L 23 and 24 final

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AIR POLLUTION CONTROL course material by Prof S S JAHAGIRDAR,NKOCET,SOLAPUR for BE (CIVIL ) students of Solapur university. Content will be also useful for SHIVAJI and PUNE university students

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L 23 and 24 final

  1. 1. L-23 Gravity settling chamber Air Pollution and Control (Elective-I)
  2. 2. Gravity settling chamber • Gravity settling chamber is used to remove large and abrasive particles greater than 50 µ from a gas stream. • This is a simple particulate collection device using the principle of gravity to settle the particulate matter in a gas stream passing through its long chamber. Prof S S Jahagirdar, NKOCET 2
  3. 3. • The primary requirement of such a device would be a chamber in which the carrier gas velocity is reduced so as to allow the particulate matter to settle out of the moving gas stream under the action of gravity. • This particulate matter is then collected at the bottom of the chamber. • The chamber is cleaned manually to dispose the waste. Prof S S Jahagirdar, NKOCET 3
  4. 4. Gas outlet Prof S S Jahagirdar, NKOCET 4
  5. 5. Prof S S Jahagirdar, NKOCET 5
  6. 6. Prof S S Jahagirdar, NKOCET 6
  7. 7. Gravity settling chamber with trays Prof S S Jahagirdar, NKOCET 7
  8. 8. • The gas velocities in the settling chamber must be sufficiently low for the particles to settle due to gravitational force. • Literature indicates that gas velocity less than about 3 m/s is needed to prevent re-entrainment of the settled particles. The gas velocity of less than 0.3 m/s will produce good results. Prof S S Jahagirdar, NKOCET 8
  9. 9. Design Parameters:For 100 % efficiency H L t  Vt VH --------------Eq -i Where, H= height of settling chamber L = Length of settling chamber Vt = Velocity of settling VH = velocity of flow Prof S S Jahagirdar, NKOCET 9
  10. 10. From equation I Settling velocity may be given by VH H Q Vt   L LW -------------Eq – ii W= width of chamber (As Q = area of inlet x velocity = W.H.VH ) For streamline flow settling velocity is given by 2 Vt  g .d p . p ------------- Eq- iii 18. Prof S S Jahagirdar, NKOCET 10
  11. 11. • Equating equations ii and iii, 2 VH H g .d p . p  L 18. therefore, we get, d p min  18. H .V H g .L. p -------Eq iv dpmin is min size of particle that can be removed with 100 % efficiency Prof S S Jahagirdar, NKOCET 11
  12. 12. For better and conservative results multiplying factor 2 can be taken d p min 18. H .VH  2 g.L. p Efficiency of settling chamber is given by d p  dp   dp  m in     2 Prof S S Jahagirdar, NKOCET 12
  13. 13. • Another equation for calculation of efficiency is 2  g .d p  p .L    1  exp     18. .V .H  H   Prof S S Jahagirdar, NKOCET 13
  14. 14. Settling chamber with trays Settling trays can be used to improve removal efficiency. Prof S S Jahagirdar, NKOCET 14
  15. 15. If, n = number of trays, then equation iv becomes d p min  18. H .V H n. g .L . p Prof S S Jahagirdar, NKOCET 15
  16. 16. Prof S S Jahagirdar, NKOCET Advantages 1. 2. 3. 4. 5. Low initial cost Simple construction Low maintenance cost Low pressure drop Dry and continuous disposal of collected solids 6. Can be constructed of any material 7. Temperature and pressure limitations are imposed by type of material used 16
  17. 17. Disadvantages 1. Large space requirement 2. Only comparatively large particles can be collected Prof S S Jahagirdar, NKOCET 17
  18. 18. Prof S S Jahagirdar, NKOCET Applications of settling chamber • Settling chambers are mostly used as pre-cleaners. They are sometimes used in the process industries, particularly in the food and metallurgical industries as the first step in dust control. • Use of settling chambers as pre-cleaners can also reduce the maintenance cost of high efficiency control equipment, which is more subject to abrasive deterioration. 18
  19. 19. Problem (Peavy -Rowe) Assume viscosity of air = 2.1 x 10-5 kg/m.s Prof S S Jahagirdar, NKOCET 19
  20. 20. Solution :- Prof S S Jahagirdar, NKOCET 20
  21. 21. Objective questions Q1. Gravity settling chamber removes _____________ particles. Q2. In gravity settling chamber, the gas velocity of less than _______ m/s will produce good results. Q3. If trays are used in settling chamber efficiency _______________. Q4. True or false? 1.Settling chamber can be connected with other control equipments in series to increase efficiency. Prof S S Jahagirdar, NKOCET 21
  22. 22. 2. Settling chamber can remove less than 1 µ particles with 90% efficiency. 3. Increase in flow velocity increases efficiency of settling chamber. Prof S S Jahagirdar, NKOCET 22
  23. 23. Theory questions Q1. Explain working of gravity settling chamber with neat sketch. Also give advantages and disadvantages. Q2. Write a note on ‘Design of gravity settling chamber’. Prof S S Jahagirdar, NKOCET 23

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