A gas containing methane, propane, and $n$-butane is to be scrubbed countercurrently in a sieve-tray tower with
Question:
A gas containing methane, propane, and $n$-butane is to be scrubbed countercurrently in a sieve-tray tower with a hydrocarbon oil to absorb principally the butane. It is agreed to design a tray for the circumstances existing at the bottom of the tower, where the conditions are
The system obeys Raoult's law; the vapor pressure of $n$-butane at $310 \mathrm{~K}$ is 3.472 bar (Reid et al., 1987).
(a) Design a suitable cross-flow sieve tray for such a tower. According to Bennett and Kovak (2000), the optimal value of the ratio $A_{h} / A_{a}$ is that which yields an orifice Froude number, $\mathrm{Fr}_{o}=0.5$. Design for the optimal value of $d_{o}$ on an equilateral-triangular pitch $12 \mathrm{~mm}$ between hole centers, punched in stainless-steel sheet metal $2 \mathrm{~mm}$ thick. Use a weir height of $50 \mathrm{~mm}$. Design for a $75 \%$ approach to the flood velocity. Report details respecting tower diameter, tray spacing, weir length, gas-pressure drop, and entrainment in the gas.
(b) Estimate the tray efficiency corrected for entrainment for the design reported in part (a).
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