SCRUBBER DESIGN (PACKED COLUMN)
Prepared by : Checked by : Date :
Column Tag No. Job No. Client Project
: : : :
HCL Scrubber 4506A JOL SR - Plant -4, 5
Input Data
Stream
:
HCL Vap.
Packin Packing g type type Packing size Packing MOC Gas pr. Drop / m bed Total packing height Gas / Vapour Properties Gas / Air flow rate
Gas pressure at entry Gas temperature at entry Gas / Air mol weight
= Intall Intallox ox Saddle Saddles s = 25 m m = PP = 15 mm mmW C / m packing height = 3.2 m (including all packed beds)
= =
1000 kg k g /h 0.2778 kg/s
= = =
1.0000 atm o 30.00 C 29
Component to be scrubbed Component Name = Component flow rate = % comp. in air/gas = Molecular weight of comp. =
=
Packing factor, Fp
=
Charac. Packing Factor,Cf = Conversion factor, J =
21 m
o
303.00 K
=
(presumed) / (given by client) / (by process cal.)
Liquid / Scrubbing media Properties Scrubbing media = 20% NaOH Liquid flow rate, L = 77 k kg g /h = 0.0214 kg/s Liquid Density, L = 1100 kg/m = 0.0035000 Ns/m
(N/m )/m )/m 147.1 (N/m
0 m /h 0 m /s
OR
HCL Vap 70 Kg K g /h 6 % (v/v) 36.5
Liquid Viscosity, µL
=
Conversion : 2
3.5 Cp
=
0.00350000 Ns/m
2
-
33 Ref. Table 6.3, Characterstics of Random packings 1.0 factor fo for ad adequate liliquid di distribution & irrigation ac across th the be 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 =
Gas in
0.009432183 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 m /s
= (m /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 = 0.277778 Kg/s 3 Selected vol. Flow rate = 0.234499 m /s Selected molar flow rate = 0.009432 Kmol/s 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 Liquid leaving = 0.0420 Kg/s L'
G
G'
L
0.5
=
Using
(molar flow rate x % comp. x mol. Wt.) (Inlet liquid flow rate + comp. Removed)
0.00497
Refer fig.6.34 using a gas pressure drop of
0.00497
as ordinate,
G' Cf µL
J
=
0.04 (from graph)
G(
G)
=
0.04
2
0.1
L
--
gc
Therefore, G'
G(
--
L
0.1
Cf µL
G)
gc
0.5
J
=
1.6665 Kg / m .s
Tower c/s area
=
0.1667 m
( c/s area = mass flow rate / G' )
Tower diameter
= =
0.4607 m 500 mm
=
Corresponding c/s area
=
0.1963 m
Sheet 2 of 11
460.7 mm
147.1
2
(N/m )/m
TO ESTIMATE POWER REQUIREMENT Efficiency of fan / blower
=
assumed / given
60 %
To calculate pressure drop 470.72 N/m
Pressure drop for irrigated = packing For dry packing, O/L Gas flow rate, G' O/L Gas pressure Gas density, G
=
CD
=
Delta P
= CD
= =
(pressure drop per m packing x total ht. of packing)
1.3095 Kg / m .s (Gas inlet flow rate - Component removed) / c/s area 100854.3 N/m (subtracting pressure drop across packing)
gas mol wt. x 273 x 22.41m3/Kmol T in kelvin = 1.1605 Kg/m
Z
96.7
gas o/l pr. 101330
Ref. Table 6.3, Characterstics of Random packings
G' G
=
142.89 N/m
Pressure drop for packing =
613.61 N/m
(irrigated packing + dry packing)
Pressure drop for internals = =
25 mmW C 245.17 N/m
(packing supports and liquid distributors)
Gas velocity Inlet expansion & outlet contraction losses
= 7.5 m/s = 1.5 x Velocity heads = 42.19 N m / Kg = 49.97 N/m 908.75 N/m
=
1.5 x (V / 2g) (divide by density)
Total pressure drop
=
(packing + internals + losses)
Fan power output
= pressure drop,N/m x (gas in - component removed) Kg/s O/L gas density, Kg/m = 201.35 N .m / s = 0.20 kW
Power for fan motor
= =
2
0.34 kW 0.45 hp
(fan power output / motor efficiency)
Sheet 3 of 11
COLUMN DIAMETER / HYDRAULIC CHECK Liq.-Vap. Flow factor, FLV
= (L / V) x ( = 0.0025
V
Design for an initial pressure drop of From K4 v/s FLV, =
0.85
K4 at flooding
=
6.50
Trial % flooding
= (
Gas mass flow rate, Vm
=
Trial column c/s area (Trial As)
Trial column dia., D
=
mm H2O /m packing
(K4 / K4 at flooding)
) x 100
36.1620 K4 .
V(
L
13.1 Fp (µL / =
L)
15
K4
=
/
--
V) L)
(1/2)
.
3.7763 kg/m .s V / Vm
=
0.0736 m
=
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, As
=
% flooding
=
0.1963 m
13.5472
As = (pi/4) x D
% 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 0.018 N/m = 18 dyne/cm Liquid-phase Surface Tension, = 20 dyne/cm Norton's Correlation Applicable Liquid Viscosity
=
3.5 cP
n
=
1.13080
ln HETP
=
0.837437
HETP
= =
2.310437 ft 0.704221 m
Norton's Correlation NOT applicable
Calculation
For separations, less than 15 theoritical stages, a 20% design safety factor can be applied. Considering 20% safety factor, HETP = 0.845065 m
For separations, requiring 15 to 25 theoritical stages, a 15% design safety factor can be applied. Considering 15% safety factor, HETP = 0.809854 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
