ECS_N2

• 1) Fluid mechanics (mixing)
• 2) Heat transfer
• 3) Chemical reaction rates

• 1) Gas combustion (Easy)
• 2) Liquid combustion (Fuel must vaporize first)
• 3) Solid combustion (Determined by carbon combustion)

• 1) Time
• 2) Temperature (T > Tign)
• 3) Turbulence (mixing)

• 1) Ash
• 2) Moisture
• 3) Volatiles
• 4) Char

• 1) Drying and heating (3s)
• 2) Volatile release (12s)
• 3) Ignition (25s)
• 4) Secondary fragmentation (100s)

• 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).

• 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.

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)

• 1) Forced ignition (uses an external source of energy).
• 2) Self ignition (reactants are raised to there Tign).

• 1) Pulverized coal (Fine suspension) ~1300C
• 2) Stoaker fired (Fixed grate) ~1100C
• 3) Fluidized bed (Semi-fluid) ~850C

• 1) Highly fuel flexible (Large thermal mass).
• 2) Low acid gas emissions (mixing allows fir low temperature combustion).

• 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

• 1) Burning velocity
• 2) Flammability limit
• 3) Flame quenching
• 4) Flame stabilization
• 5) Adiabatic flame temperature

• Fuel type
• Air fuel ratio (Highest close to stochiometric ratio)
• Inert gas (N2) amount
• Ambient pressure
• Temperature
• Fluid dynamics of flow

• 1) Type of fuel
• LFL = 1/sum(yi/LFLi) - yi is mol fraction
• 2) Temperature
• As T Up, LFL down, UFL up

• 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.

• 1) Opposed jet systems
• 2) Flame stabilization rings

• 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

• 1) Combustion is not instantaneous and heat is lost to surroundings.
• 2) Above 1650C CO2 and H2O dissociate absorbing heat.

• 1) GHGs (CO2, N2O CH4, CFC, HFC)
• 2) Acid Rain (SO2, NO, NO2)
• 3) Others (Hg, Pb, Cd)
• 4) Particulates

• 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.

• 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

• 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

• 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

• (1) Fabric filter (bag house) --best
• (2) Electrostatic precipitator
• (3) Cyclone
• (4) Inertia separator