(1) Air heavy medium fluidized bed dry coal preparation 1. Basic principle and characteristics of dry coal preparation by air heavy medium fluidized bed (1) The process of fluidization Air heavy medium fluidization is a process in which a particulate solid medium is brought into a fluid-like state by contact with a gas. As shown in Fig. 4-4-63(a), a container 1 having a vertical wall and a distributor 2 on the lower portion are stacked with a plurality of uniform fine particles 3, and a V-shaped piezometer is placed at the lower portion of the granular layer. 5. The gas stream flows from the bottom 4 through the distributor 2 into the bed of particles and is then discharged from the top of the vessel. As the gas stream passes through the bed, as the gas flow rate increases, the entire fluidization process has three basic stages: 1 fixed bed; 2 fluidized bed; 3 transport bed. See Figure 4-4-63(b), (c), (d), respectively. (2) Fluid-like properties of a fluidized bed Whether the gas-solid fluidized bed can have liquid mobility is very important for the air heavy medium fluidized bed sorting technology. Studies have shown that the gas-solid fluidized bed after complete fluidization looks like a boiling liquid and exhibits fluid-like properties in many respects. As shown in Figure 4-4-64. 1Two connected beds can be automatically adjusted to the same horizontal plane [Fig. 4- 4 - 64(a)]; 2 When the container is inclined, the upper surface of the bed remains horizontal (Fig. 4- 4 - 64(b)); The pressure difference between any two points in the three beds is equal to the static pressure difference between the two points [4-4-6) (c]], which is 4 has a liquid-like fluidity, such as opening a hole in the wall of the container, the particles will be ejected from the orifice [4 -4 - 64 [d)]; 5 Objects smaller than the bed density will float on the bed surface, and objects larger than the bed density will sink to the bottom of the bed. This process of density stratification obeys Archimedes' law [Fig. 4- 4 - 64(e), which is (3) Principle of separation of air heavy medium fluidized bed The so-called air heavy medium separation is to use the fluid-like nature of the gas-solid fluidized bed to form a uniform and stable gas-solid suspension with a certain density in the fluidized bed. The average density of the bed is: Therefore, according to Archimedes' law, light and heavy products are layered by density in the suspension, that is, light products smaller than the density of the bed are floated; heavy products larger than the density of the bed sink, separated and deproteinized to obtain two qualified product. 2. Air heavy medium fluidized bed dry sorting machine The air heavy medium fluidized bed dry sorting machine developed in China is the main equipment for material selection and separation. Its structure is shown in Figure 4-4-65. The machine consists of an air chamber, a gas distributor, a sorting chamber and a product transport scraper unit. The sorting process of the material in the sorting machine is: the sieved 6~ 50mm bulk material and the weighted material are respectively added to the sorting machine, and the pressurized gas with a certain speed from the wind pack passes the gas through the bottom air chamber. After the distributor, the fluidization is uniformly applied to the weighted material, and a uniform and stable gas-solid two-phase fluidized bed with a certain density is formed under certain process conditions. The material is stratified by density in the fluidized bed, and the material smaller than the density of the bed is floating, which is called floating material, and the material larger than the density of the bed sinks, called sinking. The stratified materials are respectively transported by the low-speed running stepless chain scraper conveying device, and the floating objects such as clean coal are discharged from the right end discharge port, and the sediment such as vermiculite or tail coal is discharged from the left end discharge port. The air chambers in the lower part of the sorting machine are connected to the air supply system, and the air pressure and the air volume adjustment and indicating devices of each room are provided. The upper part of the sorting machine is connected with the air-exhaust dust-removing system, and the design of the phoenix is ​​larger than the air supply volume, so that the inside of the sorting machine is in a negative pressure state, which can effectively prevent the powder from escaping. The air heavy medium fluidized bed sorting machine can effectively sort 6 ~ 50 (80) mm grain coal with external moisture less than 5%. The sorting accuracy is high, and the possible deviation is in the range of 0.05-0.07. Table 4-4-16 lists the main parameters of the 10 t/h, 25t/h, 50t/h air heavy medium fluidized bed sorting machine. 3. Practical application and effect of dry coal preparation by air heavy medium fluidized bed 50 t/h air heavy medium fluidized bed dry coal preparation demonstration plant in Qitaihe Taoshan Coal Preparation Plant, which is the world's first air heavy medium dry coal preparation plant with an annual processing capacity of 320,000 I, sorting The density is 1.45 g/cm 3 , and the raw coal is difficult to select or extremely difficult to select. The principle process of the coal preparation plant process system is shown in Figure 4-4-66. It mainly includes: raw coal preparation system, coal preparation system, de-intermediation and medium recovery system, supply and dust removal system and product loading and transportation system. Figure 4-4-66 Principle process of 50t/h air-weight medium coal preparation process system The fluidization characteristic curve of the fluidized bed sorting machine is shown in Figure 4-4-67. The actual product distribution curve is shown in Figure 4-4-68. The industrial continuous operation of the 50t/h air heavy medium fluidized bed sorting machine shows that at different sorting densities, the possible deviation E value is in the range of 0.05~0.07, the quantity efficiency is above 90%, and the dielectric loss is 0.5 kg/ t below. (2) Compound dry coal preparation Traditional wind jigs and wind shakers have been phased out due to their poor efficiency. China has absorbed the advantages of the airless dry shaker and the Russian wind sorter developed in the United States in recent years, and successfully developed a composite dry sorter. 1. Sorting mechanism of compound dry sorting machine (1) Sorting effect of sorting materials in spiral motion The material is piled up on the bed surface, and the bottom layer of the ore is directly in contact with the vibrating bed surface. The friction force is large, and the inertial force obtained causes the lower layer of ore to move along the bed surface to the back plate. The material is guided to move down the backing plate due to the blocking of the backing plate. The upper layer material is slid along the surface layer to the discharge side by the thrust and gravity of the backing plate, so that the upper and lower parts of the bed have opposite velocity gradients. Under the guidance of the bed grate and the constant pressure of the material, a spiral motion of the material to the side of the vermiculite is formed while rotating. Coal density formed in the peripheral large-diameter helical motion, high density and pyrite gangue is formed in the small-diameter helical movement in the bed angle and the back plate, Figure 4-4-69. Due to the different thickness of the material bed and the thinness near the discharge side, the vermiculite mixed into the surface layer can be quickly transported to the back surface near the discharge side and transported to the back sheet. Only the light material with the lowest surface layer density can be discharged over the baffle. During the whole sorting process, due to the reduction of the width of the bed surface, the material forms a spiral motion with decreasing diameter from the feed end to the end of the vermiculite, and some of the lighter surface coal is separated every cycle until the vermiculite is finally discharged. (2) Segregation and wind force complement each other The looseness and delamination of the material on the composite dry selection machine surface is achieved by the suspension of mechanical vibration and updraft. The loose strength increases with the increase of mechanical vibration strength and bottom wind speed. According to the second law of thermodynamics, any system tends to reduce free energy. The potential energy of the bed before stratification is higher than the potential energy after stratification. As long as appropriate loose conditions are given, heavy minerals will enter the lower layer. Layering is the process of reducing the potential energy by redistribution of ore particles. In a non-air-drying shaker, different density of ore particles are layered according to the principle of lowering the bit energy, which inevitably causes the ore particles to form a screen similar to a sieve opening, resulting in segregation and segregation. The densely-sized ore particles are forced to move downward due to their strong gravitational pressure, and the small-density ore particles are squeezed into the upper layer. Although the density is small, the ore particles with a small particle size will also leak to the bottom layer. In order to solve this problem, a small amount of wind is added at the bottom of the sorting bed, on the one hand, the looseness of the ore group is strengthened, and on the other hand, the layering is strengthened, so that the coal particles with small and light particle size are pushed to the surface by the wind. As a result of the combined action, the sorting process is refined and the ore particles are layered by density (see Figure 4- 4 - 70). [3] Separation of autogenous media The composite dry sorter has a feed size range of 0 to 80 mm, while the conventional air separation has a feed size of 25 to 50 mm or 13 to 25 mm). The composite dry sorting machine has a wide range of grain size, but the sorting effect is good. The main reason is that the fine-grained material and air form a gas-solid two-phase mixed medium, and a certain type is formed in the sorting bed. Density, relatively stable gas-solid suspension. In the bed of the first dry chamber of the composite dry sorter near the feed end, a large amount of fine material is contained . The volume of the chamber is reduced during operation to take full advantage of the sorting action of the autogenous medium. In summary, the sorting mechanism of the composite dry sorting machine is to make the bed loose under the condition of spiral turning motion, and the vibration and wind force are used to cause the bed to be loose, and the gravity (potential energy) is divided in different sections. Layer function, also has the role of self-generated media sorting, and the buoyancy effect that utilizes the interaction of particles, so that the segregation effect and the wind action can effectively cooperate to achieve the purpose of comprehensive sorting. At the same time, each sorting effect is different in different sections (see Figure 4-4-71). 2. Structure and technical characteristics of composite dry sorting machine 1 Structure-one composite dry sorting machine consists of sorting bed, vibrator, wind chamber, frame and hanging device, as shown in Figure 4-4-72. The sorting bed is composed of a bed surface, a back plate, a grid strip, and a discharge baffle. There are three air chambers under the bed surface that can control the air volume. The air is supplied by the centrifugal fan, and the air flow acts upwards on the sorting materials through the air holes on the bed surface. The sorting bed and the vibrator are suspended on the frame by the hanging device, and the longitudinal and lateral slopes of the sorting bed can be arbitrarily adjusted. 2 Principle of action A selected material is sent from the feeder to the feed port, into a sorting bed with a certain longitudinal and lateral slope, and a bed of material having a certain thickness is formed on the bed surface. The bottom layer material of the bed is moved to the back plate by the vibration inertia force, and the material is turned upward by the back plate. The lower density coal is flipped to the upper layer and slides down the surface of the bed under the influence of gravity. Due to the vibrational force and the pressure of the material entering the sorting bed continuously, the continuously turning material forms a spiral motion and moves toward the vermiculite end. As the width of the bed surface is gradually reduced, the coal with low density falls from the surface, and the lowermost coal is continuously discharged through the discharge baffle, while the meteorite and pyrite with higher density are gradually concentrated to the end of the vermiculite. A number of wind holes are evenly distributed on the bed surface to make the bed sufficiently loose. The material will be subjected to a sorting action during each cycle of motion. After multiple sorting, a variety of products with low to high ash content can be obtained. 3Technical Features - At present, there are two models of composite dry sorting machines. The technical characteristics are shown in Table 4- 4-17. 4 Sorting effect and application scope of composite dry coal preparation In recent years, the semi-industrial test of dry coal preparation has been carried out on different coal samples by composite dry sorting machine, and it has achieved good results in industrial production. Sorting effect. Figure 4-4-73 is the contact diagram of the dry selection system equipment of the Chaoyang side stick. Some examples are listed in Table 4-4-18, and the main sorting indicators are listed in Table 4-4-19. Table 4-4-20 is a comparison of a composite dry sorter with a conventional air sorter and a Russian wind sorter. Use self-generated medium (powder coal) as a gas-solid two-phase mixed medium instead of air alone. Therefore, the material size range of the selected materials is very wide, up to 0~80mm. Mechanical vibration is used to make the material spiral, even if there is no wind. Traditional wind selection uses wind as the main sorting condition. Only the windy loose bed layer is used and the mixed medium is composed of the fine material, and the material is not required to be blown off the surface of the bed, and the required air volume is only 1/3 or less of the conventional air selection. Take full advantage of the buoyancy effect created by particle interactions in the bed. The closer to the vermiculite end, the greater the bed density, so that a vermiculite product with a wide particle size and high purity can be obtained.
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Dry coal preparation
In China accounted for more than 2/3 of recoverable reserves of coal located in the serious water shortage areas Shanxi, Shaanxi, western Inner Mongolia and Ningxia, and therefore can not now uses a lot of water-intensive wet cleaning method to improve coal quality. China's self-developed gas-solid two-phase flow air heavy medium fluidized bed coal preparation technology and composite dry sorting machine can better meet the sorting requirements of drought-deficient areas and easy muddy coal. The biggest difference between composite dry coal preparation and traditional air selection is:
    The composite dry sorter divides the corresponding bed surface into three sections in the order of the wind chamber. When the coal is not classified, the material on the first bed near the feeding end is strongly sorted by the autogenous medium. The sorting result is more than 80% of the 0~6mm pulverized coal discharged with the large-size fine coal, and the remaining materials enter the second and third sections. Since the amount of fine coal is very small, the main sorting effect is not the separation of self-generated media, but the buoyancy effect of particle interaction. The meteorite and pyrite are dense and can sink to the bed surface; the coal blocks float on the surface of the bed. At this time, the effect of the wind is not only loose, but also the coal below the funnel needs to be pushed toward the surface, so the air volume is greater than the first segment. (4) Buoyancy effect of particle interaction