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The zinc oxide production process using a rotary kiln is an important method for manufacturing zinc oxide today. First, the zinc feedstock and coking coal are crushed into particles smaller than 40 mesh. The zinc feedstock and coking coal are then mixed in a ratio of 1:0.30–0.35 to form a mixture. This mixture is subsequently processed into particles with an effective diameter of 8–15 millimeters, before being fed into the rotary kiln for processing. When used in the smelting of zinc oxide from zinc oxide ores with a zinc content of 15% to 25% or from zinc-containing industrial slag, it can significantly reduce the use of coke or coal ； Smelting offers the advantages of high-quality products, improved productivity, and low nodulation. The main components of the rotary kiln structure include the following: 1. The kiln shell, which constitutes the core of the rotary kiln. The steel plates making up the kiln shell are approximately 40 mm thick; near the ring-shaped support structure, where the load is greater, these steel plates are thicker. The interior of the kiln shell is lined with a layer of refractory bricks about 200 mm thick. During operation, due to the high temperatures and the loads it has to bear, the kiln shell deforms into an oval shape; this exerts pressure on the kiln bricks, affecting their lifespan. A section about one meter long at the end of the kiln is conical in shape, allowing the material coming from the feed chamber of the preheater to enter the kiln more smoothly. 2. The tire ring, support rollers, bearings – all of these are used to bear the weight of the kiln. The ring is fitted over the kiln shell; it is not fixed to the kiln shell. A steel plate is placed between the kiln shell and the ring, thereby maintaining a certain gap between them – this gap should neither be too large nor too small. If the gap is too small, the expansion of the kiln shell is restricted by the ring, causing the kiln bricks to break easily. If the gap is too large, the relative movement and friction between the kiln shell and the ring cause more severe elliptical deformation of the kiln shell. Lubricant is usually applied between the two. We can estimate the degree of elliptical deformation of the kiln shell by observing the relative movement between the kiln shell and the ring. There is a difference in thermal conductivity between the kiln shell and the core ring; therefore, an external fan is necessary to help dissipate heat from the kiln shell and thus reduce the temperature difference between the two. Otherwise, the expansion of the kiln shell will be restricted by the ring. When starting up the kiln, the temperature rise rate of the kiln shell is higher than that of the refractory ring; therefore, kiln operators must control the temperature rise rate of the rotary kiln at 50°C/h, which helps to protect the kiln bricks. Typically, the idler wheels are about 50–100 mm wider than the wheel bands. The roller bearings are made of babbitt alloy; if these bearings lose lubrication, they can be damaged due to excessive heat. Cooling water is circulated for cooling at the bearings. To reduce the thermal radiation from the kiln shell to the tire ring, which causes the bearing wheels to become too hot, insulation panels are installed between them to minimize heat radiation. A rotary kiln usually has 2 to 3 sets of idler wheels. 3. Thrust rollers: Thrust rollers serve as limit switches that prevent the rotary kiln from moving too far downward or upward. Since the support roller needs to be slightly wider than the kiln body, this allows the idler rollers and the wheel band to move up and down, ensuring even wear. Thrust rollers are provided on the end face of the tire ring. The thrust roller merely serves to provide resistance; it does not have its own power. The upward and downward movement of the kiln body is achieved through the misalignment of the rollers; by setting the supporting rollers at an angle relative to the kiln’s center line, these rollers exert an upward force on the kiln body, causing the kiln shell to move upward. Sometimes, sprinkling some raw material powder or cleaning the idler wheels to increase their friction coefficient can also cause the kiln body to rise. When the kiln body is being lowered, it is sufficient to spread graphite powder between the idler wheels and the wheel bands in order to reduce the friction between them. When the rotary kiln reaches the Y1 switch, the hydraulic system starts to operate; it operates for 1 minute and then stops for 4 minutes, repeating this cycle of 1 minute of operation followed by 4 minutes of stoppage until the kiln shell reaches the Y5 position. At this point, the kiln body begins to consume energy; the hydraulic system releases pressure for 2 minutes, then stops for 4 minutes, before repeating the process. It continues feeding until the kiln body reaches position Y1. It is fine to keep repeating the above process. When the hydraulic system stops operating, the internal pressure remains unchanged. For more information on zinc oxide using the indirect method, please click » The hydraulic system also has three limit switches. When feeding begins, if the Y1 switch fails, the kiln body will come into contact with the second Y switch, and the system will issue an alarm (at this point the kiln body has exceeded the feeding range by 30 mm). If it then comes into contact with the third switch, the system will shut down (at this point the excess over the feeding range is 50 mm). When the rotary kiln moves forward, if the first switch fails, the system will issue an alarm when the rotary kiln reaches the second switch; however, the machine will not shut down, as the thrust rollers limit the maximum distance the kiln shell can move forward.