Furnace & Kilns by Fel


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Furnace & Kilns by Fel

  1. 1. FURNACE & KILNS 8/13/2013CHAPTER 12: FURNACE & KILNS 1
  2. 2. FURNACE • A furnace is a device used for heating. The name derives from Latin fornax, oven. • It is essentially a thermal enclosure and is employed to process raw materials at high temperatures both in solid state and liquid state. 8/13/2013CHAPTER 12: FURNACE & KILNS 2
  3. 3. The principle objectives are: a) To utilize heat efficiently so that losses are minimum, and b) To handle the different phases (solid, liquid or gaseous) moving at different velocities for different times and temperatures such that erosion and corrosion of the refractory are minimum. 8/13/2013CHAPTER 12: FURNACE & KILNS 3
  4. 4. • Furnaces are usually made of either insulating firebrick or firebrick covered with refractory material. The charge, or inlet material, is introduced by chutes, conveyors or pipes. The furnace can run in batch mode, or in continuous mode. The charge moves through the furnace on skids or rolls, or by gravity, rotation, slope, or mechanical pushers such as screws. 8/13/2013CHAPTER 12: FURNACE & KILNS 4
  5. 5. 8/13/2013CHAPTER 12: FURNACE & KILNS 5 • Furnaces can be direct fired, over fired, under fired, or side fired. In direct fired furnaces, the heat is produced on the inside of the furnace chamber. In over, under, and side fired furnaces, heat is produced in a chamber in the respective area and flows throughout the furnace.
  6. 6. TYPES / CLASSIFICATION / CLASSES 8/13/2013CHAPTER 12: FURNACE & KILNS 6 1. Combustion Furnace 2. Electric Furnace
  7. 7. 8/13/2013CHAPTER 12: FURNACE & KILNS 7 Table 1 Classification of Combustion Furnaces Classification Method Types and Examples Type of fuel used Combustion Type 􀂃 Oil-fired 􀂃 Gas-fired 􀂃 Coal-fired Mode of charging materials Intermittent / Batch Periodical 􀂃 Forging 􀂃 Re-rolling (batch/pusher) 􀂃 Pot Continuous 􀂃 Pusher 􀂃 Walking beam 􀂃 Walking hearth 􀂃 Continuous recirculating bogie furnaces 􀂃 Rotary hearth furnaces Mode of heat transfer Radiation (open fire place) Convection (heated through medium) Mode of waste heat recovery Recuperative Regenerative
  8. 8. TYPICAL FURNACE SYSTEM 8/13/2013CHAPTER 12: FURNACE & KILNS 8 i. Forging Furnaces The forging furnace is used for preheating billets and ingots to attain a ‘forge’ temperature. The furnace temperature is maintained at around 1200 to 1250°C. ii. Rerolling Mill Furnace a. Batch type. A box type furnace is employed for batch type rerolling mill. The furnace basically used for heating up scrap, small ingots and billets weighing 2 to 20 kg. for rerolling. b. Continuous Pusher Type. The process flow and operating cycles of a continuous pusher type is the same as that of the batch furnace.
  9. 9. 8/13/2013CHAPTER 12: FURNACE & KILNS 9 iii. Continuous Steel Reheating Furnaces The main function of a reheating furnace is to raise the temperature of a piece of steel, typically to between 900°C and 1250°C, until it is plastic enough to be pressed or rolled to the desired section, size or shape.
  10. 10. ELECTRIC FURNACE 8/13/2013CHAPTER 12: FURNACE & KILNS 10 • A chamber heated by electric current is known as Electric Furnace. Electric furnaces are cheaper than oil fired furnaces and gas fired furnaces.
  11. 11. ELECTRIC FURNACE 8/13/2013CHAPTER 12: FURNACE & KILNS 11 • Operating Principle Steel scrap and a small amount of carbon and limestone are dropped into the electric furnace through the open roof. The roof is then closed, and the electrodes are lowered. Power is turned on, and, within a period of about two hours, the metal melts. The current is then shut off, the electrodes are raised, the furnace is tilted, and the molten metal is poured into a ladle, which is a receptacle used for transferring and pouring molten metal.
  12. 12. ELECTRIC FURNACE 8/13/2013CHAPTER 12: FURNACE & KILNS 12 Fig. 1 Schematic illustration of types of Electric Furnaces: (a) direct arc, (b) indirect arc , and (c) induction.
  13. 13. COMPONENTS & PARTS 8/13/2013CHAPTER 12: FURNACE & KILNS 13 Figure 2: Typical Furnace Components
  14. 14. APPLICATION AND USES 8/13/2013CHAPTER 12: FURNACE & KILNS 14 • High temperatures soften, melt, and anneal the metals. Heating can also cause the absorption of carbon. Furnaces are used in various stages of heat treatment, as shown in the table below for steel treatment. Treatment heat-treating annealing hardening heating reheating Temperature Range up to 1200°F 1200-1600°F 1500-1600°F up to 2300°F up to 2300°F
  15. 15. APPLICATION AND USES 8/13/2013CHAPTER 12: FURNACE & KILNS 15 • Furnaces are also used to melt glass, coke coal, distill zinc, and many other processes. Hearth furnaces can be used to remove hazardous waste. They are also used in the microelectronics industry in semiconductor wafer production.
  16. 16. KILNS 8/13/2013CHAPTER 12: FURNACE & KILNS 16 • A kiln is a thermally insulated chamber, a type of oven that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. • Kilns are furnaces used for ceramic or brick heating, causing moisture and organic materials to evaporate. Kilns are heated by horizontal space burners with gas, liquid, or solid fuel.
  17. 17. TYPES / CLASSIFICATION / CLASSES 8/13/2013CHAPTER 12: FURNACE & KILNS 17 1. In using an intermittent kiln, the ware to be fired is loaded into the kiln. The kiln is closed, and the internal temperature increased according to a schedule. After the firing is completed, both the kiln and the ware are cooled. Kilns in this type include: • Clamp kiln • Skove kiln • Scotch kiln • Down-Draft kiln
  18. 18. 8/13/2013CHAPTER 12: FURNACE & KILNS 18 2. A continuous kiln, sometimes called a tunnel kiln, is a long structure in which only the central portion is directly heated. From the cool entrance, ware is slowly transported through the kiln, and its temperature is increased steadily as it approaches the central, hottest part of the kiln. From there, its transportation continues and the temperature is reduced until it exits the kiln at near room temperature. Kilns in this type include: • Hoffman kiln • Bull’s Trench kiln • Habla (Zig-Zag) kiln
  19. 19. 8/13/2013CHAPTER 12: FURNACE & KILNS 19 Ceramic Kilns • Kilns are an essential part of the manufacture of all ceramics, which require heat treatment, often at high temperatures. During this process, chemical and physical reactions occur that permanently alter the unfired body. In the case of pottery, clay materials are shaped, dried and then fired in a kiln.
  20. 20. 8/13/2013CHAPTER 12: FURNACE & KILNS 20 • Wood Drying Kiln A variety of wood drying kiln technologies exist today: 1. Conventional wood dry kilns - are either package-type (side loader) or track-type (tram) construction. 2. Dehumidification kilns - Heat comes primarily from an integral dehumidification unit that also removes humidity. 3. Solar kilns - are conventional kilns, typically built by hobbyists to keep initial investment costs low.
  21. 21. 8/13/2013CHAPTER 12: FURNACE & KILNS 21 • Rotary Kilns - is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. Materials produced using rotary kilns include: • Cement • Lime • Refractories • Metakaolin • Titanium dioxide • Alumina • Vermiculite • Iron ore pellet
  22. 22. OPERATING PRINCIPLE 8/13/2013CHAPTER 12: FURNACE & KILNS 22 • The kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner.
  23. 23. COMPONENTS & PARTS 8/13/2013CHAPTER 12: FURNACE & KILNS 23
  24. 24. APPLICATION & USES 8/13/2013CHAPTER 12: FURNACE & KILNS 24 • Tunnel kilns are used to vitrify clay bricks, particulate solids, and large solid objects. They are also used to sinter capacitors, soft ferrite, composite materials, and capacitors used in computers and cellular telephones also. Rotary kilns are used to make cement and to calcine small waste stone and free- flowing, granular solids. Downdraft kilns are used to produce brick, pipe, tile, and stoneware, while updraft kilns are used for pottery burning.
  25. 25. 8/13/2013CHAPTER 12: FURNACE & KILNS 25 Other uses of kiln include: • To dry green lumber so it can be used immediately • Drying wood for use as firewood • Heating wood to the point of pyrolysis to produce charcoal • For annealing, fusing and deforming glass, or fusing metallic oxide paints to the surface of glass • For cremation (at high temperature) • Drying of tobacco leaves • Drying malted barley for brewing and other fermentations • Drying hops for brewing (known as a hop kiln or oast house) • Drying corn (grain) before grinding or storage, sometimes called a corn kiln, corn drying kiln. • Smelting ore to extract metal • Heating limestone with clay in the manufacture of Portland cement • Heating limestone to make quicklime or calcium oxide