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Basics of bag filter based de-dusting system.

Published in: Technology


  1. 1.  Air pollution is the introduction into the atmosphere of chemicals, particulates, or biological matters that cause discomfort, disease, or death to humans, damage other living organisms such as food crops, or damage the natural environment or built environment.
  2. 2. Basic Concept
  3. 3.  Dust laden air enters through the hopper by suction or positive pressure The heavier dust particles fall immediately into the hopper, while the lighter ones deposit on the outer surface of filter bags Dust deposited on bag surface is dislodged & bag is cleaned by pulse of high pressure compressed air.
  4. 4. Penthousewith hoistDust particles Insulation toare avoidretained on the undershootingsurface of the of dew pointfilter (hot gasmedium and versionthecleaned air Top-Down flowpasses in filter housingthrough thefilter Dust collectionmedium and hopper or trayflows with materialinto the clean dischargegas screw orchamber or scraper chainduct. conveyor
  5. 5. Bagfilters : Classification based on how the fabric is cleaned1. Shaking 2. Compressed Air 3. Reverse Air Reverse Air
  6. 6. Types of Cleaning
  7. 7. Bag Filter - Basics In an industrial system of gas cleaning, the fabric is media made into either an envelope or a tube. These envelopes or tubes are called the bags and a housing of these is called Bag Filter or Bag House.
  8. 8. FACTORS GOVERNING SELECTION OF TYPE OF APC EQUIPMENT - 1 • Inlet dust load in gm/ Nm3 • Gas volume in Nm3/ hr • Gas temperature • Nature of pollutant : Gaseous /Particulate • Properties of dust : Physical (density /size fraction / temperature /‘wettability’) • Properties of gas : Physical /Chemical (nature: acidic / alkaline, moisture content critical)
  9. 9. FACTORS GOVERNING SELECTION OF TYPE OF APC EQUIPMENT - 2 • Nuisance value /Recovery value of both dust and gas • Outlet emission requirements /Efficiency required • Space availability • Economics /Budget /Fund availability /Return on Investment
  10. 10. Air-to Cloth Ratio =Total volume of gas (or air) handled by the Bag filter [m3/min] /Total filtration area provided in the Bag Filter [m2] = [ m3/min-m2 = m/min, => velocity unit; hence also called filtration velocity, and is actually the velocity at which the dust laden gases travel across the filter element ]The more critical the dust { fine, light, sticky, non-agglomerating, abrasive, etc}or higher the dust loading, the larger is the filtration area provided, i.e. lower isthe air-to-cloth ratio maintained.
  11. 11. Can Velocity = Velocity at which the gas travels upwards across the cross section of the Bag filter =Total volume of gas (or air) handled by the Bag filter [m3/min] / Cross sectional area of Bag Filter casing [m2]This is an important aspect and has to be restricted especially for fine, light,and non-agglomerating dust (lime, carbon black are typical examples) asotherwise the dust may remain in a fluidised state in the bag filter and not getdischarged from the unit at all.
  12. 12. Filter Fabric selection
  13. 13. Online type :-Cleaning is done on line ( chamber in operation)Off Line type :-Cleaning is done in the off line mode. i.e cleaning of the chamber after isolating the flue gas entry . This avoids re entrainment of dislodged dust Used in case of fine dust
  14. 14. Bag Filter – Type-Online Single module-hopper Entry
  15. 15. Bag Filter – Type-OfflineHow it works – Normal Gas Flow
  16. 16. Bag Filter – Type-OfflineHow it works – Reverse Gas Flow
  17. 17. Bag Filter – Type-Offline  In offline Pulse Jet Bag Filter which is a compartmentalized Bag Filter, one compartment is sequentially taken out for cleaning purpose. Rest all the compartments are under filtration process. Typically offline cleaning is employed for finer dust particle sizes which does not settle easily.  In Modular construction Pulse Jet Bag Filter which is Online in cleaning operation, one compartment can be taken out doe maintenance purpose if required.• The cleaning in this type of filter is online i.e. filtration and cleaning simultaneously occurs in a compartment. These type of filters are usually designed for Process application which handle large gas volumes.• In both the above types of Bag Filters outlet type poppet dampers pneumatically operated are required for isolation of compartments. PJBF-Offline
  18. 18.  Constant emission air pollution control (APC) equipment. Suspended particulate emission control using positive filtration. Possible to achieve lower outlet emission. Suitable upto gas temp. of 260 deg C. Can handle various types dust viz. explosive/non-explosive, abrasive, hygroscopic, sticky, coarse/fine. Low initial set-up cost.
  19. 19. Pulse Jet: Pulse Valve
  20. 20.  Pulse Jet Components - Diaphragm Valve
  21. 21. Pulse Jet Component – Air Manifold Tank
  22. 22. Pulse Jet Components – Tubesheet (Cell Plate)
  23. 23. Pulse Jet Components - Venturis
  24. 24. Pulse Jet Components - Bags
  25. 25. Pulse Jet Components – Bags
  26. 26. Pulse Jet Components - Cages
  27. 27. Pulse Jet Components – Cleaning system
  28. 28. Pulse Jet Components – Cleaning system
  29. 29. Pulse Jet Components – Timer or DP Based Control
  30. 30. Pulse Jet Cleaning Operation through Timer
  31. 31. 6 Ways Dust Gets to Clean Air Plenum Hole in Bag Snapband/Flange Top Welding Cracks Clean too soon (Over Cleaning) Not Cleaning (Under Cleaning) Air Leaks at Door Seal
  32. 32. Pulse Jet Component – Blowpipe Normal Holes Enlarged Holes
  33. 33. Pulse Jet– Blowpipe Misalignment Problem of Cage of Blowpipe Less than 1/4 inch (6.35 mm)
  34. 34. PROBLEM POSSIBLE SOLUTION CAUSEHigh DP Bad Gauge Check gauge by blowing into it. If needle does not move replace gauge Leaking gauge Repair leaking gauge pipe pipe Choked gauge Clean / replace gauge pipe pipe Low header Minimum required pressure is pressure 6.3kg/cm2g (90psi). Check supply pipe, drain valve for leaks. Check Diaphragm & solenoid operation
  35. 35. PROBLEM POSSIBLE SOLUTION CAUSEHigh DP Static Charge Static Electricity will interfere with the on Filter cleaning operation. Ground the filter Water in Air Remove water & clean the system. Line Check regularly the manual/Auto drain valve of Air Filter. Replace the defective one. Bag Blinding High moisture & condensation will or chocking cause dust cakes, which are difficult to remove & it blinds/chokes bags. 1)Preheat Bag Filter on start-up & use space heater ON for long shutdown. 2)Wash bags & use after drying. 3) Membrane bags – Permanent soln.
  36. 36. PROBLEM POSSIBLE SOLUTION CAUSEHigh DP Wet Humid compressed Air allows dust Compressed cake to stick to the bags. Ensure, Air clean & dry compressed air Too high Check for airflow figure. If it is very System Air high the A/C Ratio will also be very Flow high causing high DP as well as Re- entrainment Dust Particles Ask customer for actual particle size – Too fine analysis & compare with figures given in the order – Excessive fines will simply choke the pores on bag surface Pulse pipe The pulse pipe nozzle should be mis alignment concentric with the bag centre
  37. 37. PROBLEM POSSIBLE SOLUTION CAUSEHigh DP Bag-Cage For normal felt bags the bag –cage Pinch – not pinch should be within 6mm ~ 12mm. Okay Replace ‘Too tight’ bags, as well as ‘Too loose’ bags Long Pulse Adjust OFF Time by observing Bag Frequency Filter DP and set. Reduce OFF Time by 5seconds interval and watch till DP stabilize Pulse ON Pulse ON time should Typically in the Time range of 80~100ms. Some Fine dust application, it may require higher ON time, but that should be verified first
  38. 38. PROBLE POSSIBLE SOLUTION M CAUSEHigh DP Sequential Any malfunction can cause irregular Controller pulsing, causing raise in DP across Problem BF. Repair/replace card(s) RAV Leakage High Dust If actual value is higher than design, Load check everything and then increase pulse frequency till 10sec interval time. Else, advice customer to go for pre- filter Failure of solenoid valve diaphragm
  39. 39. PROBLEM POSSIBLE SOLUTION CAUSELow DP Bad Gauge Check gauge by blowing into it. If needle does not move replace gauge Leaking / Repair leaking gauge pipe choked gauge pipe Holes in Bags Replace worn bags Low System Check duct systems for deposits & air volume closed dampers – It causes work area problem for dedusting system Wrong Bag Look for dust on clean air plenum & installation blank /dummy the defective bags
  40. 40. PROBLEM POSSIBLE SOLUTION CAUSEEmission Holes in Replace damaged bags bags, cut in snapbands Precoating / Carryout proper precoat/ seeding. If seeding not not possible, wait for sometime till the done for new process stabilizes after start-up bags Wrongly Check all dummies and ensure tight fit, installed else replace them dummies Chemical Check whether bags are being torn attack just by hand pressure. If so, chemical attack is confirmed
  41. 41. PROBLEM POSSIBLE SOLUTION CAUSEPoor Bag Overcleaning Increase pulse frequency or OFF timeLife duration Abrasion Poor inlet design causing high inlet velocity and elbows at inlet can cause accelerated abrasion of bags – Bent / Replace bent / corroded cages corroded Cages High Air High A/C ratio shortens bag life. Volumes
  42. 42. PROBLEM POSSIBLE SOLUTION CAUSEPoor Bag Moisture in Moisture in compressed air might causeLife Comp air acid mist in some application and weaken bags. Moisture also shrink some fabric materials. Take corrective action to control moisture Thermal Some Fabrics like PPS (Ryton) is having Shrinkage thermal shrinkage. Over exposure of high temperature might cause such shrinkage. Setting of temperature alarm is important
  43. 43. PROBLEM POSSIBLE SOLUTION CAUSEHopper Cleaning Check pulsing system as a whole andPlugging malfunction take corrective action Dust disposal Inform customer about mal functioning system – about RAV/Screw Conveyors/ chain malfunction conveyors Wrong design Establish thru’ data collection of Dust disposal system