By Final Year Chem. Engg. (Roll no:11-20) U.I.C.T,Mumbai-400019

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By Final Year Chem. Engg. (Roll no:11-20) U.I.C.T,Mumbai-400019

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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= 1m3/hr

Impurity in inlet organic stream=10000ppm

Desired impurity in exit stream=500ppm

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

- 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)

- [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)

- 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

- 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)

- 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.

Thank You