Many different solvents, including water and organic solvents are used in coating, printing, dyeing, impregnating, sizing, papermaking, waterproofing, waxing or otherwise treating webs made of paper, plastic, metal, cloth, rubber, textiles, etc. The principal object of the invention is to provide an improved method and apparatus for drying such webs. It is a further object to provide a method and apparatus for recovering the solvent for re-use.
In the past, forced circulation of air over the surface of a web within closed vacuum chambers has been employed to dry the web as disclosed in U.S. Pat. No. 1,487,362 to O. D. Rice. It has also been known to dry the web by heating it with radiant heaters or gas flames which when organic solvents are used can also incinerate the organic solvent vapor. In the past, the recovery of a portion of the organic solvent has been accomplished by passing the solvent vapors removed from the web through a series of absorbent activated carbon beds, then passing steam through the solvent saturated activated carbon bed to remove the absorbed solvent as solvent-water mixture, which was subsequently in a secondary process fractionally distilled to separate the organic solvent from the water. However, the activated carbon beds are limited to absorbing only a small percentage of their weight in organic solvent, and, therefore, the beds must be quite large. Several of these large beds are typically required, inasmuch as the organic solvent vapors must be passed through an unsaturated bed while the organic solvent is being removed from the saturated bed or beds. In addition to large size, the activated carbon absorption method is relatively expensive in cost and use of energy and recovers only a portion of the solvent used in processing the web.