1. A review of Gasification Technology and its potential
application in the Irish waste industry
Stephen Leslie. UCD School of Biosystems Engineering,University College Dublin, Belfield,Dublin 4,
Ireland
Abstract (100 words)
Gasification isatechnologywhichcanbe usedinthe Irishwasteindustryandfurtherknowledgeabout
other gasifiers and how they operate in necessary before installing them in Ireland. An overview of
the history, chemistry, useful products obtained, design and environmental performance has been
investigatedformthe publishedliterature.Itwasfoundthat gasificationisa cleanway of processing
waste anditcan provide Irelandwithelectricity,fuelsandbuildingmaterialsandreducethe countries
dependence on landfills and imported fossil fuels. This technology should be favoured over
incineration as the main type of thermal treatment process.
Introduction
‘’Gasification, or “indirect combustion”, in particular, is the conversion of solid waste to fuel - or
synthesis-gasesthroughgas-formingreactions:itcanbe definedasapartial oxidationof the waste in
presence of an oxidant amount lower than that required for the stoichiometric combustion’’(Arena,
2012). ThisisapromisingtechnologyformanagingIreland’sfuturewaste,whileitislesscommonthan
incineration,the technologyhasbeenaroundforovertwohundred years,beforethe inventionof the
light bulb, the gasification of coal was used to create a town gas that was ignited in lanternsto light
upfactoriesandstreetsatnight (Tomory,2012),thenaboutacenturylaterthe fischerTropschprocess
wasinventedwhichallowedforthe creationof fuelsduringthe secondworld war(Davis,2005),there
was a massive step forward during the 1960’s when NASA began researching materials that could
withstandhightemperaturesformre-enteringearth’sorbit, thisledDr.Camachoin1973 tointroduce
the concept of continuous pyrolysis of household waste using plasma torches to create syngas and
slag,the firstpilotscale demonstratingthe technologywasbuiltandoperatedin1988 by Resorption
Canada Limited (Pourali,2010). Currentlythere isonly51 waste gasificationunitsinoperationandin
the planningorconstructionprocessinthe worldwhichcomparedtothe total numberof coal gasifiers
(381) is quite small (Gasification.org, 2015)
Irelandwaste hasbeendecreasingeveryyearfrom2006to2012, more waste wasrecoveredthanwas
disposed of in 2012 and the amount of waste being sent to landfill has been in steady decline since
the implementation of a landfill levy (2013). These are all signs that waste is moving up the waste
hierarchy and that these trends are set to continue into the future. It would appear however that
gasification will face challenges in finding steady streamof waste to process as there is currentlyan
incineratorinoperationinIrelandandanotheriscurrentlybeingbuiltwhichhaveacombinedcapacity
of 835,000 tonnes per year (Dublinwastetoenergy.ie, 2015), (Industrial emissions Licence Endaver
Ireland Limited, 2015).

2. Objective of this paper is to review the present state of gasification and to discuss its potential in
the Irish waste industry
Principal of Design and Operation
Design
Two of the most common types of gasifiers are updraft and downdraft. Both types have similar
chemical reactionsoccurring,asrefuse derivedfuel isaddedfromthe top, the contentgetsdriedand
heatedupinthe dryingzone,thisisfollowedbythepyrolysiszonewherelongchainorganicmolecules
are broken to form char and tar, this is followed by the oxidation zone were small amounts of the
waste are combusted toover1200°C toprovide heatforthe endothermicBoudouardreactionswhich
create hydrogenand carbon monoxide inthe reductionzone.The difference betweenthese typesof
reactors is the flow of syngas, in the updraft as seen in figure 1, fuel goes in from the top and gas
comesoutformthe topwhichbooststhermalefficiencyhowever,asthe syngashasn’tpassedthrough
the reduction zone properly, this leads to a high tar content in the gas. In a downdraft gasifier, the
syngas comes out form the bottom which means the syngas must pass through the reduction zone
leading to low tar concentrations and a reduction in thermal efficiency as heat leaves the reactor
within the gas (Belgiorno et al., 2003)
Figure 1 Diagrams of the different types of gasifiers (source: Belgiorno et al 2003).
Fluidisedbedgasifiersusesilicasandinthe reactor,airisblowninfromthe bottomwhichreducesthe
densityandincreasesthe volume andsurface areafor reactionsto occur. In a bubblinggasifier,airis
blowninfrom the bottomat around2-3m/s, fuel isfedinfrom the top and the gas isreleasedtoget
processedfurther,ina circulatinggasifierairis blowninat arounf 5-10m/s which createsa verylow
density mixture of sand and MSW, sand escapes from the reactor, gets trapped in a cyclone and is
pumped back into the reactor.
One of the mainpurposes forgasificationistogenerate electricity,one of the mostefficientmethods
of doingthisisbyusinga gas turbine thatproduceselectricityformthe ignitionof the gasandreturns
some of the heat back to the reaction, another way of doing that is by taking some of the heat and
using it to create steam which can power a steam turbine, these configurations were modelledand
the results show that 30% efficiency can be obtained for the first method and around 40% for the
second (Baratieri et al., 2009). One of the problems with using MSW as a fuel in gasification is that
plasticssuchas PVCwhichare not usuallyrecycledwill endbeingusedasa fuel,howeverplasticsare
derivedfromcrude oil (Khooet al.,2010) whichmeans that its combustionwill leadtomore carbon
dioxide entering the atmosphere, to combat this, it is possible to connect gasification systems with

3. carboncapture and storage facilitieswhich will intheorymake itcarbonneutral,howeveritwillresult
in a 10% drop of overall electrical efficiency (Mansouri Majoumerd et al., 2012).
Useful products obtained from the Process
A study was undertaken in the US to see how much electricity and fuels could be created from the
gasification process using ASPEN Plus simulations of a fluidized bed gasifier operating at 900 °C. The
results showed that by using the Fischer Tropsch process on the syngas along with refining the
syncrude, 57L of Diesel, 123L of Petrol, 25L of Kerosene, 11L of liquefied petroleum gas and 12L of
Residual fuel oil couldbe createdalongwith193Kwhof electricity.These valueswerebasedon1000kg
of RDF which consisted mainlyof shredded paper and plastic. The energy embodied in the fuel and
electricityfromthe reactionwas2.4timesgreaterthanthe energyputintothe system(Pressleyetal.,
2014). Papers have shown however that coke is required in some of the gasification processesto
achieve the necessarytemperaturesinthe reactionchamber.Foreverytonneof wasteprocessed,the
reaction chamber required 49Kg of coke derived from crude oil. This meant that by comparison, the
movinggrate gasifierwasconsideredlesscarbonintensive asitusedmethane andLPG as an axillary
fuel,itwasalsoshownthatthe incineratorproduced550Kwhof electricitywhilethe gasifierproduced
450Kwh (Arenaetal., 2015) thiscontrasts witha studyin2004 whichstatedthat the g𝐶𝑂2/𝐾𝑊𝐻 for
incineration was 220 while gasification was only 115, this was due to the fact that the electrical
efficiencyof the incineratorchosenwas15.3% and the gasifierwas 27.2%, it was probablyassumed
that the high volume of plastic, organics and paper in the waste at that time was enough and it did
notneedcoke tomaintainthe heatlevelsinthe reactor (MurphyandMcKeogh,2004).Anotheruseful
productwhichcomesfromgasificationisslagwhichisastable rocklikematerial whichmostlyconsists
of silicondioxide, calciumoxideandaluminiumoxide.A studyconductedinJapanshowedthatintwo
gasifiersthatusedthedirectmeltingprocessbetween173kgand97kg of slagwasproduced pertonne
of waste (Tanigaki et al., 2012). Slag has similar properties to gravel which means it can be used to
make precast concrete,bricks and asphaltpavementsthusgivingita value (Tanigaki etal.,2012). All
of the products discussed above could help Ireland develop a circular economy (Pan et al., 2015).
Tar and dioxin removal
One of the problemswithgasificationisthe productionof longchain hydrocarbons(Tar) that leaves
the gasifierandcondenseswithinthepipeworkandenginesinthe system.Tarcontentinsyngasmust
not exceed10mg/𝑚3 in gas turbinesand100mg/𝑚3 ingas engines (Arena,2012).It hasbeenshown
that by using pure 𝑂2 as an oxidant in the gasifier, this leads to higher retention times and higher
energydensitiesinthe gas (Arena,2012),howeverithasalsobeenshownthatthiscanreduce the tar
concentrationsinthe gas whichmeansthat lessgasprocessingisrequiredbefore itentersa fuel cell
or gas turbine, yet creating oxygen onsite is still relatively expensive (Pintoet al., 2012). It is also
important to note the more tar which is created and not broken down means that the gasification
process will become more inefficient. It is for this reason that catalysts have been developed and
studied which can convert tars into syngas at high temperatures. It has been shown that dolomite
whichcontainsCalciumOxide isaveryaffectivecatalystdue tothe increasedsurface area.Ironbased
minerals such as Olivine and Limonite have shown good results however there were contracting
resultsbasedoncalcinedandnon-calcinedOlivine.A Nickel titaniumoxidecatalysthasshown a98.1%
conversion of tar to syngas which is unsurprising due to its use in the petroleum industry (Xu et al.,
2010). Anotherwayof reducingtar productionis by choosinga downdraftgasifierasthe syngas has
to move throughthe oxidationandreduction zonesthusbreakingthe tarup into syngas.It isfor this
reason that the downdraft is one of the most common configuration of small gasifiers used today
(Simone etal.,2012).One of the problemswiththermallytreatingourwaste isthatorganicmolecules
like polychlorinated dibenzo-para-di-oxins, polychlorinated dibenzofurans and dioxin-like

4. polychlorinated biphenylscollectivelyknownasdioxinscanformwhichare knowncarcinogens.These
gasesusuallyformwhenthe gasis beingcooledandwhenthe degradationof carbonaceousmaterial
in the presence of chlorine or other metals occurs. It has been shown in Japan that bag filters can
operate at the dioxin forming temperatures (150-200°C) and can adsorb and convert 96% of dioxins
whichmeansonaverage0.0062ngtoxicequivalencyfactors/𝑚3isreleasedfromthegasificationplant
(KawamotoandMiyata,2015). These resultsare extremelypromisingformanIrishperspectiveasthe
maximum allowable concentration set by the EU is 0.1 ng/𝑚3 TEQ (AIr Quality and Climate, 2006)
Plasma Gasification
This technologyrequiresthe use of a plasmatorch whichhas a highvoltage across the nozzle outlet.
Airpassesthroughthis nozzle andbecomesionisedandheatedupto 6000°C whichcreatesa plasma
thus helping to breakdown the waste into syngas. The electricityneededto run the plasma torch
comesfromthe gas generatoronsite,apilot-scale downdraftplasmagasifierwasdevelopedinIsrael
and it had a cold gas efficiency between 30-60% (Zhang et al., 2012). One of the benefits of this
technologycomparedtoother gasifiersisthe highlevel of control it givesinrelationto temperature
as it is derivedfromelectricity (Lemmensetal.,2007). It has beenshownthat by usingan integrated
plasma gasificationfuel cell (IPGFC) an electrical efficiency of up to 33% can be achieved, it has also
been shown that high temperature fuel cells can use carbon monoxide as a fuel (cold temperature
fuel cellsare poisonedbycarbonmonoxide) andthe fuel cellhasahigherefficiencythanagasturbine
(Galeno et al., 2011).
Challenges of installing gasification technologies in Ireland
One of the major barriers that Ireland faces with gasification is the lack of trust that the public have
for the government and local authorities as most feel that they should try to be more transparent
(Fahy,2005), recentlythere have beenplansfora gasificationplantatGortadroma inLimerickat the
site of an old landfill (Eprenewable.com, 2015), (Jacques, 2015), (Ryan, 2015) which have been met
with public opposition and a group that call themselves Residents Against Gasification in our
Environment(RAGE) whobelieve thatnotenoughinformationwas giventothem, trucksenteringand
exiting the facility would create massive amount of traffic and that air quality might be reduced.
Similar findings have been seen from surveys on public perceptiontowards windturbines in Ireland
and Scotland,there was a findingthatthe closera populationwasto the turbine the lesssupportive
they would be towards the project (Ladenburg and Dahlgaard,2012), which means that Gasification
could become another NIMBY technology. Another problem with the development of any kind of
thermal treatmentof waste inIrelandis the lack of districtheatinginfrastructure intownsand cities
as thiscoulddramaticallyincreasethe efficiencyof anincineratororgasifierandreduce the countries
dependence on fossil fuels for heating (Murphy and McKeogh, 2004).
Discussion
Irelandalongwill all the otherEuropeancountriesmanagesitswaste basedonthe waste hierarchy
whichplaceslandfill asthe leastfavouredoptionfollowedbythermal treatment,recycling,reusing
and the mostfavouredbeingprevention (Gharfalkaretal.,2015)thisisway the landfill levyof €75
pertonne was introducedasitaimedto make otheroptionsmore financially competitive(2013).
Takingthisinto consideration,itcouldbecome averylucrative wayforthe firstwaste companiesto
operate gasifiersastheywill instantlysave €75 on everytonne theyprocess,ontopof that, instead
of treatingashwhichispotentiallytoxictothe environmentandexpensive todeal with,theycould
sell the slagto local constructioncompanies.Asshownby (MurphyandMcKeogh,2004) the carbon

5. intensityof gasificationelectricityislessthannatural gaswhichisthe mainsource electricityfor
Irelandwhichcouldpotentiallyreduce ourdependence onimportednatural gas andour carbon
footprint.While the price of crude oil isquite low right now itmakesnosense toinvestinalternative
fuels,howeverIrelandisalmostcompletelydependentonimportedcrude oil productswhichmeans
that itis vulnerabletoprice fluctuations (Glynnetal.,2014) , while the potential forfuel creation
viathe fischertropschprocessisquite small incomparisontothe amountof fuel usedinIreland,it
wouldstill provideasafetynetalongwithdiversifyingthe businessmodelsof refuse companies.
The safetyaspectof gasificationisanimportantfactorto considerasitwill decide whether ornot
the general publicwill supportitsimplementationintothe country.Asalreadyshownby (Kawamoto
and Miyata,2015) the level of dioxinsemittedintothe environmentinJapaniswell below safety
limitsputinplace bythe EU. It has alreadybeenshownthatthe publicinthe UK preferindirect
combustionmethodscomparedtoincinerationasaway to deal withwaste (Yangetal.,2007) which
couldbe mirroredby the Irishpeople.Ashasalreadybeenmentioned,the successorfailure of
implementingawaste managementsystemwill dependonthe government’stransparencyandon
howwell theycommunicate theirplanswiththe local residencesandthe general population(Fahy,
2005).
Conclusion
Gasificationisacleanand safe wayto processIreland’sfuture waste and effortsshouldbe made to
introduce itintothe country.While itisnot the bestoptiononthe waste hierarchypyramiditdoes
provide agood wayto reduce our dependence onlandfills,buildingmaterialsandimportedfossil
fuelsalongwithreducingthe countriescarbonfootprint.
2013, Waste Management(Landfill Levy) (amendment)regulations2013, in Environment,ed.,St.
Stephen'sGreen,Dublin.
Arena,U., 2012, Processand technological aspectsof municipal solidwaste gasification.A review:
Waste Management,v.32, p. 625-639.

6. Arena,U., F.Ardolino,andF.Di Gregorio,2015, A life cycle assessmentof environmental
performancesof twocombustion- andgasification-basedwaste-to-energytechnologies:
WASTE MANAGEMENT, v.41, p. 60-74.
Baratieri,M.,P. Baggio,B. Bosio,M. Grigiante,andG. A. Longo,2009, The use of biomasssyngasin
IC enginesandCCGTplants:A comparative analysis:AppliedThermalEngineering,v.29, p.
3309-3318.
Belgiorno,V.,G.De Feo,C. Della Rocca,and R. M. A.Napoli,2003, Energyfromgasificationof solid
wastes:Waste Management,v.23, p. 1-15.
Davis,B. H., 2005, Fischer–Tropschsynthesis:Overviewof reactordevelopmentandfuture
potentialities:TopicsinCatalysis,v.32, p.143-168.
Galeno,G.,M. Minutillo,andA.Perna,2011, Fromwaste to electricitythroughintegratedplasma
gasification/fuel cell(IPGFC) system:International Journalof HydrogenEnergy,v.36, p.
1692-1701.
Gharfalkar,M., R. Court,C. Campbell,Z.Ali,andG.Hillier,2015, Analysisof waste hierarchyinthe
Europeanwaste directive 2008/98/EC: Waste management(New York,N.Y.) U6 -
ctx_ver=Z39.88-2004&ctx_enc=info%3Aofi%2Fenc%3AUTF-
8&rfr_id=info:sid/summon.serialssolutions.com&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&r
ft.genre=article&rft.atitle=Analysis+of+waste+hierarchy+in+the+European+waste+directive+
2008%2F98%2FEC&rft.jtitle=Waste+management+%28New+York%2C+N.Y.%29&rft.au=Ghar
falkar%2C+Mangesh&rft.au=Court%2C+Richard&rft.au=Campbell%2C+Callum&rft.au=Ali%2
C+Zulfiqur&rft.date=2015-05-01&rft.eissn=1879-
2456&rft.volume=39&rft.spage=305&rft_id=info:pmid/25725949&rft.externalDocID=25725
949&paramdict=en-USU7 - Journal Article,v.39, p. 305.
Glynn,J.,A. Chiodi,M.Gargiulo,J.P. Deane,M.Bazilian,andB. O. Gallachor,2014, EnergySecurity
Analysis:The case of constrainedoil supplyforIreland:ENERGYPOLICY,v. 66, p.312-325.
Kawamoto,K.,andH. Miyata, 2015, Dioxinformationandcontrol inagasification–meltingplant:
Environmental Science andPollutionResearch,v.22,p. 14621-14628.
Khoo,H. H., R. B. H. Tan, and K.W. L. Chng, 2010, Environmental impactsof conventionalplasticand
bio-basedcarrierbags:Part1: Life cycle production:The International Journal of Life Cycle
Assessment,v.15, p. 284-293.
Ladenburg,J.,andJ.-O.Dahlgaard,2012, Attitudes,thresholdlevelsandcumulativeeffectsof the
dailywind-turbineencounters:AppliedEnergy,v.98,p. 40-46.
Lemmens,B.,H.Elslander,I.Vanderreydt,K.Peys,L.Diels,M.Oosterlinck,andM.Joos,2007,
Assessmentof plasmagasificationof highcaloricwaste streams:Waste Management,v.27,
p. 1562-1569.
Mansouri Majoumerd,M., S. De,M. Assadi,andP. Breuhaus,2012, AnEU initiative forfuture
generationof IGCCpowerplantsusinghydrogen-richsyngas:Simulationresultsforthe
baseline configuration:AppliedEnergy,v.99,p. 280-290.
Murphy,J. D., and E. McKeogh,2004, Technical,economicandenvironmental analysisof energy
productionfrommunicipal solidwaste:Renewable Energy,v.29, p. 1043-1057.
Pan,S.-Y.,M. A.Du, I. T. Huang,I. H. Liu,E. E. Chang,and P.-C.Chiang,2015, Strategieson
implementationof waste-to-energy(WTE) supplychainforcirculareconomysystem:a
review:Journal of CleanerProduction,v.108, Part A, p.409-421.
Pinto,F.,R. N.Andre,C.Franco, C. Carolino,R.Costa,M. Miranda, and I.Gulyurtlu,2012,
Comparisonof a pilotscale gasificationinstallationperformance whenairoroxygenisused
as gasificationmedium1.Tars and gaseoushydrocarbonsformation: Fuel,v.101, p.102-
114.
Pourali,M.,2010, Applicationof PlasmaGasificationTechnologyinWaste toEnergy-Challengesand
Opportunities:IEEETransactionsonSustainable Energy,v.1,p. 125-130.

7. Pressley,P.N.,T.N.Aziz,J.F. DeCarolis,M.A. Barlaz,F. He,F. Li,and A. Damgaard,2014, Municipal
solidwaste conversiontotransportationfuels:alife-cycle estimationof global warming
potential andenergyconsumption:Journal of CleanerProduction,v.70,p. 145-153.
Simone,M.,F. Barontini,C.Nicolella,andL.Tognotti,2012, Gasificationof pelletizedbiomassina
pilotscale downdraftgasifier:Bioresource Technology,v.116, p. 403-412.
Tanigaki,N.,K.Manako, andM. Osada,2012, Co-gasificationof municipalsolidwaste andmaterial
recovery ina large-scale gasificationandmeltingsystem:Waste Management,v.32,p. 667-
675.
Tomory,L., 2012, Fosteringanewindustryinthe Industrial Revolution:BoultonandWattand
gaslight1800–1812: The BritishJournal forthe Historyof Science,v.46, p.1-31.
Xu,C., J. Donald,E.Byambajav,andY. Ohtsuka,2010, Recentadvancesincatalystsforhot-gas
removal of tar and NH3 from biomassgasification:Fuel,v.89, p.1784-1795.
Yang, Y. B., V.N.Sharifi,andJ. Swithenbank,2007, Convertingmoving-grateincinerationfrom
combustiontogasification –Numerical simulationof the burningcharacteristics:Waste
Management,v.27, p.645-655.
Zhang,Q., L. Dor, D. Fenigshtein,W.Yang,andW. Blasiak,2012, Gasificationof municipal solidwaste
inthe PlasmaGasificationMeltingprocess:AppliedEnergy,v.90,p. 106-112.
Gasification.org,(2015). World Gasification Database.[online] Availableat:
http://www.gasification.org/what-is-gasification/world-
database/results/title?search:main_feed_classification=Coal[Accessed20Nov.2015].
Dublinwastetoenergy.ie,(2015). - Dublin WasteTo Energy.[online]Available at:
http://dublinwastetoenergy.ie/[Accessed19Nov.2015].
Industrial emissionsLicence EndaverIrelandLimited.(2015).1st ed.[ebook] EPA.Availableat:
http://www.indaver.ie/fileadmin/indaver/Pictures/Ireland/Downloads/Industrial_Emissions_Licence
_for_Meath__ME_1__W0167-03.pdf [Accessed19 Nov.2015].
AIr QualityandClimate.(2006).1st ed.[ebook] Availableat:
http://dublinwastetoenergy.ie/uploads/archive/files/july-
2006/technical_summary/Chapter_08_Air_quality_climate.pdf [Accessed22Nov.2015].
2013, Waste Management(Landfill Levy) (amendment)regulations2013, in Environment,ed.,St.
Stephen'sGreen,Dublin
Glynn,J.,A. Chiodi,M.Gargiulo,J.P. Deane,M.Bazilian,andB. O. Gallachor,2014, EnergySecurity
Analysis:The case of constrained oil supplyforIreland:ENERGYPOLICY,v. 66, p.312-325.