Transcript Municipal Solid Waste Incineration

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)
Waste
Flue Gas
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
Ash Conveyer
Metal Recovery
Mass Burn Facility – Pinellas County
Tipping
Floor
Overhead Crane
Turbine Generator
Fabric Filter
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Updated August 2005