Energy saving and consumption reduction has become a mainstream topic in today's social development. It not only responds to the country's macro planning, but also lays a solid foundation for reducing costs and improving benefits in various industries. The tunnel kiln of the fired brick production line is the leading thermal equipment in the fired brick industry in my country. Although the thermal energy utilization rate of modern tunnel kilns is much higher than that of previous wheel kilns, it is still a large energy consuming consumer. How the tunnel kiln can better save energy and reduce consumption is a major issue in the development of the sintered brick industry.
2 Features of tunnel kiln of sintered brick production line
The tunnel kiln is a modern continuous firing thermal equipment, which is widely used in the roasting production of refractory materials and other products. Sintered brick production line Tunnel kiln is the leading thermal equipment in my country's burning brick industry. Figure 1 shows the tunnel kiln system diagram of the sintered brick production line. Mainly using the countercurrent principle, the heat utilization efficiency is high, and the heat utilization rate is about 50% higher than that of the conventional wheel kiln. Therefore, the industry is gradually banning wheel kilns and vigorously promoting tunnel kilns. Tunnel kilns have accounted for more than 60% of the industry's market, so how to improve the heat preservation and energy saving of tunnel kilns is particularly important and more meaningful.
Figure 1. Tunnel kiln system diagram
3 Several ways of tunnel kiln heat preservation and energy saving for sintered brick production line
3.1 Reasonable selection of tunnel kiln structure can make the tunnel kiln better heat preservation and energy saving
According to factors such as raw material properties, product specifications, billet form, surrounding environment, investment cost and other factors, choose a tunnel kiln suitable for you. In order to improve the effect of energy saving and emission reduction, we must pay attention to choosing a well-structured kiln type.
3.1.1 Adopt reasonable kiln roof insulation and sealing structure There are four main types of tunnel kiln roof structures:
a. Refractory brick flat ceiling structure;
b. Flat ceiling structure of refractory castable prefabricated block;
c. Arched kiln roof structure built with refractory bricks;
d. Refractory ceramic fiber module flat ceiling structure.
The insulation and sealing of the kiln roof is a very critical step, which is related to the energy consumption of the tunnel kiln. Different kiln roof structures have different kiln roof insulation and sealing measures.
As shown in Figure 2, the roof of the tunnel kiln adopts a refractory brick flat ceiling structure (a), which requires that the gap between the hanging bricks is sealed with appropriate thermal insulation materials under the premise of ensuring the free expansion and contraction of the hanging bricks; At the same time, a castable sealing layer is laid on the hanging bricks to ensure the airtightness of the kiln roof; the aluminum foil-coated refractory ceramic fiber is laid in the middle of the insulation material, which effectively shields the convection of heat through the insulation material to the air, and effectively reflects the radiant heat , Reduce the heat loss of the kiln roof.
Figure 2. Refractory brick flat ceiling structure
The roof of the kiln is a tunnel kiln with a refractory castable prefabricated flat ceiling structure (b). The measures taken for the kiln roof insulation are similar to the refractory brick suspended brick flat ceiling structure. However, because the raw materials contain compounds of sulfur, potassium and sodium, harmful gases will erode the preform during high-temperature roasting. At the same time, it will react with some components in the preform to form low-melting minerals, causing the original preform to lose its original characteristics and strength. A series of changes in physical properties such as heat conduction and elastic coefficient will eventually cause the prefabricated block to peel off and crack. Therefore, the current roof structure of the tunnel kiln adopts a refractory brick hanging brick structure or a refractory ceramic fiber module structure, which increases the corrosion resistance of the kiln roof and reduces the probability of the kiln roof hanging plate falling off due to erosion.
Refractory brick masonry arched kiln roof structure (c) The tunnel kiln roof is made of refractory bricks, and the insulation layer above is mostly backfilled. This kind of tunnel kiln is simple to construct, but because the kiln roof is arched However, the general kiln car stacking car is a mechanical stacking car, and the top of the billet stack is flat, so the kiln head clearance cannot be guaranteed (see 3.2 billet description below). So this arched tunnel kiln is now being phased out.
As shown in Figure 3, the roof of the tunnel kiln adopts a refractory ceramic fiber module flat ceiling structure (d). The ceramic fiber module is made of ceramic fiber. A certain proportion of compression is maintained during the processing. When in use, the module expands in the compression direction, so that the modules are squeezed into a seamless whole. When the module is installed, a compensation blanket must be installed in the non-compression direction of the module, and the compensation blanket must also be installed in compression. Aluminium-clad refractory ceramic fiber is also laid on the top of the module to reduce the convection of the thermal hollow on the top of the kiln and reflect the heat radiation.
Figure 3. Flat ceiling structure of refractory ceramic fiber module
3.1.2 Adopt a reasonable insulation and sealing structure of the kiln wall
Due to site and cost issues, the current tunnel kiln is developing towards a thin kiln wall. The thermal insulation of the kiln wall is directly related to the energy consumption of the tunnel kiln. When the kiln wall is thinner, the insulation performance of the kiln wall may decrease. This requires a reasonable design of the kiln wall and its insulation structure to ensure that the insulation performance of the kiln wall will not decrease.
Figure 4. Schematic diagram of tunnel kiln wall structure
First of all, higher-grade lightweight heat-insulating materials can be used for kiln wall masonry. Although there is more investment at one time, the significant energy-saving effects after commissioning will reduce the total investment cost. We now generally use insulation materials with good insulation effect and relatively economical, such as refractory ceramic fiber, expanded vermiculite and perlite. A layer of refractory fiber covered with aluminum foil is also laid in the middle of the insulation material of the kiln wall to reflect the heat from the kiln.
Secondly, as shown in Figure 4, probe bricks are set on the kiln wall to cooperate with the kiln car lining to form a curved seal structure; at the same time, a sand sealing groove is set under the kiln wall to cooperate with the sealing plate of the kiln car for sand sealing. The tortuous seal and sand seal structure of the kiln wall and the kiln car can effectively prevent the penetration of cold air under the kiln car and enhance the sealing performance of the tunnel kiln. At the same time, during the production process, the sand sealing tank must ensure that there is enough sand to prevent the hot air above the kiln car from entering under the kiln car and causing damage to the bearings of the kiln car. Reasonable kiln wall insulation structure and effective kiln wall sealing measures will greatly reduce the energy consumption of the tunnel kiln, and at the same time reduce the investment cost.
3.1.1 Use lightweight materials to reduce heat storage loss
The heat taken away by the kiln body and the kiln car accounts for a large part of the total heat consumption of the kiln. Therefore, reducing the heat storage loss and heat dissipation loss of the kiln body has become an important measure for kiln energy saving. The use of lightweight, heat-insulating refractory materials as the lining and vehicle lining of the kiln not only makes the temperature in the kiln uniform up and down, but also saves fuel significantly due to the low accumulation and heat dissipation. Choose a good insulation material for the kiln car lining to prevent the heat in the kiln from passing through the kiln car lining to the bottom of the kiln car and causing damage to the lower wheel bearings of the kiln car.
3.2 Reasonable stacking of billets can enable better sintering of bricks and reduce energy consumption of tunnel kilns
The popular saying in the brick and tile industry "three-point firing, seven-point yard" fully illustrates the importance of the stacking process in the operation of the kiln. Especially in today's full internal combustion roasting, the stacking of the stacks should be more standardized. streamline.
The main principle of stacking the billets is dense and thin on the side and thin on the bottom, so that the reasonable and even distribution of the firing speed and temperature can be taken into account, and the coordination of processes such as heat energy can be appropriately saved. The density of the edge of the stack body can effectively increase the fire temperature there to compensate for the heat energy absorbed by the kiln wall and taken away by the gap between the edges. The dense upper part and the lower part thinner can strengthen the preheating effect of the lower part, ensure a certain speed of the primer fire, and reduce the time difference and temperature difference of the burning of the bricks. Enterprises with conditions have laid hole-shaped pad bricks on the kiln car to play the role of sparse yards at the lower part and further optimize the firing environment.
As shown in Figure 5, the gap between the stack body and the kiln wall should be between 8 cm and 10 cm, and the gap between the top of the kiln should be between 10 cm and 12 cm. When the gap between the top and the edge is too large, not only the energy consumption will increase, but also the roasting speed, that is, the fire speed of the bottom fire, the temperature difference between the top and bottom of the brick stack, and the inside and outside are also large, and the color of the product after the kiln appears to be old and tender. state. When the blank car and the blank car are discharged together, the distance between each car should be 12 cm. If the distance is too close, the stacks will easily collide with each other. If the distance is too close, the energy consumption will increase and the stacks will not be preheated during preheating. Uniform, and the temperature distribution in the firing zone is also quite different.
3.3 Choose a reasonable firing process
According to the characteristics of the bricks, the structure of the kiln and the type of fuel, a reasonable kiln operation procedure shall be formulated. When roasting in a tunnel kiln, pay attention to the changes in the three stages of drying, sintering, and cooling in different time zones, and resolutely avoid irregular production. If the temperature is not easy to control, it is easy to cause disorder in the kiln atmosphere, damage the internal structure of the tunnel kiln, affect product quality, and cause A lot of waste. For example, the yield and quality of products produced during the day and night are very different. The main reason is that the operators at night did not control and adjust the firing of the kiln well, which caused irregular production. This wastes production time, energy consumption and manpower, and also reduces the service life of the tunnel kiln.
Figure 5. Schematic diagram of stacking of tunnel kiln
3.4 Strengthen the waste heat recovery and utilization function of the tunnel kiln
The flue gas discharged from the preheating zone has a high temperature and a lot of heat. If it is directly discharged into the atmosphere, it will not only cause air pollution, but also cause a lot of waste. After processing the flue gas, we can use this part of the heat energy, which can be transported to the drying room by a fan to dry the green body to supplement the lack of residual heat in the cooling zone. The waste heat of the cooling zone accounts for about 30% to 35% of the total heat consumption of the kiln. Because this part of the heat is relatively clean, it is widely used. The waste heat of the cooling zone is mainly used to extract hot air to dry the green body. The excess waste heat can be installed in the cooling zone with a waste heat boiler for heating or bathing, and some manufacturers use it to generate electricity. This not only greatly improves the utilization rate of waste heat and saves a lot of energy, but also improves the adjustment of the kiln thermal system by means of waste heat utilization. The waste heat from the kiln bottom ventilation duct and the abdominal cavity of the kiln roof can also be conveyed to the drying room by a fan to dry the green body.
There are many ways to save energy in tunnel kilns. If we want to fundamentally solve the problem of high energy consumption in tunnel kilns in my country's sintered brick production line, we must take a comprehensive energy-saving approach. When designing and constructing new tunnel kilns or transforming old tunnel kilns with energy-saving technologies, enterprises can take the above-mentioned comprehensive energy-saving measures and use various comprehensive energy-saving technologies as much as possible. Only in this way can the energy consumption level of the tunnel kiln be greatly reduced, and the comprehensive energy consumption per unit of product firing can reach the energy-saving level of foreign advanced kilns. This has positive significance for reducing the production cost of the enterprise, improving the economic efficiency of the enterprise, and reducing energy consumption.