Municipal Solid Waste Incineration
Municipal Solid Waste Incineration
Combustion TypesIncineration (energy recovery through complete oxidation)Mass BurnRefuse Derived FuelPyrolysisGasificationPlasma arc (advanced thermal conversion)
GasificationPartial oxidation process using air, pure oxygen, oxygen enriched air, or steamCarbon converted into syngasMore flexible than incineration More public acceptance
Flexibility of Gasification
PyrolysisThermal degradation of carbonaceous materialsLower temperature than gasificationAbsence or limited oxygenProducts are gas, liquid, solid charDistribution of products depends on temperature
Waste Incineration - AdvantagesVolume and weight reduced (approx. 90% vol. and 75% wt reduction)Waste reduction is immediate, no long term residency requiredDestruction in seconds where LF requires 100s of yearsIncineration can be done at generation site Air discharges can be controlled Ash residue is usually non-putrescible, sterile, inertSmall disposal area requiredCost 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 homesBiogenic portion of waste is considered CO2 neutral (tree uses more CO2 during its lifecycle than released during combustion)Should not displace recycling
Waste Incineration - DisadvantagesHigh capital costSkilled operators are required (particularly for boiler operations)Some materials are noncombustible Some material require supplemental fuelPublic disapprovalRisk imposed rather than voluntaryIncineration will decrease property value (perceived not necessarily true)Distrust of government/industry ability to regulate
Three TsTimeTemperatureTurbulence
System ComponentsRefuse receipt/storageRefuse feedingGrate systemAir supplyFurnaceBoiler
Energy/Mass BalanceWasteFlue GasEnergy Loss (Radiation)Mass Loss (unburnedC in Ash)
Flue Gas PollutantsParticulatesAcid GasesNOxCOOrganic Hazardous Air PollutantsMetal Hazardous Air Pollutants
ParticulatesSolid 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 ControlCyclones - not effective for removal of small particulates Electrostatic precipitator Fabric Filters (baghouses)
MetalsRemoved with particulates Mercury remains volatilized Tough to remove from flue gas Remove source or use activated carbon (along with dioxins)
Acid GasesFrom Cl, S, N, Fl in refuse (in plastics, textiles, rubber, yd waste, paper) Uncontrolled incineration - 18-20% HCl with pH 2Acid gas scrubber (SO2, HCl, HFl) usually ahead of ESP or baghouse Wet scrubber Spray dryer Dry scrubber injectors
Nitrogen removalSource removal to avoid fuel NOx production T < 1500 F to avoid thermal NOx Denox sytems - selective catalytic reaction via injection of ammonia
Air Pollution ControlRemove certain waste componentsGood Combustion PracticesEmission Control Devices
DevicesElectrostatic PrecipitatorBaghousesAcid Gas ScrubbersWet scrubberDry scrubberChemicals added in slurry to neutralize acidsActivated CarbonSelective Non-catalytic Reduction
Role of Excess Air Control Three TsAmount of Air AddedT
Role of Excess Air ContdIncreasing MoistureAmount of Air Added
Role of Excess Air ContdInsufficient O2StoichiometricExcess AirPICs/ParticulatesNOxTOptimum T Range(1500 1800 oF)Amount of Air Added
AshBottom Ash recovered from combustion chamberHeat Recovery Ash collected in the heat recovery system (boiler, economizer, superheater)Fly Ash Particulate matter removed prior to sorbentsAir Pollution Control Residues usually combined with fly ashCombined Ash most US facilities combine all ashes
Schematic Presentation of Bottom Ash Treatment
Ash Reuse OptionsConstruction fillRoad constructionLandfill daily cover Cement block productionTreatment of acid mine drainage
StackRefuse BoilerTippingFloorFabric FilterSpray DryerMetal RecoveryAsh ConveyerMass Burn Facility Pinellas County
Overhead Crane
Turbine Generator
Fabric Filter
Return to Home pageUpdated August 2005