scrubber design
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design scrubberTRANSCRIPT
Column DiameterSCRUBBER DESIGN (PACKED COLUMN)Prepared by :Column Tag No.:HCL ScrubberChecked by :Job No.:4506ADate :Client:JOLProject:SR - Plant -4, 5135792468Input DataStream:HCL Vap.Packing type=Intallox SaddlesPacking size=25mmPacking MOC=PPGas pr. Drop / m bed=15mmWC / m packing height=147.09975(N/m2)/mTotal packing height=3.2m (including all packed beds)Gas / Vapour PropertiesGas / Air flow rate=1000kg/hOR0m3/h=0.2778kg/s=0m3/sGas pressure at entry=1.0000atmGas temperature at entry=30.00oC=303.00oKGas / Air mol weight=29Component to be scrubbedComponent Name=HCL VapComponent flow rate=70Kg/h% comp. in air/gas=6% (v/v)(presumed) / (given by client) / (by process cal.)Molecular weight of comp.=36.5Liquid / Scrubbing media PropertiesScrubbing media=20% NaOHLiquid flow rate, L=77kg/h=0.0214kg/sLiquid Density, L=1100kg/m3Conversion :Liquid Viscosity, L=0.0035000Ns/m23.5Cp =0.00350000Ns/m2Packing factor, Fp=21m-1Charac. Packing Factor,Cf=33Ref. Table 6.3, Characterstics of Random packingsConversion factor, J=1.0factor for adequate liquid distribution & irrigation across the bedCalculationsTO CALCULATE COLUMN DIAMETERSince larger flow quantities are at the bottom for an absorber, the diameter will be chosen toaccommodate the bottom conditions.To calculate Gas densityAvg. molecular weight=29.45Kg / KmolIf gas flow rate is given in kg/hIf gas flow rate is given in m3/hGas in =0.0094321826Kmol/sGas in= (m3/s) x 273xpr. in atmx 1kmol = mass / mol wtT in kelvin1.0 atm22.4=(kmol/s) x T in kelvin x 1.0 atm x 22.4273 pr. In atm 1=0Kmol/s=0.234499m3/s=0Kg/smass = mol wt x kmolSelect vol. flow rate and mass flow rate from above,Selected mass flow rate=0.2777777778Kg/sSelected vol. Flow rate=0.234499m3/sSelected molar flow rate=0.009432183Kmol/sTherefore, gas density=1.1846Kg/m3(mass flow rate / vol. Flow rate)To find L', G' and Tower c/s areaAssuming essentially complete absorbtion,Component removed=0.0207Kg/s(molar flow rate x % comp. x mol. Wt.)Liquid leaving=0.0420Kg/s(Inlet liquid flow rate + comp. Removed)L' G0.5=0.00497G' LUsing0.00497as ordinate,Refer fig.6.34 using a gas pressure drop of147.09975(N/m2)/mG' 2 Cf L0.1 J=0.04(from graph)G ( L -- G) gcTherefore, G'=0.04G ( L -- G) gc0.5Cf L0.1 J=1.6665Kg / m2.sTower c/s area=0.1667m2( c/s area = mass flow rate / G' )Tower diameter=0.4607m=460.7mm=500mmCorresponding c/s area=0.1963m2TO ESTIMATE POWER REQUIREMENTEfficiency of fan / blower=60%assumed / givenTo calculate pressure dropPressure drop for irrigated=470.72N/m2(pressure drop per m packing x total ht. of packing)packingFor dry packing,O/L Gas flow rate, G'=1.3095Kg / m2.s(Gas inlet flow rate - Component removed) / c/s areaO/L Gas pressure=100854.2808N/m2(subtracting pressure drop across packing)Gas density, G=gas mol wt. x 273 xgas o/l pr.22.41m3/Kmol T in kelvin101330=1.1605Kg/m3CD=96.7Ref. Table 6.3, Characterstics of Random packingsDelta P=CD G' 2ZG=142.89N/m2Pressure drop for packing=613.61N/m2(irrigated packing + dry packing)Pressure drop for internals=25mmWC(packing supports and liquid distributors)=245.17N/m2Gas velocity=7.5m/sInlet expansion & outlet=1.5 x Velocity heads=1.5 x (V2 / 2g)contraction losses=42.19N m / Kg=49.97N/m2(divide by density)Total pressure drop=908.75N/m2(packing + internals + losses)Fan power output=pressure drop,N/m2 x (gas in - component removed) Kg/sO/L gas density, Kg/m3=201.35N .m / s=0.20kWPower for fan motor=0.34kW(fan power output / motor efficiency)=0.45hpCOLUMN DIAMETER / HYDRAULIC CHECKLiq.-Vap. Flow factor, FLV=(L / V) x ( V / L)=0.0025Design for an initial pressure drop of15mm H2O /m packingFrom K4 v/s FLV,K4=0.85K4 at flooding=6.50Trial % flooding=( (K4 / K4 at flooding) ) x 100=36.1620Gas mass flow rate, Vm=K4 . V ( L -- V)13.1 Fp (L / L)0.1=3.7763kg/m2.sTrial column c/s area=V / Vm(Trial As)=0.0736m2Trial column dia., D=0.3060mD =(4/pi) x Trial AsRound off 'D' to nearest standard sizeTherefore, D=0.500mColumn C/S area, As=0.1963m2As =(pi/4) x D2% flooding=13.5472% flooding = Trial % flooding x (Trial As / As)ConclusionGenerally 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.HETP PREDICTIONNorton's Correlation :ln HETP = n - 0.187 ln + 0.213 ln Applicable when,liquid phase surface tension > 4 dyne/cm & < 36 dyne/cmliquid viscosity > 0.08 cP & < 0.83 cPConversion :Input Data0.018N/m =18dyne/cmLiquid-phaseSurface Tension,=20dyne/cmNorton's Correlation ApplicableLiquid Viscosity=3.5cPNorton's Correlation NOT applicablen=1.13080Calculationln HETP=0.8374365771HETP=2.3104367528ft=0.7042211223mFor separations, less than 15 theoritical stages, a 20% design safety factor can be applied.Considering 20% safety factor,HETP=0.8450653467mFor separations, requiring 15 to 25 theoritical stages, a 15% design safety factor can be applied.Considering 15% safety factor,HETP=0.8098542906m
&CSheet &P of &N(1/2)For values of 'n' Refer Table 6.2For values of K4 , refer fig 11.44Refer fig 6.34Refer Table 6.3Refer Table 6.3
Table 6.2Table 6.2Constant for HETP CorrelationRef.:: Random Packings and Packed Towers ---- Strigle
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Fig 11.44Ref. : : Chemical Engineering, Volume-6 , COULSON & RICHARDSON'S
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Fig 6.34Ref. : : Mass Transfer Operation : : Treybal
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Table 6.3
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