SCRUBBER DESIGN (PACKED COLUMN) Prepared by : Checked by : Date : Column Tag No. Job No. Client Project Stream = Intallox Saddles = 25 mm = PP = 15 mmWC / m packing height = 3.2 m (including all packed beds) : : : : : HCL Vap. ### Input Data Packing type Packing size Packing MOC Gas pr. Drop / m bed Total packing height = 147.1 (N/m2)/m Gas / Vapour Properties Gas / Air flow rate = = Gas pressure at entry Gas temperature at entry Gas / Air mol weight = = = 1000 kg/h 0.2778 kg/s 1.0000 atm 30.00 oC 29 OR = 0 m3/h 0 m3/s = 303.00 oK Component to be scrubbed Component Name = Component flow rate = % comp. in air/gas = Molecular weight of comp. = HCL Vap 70 Kg/h 6 % (v/v) 36.5 (presumed) / (given by client) / (by process cal.) Liquid / Scrubbing media Properties Scrubbing media = 20% NaOH Liquid flow rate, L = 77 kg/h = 0.0214 kg/s Liquid Density, L = 1100 kg/m3 Liquid Viscosity, µL Packing factor, F p = 0.0035000 Ns/m2 = 21 m-1 Conversion : 3.5 Cp = 0.00350000 Ns/m2 Charac. Packing Factor,Cf = Conversion factor, J = 33 Ref. Table 6.3, Characterstics of Random packings 1.0 factor for adequate liquid distribution & irrigation across the bed Sheet 1 of 11 Calculations TO CALCULATE COLUMN DIAMETER Since larger flow quantities are at the bottom for an absorber, the diameter will be chosen to accommodate the bottom conditions. To calculate Gas density Avg. molecular weight = If gas flow rate is given in kg/h Gas in = 0.01 Kmol/s kmol = mass / mol wt = (kmol/s) x T in kelvin x 1.0 atm x 22.4 273 pr. In atm 1 = 0.234499 m3/s 29.45 Kg / Kmol If gas flow rate is given in m3/h Gas in = (m3/s) x 273 x pr. in atm x T in kelvin 1.0 atm 1 22.4 = = 0 Kmol/s 0 Kg/s mass = mol wt x kmol Select vol. flow rate and mass flow rate from above, Selected mass flow rate = 0.28 Kg/s Selected vol. Flow rate = 0.23 m3/s Selected molar flow rate = 0.01 Kmol/s Therefore, gas density = 1.1846 Kg/m3 (mass flow rate / vol. Flow rate) To find L', G' and Tower c/s area Assuming essentially complete absorbtion, Component removed = 0.0207 Kg/s Liquid leaving = 0.0420 Kg/s L' G' Using G L (molar flow rate x % comp. x mol. Wt.) (Inlet liquid flow rate + comp. Removed) 0.5 = 0.00497 0.00497 as ordinate, = Refer fig.6.34 using a gas pressure drop of 147.1 (N/m2)/m G' 2 Cf µL0.1 J ( G -L ) gc G 0.04 (from graph) Therefore, G' = 0.04 G ( L -J G ) gc 0.5 Cf µ = Tower c/s area Tower diameter = = = = 0.1 L 1.6665 Kg / m2.s 0.1667 m2 0.4607 m 500 mm 0.1963 m2 TO ESTIMATE POWER REQUIREMENT ( c/s area = mass flow rate / G' ) = 460.7 mm Corresponding c/s area Sheet 2 of 11 Efficiency of fan / blower = 60 % assumed / given To calculate pressure drop Pressure drop for irrigated = packing For dry packing, O/L Gas flow rate, G' O/L Gas pressure Gas density, G 470.72 N/m2 (pressure drop per m packing x total ht. of packing) = 1.3095 Kg / m2.s (Gas inlet flow rate - Component removed) / c/s area = 100854.28 N/m2 (subtracting pressure drop across packing) = gas mol wt. x 273 x 22.41m3/Kmol T in kelvin = 1.1605 Kg/m3 = = CD = 96.7 G' 2 G gas o/l pr. 101330 CD Delta P Z Ref. Table 6.3, Characterstics of Random packings 142.89 N/m2 613.61 N/m2 25 mmWC 245.17 N/m2 (irrigated packing + dry packing) (packing supports and liquid distributors) Pressure drop for packing = Pressure drop for internals = = Gas velocity Inlet expansion & outlet contraction losses = 7.5 m/s = 1.5 x Velocity heads = 42.19 N m / Kg = 49.97 N/m2 = 908.75 N/m2 = 1.5 x (V2 / 2g) (divide by density) Total pressure drop Fan power output (packing + internals + losses) = pressure drop,N/m 2 x (gas in - component removed) Kg/s O/L gas density, Kg/m 3 = 201.35 N .m / s = 0.20 kW = = 0.34 kW 0.45 hp (fan power output / motor efficiency) Power for fan motor Sheet 3 of 11 COLUMN DIAMETER / HYDRAULIC CHECK Liq.-Vap. Flow factor, F LV = (L / V) x ( = 0.0025 V / L ) Design for an initial pressure drop of From K4 v/s FLV, K4 K4 at flooding Trial % flooding = = = ( = = 0.85 6.50 15 mm H2O /m packing (K4 / K4 at flooding) 36.1620 K4 . V ) x 100 (1/2) Gas mass flow rate, V m ( L -L V ) 13.1 Fp (µL / = Trial column c/s area (Trial As) = = Trial column dia., D = )0.1 3.7763 kg/m2.s V / Vm 0.0736 m2 0.3060 m D = (4/pi) x Trial As Round off 'D' to nearest standard size Therefore, D = 0.500 m Column C/S area, A s = 0.1963 m2 As = (pi/4) x D2 % flooding = 13.5472 % flooding = Trial % flooding x (Trial A s / As) Conclusion Generally packed towers are designed for 50% -- 85% flooding. If flooding is to be reduced, (i) Select larger packing size and repeat the above steps. OR (ii) Increase the column diameter and repeat the above steps. Sheet 4 of 11 HETP PREDICTION Norton's Correlation : ln HETP = n - 0.187 ln + 0.213 ln µ Applicable when, liquid phase surface tension > 4 dyne/cm & < 36 dyne/cm liquid viscosity > 0.08 cP & < 0.83 cP Conversion : Input Data 0.02 N/m = 18 dyne/cm Liquid-phase Surface Tension, = 20 dyne/cm Norton's Correlation Applicable Liquid Viscosity n = = 3.5 cP 1.13080 Norton's Correlation NOT applicable Calculation ln HETP HETP = = = 0.84 2.31 ft 0.7 m For separations, less than 15 theoritical stages, a 20% design safety factor can be applied. Considering 20% safety factor, HETP = 0.85 m For separations, requiring 15 to 25 theoritical stages, a 15% design safety factor can be applied. Considering 15% safety factor, HETP = 0.81 m Sheet 5 of 11 Table 6.2 Constant for HETP Correlation Ref.:: Random Packings and Packed Towers ---- Strigle Ref. : : Chemical Engineering, Volume-6 , COULSON & RICHARDSON'S Ref. : : Mass Transfer Operation : : Treybal