New development in alumina production technology
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With the mastery of high pressure technology, the temperature of the cooker can be greatly improved, and the dissolution of bauxite can be carried out at a higher temperature. In 1934, Austria entered Hiller and found that the temperature of the gibbsite-type bauxite was increased from 160 ° C to 190 ° C, and the rate of dissolution was greatly accelerated. The temperature of the diaspore bauxite is increased from 230 ° C to 290 ° C, the dissolution rate is greatly accelerated, and the dissolution process can be carried out in a tubular reactor like a coil. However, the high pressure pump is severely worn. In 1954, Professor B. Lanyi of Hungary connected the barrel as a reactor and pump, and dissolved at 330 ° C. The dissolution time was only 1% of the autoclave. The dissolution rate of alumina was very high, and the red mud sedimentation performance was very good. After years of experimental research, the Hungarians established the first set of pipelined dissolution devices at the Almasfuzito plant in 1965. Subsequently, in 1973, a flow rate of 60 m 3 /h and a dissolution temperature of 260 ° C were established to treat the bauxite-type bauxite, and the annual output of alumina 50,000 t industrial plant. The results of the operation provided sufficient data for industrialization. In 1981, the plant dismantled the autoclave dissolved at 210 ° C and established a new pipeline dissolution device. It was put into operation in 1982 and has an annual output of 100,000 tons of alumina. In 1987, a molten salt heating pipeline dissolving device was established, and the dissolution temperature reached 300 °C.
The Soviet Union conducted a high temperature dissolution test of diaspore bauxite from 1945 to 1947. At 315 ° C, the theoretical dissolution rate is reached in a few minutes when Na 2 O k , and the solubility of SiO 2 is very low, and the red mud sedimentation performance is good. Tubular reactors All-Union Institute of aluminum magnesium autoclave test plant, various forms (vertical, horizontal, single-tube, multi-tube), and the original slurry preparation system, the temperature can be 320 ℃, different pressures of 20MPa Testing of processes and equipment. The dissolution test of diaspore-type bauxite in Greece, Northern Ural, Yugoslavia and other places was carried out. However, its pipelined dissolution technology was only used in the 1980s, and the first pipelined dissolution unit was built in Hukolaev. Preheated with a ten-stage casing, the inner diameter of the casing is 159mm, the outer diameter is 325mm, one is 75m, and the first one is six. The tubular reactor has a diameter of 159 mm and each of 75 m has a total of 11 pieces. 4 organic heaters. The high pressure pump is a piston pump. One pipe transports the lye, and the other pipe transports the slurry and then merges.
After the Second World War, German Union Aluminum Corporation wanted to use a tubular reactor to treat a diaspore bauxite. In 1960, research began on pipeline dissolving technology. In 1966, a test device with a flow rate of 3 m 3 /h and a dissolution temperature of 320 ° C was built at the Nab plant. The process and equipment problems were systematically studied, and the basic data of industrial design was provided. In 1967, the world's first pipelined dissolution unit was established at the Nab plant with a slurry flow rate of 80 m 3 /h. In 1973, the Stade plant used four sets of pipelined dissolution units with a total capacity of 600 kt/a and a plant operating rate of 90%. The actual production capacity is 690 kt / a, the energy consumption per ton of alumina is 8.15 GJ, and the power consumption is 265 kW·h. The plant also carried out the operation of passing pure oxygen into the oxidizing circulating liquid in the tubular reactor, and the effect was good. In 1980, the most advanced RA-6 pipelined dissolution unit was built at the Lippe plant. Germany's capacity to produce alumina using pipelined dissolution technology amounts to 1140 kt/a.
In the United States in the 1980s, a pipelined dissolution apparatus was also used to treat feldspar extraction of alumina. The tubular reactor was connected vertically with a flow rate of 0.8 m 3 /h and a reaction time of 30 min. At 240 ° C, 90% of the alumina in the anorthite has been dissolved. A pilot plant with an annual output of 500,000 tons of alumina was designed. Compared with the Bayer process, which is usually made of bauxite, the direct production cost is similar, but the investment is much larger.
In 1976, France invested in the first pipelined dissolution plant at the Salinders plant to treat boehmite bauxite. The dissolution temperature is 240 ° C, the slurry flow rate is 180 m 3 /h, the mass concentration of Na 2 Ok is 160-220 g / L, and the caustic ratio of the eluate is about 1.44. 90% of the silicon was removed at 150 ° C for 15 to 30 minutes, and then preheated and heated. The heating tube has a length of 2000 m, an outer diameter of 245 mm and an inner diameter of 196 mm. Heat transfer coefficient: 1 kW / (m 3 · ° C) before cleaning, 2 kW / (m 3 · ° C) after cleaning. Pechiney Aluminium Company has created a single-tube preheating (150T °C)-autoclave dissolution technology, which was applied to the treatment of diaspore-type soil mines by Shanxi Aluminum Plant and Pingguo Aluminum Company.
In 1968, China built the first set of pipeline dissolution equipment in Guizhou Aluminum Plant. The slurry flow rate was 1~1.8m 3 /h, the pressure was 4MPa, and the dissolution temperature was 240°C. The slurry enters the eight-stage single-tube preheating to 160 ° C, then is heated by molten salt at 240 ° C, and enters 11 series of dissolvers (Φ 325 mm × 15 mm) for complete dissolution, and is discharged through eight stages of self-evaporation. The study failed to continue for various reasons. 1975 to 1982, Zhengzhou Light Metal Research studied Bayer enhanced dissolution. The slurry flow rate is 0.5 m 3 /h, the pressure is 15 MPa, and the dissolution temperature is 320 °C. The test results show that it is necessary to maintain a certain long dissolution time for the insoluble bauxite bauxite. Therefore, the use of a pipe-stop tank is the most suitable dissolution device. In 1983, the mine was awarded a flow-discharging device with a flow rate of 4 to 6 m 3 /h. In 1988, the most difficult to dissolve Guangxi Pingguo mine in China was tested and achieved good results.