Pyrolysis of rice husk and sawdust for liquid fuel

ISSN 1001-<0742Jurnd of FEnmirnmental Sciences Vol. I8, No.2, p.392- -396, 2006CN11- 2629/XArticle I. 10-0742006)02-0392-05CLC mumber: X706Document code:APyrolysis of rice husk and sawdust for liquid fuelZHU Xi-feng', ZHENG Jji-lu, GUO Qing xiang, ZHU Qing shi(Biomass Clean Energy L.aboratony, Unirersity of Science and Technology of China. Hefei 230026, China. E mail: xfzhu@ustc edu.cn)Abstract: The paper is focused on studying; how to convert ricc husk and sawdust into liquid fucl. Rice husk, sawdust and theirmixture were pyrolyzed at the temperature bctwcen 420C and 540C , and the main product of liquid fuel was obtaincd. Theexpecrimental result showed that the yield of liquid fuel heavily depended on the kind of feedstock and pyrolysis temperature. In theexperiments, thc maximum liquid yields for rice husk, sawdust and their mixture were 56% at 465C, 61% at 490C and 60% at 47SCrespectively. Allalysis with GC-MS and other apparatus indicated that the liquid fuel is a complicated organic cormpound with lowcaloric value and can be directly used as fuel oil without any up-grading. As a crude oil, the liquid fuel can be refined to be vehicle oil.Keywords: solid organic waste; rice husk; sawdust; pyrolysis; liquid fuelIntroductionEven though pyrolysis of sawdust had been studiedRice husk and sawdust from agriculture andby some researchers, there are yet many problems towood industry are abundant with an annual productionbe solved. For example, chemical composition ofof more than 900 million tons of dry mass in China.un-condensable gas from pyrolysis of sawdust is stillThe traditional methods such as composting andunknown; pyrolysis of rice busk or the mixture of riceincineration are not suitablc 10 process these organichusk and sawdust for liquid fuel in a fluidized bedsolid wastes as they contain lttle nitrogen forhave not ever been studicd. A life-cycle analysis of thecomposting and lot of solid grains and smoke will beenergetic performance of thermal conversion, whichreleased to pollute environment during incineration.has been not studied by other researchers, is presentedTherefore, an advisable method should be developedin this paper. Moreover, this paper speciallyto deal with rice husk and sawdust.emphasizes on and analyzes the significance ofIn fact, solid organic wastes such as rice husk andcnvironment protection when pyrolyzing sawdust andsawdust is a kind of renewable resource. Solid organicice husk for liquid fuel, namely the liquid fuelwastes can be pyrolyzcd and changed into liquid fuelconverted from rice husk and sawdust is much cleaner(Bridgwater et al, 1999; Bridgwater and Peacoke,than fossil fucls and un-condensable gas will not2000). For instance, wood Icaf (Zabanioto ancpollute air. .Karabelas, 1999), soybean cake (Puttn et al., 2002)The purpose on this paper was t0 find anand rapeseed cake (0zcimen and Karaosmanoglu,advisable method to deal with organic solid waste and2004) all can be converted to liquid fuel. Yi et al.present a systcmatic research about the method-(2000) obtained liquid fuel from corn stalk. Algae canpyrolysis, which will convert organic solid waste suchbe also converled into liquid fuel (Peng et al., 2000;as rice husk and sawdust into liquid fucl. Furthermore,Sawayamna el al, 1999; Ginburg, 1993). Dai et al.this paper was also aimed at that liquid fucl converted(2000) and Ren el al. (2002) studied the eficct offrom rice husk and sawdust which is cleaner comparedreaction tcmperature on the product yield whenwith fossil fuels and the proccss of pyrolysis of ricepyrolyzing sawdust. Luo et al.(2005) studiced pyrolysishusk and sawdust will not bring about polution.of rice straw, wood and obuained the kinetics models1 Experimentalof their conversion. All kinds of rcactors, such asrotating cone reactor (Wagenaar, 1987)， vacuum1.1 Materialspyrolysis reactors (Lemieux el al, 1987) and vortexThe experimental malcrials include rice husk,reactors (Diebold and Scahill, 1987), are uscd tosawdust, sand and nitrogen. Their physica! properticspyrolyze organic solid wastes. Just as wood leaf,such as density and diameter arc listed in Table I. Therapesced cake and soybean cake, rice husk andproximate analysis of rice husk and sawdust are listedsawdust are also derived from green plants and aren Table 2. Sand is used as the thermal carrier toable to be converted into liquid fuel as follows:quickly transfer hcat from hot nitrogen to rice husk orCharcolsaw中国煤化工。Rice husk: gas to fluidize ricecoolhuskJMYHC N M H Guidized-bed reactor.Organic steam- Liquid fuelSawdust1.2 Experimental deviceAs shown in Fig.l, the experimental deviceUn-condensable gasmainly consists of a hopper, two screw feeders, a1Fogp数据The National Nanual Sciene Foundation of Chin(Nol.50576091); * Crreponding auhorNo.2Pyrolysie of rice husk and sawdust for liquid fucl393Table 1 Physical property of experimental materialsconfiguration and size, among them the first one isMatcrialDensily, kgim'Avernrageneter, mused to control the fceding rate and the second oneSawdust800.000344runs at relativly high speed to avoid jamming infeeding system. The fluidized-bed reactor has theRice husk300.003192height of 2 m and the diameter of 70 mm in which riceSand26000.00045husk or sawdust is rapidly heated for pyrolysis. Theelectric heater can pre-heat nitrogen to theTable 2 Proximate analysis of rice husk and sawdusttemperature of 450C to 550"C before entering intoMaterialMoisture, Ash, Volatile, Fixed carbon, Low heat value,the fluidized-bed reactor. The two cyclones are usedw1% wt% w1%wt%MJ/kgto separate solid particles such as charcoal and ashfrom the hot gas. The condenser has some nozzles inSawdust 9.06 7.36 71.905.21its topper and a heat exchanger in its middle, in whichRice husk 7.70 18.X0) 64.309.2013.36the pyrolyzed hot gas can be quickly cooled intoliquid by scrubbing with the condensed liquid pumpedelcctric heater, a fluidized-bed reactor; two cyclones,from the bottom of condenser, and the heat ofa condenser, an oil pump, as well as some ther-pyrolyzed hot gas is carried out thc condenser bymocouples and some pressure meters. The hopper iscooling water flowed in and out the heat exchanger.used to contain the feedstock of rice husk. sawdust orThermocouples and pressure meters are used totheir mixture. The two screw feeders have the samemonitor and control the pyrolysis system.CycloneGasluidized-bed rcactorfHopper|Hot|Tiguid fhceli CondenserFeed 1Heat cxchanger一Hot waterF. CharcoalCool water-eed2Thermocouple↓.HCool HliqutdtuclPumpNitrogcnLiquid fuelHeaterFig.l FExpcrimental device1.3 Methodfecdsstock.Some ethanol for scrubbing is needed to put intoIn the equation, the wcight of pyrolyzed liquidthe condenser in the first experiment. Thereforc, thecan be measured based on the increascd liquid level inliquid fuel obtained from condenser actually is thethe bottom of condenser, and the weight of fedmixture of ethanol and pyrolyzed liquid from ricefeedstock can be measured based on the speed of thehusk or sawdust. As ethanol is easily to be volatilized,first screw feeder.its concentration in the mixture will be less and lessAs the ash in the fed feedstock should be cqual totill to zcro with experiment being carried out. Thethat in charcoal, the charcoal yield can be calculatedexperience shows that the mixture will only consist ofas follows,the pyrolyzed liquid if the experiment lasts for morcr。=“(2)than 10 h.C。Besides liquid fucl, two by-products that arewhere上is the charcoal vield. ce is ash content in thecharcoal and un-condensable gas can be obtained fed中国煤化工lent in the obtainedchawhen rice husk or sawdust is pyrolyzcd.MHCNMHG.be acquired by theThe liquid yicld can be figured out as follows:" nuld ul心11, LL gan yLIL Lunldifference as the sum of three yiclds is equal to 100%.n= Wp(1)The yield of liquid fuel is heavily affected bywhere rη is the liquid yield, wp is the weight of thecooling method. If the cooling speed is not fast, somepyglyaliquid and twr is the weight of the fedcondensable gas will be cracked into un-condensable394ZHU Xi-fenget aVol.I8gas and bitumen. Scrubbing with well-sprayedTabie4 Main properties and elements of lquid frompyrolyzed liquid from the bottom of condenser is adiferent feedstockgood way to cool the hot pyrolyzed gas as the hugePropertiesLiquid from Liquid from Liguid fromquantity of heat can be quickly absorbed by the liquidrice husksawdustmixturemist.HO, wt%25.219.00.7Rice husk, sawdust and their mixture are fed at2.82.1.6the ratcs of 7.32 kg/h, 6.9 kg/h and 7.00 kg/hDensity, kg/m'119013001255respectively in the experiments. In the mixture, theViscosity, mm/s128 .240156mass ratio of rice husk to sawdust is 1.0.LHV, MIJkg17.2417.42 Results and discussionC, wt%4.753.046.5H, w%7.6.47.3Experiments show that temperature below 420CO, wt%50.00.25.8is not suffcient for pyrolysis as some rice husk orN, wt%0.sawdust can be found in the charcoal, in contrast thes, wt%.1temperature above 540C is too high as the yield ofliquid fuel is obviously dccreased. Therefore theused as fucl oil for combustion in boiler and furmacefeasible temperature for pyrolysis should be set in thewithout any up-grading Furthermore, it can be refinedrange from 420- 540"C.to be vehicle oil as a crude oil. Some researchers areThe yields of three products varying with tem-studying how to utilize liquid fuel from pyrolysisperature are listed in Table 3 to Table 5 respectively(Chiaramonti et ol, 2003a; Adjaye and Bakhshi,for rice husk, sawdust and their mixture.1995).In the experiment, the compositions ofliquid fuelTable 6 shows that the un- condensable gas is and un-condensable gas arc analyzed with gascomplicated gascous mixture with low caloric valucchromatography-mass spectrometry, and the resultsmainly due to the dilution of carrier gas nitrogen,are listed in Table 4， Table 5 and Table 6，which implies that the carricr gas nitrogen should berespectivcly.substituted by the un-condensable gas so that theFrom Table 4 it can bc found that: (1) theproduct gas can bc used as fuel gas.pyrolyzed liquid has higher energy density much moreRelations betwecn liquid yields and temperaturethan that of rice husk or sawdust so that it isare shown in Fig.2 for rice husk, sawdust and theirconvenient for transportation and utilization, and (2)mixture respectively, from which il can be found thatthe pyrolyzed liquid contains litle S, N and other(1) liquid yiclds for all feedstock first increase andpollutants.then decreasc with temperature increasing, and itsTable 5 indicates that the pyrolyzed liquid fuel ismaximum ones are 56%, 61% and 60% for rice huska complicated organic compound that mainly consistsal 465C, sawdust at 490C and their mixture at 475Cof water, acids and heterocyclic substances. It can beLiyuid fuctTable 3 Relationship between temperature and the product yieldsfrom rice huskMaterialTempera-_GaCharcoalLiquid fuelturc,Cwt% kg/h w% kgh wt% kghRice husk 42012 0.88 35 2.56 53 3.8842045080540505 1.10 29 2.12 564.1020 1.46 24 1.76 500t1026 1.90 21 1.54 s33.883 2.41 18 1.32 493.59Sawdust 42012 0.8830 2.20 s84.254 1.02 25 1.83 61204591s4018 1.32 21 1.54 61 4.4723 1.618 1.32 59 4.3230 220 16 117 54 3.95中国煤化工Mixture 42032 2.34 56 4.10MYHCNMHG__.14 1.02 25 1.83 61 4.47RO51020 1.4624 1.76 5?4.1724 1.76 19 1.39 5Fig.2 Rclationship between pyrolysis temperaturc and product yields312.2717 1.24 52 3.81a. rice husk; b. sawdust; c mixlureNo.2Pyrolysis of nice husk and sawdust for liquid fue!395Table 5 Compositions of liquid from diferent fecdstockLiquid fucl from ricc huskLiquid fuel from sawdustLiquid fuel from mixtureCompositionw%wt%Formic acid7.697.20β- Hydroxybutyric acid2.31Fithane, methoxy-1.54B-Hydroxybutyric acid1.50Toluene5.004.20Tolucnc4.80Benzoic acid, 3-mcthyI-15Benzoic ucid, 3-metbyl-20Benzoic acid, 3-metby-1.301.2-Bencenedicarboxylic acid,Ethyl bydrogen fiumarate1901,2-Benzenedicarboxylic acid,2-Cyclopcntanc-1-one, 3-mcthlyl1.42Cyclohexanol, 2 amino-, cis-1.44Cyclohexanol, 2-amino-, cis-1.014H-pyran-4-one, 2, 6-dimnethyl.2.154H-pyran-4-one, 2,6-dimethyl- 1.654H-pyran-4-one, 2.6-dimethyI-1.80Acetophenone. 1-(4-hydroxy-3-methxy) 1.00.2-Cyclobutanedionc.731,2-Cyclobutanedione0.98Benzaldeltydc, 2- hydroxyl1.85Benzaldehyde, 2-hydroxyl.03Propane, 13-dimethoxy-0.69Bencaldehyde, 3. 5-dimethyl 4 -hydroxyl 1.92Propanal, 23-dihydroxy-1.483-0ctyn-2-one0.92Table 6 Compositions of uncondensed gus from difterenetall feedstock always decrease with tempcrature.feedstockAbove results are similar with the other' sCias from rice husk Gias from sawdustGas from mixtureresearch. For instancc, Putin et al. (2002) found theComposition wt% Composition wt% Composition wl%maximum liquid yield is 42.7% at 550C for soybeanN:88S:86Nz87cake and Ozcimen et al.(2004) obtained the maximum.0lH20.02.02liquid yield of 59.7% at 500C for rapeseed cake.o2.24co3.402.58Energctic pcrformance of the conversion isO27.629.20:O28.42analyzed and the result is listed in Table 7, from which:H,0.54CH,0.63CH，0.57it can be found that: (1) the energy cascade is about_CHCH0.300.2849% for liquid fuel and about 86% for all products, (2)the thermal energy contained in charcoal is more thanrespectively; (2) gas yields for all fccdstock alwaysthe energy consumed by electric heating. As we allincrease with temperature; and (3) charcoal yields forknow that electric is the most expensive one in allTable 7 Analysis of the energetic performance for thermal conversionFeedstockA. MIhB, M/hC, MJ/hD, M/hF, MJ/hF, MIJh .G, MJhIL,%I,%Rice husk97.8043.2.63.671.418.6846.9848.1887.77Sawdust104.9576.609.0248.0949.3186.61Mixture100.008.7474.3349.2686.54Notes: A. energy inlow from feedslock; B. energy consumed by electric beating; C. energy consumcd by feeding feedstock; D. energy consumed bypumping liquid; E. energy contained in liquid; F. energy contained in gas; G. energy contained in charcoal; H. energy cascade only for liquid; 1. energycascade for all productsforms of energy, the process cost of conversion will berespectively at 465C, 490C and 475C. Scnubbinggreatly reduced if electric heating is replaced bywith well-sprayed liquid from the bottom of condensercharcoal combustion and the carrier gas nitrogen isis a good way to cool the hot pyrolyzed gas as thereplaced by the hot fue gas.hugc quantity of heat can be quickly absorbed by theliquid mist. The liquid fuel is a complicated organic3 Conclusionscompound that mainly consists of water, acids andheterocvclic substances. It can be used as fucl oil forSolid organic wastes such as rice husk andcom中国煤化工nace without anysawdust can be converted into liquid fuel by pyrolyis.up-YHC NMHGude oil, it can beLiquid yield first increases and then decreases withtemperature increasing, and there is an optimumrefinea to be venicle 011. II IS possible for electrictcmperalurc for pyrolyis of rice husk or sawdust intoheating and the carrier gas nitrogen to be replaced byliquid fuel. The maximum liquid yields for rice husk,charcoal combustion and its hot flue gas. In this way,sawdust and thcir mixturc arc 56%，61% and 60%pyrolysis cost will be greatly reduced.3967IIU Xi-fenget oal.Vol.l8Fnergy, 29: 779- -787.References:Peng W M, Li X s, WuQ Y er al, 2000 Recovery of planktonic algae :from lakes 1o produce fuels by pyrolysis []. Techniqucs andAdjaye J D, Bukhshi N N, 1995. 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