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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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1538 Klaus-Dirk Henning<br />

Figure 22.1.21. H 2S and CS 2 removal in the filament yarn production (After reference 34).<br />

H 2S-removal<br />

The exhaust air, saturated with water vapor, is first treated in an absorption unit for removal<br />

<strong>of</strong> H 2S by routing it through two successive jet scrubbers working with dilute caustic<br />

soda solution. Downstream <strong>of</strong> these, a centrifugal scrubber is installed as an entrainment<br />

separator. The sulphide-containing solution rejected from the scrubbers is used to precipitate<br />

zinc in the waste water treatment system <strong>of</strong> the production plant. By products adsorbed<br />

on the activated carbon, such as sulphuric acid and elemental sulphur, are removed periodically<br />

by water and alkaline extraction.<br />

CS 2-removal and recovery<br />

The pre-cleaned airstream containing carbon disulfide vapors passes through two or<br />

three parallel adsorbers, in which the CS 2 is absorbed on a bed <strong>of</strong> Supersorbon � activated<br />

carbon. As soon as the adsorbent is saturated it is regenerated by desorbing the solvent with<br />

a countercurrent flow <strong>of</strong> steam. The resulting mixture <strong>of</strong> water and CS 2 vapors is condensed<br />

and separated in gravity settlers. The recovered CS 2 is returned to the viscose production<br />

without further treatment. The condensed steam is stripped <strong>of</strong> residual CS 2 in the centrifugal<br />

scrubber and used as dilution water for operation <strong>of</strong> the jet scrubbers.<br />

Operating experience<br />

The specified purity <strong>of</strong> the treated exhaust air is reliably achieved with the<br />

Supersorbon � process 34 with respect to both CS 2 and H 2S. The CS 2 recovery rate is about<br />

95%. The purity <strong>of</strong> the recovered solvent meets viscose production specifications. A widely<br />

varying CS 2 concentration in the exhaust air has not adversely affected operation <strong>of</strong> the adsorption<br />

system.

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