A scheme for the removal of $\mathrm{H}_{2} \mathrm{~S}$ from a flow of $1.0 \mathrm{std} \mathrm{m}^{3} / \mathrm{s}$ of natural gas by scrubbing with water at $298 \mathrm{~K}$ and 10 atm is being considered. The initial composition of the feed gas is $2.5 \mathrm{~mol} \% \mathrm{H}_{2} \mathrm{~S}$. A final gas stream containing only $0.1 \mathrm{~mol} \%$

$\mathrm{H}_{2} \mathrm{~S}$ is desired. The absorbing water will enter the system free of $\mathrm{H}_{2} \mathrm{~S}$. At the given temperature and pressure, the system will follow Henry's law, according to $Y_{i}=48.3 X_{i}$, where $X_{i}=\mathrm{mol} \mathrm{H}_{2} \mathrm{~S} / \mathrm{mol}$ of water; $Y_{i}=\mathrm{mol} \mathrm{H}_{2} \mathrm{~S} / \mathrm{mol}$ of air.

(a) For a countercurrent absorber, determine the flow rate of water that is required if 1.5 times the minimum flow rate is used.

(b) Determine the composition of the exiting liquid.

(c) Calculate the number of ideal stages required.

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Vs Vs Vs Y3 12 3 LS LS 2 LS X3 LS X2 VS X1 Yo Y Yo Equilibrium Slope LSVS Yo Y . Y3 X3 X2 X1 Figure 3.30 Cross-flow cascade of three ideal stages.