Roller hearth kiln for firing foamed ceramics

Abstract

The application discloses a roller kiln for sintering foamed ceramics, which comprises a kiln chamber and a transmission mechanism and a heating mechanism arranged in the kiln chamber. The kiln chamber comprises, in sequence along the transmission direction of the transmission mechanism, an exhaust section, an oxidation section, a sintering section and a cooling section. The heating mechanism is arranged in the oxidation section and the sintering section. The transmission mechanism divides the kiln chamber into an upper kiln chamber and a lower kiln chamber. The heating mechanism arranged in the oxidation section is arranged in the upper kiln chamber or the lower kiln chamber of the oxidation section. The heating mechanism arranged in the sintering section is arranged in the upper kiln chamber and the lower kiln chamber of the sintering section. The heights of the kiln chambers of the exhaust section, the oxidation section and the sintering section are the same, so that the temperature difference between the lower kiln chamber and the upper kiln chamber of the oxidation section is greater than or equal to 60 DEG C. The application can shorten the sintering time of foamed ceramics, reduce the unit sintering energy consumption, improve the uniformity of the air bubbles in the foamed ceramic product, thereby reducing the thermal conductivity and improving the compressive strength.

Description

Technical Field

[0001] This invention relates to the field of ceramic machinery and equipment, and more particularly to a roller kiln for firing foamed ceramics. Background Technology

[0002] In the traditional building materials industry, roller kilns are generally used for firing ceramic bricks. Functionally, roller kilns for firing ceramic bricks are generally divided into a preheating section, an oxidation section, a firing section, and a cooling section. The preheating section is mainly used to dry the residual moisture (around 1%) in the ceramic brick body, with an outlet temperature of approximately 500–600℃. The oxidation section is mainly used to remove carbonates, sulfates, and organic matter from the ceramic brick body, with an outlet temperature generally between 850–1000℃. The firing section's main function is to fire the brick body and glaze, with a maximum temperature generally between 1100–1240℃. Structurally, they generally have two characteristics: firstly, the height of the preheating section is less than the height of the oxidation and firing sections; this is because a lower kiln height means a higher pressure gradient, i.e., a faster gas flow rate, which translates to a faster drying rate. Especially now, with the pursuit of high production volume, the height of the preheating section has been further reduced. Furthermore, a key reason why the existing structure sets the preheating section lower than the firing section is that the oxidation section needs to discharge some of the waste gas generated during oxidation. If the negative pressure is too low, it will be difficult to discharge the waste gas in a timely manner. The waste gas in the oxidation section is mainly extracted by the exhaust fan located in the preheating section. If the preheating section is too high, the negative pressure provided by the exhaust fan will be significantly lost in the preheating section, making it difficult to meet the negative pressure requirements of the oxidation section. The second characteristic is the relatively high kiln height of the oxidation and firing sections. For a kiln of approximately 200m, the internal height of the oxidation and firing sections is around 800-900mm. This is mainly because the higher the kiln height, the smaller the temperature gradient across the kiln cross-section. For the oxidation section, a smaller temperature difference across the cross-section means more uniform oxidation of the ceramic tile body; for the firing section, a smaller temperature difference across the cross-section means less stress difference in the body cross-section, making it less prone to defects such as warping. In other words, it is common knowledge among those skilled in the art that increasing the kiln height of the oxidation and firing sections means improving the quality of the fired ceramic tiles; reducing the kiln height of the preheating section is beneficial for increasing production output. However, excessively high kiln height can also lead to a significant increase in fuel costs. Therefore, the general design principle for kilns in the ceramic tile industry is to use as large a kiln height as possible (especially in the oxidation and firing sections) while ensuring that the firing energy consumption is tolerable.

[0003] On the other hand, for the roller kiln for firing foamed ceramics, based on a full consideration of the characteristics of the structure and formula of the foamed ceramics themselves, and combined with the technical knowledge accumulated in the field of roller kilns for ceramic bricks, those skilled in the art have further increased the height of the firing section and the oxidation section (see...). Figure 1This is mainly because: firstly, the height of foamed ceramic blanks is relatively large after foaming (the thickness of finished foamed ceramic products is ≥100mm, while traditional ceramic tiles are only 5-20mm), requiring a higher kiln height; secondly, it is generally believed that the greater the height of foamed ceramics, the greater the temperature difference across its cross-section, making it more prone to defects due to temperature differences; especially since foamed ceramics themselves have a low thermal conductivity (during the foaming process in the firing stage and after foaming), heat transfer is more difficult, further amplifying this temperature difference. Therefore, in conventional technology, the internal height of roller kilns used for foamed ceramics is generally around 1m, with the upper kiln chamber approximately 580-600mm and the lower kiln chamber approximately 380-450mm. Furthermore, for foamed ceramic roller kilns, since the foamed ceramics are not pre-dried before entering the kiln, their moisture content is around 6-8% (ceramic bricks generally have a moisture content of about 7% after pressing, but after pre-drying, glazing, and other decorations, the moisture content is about 1%). The drying pressure is relatively high, therefore, the height and length of the preheating section are generally further reduced. In existing technology, the height of the preheating section is approximately 300-350 mm. In addition, for foamed ceramics, the powder is generally arranged in kiln cars, which then enter the roller kiln for firing. During the firing section, since the spray guns are all located in the lower kiln chamber, the hot airflow rises from the bottom of the kiln to the top. Kiln cars can obstruct some of the hot airflow, easily causing hot air to surge upwards from both sides of the kiln. This upward surge is especially pronounced when the preheating section is low and the overall negative pressure is high, leading to rapid heating of the kiln furniture sidewalls. This causes the powder near the kiln furniture sidewalls to melt first, obstructing the oxidation and exhaust pathways of the powder. The liquid phase generated by the melting powder encapsulates the gases produced during the exhaust process. In subsequent high-temperature sintering, the gases generated by the foaming agent also mix with the exhaust gases, easily forming large or interconnected pores, affecting the quality of the foamed ceramics. Therefore, existing technologies often maintain a sufficient length of the oxidation section to prevent the formation of large local bubbles, which prolongs the production cycle. The optimal firing cycle for existing roller kilns is approximately 10–15 hours.

[0004] Overall, existing kilns for firing foamed ceramics have long firing cycles and high energy consumption. Furthermore, attempts to further shorten the firing cycle often result in defects such as large localized bubbles. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a roller kiln for firing foamed ceramics, which has low energy consumption and produces foamed ceramics with uniform cross-section bubbles.

[0006] To address the technical problem of this invention, the present invention provides a roller kiln for firing foamed ceramics, comprising a kiln chamber and a conveying mechanism and a heating mechanism disposed within the kiln chamber. The kiln chamber sequentially comprises a flue gas section, an oxidation section, a firing section, and a cooling section along the conveying direction of the conveying mechanism. The heating mechanism is disposed within the oxidation section and the firing section. The conveying mechanism divides the kiln chamber into an upper kiln chamber and a lower kiln chamber. The heating mechanism located in the oxidation section is disposed in either the upper or lower kiln chamber of the oxidation section, and the heating mechanism located in the firing section is disposed in both the upper and lower kiln chambers of the firing section. The flue gas section, oxidation section, and firing section are at the same height, such that the temperature difference between the lower and upper kiln chambers of the oxidation section is ≥60℃.

[0007] As an improvement to the above technical solution, the height of the upper kiln chamber is 385-450mm, and the height of the lower kiln chamber is 325-390mm.

[0008] As an improvement to the above technical solution, the heating mechanism located in the oxidation section is located in the lower kiln chamber of the oxidation section, and the distance between the heating mechanism and the transmission mechanism is 90-100mm.

[0009] As an improvement to the above technical solution, the heating mechanisms in the oxidation section are evenly spaced, with a distance of 1000-1500mm between adjacent heating mechanisms, so that the temperature difference between the lower and upper kiln chambers of the oxidation section is ≥80℃.

[0010] As an improvement to the above technical solution, the heating mechanisms in the firing section are evenly spaced in the upper and lower kiln chambers of the firing section so that the temperature difference between the lower and upper kiln chambers of the firing section is ≤30℃.

[0011] As an improvement to the above technical solution, the distance between the heating mechanism located in the lower kiln chamber of the firing section and the transmission mechanism is 90-100mm; the distance between the heating mechanism located in the upper kiln chamber of the firing section and the transmission mechanism is 300-360mm.

[0012] As an improvement to the above technical solution, the distance between the heating mechanisms located in the firing section is 1400-1600mm, so that the temperature difference between the lower and upper kiln chambers of the firing section is ≤20℃.

[0013] As an improvement to the above technical solution, the height of the upper kiln chamber is 440mm, and the height of the lower kiln chamber is 325mm;

[0014] The distance between the heating elements in the oxidation section is 1080 mm, and the distance between the heating elements in the firing section is 1500 mm.

[0015] As an improvement to the above technical solution, the temperature of the foamed ceramic blank at the inlet of the flue gas section is 60-100℃, the temperature of the foamed ceramic blank at the outlet of the flue gas section is 400-500℃, the temperature of the foamed ceramic blank at the outlet of the oxidation section is 900-1150℃, and the maximum temperature of the firing section is 1150-1250℃.

[0016] As an improvement to the above technical solution, the residence time of the foamed ceramic green body in the flue gas section is 5-10 min, the residence time in the oxidation section is 30-90 min, and the residence time in the firing section is 100-240 min.

[0017] Implementing this invention has the following beneficial effects:

[0018] 1. This invention sets the heights of the exhaust section, oxidation section, and firing section to be the same. With this structure, the temperature difference between the lower and upper kiln chambers of the oxidation section can reach more than 60°C, allowing the oxidation reaction to proceed gradually from the bottom to the top of the kiln car powder. This effectively reduces the probability of local large bubbles and ensures the quality of the foamed ceramic product. At the same time, it also effectively shortens the residence time of the foamed ceramic body in the firing section and improves production efficiency.

[0019] 2. The roller kiln of the present invention for firing foamed ceramics has a low overall height and low energy consumption. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a roller kiln used in the prior art for firing foamed ceramics;

[0021] Figure 2 This is a schematic diagram of the structure of a roller kiln used for firing foamed ceramics in one embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0023] refer to Figure 2This invention provides a roller kiln for firing foamed ceramics, comprising a kiln chamber 1, a conveying mechanism 2 disposed within the kiln chamber 1, and a heating mechanism 3; wherein the kiln chamber 1 is divided into an upper kiln chamber 11 and a lower kiln chamber 12 by the conveying mechanism 2. Functionally, the kiln chamber 1 sequentially includes a flue gas section 4, an oxidation section 5, a firing section 6, and a cooling section 7 along the conveying direction of the conveying mechanism 2. The heating mechanism 3 is disposed within the oxidation section 5 and the firing section 6. The heating mechanism 3a located in the oxidation section 5 is disposed in the upper kiln chamber 11a or the lower kiln chamber 12a of the oxidation section 5, and the heating mechanism 3b located in the firing section 6 is disposed in the upper kiln chamber 11b and the lower kiln chamber 12b of the firing section 6; the kiln chamber 1 of the flue gas section 4, the oxidation section 5, and the firing section 6 has the same height. Based on the above structure, the temperature difference between the lower kiln chamber 12a and the upper kiln chamber 11a of the oxidation section 5 can be increased to over 60°C, and the absolute pressure of the oxidation section 5 can be controlled below 101295Pa. This allows the oxidation reaction to proceed gradually from the bottom to the top of the kiln car powder, reducing the probability of local large bubbles, shortening the residence time of the oxidation section, shortening the firing cycle, reducing energy consumption, and improving production efficiency.

[0024] Furthermore, it should be noted that the temperature difference between the lower kiln chamber 12 and the upper kiln chamber 11 in this invention refers to the difference between the temperature at the lower kiln chamber 20mm away from the transmission mechanism and the temperature at the center of the upper kiln chamber 11. The absolute pressure refers to the absolute pressure located at the top 1 / 3 of the upper kiln chamber 11.

[0025] Specifically, the height of the upper kiln chamber 11 is 385–450 mm. When the height of the upper kiln chamber 11 is greater than 450 mm, the exhaust gas section 4 is difficult to dry effectively, and the exhaust gas from the oxidation section 5 is also difficult to discharge in time, reducing the oxidation rate. When the height of the upper kiln chamber 11 is less than 385 mm, the negative pressure in the oxidation section 5 is high (< -50 Pa), which easily causes the powder near the kiln car wall to liquefy first; and the temperature difference between the upper and lower parts of the firing section 6 is too large, which easily leads to uneven foaming defects. For example, the height of the upper kiln chamber 11 is 390 mm, 395 mm, 400 mm, 405 mm, 410 mm, 415 mm, 420 mm, 425 mm, 430 mm, 435 mm, 440 mm, or 445 mm, but is not limited to these. Preferably, the height of the upper kiln chamber 11 is 440 mm. The height of the lower kiln chamber 12 is 325-390mm, and exemplary values ​​are 330mm, 335mm, 345mm, 350mm, 355mm, 360mm, 365mm, 370mm, 375mm, 380mm or 385mm, but it is not limited to these. Preferably, the height of the lower kiln chamber 12 is 325mm.

[0026] Compared to conventional roller kilns for firing foamed ceramics, this invention lowers the height of the oxidation section 5 and raises the height of the exhaust section 4. Lowering the height of the oxidation section 5 increases the internal temperature difference, allowing the oxidation exhaust to gradually rise from the bottom to the top of the foamed ceramic body, resulting in more complete and thorough oxidation exhaust. On the other hand, raising the height of the exhaust section 4 reduces the negative pressure within the oxidation section 5 to some extent, mitigating the adverse effects of the kiln head negative pressure on the rising hot airflow within the oxidation section 5 and preventing rapid melting of powder near the kiln car wall, which could affect exhaust and cause localized large bubbles. Testing has shown that even with the roller kiln height described in this invention, the drying requirements of the exhaust section 4 and the exhaust gas discharge requirements of the oxidation section 5 can still be met. Specifically, with the aforementioned heights of the exhaust section 4 and oxidation section 5, the absolute pressure of the oxidation section can be controlled between 101280 and 101290 Pa (i.e., a negative pressure of -45 to -35 Pa).

[0027] Specifically, the heating mechanism 3a in the oxidation section 5 is located in the lower kiln chamber 12a, and the distance between it and the transmission mechanism 2 is 90-100 mm. When the distance is greater than 100 mm, the heating efficiency is low; when the distance is less than 90 mm, a hot airflow that quickly circulates around both sides of the kiln furniture is easily formed in the upper kiln chamber 11a. For example, the distance between the transmission mechanism 2 and the heating mechanism 3a is 92 mm, 94 mm, 96 mm, 98 mm, or 99 mm, but is not limited to these. The heating mechanisms 3a in the oxidation section 5 are evenly spaced, and the distance between adjacent heating mechanisms 3a is 1000-1500 mm, for example 1050 mm, 1100 mm, 1150 mm, 1200 mm, 1250 mm, 1300 mm, 1350 mm, 1400 mm, or 1450 mm, but is not limited to these. Preferably, the distance between the heating mechanisms 3a in the oxidation section 5 is 1080 mm. By arranging the heating mechanisms 3a at the above-mentioned intervals, the temperature difference between the lower kiln chamber 12a and the upper kiln chamber 11a of the oxidation section 5 can be ≥80℃, more specifically 80~160℃. Specifically, when water gas is used as the fuel, the temperature difference can reach 80~90℃; when natural gas is used as the fuel, the temperature difference can reach 140~150℃. Based on this temperature difference, the oxidation quality of the oxidation section 5 can be effectively improved, and the firing cycle can be shortened.

[0028] It should be noted that while reducing the height of kiln chamber 1 generally improves energy utilization efficiency and enhances oxidation quality and rate, it also means a larger temperature difference between the upper and lower parts of firing section 6. This can lead to uneven foaming, affecting the compressive strength and thermal conductivity of the foamed ceramics, and reducing their yield. To eliminate these adverse effects, this invention mainly makes the following structural improvements:

[0029] First, the heating mechanisms 3 of the firing section 6 are evenly spaced within the upper kiln chamber 11b and lower kiln chamber 12b of the firing section 6. This ensures that the temperature difference between the lower kiln chamber 12b and the upper kiln chamber 11b of the firing section 6 is ≤30℃. Second, the distance between the heating mechanism 3b of the lower kiln chamber 12b and the transmission mechanism 2 of the firing section 6 is controlled to be 90-100mm, exemplarily 92mm, 94mm, 96mm, 98mm, or 99mm, but not limited to these. Third, the distance between the heating mechanism 3 of the upper kiln chamber 11b and the transmission mechanism 2 of the firing section 6 is controlled to be 300-360mm, exemplarily 305mm, 310mm, 315mm, 320mm, 325mm, 330mm, 335mm, 340mm, 345mm, 350mm, or 355mm, but not limited to these. Finally, the distance between the heating mechanisms 3b located in the firing section 6 is controlled to be 1400-1600mm, with exemplary values ​​of 1400mm, 1430mm, 1460mm, 1520mm, 1550mm, 1580mm, or 1590mm, but not limited to these. Through the combined control of the above aspects, the temperature difference between the lower kiln chamber 12b and the upper kiln chamber 12a in the firing section 6 can be ≤20℃, specifically 3-20℃. Specifically, when water gas is used as fuel, the temperature difference is controlled at 3-10℃, and when natural gas is used as fuel, the temperature difference is controlled at 15-20℃.

[0030] The conveying mechanism 2 can be a roller, but is not limited to it. The distance between the center lines of adjacent rollers is 300-400 mm, preferably 340-370 mm. The roller material can be a high-alumina roller or a SiC roller, but is not limited to it.

[0031] The heating mechanism 3 is a combustion mechanism using natural gas, water gas, or heavy oil as fuel, or an electrically heated structure. Preferably, it is a combustion mechanism using natural gas or water gas as fuel. Furthermore, it should be noted that the heating mechanism 3 referred to in this invention mainly refers to the spray gun of the combustion mechanism.

[0032] Based on the aforementioned roller kiln structure, this invention further modifies the specific firing regime of the roller kiln. Specifically, the temperature of the foamed ceramic green body at the inlet of the flue gas section 4 is controlled at 60–100°C, and the temperature of the foamed ceramic green body at the outlet of the flue gas section 4 is controlled at 400–500°C, so that the residence time of the foamed ceramic green body in the flue gas section 4 is 5–10 min. The temperature of the foamed ceramic green body at the outlet of the oxidation section 5 is 900–1150°C, and the residence time of the foamed ceramic green body in the oxidation section 5 is 30–90 min; the maximum temperature of the firing section 6 is 1150–1250°C, and the residence time of the foamed ceramic green body in the firing section 6 is 100–240 min.

[0033] Based on the above-mentioned roller kiln and firing system, the parameters of the roller kiln of the present invention are compared with those of existing roller kilns as follows:

[0034]

[0035]

[0036] As can be seen from the table, this invention reduces the height of the oxidation and firing sections while increasing the height of the exhaust section. This results in more thorough exhaust in the oxidation section, accelerates the oxidation reaction, shortens the firing cycle, and avoids defects such as large local bubbles while shortening the firing cycle. This maintains the stability of the foamed ceramic product's performance, improves the compressive strength of the finished foamed ceramic, and reduces its thermal conductivity.

[0037] The above description is a preferred embodiment of the invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the invention, and these improvements and modifications are also considered to be within the scope of protection of the invention.

Claims

1. A roller hearth kiln for sintering foamed ceramics, comprising a kiln chamber and a conveying mechanism and a heating mechanism arranged in the kiln chamber, the kiln chamber comprising, in the conveying direction of the conveying mechanism, in succession, a fume removal section, an oxidation section, a sintering section and a cooling section, the heating mechanism being arranged in the oxidation section and in the sintering section, the conveying mechanism dividing the kiln chamber into an upper kiln chamber and a lower kiln chamber, the heating mechanism arranged in the oxidation section being arranged in the upper kiln chamber or in the lower kiln chamber of the oxidation section, the heating mechanism arranged in the sintering section being arranged in the upper kiln chamber and in the lower kiln chamber of the sintering section, characterized in that The heights of the smoke exhausting section, the oxidizing section and the sintering section are the same; The height of the upper kiln chamber is 385-450 mm, and the height of the lower kiln chamber is 325-390 mm; The heating mechanisms in the sintering section are uniformly arranged in the upper kiln chamber and the lower kiln chamber of the sintering section, the distance between the heating mechanism in the lower kiln chamber of the sintering section and the conveying mechanism is 90-100 mm, and the distance between the heating mechanism in the upper kiln chamber of the sintering section and the conveying mechanism is 300-360 mm.

2. The roller hearth kiln for firing foamed ceramics of claim 1, wherein, The heating mechanism in the oxidizing section is arranged in the lower kiln chamber of the oxidizing section, and the distance between the heating mechanism and the conveying mechanism is 90-100 mm.

3. The roller hearth kiln for firing foamed ceramic of claim 2, wherein, The heating mechanisms in the oxidizing section are uniformly arranged, and the distance between adjacent heating mechanisms is 1000-1500 mm.

4. The roller hearth kiln for firing foamed ceramic of claim 1 wherein, The distance between the heating mechanisms in the sintering section is 1400-1600 mm.

5. The roller hearth kiln for firing foamed ceramic of claim 1 wherein, The height of the upper kiln chamber is 440 mm, and the height of the lower kiln chamber is 325 mm; The distance between the heating mechanisms in the oxidizing section is 1080 mm, and the distance between the heating mechanisms in the sintering section is 1500 mm.

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