ECS_NB_Chunk_1

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Author:
ChrisC
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78836
Filename:
ECS_NB_Chunk_1
Updated:
2011-04-11 11:07:50
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ECS
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ECS
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  1. What are the steps of the gasification process?
    • 1) Drying (>150C)
    • 2) Pyrolysis (Heating in absence of oxygen, 150-700C)
    • Products are:
    • Liquid Tar ---> BioOil
    • Solid Char ---> Gasification (800 -1100C)
    • Gas Tar
    • 3) Combustion (700 - 1500C)
  2. What is the difference between gasification and combustion?
    • Combustion releases heat packed in chemical bonds while gasification
    • packs more energy into the chemical bonds.
  3. What are the 5 (4+1) main gasification reactions?
    • 1) Water gas Rxn C + H20 -> H2 +CO
    • 2) Boudard Rxn CO2 + C -> 2CO
    • 3) Shift Rxn CO + H20 -> CO2
    • 4) Methanation C + H2 -> CH4

    5) Partial Combustion C + 0.502 -> C02
  4. What is the typical value for equivalence ratio?
    0.2 -> 0.3

    • <0.2 - Incomplete gasification, excess char, low HV
    • >0.4 - Too much combustion Excess CO2, H20, low HV
  5. What are the four main applications for gasifiers?
    • 1) Chemical production (CO2, Methanol, Hydrogen, Amonia)
    • 2) Syngas production (H2 and CO)
    • 3) Electricity/heat production (IGCC)
    • 4) Transport fuel production (Kerosene, Bio-disel)
  6. Give 6 benefits of gasification over direct combustion.
    • 1) Allows for use of high efficiency combined cycle over typical Rankine Cycle.
    • 2) Generates less CO2, NOx, and particulates.
    • 3) For high sulfer coal the elemental sulfer can be retained with limestone during gasification.
    • 4) Gasification/compression may be cheaper than boiler, condenser, engine required for small scale Rankine Cycle
    • 5) Requires less water.
    • 6) Allows for cleaning of dirty fuels for applications like glass manufacturing.

    **If heat is the only product desired combustion may be preferable, especially at small scale.
  7. What effect does temperature have on CO/CO2 concentration at gasification equilibrium?
    • As T increases
    • CO2 Conc (up)
    • CO Conc (down)

    **s shaped curve
  8. What effect does pressure have on CO/CO2 concentration at gasification equilibrium?
    • As P increases
    • CO2 Conc (up)
    • CO Conc (down)

    **exponential curve
  9. What effect does equivalence ratio have on carbon conversion efficiency?
    • As ER increases CCE increase until approximately 0.27.
    • It then decreases again.
  10. What are the four types of gasifiers?
    • 1) Updraft (Medium in bottom, Gas flows out top)
    • 2) Downdraft (Medium in top, Gas flowes out bottom
    • Up and down are both considered moving bed.
    • 3) Fluidized Bed (Best for Biomass)
    • 4) Entrained (High Capacity)
  11. Rank FBB by capacity.
    • 1) Entrained (>100 MW)
    • 2) Fluidized Bed (10 - 100 MW)
    • 3) Updraft (<20 MW)
    • 4) Downdraft (<5 MW)
  12. Rank FBB by temperature.
    • 1) Entrained (1000 - 1500 C)
    • 2) Fluidized Bed (800 - 900 C)
    • 3) Updraft (700 - 900)
    • 4) Downdraft (700 - 1200)
  13. Rank FBB by tar generation.
    • 1) Updraft (High)
    • 2) Fluidized Bed (Medium)
    • 3) Downdraft (Low)
    • 4) Entrained (Absent)
  14. What are the 6 steps to gasifier design?
    • 1) Choose type
    • 2) Design choices (medium and temperature)
    • 3) Energy Balance (How much hydrocarbon is used for combustion?)
    • 4) Process design (mass balance, equilibrium calculation)
    • 5) Gasifier Sizing
    • 6) Optimization (Kinetic modeling)
  15. What are the three types of gasifiing medium?
    • 1) Air - Cheap, convenient, 4-7 MJ/nm3
    • 2) Steam - Increased hydrogen, 10 - 18MJ/nm3
    • 3) Oxygen - Expensive (Requires O2 Plant), 12 - 28MJ/nm3
  16. What are the two things temperature effects during gasification?
    • 1) Composition of gas.
    • 2) Gasification efficiency.

    **Hydrogen yield increase with temperature.
  17. What are the limiting assumptions for equilibrium calculations?
    • 1) Tar effects are ignored.
    • 2) Assume infinite speed.
    • 3) Neglect heat and mass transfer losses.
  18. How is performance determined during optimization?
    • 1) Indicated by cold and hot gas efficiency.
    • 2) Amount of unconverted tar and carbon concentration.
    • 3) Composition and heating value of the product.
  19. What are the three components of kinetic modeling?
    • 1) Hydrodynamic model of the reactor
    • 2) Reaction kinetic models
    • 3) Heat and mass transfer models
  20. What are the three components of kinetic modeling?
    • 1) Hydrodynamic model of the reactor
    • 2) Reaction kinetic models
    • 3) Heat and mass transfer models
  21. What is an advantage of the increased residence time in circulating FB over bubbling FB?
    Prevents back mixing

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