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What are the special features of the annular mobile tunnel kiln? Better to know these before choosing a mobile tunnel kiln for your brick factory

1. The place to build the mobile kiln must be square
The kiln body of the mobile kiln moves along a circular track formed by two concentric circles with different diameters. Not only does the kiln building site need to be large, but it must also be square.
For example: a mobile kiln with an inner width of 9.6m and an outer rail diameter of 120m. Including outer ring roads and drainage ditches, it requires at least a 138m*138m site, which is 19044m2; another example is a mobile kiln with an inner width of 12.4m and an outer rail diameter of 120m. The track diameter is 128m, which requires at least a 145*145m site, that is, 21025m2.

2. More suitable for frost-free warm area
The wet green bricks after molding need to be stored on the ring road outside the kiln for a period before entering the mobile kiln. In the warm area, the temperature is higher and there is no frost period, the green brick can slowly lose some moisture through natural drying outside the kiln. This not only saves the consumption of heat energy entering the drying section of the kiln, but also reduces drying cracks and collapse of the green body, which is beneficial to improve drying quality. However, in cold areas and severe cold areas with frost periods, the kiln might only be used for 5-7 months per year due to frost, and its annual effective trial period is very short.
However, in order to overcome this shortcoming, some mobile kiln manufacturers set up retaining walls around the kiln building.

3. Only applicable for once stack one stage baking technology
In mobile tunnel kiln, the green bricks are stacked directly on the bottom of kiln and be baked into red bricks once and all. In case that the drying sensitivity coefficient of the raw material is high, or the product is a block with high porosity, the secondary burning process should be used. At this time, the mobile kiln cannot be used.

4. Better use solid fuel
Because the kiln body needs to be moved frequently, if gas or liquid fuel is used, the pipeline layout is more complicated, so it is best to use solid fuel like coal or wood. Of course, China already has mature rotary tunnel kilns that use natural gas sintering to catering customer’s requirement.

5. On the premise of meeting the drying and roasting system, do not lengthen the kiln body casually
Because lengthening the kiln body increases the weight of the kiln body, it also increases the length of the sand blast plate inserted into the sand sealing groove, thus increasing the resistance between the sand blast plate and the sand in the sand sealing groove, fatherly increasing the movement resistance of the kiln body and consuming more energy.

6. Track installation requires high accuracy and stability
Because the diameters of the concentric circles of the inner and outer rails are very large, the rails are required to be installed with high precision and good stability to avoid causing some wheels to hang in the air and derail, which would increase the burden on the other wheels and increase local resistance.

7. Kiln walking wheels can only be casting steel wheels
Due to the heavy load on the wheels that the kiln body travels on, whether it is the driving wheel or the driven wheel, it is not suitable to use steel wheels processed by machine tools to avoid deformation after being stressed. It is also not suitable to use cast iron wheels. Cast iron wheels have poor flexural strength and are not wear-resistant. It could only be cast steel wheels.

8. The insulation material should be of high purity and the installation should be reliable.
In order to reduce the weight and power consumption when the kiln is moved, the inner roof and inner wall materials of the kiln generally use aluminum silicate fiber modules. It is hoped that the impurity content of the material will be less (as much as possible to increase the purity), otherwise sulfur-containing gas will easily enter the module pores and react chemically with these impurities, causing the fiber material to pulverize and fall off. In addition, because the fibers are very thin, they will also wear out and fall off under the long-term erosion of high-speed dust-containing gas. Therefore, some factories need to replace the vulnerable parts of the kiln every five years or so. The installation of the inner wall module must be fixed firmly to prevent bulging during use, which may cause the stack to collapse and damage the inner wall of the kiln when the kiln body is moved.

9. The pressure of the extruder should be high
Because the billet distribution platform is moved accordingly to the kiln, the green bricks are clamped up and down for 3 times by robots or manipulators. So the wet blanks should have high mechanical strength.

10. Sand duct height and sand size requirements
The sand air ducts inside and outside the mobile kiln are very long. In order to prevent erroneous air from leaking into the kiln body, the sand air ducts should be filled with enough sand. The height of the sand surface should not be less than 50-60mm. The ideal particle size of the sand is 5- 7mm accounts for 30%, and the remaining 70% is dust-free fine particles.

11. If conditions permit, try to make the circumference of the ring as long as possible
Generally, the wet green bricks need to be stationary for a period of time on the external track of the kiln. By naturally and slowly evaporating part of the water, it can not only reduce the heat energy consumption in the kiln, but also because the moisture in the green body has moved closer to the critical moisture before entering the kiln. It can reduce the occurrence of wet collapse and drying cracks of the green body in the kiln. Therefore, if conditions permit, the circumference of the annular track should be made as long as possible. This can also make the static stop time of the wet green body longer.

12. Circular Road
The circular road of the mobile kiln should be about 0.15m higher than the road to prevent rainwater from flowing into the ring road of the kiln, destroying the established thermal system and increasing heat energy consumption. Reinforcement measures should be taken at the edge of the ring road, or steel plates should be temporarily placed as entrance and exit the driveway to protect the edge of the roundabout from being crushed by transport vehicles.

13. Flue gas desulfurization device
Since the kiln body of the mobile kiln needs to be moved frequently, it brings certain difficulties to the flue gas desulfurization device. Currently, the most commonly used method is to place the desulfurization tower near the center point and build an annular main flue inside the annular channel. There are several interfaces with gate valves on the main flue. After the kiln is moved, the exhaust gas will enter the annular main flue and then enter the desulfurization tower. The disadvantages of this approach are: 1) Since the flue fed into the desulfurization tower is long and has many turns, it generates greater resistance; 2) There are many possible air leakage points. Some brick factories in China place the desulfurization tower on the top of the mobile kiln, which moves with the kiln body, and the desulfurization effect is better.