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