Metal sulphide ores (pyrite, yellow copper ore, galena and sphalerite, etc.) is an important industrial raw material and metallurgical industry sulfate concentrate (sulfur concentrate, copper concentrate, a nickel fine after flotation ore, molybdenum concentrate and zinc concentrate, etc.) need to be dried before entering the subsequent firing and melting equipment. In China, with the construction of large iron ore roasting sulfur and non-ferrous smelting apparatus, the concentrate drying urgent need to improve the processing capacity of a single apparatus, and the requirements for implementation of the depth dried concentrate. 1 Drying characteristics and drying requirements of concentrate The wet copper sulphide concentrate is generally taupe and has a particle size of about 200 mesh (74 m). Due to the high metal content, the bulk density is large and the wear resistance of the equipment is strong. Concentrates produced by flotation are generally 10% to 15%. Concentrates are loose; when higher, concentrates are more viscous. In addition, sulfides in concentrates are susceptible to acid corrosion during heating. The water content of the incoming concentrate has a great influence on the smelting operation. The general smelting process requires that the concentrates in the furnace have lower requirements, such as flash furnace smelting requires less than 0.3% of the copper concentrate. If the water content is too high, the concentrate will have poor fluidity and block the hopper L2], which is also not conducive to the smelting of non-ferrous metals. In addition, the smelting operation also has certain requirements on the particle size of the concentrate after drying. 2 drying methods and equipment The drying of metal sulfide concentrates is generally divided into direct drying and indirect drying. 2.1 Direct drying Direct drying of concentrates refers to the drying process in which the drying medium comes into contact with the concentrate during the drying process, such as cylinder drying and air drying. Direct drying generally uses hot air or hot flue gas as the heating medium, and the first or second stage is dried according to the process requirements. In the early days, smelters generally used cylinder drying or airflow drying, in which airflow drying was divided into two-stage (squirrel cage disperser + drying tube) and three-stage (short cylinder dryer + squirrel cage disperser + drying tube) ). Although the two methods have large processing capacity and uniform product size, they all have the disadvantages of low thermal efficiency, large floor space and complicated process. In addition, due to the vertical conveying of materials, the rotary kiln has high power consumption; the squirrel cage disperser is easy to wear due to high-speed rotation (250-300 r/rain), and the maintenance workload is large, generally 2-3 weeks. That is, it needs to be repaired once -3]. In view of the above reasons, some manufacturers have begun to use rotary flash dryers to dry certain concentrates (such as molybdenum concentrate) in recent years. However, the rotary flash dryer generally uses high temperature gas as a drying medium, which is easy to form SO: causing corrosion to the equipment, and the lower agitator has a high rotation speed and is prone to wear. In addition, the rotary flash dryer also has the problems of low thermal efficiency and low processing capacity. It is particularly important to note that the direct drying method generally has problems with exhaust gas treatment. The exhaust gas flow is large, the dust content is high, and improper treatment may cause environmental pollution. 2.2 Indirect drying Indirect drying of concentrate refers to the drying process in which the drying medium does not come into contact with the concentrate during the drying process. The equipment includes a multi-layer steam coil dryer, a tray dryer, a paddle dryer and a steam tube rotary dryer. . Indirect dryers generally use saturated steam as the heating medium, and their thermal efficiency is much higher than direct drying, and the amount of exhaust gas is small and the dust content is low, so the process is relatively simple. The multi-layer steam coil dryer is the first indirect dryer used to dry concentrates. It consists of a multi-coil rotor and a fixed casing, and the concentrate advances as the rotor rotates. Due to the strong wear of the concentrate, coil damage, guard plate and scraper wear are prone to occur, and maintenance work is very frequent. In general, the dryer is shut down once a week. The disc dryer has been used to dry sulphur concentrate, but there have been many production failures: the material on the upper several layers of the drying tray is crusted, the material is easily dropped from the outer edge of the drying tray directly to the chassis and short-circuited, and the eucalyptus leaves are easily worn. Causes the mast to break. These problems directly affect the drying effect and the normal operation of the drying equipment. Finally, the manufacturer is forced to pre-dry the material and then send it to the tray dryer for drying, which not only lengthens the process, but also increases the investment. In addition, its processing power is also small. The paddle dryer is particularly suitable for drying viscous and paste materials. According to the experimental research, the drying effect of the paddle dryer on the concentrate is very good. Due to the self-cleaning effect of the blade, the material is basically not bonded, the flow state is good, and the moisture content and particle size of the exported product can meet the industrial requirements. However, due to the nature of the material, the blades are prone to wear and the power consumption is large, which is not suitable for large installations. Steam tube rotary dryer has gradually become the first choice for concentrate drying due to its energy saving and environmental protection, single processing capacity and low power consumption. The following focuses on the steam tube rotary dryer. 3 steam tube rotary dryer Since 1992, Lanzhou Ruide Drying Technology Co., Ltd. has started the localization of high-density polyethylene (HDPE) equipment steam tube rotary dryer. After continuous improvement and optimization, it has formed its own patented technology. The company has completed the localization of large-scale HDPE and PTA (pure phthalate) steam tube rotary dryers, and successfully applied this technology to the drying of wet concentrates in the metallurgical industry. 3.1 Structure and working principle As mentioned above, the steam tube rotary dryer is an indirect heating type rotary dryer whose structure is shown in Fig. 1. The steam tube rotary dryer is mainly composed of a simplified body, a steam pipe, a feed screw, a feed end seal, a discharge end seal, a steam system, a transmission system and a support member. The steam heat exchange tubes are arranged in a circle in a concentric manner and arranged in the cylinder body throughout the dryer. The heat required for drying is provided by the steam passing into the heat exchange tubes. In addition, a small amount of carrier gas (air) is introduced into the body, and the water evaporated from the drying process is carried outside the cylinder. 3 2 experimental research Tianhua Chemical Machinery and Automation Research and Design Institute used a steam tube rotary dryer to conduct detailed experimental research on the drying of copper concentrate. The dryer is 00 mm X 3 500 mm and uses saturated steam as the heating medium. The purpose of the test is to understand the flow and bonding of materials with different water contents and the particle size distribution of the materials after drying. The test uses five kinds of raw materials provided by the manufacturer at home and abroad, and its W(H 0) is 5% to 6%. Due to the low water content, there is no sticking wall in the drying process, the fluidity of the material is very good, the product can meet the water content requirement of the flash furnace smelting, but the particle size distribution of the copper concentrate before and after drying does not change much. The copper concentrate drying curve and drying rate curve are shown in Figures 2 and 3, respectively. It can be seen from Fig. 2 that the residence time is about 30 min, so that the product can reach 0.3% or less. From the experimental research, the steam tube rotary dryer has the advantages of large processing capacity and low power consumption, and the particle size requirement can be satisfied by appropriately controlling the moisture content of the feed. If the product is pneumatically transported after drying, the loose particles formed during drying can be completely broken up without adversely affecting subsequent equipment. 3.3 drying process The steam tube rotary dryer uses medium and low pressure saturated steam as the heating medium, and the drying temperature is low, so it does not cause decomposition and oxidation of sulfide in the concentrate. The process of the copper concentrate rotary dryer is as follows: the wet concentrate enters the interior of the dryer through the screw feeder, the dryer cylinder has a certain inclination, and the material rolls forward and moves along with the rotation of the cylinder, while the side and the edge The steam pipe arranged around the simplified body is heat-exchanged and dried, and the dried concentrate is discharged through the discharge bin; a small amount of carrier gas enters the interior of the dryer from the discharge end, and the moisture evaporated by the drying process is discharged from the feeding end; After the dust collector is separated and dusted, the exhaust gas is evacuated, and the collected dust is returned to the feed spiral. The process has the advantages of simple process, low equipment quantity, low investment, high thermal efficiency, small dust and harmful gas emission, easy operation and maintenance management. 3.4 Industrial applications The copper concentrate rotary steam dryer developed by Jinhua Chemical Machinery and Automation Research and Design Institute for Jinchuan Company has a specification of .2m X 17.5 m and a processing capacity of over 100 t/h. The drying equipment is applied to the company's 250 kt/a copper synthesis furnace project. It is the largest steam tube rotary dryer developed in China and the first large-scale domestic concentrate drying equipment in the metallurgical industry. It uses the medium and low pressure steam of the waste heat boiler as the heat source, and the energy saving effect is very obvious. Since the start of the car in September 2005, the dryer has been in good condition. Its successful application has saved the country nearly 40 million yuan in foreign exchange. In August 2006, Tongling Nonferrous Metals (Group) Co., Ltd. successfully completed the 400 kt/a sulfuric acid project. This project is the first in China to use steam pipe rotary spray drying equipment to dry sulfur concentrate, equipment specifications of .4 m X 21 m, processing capacity of 65 t / h L1. Practice has proved that the steam tube rotary dryer is very suitable for large-scale processing and deep drying of concentrates, and has the advantages of environmental protection and energy saving, and is worth promoting.
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