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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

slide2
An Overview
  • Same packing as used in G-L operations
  • Advantage of using Packings
  • Material of Packing to be used
slide3
Tower design
  • The Problem statement:

Flow rate of organic stream= 1m3/hr

Impurity in inlet organic stream=10000ppm

Desired impurity in exit stream=500ppm

slide4
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
slide5
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)

slide6
[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.
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