ECS_N2

Card Set Information

Author:
ChrisC
ID:
65836
Filename:
ECS_N2
Updated:
2011-02-12 14:05:29
Tags:
Energy Conversion Systems
Folders:

Description:
Energy Conversion Systems - Mechanical Engineering
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user ChrisC on FreezingBlue Flashcards. What would you like to do?


  1. What effects the finite rate of combustion?
    • 1) Fluid mechanics (mixing)
    • 2) Heat transfer
    • 3) Chemical reaction rates
  2. What are the three types of combustible fuels?
    • 1) Gas combustion (Easy)
    • 2) Liquid combustion (Fuel must vaporize first)
    • 3) Solid combustion (Determined by carbon combustion)
  3. What are the requirements for combustion (3Ts)?
    • 1) Time
    • 2) Temperature (T > Tign)
    • 3) Turbulence (mixing)
  4. What are the components of solid fuel?
    • 1) Ash
    • 2) Moisture
    • 3) Volatiles
    • 4) Char
  5. What are the steps of solid fuel combustion?
    • 1) Drying and heating (3s)
    • 2) Volatile release (12s)
    • 3) Ignition (25s)
    • 4) Secondary fragmentation (100s)
  6. What are the two types of volatilzation?
    • 1) Volatile burns close to the surface (O2 is readily available, and VM release is moderate).
    • 2) Volatile burns away from the surface (O2 is limited, and VM release is fast).
  7. What is the char burning process and equation?
    • 1) O2 diffuses to the surface of the particle.
    • 2) The O2 reacts with C to form CO or CO2

    • q = Cg/(1/Hm +1/Rc)
    • Hm is the mass transfer coefficient
    • Rc is the Arrhenius reaction rate.
  8. What is the mechanism factor
    Phi is a term in the mass transfer coefficient which is different depending on if CO or CO2 is the main product of the combustion reaction.

    • Phi = 1 when we have primarily CO2 (Low Temp)
    • Phi = 2 when we have primarily CO (High Temp)
  9. What are the two types of ignition?
    • 1) Forced ignition (uses an external source of energy).
    • 2) Self ignition (reactants are raised to there Tign).
  10. Give three types of industrial combustors.
    • 1) Pulverized coal (Fine suspension) ~1300C
    • 2) Stoaker fired (Fixed grate) ~1100C
    • 3) Fluidized bed (Semi-fluid) ~850C
  11. What are some benefits to fluidized bed boilers?
    • 1) Highly fuel flexible (Large thermal mass).
    • 2) Low acid gas emissions (mixing allows fir low temperature combustion).
  12. What are the two types of flame groupings?
    • 1) Named by mixing
    • Premixed flame - Mixed before ignition(Blue, intense)
    • Diffusion flame - Fuel is ignited and air mixes with it as it burns (Orange, Less intense)
    • 2) Name by fluid flow
    • Laminar - Longer flame
    • Turbulent - Shorter flame
  13. What are the major characteristics and issues with flames?
    • 1) Burning velocity
    • 2) Flammability limit
    • 3) Flame quenching
    • 4) Flame stabilization
    • 5) Adiabatic flame temperature
  14. What does the flame velocity depend on?
    • Fuel type
    • Air fuel ratio (Highest close to stochiometric ratio)
    • Inert gas (N2) amount
    • Ambient pressure
    • Temperature
    • Fluid dynamics of flow
  15. What effects the flammability limit?
    • 1) Type of fuel
    • LFL = 1/sum(yi/LFLi) - yi is mol fraction
    • 2) Temperature
    • As T Up, LFL down, UFL up
  16. What are the two aspects of flame quenching
    • 1) Hot gases and flames lose heat if they come in contact with a cooler surface.
    • 2) Free radicals tend to diffuse towards the surface of solid walls.
  17. Name two ways to get flame stabilization.
    • 1) Opposed jet systems
    • 2) Flame stabilization rings
  18. What is the adiabatic flame temperature equation?
    • HrTr = HpTp
    • Tp ~ Tr + fHc/Cp

    • Hc - heat of combustion of fuel
    • Cp - specific heat of the products
    • f - mass ratio of products and reactants
  19. Why is the actual flame temperature lower than adiabatic?
    • 1) Combustion is not instantaneous and heat is lost to surroundings.
    • 2) Above 1650C CO2 and H2O dissociate absorbing heat.
  20. What are the types of air pollutants?
    • 1) GHGs (CO2, N2O CH4, CFC, HFC)
    • 2) Acid Rain (SO2, NO, NO2)
    • 3) Others (Hg, Pb, Cd)
    • 4) Particulates
  21. Briefly describe smog, VOC, smoke, haze
    • Smog - Ozone that forms through reaction of NOx and VOC with other chemicals, especially in sunlight.
    • VOC - Unburnt hydrocarbons.
    • Smoke - Solid + Liquid + Gas (Near source).
    • Haze - Far away from source.
  22. Give three ways which NOx forms
    • 1) Thermal NOx - Oxidation of atmospheric N2 at high temperatures (T > 1000C)
    • N2 + O2 -> 2NO
    • 2) Prompt NOx - Reaction with hydrocarbon radicals (T > 1000C)
    • 3) Fuel Nitrogen - N + O -> NO2 at all temperatures
  23. Give 5 (3 and 2) ways to control SO2 emissions.
    • In Situ
    • Low surfer fuel
    • Desulferize the fuel (coal cleaning)
    • Capture SO2 in combustion using sorbents
    • Post Combustion
    • Wet scrubbing
    • Ca/S = 1.5, produces high quality CaSO4 (gypsom), disposal of wet slurry is an issue.
    • Dry scrubbing
    • Contains untreated CaO, Ca/S =2.5
  24. Give 5 (3 and 2) ways to control NOx emissions.
    • In Situ
    • (1) Fluidized combustion --best
    • (2) Low NOx burners with staged air supply (40 -60%)
    • (3) Flue gas recirculator
    • Post Combustion
    • Selective catalytic reactor (SCR)
    • >90%, uses amonium and catalysts (Ti - oxides)
    • Selective non-catalytic reactor (SNCR)
    • Cheaper alternative, not as effective
  25. Give 4 ways to control particulates post combustion.
    • (1) Fabric filter (bag house) --best
    • (2) Electrostatic precipitator
    • (3) Cyclone
    • (4) Inertia separator

What would you like to do?

Home > Flashcards > Print Preview