Item b bed operations packed bed fluidized bed
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Item B: Bed Operations packed bed & fluidized bed 填充 床與流體化 床 PowerPoint PPT Presentation


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Item B: Bed Operations packed bed & fluidized bed 填充 床與流體化 床. 填充床 (packed bed, fixed bed 固定床 ), 流體化床 (fluidized bed) – solid phase, gas phase, liquid phase 用途 : 吸附 / 吸收 / 蒸餾 (mass transfer 質傳操作 ), 反應 (e.g. 燃燒 / 煆燒 ), ion-exchange bed 逆洗去除雜質 , ….

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Item B: Bed Operations packed bed & fluidized bed 填充 床與流體化 床

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Item b bed operations packed bed fluidized bed

Item B: Bed Operationspacked bed & fluidized bed填充床與流體化床


Item b bed operations packed bed fluidized bed

  • 填充床 (packedbed,fixedbed固定床), 流體化床 (fluidizedbed)–solidphase,gasphase,liquidphase

  • 用途: 吸附/吸收/蒸餾 (mass transfer 質傳操作), 反應 (e.g. 燃燒/煆燒), ion-exchange bed逆洗去除雜質, ….

  • 關心的項目:pressuredrop(flowresistance),reactionrate(oradsorptionrate,or..)(extentofreaction);mass transfer rate (質傳速率 ~ in general related to diffusion rate, surface area of solid); materialloss(solidmaterial);

  • 單操實驗:先關心基本的壓降(壓降不正常的後果?)


Item b bed operations packed bed fluidized bed

  • 堆積物當然也可以是粉粒體, e.g. 觸媒粒子

  • 此圖例子為氣液相逆流, 所示堆積物多用於蒸餾


Item b bed operations packed bed fluidized bed

  • 原則上影響填充床壓降者: 填充物尺寸, 堆積密度 (random packing, ordered packing, etc. 壓降與接觸面積之間的妥協), 流體速度, 流體特性 (especiallyviscosity);

  • 單一流體時的壓降 Ergunequation:viscous force and inertia force之和

  • R/ρu2 = 4.17/Re + 0.29 (f = 64/Re for flow through a pipe) R: drag force on unit area of packed material


Item b bed operations packed bed fluidized bed

  • L’ 表示也有液體流過;G‘superficialgasmassvelocity

  • 乾溼塔操作不同


Item b bed operations packed bed fluidized bed

  • Loading point – 此時壓降斜率開始明顯增加; 氣體實際流速必然快許多;液體holdup也比然增加許多;

  • Flooding point - 液體開始流不下去,stayontop; 氣體開始以bubble方式通過; 逐漸開始出現泡沫, 氣體會帶走一些液體;

  • idealoperation: 應該稍低於loadingpoint


Item b bed operations packed bed fluidized bed

  • GeneralizedpressuredropandfloodingpointcurvesfromEckert

  •  主要correlateL'&G'


Item b bed operations packed bed fluidized bed

  • 流體化床: 基本上以氣固相為主; 流體與固體粒子充分接觸, 但接觸時間可能很短 (反應速度必須快)

  • 底部多為porous plate 除一開始支撐粒子外, 也可以順便均勻分散氣體之流動

  • 固體粒子有被帶出的可能性; 一般操作都需要加裝回收粒子設備, 諸如cyclone

  • 實驗項目: 最小流體化速度, 終端速度(terminalvelocity)


Item b bed operations packed bed fluidized bed

Fixedbedtoexpandedbedtominimumfluidizationtopneumatictransport; bubbling fluidization; two-phase theory of fluidization; slurry transport or pneumatic transport


Item b bed operations packed bed fluidized bed

  • 堆積情形會影響壓降

  • 正常操作壓降即為weightofbed/crossarea=W/A

  • bedheight 會逐漸增加, 最後粒子會被吹走


Item b bed operations packed bed fluidized bed

emf and umf: minimum fluidization 對應的狀況

  • 為精確的得到umf宜先讓bedfluidized, 然後再重複之

  • Φs sphericity球型度 (為求簡化可以假設為1)

  • Forroughlysphericalparticles,εmf~0.40-0.45


Item b bed operations packed bed fluidized bed

Terminal velocity 的一些經驗式

Forspheres&εm=0.45,terminalvelocity 大約是minimumfluidizationvelocity的50倍, Rep > 103, 則只有7.7倍


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