aLeTec

, Qin

omamomtoER

n efr t 0

fuel gas was 4163 kJ/N m .

d as atural wbiomae it proe effect effect4]. In g

since the volatile matter content was eliminated during thepyrolysis [9]. Furthermore, biomass char contained the highercontent of xed carbon, which had a high reactivity during thegasication.

was provided by partial combustion of the feedstock with a hypo-stoichiometric amount of air. Because the furnace was similar toa cyclone dust catcher, the separation of residual ash from the gasow was achieved in the reactor without additional cleaningequipment. Compared with the conventional uidized bedgasiers, it was simple, low-cost and easy to operate. Sun et al. [15]investigated the cyclone air gasication of wood powder forproducing fuel gas. The results showed that the peak gas temper-ature in cyclone gasier was higher than that in uidized bed

* Corresponding author. Tel./fax: 86 027 87557464.

Contents lists availab

Renewable

els

Renewable Energy 37 (2012) 398e402E-mail address: xiaobo1958@126.com (B. Xiao).pyrolyzed to the fuel products consisted of approximately 70 wt%liquid, 15 wt% char, and 15 wt% gas [5]. As a byproduct, the charproduced during the fast pyrolysis of biomass needed to be utilized.

Extensive studies had been reported on the gasication ofbiomass char using several agents such as air, steam and carbondioxide [6e8]. Compared to the raw biomass, biomass char wasrecognized as a preferable feedstock for gasication. The obtainedgas from direct gasication of raw biomass was usually rich in tar,because of the high volatile matter content. In the case of chargasication, gas products with lower content of tar can be obtained,

gasication were 200e250 kJ/mol and 130e170 kJ/mol, respec-tively. Yan et al. [12] studied the steam gasication of char derivedfrom cyanobacterial blooms in a xed-bed reactor. The resultsshowed that solid residence time played an important role onsteam gasication process, while particle size presented less effecton gasication process.

Cyclone furnace, a kind of gasier with the energy self-sufciency, was widely applied in combustion and gasication ofbiomass [13,14]. The furnace combined combustor and gasier intoone reactor, in which the thermal energy for gasication reactions1. Introduction

Biomasswaste, which is considerederives from plants including agriculwaste, etc. Recently, the interest onpower generation has increased sincemissions for limiting the greenhousconversion of biomass was the mosenergy to replace the fossil fuel [2e0960-1481/$ e see front matter 2011 Elsevier Ltd.doi:10.1016/j.renene.2011.07.001potential energy source,aste and forestry woodss waste utilization forvides low SO2 and CO2t [1]. Thermo-chemicalive technology for bio-eneral, biomass can be

Gasication of biomass char using steam agent had notableadvantages for the wide application. On the one hand, the gasi-cation reaction was much more rapid using H2O rather than CO2 asan oxidant [10]. On the other hand, the produced gas with highcontent in H2 and CO could be used as fuel gas or syngas accordingto the gas composition [8]. Marquez-Montesinos et al. [11] per-formed a kinetic study on the gasication of grapefruit skin charwith CO2 and with steam. The results indicated that the apparentactivation energy values obtained for CO2 gasication and for steam 2011 Elsevier Ltd. All rights reserved.Gasication of biomass char with air-ste

Pi-wen He a,b, Si-yi Luo c, Gong Cheng a, Bo Xiao a,*,a School of Environmental Science and Engineering, Huazhong University of Science andb School of Urban Construction, Yangtze University, Jingzhou 434023, PR Chinac School of Environmental and Municipal Engineering, Qingdao Technological University

a r t i c l e i n f o

Article history:Received 2 March 2011Accepted 2 July 2011Available online 28 July 2011

Keywords:GasicationCharCyclone furnace

a b s t r a c t

Biomass char, obtained frgasication using an air-stea cyclone furnace where calence ratio (ER) and steamshowed that the increasingyield and carbon conversiosteam would lower reactoconditions (ER 0.36, S/C

3

journal homepage: www.All rights reserved.m in a cyclone furnace

i Cai a, Jin-bo Wang a

hnology, Wuhan 430074, PR China

gdao 266035, PR China

the residues of biomass pyrolysis, was employed as feedstock for theagent. The gasication with the energy self-sufciency was carried out in

bustor and gasier were combined into one reactor. The effects of equiv-char ratio (S/C) on gasication performance were investigated. The resultsled to the increasing reactor temperature and increased dry gas yield, H2ciency. The introduction of steam promoted the gas quality, but excessiveemperature and degrade gas quality. Under the optimum experimental.45), the yield of the tar-free gas reached 3.72 N m3/kg and the LHV of the

le at ScienceDirect

Energy

evier .com/locate/renene

gasiers. The LHV of the producer gas was 3.64e5.76 MJ/Nm3, andthe tar content of the producer gas decreased to 5.6 g/Nm3 with thesecondary air.

The aim of this study was to examine the feasibility of the air-steam gasication of biomass char in the cyclone furnace. Theeffects of equivalence ratio (ER) and steam to char ratio (S/C) onreactor temperature, gas composition and gasication performancewere studied.

Table 1Ultimate analysis and proximate analysis of the samplea

Ultimate analysis (%)

C H O N S

Raw biomass 44.54 5.36 47.81 0.41 0.06Char 79.31 2.52 10.45 0.15 0.03

a Dry basis.

P.-w. He et al. / Renewable En2. Experimental section

2.1. Materials

The char used in this study was the byproduct of the bio-oilproduction through a fast pyrolysis of ramie residues at 500 C.The samples were shredded into particles of sizes of approximately0.125e0.25 mm. The proximate and ultimate analyses of thesample were listed in Table 1. Ultimate analysis of the sample wasobtained with a CHNS analyzer (Vario Micro cube, Elementar). Suchanalysis gave the weight percent of carbon, hydrogen, nitrogen, andsulfur in the sample simultaneously, and the weight percent ofoxygen was determined by difference. The thermogravimetricanalyzer was used to carry out the proximate analysis which wasexpressed in terms of moisture, volatile matter, xed carbon [16].

2.2. Apparatus and procedures

The equipment included cyclone furnace, screw feeder, aircompressor, owmeter, gas sampling, thermocouple (K-type) andsteam generator. The schematic conguration was illustrated inFig. 1. The cyclone furnace (high 600 mm, outer diameter 300 mm)was made of heat-resistant stainless steel tubing with a 5 mm ofwall thickness and wrapped with insulation materials.

At the start-up of each experimental run, the screw feeder wasturned on at the desired rotate speed to keep a 12 kg/h of feedstockFig. 1. Experimental apparatus: 1, air compressor; 2, screw feeder; 3, cyclone furnace;4, thermocouples; 5, ow meter; 6, gas sampling port; 7, temperature measurementsystem; 8, ow pipe; 9, steam generator; 10, water inlet; 11, steam ow meter.ow rate, and the air compressor was turned on to provide anexcessive amount of air. Then oxy-acetylene ame was used toignite char powder in the furnace. After 15 min of completecombustion, the reactor temperature reached about 800 C. At thismoment, the air ow was adjusted by adjusting valve of aircompressor to obtain theequivalence ratioof 0.25, 0.27, 0.32, 0.36,0.41. The surplus heat energy of the produced gas was reutilized forsteam generation.When the reactor temperature kept a stable statefor 3 min, the tests began and experimental data were recorded.Each test was repeated three times. Because of the energy suppliedby partial combustion, the temperature in the reactor might havethe difference of 10e30 C among parallel tests. The product gaswas analyzed by GC 9800T. Permanent gases (H2, CH4, N2, CO andCO2) were analyzed with TCD using 5A, porapak Q column. Thecarrier gas was argon in all analyses.

2.3. Methods of data processing

The lower heating value (LHV) of the gas is calculated by [17],

LHVkJ=Nm3

CO 126:36 H2 107:98 CH4

358:18 (1)where, CO, H2, and CH4 are themolar percentages of components ofthe product gas.

The carbon conversion efciency is calculated by,

XC% 12YCO% CO2% CH4%=22:4 C% 100% (2)where, Y is the product gas yield (N m3/kg), C% is the masspercentage of carbon in ultimate analysis of the sample, and theother symbols are the molar percentages of components of theproduct gas.

Steam conversion, SC (%) is calculated by,

SC 18Y1000H2%2CH4%=22:4W1W2100% (3)whereW1 is steam ow rate andW2 is the total moisture content inthe feed.

3. Results and discussion

3.1. Gasication reactions in the cyclone furnace

Gasication of the char in the cyclone furnace can be divided

Proximate analysis (%) LHV (MJ/kg)

Volatile matter Fixed carbon Ash

78.98 19.20 1.82 16.6216.91 75.55 7.54 28.4

ergy 37 (2012) 398e402 399into two steps. As soon as the char powder were fed along thetangent direction of the furnace wall with air, combustion andincomplete combustion reactions (Eqs. 4, 5) promptly took place,which effectively provided the thermal energy for gasicationreactions.

Oxidation:

C O2 CO2 408:8 kJ=mol (4)

2C O2 2CO 246:6 kJ=mol (5)

CH4 H2O g CO 3H2 206 kJ=mol (11)

3.2. Reactor temperature

Temperature is considered as the main parameter for estimating

Table 2Effect of ER on gasication performance.

Air (Nm3/h) 22 24 28 32 36

ER 0.25 0.27 0.32 0.36 0.41

Dry gas yield (N m3/kg) 2.19 2.39 3.00 3.52 3.87Liquid product yield

(g/N m3)132.4 92.1 33.3 5.7 2.6

H2 yield (mol/kg) 1.95 4.59 9.90 15.70 17.12H2/CO 0.09 0.20 0.38 0.53 0.56LHV(kJ/N m3) 3080 3602 3668 3755 3497Steam conversion (%) 12.05 34.57 67.43 93.66 96.93Carbon conversion

efciency (%)51.91 60.40 71.40 86.48 93.27

Feed rate 12 kg/h; S/C 0.35.

e Energy 37 (2012) 398e402P.-w. He et al. / Renewabl400Then, combined with the ow, the residues revolved anddropped along the furnace wall. During this process, most particleswere mixed with vapor and gasication reactions occurred asfollows (Eqs. 6e11). In the end, ash separated from the ow and fellinto the taper container, and the produced gas ew into the pipewith high temperature. The nal gas composition was the result ofthe combination of a series of complex and competing reactions[18].

Boudouard:

C CO2 2CO 172 kJ=mol (6)Water gas:

Primary : C H2Og CO H2 131 kJ=mol (7)

Secondary : C 2H2O g CO2 2H2 76 kJ=mol (8)Methanation:

C 2H2 CH4 88 kJ=mol (9)Wateregas shift:

COH2O g H2 CO2 42:2 kJ=mol (10)Steam reforming:

Fig. 2. (a) Effect of ER on reactor temperature: Feed rate 12 kg/h, S/C 0; (b) Effectof S/C on reactor temperature: Feed rate 12 kg/h, ER 0.36.on biomass gasier. In this study, reactor temperature was inves-tigated under the different experimental conditions. The temper-atures measured at different points of the furnace (upper-reactor,middle-reactor and bottom-reactor) were compared in Fig. 2.

The effect of ER on reactor temperature is shown in Fig. 2(a). Itwas found that the temperature at each point was very sensitive toER and it rapidly increased with the increasing ER. At the higher ER,more oxygen reacting with the char resulted in the higher reactortemperature. The values in the upper-reactor, middle-reactor andbottom-reactor reached 832e1016 C, 783e993 C, 721e952 C,respectively. The peak temperature appeared in the upper of thereactor suggested that the upper-reactor was the main combustionzone. The average reactor temperature in this test ranged from 779to 987 C, which was higher than that in our previous study on thegasication of raw biomass feedstock [19]. The possible reasonsascribed to the higher LHV of char for releasing more heatingenergy. For a uidized bed gasier, the temperature of thecombustion zone generally maintained 750e900 C, while thetemperature at the exit of the gasier was always below 600 C[2,20]. However, the temperature distribution in the cycloneFig. 3. Effect of ER on gas composition: Feed rate 12 kg/h, S/C 0.35.

furnace showed that the temperature difference between upper-reactor and bottom-reactor was very small, just only 60e100 C.It meant the residence time of feedstock in the high temperaturezone was prolonged for gasication.

Fig. 2 (b) shows the effect of S/C on reactor temperature at thexed ER of 0.36. The temperatures in different parts of the reactordramatically decreased, due to the cooling effect of the introduced

quite low when ER was below 0.27, then it remarkably increased

2conversion and carbon conversion efciency rapidly increased.

3.4. Effect of S/C on gasication

4. Conclusions

Table 3Effect of S/C on gasication performance.

Steam rate (kg/h) 3.0 4.2 5.4 6.6 7.8

S/C 0.25 0.35 0.45 0.55 0.65

Dry gas yield (N m3/kg) 3.22 3.52 3.72 3.4 3.13H2 yield (mol/kg) 10.20 15.70 19.25 9.71 3.08H2/CO 0.46 0.53 0.57 0.38 0.14LHV(kJ/N m3) 3132 3755 4163 3113 2459Steam conversion (%) 96.16 93.66 90.26 39.74 13.95Carbon conversion

efciency (%)79.38 86.48 95.19 80.43 76.52

Feed rate 12 kg/h; ER 0.36.

P.-w. He et al. / Renewable Enwith the increased ER and reached the maximum at ER of 0.36.From Table 2, H2 yield was only 4.59 mol/kg at ER below 0.27,

since the lower steam conversion. It revealed that the gasicationsteam. The change in temperature indicated that a series of endo-thermic reactions (reforming and wateregas shift reaction)occurred.

3.3. Effect of ER on gasication

Generally, the gasication of biomass was affected by twocontradictory factors of ER, because ER was not only related to thegasication temperature but also represented the oxygen quantityintroduced into the reactor [17]. Table 2 shows the effect of ER onair-steam gasication performance of char in the cyclone furnace.The dry gas yield increased from 2.19 to 3.87 N m3/kg with theincreasing ER from 0.25 to 0.41. The incondensable gas composi-tions at different ER values are shown in Fig. 3. It can be seen thatthe increased ER leads to a decrease in CO concentration and anincrease in CO2 concentration. The H2 concentration in fuel gas wasFig. 4. Effect of S/C on gas composition: Feed rate 12 kg/h, ER 0.36.The tar-free fuel gas was produced from the air-steam gasica-tion of biomass char in a cyclone furnace with the energy self-sufciency. The higher ER resulted in higher reactor temperatureto increase H2 yield, steam decomposition and carbon conversionefciency. The optimal value of S/C was found to be 0.45. Excessivesteam would lower reactor temperature and degrade fuel gasquality. The maximum dry gas yield reached 3.72 N m3/kg with4163 kJ/N m3 of the LHV.

Acknowledgments

This research is supported by the National Natural ScienceFoundation of China (No. 20876066). The authors are grateful to theAnalytical and Testing Center of Huazhong University of Scienceand Technology for carrying out the ultimate analysis of theThe inuence of S/C on gasication performance is shown inTable 3. It is obvious that the whole gasication process can bedivided into two stages. The S/C of the rst stage was from 0.25 to0.45. In this stage, the presence of steam contributed to the reac-tions of (7), (8), (10) and (11) under the high reactor temperature.The higher steam conversion indicated that more steam introducedduring the gasication process to improve the quality of fuel gas. Asshown as in Fig. 4, both H2 and CO concentrations in the productgas gradually increased with the increasing S/C in the rst stage.When S/C varied from 0.55 to 0.65, the reactor temperature rapidlydecreased and maintained 650e750 C. In this stage, excessivesteam resulted in the degraded gas quality. It can be seen thenegative effect of S/C on dry gas yield, H2 yield and the LHV of fuelgas. Thus, there existed an optimal value for S/C. Similar resultswere reported on steam gasication of biomass char in a xed-bedreactor [21]. In this test, dry gas yield reached the maximum of3.72 N m3/kg at S/C of 0.45, which also corresponded to themaximum H2 yield of 19.25 mol/kg and the maximum LHV of4163 kJ/N m3.

In particular, an analysis on the liquid product under theexperimental conditions showed that the weight of dissolvedmatter by dichloromethane was not determined. It suggested thatthe liquid product should be from the surplus steam and the tar-free fuel gas was produced from the air-steam gasication ofbiomass char.Table 2 also indicates that the maximum LHV of the produced gas ispresented at ER of 0.36. Too small or too large ER was unfavorablefor fuel gas quality in the cyclone furnace.

The obtained results suggested that ER was an importantcontrolling parameter for air-steam gasication of biomass char inthe cyclone furnace. However, the variation of temperature atdifferent ER values played a more prevailing role in inuencing thegasication performance including H2 yield, carbon conversionefciency and the LHV of fuel gas.reactions (Eqs. 7, 8, 10) could not play a prevailing role at the lowerreactor temperature. According to the literature [18], thewateregasshift reaction (Eq. (7)) appeared to be more dominant for thetemperature range 730e830 C. When ER varied from 0.32 to 0.41,the reactor temperature reached the value, which could meet therequirement of water shift reactions. Thus, H yield, steam

ergy 37 (2012) 398e402 401samples.

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P.-w. He et al. / Renewable Energy 37 (2012) 398e402402

Gasification of biomass char with air-steam in a cyclone furnace1 Introduction2 Experimental section2.1 Materials2.2 Apparatus and procedures2.3 Methods of data processing

3 Results and discussion3.1 Gasification reactions in the cyclone furnace3.2 Reactor temperature3.3 Effect of ER on gasification3.4 Effect of S/C on gasification

4 Conclusions Acknowledgments References