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Metal sulphide concentrate drying characteristics and selection of
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In this paper, sulfide concentrate as an example to illustrate concentrate drying characteristics, drying equipment selection and industrial application.

Metal sulphide ore (pyrite, chalcopyrite, galena and sphalerite, etc.) is the sulfuric acid industry and metallurgical industry an important raw material, after the flotation concentrate (pyrite concentrate, copper concentrate, nickel concentrate , molybdenum and zinc concentrates, etc.) need to enter the follow-up dry roasting and smelting equipment. In China, with large-scale pyrite and non-ferrous metal smelting plant of the building, an urgent need to improve concentrate drying equipment, a single processing capabilities, and called for the implementation of the depth of dry concentrate.

A concentrate drying characteristics and drying requirements

Wet sulfide copper concentrate is generally grayish brown, particle size of about 200 mesh (74 m). Due to the higher metal content, bulk density greater wear and tear on equipment is stronger. Concentrates produced by flotation of its W (H2O) is usually 10% to 15%. When W (H2O) for about 10%, the ore is relatively loose; as w (H: O) higher, concentrate more sticky. In addition, the concentrates in the sulphides in the heating process could easily lead to acid corrosion.

The water content of concentrate into the furnace to the smelting operations have greatly affected. General requirements into the furnace smelting process concentrates W (H: O) 6% 1 8%, while others are calling for lower, such as flash smelting of copper concentrate requirements into the furnace W (H: O) less than 0.3% . Will cause excessive water content Concentrates poor mobility, plug plus hopper L2], is not conducive to non-ferrous metals smelting. In addition, the smelting operations on the particle size after drying concentrates have certain requirements.

Two drying methods and equipment

Metal sulphide concentrates drying normally takes the direct and indirect drying drying in two ways.

2.1 Direct Drying

The direct dry concentrate is dried in the drying process in the media come into contact with the concentrate drying processes, such as cylinder-drying and air drying. Direct drying generally use hot air or hot flue gas as a heating medium, according to the technical requirements of one or two dry. Early, smelters generally use the cylindrical dry or air dry, which was divided into two-stage air drying (Cage dispersed machine + drying tube) and the three-step (short cylinder drying machine + machine + drying tube cage broke up ). Both of these methods concentrate processing capacity while a larger particle size and uniform, but all there is low thermal efficiency, an area of large and complex process shortcomings.

In addition, the air drier due to the vertical transportation of materials, rotary power consumption is high; one of the squirrel cage broken up due to high-speed rotating machines (250-300 r / rain), the rotor easy to wear and tear, maintenance workload, generally 2-3 weeks that is required to repair welding a -3]. For these reasons, in recent years some manufacturers began to use spin flash dryer to dry some of concentrates (such as molybdenum concentrate). However, spin flash dryer generally use high-temperature gas as drying medium, easy to form SO:, caused by corrosion of equipment, and the lower part of a high speed mixer, prone to wear and tear. In addition, the spin flash dryer also exists a low thermal efficiency and processing power of small problems. Of particular note is the prevalence of the direct drying exhaust gas deal with problems. The exhaust flow of large dust content was high, environmental pollution caused by improper handling easily.

2.2 Indirect Drying

Concentrate indirect drying is the drying medium in the drying process does not come into contact with the concentrate drying process, its equipment has multi-layer coil steam dryer, tray dryer, paddle dryer and steam tube rotary dryer, etc. . Indirect dryers generally use saturated steam as the heating medium, the thermal efficiency is much higher than the direct dry, and the small amount of exhaust, dust content is low, and thus relatively simple process. Multi-Steam coil dryer used to dry and concentrate is the first indirect dryer. It consists of a multi-coil structure of the rotor and a fixed shell composition, concentrate with the rotation of the rotor to move forward. Concentrate is stronger because of wear and tear, high incidence of coil damage, protection board and scraper wear, repair work is very frequent. Under normal circumstances, dryers inspected once a week downtime. Tray dryer was used to dry sulfur fine sand, but there have been many product failures: the upper layers of dry material on the disc scarring, the material easy to fall directly from the dry plate in the end plate outer edge of the short-circuit, as well as rake leaves easy to wear and tear rod fracture caused by rake. These issues directly affect the drying effect and drying equipment, the normal operation of the last manufacturers are being forced on the material pre-drying and then be sent to disc dryer drying process is not only longer, but also investment. In addition, its processing power is also smaller. Paddle dryer is particularly suitable for drying and paste adhesive materials. Under the pilot study, paddle dryer works well on the dry concentrate, due to the blade self-cleaning effect, the material basically no bonding, mobility in good condition, and the export of moisture content and particle size can meet the industrial requirements . However, material properties, easy to wear and blade power consumption, large, does not apply to large-scale installations. Rotary steam tube dryer because of its energy-saving environmental protection, a single processing advantages of low power consumption, Japan has gradually become the preferred concentrate drying equipment. The following highlights the steam tube rotary dryer.

3 rotary steam tube dryer

Lanzhou Reid Drying Technology Co., Ltd. Since 1992, the high-density polyethylene (HDPE) plant steam tube rotary dryer localization of research, through continuous improvement and optimization, formed its own patented technology. The company has completed large-scale HDPE and PTA (terephthalic acid on the sperm) devices, rotary steam tube dryer localization, and the technology used in the metallurgical industry to successfully dry the wet concentrate.

3.1 Structure and working principle of

As mentioned above, the steam tube rotary dryer is an indirect heat rotary dryer, its structure shown in Figure 1. Rotary Steam Tube Dryer mainly by the Simplified, steam pipes, feed screw, feed-side sealing, discharging-side sealing, steam systems, powertrain solutions and support pieces so on. Steam heat exchange tube in concentric circles arranged in a number of ways ring, arranged in the cylinder body, throughout the dryer. The heat needed to dry by-pass into the heat exchange tubes within the steam to provide. In addition, the Simplified intercom into a small amount of carrier gas (air), the drying process will evaporate the moisture out of things to bring to the tube.

32 Experimental Study

Tianhua Chemical Machinery and Automation Research and Design Institute steam tube rotary dryer for drying of copper concentrate in detail studied. Dryer specification 00 mm X 3 500 mm, using saturated steam as the heating medium. The purpose of testing is to understand the different water content in the flow of materials, bonding, as well as dry materials, particle size distribution. Experiment with domestic and foreign manufacturers with a total of five kinds of raw materials, the W (H 0) 5% 1 6%. As the water content low, the drying process is not sticky wall phenomenon, the flow of materials is very good, the product can meet the flash smelting furnace of the water content requirements, but before and after the dry little change in particle size distribution of copper concentrate. Copper concentrate drying curve and drying rate curves are shown in Figure 2 and Figure 3. Can be seen from Figure 2, residence time of about 30 rain can make the products of the (H20) up 0.3%.

From the pilot studies, the rotary steam tube dryer with a handling capacity of large and low power consumption advantages, as long as proper control of moisture content on the feed to meet the size requirements. If dry products are pneumatic conveying, drying the formation of loose particles can be dispersed, the follow-up device is not adversely affected.

3.3 Drying Process

Rotary steam tube dryer is in low-pressure saturated steam as the heating medium, drying at lower temperatures, it will not cause the decomposition of sulfide concentrates and oxidation. Concentrate rotary dryer process is as follows: Wet concentrate through screw feeder into the dryer inside the dryer cylinder has a certain slope, the material side of the roll with the rotating cylinder to move forward, side and along the Simplified layout of steam around the heat exchanger tubes were dry, dried concentrate feed tank through a discharge; a small amount of carrier gas from the discharge end into the dryer inside, carrying the drying process of water evaporation from the feed side discharge; through the bag After the dust separation of dust, exhaust venting of collected dust back into the feed screw. The process has a simple process, a small amount of equipment, low investment, high heat efficiency, dust and harmful gas emissions, a small, easy operation and maintenance and management and so on.

3.4 Industrial Applications

Tianhua Chemical Machinery and Automation Research and Design Institute of Jinchuan copper concentrate steam pipes developed rotary flash dryer specifications .2 m X 17.5 m, with a capacity exceeding 100 t / h. The drying equipment used in the company's 250 kt / a of copper synthesis furnace project, is currently the largest domestic development of the steam tube rotary dryer size machine, is also the metallurgical industry with the introduction of the first large-scale flash furnace supporting domestic concentrate drying equipment. It uses waste heat boiler in low pressure steam as the heat source, energy-saving effect is very obvious. Since the September 2005 car since the dryer is running in good condition. The successful application of it to save foreign exchange for the country almost 4 000 million yuan. In August 2006, Tongling Nonferrous Metals (Group) Co., Ltd. 400 kt / a sulfuric acid test the success of the project. This project is the first time using spray drying equipment, steam tube rotary drying sulfur concentrates, equipment specifications for the .4 m X 21 m, capacity 65 t / h L1. Practice has proved that the steam tube rotary dryer is ideal for large quantities of ore processed and the depth of drying, and has environmental protection and energy saving advantages, it is worth promoting.

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