Filtration of pulp mill liquids

Abstract

A fiber mat is formed on a screen cylinder of a pressurized fiber filtering device used to filter particles from a liquid stream. The fiber mat is a fine particle filter to remove small particles from the liquid stream. The fiber mat is formed by injecting cellulosic fibers into the liquid stream flowing into the fiber filtering device. These fibers collect on the screen cylinder as the liquid flows through the cylinder. The collection of fibers forms the fine filtering mat.

1 . A process for removing solid particles from a liquid stream in a pulp or paper mill having a filtering device having an inlet for liquid having at least some undesirable materials, an outlet for treated liquid having reduced concentration of undesirable material, an outlet for undesirable material, and a perforated screen element, comprising: 
 (a) introducing a first liquid having an undesirable material content to the inlet;    (b) introducing a second liquid having at least some comminuted fibrous material to the inlet to form a mixture of the first and second liquids;    (c) passing the mixture of the first and second liquids through the screen element to produce a third liquid having little or no undesirable material;    (d) discharging the third liquid from the filtering device, and    (e) practicing steps (a)-(d) so that at least some of the comminuted cellulosic fibrous material introduced with the second liquid is retained on the screen element to form a permeable mat of cellulose material which acts as a filtering medium for the undesirable material in the first liquid.    
     
     
         2 . A process as recited in  claim 1  wherein steps (a)-(d) are practiced using a cylindrical screen element as the screen element.  
     
     
         3 . A process as recited in  claim 1  wherein (b) is practiced so that the second liquid is mixed with the first liquid prior to being introduced to the inlet.  
     
     
         4 . A process as recited in  claim 1  wherein step (b) is practiced by continuously introducing the second liquid.  
     
     
         5 . A process as recited in  claim 1  wherein step (b) is practiced by intermittently introducing the second liquid.  
     
     
         6 . A process as recited in  claim 1  wherein in step (b) the introduction of the second liquid is regulated as a function of the introduction of the first liquid.  
     
     
         7 . A method as recited in  claim 1  wherein (a)-(d) are practiced so as to sense undesirable material in the liquid and to automatically adjust a mat formed on the screen element in response to that sensing.  
     
     
         8 . A system for treating a liquid stream in a pulp and paper mill to remove undesirable material from the liquid stream, comprising: 
 a filtering device including a perforated screen element having a filtering surface, an inlet, and a filtered liquid outlet;    said inlet connectable to a source of liquid containing undesirable material;    said inlet connectable to a source of liquid containing at least some comminuted cellulosic fibrous material to the inlet; and    a bed of comminuted cellulosic fibrous material on the filtering surface of the screen element to provide a fine screening medium.    
     
     
         9 . A system as recited in  claim 8  wherein said screen element is a cylindrical screen element.  
     
     
         10 . A system as recited in  claim 9  wherein said screen element rotates.  
     
     
         11 . A system as recited in  claim 9  wherein said screen element is stationary.  
     
     
         12 . A system as recited in  claim 8  wherein said filtering surface is a concave or external surface.  
     
     
         13 . A system as recited in  claim 8  wherein said filtering surface is a convex or internal surface.  
     
     
         14 . A system for treating a liquid stream in a pulp and paper mill to remove undesirable material from the liquid stream, comprising: 
 a filtering device having a perforated screen element having a perforated filtering surface, an inlet and a filtered liquid outlet, a liquid containing undesirable material, and a liquid containing at least some comminuted cellulosic fibrous material, introduced to the inlet; and    a bed of comminuted cellulosic fibrous material on the perforated filtering surface of the screen element which provides a finer screening medium than the perforated filtering surface of the screen element without the bed of comminuted cellulosic fibrous material present.    
     
     
         15 . A system as recited in  claim 14  wherein said screen element is a cylindrical screen element.  
     
     
         16 . A system as recited in  claim 14  wherein said screen element rotates.  
     
     
         17 . A system as recited in  claim 14  wherein said screen element is stationary.  
     
     
         18 . A system as recited in  claim 14  wherein said filtering surface is a concave or external surface.  
     
     
         19 . A system as recited in  claim 14  wherein said filtering surface is a convex or internal surface.