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LT Dust Briquetting Process



Source: internal company

LT Dust Briquetting Process

  After digestion, the properties of the dust have changed, mainly as follows: 1. The volume will expand during the conversion of calcium oxide into calcium hydroxide. The bulk density of the dust before digestion is 0.87 t/m3, and after digestion, it drops to 0.75 t/m3. The density of finished briquetts is generally 2.5-3.0 t/m3, which means that the compression ratio becomes larger and the difficulty of pelletizing increases. 2. The moisture content of the dust has changed. After digestion, the moisture content of the dust is about 3%-4%, which is between dry hot pressing and wet cold pressing. In this state, a certain amount of binder must be used for briquetting , and the process parameters of briquetting will also change. 

Determination of Binder 
  The key to dry cold briquetting technology lies in the selection and addition method of the binder. There are many kinds of binders studied and tested at home and abroad. In industrial applications, there are mainly cement, sodium silicate, bentonite, sodium humate, asphalt, etc. The fatal problem with inorganic binders such as cement, sodium silicate, and bentonite is that in order to maintain the strength of the lump, the amount of inorganic binders added is large, which brings a large number of impurities into the lump products, resulting in a significant decrease in iron grade and an increase in the amount of converter smelting slag. Although the briquetting method using sodium humate, asphalt, and the like as binders has high normal temperature strength and good moisture resistance and water resistance, its disadvantages are high price, softening, and deformation of briquetting in high-temperature process, poor high-temperature strength, and serious pollution. 

Selection of Process Parameters for Briquetting
  LT dust is formed by a high-pressure counter-roller ball press, and the working diagram is shown in the figure. On the one hand, the ball press feeds by the self-weight of the material and the preloading screw, and on the other hand, it depends on the friction force of the rotating roller of the ball press. The original dispersed dust is pressed into blocks with small volume and high density under high pressure. In this process, the gap of the material is compressed, resulting in plastic deformation, and its deformation energy is transferred to the material to generate heat, and the briquette is in a hot state when it leaves the press roller. Dust is pressed into a single ball in the form of a ball mold, with flaky connected briquettes, or all of them are pressed. 

  The main working parameters of the ball press include feed rate, pressing speed, and pressure, and the selection of parameters directly affects the quality and output of the ball. 
1. Feed quantity 
   Under the condition that the material ratio is determined, the amount of feed determines the pelletizing rate and the initial strength of pelletizing. When the feed quantity is too small, it cannot form balls. The material quantity is small, the ball is flat, the spherical surface has no luster and heat, and the initial strength is poor. When the feed rate is appropriate, the thickness of the pelletizing intermediate layer is 2-5mm, and the spherical surface has a luster and good temperature and strength. When the feed rate is too large, the thickness of the middle layer of the ball reaches 4-6mm, and the spherical surface has luster, good temperature, and strength. When the feeding amount is too large, the ball will be pressed into a whole piece, and the strength will decrease. In serious cases, the preloading motor will be locked or the main motor of the ball pressing machine will be stuck. 

2. Pre-pressing and rotation speed of the main roller 
   Pre-pressing is the pre-compaction before the material is supplied to the rolling ball. The compactness of materials before they are supplied to the pair rollers depends on the extrusion between materials and external mechanical extrusion. If the opposite roller is fed directly by gravity, for the same material, the feeding amount can only depend on the height of the material column, and if a preloading device is added, the opposite roller can be forced to feed. Principle: By adjusting the rotation speed of the preloading motor and controlling the rotation speed of the preloading screw, the compactness of the materials delivered to the counter rollers can be adjusted. As shown in the figure, the screw is a variable diameter and variable pitch screw. After the material enters the screw, it is gradually compressed from top to bottom. Before entering the counter-roller ball press, the volume has been greatly reduced, which is equivalent to a preliminary briquette, and then it is rolled and formed under high pressure, thus obtaining a high-quality briquette. 
   The initial strength of pelletizing will increase with the increase of preloading speed. If continuous feeding, when the material quantity is insufficient, increasing the preloading speed can compensate for the influence of insufficient feeding to a certain extent. If continuous feeding, when the material quantity is insufficient, increasing the preloading speed can compensate for the influence of insufficient feeding to a certain extent. If the material quantity is very large, the preloading speed can be appropriately reduced, and the roller is fed by extrusion between materials. 

                                                               1. Hopper 2. Reducer 3. Motor 4. Coupling 5. Supporting device 6. Preloading screw 7. Material guide device 

Determine the Pressure 
  The pressure of the briquette machine is provided by the hydraulic system, and the test pressure is measured by oil pressure. In the range of 13-25MPa, the influence of the pressure of ball press on the initial strength of ball forming is studied. When the preloading feed amount is small, the initial strength of pelletizing is inversely proportional to the pressure to a certain extent. With the increase of pressure, the initial strength of pelletizing decreases. The main reason is that with the increase of pressure, the distance between the rollers becomes smaller, resulting in a smaller amount of materials that are not dense enough to enter the ball mold, and the strength decreases instead. When the preloading feed amount is appropriate, the initial strength of pelletizing is proportional to the hydraulic pressure. When the preloading feed amount is too large, the pelletizing with better initial strength can be obtained at lower pressure. If the pressure continues to increase, the initial strength of the ball will not increase significantly, and because the ball is pressed into a sheet shape, it will be broken due to gravity when falling, with more leftover materials, the strength of the ball will decrease instead.

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