ECS_NB_Chunk3

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Author:
ChrisC
ID:
78834
Filename:
ECS_NB_Chunk3
Updated:
2011-04-11 11:04:43
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ECS
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ECS
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  1. What are the four types of pulverized coal plants?
    • Wet bottom (slagging T>Tmelt ash)
    • Dry bottom ( >85% fly ash)
    • Front Fired
    • Tangental Fired
  2. Give the steps in pulverized coal firing.
    • Coal -> Crushed -> Screen -> Pulverized -> Burner -> Ash
    • 0.3-0.4m <10mm <74micron air^
  3. Rank fuels on volumetric heat release rate (High to Low)
    Gasoline, Oil, Anthracite, Bituminous, Lignite, Biomass
  4. Rank fuels on capacity required (high to low)
    Lignite, High VOC Bituminous, Medium Bituminous
  5. Rank fuels on Height to pipes distance.
    Anthracite, Bituminous, Oil
  6. What effect does capacity and temperature have on grate heat rate?
    As both increase heat rate increases.
  7. How do you convert to steam boiler capacity?
    t/h(steam) = 0.75 MWth heat input
  8. Give three characteristics of Fluidized Bed Boilers
    • 1) Fuel burns in fluidized suspension of inert particles.
    • 2) Combustion zone is kept low by extracting heat directly from combustion zone.
    • 3) Exceptionally high degree of heating.
  9. What is the difference between FB and other boilers?
    Difference lies in how the gas and solids move around in the furnace.
  10. What are the main advantages of FB boilers?
    • 1) Low emission of SO2 and NOx
    • 2) Very fuel flexible
    • 3) Easy to operate and stable
    • 4) Lower maintenance
    • 5) Cost less than PC for lignite fuels
    • 6) Cost less than PC if FGD and SCR is required?

    **Note FB has a higher N20 (GHG) emssion than PC.
  11. What are the two main types of FB?
    • 1) Bubbling - Low Speed (1-2m/s), 10mm dp
    • 2) Circulating - High speed (4.5-5.5m/s), 6mm dp
  12. What kind of fuel can FB IDEALLY burn?
    FB can burn any fuel that has energy sufficient to raise itself and combustion gas above its ignition temperature.
  13. Why is FB insensitive to quality of fuel (2)?
    • 1) Large thermal inertia allows most fuels to be heated to ignition without losing too much heat from the boiler.
    • 2) Mixing makes it possible to dissipate the released heat and fresh fuel particles around the bed for easy ignition.
  14. Why is FB low acid rain emissions (2)?
    • 1) Low combustion temp allows limestone to capture Sulfur in combustion zone.
    • 2) Low temp and stagged air does not allow nitrogen to form NOx.
  15. Rank fuels on volumetric heat release rate (High to Low)
    Gasoline, Oil, Anthracite, Bituminous, Lignite, Biomass
  16. Rank fuels on capacity required (high to low)
    Lignite, High VOC Bituminous, Medium Bituminous
  17. Rank fuels on Height to pipes distance.
    Anthracite, Bituminous, Oil
  18. What effect does capacity and temperature have on grate heat rate?
    As both increase heat rate increases.
  19. How do you convert to steam boiler capacity?
    t/h(steam) = 0.75 MWth heat input
  20. Give three characteristics of Fluidized Bed Boilers
    • 1) Fuel burns in fluidized suspension of inert particles.
    • 2) Combustion zone is kept low by extracting heat directly from combustion zone.
    • 3) Exceptionally high degree of heating.
  21. How does circulating fluidized bed boiler work (2)?
    • 1) CFD Loop of solids
    • 2) Convection loop of gas
  22. Give the steps to operate a FB boiler (4).
    • 1) Preheat bed solids
    • 2) Let T increase until > Tign
    • 3) Extract heat
    • Water tubes in bed
    • Regulating air passing through bed
    • 4) Ash either stays in bed or entrained as fly ash.
  23. Give 3 advantages to keeping FB temperature low.
    • 1) Avoid melting or agglomerating bed solids
    • 2) Reduction of NOx
    • 3) Allows for Sulfur removal.
  24. What are the FB rules of thumb (6)?
    • 1) A = Vgas/Uf
    • 2) Hb = 0.4 - 1.5m (Hb = 0.7Uf - Gives residence time of 0.7s)
    • 3) Dp ~ 0.75mm
    • 4) Uf = 2.5Umf
    • 5) Qgrate = 3.3*Uf|300k/excess air (1.2 = 20% excess) (Mw/m2)
    • 6) About 2.908 MJ/kg heat is generated when 1kg of dry air is consumed.

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