Sheet 1 of 15

SCRUBBER DESIGN (PACKED COLUMN)

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

Project :

### Input Data Stream : HCL Vap.

Packing type = Intallox SaddlesPacking size = 25 mmPacking MOC = PP

Gas pr. Drop / m bed = 15 mmWC / m packing height = 147.1Total packing height = 3.2 m (including all packed beds)

Gas / Vapour Properties

Gas / Air flow rate = 1000 kg/h OR 0

= 0.2778 kg/s = 0

Gas pressure at entry = 1.0000 atm

Gas temperature at entry = 30.00 = 303.00Gas / Air mol weight = 29

Component to be scrubbedComponent Name = HCL VapComponent flow rate = 70 Kg/h% comp. in air/gas = 6 % (v/v)Molecular weight of comp. = 36.5

Liquid / Scrubbing media PropertiesScrubbing media = 20% NaOHLiquid flow rate, L = 77 kg/h

= 0.0214 kg/s

= 1100 Conversion :

= 0.0035000 3.5 0.00350000

= 21

= 33 Ref. Table 6.3, Characterstics of Random packingsConversion factor, J = 1.0 factor for adequate liquid distribution & irrigation across the bed

(N/m2)/m

m3/h

m3/s

oC oK

(presumed) / (given by client) / (by process cal.)

Liquid Density, L kg/m3

Liquid Viscosity, µL Ns/m2 Cp = Ns/m2

Packing factor, Fp m-1

Charac. Packing Factor,Cf

Sheet 2 of 15

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 densityAvg. 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 = 0.0094321826 Kmol/s Gas in x pr. in atm x 1kmol = mass / mol wt T in kelvin 1.0 atm 22.4

= 273 pr. In atm 1 = 0 Kmol/s

= 0.234499 = 0 Kg/smass = mol wt x kmol

Select vol. flow rate and mass flow rate from above,Selected mass flow rate = 0.2777778 Kg/s

Selected vol. Flow rate = 0.234499Selected molar flow rate = 0.0094322 Kmol/s

Therefore, gas density = 1.1846 (mass flow rate / vol. Flow rate)

To find L', G' and Tower c/s areaAssuming 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 = 0.00497

Using 0.00497 as ordinate, 147.1

= 0.04 (from graph)

Therefore, G' = 0.04 0.5

= 1.6665

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

Tower diameter = 0.4607 m = 460.7 mm= 500 mm

= (m3/s) x 273

(kmol/s) x T in kelvin x 1.0 atm x 22.4

m3/s

m3/s

Kg/m3

L' G

G' L

Refer fig.6.34 using a gas pressure drop of (N/m2)/m

G' 2 Cf µL0.1 J

G ( L -- G) gc

G ( L -- G) gc

Cf µL0.1 J

Kg / m2.s

m2

Sheet 3 of 15

Corresponding c/s area = 0.1963

TO ESTIMATE POWER REQUIREMENT

Efficiency of fan / blower = 60 %

To calculate pressure drop

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

For dry packing,

O/L Gas flow rate, G' = 1.3095 (Gas inlet flow rate - Component removed) / c/s area

O/L Gas pressure = 100854.28 (subtracting pressure drop across packing)

= gas mol wt. x 273 x gas o/l pr. 22.41m3/Kmol T in kelvin 101330

= 1.1605

= 96.7 Ref. Table 6.3, Characterstics of Random packings

Delta P =

Z

= 142.89

Pressure drop for packing = 613.61 (irrigated packing + dry packing)

Pressure drop for internals = 25 mmWC (packing supports and liquid distributors)

= 245.17

Gas velocity = 7.5 m/s

Inlet expansion & outlet = 1.5 x Velocity heads =contraction losses = 42.19 N m / Kg

= 49.97 (divide by density)

Total pressure drop = 908.75 (packing + internals + losses)

Fan power output =

= 201.35 N .m / s= 0.20 kW

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

m2

assumed / given

N/m2

Kg / m2.s

N/m2

Gas density, G

Kg/m3

CD

CD G' 2

G

N/m2

N/m2

N/m2

1.5 x (V2 / 2g)

N/m2

N/m2

pressure drop,N/m2 x (gas in - component removed) Kg/s

O/L gas density, Kg/m3

Sheet 4 of 15

COLUMN DIAMETER / HYDRAULIC CHECK

== 0.0025

Design for an initial pressure drop of 15 mm H2O /m packing

= 0.85

= 6.50

Trial % flooding == 36.1620

=

= 3.7763

Trial column c/s area =

= 0.0736

Trial column dia., D = 0.3060 m D =

Round off 'D' to nearest standard sizeTherefore, D = 0.500 m

= 0.1963

% flooding = 13.5472

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.

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

From K4 v/s FLV,

K4

K4 at flooding

( (K4 / K4 at flooding) ) x 100

Gas mass flow rate, Vm K4 . V ( L -- V)

13.1 Fp (µL / L)0.1

kg/m2.s

V / Vm

(Trial As)

m2

(4/pi) x Trial As

Column C/S area, As m2 As = (pi/4) x D2

% flooding = Trial % flooding x (Trial As / As)

(1/2)

Sheet 5 of 15

HETP PREDICTION

Norton's Correlation : ln HETP = n - 0.187 ln + 0.213 ln µApplicable when, liquid phase surface tension > 4 dyne/cm & < 36 dyne/cmliquid viscosity > 0.08 cP & < 0.83 cP

Conversion :Input Data 0.018 N/m = 18 dyne/cmLiquid-phase Surface Tension, = 20 dyne/cm Norton's Correlation Applicable

Liquid Viscosity = 3.5 cP Norton's Correlation NOT applicable

n = 1.13080

Calculation

ln HETP = 0.8374366

HETP = 2.3104368 ft= 0.7042211 m

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

Considering 20% safety factor, HETP = 0.8450653 m

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

Considering 15% safety factor, HETP = 0.8098543 m

Table 6.2Constant for HETP Correlation

Ref.:: Random Packings and Packed Towers ---- Strigle

Ref. : : Chemical Engineering, Volume-6 , COULSON & RICHARDSON'S

Ref. : : Mass Transfer Operation : : Treybal

http://www.engineeringtoolbox.com/scrubbers-air-washers-d_139.html

Scrubber humidifying efficiency

Some industrial processes need more cleaning than a single scrubber can provide. In smell polluted processes, like exhaust air from fish meal or fish feed dryers, bio beds are commonly used. A bio bed, which is an organic organism, require process air with as little dust as possible and temperature and humidity within certain limits.

The humidifying efficiency of the scrubber may be expressed as:

where

Scrubber Efficiencies

Typical nozzle scrubber efficiencies

Cleaning efficiency: 70% of fine dust and 80% of coarse dirt

Air velocity through the washer: 2 - 3 m/s

Air flow pressure drop resistance: 50 - 140 N/m2

Water pressure before nozzles: 100 - 170 kN/m2

Water consumption: 0.45 - 0.55 l/m3 air (depends on the temperature of the process air)

μh = (t1 - t2) / (t1 - tw) 100% (1)

μh = scrubber humidifying efficiency (%)

t1 = initial dry bulb temperature (oC)

t2 = final dry bulb temperature (oC)

tw = initial wet bulb temperature (oC)

60-70 % with one bank of nozzles downstream

65-75 % with one bank of nozzles upstream

85-100 % with two banks of nozzles

Some industrial processes need more cleaning than a single scrubber can provide. In smell polluted processes, like exhaust air from fish meal or fish feed dryers, bio beds are commonly used. A bio bed, which is an organic organism, require process air with as little dust as possible and temperature and humidity within certain limits.

Some industrial processes need more cleaning than a single scrubber can provide. In smell polluted processes, like exhaust air from fish meal or fish feed dryers, bio beds are commonly used. A bio bed, which is an organic organism, require process air with as little dust as possible and temperature and humidity within certain limits.

Some industrial processes need more cleaning than a single scrubber can provide. In smell polluted processes, like exhaust air from fish meal or fish feed dryers, bio beds are commonly used. A bio bed, which is an organic organism, require process air with as little dust as possible and temperature and humidity within certain limits.