制粒工艺过程的水分控制（PPT51页)

影响颗粒稳定度的因素调制20％环模15％粉碎粒度20％配方/原料40％冷却5%蒸汽调制的关键•蒸汽质量：什么是蒸汽质量？如何得到高质量蒸汽•根据饲料类型和调制时间长短正确设定调制气压•原料与成品水分控制蒸汽调制过程的热交换•蒸汽热量的组成：表观热与潜热•潜热---物料升温的主要热量来源:–每凝结一个百分数单位的优质蒸汽，物料温度大约上升150C•蒸汽表•蒸汽质量蒸汽表over压力温度表观热潜热总热kg/cm20C----kcal/kg----0.51121125316431.01201205266461.51271275216482.0134134517651蒸汽质量•湿蒸汽－蒸汽中含液态水,热量低，易堵塞模孔•蒸汽质量可用气态水在蒸汽中的百分数来表示•测定蒸汽质量的方法•过热蒸汽或不饱和蒸汽•判定过热蒸汽的方法•理想的蒸汽：100％饱和蒸汽蒸汽质量的计算蒸汽质量%={[(W2xT2-W1xT1)/(W2-W1)-Hf]/Hfg}x100%W1=注入蒸汽前水重W2=注入蒸汽前水重T1=注入蒸汽前水温T2=注入蒸汽前水温Hf=测试压力下的表观热(查蒸汽表)Hfg=测试压力下的潜热(查蒸汽表)蒸汽表over压力温度表观热潜热总热kg/cm20C----kcal/kg----0.51121125316431.01201205266461.51271275216482.0134134517651蒸汽系统主要设备的选择与设定•锅炉•输汽管道内径的确定•汽水分离器•疏水阀•减压(稳压)器•流量控制阀锅炉的选择与设置BoilerSelectionandLayout•燃料的选择要全面考虑供气稳定性、人工、燃料价格及环境等因素FuelType•锅炉的功率或供气量要留有余地BoilerSize:Leavesufficientroom•尽可能缩短锅炉与用汽设施之间的距离Locationoftheboiler:closetothepelletmillID(cm)=Wx3.53v/30W=蒸汽流量(Steamflow),kg/minv=给定气压下的比体积(Specificvolumeundergivensteampressure),m3/kg(查表)30=最大流速(allowedsteamflowvelocity),m/s输汽管道内径的确定SizingthePipe气水分离器SteamSeparator•根据机械原理将蒸汽中的水滴与蒸气分开以得到优质蒸汽.Usingamechanicaladvicetoremovewaterdrip-letsfromthesteamandobtainhighqualitysteam.•好的气水分离器可移走98%的水滴.Goodseparatorcanremovemorethan98%ofthewaterdrip-lets•其功能为将凝积水(在进入调制器前)从蒸汽系统中排出.Toremovewatercondensateoutofthesteamsystem(beforethesteamgoingintotheconditioner).•疏水阀应不时启闭使一定压力下的凝积水移到常压的回收系统且不丢失蒸気.Itmustperiodicallyopenandclosetoallowthepressurizedcondensatetoberemovedintoanatmosphericcondensatereturnsystemwithoutlosingsteam.疏水阀CheckValve•只有气压稳定才能使气流稳定,从而保证制粒过程稳定.Steadypressureiscriticalforsmoothsteamflowandhencesmoothpelletingoperation.•减压有助于提高蒸汽质量.Pressurereductionhelpsimprovingsteamquality.•减压(稳压)器的主要参数:流量、调压范围及控制的稳定性(可用变异系数度量).Parametersforconsideration:Maximumflow(kg/hour),pressurerange,pressurestability(expressedasCV%).减压(稳压)器SteamPressureReducer-Regulator•控制进入调制器的蒸汽流量.只有物料流量与蒸汽流量同步控制才能实现稳定的制粒作业.Itmetersthesteamflowgoingintotheconditioningchamber-animportantdeviceforoperator•调制器操作与流量应是线性关系.Alinearresponseisrequiredbetweencontrolvalveandsteamflow.•一般的控制阀的操作与实际流量不是线性关系.Thegatevalveisnon-linear-athalfopening,smallchangesinsettingresultslargesteamflowvariation.流量控制阀SteamFlowControlValve•减压、分水、气压控制三合一Aseparator-trap-pressureregulator“threeinone”device.•流量控制阀在自动和手动控制条件下均与流量呈线性关系.Linearsteamflowcontrolvalvesforbothmanualandautomaticcontrolsystem-CospectValve蒸汽调制系统参数的设定ParameterSettingsinSteamConditioning•考虑因素：调制时间、蒸汽质量、饲料配方.Factorstobeconsidered:Retentiontime,steamqualityandformulation/ingredients.•对于一般饲料配方，应在不塞机的前提下，尽可能提高料温.Ingeneral,mashtemperatureshouldbeconditioned“ashighaspossible”beforereachingthe“chockpoint”.减压前后的压力比PressureRatiobefore–afterPressureReducingValve-减压可使蒸汽中的水滴挥发.减压幅度过大,在蒸汽质量好时,可形成过热(不饱和)蒸汽.Pressurereductionhelpswaterdripletsflashoffbutmayalsoproduceasupper-heatedsteamifthepressuredropistoomuchandthesteamqualityalreadyveryhigh.•一般推荐:3.5-4:1GeneralRecommendation:3-4to1进入调制室的蒸汽压力设定SteamPressureSettingbeforeConditioner•调制时间短，蒸汽质量好，宜采用低蒸汽压(1.5-0.5kg/cm2或更低)，以争取热交换时间(并降低能耗).Lowpressure(0.5-1.5kg/cm2)ispreferredifretentiontimeisshort(20secorless).•调制时间长，可采用较高蒸汽压力。Higherpressureworkswell(2-4kg/cm2)ifretentiontimeislong(40secormore).•关键在于有足够时间完成热交换-释放潜热.Thekeyistogivesufficienttimeforheattransfer-releasinglatentheat.•调制温度≤700C以控制水分避免塞机Keepmashtemperature≤700Ctoavoidmoistureincreasecausedstickiness•可考虑采用较高蒸汽压力甚至过热蒸汽Highersteampressure-lowsteamflow,orsupperheatedsteammayhelp高乳清粉乳猪料蒸汽参数的设定SteamSettingforHighWheyDiet•延长调制时间有助于水分进入并软化粉料以提高颗粒质量Extendedretentiontimehelpsmoisturepenetrationandsoftensparticlesforbetterpellets.•调制时间测定(Measuringmeanretentiontime):MRT(Sec.)=(3600xW)/(1000xP)where,W=调制器内水分校正的物料量,kgMoistureadjustedmashweightinconditioner,kgP=产量,MT/hProductionrate,MT/h蒸汽调制时间RetentionTime蒸汽调制时间RetentionTime•延长常规调制器调制时间的简易办法:通过调节浆片角度提高物料在调制器内的充满度.ExtendingRetentionTimebyAdjustingPitchAngle•夹层(间接)蒸器的作用Theroleofindirectsteam.ExtendingRetentionTimebyAdjustingPitchAngle•Mashfillbeforeadjustment•thermometerConditionerPaddlePitchAdjustment(TopView)MashFillafterAdjustment延长调制时间的设备•多层调制器•可变仰角调制器•熟化调制器Ripenner•DDC制粒过程的自动控制•料流控制•蒸汽流控制•料温反馈控制，电流反馈控制常规蒸汽调制的局限性LimitstoTraditionalSteamConditioning•高水分、低温原料限制料温升高。Cannotachievehighmashtemperaturewheningredientmoistureishighandtemperatureislow.•解决途径：烘干-预热？投入机械能?加压调制?Solution:Drying?Pre-heating?Mechanicalenergyinput?Pressurizing?What’sNew?-ForBetterPellets-制粒工艺过程的水分控制控制关键点•调制前粉料水分:水分低于12%在混合物机加水(一般不超过一个百分点)•调制后水分可通过料温上升估测•成品水分:通过冷却时间－料层高度调节•以电容为基础的快速水分测定器：–不需样品粉碎–不需称量–测定误差不超过0.5百分数单位–手工操作系统，六秒中得结果,电脑自动监测系统，每秒20个以上读数关键设备制粒问题解难案例PelletingTroubleShooting-CasebyCaseAnalyses例1(广东,1985)Case1(Guangdong)•问题:产量偏低,爱环镆寿命低Problem:lowproductionrate.,diewearingtofast•现场观察:进入调制器蒸汽压:2.7kg/cm2,On-siteobservation:Steampressureatconditioner2.7kg/cm2•问题所在?如何解决?Solution?例2(美国,1990)Case2(US-1990)•问题:兔颗粒质量差,含粉多.Problem:poorpelletqualityinarabbitdiet.•现场观察:未发现明显异常.与工人座谈得知唯一改变是粉碎玉米由厂外带加工.Nosignificantproblemfoundinpelletingoperation.Onlychangesrecentlymadewascornmealsuppliedfromtoll-millingbyanoutsidecontractor.•问题所在?如何解决?Solution?例3(美国,1994)Case3(US-1994)•问题:料温上不去,颗粒质量差,含粉多,产量低P