Biomass residues revaluation with energy production in a nursery company

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Contents lists available atScienceDirect

Ecological

Engineering

j o u r n a l h o m e p a g e :w w w . e l s e v i e r . c o m / l o c a t e / e c o l e n g

Biomass

residues

revaluation

with

energy

production

in

a

nursery

company

Carlo

Carcasci

∗

,

Leonardo

Mussato,

Matteo

Neri

DIEF:DepartmentofIndustrialEngineering,UniversityofFlorence,viaSantaMarta,3-50139Florence,Italy

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received13February2017

Receivedinrevisedform27April2017 Accepted5May2017 Keywords: Nurserywaste Biomasschipper Greenhouseheater Biomassheater

ORC(Organicrankinecycle) Residuesrevaluation

a

b

s

t

r

a

c

t

IntheTuscanyregion,Italy,nurseriesproducealargeamountofbiomassresidualandtreatitaswaste

productfromworkingactivity,usually.Theaimofthisstudyistoevaluateadifferentwaytouseresiduals

forthenurserycompanyVannucciPiante(Pistoia),fromtheavailabilityofresidualstothethermaldemand

ofthecompany.Thepossibilityofinternallytreatingthebiomassinordertotransformitintosolidfuel

hasalsobeentakenintoaccount.Thethermaldemandderivesfromtheheatingofgreenhousesand

ofﬁcesduringthewinterperiod.Thethermalenergyrequirementandthesolidbiomassfuelavailability

arestudiedinordertobeconciliated.Threedifferentsolutionshavebeenevaluated,considering

co-generationandincentivebonusfortheproductionofthermalandelectricenergy,asprovidedbythe

Italianlaw.Thefeasibilityofthesolutionshasbeenanalysedandtheresultshavebeencompared,in

ordertodescribethebestsolutionineconomicterms.Asemergedinthisstudy,policiesforrenewable

energyinItalyarenotuptothetaskofsupportingthosetypeofinvestment,inparticularforagricultural

wasterevaluation.

1. Introduction

ThenurserysectorinEuropeinvolves90,000haofcultivated

landand120,000hafornurseries.Productionreached19.8billion

Eurosin2011,mainlyconcentratedintheNetherlands(33%),Italy

(13%),France(12%),Germany(12%)andSpain(11%).AsforItaly,up

to13,000haconcernpottedﬂowersandplants.Despitethelarge

areatakenbynurseriesandthesector’seconomicrelevance,most

Italiancompaniesarecharacterizedbytheirlimitedsize:64%of

nurserieshavelessthan1haofextension(Sarrietal.,2013).

Agriculturalgreenhousesareas havegreatlyrisen worldwide

over the last few decades. A large amount of energy input is

required,inordertomaintainanappropriatetemperatureforcrop

growthduringthewinterandsummerseasons.Energydemand

predictionneedstoenhanceenergymanagementandenergy

sav-ingsoftheagriculturalgreenhouses.

Thedemandforenergyinagriculturehasincreasedconsiderably

withtheintroductionofhigh-yieldingvarietiesandmechanized

crop-productionpractices.Therefore,itisnecessarytoimplement

aswitchfromconventionaltoalternativeenergysources.

Gener-∗ Correspondingauthor.

E-mailaddresses:carlo.carcasci@uniﬁ.it,[email protected]ﬁ.it (C.Carcasci).

ally,studieshavebeenconcentratedonworldwideproductionof

ﬁeldcropssuchaswheat,rice,soybean,cotton,maize,mustard,

clusterbean,greengram,pearlmillet,sugarcane,etc.inorderto

improvetheenergyoutput–inputanalysesandtoinvestigatetheir

relationships(Unmoleetal.,1987;Satpathyetal.,1991;Singhetal.,

1999;Singhetal.,2000;Sahaetal.,2002).Atthesametime,

agricul-turalcompanies’residualsaremainlycomposedbybiomass,and

smallerpercentagesbyplastic,paperandiron.

EvenifItaliannurseries’areaisonly1.2%oftheutilized

agri-culturearea(ISTAT, 2013(istitutonazionale distatistica),2013),

nurseries represent the most considerableworking activity for

someItaliandistricts.

Overthelastfewyears,severalmachinemanufacturershave

beenofferingdedicatedimplementsforcollectingpruningresidue.

These machines generally derive from conventional mulchers,

equippedwithastoragebinorwithablower,thelatterdesigned

todirecttheﬂowofcomminutedresiduestoaconveyorbelt(Daou

etal.,2009).Inorder toseparatebiomassfromsoilpart,many

authorsproposetouseinnovativeshakermachineforoptimizing

theprocess(Boncinellietal.,2015).

Theinputenergy(anditscost)ofafarm isstudiedinmany

paper.MohammadiandOmid(2010)determinedtheenergyuse

efﬁciency for theproduction of cucumber and compared input

energy usewithinputcosts inthe Tehranprovince, Iran.They

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Nomenclature

Ci Thermalenergyvalorisationcoefﬁcient(from

ital-ianlaw“Contotermico”)[D/kWh]

Ce Emissionvalorisationcoefﬁcient(fromitalianlaw

“Contotermico”)[−]

E Annualenergy[MJ/y]

ﬂowbio Flowrateofdrummachine

i Interestrate[−]

Ia Annual incentivefor biomass boiler(from italian

law“Contotermico”)

Mo Moistureondrybasis[%]

M Mass[kg]

Mbio Quantityofgreenresiduesprocessed;

LHV Lowerheatingvalues[MJ/kg₋MJ/Sm3_]

n Yearofinvestment[y]

NPVn Netpresentvalueatyearn[D]

Pn Nominal thermal power(from italianlaw“Conto

termico”)[kW]

Powdrum Mechanicalpowersupplybydrummachine

PI Proﬁtabilityindex[−]

PBP Paybackperiod[y]

Q Thermalpower[kW]

r Latentheatofvaporization[MJ/kg]

S0 Initialcosts[D]

Sdiesel Costofdieselusedbydrummachine

Sk Annualcashﬂow[D]

t Timeofestimatedannualworkofboilers[h](from

italianlaw“Contotermico”)

twork Timeofworkingmachinetoprocessacertain

quan-tityofbiomass[h] Greeksymbols ␩ Efﬁciency Subscripts bio Biomass d Dieselfuel dry Dry ng Naturalgas w Water wet Wet Acronyms

LHV LowerHeatingValues

NPV NetPresentValue

ORC OrganicRankineCycle

PBP PayBackPeriod

PI ProﬁtabilityIndex

alsointroducedamathematicalmodelbasedongreenhousefarms.

Hamedanietal.(2011)examinedtheenergyusepatternsandthe

relationshipbetweenenergyinputandyieldforgrapeproduction

inMalayerregionofHamadanProvince,Iran.Otherresearchers

Raﬁeeetal.,(2013)examinedenergyusepatternsandthe

relation-shipbetweenenergyinputsandyieldforpruneproductioninthe

TehranprovinceofIranandtheypresentedacomprehensive

pic-tureofthecurrentstatusofenergyconsumptionandsomeenergy

indices.

Otherstudiesfocusedonenergyconsumptionofgreenhouses.

(B.OzkanC.F.,2007)examinedtheenergyusepatternsandcost

ofproductionina greenhouseand open-ﬁeldgrapeproduction.

Canakci andAkinci(2006) investigatedtheenergy usepatterns

in greenhousevegetable production, in order todeterminethe

energy output–inputratioand theirrelationships.Kuswardhani

etal.(2013)estimatedenergyconsumptionperunitﬂoorareaof

greenhouseandopenﬁeldfortomato,chiliandlettuceproduction

inIndonesia.Amodel-optimizedprediction(MOP)methodology

is proposed (Yang et al., 2016), in order to predict theenergy

demand ofgreenhouses witha better performanceof accuracy

andcost.(B.OzkanA.K.,2004)examinedtheenergyequivalents

ofinputsandoutputingreenhousevegetableproduction inthe

Antalyaprovince,Turkey,fortheproductionoffourgreenhouse

crops(tomato,cucumber,eggplantandpepper).

Manyotherresearchersstudiedtheuseofpruning.Pruningcan

betreatedinordertorecovermajorquantitiesoforganicmaterials,

inparticularwood-chipandsubstrate.Wood-chipcanbeusedasa

bio-ﬁlterorasabio-fueldependingontheefﬁciencyofseparation

andthequalityintermsoftype,heatvalue,moistureandsize.

Sub-stratecanbereintroducedinﬁeld,inordertomaintaingroundlevel

ormixitwithvirginsubstrate(Sarrietal.,2013).Someresearchers

studiedpruningharvesters(PicchiandSpinelli,2010;Croceetal.,

2013)orproductionofcompostandbiogasfromgreen residues

(Chilosietal.,2015;Baldietal.,2016).Otherresearchersproposed

a prune recycling.In fact, (Z.González,A. Rosal, A. Requejo,A.

Rodríguez,2011)characterizedchemicallyorangetreepruningand

useitinpulpingandcombustionprocesses.Moreover,they

pro-poseditasasuitablecheapenergysourcebycombustion.Energetic

andeconomicanalysisofatri-generationsystemfueledonlywith

treepruningresiduesareproposed(Denticed’Accadiaetal.,2016;

Clodoveoetal.,2016).

Pistoia(43◦54N,10◦41E.30a.s.l.),isacitylocatedinthe

Tus-canyregion,inthecenter-northofItaly, andithasthegreatest

plantnurserydistrictinthecountry.Thisareaischaracterizedby

anaveragerainfallof1300mmperyear,averagewinter

temper-aturearound5/7◦Cwithminimumpeaksof−10◦_C_and_summer

temperaturearound21/23◦Cwithmaximumpeaksof40◦C.The

soilconsistsofalluvialdepositswhicharefertileandrichinsand

and silt.Theabove-mentionedconditionsareidealfor

cultivat-ingoutdoorornamentalplants.ThisisthereasonwhyPistoiahas

becomethemostimportantnurserydistrictinItalyandamajor

oneinEuropeallovertheyears(Lucchettietal.,2016).

Currently,thisdistricthasabout4100haofﬁeld-grownplants,

1000haofpot-grownplants,andabout100haforgreenhouse

culti-vations.Thecompaniesoperatinginthissectoraremorethan1500,

with5500workers.Halfofthemareemployees,whiletheothers

areentrepreneursandindependentsmallfarmers.Theestimated

grosssaleableproductionisaround500millioneuros,with300

mil-lioneurosofexport.Pistoia’snurseryproductionrepresentsabout

25%ofthenationalproductionandmorethanhalfofitisexported

(Lucchettietal.,2016).

GreenresiduesinthePistoiadistrictaregenerallytreatedlike

wastesbynurseries,eveniftheItalianlawcouldacknowledgethis

typeofresiduesasaby-productofnurseryactivity.

Reusingbiomassasenergysupplyforthenurserycanreduce

CO2emission,butisitaneconomicallycompetitivealternativeto

fossilfuel?

Theaimofthepresentstudyistoanalyzethebeneﬁtsof

differ-enttreatmentsofbiomass,intermsofwasterecycling,revaluation

ofbiomasswasteandenergysaving,aswellasthepossibilityto

usedifferentenergy sources.Thermaland electric energiescan

beproducedstartingfromthewood-chipsource:theirquantities

areevaluatedinordertocovertheenergyneedsofthecompany.

Biomassproductionsystemandenergygenerationplantsare

deter-minedintermsoftechnicaldataandeconomiccosts.

ThisstudyisreferredtoVannucciPiante,oneofthelargest

nurs-eries locatedinPistoia.Evenifthestudyis referredtoa single

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nurs-Fig.1.−Costsfordisposingofbiomasswasteproductsin2014forVannucciPiante.

Fig.2.−Thermalenergyplantatpresent.

erycompanies.InthespeciﬁccaseofPistoia,beneﬁtscaninvolve

theentirenurserydistrictandthelocaleconomy.

2. Currentsituation

Datausedinthisresearchlikedisposalcost,wastevolume

pro-ductionand fuelconsumption have beenprovided byVannucci

Pianteandtheyarereferredtotheyear2014(Fig.1).

Biomassresidualiscurrentlybeingtreatedasawasteproduct,

soitisdisposedbyanexternalcompany.Thepartofsoilpresentin

thewasteisseparatedfromthebiomasspartanditisbroughtback

toVannucciPiante.Thisservicerepresentsacostforthecompany:

theservicecosts12D/t.Annualbiomassdisposalcostsaremore

relevantinthesummerseasonwhentheplantsarepruned(Fig.2).

Ontheotherside,thermalenergyproductionisnecessary

dur-ingthewinterseason(Fig.3),mainlyinorder160to:

–Servegreenhousesinordertopreserveandimprovethegrowth

ofsomevarietiesofplants;

–Heatcompanyofﬁcesandindoorworkingbuild.

Greenhousesareheatedbyanumberofdieselfuelheaters(90%

efﬁciency)evenlydistributedineachgreenhouseandsuppliedby

pipeplantsthatstartfromexternalstoragetanks.Ofﬁcesareserved

bynatural gasboilers(95%efﬁciency). Fig.4 shows theannual

energycosts,limitedtocoldmonths.Thesecostsaremore

rele-vantfromNovembertoFebruary,whentheambienttemperature

islow.

2.1. Biomassproduction

Biomassresidualsproductionisduetodifferentworkingand

maintenanceoperationsinnurserycompany:

• Pruningandfelling;

• Unsoldplantswhichcannotbesoldduringnextseason;

• Plantsdamagedbychemical,biologicorweatheragents

compro-misingtheirappearance.

Biomassphysicalfeaturesdependontheproductionperiodof

theyear(Fig.5).MostplantsaresoldtoforeignandItalianbuyers

duringthewinterandspringseasons.Attheendofthisperiod,a

Table1

–Installedthermalpower.

Site Power[kW]

GreenhousessiteA 2300

GreenhousessiteB 3900

Ofﬁces 200

TOTAL 6400

largepartofunsoldplantscannotbecultivatedasecondtime,and thisiswhypruningproductionincreasesfromMaytoJuly.In2014 VannucciPiantehasproduced5407tofwastelinkedtobiomassand soil.

The moisturelevel is a fundamental parameter,in order to evaluatewood-chipquality.Moistureonadrybasisisdeﬁnedas ((AssociazioneItalianaEnergieAgroforestali),2009):

M0= mmbiow

kgw/kgbio,dry

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Theaverageannualmediumvalueofmoistureofnewbiomass

residuals isabout70% (Francescato, 2009(AssociazioneItaliana

Energie Agroforestali), 2009). Wood-chip produced with

nurs-ery’sresiduesisconsideredofB1categoryinwood-chipmarket

((AssociazioneItalianaEnergieAgroforestali),2009).

Moistureleveldeterminestheheatvalueofthistypeof

wood-chipandthesellingandbuyingprice(Fig.6)(Franceschi,2015).

Its value depends on the time of production and the variety

of plant residuals. The lower heating value for dry biomass is

assumed LHVbio,dry=17MJ/kgdry (Francescato, 2009(Associazione

ItalianaEnergieAgroforestali),2009).TheLHVofwetbiomassis

obtainedbyenergybalance,takingthelatentheatofvaporization

intoaccount.

LHVwet=

LHVdry+Mo·r

1+Mo (2)

Thebuyingpriceisgivenbywood-chipmarket.Thesellingprice

isconsideredthe2/3ofbuyingprice(Franceschi,2015).

Moisturevalueschangeduringstoragetime:therateofchange

depends on the place and time of storage, weather conditions

during thestorage period and thesize of wood-chip. Moisture

reductiondeterminesa massdecreaseduringthedryingperiod

((Associazione Italiana Energie Agroforestali), 2009) (Simpson, 1998).

2.2. Thermalenergydemand

Therearetwodifferentgreenhousessites.Theyare450mfar

fromeachotherandtheycover11,230m2_and_21,270_m2_of_area

respectively.Atpresent,eachgreenhousehas4/5heaters(using

dieselfuel)of100kWand140kWsizeforatotalof20x100kW

and30x140kW.Thermalpowerofgeneratorsis2300kWforthe

ﬁrstsiteand3900kWforthesecondsite.Ofﬁcesarelocatedina

twoﬂoorbuildingandhaveatotalareaof2170m2_._They_are_served

bytwonaturalgasboilersof100kW.Theentireinstalledthermal

poweris6400kW(Table1).

Theannualconsumptionofnaturalgasanddieselfuelsis

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Fig.3.−Thermalenergycostsin2014forVannucciPiante.

Fig.4. −Annualbiomasswasteandsoilfractionproductionin2014forVannucciPiante.

Fig.5. −LowHeatingValue,SellingandBuyingPricesofB1categorywoodchipvaryingmoisture(Franceschi,2015),((AssociazioneItalianaEnergieAgroforestali),2009).

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Table2

–TechnicaldataandcostsofBiomasstreatmentmachines.

DrumscreenerPezzolatoL3000mini DrumchipperPezzolatoPZ250

Workingpower[kW] 15 60

Biomassﬂow[t/h] 6 8

Price[D] 30,400. 30,000.

Annualfuelcost[D/year] 5290. 13,750.

Annuallaborcost[D/year] 27,030. 17,580.

energyisdeterminedusingtheannualconsumptionsofdieselfuel andnaturalgasfuel,theirlowerheatingvalues(LHV−fordiesel fuelis43MJ/kgand35MJ/Sm3_for_natural_gas_fuel)_and_the_boilers

thermalefﬁciencies:

EH=LHVd·md·d+LHVng·mng·ng (3)

3. Alternativesolutions

Biomassnurseryresidualscanbetreatedandrevaluedin dif-ferentways. Italianlawsallowtheuseofbiomass residualas a by-productofthenursery.Therefore,residualsarenotconsidered wastematerialsandthecompanydoesnotneedtodisposeofthe biomassas waste.In ordertoreevaluate biomassand different heatingsupplies,theidentiﬁedpossibilitiesare:

1.Production of wood-chip used to supply wood-chip boilers. Biomassprocessingtakesplacewithinthecompanyandit pro-duces substrate which is fed back to ﬁelds and wood-chip. Wood-chipisstoredintoanopen-sides speciﬁcallydedicated warehouse.Dieselfuelheatersarereplacedbywood-chip boil-ers, positioned into boilers sites, and the heating supply is performedbyhotwaterpipesplants.

2.Production of wood-chip,which is entire soldto wood-chip tradersandproviders.Thermalenergyforgreenhousesis gener-atedbynaturalgasheatersthatreplaceactualheaters.

3.Productionofwood-chipusedtofeedanOrganicRankineCycle (ORC)plantinordertocogenerateelectricpowerandthermal power.

Eachsolutionisoptimizedintermsofinvestmentreturns, fol-lowingthreeindicators(especiallywarehouse’ssize):

NPVn=−S0+ n

k=1 Sk (i+1)k (4) PI=NPV20 S0 (5) PBP=n0:NPVn0=0 (6)

whereNPVnis NetPresent Valueindicatorrelatedtonyears of

investment,S0 isinitialcosts,Sk isannualcashﬂow,PIisProﬁt

IndexindicatorandPBPisPayBackPeriodindicator. 3.1. Biomassprocessing

Inordertoobtainusefulandsaleableproducts,biomassis pro-cessedwithtwosequentiallytreatments:

• Separationofwoodpartsfromthesubstrate:thetreatmentis performedbyaseparatingmachine,whichhasarotatingdrum screener.Forthispurpose,thedrumscreener“PezzolatoL3000 mini”hasbeenchosen(Table2).

• Woodpartsarechippedinordertoobtainlittlepartsof

wood-chip.Sizereductionensuresabetterdryingandabetteruseofthe

warehouse.Actually,wood-chiphasahigherdensitythan

pre-chippedwoodandittakeslessspace.Drumchipper“Pezzolato

PZ250”hasbeenchosenforchippingtreatment(Table2).

Inordertoestimateannualdieselandlaborcostsforthese

oper-ations,costoflaborperhourslabor=25D/hhasbeenconsidered.

Then,themediumcostofdieselfuel,whichissdiesel=0.827D/l.The

followingequationshavebeenappliedwiththesevalues:

twork=

Mbio

flowbio

Sdiesel=

twork·Powdrum

·LHVdiesel

Slabor=twork·slabor

Where:

• twork isthetimethedrummachinetakestoprocessacertain

quantityofbiomass/residues

• Mbioisthequantityofbiomass/residuesprocessed

• ﬂowbioistheﬂowrateofthedrummachine

• Sdieselisthecostofdieselusedbythemachinefortworkoftime

• ␩ is the efﬁciency of machine, assumed to be 25% for both

machines

• LHVdieselisthelowerheatingvalueofdieselfuel

• Powdrumisthemechanicalpoweroutcomeofdrummachine

Separationprocesswithdrumscreenerhandlesagreater

quan-tityof mass than drum chipper becauseat this stage,biomass

containsanimportantpartofsoil(Fig.5).

3.2. Solution1–Heatingplantofgreenhousespoweredby

producedwood-chipandsaleofsurplusoflatter

Inordertosupplythermalenergytogreenhousesandofﬁces

therearetworeferenceconﬁgurations:centralizedand

decentral-ized.Aheatingplantimplementedbywood-chipboilersrequires

additionalcomponents,forexamplewood-chiptanksand

auto-maticsystemsforfuelsupply,waterthermalstorages,ashremoval

systems,andmanyothers.Forthisreason,thecentralized

conﬁgu-rationisnormallychosen.Consideringthelocationofgreenhouses

andofﬁces,twothermalcentralsareneeded:oneforagreenhouses

groupandonefortheofﬁces.Theconsideredpowerboilershave

asizeof500kW.Thisisthebestcompromisebetweenmachine

costandincentivesprovidedbyItalianlaw.Inparticular,for

refer-encemodel,the“TurbomatTM500”(Table3),producedbyFroling,

hasbeenchosen.Then,Centralizedconﬁgurationisnecessaryfor

transportingtheheatfromthecentralstogreenhousesandofﬁces

usinghotwaterasheattransferﬂuid(Figs.7and8,Table4).

Thecostofsuchaplantis580,000D,estimatedbythecompany

TIESSEIS.R.L.(Pistoia,IT).

ItalianEconomicandIndustryMinistrypromotesenergysaving,

introducing“ContoTermico”decree(DM28/12/12)whichprovides

anincentivebonusIafortheﬁrst5yearsofoperation.Thisincentive

isaimedatbiomassheaters.Theamountoftheincentiveforeach

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Fig.7.–Biomass-fedthermalenergyplant.

Fig.8.−VariationofNPV20andPIbyvaryingthesizeofwarehouse.

Table3

–TechnicaldataofTurbomatTM500. TurbomatTM500SPS4000−Froling

NominalPower(KW) 500

Efﬁciency(Mo≤50%) 94%

Temperatureofexhaustgasatnominalcondition[◦_C] ₁₄₀

MaxPressure[bar] 6

MinTemperaturereturn[◦_C] ₆₅

MaxwaterTemperature[◦C] 90

Totalweight[Kg] 8400

Ia=Pn·t·Ci·Ce

Ci[D/kWh]isacoefﬁcientaboutthermalenergyvalorization,

whichdependsonthethermalpowerofeachboiler.Inthepresent caseCi=0.020D/kWh(Pn=35.÷500.kW).

tistheoperationtime(hoursperyear)anditdependsonthe plantlocation’sclimaticzone.t=1400hbecausePistoiaisinthe“D” climaticzone(eachdistrictofItalyisclassiﬁedonclimaticzone from“A”to“F”).

Ce is a coefﬁcientaboutemission ofprimary particulateper

Sm3_of_air._In_this_analysis_C

e=1.2becausetheboileremissionsare

between15mg/Sm3_and₂₀_mg/Sm3_.

Table5

–Technicaldataofnaturalgasheaters.

Nominalpower[kW] 85.0

Heaternaturalgasconsumption[Sm3_/h] _8.767

Efﬁciency 95%

Table6

−ComparisonofNPV20andPIinopenﬁeldsolutionstorageand350m2warehouse

storage.

Openﬁeldstorage Warehouse350m2_storage

NPV20 D1,064,537 D732,187

PI 3.23 1.75

Thewood-chipproducedbytransformationofbiomassisstored inawarehouse,implementedbyafarmbuildingopenedonthree sideswithusefulheightof5.m,speciﬁccapacityestimatedof2. t/m2_and_a_speciﬁc_cost_of_250.

D/m2_(Agenzia_delle_Entrate_-Ufﬁcio

Provinciale,2015).Itisassumedthatwood-chipisstoredmonthly

andthatthemoistureofwood-chipdecreasesby10%permonth

((AssociazioneItalianaEnergieAgroforestali),2009).Ifitisnotused

Table4

−Thermalpowerrequirement.

ThermalunitA ThermalunitB

Users GreenhousesgroupA+Ofﬁces GreenhousesgroupB

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Fig.9.−Naturalgasfeedingathermalenergyplant.

Table7

−ThermalpowerrequirementinORCsolution.

ThermalunitA ThermalunitB+ORC Users GreenhousesgroupA+Ofﬁces GreenhousesgroupB Powerrequirement(kW)2300+200=2500 3900

Table8

–TechnicaldataofORCmodule. ORCTurboden3CHPMode

ThermalpowerIN[kW] 1971

Electricpowergenerated[kW] 300

Electricefﬁciency 15.5%

Thermalpowerforcogeneration[kW] 1636

ThermalefﬁciencyCOG 83%

Watertouserstemperature[◦C] 75

Waterreturntemperature[◦C] 55

OperatingTime[hours] 4661

Table9

−NPV20andPIofORCsolution.

ORC

NPV20 D1,085,558

PI 0.24

orsoldbeforehand,themoisturereachesatleasta20% stabiliza-tion(Simpson,1998).Ifthewoodchipstockedinthewarehouse

hasMo≤50%,itisutilizedforsatisfyingthethermalrequirement.

OtherwisethenecessarywoodchipispurchasedatMo=20%.The

warehousehasamaximumcapacitythatdependsonitssize.This

limitcanbeovercomebysellingthesurplusofthedriestwood-chip

availableinstock.Theproﬁtabilityofinvestmentinthissolutionis

studiedvaryingthesizeofwarehousetoidentifytheoptimalsize

(Fig.9);amaximumofNPV20forthesize450m2andamaximum

ofPIforthesize400m2_are_present._The_{conﬁguration}_of_“0_m2_”

representsavirtualsituationinwhichthewood-chip,produced

duringthemonth,isentirelysoldandthethermalrequirementis

satisﬁedpurchasingdrywood-chip(Mo=20%).

InthisconﬁgurationPIassumestheabsolutemaximumvalue.

It is reasonablethat buildingnew warehouses is not

economi-callyproﬁtable.Moreover,thebestconﬁgurationforthissolution

isassumedtobea450m2_warehouse.

3.3. Solution2–Sellingofallproducedwoodchipandsupplying

thermaldemandbynaturalgasheatgenerators

Adifferentsolutionisproposedinordertoreduceinitialcosts

andsimplifytheplant.Inthissolution,allwoodchipisstoredin

awarehouseandsoldwhenwoodchipreachesMo=20%orwhen

thewarehouseisfull.Thermalenergyforgreenhousesisproduced

bythecombustionofnaturalgas.Thefeasibilityofanaturalgas

heatingsystemdependsonthenaturalgasgridandthelocation

ofgreenhouses.Naturalgasheatersareplacedintogreenhouses

asreplacementofdieselfuelheaters:theydirectlytransferheatto

air,withoutneedingahotwaterdistributionsystem.Bydoingso,

heatingplantresultscheaperthantheprevioussolutionandthere

isnolostheatduetoheattransportation.Thenaturalgassupply

isperformedbyapipesystemthatlinkseverygreenhousetomain

gaspipe(Fig.10).

Incomparisonwiththepreviousplant,thereisnolabor

require-mentforwoodchipsupply andheatingboilerscleaning,and no

labor for biomass storage place and systems either. Moreover,

biomasstreatmentiscompletelyseparatedfromthermalenergy

production.Thereisnopossibilitytobeneﬁtofincentivesinthis

case,andnaturalgasismoreexpensivethanwoodchip.Asforthe

thermalenergydemand,73heatersof85kWeachhavebeentaken

intoaccount(Tables4and5).

AsinSolution1,Fig.11showstheproﬁtabilityoftheinvestment,

varyingthesizeofthewarehouse.

Fig.11 showsthatthebestsolutionintermsofNPV20hasa

warehouseof350–400m2_.

Biomassstoragewarehouseisaconsiderablecostofthe

invest-ment. Its feasibility also depends on the availability of areas

necessarytorealizeit.Adifferentsolutionisproposedinorder

toreduceinitialcostsandsimplifytheplant.Biomassresidualsare

storedinanopenﬁeldareaacrosstheyear,duringproductiontime.

Naturaldehumidiﬁcationoccursduringthestorageperiod,in

par-ticularduringspringandsummermonths.Treatmentofbiomassis

carriedoutduringsummermonths,whenaveragemoisturelevelis

atitslowest.Inthiscasebiomassissubjecttoweatheragentsandis

directlyincontactwiththeground,evenifinmostoftheyearit

pre-servesitsoriginalsizeanditislessdecomposablethanwoodchip.

Producedwoodchipisimmediatelysoldtotraders.Consideringthe

amountofbiomassproducedbyVannucciPiante,biomasscouldbe

workedinJuly,AugustandSeptember,hypothetically.Theaverage

moisturelevelisconsidered50%andtheestimatedmassreduction

duetodecompositionisof20%(Simpson,1998).Soldwoodchip

ispriced30D/ton(Franceschi,2015).Consideringmassreduction

due todehumidiﬁcation and decomposition, woodchip

produc-tionis about 2978ton/year. Woodchip sale proceedsstands at

89,949D/year.NPV20andPIarereportedinTable.

3.4. Solution3–ORCincogenerationwithboilerpoweredby

wood-chipbyproduct

Inthissolution,electricenergyisproducedinordertoextract

thehighesteconomicvaluefromthebiomass.Thermaland

elec-tricenergiesareproducedinaco-generativeplant.Twothermal

energyunitsandoneORC(Organic-ﬂuidRankineCycle)systemare

assumedtobenecessary(Fig.12,Table6).Theheatgeneratedby

ORCcanbeusedtosatisfyathermaldemandwhenitisrequested,

orcanbedissipatedbyadrycoolingtower.

Asforthechoiceofthermalboilers,thesameconsiderationsof

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Fig.10.−VariationofNPV20andPIvaryingthesizeofwarehouse.

Fig.11.−ThermalandelectricenergyproductionplantwithORC.

heatpipeplantdescribedinSolution1havebeenused.

Consid-eringthequantityofwoodchipproducedinayearandinorder

tomaximizetheworkingtime,theelectricpowersizeofORC

co-generatorisof300·kWel(Table6).Theannualquantityofproduced

woodchippermitstheORCmoduletoworkonly4661hperyear

(Tables7and8).

Woodchipproducedbytransformingofbiomassisstoredina

warehouse,thatinthiscaseisdesignedtomaximizeitsuse.

Boil-ersofthermalcentralsguaranteetherighttoreceiveanincentive

bonus,asmentioned for Solution1. Theministerial decree DM

23/6/2016givestherighttoreceiveabasicincentiverateforelectric

energyproducedfor20years,inordertorealizeanelectricenergy

plantgeneratorpoweredbywoodchip.TheratethattheVannucci

Piantecompanypaysfortheelectricenergyislowerthantherate

providedbyincentives.Therefore,theanalysisofproductivityof

thissolutioncanbeobtainedfromtheelectricityconsumptionof

company.

4. Results

All proposed solutions are compared in terms of economic

returnswiththreeindicatorsofequations1,2,3.

Theeconomicvaluationofthesolutionshasbeenreportedin

Fig.13andTable9.

Initialcostsareextremely different.Naturalgassolutionhas

thelowestcostandthisismostlyduetothelowcostofnatural

gasheaters.ORCsolutionisthemostexpensiveone:initialcosts

amounttoD 4,500,000.ThisisduetothehighcostofORCmodule

respecttootherinitialcostsofthesolution.Suchasolutioncould

befavourableonlyifcashﬂowisgoodduringtheinvestmentyears.

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Fig.12.−Initialcostsoftheproposedsolutions.

Fig.13.−Annualcashﬂowforeachproposedsolution.

hasanintermediateinitialcost:inthiscasethemostrelevantcost

derivesfromthewoodchipboilers.Thebiomasstreatment

machin-erycostisnotsosigniﬁcant,incomparisonwiththeothercostsof

investments.Inthisway,thewoodchipproductioncanbeeasily

performedineconomicterms.

AnnualcashﬂowsarereportedinFig.14,anddetailsinTable10.

AlthoughtheNaturalgasheaterssolutionhasthelowestinitial

costs,annualcostsarehigherthanintheothertwosolutions.This

isduetothenaturalgaspurchasecost.Theannualcostsforthe

othertwosolutionsarecomparable.

Thesolutionwith ORChashighest annual returns.The best

annualreturnforthissolutionisthesaleofelectricenergy

pro-duced,which amountsto aboutD 344,000.Anothersigniﬁcant

returnintheﬁrstandthethirdsolutionsisgivenbybonus

incen-tives. Moreover, saving fuel currently used by the company is

anotherimportantreturninallthreesolutions.Lessconsiderable

returnsarethewoodchipsellingandthesavingonbiomasswaste

disposal.

AsshowninFig.14andTable11,NPV20 ofthesolutionsare

similar.Naturalgashasthebestone,theothershavesigniﬁcantly

differenttrends.ThetrendofORCsolutionNPVhasthebestrise

during the given period, because this solution hasthe highest

annualreturn.DespiteofNPV20,thePBPsofthesolutionsarevery

different.Naturalgassolutionhasthelowestvalue(2years).The

woodchipboilerssolution’sPBPis7yearsandtheORCsolutionis

theworstonewith13yearsofPBP.AsTable11shows,thebestPI

istheoneforthenaturalgassolution.

5. Conclusions

Theresultsofthisstudyshowthatnaturalgassolutionisthebest

oneineconomicterms,consideringthethreeindicatorsinTable11.

EveniftheNPV20ofwoodchipboilerssolutionisthehighest,the

PBPandPIareconsiderablybetterinnaturalgassolution(Table12).

Theotherstwosolutions,woodchipboilersandORC,exploit

thebiomassby-productsource,representingtwowaysto

imple-mentrenewableenergyproduction.Thistypeofsolutionshashigh

initialcosts.EveniftheItalianEconomicMinistryguarantees

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Fig.14. −NPVtrendin20years-longinvestmentforeachproposedsolution.

Table10

−Detailsofinitialcostsforeachproposedsolution.

Woodchipsboilerswarehouse450m2 _Natural_gas_heaters₊_woodchip_sale _ORC_cogeneration₊_woodchip_boilers

Thermalunits D1,312,000 D208,780 D1,010,000

Heatpipesystem D580,000 D0 D580,000

Biomasstreatmentmachinery D60,400 D60,400 D60,400

Wood-chipwarehouse D112,500 D0 D343,750

Naturalgasdistributionplant D0 D60,000 D0

ORCPlant D0 D0 D2,500,000

Total D2,064,900 D329,180 D4,494,150

Table11

−Detailsofannualcashﬂowforeachproposedsolution.

AnnualCosts Biomasstreatment -D71,400 -D63,345 -D63,345

Wood-chippurchase -D10,985 D0 D0

Naturalgaspurchase D0 -D123,160 D0

Plantmaintenance -D20,000 -D10,000 -D30,000

Totalcosts -D102,385 -D196,505 -D93,345

AnnualReturns Savingonwastedisposal D64,880 D64,880 D64,880

Savingonactualfuelpurchase D194,038 D181,940 D194,038

Wood-chipselling D61,619 D89,949 D0

Bonusincentives D218,400 D0 D168,000

Electricenergyselling D0 D0 D343,957

Totalreturns D538,937 D336,769 D770,875

Annualcashﬂow D436,552 D140,264 D677,530

Table12

−Economicindicatorusedforproﬁtabilityanalysisofinvestmentsforeachproposedscenario.

NPV20 D1,131,932 D1,064,537 D1,085,558

PI20 0.55 3.23 0.24

PBP 7years 2years 13years

tomake thesesolutions competewithconventional fossilfuels alternatives.

Thisstudy highlights that sellingwood chipproduced with biomassby-productismorereasonablethanusingitinternallyin anurserycompany.

Accordingtotheresultsof this work,policiesonrenewable energies incentives should be strengthen in Italy. Not surpris-ingly,companieslikeVannucciPiantetreatbiomassby-productas awaste.

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