Process arrangement in the short circulation of a paper machine

Abstract

A process arrangement in the short circulation of a paper machine comprises a feed pump ( 10 ), a headbox ( 11 ), means ( 12 ) for passing a pulp suspension jet (J) in a closed space from the headbox ( 11 ) into a forming gap defined by two wires ( 13, 14 ), dewatering elements ( 15, 16 ) placed against the wires ( 13, 14 ) a dilution duct ( 17 ) for passing wire water from the dewatering elements ( 15, 16 ) to stock dilution, and an outlet duct ( 18 ) for passing excess wire water out of the short circulation. The dilution duct ( 17 ) and the outlet duct ( 18 ) are in flow communication, and the outlet duct ( 18 ) has means ( 19, 22 ) for keeping the pressure in the dilution duct ( 17 ) even. For controlling the pressure in the short circulation of a closed former, excess wire water is passed out through a tank ( 19 ) provided with an overflow or other control.

1 - 13 . (canceled)  
     
     
         14 . A short circulation of a paper machine comprising: 
 a feed pump having an inlet side and an outlet side;    a headbox in flow receiving relation to the feed pump outlet side;    means for passing a pulp suspension jet in a closed space from the headbox into a forming gap defined by a first wire and a second wire;    a first plurality of dewatering elements placed against the first wire;    a second plurality of dewatering elements placed against the second wire;    a dilution duct connected to pass wire water from the first plurality of dewatering elements and the second plurality of dewatering elements to the pump inlet side    a source of thick stock joining the dilution duct before the pump inlet side;    an outlet duct arranged to pass wire water from the first plurality of dewatering elements and the second plurality of dewatering elements, out of the short circulation through a means for keeping the pressure in the dilution duct even; and    wherein the dilution duct and the outlet duct are in flow communication with each other.    
     
     
         15 . The short circulation of a paper machine of  claim 14 , wherein the means for keeping the pressure in the dilution duct even comprises a tank having an overflow to which the outlet duct is connected.  
     
     
         16 . The short circulation of a paper machine of  claim 15 , wherein the tank is placed at a selected level higher than the first plurality of dewatering elements and the  
     
     
         17 . The short circulation of a paper machine of  claim 14  further comprising a device producing a pressure loss positioned in the outlet duct.  
     
     
         18 . The short circulation of a paper machine of  claim 14  further comprising a valve producing a pressure loss positioned in the outlet duct.  
     
     
         19 . The short circulation of a paper machine of  claim 14  further comprising a means for centrifugal cleaning placed between the pump inlet side and where the source of thick stock joins the dilution duct.  
     
     
         20 . The short circulation of a paper machine of  claim 14  further comprising a machine screen through which the source of thick stock passes before joining the dilution duct.  
     
     
         21 . The short circulation of a paper machine of  claim 14  wherein the headbox is a dilution headbox, and further comprising: 
 a deaeration device; and    a pipe line in communication with wire water from the first plurality of dewatering elements and the second plurality of dewatering elements, wherein the deaeration device is in wire water supplying relation to the dilution headbox, to supply wire water as dilution water.    
     
     
         22 . The short circulation of a paper machine of  claim 14  wherein the first plurality of dewatering elements and the second plurality of dewatering elements are divided into compartments, each compartment being provided with a valve for controlling the dewatering pressure in said compartment.  
     
     
         23 . A method for controlling pressure in a short circulation of a closed former comprising the steps of: 
 passing wire water from a wire section of the closed former through a dilution duct, the dilution duct having a pressure;    diluting thick stock with the wire water in the dilution duct;    passing a portion of the wire water out of the short circulation through an outlet duct, the outlet duct having a pressure, and wherein the dilution duct and the outlet duct are in flow communication with each other;    wherein the portion of the wire water passed out of the short circulation is passed through a tank in which the pressure of the outlet duct is controlled by an overflow and thus the pressure in the dilution duct is also controlled.    
     
     
         24 . The method of  claim 23 , wherein wire water from the wire section is taken from a plurality of dewatering elements, and wire water passed out of the short circulation is taken from dewatering elements at a downstream end of the wire section.  
     
     
         25 . The method of  claim 23 , further comprising the steps of: 
 passing half or less of the wire water used for stock dilution to a deaeration device; and    controlling a fiber weight profile of a dilution headbox with wire water coming from the deaeration device.    
     
     
         26 . The method of  claim 23  wherein the thick stock is screened before it is introduced into the dilution duct and, after dilution takes place in the dilution duct, the stock flow is passed into a headbox without a new screening stage.  
     
     
         27 . The method of  claim 23  wherein the thick stock is screened before it is introduced into the dilution duct and, after dilution takes place in the dilution duct, the stock flow is passed to a centrifugal cleaning stage.  
     
     
         28 . A method for controlling pressure in a short circulation of a closed former comprising the steps of: 
 passing wire water from a wire section of the closed former through a dilution duct, the dilution duct having a pressure;    diluting thick stock with the wire water in the dilution duct;    passing a portion of the wire water out of the short circulation through an outlet duct, the outlet duct having a pressure, and wherein the dilution duct and the outlet duct are in flow communication with each other;    wherein the portion of the wire water passed out of the short circulation is passed through a tank in which the pressure of the outlet duct is controlled by a means for keeping the pressure in the dilution duct even, and thus the pressure in the dilution duct is also controlled.    
     
     
         29 . A short circulation of a paper machine comprising: 
 a feed pump having an inlet side and an outlet side;    a headbox in flow receiving relation to the feed pump outlet side;    a slice mounted to the headbox, the slice having walls for passing a pulp suspension jet from the headbox into a forming gap defined by a first wire and a second wire so that the jet does not contact ambient air;    a first plurality of dewatering elements sealed against the first wire and arranged to receive wire water at a pressure above ambient pressure;    a second plurality of dewatering elements sealed against the second wire and arranged to receive wire water at a pressure above ambient;    a dilution duct connected to pass wire water from the first plurality of dewatering elements and the second plurality of dewatering elements to the pump inlet side;    a source of thick stock joining the dilution duct before the pump inlet side;    an outlet duct arranged to pass wire water from the first plurality of dewatering elements and the second plurality of dewatering elements out of the short circulation through a structure which forms a pressure regulating overflow which keeps the pressure of wire water in the dilution duct even; and    wherein the dilution duct and the outlet duct are in flow communication with each other so the pressure of wire water fed to the pump is even.    
     
     
         30 . The short circulation of a paper machine of  claim 29 , wherein the structure which forms the pressure regulating overflow is placed at a selected level higher than the first plurality of dewatering elements and the second plurality of dewatering elements.  
     
     
         31 . The short circulation of a paper machine of  claim 29  further comprising a device producing a pressure loss positioned in the outlet duct.  
     
     
         32 . The short circulation of a paper machine of  claim 29  further comprising a valve producing a pressure loss positioned in the outlet duct.  
     
     
         33 . The short circulation of a paper machine of  claim 29  further comprising a means for centrifugal cleaning placed between the pump inlet side and where the source of thick stock joins the dilution duct.  
     
     
         34 . The short circulation of a paper machine of  claim 29  further comprising a machine screen through which the source of thick stock passes before joining the dilution duct.  
     
     
         35 . The short circulation of a paper machine of  claim 29  wherein the headbox is a dilution headbox and further comprising a deaeration device and a pipe line in communication with wire water from the first plurality of dewatering elements and the second plurality of dewatering elements, the deaeration device being in wire water supplying relation to the dilution headbox, to supply wire water as dilution water.  
     
     
         36 . The short circulation of a paper machine of  claim 29  wherein the first plurality of dewatering elements and the second plurality of dewatering elements are divided into compartments, each compartment being provided with a valve for controlling the dewatering pressure in the compartment.