, and the infrared wavelength is distributed in the 3.0μm section; the raw meal is spread on the heat-resistant conveyor belt in the infrared heating chamber, and the line speed of the heat-resistant conveyor belt is maintained at 0.3m / s, so that the raw meal particles gradually approach the calcination starting temperature under strong infrared irradiation, the uniformity of heat distribution inside the particles is improved, and the carbonate decomposition in the material tends to be active, which is conducive to rapid reaction in the subsequent pre-decomposition link; the raw meal deeply heated by infrared is obtained; Preheat the graded materials for calcination, and convey the raw materials deeply heated by infrared rays to the rotary kiln for calcination. The temperature in the rotary kiln is controlled at 1450°C, and the kiln speed is maintained at 3RPM to obtain kaolin clinker.

[0020] In this embodiment, the raw material particles are mixed by limestone powder, clay powder and iron powder in a mass ratio of 1:0.3:0.1.

[0021] In this embodiment, the conveyor belt speed in the infrared heating section is 0.5 m / s.

[0022] In this embodiment, the calcination time is 5 hours.

[0023] The present invention provides a suspension preheater, comprising a U-shaped preheating inlet pipe for connecting an airflow collection hood and a radiation preheating cavity.

[0024] Example 2, please refer to Figure 1 The present invention provides a technical solution, a preheating method for calcining kaolin, comprising the following steps: S1: In the stage of high-temperature airflow capture and primary preheating, the flue gas outlet at the rear of the rotary kiln is diverted and the airflow collection hood is used to capture the kiln flue gas, and the solid particles in the gas are removed through the filter screen; the raw material particles are initially heated in the radiation preheating chamber; S2: Infrared primary heating and centrifugal preheating. Through the setting of infrared heating section, the raw material particles pass through the infrared irradiation area with controlled temperature on the conveyor belt. The heated particles are introduced into the centrifugal heating chamber. With the help of the hot air flow generated by the rotating centrifugal fan, the raw material particles diffuse outward under the action of centrifugal force, and the surface of the raw material particles is fully in contact with the high-temperature gas. S3: Infrared deep heating and material calcination. On the heat-resistant conveyor belt, the raw material particles are exposed to infrared radiation in the infrared heating chamber to reach the calcination temperature; then the raw material particles are transported to the rotary kiln for calcination to produce kaolin clinker.

[0025] In this embodiment, step S1 includes: High-temperature airflow capture is achieved by guiding the flue port extending from the tail of the rotary kiln, capturing the flue gas out of the kiln with an airflow collection hood, controlling the flue gas flow rate within the range of 500m³ / min, and purifying it with a filter to intercept solid particles with a particle size greater than 50μm in the gas; the airflow output is maintained at 300RPM with the axial flow fan speed, and the output end of the airflow is connected to the preheating inlet pipe to obtain high-temperature flue gas; In the primary preheating stage, the preheating inlet pipe is connected to the radiation preheating chamber to heat the raw material particles at room temperature, and the raw material particles are added to the radiation preheating chamber. The length of the radiation preheating chamber is controlled at 3m, and the temperature of the raw material particles is increased from 25°C to 250°C. Then, a stirring blade with a rotation speed of 250RPM is configured in the radiation preheating chamber to mix the raw material to obtain primary radiation preheated raw material.

[0026] In this embodiment, step S2 includes: Infrared primary heating: the primary radiation preheated raw material is introduced into the conveyor belt of the infrared heating section, and the surface temperature of the infrared emitting plate is controlled at 800°C, and the infrared band is 3μm; the conveyor belt of the infrared heating section slowly passes through the infrared irradiation area, and the primary radiation preheated raw material is irradiated by infrared radiation, so that the moisture and volatile components in the internal microporous structure are desorbed. After the average temperature of the primary radiation preheated raw material reaches 350°C, the raw material that has been preheated by infrared primary heating is obtained; Centrifugal primary preheating: the raw meal that has been primarily heated by infrared rays is introduced into a centrifugal heating chamber, and a centrifugal fan is used to rotate to generate an annular hot air flow, so that the raw meal particles diffuse outward in a centrifugal manner; the speed of the centrifugal fan is controlled at 1500RPM, and the high-speed airflow suspends the raw meal particles in the centrifugal chamber, and the average gas flow rate is maintained at 10m / s; in this way, the raw meal is evenly dispersed in the chamber, the particles collide with each other and the heat transfer rate is accelerated, the particle surface is fully in contact with the high-temperature gas, and the raw meal temperature is raised to 500℃ to obtain the raw meal that has been primarily preheated by centrifugal force.

[0027] In this embodiment, step S3 includes: Infrared deep heating, the raw meal preheated by centrifugal force is introduced into the infrared heating chamber, the emission surface temperature is controlled at 1000℃, and the infrared wavelength is distributed in the 3.0μm section; the raw meal is spread on the heat-resistant conveyor belt in the infrared heating chamber, and the line speed of the heat-resistant conveyor belt is maintained at 0.2m / s, so that the raw meal particles gradually approach the calcination starting temperature under strong infrared irradiation, the uniformity of heat distribution inside the particles is improved, and the carbonate decomposition in the material tends to be active, which is conducive to rapid reaction in the subsequent pre-decomposition link; the raw meal heated by infrared deep heating is obtained; Preheat the graded materials for calcination, and convey the raw materials deeply heated by infrared rays to the rotary kiln for calcination. The temperature in the rotary kiln is controlled at 1300°C, and the kiln speed is maintained at 3RPM to obtain kaolin clinker.

[0028] In this embodiment, the raw material particles are mixed by limestone powder, clay powder and iron powder in a mass ratio of 1:0.3:0.1.

[0029] In this embodiment, the conveyor belt speed in the infrared heating section is 0.5 m / s.

[0030] In this embodiment, the calcination time is 3 hours.

[0031] In the above-mentioned embodiments, the high-temperature airflow capture and primary preheating stage filters solid particles while recycling kiln flue gas and uses a radiation preheating chamber for initial heating to ensure that the temperature distribution of the raw material particles is uniform. In the infrared primary heating and centrifugal preheating stage, the initial heating effect of the particles is improved by controlling the infrared irradiation temperature, and the hot air flow generated by the rotating centrifugal fan is used to make the particles fully contact with the high-temperature gas under the action of centrifugal force, thereby improving the heating efficiency. In the infrared deep heating and material calcination stage, the raw material particles quickly reach the calcination temperature through deep heating on the heat-resistant conveyor belt, ensuring the stability and controllability of the calcination process. The entire preheating method shortens the preheating time and reduces energy consumption, while improving the particle recovery rate and fineness distribution, thereby improving the efficiency of the kaolin calcination process and product quality.

[0032] Experimental methods: Preheating temperature uniformity test: The preheating temperature uniformity test method is carried out in accordance with the national standard GB / T 12345. In the experiment, temperature sensors are arranged at different positions of the preheating chamber to record the temperature distribution data of the raw material particles during the preheating process. The preheating temperature uniformity percentage is obtained by calculating the ratio of the standard deviation of the temperature at each measuring point to the average temperature.

[0033] Energy consumption experiment: Energy consumption is measured in accordance with the energy management standard ISO 50001. The power consumption during the entire preheating process is recorded, including the energy consumption data of the airflow system, infrared heating system and conveyor belt. The total energy consumption per ton of raw material is calculated and expressed in kWh / t.

[0034] Preheating time experiment: The preheating time is measured according to the production line operation process. The total time required for the raw material to enter the primary preheating stage and complete the deep heating is recorded to ensure that the preheating efficiency of different methods can be compared under the same production conditions.

[0035] Particle recovery rate experiment: The particle recovery rate is determined according to the standard method for solid particle recovery rate. The recovery rate percentage is calculated by collecting and weighing the mass of particles before and after preheating during the preheating process, reflecting the system's recovery efficiency of particles.

[0036] Particle size distribution experiment: Particle size distribution is determined by a laser particle size analyzer in accordance with the national standard GB / T14684. Take the raw material sample after preheating, perform particle size analysis, and count the percentage of particles ≤50μm to evaluate the effect of preheating method on particle size.

[0037] The kaolin clinker prepared in Examples 1-2 was tested, wherein Comparative Example 1 was a commercially available product, and the test results were as follows: Table 1 Performance test data Performance Indicators Comparative Example 1 Example 1 Example 2 Preheating temperature uniformity (%) 85 92 90 Energy consumption (kWh / t) 150 130 125 Warm-up time (minutes) 60 50 48 Particle recovery rate (%) 80 88 85 Particle size distribution (≤50μm, %) 70 85 83 As can be seen from Table 1, Examples 1-2 have higher preheating temperature uniformity, lower energy consumption, shorter preheating time, higher particle recovery rate and better particle fineness distribution than Comparative Example 1. These advantages indicate that the preheating method of the present invention is superior to the prior art in terms of efficiency and performance.

[0038] The above are only preferred embodiments of the present invention and are not intended to limit the present invention in other forms. Any technician familiar with the profession may use the technical contents disclosed above to change or modify them into equivalent embodiments with equivalent changes and apply them to other fields. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A preheating method for calcining kaolin, characterized in that: The following steps are involved: S1: In the stage of high-temperature airflow capture and primary preheating, the flue gas outlet at the rear of the rotary kiln is diverted and the airflow collection hood is used to capture the kiln flue gas, and the solid particles in the gas are removed through the filter screen; the raw material particles are initially heated in the radiation preheating chamber; S2: Infrared primary heating and centrifugal preheating. Through the setting of infrared heating section, the raw material particles pass through the infrared irradiation area with controlled temperature on the conveyor belt. The heated particles are introduced into the centrifugal heating chamber. With the help of the hot air flow generated by the rotating centrifugal fan, the raw material particles diffuse outward under the action of centrifugal force, and the surface of the raw material particles is fully in contact with the high-temperature gas. S3: Infrared deep heating and material calcination. On the heat-resistant conveyor belt, the raw material particles are exposed to infrared radiation in the infrared heating chamber to reach the calcination temperature; then the raw material particles are transported to the rotary kiln for calcination to produce kaolin clinker.

2. The preheating method for calcining kaolin according to claim 1, characterized in that: The S1 step includes: High-temperature airflow capture: by guiding the flue port extending out of the rear of the rotary kiln, the flue gas out of the kiln is captured by the airflow collection hood, the flue gas flow is controlled within the range of 500-800m³ / min, and the filter is used for purification to intercept solid particles with a particle size greater than 50μm in the gas; the airflow output is maintained at a speed of 230-500RPM by the axial flow fan, and the output end of the airflow is connected to the preheating inlet pipe to obtain high-temperature flue gas; In the primary preheating stage, the preheating inlet pipe is connected to the radiation preheating cavity, the raw material particles at room temperature are heated, and the raw material particles are added to the radiation preheating cavity. The cavity length of the radiation preheating cavity is controlled at 3-5m, and the temperature of the raw material particles is increased from 25°C to 200-300°C; and then the radiation preheating cavity is equipped with a stirring blade with a rotation speed of 230-500RPM for mixing to obtain primary radiation preheated raw material.

3. The preheating method for calcining kaolin according to claim 2, characterized in that: The S2 step includes: Infrared primary heating, the primary radiation preheated raw material is introduced into the conveyor belt of the infrared heating section, the surface temperature of the infrared emitting plate is controlled in the range of 800-1000°C, and the infrared band is between 2.5-3.5μm; the conveyor belt of the infrared heating section slowly passes through the infrared irradiation area, the primary radiation preheated raw material is irradiated by infrared radiation, so that the moisture and volatile components in the internal microporous structure are desorbed, and after the average temperature of the primary radiation preheated raw material reaches 300-400°C, the raw material that has been primarily heated by infrared is obtained; Centrifugal primary preheating: the raw material that has been primarily heated by infrared rays is introduced into a centrifugal heating chamber, and a centrifugal fan is used to rotate to generate an annular hot air flow, so that the raw material particles diffuse outward in a centrifugal manner; the speed of the centrifugal fan is controlled within the range of 800-1500RPM, and the high-speed airflow suspends the raw material particles in the centrifugal chamber, and the average gas flow rate is maintained within the range of 5-10m / s. After the raw material temperature is raised to 400-500℃, the raw material that has been primarily preheated by centrifugal force is obtained.

4. The preheating method for calcining kaolin according to claim 3, characterized in that: The S3 step includes: Infrared deep heating, the raw meal preheated by centrifugal force is introduced into an infrared heating chamber, the emission surface temperature is controlled within the range of 900-1100°C, and the infrared wavelength is distributed within the range of 2.0-3.0 μm; the raw meal is spread on a heat-resistant conveyor belt in the infrared heating chamber, and the line speed of the heat-resistant conveyor belt is maintained at 0.1-0.3 m / s to obtain the raw meal deeply heated by infrared; Preheat the graded materials for calcination, and convey the raw materials deeply heated by infrared rays to a rotary kiln for calcination. The temperature in the rotary kiln is controlled in the range of 1200-1450°C, and the kiln rotation speed is maintained at 1-3RPM to obtain kaolin clinker.

5. The preheating method for calcining kaolin according to claim 2, characterized in that: The raw material particles are prepared by mixing limestone powder, clay powder and iron powder in a mass ratio of 1:0.3:0.

1.

6. The preheating method for calcining kaolin according to claim 3, characterized in that: The conveyor belt speed in the infrared heating section is 0.2-0.5 m / s.

7. The preheating method for calcining kaolin according to claim 4, characterized in that: The calcination time is 1-5 hours.

8. A suspension preheater for the preheating method for calcining kaolin according to any one of claims 1 to 7, characterized in that: The utility model comprises a U-shaped preheating inlet pipe for connecting an airflow collection hood and a radiation preheating cavity.

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