Design and application of high temperature tunnel kiln:
1 Main technical parameters and economic indicators
The tunnel kiln is open flame intermittent combustion, intermittently entering the car, the fired products are corundum mullite refractory bricks, the full kiln length is 50m, the kiln width is 1.5m, the height of the kiln car platform to the kiln top is 0.95 / 0.75m, kiln content There are 25 kiln cars, each kiln car is packed with 2 brick stacks, firing temperature is 1650 ℃, firing period is 46h, fuel is natural gas, energy consumption per ton brick is 1500kcal, kiln temperature and pressure are automatically controlled, and temperature control accuracy is ≤ ± 2 ℃.
2 Kiln main structure and working system
The entire kiln mainly includes the main structure of the kiln, the closed air curtain of the kiln head and the smoke exhaust system, the stirring air system, the combustion system, the kiln tail cooling system, the under-vehicle cooling air system, the waste heat utilization system, the kiln car, the automatic control system, etc. As shown in Figure 1. This kiln adopts some new technologies in the kiln body structure, high temperature hot air combustion support, waste heat utilization and automatic control. Compared with the traditional high temperature kiln, it has the characteristics of high temperature firing control accuracy and remarkable energy saving effect.
2.1 The main structure of the kiln
The steel structure of the kiln body is reinforced with profiled steel columns, and the outer surface is decorated with high-quality steel plate paint. The kiln has a total length of 50m and is divided into three parts: pre-heating zone, firing zone and cooling zone. The sintered belt is lined with corundum mullite bricks, followed by high-temperature light-weight heat-insulating bricks, heat-insulating fillers, and non-asbestos silicate calcium boards. The structure of the kiln roof is arch-shaped. In order to reduce the high-temperature expansion of the arch roof, the lining should be made of refractory bricks with a slightly lower density, a smaller expansion coefficient, and the same quality as the firing zone. Three interleaved baffles are built on the pre-tropical vault to make the hot air flow above the arch foot deflect downward, which only reduces the temperature difference between the upper and lower parts of the pre-tropical zone, but also does affect the smoke extraction force too much. Due to the large lateral thrust of the vault, the outside of the arch foot bricks of traditional tunnel kilns are made of heavy bricks, and this part has poor thermal insulation. The outside of this design arch brick is made of high-quality flat bricks with a certain distance between them. The flat bricks are filled with light insulation bricks and bulk insulation materials, which can effectively improve the heat insulation performance of this part.
High-temperature kilns have stricter requirements for burner bricks. Due to the large temperature difference between the hot and cold ends of the integral burner brick, it cracks during use, has a short service life, and is troublesome to replace. The burner brick of the kiln is divided into 4 pieces during the manufacture, and then the masonry is put together into a whole, which greatly prolongs the service life of the burner brick. After a period of production and operation of a traditional high-temperature tunnel kiln, the inner walls on both sides of the firing zone will protrude into the kiln to varying degrees due to high-temperature expansion. To overcome this problem. The kiln wall lining refractory bricks of the firing zone are designed as meshing structure, and the use result proves that the kiln wall is basically free of inner convexity.
2.2 Closed air curtain and smoke exhaust system of kiln head
In order to keep the pressure in the kiln stable and avoid fluctuations in firing temperature, the kiln head and the kiln tail of the kiln are provided with a kiln door, and an air curtain air hood is provided on each side wall of the kiln head and the kiln top, and the air is used as a closed gas Curtain, changing the traditional kiln door and air-sealed air curtain form, is also conducive to the product clean into the kiln and fired. The smoke exhaust system adopts the form of multi-point smoke exhaust in the kiln and centralized smoke exhaust by the fan outside the kiln. On the kiln walls on both sides of the pre-tropical zone, multiple pairs of smoke vents are provided. The smoke exhaust port is located near the kiln wall of the kiln wall. At the same time, the temperature curve of the pre-tropical zone is adjusted by adjusting the opening of the exhaust port. A cold air dilution port is provided on the outside of each smoke exhaust port. If necessary, part of the air outside the kiln can be sucked in to reduce the temperature of the smoke exhaust.
2.3 Stirring air system
The traditional tunnel kiln pre-tropical zone has a large temperature difference due to gas stratification. In addition to the kiln roof effluent and multi-point smoke exhaust measures, this design also has a stirring air system on the walls of the two sides of the pre-tropical zone, and the ambient cold wind is drawn through the fan, passes through the main pipe, branch pipe, and ball valve, and enters the kiln. The upper channel of the mixer stirs the air flow to prevent the air flow stratifying, thereby reducing the temperature difference between the upper and lower parts of the pre-tropical zone. The air inlets are small and numerous, and are staggered on both sides.
2.4 Combustion system
Because the high-temperature constant time of the fired products requires a long time, the firing zone in this design accounts for a slightly larger proportion of the total length of the kiln body, and the number of burners arranged is also slightly larger. The firing can be adjusted by changing the number and location of burnt burners The location of the high temperature point and the high temperature constant temperature time of the belt can be adapted to the requirements of the firing process of different formula products, and have greater adaptability and flexibility of the firing process.
The burners are staggered along the two sides of the kiln and face the combustion channel between the brick stacks of the kiln. Therefore, the high-speed combustion airflow does flow relatively and interferes with each other, but generates a certain circulation in the horizontal and vertical directions of the kiln. Make the temperature inside the kiln uniform. The combustion chamber is provided on the side wall of the kiln body, but the direct combustion method among the products in the kiln can make the structure of the side wall simpler and can fully insulate heat.
It should be noted that the combustion method of this kiln is very different the traditional tunnel kiln. Even if the traditional high-temperature tunnel kiln does have a combustion chamber, the inner cavity of the burner brick is also larger, and most all of the combustion-supporting air enters the kiln through the burner the combustion chamber burner brick to support combustion. The heat exchange of the combustion-supporting air mainly depends on It is realized by metal heat exchangers hollow arches and hollow walls of the kiln body. The heat exchange temperature is up to 1000 ℃, and the lowest is only 200 ~ 300 ℃. Moreover, the pressure of the combustion-supporting air using the kiln brick masonry heat exchange method is high, and it is easy Cause the kiln body to ventilate and leak air. The new high-temperature kiln of this design has no combustion chamber, the burner brick is shorter and the inner and cavity are smaller. Only a small part of the cold air enters the kiln through the burner, which functions as a cooling burner and a blowing aid. Most of the combustion air comes Cooling air blown into the cooling belt. After the hot air after cooling the product reaches the firing zone, its temperature approaches reaches the highest temperature. Obviously, the energy-saving effect of this kiln is remarkable, and it is easier to operate at high temperature and constant temperature.
2.5 Cooling system of kiln tail
The kiln is provided with a cold air port on both sides of the wall and the top of the kiln, and a large amount of cold air cooling products are blown into the kiln by the fan. In addition, several pairs of high-speed and low-flow cold air blowing pipes are staggered up and down on both sides of the kiln wall at the joint of the two kiln cars of the cooling zone. The cold air blown in forms a cooling section at the joint of the kiln car, which helps to cool the entire product evenly. . Most of the hot air after cooling the product moves to the burning zone to support combustion, and the remaining part is drawn out by the heat exhaust fan through the cooling zone kiln wall exhaust port and sent to the drying kiln.
2.6 Under-car cooling air system
The kiln is a high-temperature kiln. In order to prevent the temperature under the car being too high, a cooling air system is provided under the car. In the firing zone and cooling zone, a blower tube is provided at the lower part of the kiln car to blow cold air under the car, pass through the air outlet at the bottom of the kiln wall, and use the natural suction force formed by the height difference between the internal and external air outlets to eliminate.
2.7 Waste heat utilization system
The waste heat utilization system of this design includes four parts: the cooling hot air in the cooling zone, the cooling air under the car, the heat dissipation cooling air on the outer surface of the kiln wall and the top of the kiln wall, and the flue gas heat exchange air. Because the surface temperature of the high-temperature kiln is slightly higher than that of the general tunnel kiln, in order to make full use of the residual heat, the high-temperature belt kiln roof is covered with a corrugated steel plate to form a heat exchange space with the outer vault; the outer layer of the kiln wall is built into a hollow wall. The cold air enters the hollow wall a row of small holes close to the ground, mixes with the heat exchange wind at the top of the kiln, and is pumped out intensively. A metal heat exchanger is installed on the main smoke exhaust pipe outside the kiln, which can make full use of part of the waste heat of the flue gas. The four parts of the above residual heat air are sent to the drying kiln, which can fully meet the needs of product drying.
2.8 Kiln car
The kiln car is made of profiled steel, and the bearings are made of high-temperature bearings with a maximum temperature resistance of 300 ° C. The refractory material of the car body is: the sintered mullite brick with good thermal shock resistance is used for the car deck bricks, and the surrounding bricks are meshed. Build; choose insulated bricks in the middle. The advantage of dry-laying the bricks on the platform is that it can greatly reduce the number of kiln car repairs and extend the service life of the kiln car.
2.9 Automatic control system
The automatic control system of the kiln includes temperature control, pressure control and safety alarm.
The firing temperature is controlled by computer, including computer, AI artificial intelligence regulator, solenoid valve, electric actuator and thermocouple, etc., and is equipped with a data acquisition card and isolation devices inside and outside the machine. . The temperature is detected by the thermocouple, and the fire flame is adjusted by the electric actuator. They are controlled by the computer and the AI artificial intelligence regulator according to the set firing curve. The computer control system can only realize the automatic control of the kiln temperature. It can also achieve comprehensive control of various kiln systems, and can automatically record, print, and screen language prompts; in addition, the computer can simulate and store a variety of firing system curves according to firing requirements, and the parameters of the firing curve can be Need to modify at any time.
The kiln pressure control is achieved by frequency conversion control of exhaust fans, cooling fans and hot air extraction fans. The pressure signal in the kiln and the pressure signal of the main pipeline of the fan are collected by the pressure transmitter and sent to their respective AI intelligent regulators to automatically adjust the speed of the fan by frequency conversion, which has high control accuracy and saves power. A pressure transmitter can be used to measure the pressure signals of multiple parts in the kiln by manual switching, and both the manual operator and the frequency converter can be switched to the manual operating environment, so as to facilitate process exploration and cope with emergencies.
The fuel used in the kiln is natural gas. In order to ensure the safety of gas supply, a solenoid main valve is provided on the main gas supply line, and an interval solenoid valve is also provided on each ring pipe. When the system is powered off, the solenoid valve automatically cuts off the gas path to prevent natural gas entering the kiln; when the fan system fails, the alarm system sends an alarm signal and the solenoid valve automatically cuts off the gas path to ensure safety.
3 Conclusion
The designed new high-temperature tunnel kiln adopts unique new technology in the structure and combustion mode of the kiln body, with advanced and reliable performance, and it is successfully commissioned and put into normal operation. After being put into production, the technical and economic indicators of the kiln have reached the design requirements, and the energy-saving effect is remarkable. It is worth adopting learning when the relevant manufacturers build rebuild high-temperature tunnel kilns.
