Pressurised water pressure-reducing nozzle for generating microbubbles in a flotation plant

Abstract

The inventive nozzle comprises a first releasing stage ( 1 ) for producing a pre-release by absorbing from 5 to 20% of available pressure, a second releasing stage ( 2 ) wherein a substantial release is carried out and the pressurised water passes from a saturation pressure to an output nozzle pressure, an intermediate chamber ( 3 ) in the form of a transition chamber in which the pressurised water approaches the saturation pressure by absorbing from 5 to 30% of the available pressure and an outlet tube ( 3 ) consisting of a sudden release and cavitation confinement tube whose minimum length ( 1 ) substantially corresponds to a distance separating the end of said tube on the second release stage side from a readhesion point of jets to the tube wall at the angle of divergence (alpha) thereof ranging from 3 to 12 DEG before readhesion.

1 . A pressurized water pressure-reducing nozzle for generating microbubbles in a flotation plant comprising a first pressure reduction stage ( 1 ), an intermediate transfer chamber ( 3 ), a second pressure reduction stage ( 2 ) and an outlet pipe ( 4 ), this nozzle being characterized in that: 
 the first and second pressure reduction stages are produced in the form of a diaphragm comprising one or more orifices, the hydraulic diameter (d 1 ) of the orifice of the first stage ( 1 ), or of the equivalent orifice if this stage comprises several orifices, being greater than the diameter (d 2 ) of the orifice of the second stage, or of the equivalent orifice if this stage comprises several of them, the aforementioned orifices being able to be of any shape, but preferably circular,    and in that:    the first pressure reduction stage ( 1 ) performs a preliminary pressure reduction by absorbing 5 to 20% of the available pressure;    the second pressure reduction stage ( 2 ), in which most of the pressure reduction occurs, causes the pressurized water to pass from saturation pressure to the nozzle outlet pressure;    the intermediate chamber ( 3 ) is a transition chamber in which the pressurized water approaches saturation pressure by absorbing 5 to 30% of the available pressure and    the outlet pipe ( 4 ) consists of a sudden pressure reduction and cavitation confinement pipe, whose minimum length (L) substantially corresponds to the distance separating the end of said pipe on the second pressure reduction stage side from the point of reattachment of the jets onto the walls of the pipe, with an angle of divergence (a) of the jets, before reattachment, between 3 and 12°, preferably between 6 and 9°.    
   
   
       2 . The nozzle as claimed in  claim 1 , wherein the orifice of the first pressure reduction stage consists of a valve, a baffle or any other flow restriction device.  
   
   
       3 . The nozzle as claimed in  claim 1 , wherein the intermediate or transition chamber ( 3 ) has a height (e), i.e. a distance separating the first pressure reduction stage ( 1 ) from the second stage ( 2 ), which is less than the diameter (d 1 ) of the orifice of the diaphragm forming the first pressure reduction stage, preferably equal to half this diameter.  
   
   
       4 . The nozzle as claimed in  claim 1 , wherein the diaphragm forming the second stage comprises a single central orifice.  
   
   
       5 . The nozzle as claimed in  claim 1 , wherein the diaphragm forming the second stage comprises a plurality of orifices situated at an equal distance from the center of the diaphragm.  
   
   
       6 . The nozzle as claimed in  claim 1 , wherein the hydraulic diameter (d 1 ) of the orifice of the first pressure reduction stage ( 1 ) or of the equivalent orifice if this stage comprises several orifices, is between 1.6 and 1.1 times the diameter of the orifice of the second pressure reduction stage or of the equivalent orifice if this stage comprises several orifices.  
   
   
       7 . The nozzle as claimed in  claim 1 , wherein the second pressure reduction stage ( 2 ) has sudden widening, the outlet angle of the orifice or orifices of the diaphragm forming it being level (180°) or between 90° and 270°.  
   
   
       8 . The nozzle as claimed in  claim 1 , wherein the outlet pipe ( 4 ) terminates in a trumpet-shaped end divergent ( 5 ).