Patent Publication Number: US-2006016731-A1

Title: Reactor particularly suitable for cleaning fibrous suspensions dispersed in liquids

Description:
BACKGROUND OF THE INVENTION  
      The invention concerns an improved reactor for cleaning fibrous suspensions dispersed in liquids.  
      In particular the reactor object of the invention has been designed to be employed in the paper manufacturing sector, where it is used to remove ink from fibrous suspensions deriving from recycled paper.  
      It is known that in the paper processing sector the cleaning of fibrous suspensions, and particularly the cleaning of and ink removal from fibrous suspensions obtained from recycled paper, is performed by flotation inside purposely designed reactors.  
      Essentially, said known flotation treatment consists in introducing into the reactor the fibrous suspension to be cleaned together with air and maintaining the fluid mass in agitation in order to favour contact between the air bubbles and the fibrous suspension.  
      The air bubbles pick up the impurities present in the suspension which they encounter during movement inside the reactor, creating foam which floats on the free surface of the suspension; said foam is continuously removed by means of appropriate skimming devices.  
      Reactors of the known type which clean fibrous suspensions deriving from recycled paper by means of the flotation method described above are illustrated in the patents WO98/54402 and WO98/54403, whose holder is the applicant for the present invention.  
      In both patents the reactor essentially consists of a cylindrical container provided with a series of injectors arranged around its circumference and at different heights.  
      The suspension to be cleaned is introduced into the container by pumping from the outside towards the inside via the injectors arranged at the level of the free surface of the suspension already present, each injector being also connected in parallel to an air suction pipe which communicates with the external environment.  
      During injection, the suspension sucks in air from the outside by Venturi effect, so that an emulsion is introduced into the container consisting of the suspension to be cleaned, in which air bubbles are dispersed.  
      The air bubbles, owing also to the presence of chemical reagents, pick up the impurities present in the suspension and generate foam which floats on the free surface of the suspension: it is this “picking up” of the impurities by the air bubbles which is called flotation.  
      The foam is removed from the free surface of the suspension by means of one or more rotating blades and then conveyed away via an outlet pipe.  
      The suspension which has undergone the first flotation inside the container drops by gravity towards the bottom of the container and enters the interception means, which in the patent WO98/54403 are present only on the bottom, while in the patent WO98/54402 they are also present in an intermediate position in the container; the suspension is pumped back into the container at different heights via further injectors connected in parallel to the same number of air suction pipes.  
      In this way the suspension, already partially cleaned during the first flotation, by dropping again towards the bottom of the container undergoes backwashing by the air bubbles which move upwards and absorb the impurities according to the process previously described.  
      In this way further flotation of the fibrous suspension is obtained.  
      The suspension drops towards the bottom of the container and when it enters the interception means arranged on the bottom for the second time, it has basically terminated its cleaning cycle and is conveyed away for use by means of pumps.  
      All the reactors of the known type described and also others equivalent to them have some recognised drawbacks and limitations.  
      A first drawback consists in the fact that introduction of the fibrous suspension to be cleaned is performed radially from the outside towards the inside of the container and this makes construction of the reactor complex and costly since it requires the installation, circumferentially and at various heights of the container, of a large number of injectors with related valves and air feed pipes.  
      A further drawback consists in the fact that the presence of such a large number of components also requires lengthy assembly work with consequent increase in costs, which influence the sale price and therefore the competitiveness of the company on the market.  
      A further drawback due to said large number of components is represented by the high maintenance costs which the purchaser has to sustain after installation to keep the reactor in efficient working order at all times.  
      A further drawback consists in the fact that said large number of component elements obliges the manufacturer to perform pre-assembly and subsequent disassembly of the reactor prior to shipment.  
      This obviously also contributes to increasing the production costs and the sale price.  
      Last but not least, a further drawback consists in the difficulty in setting reactors of the known type, due to the presence of a large number of pipes, valves and injectors to be set.  
      The aim of this invention is to overcome the above-mentioned drawbacks.  
     SUMMARY OF THE INVENTION  
      In particular the first aim of the present invention is to produce a reactor which has the same dimensions as the reactors of known type equivalent to it, and in particular the reactors of the patents mentioned, but fewer components.  
      A further aim is that the reactor of the invention does not have to be pre-assembled at the workshop and then disassembled prior to shipment to the purchaser.  
      A further aim is to produce a reactor which is simpler and quicker and therefore cheaper to construct than the known reactors with equivalent characteristics.  
      A further aim is to make assembly of the reactor of the invention at the user&#39;s premises simpler and quicker and therefore cheaper compared to the known reactors with equivalent characteristics.  
      A further aim of the invention is to produce a reactor which, with respect to known reactors with equivalent characteristics, has smaller overall dimensions.  
      A further aim of the invention is to allow the reactor to be produced using any container that may also have already been used in another plant and discarded.  
      Last but not least, a further aim is to make the reactor of the invention less difficult to stow in the transport container than the reactors of known type with equivalent characteristics.  
      Said aims are achieved by producing a reactor for cleaning fibrous suspensions dispersed in liquids which according to the main claim comprises: 
          a substantially cylindrical container with substantially vertical longitudinal axis to contain said suspension to be cleaned;     one or more blades arranged inside said container and connected to a drive shaft which defines a substantially vertical rotation axis;     drive elements combined with said drive shaft and designed to rotate it around said vertical axis;     a plurality of feed units for introducing into said container said suspension to be cleaned, together with a gaseous substance dispersed in it in the form of bubbles, said feed units being arranged in succession one above the other at different heights inside said container;     means for intercepting said suspension positioned inside said container and communicating with one or more of said feed units;     devices for skimming off the foam formed by the impurities picked up by said bubbles;     and wherein each of said feed units comprises at least one feed pipe which extends towards the inside of said container and is provided with a plurality of ejectors, each of said ejectors having a spray direction facing towards the inner surface of said container to distribute said suspension to be cleaned starting from the inside of the cross section of said container.        

      Each of the above feed units comprises a substantially rectilinear feed pipe which defines a substantially horizontal longitudinal axis and is arranged substantially radially to the cross section of the container.  
      According to one form of embodiment the feed pipe is provided at the end inside the container with a C-shaped tubular connection on which the ejectors are arranged.  
      Advantageously the reactor of the invention, since it comprises fewer components than the reactors of known type, is simpler to construct, costs less and is more reliable in terms of operation.  
      Again advantageously, for the same reasons described above, the reactor of the invention also requires less maintenance.  
      Equally advantageously, the reactor of the invention is simpler to transport and assemble than the known reactors equivalent to it.  
      Lastly, advantageously, the reactor of the invention permits the use of containers discarded from old plants. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The aims and advantages mentioned above will be illustrated in greater detail during the description of some preferred forms of embodiment of the invention, which are provided as non-restrictive examples and are shown in the attached drawings, wherein:  
       FIG. 1  shows the longitudinal section of the reactor of the invention, indicating the flow directions during operation;  
       FIG. 2  shows the longitudinal section of a variant of the reactor of the invention, indicating the flow directions during operation;  
       FIG. 3  shows a cross section of the reactor of the invention with the injectors produced according to a preferred form of embodiment;  
       FIG. 4  shows the cross section of the reactor of the invention with the injectors produced according to a variant;  
       FIG. 5  shows an intermediate cross section of the reactor of the invention illustrated in  FIG. 1 ;  
       FIG. 6  shows a detail of the reactor of the invention illustrated in  FIG. 1  or in  FIG. 2 ;  
       FIG. 7  shows another cross section of the reactor of the invention illustrated in  FIG. 1  or in  FIG. 2 ;  
       FIG. 8  shows a partial axonometric view of the reactor of the invention illustrated in  FIG. 1 ;  
       FIG. 9  shows the reactor of the invention disassembled, with the parts already loaded in a container. 
    
    
     DESCRIPTION OF THE INVENTION  
      As can be seen in  FIG. 1 , the reactor of the invention, indicated as a whole by  1 , consists of a substantially cylindrical container  2 , defining a substantially vertical longitudinal axis Y, provided with one or more blades  3  arranged inside it, one of which can be seen in the cross section of  FIG. 7 .  
      The blades are connected to a drive shaft  4  which defines a substantially vertical rotation axis Y′ coinciding with the longitudinal axis Y of the container  2 .  
      In different forms of embodiment not represented, the axis of the container and the rotation axis may not coincide.  
      Drive elements set the drive shaft  4  rotating around the above-mentioned vertical axis in order to keep in motion the suspension to be cleaned contained inside the container  2 .  
      A plurality of feed units, indicated as a whole by  5 , which can be seen also in  FIG. 8 , are arranged inside the container  2 , in succession one above the other and at different heights, in order to feed the suspension to be cleaned into the container, together with a gaseous substance dispersed in it in the form of bubbles.  
      More precisely, the feed units  5  comprise a main feed unit indicated as a whole by  6  and positioned at the level of the free surface of the fibrous solution to be cleaned, as well as a plurality of secondary feed units  7 ,  8 ,  9  arranged below the main feed unit  6 .  
      According to the invention, each of the above feed units  6 ,  7 ,  8 ,  9 , comprises a feed pipe  6   a ,  7   a ,  8   a ,  9   a  which extends towards the inside of the container  2  and is provided with a plurality of ejectors  6   d ,  7   d ,  8   d ,  9   d , each of which has a spray direction Z facing towards the inner surface  2   a  of the container  2  for the distribution of the suspension to be cleaned starting from the inside of the cross section S of the container  2 .  
      According to the form of embodiment shown in  FIGS. 1, 3  and  8 , each feed pipe  6   a ,  7   a ,  8   a ,  9   a  is substantially rectilinear, defines a longitudinal axis X arranged substantially radially to the cross section S of the container  2  and is provided, at the end extending towards the inside of the container  2 , with a C-shaped tubular connection  6   b ,  7   b ,  8   b ,  9   b.    
      Said C-shaped tubular connection has its centre coinciding with the longitudinal axis Y of the container  2  and the ejectors  6   d ,  7   d ,  8   d ,  9   d  are applied to it.  
      According to a variant shown in  FIG. 4 , each feed pipe  6   a ,  7   a ,  8   a ,  9   a  is substantially rectilinear and also defines a longitudinal axis X arranged substantially radially with respect to the cross section S of the container  2 , but differs from the above form of embodiment due to the fact that the ejectors  6   d ,  7   d ,  8   d ,  9   d  are arranged on the outer surface of the feed pipe.  
      In both forms of embodiment referred to, the ejectors can consist indifferently of precision-sized through holes made directly in the respective tubular elements, or fixed or removable jets applied to the tubular elements by means of screw or pressure coupling.  
      Furthermore each ejector has a spray direction Z facing towards the inner surface  2   a  of the container  2 .  
      Said spray direction Z can be parallel to the plane defined by the cross section S of the container  2  or preferably, as shown in detail in  FIG. 5 , intersect the cross section at an angle. In particular the spray direction Z slightly slopes downwards in order to compensate for the fact that the air incorporated in the jet tends to move the jet upwards, displacing it along a curved path Z′ which bends towards the top.  
      In this way, in the cross section S of the container  2 , the layer formed by the jets is of limited thickness with reference to the longitudinal axis Y of the container in which the suspension is uniformly distributed.  
      The main aim of the invention, that of feeding the suspension into the container with a reduced number of feed pipes and ejectors, has therefore been achieved.  
      It can be observed in particular that the main feed unit  6  comprises the feed pipe  6   a  to which a suction pipe  6   c  is connected in parallel, said pipe sucking air from the outside by Venturi effect when the suspension to be cleaned runs through the feed pipe  6   a  in the direction indicated by the arrow I to reach the ejectors  6   d.    
      In this way an emulsion consisting of the suspension to be cleaned mixed with air is fed into the container  2 , wherein the air bubbles, assisted by the chemical reagents present, pick up the impurities dispersed in the suspension.  
      In this way a first flotation is obtained, which generates foam floating on the free surface of the suspension, said foam being removed from said surface by means of skimming devices indicated as a whole by  10 .  
      These comprise a rotating arm  11  connected to the drive shaft  4  which during rotation conveys the foam towards the outlet  12  of a drain pipe  13 .  
      The outlet  12  is obtained in the side surface  2   a  of the container  2 , at the level of the circle described by the rotating arm  11  during rotation.  
      The liquid which drops vertically inside the container in the direction indicated by the arrow D is collected midway through its descent by second interception means  14  which, as can be seen in  FIG. 1 , consist of a collecting tank  14   a  with a tapered base  14   b  converging downwards towards the centre, arranged substantially halfway up the container  2 .  
      In particular, the collecting tank  14   a  is positioned between the above-mentioned secondary feed units  7 ,  8 ,  9  and communicates with the first secondary feed unit  7 , which is positioned immediately above the collecting tank  14   a  and immediately below the main feed unit  6 .  
      More precisely, a delivery pipe  15 , via pumping means not shown, takes the liquid from the collecting tank  14   a  and conveys it in direction  15   a  to the feed pipe  7   a  of the above-mentioned first secondary feed unit  7 .  
      Also in this case a suction pipe  7   c  is connected parallel to the feed pipe  7   a  and communicates with the external environment, enabling the liquid that flows through the feed pipe  7   a  to suck in air by Venturi effect.  
      The suspension crosses the feed pipe  7   a  and reaches the injectors  7   d  which feed it in immediately above the collection tank  14   a.    
      The suspension is sprayed by the injectors  7   d  from the inside of the section of the container  2  towards its inner surface  2   a , according to the directions shown in the drawings in  FIGS. 3 and 4 .  
      In particular, if the injectors are of the type shown in  FIG. 3 , the injection directions Z are substantially radial, whereas if the injectors are of the type shown in  FIG. 4 , then the directions Z are not radial, but in any case facing the inner surface of the container  2 .  
      The suspension that has already been cleaned previously, having undergone the first flotation, drops by gravity in the direction shown by the arrows D and undergoes a second flotation during which the air bubbles which combine with the impurities still present in the suspension are transformed into foam which rises by gravity to the free surface and is eliminated as already explained.  
      The suspension that is fed back into the container  2  above the collecting tank  14   a  drops towards the bottom of the container  2 , where first interception means are present, indicated as a whole by  16  and comprising a collecting hood  16   a  tapering upwards provided with at least one delivery pipe  17  connected to it, said pipe allowing the cleaned liquid to be extracted by means of pumping means with which it is provided and which are not shown.  
      A part of the cleaned liquid indicated by the arrow  18  is conveyed away for use and constitutes the so-called “accepted” liquid, while the remaining part indicated by the arrow  19  flows into the feed pipes  8   a  and  9   a  of the second  8  and third  9  secondary feed unit respectively, which are arranged above the first interception means  16 .  
      From the second  8  and third  9  secondary feed unit the suspension is fed in at an intermediate position in the container  2  via further ejectors  8   d  and  9   d  respectively, after emulsification with air that, also in this case, is taken in by Venturi effect through respective suction pipes  8   c ,  9   c  arranged parallely to the secondary feed pipes.  
      The liquid that flows towards the bottom of the container in the direction indicated by the arrows  20  undergoes further flotation and is completely cleaned when it enters the first interception means  16  for the second time.  
      The fibrous suspension passes through the inside of the container  2  several times thus undergoing several flotation operations, assisted also by the rotation of the blades  3 .  
      In this regard each blade  3  consists of a flat laminar body or, alternatively, of a rectilinear or curved tubular body as shown in  FIG. 7 .  
      To stabilise the ascending and descending flows, grille sectors  21  are provided inside the container  2 , which are arranged between the intermediate tank  14   a  and the inner surface of the container  2  as can be seen in  FIG. 5 .  
      The insertion of said grille sectors  21  is possible since, to reduce the dimensions of the intermediate tank  14   a  and facilitate loading and transport of the reactor via container A, the intermediate tank  14   a  and also the hood  16   a  which constitutes the first collecting means  16  are quadrangular in shape as can be seen in  FIG. 5 .  
      The intermediate tank  14   a  will be preferably square-shaped.  
      Furthermore, as can be seen in the axonometric representation of  FIG. 8 , all the feed pipes  6   a ,  7   a ,  8   a ,  9   a  are vertically aligned on one single shaped metal sheet  22 , which is assembled by welding to further shaped metal sheets complementary to it to constitute the cylindrical container  2 .  
      The disassembled reactor is loaded in a container A by arranging the elements as shown in  FIG. 9 .  
      In a simplified variant shown in  FIG. 2 , the reactor of the invention, indicated as a whole by  30 , differs from the form of embodiment just described due to lack of the intermediate tank.  
      In said case, with reference to the fibrous suspension indicated by the arrow U which comes out of the first interception means  16  arranged on the bottom, the part indicated by the arrow  19  is conveyed away for use and the remaining part indicated by the arrow  19   a  is conveyed through all the feed pipes  7   a ,  8   a ,  9   a  of the secondary feed units  7 ,  8 ,  9  which in this case, as can be seen, are all arranged below the main feed unit  6  and above the first interception means  16 .  
      On the basis of what has been described, the reactor of the invention achieves all the set aims.  
      In particular, the presence of the feed units each consisting of one single feed pipe with injectors that inject the suspension from the inside of the container permits the production of a reactor with fewer components compared to the known technique.  
      Said construction simplicity also permits achievement of the aim to avoid pre-assembly of the reactor at the factory prior to shipment to the customer.  
      Furthermore the aim to produce a reactor with simpler, quicker and therefore cheaper construction compared to the known reactors with equivalent characteristics is also achieved.  
      The aim to produce a reactor with smaller overall dimensions than the known reactors with equivalent characteristics is also achieved.  
      Lastly, advantageously for the users, the reactor of the invention requires less maintenance and can also be produced using any discarded container that has already been used in another plant.  
      It should be pointed out that in the reactor of the invention the number of feed units, their arrangement, the number of blades, their arrangement and their shape can be different from what has been described and illustrated herein.  
      Modifications can also be made to the reactor of the invention and it can be produced according to construction variants which, if they fall within the scope of the following claims, must all be considered protected by this patent.