Methods and apparatus for dewatering paper webs

Abstract

A wet paper web or other wet porous web exiting a web former is supported on a vented press roll and sequentially subjected to a relatively high pressure mechanical nip pressing force and a relatively low pressure water displacement-pressing force. The combination of the two diverse pressing forces applied in sequence to the web is very effective in efficient and economical de-watering of the web and at the same time provides a de-watered web having high bulk, high solids content and high mechanical strength. The low pressure fluid displacement pressing force is applied immediately contiguous to the high pressure mechanical nip pressing force and may be applied upstream or downstream or both upstream and downstream of the mechanical nip pressing force.

What is claimed is:  
     
         1 . A method of dewatering a moving wet paper web comprising the steps of contiguous application of mechanical pressing and displacement dewatering to the web.  
     
     
         2 . A method as set forth in  claim 1  wherein the web is subjected to the displacement dewatering prior to the mechanical pressing.  
     
     
         3 . A method as set forth in  claim 1  wherein the web is subjected to the displacement dewatering after the mechanical pressing.  
     
     
         4 . A method as set forth in  claim 1  wherein the web is subjected to the displacement dewatering both prior to and after the mechanical pressing.  
     
     
         5 . A method as set forth in  claim 1  wherein the mechanical pressing is applied at a nip formed between two press rolls.  
     
     
         6 . A method as set forth in  claim 5  wherein the mechanical pressing is applied over a nip length of from about one-half to about four inches and at a load of from about 300 to about 1200 pounds per lineal inch.  
     
     
         7 . A method as set forth in  claim 1  wherein the mechanical pressing is applied at the nip between a press roll and an extended nip press shoe.  
     
     
         8 . A method as set forth in  claim 7  wherein the mechanical pressing force is applied over a nip length of from about 8 to about 14 inches at a load of from about 1400 to about 7000 pounds per lineal inch.  
     
     
         9 . A method as set forth in  claim 1 , wherein the displacement dewatering is applied over a length of from about 0.5 to about 50 inches at a fluid pressure of from about 20 to about 300 pounds per square inch.  
     
     
         10 . A method as set forth in  claim 1  wherein the mechanical pressing is applied at the nip of a vented roll and an associated mechanical press element, and the displacement dewatering is applied over an arc of the vented roll contiguous to the nip.  
     
     
         11 . A method as set forth in  claim 1  wherein the mechanical pressing and contiguous displacement dewatering of the moving web are first applied to one side of the web and subsequently applied to the other side of the web, without open draw, to mitigate two-sidedness of the web.  
     
     
         12 . A method of dewatering a wet paper web comprising the steps of: 
 supporting the wet web on a vented roll;    passing the wet web through a mechanical press nip formed between the vented roll and an associated press element; and    passing the web through a displacement dewatering zone formed between the vented roll and an associated pressure chamber.    
     
     
         13 . A method as set forth in  claim 12  including the step of passing the web through the mechanical press nip and immediately thereafter passing the web through the displacement dewatering zone.  
     
     
         14 . A method as set forth in  claim 12  including the steps of sequentially passing the web through a first water displacement zone, a mechanical press nip, and a second displacement dewatering zone, all on the one vented roll.  
     
     
         15 . Apparatus for dewatering a wet paper web comprising, 
 means for mechanically pressing the wet web, and    means defining a displacement press for applying fluid pressure to the web, said displacement press means being contiguous to said mechanical press means.    
     
     
         16 . Apparatus as set forth in  claim 15  wherein said mechanical pressing means and said displacement press means are located on a single roll.  
     
     
         17 . Apparatus as set forth in  claim 15  wherein 
 said mechanical pressing means comprises a vented roll and an associated mechanical press element defining a press nip there between, and  
 said displacement press means comprises a pressure chamber extending over an arc of said vented roll contiguous to said nip and means for applying fluid pressure within said chamber.  
 
     
     
         18 . Apparatus as set forth in  claim 17  wherein said pressure chamber is located upstream of said nip.  
     
     
         19 . Apparatus as set forth in  claim 17  wherein said pressure chamber is located downstream of said nip.  
     
     
         20 . Apparatus as set forth in  claim 17  wherein said press nip is within said pressure chamber.  
     
     
         21 . Apparatus for dewatering a wet paper web comprising, 
 a vented roll for supporting the web,    a press member loaded on said vented roll forming a press nip there between, and    a pressure chamber on said vented roll, said pressure chamber being pressurized with a fluid and applying a displacement dewatering pressure on the web.    
     
     
         22 . Apparatus as set forth in  claim 21 , wherein said pressure chamber is contiguous with and downstream of said press nip.  
     
     
         23 . Apparatus for dewatering a wet paper web comprising, 
 a vented roll for supporting the web,    a press roll loaded on said vented roll forming a press nip there between, and    a pair of cap rolls on at least one side of said press nip, one said cap roll engaged with said vented roll and the other said cap roll engaged with said first cap roll and said press roll, said pair of cap rolls, vented roll and press roll defining a pressure chamber.    
     
     
         24 . Apparatus for dewatering a wet paper web comprising, 
 a vented roll for supporting the web,    a non-vented roll radially spaced from said vented roll,    a press roll between and engaged with both said vented and non-vented rolls, said vented roll and said press roll forming a press nip there between, and    a cap roll on at least one side of said press nip, said cap roll engaged with said vented roll and said non-vented roll, said cap roll, vented roll, non-vented roll and press roll defining a pressure chamber.    
     
     
         25 . Apparatus for dewatering a wet web comprising, 
 a vented roll for supporting the web,    an extended nip press loaded against said vented roll forming an extended press nip there between,    a cap roll engaged with said vented roll and spaced from said extended nip press, and    a member extending between said extended nip press and said cap roll, said vented roll, extended nip press, cap roll, and said member defining a pressure chamber.    
     
     
         26 . Apparatus for dewatering a wet web comprising, 
 a first press for dewatering the web having a first set of endless belt runs, said web being carried between said first set of endless belts, said first press having at least one displacement dewatering zone for applying fluid pressure to a first side of the web; and    a second press for dewatering the web having a second set of endless belt runs, said web being carried between said second set of endless belts, said second press having at least one displacement dewatering zone for applying fluid pressure to a second side of the web.    
     
     
         27 . Apparatus as set forth in  claim 26 , further comprising a belt guide roll on one of said belt runs of one of said presses, said guide roll urging said one belt run into contact with the web as the web is being carried on the other said press, whereby said web is transferred from said first press to said second press without open draw.