Tunnel kiln is generally a long and straight tunnel with fixed walls and vaults on both sides and at the top, and the kiln car runs on the track laid at the bottom. Combustion equipment is located on both sides of the middle of tunnel kiln, forming a fixed high temperature zone-firing zone. Under the action of chimney or induced draft fan at the front end of tunnel kiln, the high-temperature flue gas produced by combustion flows along the tunnel to the kiln head, and the products entering the kiln are gradually preheated, which constitutes the preheating zone of tunnel kiln. Cold air is blown into the end of the tunnel kiln to cool the products in the back section of the tunnel kiln. The blown cold air flows through the product and is heated, then it is pumped out and sent to the dryer as the heat source for drying the blank. This part constitutes the cooling zone of the tunnel kiln.
Compared with intermittent old inverted flame kiln, tunnel kiln has a series of advantages.
1, continuous production, short cycle, large output and high quality.
2. It works by using the counter-current principle, so the heat utilization rate is high and the fuel is economical. Because of good thermal insulation and waste heat utilization, the fuel is very economical, which can save about 50-60% compared with the inverted flame kiln.
3. The firing time is shortened. Compared with ordinary large kilns, it takes 3-5 days from kiln loading to kiln discharging, while tunnel kilns can be completed in about 20 hours.
4. Save labor. It is not only convenient to operate during firing, but also convenient to load and unload the kiln outside the kiln, which improves the working conditions of operators and reduces the labor intensity.
5. Improve the quality. The temperature of preheating zone, sintering zone and cooling zone is often kept in a certain range, so it is easy to master the sintering law, so the quality is better and the breakage rate is less.
6. Kilns and kiln furniture are durable. Because the kiln is not affected by rapid cooling and rapid heating, the kiln body has a long service life and is generally repaired once every 5-7 years.