Transcript Municipal Solid Waste Incineration

Thermochemical Conversion
Technologies
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, hydrogen, or
steam
 Produces electricity, fules (methane,
hydrogen, ethanol, synthetic diesel), and
chemical products
 Temperature > 1300oF
 More flexible than incineration, more
technologically complex than incineration or
pyrolysis, more public acceptance
Flexibility of Gasification
Pyrolysis
Thermal degradation of carbonaceous materials
Lower temperature than gasification (750 – 1500oF)
Absence or limited oxygen
Products are pyrolitic oils and gas, solid char
Distribution of products depends on temperature
Pyrolysis oil used for (after appropriate posttreatment): liquid fuels, chemicals, adhesives, and
other products.
 A number of processes directly combust pyrolysis
gases, oils, and char
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Pyrolyzer—Mitsui R21
Thermoselect (Gasification and
Pyrolysis)
 Recovers a synthesis gas, utilizable glass-like
minerals, metals rich in iron and sulfur from
municipal solid waste, commercial waste,
industrial waste and hazardous waste
 High temperature gasification of the organic
waste constituents and direct fusion of the
inorganic components.
 Water, salt and zinc concentrate are produced
as usable raw materials during the process
water treatment.
 No ashes, slag or filter dusts
 100,000 tpd plant in Japan operating since
1999
Thermoselect
(http://www.thermoselect.com/index.cfm)
Fulcrum Bioenergy MSW to Ethanol Plant
Plasma Arc
 Heating Technique using electrical arc
 Used for combustion, pyrolysis, gasification, metals
processing
 Originally developed by SKF Steel in Sweden for
reducing gas foriron manufacturing
 Plasma direct melting reactor developed by
Westinghouse Plasma Corp.
 Further developed for treating hazardous feedstocks
(Contaminated soils, Low-level radioactive waste,
Medical waste)
 Temperatures (> 1400oC) sufficient to slag ash
 Plasma power consumption 200-400 kWh/ton
 Commercial scale facilities for treating MSW in Japan
Plasma Arc Technology in Florida
 Green Power Systems is proposing to build
and operate a plasma arc facility to process
1,000 tons per day of municipal solid waste
(garbage) in Tallahassee, Florida.
 Geoplasma is proposing to build a similar
facility for up to 3,000 tons of solid waste per
day in St. Lucie County, claims 120 MW will
be produced
 Health risks, economics, and technical issues
still remain
Process
Heated using
– direct current arc plasma for high T organic
waste destruction and gasification and
– Alternating current powered, resistance
hearing to maintain more even T
distribution in molten bath
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
Waste Incineration Disadvantages
High capital cost
Skilled operators are required
(particularly for boiler operations)
Some materials are noncombustible
Some material require
supplemental fuel
Waste Incineration Disadvantages
 Air contaminant potential (MACT standards have
substantially reduced dioxin, WTE 19% of Hg
emissions in 1995 – 90% reduction since then)
 Volume of gas from incineration is 10 x as great
as other thermochemical conversion processes,
greater cost for gas cleanup/pollution control
 Public disapproval
Risk imposed rather than voluntary
Incineration will decrease property value
(perceived not necessarily true)
Distrust of government/industry ability to
regulate
Carbon and Energy
Considerations
 Tonne of waste creates 3.5 MW of energy
during incineration (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)
 Unlike biochemical conversion processes,
nonbiogenic CO2 is generated
 Should not displace recycling
WTE Process
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
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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
Conclusions
 Combustion remains predominant thermal
technology for MSW conversion with
realized improvements in emissions
 Gasification and pyrolysis systems now in
commercial scale operation but industry
still emerging
 Improved environmental data needed on
operating systems
 Comprehensive environmental or life cycle
assessments should be completed
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Updated August 2008