Method and process arrangement in the short circulation of a paper machine

Abstract

A process arrangement in the short circulation of a paper machine comprises devices ( 10 - 13 ) for dilution of thick stock, centrifugal cleaners ( 14 ), and a headbox fan pump ( 16 ), as well as a pipe system connecting these. There is a direct flow connection from the centrifugal cleaners ( 14 ) along a pipeline ( 30 ) to the headbox fan pump ( 16 ), through which pipeline ( 30 ) a centrifugally cleaned stock flow (F 6 ) is passed direct to the headbox fan pump ( 16 ) without any deaeration or dilution stages in between. A secondary line ( 32 ) is connected to the pipeline ( 30 ) for passing through it part of the centrifugally cleaned stock flow as a return flow (F 7 ) back to the thick stock dilution devices ( 10 - 13 ). By this arrangement it can be ensured that the pressure on the suction side of the fan pump ( 16 ) remains substantially constant.

1 . A process arrangement in the short circulation of a paper machine comprising devices ( 10 - 13 ) for dilution of thick stock centrifugal cleaners ( 14 ), and a headbox fan pump ( 16 ), as well as a pipe system connecting these, and in which there is a direct flow connection from the centrifugal cleaners ( 14 ) along a pipeline ( 30 ) to the headbox fan pump ( 16 ), through which pipeline ( 30 ) a centrifugally cleaned stock flow (F 6 ) is passed direct to the headbox fan pump ( 16 ) without any deaeration or dilution stages in between, characterized in that a secondary line ( 32 ) is connected to said pipeline ( 30 ) for passing through it part of the centrifugally cleaned stock flow as a return flow (F 7 ) back to the thick stock dilution devices ( 10 - 13 ), by which arrangement it is ensured that the pressure on the suction side of the fan pump ( 16 ) remains substantially constant.  
     
     
         2 . A process arrangement as claimed in  claim 1 , characterized in that the thick stock dilution devices comprise a mixing pump ( 12 ), an incoming flow (M) of the thick stock, a wire water flow (F 10 ) and the return flow (F 7 ) of the centrifugally cleaned stock being passed to a mixing space ( 11 ,  13 ) situated on the suction side of the mixing pump.  
     
     
         3 . A process arrangement as claimed in  claim 2 , characterized in that the return flow (F 7 ) is passed centrally and parallel to the wire water flow (F 10 ) to the suction side of the mixing pump ( 12 ).  
     
     
         4 . A process arrangement as claimed in any one of the preceding claims, characterized in that the mixing pump ( 12 ) and the headbox fan pump ( 16 ) have common pressure control, i.e. feedforward control, to control the operating speed.  
     
     
         5 . A process arrangement as claimed in any one of the preceding claims, characterized in that other process flows smaller than that of the main line are connected to the secondary line ( 32 ).  
     
     
         6 . A method in the short circulation of a paper machine for keeping the pressure constant on the suction side of a headbox fan pump ( 16 ), in which method the stock is diluted to headbox consistency, cleaned by centrifugal cleaners ( 14 ) and pumped through a headbox ( 20 ) to a wire section of the paper machine, and in which a stock flow (F 6 ) is passed from the accept side of the centrifugal cleaners ( 14 ) direct to the headbox fan pump ( 16 ) without any deaeration or dilution stages in between, characterized in that the pressure in a pipeline ( 30 ) leading from the centrifugal cleaners ( 14 ) to the fan pump ( 16 ) is kept substantially constant by passing part of the stock coming from the centrifugal cleaners ( 14 ) as a return flow (F 7 ) back to the dilution of the thick stock.