Non-isothermal Kinetics of Pyrolysis of Three Kinds of Fresh Biomass

Mar. 2007Journal of China University of Mining & TechnologyVo1.17 No.1Available online at www.sciencedirect.comSCIENCE; @oinEcr.J China Univ Mining & Technol 2007, 17(1): 0105- 0111Non-isothermal Kinetics of Pyrolysis ofThree Kinds of Fresh BiomassMIN Fan-feil'2, ZHANG Ming-xu'2, CHEN Qing-ru3'Department of Material Science and Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001, China2Key Laboratory of Modern Mining Engineering of Anhui Province, Huainan, Anhui 232001, ChinaSchool of Chemical and Engineering Technology, China University of Mining & Technology, Xuzhou, Jiangsu 221008, ChinaAbstract: The pyrolysis kinetics of three different kinds of fresh biomass (grass: triple A, wheat straw, corn straw) innitrogen flow were studied by thermogravimetric analysis at five different heating rates. The kinetic parameters of thepyrolysis process were calculated using the method of Ozawa -Flynn-Wall and the mechanism of reactions were investi-gated using the method of Popescu. It was found that the values of activation energy varied in different temperatureranges. The pyrolysis processes are well described by the models of Zhuravlev (Zh) and valid for diffusion-controlledbetween 200。C and 280 °C, by Ginstling-Brounshtein (G-B), valid for diffusion-control between 280。C and 310 °C, forfirst- order chemical reaction between 310°C and 350。C, by Zhuravlev (Zh) valid for diffusion-control between 350。Cand 430 °C and by the one-way transport model when temperatures are over 430。C.Key words: non-isothermal kinetics; fresh biomass; pyrolysis; thermogravimetric analysisCLC number: TQ 351.21 Introductionnism must be known so that the design and control ofthese processes can be carried out.Renewable energy is of growing importance insolving environmental concerms over fossil fuel usage. study the kinetics of the thermal decomposition ofBiomass is potentially the most attractive renewablebiomass. Most of the research has focused on the ki-energy resource available because it is widely dis-netics of cellulose pyrolysisMost of the kineticpersed and could contribute zero net carbon dioxidemodels in the literature for the pyrolysis of biomassemission to the atmosphere. Biomass is already theare simple first or nth-order reaction models-t .fourth largest source of energy in the world supplyingVlaev et al. estimated kinetic parameters from theabout 14% of primary energy. It is considered thethermogravimetric analysis (TGA) of pyrolysis ofrenewable energy source with the highest potential torice husk by using the method of Coats-Redfern andmeet the energy demand of modern society for bothfourteen equations. The pyrolysis process can be bestthe developed and developing economies world-described by the equation of Ginsting- Brounshtein,widel-valid for diffusion-controlled reactions. Values ofBiomass can be used as raw material to generateactivation energy, frequency factor, change of entropy,liquid, gaseous and solid fuels. To achieve this, ther-enthalpy and Gibbs energy have been calculatedmochemical methods such as pyrolysis and gasifica-Safi determined the kinetic parameters of thermaltion are the most appropriate and therefore, the mostdecomposition of pine needles in air by using severalcommercially used. The increased interest in themethods. Agrawal and Sivasubramanian's methodconversion of biomass for producing alternative fuelswas found to be the most consistent. For the totalnecessitates fundamental understanding of processesdegradation zone, the orders of reaction were foundinvolving pyrolysis of biomass. Knowledge of theto be in the range of 0.00- 2.50 by using Agrawal andkinetics of thermal reactions is vital to predicting theSivasubramanian's method and the activation energybehavior of biomass. Thermal decomposition mecha-in the range of中国煤化Ilowever, theReceived 22 September 2006; accepted 28 November 2006MYHCNMH G .Project 50474056 supported by the National Natural Science Foundation of ChinaCorresponding author. Tel: +86-554-6668649; E-mail address: ffmin@ aust.edu.cn.106Journal of China University of Mining & TechnologyVol.17 No.kinetic parameters of pyrolysis of biomass, especiallyof fresh biomass samples during drying and thermalfresh biomass, have rarely been studied using thedecomposition as the samples went through a linearmethods based on experiments under various heatingheating program. The instrument also provided con-rates.tinuous recording of the DTG and DSC curves. In thePyrolysis gasification of fresh biomass, whichpresent study, the flow rate of the purge nitrogen wascontains more moisture in its original state and isfixed at 100 mL/min and the heating rate was variedstored for brief periods, can produce hydrogen richfrom 2 to 10 K/min. Temperatures were raised fromgas. This work aims to determine the kinetic parame-25 °C to 800 °C. The uniformity of the samples wasters for the thermal decomposition of three differentmaintained by using 5 mg samples and spreadingtypes of fresh biomass. The kinetic parameters of thethem uniformly over the alumina crucible base in allprocess were calculated using the method of Ozawa-experiments.Flynn-Wall and the mechanisms of reactions were2.1 Materials and measurementinvestigated using the method of Popescu. It is con-sidered that methods based on experiments carriedIn the experiments, three fresh biomass samples,out under various heating rates give more reliableGrass: Triple A (GR), Wheat Straw (WS) and Cornresults than those based on data from a single heatingStraw (CS) were used.Samples were grounded andrate. Moreover, the integral methods are subjected tosieved into a powder with a particle size of less thanfewer experimental errors. The methods of Ozawa-0.2 mm.Flynn-Wall and Popescu have both virtues mentionedAn Elementar Vario EL- II elemental analyzer andabove [17-181.a thermogravimetric method calibrated to ASTMstandards were used to carry out ultimate and proxi-2 Experimentalmate analysis, respectively. The results of proximateand ultimate analyses of three fresh biomass samplesA SDT2960 thermal analyzer was used in the pre-are given in Table 1.sent study to monitor continuously the weight changeTable 1 Results of proximate and ultimate analyses of three fresh biomass samplesBiomassProximate analysis (air dried basis) (%)Ultimate analysis (dry ash free basis) (%)sampleVMAsh(kJ/g)CN3R8.6468.7413.089.5414.7049.457.572.3740.520.09VS9.4267.0413.210.2914.0449.69500.2642.420.12iS13.114.8414.957.940.4142.85Note: VM: volatile matter; FC: fixed carbon; Qnet ,ad:; air dried basis, low heating value2.2 TheoreticalBy using Doyle's rule andData from TG curves were used to determine thekinetic parameters. Mathematical analysis was perg(a)=f["dc_(3)J0 f(a)formed by. using the integral method of Ozawa-Flynn-Wall [19].Eq. (2) can be transformed toThe biomass pyrolysis process may be representedEby the following reaction scheme:lgβ= lg|- 2.313 - 0.4567-(4Biomass - > Solid residue +VolatilesRg(a))RTThe common kinetic equation of can be written as .Since the degrees of conversion a are the same forfollowsdifferent heating rates β, according to Eq. (4) it fol-da_ AE )f(a)(1AETlows that IgRg(a),is constant and a plotof lg β15.10x) is a function, such as that given in Tableagainst 1/T should be a straight line with slope, the type of which depends on the reaction-0.4567. Emechanism, T is the absolute temperature， a thedegree of conversion, A the pre-exponential or fre-[ he mechanisms of reactions were investigatedquency factor, E the activation energy, R the universalusing the method of Popescu, which is elaborated ingas constant 8.314 J/(mol.K) and β the heating rate.the literature [171The integral form of Eq. (1) is, then中国煤化工exp(-EIRT)dT(2)MHCNMH G.MIN Fan-fei et alNon-isothermal Kinetics of Pyrolysis of Three Kinds of Fresh BiomassTable 2 Algebraic expressions of functions of the most common reaction mechanisms for gas solid reactionsSymbolMechanismg(a)f(a)Diffusion One-way transporta1/2aTwo-way transporta+(1-a)In(1-a)[-ln(1-a)]'Three-way transport[1-(1-a)部(3/2)(1-a)[1-(1-a)所GBGinstling- Brounshtein equation1-(2/3)a -(1-a)(3/2(0 -a)11"'thZhuravlev equation(1-a)+-1' .(3/2)(1-a)*[(1-a) 5-11'Random nucleation and nuclei growth Bi-dimensional[- In(1 - a))f2(1-a)-ln(l- a)}Tree-dimensional[- ln(1- a))'3(1- a)[-In( - a)‘P-1Prout- Tompkins (m =0.5)In(1+ai )/(1-a3)](1- a)a'-T2Prout- Tompkins (m =1)ln[a/(1-a)](1-a)aChemical reaction First-order-In(1 -a)Second-order(1-a)"-1(1-a)'Limiting surface reaction between both phase One dimensionTwo dimension1-(1-a)2(1-a)户Three dimension1-(1-a)i30-a)3 Results and Discussiondecomposition of cellulose and hemicelluloses. Thethird plateau starts around >370 °C which largely re-3.1 Calculation of the values of activation energyflects the thermal decomposition of lignin20 21. WithThe TG and DTG curves of GR, WS and CS atthe heating rate increases the thermal decompositionheating rates of the 2, 4, 6, 8 and 10 K/min heatingtemperature zone also increases. The nature of a TGrates are shown in Fig. 1. The TG curves have threecurve with the corresponding DTG peaks gives aplateaus each. The first and smaller plateau show thatclear indication of the number of stages of the ther-there is an initial loss of moisture from the samplesmal degradation. The kinetic studies in this work arestarting at around 25 °C and continuing up to aboutdevoted to the second stage and third one stage. The180 °C. Higher temperature drying (> 100 °C) occursconversion degrees of the two stages are calculated.due to the loss of surface tension bound water of theThe largest conversion degree of the third stage is 0.5ground sample particles. The second plateau occursfor the 10 K/min heating rate.around 180- 370 °C which largely reflects the thermalG、DIG)β-2 K/min| 0 g50 DIβ=2K/min 105S0-、DIG_β-2 K/min 105! TGTG50f~ DTG50↑ DI。 β-4Kmin元三β=4 K/min冒1o06100 "50f- DIG月-6Kmin 3量看50-DITG--_ B=6K/min 3营SO[DTGβ= 6K/minSO[ TGβ-8K/min 4190[~ TGβ=8K/min 49β=8 K/min[-DIG-DIG[~ DIG100[~DIG8=10 K/minx_ A-=1Kminβ= 10 K/min200 400 600 8000 200 400 600 800200 400600 800Temperature(C)(a) Curves of GR degradation(b) Curves of Ws degradation(C) Curves of CS degradationFig. 1 TG and DTG curves in nitrogen at different heating ratesAccording to Eq. (4), based on the experimentalfound by other investigators for various biomass ma-data, the plot of lgβ against 1/T leads to a straightterials and their components. The values of E are dif-ferent in some reaction zones. The values of E corre-line whose slope is the value of - -0.4567号. Valuessponding to the conversion degrees ranges of 0.2-0.9of the activation energy calculated this way are pre-in the second reaction zone are in good agreementsented in Table 3. The values of activation energy arewith the valuesi中国煤化工dation fromthe literature [: values of Ein the range of 35- -207 kJ/mol for the entire tempera-correspondingMYHCNM H Gs ranges ofture range. These values are in the range of values>0.3 in the third reaction zone are in excellent.108Journal of China University of Mining & TechnologyVol.17 No.1agreement with the values of lignin thermal degrada-for three different fresh biomass samples show lttletion from the literature [6, 21]. In other words, thedifference in the range of thermal decomposition, thetwo reaction zones reflect the thermal decompositionaverage value of E of GR is the largest and that of CSof cellulose and lignin, respectively. The values of Eis the least. .Table 3 Values of activation energy computed by Eq. (4)_GIWsE (kJ/mol)Correlation coff.Correlation cofff.0.10162.29- 0.998 91181.82- 0.999 46169.39- 0.999 150.15177.3- 0.999 62182.36- 0.999 83177.83- 0999280.2087.54- 0.999 08183.28- 0.999 87182.14. 0.999 14 .025196.89.0.999 44185.40.0.999 84181.42- 0.999 30205.51 .0.999 07185.620.35208.63186.99.0.999 91186.79- 0.999 700.40205.33- 0.999 32184.99186.97- 0.999 360.45201.12- 0.99931182.96- 0.999 88179.38- 0.999 250.50206.58180.36173.58- 0.999 670.55194.08- 0.999 28178.90- 0.999 95172.06- 0.999 60194.85178.32168.49- 0.999 520.65187.35169.690.70185.42.0.999 38180.03.0.99996169.45.0.999 85.0.75186.46182.39.0.999 98172.44.0.999 190.80186.95- 0.999 37186.06- 0.999 98173.82- 0.999 570.85188.1 1192.43- 0.999 93178.310. 90190.10- 0.999 59203 .99- 0.999 81180.39- 0.999 27143.35-0.99907184.77110.93- 0.999 78126.26- 0.999 09140.51- 0.999 42122.06104.80105.59- 0.999 39110.93 .- 09997885.35- 0.999 970.3089.63- 0.999 0169.26.0.999 6765.56- 0.998 8768.80- 0.999 1457.01- 0.998 9352.73- 0.998 27.4054.710.999 1048.39- 0.998 4944.05 ..0.998 392 0.4546.6642.18- 0.998 3138.46- 0.997 9242.12.0.999 2639.13. 0.998 7635.70.0.998 67can be confirmed by TG and DTG curves (Fig.1). As3.2 Mechanism of thermal decompositioncan be seen in Tables 4 -6 the highest correlation co-The formal expressions of the functions f(a) andefficients of the three samples are obtained with theg(a) depend on the conversion mechanisms and theirfirst-order chemical reaction around 310- -350 °C. Asmathematical models. These models represent thethe thermal decomposition of hemicelluloses andlimiting stages of the reactions which include chemi-cellulose are nearly completed, the release of volatilecal reactions, random nucleation and nuclei growthmatter decreases; the reaction occurs under thand phase boundary reactions or diffusion. Table 2first-order chemical reaction in this temperature range.shows the most common kinetic models and theirBetween 350 and 430。C, the best correlation coeffi-algebraic expressions for solid thermal decompositioncients of three samples are obtained with the equationreaction.of Zhuravlev. It suggests that the thermal degradationWith the help of the functions from Table 2 and byoccurs under kinetic-diffusion control again in theusing the least squares method, Tables 4 -6 are ob-temperature range. It can be observed in Fig. 1 thattained.there is a smaller peak in the DTG curves in the sameIt can be observed in Tables 4-6 that the highesttemperature range. It indicates that the release rate ofcorrelation coefficients of the three samples are ob-volatile matter increases. One may notice that thetained with the equation of Zhuravlev between 180 °Chighest correlation coefficients are obtained for theand 280 °C and the equation of Ginstling- Brounshteinone-way transport model in Tables 4- 6 of the threearound 280- 310°C. It indicates that pyrolysis of threesamples around 430- -750°C. This may be ascribed totypes of fresh biomass takes place under typical dif-the fact that the thermal degradation of lignin domi-fusion control in the studied temperature range. Thenates and it mainly yields charcoal and the release ofhigher values of E (Table 3) are observed in the reac-volatile matter中国煤化工rature rangetion zone. Thermal decomposition in this temperature81. In a higher 1Ensfer effectsrange is subjected to kinetic diffusion control due toshould be conCNMHGlopmentofthe release of large amounts of volatile matter. Thisstrong temperature gradients within samples..MIN Fan-fei et alNon-isothermal Kinetics of Pyrolysis of Three Kinds of Fresh BiomassTable 4 Correlation cofficients corresponding various kinetic mechanisms using the GR data setTm(K)503.15513.15523.15533.15543.15553.15563.15573.15583.15593.15T(K573.15_593.15 603.150.9740 0.947 90.923 70.932 90.961 9 0.985 10.977 10.727 60.7952 0.911 90.9780 0.956 60.938 70.951 00.97780.994 70.997 70.909 10.93500.992 60.981 7; 0.96450.952 10.966 30.988 90.991 50.996 10.997 909805.G.R0.979 3; 0.95940.943 40.982 30.995 9.0.998 40967 40.97710.0988G-B09877 0 977 00972 4.0096，0.99630 9797.094770. 029 q0.8780086100.81790693 30. 8208.0 09670973 000680098860.985 60.988 6.0.7622 0.680 00.947 50.97320.984 20.8290 0.764 80.719 70.755 80.85760.951 10.98640.992 80.99750.975 5P-T20.6352 0.54780.63760.839 9.0.949 20.97790.99190.976 20.9159 0.872 60.8432 0.87480.93880.984 10.9948 0.997 40.99740.97230.89710.9809 0.989 00.95980.929 30.87010.8466 .0.8901 0.826 50.7696 0.776 80.8357 0.898 9.0.875 70.497 20.6159 .0.721 20.9037 0.850 90.8092 0.831 5.0.89780.958 40.97620.890 20.934 0.0.986 10.9079_ 0.858 50.8211 0.84710.9134 0.9698 .0.9882_ 0.953 2.0.9776_0.993 9623.15663.15703.15743.15783.15 823.15863.15903.15943.15983.15T,(K)783.15823.15 _903.15_ 943.15983.15_ 1 023.150.869 10.899 10.9780 0.993 80.998 00.998 50.998 10.997 4.0.996 50.956 60.8854 0.91680.9855 0.996 50.995 90.988 50.98200.9709 0.984 40.9006 0.932 70.9909099620.989 80.981 7.0.971 30.9564 .0.933 10.91680.890 70.922 40.987 60.99670.994 10.989 30.982 90.973 10.95640. 9569.0.926 77 0.957 20.995 80.973 40.95700,939 20.91830.895 5.0882 40.1678 0.487 20.848 4 0. 929 00.972 40_ 989 30.997 10995 10.971 2 .093890.0734 0.401 508079 0 899 60853 80 97700991 60007 50.98050 05000.943 80090 a .00730.955 5心00P-Ti0.9823 .0.05940.282 30.872 30.992 30.96740.927 30.49150.71450.980 20.99590.99700.99090.94460.91400.5664 0.791 40.994 40.97690.95650.929 60.89890.882 0.0.4159 0.623 50.88190.936 3.0.96550.9736097670.979 70.98160.796 00.45370.6706 .0.91100.96300.98750.9986098530.4663 0.68560.919 4_ 0.969 70.9916 0.997 60.9979 0.991 70.97140.954 9Tm，T。 are two different degrees of conversion corresponding temperatures.Table 5 Correlation coefficients corresponding various kinetic mechanisms using the WS data setT(K)583. 15_513.15_523.15_533.15_543.15_563.15_583.15_593.15__603.150.97130.957 70.96050.97540.886 00.541 50.145 1D20.9940 0.9906097870.97010.97550.987 80.99320.967 8.0.796 50.880 20.9955 0.993 50.985 10.98040.98650.993 0.0.99340.99760.98390.96010.9946 0.991 70.9810 0.97390.99050.995 10.89320.9472Zh0.997 30.9938 0.993 20.98700.96780.95900.94850.92310.7815 0.793 00.7474 0.719 70.760 10.857 80.926 30.934 20.91230.97420.6729 0.708 40.660 10.623 20.663 00.77990.874 00.887 30.859 70.950 6PT，0.7943 0.807 80.768 90.750 50.7984 0.893 50.954 70.970 60.97030.995 5PT20.38160.495 90.4748 0.448 20.513 10.686 90.8477 0.91500.941 70.985 80.93210.92450.8958 0.884 00.9852 0.99030.9848 0.99900.9488 0.94760.9332 0.936 00.964 80.98790.9816 .0.969 50.9460 0.890 10.9151 0.894 40.844 90.805 70.811 40.857 50.8626 0.68420.2625 0.11210.92240.91040.87220.84860.869 30.922 80.951 80.913 70.767 70.884 30.925 7_ 0.915 30.88040.861 20.88520.937 90.9675 .0.952 30.8777_ 0.9837743. 15mK)663 15702 1s74315783 1582315903. 15043 1ζ.1023 15T.(K)_703.150.99410.97940.9749 0.998 00.99820.998 80.998 00.997 40.999 20.768 70.99620.983 90.996 0.0.99310.990 10.98340.975 10.970 90.995 60.9978 0.9870 .0.97780.9908 .0.983 10.974 50.9605 .0.943 10.924 70.92590.9968 0.985 10.99460.99000.985 0.0.97560.963 30.952 20.97680.99950.976 o .0.96020.944 0.0.92420.904 70.88880.888 3A20.44460.09910.5610 0.927 70.96150.985 50.995 6.0.987 70.96250.953 30.31700.07000.391 30.886 10.93020.966 40.98980.992 9.0.97340,966 3.0.45890.134 60.61450.946 90.97700.993 80.993 60.975 60.944 30.929 7P-T,0.11950.240 60.16280.843 30.901 00.962 20.99010.986 70.95630.938 50.792 80.719 70.876 70.988 50.9958 0.995 40,983 80.962 10.933 70.921 90.8367 0.822 90.9334 0.994 90.9844 0.9666中国煤化工0.88230.744 0.581 10.7613 0.93990.95070.959 I0.435 80.769 10.654 40.8280 0.971 60.9853 0.994 6fH.CNMHG0.777 10.677 10.846 10.978 70.9909 0.99740.995 6__ 0984 30.965 80.973 5.110Jourmal of China University of Mining & TechnologyVol.17 No.1Table 6 Correlation cofficients corresponding various kinetic mechanisms using the CS data set"m(K)503.15513.15523.15533.15543.15 553.15563.15573.15583.15593.15Tn(K)543.15553.15563.15 .593.1603.15D10.98650.97320.945 20.91380.925 50.973 70.9910.961 50.625 20.723 4)20.989 10.978 70.956 30.932 3.0.94650.984 10.991 80.995 20.870 80.89440.991 50.966 20.963 80.988 90.982 5.0.987 30.9960.9969G-B0.99000.98050.95980.938 20.952 90.98640.98940.997 00.95450.954 0.Zh0.9950 0.991 10.981 30.973 0.0.985 00.98540.953 90.931 00.901 40.883 00.791 80.761 60.697 00.670 10.83520.943 20.978 00.9850.978 10.7046 0.676 90.60190.517 50.54690.741 70.901 10.955 5.965 10.957 42-T，0.803 90.778 20.7216 0.667 80.71800.874 50.960 90.989 0099740.996 00.468 20.406 30.367 10.624 80.868 40.962 50.992 60.988 8.0.92250.899 3.0.85940.826 10.86570.954 10.98340.993 30.996 40.997 820.941 30.928 20.905 20.892 70.934 70.981 90.967 60.941 60.896 50.873 00.89940.862 40.798 60.730 50.742 30.853 90.921 50.836 20.389.0.528 70.91150.8819 .0.831 10.782 40.8125 0.91780.97120.9743088140.897 0.0.9153 0.887 9.0.840 90.797 80.8319 0.93240.962 00.957 5623.15663.15703.15743.15783.15823.15863.15943.15T.(K)663.15 703.15743.15 783.15903.15983.151 023.150.986 80.989 30.99600.997 30.997 10.996 9.997 80.995 60.99030.992 10.995 30.99480.991 10.987 70.983 00.969 80.9932 0.993 70.9928 0.989 00.9806 0.97190.946 50.93020.911 1iB0.991 30.994 60.987 8.0.982 50.975 40.965 40.954 30.943 10.9938 .0.98460.9736 .0.957 60.94200.92550.893 6A20.377 20.769 90.896 90.928 20.9636 0.98440.994 50.990 80.97240.936 60.248 10.699 10.849 20.885 30.932 90.964 80.984 70.993 50.982 00.947 30.394 30.789 30.91460.94770.97840.99380.955 8P-T20.0569 0.586 10.7823 0.840 50.9122 0.959 30.986 90.989 70.968 80.9274 .0.749 60.917 70.97610.995 40.993 80.984 80.96740.943 50.91250.803 70.95220.991 8.0.982 30.942 80.897 4R，0.699 50.867 70.935 40.940 70.9540 0.960 3.0.9654 0.969 20.965 10.899 00.7202 0.894 80.9596 0.97260.986 50.994 00.994 90.986 70.971 80.73020.902 90.965 90.979 50.996 30.972 00.947 24 Conclusionstemperature ranges; the values of activation energyare in the ranges of 35- -207 kJ/mol for the entire1) The pyrolysis process of fresh biomass can betemperature range.divided into three stages. The first stage is loss of3) The Popescu method was successfully applied tomoisture from the samples. The second thermal deg-determine the reaction mechanism of samples. It in-radation occurs around 180- -370 °C and reflectsdicates that the pyrolysis process of fresh biomasslargely the thermal decomposition of cellulose andcannot be well described using only one reactionhemicelluloses. The third one starts around >370。Cmechanism function.which largely reflects the thermal decomposition of4) The pyrolysis process is well described by thelignin.mechanism of a first-order chemical reaction and ki-2) The values of activation energy of three types ofnetic-diffusion control. Kinetic-diffusion control isfresh biomass vary in different thermal degradationthe dominating reaction mechanism.References1] Agblevor F A, Besler S, Wiselogel A E. Fast pyrolysis of stored biomass feedstocks. Energy & Fuels, 1995, 9: 635- -640.[2] Min F F, Zhang M X. 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