FR2536305A1 - PROCESS AND INSTALLATION FOR FLOATING SUSPENSION OF FIBERS - Google Patents

Abstract

A.PROCESS AND INSTALLATION FOR FLOTATION OF FIBER SUSPENSION. B. INSTALLATION CONSISTING OF A TANK 1 WITH A DIFFUSER 15 SUPPLIED BY DUCT 9, THE BASE OF THE DIFFUSER BEING EQUIPPED WITH A CLOSING PLATE 14 SEPARATING THE JET OF LIQUID INTO A RISING JET AND A DOWN JET. C. THE INVENTION CONCERNS IN PARTICULAR THE CLEANING OF SUSPENSIONS OBTAINED FOR EXAMPLE FROM OLD PAPER.

Description

25363 5

  "Method and installation for the floating of

fiber suspension "e -

  The invention relates to a method of floating fiber suspension in a flotation tank - with extraction of at least part of the suspension, at least near the bottom of the flotation tank and reintroduction of part of the suspension injected into the flotation tank, also at least near the bottom of the flotation tank at

using at least one injector.

  We already know an installation for setting

  implementing the method according to document DE-AS 29 14 392.

  In this installation, the entire volume of the sus-

  pension is extracted at the bottom of the flotation tank.

  Feeding both the fresh suspension that is-

  ie the one to be cleaned as well as the suspension

  Zion which circulates in the circuit is done using injections

  teurs which are distributed substantially radially at the periphery and have a tangential ejection direction,

  however in these separate systems in this installation

  lation, many injectors are required and the assembly is

  very complex The flow conditions in the reservoir

  see floatation of this installation do not appear

  not as favorable at least not decisive for assu-

  rer an advantageous separation of dirt particles O The operation of the installation appears, according to the explanations given in this document, not to be

  interesting because according to the operating scheme of the ins-

  tallation, the flow up and down of the suspension must cross, which is not possible in itself. The object of the present invention with respect to the prior art is to create a flotation process which presents clear conditions and generates a

  flotation as efficient as possible as well as ins-

  installations allowing this advantageous effect to be obtained

  or its amplifications with an extremely simple assembly.

  This is important because the cost of such installations

  flotation measures, insofar as they must

  treat old paper, be part cost

11 days very reliable.

  To this end, the invention relates to a method of the above type characterized in that a smaller part of the suspension is extracted at the bottom of the tank and is again supplied to that or those of the injectors

of the same cell.

  According to another characteristic of the invention, after the exit from the injector, there is a flow of the suspension both towards the upper surface of the suspension than towards the oand of the flotation tank, and the quantity of suspension , to return, which flows down, is extracted from the remaining part of the suspension at the bottom of the tank and is chosen so that the sedimentation speed of the suspension is less than the rising speed of the bubbles. air

  where appropriate also of those which have already grown

  dirt particles, and the rising flow

  at least reaches the level of the upper surface.

  liquid in the flotation tank.

  The invention also relates to an installation for implementing this method, this installation 53635 i is characterized in that it only comprises an injector

  which includes a diffuser generating a horizontal flow

  zontal of the suspension, diffuser which is provided itself

  at the end of an essentially vertical mixer path

  cal, after a point of narrowing of the suspension supply line, and in that the bypass line for the part of the suspension passing through

  the circuit and the supply line for the suspension

  ion to be treated, newly introduced into the tank

  flotation are gathered upstream of the restriction zone

  cissement of the suspension supply line, and in that the bypass line comes out at the bottom of the floatation tank. According to another characteristic of the invention, the bypass line and the suspension supply line for the new suspension to be introduced are assembled upstream of the pressure raising pump

of the injector.

  According to another characteristic of the invention,

  the flotation tank is shaped like a green cylinder

  tical whose bottom is in the shape of a truncated cone whose

the top is pointing down.

  According to another characteristic of the invention, the lower part of the radial diffuser is an essentially horizontal closing plate, which is located at a certain distance above the bottom of the flotation tank. Finally, according to another characteristic of

  the invention, the point of extraction of the net suspension

  toyée is located in the highest part of the tank.

  The invention allows the passage of a relative flow

  significant through the injector, -if a significant amount of air is drawn in due to the

  high flow velocity resulting therefrom

  -to say that a given quantity of air is introduced in an advantageous way in terms of energy since the power requested by an injector is proportional

squared the air / liquid ratio.

  The method and the installation according to the invention will be described below with the aid of the appended drawings which

  show different embodiments of the installation

  tion: Figure la is a vertical sectional view

  of a first embodiment of the invention.

  FIG. 1B is a top view corresponding to

in figure -la -

  Figure 2a is a vertical sectional view

  of a second embodiment of the invention.

  Figure 2b is a top view corresponding

Figure 2a.

  Figure 3a is a vertical sectional view

  of a third embodiment of the invention.

  Figure 3b is a top view corresponding

  in FIG. 3 a According to the figures, the references 1, 1 ′ or 1 "designate the flotation tank into which dives

  a mixing hose 15 This mixing hose includes a -

  mixer path between the outlet of the injector and the reduced section 12, path in which the suspension mixes with the air bubbles The outlet of the injector is formed by a radial diffuser 13 which carries on the side

  facing the bottom 7, 7 'of the flotation tank cor-

  corresponding, a closing plate 14, essentially horizontal This assembly results in a flow at the outlet of the injector along flow lines which are at least close to the horizontal direction Then the flow is divided into an upward flow and a flow downward The fraction of the upward flow is chosen so that the vertical component is lower than the rate of rise of the air bubbles even of those which have already clung to the particles

of dirt.

  At the narrowing point 12 of the injector 6,

  there is a small air tube 11, projecting in posi-

  central, and which sucks in the air necessary for floating It is possible to provide other small tubes

  of this type of air directly below the shrinking point

  cementing of the tube in the mixer path 15 The suspension supply line 9 is connected to a

  compression 10 which provides the necessary pressure height

  match the injector and other pressure drops in the lines The amount of suspension flowing down arrives in the bypass line 8 or 8 '

  then also to the pressure raising pump 10.

  Upstream of this pressure raising pump, the con-

  pick for the new suspension to be introduced (indicated here by an arrow referenced Q) is joined to the pipe zu

  bypass 8 for suspension circulating-in circuit.

  Thanks to this arrangement, a reduced residence time is obtained, which is very advantageous for all the particles including the suspension, that is to say water and fibers, in the flotation tank O This time cannot

  in no case be less than the average residence time

  both of the relation V Z / QZU of all the particles Darns this equation, Vz represents the volume of the flotation tank and Qzu the quantity of suspension which is ch Iaque

  once again introduced into the float tank.

  its that is to say as shown in the figures

  binds the result of the flotation very strongly because all the dirt particles thus have the greatest chance of being fixed on air bubbles In addition, the installations according to the invention have clear flow conditions, which is also advantageous

  for the flotation effect In addition, a pos-

  very easy to evacuate the foam The quantity

2536305 1

  of suspension which rises is first of all guided to a place very little distant below the level of liquid and is evacuated there by an overflow In this way, the flow takes place radially towards the outside and also causes the foam Thanks to another overflow bearing the reference 3 in the figures, it is then possible

  extract the foam Extraction of the suspension net-

  toyée is then done for example as indicated in Figures la and 2a, by a box-extractor 2 which is connected a pipe 5 In the case of Figures 3a and

  3 b, the cleaned suspension is extracted slightly in

  below the level of the suspension and is evacuated by a

  line 5 while the foam is extracted by an overflow

  full located directly at the edge of the tank

  see in a foam extraction channel 4 and by a

foam line 6.

  It is thus possible by the choice of different

  rents partial flows of the suspension, adjust the conditions as necessary In each case, we obtain a relatively long average residence time for the particles in the flotation tank

  in other words, statistically, we have a

  the residence times of all of the following particles

  in front of a Gaus bell curve, a relative fraction-

  weak suspension, the particles of which have relatively short residence times This allows a much more advantageous flotation effect than that rendered

  possi'ble by the installations known until now.

Claims (7)

R E V E N D I C A T I O N S   1) Flotation process of fiber suspension in a flotation tank with extraction   at least part of the suspension, at least near   mapped from the bottom of the floatation tank and reintroduction   of a part of the suspension injected into the reservoir-   flotation device, also at least in the vicinity of the bottom of the flotation tank using at least one injector, method characterized in that a smaller part of the suspension is extracted at the bottom of the tank and is again supplied - to that or those of the injectors of the same cell -   2) Method according to claim 1, character-   risé in that after the exit of the injector, there is a flow of the suspension both towards the upper surface of the suspension than towards the bottom of the tank   flotation, and the amount of suspension, to be reve-   nir, which flows downwards, is extracted from the remaining part of the suspension at the bottom of the tank and is chosen so that the sedimentation speed of the suspension is less than the rising speed of the air bubbles. if necessary also of those, which have already caught on dirt particles, and the rising flow arrives at least to the level of   the upper surface of the liquid in the float tank taison.   3) Installation for the implementation of -pr-o-   assigned according to any one of claims I or Z 2   characterized in that it only has one injector   (6) which comprises a diffuser (13) generating a flow   horizontal suspension, diffuser provided   itself at the end of a mixer path (15) essen-   -so vertical, after a point of narrowing (12) of the suspension supply line (9), and in that the bypass line (8, 8 ') for the part of the 2536305 i   suspension passing through the circuit and supply line   ment (9) for the suspension to be treated, introduced newly into the flotation tank (1, 1 ′, 1 ") are joined upstream of the narrowing zone (12) of the suspension supply line (9), and in that the bypass line (8, 8 ') comes out at the   bottom (7, 7 ') of the flotation tank (1, 1', 1 ").   4) Installation according to claim 3, characterized in that the bypass line (8, 8 ') and the suspension supply line (9) for the new suspension to be introduced are joined upstream of   the pressure raising pump (O 10) of the injector (6).    ) Installation according to one of the claims   3 or 4, characterized in that the flotation tank (1, 1 ', 1 ") is in the form of a vertical cylinder whose bottom (7) is in the form of a trunk of c 8 ne whose top is directed down.   6) Installation according to any one of   claims 3 to 5, characterized in that the part   bottom of the radial diffuser (13) is an iron plate   essentially horizontal measurement (14) which is located   a certain distance above the bottom (7, 7 ') of the tank see waterline.   7) Installation according to any one of   claims 3 to 6, characterized in that the point   of the cleaned suspension is in the highest part of the tank.