A rotary kiln, commonly known as a rotating calcination kiln, belongs to the category of building material equipment. Based on the materials processed, rotary kilns can be classified into cement kilns, metallurgical and chemical kilns, and lime kilns. Cement kilns are primarily used for calcining cement clinker and are divided into dry-process and wet-process cement kilns. Metallurgical and chemical kilns are mainly used in the metallurgical industry for magnetizing roasting of lean iron ore in steel plants, oxidizing roasting of chromium and nickel iron ores, calcining high-alumina bauxite in refractory material plants, and calcining clinker and aluminum hydroxide in aluminum plants. They are also used in chemical plants for roasting chromite sand and powder. Lime kilns (active lime kilns) are used to calcine active lime and lightly burned dolomite for steel plants and ferroalloy plants.
Industries of Application:
Rotary kilns are widely used in many production industries, including building materials, metallurgy, chemicals, and environmental protection. In the early stages, rotary kilns were most extensively applied in the cement industry. Currently, the rotary kiln series products manufactured by Henan Zhengzhou Mining Machinery Co., Ltd. are widely used in the following industries:
Functions:
1. Its technical performance and operational conditions largely determine the quality, output, and cost of a company's products. The folk saying, "As long as the kiln rotates, there will be thousands and thousands," vividly describes the importance of rotary kilns in production.
2. In the building materials industry, rotary kilns are used not only for calcining cement clinker but also for calcining clay, limestone, and drying slag. In refractory material production, rotary kilns are used to calcine raw materials to stabilize their dimensions and increase strength before further processing. They are also used in the production of lightweight aggregate ceramsite.
3. In the mineral processing industry, rotary kilns are used for magnetizing roasting of lean iron ore, transforming the ore's weak magnetism into strong magnetism to facilitate magnetic separation.
4. In the chemical industry, rotary kilns are used to produce soda ash, calcine phosphate fertilizers, and barium sulfide. In the 1960s, LapPle and others in the United States invented a new process for producing phosphoric acid using rotary kilns. This method offers advantages such as low energy consumption, reduced electricity usage, no need for sulfuric acid, and the ability to utilize medium and low-grade phosphate ores.
5. The entire cement production process can be summarized as "two grindings and one burning," where the "one burning" refers to the process of calcining the finely ground raw materials into clinker under high temperatures in a rotary kiln. Therefore, the rotary kiln is the core equipment in cement production, often referred to as the "heart" of a cement plant.
6. In environmental protection, developed countries have been using cement kilns to incinerate hazardous waste and garbage for over 20 years. This not only reduces waste volume and harm but also utilizes waste as fuel, saving coal and achieving waste resource utilization.
7. In the metallurgical industry and emerging industries, rotary kilns are widely used in the processing of raw materials and tailings for metals such as lithium, magnesium, and aluminum.
Classification:
Rotary kilns can be classified based on their shape into variable-diameter rotary kilns and straight-diameter rotary kilns. Based on their applications, they can be classified into cement rotary kilns, ceramsite sand rotary kilns, kaolin rotary kilns, and lime rotary kilns. Based on energy sources, they can be classified into gas-fired rotary kilns, coal-fired rotary kilns, and mixed-fuel rotary kilns.
1. **Variable-Diameter Rotary Kiln**
A rotary kiln with varying diameters at the front and rear. Typically, the diameter changes by about 30 cm. Compared to traditional straight-diameter rotary kilns, variable-diameter kilns offer energy-saving and high-yield advantages. However, they are more difficult to manufacture and require stricter equipment standards.
2. **Straight-Diameter Rotary Kiln**
A rotary kiln with the same diameter at the front and rear. This is the most common type of rotary kiln, invented by German engineer Dietz in 1883. After over a century of evolution, rotary kilns have become versatile equipment. They offer better performance and higher yields compared to traditional vertical kilns. Although easier to manufacture, they are more energy-intensive than variable-diameter rotary kilns.
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Main Structure:
1. **Kiln Head**
The kiln head is the discharge section of the rotary kiln, with a diameter larger than that of the kiln body. It is sealed with stainless steel fish-scale plates and mainly consists of inspection ports, coal injection nozzles, carts, and observation holes.
2. **Kiln Body**
The kiln body is the main part of the rotary kiln, typically 30–150 meters long and cylindrical in shape, with 3–5 riding rings. The cylinder is usually processed into 3–10 segments in the factory and transported by large trucks to the site for welding. The riding rings, also known as tire rings, are cast from molten steel. The section of the kiln body with riding rings has slightly thicker steel plates due to the load-bearing requirements. The supporting rollers, which are part of the kiln body, correspond to the riding rings and are connected to the foundation, serving as the main load-bearing pillars of the rotary kiln. A set of rollers typically consists of two support rollers and two thrust rollers. Refractory bricks are laid inside the rotary kiln during normal operation.
3. **Kiln Tail**
The kiln tail is an essential part of the rotary kiln, resembling a cover at the feed end. Its main functions are feeding and sealing.
4. **Rotary Kiln Support Frame**
- The support frame makes the rotary kiln more robust, ensuring stable operation without shaking.
- It fixes the rotary kiln equipment, preventing deformation during operation. Improper operation can cause deformation, and the support frame helps avoid this.
- The support frame facilitates the lifting and transportation of the rotary kiln equipment.
5. **Preheater Tower**
Also known as the preheater, it is a vertical structure that preheats materials using the waste heat from the exhaust gas of the rotary kiln before the materials enter the kiln. The principle involves passing the exhaust gas from the kiln tail through the preheater tower filled with raw materials to achieve preheating. The preheater effectively reduces energy consumption and improves the quality of the final product.
6. **Cooler**
The cooler is the opposite of the preheater and is used to rapidly cool the materials after they are calcined in the rotary kiln. It resembles a smaller rotary kiln but with a smaller diameter and shorter length. Unlike the kiln, it does not require refractory bricks and is equipped with lifting plates inside. Its main function is to quickly cool the finished product.
7. **Burner**
The burner is the heat source of the rotary kiln and a key piece of equipment for providing the heat needed to calcine the raw materials. Fuel is injected into the kiln through the nozzle and ignited. Common fuels include rice husks, natural gas, coal oil, and pulverized coal.
