Abstract:
A treatment vessel for separating contaminants from a base liquid is provided. The vessel comprises a first cylindrical portion, a frusto-conical portion, a second cylindrical portion and a conical portion, the conical portion having a bottom outlet arranged to discharge heavy contaminants from the vessel. Over time, the heavy contaminants settle on the sides of the conical and frusto-conical portions. In order to remove the settled contaminants, the vessel is provided with at least one clarified liquid inlet disposed at or proximate to the frusto-conical portion. The clarified liquid is sourced from either the treatment vessel itself, or another treatment vessel in the same system. The clarified liquid is reintroduced into the vessel in a manner so as to cause a downward circular flow to scour out the frusto-conical portion and the conical portion so as to assist in removal of heavy contaminants that settle on the sides thereof.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an apparatus for treatment of contaminated liquids particularly, but not exclusively, treatment of industrial, agricultural and municipal effluent. 
   BACKGROUND OF THE INVENTION 
   Vessels for separating contaminants from liquids are well known in the art and are generally in the form of a cylindrical tank with a conical bottom, where the apex of the conical bottom is lower than the outer side thereof. 
   Inlets may be positioned so as to produce a spiral flow of the liquid in the vessel and outlets may be positioned at the bottom, top and sides of the vessel to enable the drawing off of various fractions of the separated liquid stream, depending on its relative specific gravity. 
   For the purposes of this specification, a vessel or vessels of aforementioned type will be hereinafter referred to as a “treatment vessel” or “treatment vessels”. 
   The inlet of a treatment vessel is typically situated at the outer edge of the treatment vessel, and is typically arranged in such a manner so as to introduce liquid tangentially and thereby create laminar, spiral flow within the treatment vessel. As the liquid nears the centre of the treatment vessel, the speed decreases and the direction of the flow is changed to a vertical up and down flow towards the top and bottom outlets. 
   It is preferred that no spiral flow takes place at the centre part of the treatment vessel so as to allow the contaminants to separate. 
   Separation takes place within the treatment vessel as the speed of flow slows toward the centre of the treatment vessel. Thus, while contaminants are suspended at the rate of flow at the outer part of the treatment vessel, these will be released as the speed of flow decreases toward the centre of the treatment vessel and will separate into their fractions depending on their specific gravity. 
   Separation can be aided by the prior addition of a variety of chemical substances. The methods for introducing contaminated liquids tangentially into a treatment vessel so as to produce spiral flows and the methods for operating such treatment vessels are well known. 
   It is often the practice to use more than one treatment vessel within a single separator system where more than one operation is required within the separator system. Thus, one treatment vessel may be used for removing those contaminants where the specific gravity of the contaminants is heavier than the carrying liquid, and another treatment vessel may be used to concentrate the contaminants removed. 
   A problem with existing treatment vessels used in separator systems is that the heaviest contaminants are directed downward toward the apex of the conical bottom of the treatment vessel and can build up a plug which does not flow out of the treatment vessel as desired. 
   The inventor of the present invention has previously provided a method of mitigating plugging of the bottom outlet of the treatment vessel by reintroducing clarified liquid obtained from a treatment vessel within the separator system in a manner so as to produce a downward spiral flow to scour out the conical portion of the treatment vessel. However, it has been found that the effectiveness of the method over prolonged periods of time can sometimes be compromised by the formation of “rat-holes” within the settling sediment, since upon its mechanical removal the sediment adheres to the walls of the conical portion. Further, access to the bottom portion of the treatment vessel for maintenance and cleaning, in the eventuality of “rat-hole” formation can sometimes be very difficult. 
   The present invention seeks to mitigate the possibility of “rat-holing” and subsequent plugging in treatment vessels by the separation of heavy contaminants therein and which increases the efficiency of operation of same beyond that of prior treatment vessels and clarifiers. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the present invention there is provided a treatment vessel for separating contaminants from a base liquid treated therein, the treatment vessel comprising: 
   a first cylindrical portion; 
   a frusto-conical portion adjacent a lower end of the first cylindrical portion; and 
   a base portion comprising a second cylindrical portion adjacent a lower end of the frusto-conical portion and a conical portion adjacent a lower end of the second cylindrical portion, the conical portion having a bottom outlet arranged to discharge heavy contaminants from the treatment vessel; 
   a clarified liquid source derived from the treatment vessel or another treatment vessel in a treatment system; and 
   at least one clarified liquid inlet disposed at a side of the treatment vessel to reintroduce clarified liquid into the treatment vessel from the clarified liquid source at, or proximate to, the frusto-conical portion thereof; 
   wherein, in use, the clarified liquid is reintroduced in a manner so as to cause a downward circular flow to scour out the frusto-conical portion and the conical portion of the base portion and assist in removing heavy contaminants that accumulate adjacent the bottom outlet of the treatment vessel. 
   In accordance with a second aspect of the present invention, there is provided a treatment system for separating contaminants from a base liquid treated therein, the system comprising; 
   a plurality of treatment vessels each including a frusto-conical portion and a base portion comprising a second cylindrical portion adjacent a lower end of the frusto-conical portion and a conical portion adjacent a lower end of the second cylindrical portion, the conical portion having a bottom outlet arranged to discharge heavy contaminants from the treatment vessel; 
   at least one clarified liquid source derived from one or more of the treatment vessels, a clarified liquid inlet disposed at a side of the or each treatment vessel to re-introduce the clarified liquid into the treatment vessel from one of the clarified liquid sources at, or proximate to, the frusto-conical portion thereof; 
   wherein, in use, the clarified liquid is reintroduced in a manner so as to cause a downward circular flow to scour out the frusto-conical portion and the conical portion of the base portion and assist in removing the heavy contaminants that accumulate at a bottom outlet of the treatment vessel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a cross sectional side elevation of the vessel in accordance with the first and second aspect; and 
       FIG. 2  is a plan view of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the Figures, wherein like numerals and symbols refer to like parts throughout, there is shown a treatment vessel  11 . The first and second aspects of the present invention are directed towards a separator system using one or more treatment vessels  11 . 
   The treatment vessel  11  comprises a right circular first cylindrical portion  13  having a frusto-conical portion  15  at a lower end thereof, and a right circular second cylindrical portion  17  having a conical portion  19  at a lower end thereof. 
   The frusto-conical portion  15  has an apex  15   a  lower than the side  15   b  thereof. The second cylindrical portion  17  is integral with the apex  15   a , the diameter of the second cylindrical portion  17  being coincident with the diameter of the apex  15   a . The conical portion  19  has an apex  19   a  lower than the side  19   b  thereof. 
   The height of the first cylindrical portion  13  is preferably no more than one and a half times the diameter of the first cylindrical portion  13 . 
   The diameter of the second cylindrical portion  17  is preferably from about 22% to about 40% of the diameter of the first cylindrical portion  13 . 
   The angle of inclination of side  19   b  is preferably twice the angle of inclination of side  15   b . Preferably, the angle of inclination of side  19   b  is about 60° and the angle of inclination of side  15   b  is about 30°. 
   In a preferred embodiment of the invention, the conical portion  19  is removable from the treatment vessel  11 . To this purpose, a lower edge of the second cylindrical portion  17  is preferably provided with a flange member  18   a  and an upper edge of the conical portion  19  is provided with a complementary flange member  18   b  for mating thereof. The flange members  18   a ,  18   b  are fixed together with conventional fixing means. 
   A top  12  of the first cylindrical portion  13  is open and has an annular gutter  14  disposed around an upper edge  13   b  of the first cylindrical portion  13 , the latter defining an intermediate lip between the annular gutter  14  and the top  12  of the first cylindrical portion  13 . In an alternative embodiment of the invention, the annular gutter  14  is disposed around an inside upper edge of the first cylindrical portion  13 . Inlets  21  for the vessel  11 , defined by a pair of conduits  21   a  and  21   b , are tangentially disposed at the side of the first cylindrical portion  13  to introduce contaminated base liquid into the vessel  11  so as to produce a spiral flow of liquid within the treatment vessel  11 . The conduits  21   a  and  21   b  are spaced apart from each other vertically, with the conduit  21   a  disposed approximately midway along the length of the first cylindrical portion  13  of the treatment vessel  11 , and the conduit  21   b  disposed proximate to midway between the conduit  21   a  and the top of the frusto-conical portion  15  of the treatment vessel  11 . Furtherstill, the openings of the conduits  21   a  and  21   b  are angularly spaced apart around the circumference of the first cylindrical portion  13  by approximately 90° as shown in  FIG. 1  of the drawings. 
   It will be understood that in an alternative embodiment of the invention the vessel  11  is provided with only one inlet  21  tangentially disposed at the side of the first cylindrical portion  13  to introduce contaminated base liquid into the vessel  11  so as to produce a spiral flow of liquid within the treatment vessel  11 . 
   A plurality of different sets of outlets are provided for the treatment vessel  11 . Bottom outlets  23  are disposed at the apex  19   a  and are defined by a pair of conduits  23   a  and  23   b  for discharging liquid through the apex  19   a  from the treatment vessel  11 . An upper outlet  25  (or set of outlets not shown) is provided proximate to the top  12  of the treatment vessel  11  and is defined by a conduit connected to a bottom of the annular gutter  14  in order to discharge liquid therefrom. 
   A further set of outlets  27  are disposed about the periphery of the first cylindrical portion  13  intermediate the top  12  and bottom of the first cylindrical portion  13 . These outlets in the present embodiment are defined by four conduits  27   a ,  27   b ,  27   c  and  27   d  which are axially spaced apart along the treatment vessel  11  to discharge different fractions of the liquid from within the treatment vessel  11 , depending upon the relative specific gravity thereof, as will be described in more detail later. 
   Preferably, the vessel  11  is provided with flow modifying means  29  comprising a pair of centrally disposed vanes  29   a ,  29   b  adjacent the top of the first cylindrical portion  13 . In the present embodiment, two vanes  29   a  and  29   b  are disposed in an orthogonally intersecting relationship. The radial extent of the vanes  29   a ,  29   b  increases progressively towards the circumference of the first cylindrical portion  13  as shown in  FIG. 1 , as the vane  29  extends axially towards the top  12  of the vessel  11 . The vanes  29   a ,  29   b  are fixedly mounted to the inner wall of the first cylindrical portion  13  at the outer radial ends of the fully extended radial portion thereof for fixedly disposing the flow modifying means  29  within the treatment vessel  11 . 
   Preferably, the vessel  11  is also provided with a cylindrical skirt  40  depending from adjacent outer radial ends of the flow modifying means  29 , as shown in  FIG. 1 . A lowermost edge  42  of the cylindrical skirt  40  is disposed adjacent the uppermost of the pair of conduits  21   a  and  21   b . The purpose of the cylindrical skirt  40  is to encourage flow of separated liquid, containing light weight contaminants in the form of flotation material, to be drawn up an outer side of the cylindrical skirt  40  so as to be discharged through the uppermost outlet  27   a.    
   In  FIGS. 1 and 2  there are shown a plurality of first clarified liquid inlets  31  disposed at the side of the treatment vessel  11  proximate to the frusto-conical portion  15  in a tangential manner so as to reintroduce the clarified liquid into the treatment vessel  11  tangentially in this region. The first inlets  31  are connected to a clarified liquid source being a branch from one or more of the outlet conduits  27   a,    27   b,    27   c  or  27   d  of another treatment vessel  11  provided in the separator system or the upper outlet  25  of the same treatment vessel  11 . 
   As can be seen in  FIGS. 1 and 2 , the first inlets  31  are spaced equiangularly around the side  15   b  of the frusto-conical portion  15  at a position intermediate the top of the frusto-conical portion  15  and the apex  15   a  Furthermore, the first inlets  31  are oriented slightly lower at ends adjacent the treatment vessel  11  so that clarified liquid introduced into the treatment vessel  11  therethrough is directed with a downward directional component towards the apex  15   a  of the frusto-conical portion  15  in a manner to be described in more detail later. 
   In  FIGS. 1 and 2  there are shown a plurality of second clarified liquid inlets  33  disposed at the side of the treatment vessel  11  proximate to the second cylindrical portion  17 . The second inlets  33  are oriented in a downward longitudinal manner so as to reintroduce the clarified liquid into the treatment vessel  11  longitudinally in this region. The second inlets  33  are connected to a clarified liquid source being a branch from one or more of the outlet conduits  27   a,    27   b,    27   c  or  27   d  of another treatment vessel  11  provided in the separator system or the upper outlet  25  of the same treatment vessel  11 . 
   As can be seen in  FIGS. 1 and 2 , the second inlets  33  are spaced equiangularly around the second cylindrical portion  17  at a position intermediate the top and the bottom of the second cylindrical portion  17 . 
   In a preferred embodiment of the present invention the first and second inlets  31 ,  33  are spray nozzles which reintroduce the clarified liquid into the treatment vessel  11  under pressure. Typically, for example, each spray nozzle would reintroduce clarified liquid into the treatment vessel  11  at a flow rate of 17 L/minute at a pressure of 68 kPa. It will be understood that the number of first and second inlets  31 ,  33  provided to the treatment vessel  11 , and the flow rate and pressure under which they operate will vary according to the size of the treatment vessel  11  and the sedimentary characteristics of the contaminated liquids introduced into the treatment vessel  11  for treatment. 
   The separator system of  FIGS. 1 and 2  comprises one or more treatment vessels  11 , as described above. Accordingly, the conduits  31   a  and  31   b  are connected either to a clarified liquid source being a branch from one or more of the outlet conduits  27   a ,  27   b,    27   c  or  27   d  from a treatment vessel  11  disposed subsequently in the series of treatment vessels  11  constituting the separator system, the upper outlet  25  of the same treatment vessel  11 , or both. 
   Now describing the manner of operation of the separator system, contaminated base liquid is supplied to a treatment vessel via the inlets  21 . 
   In the case of a single treatment vessel separator system, the inlets  21  are connected to some contaminated base liquid source and the outlets  25  provide different fractions of the clarified decontaminated base liquid. 
   In the case of the separator system comprising a plurality of treatment vessels  11 , the treatment vessels  11  are connected in series so that the inlets  21  of all subsequent treatment vessels  11  are connected to one or more of the outlets  27  or a preceding treatment vessel  11 — or in the case of a preceding treatment vessel dedicated to treating a low volume of light contaminants, to the upper outlet  25  and/or in the case of a preceding vessel dedicated to treating a low volume of heavy contaminants, to the bottom outlet  23   b  additionally or alternatively to the outlets  27 . Thus, the outlets  27  of all preceding treatment vessels  11  in the series are connected to the inlets  21  of a subsequent treatment vessel  11 , additionally and/or alternatively to the outlets  25  and  23   b,  depending upon whether the treatment vessel  11  is dedicated to handling low volumes of light or heavy contaminants, respectively. 
   In the interests of risk management, it is preferable that the separator system comprise a plurality of treatment vessels  11  connected in series as described previously, wherein the series of connected vessels  11  are themselves connected in a parallel configuration. In this way, the failure of one treatment vessel  11  will not entirely interrupt process control within the system. Furthermore, a parallel configuration of several serially connected treatment vessels  11  allows for operational flexibility in that one or more vessels  11  can be readily added or subtracted from the system to account for volume capacity changes in a treatment plant. 
   The tangential positioning of the inlets  21  is provided to introduce base liquid containing heavy and light contaminants into the treatment vessel  11  in a tangential manner so as to produce a circular flow therein. Frictional forces between the circulating flows and the internal surfaces of the treatment vessel  11  produce laminar flows within the circulating liquid which facilitate the displacement of the heavy and light contaminants, under gravity, through the liquid. Heavy contaminants, having a relative specific gravity greater than that of the residual decontaminated base liquid, travel down towards the apex  19   a  or the conical portion  19 , whilst light contaminants, having a specific gravity lighter than the contaminated base liquid, travel upward towards the top  12  of the treatment vessel  11 . 
   This separation of heavy and light contaminants allows relatively clarified, decontaminated base liquid to remain midway between the top and bottom of the first cylindrical portion  13 , allowing this to be drawn off and discharged via the outlets  27 . As described, the outlets  27  are spaced apart axially of each other to enable different fractions of clarified decontaminated base liquid to be drawn off from the treatment vessel  11 . In this way, the treatment vessel  11  of the present invention affords a threefold separation of heavy contaminants, light contaminants such as in the form of flocculatory material, and clarified decontaminated base liquid. 
   Importantly, the first clarified liquid inlets  31  reintroduce clarified liquid to the treatment vessel  11  in a tangential manner, so as to circulate the liquid containing heavy contaminants proximate to the frusto-conical portion  15  of the treatment vessel  11  in a downward direction which causes a downward circular flow of liquid to scour out the frusto-conical portion  15  and assist in removing the heavy contaminants accumulating at the bottom outlet  23  of the treatment vessel  11 . 
   Further, the removal of heavy contaminants which accumulate at the bottom outlet  23  of the treatment vessel  11  is also assisted by reintroduction of clarified liquid through the second inlets  33  in a downward direction to scour out the conical portion  19 . 
   In this way, plugging of the apex  19   a  and hence the bottom outlets  23  is avoided by fluidising the heaviest contaminants continuously, enabling them to flow through one or other of the outlets  23   a  or  23   b,  which ever is connected into the system. 
   The scouring action produced by the flow of reintroduced clarified liquid is further assisted by the force of the flow of clarified liquid as it is reintroduced into the treatment vessel  11  under pressure through the spray nozzles at inlets  31 ,  33 . 
   Furthermore, the accumulation of sediments on the frusto-conical portion  15  and the conical portion  19  through “rat-holing” over prolonged periods of time is minimised by the augmentation of the treatment vessel  11  with the second cylindrical portion  17  and the conical portion  19 , particularly since the angle of inclination of side  19   b  is greater than the angle of inclination of side  15   b.    
   In the preferred embodiment of the invention, the conical portion  19  can be easily removed by loosening the fixing means which hold flange members  18   a,    18   b  together, thus providing ease of access to the frusto-conical portion  15  of the treatment vessel  11  and the second cylindrical portion  17 , and the conical portion  19  for maintenance and cleaning purposes. 
   It should be appreciated that the scope of the present invention is not limited to the particular embodiments herein described and that minor modifications or changes to the vessel design are envisaged to fall within the scope of the present invention and do not depart from the spirit of the same.