Hydrocyclone, system and method for cleaning cellulose suspensions

Abstract

The present invention concerns a hydrocyclone for cleaning cellulose suspensions from light impurities i.e. a so called reverse hydrocyclone, having a base end and an apex end and a separation chamber having an elongated shape between the base end and the apex end, at least one inlet arranged at the base end and at least one underflow outlet at the apex end and at least one overflow outlet at the base end. The overflow outlet is provided with an additional, light reject outlet arranged concentrically to a length axis of the hydrocyclone. The invention also concerns a system and a method for producing and/or treating cellulose suspension comprising at least a reverse cleaning stage and at least a dewatering stage.

1 . A hydrocyclone for cleaning cellulose suspensions from light impurities, called a reverse hydrocyclone, having a base end and an apex end and a separation chamber having an elongated shape between the base end and the apex end, at least one inlet arranged at the base end and at least one underflow outlet at the apex end and at least one overflow outlet at the base end, the overflow outlet being provided with an additional, light reject outlet arranged concentrically to a length axis of the hydrocyclone. 
     
     
         2 . The hydrocyclone according to  claim 1 , wherein the overflow outlet comprises a vortex finder. 
     
     
         3 . The hydrocyclone according to  claim 2 , wherein the light reject outlet comprises a vortex finder. 
     
     
         4 . The hydrocyclone according to  claim 2 , wherein the hydrocyclone has a strongly decreasing cross sectional diameter for a first portion of its length from at least near the base end towards the apex end and a slowly decreasing cross sectional diameter for a second portion of its length from a transition between the first portion and the second portion towards the apex end, the transition between the first and the second portions having a diameter Dt, and the relation between the transition diameter Dt and a base end diameter D is between 0.35 and 0.7. 
     
     
         5 . The hydrocyclone according to  claim 2 , wherein a base end diameter is at least 60 mm. 
     
     
         6 . The hydrocyclone according to  claim 2 , wherein the relation between the length of the hydrocyclone L and the base end diameter D is at least 10. 
     
     
         7 . The hydrocyclone according to  claim 2 , wherein the overflow vortex finder protrudes into the separation chamber at the base end. 
     
     
         8 . The hydrocyclone according to  claim 2 , wherein the overflow vortex finder decreases in diameter from the base end and outwards. 
     
     
         9 . The hydrocyclone according to  claim 2 , wherein the overflow vortex finder has a diameter Do near the base end in the range of 0.17*D to 0.37*D, preferably 0.23*D to 0.33*D. 
     
     
         10 . The hydrocyclone according to  claim 3 , wherein the light reject vortex finder protrudes into the overflow vortex finder at the end of said overflow vortex finder which is furthest away from the base end. 
     
     
         11 . The hydrocyclone according to  claim 10 , wherein the light reject vortex finder has a diameter Dr at the end closest to the base end in the range of 0.25*Do to 0.4*Do. 
     
     
         12 . The hydrocyclone according to  claim 1 , wherein the outlet flow from the light reject outlet is 3-15% of the total inlet flow. 
     
     
         13 . The hydrocyclone according to  claim 1 , wherein the outlet flow from the overflow outlet is 25-65% of the total inlet flow. 
     
     
         14 . The hydrocyclone according to  claim 1 , wherein the outlet flow from the underflow outlet is 30-60% of the total inlet flow. 
     
     
         15 . The hydrocyclone according to  claim 1 , wherein the concentration of fibers in the cellulose suspension in the inlet flow is between 0.5-1.5% and the concentration of fibers in the underflow outlet flow is 1.2-3% and the relation between the inlet concentration and the underflow concentration is between 1.5-3.3 times. 
     
     
         16 . A system for producing and/or treating cellulose suspension, comprising at least a reverse cleaning stage and at least a dewatering stage, the reverse cleaning stage comprising at least one hydrocyclone for cleaning cellulose suspensions from light impurities, called a reverse hydrocyclone, having a base end and an apex end and a separation chamber having an elongated shape between the base end and the apex end, at least one inlet arranged at the base end and at least one underflow outlet at the apex end and at least one overflow outlet at the base end, the overflow outlet being provided with an additional, light reject outlet arranged concentrically to a length axis of the hydrocyclone. 
     
     
         17 . The system according to  claim 16 , wherein at least one hydrocyclone for cleaning cellulose suspensions from light impurities, called a reverse hydrocyclone, having a base end and an apex end and a separation chamber having an elongated shape between the base end and the apex end, at least one inlet arranged at the base end and at least one underflow outlet at the apex end and at least one overflow outlet at the base end, the overflow outlet being provided with an additional, light reject outlet arranged concentrically to a length axis of the hydrocyclones, the light reject outlet being provided in a primary cleaning stage of the reverse cleaning stage. 
     
     
         18 . The system according to  claim 17 , wherein a light reject fraction from the primary cleaning stage is lead to a secondary cleaning stage comprising any type of reverse hydrocyclone. 
     
     
         19 . The system according to  claim 16 , wherein an overflow fraction (MF) from said hydrocyclone is used for dilution. 
     
     
         20 . The system according to  claim 19 , wherein the overflow fraction (MF) is lead to any position upstream said reverse cleaning stage for dilution. 
     
     
         21 . The system according to  claim 16 , wherein the system also comprises at least a forward cleaning stage, a screening stage or a floatation stage. 
     
     
         22 . The system according to  claim 16 , wherein any of the light reject fractions are sent to an air separation tank kept at below −30 kPa under pressure. 
     
     
         23 . The system according to  claim 16 , wherein a light reject fraction is lead to a last clarification stage comprising a dissolved air water flotation. 
     
     
         24 . A method for producing or treating cellulose suspension by means of cleaning the cellulose suspension from light impurities in a reverse cleaning stage and dewatering the cellulose suspension in a dewatering stage, the method comprising cleaning the cellulose suspension from light impurities by means of at least one hydrocyclone for cleaning cellulose suspensions from light impurities, called a reverse hydrocyclone, having a base end and an apex end and a separation chamber having an elongated shape between the base end and the apex end, at least one inlet arranged at the base end and at least one underflow outlet at the apex end and at least one overflow outlet at the base end, the overflow outlet being provided with an additional, light reject outlet arranged concentrically to a length axis of the hydrocyclone. 
     
     
         25 . The method according to  claim 24 , whereby at least one hydrocyclone of the type in  claim 24  is positioned in a primary cleaning stage of the reverse cleaning stage. 
     
     
         26 . The method according to  claim 25 , whereby a light reject fraction from a hydrocyclone of the primary cleaning stage is lead to a secondary cleaning stage comprising any type of reverse hydrocyclone. 
     
     
         27 . The method according to  claim 24 , whereby an overflow fraction (MF) from said hydrocyclone is used for dilution. 
     
     
         28 . The method according to  claim 27 , whereby the overflow fraction (MF) is used for dilution in any position upstream said reverse cleaning stage. 
     
     
         29 . The method according to  claim 24 , whereby the cellulose suspension is cleaned in at least one of a forward cleaning stage, a screening stage and a flotation stage.