Question

column 0.6 m diameter and 6 m high is packed with 25 mm ceramic Raschig rings and used in a gas absorption process carried out at 101 KPa and 300 K. If the liquid and gas properties approximate to those of water and air (water viscosity=1 mNs/m2, air viscosity=0.02 mNs/m2) and their flowrates are 2.4 and 0.95 kg/m2s respectively. The packing properties are the following: voidage (e) is 0.71, specific surface area (S) is 190 m2/m3. Calculate the wet pressure drop across the column using ROSE and YOUNG correlation (use Carman Approach-ERGUN equation to calculate the dry pressure drop).

Answer 1

Data provided in problem statement

Raschig rings nominal size ( d_n ) = 25 mm

Operating Tempearure ( T ) = 300 K

Height of column ( l ) = 6 m

Gas flowrate ( G ) = 0.95 kg/ m2s

Air density ( ) can be given as

= ( MW / V_stp ) * ( T_stp / T )

Here

MW = molecular weight of air = 29 kg / kmol

V_stp = Ideal gas volume at STP = 22.4 L

T_stp = Temperature STP = 273 K

= ( 29 / 22.4 ) * ( 273 / 300 ) = 1.178 kg / m3

so

Velocity of air ( u) = G / = ( 0.95 kg/ m2s ) / ( 1.178 kg / m3 ) = 0.806 m /s

Voidage ( e) = 0.71

Specific surface are ( S) = 190 m2/ m3

Now Carman correlation for flow through packed bed can be given as

Wet pressure drop across the  column = 411.7084 N/ m2