Question

A 2-in-ID wetted wall column is being used to strip CO2 from an aqueous solution by an air stream at 1.0 m/s. At one point in the column, the concentration of CO2 in the air stream is 1.5 mole percent. At the same point in the column, the concentration of CO2 in the water is 0.5 mole percent. Determine the gas-mass-transfer coefficient kG (kg mole/atm-m2-s) and the mass flux at the point in the column. The column is operated at 10 atm and 25°C. The Henry’s constant of CO2 in water at 25°C is 1.64 × 103 atm/mole fraction CO2 in solution.

Answer 1

The mass transfer coefficient correlation in wall-wetted column is given by the equation,

Here Re is the reynold's number and is calculated using the equation,

Diameter of the tube is given as,

Velocity of gas stream,

From the table,

Density of the air at our temperature of and is

viscosity of the air at our temperature of and is  

So.

is the Schimdt number given as,

kinematic viscosity of the air at our temperature of is

Diffusivity of the gas system is found out from the table as at our temperature of and ,

So,

Now is the logarithmic mean pressure of the non diffusing gas that is air at our given point, between the bulk gas and at the interface of air-water

Now, is the total pressure of the system given as also.

total pressure = pressure of CO2 + pressure of air

Now the pressure of CO2 inbulk air can be calculated using dalton's law,

Here mole fraction of CO2 inbulk air is given as,

So

Now the partial pressure at the interface is given by Henry's law as,

Henry's law constant is given as,

mole fraction of CO2 in water is given as,

So,

So

So coming to our main equation,

So the mass transfer coefficient of the given gas system is 0.03105 m/s

Now,  gas-mass-transfer coefficient kG (kg mole/atm-m2-s) can be calculated using the comparison,

R is the universal gas constant given as,

So, the  gas-mass-transfer coefficient is 0.00127 kmol/atm-m2-s