www.elsevier.com/locate/enconman

Energy Conversion and Management 48 (2007) 1132–1139

Bio-syngas production from biomass catalytic gasification

Pengmei Lv a,*, Zhenhong Yuan a, Chuangzhi Wu a, Longlong Ma a,Yong Chen a, Noritatsu Tsubaki b

a Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, No. 2 Nengyuan Road, Tianhe, Wushan,

Guangzhou 510640, People’s Republic of Chinab School of Engineering, Nagoya University, Gofuku, Toyama, Japan

Received 26 December 2004; received in revised form 23 April 2006; accepted 29 October 2006Available online 12 December 2006

Abstract

A promising application for biomass is liquid fuel synthesis, such as methanol or dimethyl ether (DME). Previous studies have studiedsyngas production from biomass-derived char, oil and gas. This study intends to explore the technology of syngas production from directbiomass gasification, which may be more economically viable. The ratio of H2/CO is an important factor that affects the performance ofthis process. In this study, the characteristics of biomass gasification gas, such as H2/CO and tar yield, as well as its potential for liquidfuel synthesis is explored. A fluidized bed gasifier and a downstream fixed bed are employed as the reactors. Two kinds of catalysts: dolo-mite and nickel based catalyst are applied, and they are used in the fluidized bed and fixed bed, respectively. The gasifying agent used isan air-steam mixture. The main variables studied are temperature and weight hourly space velocity in the fixed bed reactor. Over theranges of operating conditions examined, the maximum H2 content reaches 52.47 vol%, while the ratio of H2/CO varies between 1.87and 4.45. The results indicate that an appropriate temperature (750 �C for the current study) and more catalyst are favorable for gettinga higher H2/CO ratio. Using a simple first order kinetic model for the overall tar removal reaction, the apparent activation energies andpre-exponential factors are obtained for nickel based catalysts. The results indicate that biomass gasification gas has great potential forliquid fuel synthesis after further processing.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Syngas; Biomass; Catalytic gasification

1. Introduction

Syngas plays an important role as an intermediate in theproduction of several industrial products, such as Fischer–Tropsch liquids, methanol and ammonia. Currently, syn-gas is produced from fossil fuels, mainly coal, natural gasand naphtha. Syngas from renewable resources, such asbiomass, exhibits a promising prospective [1–7]. This isbecause biomass is a CO2 neutral resource and is distrib-uted extensively in the world. Several biomass to methanoldemonstration projects have been developed recently, suchas the Hynol project in the United States, the BioMeet and

0196-8904/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.enconman.2006.10.014

* Corresponding author. Tel.: +86 20 87057729; fax: +86 20 87057737.E-mail address: lvpm@ms.giec.ac.cn (P. Lv).

Bio-Fuels projects in Sweden and the BGMSS project inJapan [8–10]. Although more and more interest has beenfocused on this subject, little study was found to addressthis topic [11–14]. Classifying the literature involved in thissubject, it can be found that three different routes of syngasfrom biomass were studied. They were syngas from bio-mass-derived oil [11], syngas from biomass-derived char[12,13] and syngas from reforming of biomass gasificationgas [14]. Panigrahi et al. [11] explored synthesis gas produc-tion from steam gasification of biomass-derived oil. Differ-ent gasifying agents, mixtures of CO2 and N2, H2, N2 andsteam were used. In their study, syngas (H2 + CO) rangedfrom 75 to 80 mol%. Chaudhari et al. [12,13] investigatedsynthesis gas production from biomass-derived char. Theirobjective was to provide information on different optimumconditions for producing gases for different applications.

Nomenclature

k kinetic constant for tar elimination (m3 (Tb,wet)/kg h)

A pre-exponential factor for k (m3 (Tb,wet)/kg h)R gas constant (kJ/mol K)E apparent activation energy for overall tar re-

moval (kJ/mol)Q gas flow rate [m3 (Tb,wet)/h]T = Tb temperature measured in center of fixed bed (�C)

X tar conversion, dimensionlessW weight of catalyst in fixed bed (kg)

Greek Symbols

o tar concentration in flue gas (kg/m3)s space time, defined as W/Q [kg h/m3(Tb,wet)]

P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139 1133

Wang et al. [14] studied syngas from reforming of biomassgasification gas by adding of biogas.

From the above discussion, it was easily discovered thatfew studies referred to syngas from direct gasification ofbiomass. Hence, there is a need for a systematic study inthis direction. Therefore, the purpose of this study is to testthe feasibility of syngas from direct biomass gasification,which is a more compact process because pure biomassair gasification produces a gas with a low H2/CO ratio,which is not suitable for further synthesis of liquid fuel.Therefore, gasifying agents air and steam were used in thisstudy and common catalysts were applied to improve theH2/CO ratio as well as to decrease tar yield.

2. Experimental section

2.1. Feed materials and catalysts

Pine sawdust obtained from a timber mill in GuangzhouCity, China, was used as the feedstock for experimentalruns. The particle size of this pine sawdust is between 0.3and 0.45 mm. Its proximate and ultimate analyses arereported in Table 1.

Calcined dolomite and nickel based catalysts were usedin the experiments, which were proved to be quite active fortar elimination [15–17]. The dolomite was first crushed andsieved to obtain a fraction with a particle sized 0.3–0.45 mm and then calcined in air at 900 �C for 4 h. Itschemical composition is presented in Table 2. Nickel based

Table 1Proximate and ultimate analysis of pine sawdust

Moisture content (wt% wet basis) 8Higher heating value (MJ/kg) 20.2Proximate analysis (wt% dry basis)

Volatile matter 81.0Fixed carbon 18.5Ash 0.5Ultimate analysis (wt% dry basis)

C 51.26H 5.54O 42.29N 0.18S 0.23

catalysts of Z409R were used in the catalytic reactor, whichwere produced in Qilu PetroChemical Company, Shan-dong Province, China. Z409R is annular with a size of /16 · /6 · 6.0–6.8 mm and a composition of NiO P22 wt%, K2O of 6.5 ± 0.3 wt%.

2.2. Apparatus

The tests were performed in an atmospheric pressure,indirectly heated, fluidized bed gasification system, whichis shown schematically in Fig. 1. Its major componentsare: a fluidized bed gasifier, a biomass feeder, a steam gen-erator, an air compressor, a cyclone and a catalytic fixedbed reactor.

The reactor is made of 1Cr18Ni9Ti stainless steel pipeand is externally heated by two electric furnaces. The totalheight of the reactor is 1400 mm, with a bed diameter of40 mm and a freeboard diameter of 60 mm. Along the totalheight of the reactor, there are 5 temperature and pressuretaps for temperature and pressure detection. Below thereactor, one air distributor is installed for better air distri-bution. The distributor is 3 mm in thickness and 25 holes(i.d. 1 mm) are perforated uniformly in it. The biomass isfed into the reactor through one screw feeder driven by avariable speed metering motor. Air is used as the fluidizingagent and comes from the air compressor. Before the airenters the reactor, it is preheated to 65 �C for better perfor-mance. The steam of 154 �C is produced in a steam gener-ator (Model SZ0.015-0.40, Guangzhou Zhongli BoilersAuxiliary Machine Co., Ltd., Guangdong, China). Beforethe steam flows into the reactor above the biomass feedingpoint, it is metered by a steam flow meter. The producedgas flow exits the reactor, then passes through a cyclone,which is heated to 200 �C to prevent the tar contained inthe gas from condensing in it. The fixed bed reactor isexternally heated by an electric furnace. Its length is400 mm with an inner diameter of 38.5 mm.

Table 2Chemical composition of uncalcined dolomite (wt%)

Sample CaO MgO SiO2 Al2O3 Fe2O3 Loss Total

Dolomite 31.2 19.5 2.35 0.34 0.24 46.15 99.78

Air distributor

Gasflowmeter

Aircompressor

Hopper

GasifierCyclone

Fixed-bedreactor

Valve Toexhaust burner

Gas and tar sampling

Steamflowmeter

Heators

Gas and tar sampling

Steamgenerator

T,P

T

T

T P

T

T,P

T

Fig. 1. Schematic diagram of biomass catalytic gasification for syngas production.

1134 P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139

Prior to each test, an amount of 120 g/(kg h�1) bio-mass calcined dolomite mixed with 30 g silica sand (0.2–0.3 mm) were put in the gasifier. Since calcined dolomiteis soft, it erodes during the test and is eluted out of thebed with the flue exit gas. Therefore, some calcined dolo-mite was mixed with the pine sawdust carefully by handand continuously fed into the gasifier to attain a steadystate. The feeding rate of calcined dolomite was deter-mined by preliminary test. At the end of each test, cal-cined dolomite left in the gasifier is separated andmeasured. Thus, the weight percent of calcined dolomitein the gasifier bed during operation can be known, andit is about 65–71 wt% over the ranges of experimentalconditions examined.

Electricheating Qu

Volume flow meter

Silica gel

Fig. 2. Schematic diagram

The measurement accuracy for the gas flow meter, tem-perature sensor, manometer, steam flow meter is ±0.06N m3/h, ±10 �C, ±0.25 kPa, ±0.05 kg/h, respectively.

To ensure the reliability of the test data, each experi-ment was repeated 2 times and the results had good agree-ment. The data reported in this paper is average values ofthe two times.

2.3. Gas and tar analysis

The cool, dry, clean gas was sampled using gas bags andanalyzed on a gas chromatograph (Model GC-2010, Shi-madzu, Japan), which is fitted with a GS carbon plotcolumn (30 m · 0.530 mm · 3.00 lm), flame ionization

artz fiber filter

Steel tube

Ice bath Cool bath

Gas washing bottles content CH2C 2

of tar sampling system.

650 700 750 800 8503.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

Val

ue o

f H2/

CO

Temperature (˚)

Fig. 3. Effect of temperature on the value of H2/CO.

P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139 1135

detector (FID) and thermal conductivity detector (TCD),and standard gas mixtures are used for quantitativecalibration.

The tar sampling line is shown in Fig. 2. Dichlorometh-ane cooled to approximately �10 �C is used to condenseand collect the tar.

A gas chromatograph HP-4890 is used to analyze the tarsample. The operating conditions are: 30 m · 0.25 mm ·0.25 lm, HP-5 capillary column; carrier gas, N2; tempera-ture program: 75 �C (hold 5 min) to 285 �C at 3 �C/min(hold 40 min); injector and detector temperature, 280 �C.

3. Results and discussion

3.1. Effects of different fixed bed reactor temperature

As listed in Table 3, run no. 1, the operating conditionsin the fluidized bed were kept constant, while the tempera-ture in the catalytic reactor was varied to perform a seriesof tests. In Table 3, equivalence ratio is defined as theactual oxygen to fuel ratio divided by the stoichiometricoxygen to fuel ratio needed for complete combustion.The experimental results are presented in Table 4.

Table 4 shows that the content of H2 exhibits an increas-ing trend with temperature. This is an expected resultbecause most H2 production reactions are endothermic.The content of CH4 decreases with temperature because ahigher temperature strengthens the steam reforming reac-tion of CH4. The content of CO first decreases and thenincreases with temperature, which indicates reactions (1)–(4) happen simultaneously in the process. As a result ofthe variation trend of H2 and CO, the ratio of H2/CO also

Table 3Operating conditions in the fluidized bed reactor

Run no. 1 2 R

Biomass feed rate (kg/h) 0.47 0.54 SAir (N m3/h) 0.65 0.65 CSteam (kg/h) 0.4 0.4 CEquivalence ratio 0.30 0.25 GGasifier bed outlet gas composition(dry, inert-free, vol%)

Run no. H2 CH4 CO CO2 C2

1 38.38 7.02 24.89 27.62 2.092 38.13 7.48 26.06 26.20 2.14

Table 4Experimental results of different fixed bed temperature at the condition of run

Reactor temperature (�C) 650 70

Dry, inert-free, gas composition (vol%)H2 46.28 4CH4 5.24CO 14.89 1CO2 32.16 3C2 1.42Gas yield (N m3/kg biomass) (wet basis) 1.87Tar yield (g/kg biomass) (wet basis) 6.43

first increases and then decreases with temperature andreaches the maximum value of 4.45 at the temperature of750 �C, as shown in Fig. 3. Fig. 3 indicates that the valueof H2/CO ranges between 3.11 and 4.45, a quite high ratio.Fig. 3 also indicates that temperature is an important fac-tor for controlling H2/CO ratio

COþH2O ¼ CO2 þH2 þ 41 kJ=mol ð1ÞCH4 þH2O ¼ COþ 3H2 � 206 kJ=mol ð2ÞCþH2O ¼ COþH2 � 131 kJ=mol ð3ÞCþ CO2 ¼ 2CO� 172 kJ=mol ð4Þ

un no. 1 2

team-to-biomass ratio 0.85 0.75alcined dolomite feeding rate (g/h) 14 16alcined dolomite in the gasifier (g) 56 65asifier bed temperature (�C) 800 800

Gas yield (N m3/kg biomass, wet basis) Tar yield (g/kg biomass)

1.56 13.851.54 19.05

no. 1

0 750 800 850

9.33 49.65 50.23 52.474.89 4.37 4.3 2.92.28 11.15 12.3 14.822.81 34.37 32.56 29.650.69 0.46 0.6 0.162.12 2.15 2.24 2.415.53 4.42 4.29 2.35

Table 5Experimental results of different reactor WHSV (h�1) at the condition of run no. 2, Tb = 700 �C

WHSV (h�1) 10.7 7.2 5.4 4.3 3.6 3.1 2.7

Dry, inert-free, gas composition (vol%)H2 42.84 46.67 47.61 47.62 47.84 48.93 49.09CH4 6.59 5.67 5.18 4.79 5.12 5.14 4.72CO 20.35 17.35 16.44 16.87 15.93 15.33 14.78CO2 28.62 29.42 30.12 30.08 30.18 29.99 30.73C2 1.61 0.9 0.66 0.65 0.94 0.62 0.64Gas yield (N m3/kg biomass) (wet basis) 1.86 1.97 2.01 2.09 2.13 2.19 2.22

1136 P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139

3.2. Experimental results of different Weight Hourly Space

Velocity (WHSV)

Weight hourly space velocity (WHSV) is defined as themass flow rate of biomass fed to the gasifier divided bythe mass of catalyst in the catalytic reactor. Keeping theoperating conditions listed in Table 3, run no. 2 constant,the experimental results of different WHSVs in the catalyticreactor is presented in Table 5. As shown in Table 5, thecontent of H2 shows an upward trend with increasing res-idence time, while the content of CH4 and CO decreaseswith increasing residence time. The content of CO2 has lit-

2 4 6 8 10 12

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4 Tb=700˚ Tb=800˚

Val

ue o

f H2/

CO

Weight Hourly Space Velocity (h-1)

Fig. 4. Effect of WHSV on the value of H2/CO.

Table 6Comparison of different routes for bio-syngas production

Process A [11] B [13]

Feedstock Biomass-derived oil BiomaGasifying agent H2 and N2 SteamReforming method – –Use of catalyst No NoTypical gas composition (dry, inert-free,

mol%)H2 33.3 70.0CO 29.0 14.8CO2 4.9 14.1CH4 17.0 1.1Others 15.8 –Range of H2/CO 1.15–2.41 4.0–7.

tle change. The above phenomena indicate that applyingmore catalysts is favorable for H2 production.

The value of H2/CO for two different temperatures inthe fixed bed reactor is shown in Fig. 4. For the tempera-tures of 700 �C and 800 �C, the values of H2/CO varybetween 2.11 and 3.32, 1.87 and 2.78, respectively. Fig. 4indicates that the ratio of H2/CO increases with residencetime. This is an obvious result, which can be seen fromTable 5. Another phenomena found from Fig. 4 is thatthe ratio of H2/CO at 700 �C is higher than that at800 �C. This result is in accordance with the conclusiondrawn from Fig. 3. That is, there exists a maximum valueof H2/CO for the different temperatures. This is possiblycaused by the water gas shift reaction (1) being exothermic;so a higher temperature is not favorable for CO consump-tion, which lowers the CO transformation rate, whichresults in a smaller value of H2/CO.

Observing Fig. 4, we can also find that there appears anextraordinary decrease in the H2/CO ratio at WHSV justhigher than 4 h�1. This can be explained by the residencetime being shorter than the minimum time needed for somesecondary reactions of biomass gasification gas to proceedwhen WHSV is higher than 4 h�1. This results in a slightincrease of H2 content and, thus, makes a quite small incre-ment of H2/CO ratio when WHSV is higher than 4 h�1.

3.3. Comparison of different routes for bio-syngas production

Table 6 lists a comparison of the different routes for bio-syngas production and process D represents this study. AsTable 6 indicates, process A yields the least hydrogen,

C [14] D

ss-derived char Biomass-derived gas BiomassAir-steam Air-steamBiogas or CH4 reforming –Yes Yes

57.64 52.4736.62 14.823.07 29.652.38 2.9– 0.16

0 1.42–1.57 1.87–4.45

P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139 1137

while process B produces a maximum H2 content andthereby the highest H2/CO ratio. Processes C and D pro-duce comparable H2 quantities. From Table 6, we canknow that the H2/CO ratio is quite high from direct bio-mass catalytic gasification. Process D has the highest con-tent of CO2, which is caused by the catalytic activity ofnickel catalysts on the water gas shift reaction (1). Thiscan be settled by controlling operation conditions and

Fig. 5. Gas chromatogram of tar samp

Fig. 6. Gas chromatogram of tar samp

modifying the nickel catalyst to make it have low selectivityon the WGSR. The advantage of process D is that it pro-duces syngas in one step, while the other processes needtwo steps. This means it has more compact equipmentand may be more economically viable.

Based on the above analysis, it can be concluded thatbiomass catalytic gasification has great potential for syngasproduction and has a good economic outlook.

le in the inlet of fixed bed reactor.

le in the exit of fixed bed reactor.

0.00090 0.00095 0.00100 0.00105 0.00110

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

ln(k

)

1/T(1/K)

Fig. 7. Arrhenius plot for tar catalytic cracking.

1138 P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139

3.4. Tar yield analysis and kinetic model construction for tarcracking

Figs. 5 and 6 show the gas chromatogram of tar samplestaken from the inlet and outlet of the fixed bed reactor,respectively. It is obvious that both the species and thequantity of tar are reduced greatly in the presence of nickelbased catalysts.

Although there are hundreds of species in the tar sam-ple, in order to simplify the analysis, all the species are trea-ted as a single one lump. This approach has been acceptedby many institutions working worldwide in catalytic hotgas cleaning [18]. It uses the following single first orderkinetic equation:

� d@

dt¼ k@ ð5Þ

which can be used in integrated form, working under pis-ton or plug flow conditions, as

k ¼ ½� lnð1� X Þ�=s ð6ÞAlso, for k, it abides by the Arrhenius equation as

k ¼ A expð�E=RT Þ ð7ÞEq. (7) can be further transformed as

lnðkÞ ¼ lnðAÞ þ �ER

� �1

Tð8Þ

Eq. (8) is linear. By applying k (determined by Eq. (6)) andT to it; the values of E and A can be determined. A calcu-lation result for the condition listed in Table 4 is presentedin Fig. 7, which shows good linearity. The E and A valuesdetermined by Fig. 7 are 51 kJ/mol and 14476 (m3 (Tb,wet)/kg h), respectively. This value of E is in near agreementwith Aznar et al.’s experimental data, 58 kJ/mol [18].

4. Conclusion

The results show that quite a high ratio of H2/CO, rang-ing between 1.87 and 4.45, can be obtained from biomass

catalytic gasification, which is favorable for methanol orDME synthesis. However, besides H2 and CO, there is alsoa lot of CO2 and CH4 in the gases, which needs to bedecreased through modifying the catalysts and controllingoperating conditions. The maximum H2 content reaches52.47 vol%. An appropriate temperature (750 �C for thecurrent study) and more catalyst are more favorable forgetting a higher H2/CO ratio.

From the comparison of this technology with others, itcan be seen that great potential exists for syngas produc-tion from direct biomass gasification.

A single one lump model is perfect for tar destructionanalysis. Applying this model, E and A can be determinedas 51 kJ/mol and 14476 (m3 (Tb,wet)/kg h), respectively.

Acknowledgements

The financial support received from the National Natu-ral Science Foundation of China (Project No. 50576100),Guangdong Province Key Laboratory Open Foundation(Project No. 50610117) and Guangdong Province NaturalScience Foundation (Project No. 003045) is gratefullyappreciated.

References

[1] Bridgwater AV, Double JM. Production costs of liquid fuel frombiomass. Fuel 1991;70(10):1209–24.

[2] Dong Y, Steinberg M. Hynol—an economic process for methanolproduction from biomass and natural gas with reduced CO2 emission.Int J Hydrogen Energy 1997;22(10–11):971–7.

[3] Hamelinck CN, Faaij APC. Future prospects for production ofmethanol and hydrogen from biomass. J Power Sources2002;111(1):1–22.

[4] Chmielniak T, Sciazko M. Co-gasification of biomass andcoal for methanol synthesis. Appl Energy 2003;74(3–4): 393–403.

[5] Tijmensen MJA, Faaij APC, Hamelinck CN, van Hardeveld MRM.Exploration of the possibilities for production of Fischer–Tropschliquids and power via biomass gasification. Biomass Bioenergy2002;23(2):129–52.

[6] Faaij A, Hamelinck C, Tijmensen M. Long term perspectives forproduction of fuels from biomass; integrated assessment and R&Dpriorities – preliminary results. In: Kyritsis S et al., editors. In:Proceedings of the first world conference on biomass for energyand industry. London, UK: James & James Ltd., 2001. vol. 1/2,p. 687.

[7] Larson ED, Jin H. Biomass conversion to Fischer–Tropsch liquids:preliminary energy balances. In: Overend R, Chornet E, editors.Proceedings of the fourth biomass conference of the Ameri-cas. UK: Elsevier Science Kidlington; 1999. p. 43.

[8] Norbeck JM, Johnson K. http://www.methanol.org/pdf/Hynolexec.pdf, 2000.

[9] Brandberg ARL, Ekbom T. http://www.ecotraffic.se/pdf/isafxii.pdf.[10] Mitsubishi Heavy Industries. Biomass gasification methanol synthesis

system. http://www.mhi.co.jp/power/e_power/techno/biomass/,April, 2006.

[11] Panigrahi S, Dalai AK, Chaudhari ST, Bakhshi NN. Synthesis gasproduction from steam gasification of biomass-derived oil. EnergyFuels 2003;17(3):637–42.

[12] Chaudhari ST, Bej SK, Bakhshi NN, Dalai AK. Steam gasification ofbiomass-derived char for the production of carbon monoxide-richsynthesis gas. Energy Fuels 2001;15(3):736–42.

P. Lv et al. / Energy Conversion and Management 48 (2007) 1132–1139 1139

[13] Chaudhari ST, Dalai AK, Bakhshi NN. Production of hydrogen and/or syngas (H2 + CO) via steam gasification of biomass-derived chars.Energy Fuels 2003;17(4):1062–7.

[14] Wang TJ, Chang J. Lv PM. Synthesis gas production via biomasscatalytic gasification with addition of biogas.

[15] Delgado J, Aznar MP, Corella J. Calcined dolomite, magnesite andcalcite for cleaning hot gas from a fluidized bed biomass gasifier withsteam: life and usefulness. Ind Eng Chem Res 1996;35(10):3637–43.

[16] Corella J, Orıo A, Aznar P. Biomass gasification with air influidized bed: reforming of the gas composition with commercial

steam reforming catalysts. Ind Eng Chem Res 1998;37(12):4617–24.

[17] Courson C, Makaga E, Petit C, Kiennemann A. Developmentof Ni catalysts for gas production from biomass gasificationreactivity in steam- and dry-reforming. Catal Today 2000;63:427–37.

[18] Aznar MP, Caballero MA, Gil J, Martın JA, Corella J. Commercialsteam reforming catalysts to improve biomass gasification withsteam–oxygen mixtures. 2. Catalytic tar removal. Ind Eng Chem Res1998;37(7):2668–80.