a$.$ A gas mixture of $60$mol$\%$ of $N_2$ and $40$mol$\%$ of $O_2$ is held at a

constant temperature of $2050K$ in the combustion chamber.

Assume the Zeldovich thermal mechanism is valid and the molar

density for the gas mixture is $6\mathrm{.}1{10}^{-6}mo\frac{l}{c}{m}^3.$ Estimate the

maximum residence time $(s)$ for the gas mixture in the chamber

if the nitric oxide $($NO$)$ emission limit is $1000$ ppm $($mol$).$

Suggest ONE $(1)$ strategy to further reduce the NO emission

under a constant gas mixture composition and residence time.

Support your answer with calculation and explanation.

$[13$ marks$]$

b$.$ A flue gas stream $(5\frac{m^3}{s})$ from coal fired power plant contains

$15,000ppm($mol$)$ of sulphur dioxide $(S{O}_2).$ The emission limit

for $S{O}_2$ is $70ppm($mol$).$ In order to meet the emission limit$,$ an

absorption column is used to remove the $S{O}_2$ in the flue gas

stream using $0\mathrm{.}001\frac{m^3}{s}$ of water at a pressure and temperature

of $30C$ and $150$atm, respectively. It is given that the molar

volume for the flue gas, Henry constant for $S{O}_2$ in water and

molar density of water are $0\mathrm{.}02\frac{m^3}{m}ol,250$atm and

$55\mathrm{.}6$kmo$\frac{l}{m^3},$ respectively. Assume the equilibrium composition

at the top and bottom of the absorber$,y_i^{**}=0\mathrm{.}8y_i.$

Using appropriate calculation and explanation, justify whether

the above operating conditions for the absorption column could

meet the emission limit$.$

Recommend Two $(2)$ methods to reduce the solvent

consumption rate.