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Energy 44 (2012) 1067e1077

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Energy

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Fast pyrolysis of sugarcane and cassava residues in a free-fall reactor

Adisak Pattiya a,*, Sittha Sukkasi b, Vituruch Goodwin b

aBio-Energy and Renewable Resources Research Laboratory, Faculty of Engineering, Mahasarakham University, Kamriang, Kantharawichai District, Maha Sarakham 44150, ThailandbNational Metal and Materials Technology Center, 114 Thailand Science Park, Phahonyothin Rd., Klong 1, Klong Luang, Pathumthani 12120, Thailand

a r t i c l e i n f o

Article history:Received 9 December 2011Received in revised form24 February 2012Accepted 14 April 2012Available online 28 May 2012

Keywords:Agricultural residuesBio-oilBiomassFast pyrolysisFree-fall pyrolyser

* Corresponding author. Tel.: þ66 4 375 4321x3036E-mail address: adisak_pattiya@yahoo.com (A. Pat

0360-5442/$ e see front matter � 2012 Elsevier Ltd.doi:10.1016/j.energy.2012.04.035

a b s t r a c t

Fast pyrolysis of agricultural residues from sugarcane and cassava plantations was carried out ina laboratory-scale free-fall reactor unit. The objectives of this work were to investigate the effects ofbiomass types and pyroysis conditions, such as reactor temperature, condensation temperature, nitrogenflow rate and run duration, on pyrolysis product distribution, as well as to study the basic properties ofthe products. The results showed that all of the parameters affected the product distribution. Theoptimum reactor temperatures for maximising bio-oil yield were in the range of 350e450 �C. About70 wt% of bio-oil yield could be obtained by pyrolysis of cassava stalk at a reactor temperature of 450 �Cand a primary condensation temperature of 10 �C. It was also found that the minimum flow rate ofnitrogen for obtaining high bio-oil yield was 1.5 l/min. The product characterisation showed that the bio-oil and char produced from the agricultural residues with the free-fall reactor unit were to a certainextent similar to those produced from different types of biomass with different types of pyrolysis reactorconfigurations.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Due to the decline in fossil fuels coupled with the growingdemand for energy, a quest for alternative sources of energy andfuel is inevitable. One of those alternative sources is biomass, whichis regarded as clean and renewable. Among the many types ofbiomass, the non-food ones, such as agricultural residues, arepromising and less likely to cause conflicts. Sugarcane and cassavaplants are normally grown for food (e.g. sugar and tapioca) in manycountries including Thailand. The world’s sugarcane and cassavaproductions are 1,661,251,480 and 233,795,973 tonnes per year in2009 [1]. This corresponds to sugarcane and cassava residues ofapproximately 500 and 100 million tonnes per year, respectively.The agricultural residues from sugarcane plantations, also calledsugarcane trash, include leaves and tops. Another residue fromsugarcane production is sugarcane bagasse, which was previouslyinvestigated in vacuum pyrolysis experiments [2]. However, it is notconsidered in this work because the sugar factories typically use itas boiler fuel for heat and power generation. Cassava residues leftfor energy usage are mainly stalk and rhizome. The cassava leavesare usually left on the fields for soil conditioning.

; fax: þ66 4 375 4316.tiya).

All rights reserved.

Biomass can be used for energy directly by combustion orconverted into a more flexible form such as liquid. One of thebiomass-to-liquid conversion technologies is fast pyrolysis inwhichbiomass is thermally decomposed in the absence of oxygen underprecisely controlled conditions. Fast pyrolysis of biomass has threeproducts, namely char, gas, and bio-oil, which is the main productin liquid form that allows more convenient storage and trans-portation than the original solid biomass.

The key component of fast pyrolysis process is a pyrolysisreactor or pyrolyser in which pyrolysis reactions take place. Thereare several types of fast pyrolysis reactors currently being used ortested, such as bubbling fluidised-bed [3,4], circulating fluidised-bed [5], rotating cone, ablative, vacuum [2], auger and entrainedflow reactors. The details of a wide range of fast pyrolysis reactorconfigurations are provided by Bridgwater and Peacocke [6] andmost updated information about the reactors is given by Bridg-water [7]. One of the most interesting configurations of pyrolysisreactors is an entrained flow reactor, which is also called “a free-fallreactor”, “a drop-tube reactor” [8], “a flow reactor” [9], “a downflowreactor” [10] or “a tubular reactor” [11]. The technical concept ofthis reactor is very simple compared with the other types. Biomassparticles are allowed to drop or move downward under gravita-tional force together with some entrained flow of inert gas insidea tubular reactor. The temperature of the reactor can be controlledin the range of 300e600 �C. When each biomass particle passes thehot zone of the reactor, thermal decomposition occurs, thus

Table 1Main characteristics of biomass samples.

Analysis Sugarcaneleaves

Sugarcanetops

Cassavastalk

Cassavarhizome

Proximate analysis (wt%, as-received basis)Moisture 6.7 6.6 8.5 8.8Volatile matter 79.0 74.9 69.7 65.0Fixed carbon 8.6 12.5 14.7 15.0Ash 5.7 6.0 7.1 11.2Ultimate analysis (wt%, dry ash-free basis)Carbon 48.9 49.0 48.8 49.5Hydrogen 6.5 6.6 6.7 6.5Nitrogen 0.2 0.6 1.1 1.1Oxygen 44.4 43.8 43.4 42.9Molecular formula CH1.58O0.68 CH1.6O0.67 CH1.64O0.67 CH1.57O0.65

Heating valuea (MJ/kg, dry basis)HHV 18.4 18.3 18.1 17.1LHV 17.0 17.0 16.8 15.9Density (kg/m3)Bulk 230 160 230 260Apparent 800 670 1000 1000

a Calculated from a correlation suggested by Sheng and Azevedo [23].

A. Pattiya et al. / Energy 44 (2012) 1067e10771068

producing pyrolysis vapour. The vapour is rapidly cooled to becomebio-oil. The solid residue is collected as char. The advantage of thisreactor configuration is the reduction of sweep gas, compared tofluidised-bed reactors, which would increase in efficiency of bio-oilcondensation, due the higher partial pressure of the pyrolysisvapour.

Free-fall reactors were previously applied for fast, rapid or flashpyrolysis of biomass like wood, oilseed and agricultural residues[10e16], cellulose [9], polystyrene waste [17] and coal [14,18] attemperatures from 400 �C to 1100 �C under different sweep gas oratmosphere such as nitrogen [10,11,14e16,18e20], hydrogen [14],a mixture of nitrogen and steam [20] or even under vacuum [17].The purposes of the previous studies were to investigate the effectsof process parameters such as biomass or solid fuel types[10,12e14,16,18], heating rate [12], temperature [9e20], particlesize [9e13,15e17,19,20], residence time [12,14,20], sweep gas flowrate [15,19], addition of steam [10,20], pressure [14], solid fuel feedrate [9,19] and solids/gas ratio [9] on pyrolysis product distribution[9e20], gas composition [10,12,13,16,18,20], or char reactivity[12,13,18]. Although it is typically accepted that fast, rapid or flashpyrolysis of biomass or other solid fuels aims to maximise thepyrolysis liquid or bio-oil yield, the majority of the previousresearch [9,10,12e14,16e18,20] on fast pyrolysis using free-fallreactors did not give emphasis on the bio-oil product, but ratherfocused on gas yield and composition or other purposes such aschar activity or kinetic studies. Only few studies [11,15,19] consid-ered bio-oil produced with free-fall reactors as the main product.Acikgoz and Kockar [11] as well as Onay and Kockar [15] performedpyrolysis experiments of oil seeds (linseed and rapeseed) in a free-fall reactor under nitrogen atmosphere to investigate the effects ofpyrolysis temperature and biomass particle size on product yields.They found that pyrolysis temperature of 550 �C and particle size ofhigher than 180 mm gave a maximum linseed bio-oil yield of 68.8%,and pyrolysis temperature of 600 �C and particle size of224e600 mm gave a maximum rapeseed bio-oil yield of 75%. Theyconcluded that the pyrolysis temperature and solid particle sizesignificantly affect bio-oil yields. Recently, Ellen and Brown [19]examined the optimisation of four process parameters in fastpyrolysis of red oak using a free-fall reactor. Bio-oil yields in therange of 64.4e72 wt% were obtained at the heater set-pointtemperatures of 450e650 �C, the average biomass particle sizesfrom 200 to 600 mm, the sweep gas flow rates from 1 to 5 sL/minand the biomass feed rates from 1 to 2 kg/h.

The production of bio-oil from fast pyrolysis in free-fall reactorshas already been investigated on oil seed [11,15] and wood [19], butno published research study has been carried out on agriculturalresidues. Therefore, it is the purpose of the current study toinvestigate the bio-oil production of agricultural residues fromsugarcane and cassava plantations by fast pyrolysis in a free-fallreactor. These types of biomass were previously pyrolysed influidised-bed reactors [21,22]. However, their pyrolysis behaviourin a free-fall reactor is still not fully known and thus a subject ofpresent research. In this work, the effects of process parameterssuch as reactor temperature, condensation temperature, sweep gasflow rate and run duration on product yields were examined.Additionally, basic properties of bio-oil and char are analysed andcompared with literature data.

2. Materials and methods

2.1. Biomass feedstock

Biomass residues from sugarcane and cassava plants, namelysugarcane leaves (SL), sugarcane tops (ST), cassava stalk (CS) andcassava rhizome (CR), were taken from northeast region of

Thailand. The feedstock materials were ground to a particle size of250e450 mm and dried in an oven at 105 �C for 24 h prior topyrolysis experiments. The drying could ease the feeding andreduce the tendency of the particles sticking to the reactor wall.Table 1 summarises their main characteristics [23].

2.2. Fast pyrolysis apparatus

Fast pyrolysis experiments were carried out with a bench-scalefree-fall reactor unit. Fig. 1 shows a schematic diagram of thepyrolysis unit. It is composed mainly of a feeding unit, a reactor anda product collection system. The feeding unit consists of a biomasshopper, a stirrer with paddles, a screw feeder and a water coolingjacket. The main part of this unit was made of 304 stainless steel.Both the stirrer and screw feeder were driven by two separatemotors. The speed of each motor could be adjusted in conjunctionwith the nitrogen entrained flow rates in order to control biomassfeed rate. The water cooling jacket was used to prevent prematurepyrolysis of the biomass particles prior to entering the reactor zone,which would otherwise cause the blockage in the feeding tube.The reactor was constructed of a 304 stainless steel tube with aninternal diameter of 7.7mm and a height of 100 cm. The reactor washeated by an FeeCreAl electric heating wire (0.7 U/m) that deliversabout 250 W at 60 V. The heating wire was electrically insulated byfish spine ceramic beads and thermally insulated by ceramic fiberblanket. A K-type thermocouplefit to the externalwall of the reactorand located at the middle of the reactor height was used to controland monitor the operating temperature. The product collectionsystem comprised three char pots, two cyclone separators, a hotfilter for collecting solid products, a water-cooled condenser, anelectrostatic precipitator (ESP), a dry-ice/acetone condenser, twobio-oil pots and a cotton wool filter for collecting liquid products.The material used for most parts of the product collection systemwas 304 stainless steel, except for the ESP and the dry-ice/acetonecondenser, which were made of a clear acrylic tube and borosilicateglass, respectively. All pipeline parts from char pot 1 to the inlettube of thewater-cooled condenserwere electrically heated to keepthe temperatures inside the tubes (or temperatures of pyrolysisvapour) around 400 �C to avoid condensation of the vapour.

2.3. Fast pyrolysis experiments

Each experiment was initiated by preheating the pyrolysis unitto a target temperature. Then nitrogen flow was turned on to

Fig. 1. Schematic diagram of fast pyrolysis apparatus.

A. Pattiya et al. / Energy 44 (2012) 1067e1077 1069

remove oxygen or air in the system. Once the systemwas at steadystate as noticed from the constant reading of temperatures, themotors were switched on to begin feeding the biomass into thereactor. Biomass particles moved downward due to gravitationalforce and the nitrogen entrained flow, while simultaneouslydecomposed in the reactor producing pyrolysis vapour and theresidues turned into char. The large char particles dropped into thechar pot 1, whereas char fines were carried over together with thepyrolysis vapour by the nitrogen flow passing the two cycloneseparators and the hot filter where the majority of char fines werecaptured and then kept in the char pots 2 and 3. The pyrolysisvapour subsequently flew through the water-cooled condenser andthe ESP and was condensed into liquid product. Most of the liquidproduct was collected in the bio-oil pot 1. In addition, lowermolecular weight or light bio-oil could be condensed by the verylow temperature (around�78 �C) dry-ice/acetone condenser. Someliquid product was also trapped in the cotton wool filter.

Experiments were carried out in three sets. The first one was toinvestigate the effects of reactor temperature on yields of pyrolysisproducts, for the four types of biomass. Sugarcane leaves, sugarcane

tops, cassava stalk and cassava rhizome samples were pyrolysed at350, 400, 450, 500 and 550 �C. The aim of this set of experimentswas to find out the optimum temperatures for obtaining highestbio-oil yields for each feedstock. Other parameters such as coolingwater temperature and nitrogen flow rate were kept constant at30 �C and 3 l/min, respectively. This flow rate of nitrogen wasselected as it could partially prevent the biomass from sticking tothe reactor wall, which would otherwise block the feeding. Thesecond set of experiments was to investigate the effects of watertemperature used in the water-cooled condenser. In this set, onlyone type of biomass was selected for testing according to the resultsof the first experimental set. Specifically, the chosen biomass typewas the one that gave high bio-oil yield and was easy to feed. Thecooling water temperatures studied were 10, 30 and 50 �C, whilenitrogen flow rate was kept constant at 3 l/min. The reactortemperature applied in this set of experiments was the one thatgave highest bio-oil yield. The third set of experiments wasdesigned to investigate the effects of nitrogen flow rate on pyrolysisproduct distribution by applying a selected biomass and operatingtemperature according to the results from the first set of

A. Pattiya et al. / Energy 44 (2012) 1067e10771070

experiments. The nitrogen flow rates were 0.1, 0.6, 1.5, and 3 l/min.The cooling water temperature was kept constant at 30 �C. For allexperiments, the biomass-feeding rate was approximately 100 g/hand the nitrogen flow was at around atmospheric pressure.

2.4. Mass balance calculation

All parts of the fast pyrolysis apparatus were weighed beforeand after experimentation in order to find the yields of pyrolysisproducts. The difference in theweight of the feeder before and afterthe experiment is the quantity of biomass input. The difference inthe total weight of the reactor, char pot 1, cyclone separator 1, charpot 2, cyclone separator 2, char pot 3, hot filter and all of the con-necting tubes before and after the experiment indicates the amountof char produced. The calculated char yield also includes the charfines present in the bio-oil which was determined by solids contentanalysis (see section 2.5.1). The liquid or bio-oil yield was calculatedfrom the difference in the weight of the water-cooled condenser,ESP, bio-oil pot 1, dry-ice/acetone condenser, bio-oil pot 2 andcotton wool filter before and after the experiment. The majority ofthe bio-oil was collected from the water-cooled condenser, ESP andbio-oil pot 1 and was somewhat different in characteristic fromthose collected from the dry-ice/acetone condenser, bio-oil pot 2and cotton wool filter. The former bio-oil was sticky and dark-brown in colour, whereas the latter was aqueous and yellowish.While the former bio-oil looked like typical bio-oil, the lattercontained mainly water and light or low molecular weight organiccompounds. Since the main liquid product was the former bio-oil,only that part of bio-oil was subjected to characterisation.

2.5. Analysis of pyrolysis products

2.5.1. Bio-oil analysis2.5.1.1. Water content. Volumetric KarleFischer titration, which iswidely used and recommended for determination of watercontent of bio-oil, was applied using a Metrohm automatic titra-tion instrument. Prior to the measurement, a KarleFischer reagent(Hydranal Composite 5) used as a titrant was standardised withdeionised redistilled water. A mixture of bio-oil obtained from bio-oil pot 1, water-cooled condenser and ESP from each experimentwas tested in triplicate and the average results were reported.

2.5.1.2. Solids content. Solids content of bio-oil was determined asethanol insolubles by using vacuum filtration technique. Approxi-mately 2e3 g of bio-oil was filtered through a pre-dried and pre-weighed Whatman No. 3 qualitative filter paper with particleretention of 6 mm. The bio-oil was thenwashed with excess amountof ethanol until the filtrate was clear to ensure that there was noorganic liquid left on the filter paper. The filter paper with theresidues was air-dried for 15 min, dried in an oven at 105 �C for30 min, cooled in a desiccator and weighed. The solids content wasthen calculated as the percentage of the solid residues in the bio-oil.This method was suggested by Oasmaa and Peacocke (2001) [24].

2.5.1.3. pH value. The pH value of bio-oil was determined usinga Hanna HI 98107 (pHep) pocket pHmeter with an accuracy of�0.1pH unit. Prior to the measurement, the instrument was calibratedwith a liquid calibration standard of pH 7.

2.5.1.4. Specific gravity. The specific gravity of bio-oil samples wasmeasured according to ASTM D 4052 at 15 �C by a digital densitymeter (Anton Paar DMA 4500). Prior to the analysis, the densitymeter was calibrated with deionised redistilled water and air.Approximately 0.7 ml of each sample was injected into a U-shapedoscillating sample tube.

2.5.1.5. Elemental analysis. Elemental analysis of bio-oil sampleswas carried out by the Laboratory Equipment Center, Mahasarak-ham University, Thailand, to determine the percentages of carbon,hydrogen, nitrogen and sulphur. The Leco TruSpec Micro CHNSelemental determinators were applied for the analysis. The oxygencontent was calculated by difference.

2.5.1.6. Heating value. The higher heating values (HHV) of bio-oilsamples were calculated based on a correlation developed byChanniwala and Parikh [25] as shown by the following equation:

HHVdry

�MJkg

�¼0:3491 Cþ 1:1783 Hþ 0:1005 S� 0:1034 O

� 0:015 N� 0:0211 A ð1ÞWhere C, H, S, O, N and A represent mass percentages on dry

basis of carbon, hydrogen, sulphur, oxygen, nitrogen and ashcontents of bio-oil (organics and solid fine particles) on water-freebasis, respectively.

The lower heating values (LHV) were calculated from HHV andthe hydrogen content by the following equation [26]:

LHVdry

�MJkg

�¼ HHVdry � 2:442� 8:936

H100

(2)

where H is weight percentage of hydrogen on dry basis.To calculate the values on as-produced or wet basis, the

following equations [26] were applied, taking into account thewater content of bio-oil (H2O, wt%):

HHVar ¼ HHVdry

�1� H2O

100

�(3)

LHVwet

�MJkg

�¼ LHVdry

�1� H2O

100

�� 2:442

H2O100

(4)

2.5.1.7. GC/MS analysis. Bio-oil was diluted in ethanol to obtainapproximately 17.5 wt% of organics. The samples were filteredthrough a Filtrex nylon filter with 0.2 mm pore size prior to theinjection. The gas chromatography/mass spectrometry (GC/MS)analysis of bio-oil was conducted using an SHIMADZU Gas Chro-matograph Mass Spectrometer model GCMS-QP2010 Plus. Theseparation was made on a 60 m � 0.25 mm id DB-1701 columnwith 0.25 mm film thickness. Its phase composition was 14%-cya-nopropyl-phenyl-86%-dimethylpolysiloxane. In addition, a fusedsilica capillary column (5 m � 0.25 mm) was used as a guardcolumn and placed before the main column. The GC oventemperature was held at 45 �C for 4 min and programmed to risefrom 45 �C to 240 �C at 4 �C/min and from 240 �C to 270 �C at 5 �C/min. The oven was maintained at this final temperature for15 min. The injector temperature was 280 �C with a split ratio of1:25. Helium was the carrier gas with a linear velocity of 38 cm/s.The capillary column was directly connected to a metal quardru-pole mass filter with pre-rod Mass Analyser and Electron multi-plier detector. The mass spectrometer was operated with electronimpact (EI) mode at ion source and interface temperatures of 280and 250 �C, respectively, with ionisation energy of 70 eV. The massrange from m/z 35 to 400 was scanned with a scan event of 0.3 s.Data acquisition and processing was performed using SHIMADZULabSolutions GCMSsolution version 2.50 software. Identification ofthe compounds was achieved by comparing the mass spectrum(m/z distribution) with Wiley and NIST mass spectral database andliterature data [27e38].

0

5

10

15

20

25

30

35

40

45

50

55

60

300 350 400 450 500 550 600

ProductYield(wt%,drybasis)

Temperature(°C)

Bio Oil

Gas

Char

0

5

10

15

20

25

30

35

40

45

50

300 350 400 450 500 550 600

ProductYield(wt%,drybasis)

Temperature (°C)

Bio Oil

Gas

Char

a

b

Fig. 2. Effect of reactor temperature on yields of products derived from sugarcaneagricultural residues: (a) Sugarcane leaves and (b) Sugarcane tops.

A. Pattiya et al. / Energy 44 (2012) 1067e1077 1071

2.5.2. Char analysisSolid or char products were analysed for their ash and elemental

contents as well as heating values. The method used for determi-nation of the ash content of the char was ASTM E 1755-01. The ashcontent was expressed as the mass percent of residue remainingafter dry oxidation at 575 � 25 �C. The elemental analysis andheating values determination of the char were carried out in thesame way as those applied for bio-oils (see section 2.5.1.5 and2.5.1.6).

3. Results and discussion

3.1. Effects of process parameters on pyrolysis product distribution

There are several process parameters affecting the pyrolysisproduct distribution. These parameters can be grouped into 3categories: independent, dependent and controlled variables. Thispaper focuses on four independent variables, namely reactortemperature, primary condensation temperature, nitrogen flowrate and run duration. The dependent variables are yields of bio-oil,char and gas. The controlled variables include reactor size andconfiguration, biomass feed rate, voltage supply to the ESP, insu-lation material, the quantities of glass wool and cotton wool (hotand cold filter media) and temperatures of cooling water andtransfer line (from reactor exit to condenser). The experimentalresults based on the four independent variables are given anddiscussed below.

3.1.1. Reactor temperatureTo investigate the influence of reactor temperature on pyrolysis

product yields, a total of 20 experimental runs were carried out on4 biomass types (sugarcane leaves (SL), sugarcane tops (ST), cassavastalk (CS) and cassava rhizome (CR)) at reactor temperatures of 350,400, 450, 500 and 550 �C and the flow rate of nitrogenwas 3 L/min.As mentioned earlier, the pipelines temperature was kept constantat around 400 �C. It is therefore important to note that for thereactor temperature of 350 �C, it is possible that post-pyrolysis ofthe residual solid at 400 �C could take place outside the reactorzone, especially in the char pots. The main objective of theseexperiments was to determine the optimum pyrolysis reactortemperature for maximising the yield of bio-oils derived from eachfeedstock. The results are illustrated in Figs. 2 and 3. All of thefigures show that the temperature of the free-fall reactor greatlyinfluences pyrolysis product distribution. Virtually all of the bio-oilyields tended to increase from 350 �C to a certain temperature(either 400 �C or 450 �C) and further increase of the temperature to550 �C reduced bio-oil yields. An exception was for ST bio-oil. Theyields of char from all feedstock types decreased when increasingreactor temperature. This is probably due to the increase in theprimary decomposition of the biomass particles and/or thesecondary decomposition of char at higher temperature. The gasyields increased significantly with temperature. This increase isspeculated to be owing to the secondary cracking of char andpyrolysis vapour. Similar trends for the effect of pyrolysis temper-ature on product distribution were previously reported[11,22,39,40], although with regard to different biomass types and/or reactor configurations.

When comparing bio-oil yields from sugarcane residues (SL andST), it was found that the maximum SL bio-oil yield occurred at400 �C with 53.3 wt%, while ST bio-oil yield reached its maximumat 350 �C with 44.1 wt%. Since the other pyrolysis process param-eters for both feedstock were controlled, the two possible reasonswhy the ST bio-oil yield was lower than that of SL may be related tothe biomass composition and particle density. According to Table 1,the ST contained slightly higher ash and lower volatile than the SL.

Higher ash content of biomass would normally lead to higher charand gas in pyrolysis reactions. The volatile matter content ofbiomass could be an indication of bio-oil yield. It is expected thatthe higher this value, the higher the bio-oil yield. Comparing Fig. 2(a) and (b), the char yields for both materials were similar and theSTgas yield was higher than that of the SL. Therefore, the lower bio-oil yield of the ST could be partly due to the higher ash content andthe lower volatile matter content. The particle apparent density ofbiomass is also important in fast pyrolysis, especially in a free-fallreactor. If the particle apparent density is high, it means that theparticle is heavy and could fall down the reactor tube more easilyand rapidly than the light or low-density biomass particles. Table 1shows that the particle apparent densities of SL and ST are 800 and670 kg/m3, respectively. This means that the ST particles are lighterthan those of the SL. Accordingly, the ST particles would tend tothermally decompose near the inlet of the free-fall reactor. Theevolved vapour would then have longer residence time to travel tocondensation unit. This could also explain the reason why the STgave lower bio-oil yield and higher gas yield than the SL.

Biomass residues from sugarcane plants were previously pyro-lysed in a fluidised-bed reactor by Xu et al. [22]. The residuesinvestigated include the internal bagasse, external and whole plant.The internal bagasse was defined as the finest sugarcane bagassefrom the mills once the juice is extracted. The external was the partthat is left over after being chopped with machete once thesugarcane is harvested, which is similar to the sugarcane tops. Thewhole plant was the dried residue remained on the land, whichprobably means the sugarcane leaves. The reported maximumliquid yields for the ST and SL were 52.6 wt% and 55.5 wt%,

a

b

Fig. 3. Effect of reactor temperature on yields of products derived from cassava agri-cultural residues: (a) Cassava stalk and (b) Cassava rhizome.

A. Pattiya et al. / Energy 44 (2012) 1067e10771072

respectively, at a pyrolysis temperature of 400 �C. It can be seenthat the maximum SL bio-oil yield and optimum pyrolysistemperature obtained from the free-fall reactor (53.3 wt% at400 �C) were similar to that obtained from the fluidised-bed reactor(55.5 wt% at 400 �C). However, the maximum bio-oil yields andoptimum pyrolysis temperatures of the sugarcane tops when usingdifferent reactor configurations are apparently different. The free-fall reactor gave lower bio-oil yield and pyrolysis temperaturethan the fluidised-bed reactor. This discrepancy could be related tothe heat transfer of the biomass particles when undergoing ther-molysis inside the two reactor types.

Fig. 3 shows that the maximum bio-oil yields for CS and CRbiomass are 52.3 wt% and 50.3 wt%, obtained at reactor tempera-tures of 450 �C and 400 �C, respectively. The reasonwhy the CS gaveslightly higher bio-oil yield than the CR could be the lower ashcontent of the CS biomass, since the inorganic salts in the ash couldact as catalysts for secondary reactions such as char forming andvapour cracking. Fast pyrolysis of the CS and CR biomass sampleswere previously studied in a fluidised-bed reactor [40] and it wasfound that themaximumyields of the liquid bio-oil derived fromthestalk and rhizome were 62 wt.% and 65 wt.% on dry basis, respec-tively. The pyrolysis temperatures in the fluidised-bed reactor thatgave the highest bio-oil yields for both feedstock types were in therange of 475e510 �C [40]. Therefore, it is obvious that the CS and CRbio-oil yields obtained with the free-fall reactor (50.3e52.3 wt%)were lower than those obtained with the fluidised-bed reactor(62e65wt%). This shows that the pyrolysis reactor design isimportant for achieving high yield of liquid product.

When comparing the current findings of SL, ST, CS and CR bio-oil yields with the results from literature data [11,15,19] using thesame type of pyrolysis reactor (free-fall reactor configuration)which gave maximum bio-oil yields of 68.8 wt%, 75 wt% and 72 wt% for linseed, rapeseed and red oak, respectively, it was found thatthe SL, ST, CS and CR gave lower bio-oil yields. The lower bio-oilyields in this study could be mainly due to the biomass compo-sition because the biomass types investigated here are agriculturalresidues, which normally contain high amounts of ash comparedto wood. Unlike linseed and rapeseed, the sugarcane and cassavaresidues contain no oil. This also explains the lower bio-oil yieldsof the SL, ST, CS and CR.

3.1.2. Primary condensation temperatureAccording to Fig. 1, the bio-oil collecting unit is composed of

a water-cooled condenser, an ESP, a dry-ice/acetone condenser,a cottonwool filter and two bio-oil pots. The majority of bio-oil wascollected in Bio-oil Pot 1 by the water-cooled condenser and an ESP.This part of bio-oil is referred to as “primary bio-oil”. The water-cooled condenser is a double-pipe counter-flow heat exchanger.The temperature of the cooling water is called “primary conden-sation temperature”. The light organic volatiles together with waterwere also collected in a dry-ice/acetone condenser at a temperaturearound �78 �C (“secondary condensation temperature”). Thisliquid product was collected in Bio-oil Pot 2. The Pot 2 Bio-oilcombined with the liquid in the cotton wool filter is named“secondary bio-oil”.

To investigate the influence of primary condensation tempera-ture (2e50 �C) on pyrolysis product distribution, a total of 7experimental runs were carried out using cassava stalk (CS) ata reactor temperature of 450 �C and a feeding rate of about 100 g/h.The first three experiments were performed for 1 h (Fig. 4 (a)) andthe rest were run for 3 h (Fig. 4 (b)). Fig. 4 (a) and (b) show the sametrend for pyrolysis product distribution that the bio-oil yields wereenhanced when increasing or decreasing the primary condensationtemperatures from room temperature (around 30 �C). The CS bio-oil yield reached its maximum at 69.6 wt% with the primarycondensation temperature of 10 �C (Fig. 4 (a)). Normally, one wouldexpect that the increase in the primary condensation temperaturewould allow part of the water to shift from the Bio-oil Pot 1 to theBio-oil Pot 2. If so, the primary bio-oil would reduce, the secondarybio-oil would increase and the summation of both yields would bemore or less constant. However, the results show that the primarycondensation temperaturemainly affected the primary bio-oil yieldas can be seen from Fig. 4 that the secondary bio-oil yields wereonly slightly changed with the primary condensation temperature.This is due to the fact that the majority of the bio-oil productderived from the primary bio-oil.

The reduction or increase in the bio-oil yields with the primarycondensation temperature was corresponding to the changes in thegas yield, while the char yields were nearly constant. Based on thecurrent findings, it could be inferred that the primary condensationtemperature did not only influence the collection efficiency of thebio-oil, but could be involved in some chemical reactions occurringupon condensation of the pyrolysis vapour. These might be relatedto the formation of organic compounds from free radicals, which isdependent on temperature. In the current study, it has been shownthat lower or higher condensation temperature than 30 �C favouredthe formation of liquid compounds.

3.1.3. Nitrogen flow rateNitrogenwas used to remove oxygen in the system, to sweep the

pyrolysis vapour to the condensation unit and to entrain somebiomass particles clinging to the reactor wall. Nitrogen flow rate ina free-fall reactor normally affects the solid and vapour residence

Fig. 4. Effect of primary condensation temperature on yields of products from pyrol-ysis of cassava stalk at 450 �C for (a) 1 h and (b) 3 h.

A. Pattiya et al. / Energy 44 (2012) 1067e1077 1073

times. In this work, the effect of nitrogen flow rate in the range of0.1e3.0 l/min on product distributionwas examined and the resultsare shown in Fig. 5. It is apparent that increasing the nitrogen flowrate from 0.1 l/min to 1.5 l/min increased the bio-oil yield from48 wt% to 53 wt% and a further increase of the flow rate to 3.0 l/min

Fig. 5. Effect of nitrogen flow rate on yields of products from pyrolysis of cassava stalkat 450 �C operated for 1 h.

did not affect the bio-oil yield. The increase of the bio-oil yield withthe flow rate occurred at the expense of the char and gas yields. Thereduction of the char yield when increasing the nitrogen flow ratefrom 0.1 to 1.5 l/min could be due to the dropping behaviour of thebiomass particles in the reactor tube. At low nitrogen flow rate,biomass particles may fall down slowly and stick to the reactor walland the accumulation of the solid residues or char on the wall couldlower the heat transfer of the reactor. Consequently, increasing thenitrogen flow rate to a certain extent would allow continuousdropping of the biomass particles down to the char pot. Thedecrease of the gas yield with the increase of the nitrogen flow ratefrom 0.1 to 1.5 l/min could be related to the vapour residence time.Higher flow rate of nitrogen led to shorter vapour residence time,thus reducing the secondary reactions such as vapour cracking andchar forming, which would otherwise induce the production ofnon-condensable gases and char, respectively.

3.1.4. Run durationThe run duration is equal to the period of time spent feeding

biomass into the reactor. This duration was expected to influencethe pyrolysis product distribution. The run duration for typicalexperiments was 1 h at a fixed biomass feed rate of around 100 g/h.To investigate the effect of the run duration, the duration wasincreased to 3 h, while fixing the solid feed rate. This means that thetotal amount of the biomass fed was increased from about 100 g to300 g. Therefore, the impact of the run durationwould be along theline of that of the biomass quantity. To confirm the trends of theresults, two biomass samples were applied including the CS and CR.The reactor temperatures for pyrolysing the CS and CR in this studywere chosen from the optimum conditions previously found, whichwere 450 �C and 400 �C, respectively, and the nitrogen flow ratewas constant at 3 L/min. The results are illustrated in Fig. 6. Fig. 6 (a)shows that when increasing the experimental run duration from1 h to 3 h, the CS bio-oil yield decreased from 52.3 wt% to 39.7 wt%on dry basis. This accounts for the reduction of 12.6%. Likewise,from Fig. 6 (b), the CR bio-oil yield decreased from 50.3 wt% to41.9 wt% on dry basis, which is equivalent to the reduction of 8.4%,when extending the run duration from 1 h to 3 h. The reduction ofbio-oil yields occurred concurrently with the rising of the gasyields, whereas the char yields were almost unchanged (Fig. 6). Itcould be therefore deduced that part of the pyrolysis vapour thatwould otherwise be condensed into bio-oil was transformed intonon-condensation gas for long duration runs. This transformationis expected to be due to the secondary cracking reactions of thepyrolysis vapour. These reactions were enhanced when operatedfor long time because the longer the experiments went on, thehigher the amount of the biomass had been fed. This in turn led tothe increase in the quantity of char fines accumulated inside thereactor tube, transfer line, as well as at hot filter.When the pyrolysisvapour passed the char fines, secondary cracking could take place,especially if the char fines contain high inorganic species such asalkali and alkaline earth metals. The metals in the char finestogether with the char porous structure could act as catalysts forsecondary reactions, thus reducing the liquid yield and changing itscomposition [41]. One way to mitigate this problem is to eitherincrease the size of the reactor unit or to design a new hot filtrationunit that can continuously remove the accumulated char particlesfrom the pyrolysis vapour pathway.

3.2. Characteristics of bio-oils

Basic properties of bio-oil produced from four types of biomassin comparison to literature data using wood [42], rice straw [43]and rapeseed [15] are summarised in Table 2. The table showsthat the water contents of bio-oil samples produced in this work

Fig. 6. Effect of run duration on yields of products from pyrolysis of (a) Cassava stalk at450 �C and (b) Cassava rhizome at 400 �C operated for 1 h (short duration) and 3 h(long duration).

A. Pattiya et al. / Energy 44 (2012) 1067e10771074

were in the range of 15.0e24.2 wt%, which is similar to those of bio-oil samples produced from wood and rice straw, although theywere produced with different reactor configurations. The rapeseedbio-oil produced from a free-fall reactor contained very little water.This may be due to the nature of the oil seed feedstock. Watercontent of bio-oil depends on several factors such as moisture

Table 2Characteristics of bio-oils.

Characteristics This work

Sugarcane leaves Sugarcane tops Cassava sta

Water content (wt%) 18.1 24.2 15.0Solids content (wt%) 2.9 3.7 2.9pH 3.3 3.2 3.3Specific gravity 1.09 1.07 1.13Elemental composition (wt%, as-produced basis)Carbon 60.0 65.4 47.0Hydrogen 7.5 7.7 6.2Nitrogen 1.9 1.8 1.2Oxygen 29.5 24.2 44.7Ash 1.1 1.0 0.9Molecular fomula CH1.51O0.37 CH1.4O0.28 CH1.58O0.71

Heating value (MJ/kg, as-produced basis)HHV 26.7 29.3 19.0LHV 22.7 24.1 15.7

content of the feedstock, pyrolysis reactor configuration, heatingrate, pyrolysis temperature and condensation temperature. Thewater content of bio-oil affects its use as fuel. If the water content istoo high, the bio-oil would be difficult to ignite and the heatingvalue would be low. Nevertheless, water in bio-oil has somebenefits such as reducing its viscosity and flame temperatureduring combustion, thus reducing chances for some unwantedgases such as NOx to form. The water contents of bio-oil producedfrom sugarcane and cassava residues were in the range of typicalfast pyrolysis liquid. Consequently, the bio-oil may be used as fuel.

Apart from the water content, solids content of bio-oil is alsoimportant in applications. Ideally, the solids content should beminimised as they could cause problems such as clogging anderosion of pipelines, vessels or pumping system. Solids in bio-oilare char fines that could not be removed from the vapour in theseparation process because of the low efficiency of the cyclones andhot filter. The char fines could also lower the bio-oil stability, whichis normally measured by changes in viscosity over the period oftime, because char fines containing active catalysts such as alkaliand alkaline earth metals for polymerisation reactions. This couldincrease the bio-oil molecular weight and therefore its viscosity. Ifthe polymerization reactions continue, eventually phase separationmay occur and the bio-oil’s application would be problematic.According to Table 1, the solids contents of the bio-oils produced inthis study were relatively high (2.9e4.3 wt%) compared to previousstudies [42,43]. Future work is therefore needed to improve thechar collection efficiency in the free-fall reactor unit. A moving-bedhot filter is under development by the authors at the Bio-Energyand Renewable Resources Research Laboratory, MahasarakhamUniversity, Thailand.

The pH values of bio-oils are tabulated in Table 2. The SL, ST, CSand CR bio-oil samples had pH of 3.2e3.5, which is in agreementwith previous data [15,42,43]. The bio-oils were acidic because ofthe presence of some acids such as formic, acetic, propanoic andhexadecanoic acids (Table 3).

Table 2 shows that the specific gravity of bio-oil produced in thiswork was approximately 1.1, which is similar to bio-oil producedfrom different raw materials with different reactor types. Thisshows that biomass types or pyrolysis process parameters had littleinfluence on bio-oil specific gravity or density. Table 2 also providesthe elemental content of bio-oil. Generally, the main elementalcomposition of bio-oil includes carbon, hydrogen, nitrogen andoxygen, which are derived from the original biomass. Bio-oil alsocontains trace elements such as sodium, potassium, calcium,phosphorus and silicon, collectively in the form of ash. The mainelemental compositions of the SL, ST, CS and CR bio-oil were similar

Ref [38]. Ref [39]. Ref. [11]

lk Cassava rhizome Wood Rice straw Rapeseed

24.1 15e30 25e45 <0.054.3 0.2e1 0.1e3 N/A3.5 2.5 4.2 3.21.08 1.2 N/A 0.984

59.4 54e58 65.5 72.87.7 5.5e7.0 7.7 10.82.0 0e0.2 1.2 3.329.8 35e40 25.7 13.11.1 0e0.2 0.1 N/ACH1.56O0.38 CH1.34O0.50 CH1.41O0.29 CH1.78O0.13

26.7 16e19 17.3 37.921.4 14.3e18.2 12.6e18.1 N/A

A. Pattiya et al. / Energy 44 (2012) 1067e1077 1075

to the literature data. The ash contents of the bio-oil produced inthis work were in the range of 0.9e1.1 wt%, which are higher thanthose produced from wood and rice straw. The high ash contentcould be related to the high solids content because the solids or

Table 3Percentages of the chromatographic peak areas.

Peak no. Retention time (min) Compound name

1 5.32 2-Butanone2 6.44 Formic acid3 7.25 Acetic acid4 8.48 2-Propanone, 1-hydroxy-5 8.62 Toluene6 9.76 2-Butanone, 3-hydroxy-7 10.67 Propanoic acid8 11.85 Cyclopentanone9 12.05 1-Hydroxy-2-butanone10 12.25 3-Hydroxypropanal11 12.81 o-Xylene12 13.36 3-Furaldehyde13 13.94 Furfural14 13.48 Cyclohexanone15 13.92 Styrene16 13.78 Cyclopentanone, 3-methyl-17 14.11 Butanoic acid18 14.49 Furan, 3-methyl-19 16.39 2-Furanmethanol20 16.72 2-Propanone, 1-(acetyloxy)-21 16.78 2-Cyclopenten-1-one, 2-methyl-22 17.42 Ethanone, 1-(2-furanyl)-23 17.96 2-Cyclopentene-1,4-dione24 18.02 Pentanoic acid25 19.03 Benzaldehyde26 19.51 2,5-Hexanedione27 20.07 2-Furancarboxaldehyde, 5-methyl-28 20.68 2-Cyclopenten-1-one, 3-methyl-29 20.89 Butyrolactone30 21.21 2(5H)-Furanone31 21.75 2(5H)-Furanone, 5-methyl-32 22.88 2-Cyclopenten-1-one, 2-hydroxy-3-methyl-33 29.98 Benzofuran, 2-methyl-34 24.1 Phenol35 24.69 Phenol, 2-methoxy-36 25.86 Phenol, 2-methyl-37 26.27 Maltol38 26.38 Phenol, 2,6-dimethyl-39 29.55 Phenol, 2,5-dimethyl-40 26.73 Naphthalene41 34.54 2-Furancarboxaldehyde, 5-(hydroxymethyl)-42 27.14 Phenol, 4-methyl-43 27.2 Phenol, 3-methyl-44 28.4 Phenol, 2-methoxy-4-methyl-45 28.59 Phenol, 2-ethyl-46 28.79 Phenol, 2,3-dimethyl-47 29.46 Phenol, 2,3,5-trimethyl-48 30.22 Phenol, 3-ethyl-49 31.07 Phenol, 2,4-dimethyl-50 13.31 Phenol, 4-ethyl-2-methoxy-51 31.08 Phenol, 2,4,6-trimethyl-52 33.21 2-Methoxy-4-vinylphenol53 33.67 1-Tridecene54 34.02 Eugenol55 34.11 Phenol, 2-methoxy-4-propyl-56 34.71 1,2-Benzenediol57 34.99 Phenol, 2,6-dimethoxy-58 35.8 Phenol, 2-methoxy-4-(1-propenyl)-59 36.2 1,2-Benzenediol, 4-methyl-60 36.73 Phenol, 4-(2-propenyl)-61 37.41 Phenol, 2-methoxy-4-(1-propenyl)-, (E)-62 38.12 Vanillin63 38.27 Hydroquinone64 40.58 Ethanone, 1-(4-hydroxy-3-methoxyphenyl)-65 45.39 Phenol, 2,6-dimethoxy-4-(2-propenyl)-66 46.23 Benzaldehyde, 4-hydroxy-3,5-dimethoxy-67 48.06 Ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl)68 50.54 n-Hexadecanoic acid

char contained ash. Removing the solids from bio-oil would reduceits ash content as well. The heating value calculation showed thatthe HHV of bio-oil produced from sugarcane and cassava residueswere in the range of 19.0e29.3 MJ/kg, which are somewhat higher

Sugarcane leaves Sugarcane tops Cassava stalk Cassava rhizome

0.37 1.04 0.87 0.510.00 0.21 0.64 0.00

11.68 12.25 16.29 16.547.77 7.02 7.73 8.630.00 0.51 0.30 0.220.57 0.45 0.29 0.271.23 0.93 0.81 0.760.42 0.78 0.55 0.461.43 1.22 0.59 0.840.67 0.45 1.48 1.090.00 0.29 0.00 0.130.24 0.00 0.00 0.264.73 0.21 0.37 2.310.11 0.46 0.17 0.150.22 0.19 0.11 0.060.11 0.44 0.00 0.000.84 0.33 0.75 0.584.73 0.00 4.73 1.781.03 1.75 0.66 0.743.33 1.28 1.21 1.290.00 2.17 1.32 1.490.52 0.00 0.40 0.440.00 0.00 0.23 0.130.21 0.16 0.00 0.000.42 0.56 0.47 0.270.48 0.25 0.00 0.000.67 0.23 0.50 0.352.24 2.29 1.50 1.581.05 1.03 0.71 0.540.00 0.00 1.36 1.580.00 0.00 0.44 0.336.54 3.26 3.81 4.450.00 1.28 0.00 0.145.66 6.47 2.44 2.681.60 4.47 2.78 4.932.12 2.61 1.88 2.000.00 0.38 0.41 0.381.66 1.31 0.00 1.190.58 0.00 2.02 0.410.00 0.59 0.20 0.090.00 0.00 0.83 0.005.83 3.13 2.47 2.160.00 2.41 1.93 2.040.76 1.05 1.46 2.400.00 2.21 0.00 1.041.55 1.98 2.02 1.950.19 0.31 0.29 0.278.82 7.86 0.73 0.570.48 0.62 0.30 0.412.17 2.90 1.25 2.030.35 0.35 0.75 0.100.00 4.74 1.68 2.850.70 0.61 0.64 0.000.75 0.69 1.26 2.140.00 0.18 0.27 0.514.82 1.76 5.73 2.121.58 3.16 1.78 3.670.00 0.46 0.00 0.000.45 0.22 3.72 0.241.68 0.59 0.00 0.001.13 1.96 3.33 6.192.07 1.14 3.09 2.532.71 1.52 1.72 0.980.00 0.00 2.26 1.700.50 0.81 1.12 2.960.00 0.00 0.86 1.01

- 0.21 0.18 0.47 0.530.00 2.27 2.03 0.00

5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.00.00

0.25

0.50

0.75

1.00

1.25

1.50

(x10,000,000)

Cassava Stalk

Cassava Rhizome

Sugarcane Tops

Sugarcane Leaves

Fig. 7. Chromatograms of bio-oils produced from the four biomass samples.

Table 4Characteristics of char.

Characteristics This work Ref [40] Ref [41]

Sugarcane leaves Sugarcane tops Cassava stalk Cassava rhizome Radiata pine Rice straw Bamboo sawdust

Elemental composition (wt, as-produced basis)Carbon 53.7 60.9 54.8 64.7 73.5 40.98 35.5Hydrogen 2.2 3.4 2.5 3.0 3.1 2.37 1.81Nitrogen 0.6 1.5 1.0 1.3 N/A 0.35 1.16Sulphur N/A N/A N/A N/A N/A 0.32 0.02Oxygen 4.6 7.9 10.3 5.9 N/A 6.08 26.91Ash 38.9 26.3 31.4 25.1 23.4 49.9 34.6Molecular fomula CH0.5O0.06 CH.67O0.1 CH0.54O0.14 CH0.56O0.07 CH0.51O0.24 CH0.69O0.11 CH0.61O0.57

Heating value (MJ/kg, as-produced basis)HHV 20.1 23.9 20.3 25.0 26.0 17.0 14.4LHV 18.6 22.4 19.1 23.5 25.3 16.5 14.0

A. Pattiya et al. / Energy 44 (2012) 1067e10771076

than those of wood and rice straw bio-oil, but lower than that ofrapeseed bio-oil. Since rapeseed contains some oil in nature. Thehigh heating value of its bio-oil is then not surprising.With the highenergy content, the bio-oil produced in this workmay be used as analternative fuel.

Four bio-oil samples obtained from fast pyrolysis of the fourtypes of biomass at their optimum reactor temperature werefurther examined with GC/MS technique in order to identify theirchemical compounds. The chromatograms are shown in Fig. 7. Ingeneral, the four chromatograms look similar and are difficult todifferentiate. The main 68 peaks were identified and the results inTable 3 shows that different biomass materials gave similarchemical compounds, but with different proportions. Most of theidentified peaks are oxygenated compounds, whereas some peaksare hydrocarbons such as toluene, o-xylene, styrene and 1-tride-cene. The oxygenated compounds included acids, aldehydes,ketones and phenols. It was these acids that caused the low pHvalue of the bio-oil. Since the oxygenated compounds are non-polar, the bio-oil samples are not miscible with petroleum oil.Nevertheless, bio-oil could be blended with petroleum fuel viaemulsification.

3.3. Characteristics of char

Char is a secondary product from fast pyrolysis of biomass andcan be used as an alternative solid fuel. Basic properties of charobtained from pyrolysis of SL, ST, CS and CR at their optimumtemperatures in comparison to those of radiata pine [44], rice straw

and bamboo sawdust [45] are summarised in Table 4. The carboncontents of char produced in this work were in the range of54e56 wt%, which are higher than those of the rice straw andbamboo sawdust char, but lower than that of the pine char. Thehydrogen and nitrogen contents of all chars were not significantlydifferent. The oxygen contents of the SL, ST, CS and CR chars were inthe range of 4.6e10.3 wt%, which are similar to that of the ricestraw char, but much lower than the bamboo char. Ash contentanalysis shows that at least a quarter of the chars was actually ash.The high ash content of the chars implies that the ash in the originalbiomass was concentrated in the form of char after pyrolysis.Table 4 also shows that the heating values of chars produced in thework were higher than those of the rice straw and bamboo chars,but slightly lower than that of the pine char. The chars producedfrom fast pyrolysis could be used as solid fuel for process heat orupgraded to activated carbon. The char may also be used as soilimprovement agent as it contains significant amount of mineralmatter. This application of char is one of the carbon negativetechnologies that can reduce carbon in the atmosphere.

4. Conclusions

Fast pyrolysis of agricultural residues from sugarcane and cas-sava plantations was carried out with a bench-scale free-fall reactorunit in order to investigate the effect of reactor temperature,primary condensation temperature, nitrogen flow rate and exper-imental run duration on yields of the three products including bio-oil, char and non-condensable gas. It was found that the optimum

A. Pattiya et al. / Energy 44 (2012) 1067e1077 1077

reactor temperatures for obtaining highest bio-oil yield for sugar-cane leaves, sugarcane tops, cassava stalk and cassava rhizomewere 400 �C, 350 �C, 450 �C and 400 �C which gave maximum bio-oil yields of 53.3 wt%, 44.1 wt%, 52.3 wt% and 50.3 wt%, respectively.The primary condensation temperature also affected the pyrolysisproduct distribution. The yield of cassava stalk bio-oil wasincreased from 52.3 wt% to a maximum of 69.6 wt% whendecreasing the primary condensation temperature to 10 �C. Inaddition, increasing the nitrogen flow from 0.1 to 1.5 l/min couldincrease bio-oil yield at the expense of char and gas yields. Thestudy of run duration showed that when extending the run timefrom 1 h to 3 h, approximately 8e13 wt% of bio-oil yields werereduced and the gas yield was increased. Some properties of bio-oiland char products were determined and reported. The data showedthat the bio-oil and char would be valuable not only as renewableenergy, but also for the environment.

Acknowledgements

Financial supports from the National Science and TechnologyDevelopment Agency (NSTDA) and the Faculty of Engineering,Mahasarakham University, Thailand, are gratefully acknowledged.Thanks also to Mr. Boonsiri Pidtasaeng, Mr. Chartree Bongkaew, Mr.Pairoad Boonchuay and Mr. Suntorn Suttibak for their researchassistance.

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