By final year chem engg roll no 11 20 u i c t mumbai 400019
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Packed Column Extractor. By Final Year Chem. Engg. (Roll no:11-20) U.I.C.T,Mumbai-400019. An Overview. Same packing as used in G-L operations Advantage of using Packings Material of Packing to be used. Tower design. The Problem statement : Flow rate of organic stream= 1m 3 /hr

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By final year chem engg roll no 11 20 u i c t mumbai 400019

Packed Column Extractor

By

Final Year Chem. Engg. (Roll no:11-20)

U.I.C.T,Mumbai-400019


By final year chem engg roll no 11 20 u i c t mumbai 400019

An Overview

  • Same packing as used in G-L operations

  • Advantage of using Packings

  • Material of Packing to be used


By final year chem engg roll no 11 20 u i c t mumbai 400019

Tower design

  • The Problem statement:

    Flow rate of organic stream= 1m3/hr

    Impurity in inlet organic stream=10000ppm

    Desired impurity in exit stream=500ppm


By final year chem engg roll no 11 20 u i c t mumbai 400019

Approach

  • We assume that the dispersed and the continuous phases are in plug flow

  • We find the minimum value of Ud/Uc

  • Then we assume different values for Ud/Uc

  • Calculate hold up at flooding using

  • εf={[(Ud/Uc)2+8 (Ud/Uc)]0.5-3(Ud/Uc)}/[4*(1- Ud/Uc)]

  • Assume a certain percentage of flooding hold up as operating hold up and hence calculate ε

  • We find the terminal velocity of a drop using

  • eUo=C(a*ρc/(e3*g*Δ ρ)) (-0.5) formula given in the book by Degallson and Laddha where C=0.637

  • Then we calculate Ud using the correlation for slip velocity


By final year chem engg roll no 11 20 u i c t mumbai 400019

  • Find diameter of the column:

  • D=((Qc/Uc)*(4/3.142))0.5

  • Drop diameter is found using

  • d=1.6(γ/(ρc-ρd)g) 0.5

  • Size of Raschig rings were taken as 1”,0.75” and 0.5”.

  • Overall Height of transfer unit:

    Koc.a=0.06* φ*(1- φ)/[(a*ρc/(g*e 3 *Δρ))0.5*(γ/(Δρ*g)) 0.5 *{(Sc)c 0.5 +(Sc)d 0.5 /m}]

    (This corellation is for packing size greater than drop size)


By final year chem engg roll no 11 20 u i c t mumbai 400019

  • [HTU oc]plug flow = Uc/Koc.a

  • [NTU oc]plug flow=(Cc1-Cc2)/(ΔC)LM

  • Height of column:

    Zt=[HTU oc]plug flow * [NTU oc]plug flow

  • Distributor design:

    We take nozzle velocity = 0.5*eUo

    Nozzle diameter value should be comparable with droplet diameter value. Hence, we take nozzle diameter= 6 mm.

    No of orifices = Qd/( Area of nozzle*Vn)


Sample calculations
Sample Calculations

  • Overall mass balance

  • Qo*ρo*(10,000-500)=Qa*ρa*(50,000-0)

  • 1*900*9500= Qa*1000*50000

  • Thus

    Qa= .9*9500/50000

    = 0.171

  • Thus, the flow rate ratio (aq:org) or velocity ratio should be > 0.171


Sample calculations continued
Sample calculations- continued

  • Consider Raschig ring packings of size 1”.

  • Let the operating holdup=60% of holdup at flooding.

  • Let Ud/Uc=1.1.

  • εf = 0.3403

  • Operating holdup = 0.2042

  • Terminal velocity = 0.03191 m/s

  • By slip velocity relation, Ud= 0.00385 m/s

  • Uc= 0.0035 m/s

  • Column diameter: 0.318m

  • Drop diameter: 8 mm

  • Koc.a= 12.407

  • HTU=3.327 ft=1.01m

  • NTU=3.429

  • Column height=11.41 ft = 3.477 m

  • No of orifices for the distributor (orifice diameter=6 mm)= 70(approx)


Observations
Observations

  • With increase in Ud/Uc, height of column decreases, diameter increases.

  • The diameter of the column increases when packings of smaller nominal diameter are used.

  • With increase in %flooding the total height of the column decreases.