Municipal Solid Waste Incineration

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Municipal Solid Waste Incineration
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Combustion Types

• Incineration (energy recovery through complete
  oxidation)
• Mass Burn
• Refuse Derived Fuel
• Pyrolysis
• Gasification
• Plasma arc (advanced thermal conversion)

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Gasification

• Partial oxidation process using air, pure oxygen,
  oxygen enriched air, or steam
• Carbon converted into syngas
• More flexible than incineration
• More public acceptance

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Flexibility of Gasification
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Pyrolysis

• Thermal degradation of carbonaceous materials
• Lower temperature than gasification
• Absence or limited oxygen
• Products are gas, liquid, solid char
• Distribution of products depends on temperature

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Waste Incineration - Advantages

• Volume and weight reduced (approx. 90 vol. and
  75 wt reduction)
• Waste reduction is immediate, no long term
  residency required
• Destruction in seconds where LF requires 100s of
  years
• Incineration can be done at generation site
• Air discharges can be controlled
• Ash residue is usually non-putrescible, sterile,
  inert
• Small disposal area required
• Cost can be offset by heat recovery/ sale of
  energy

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Incineration
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Environmental Considerations

• Tonne of waste creates 3.5 MW of energy (eq. to
  300 kg of fuel oil) powers 70 homes
• Biogenic portion of waste is considered CO2
  neutral (tree uses more CO2 during its lifecycle
  than released during combustion)
• Should not displace recycling

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Waste Incineration - Disadvantages

• High capital cost
• Skilled operators are required (particularly for
  boiler operations)
• Some materials are noncombustible
• Some material require supplemental fuel
• Public disapproval
• Risk imposed rather than voluntary
• Incineration will decrease property value
  (perceived not necessarily true)
• Distrust of government/industry ability to
  regulate

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Three Ts

• Time
• Temperature
• Turbulence

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System Components

• Refuse receipt/storage
• Refuse feeding
• Grate system
• Air supply
• Furnace
• Boiler

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Energy/Mass Balance
Energy Loss (Radiation)
Flue Gas
Waste
Mass Loss (unburned C in Ash)
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Flue Gas Pollutants

• Particulates
• Acid Gases
• NOx
• CO
• Organic Hazardous Air Pollutants
• Metal Hazardous Air Pollutants

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Particulates

• Solid
• Condensable
• Causes
• Too low of a comb T (incomplete comb)
• Insufficient oxygen or overabundant EA (too high
  T)
• Insufficient mixing or residence time
• Too much turbulence, entrainment of particulates
• Control
• Cyclones - not effective for removal of small
  particulates
• Electrostatic precipitator 
• Fabric Filters (baghouses) 

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Metals

• Removed with particulates
• Mercury remains volatilized
• Tough to remove from flue gas
• Remove source or use activated carbon (along with
  dioxins)

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Acid Gases

• From Cl, S, N, Fl in refuse (in plastics,
  textiles, rubber, yd waste, paper)
• Uncontrolled incineration - 18-20 HCl with pH 2
• Acid gas scrubber (SO2, HCl, HFl) usually ahead
  of ESP or baghouse
• Wet scrubber
• Spray dryer
• Dry scrubber injectors

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Nitrogen removal

• Source removal to avoid fuel NOx production
• T lt 1500 F to avoid thermal NOx
• Denox sytems - selective catalytic reaction via
  injection of ammonia

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Air Pollution Control

• Remove certain waste components
• Good Combustion Practices
• Emission Control Devices

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Electrostatic Precipitator
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Recovery of metals from Ash

• (Fe, Al, Cu, Zn, Cr, and Pb) concentrated in
  bottom ash mostly,
• while Cd existed primarily in fly ash.
• Fe, 2.69  102,
• Al, 1.46  104,
• Cu, 4.91  104,
• Zn, 6.92  101,
• Cr, 5.10  104,
• Pb 1.85  104

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Ash

• Bottom Ash recovered from combustion chamber
• Heat Recovery Ash collected in the heat
  recovery system (boiler, economizer, superheater)
• Fly Ash Particulate matter removed prior to
  sorbents
• Air Pollution Control Residues usually combined
  with fly ash
• Combined Ash most US facilities
• combine all ashes

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Schematic Presentation of Bottom Ash Treatment
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Ash Reuse Options

• Construction fill
• Road construction
• Landfill daily cover
• Cement block production
• Treatment of acid mine drainage

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Refuse Boiler
Fabric Filter
Stack
Spray Dryer
Tipping Floor
Ash Conveyer
Metal Recovery
Mass Burn Facility Pinellas County
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Overhead Crane
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Turbine Generator
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Fabric Filter
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