Bauxite, also known as bauxite or bauxite, is mainly composed of alumina (Al2O3), which is hydrated alumina containing impurities and is an earthy mineral. White or off-white, brownish-yellow or light red due to iron content. Density 3.9-4g/cm3, hardness 1-3, opaque and brittle. Extremely difficult to melt. Insoluble in water, soluble in sulfuric acid and sodium hydroxide solution. It is mainly used for aluminum smelting and refractory materials.
The bauxite calcination process is a complex process in which raw bauxite is calcined at high temperature (1200-1700°C) and called clinker. The material enters the kiln for calcination from the kiln tail (the higher end of the cylinder), and due to the inclination and slow rotation of the cylinder, the material rolls in the circumferential direction and moves in the axial direction (from the higher end to the lower end) , to continue to complete the process, the raw clinker enters the cooler through the kiln hood for cooling. As the calcination temperature increases and the holding time prolongs, the aluminum content increases and the grade increases accordingly.
Calcination process: raw materials entering the factory → warehouse → crushing → grinding → filter press → mud refining → extrusion molding → drying → calcining → crushing → finished products. Due to the instability of its raw material composition, the clinker obtained by this traditional calcined clinker production process is not high in quality, and the product quality is unstable. In order to obtain high-quality products, a new homogenized material calcined process is proposed. : Raw materials enter the factory→storage→crushing→grinding→desiliconization→wet homogenization→press filtration→sliming→extrusion molding→drying→calcination→crushing→finished products.
Calcination process specific steps:
1. Crushing system
The bauxite entering the factory has a block size of about 300~500mm and a moisture content of about 8%. After entering the factory, it is stacked in the shed. The storage capacity is generally about one month. The forklift shovels it into the silo, and feeds it into the jaw crusher evenly and continuously through the apron feeder. After crushing, the particle size becomes 50~80mm, and then it is transported to the impact crusher through the belt conveyor, and the particle size is less than 20mm. After crushing, it is stored in the buffer silo.
2. Bauxite drying system
The crushed bauxite in the buffer silo enters the round silo on the top of the fluidized furnace through the belt conveyor and hoist, and a weighing belt feeder is installed under the silo to make the crushed bauxite evenly enter the dryer. After drying, it is sent to the batching warehouse, and it can also be sent to the stacking shed. The storage time is generally about 5 days. The fluidized fluidized furnace produces hot flue gas at 800-900°C to dry materials, and uses low-volatile coal as fuel. The crushed coal particles are 5~8mm, and are fed into the fluidized furnace furnace by the disc feeder, and the automatic temperature control system is used to control the feeding speed of the disc feeder to stabilize the combustion temperature of the fluidized furnace. The bag filter is used to purify the waste gas exiting the dryer to achieve dust discharge up to standard.
3. Batching station
Bauxite and additives are used for batching. All kinds of materials are transported to the batching warehouse. A speed-regulating belt weighing feeder is installed under the warehouse, and the automatic proportioning of materials is realized by the computer batching system. The proportioned materials enter the grinding system through the belt conveyor.
4. Grinding system
The grinding system adopts a closed-circuit system to produce raw meal powder with a fineness of more than 500 mesh. The mill adopts three warehouse tube mill. O-sepa type * eddy current powder separator is selected as the powder separator, and the fineness of the product can be easily adjusted by changing the speed of the powder separator. The selected finished raw meal powder is collected by a high-concentration air box pulse bag filter and sent to the raw meal round storage.
5. Granulation system
The granulator has the characteristics of fast ball forming, high efficiency, good roundness and clean production. After the raw meal is unloaded from the raw meal round warehouse, it is transported to the silo on the top of the new pellet mill by a screw conveyor and an elevator, and a screw weighing feeder is used under the silo to feed the raw meal into the pellet mill. The granulation water is measured and put into the granulator. The ratio of raw meal and water can be adjusted. The raw meal and water in the granulator form raw meal pellets under the action of the high-speed rotating stirring rod and the low-speed rotating inner cylinder in the machine. After a certain period of time, the granulation is finished, and the raw meal pellets are discharged from the lower discharge pipe and fall onto the belt feeder. The raw meal pellets are transported to the dryer at the end of the kiln.
6. Kiln tail dryer system
The water content of the newly made pellets is about 15%. Using the waste heat of the exhaust gas at the kiln tail, the moisture of the pellets can be reduced to about 8% in the kiln tail dryer, and then put into the kiln for calcination. The kiln tail dryer adopts counter-flow type. The hot air end of the dryer is additionally equipped with a burner to provide hot air for the dryer when the heat of the exhaust gas at the kiln tail is insufficient. The temperature of the exhaust gas at the kiln tail used by the dryer is about 500°C. After being used by the dryer, the temperature drops to about 150°C, which is suitable for the working condition of the bag filter at the end of the kiln. The raw material pellets out of the dryer are stored in the intermediate warehouse for use in the rotary kiln.
7. Rotary kiln system
The dried raw meal pellets are unloaded from the intermediate bin, and lifted to the kiln tail by the elevator, and the raw meal pellets are divided into qualified and unqualified by the vibrating screen. Qualified raw meal pellets enter the rotary kiln for calcination, and unqualified raw meal pellets return to the grinding system. In the rotary kiln, the raw material particles gradually move towards the kiln head with the rotation of the rotary kiln, and are calcined into petroleum proppant ceramsite sand at a temperature of 1400°C~1600°C in the firing zone. The ceramsite sand enters the single cylinder cooler for cooling, and the secondary air of the cooler enters the rotary kiln.
8. Kiln tail dust collection system
The bag dust collector is used to purify the exhaust gas at the kiln tail (including the exhaust gas of the kiln tail dryer). A humidification tower is also installed at the end of the rotary kiln to cool down the exhaust gas at the kiln end, so that the temperature of the exhaust gas can be reduced to the required temperature of the bag filter. The emission concentration of the bag filter can reach below 30mg/Nm3, achieving standard emission and clean production.
9. Finished system
The bauxite material exiting the cooling machine is lifted to the vibrating screen, divided into different particle sizes according to the standard requirements, and enters different finished product bins.
