NSEN 618 Class 12

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NSEN 618 Class 12

• Combustion -- all of Chapter 4 and some of
  Chapter 5
• Learn how to calculate combustion events
• Temperature
• Ignition
• Volume increase
• Pressure
• Explosions
• Apply to Incinerator types
• Starved air
• Excess air
• Pyrolysis
• Reduction.

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Terminology

• Reactions All chemical transformations
• Combustion Rapid oxidation generally of
  hydrocarbons
• Incineration Controlled combustion to
  destruction
• Deflagration Explosive burning but vr lt vs
• Explosion Destructive pressure release
• Detonation Special case Deflagration vr gt vs

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Special Combustion Processes

• Combustion
• C O2 --gt CO2
• C H2 O2 --gt CO2 2H2O
• H2 O2 --gt 2H2O
• Explosives - Anything that has a destructive
  pressure increase is an explosion)
• NaNO2 C --gt CO2 N2
• NH4NO3 --gt 2 H2O 1/2 N2 NO

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Calculations

• One needs to understand chemistry
• Phase changes
• Thermodynamics
• Physics
• Operations

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Combustion

• The Governing Adiabatic Equation
• Disposition of various components
• H2 --gt H2 O
• C --gt CO2
• N --gt N2
• Cl, S, P, F --gt Acids, i.e., HCl, H2SO4, HF
• Metals --gt Oxides --gtAshes
• SiO2 --gt SiO2 Dust to Dust

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Method

• Set up Chemical Equation
• Select the least amount that is of interest
• Assign that to be 1 mole
• Adjust molar volume of the remaining reactants
  and POCs
• Calculate weight percent if necessary (it usually
  is, since we think of our real world in terms of
  weight percent although, in fact it is mass
  percent)

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Method (continued)

• Given the calculated T, is it above ignition
  temperature?
• Where does ignition temperature come from?
• Generally around 250 C for flammables
• 400 C for nitrate
• 800 C for almost everything
• If T gt 1000 C, should reevaluate specific heats
  depending on the degree of accuracy you need

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Method (continued)

• Double check the heats of reaction and make sure
  they make sense
• Negative heats of formation for reactants
  decrease the heat of reaction
• Positive heats of formation for reactants
  increase the heat of reaction over and above that
  of the heat of formation of the POCs
• Evaluate the gaseous products
• Compute pressure increases or volume increases of
  the POCs against the Reactants as desired
• Use PV nRT as necessary

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Examples using Excel Combustion Files

• H2 O2
• C O2
• C2H4
• NaNO3 C
• Ammonium Nitrate
• TNT

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Types of Combustion

• Combustion (low velocity - constant pressure)
• Stoichemetric, Starved air, Excess air
• Deflagration (high velocity - pressure build-up)
• Detonation (reaction velocity gt velocity of sound
  - pressure build-up)

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Special Conditions

• Ignition Temperature
• Flame Temperature
• Flash point
• Flash over
• LEL, UEL (Lower and upper explosion limit)

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LEL, UEL

• Concentration of a gaseous fuel (CH4, C2H2, H2 ,
  for example) at which the reaction will
  propagate unassisted. Generally this is equal
  the concentration at which the calculated
  adiabatic temperature equals the ignition
  temperature.
• Note however that ignition temperature is
  pressure sensitive, sensitive to catalytic
  influences.
• Note also that Temperature adiabatic delta T
  initial T
• Nevertheless, the adiabatic calculation is very
  close to correct.

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Why Incinerate??

• Satisfies all 10 CFR 61 WAC except finely divided
  Particulates
• Volume Reduction - Mostly a Cost Issue
• Destroys organics not conducive to good
  cementation
• Mostly imposed by 40 CFR 268 Hazardous Waste
  Treatment Standards
• Required for 40 CFR 761 PCB

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Equipment Issues

• Feeding
• Ash removal
• Filtration (particularly Cl, NOx, dioxins, SOx
• High temperature materials
• Contamination spread
• Repair and maintenance
• Uniform feed - trash vs. known input

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Operational Conditions

• 800 - 1100 C First Stage
• 2000 C volatile destruction
• Sub atmospheric conditions

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Alternative Incinerator Variants

• Fixed hearth
• Moving hearth
• Rotary kiln
• Dual stage
• Cyclone furnaces
• Pyrolysis

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More Alternative Incinerator Variants

• Slagging pyrolysis
• Gravity feed
• Molten salt
• Acid bath
• Fluidized bed
• Glass furnace based
• Plasma driven