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Solid Waste Management through the Application of Thermal Methods

Waste Mamthe description of the alternative thermal practices for muninversion of waste into harmless materials and the utilization of thewithin waste as heat, steam, electrical energy or coey include all processes converting the waste content into gas, liquid and solid productsor consequent release of thermal energyAccording to the New Waste Framework Directive 2008/98/EC, the waste treatmentpanied by signifincluded in thehe priorities in the wastegementsector shows that energy recovery is more desired option in relation to the final disposalMunicipal solid WastePreyerecyclingREnergy recoveryDisposalFig 2 Pyramid of the priorities in the wastearound the world deTechnologically advanced countries in the domain of waste management are characterizedbasis of Eurostat data the percentages of municipal waste treated with thermal methods forthe year 2007 in Denmmbourg, Netherlands, France(Autret et al, 2007)Germany, Belgium and Austria were 53 % 47%, 47%, 38%o, 36%, 35%6, 34% and 28%espectively On the other hand, there are still Member-States that do not apply thermalniques in order to handle the generated municipal waste, especially in the southernEurope and the Baltic Sea Such countries include Bulgaria, Estonia, Iceland, Cyprus, Latvia,Lithuania, Slovenia, Malta, poland, Romania and Greecend Europe and worldwide is provided, Data referring to incineration -mass buris, gasification and plasma technologyted theects of each technology, the indicative respective reactions, as well as the peach thermal process,bed Theeaning systems are also discussed

Solid Waste Management through the Application of Thermal MethodsFEEDSTOCKC OxYGEN PLAGASIFIERO GAS CLEAN-UPCLEAN SYNGASTO POWERFig 7 A schematic diagram of gasification processSolids: All types of coal and petroleum coke (a low value byproduct of refining) andbiomass, such as wood waste, agricultural waste and household wasteLiquids: Liquid refinery residuals (including asphalts, bitumen, and otherresidues)and liquid waste from chemical plants and refineriesas: Natural gas or refinery/chemical off-gasB)Gasifierterial reacts with oxygen (or air) and steam at highgasifier designs, distinguished by the use of wet or dry feed, the use of air or oxygen, theactors flow direction (up-flCurrently, gasifiers are capable of handling up to 3, 000 tons/day of feedstock throughputture After befed directly (in the case of gas or liqthe feedstockected into the gasifier, alongamount of air or oxygen and steam Temperatures in a gasifi1, 400-2,800 degrees Fahrenheit The heat and pressure inside the gasifier break apart thehemical bonds of the feedstock, forming syngas The syngasmanily of H? andCO and, depending upoication technology,quantities of CHD2, H2S, and water vapour Syngas can be combusted to proder and steam

or used as a building block for a variety of chemicals and fuels Syngas generally has aheating value of 250-300 Btu/scf, compared to natural gas at approximately 1,000Typically, 70-85% of the carbon in the feedstock is converted into the syngas The ratio ofbon monoxide to hydrogen depends in part upon the hydrogen and carbon content of thefeedstock and the type of gasifier usedification systems use almost pure oxygen(as opposed to air) to help facilitate theThe oxyger through separate co-feed portn the feed injectorvegas produced in the gasifilevels ofLies thatt beer the gas is cooled, the trace minerals, particulateaning processes common to the chemical and refining industriesFor feeds(such as coal) containing mercury, more than 95% of the mercury can be removedfrom the syngas using relatively small and commercially available activated carbon bedE)By-productsfeed gasifiers produce a glass-like by-product called slag, which isng material Also,most gasification plants, more than 99% of the sulphur is removed and recovered either asmental sulphurand carbon monoxide, the major components of syngas, are the basic buildingblocks of a number of other products, such as chemicals and fertilizers In addition,gasification plant can be designed to produce more than one product at a time(co-ductiontion), such as the production of electricity, steam, and chemicals( eg methannia) This polygeneration flexibility allows a facilityefficiency and inof itsThe basic types of the gasifiersHorizontal steady bedFluidized bed (Groi et al, 2006)Multiple hearthsRotary ksteady bed facilities, as well as fluidized bed ones ishe facilities of vertical steady bedhe fad have ltal cost but thens in theaste(it has to be homogenous, eg On the basis of the results of pilot applications for units that were operating at temperatures

Solid Waste Management through the Application of Thermal Methods0The produced solid residue has high absorption ability and can be used in facilities forthe engine perforreaching 76% of the performance in the case that onused( Belgiorno et al, 2003)Summarizing, gasification is not an incineration or combustion process If gasification wasthat produces more valuable and useful products from carbonaceous material bothgasification and combustion processes convert carbonaceous material to gases

Gasificationn the abswithgen, whileThe objectives of combustion are to thermally destruct the feed material andivert the feed mateluable, environmentally friendly intermediate products that can be used forpurposes including chemical, fuel, and eneduction Elements generally foundO, sCl are converted to aCO, H,, H o, CO,, NH3, n2, CHi, H2S, HCL, Cos, HCN, elemental carbon, and traces ofheavier hydrocarbon gases The products of combuprocesses are CO2, H2O, SO, NO,NO, and HCIombustion of solids, heavy oils, and carbonaceous industrial and domestic waste First,sulphur and nitroto acid rainreduced significantly due to the cleanup of syngas Sulphur in the gasifi2 s, while nitrogen in the feed is converted to diatomic nitrogen(n:nd NH3, Both H25 and NH3 are removed in downstream prodTherefore, if the resulting clean syngas is combusted in a gas turbine to generateity or in a boiler to produce steam or hot water, the production of sulphur andoxides are reduced significantly If the clean syngas is used as an intermediatet folufacture of chemicals, these acid-rain precursors are not formed

The particulates in the raw syngas are also significantly reduced due to multiple gassystems used to meet gas turbine manufacturers speons, Particulatelace in primary cycloneor dry filters and thenooling and acid gasA second major advantage is that furan and dioxin compounds are not formed duringgasification Combustion of organic matter is aogenic pollutants, The1 The lack of oxygen in the reducing environment of the gasifier pretformation ofand limits chlorination of any2 High temperature of gasification processes effectively destroys any furan or dioxinFurthermore, if thecombustturbine where excess oxygen is present, thenot favor formation of free chlorine In addition, postombustion formation of dioxin or furan is not expected toery little of thethat are required for post-combustion formation of these compounds arepresent in the flue gLimited data is available on the concentration of volatile organic compounds, semi-volatileganic compounds (SVoCs), and polycyclic aromatic hydrocarbons (PAHs) fromprocesses, The data thavailable indicate that vOcs, SvOCs, and Pahs areels(on the order of parts per biof syngas also indicates greater than 9999 percent chlorobenzene andpart perof selected PAHs and VOCs(Rezaiyan Cheremisinoff, 2005; Klein, 2002,Radian International LLC 20004is the thermal degradaals through the use of anmperatures of 450 to 750C, in the absencerials, resultingmarily of H2, CO, CO CHa and comphydrocarbons The syngas can be utilized in boilers, gas turbines or internaof the organic materials thattileeft as char material Ibottom ash that requires disposal, althoughme pyrolysis ashused for manufacturing brick materials Pyrolysis involves thethermal degradation of organic waste in the absence of free oxygen to produce abonaceous char, oils and combustible gaseshough pyrolysis is an age-oldrelativeolysis is thermolysis, whichtechnically more accurate fuallystarved-air rather than the total absence of oxygen Although all the products of pyrolysisfuel for power gethecess, this oil may be used as liquid fuel for burning in a boiler or as a substitute for dieselin reciprocating engines, although this normally requires further processing(Institutionof Mechanical Engineers, 2007)

Solid Waste Manageh the Application of Thermal MethodsThe reactions taki如ptially are decomposition ones, where organic components ofCxHv→CcHd+CmHnhydroctions that lfrCxHy→CH2+ cokeIn the case of existence of oxygen, CO and CO2 are produced or the interaction with water ispossible The produced coke can be vaporized into O2 and CO2products can be liquid, solid and gaseous The majority of theis by 75-90 into volatile substa%o to solid residue(coke) However, due to the existence of humidity andsubstances, the quantity of volatile substances varies from 60 to 70% and the coke betw30and40%In order to achieve the successful operation of a pyrolysis facility, continuous control isMoreovwith no processes taking Place duing the method developmentor composition variation that does not include metals andseparation at source or mechanical separation) In addition, specialis needed aboutSolid Carbon tted into several inertproductsGasDust particles, CO, CO2, CH+, H700 m3off-gases/tone of wasteCH3COOH, CH3COCH3,CH3OH,compleTable 1 Brief description of the solid, liquid and gas products from the operation of apyrolysis unPyrolysis temperature(C)3363413182061652863241253031312403385(btu/St/t)Table 2 Composition of the produced gas at different pyrolysis temperatures Waste Mawhetherproducts satisfy the specifications of commercial fuel (mainly due to thee productsThe product proportions depend on the waste nature, the temperature conditions and theusing materials are a solid residue and a synthetic gasponents form tars andbe removed anddue (sometimes described as a char)isThe syngasstituents include carbon monoxideOCsroportion of these can be cortypically haalorificondensable fraction can be collected byTypical Pyrolysis Facilityhe following are taking placeDrying of solid(100-200CInitial decomposition of substances, initiation of the decomposition of Has and CO2Break of the bonds of aliphatic substances- Start of the separation of CH4 and otherEnrichment of the produced mConversion of coal tar materials into fuel material and tar (400-600oC)Decommaterials resistanat- Formation of aromatic substances(600Ctic substances, processes for hydrogenfrom organics likeutadiene, etc(600C)Size reductionDfetal 60 kg1000kgokg Thermolyser nert g0 kgWater 220 kgThermolysis Gas 380 kgg 8a schematic diagram of gasification process

Solid Waste Management through the Application of Thermal MethodsThe main advantages of pyrolysis in comparison to incineration areposition temperature is lower than the incineration temperature, so thele facilitytense than in incinerateThe decion takes place in reducing atmosphere and not in oxidizing like inincineration, The demandalso the reason for less air emissipyrolyseThe ash content in carbon is much higher than in the case ofThe metals that are included in waste are not oxidized during pyrolysis and havehigher commercial vaNo ash is produced from the combustion of thelysis gas and the cleaning of themain disadvantages of pyrolysis include:The big problem of this technique is that pre-treatment is required including cuttingdhe cost for thenstallation and operation of such units substantiallyThe pyrolysis products cannot be disposed without further tre

atmentThe facilities for cleaning the gases and wastewater require extremely high costAt present, the application of the method at large scale is limited Nevertheless, theprospects for reactors of average temperature with the form of rotary drum or fluidized5 Plasma technology51 Generaevery gas of which at least a percentage of itsand the charges of elecbalanced bAs a resulutral itted from electric dischargfrom the passacurrent(continuous, alternate or high frequency) through the gas and from theresistivelaracterized as the fourth state of matter and differs from the ideal gases, because it isnaracterized by collective phenomenaoriginate fromnot interact only withneighbouring particles through collisions, but they also bear the influence of an averageomagnetic field, which is generated by the rest charges In a large numbercollective phenomena take placech faster than the characteristic collchnology can be used as a tool for green chemistry and wastlety of chemical processes They are characterized by high electron densityelevated temperatures and pressures, thechemical reactivity and quenchingPlasma technology is very drasticperahur Ce of highly reactive atomic ande characteristic of these plasmas is far grees in comparison with other thermal

Solid Waste Managh the Application of Thermal MethodsFinally, the firstt attempt to trtreat municipal waste in Greece with the use of gasificationGenerbustion)-basedgreater than stoichiometric), typically at temperatures hia wastegas composed primarily of carbonide(CO2)and water(H2O) OtheDuring the full combustion there is oxygen in exceconsequently, the stoichiometricustion reactionan the value“1" In thecoefficient is equal to"1", no carbon monoxide(Co)iserage gas200C The reactions that are then taking place arCxHy +(x+ y/4)O2-xCO2+y/ H2OIcorwhere the produced co, reacts with c that has not been coCO at higher temperaturC+OO2+17258→2C0(3)The object of this thermal treatment method is the reduction of the volume of the treated wastewith simultaneous utilization of the contained energy The recovered energy could be used forelectric energy productionhebeton of domestic waste07 MWh of electricity and 2 MWh of district heating Thus, incinerating about 600 tones ofwaste per day,MW of electrical power200 MWh district heating could behnology isof the municipal solid waste byand itsby 75%, Theof high quantities of solid waste(more than 100,000 tones per year)nditions have tosfied so that the complete combustion of thefuel material and oxidations at the combustion heartaturebustiontable temperature within the furnaceadequate residence time of waste at the combustion area( Gidarakos, 2006)

LandfillFur ther Ash ProcessingFig 3A schematic diagram of incineration processIntosoil, surfacerisks to humahealth, from the incineration and co-incineration of waste(Europeanission, 2000)

Solid Waste Management through the Application of Thermal MethodsWeighing SystemThe system for weighing acticalat the control and recording of theto minimize the time that vehicles remain at thisReceptionDue to the fact that waste does not arrive onbasisry to the feeding of thefacility), the existence of waste reception and temporary storage site is considered necessarway that the following are ensuredtransferrede is receivedthe homogeneity of the waste thatused as feeding material is achievedthe smooth feeding of the facility is ensuredMoreover, the design of the reception site should be based on the minor instance, the solid waste shoulddays so as to avoid odours, while the bottom of the site has to beweathering to allow the leachates and washing wastewater to go awayFeeding Systempted to the rate and feeding velocity of the installationCombustion hearthsaste at incineration facilities is achieved through theburner, which operates with secondary fuel Basic parameters for the appropriate operationhievement of the minimum desired temperatureadequate combustion timehievement of turbulence conditions/ homogenous waste incinerationwhich the energy content of theway through steam production (eghbouring industrialfacilities or for the heating of urban areas Pressure, temperature and steam production ratere basic parametethe effective operation of the boileSystem for the removal of residuesResid20-40% of the weight of thethatcollected at hoppers where they are transferred with speEmission control systemrticles, HCl, HF sO,, dioxins and Waste MaThe generated air emissions contain the typical combustion products (CO, COz, NO, sO2),cess of oxygen, dust particles as well as other compod thetion of other compounds, such as HCl, HE, suspended particles which contaheavy metals, dioxins and furans, depend on the composition of the waste that is subjectedIncinerationquantity of 4,000tedust be controlled by applying appropriate anti-pollution systems, such asElectrostatic filtersWet cleaninng towers, rotate spraDioxin or furan refers to molecules or compounds composed of carbon and oxygen Theseflorine or breproperties Most research on halogenated dioxin and furan has been concerned withdioxin and furambustion processes including domestic and medical waste combustion or incinerationpost-combustion flue gas cooling system due to the pisor compounds, freechlorine, or unburned carbon and copper species in the fly ashThe toxic influence of dioxins and fhad not been made clear until the end of theappTEQ-Toxic equivalent of the dioxin emissions

As a result, the dioxin emissions have beemited to one thousandth in relation to the year 1987, reaching values lower than 10 gr TEnoted that on the basis of datd by the us epelled burning oftheound 600 gr annualland furans are produced in almost all combustion processes, in the gas phase, whilemperature is 300Cre possible, formation andtheir content in oxygen encourage their formation Consequently, the operating conditionse the dioxin formation at higher degree than the waste compositiontribution of dfurans to humanct thatary to take basic and secondary measures so as to limit such emissicis removed, cyclones (removal effieelectrostatic precipitators(removal efficiency 99995%)andApart from the removal of suspendproducts during incineration are briefly described

Solid Waste Management through the Application of Thermal Methods90Backyard trashn(hero Backyard Barrel BurningnMetal smeitingDecrease in WTEation (edcatemissions 1987-20022D024Fig 4 dioxssion in the USA(Deriziotis, 2004)Fig 5 Cyclones (left), electrostatic precipitators(middle)& bagfilter(rightBagfilter: Theterials, where the suspended particlesdetained

Depending on the requirements, the material of the filters is from natural fibres,Electrostatic Precipitators(Electro filters: They are consisted of the cathode that can be aple thin wire and the anode Another configuration includes a systbetween the anode and the cathode When the particles enter the cathode field, they edthe positive pole (anode) The velocity of theparticles depends on the weight and the Coulomb forces that are developed

d on the development of centrifugal force at thThe particles due to the centrifugal force and the rotary floralls and then moved downward Cyclones are often applied together withWastewater is generated by the use of water during the incineration process and int absorbance towers(2 mf waste)ters(precipitatorsThe wastewater stream containsnded solids as well as dissolved organic andorganic substances It is characterized as hazardous wastewater and specific treatment isred prior to its final disposndary solid residues that are generated during incineration can be categorizedFly ash: It is the lightest fraction of the generated solid residues anncentrations of heavy metals and is characterized as hazardouof the incineration process (inorganic matter) andollected at the bottom of theFilter dustThe solid residues stream must be treated prior to their final disposal, while a main portionof their quanuld be recycled by applying specific processesTypes ofus types of incinerators, such as moving grate, fixed grate, rotaryfluidized bed, etc(Fig

6)Moving gratThe typiction plant for domestic solid waste is a moving grate incinerator Theing grate enables the movement of waste through the combustion chamber to behandle up to 35 tones of wasteand can operate 8,000 hours perand maintenance of aboutth's durationmes referred to as municipal solid Waste IncineratorsThe waste is introduced by a wastethrough the" throat" at one end of the grate, fromthe ash pit in the otherremoved through a water lockPart of the combustion air (primary combustionsupplied through the grate fromso has the purpose of cooling the grate itself Ct fothe mechanical strength of the grate, and mmoving ge also wat

Solid Waste Management through the Application of Thermal MethodsSecondary combustion air is supplied into the boiler at high speedte combustion of the flue gases by inbetter mixinguring a surplus of oxygen In multthe secondary combustion air is introduced in a separate chamber downstream the primaryAccording to the European Waste Incineration Dicineration plants mustt is required to install backup auxiliary burners(oftend bywhichach thisThe flled in the superheaters, where the heat is transferred to steamally 400C at a pressure of 40 barhe electricity generation inOften incineration plants consist of several separate boiler lines'(boilers and flue gastreatment plants), so that waste receival can continue at one boiler line, while the others areFixed grateThe older and simpler type of incinerator tbrick-lined cell with a fixed metal srate overpening in the top or side for loading and another opening in theincombustible solids called clinkersRotary-kilnype of incinerator has two chambers, a primary chamber and secondary chamber Theprimary chamber consists of an inclined refractory lined cylindrical tube Movement of themilitates movement of wastevolatcessaryThe clinkers spill out at the end of the cylinder A tall flue gas stack, fan, or steam jetlies the needed draft

ash drolgh the grate, but many particlesth the hot gases The particles andcombustible gases mayafterburner'Fluidized bedAccording to the technology that is applied for this type of incinerator, a strong airflow isforced through a sand bed The air seeps through the sand until a point is reached where thend particles separate to let the air through and mixing and churning occurs, thus a fluidized3 Gasificat31 GeneraOCIke biomass, sludge domestic solid waste toelectric power, valuable products, such as chemicals, fertilizers, substitute natural gas,Waste MaFig 6 three types of incinerators: (a)fixed grate, (b) rotary kiln, (c) fluidized bedydrocarbons (compounds of carbonhydrogen and oxygen molecules) to COz and HO

This is a partial oxidation process whichduces a composite gas(syngas) comprised primarily of hydrogen( H2) and carbonnefit ofthat the prodbe used directlart ofCombined Heat and P(CHP)or Combined-Cycle Gas Turbine systerheoretically improving the overall thermal efficiency of the plant The main disadvantage isthat thered the capital investmentThe main reactions taking place during gasification areOxidation(exothermic)C+ O-CO2(4Water evaporation reaction(endothermic)C+ H2O-C0+Houdouard Reaction(endothermic)C+ CO2+ 2Creaction(exothermic)C+ 2H2-+CHa32 Typical gasifiedtypical gasification plant inclue)FeedstockGasification enables the capturetally beneficialf low-grade hydrocarbon materials ("feedstocksdesigned to run on a single material or a blend of feedstocks