稻谷深床干燥工艺参数对干燥比能耗的影响.pdf

第 28 卷增刊 2农 业 工 程 学 报Vol.28Supp.22012 年10 月Transactions of the Chinese Society of Agricultural EngineeringOct.2012285Influences of drying parameters on efficiency rate of paddyrice in deep fixed-bedWang Danyang1,2,Li Chenghua3,Tong Ling1,Zhang benhua1,Liu Qing2,Hu Yanqing1(College of Engineering,Shenyang Agricultural University,Shenyang 110866;2.Institute of Agricultural Product Processing,Chinese Academy of Agricultural Engineering,Beijing 100125;3.College of mechanical Engineering,Shenyang Ligong University,Shenyang 110168)Abstract:In order to reduce drying energy consumption for paddy rice and enhance the production efficiency,a newconcept of efficiency rate which showed thermodynamic characters was defined for paddy drying in a deep fixed-bedbased on analyzing the existing indexes.A series of paddy drying experiments were conducted in a deep fixed-bed.Influencing laws of each experiment factor on the new index were investigated.Five-factor quadratics rotary orthogonalcombination was adopted to establish the relationship between performance function and each factor,and the effects ofeach factor on the efficiency rate were investigated.An optimum range under 95%probability of efficiency rate lowerthan 2000 kJ/(kg h)was obtained as follows:drying air temperature,drying air velocity,paddy thickness,originalmoisture content and tempering time were 56.2-57.7,0.89-0.96 m/s,35.3-37.0 cm,21.31%-21.86%,2.87-3.16 h,respectively.The results provide a reference for saving energy of paddy drying in the practice and the research of paddydrying process simulation.Key words:efficiency,grains,dyers,paddy rice,deep fixed-bed drying,drying parametersdoi：10.3969/j.issn.1002-6819.2012.z2.050CLC number:S511,S226.6Document code:AArticle ID:1002-6819(2012)-Supp.2-0285-06Wang Danyang,Li Chenghua,Tong Ling,et al.Influences of drying parameters on efficiency rate of paddy rice in a deepfixed-bedJ.Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2012,28(Supp.2):285290.(in English with Chinese abstract)王丹阳，李成华，佟玲，等.稻谷深床干燥工艺参数对干燥比能耗的影响J.农业工程学报，2012，28(增刊2)：285290.0IntroductionPaddy rice drying costs more energy in paddyprocessing,low energy consumption is an importantfactor for economic competitiveness of paddy processingbesides drying quality and efficiency improvement.The weight of energy consumption index is thebiggest in the whole evaluation index system of paddyrice drying1.So energy saving and lower consumptionhave great significance for paddy rice production.Received date：2012-07-01Revised date：2012-09-23Foundation item：The youth science fund of Shenyang AgriculturalUniversity（20121001）Biography：Wang Danyang(1977),doctor,research field:agriculturalproductsengineering.ShenyangCollegeofEngineering,ShenyangAgricultural University,110866 and Institute of Agricultural ProductProcessing,Chinese Academy of Agricultural Engineering,Beijing 100125.Email:Corresponding author：Li Chenghua(1958),doctor,professor,researchfield:agriculturalmechanizationengineering.ShenyangCollegeofMechanical Engineering,Shenyang Ligong University 100168.Email:In the previous study,the energy consumptionindex for paddy drying was not uniform,with someresearchers using the terms unit energy consumption1,others dryer output2,dry strength3,drying capacity4,standard coal consumption5and still others powerconsumption6.These terms laid different emphasison energy consumption assessment,while there wasambiguity in their application.For example,accordingto the same phenomenon describing that is energyconsumption for drying 1 kg water of wet paddy rices,there are many different names such as unit energyconsumption,unitheatconsumption,unitheatconsumptionamountetc.Inaddition,waterevaporation amount per hour,dryer output,dryingstrength,drying ability and etc,which all evaluate thedryer only from the aspect of efficiency rather thanenergy consumption.This has brought inconvenienceto the academic exchanges.Therefore,a new energyconsumption index of efficiency rate was proposedbased on those terms comprehensively considered.Thatwas the energy consumption per unit time and unit of农业工程学报2012 年286waterdrying.Aimingattheefficiencyrate,experiments of paddy drying in a deep fixed-bed wereconducted and the parameters of drying process wereoptimized to seek an evaluation index which candescribetheinternalrelationsbetweenenergyconsumption and paddy drying in a deep-fixed bedmorereasonably.Thestudyprovidesausefulformation for saving energy,the operation andadjustment of existing drying equipment.1Materials and methods1.1MaterialsPaddies of rice CV L-294(main-grain)wereharvested in Liaoning 2008.The initial moisturecontents measured by oven method were between12%and 14%(w.b.).Sprayed with water required48 h before experiments,the samples were sealed inmultilaminated bags,and were overturned every threeor four hours to insure the uniformity of moisturecontent.The moisture content of drying rice samplesbefore each drying treatments were between 23.4%and 24.2%(w.b.).1.2MethodsEnvironmental temperature was 9-11 andrelativehumiditywas43%-52%duringtheexperiment.A deep-fixed bed was used for singlefactor and multi-factor experiments.The structure ofthe deep-fixed bed is as Fig.1.1.Drying chamber2.Rotary separater3.Feed inlet4.Sensors5.Material discharge6.Electronic digital temperature measurer7.Mcusystem8.Master computer9.Heater10.Control valve11.Exhaustpipe for stable pressure12.Air compressor13.Pressure gauge14.RotameterFig.1Structure of drying test bedComing from the air compressor by the systemworking,the airflow of stable pressure flew throughthe control valve and the rotameter,and then it wastransportedtothedryingchambertodrytheinside-materials after it was heated by the heater.There were some test holes in the drying chamber,which are used for measuring temperature,humidityand other parameter values of each grain layer.In eachdrying experiment,moisture contents of each testpoint in each grain-layer were obtained throughweight measurement of each test point by a specialsampler in every certain interval which was changedfrom 5 to 30 min with the increasing of drying timeuntil all the moisture contents of paddies in test pointswere of 14%(w.b.),which had met the safe storagestandard.A series of single factor experiments,whichincluded air temperature,air velocity,paddy thickness,original moisture content and tempering time,hadbeenconducted,andtheefficiencyratewasdetermined as evaluation index.According to thecomprehensive results of the single factor experiments,each unremarkable factor interval had been rejected,and each factor coding level for quadratic orthogonalrotation experiments were determined(Table 1).Table 1Coding of factor levelFactorsFactorlevelAir tem-peratureX1/Air velocityX2/(m s-1)PaddythicknessX3/cmOriginal moisturecontentX4/%Temperingtime X5/h+2851.2060286+1751.0150254.50650.8340223-1550.6430191.5-2450.45201601.3Energy consumption indexThe total energy consumption consists of twoparts:the energy consumption of air compressors andair heaters.According to the drying technology,thethermodynamic system of drying cylinder is known asan opened thermodynamic system,and in order toanalyze the influences of drying parameters on energyconsumption more efficiently,the energy consumptionof drying cylinder section is concerned alone.Dryingcylinder section of each experiment was divided into3-5 layers according to the thickness of paddy rice.During the drying process,energy consumption ofeach layer which in different time section wasdetermined by the measurement of hot air temperatureand moisture contents of paddy rice in each layer.Then,thetotalenergyconsumptionofeachexperiment was just the cumulative energy sum ofeach layer.According to the first law of thermodynamics：2211()()rQEememW As E consists of kinetic energy and potential energy22iiiiiTqhgzl(i=1,2.4,5)（1）Where iq is the difference of import heat and exportheat of each layer,kJ/kg.ih is the difference ofimport air enthalpy and export air enthalpy of each增刊 2王丹阳等：稻谷深床干燥工艺参数对干燥比能耗的影响287layer,kJ/kg.22iis the difference of import kineticenergy and export kinetic energy of each layer,kJ/kg.g iz is the difference of import potential energy andexport potential energy of each layer,kJ/kg.liTis theenergy exchange of system with external,kJ/kg.While,each virtual thin layer is only 6 cm,so windpressure drop of each thin layer is small enough thatthe difference of kinetic energy can be neglected.Furthermore,drying cylinder section was selected asthe research object of thermodynamic system,andheat transfer coefficient of cylindrical wall is so smallthat energy exchange can be neglected.So the total energy consumption Q of the wholedrying process is()1()3600()iitijrQVq（2）Where Viis the volume of each layer,m3.(t)is the airdensity,kg/m3.So the efficiency rate(E)is determined as follow1()1/iijrEQwt（3）Where()irwis evaporation of each layer in dryingprocess,kg;t is drying time,h.2 Results and discussion2.1 Establishment of regression equationThe regression equation in the code space,whichrevealed the relation of the affecting parameters anddrying efficiency rate,was established based on 36groups of measurement results of the quadraticorthogonal rotation experiments.Through varianceanalysis and significant test for regression coefficients,the equation fitting is good and remarkable(=0.1).Inthe coding space is a significant regression equation asfollows:E=2677.2577+809.1963x1 72.5289x2+600.5163x3+432.8866x4 245.256x2x5 253.345x3x4+191.6757x12+162.1808x22 94.708x32 144.19x42135.9351x52（4）The predicted values obtained by the regressionequation and measured values are as shown in Fig.2.The results proved that the regression equation has ahigh forecast precision.According to the equation(4),the contribution degree of each factor was calculatedand the results were as follow:1=3.5599,2=2.3195,3=2.4483,4=2.4417,5=1.5859.Theresults indicated that efficiency rate was affectedobviously in successive order of air temperature,paddythickness,originalmoisturecontent,airvelocity and tempering time.Fig.2Relationship between predicted and observed value2.2Influences of the parameters on efficiency rateThe fixed factor is zero level.And the influencesof any two factors on the index according to theregression equation are as shown in Fig.3,4.a.Efficiency rate with air temperature and paddy thicknessb.Efficiency rate with air temperature and paddy original moisture contentc.Efficiency rate with air temperature and air velocityFig.3Efficiency rate with air temperature and the otherfactors农业工程学报2012 年288Fig.3 a,b show almost the same influencing lawsofairtemperatureandpaddy thicknessorairtemperature and paddy original moisture content onefficiency rate.The thinner paddy thickness with thelower air temperature or the fewer paddy originalmoisture content with the lower air temperature willboth cause the less efficiency rate,and vice versa.Onthe same conditions of the other parameters,thehigher the air temperature or the thicker the paddythickness or the more the paddy original moisturecontent,the more the drying efficiency rate.Fig.3c indicated that the higher the drying airtemperature the more the drying efficiency rate underthe same conditions.The weaker the drying airvelocity the more the drying efficiency rate with thedrying air velocity below 0 level.The efficiency ratewere little change with the air velocity above 0 leveland changed in small range,while it was largelyincreased with the substantial increasing of the airvelocity,specifically high air temperature.Thus theair velocity about 0 level is recommended for thepaddy rice actual production.a.Efficiency rate with paddy thickness and original moisture contentb.Efficiency rate with paddy thickness and air velocityFig.4Efficiency rate with paddy thickness and the otherfactorsFig.4 a indicated that the less paddy rice originalmoisture content with the thinner paddy rice thicknesscauses the less efficiency rate.The efficiency rate willbe greatly increased with the paddy original moisturecontent or the increasing of paddy thickness,andefficiency rate is higher under the effect of less paddyoriginal moisture content and higher drying airtemperature,while slightly higher paddy originalmoisture will affirmatively cause higher efficiencyrate.Consequently more paddy original moisturecontent for drying equipment must be avoided inproduction.Fig.4 b indicated that the efficiency rate isproportional to paddy thickness when other conditionsremain unchanged,while the relationship betweenefficiency rate and air velocity is divided into twostages.According to the air velocity above and belowthe level of zero,efficiency rate is proportional andinverselyproportionaltodryingairvelocityrespectively.a.Efficiency rate with air temperature and tempering timeb.Efficiency rate with air velocity and tempering timec.Efficiency rate with paddy thickness and tempering timeFig.5Efficiency rate with tempering time and the otherfactorsFig.5a indicated that efficiency rate is largelyincreased with other parameters of constant and air增刊 2王丹阳等：稻谷深床干燥工艺参数对干燥比能耗的影响289temperature above the level of zero.Efficiency rate isnormally less under the condition that air temperatureis below the level of zero and especially below thelevel of-0.55.the influences of tempering time on efficiencyrate is greater than that of air velocity(Fig.5 b).Efficiency rate is proportional to air velocity withtempering time below the level of zero,and vice versa.As well as efficiency rate is proportional to temperingtime if the air velocity is below the level of zero,andvice versa.Fig.5 c indicated that efficiency rate isproportional to paddy thickness if the other parametersare constant,and small changes in tempering time haslittle effect on efficiency rate,but the tempering timeof particularly high or low level can effectively reducedrying efficiency rate.3Parameter optimizationThemethodofcomputersimulationandoptimization was used based on the quadratic regressionequation.Each experimental factor was designed for 5levels:2，1 and 0.With less than 2000 kJ/(kg h)oftheefficiencyratein95%probability,947optimization schemes were obtained based on theoptimization of the corresponding 3215 schemes.Variable values and frequency distribution are asshown in table.2.The results showed that the standarderror were very low,the confidence of the distributioninterval of 95%probabilities were good.Table 2Variable values and frequency distribution forefficiency rate less than 2000 kJ(kg h)-1Factor frequencyCodex1x2x3x4x5-2329111257215233-12911642392111560188234191184148194239131164190245199129173220Mean-0.807810.265048-0.38437-0.138330.008448Standard error0.0328460.0366960.0389280.040380.042933Distributionintervalof95%probabilities(-0.8814,0.7343)(0.1829,0.3472)(-0.4716,-0.2972)(-0.2288,-0.0479)(-0.0877,0.1046)processparameter ranges(56.19,57.66)(0.89,0.96)(35.28,37.03)(21.31,21.86)(2.87,3.16)4ConclusionsThe experiments of paddy drying in a deepfixed-be