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

Same packing as used in G-L operations Advantage of using Packings Material of Packing to be used

The Problem statement: Flow rate of organic stream= 1m 3 /hr Impurity in inlet organic stream=10000ppm Desired impurity in exit stream=500ppm Continuous phase:SI units Flow rate(Qc) Viscosity ( µ c) Density( ρ c) Diffusivity(Dc) Concentration of impurity in feed(Cc1)10000 Dispersed phaseSI units Flow rate(Qd) Viscosity ( µ d) Density( ρd) Diffusivity(Dd) Interfacial tension( γ ) Equilibrium distribution coefficient (Cd/Cc)55 Concentration of impurity at inlet(Cd1)00

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 ε f ={[(Ud/Uc) 2 +8 (Ud/Uc)] (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*ρ c /(e 3 *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/(ρ c -ρ d )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/K oc.a [NTU oc ] plug flow =(C c1 -C c2 )/(ΔC) LM Height of column: Z t = [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 Overall mass balance Q o *ρ o *(10, )=Q a *ρ a *(50,000-0) 1*900*9500= Q a *1000*50000 Thus Q a =.9*9500/50000 = Thus, the flow rate ratio (aq:org) or velocity ratio should be > 0.171

Sample calculations- continued Consider Raschig ring packings of size 1”. Let the operating holdup=60% of holdup at flooding. Let Ud/Uc=1.1. ε f = Operating holdup = Terminal velocity = m/s By slip velocity relation, Ud= m/s Uc= m/s Column diameter: 0.318m Drop diameter: 8 mm Koc.a= HTU=3.327 ft=1.01m NTU=3.429 Column height=11.41 ft = m No of orifices for the distributor (orifice diameter=6 mm)= 70(approx)

Variation with Ud/Uc for 70% flooding - 1 inch raschig ring Ud/Uc ε HTU OC [(NTU)plug flow]continuous Height of column (based on plug flow),(Zt)plug D (column dia) m Variation with nominal diameter of packing for 70% flooding - for Ud/Uc=1.5 1 inch 0.75 inch es 0.5 inc he s D (column dia) m

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.