Chapter Ii


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Chapter Ii

  1. 1. Chapter II SIZE REDUCTION
  2. 2. OBJECTIVES 1. To obtain solid particles in a specific range size and specific surface area 2. To destruct mineral or crystal of chemical bounded in a solid compounds 3. To make separation of desirable components is possible 4. To reduce fibrous materials size to ease their treatments 5. To enhance specific surface area
  3. 3. Solid Raw Materials Solid in fluid processing Solid Materials Industries Size reduction Cracking Crushing Grinding Smaller particle
  4. 4. Large size raw solid particles Synthetic solid materials Treatable/process able solid particles sheet, cubic, powder
  5. 5. <ul><li>Coarse Size Reduction </li></ul><ul><li>Designated for hard, irregular solid particles having 2 – 96 inches or larger. </li></ul><ul><li>Equipments: Jaw crusher, gyratory crusher, toothed roll crusher, hammer mill </li></ul>2. Intermediate Size Reduction Designated for hard, irregular solid particles having 1 – 3 inches. Equipments: cone crusher, crushing rolls, stamp hill, disintegrator CLASSIFICATON OF SIZE REDUCTION Basic: Feed/Original Size
  6. 6. 3. Fine Size Reduction Designated for hard, irregular solid particles having 0.25 – 0.5 inches. Equipments: ball mill, tube mill, rollers mill
  7. 7. 1. Crusher Designated for crushing of large solid particles into smaller particles of about several inches These equipments are divided into: a. Primary Crusher Designated for crushing of feed having any size of solid particles to obtain smaller particle products having 6 – 10 inches in size. b. Secondary Crusher Designated for crushing of feed having any size of solid particles to obtain smaller particle products having 1/4 inches in size. CLASSIFICATON OF SIZE REDUCTION Basic: Product size
  8. 8. 2. Grinder Designated for size reduction of large solid particles produced by crusher. These equipments are divided into: a. Intermediate Grinder Designated for obtaining smaller particle products having 40 mesh in size. b. Ultra fine Grinder Designated for size reduction of feed having smaller than ¼ inch in size to obtain smaller particle products having 200 mesh in size. 3. Cutter/Disintegrator Designated for size reduction of solid particles by cutting and tearing. Suitable for fibrous materials, such as asbestos and wood
  9. 9. Size reduction Irregular particle shape Irregular particle size (non- uniform) Pre-processing I WANT REGULAR SHAPE AND PARTICLE SIZE
  10. 10. SEPARATION 1. Free Crushing Fine particles are discharged from the crusher immediately. Discharging can be done by gravitational force. Particles are blown using pressurised air, washed with water and discharged by centrifugal force. This operation may prevent the formation of more fine particles by reducing contact intensity. <ul><li>Choke Feeding </li></ul><ul><li>It is reverse of free crushing operation. </li></ul><ul><li>Crusher is equipped with feed catcher and maintained to be fulfilled to prevent immediate product release. </li></ul><ul><li>This operation may perform a very economical operation as more fine particles may be produced and reduce size reduction operation steps. </li></ul>
  11. 11. Operating Variables: 1. Moisture Content (MC) Should be less than 3-4 %, as pasting and agglomeration may occur. For low MC solid materials, coarse and intermediate size reduction is applicable. For high MC (>50 %), fine size reduction is ore suitable. 2. Reduction Ratio (RR) RR = ratio of feed to product particle diameter. Coarser: RR 3 to 7 Fine Grinder: RR >100
  12. 12. 3. Material Structures Toughness, brittleness, fibrous, etc. 4. Material Hardness Measured by Mosh Degree (1 to 10). Scale 1 – 4 : Soft More than 4: Hard
  13. 13. THE SIZE REDUCTION PROCESS 1. Batch <ul><li>Continue </li></ul><ul><li>Is a sustainable operation. It Can be grouped into: </li></ul><ul><li>a. Continuous Open Circuit (No material is recycled to be processed) </li></ul><ul><li>b. Continuous Closed Circuit (Oversize products are recycled into process, economical of crushing power, uniform product size) </li></ul>Crusher Crusher Raw material Products a Raw material Products b Screen Over Size
  14. 14. THE SIZE REDUCTION LAWS During size reduction process, with the application of mechanical energy materials experience: Distortion, Tensile/loose, and crack. Every unit area of solid has it’s specific energy, the formation of new surface needs energy released from stress energy when the solid materials crack. Terms: 1. Grindability: amount of solid reduced into a specific size using a specific equipment, (Ton/Hour). 2. Relative Grindability: ratio of grindability of a solid material to grindability of a standard material
  15. 15. <ul><li>Kicks Law </li></ul><ul><li>Energy required to grind a specific material is constant for the same reduction ratio irrespective of it’s original size </li></ul><ul><li>Hp = Energy, K= constant, D= initial diameter, d = final diameter </li></ul><ul><li>Energy to grind particle 1 inch into 0.5 inch = Energy to grind particle 3 inch into 1.5 inch </li></ul>2. Rittinger Law Energy required to grind a specific material is proportional to the new surface are formed. The Rittnger numbers are shown in table 2.1
  16. 16. Table 2.1 The Rittnger numbers of some minerals on Drp Weight Crusher 75.9 1053 163.3 Calcite (CaCl 2 ) 93.8 1300 201.5 Galena (PbS) 56.2 780 121 Sphalerite (ZnS) 22.57 314 47.7 Pyrite (FeS 2 ) 17.56 243 37.7 Quartz (SiO 2 ) cm 2 /kg-cm cm 2 /ft-lb in 2 /ft-lb Rittinger Number Minerals
  17. 17. The two laws only consider the energy required for the size reduction for a given reduction ratio. In fact, the total energy should be summation of energy to drive the machine, reduction size energy and friction energy. 3. Bond law Energy required to grind a specific material into a specific particle size is proportional to square root of product’s surface area to volume ratio. Ei = Bond’s working index E i = Nett energy in KWH/ton of feed required to reduce solid material into a specific size so that 80% of products can through 100 µ screen
  18. 18. X f = feed particle size X p = product particle size N = 1, Kick’s Law N = 2, Rittinger Law N = 3, Bond Law General Equations: X = particle size
  19. 19. SIZE REDUCTION EQUIPMENTS Machines for size reduction are divided into two groups, namely: <ul><li>Coarse crusher for hard materials, such as: jaw crusher, gyratory crusher or disk crusher </li></ul><ul><li>Coarse crusher for soft materials, such as : hammer mill or toothed roll crusher </li></ul><ul><li>Jaw Crusher </li></ul><ul><li>Consists of Blake type and Dodge type crushers, Blake type is easily encountered in industries, but not for the Dodge type </li></ul>
  20. 20. <ul><li>Blake Type Jaw Crusher (BTJC) </li></ul><ul><li>- Developed by E. W. Blake (1858) </li></ul><ul><li>- usually also called as Double Toggle Crusher </li></ul><ul><li>- suitable for reduction of hard materials having 2-96 inches in size </li></ul><ul><li>- the biggest size is 8 x 6 ft, cap.1250 ton/hr, requires 400hp (300KW), able to prepare 18 inches particle. </li></ul><ul><li>- made of cast steel lined with a tough abrasion resistant metal such as Manganese Steel </li></ul><ul><li>- operational cost: expensive </li></ul><ul><li>- advantages: able to crack hard materials, large capacity, seldom product discharge clogging </li></ul>
  21. 21. Working Principles of Blake Type Jaw Crusher - It works based on PRESSURE - Two main parts of BTJC: a. Frame: function as a fixed Jaw b. Movable Jaws is pivoted at the top ad operated by eccentric, pitman, and toggles
  22. 22. The pitman is given a nearly Vertical motion by eccentric, and since one of the toggles is mounted in rigid journals at one end of the crusher frame, the reciprocating motion of the pitman causes he other toggle to move the jaw back and forth. The jaw is held against the toggle by a tension link and spring. Crushing is accomplished if the movable jaw moves toward the fixed jaw. That means an intermittent power requirement. In order to equalize this, one or two heavy wheels are mounted on the main shaft of the crusher. The machine is driven by flat belts or V-belts
  23. 23. 2. Dodge Crusher - subject to uneven stresses inherent in its design - only designed in SMALL size - Movable jaw is pivoted at the bottom and the width of the discharge opening remain constant, therefore yielding a more closely sized product. - No toggles are required. - The jaw is operated through pitman by eccentric. - If only one size reducing machine is employed, the uniformity of product size is an advantage, otherwise it is of limited use. - The power is applied through along lever, if the crusher becomes clogged enormous stress are set up in the members which become excessive in machines with gape above 11 inch. - The constant opening of the jaws at the discharge end gives this equipmnt an annoying tendency of CLOG….Not happen in BTJC
  24. 24. Dodge Crusher