Research ArticleNot Reacted Core Model Applied in Palm Nut Shell Pyrolysis
Ernesto de la Torre and Sebastian Gamez
Department of Extractive Metallurgy Escuela Politecnica Nacional Quito 170517 Ecuador
Correspondence should be addressed to Sebastian Gamez sebastiangamezepneduec
Received 29 September 2018 Revised 24 November 2018 Accepted 27 November 2018 Published 2 January 2019
Academic Editor Evangelos Tsotsas
Copyright copy 2019 Ernesto de la Torre and Sebastian Gamezis is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in anymedium provided the original work isproperly cited
One of the main sources of activated carbon is biomass which can be transformed into char by pyrolysis Apart from the obtainingcoal the pyrolysis of biomass can be used for the preparation of fuels and this is why it is very important to determine its kineticparameters for modelling In the present research the pyrolysis enthalpy of palm nut shells (Elaeis guineensis) was determinedwith the use of a differential scanning calorimetry study (DSC) To determine the kinetic parameters the Not Reacted Core modelwas employed is model considers that there is a heat and mass gradient between the furnace atmosphere and the interfaceformed during pyrolysis To obtain the required data for the model palm nut shells were submitted to pyrolysis in a Nicholsfurnace under reducing atmosphere Samples were taken every 10 minutes to calculate char conversion e experimentalpyrolysis enthalpy resulted to be 30181 Jg and then the monomeric units of cellulose hemicellulose and lignin were employed inorder to determine the pyrolysis enthalpy per mole e three biopolymers react with different mechanisms at different tem-peratures e molecular weight resulted to be 17238 gmole and the enthalpy for pyrolysis was 5203 kJmol For the applicationof the Not Reacted Coremodel the amorphous char heat transfer coefficient was selected and the value is 16 JsmiddotmmiddotKe reactionrate constant was 664 times 10minus91s assuming a first-order reaction whereas the effective diffusion across the char layer was 483times 10minus7m2s
1 Introduction
e search for new sources of energy has provoked thegeneral interest for the use of biomass e pyrolysis ofbiomass is a complex thermal process that allows obtainingfuels [1] However the process is very complex and it de-pends on several factors It should also be noted that eachlignocellulosic material to be used tends to vary enormouslyin its chemical composition As it is of general knowledgebiomass is composed of several components and the threemore representatives are cellulose hemicellulose and lignin[2] According to biomass chemical composition pyrolysiscould be endothermic or exothermic Generally lignocel-lulosic materials that have a higher concentration of ligninwill tend to show endothermic pyrolysis On the contrarylignocellulosic materials have a lower concentration of ligninand a greater quantity of cellulose and hemicellulose andthey will show an exothermic behaviour during pyrolysisUsually the lignocellulosic substances that come from the
stems have a higher concentration of lignin in their structure[3]
In order to understand the pyrolysis of lignocellulosicmaterials such as palm nut shells it is necessary to un-derstand how the decomposition of the main constituentsoccurs us the process of pyrolysis of palm nut shells canbe divided into four major stages dehydration of the beandecomposition of hemicellulose decomposition of celluloseand decomposition of lignin [4] Depending on whichcomponent is in greater concentration with respect to theothers biomass will have an exothermic or endothermicbehaviour during pyrolysis us in many articles it isfrequently discussed whether the nature of the pyrolysis isexothermic or endothermic According to several authors ifthe content of lignin is high the pyrolysis process will beendothermic [3 5ndash7]
Cellulose and hemicellulose may have the same mech-anisms of thermal decomposition e mechanisms pro-posed for the pyrolysis of cellulose consider dehydration and
HindawiInternational Journal of Chemical EngineeringVolume 2019 Article ID 9561265 8 pageshttpsdoiorg10115520199561265
depolymerization reactions with breakdown of glycosidicbonds and bonds which produce tar levoglucosan furfuraland heterocyclic compounds as well as CO CO2 CH4CnHm and H2 [8] e coal is produced by low temperaturedehydration reactions and secondary reactions of repoly-merization (reforming) In addition carbon in the form ofgraphene layers is produced by aromatization reactionswhich occur via dehydration reactions that produce coalese reactions are exothermic while reactions that generatetar and gases are highly endothermic [9]
Lignin on the contrary has a much more complexstructure It is made up of dierent phenolic molecules andcarbonyl compounds and when they are fragmented duringpyrolysis these molecules give rise to dierent aromaticcompounds e mechanisms of thermal decomposition oflignin are much more complex [10 11] ey are based ondehydration and on depolymerization reactions similar tothose proposed for cellulose Due to the chemical compo-sition of the lignin the production of tar and levoglucosan isless than in the case of cellulose which results in a higherproduction of coal in the pyrolysed material However thereare three components that are repeated throughout thechemical structure with dierent forms of polymerizationese are p-coumaryl alcohol (C9H10O2) coniferyl alcohol(C10H12O3) and synapyl alcohol (C11H14O4) [12 13]
In the literature the three organic compounds are ac-cepted as the main components of lignin ese componentspossess the main functional groups (hydroxyl groups andmethoxy groups) that participate in the formation anddecomposition reactions of lignin In fact it is consideredthat 90 of the functional groups found in the structure oflignin are the methoxy groups while the remaining 10correspond to the hydroxyl groups [14] In order to evaluatethe rate of decomposition of biomass in the case of ther-mogravimetric analysis the Not Reacted Core model wasapplied considering simple reactions to succeed simulta-neously According to the reaction mechanisms proposed byseveral authors the carbonization reaction of palm nut shellscan be simplied as follows
Cq(s)⟶ Ch(s) + Gas(g) (1)
where Cq(s) is the solid reagent (the palm nut shell) Ch(s)is the carbonizedmaterial (residual solid coal) and Gas(g) isgas produced during carbonization
e mechanism of cellulose carbonization proposed byZickler et al [15] considers an unreacted nucleus which isreduced as a function of time and the phenomenologicalmodel proposed for palm kernels pyrolysis is shown inFigure 1
In the middle there is the not reacted core representedby Cq Surrounding the not reacted core is the carbon layer(Ch) formed during palm nut shells pyrolysis Heat istransferred from the oven to the interface in order to initiatethe pyrolysis erefore To (outside temperature) must behigher than Ti (interface temperature) in order to maintain agradient During pyrolysis several gases are produced whichincrease Pi (interface pressure) is pressure must begreater than Po (outside pressure) to permit gases to diuse
from the interface to the outside us heat and masstransport phenomena are crucial stages for palm nut shellspyrolysis
e mechanism of palm nut shells pyrolysis is verycomplex its decomposition rate depends on many dierentfactors the most signicant being the heat transport to theCqCh interface (being endothermic) reaction rates in-volved in the pyrolysis and the diusion of gases throughthe coal layer that should be porous pore blockage by tarreduction of particle size and fracturing of particles[16ndash18]
2 Materials and Methods
e STA 8000 thermogravimetry equipment was used toobtain the TGA-DSC thermograms All the samples weresubjected to pyrolysis for which nitrogen was used as inertgas Gas ow of 80mLmin and a heating ramp of 10degCminfrom 50 to 900degC were employed in each experiment Todetermine the kinetic parameters the Not Reacted Coremodel was employed is model considers that there is aheat and mass gradient between the furnace atmosphere andthe interface formed during pyrolysis e molecular weightof palm kernels was estimated considering the chemicalcomposition of the monomeric units within each bio-polymer erefore glucose p-coumaryl alcohol coniferylalcohol and synapyl alcohol were considered for molecularweight calculation according to their percentage in weightwithin palm kernels
To obtain the required data for themodel pilot scale testswere carried out in a 12 kg Nichols furnace Combustion iscarried out in the presence of air and liqueed petroleum gas(LPG) composed by 50 C3H8 and 50 C4H10 within aburner which has a heat capacity of 315 000 kJh e ovenhas a sheet of 4mm thick and refractory-insulating brickswhich comprise a combustion chamber coupled to a 457mmdiameter reaction chamber is chamber is provided with a
Notreacted
coreCq
Ch Gas
Plowast
PiTo
Po
Ti
riro
Heat
Figure 1 Not Reacted Core model (Cq palm kernel Ch coal plowastgas equilibrium pressure Po atmospheric pressure Pi gas pressureat the interface To outside temperature Ti temperature at theinterface ro radius of the particle ri radius of the interface rocradius of the particle after decreasing volume)
2 International Journal of Chemical Engineering
100mm height blade stirrer with a rotating speed of 4revolutions per minute e atmosphere of the Nicholsfurnace is controlled by the lambda factor (λ) which is theratio between the air supplied to the burner and the airstoichiometrically necessary for a complete combustion ofthe gas e air is supplied by a fan whose flow rate is166Nm3min e pilot scale pyrolysis tests were carriedout on samples with a particle size between 5 and 20mm Foreach test the Nichols furnace was heated to the desiredtemperature (heating rate 07ndash15 and 10degCmin) with areducing atmosphere λ 076 (chemical analysis of com-bustion gases 10 CO2 4 CO 11 H2 001 O2 and 9H2O) e samples were loaded at the start of the oveneither in a fixed bed with 12 kg of sample or in mixed bedwith 3 or 4 kg Tests were also carried out by introducing thesample into the preheated oven at the desired temperatureAt the end of the test the material is discharged cooled in aclosed metal container and weighed Samples were takenevery 10 minutes to calculate char conversion and to in-corporate those data in the modele reaction rate constantand the effective diffusion coefficient across the char layerwere calculated as well
Tests on an industrial scale were carried out in a rotarykiln which runs on fuel oil with an excess of air of 20 (λ
12) and whose burner has a heat capacity of 8 times 106 kJhe solids were introduced into the furnace by an endlessscrew that moves in the same direction as the flue gas(cocurrent) forming a layer of about 15 cm in height whenthe furnace works without lift Treated solids are dis-charged at the opposite end of the feed through a water-cooled endless screw while gases came out at the top andwent through an afterburner a plate heat exchanger acyclone a draft fan and finally the chimney e nominalcapacity of the solids supply in the oven is 1m3h anddepending on the speed of rotation and the use of the liftersor without the use of the lifters the residence time can varybetween 03 and 80 hours Palm kernels of 5 to 20mmwereintroduced to a rotary kiln which was heated for 7 days at850degC in an oxidizing atmosphere (λ 12) the fuel oilconsumption was 2650 Lday In these tests incominggases contained 10 CO2 5 O2 and 15 H2O Asmentioned above the tests were performed in the presenceor absence of levers the rotational speed was set at 3 rpmwith a feed of 900 kgh e duration of each trial was 35days in order to obtain samples in sufficient quantity toprovide them to potential customers e output rate of thecarbonized materials was measured and their volatilecontent was measured regularly in order to use in the NotReacted Core model
3 Results and Discussion
31 Not Reacted Core Model In order to develop the NotReacted Core model TGA-DSC analysis of pulverized palmkernels were carried out under inert atmosphere of nitrogenPyrolyzed samples were analysed by scanning electronmicroscopy (SEM) to verify the existence of an unreactedcore SEM image of palm nut shells after pyrolysis is shownin Figure 2
e black core corresponds to the unreacted palm nutshell whereas the surrounding material is the residual solidcoal is image confirms the idea that biomass pyrolysisoccurs according to the not reacted core At the first stageheat is transferred through the char layer to the interface upto the interface en chemical reactions of biomass de-composition (different mechanisms for the three bio-polymers) occur at the interface which results in thegeneration of residual coal and various gases Finally thesegases diffuse through the char layer towards the externalatmosphere e relevance of these model lies in the in-corporation of all the three known mechanisms that mayoccur during biomass pyrolysis heat transfer chemicalreaction at the interface and mass transfer
e Not Reacted Core model for palm nut shells py-rolysis was employed considering that the particles arespherical erefore there is no accumulation of heat andmass during pyrolysis and the amount of heat carried by thegases is negligible First the equilibrium constant of reaction(1) was calculated using the following equations
ΔGo minusRT ln Keq
Keq aCh middot plowastgas
aCq plowastgas
(2)
where Keq is an equilibrium constant of equation (1) aCh isthe activity of carbonized product or solid coal (equal to 1)plowastgas is the partial pressure of the gases produced by car-bonization aCq is the activity of solid shells (equal to 1) R isthe universal gas constant (831 JKmiddotmol) and T is thetemperature (K)
On the contrary the conversion (χ) for the carbonizationof palm nut shells (equation (1)) can be estimated as the GasmolesCq moles ratio assuming that all palm nut shells arespherical erefore the moles of solid shells can be de-termined by the product between the sphere volume andpalm nut shells density
χ gas molesCq moles
1113938
t
0 ngRx dt
(43)π middot ro middot ρCq (3)
For pilot and industrial essays in the Nichols furnace androtary kiln respectively the achieved conversion can bedetermined bymeasuring the amount of the volatile materialduring pyrolysis e amount of the volatile material is thedifference between the initial palm nut shells mass and the
Figure 2 Palm kernelrsquos not reacted core SEM image (200 microm)
International Journal of Chemical Engineering 3
mass weighed at different intervals of time Equation (4)shows how to calculate conversion in experimental tests formodels validation
χ ( volatile material)0 minus ( volatile material)t
( volatile material)0
(4)
In order to estimate the specific reaction rate constant(kr) and the effective gas diffusion (Def ) a geometric ap-proach is proposed based on the phenomenological model(equation (1) Figure 1) and the calculation of the number ofmoles of gas produced by the chemical reaction (ngRx) can beobtained by the following equation
ngRx 4πr2i minus
dri
dt1113888 1113889ρCq kr 4πr
2i1113872 1113873 plowast minus pi( 1113857 (5)
where ngRx is the number of moles of gas produced by thereaction chemical (moles) ri is the radius of the interface(cm) t is the time (s) ρCq is the molar density of the shells(molecm3) kr is the specific reaction rate constant (cms)plowast is the equilibrium partial pressure of the gases producedby the carbonization (Pa) (equation (1)) and pi is the partialpressure of gases at the interface (Pa)
Grouping the terms of equation (5) and integrating weget
dri
dt1113888 1113889 minus
kr plowast minus pi( 1113857
ρCq minusB (6)
1113946ri
ro
dri minusB 1113946t
0dt (7)
ri ro minusB (8)
ngRx 4πρCqB ro minusBt( 11138572 (9)
On replacing equation (9) in equation (3)
ro 1minus(1minus χ)13
1113960 1113961 B (10)
χ 3B
rot minus
3B2
r2ot2
+B3
r3ot3 (11)
By solving equation (10) the B constant is found andthen by solving equation (6) the specific reaction rateconstant can be estimated
Finally the effective diffusion constant can be de-termined by solving the next equation
where ngDf is the number of moles of gas leaving the particleby diffusion through the porous coal layer (moles) Def is theeffective diffusion constant of gases through the porous coallayer (cm2s) pi is the pressure at the interface (Pa) po is theexternal pressure (Pa) ri is the interface radius (cm) and roc isthe radius of the particle after volume contraction (cm)
32 TGA-DSC Analysis In order to understand palm nutshells pyrolysis TGA-DSC analyses were performed InFigure 3 it is shown that the thermogram is obtained
According to Yang et al carbonization of the palm nutshells takes place as follows
(i) Zone I (lt131degC) removal of moisture
(ii) Zone II (217ndash335degC) decomposition of hemicellulose(iii) Zone III (335ndash392degC) decomposition of cellulose(iv) Zone IV (gt392degC) decomposition of lignin
At the beginning the weight loss is very low since thehumidity present on palm nut shells evaporates en thehemicellulose decomposes over 217degC followed by cellulosedecomposition Both biopolymers have the same monomerwhich is glucose and over 335degC this substance transformsto levoglucosan tar and several gases such as CO CO2 CH4and H2 among others On the contrary pyrolysis enthalpy iscalculated from the DSC analysis shown in Figure 4
Between 50 and 100degC an endothermic peak can beobserved which corresponds to the evaporation of hu-midity Afterwards the other endothermic peak is detectedat 243degC which may be assigned to hemicellulose de-composition en a bigger endothermic peak is foundupon 400degC and the other at 441degC ose peaks couldcorrespond to cellulose and lignin decomposition Finallyit was determined that lignin may decompose upon 392degC(Figure 3) and in our DSC study we detected the largestendothermic peak upon 500degC which may be assigned tolignin decomposition
en as it can be observed palm nut shells pyrolysis hasan endothermic behaviour is result confirms that thecontent of lignin within biomass determines if pyrolysis isexothermic or endothermic In this case the process resultedto be endothermic since the content of lignin within palmnut shells is high (504) Pyrolysis enthalpy was calculatedfrom the DSC analysis which was 30181 Jg is valuecannot be implemented in the Not Reacted Core model sincethis model uses values per mole instead of per gram uspalm nut shells molecular weight was estimated consideringits chemical composition
Nevertheless palm nut shells are not a pure chemicalcompound therefore the molecular weight was estimatedconsidering monomeric units of the three biopolymers thatconform to biomass (cellulose hemicellulose and lignin)Since lignin is a biopolymer too complex to estimate itsmolecular weight it was assumed that all monomeric unitsof the palm nut shells are involved in pyrolysis ereforeglucose is proposed as the monomeric unit of cellulose andxylene was selected as the monomeric unit of hemicelluloseIn the case of lignin the main monomeric units resulted tobe coumaryl sinapyl and coniferyl alcohols since they arethe major units in this biopolymer In Table 1 lignincomposition of palm nut shells is shown
Ligninrsquos average molecular weight was incorporated forpalm nut shells molecular weight estimation In Table 2 themolecular weight calculated using palm nut shells chemicalcomposition can be observed
4 International Journal of Chemical Engineering
e estimated molecular weight resulted to be 17238 gmole and this value was employed to determine the py-rolysis enthalpy per mole in order to incorporate it to theNot Reacted Core model
33 Not Reacted Core Modelrsquos Results and Validation eresults obtained with the model can be applied for calcu-lating pyrolysis kinetic and thermodynamic parameters InTable 3 it is shown the results are obtained with the NotReacted Core model
Pyrolysis enthalpy was estimated by the product betweenthe enthalpy obtained in the DSC analysis and the molecularweight determined with palm nut shells chemical compo-sition Pyrolysis entropy was estimated considering thedecomposition temperature for each biopolymer found inthe TGA analysis Afterwards Not Reacted Core modelsequations were applied for kinetic parameters de-termination In this case the pressure in the equilibriumresulted to be 883 atm (894 kPa) which is necessary for gasdiusion e reaction rate constant was 664 times 10minus91sassuming a rst-order reaction whereas the eective dif-fusion across the char layer was 483 times 10minus6m2s In order toevaluate the inuence of a high carbonization temperatureand a high heating rate pyrolysis tests of palm nut shellswere carried out in the Nichols furnace preheated to 850degCPalm nut shells were fed at this temperature in the reaction
chamber and at dierent periods of time shells are dis-charged cooled in a closed metal container and weighed forvolatile material calculation Afterwards conversion wascalculated with equation (4) whereas equation (3) wasemployed for conversion estimation with the Not ReactedCore model In Figure 5 there is a comparison of the volatilematerial removal esectciencies (χ) calculated by the applica-tion of the Not reacted Core Model and those obtainedexperimentally during pyrolysis of palm nut shells in theNichols furnace at 850degC
As it can be observed in Figure 5 this model ts quite wellwith experimental results obtained during pyrolysis of palmnut shells in the Nichols furnace Since palm nut shells py-rolysis is highly endothermic a high heat ux is required at theinterface as it is shown in Figure 6 Considering a temperaturegradient between the interface and the furnace temperature of50degC the amount of heat transported is not susectcient toovercome the energy requirements of the reaction
ese results suggest that palm nut shells pyrolysis islimited by heat transport to the reaction interface It waspossible to prove this hypothesis by industrial tests in acontinuous rotary kiln where the gassolid contact is dif-ferent compared to that of the Nichols furnace and con-sequently can also change the heat transport rate to interfaceand the diusion of the gases produced by carbonizationKunni and Chisaki [19] and Perry et al [20] proposeddierent methods for calculating the residence time in arotary kiln a very important parameter for the control of thequality of the carbonized product Equation (13) which is anempirical relation is the most used relation for the esti-mation of residence time of a solidmaterial in a rotary kiln asa function of its rotational speed
tsj 177L
θ
radicF
PDn (13)
where tsj is the residence time (min) L is the oven length(14m) θ is the angle of repose of palm nut shells (347deg) F isthe characteristic factor of the inside of the rotary kiln (1 foroven without lift 2 for oven with lifters) P is the oven slope(2deg)D is the inside diameter of the oven (15m) and n is thespeed of rotation of the oven (revolutions per minute)
With equation (13) which involves the residence timeand the kiln length) equation (11) and kinetic parameterslisted in Table 3 conversion (χ) can be calculated andcompared with the experimental conversions obtained withthe industrial rotary kiln as it can be observed in Figure 7
Given the consistency of the results obtained with theapplication of the Not Reacted Core model for palm nut
shells carbonization this model may be applied to calculatethe variation of the ow of gases produced by carbon-ization as a function of kiln lengthese data very disectcult
Table 3 Not Reacted Core model results
Parameter Value UnitsΔHdeg 5207406 JmoleΔSdeg 8531 JmolemiddotKΔGdeg minus1393675 Jmoleplowast 89469975 PaMolecular weight estimated 17238 gmolekr 664 times 10minus9 1sDf 483 times 10minus7 m2s
0
20
40
60
80
100
0 02 04 06 08 1Carbonization time at 850degC (h)
ModelExperimental results
χ (
)
Figure 5 Conversion according to experimental results and NotReacted Core model
0
200
400
600
800
1000
0 02 04 06 08 1 12
Hea
t (kJ
h)
Radius interface (cm)
Heat transport with TiRequired heat for reaction
Figure 6 Calculation of heat required for reaction and heattransfer to interface as a function of interface radius (ri) duringpalm nut shells pyrolysis (ro 12 cm To 850degC)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16Kiln length (m)
Calculated by the modelExperimental results (with liers)
χ (
)
Figure 7 Comparison between experimental conversion in therotary kiln (χ) with lifters and conversion calculated with the NotReacted Core model (d80 12mm feed 900 kgh T 850degC n 29 rpm)
6 International Journal of Chemical Engineering
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
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Navigation and Observation
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Submit your manuscripts atwwwhindawicom
depolymerization reactions with breakdown of glycosidicbonds and bonds which produce tar levoglucosan furfuraland heterocyclic compounds as well as CO CO2 CH4CnHm and H2 [8] e coal is produced by low temperaturedehydration reactions and secondary reactions of repoly-merization (reforming) In addition carbon in the form ofgraphene layers is produced by aromatization reactionswhich occur via dehydration reactions that produce coalese reactions are exothermic while reactions that generatetar and gases are highly endothermic [9]
Lignin on the contrary has a much more complexstructure It is made up of dierent phenolic molecules andcarbonyl compounds and when they are fragmented duringpyrolysis these molecules give rise to dierent aromaticcompounds e mechanisms of thermal decomposition oflignin are much more complex [10 11] ey are based ondehydration and on depolymerization reactions similar tothose proposed for cellulose Due to the chemical compo-sition of the lignin the production of tar and levoglucosan isless than in the case of cellulose which results in a higherproduction of coal in the pyrolysed material However thereare three components that are repeated throughout thechemical structure with dierent forms of polymerizationese are p-coumaryl alcohol (C9H10O2) coniferyl alcohol(C10H12O3) and synapyl alcohol (C11H14O4) [12 13]
In the literature the three organic compounds are ac-cepted as the main components of lignin ese componentspossess the main functional groups (hydroxyl groups andmethoxy groups) that participate in the formation anddecomposition reactions of lignin In fact it is consideredthat 90 of the functional groups found in the structure oflignin are the methoxy groups while the remaining 10correspond to the hydroxyl groups [14] In order to evaluatethe rate of decomposition of biomass in the case of ther-mogravimetric analysis the Not Reacted Core model wasapplied considering simple reactions to succeed simulta-neously According to the reaction mechanisms proposed byseveral authors the carbonization reaction of palm nut shellscan be simplied as follows
Cq(s)⟶ Ch(s) + Gas(g) (1)
where Cq(s) is the solid reagent (the palm nut shell) Ch(s)is the carbonizedmaterial (residual solid coal) and Gas(g) isgas produced during carbonization
e mechanism of cellulose carbonization proposed byZickler et al [15] considers an unreacted nucleus which isreduced as a function of time and the phenomenologicalmodel proposed for palm kernels pyrolysis is shown inFigure 1
In the middle there is the not reacted core representedby Cq Surrounding the not reacted core is the carbon layer(Ch) formed during palm nut shells pyrolysis Heat istransferred from the oven to the interface in order to initiatethe pyrolysis erefore To (outside temperature) must behigher than Ti (interface temperature) in order to maintain agradient During pyrolysis several gases are produced whichincrease Pi (interface pressure) is pressure must begreater than Po (outside pressure) to permit gases to diuse
from the interface to the outside us heat and masstransport phenomena are crucial stages for palm nut shellspyrolysis
e mechanism of palm nut shells pyrolysis is verycomplex its decomposition rate depends on many dierentfactors the most signicant being the heat transport to theCqCh interface (being endothermic) reaction rates in-volved in the pyrolysis and the diusion of gases throughthe coal layer that should be porous pore blockage by tarreduction of particle size and fracturing of particles[16ndash18]
2 Materials and Methods
e STA 8000 thermogravimetry equipment was used toobtain the TGA-DSC thermograms All the samples weresubjected to pyrolysis for which nitrogen was used as inertgas Gas ow of 80mLmin and a heating ramp of 10degCminfrom 50 to 900degC were employed in each experiment Todetermine the kinetic parameters the Not Reacted Coremodel was employed is model considers that there is aheat and mass gradient between the furnace atmosphere andthe interface formed during pyrolysis e molecular weightof palm kernels was estimated considering the chemicalcomposition of the monomeric units within each bio-polymer erefore glucose p-coumaryl alcohol coniferylalcohol and synapyl alcohol were considered for molecularweight calculation according to their percentage in weightwithin palm kernels
To obtain the required data for themodel pilot scale testswere carried out in a 12 kg Nichols furnace Combustion iscarried out in the presence of air and liqueed petroleum gas(LPG) composed by 50 C3H8 and 50 C4H10 within aburner which has a heat capacity of 315 000 kJh e ovenhas a sheet of 4mm thick and refractory-insulating brickswhich comprise a combustion chamber coupled to a 457mmdiameter reaction chamber is chamber is provided with a
Notreacted
coreCq
Ch Gas
Plowast
PiTo
Po
Ti
riro
Heat
Figure 1 Not Reacted Core model (Cq palm kernel Ch coal plowastgas equilibrium pressure Po atmospheric pressure Pi gas pressureat the interface To outside temperature Ti temperature at theinterface ro radius of the particle ri radius of the interface rocradius of the particle after decreasing volume)
2 International Journal of Chemical Engineering
100mm height blade stirrer with a rotating speed of 4revolutions per minute e atmosphere of the Nicholsfurnace is controlled by the lambda factor (λ) which is theratio between the air supplied to the burner and the airstoichiometrically necessary for a complete combustion ofthe gas e air is supplied by a fan whose flow rate is166Nm3min e pilot scale pyrolysis tests were carriedout on samples with a particle size between 5 and 20mm Foreach test the Nichols furnace was heated to the desiredtemperature (heating rate 07ndash15 and 10degCmin) with areducing atmosphere λ 076 (chemical analysis of com-bustion gases 10 CO2 4 CO 11 H2 001 O2 and 9H2O) e samples were loaded at the start of the oveneither in a fixed bed with 12 kg of sample or in mixed bedwith 3 or 4 kg Tests were also carried out by introducing thesample into the preheated oven at the desired temperatureAt the end of the test the material is discharged cooled in aclosed metal container and weighed Samples were takenevery 10 minutes to calculate char conversion and to in-corporate those data in the modele reaction rate constantand the effective diffusion coefficient across the char layerwere calculated as well
Tests on an industrial scale were carried out in a rotarykiln which runs on fuel oil with an excess of air of 20 (λ
12) and whose burner has a heat capacity of 8 times 106 kJhe solids were introduced into the furnace by an endlessscrew that moves in the same direction as the flue gas(cocurrent) forming a layer of about 15 cm in height whenthe furnace works without lift Treated solids are dis-charged at the opposite end of the feed through a water-cooled endless screw while gases came out at the top andwent through an afterburner a plate heat exchanger acyclone a draft fan and finally the chimney e nominalcapacity of the solids supply in the oven is 1m3h anddepending on the speed of rotation and the use of the liftersor without the use of the lifters the residence time can varybetween 03 and 80 hours Palm kernels of 5 to 20mmwereintroduced to a rotary kiln which was heated for 7 days at850degC in an oxidizing atmosphere (λ 12) the fuel oilconsumption was 2650 Lday In these tests incominggases contained 10 CO2 5 O2 and 15 H2O Asmentioned above the tests were performed in the presenceor absence of levers the rotational speed was set at 3 rpmwith a feed of 900 kgh e duration of each trial was 35days in order to obtain samples in sufficient quantity toprovide them to potential customers e output rate of thecarbonized materials was measured and their volatilecontent was measured regularly in order to use in the NotReacted Core model
3 Results and Discussion
31 Not Reacted Core Model In order to develop the NotReacted Core model TGA-DSC analysis of pulverized palmkernels were carried out under inert atmosphere of nitrogenPyrolyzed samples were analysed by scanning electronmicroscopy (SEM) to verify the existence of an unreactedcore SEM image of palm nut shells after pyrolysis is shownin Figure 2
e black core corresponds to the unreacted palm nutshell whereas the surrounding material is the residual solidcoal is image confirms the idea that biomass pyrolysisoccurs according to the not reacted core At the first stageheat is transferred through the char layer to the interface upto the interface en chemical reactions of biomass de-composition (different mechanisms for the three bio-polymers) occur at the interface which results in thegeneration of residual coal and various gases Finally thesegases diffuse through the char layer towards the externalatmosphere e relevance of these model lies in the in-corporation of all the three known mechanisms that mayoccur during biomass pyrolysis heat transfer chemicalreaction at the interface and mass transfer
e Not Reacted Core model for palm nut shells py-rolysis was employed considering that the particles arespherical erefore there is no accumulation of heat andmass during pyrolysis and the amount of heat carried by thegases is negligible First the equilibrium constant of reaction(1) was calculated using the following equations
ΔGo minusRT ln Keq
Keq aCh middot plowastgas
aCq plowastgas
(2)
where Keq is an equilibrium constant of equation (1) aCh isthe activity of carbonized product or solid coal (equal to 1)plowastgas is the partial pressure of the gases produced by car-bonization aCq is the activity of solid shells (equal to 1) R isthe universal gas constant (831 JKmiddotmol) and T is thetemperature (K)
On the contrary the conversion (χ) for the carbonizationof palm nut shells (equation (1)) can be estimated as the GasmolesCq moles ratio assuming that all palm nut shells arespherical erefore the moles of solid shells can be de-termined by the product between the sphere volume andpalm nut shells density
χ gas molesCq moles
1113938
t
0 ngRx dt
(43)π middot ro middot ρCq (3)
For pilot and industrial essays in the Nichols furnace androtary kiln respectively the achieved conversion can bedetermined bymeasuring the amount of the volatile materialduring pyrolysis e amount of the volatile material is thedifference between the initial palm nut shells mass and the
Figure 2 Palm kernelrsquos not reacted core SEM image (200 microm)
International Journal of Chemical Engineering 3
mass weighed at different intervals of time Equation (4)shows how to calculate conversion in experimental tests formodels validation
χ ( volatile material)0 minus ( volatile material)t
( volatile material)0
(4)
In order to estimate the specific reaction rate constant(kr) and the effective gas diffusion (Def ) a geometric ap-proach is proposed based on the phenomenological model(equation (1) Figure 1) and the calculation of the number ofmoles of gas produced by the chemical reaction (ngRx) can beobtained by the following equation
ngRx 4πr2i minus
dri
dt1113888 1113889ρCq kr 4πr
2i1113872 1113873 plowast minus pi( 1113857 (5)
where ngRx is the number of moles of gas produced by thereaction chemical (moles) ri is the radius of the interface(cm) t is the time (s) ρCq is the molar density of the shells(molecm3) kr is the specific reaction rate constant (cms)plowast is the equilibrium partial pressure of the gases producedby the carbonization (Pa) (equation (1)) and pi is the partialpressure of gases at the interface (Pa)
Grouping the terms of equation (5) and integrating weget
dri
dt1113888 1113889 minus
kr plowast minus pi( 1113857
ρCq minusB (6)
1113946ri
ro
dri minusB 1113946t
0dt (7)
ri ro minusB (8)
ngRx 4πρCqB ro minusBt( 11138572 (9)
On replacing equation (9) in equation (3)
ro 1minus(1minus χ)13
1113960 1113961 B (10)
χ 3B
rot minus
3B2
r2ot2
+B3
r3ot3 (11)
By solving equation (10) the B constant is found andthen by solving equation (6) the specific reaction rateconstant can be estimated
Finally the effective diffusion constant can be de-termined by solving the next equation
where ngDf is the number of moles of gas leaving the particleby diffusion through the porous coal layer (moles) Def is theeffective diffusion constant of gases through the porous coallayer (cm2s) pi is the pressure at the interface (Pa) po is theexternal pressure (Pa) ri is the interface radius (cm) and roc isthe radius of the particle after volume contraction (cm)
32 TGA-DSC Analysis In order to understand palm nutshells pyrolysis TGA-DSC analyses were performed InFigure 3 it is shown that the thermogram is obtained
According to Yang et al carbonization of the palm nutshells takes place as follows
(i) Zone I (lt131degC) removal of moisture
(ii) Zone II (217ndash335degC) decomposition of hemicellulose(iii) Zone III (335ndash392degC) decomposition of cellulose(iv) Zone IV (gt392degC) decomposition of lignin
At the beginning the weight loss is very low since thehumidity present on palm nut shells evaporates en thehemicellulose decomposes over 217degC followed by cellulosedecomposition Both biopolymers have the same monomerwhich is glucose and over 335degC this substance transformsto levoglucosan tar and several gases such as CO CO2 CH4and H2 among others On the contrary pyrolysis enthalpy iscalculated from the DSC analysis shown in Figure 4
Between 50 and 100degC an endothermic peak can beobserved which corresponds to the evaporation of hu-midity Afterwards the other endothermic peak is detectedat 243degC which may be assigned to hemicellulose de-composition en a bigger endothermic peak is foundupon 400degC and the other at 441degC ose peaks couldcorrespond to cellulose and lignin decomposition Finallyit was determined that lignin may decompose upon 392degC(Figure 3) and in our DSC study we detected the largestendothermic peak upon 500degC which may be assigned tolignin decomposition
en as it can be observed palm nut shells pyrolysis hasan endothermic behaviour is result confirms that thecontent of lignin within biomass determines if pyrolysis isexothermic or endothermic In this case the process resultedto be endothermic since the content of lignin within palmnut shells is high (504) Pyrolysis enthalpy was calculatedfrom the DSC analysis which was 30181 Jg is valuecannot be implemented in the Not Reacted Core model sincethis model uses values per mole instead of per gram uspalm nut shells molecular weight was estimated consideringits chemical composition
Nevertheless palm nut shells are not a pure chemicalcompound therefore the molecular weight was estimatedconsidering monomeric units of the three biopolymers thatconform to biomass (cellulose hemicellulose and lignin)Since lignin is a biopolymer too complex to estimate itsmolecular weight it was assumed that all monomeric unitsof the palm nut shells are involved in pyrolysis ereforeglucose is proposed as the monomeric unit of cellulose andxylene was selected as the monomeric unit of hemicelluloseIn the case of lignin the main monomeric units resulted tobe coumaryl sinapyl and coniferyl alcohols since they arethe major units in this biopolymer In Table 1 lignincomposition of palm nut shells is shown
Ligninrsquos average molecular weight was incorporated forpalm nut shells molecular weight estimation In Table 2 themolecular weight calculated using palm nut shells chemicalcomposition can be observed
4 International Journal of Chemical Engineering
e estimated molecular weight resulted to be 17238 gmole and this value was employed to determine the py-rolysis enthalpy per mole in order to incorporate it to theNot Reacted Core model
33 Not Reacted Core Modelrsquos Results and Validation eresults obtained with the model can be applied for calcu-lating pyrolysis kinetic and thermodynamic parameters InTable 3 it is shown the results are obtained with the NotReacted Core model
Pyrolysis enthalpy was estimated by the product betweenthe enthalpy obtained in the DSC analysis and the molecularweight determined with palm nut shells chemical compo-sition Pyrolysis entropy was estimated considering thedecomposition temperature for each biopolymer found inthe TGA analysis Afterwards Not Reacted Core modelsequations were applied for kinetic parameters de-termination In this case the pressure in the equilibriumresulted to be 883 atm (894 kPa) which is necessary for gasdiusion e reaction rate constant was 664 times 10minus91sassuming a rst-order reaction whereas the eective dif-fusion across the char layer was 483 times 10minus6m2s In order toevaluate the inuence of a high carbonization temperatureand a high heating rate pyrolysis tests of palm nut shellswere carried out in the Nichols furnace preheated to 850degCPalm nut shells were fed at this temperature in the reaction
chamber and at dierent periods of time shells are dis-charged cooled in a closed metal container and weighed forvolatile material calculation Afterwards conversion wascalculated with equation (4) whereas equation (3) wasemployed for conversion estimation with the Not ReactedCore model In Figure 5 there is a comparison of the volatilematerial removal esectciencies (χ) calculated by the applica-tion of the Not reacted Core Model and those obtainedexperimentally during pyrolysis of palm nut shells in theNichols furnace at 850degC
As it can be observed in Figure 5 this model ts quite wellwith experimental results obtained during pyrolysis of palmnut shells in the Nichols furnace Since palm nut shells py-rolysis is highly endothermic a high heat ux is required at theinterface as it is shown in Figure 6 Considering a temperaturegradient between the interface and the furnace temperature of50degC the amount of heat transported is not susectcient toovercome the energy requirements of the reaction
ese results suggest that palm nut shells pyrolysis islimited by heat transport to the reaction interface It waspossible to prove this hypothesis by industrial tests in acontinuous rotary kiln where the gassolid contact is dif-ferent compared to that of the Nichols furnace and con-sequently can also change the heat transport rate to interfaceand the diusion of the gases produced by carbonizationKunni and Chisaki [19] and Perry et al [20] proposeddierent methods for calculating the residence time in arotary kiln a very important parameter for the control of thequality of the carbonized product Equation (13) which is anempirical relation is the most used relation for the esti-mation of residence time of a solidmaterial in a rotary kiln asa function of its rotational speed
tsj 177L
θ
radicF
PDn (13)
where tsj is the residence time (min) L is the oven length(14m) θ is the angle of repose of palm nut shells (347deg) F isthe characteristic factor of the inside of the rotary kiln (1 foroven without lift 2 for oven with lifters) P is the oven slope(2deg)D is the inside diameter of the oven (15m) and n is thespeed of rotation of the oven (revolutions per minute)
With equation (13) which involves the residence timeand the kiln length) equation (11) and kinetic parameterslisted in Table 3 conversion (χ) can be calculated andcompared with the experimental conversions obtained withthe industrial rotary kiln as it can be observed in Figure 7
Given the consistency of the results obtained with theapplication of the Not Reacted Core model for palm nut
shells carbonization this model may be applied to calculatethe variation of the ow of gases produced by carbon-ization as a function of kiln lengthese data very disectcult
Table 3 Not Reacted Core model results
Parameter Value UnitsΔHdeg 5207406 JmoleΔSdeg 8531 JmolemiddotKΔGdeg minus1393675 Jmoleplowast 89469975 PaMolecular weight estimated 17238 gmolekr 664 times 10minus9 1sDf 483 times 10minus7 m2s
0
20
40
60
80
100
0 02 04 06 08 1Carbonization time at 850degC (h)
ModelExperimental results
χ (
)
Figure 5 Conversion according to experimental results and NotReacted Core model
0
200
400
600
800
1000
0 02 04 06 08 1 12
Hea
t (kJ
h)
Radius interface (cm)
Heat transport with TiRequired heat for reaction
Figure 6 Calculation of heat required for reaction and heattransfer to interface as a function of interface radius (ri) duringpalm nut shells pyrolysis (ro 12 cm To 850degC)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16Kiln length (m)
Calculated by the modelExperimental results (with liers)
χ (
)
Figure 7 Comparison between experimental conversion in therotary kiln (χ) with lifters and conversion calculated with the NotReacted Core model (d80 12mm feed 900 kgh T 850degC n 29 rpm)
6 International Journal of Chemical Engineering
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
Propagation
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Advances in
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Submit your manuscripts atwwwhindawicom
100mm height blade stirrer with a rotating speed of 4revolutions per minute e atmosphere of the Nicholsfurnace is controlled by the lambda factor (λ) which is theratio between the air supplied to the burner and the airstoichiometrically necessary for a complete combustion ofthe gas e air is supplied by a fan whose flow rate is166Nm3min e pilot scale pyrolysis tests were carriedout on samples with a particle size between 5 and 20mm Foreach test the Nichols furnace was heated to the desiredtemperature (heating rate 07ndash15 and 10degCmin) with areducing atmosphere λ 076 (chemical analysis of com-bustion gases 10 CO2 4 CO 11 H2 001 O2 and 9H2O) e samples were loaded at the start of the oveneither in a fixed bed with 12 kg of sample or in mixed bedwith 3 or 4 kg Tests were also carried out by introducing thesample into the preheated oven at the desired temperatureAt the end of the test the material is discharged cooled in aclosed metal container and weighed Samples were takenevery 10 minutes to calculate char conversion and to in-corporate those data in the modele reaction rate constantand the effective diffusion coefficient across the char layerwere calculated as well
Tests on an industrial scale were carried out in a rotarykiln which runs on fuel oil with an excess of air of 20 (λ
12) and whose burner has a heat capacity of 8 times 106 kJhe solids were introduced into the furnace by an endlessscrew that moves in the same direction as the flue gas(cocurrent) forming a layer of about 15 cm in height whenthe furnace works without lift Treated solids are dis-charged at the opposite end of the feed through a water-cooled endless screw while gases came out at the top andwent through an afterburner a plate heat exchanger acyclone a draft fan and finally the chimney e nominalcapacity of the solids supply in the oven is 1m3h anddepending on the speed of rotation and the use of the liftersor without the use of the lifters the residence time can varybetween 03 and 80 hours Palm kernels of 5 to 20mmwereintroduced to a rotary kiln which was heated for 7 days at850degC in an oxidizing atmosphere (λ 12) the fuel oilconsumption was 2650 Lday In these tests incominggases contained 10 CO2 5 O2 and 15 H2O Asmentioned above the tests were performed in the presenceor absence of levers the rotational speed was set at 3 rpmwith a feed of 900 kgh e duration of each trial was 35days in order to obtain samples in sufficient quantity toprovide them to potential customers e output rate of thecarbonized materials was measured and their volatilecontent was measured regularly in order to use in the NotReacted Core model
3 Results and Discussion
31 Not Reacted Core Model In order to develop the NotReacted Core model TGA-DSC analysis of pulverized palmkernels were carried out under inert atmosphere of nitrogenPyrolyzed samples were analysed by scanning electronmicroscopy (SEM) to verify the existence of an unreactedcore SEM image of palm nut shells after pyrolysis is shownin Figure 2
e black core corresponds to the unreacted palm nutshell whereas the surrounding material is the residual solidcoal is image confirms the idea that biomass pyrolysisoccurs according to the not reacted core At the first stageheat is transferred through the char layer to the interface upto the interface en chemical reactions of biomass de-composition (different mechanisms for the three bio-polymers) occur at the interface which results in thegeneration of residual coal and various gases Finally thesegases diffuse through the char layer towards the externalatmosphere e relevance of these model lies in the in-corporation of all the three known mechanisms that mayoccur during biomass pyrolysis heat transfer chemicalreaction at the interface and mass transfer
e Not Reacted Core model for palm nut shells py-rolysis was employed considering that the particles arespherical erefore there is no accumulation of heat andmass during pyrolysis and the amount of heat carried by thegases is negligible First the equilibrium constant of reaction(1) was calculated using the following equations
ΔGo minusRT ln Keq
Keq aCh middot plowastgas
aCq plowastgas
(2)
where Keq is an equilibrium constant of equation (1) aCh isthe activity of carbonized product or solid coal (equal to 1)plowastgas is the partial pressure of the gases produced by car-bonization aCq is the activity of solid shells (equal to 1) R isthe universal gas constant (831 JKmiddotmol) and T is thetemperature (K)
On the contrary the conversion (χ) for the carbonizationof palm nut shells (equation (1)) can be estimated as the GasmolesCq moles ratio assuming that all palm nut shells arespherical erefore the moles of solid shells can be de-termined by the product between the sphere volume andpalm nut shells density
χ gas molesCq moles
1113938
t
0 ngRx dt
(43)π middot ro middot ρCq (3)
For pilot and industrial essays in the Nichols furnace androtary kiln respectively the achieved conversion can bedetermined bymeasuring the amount of the volatile materialduring pyrolysis e amount of the volatile material is thedifference between the initial palm nut shells mass and the
Figure 2 Palm kernelrsquos not reacted core SEM image (200 microm)
International Journal of Chemical Engineering 3
mass weighed at different intervals of time Equation (4)shows how to calculate conversion in experimental tests formodels validation
χ ( volatile material)0 minus ( volatile material)t
( volatile material)0
(4)
In order to estimate the specific reaction rate constant(kr) and the effective gas diffusion (Def ) a geometric ap-proach is proposed based on the phenomenological model(equation (1) Figure 1) and the calculation of the number ofmoles of gas produced by the chemical reaction (ngRx) can beobtained by the following equation
ngRx 4πr2i minus
dri
dt1113888 1113889ρCq kr 4πr
2i1113872 1113873 plowast minus pi( 1113857 (5)
where ngRx is the number of moles of gas produced by thereaction chemical (moles) ri is the radius of the interface(cm) t is the time (s) ρCq is the molar density of the shells(molecm3) kr is the specific reaction rate constant (cms)plowast is the equilibrium partial pressure of the gases producedby the carbonization (Pa) (equation (1)) and pi is the partialpressure of gases at the interface (Pa)
Grouping the terms of equation (5) and integrating weget
dri
dt1113888 1113889 minus
kr plowast minus pi( 1113857
ρCq minusB (6)
1113946ri
ro
dri minusB 1113946t
0dt (7)
ri ro minusB (8)
ngRx 4πρCqB ro minusBt( 11138572 (9)
On replacing equation (9) in equation (3)
ro 1minus(1minus χ)13
1113960 1113961 B (10)
χ 3B
rot minus
3B2
r2ot2
+B3
r3ot3 (11)
By solving equation (10) the B constant is found andthen by solving equation (6) the specific reaction rateconstant can be estimated
Finally the effective diffusion constant can be de-termined by solving the next equation
where ngDf is the number of moles of gas leaving the particleby diffusion through the porous coal layer (moles) Def is theeffective diffusion constant of gases through the porous coallayer (cm2s) pi is the pressure at the interface (Pa) po is theexternal pressure (Pa) ri is the interface radius (cm) and roc isthe radius of the particle after volume contraction (cm)
32 TGA-DSC Analysis In order to understand palm nutshells pyrolysis TGA-DSC analyses were performed InFigure 3 it is shown that the thermogram is obtained
According to Yang et al carbonization of the palm nutshells takes place as follows
(i) Zone I (lt131degC) removal of moisture
(ii) Zone II (217ndash335degC) decomposition of hemicellulose(iii) Zone III (335ndash392degC) decomposition of cellulose(iv) Zone IV (gt392degC) decomposition of lignin
At the beginning the weight loss is very low since thehumidity present on palm nut shells evaporates en thehemicellulose decomposes over 217degC followed by cellulosedecomposition Both biopolymers have the same monomerwhich is glucose and over 335degC this substance transformsto levoglucosan tar and several gases such as CO CO2 CH4and H2 among others On the contrary pyrolysis enthalpy iscalculated from the DSC analysis shown in Figure 4
Between 50 and 100degC an endothermic peak can beobserved which corresponds to the evaporation of hu-midity Afterwards the other endothermic peak is detectedat 243degC which may be assigned to hemicellulose de-composition en a bigger endothermic peak is foundupon 400degC and the other at 441degC ose peaks couldcorrespond to cellulose and lignin decomposition Finallyit was determined that lignin may decompose upon 392degC(Figure 3) and in our DSC study we detected the largestendothermic peak upon 500degC which may be assigned tolignin decomposition
en as it can be observed palm nut shells pyrolysis hasan endothermic behaviour is result confirms that thecontent of lignin within biomass determines if pyrolysis isexothermic or endothermic In this case the process resultedto be endothermic since the content of lignin within palmnut shells is high (504) Pyrolysis enthalpy was calculatedfrom the DSC analysis which was 30181 Jg is valuecannot be implemented in the Not Reacted Core model sincethis model uses values per mole instead of per gram uspalm nut shells molecular weight was estimated consideringits chemical composition
Nevertheless palm nut shells are not a pure chemicalcompound therefore the molecular weight was estimatedconsidering monomeric units of the three biopolymers thatconform to biomass (cellulose hemicellulose and lignin)Since lignin is a biopolymer too complex to estimate itsmolecular weight it was assumed that all monomeric unitsof the palm nut shells are involved in pyrolysis ereforeglucose is proposed as the monomeric unit of cellulose andxylene was selected as the monomeric unit of hemicelluloseIn the case of lignin the main monomeric units resulted tobe coumaryl sinapyl and coniferyl alcohols since they arethe major units in this biopolymer In Table 1 lignincomposition of palm nut shells is shown
Ligninrsquos average molecular weight was incorporated forpalm nut shells molecular weight estimation In Table 2 themolecular weight calculated using palm nut shells chemicalcomposition can be observed
4 International Journal of Chemical Engineering
e estimated molecular weight resulted to be 17238 gmole and this value was employed to determine the py-rolysis enthalpy per mole in order to incorporate it to theNot Reacted Core model
33 Not Reacted Core Modelrsquos Results and Validation eresults obtained with the model can be applied for calcu-lating pyrolysis kinetic and thermodynamic parameters InTable 3 it is shown the results are obtained with the NotReacted Core model
Pyrolysis enthalpy was estimated by the product betweenthe enthalpy obtained in the DSC analysis and the molecularweight determined with palm nut shells chemical compo-sition Pyrolysis entropy was estimated considering thedecomposition temperature for each biopolymer found inthe TGA analysis Afterwards Not Reacted Core modelsequations were applied for kinetic parameters de-termination In this case the pressure in the equilibriumresulted to be 883 atm (894 kPa) which is necessary for gasdiusion e reaction rate constant was 664 times 10minus91sassuming a rst-order reaction whereas the eective dif-fusion across the char layer was 483 times 10minus6m2s In order toevaluate the inuence of a high carbonization temperatureand a high heating rate pyrolysis tests of palm nut shellswere carried out in the Nichols furnace preheated to 850degCPalm nut shells were fed at this temperature in the reaction
chamber and at dierent periods of time shells are dis-charged cooled in a closed metal container and weighed forvolatile material calculation Afterwards conversion wascalculated with equation (4) whereas equation (3) wasemployed for conversion estimation with the Not ReactedCore model In Figure 5 there is a comparison of the volatilematerial removal esectciencies (χ) calculated by the applica-tion of the Not reacted Core Model and those obtainedexperimentally during pyrolysis of palm nut shells in theNichols furnace at 850degC
As it can be observed in Figure 5 this model ts quite wellwith experimental results obtained during pyrolysis of palmnut shells in the Nichols furnace Since palm nut shells py-rolysis is highly endothermic a high heat ux is required at theinterface as it is shown in Figure 6 Considering a temperaturegradient between the interface and the furnace temperature of50degC the amount of heat transported is not susectcient toovercome the energy requirements of the reaction
ese results suggest that palm nut shells pyrolysis islimited by heat transport to the reaction interface It waspossible to prove this hypothesis by industrial tests in acontinuous rotary kiln where the gassolid contact is dif-ferent compared to that of the Nichols furnace and con-sequently can also change the heat transport rate to interfaceand the diusion of the gases produced by carbonizationKunni and Chisaki [19] and Perry et al [20] proposeddierent methods for calculating the residence time in arotary kiln a very important parameter for the control of thequality of the carbonized product Equation (13) which is anempirical relation is the most used relation for the esti-mation of residence time of a solidmaterial in a rotary kiln asa function of its rotational speed
tsj 177L
θ
radicF
PDn (13)
where tsj is the residence time (min) L is the oven length(14m) θ is the angle of repose of palm nut shells (347deg) F isthe characteristic factor of the inside of the rotary kiln (1 foroven without lift 2 for oven with lifters) P is the oven slope(2deg)D is the inside diameter of the oven (15m) and n is thespeed of rotation of the oven (revolutions per minute)
With equation (13) which involves the residence timeand the kiln length) equation (11) and kinetic parameterslisted in Table 3 conversion (χ) can be calculated andcompared with the experimental conversions obtained withthe industrial rotary kiln as it can be observed in Figure 7
Given the consistency of the results obtained with theapplication of the Not Reacted Core model for palm nut
shells carbonization this model may be applied to calculatethe variation of the ow of gases produced by carbon-ization as a function of kiln lengthese data very disectcult
Table 3 Not Reacted Core model results
Parameter Value UnitsΔHdeg 5207406 JmoleΔSdeg 8531 JmolemiddotKΔGdeg minus1393675 Jmoleplowast 89469975 PaMolecular weight estimated 17238 gmolekr 664 times 10minus9 1sDf 483 times 10minus7 m2s
0
20
40
60
80
100
0 02 04 06 08 1Carbonization time at 850degC (h)
ModelExperimental results
χ (
)
Figure 5 Conversion according to experimental results and NotReacted Core model
0
200
400
600
800
1000
0 02 04 06 08 1 12
Hea
t (kJ
h)
Radius interface (cm)
Heat transport with TiRequired heat for reaction
Figure 6 Calculation of heat required for reaction and heattransfer to interface as a function of interface radius (ri) duringpalm nut shells pyrolysis (ro 12 cm To 850degC)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16Kiln length (m)
Calculated by the modelExperimental results (with liers)
χ (
)
Figure 7 Comparison between experimental conversion in therotary kiln (χ) with lifters and conversion calculated with the NotReacted Core model (d80 12mm feed 900 kgh T 850degC n 29 rpm)
6 International Journal of Chemical Engineering
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Navigation and Observation
International Journal of
Hindawi
wwwhindawicom Volume 2018
Advances in
Multimedia
Submit your manuscripts atwwwhindawicom
mass weighed at different intervals of time Equation (4)shows how to calculate conversion in experimental tests formodels validation
χ ( volatile material)0 minus ( volatile material)t
( volatile material)0
(4)
In order to estimate the specific reaction rate constant(kr) and the effective gas diffusion (Def ) a geometric ap-proach is proposed based on the phenomenological model(equation (1) Figure 1) and the calculation of the number ofmoles of gas produced by the chemical reaction (ngRx) can beobtained by the following equation
ngRx 4πr2i minus
dri
dt1113888 1113889ρCq kr 4πr
2i1113872 1113873 plowast minus pi( 1113857 (5)
where ngRx is the number of moles of gas produced by thereaction chemical (moles) ri is the radius of the interface(cm) t is the time (s) ρCq is the molar density of the shells(molecm3) kr is the specific reaction rate constant (cms)plowast is the equilibrium partial pressure of the gases producedby the carbonization (Pa) (equation (1)) and pi is the partialpressure of gases at the interface (Pa)
Grouping the terms of equation (5) and integrating weget
dri
dt1113888 1113889 minus
kr plowast minus pi( 1113857
ρCq minusB (6)
1113946ri
ro
dri minusB 1113946t
0dt (7)
ri ro minusB (8)
ngRx 4πρCqB ro minusBt( 11138572 (9)
On replacing equation (9) in equation (3)
ro 1minus(1minus χ)13
1113960 1113961 B (10)
χ 3B
rot minus
3B2
r2ot2
+B3
r3ot3 (11)
By solving equation (10) the B constant is found andthen by solving equation (6) the specific reaction rateconstant can be estimated
Finally the effective diffusion constant can be de-termined by solving the next equation
where ngDf is the number of moles of gas leaving the particleby diffusion through the porous coal layer (moles) Def is theeffective diffusion constant of gases through the porous coallayer (cm2s) pi is the pressure at the interface (Pa) po is theexternal pressure (Pa) ri is the interface radius (cm) and roc isthe radius of the particle after volume contraction (cm)
32 TGA-DSC Analysis In order to understand palm nutshells pyrolysis TGA-DSC analyses were performed InFigure 3 it is shown that the thermogram is obtained
According to Yang et al carbonization of the palm nutshells takes place as follows
(i) Zone I (lt131degC) removal of moisture
(ii) Zone II (217ndash335degC) decomposition of hemicellulose(iii) Zone III (335ndash392degC) decomposition of cellulose(iv) Zone IV (gt392degC) decomposition of lignin
At the beginning the weight loss is very low since thehumidity present on palm nut shells evaporates en thehemicellulose decomposes over 217degC followed by cellulosedecomposition Both biopolymers have the same monomerwhich is glucose and over 335degC this substance transformsto levoglucosan tar and several gases such as CO CO2 CH4and H2 among others On the contrary pyrolysis enthalpy iscalculated from the DSC analysis shown in Figure 4
Between 50 and 100degC an endothermic peak can beobserved which corresponds to the evaporation of hu-midity Afterwards the other endothermic peak is detectedat 243degC which may be assigned to hemicellulose de-composition en a bigger endothermic peak is foundupon 400degC and the other at 441degC ose peaks couldcorrespond to cellulose and lignin decomposition Finallyit was determined that lignin may decompose upon 392degC(Figure 3) and in our DSC study we detected the largestendothermic peak upon 500degC which may be assigned tolignin decomposition
en as it can be observed palm nut shells pyrolysis hasan endothermic behaviour is result confirms that thecontent of lignin within biomass determines if pyrolysis isexothermic or endothermic In this case the process resultedto be endothermic since the content of lignin within palmnut shells is high (504) Pyrolysis enthalpy was calculatedfrom the DSC analysis which was 30181 Jg is valuecannot be implemented in the Not Reacted Core model sincethis model uses values per mole instead of per gram uspalm nut shells molecular weight was estimated consideringits chemical composition
Nevertheless palm nut shells are not a pure chemicalcompound therefore the molecular weight was estimatedconsidering monomeric units of the three biopolymers thatconform to biomass (cellulose hemicellulose and lignin)Since lignin is a biopolymer too complex to estimate itsmolecular weight it was assumed that all monomeric unitsof the palm nut shells are involved in pyrolysis ereforeglucose is proposed as the monomeric unit of cellulose andxylene was selected as the monomeric unit of hemicelluloseIn the case of lignin the main monomeric units resulted tobe coumaryl sinapyl and coniferyl alcohols since they arethe major units in this biopolymer In Table 1 lignincomposition of palm nut shells is shown
Ligninrsquos average molecular weight was incorporated forpalm nut shells molecular weight estimation In Table 2 themolecular weight calculated using palm nut shells chemicalcomposition can be observed
4 International Journal of Chemical Engineering
e estimated molecular weight resulted to be 17238 gmole and this value was employed to determine the py-rolysis enthalpy per mole in order to incorporate it to theNot Reacted Core model
33 Not Reacted Core Modelrsquos Results and Validation eresults obtained with the model can be applied for calcu-lating pyrolysis kinetic and thermodynamic parameters InTable 3 it is shown the results are obtained with the NotReacted Core model
Pyrolysis enthalpy was estimated by the product betweenthe enthalpy obtained in the DSC analysis and the molecularweight determined with palm nut shells chemical compo-sition Pyrolysis entropy was estimated considering thedecomposition temperature for each biopolymer found inthe TGA analysis Afterwards Not Reacted Core modelsequations were applied for kinetic parameters de-termination In this case the pressure in the equilibriumresulted to be 883 atm (894 kPa) which is necessary for gasdiusion e reaction rate constant was 664 times 10minus91sassuming a rst-order reaction whereas the eective dif-fusion across the char layer was 483 times 10minus6m2s In order toevaluate the inuence of a high carbonization temperatureand a high heating rate pyrolysis tests of palm nut shellswere carried out in the Nichols furnace preheated to 850degCPalm nut shells were fed at this temperature in the reaction
chamber and at dierent periods of time shells are dis-charged cooled in a closed metal container and weighed forvolatile material calculation Afterwards conversion wascalculated with equation (4) whereas equation (3) wasemployed for conversion estimation with the Not ReactedCore model In Figure 5 there is a comparison of the volatilematerial removal esectciencies (χ) calculated by the applica-tion of the Not reacted Core Model and those obtainedexperimentally during pyrolysis of palm nut shells in theNichols furnace at 850degC
As it can be observed in Figure 5 this model ts quite wellwith experimental results obtained during pyrolysis of palmnut shells in the Nichols furnace Since palm nut shells py-rolysis is highly endothermic a high heat ux is required at theinterface as it is shown in Figure 6 Considering a temperaturegradient between the interface and the furnace temperature of50degC the amount of heat transported is not susectcient toovercome the energy requirements of the reaction
ese results suggest that palm nut shells pyrolysis islimited by heat transport to the reaction interface It waspossible to prove this hypothesis by industrial tests in acontinuous rotary kiln where the gassolid contact is dif-ferent compared to that of the Nichols furnace and con-sequently can also change the heat transport rate to interfaceand the diusion of the gases produced by carbonizationKunni and Chisaki [19] and Perry et al [20] proposeddierent methods for calculating the residence time in arotary kiln a very important parameter for the control of thequality of the carbonized product Equation (13) which is anempirical relation is the most used relation for the esti-mation of residence time of a solidmaterial in a rotary kiln asa function of its rotational speed
tsj 177L
θ
radicF
PDn (13)
where tsj is the residence time (min) L is the oven length(14m) θ is the angle of repose of palm nut shells (347deg) F isthe characteristic factor of the inside of the rotary kiln (1 foroven without lift 2 for oven with lifters) P is the oven slope(2deg)D is the inside diameter of the oven (15m) and n is thespeed of rotation of the oven (revolutions per minute)
With equation (13) which involves the residence timeand the kiln length) equation (11) and kinetic parameterslisted in Table 3 conversion (χ) can be calculated andcompared with the experimental conversions obtained withthe industrial rotary kiln as it can be observed in Figure 7
Given the consistency of the results obtained with theapplication of the Not Reacted Core model for palm nut
shells carbonization this model may be applied to calculatethe variation of the ow of gases produced by carbon-ization as a function of kiln lengthese data very disectcult
Table 3 Not Reacted Core model results
Parameter Value UnitsΔHdeg 5207406 JmoleΔSdeg 8531 JmolemiddotKΔGdeg minus1393675 Jmoleplowast 89469975 PaMolecular weight estimated 17238 gmolekr 664 times 10minus9 1sDf 483 times 10minus7 m2s
0
20
40
60
80
100
0 02 04 06 08 1Carbonization time at 850degC (h)
ModelExperimental results
χ (
)
Figure 5 Conversion according to experimental results and NotReacted Core model
0
200
400
600
800
1000
0 02 04 06 08 1 12
Hea
t (kJ
h)
Radius interface (cm)
Heat transport with TiRequired heat for reaction
Figure 6 Calculation of heat required for reaction and heattransfer to interface as a function of interface radius (ri) duringpalm nut shells pyrolysis (ro 12 cm To 850degC)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16Kiln length (m)
Calculated by the modelExperimental results (with liers)
χ (
)
Figure 7 Comparison between experimental conversion in therotary kiln (χ) with lifters and conversion calculated with the NotReacted Core model (d80 12mm feed 900 kgh T 850degC n 29 rpm)
6 International Journal of Chemical Engineering
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Navigation and Observation
International Journal of
Hindawi
wwwhindawicom Volume 2018
Advances in
Multimedia
Submit your manuscripts atwwwhindawicom
e estimated molecular weight resulted to be 17238 gmole and this value was employed to determine the py-rolysis enthalpy per mole in order to incorporate it to theNot Reacted Core model
33 Not Reacted Core Modelrsquos Results and Validation eresults obtained with the model can be applied for calcu-lating pyrolysis kinetic and thermodynamic parameters InTable 3 it is shown the results are obtained with the NotReacted Core model
Pyrolysis enthalpy was estimated by the product betweenthe enthalpy obtained in the DSC analysis and the molecularweight determined with palm nut shells chemical compo-sition Pyrolysis entropy was estimated considering thedecomposition temperature for each biopolymer found inthe TGA analysis Afterwards Not Reacted Core modelsequations were applied for kinetic parameters de-termination In this case the pressure in the equilibriumresulted to be 883 atm (894 kPa) which is necessary for gasdiusion e reaction rate constant was 664 times 10minus91sassuming a rst-order reaction whereas the eective dif-fusion across the char layer was 483 times 10minus6m2s In order toevaluate the inuence of a high carbonization temperatureand a high heating rate pyrolysis tests of palm nut shellswere carried out in the Nichols furnace preheated to 850degCPalm nut shells were fed at this temperature in the reaction
chamber and at dierent periods of time shells are dis-charged cooled in a closed metal container and weighed forvolatile material calculation Afterwards conversion wascalculated with equation (4) whereas equation (3) wasemployed for conversion estimation with the Not ReactedCore model In Figure 5 there is a comparison of the volatilematerial removal esectciencies (χ) calculated by the applica-tion of the Not reacted Core Model and those obtainedexperimentally during pyrolysis of palm nut shells in theNichols furnace at 850degC
As it can be observed in Figure 5 this model ts quite wellwith experimental results obtained during pyrolysis of palmnut shells in the Nichols furnace Since palm nut shells py-rolysis is highly endothermic a high heat ux is required at theinterface as it is shown in Figure 6 Considering a temperaturegradient between the interface and the furnace temperature of50degC the amount of heat transported is not susectcient toovercome the energy requirements of the reaction
ese results suggest that palm nut shells pyrolysis islimited by heat transport to the reaction interface It waspossible to prove this hypothesis by industrial tests in acontinuous rotary kiln where the gassolid contact is dif-ferent compared to that of the Nichols furnace and con-sequently can also change the heat transport rate to interfaceand the diusion of the gases produced by carbonizationKunni and Chisaki [19] and Perry et al [20] proposeddierent methods for calculating the residence time in arotary kiln a very important parameter for the control of thequality of the carbonized product Equation (13) which is anempirical relation is the most used relation for the esti-mation of residence time of a solidmaterial in a rotary kiln asa function of its rotational speed
tsj 177L
θ
radicF
PDn (13)
where tsj is the residence time (min) L is the oven length(14m) θ is the angle of repose of palm nut shells (347deg) F isthe characteristic factor of the inside of the rotary kiln (1 foroven without lift 2 for oven with lifters) P is the oven slope(2deg)D is the inside diameter of the oven (15m) and n is thespeed of rotation of the oven (revolutions per minute)
With equation (13) which involves the residence timeand the kiln length) equation (11) and kinetic parameterslisted in Table 3 conversion (χ) can be calculated andcompared with the experimental conversions obtained withthe industrial rotary kiln as it can be observed in Figure 7
Given the consistency of the results obtained with theapplication of the Not Reacted Core model for palm nut
shells carbonization this model may be applied to calculatethe variation of the ow of gases produced by carbon-ization as a function of kiln lengthese data very disectcult
Table 3 Not Reacted Core model results
Parameter Value UnitsΔHdeg 5207406 JmoleΔSdeg 8531 JmolemiddotKΔGdeg minus1393675 Jmoleplowast 89469975 PaMolecular weight estimated 17238 gmolekr 664 times 10minus9 1sDf 483 times 10minus7 m2s
0
20
40
60
80
100
0 02 04 06 08 1Carbonization time at 850degC (h)
ModelExperimental results
χ (
)
Figure 5 Conversion according to experimental results and NotReacted Core model
0
200
400
600
800
1000
0 02 04 06 08 1 12
Hea
t (kJ
h)
Radius interface (cm)
Heat transport with TiRequired heat for reaction
Figure 6 Calculation of heat required for reaction and heattransfer to interface as a function of interface radius (ri) duringpalm nut shells pyrolysis (ro 12 cm To 850degC)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16Kiln length (m)
Calculated by the modelExperimental results (with liers)
χ (
)
Figure 7 Comparison between experimental conversion in therotary kiln (χ) with lifters and conversion calculated with the NotReacted Core model (d80 12mm feed 900 kgh T 850degC n 29 rpm)
6 International Journal of Chemical Engineering
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Navigation and Observation
International Journal of
Hindawi
wwwhindawicom Volume 2018
Advances in
Multimedia
Submit your manuscripts atwwwhindawicom
chamber and at dierent periods of time shells are dis-charged cooled in a closed metal container and weighed forvolatile material calculation Afterwards conversion wascalculated with equation (4) whereas equation (3) wasemployed for conversion estimation with the Not ReactedCore model In Figure 5 there is a comparison of the volatilematerial removal esectciencies (χ) calculated by the applica-tion of the Not reacted Core Model and those obtainedexperimentally during pyrolysis of palm nut shells in theNichols furnace at 850degC
As it can be observed in Figure 5 this model ts quite wellwith experimental results obtained during pyrolysis of palmnut shells in the Nichols furnace Since palm nut shells py-rolysis is highly endothermic a high heat ux is required at theinterface as it is shown in Figure 6 Considering a temperaturegradient between the interface and the furnace temperature of50degC the amount of heat transported is not susectcient toovercome the energy requirements of the reaction
ese results suggest that palm nut shells pyrolysis islimited by heat transport to the reaction interface It waspossible to prove this hypothesis by industrial tests in acontinuous rotary kiln where the gassolid contact is dif-ferent compared to that of the Nichols furnace and con-sequently can also change the heat transport rate to interfaceand the diusion of the gases produced by carbonizationKunni and Chisaki [19] and Perry et al [20] proposeddierent methods for calculating the residence time in arotary kiln a very important parameter for the control of thequality of the carbonized product Equation (13) which is anempirical relation is the most used relation for the esti-mation of residence time of a solidmaterial in a rotary kiln asa function of its rotational speed
tsj 177L
θ
radicF
PDn (13)
where tsj is the residence time (min) L is the oven length(14m) θ is the angle of repose of palm nut shells (347deg) F isthe characteristic factor of the inside of the rotary kiln (1 foroven without lift 2 for oven with lifters) P is the oven slope(2deg)D is the inside diameter of the oven (15m) and n is thespeed of rotation of the oven (revolutions per minute)
With equation (13) which involves the residence timeand the kiln length) equation (11) and kinetic parameterslisted in Table 3 conversion (χ) can be calculated andcompared with the experimental conversions obtained withthe industrial rotary kiln as it can be observed in Figure 7
Given the consistency of the results obtained with theapplication of the Not Reacted Core model for palm nut
shells carbonization this model may be applied to calculatethe variation of the ow of gases produced by carbon-ization as a function of kiln lengthese data very disectcult
Table 3 Not Reacted Core model results
Parameter Value UnitsΔHdeg 5207406 JmoleΔSdeg 8531 JmolemiddotKΔGdeg minus1393675 Jmoleplowast 89469975 PaMolecular weight estimated 17238 gmolekr 664 times 10minus9 1sDf 483 times 10minus7 m2s
0
20
40
60
80
100
0 02 04 06 08 1Carbonization time at 850degC (h)
ModelExperimental results
χ (
)
Figure 5 Conversion according to experimental results and NotReacted Core model
0
200
400
600
800
1000
0 02 04 06 08 1 12
Hea
t (kJ
h)
Radius interface (cm)
Heat transport with TiRequired heat for reaction
Figure 6 Calculation of heat required for reaction and heattransfer to interface as a function of interface radius (ri) duringpalm nut shells pyrolysis (ro 12 cm To 850degC)
0
20
40
60
80
100
0 2 4 6 8 10 12 14 16Kiln length (m)
Calculated by the modelExperimental results (with liers)
χ (
)
Figure 7 Comparison between experimental conversion in therotary kiln (χ) with lifters and conversion calculated with the NotReacted Core model (d80 12mm feed 900 kgh T 850degC n 29 rpm)
6 International Journal of Chemical Engineering
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Navigation and Observation
International Journal of
Hindawi
wwwhindawicom Volume 2018
Advances in
Multimedia
Submit your manuscripts atwwwhindawicom
to obtain experimentally are useful for the dimensioningand the selection of industrial rotary kiln operating con-ditions in order to optimize its geometry as well as thedistribution and the position of the lifters Finally thisproposed model for the carbonization of palm nut shellscan be generalized for the carbonization of the other lig-nocellulosic material
4 Conclusions
Palm nut shells pyrolysis resulted to be endothermic due tothe high content of lignin within its structure e TGA andDSC analysis demonstrated that palm nut shells present apositive enthalpy of 30181 Jg is value accords withseveral enthalpies presented in literature which suggests thatlignocellulosic materials rich in lignin have an endothermicbehaviour
For palm nut shells molecular weight calculation allmonomeric units that conform to the main biopolymers ofbiomass were considered for the calculation ereforeglucose and xylene were chosen as monomeric units forcellulose and hemicellulose respectively In the case oflignin p-coumaryl alcohol coniferyl alcohol and synapylalcohol were selected for lignin molecular weight estimationsince these substances repeat along its structure e mo-lecular weight resulted to be 17838 gmole and this valuewas possible to incorporate in the Not Reacted Core modelfor thermodynamic and kinetic parameters determinatione reaction rate constant was 664 times 10minus91s assuming afirst-order reaction whereas the effective diffusion across thechar layer was 483 times 10minus7m2s
e validity of the Not Reacted Core model was con-firmed with the experimental results obtained in the Nicholsfurnace and the rotary kiln During the pilot and industrialtests the Not Reacted Core model adjusted very well toexperimental resultse reason lies in the conceptualizationof the model In this modelling not only chemical reactionsare involved but also heat transfer to the interface and gasdiffusion as well In the case of palm nut shells pyrolysis heattransfer resulted to be the critic stage during pilot and in-dustrial essays
e Not Reacted Core model allows to scale-up pyrolysisoperations to the industrial scale During industrial essayswith the rotary kiln conversions obtained experimentallyand those estimated by applying the model resulted to bevery similaris finding allows to predict the necessary datafor industrial kilns dimensioning
Data Availability
e data used to support the findings of this study areavailable from the corresponding author upon request
Conflicts of Interest
e authors declare that there are no conflicts of interestregarding the publication of this paper
Acknowledgments
e authors show their gratitude to the Escuela PolitecnicaNacional Ecuador and to the personnel of the Departmentof Extractive Metallurgy is research was funded by theproject CONUEP (1215) ldquoActivated Carbon Productionfrom Oil Palm Shellsrdquo
Supplementary Materials
Data obtained for Not Reacted Core model application aredetailed in Table S1 en equation (10) was employed for Bconstant calculation by lineal regression as it is shown inFigure S1 Finally Table S2 shows conversions obtained withthe Not Reacted Core model and those obtained experi-mentally ese data support the results demonstrated inFigure 5 (Supplementary Materials)
References
[1] H Yang R Yan H Chen D H Lee and C ZhengldquoCharacteristics of hemicellulose cellulose and lignin pyrol-ysisrdquo Fuel vol 86 no 12-13 pp 1781ndash1788 2007
[2] A Gomez W Klose and S Rincon Pirolisis de BiomasaKassel University Press GmbH Kassel Germany 2008 httpwwwuni-kasseldeupressonlinefrei978-3-89958-457-8volltextfreipdf
[3] S Gu and D K Shen ldquoe mechanism for thermal de-composition of cellulose and its main productsrdquo BioresourceTechnology vol 100 no 24 pp 6496ndash6504 2009
[4] H Yang R Yan T Chin D T Liang H Chen and C Zhengldquoermogravimetric analysisminusfourier transform infraredanalysis of palm oil waste pyrolysisrdquo Energy amp Fuels vol 18no 6 pp 1814ndash1821 2004
[5] M Van de Velden J Baeyens A Brems B Janssens andR Dewil ldquoFundamentals kinetics and endothermicity of thebiomass pyrolysis reactionrdquo Renewable Energy vol 35 no 1pp 232ndash242 2010
[6] D E Daugaard and R C Brown ldquoEnthalpy for pyrolysis forseveral types of biomassrdquo Energy amp Fuels vol 17 no 4pp 934ndash939 2003
[7] G Wang W Li B Li and H Chen ldquoTG study on pyrolysis ofbiomass and its three components under syngasrdquo Fuelvol 87 no 4-5 pp 552ndash558 2008
[8] K Lazdovica L Liepina and V Kampars ldquoComparativewheat straw catalytic pyrolysis in the presence of zeolites PtC and PdC by using TGA-FTIR methodrdquo Fuel ProcessingTechnology vol 138 pp 645ndash653 2015
[9] S Yaman ldquoPyrolysis of biomass to produce fuels and chemicalfeedstocksrdquo Energy Conversion and Management vol 45no 5 pp 651ndash671 2004
[10] J Perez J Muntildeoz-Dorado T de la Rubia and J MartınezldquoBiodegradation and biological treatments of cellulosehemicellulose and lignin an overviewrdquo International Mi-crobiology vol 5 no 2 pp 53ndash63 2002
[11] K Wang Pyrolysis and catalytic pyrolysis of protein- and lipid-rich feedstock PhD dissertation Iowa State UniversityAmes Iowa 2014
[12] T Hosoya H Kawamoto and S Saka ldquoSecondary reactionsof lignin-derived primary tar componentsrdquo Journal of Ana-lytical and Applied Pyrolysis vol 83 no 1 pp 78ndash87 2008
[13] S Yoo and J Jane ldquoMolecular weights and gyration radii ofamylopectins determined by high-performance size-exclusion
International Journal of Chemical Engineering 7
chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawiwwwhindawicom Volume 2018
Hindawiwwwhindawicom Volume 2018
Navigation and Observation
International Journal of
Hindawi
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chromatography equipped with multi-angle laser-light scat-tering and refractive index detectorsrdquo Carbohydrate Polymersvol 49 no 3 pp 307ndash314 2002
[14] A Tolbert H Akinosho R Khunsupat A K Naskar andA J Ragauskas ldquoCharacterization and analysis of the mo-lecular weight of lignin for biorefining studiesrdquo BiofuelsBioproducts and Biorefining vol 8 no 6 pp 836ndash856 2014
[15] G A Zickler W Wagermaier S S Funari M Burghammerand O Paris ldquoIn situ X-ray diffraction investigation ofthermal decomposition of wood celluloserdquo Journal of Ana-lytical and Applied Pyrolysis vol 80 no 1 pp 134ndash140 2007
[16] W Moffat and M R W Walmsley ldquoUnderstanding limecalcination kinetics for energy cost reductionrdquo in Proceedingsof 59th Appita Conference Auckland New Zealand 2006
[17] D Hai Do and E Specht ldquoDetermination of reaction co-efficient termal conductivity and pore diffusivity in de-composition of limestone of different originrdquo in Proceedingsof Word Congress on Engineering and Computer ScienceWCECS 2011 San Francisco CA USA October 2011
[18] B R Stanmore and P Gilot ldquoReviewmdashcalcination and car-bonation of limestone during thermal cycling for CO2 se-questrationrdquo Fuel Processing Technology vol 86 no 16pp 1707ndash1743 2005
[19] D Kunii and T Chisaki Rotary Reactor Engineering ElsevierAmsterdam e Netherlands 2008
[20] R Perry D Green and J Maloney Manual del IngenieroQuımico Mc Graw Hill Mexico City Mexico 2001
