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Design of Spray column with Chemical Reaction Problem To reduce the impurity (A) level in an organic liquid from 10000ppm to 500ppm using an aqueous solvent containing a solute (B) which reacts with A following the rate equation, rate = Kmn*[A]m * [B]n Given data • • • • • • • Organic phase flow rate = 1m3/hr ρaq =1000 kg/m3 ρorg = 900 kg/m3 µaq = 1 mPas µorg = 5 mPas σ = 0.025 N/m Distribution coefficient = 5 Co-relations used • u0 = • dp = • kd = (0.00375*u0)/(1+µd/µc) • kc = 0.725* (dp*u0*ρ/µc)^-0.43*(µc/ρcD)^-0.58*(1-Φd) Approach • Case 1- The rate of chemical reaction is very slow as compared to rate of mass transfer • Case 2- The rate of mass transfer is comparable to the rate of chemical reaction • Case 3- The rate of chemical reaction is very high as compared to rate of mass transfer Case 1 • As the rate of chemical reaction is very low as compared to rate of mass transfer the concentration profile will be as below Case 2 • When the rate of chemical reaction is comparable to the rate of mass transfer Case 3 • As the rate of chemical reaction is very high the concentration of A in aqueous phase will be zero Assumption • The dispersed phase mass transfer co-efficient is very high as compared to continuous phase mass transfer co-efficient • Hence, resistance to mass transfer on the dispersed side is neglected Calculations • Calculate minimum flow rate for aqueous liquid from given data • Assume flow rate of aqueous liquid higher than the minimum value calculated • Calculate u0 • Calculate dp • Calculate Φf • Assume Φd value ranging from 0.1 times Φf to 0.9 times Φf increasing it by 0.1 every time • Hence calculate vc and vd • From the values of vc and Qc we get the column diameter. • Then we calculate a = 6 Φd/d • Then we find the no of orifices in the distributor • Then we find the values of kd and kc • Then we find the relative rate of reaction as regards to the rate of mass transfer • Based on the relative values, we can find the volume of the contactor and the height of the contactor Effect of water flow rate on volume V vs vd 12 10 8 4 5 8 6 Poly. (4) Poly. (5) 4 Poly. (8) 2 0 0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 When the phases are interchanged • When water is the continuous phase, due to Morongani effect we consider only regimes 3 and 4 • Calculations similar to the previous case • Continuous phase mass transfer is the controlling mechanism Effect of %flooding on Volume 0.014 0.012 0.01 1 0.008 2 3 Poly. (1) 0.006 Poly. (2) Poly. (3) 0.004 0.002 0 0 10 20 30 40 50 60 70 80 90 100 Effect of %flooding on Height 0.09 0.08 0.07 0.06 1 0.05 2 Poly. (1) 0.04 Poly. (2) 0.03 0.02 0.01 0 0 10 20 30 40 50 60 70 80 90 100