Scale Prevention and Water Softening

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Scale Prevention and Water Softening
2012-10-27 13:24:04

Review for midterm, taken mainly from Unit 2 powerpoint "Part V: Scale Prevention and Water Softening"
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  1. 1. Name four ways to deal with scale
    • 1.Manage scale
    • 2.Chemical addition
    • 3.Remove ions
    • 4.Remove water – leave solids behind
  2. 2. LS
    Lime soda softening
  3. 3. IX
    Ion exchange
  4. 4. RO
    Reverse osmosis
  5. 5. EVAP
  6. 6. NF
  7. 7. Process that converts quick lime into Ca(OH)2
    • Slaking (produces slaked lime)
    • CaO + H2O --> Ca(OH)2
  8. 8. Why not use NaOH to soften water?
    It's more expensive than Lime
  9. 9. NCH
    Non carbonate hardness (permanent)
  10. 10. CH
    Carbonate hardness (temporary)
  11. 11. If there is excess hardness, add...
    Soda ash (sodium carbonate, Na2CO3)
  12. 12. If there is excess alkalinity, add...
    Calcium (e.g. CaCl2) (excess alkalinity can cause damage if it becomes carbon dioxide)
  13. 13. Process used to remove silica
    MAGOX magnesium oxide forms a magnesium hydroxide sludge blanket
  14. 14. CL
    • Cold lime softening
    • Less effective 35-50 ppm
  15. 15. WLS
    • Warm lime softening
    • Effective. (20-30 ppm), used when energy is available
  16. 16. HLS
    • Hot lime softening
    • most effective but uses energy
  17. 17. Historical type of ion exchange medium
    Alumina silicates (zeolites)
  18. 18. SAC
    Strong acid cation exchange
  19. 19. WAC
    Weak acid cation exchange
  20. 20. SBA
    Strong base anion exchange
  21. 21. WBA
    Weak base anion exchange
  22. 22. What kind of ion exchange is used for brine waters?
  23. 23. Three things that can cause fouling of an ion exchange resin
    • Silica
    • Microorganisms
    • Oils
  24. 24. MBIX
    Mixed bed ion exchange (cation and anion exchangers back to back)
  25. 25. The purified water from an RO system
  26. 26. The waste solution from an RO, high in ions
  27. 27. If the pressure spikes on a RO setup, this could mean....
    The filter has been fouled and is getting plugged up
  28. 28. Flux
    The throughput, or flow rate
  29. 29. Which requires a larger pressure: RO or nano filtration?
  30. 30. Order the three filtration methods we've covered from smallest particles filtered to largest particles filtered
    • Nanofiltration
    • Ultrafiltration
    • Microfiltration
  31. 31. MVC
    Mechanical vapor compressor (a type of evaporation unit)
  32. Chemical equation for lime softening to remove calcium
    Ca(HCO3)2 + Ca(OH)2 --> 2CaCO3 +2H2O
  33. Chemical equation for lime softeneing to remove magnesium
    Mg(HCO3)2 + 2Ca(OH)2 --> 2CaCO3 + Mg(OH)2 +2H2O
  34. What chemical is used to improve the effectiveness of lime-soda softening?
    • Sodium Aluminate (Na2Al2O4)
    • (it forms a good sludge blanket)
  35. Why does Silica need to be removed?
    • It can form hard, glassy precipitates quickly and unpredictably
    • Even small amounts of scale can unbalance turbine blades and cause damage
  36. In a lime softener, the part of the process where the precipitate is emptied from the unit
  37. The small crystals that start to form in the slow mix portion of a lime-soda softener
    pin floc
  38. Which works in a wider range of pH?
    SAC is still effective through a wide pH range
  39. DCS
    Digital Control System
  40. A term for the water which does not pass through a filter
  41. What time of filtration is able to remove some multivalent ions?
    Nano filtration
  42. HRSG
    Heat Reused Steam Generators
  43. Can WAC resins be used for OTSGs (Once Through Steam Generators)?
  44. Can WAC resings be used for HRSGs?
    No. TDS mus be 0 for Heat Reused Steam Generators