Fluidized-bed pyrolysis of waste bamboo

Xiao et al. 1J Zhejiang Univ SciA 2007 8(9):1495- 14991495Journal of Zhejiang University SCIENCE AISSN 1673-565X (Print); ISSN 1862- 1775 (Online)www.zju.edu. cnjzus; www.springertink .comnine)JzUsE-mail. jzus@zju. edu.cnFluidized-bed pyrolysis of waste bambooXIAO Gang", NI Ming-jiang', HUANG He', CHI Yong', XIAO Rui', ZHONG Zhao-ping', CEN Ke-fa'('Key Lab. on Clean Coal Power Generation and Combustion Technology of Ministry of "Education,Schoo of Energy and Environment, Southeast University Nanjing 210096, China)(State Key Lab. of Clean Energy Urilizarion, Collee of Mechanical and Energv Engineering. Zhejiang Universiy. Hangzhou 310027, China)(Collge of Life Science and Pharmaceunical Enginering, Nanjing Universily 0f Technolog. Nanjing 210009 China)'E-mail: xiaogangtianmen@seu.edu.cnReceived Feb. 10, 2007; revision accepted Mar. 24, 2007Abstract: Bamboo was a popular material substituting for wood, especially for one-off commodity in China. In order to recoverenergy and materials from waste bamboo, the basic characteristics of bamboo pyrolysis were studied by a thermogravimetricanalyzer. It implied that the reaction began at 190-210 °C, and the percentage of solid product deceased from about 25% to 17%when temperature ranged from 400 °C to 700 °C. A lab-scale fluidized-bed furmace was setup to research the detailed properties ofgascous, liquid and solid products respectively. When temperature increased from 400。C to 700 °C, the mass percent of solidproduct decreased from 27% to 17% approximately, while that of syngas rose up from 19% to 35%. When temperature was about500°C, the percentage of tar reached the top, about 31%. The mass balance of these experiments was about 93%~95%. It indicatedthat three reactions involved in the process: pyrolysis of exterior bamboo, pyrolysis of interior bamboo and secondary pyrolysis ofheavy tar.Key words: Bamboo, Pyrolysis, Fluidized beds, Syngas, Tardoi: 10.1631/jzus.2007.A1495Document code: ACLC number: TK229INTRODUCTIONstituting for wood, especially for one-off commodity.A great deal of waste bamboo was produced everyBamboo was one of the fastest-growing plants,year and it always clustered at specific locations, likeand it could be harvested in 1~3 years generally. Thefurniture plants, noshery, restaurants, etc. It facilitatedarea of bamboo forests was up to 140000 km2 in thewaste bamboo to be collected and recovered. But byworld, and most was distributed over Southeast Asia,now, few researches were focused on how to make useCanada and West Africa. In China, bamboo was theofit.second woody resource, about 50000 km' and sharingPyrolysis was one of the efficient means with1/10 market of woody materials. Researches (Du etless emission to recover energy from waste biomassal, 2004; Li et al, 2004; Li et al, 2006; Wang etal, (Ayse et al, 2005; Li et al, 2000; Ni et al, 2006a;1999; Zhou and Xu, 2004) indicated that cellulose，2006b; Xiao et al, 2007; Yan et al., 2006; Zhang et al.,hemi-cellulose and lignin were the main components2005; Zhou et al, 2006). This technique could bein bamboo and their percentages were 35%~ -45%,applied to waste bamboo also. Du et al.(2004) studied15%~ 20% and 15%~ 25% respectively.on bamboo pyrolysis at 300~600。C in a fixed bed,Bamboo was a kind of popular materials sub-and researched the main components in the liquidprod中国煤化工C2H4O2 (acetic acid),C.H, CgHsO3 (2,6-dime-' Projeet spported by the National Basic Research Program (973) ofChina (Nos. G199902210534, 2005CB221202 and 2007CB2 10208)thoxYHC N M H Gnethano) were thethe Hi-Tech Research and Development Program (863) of China (No.main components, and the percentages were 15%~2006AA020101), and the Open Foundation of State Key Laboratoryof Clean Energy Utiliztion of China (No. ZJUCEU2006004)35%, 7%~20%, 8%~12%, 3%~8% respectively.1496Xiao et al. / J Zhejang Univ SciA 2007 8(9):1495- 1499In order to provide more comprehensive0.250~0.355 mm. The thickness of bed materials wasknowledge of waste bamboo pyrolysis, in this paper,about 80 mm. Feedstock was fed by batch from the topexperiments were carried out in a thermogravimetricof the reactor, where equipped with a valve. As soonanalyzer and a lab-scale fluidized bed. The charac-as the feedstock was fed, the valve was closed quickly.teristics of gaseous, liquid and solid products wereThe gaseous product came into the cooler firstly;analyzed in detail. It was looking forward to facilitatecondensable tar was collected in vessels, and afterthe technology for recovering energy and materialbeing dried, un-condensable syngas was collected in afrom waste bamboo.gas-bag. This process was going on for about 2 minuntil the reaction was almost finished. The fluidizedbed was airproofed and cooled quickly. Then it wasEXPERIMENTAL METHODOLOGYcleaned up and solid product was collected.One-off chopsticks of bamboo were selected asTemperature Nitrogenthe feedstock for the experiments. The proximate andGas-bagriernFumacerolls suplierultimate analysis was reported in Table 1. In the ex-品periments of thermogravimetire analysis bamboo wastreated less 0.1 mm, and in the experiments of fluid-Gas meter△△ized-bed pyrolysis, the size was about 5 mmx5 mmx5Vacum pumpTar clletor| BuffierFlowmetermm.Fig.1 The ilustration of nuidized bed pyrolysis reactorTable 1 Proximate and ultimate analysis of bambooItemValueIn experiments, precise flux was measured by aMoisture (%)9.15gas meter (G1.6 membrane type, minimal precision:Ash (%)1.63Volatile (73.920.2 L), which was made by Hangzhou Beta Gas MeterFixed carbon (%)15.30Co. Ltd. The un-condensable syngas was detected byHigh heat value (kJ/kg)17821Trace 2000 gas chromatography (GC). It was made byC (%)45.885.36Thermo Finnigan in Italy, equipped with FlameN(%)0.32lonization Detector (FID) to detect hydrocarbonsS(%)0.26(C1_gHn) and two Thermal Conductivity Detectors0(%)37.40(TCD) to detect CO, CO2, H2, N2, etc. The yields ofThe thermogravimetric analysis was made insyngas were calculated by N2 balance. The heat val-such procedure: At first, feedstock was put into theues of tar and solid product were measured byanalyzer and the beginning temperature was 25。C;5E- IAC/P oxygen bomb calorimeter produced bythe furmace was heated at 100 °C/min, and when theKaiyuan Instrument Company in Changsha, China.temperature achieved 100。C it was kept for 1 min toeliminate moisture in feedstock; then, the furnace wasRESULTS AND DISCUSSIONheated at 100 °C/min until the temperature reached400 °C/500 °C/600 °C/700 °C; at last, the temperatureThe pilot study was carried out in a thermogra-was kept until the total time reached 700 s to makevimetric analyzer. And the results were reported insure the reaction was completed.Fig.2. At the beginning of 0~300 s, the loss curve wasThe fluidized-bed pyrolysis reactor was equippedsimilar; there was a obvious loss at 50~100s (100 °C),with a steel tube of inside diameter of 30 mm and totalwhich meant the moisture was moved out fromheight of 250 mm, as shown in Fig. I, which wasbamboo; the reaction began at 200 s (about 250 °C);placed in an electrical heater (about 1 kW). A K-typethe中国煤化工200 -300 s, whichthermocouples was assembled at about 150 mm abovemearEied out at 250-400the gas distributor. N2 was acted as fluidized medium。C; aMHC N M H G), the percentage ofand the velocity was about 0.48 m/s. Sand was se- solid products reached about 25% and decreasedlected as bed materials and its diameter wasslowly, which meant pyrolysis was almost completed.Xiao et al. 1J Zhejiang Univ SciA 2007 8(9): 1495-14991497If the temperature increased continuously from 400 ture, or the temperature was not high enough for。C to 700 °C, the percentage of solid products would granule pyrolysis.decrease from 25% to 17%, which indicated there wasa further pyrolysis of solid product (Wang et al,Characteristics of tar from fluidized-bed pyrolysis2006).Different appearance of tar was deserved fromvarious pyrolysis temperatures, as shown in Fig.3.100The tar was more liquid and less fuscous with tem-80perature increasing.Due to the fact that the tar was very hydrophilic50 tnd thermo-active, it was difficult to measure themoisture of it. In this paper, silica gel was used to400°C 500°C 600°Cabsorb the moisture in it, however there may induce20some errors in measuring. HHV of the tar was also700Cdetected by oxygen bomb calorimeter. The results0100200300400500600700Time (s)were displayed in Table 3. With temperature increas-Fig.2 The TG curve of bamboo pyrolysising, percentage of moisture increased, while HHV oftar decreased. It was because more tar was involved inCharacteristics of solid product from fluid-secondary pyrolysis and more H2O was producedized-bed pyrolysis(Chen et al, 2003b; Wang et al, 2006).The proximate and ultimate analysis of solidproduct was carried out and reported in Table 2Characteristics of syngasGenerally, the percentage of carbon and fixed carbonInorganic gas and hydrocarbon were the mainrose up respectively with temperature increasing,components of syngas, and the yields were displayedwhile that of volatile, hydrogen and oxygen reduced.in Fig.4. In Fig.4a, steam was free, which would beThis meant pyrolysis of solid product was going ondiscussed in Section 3.4. In Fig.4b, C.H, meant otherwith temperature increasing, which was correspond-hydrocarbons, including C2H6, C;Hg, C4Hlo, CsH10,ing to the conclusion of TG experiments. The HHVCsH12, C6H14, etc. The main reactions as follows:increased from 25000 to 30000 kJ/kg approximately.It was worthy to report that, when the solidExterior bamboo- +CO2+CO+H2O+heavy tar+char,(1)product of 400~-500 °C was treated into powder, therewas some un-reacted bamboo remained inside it ob-Interior bamboo-→light tar+CO+H2+char,(2)viously. This indicated that two minutes was noHeavy tar-→>CO+H2+ H2O+CH4+C2H4+C;H,+light tar.enough for the reaction of pyrolysis at this tempera-(3)Table 2 Proximate and ultimate analysis of solid productTemperature MoistureAshVolatile Fixed carbon High heat valueCHN0(°C)(%)(kJ/kg)6.155.8222.8265.212515367.40 3.460.540.22 16.416.706.5620.6567.092766069.54 3.050.800.25 13.096005.908.4912.7672.852957074.64 1.900.55 0.278.247006.218.7010.9174.18 _3003276.67 1.690.570.285.87Table 3 Characteristics of tar400 °C500%C600°C700°CTemperature (°C)Moisture (%)HHV (kJkg)中国煤化工2815327738MHCNMHGDU010.002254620.4621411Fig.3 Tar from bamboo pyrolysis at different temperatureXiao et al. 1 J Zhejiang Univ SciA 2007 8(9):1495-149912the exterior char could act as catalysis and reducing。100agent (Chen et al, 2003a; Tan et al, 2005), light tarand co were produced rather than heavy tar or CO2.Higher temperature could enhance the heating ratioand facilitate pyrolysis of heavy tar, which induced，豆40-reaction Eq.(3).20个otMass balance of pyrolysis50060700In order to verify the accuracy of these experi-Temperature (°C)ments, mass balance was fulfilled and the result was(adisplayed in Fig.5. The mass percent of solid productdecreased with temperature increasing, which indi-cated the reaction of pyrolysis was going on with已30上-0- CH4CItemperature increasing. And reaction Eq.(2) was tes-莒20tified in a certain extent.101008C-0- Solid product-品一Syngas400601 -- Steam in syngasThe lotal(b)4020Fig.4 Yield of main components in syngas. (a) Inorganiccomponents; (b) Hydrocarbon是ol5060000Generally, the yield of inorganic gas was higherthan that of hydrocarbon. Excluding CO2, all yields ofFig.5 Mass balance of bamboo pyrolysisthe components went up with temperature increasing.CO2 and CO was the predominant component inThe mass percent of tar achieved the highest,syngas. At 400~500。C, the total percentage of CO2about 32%, when temperature was 500 °C. And whenand CO was over 90%, which meant reaction Eq.(1)temperature increased over 500 °C, the yield of tarwas the primary reaction. In this reaction, the tar wasreduced, while the yield of syngas increased sharply.fuscous and slimy, so it was called heavy tar in thisThis meant reaction Eq(3) became the principalpaper, while the liquid tar was called light tar, whichequation at 500~700 °C.was mainly produced at higher temperature. ThereThe mass percent of steam in syngas was stablewas still some un-reacted bamboo remained inside theunder the experimental conditions, which implied lesssolid products, when temperature was 400~500 °Csteam involved into the secondary reactions.and reaction time was 2 min. The reacted bamboo wasIn spite of carefulness, the mass balance reachedcalled exterior bamboo in this paper. While at higher 93%~ -95% due to the limit of collection and meas-temperature, the un-reacted bamboo would pyrolyzedurement. The errors of experiments were analyzed asfurther, it was called interior bamboo.following: During the cooling process, pyrolysis ofWhen temperature was enhanced at over 500 °Cthe solid product would be going on, although whichand up to 700 °C, the yields of CO2 decreased tardily,happened slowly. This would result in some loss ofwhile that ofCO, H2, CH4 and C2H4 increased sharply.syngent of syngas, onlyFurthermore, with temperature increasing, tar became CO2,中国煤化工bons (C- sH) weremore lucid and liquid, and less 0 remained in char.detecTYHC N M H Gm, CH2O, C2H4O2,This indicated reactions Eqs.(2) and (3) were taken et.,. could not be dected by GC. It also reduced theplace during this process. In reaction Eq.(2), due to mass balance.Xiao et al. 1s Zhejiang Univ SciA 2007 8(9):1495-14991499CONCLUSIONLi, A.M., Yan, J.H., Li, s.Q., Gu, Y.L,, Li, X.D., Ren, Y., Chi,Y, 2000. Pyrolysis of municipal solid waste in rotary klin:studies on characteristics of pyrolytic tar. Journal ofIn this paper, bamboo was pyrolyzed in a fluid-Combustion Science and Technology, 6(3):195-199 (inized bed at 400~700 °C, and the gaseous, liquid andChinese).solid products were studied in detail.Li, S.G, Xu, S.P., Liu, S.Q., Yang, C, Lu, Q.H，2004. Fast(1) With temperature increasing, the mass per-pyrolysis of biomass in free-fall reactor for hydrogen-richcentage of solid product decreased from 27% to 17%gas. Fuel Processing Technology, 85(8-10):1201-1211.[doi:10.1016/j.fuproc.2003. 10.043]approximately, while that of syngas increased fromLi, ZJ, Lin, P, He, J.Y, Yang, Z.W, Lin, Y.M., 2006.about 19% to 35%. When temperature was about 500Silicon's organic pool and biological cycle in moso°C, the percent of tar reached the highest (about 31%).bamboo community of Wuyishan Biosphere Reserve.The mass balance of these experiments was aboutJournal of Zhejiang University SCIENCE B, 711):93%~ 95%.849-857. (doi: 10.1631/zus.2006 B0849](2) In analysis of solid product, the percent ofNi, M., Leung, D.Y.C, Leung, M.K.H, Sumathy, L.K., 2006a.An overvicw of hydrogen production from biomass. Fuelfixed carbon and carbon rose up with temperatureProcessing Technology, 87(5):461-472. [doi:10.1016/j.increasing, while that of volatile, hydrogen and oxy-fupro. 2005.11.003]gen reduced. Its HHV increased from 25000 to 30000Ni, M.J., Xiao, G, Chi, Y, Yan, J.H, Miao, Q.. Zhu, W.L, Cen,kJ/kg approximately.K.F, 2006b. Study on pyrolysis and gasification of wood(3) The tar was more liquid and less fuscous within MSW. Journal of Environmental Sciences, 18:407-415.temperature increasing. The percent of moisture in tarTan, H, Wang, S.R., Luo, Z.Y, Yu, C.J, 2005. Experimentalstudy of lignin flash pyrolysis. Journal of Zhejiang Uni-rose from about 13% to 20% while the HHV of it .versity (Engineering Science), 39(5);:710-714 (in Chi-decreased from 28000 to 21000 kJ/kg roughly, whentemperature was increased from 400 °C to 700 °C.Wang, WJ, Hui, C.M., Liu, C, Wang, C.M., Chen, Y.H, Fu,(4) Generally, the yield of inorganic gas wasH, 1999. A study on the chemical components of 14higher than that of hydrocarbon. The yield ofCO, H2,timber bamboo species in Yunnan Province. Journal ofCH4 and C2H4 increased largely with temperatureBamboo Research, 18(2):74-78 (in Chinese).Wang, S.R., Liu, Q., Luo, ZY., Wen, L.H., Cen, K.F, 2006.increasing, while that of CO2 was stable roughly.Mechanism study of cellulose pyrolysis using thermo-(5) The results indicated that the pyrolysis con-gravimetric analysis coupled with infrared spectroscopy.sisted mainly of three reactions: pyrolysis of exteriorJournal of Zhejiang University (Engineering Science), .bamboo, interior bamboo and heavy tar at 400- -70040(7):1154-1157 (in Chinese).°C. And the pyrolysis of interior bamboo was cata-Xiao, G, Chi, Y, Ni, M.J, Miao, Q, Zhu, W.L., Zheng, J., Tu,H.B., Cen, K.F, 2007. Fluidized-bed pyrolysis and gasi-lyzed by the char, which was produced from pyrolysisfication of waste paper. Journal of Engineering Ther-of exterior bamboo.mophysics, 28():161-163 (in Chinese).Yan, J.H, Peng, Z., Lu, S.Y., Li, X.D., Cen, K.F, 2006. 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