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					Municipal Solid Waste
Incineration
Combustion Types
Incineration (energy recovery through
 complete oxidation)
  – Mass Burn
  – Refuse Derived Fuel
Pyrolysis
Gasification
Plasma arc (advanced thermal
 conversion)
Gasification
Partial oxidation process using air, pure
 oxygen, oxygen enriched air, or steam
Carbon converted into syngas
More flexible than incineration
More public acceptance
Flexibility of Gasification
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
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
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
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
Three Ts
Time
Temperature
Turbulence
System Components
Refuse receipt/storage
Refuse feeding
Grate system
Air supply
Furnace
Boiler
Energy/Mass Balance

            Energy Loss (Radiation)



                           Flue Gas
Waste




            Mass Loss (unburned
            C in Ash)
Flue Gas Pollutants
Particulates
Acid Gases
NOx
CO
Organic Hazardous Air Pollutants
Metal Hazardous Air Pollutants
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)
Metals
Removed with particulates
Mercury remains volatilized
Tough to remove from flue gas
Remove source or use activated carbon
 (along with dioxins)
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
Nitrogen removal
Source removal to avoid fuel NOx
 production
T < 1500 F to avoid thermal NOx
Denox sytems - selective catalytic
 reaction via injection of ammonia
Air Pollution Control
Remove certain waste components
Good Combustion Practices
Emission Control Devices
Devices
 Electrostatic Precipitator
 Baghouses
 Acid Gas Scrubbers
   – Wet scrubber
   – Dry scrubber
   – Chemicals added in slurry to neutralize acids
 Activated Carbon
 Selective Non-catalytic Reduction
Role of Excess Air – Control
Three Ts
                       Stoichiometric



 T




     Insufficient O2            Excess Air
              Amount of Air Added
Role of Excess Air – Cont’d

                     Stoichiometric




                                           Increasing Moisture




   Insufficient O2            Excess Air
       Amount of Air Added
           Role of Excess Air – Cont’d

                                     Stoichiometric


                                            NOx
             T
  Optimum T
     Range
(1500 – 1800 oF)
                   PICs/Particulates

                   Insufficient O2            Excess Air
                        Amount of Air Added
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
Schematic Presentation of
Bottom Ash Treatment
Ash Reuse Options
Construction fill
Road construction
Landfill daily cover
Cement block production
Treatment of acid mine drainage
                                             Refuse Boiler
    Stack        Fabric Filter
                          Spray Dryer
                                                             Tipping
                                                             Floor
Ash Conveyer




               Metal Recovery


      Mass Burn Facility – Pinellas County
Overhead Crane
Turbine Generator
Fabric Filter
       Return to Home page




Updated August 2005

				
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