Abstract:
A separating device is provided for separating liquid from a slurry of liquid and solid particles. The device has a settling chamber including a filter screen spanning a liquid outlet opening at the open top end of the settling chamber. A slurry inlet, in communication with the settling chamber below the filter screen, introduces a slurry of liquid and solid particles into the settling chamber. Liquid is urged to escape from the settling chamber upwardly through the filter screen. The filter screen, being located at the top of the settling chamber, provides a more natural separation of the liquid from the solid particles by permitting the liquid to rise upwardly through the screen while the solid particles settle out in the settling chamber to be compacted at the bottom of the chamber for removal of the compacted solids from the bottom of the chamber.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a device for separating liquid from a slurry of liquid and solid particles.  
         BACKGROUND  
         [0002]    Slurries of liquid and solid particles are commonly found in many industries where it is desirable to separate the liquid and solid components of the slurry. These industries include waste water processing, industrial sludge, food processing and pulp mills.  
           [0003]    Known systems for de-watering generally include a filter screen into which the slurry or sludge is forced so that the liquid is able to pass through the filter screen leaving the solid particles trapped by the screen. The solid particles however must be removed when the screen becomes plugged in order to maintain efficiency of the filter screen. Screens in this arrangement are commonly plugged because the liquid and solid particles are forced in the same direction into the screen during the filtering process.  
           [0004]    U.S. Pat. No. 5,009,795 to Eichler and U.S. Pat. No. 5,833,851 to Adams provide examples of a screw press for de-watering solids suspended in liquid. In each of these devices an auger is provided for pressing a slurry of solid particles suspended in liquid against the surrounding walls of the auger which includes a screen therein for permitting the liquid to escape. The solid particles however are continuously pressed against the filter screen thus reducing the efficiency of the screen by causing the screen to be plugged up with solid particles.  
           [0005]    U.S. Pat. No. 6,135,293 to Herbst provides a water and sludge filter press in which a filter bag filled with water and sludge is pressed between a pair of opposing screens arranged so that the water is permitted to escape through the filter bag which traps the sludge and solid particles therein. The press requires the filter bags to be emptied when the sludge accumulates therein in use.  
           [0006]    U.S. Pat. No. 5,997,750 to Rozelle provides a drinking water purification system for producing purified drinking water from surface or ground water sources. Positively charged filtration media are used to attract typically negatively charged suspended solids present in the water source. A filter column is used having screens therein which require periodic cleaning due to the accumulation of solid particles thereon because the liquid and solid particles suspended therein are forced to flow in the same direction into the screen.  
         SUMMARY  
         [0007]    According to one aspect of the present invention there is provided a separating device for separating liquid from a slurry of liquid and solid particles, the device comprising:  
           [0008]    a settling chamber arranged for containing liquid therein having a liquid outlet opening at a top end thereof;  
           [0009]    filter means spanning the liquid outlet opening at the top end of the chamber; and  
           [0010]    a slurry inlet in communication with the settling chamber below the filter means arranged to introduce the slurry of liquid and solid particles into the settling chamber;  
           [0011]    whereby introduction of the slurry of liquid and solid particles into the settling chamber urges liquid to escape from the settling chamber upwardly through the filter means spanning the liquid outlet opening.  
           [0012]    The arrangement of a separating device wherein the filter screen is located at the top of a settling chamber located therebelow provides a more natural separation of the liquid from the solid particles by permitting the liquid to rise upwardly through the screen while the solid particles settle out in the settling chamber to be compacted at the bottom of the chamber.  
           [0013]    In further variations, compaction of the solid particles is improved by providing a filter screen which is movable upwardly and downwardly to press the solid particles down into the settling chamber when the screen is lowered while permitting fresh liquid to flush the bottom side of the screen when the screen is raised. The solid particles may be removed from the settling chamber by a solid particle outlet located at the bottom of the chamber. Tapering the settling chamber downwardly and inwardly towards the solid particle outlet and providing an auger to urge the solid particles out through the solid particle outlet assists in compaction of the solid particles within the settling chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]    In the accompanying drawing, which illustrates an exemplary embodiment of the present invention:  
         [0015]    [0015]FIG. 1 is a schematic view of the separating device for separating liquid from a slurry of liquid and solid particles. 
     
    
     DETAILED DESCRIPTION  
       [0016]    Referring to the accompanying drawing, there is illustrated a separating device generally indicated by reference numeral  10 . The separating device  10  is intended for separating liquid from a slurry of liquid and solid particles which has particular application in the treatment of waste water as well as many other similar process in which it is desirable to de-water slurries or sludge.  
         [0017]    The device generally includes a settling chamber  12  which is generally conical in shape having a large open top end  14  and walls  16  which taper downwardly and inwardly to an apex at a bottom end  18  of the chamber. A solid particle outlet  20  is located at the bottom end  18  of the chamber while the open top end  14  defines a liquid outlet  22 .  
         [0018]    A slurry is introduced into the settling chamber  12  by a slurry inlet  24  coupled to communicate through a wall of the settling chamber  12  spaced upwardly from the bottom end  18  of the chamber adjacent the open top end  14  thereof. Coupling the slurry inlet  24  to the chamber at a location spaced upwardly from the bottom end of the chamber reduces the possibility of liquid becoming trapped within the compacted solids at the bottom end of the chamber.  
         [0019]    The slurry inlet  24  is coupled between the chamber  12  and a source of the slurry at a reservoir  26 . The reservoir  26  is arranged to be substantially higher in elevation than the open top end of the settling chamber such that the resulting hydrostatic head between the reservoir  26  and the chamber  12  causes the slurry to flow through the slurry inlet into the chamber.  
         [0020]    The slurry inlet  24  is in the form of an enclosed pipe which extends downwardly from the reservoir  26  at a first portion  28  and then extends at a downward incline through a second portion  30  which communicates with the chamber  12 . An angle between the first and second portions of the slurry inlet pipe is an obtuse angle so as to reduce the possibility of obstruction at the bends in the pipe with the second portion  30  of the pipe entering the chamber  12  at a downward incline of approximately 45 degrees from horizontal to direct solid particles in the slurry away from the open top end of the chamber.  
         [0021]    The liquid outlet  22  at the open top end of the chamber is arranged to be substantially greater in cross sectional area then the slurry inlet  24  so as to reduce upward velocity of the slurry entering the chamber to induce settling and minimize mixing of the liquid and solid particles.  
         [0022]    The open top end  14  of the chamber  12  includes a support flange  32  extending laterally outwardly from a periphery of the chamber for supporting a filtering screen  34  at the liquid outlet  22 . The filtering screen  34  is a conventional type screen which may be formed of stainless steel or Teflon for example.  
         [0023]    A series of springs  36  are mounted about a periphery of the filter screen  34  for supporting the periphery of the screen on the support flange  32 . The screen  34  is thus supported to span horizontally across the liquid outlet  22  while being movable relative to the settling chamber  12  on the springs  36  in a vertical direction transversely to the direction in which the screen spans. The springs  36  are supported between the screen  34  and the flange  32  so as to be oriented in a direction to urge the screen upwardly and away from the settling chamber.  
         [0024]    A flexible baffle  38  is coupled between the periphery of the screen  34  and the walls  16  of the settling chamber for sealing therebetween such that the screen is sealed with respect to the chamber walls so that the liquid is forced to pass through the screen  34  in order to escape through the open top end of the chamber  12 . The springs  36  are mounted externally of the baffle  38  so as to be shielded from the liquid and slurry within the chamber  12 .  
         [0025]    A collecting pan  40  spans laterally outwardly from the periphery of the screen  34  for supporting the periphery of the screen on the springs  36 . The pan  40  includes side walls  42  which extend upwardly from a flat bottom  44  of the pan which is in horizontal alignment with the screen  34 . The side walls  42  are enclosed at a top end by an enclosure  46  spanning the side walls spaced upwardly from the screen, defining an outlet chamber within the enclosure  46  of the collecting pan  40  adjacent an outer side of the screen  34 . The enclosure includes a gas vent  48  which is coupled to a gas line and arranged to release gases collected within the enclosure  46  in a controlled manner. The gas vent  48  communicates with the outer side of the screen and is open and closed by a controller for venting gas therefrom as required.  
         [0026]    The flat bottom  44  of the collecting pan  40  includes a liquid drain line  50  coupled thereto having an opening which is level with the screen  34  at an elevation which is well below the reservoir  26  of the slurry inlet such that hydrostatic head from the slurry within the reservoir urges the liquid through the screen  34  to be subsequently drained through the liquid drain line  50 . The liquid drain line  50  being coupled with the collecting pan  40  is thus also arranged to communicate with the outer side of the filter screen  34 .  
         [0027]    The solid particle outlet  20  includes an outlet pipe coupled to communicate with the bottom end  18  of the settling chamber to extend downwardly and outwardly therefrom. A ball valve  54  is mounted within the outlet pipe  52  spaced below the bottom end  18  of the chamber  12  for selectively discharging compacted solid particles from the settling chamber when the ball valve  54  is opened.  
         [0028]    A screw press is provided in the form of an auger  56  mounted within the outlet pipe  52  above the ball valve  54  for communication with the compacted solid particles in the bottom end of the chamber  12 . The auger  56  is mounted for rotation about a longitudinal axis of the outlet pipe  52  containing the auger therein for urging the compacted particles through the outlet pipe  52  when the ball valve  54  is opened and the auger is rotated.  
         [0029]    A compaction mechanism is provided in the form of an actuator  58  coupled to the collecting pan  40  above the settling chamber  12 . The actuator  58  is mounted between the enclosure  46  on a top side of the collecting pan and a support arm  60  which is fixed in relation to the settling chamber  12 . Actuation of the actuator  58  causes the actuator above the enclosure  46  to be extended for urging the collecting pan and the screen  34  connected thereto to move together downwardly against the slurry of liquid and solid particles within the settling chamber.  
         [0030]    The actuator  58  is thus oriented to act against the springs  36  to compact the solid particles within the chamber  12 . The springs  36  urge the screen back up to a starting position when the actuator  58  is released. A controller is provided to actuate displacement of the screen and collecting pan  40  coupled thereto at a prescribed frequency of oscillation which can be adjusted and pre-set as required.  
         [0031]    Displacement of the screen involves compression of the flexible baffle  38  in the order of approximately eighty percent of the height of the baffle which corresponds to possibly three to four inches as an example. In use, the actuator  58  would be actuated to displace the screen  34  downward into a compacted position of the solid particles in the chamber in the order of once every thirty seconds.  
         [0032]    A vibrator  62  may be coupled to the walls of the settling chamber  32  in a manner so as to be arranged to transmit vibrations through the chamber walls  16  to the slurry therein for assisting in the separation of liquid and solid particles while also assisting in compaction of the solid particles at the bottom end of the settling chamber.  
         [0033]    A mass sensor  64  may be provided which is coupled to the settling chamber  12  in a manner so as to measure a mass of the slurry within the settling chamber or a specific gravity thereof. The mass sensor  64  is used to determine when a specific gravity of the settling chamber contents are greater than a prescribed solid particle threshold which is pre-set for indicating when sufficient solid particles have been collected that the ball valve  54  of the solid particle outlet can be opened to remove at least some of the compacted solid particles. For example if the solid particles in question have a specific gravity of four relative to the liquid within which it is suspended, the prescribed solid particle threshold would be a magnitude which would be close to but below the expected specific gravity of the solid particles. In this example, a suitable threshold may be a specific gravity of three.  
         [0034]    In alternate arrangements the chamber  12  is determined to be requiring emptying of compacted solid particles based upon the expiry of a timer if the slurry conditions are constant or predictable. For greater accuracy, measurement of the amount of solid particles compacted within the settling chamber can be determined using an ultrasonic monitor for example or a pressure sensor on the screen  34  for sensing when the pressure of compacted solids exerted on the screen when the screen is lowered reaches a prescribed pressure threshold.  
         [0035]    In use, the slurry of liquid and solid particles is introduced into the settling chamber through the slurry inlet  24  at a sufficiently slow rate so as not to induce turbulence or mixing within the settling chamber but rather to induce settling of solid particles. This is encouraged by having a slurry inlet  24  with a small cross-sectional area relative to the cross-sectional area of the chamber  12  and more particularly the liquid outlet  22 . Positioning the slurry inlet  24  as close to the open top end  14  of the settling chamber  12  as possible prevents liquid from being trapped within the layers of compacted solid particles at the bottom end of the settling chamber while ensuring a continuous supply of liquid near the screen  34  for flushing solid particles from the screen in operation.  
         [0036]    The inflow through the slurry inlet  24  may be provided by a pump in an alternate arrangement, however the inflow must be at a sufficiently slow rate so as not to induce to much turbulence or mixing as noted above, and therefore an induced flow due to the hydrostatic head of the reservoir  26  is preferred.  
         [0037]    During a separating operation, the screen  34  is oscillated in a vertical direction for compacting the solid particles downwardly to the bottom end of the settling chamber. Oscillations of the screen  34  follow a prescribed period which can be constant or varied depending upon conditions sensed within the settling chamber  12 . Oscillation of the screen  34  is much slower than the vibrations induced within the chamber  12  by the vibrator  62 .  
         [0038]    As determined by appropriate sensors noted above, the solid particles compacted within the settling chamber are periodically dumped when a controller determines that the solid particle threshold has been exceeded. The controller then opens the ball valve  54  upon which the auger  56  is responsive so that the auger begins to rotate when the valve is opened to urge the compacted solid particles out of the settling chamber through the outlet pipe  52 . A suitable valve or control may be provided on the slurry inlet  24  to stop inflow when the ball valve  54  is opened. Once a predetermined amount of solid particles are removed from the settling chamber  12  the ball valve  54  is again closed and the inflow through the slurry inlet  24  is again arranged to introduce slurry into the settling chamber. As the slurry is introduced, pressure from the slurry entering urges the lighter liquid at the open top end of the settling chamber  12  to pass upwardly through the screen  34  and overflow into the liquid drain line  50 . The gas vent  48  is controlled by appropriate sensors for determining when sufficient gas has built up within the enclosure  46  that the release of gas is required.  
         [0039]    This device ensures that the liquid and solid particles are displaced in different directions with the heavier solids being directed towards the bottom end of the settling chamber while the lighter liquid is permitted to overflow upwardly through the screen. The location of the screen at the top end of the settling chamber ensures that the lighter fluids constantly gravitate to the screen for flushing the screen and reducing clogging of the inside of the screening surface by solid particles within the settling chamber. After the liquid has been separated from the settling chamber  12  for overflowing through the liquid drain line  50 , the liquid may be passed through subsequent treating operations as required depending upon the process within which the separating device is a component.  
         [0040]    While one embodiment of the present invention has been described in the foregoing, it is to be understood that other embodiments are possible within the scope of the invention. The invention is to be considered limited solely by the scope of the appended claims.