Scrubber Designing Spreadsheet by kapare9055

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```									                               SCRUBBER DESIGN (PACKED COLUMN)

Prepared by :                                                Column Tag No.          :
Checked by :                                                 Job No.                 :
Date :                                                       Client                  :
Project                 :

Input Data                                                   Stream                  :       HCL Vap.

Packing type               = Intallox Saddles
Packing size               =           25 mm
Packing MOC                =          PP
2
Gas pr. Drop / m bed       =           15 mmWC / m packing height                    =         147.1 (N/m )/m
Total packing height       =          3.2 m (including all packed beds)

Gas / Vapour Properties
3
Gas / Air flow rate     =          1000 kg/h          OR                            0 m /h
3
=        0.2778 kg/s                      =                 0 m /s

Gas pressure at entry      =     1.0000 atm
o                                           o
Gas temperature at entry   =      30.00 C                        =            303.00 K
Gas / Air mol weight       =         29

Component to be scrubbed
Component Name            =    HCL Vap
Component flow rate       =         70 Kg/h
% comp. in air/gas        =          6 % (v/v)      (presumed) / (given by client) / (by process cal.)
Molecular weight of comp. =       36.5

Liquid / Scrubbing media Properties
Scrubbing media          = 20% NaOH
Liquid flow rate, L      =          77 kg/h
=     0.0214 kg/s
3
Liquid Density, L        =       1100 kg/m                   Conversion :
2                                                        2
Liquid Viscosity, µL       = 0.0035000 Ns/m                          3.5 Cp     =        0.00350000 Ns/m

-1
Packing factor, Fp         =          21 m
Charac. Packing Factor,Cf =          33 Ref. Table 6.3, Characterstics of Random packings
Conversion factor, J      =          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    =             29.45 Kg / Kmol

If gas flow rate is given in kg/h                                If gas flow rate is given in m3/h

Gas in =        0.009432183 Kmol/s                               Gas in        = (m3/s) x     273       x pr. in atm x    1
kmol = mass / mol wt                                         T in kelvin   1.0 atm         22.4
= (kmol/s) x T in kelvin x 1.0 atm x 22.4
273         pr. In atm  1                             =                  0 Kmol/s
3
=       0.234499 m /s                                              =                  0 Kg/s
mass = mol wt x kmol

Select vol. flow rate and mass flow rate from above,
Selected mass flow rate     = 0.277778 Kg/s
3
Selected vol. Flow rate     = 0.234499 m /s
Selected molar flow rate    = 0.009432 Kmol/s

3
Therefore, gas density         =      1.1846 Kg/m                              (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                                  (molar flow rate x % comp. x mol. Wt.)
Liquid leaving             =      0.0420 Kg/s                                  (Inlet liquid flow rate + comp. Removed)

0.5
L'    G                      =    0.00497
G'    L

Using                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              =        0.04 (from graph)
G(    L --         G ) gc

0.5
Therefore, G'                  =        0.04     G(     L   --       G)   gc
Cf µL0.1 J

2
=      1.6665 Kg / m .s

2
Tower c/s area                 =      0.1667 m                   ( c/s area = mass flow rate / G' )

Tower diameter                 =      0.4607 m                   =                 460.7 mm
=         500 mm

2
Corresponding c/s area         =      0.1963 m

Sheet 2 of 11
TO ESTIMATE POWER REQUIREMENT

Efficiency of fan / blower   =          60 %          assumed / given

To calculate pressure drop

2
Pressure drop for irrigated =       470.72 N/m        (pressure drop per m packing x total ht. of packing)
packing

For dry packing,
2
O/L Gas flow rate, G'        =     1.3095 Kg / m .s (Gas inlet flow rate - Component removed) / c/s area
2
O/L Gas pressure             =  100854.3 N/m           (subtracting pressure drop across packing)
Gas density,     G           =  gas mol wt. x       273    x    gas o/l pr.
22.41m3/Kmol T in kelvin          101330
3
=     1.1605 Kg/m

CD                           =        96.7     Ref. Table 6.3, Characterstics of Random packings

Delta P                      = CD    G' 2
Z                                      G
2
=      142.89 N/m

2
Pressure drop for packing =         613.61 N/m        (irrigated packing + dry packing)

Pressure drop for internals =           25 mmWC       (packing supports and liquid distributors)
2
=       245.17 N/m

Gas velocity                 =         7.5 m/s
Inlet expansion & outlet     = 1.5 x Velocity heads      =     1.5 x (V2 / 2g)
contraction losses           =       42.19 N m / Kg
2
=       49.97 N/m                 (divide by density)

2
Total pressure drop          =      908.75 N/m        (packing + internals + losses)

2
Fan power output             = pressure drop,N/m x (gas in - component removed) Kg/s
O/L gas density, Kg/m3
=     201.35 N .m / s
=       0.20 kW

Power for fan motor          =        0.34 kW         (fan power output / motor efficiency)
=        0.45 hp

Sheet 3 of 11
COLUMN DIAMETER / HYDRAULIC CHECK

Liq.-Vap. Flow factor, FLV   = (L / V) x (       V   /        L)

=      0.0025

Design for an initial pressure drop of                   15           mm H2O /m packing
From K4 v/s FLV,
K4                           =           0.85

K4 at flooding               =           6.50

Trial % flooding             = ( (K4 / K4 at flooding)                     ) x 100
=   36.1620
(1/2)
Gas mass flow rate, Vm       =      K4 .    V(       L   --           V)
0.1
13.1 Fp (µL /              L)

2
=      3.7763 kg/m .s

Trial column c/s area        =     V / Vm
(Trial As)
2
=      0.0736 m

Trial column dia., D         =      0.3060 m                               D = (4/pi) x Trial As

Round off 'D' to nearest standard size
Therefore, D                =        0.500 m

2                                             2
Column C/S area, As          =      0.1963 m                               As = (pi/4) x D

% flooding                   =     13.5472                            % flooding = Trial % flooding x (Trial As / 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                                                  0.018 N/m =      18 dyne/cm
Liquid-phase
Surface Tension,             =         30 dyne/cm              Norton's Correlation Applicable

Liquid Viscosity            =          3.5 cP                     Norton's Correlation NOT applicable

n                           =     1.13080

Calculation

ln HETP                     =   0.761615

HETP                        =   2.141731 ft
=      0.6528 m

For separations, less than 15 theoritical stages, a 20% design safety factor can be applied.

Considering 20% safety factor,
HETP                     =     0.78336 m

For separations, requiring 15 to 25 theoritical stages, a 15% design safety factor can be applied.

Considering 15% safety factor,
HETP                     =     0.75072 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

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