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Air gasification of empty fruit bunch for hydrogen-rich gas production in a

fluidized-bed reactor

M.A.A. Mohammed, A. Salmiaton , W.A.K.G. Wan Azlina, M.S. Mohammad Amran, A. Fakhrul-Razi

Department of Chemical & Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

a r t i c l e i n f o

Article history:Received 9 November 2009

Received in revised form 23 August 2010

Accepted 4 October 2010

Available online 30 October 2010

Keywords:

Biomass

Empty fruit bunch

Gasification

Hydrogen

Yield

Energy source

a b s t r a c t

A study on gasification of empty fruit bunch (EFB), a waste of the palm oil industry, was investigated. Thecomposition and particle size distribution of feedstock were determined and the thermal degradation

behaviour was analysed by a thermogravimetric analysis (TGA). Then fluidized bed bench scale gasifica-

tion unit was used to investigate the effect of the operating parameters on EFB air gasification namely

reactor temperature in the range of 7001000 C, feedstock particle size in the range of 0.31.0 mm

and equivalence ratio (ER) in the range of 0.150.35. The main gas species generated, as identified by

a gas chromatography (GC), were H2, CO, CO2 and CH4. With temperature increasing from 700 C to

1000C, the total gas yield was enhanced greatly and reached the maximum value (92 wt.%, on the

raw biomass sample basis) at 1000 C with big portions of H2 (38.02 vol.%) and CO (36.36 vol.%). Feed-

stock particle size showed an influence on the upgrading of H 2, CO and CH4yields. The feedstock particle

size of 0.30.5 mm, was found to obtain a higher H2 yield (33.93 vol.%), and higher LHV of gas product

(15.26 MJ/m3). Equivalence ratio (ER) showed a significant influence on the upgrading of hydrogen pro-

duction and product distribution. The optimum ER (0.25) was found to attain a higher H2 yield

(27.31 vol.%) at 850 C. Due to the low efficiency of bench scale gasification unit the system needs to

be scaling-up. The cost analysis for scale-up EFB gasification unit showed that the hydrogen supply cost

is RM 6.70/kg EFB ($2.11/kg = $0.18/Nm3).

2010 Elsevier Ltd. All rights reserved.

1. Introduction

Dependence on fossil fuels as the main energy sources has led

to serious energy crisis and environmental problems. Therefore,

due to the environmental considerations as well as the increasing

demand for energy in the world, more attention has been paid to

develop new energy sources [1]. Owing to that, there has been

interest in the utilization of biomass for production of environmen-

tal friendly biofuels. As known, biomass is a CO2neutral resource in

the life cycle, while CO2 is a primary contributor to the global

greenhouse effect. Hence, increasing attention is being paid to bio-mass as a substitute for fossil fuel to reduce the global greenhouse

effect, particularly under the commitment of the Kyoto Protocol.

Biomass used as an energy resource can be efficiently achieved

by thermo-chemical conversion technology: pyrolysis, gasification

or combustion. Gasification process is one of the most promising

thermo-chemical conversion routes to recover energy from bio-

mass. During gasification process, biomass is thermal decomposed

to small quantities of char and ash, liquid oil and high production

of gaseous products under limited presence of oxygen following

Eq.(1). The yields of end products of gasification and the composi-

tion of gases are dependent on several parameters including tem-

perature, biomass species, particle size, heating rate, operating

pressure and reactor configuration[2].

Biomass heat! H2 CO CO2 CH4 Hydrocarbon

Char 1

The concern of using biomass in gasification to produce a

hydrogen rich product has been getting particular attention in re-

cent years. The reasons may be attributed to: (1) hydrogen is a

clean and efficient energy source and is expected to take an impor-

tant role in a future energy demand; (2) hydrogen is a safe source

and can be easily stored as a gas or a liquid; (3) hydrogen has good

properties in fuelling engines in automobiles; and (4) most impor-

tant, current and future energy technologies are extensively

increasing the possibility of utilizing hydrogen with economic

acceptance. Apparently, how to force the biomass gasification pro-

cess into shift towards the maximum hydrogen rich end product is

becoming a priority topic[3].

Various types of biofuels can be produced from gasification pro-

cess after catalytically upgrading the syngas by using Fischer

Tropsch (FTS) synthesis and Higher Alcohol synthesis (HAS)

technologies [4]. Through the FTS reaction, syngas can be

0196-8904/$ - see front matter 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.enconman.2010.10.023

Corresponding author. Tel.: +60 3 89466297; fax: +60 3 86567120.

E-mail address: mie@eng.upm.edu.my(A. Salmiaton).

Energy Conversion and Management 52 (2011) 15551561

Contents lists available at ScienceDirect

Energy Conversion and Management

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

http://dx.doi.org/10.1016/j.enconman.2010.10.023mailto:mie@eng.upm.edu.myhttp://dx.doi.org/10.1016/j.enconman.2010.10.023http://www.sciencedirect.com/science/journal/01968904http://www.elsevier.com/locate/enconmanhttp://www.elsevier.com/locate/enconmanhttp://www.sciencedirect.com/science/journal/01968904http://dx.doi.org/10.1016/j.enconman.2010.10.023mailto:mie@eng.upm.edu.myhttp://dx.doi.org/10.1016/j.enconman.2010.10.023

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converted to a wide range of long chain hydrocarbon products, like

gasoline, naphtha, diesel and wax. The long chain hydrocarbons

produced from the FTS reaction are distilled and hydro-cracked be-

fore being used as a liquid transportation fuel [5]. There are also

many types of alcohols such as methanol and ethanol that can be

produced using HAS technology. The syngas produced from gasifi-

cation process will be catalytically converted to alcohols under this

technology. Ethanol is an important renewable liquid fuel for mo-tor vehicles. The production of ethanol from biomass can signifi-

cantly reduce both the dependency on fossil fuel sources and

environmental pollution[6].

Oil palm (Elaeis guianensis) originally originates from West

Africa. It grows well in wet and humid places like Malaysia. In

the present time Malaysia is the worlds largest producer and ex-

porter of palm oil. Its currently accounts for 51% of the world palm

oil production and 62% of the world exports. Palm oil production in

Malaysia has increased from 2.57 million metric tons in 1980 to

17.8 million metric tons in 2009[7]. Beside palm oil availability,

Malaysian palm oil also generates huge quantity of oil palm bio-

mass including oil palm trunks, oil palm fronds, empty fruit

bunches (EFB), shells and fibers in the production of palm oil. There

was annual generation of 9.66, 5.20 and 17.08 million tons for fi-

ber, shell and empty fruit bunches respectively[8]. Oil palm is a

multipurpose plantation and also a prolific producer of biomass

as raw materials for value-added industries[9]. For example, fresh

fruit bunch contains only 21% palm oil, while the rest 67% palm

kernel, 1415% fiber, 67% shell and 23% empty fruit bunch (EFB)

are left as biomass[10].

In Malaysia, there has been a strong interest in the utilization of

oil palm biomass for the production of environmental friendly bio-

fuels. The implementation of biofuels program in Malaysia is in

line with the government policy in ensuring a sustainable develop-

ment of the energy sector as well as promoting a clean environ-

ment. For examples, the government has embarked on the

growth of renewable energy as the fifth fuel after oil, gas, hydro,

and coal, initiated earlier under the Third Outline Perspective Plan

(OPP3), 20002010 [11], and the ninth Malaysian plan (9MP),20062010[12].

Till now, a lot of work has been done and many processes are

being investigated on hydrogen-rich gas production from bio-

masses[1318]. Among them, thermo-chemical processes (gasifi-

cation and pyrolysis) are the most promising and applied

solutions for second generation fuels.

Presently, many research works related to the gasification of

biomass using different operating processes such as types of gasifi-

ers (fixed bed, moving bed and fluidized bed), gasification agents

(air, oxygen, steam or their mixtures) and operating conditions

(temperature, pressure, equivalent ratio (ER)) have been presented

and extensive researches have been conducted on small and

medium size air gasifiers to produce low BTU fuel gas and power

[1926].Gasifying agent is one of the most important parameters in the

gasification process. It plays an important role during the gasifica-

tion reactions. The agent can be air, pure oxygen, steam or their

mixtures. Air is cheap and widely used in the gasification process,

however, it contains large amount of nitrogen, which reduces the

heating value of the syngas produced. On the other hand, if pure

oxygen is used, the heating value of syngas will increase but at

the same time, the operating costs will also increase due to the

oxygen production[27], and the same can be said for using steam

as gasifying agent. The low calorific value syngas produced from air

gasification can be directly utilized as fuel for gas turbines and gas

engines [28] or can used as an industrial feedstock for heat and

power generation. Yet, the condensable organic compounds (tar)

need to be removed using hot gas cleaning method or catalyticreforming of tar.

Currently, oil palm biomass (shell, fiber and EFB) can be con-

verted to the high-value products via thermo-chemical conver-

sion processes. Yang et al. [21] have investigated the use of the

palm oil wastes as a feedstock to produce hydrogen-rich gas via

pyrolysis process in fixed bed reactor. The authors reported that

the palm oil wastes could be ideal biomass sources for biofuels

production The total gas yield was enhanced by increasing reactor

temperature with the maximum

70 wt.% of gas yield achievedper raw biomass sample with good portions of H2 (33.49 vol.%).

Kelly-Yong et al. [29] have studied the thermodynamic analysis

of hydrogen production from oil palm biomass in gasification

reaction using supercritical water (SCW) technology. The authors

reported that the utilization of SCW medium in biomass gasifica-

tion can directly deal with high moisture content of biomass

(>50%). Therefore, preliminary treatment such as biomass drying

could be avoided which will automatically reduce the operating

cost of the process. In addition, the feasibility study of obtaining

hydrogen from palm oil biomass (0.117 kg H2kg1 biomass) was

obtained. Abdullah et al. [30] investigated the fast pyrolysis of

EFB using 150 g/h fluidized-bed reactor to produce bio-oil. The re-

sults showed that the maximum bio-oil production was 55.1 wt.%

at 450C at only 1.03 s vapor residence time.

This study focuses on using EFB, a waste from the palm oil

industry as a feedstock material using air gasification process in

bench scale fluidized bed gasifier. Different operation conditions

namely reactor temperature, feedstock particle size and equiva-

lence ratio will be investigated to achieve an improved perfor-

mance of EFB conversion to energy with a high yield of

hydrogen-rich gas.

2. Materials and methods

2.1. Feedstock preparation and properties

The EFB sample investigated in this study was collected from

Seri Ulu Langat palm oil mill, Dengkil, Selangor. EFB used in thiswork is the biomass remaining as a by-product of industrial pro-

cess after removal of the nuts. Samples received were relatively

dry having less than 10 wt.% moisture, and were in the form of

whole bunches. Particle size reduction was required to allow gasi-

fication of the EFB on the available 600 g/h reactor. The bunches

were first manually chopped into small pieces that could be fed

in a shredder. After that, a Fritsch grinder with a screen size of

1.0 mm was used to obtain the feedstock size of less than

1.0 mm. The distribution of feed particle size after grinding is given

inTable 1. After extensive feeding trials, it is found that only par-

ticles between 0.3 and 1.0 mm were easily fed. Both the size frac-

tion below and above this range frequently led to blockage of the

available feeder.

The proximate and elemental analyses were carried out in aTGA (Mettler-Toledo TGA/SDTA 851) and CHNS/O analyzer (LECO

CHNS932), respectively. The results are listed inTable 2. EFB had

a very high volatile content (>80 wt.%) and low amounts of fixed

carbon (

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environmental friendly, with trace amounts of nitrogen, sulfur and

mineral matter.

3. Experimental procedure

A fluidized bed bench scale gasification unit operating at atmo-

spheric pressure was employed for all runs. Fig. 1shows a sche-

matic diagram of this unit, which consists of three main systems:

reactor (gasification reactor and heating furnace), condenser and

purification (condenser, glass wool filter and dryer) and gas storage(gasbags). The reactor is a cylindrical configuration made of stain-

less steel with a length of 600 mm and a diameter of 40 mm. Three

thermocouples were inserted in the middle of the heating furnace,

middle of the reactor tube and bottom of the reactor tube, respec-

tively. Biomass was fed into the reactor by a feeder on the top of

the reactor, which were continuously carried out at a constant flow

rate. The feeding capacity of biomass was 10 g/min. The heating

medium in the reactor was inert sand of size between 0.3 and

0.5 mm. The fluidizing gas was air, entering from the base of the

reactor.

The condensable part of the product gas was collected from the

ice water condenser, whereas the incondensable gases leaved the

system through glass wool/silica gel filter and then were collected

by gasbags for gas chromatography (GC) analysis. The tar productwas trapped in the water cooler, ice condenser walls and glass

wool/silica gel filter. Dichloromethane (DCM) was used to remove

the tar from condenser walls and filter. The dissolved product was

then filtered using filter paper and the filtrate was heated in an

oven at 70C for about 2 h to evaporate any rising solution. The

heated filtrate was then weighed to get the weight of tar.

The yield of the products was quantified as mass basis. The solid

product called charcoal was removed from the reactor and sepa-

rated from the sand bed then weighed to get the solid mass. The

yield of the total product gas was then calculated by difference.

3.1. Product gas analysis

0.5 mL of the product gas was analyzed in gas chromatography(GC) Agilent Technologies model HP6890 N with TCD and FID

detectors. A 30 m HP-Molesieve capillary column was used to sep-

arate the permanent gases. The internal diameter and film thick-

ness of the column were 0.53 mm and 0.5lm, respectively. The

oven temperature was set at 70C and carrier gas flow rate (Argon)

was 6 mL/min. The splitless inlet and TCD detector temperature

were 60 and 200 C, respectively. The TCD was calibrated with

standard gas (Air Product, Malaysia) mixture containing CO, CO2,

H2 and CH4 in nitrogen at periodic intervals.

4. Results and discussion

4.1. Thermogravimetric analysis of EFB

The thermogravimetric analysis (TGA) was performed under

10 mL/min air with a heating rate of 10 C/min. The thermal degra-

dation characteristics of different particle size dried feedstock are

displayed inFig. 2by thermogravimetry (TG) and differential ther-

mogravimetry curves (DTG), respectively. The EFB samples showed

a small DTG peaks around 100 C, which are indicative to the mois-

Table 2

Properties of EFB.

Component Measured (wt.%)

Cellulose 22.24

Hemicellulose 20.58

Lignin 30.45

Asha 8.28

Extractivesa 18.45

Elemental analysis

C 46.62

H 6.45

N 1.21

S 0.035

Ob 45.66

Proximate analysis

Mad 5.18

Vad 82.58

Ad 3.45

FCad 8.79

Calorific value (MJ/kg) 17.02

M: moisture;V: volatile matters;A: ash;FC: fixed carbon; ad:

on air dried basis; d: on dry basis.a Remaining value obtained from Acid Detergent Fiber

(ADF), Neutral Detergent Fiber (NDF) and Acid Detergent

Lignin (ADL) analysis method.b The oxygen content was determined by difference.

Fig. 1. Schematic diagram of biomass air gasification in a fluidized bed: (1) lab-scale gratifier, (2) electric furnace, (3) air pump, (4) biomass feeder, (5) flange, (6)

thermocouples, (7) air distributor, (8) temperature recorder, (9) gas discharge, (10) water cooler, (11) ice trap, (12) cooling water supply, (13) glass wool filter, (14) fuel gassampling point, and (15) gas flow meter.

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ture content, followed by big peaks around 300 C, which are indic-

ative to the decomposition of cellulose and hemicellulose, while

the humps apparent around 450C are indicative to the decompo-

sition of lignin. Similar weight loss rate was observed in other re-

searches [32,33]. The distinction between hemicellulose and

cellulose breakdowns was not fully understood but it had been

established that hemicellulose broke down at lower temperature

compared to cellulose[34].

4.2. Effect of reactor bed temperature on product yields

The yields of final products from EFB gasification under differ-

ent temperatures are shown inFig. 3. As shown inFig. 3a with tem-

perature increasing from 700 to 1000C, the total gas yields

increased sharply from 62.68 to 91.7 wt.%, while liquid, char and

tar yields reduced gradually. Meanwhile, varying temperature

showed a great influence on gas product components. The main

gas products are H2, CO, CO2, CH4and some C2hydrocarbons traces

(C2H4 and C2H6).

As shown in Fig. 3b, H2 content increased progressively from

10.27 to 38.02 vol.% as temperature increased from 700 to

1000 C. CH4 yield also increased from 5.84 to 14.72 vol.%., whilstCO2 content decreased in general with temperature increasing,

particularly at 1000C. The CO yield was initially increased from

21.87 to 33.35 vol.% as temperature increased to 800C, then de-

creased to 33.08 vol.% at temperature 900C, before it increased

again to 36.36 vol.% as temperature continuously increased to

1000C. The C2H4 and C2H6 yields were relatively small and the

influence of temperature was insignificant. The thermal cracking

of gas-phase hydrocarbons at high temperature might explain

the variation of gas product distribution observed [35]. At high

furnace temperature, the gas species generated from biomass at

pyrolysis zone could undergo further reactions (secondary reac-

tions) such as tar cracking and shifting reaction, leading to muchmore incondensable gases (including H2) generated. Therefore,

the total yield of gases products increased significantly as tem-

perature increased from 700 to 1000 C. The main reactions in-

volved could be expressed using the following Eqs. (2)(10)

[35,36]. Among them, Eqs. (2)(6) are principle or heterogenous

gasification reactions whilst Eqs. (7)(11) are homogenous and

secondary reactions. In terms of increasing H2 production, Eqs.

(5), (7)(10) are the main reactions of interest for EFB gasification

at atmospheric pressure and temperature between 700 and

1000C. The other gases component might increase or decrease

with the occurring of secondary reactions. As a result, more H2can be obtained when secondary reactions occur significantly.

From the above analysis, it can be concluded that higher temper-

ature (1000C) is favorable for thermal cracking of tar and shiftreaction.

Fig. 2. Thermal degradation characteristics of EFB: (a) thermogravimetric analysisof EFB, (b) differential thermogravimetric analysis of EFB.

Fig. 3. Effect of temperature on EFB gasification yield: (a) effect of temperature on

product yield, (b) effect of temperature on product gas composition.

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C O2! CO2 2

C 1=2O2! CO 3

C CO2! 2CO 4

C H2Og !CO H2 5

C 2H2! CH4 6

CO H2O!CO2 H2 7

CH4 H2Og ! CO 3H2 8

CH4 CO2! 2CO 2H2 9

Tar H2Og ! CO H2O CH4 H2 CmHn 10

CmHn nH2O! nCO n m=2H2 11

The lower heating value (LHV, MJ/m3) of the gas products can be

calculated using the following equation[21,35].

LHV 30:0xCO 25:7xH2 85:4xCH4 151:3xCnHmx4:2 12

CO, H2, CH4and CnHmin the above equation are the molar ratio

of the CO, H2, CH4 and other hydrocarbon (C2H2 and C2H6) in the

gas product. As shown in Fig. 3a, the heating value of total gas

products increase steadily as the temperature increases. At

1000 C, LHV of gas products reached 15.55 MJ/m3, which belongs

to be medium level of heat values for gas fuels that can be directly

used for gas engine, gas turbine or boiler for power generation.

Also it can be used for the chemical formation of methanol and

methane[31].

4.3. Effect of feedstock particle size on product yields

The second series of experiment was performed to establish the

effect of feedstock particle size on the EFB gasification productyields. In this study, the experiments were conducted by using

three different feedstock particle size ranges, namely

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the analysis on the experimental results of varying ER, it can be

understood that the optimum value for ER is 0.25, which maxi-

mum hydrogen content can be obtained.

5. Cost analysis

Performance data of fluidized bed biomass gasifier system used

in this study is given inTable 3. Due to the low efficiency of benchscale gasification unit, the system needs to be scaling-up. The prin-

cipal costs of H2production from EFB biomass using fluidized bed

gasifier are estimated as follows: It is assumed that 6 kg/h (144 kg/

d) of EFB would be the raw material for gasification process to pro-

duce 0.052 kg H2/kg EFB (7.48 kg H2/d = 84.13 Nm3/d). The capital

cost of this system covers fluidized bed gasifier, furnace and con-

struction expenditure. Costs of operation, interest, maintenanceand other expenses are assumed as shown in Table 4.

Based on the operating parameters and data of capital cost, the

calculation result of H2product cost from this system is RM 6.7 for

every kilograms of EFB which is equal to $2.11/kg EFB ($0.18/Nm3).

For comparison,Table 5presents other researchers cost analy-

sis on H2 through different processes.

6. Conclusions

In this study, air gasification of EFB, one of the most abundant

biomass found in Malaysia, was carried out in bench scale fluidized

bed gasifier. The operating parameters namely reactor tempera-

ture, biomass particle size and equivalence ratio were tested todetermine their effects on total products yields, product gas com-

position and LHV gas. The main products of EFB air gasification

were solid charcoal, liquid oil, tar and hydrogen-rich gas product.

Temperature was an important factor in this process. As the tem-

perature increased from 700 to 1000 C the gas yield increased sig-

nificantly whilst solid, liquid and tar yields progressively

decreased. The gas products mainly consisted of H2, CO, CO2 and

CH4. High temperature is favorable for the increasing gas products

including H2, CO, CH4. The LHV gas increased with temperature and

reached to 15.55 MJ/m3 at 1000C. The EFB particle size had an

influence on the total gas yield and gas composition; smaller EFB

particle size produced more CH4, CO and less CO2. On top of that,

LHV gas increased with smaller EFB particle size. ER had complex

effect on the gasification products. The ER of 0.25 was found tobe optimum to yield a maximum H2 production of 27.31 vol.% at

0

10

20

30

40

50

0.1 0.15 0.2 0.25 0.3 0.35 0.4

Yield,

Vol.%

ER

H2 CO CH4 CO2

(a)

(b)

Fig. 5. Effect of equivalence ratio (ER) on EFB gasification yield at temperature of

850C and feedstock particle size of 0.30.5 mm: (a) effect of equivalence ratio (ER)

on product yield, (b) effect of equivalence ratio (ER) on product gas composition.

Table 3

Performance data on fluidized bed EFB gasifier.

Feed rate of EFB (kg/h) 6.0

Feed rate of air (Nm3/h) 7.2

Gasifier temperature (C) 850

Gas composition (vol.%)

H2 26.70

CO 33.36

CH4 16.04

CO2 26.11

LHV of gas (MJ/m3) 12.84

Table 4

Basis of cost analysis.

Items Data Note

Capacity EFB: 1 44 kg/d

(51.84 t/y)

H2: 7.488 kg/d

(2.69 t/y)

Capital Gasifier RM 3119

Furnace RM5865Construction

expenditure

RM1746

Total RM10730

Operation Feed RM2592 RM50/t, including

collection and

transportation

Electricity RM3000/

y

RM0.28/kWh

Interest 10% of capital cost RM1073/

y

Maintenance 5% of capital cost RM536.5/

y

Other 1% of capital cost RM107.3/

y

H2 product

cost

RM 6.7/kg = $2.11/

kg: $0.18/Nm3

Table 5

Hydrogen cost through different process.

H2 cost Process Reference

$10/ kg Electrolyzed hyd rogen [42]

$4.28/kg Biomass pyrolysis with high-pressure [43]

$1.69/kg Biomass gasification with CO-shift [44]

$2.11/kg EFB air gasification This study

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850C in this work. Based on the operating parameters and data of

capital cost, the estimation cost of H2from this system is RM 6.7/kg

EFB ($2.11/kg EFB = $0.18/Nm3).

Acknowledgements

The authors would like to thank Department of Chemical &

Environmental Engineering, Faculty of Engineering, Universiti Pu-tra Malaysia for financial support on this project.

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