Asked Nov 18, 2019

A packed tower uses an organic amine to absorb CO_2. The entering gas, which contains 1.26 mol % CO_2 is to leave with only 0.04 mol % CO_2. The amine enters pure, without CO_2. If the amine left in equilibrium with the entering gas (which it doesn't), it would contain 0.80 mol % CO_2. The gas flow is 2.3 mol/s, the liquid flow is 4.8 mol/s, the tower's diameter is 40 cm, and the overall mass transfer coefficient times the area per volume (Kya) is 5x10^-5 mol/cm^3*s. How tall should the tower be?

Use the following equation:


yo -ПХО

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LG Kya yo -ПХО


Expert Answer

Step 1

The data given for the process are:


Flowrate of entering gas, GA = 2.3 mol/s

Flowrate of entering liquid, LA = 4.8 mol/s

Mole fraction of CO2 entering the tower in gas, Y0 = 0.0126

Mole fraction of CO2 leaving the tower in gas, Y1 = 0.0004

Mole fraction of CO2 entering the tower in liquid, X1 = 0.00

Mole fraction of CO2 leaving the tower in liquid in equilibrium, X*0 = 0.008

Mole fraction of CO2 leaving the tower in liquid, X0

Tower diameter, D = 40 cm

Overall mass transfer coefficient times the area per volume, Kya = 5x10-5 mol/(cm3.s)

Step 2

Apply overall mass balance on carbon dioxide (CO2) to calculate the value of X0 as:

G (Y) L (Xx)
2.3(0.0126-0.0004)= 4.8(X-0)
Xo 0.00585

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G (Y) L (Xx) 2.3(0.0126-0.0004)= 4.8(X-0) Xo 0.00585

Step 3

Now, calculate the value of m which is the local slo...


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dy т dx 0.0126 0.008 1.575


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Mass Transfer

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