Differential pressure drying and solvent recovery unit

The method of removing solvent from a web of material bearing such solvent which comprises:

• a. introducing a web of material bearing solvent through an entrance opening into the interior of a web dryer;
• b. moving the web past a radiant heat source which directs radiant heat upon the web thus enhancing the removal of said solvent from the web by vaporization;
• c. moving said web through a chamber in which dry inert gas is being introduced to enhance the vaporization of the solvent from the web and to carry the solvent vapor from the web;
• d. moving the web from said chamber through a solvent stripping slot which effectively accelerates the flow of gas over the surface of the web so as to disturb the boundary layer of solvent vapor which is attached to the surface of the web thus preventing the formation of a solvent vapor pressure concentration of the web surface which interferes with vaporization of the solvent from the web into a vacuum chamber in which a reduced pressure exists which further enhances the vaporization of the solvent from the web;
• e. collecting the solvent vapor bearing gas from the vacuum chamber;
• and
• f. then recovering the vaporized solvent from the gas.

A web dryer apparatus for drying a web bearing a solvent, said dryer comprising,

• a. a housing having a web entrance and a web exit;
• b. a plurality of chambers located within said housing, said chambers including a first chamber located adjacent the web entrance, said chamber being provided with at least one gas introduction port so that dry gas may be introduced into said chamber to pick up solvent vapors, a second chamber located adjacent the web exit, said chamber being provided with at least one gas introduction port whereby dry gas may be introduced into said chamber to pick up solvent vapors, and an intermediate vacuum chamber located between said first and second chambers, said intermediate chamber being provided with at least one gas exit port adapted to be connected to a vacuum creating source so that upon creation of a vacuum the gas introduced into the first and second chambers will flow downstream from said first chamber and upstream from said second chamber to said intermediate chamber picking up solvent vapors along the way, and
• c. at least one solvent stripping slot located between the first chamber and the intermediate chamber and at least one additional solvent stripping slot located between said intermediate chamber and said second chamber, said solvent stripping slot providing a passageway whereby the web may move downstream toward the web exit and the gas introduced into the first chamber may also move downstream to the intermediate chamber and said additional solvent stripping slot providing a passageway whereby web may move downstream toward the web exit and the gas introduced into the second chamber may move upstream to the intermediate chamber so that the gas carrying solvent vapors may be exhausted from said dryer via the gas exit port in the intermediate chamber.

A web dryer apparatus for drying a web bearing solvent, said dryer comprising:

• a. a housing having a web entrance and a web exit;
• b. a plurality of chambers located within said housing, said chambers including a first chamber located adjacent the web entrance, said chamber being provided with at least one gas introduction port so that dry gas can be introduced into said chamber to pick up solvent vapors, and a vacuum chamber located downstream of said first chamber, said vacuum chamber being provided with at least one exit port adapted to be connected to a vacuum creating source so that upon creation of a vacuum the gas introduced into the first chamber will flow downstream from said first chamber to the vacuum chamber picking up solvent vapors along the way;
• c. at least one solvent stripping slot located between the first chamber and the vacuum chamber, said solvent stripping slot providing a passageway whereby the web may move downstream towards the web exit and the gas introduced into the first chamber may move downstream to the vacuum chamber so that the gas carrying solvent vapors may be exhausted from the dryer via the gas exit port of the vacuum chamber, said solvent stripping slot being sized to permit the passage of the web and to increase the velocity of gas flow from the first chamber to the vacuum chamber over the web surface so as to disturb the boundary layer of solvent vapor on the web surface and prevent the formation of a solvent vapor pressure concentration on the web surface which can interfere with the evaporation of the solvent from the web;
• d. a radiant heat source within the web dryer positioned to direct radiant heat upon the web and to thus enhance the vaporization of the solvent from said web;
• and
• e. means located downstream of said vacuum chamber adapted to permit the web to exit from the dryer without the loss of any substantial amounts of the solvent vapor bearing gas from the dryer.

In an apparatus for drying a continuously moving web bearing a solvent, the combination of:

• a web dryer comprising a housing with web entry and exit openings, a number of chambers successively arranged between the openings through which a web is transported, narrowed solvent stripping slot means between the chambers, a dry gas inlet for one of said chambers, a gas outlet for another of said chambers, and a radiant heater in one of said chambers disposed to radiate upon a web within the chamber;
• a solvent condenser connected to said gas outlet for selectively condensing solvent from the gas flowing out of said web dryer;
• return connections between said condenser and said dry gas inlet of said web dryer to form a closed loop of gas flow;
• and
• a pump in said closed loop to impel gas through the loop.