Section B $-$ answer ANY TWO questions from this section

B$1.$ A stream of air $(100kmol{h}^{-1})$ enriched with $C{O}_2$ needs to be

scrubbed to reduce the $C{O}_2$ concentration. Water has been chosen as

the liquid phase for this process. You may assume the process takes

place at ambient pressure and $293K.$

$($a$)$ Consider the case where the $C{O}_2$ content of the inlet air is $1$vol$\%$

$($you may assume the rest of air consists of $20\%O_2$ and $79\%N_2)$

and at least $50\%$ of this $C{O}_2$ needs to be removed. What is the

minimum amount of pure water required to achieve this?

$[15$ marks$]$

$($b$)$ Under the conditions in $($a$),$ how much $O_2$ and $N_2$ are absorbed by

the water stream?

$[10$ marks$]$

$($c$)$ Water usually contains a small amount of dissolved gases.

Assuming the $C{O}_2$ level in the water being used is in equilibrium

with ambient air $($i$.$e$.$ air containing $400ppmC{O}_2),$ what is the

minimum flow rate of water required to achieve $50\%$ removal?

$[10$ marks$]$

Additional information for question B$1$ is given on the next page.Data:

Solubility of gases in water

The constants can be used to calculate solubility, $x($i$.$e$.$ the mole fraction

of the gas dissolved in water under a gas partial pressure of $1$atm $),$

through the equation

$lnx=A+\frac{B}{T}+ClnT+DT$

where $T$ is the temperature measured in $K.$

The Henry's Law constant can be calculated as

$H=\frac{1}{x}$

and it has the unit of atm.

Saturated vapour pressure of steam at $293K$ is $2339Pa.$

Useful equations:

The symbols have their usual meanings in the Kremser equation.

$v_1={}_A{v}_{N+1}+(1-{}_S)l_0$

${}_A=\frac{A-1}{A^{N+1}-1},A=\frac{L}{KV}$