UNIT$-$II

$3.($a$)$ Write a note on pressure drop in packed towers for absorption$.$

$($b$)$ A gas from a petroleum distillation column has its concentration of $H_{2}S$ reduced from $0\mathrm{.}03kg$ mole $H_2\frac{S}{k}g$ moles inert gas to $1\%$ of its value by scrubbing with a tri ethanol amine with water as a solvent in a counter current tower of height $7\mathrm{.}79m$ operating at $300C$ and $1$atm. The equilibrium relation is $Y=2x.$ Pure solvent enters the tower and leaves containing $0\mathrm{.}013kg$ mole $H_2\frac{S}{k}g$ mole of solvent. If the flow of inert hydrocarbon gas is $0\mathrm{.}015$kgmol$\frac{e}{m^2}s$ and the gas phase controls the mass transfer. Calculate the overall coefficient for absorption$.$

$4.($a$)$ Explain sieve trays and bubble cap trays.

$($b$)$ It is desired to recover $98\%$ ammonia from air$-$ammonia mixture containing $2\%$ ammonia at $20C$ and at $1$atm by scrubbing with water in a tower packed with $2\mathrm{.}54cm$ rasching rings. If the gas flow rate is $19\mathrm{.}5k\frac{g}{m^2}$min at the inlet and liquid flow rate is $1\mathrm{.}8$ times the minimum. Estimate the height of packed tower for countercurrent operation. Absorption is assumed to be isothermal. The equilibrium relation is given by $y=0\mathrm{.}764x,$ where $y,x$ are gas and liquid phase composition of ammonia in mole fraction respectively. The overall mass transfer coefficient is $1\mathrm{.}04kg$ mole $\frac{?}{m^3\text{a}\text{t}\text{m}\text{.}\text{m}\text{i}\text{n}}.$