Absence of an Expected Component

A distillation system may perform unsatisfactorily if one of the feed components is missing, present in insufficient quantity (or concentration), or is vaporized too early upon entering the column. This component may be required for the formation of a volatile azeotrope, or for preventing other materials from precipitating out of solution, or for keeping certain components in the bottom liquid. 

Cures which may overcome problems of absence of an expected component are  

Modifying the system to live with the problem In one instance (98), removal of a volatile solvent from an aqueous solution caused precipitation of dissolved solids in the section below the feed, thus plugging the column. The problem was solved by replacing packings by trays to prevent plugging. 

Injecting the absent component In one instance (13), water was essential for converting some heavy components into volatile azeotropes, which would leave with the top product. When water was absent, the azeotropes would not form, and the heavy components would leave with the bottom product. During periods when the quantity of water in the column feed was insufficient for azeotrope formation, or when excess reboil boiled off the water in the feed, steam was injected below the feed to assure azeotrope formation. 

Modifying control system In the instance described above (13), the main problem was excessive reboil causing water to boil off and dry 

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