ECS_NB1

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Author:
ChrisC
ID:
78575
Filename:
ECS_NB1
Updated:
2011-04-10 18:15:30
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Energy Conversion Systems
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Engineering energy conversion systems
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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
  22. What are the three ways to characterize biomass?
    • 1) Biochemical (Protein, oil, starch, sugar, fiber)
    • 2) Elemental (C,H,O,N,S,Cl,Ash)
    • 3) Proximate (Volatile, fixed ash, fixed carbon)
  23. What are the constituents of fiber?
    • 1) Cellulose
    • 2) Hemicellulose
    • 3) Lingin
  24. What are the three types of biomass conversion?
    • 1) Thermochemical (Fast ->Combustion, gasification, methanol production.
    • 2) Biochemical (Slow -> Digestion, ethanol production)
    • 3) Chemical (Biodisel from seed oils, animal fats, and waste oils)
  25. What are three things that the government has done to encourage ethanol expansion?
    • 1) Contingent loan guarantees.
    • 2) Public awareness
    • 3) Subsidies for production facilities
  26. What is the chemical mixture of ethanol and what percentage of heating value of gasoline does it have?
    C2H6O

    HHV = 0.75*HHV(gas)
  27. What blend with gasoline is required to be termed flex fuel?
    85%
  28. Give the basics of the bio-refinery concept.
    Biomass is used both to produce fuels (ethanol - biochemical) and gasification (Thermochemical). These are used for fuels, chemicals and materials, while the residue and waste material is used to supply combined heat and power requirements.
  29. What are the 5 steps in ethanol production?
    • 1) Preprocessing
    • milling, grinding, liquefying
    • Get cellulose ready
    • 2) Hydrolysis
    • Enzymes are used to break cellulose chains into glucose
    • 3) Fermentation
    • C6H12O2 + yeast --> 2C2H6O + 2CO2
    • 4) Distillation
    • Remove impurities
    • 5) Dehydration
  30. What do lignocellulose require before being converted to ethanol?
    Ligno cellulose does has lignin which must be preprocessed. Steam explosions are used to make celloulose available for hydrolysis.
  31. What are the approximate heating values (MJ/kg) of some various fuels?
    • Gasoline (44)
    • Heating oil(45.5)
    • Diesel (42)
    • Ethanol (38)
    • Bio-disel (37)
    • Bio-oil (18-20)
  32. How is biodesil formed?
    Oil + (A)CH3OH ---> (B)C17H33CO2CH3 + (C) C3H(OH)3

    Oil + Methanol ---> FAME (biodisel) + Glycerol

    **FAME stands for Fatty Acid Methyl esters
  33. What are some benefits of Bio-Diesel?
    • 1) Burns more completely due to high O2 content.
    • 2) Offers more lubrication.
    • 3) Higher flash point
    • 4) Reduced CO, Sulfate, soot.

    **Has a smaller heating value but above bio-oils.
  34. Give some characteristics of torrefaction process.
    • 1) Slow roasting between 200 - 300C.
    • 2) Anaerobic environment.
    • 3) Heating rate < 50C/min
    • 4) Residence time ~ 30min at T>200C
    • 5) Ambient pressure
  35. Describe the torrefaction process steps
    • 1) 125C - Majority of moisture evaporates
    • 2) 175C - Devolitisation of hemicellulose begins
    • Wood is unbound
    • 3) 240C - Hemicellulose, VOCs and extractants are burned off
    • Wood becomes friable (40 on Hardgrove)
    • 4) 470C - Final torrefaction occurs, wood becomes hydrophobic.
  36. Give some benefits of torrefaction.
    • Lower transport cost
    • Inert (no mold)
    • Less moisture absorbing
    • Brittle (80-90% easy to pulverize)
    • Higher energy density
    • More uniform than regular stock
    • low moisture content (hydrophobic)
    • does not get very wet when exposed to moisture (hydrophobic)
    • No smoking during combustion
    • Stable flame during combustion
  37. Give 6 different torrification technologies.
    • 1) Rotary drying drum (Rotary kiln)
    • 2) Screw convener
    • 3) Multiple hearth furnace (In use and scalable)
    • 4) Torbed flash (Fast 90s-5min, risk or carbonization and tar formation. Relatively new technology)
    • 5) Compact moving bed
    • 6) Belt dryer (Simple and proven, consistent)
  38. Give 7 difficulties in operating a coal boiler on biomass.
    • 1) Changed emissions
    • 2) Increased corrosion and fouling
    • 3) Change in performance
    • 4) Change in furnace heat absorption
    • 5) Storage
    • 6) Fuel pulverization is more difficult
    • 7) More moisture
  39. What index is used to measure the grind ability of a fuel?
    Hardgrove index
  40. Give 3 types of co-firing.
    • 1) Direct - Simple, cheap
    • 2) Indirect - Totally independent of main boiler
    • 3) Parallel - Feed separate but burned together
  41. Describe lingan power plant
    • 1) Coal is pulverized and sent to the boiler
    • 2) Coal is fired generating steam. Particulates are removed and SO2 scrubber is used before exhaust goes to stack.
    • 3) Steam drives a turbine generator then goes through a condensation pump, a feed pump and back to the boiler.
    • 4) Electricity is generated. Ocean water is used to cool turbine when required.

    **25% of NSP generating capacity and provides 40% of electricity generation.
  42. Give the 5 carbon abatement options outlined in class
    • 1) Energy conservation (Manage the demand)
    • 2) Efficient generation technology (e.g. Supercritical or IGCC)
    • 3) Carbon free energy use (Electrical where energy comes from non carbon source)
    • 4) Biomass combustion (or co-firing)
    • 5) Carbon capture and sequestration
  43. Give the 3 types of carbon capture in increasing maturity.
    • 1) Amine Scrubbing (NH4 or other amine solvent captures CO2)
    • 2) Oxygen combustion
    • 3) Chemical looping combustion
    • 2 and 3 are in-situ techniques
  44. Give the 3 types of carbon sequestration (storage)
    • 1) Ocean - Depth >1Km, Occurs naturally, very new
    • 2) Coal mines - Pump in CO2, Methane comes out and can be used to generate energy
    • 3) Oil and Gas Reserves - (Enhance oil recovery) CO2 disolves in oil and reduces its viscosity (increasing recovery by (30-60%). Reservoir acts as a storage site for future CO2. Mature Technology.
    • 4) Geological Reservoir
  45. Give some disadvantages to CCS
    • 1) 10 times larger plant required for 0.75 emissions
    • 2) 1.5 c/kwh increase in generation cost
    • 3) 10 to 15% reduction in efficiency

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