Municipal Solid Waste Incineration. Combustion Types Incineration (energy recovery through complete...
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Transcript of Municipal Solid Waste Incineration. Combustion Types Incineration (energy recovery through complete...
Municipal Solid Waste Incineration
Combustion Types
Incineration (energy recovery through complete oxidation)– Mass Burn– Refuse Derived Fuel
PyrolysisGasificationPlasma arc (advanced thermal
conversion)
Gasification
Partial oxidation process using air, pure oxygen, oxygen enriched air, or steam
Carbon converted into syngasMore flexible than incineration More public acceptance
Flexibility of Gasification
Pyrolysis
Thermal degradation of carbonaceous materials
Lower temperature than gasificationAbsence or limited oxygenProducts are gas, liquid, solid charDistribution 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 ConsiderationsTonne 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
TimeTemperatureTurbulence
System Components
Refuse receipt/storageRefuse feedingGrate systemAir supplyFurnaceBoiler
Energy/Mass Balance
Waste Flue Gas
Energy Loss (Radiation)
Mass Loss (unburnedC in Ash)
Flue Gas Pollutants
ParticulatesAcid GasesNOx
COOrganic Hazardous Air PollutantsMetal 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 componentsGood Combustion PracticesEmission Control Devices
Devices
Electrostatic PrecipitatorBaghousesAcid Gas Scrubbers
– Wet scrubber– Dry scrubber– Chemicals added in slurry to neutralize
acids
Activated CarbonSelective Non-catalytic Reduction
Role of Excess Air – Control Three Ts
Amount of Air Added
Insufficient O2
Stoichiometric
Excess Air
T
Role of Excess Air – Cont’d
Insufficient O2
Stoichiometric
Excess Air
Increasing Moisture
Amount of Air Added
Role of Excess Air – Cont’d
Insufficient O2
Stoichiometric
Excess Air
PICs/Particulates
NOxT
Optimum T Range
(1500 – 1800 oF)
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 fillRoad constructionLandfill daily cover Cement block productionTreatment of acid mine drainage
StackRefuse Boiler
TippingFloor
Fabric FilterSpray Dryer
Metal Recovery
Ash Conveyer
Mass Burn Facility – Pinellas County
Overhead Crane
Turbine Generator
Fabric Filter