What is Circular Tunnel Kiln?

From '800 Questions about Sintered Bricks', Editor-in-Chief: Mr. Zhao Zhenkui, China Construction Industry Press

In January 1972, an automated circular tunnel kiln was completed and put into operation at the Risboroa factory in Sikeborg, Denmark. The shape of the kiln tunnel is a circular cross-section, which is used for burning tiles. But it still use kiln cars. Its characteristics were: the kiln body and the track move relative to each other, and the kiln car is loaded and unloaded on the same side, which is convenient for transportation. The fuel is liquefied gas. The heat consumption is 1380kJ/kg finished tile (330Kcal/kg finished tile).

In addition, some brick factories in France use annular kilns with automatic rotating kiln bottoms. This type of kiln uses a continuous annular rotating kiln to replace the kiln car. Its characteristics are: (1) Due to the use of a two-chamber kiln bottom, the joints between kiln cars are eliminated, improving the sealing performance of the kiln bottom and reduce heat loss; (2) The bottom of the kiln is equipped with a 'continuous sand seal' to store sand, so there is no problem of sand leakage. This eliminates the need to frequently replenish sand; (3) The rotating kiln bottom can be used to continuously load and unload at a fixed position on the same side. Easy to carry. The disadvantage is that the kiln bottom sometimes shifts during rotation. The fuel is gasified fuel oil or gas.

After years of painstaking research, Mr. Baifei of China Xi'an Liyuan Kiln Co., Ltd. invented the annular mobile tunnel kiln, referred to as the mobile kiln. The first mobile kiln was built in 1997. The internal width of the kiln is 4m, the internal height is 1.5m, the length of the kiln body is 120m, and the diameter of the annular centerline of the kiln body is 85m (circumference is approximately 251m). At the end of 1998, the kiln was successfully ignited and tested, and won many inventions such as "Mobile tunnel kiln and the process layout of using the tunnel kiln to produce clay products" and "Ring-shaped billet conveyor and mobile tunnel kiln brick-burning process system" patent.

First mobile circular tunnel kiln in Shandong, China. 

The main differences between China's invented mobile kiln and the Danish circular tunnel kiln and the French rotating ring kiln are: (1) The former's kiln body only accounts for 40%-45% of the ring kiln tunnel, while the latter's kiln The kiln body basically occupies the entire annular kiln road, leaving only a gap for loading and unloading the kiln; (2) the former does not require kiln cars and ancillary equipment, while the latter requires kiln cars and ancillary equipment; (3) the former kiln body moves, billet does not move, the latter kiln body does not move and the billet stack moves.

Since the invention of the straight-running fixed tunnel kiln in 1751, it has not been used in production for 129 years. One of the key problems is that the problem of sand sealing in the upper and lower spaces of the kiln car has not been solved. Due to air leakage from the upper and lower parts of the kiln car, the temperature difference between the sections in the kiln increases, which affects the normal operation of the kiln car and ancillary equipment, reduces the output of the kiln car and product quality, and increases the energy consumption of the kiln. The annular mobile tunnel kiln has completely got rid of the burden of kiln cars and ancillary equipment. This is a success and has also injected strong vitality and temptation into the annular mobile tunnel kiln.

Based on Mr. Baifei's invention, the annular tunnel kiln has developed rapidly in the past ten years, and hundreds of them have been built and put into production in more than 20 provinces and cities in China. According to the raw material performance, product specifications, output and other requirements, the kiln car ranges from 120m to 160m; the internal width is also varied, including 4.5m, 5.5m, 6.8m, 7.9m, 8.8m, 9.6m, 10.8m , 12.8m, 14m, etc. The daily output of ordinary solid bricks is as high as 800,000 pieces, which is impossible to achieve for a tunnel kiln with kiln cars.