Abstract:
A method and apparatus for particulate removal from liquids is disclosed and includes a Coanda tilted wedge wire screen in combination with a liquid-flow velocity control orifice mounted within a cylindrical air-tight vessel that can be operated under pressure. The liquid flow velocity control orifice and Coanda tilted wedge wire screen in combination with the pressurized system provides for highly efficient and uniform removal of particulate matter that includes a self-cleaning feature.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates in general to an apparatus designed to remove particulates from a liquid and, in particular, a method and apparatus for particulate removal utilizing a pressurized system in combination with a wedge wire screen filter.  
           [0002]    Traditional filtration systems are usually made of a standard woven wire string or basket, perforated plate basket, mesh bags, granular media, sintered cartridges, centrifugal or cyclone separators. With the exception of the centrifugal and cyclone units, all of these systems operate in a submerged enclosure with particulates being trapped by the small openings or orifices in the filter element.  
           [0003]    The submerged systems have several shortcomings: These systems all plug rapidly when heavily loaded and must be removed to be cleaned or require back flushing to remove debris and particulate. This requires substantial maintenance costs to service the submerged systems. All of these units rapidly lose filtration efficiency as debris becomes trapped in the filter and often require a high liquid pressure to function normally. Because of the thin layer of filtrate that is required to plug a normal filter element, the element must be replaced or cleaned frequently. As the process stream must not be interrupted, maintenance and cleaning often create a dangerous and unfavorable condition. Additionally, the filter element grids must be large enough to pass the liquid yet small enough to trap particulates. In some filter mediums, the uniformity of plugging is uneven resulting in areas of high velocity, plugging and breakthroughs. This inconsistent flow rate can affect the efficiency of the filtration system resulting in poor particulate removal from the liquid due to plugging and leakage.  
           [0004]    The conventional, non-submerged systems also manifest several deficiencies: First, the liquid flow onto an inclined screen typically results in particulates becoming trapped in the filter, particularly at the upper surface area of the angled screen. This requires frequent cleaning and maintenance in order to assure efficient filtration. Non-submerged systems also tend to plug and have surface overflow, resulting in a lower efficiency and poor filtration. Further, they do not provide for uniform filtration of particulate matter.  
           [0005]    It is desirable to provide for enhanced particulate removal, a self-cleaning filter as well as consistent velocity flow of the liquid by employing an elongated, pressure competent housing incorporating a Coanda tilted wedge wire screen as a filtration device which enables self-cleaning as well as the introduction of air into the system causing the filtration device to work under pressurized conditions and to regulate the water level for most effective removal of debris.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide for a novel and improved particulate removal apparatus adaptable for use with industrial waste water, process water and other liquid processing requiring filtration.  
           [0007]    It is another object of the present invention to provide for a particulate removal method and apparatus operating under pressurized conditions allowing for a non-submerged system.  
           [0008]    It is another object of the present invention to provide for a particulate removal method and apparatus that is self-cleaning and does not require frequent back washing to remove debris.  
           [0009]    It is still another object of the present invention to provide for a particulate removal system wherein the velocity of the flowing liquid is controllable.  
           [0010]    It is another object of the present invention to provide selective particulate removal through use of a Coanda tilted wedge wire screen.  
           [0011]    A further object of the present invention is to provide for a novel and improved method of particulate removal in which the liquid is passed through a Coanda tilted wedge wire screen in a pressurized atmosphere.  
           [0012]    In accordance with the present invention, a filtration system has been devised for separating particulate matter from a liquid such as wastewater, processed water, or other processed liquids. A preferred embodiment includes an elongated, pressurized housing member containing filter means, an inlet port disposed on the housing member to receive unfiltered liquid, a first baffle forming a passage in the housing member for directing the liquid from the inlet port upwardly to the filter means, collecting means for storage of debris, and discharge means for removing filtered liquid from the housing member. The housing member can be operated in a pressurized piping system while the liquid level within the housing can be controlled so that the filter means can be operated in a non-submerged state.  
           [0013]    A method of particulate removal is also provided utilizing an air-tight housing member, pressurizing the housing member through introduction of air, directing liquid from an inline conduit to an inlet port disposed on the lower end of the housing member, forcing liquid through the inlet port and upwardly through an influent passage through a velocity orifice then downwardly by pressure or under gravity across a filter in order to remove particulate matter from the liquid, catching and draining filtered liquid from the housing.  
           [0014]    There has been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a side elevational view of the device;  
         [0016]    [0016]FIG. 2 is a top plan view with ceiling plates removed to show the top of the wedge wire screen;  
         [0017]    [0017]FIG. 3 is a front view in elevation of the device;  
         [0018]    [0018]FIG. 4 is a schematic view illustrating the path of liquid flow through the Coanda wedge wire screen of the device;  
         [0019]    [0019]FIG. 5 is a side perspective view of the velocity orifice plate and support plates; and  
         [0020]    [0020]FIG. 6 is a cross-sectional side view of the velocity orifice. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    In accordance with the present invention, a highly effective liquid filtration system for industrial waste water treatment or similar types of liquid filtration is provided. Referring now to FIGS. 1 through 6, a preferred apparatus  11  according to the present invention is broadly comprised of an elongated vessel  13  made up of bottom plate  15 , top ceiling plates  43 ,  45  and elongated pipe or casing  14 . Gas, preferably air, is introduced into the vessel  13  through gas inlet valve  37 , as seen in FIG. 3. This gas is used to control the liquid level within the pressurized vessel, the vessel  13  also having gas relief valve  39 , allowing for removal of gas from the pressurized vessel in the event that excess gas is present within the vessel  13 . The vessel  13  may also include a liquid level sensor  30  which serves to determine the level of liquid present in the vessel  13 .  
         [0022]    Referring back to FIG. 1, waste water, process water or a liquid to be filtered is introduced into the vessel  13  through inlet valve or port  17  which allows liquid to pass into influent passage  19  in the casing  14  which is formed by a first baffle  21 . The liquid pressure is preferably in the range of 30-100 psi, although it can be higher if necessary. The inlet port  17  may be connected inline to a water or liquid conduit  63  for industrial waste or process liquids. The influent passage  19  also includes the bottom plate  15  which forms a receptacle or container for the liquid with open end  18 . Due to the design of the influent passage  19 , liquid flows upwardly through the influent passage  19 , passes through liquid flow orifice  41 , which will be described in greater detail, then passes along screen surface  26  of filtration screen  25 , which may be comprised of a Coanda tilted wedge wire screen. This will also be described in greater detail at a later point. As shown in FIG. 2 and FIG. 3, side plates  49  and  49 ′ prevent liquid from spilling over screen edges  52 ,  52 ′, thereby confining liquid flow along the screen surface  26 .  
         [0023]    The liquid containing particulate matter flows under gravity or is jetted over the screen surface  26 . Particulate matter greater than a determinate size does not pass through the screen  25  and is temporarily retained on the screen surface  26 . Liquid with particulate matter removed, i.e., filtered liquid, passes through the screen  25  downwardly into effluent passage  27 . The effluent passage  27  contains air shield  36  which is preferably plastic moulded into an arc or semi-circular wedge that may be attached to an upper portion of effluent port  31 , preventing gas bubbles from becoming entrained in the filtered liquid and passing through the effluent port  31 . Due to pressurization, some liquid becomes super-saturated with gas and as liquid flows through the screen  25  and into the effluent container  27 , it strikes the surface of liquid level  32 , physically creating air bubbles. The air shield  36  prevents these entrained gas bubbles from escaping through the effluent port  31 , thereby maintaining a constant fluid level within the vessel  13 . The filtered liquid will exit the vessel  13  through the effluent port  31 . Particulate matter or debris  61  trapped on the screen surface  26  is collected in debris storage receptacle  33  for later removal through purge valve  35 .  
         [0024]    Referring to FIGS. 5 and 6, liquid flow control plate  23  is preferably made of a metal substance, such as, stainless steel but may also be made up of a plastic or plastic-like substance. The plate  23  is located on an upper end of the screen  25  creating a liquid flow control orifice  41  between the screen surface  26  and the plate  23 . The plate  23  is preferably rectangular in shape with an adjustable setting  38 . The adjustable setting  38  comprises a rear support member  34  having at least two holes  44 ,  44 ′ bored through the rear member  34 . There is a corresponding front support member  40  with larger corresponding openings  46 ,  46 ′ to receive a screw  48  or similar device inserted through the front support member  40  as well as the rear support member  34 . The larger openings  46  and  46 ′ permit the front support member  40  and the attached control plate  23  to be raised or lowered, thereby increasing or decreasing, respectively, the area of the orifice  41 , while the rear support member  34  remains stationary.  
         [0025]    Raising the control plate  23  increases the height and cross-sectional area of the orifice  41 , thereby decreasing the velocity of the liquid. A decrease in the cross sectional area of the orifice  41  increases the velocity of the liquid. The function of the orifice  41  is to provide for controlled velocity of the liquid as it passes onto the screen surface  26 . Where greater flows are required through the apparatus  11 , the influent passage  19  can be closed and sealed with the exception of the orifice  41  created by the control plate  23  and the screen surface  26 . The quantity of liquid that a given area of the screen  25  will pass is a function of the velocity of the liquid flowing over the screen surface  26 . While the velocity created by the acceleration due to gravity is usually adequate, reducing the cross sectional area of the orifice  41  will enhance the capacity and efficiency of the screen  25  by increasing the velocity of the liquid contacting the screen surface  26 . Care should be taken to assure that the orifice  41  is larger than all of the particulates to be filtered out.  
         [0026]    Referring back to FIG. 1, the screen  25  is placed diagonally across the effluent passage  27  and with respect to the first baffle  21 . The plane of the screen  25  is tilted at an angle in the range of 35° to 70°, dependent upon the function of the screen. The screen  25  is supported by lower screen support baffle  29  and the first baffle  21 . The support baffle  29 , horizontal side plates (not shown), and the first baffle  21  form the effluent passage  27  and allow filtered liquid to remain in the effluent passage  27 . The horizontal side plates extend horizontally, and the debris storage receptacle  33  is separated from the effluent passage  27  by the support baffle  29  and is designed to store particulate matter for later removal through purge valve  35 .  
         [0027]    [0027]FIG. 4 is an exploded schematic view of a Coanda wedge wire screen  25 . The Coanda tilted wedge wire screen  25  has the screen surface  26 , a lower surface  28 , an upper portion of the screen  51  and a lower portion of the screen  53 . See also FIG. 3. The Coanda screen  25  includes walls or wires  58  that are wedge-shaped extending chordally in spaced relation along the screen surface  26 . The screen is manufactured of small stainless steel wedge-shaped wires  58  that are either tungsten, inert gas, or resistance welded to supporting rods or bars located in a plane beneath the indexed and tilted wires  58 . The screen  25  may also be manufactured using plastic or plastic-like substances. Although the angle of tilt on the wire  58  is variable, optimal tilt is approximately 5°, although a tilt of between 3° to 10° would be the approximate range of tilt. The function of the tilted wire  58  is to create an exposed shearing plane along a leading edge  60  of the wire that will shear a layer of the liquid that is flowing across the surface of the screen surface  26 . It is important to have sharp, upstream edges  60  on the wires  58 , in order to have effective shearing. Particulates that are entrained in the liquid continue down the screen surface  26 . The Coanda screen is described in an article titled “Hydraulic Performance of Coanda-Affect Screens” by Tony Wahl, for publication in the Journal of Hydraulic Engineering, Volume 127, No. 6, June 2001, the entire contents of which are expressly incorporated herein by reference as if set forth in full. As described in Wahl, the Coanda-effect screens utilize a tilted wire screen panel which produces shearing offsets into the flow above the screen. The shearing action is enhanced by the fact that flow remains attached to the top surface of each wire  60 , and is thus directed into the offset created by the next downstream wire. See FIG. 4. This attachment of the flow to the top surface  60  of each wire  58  is an example of the Coanda effect, the tendency of a liquid jet to remain attached to a solid flow boundary. The placement of the wires  58  are horizontal and perpendicular to the flow across the screen. Gravity accelerates the liquid as it moves down the face of the screen  26  and the shearing action is proportional to the velocity of the liquid flow.  
         [0028]    [0028]FIG. 3 details further components of the apparatus. The vessel  13  in combination with the securing plates  43 ,  45 , results in a pressure competent system. Pressurized gas may be introduced through the gas inlet valve  37 . Such pressurized gas is used to control the liquid level within, the apparatus, thus preventing the screen element from being flooded or submerged. Once the plates  43  and  45  are secured using securing devices  47 ,  47 ′, gas may be introduced through the gas inlet valve  37  and, if desired, gas may be released through the gas relief valve  39 . The vessel  13  may also contain the liquid level sensor  30  located preferably on the inlet port  17  or the effluent port  31  or both, to indicate the level of fluid within the housing, to prevent submersion of the screen  25 . Flow passing through the screen  25  is collected in the effluent container  27  beneath the screen  25 , while overflow, particulate matter  61  pass off the lower end  53  of the screen into the debris chamber  33 . Flow velocities across the screen  25  are typically 2 to 3 meters per second depending upon the setting of the control plate  23  or the velocity due to acceleration of the fluid by gravity (32 ft./sec./sec.), increasing toward the toe or lower end of the screen  53 .  
         [0029]    The screen face  26  is kept “dry” 8  through the introduction of gas into the vessel  13  through the gas inlet valve  37 . The critical variable for the operation of the system is to control or regulate the level  32  of liquid in the pressurized effluent container  27 . If the liquid level  32  in the effluent container  27  covers the screen surface  26 , it will operate in a conventional, submerged mode and plug as liquid passes between the wires  58 . There must also be excess gas in the vessel  13  so that the critical liquid level  32  can be maintained by simply releasing gas from the housing member through the gas relief valve  39  or adding gas through the gas inlet valve  37 . If the screen surface  26  should ever become submerged it will be backwashed by the flow of liquid from the back side  28  of the screen  25 , through the screen surface  26  and out through the purge valve  35 .  
         [0030]    In certain operations of the unit it may be desirable to automate the debris removal process. This can be accomplished by putting a valve operator  56  including valve operators sold under the trademark ASCO® owned by Automatic Switch Company, Inc., to control the on/off cycles of the purge valve  35 . The purge valve  35  is a typical commercial valve such as an Asco® solenoid valve. The valve operator  56  can be either electric or pneumatic and is driven by cycle timer  57  and duration timer  59 . A typical operation would be to set the cycle timer  57  for one-hour intervals and the duration timer  59  for a 30-second interval. Each hour the purge valve  35  would open for a period of 30 seconds. During this 30-second period of time the debris  61  would be flushed out to waste. At the end of the 30 second time interval the purge valve  35  would close and the apparatus  11  would return to normal operation.  
         [0031]    Another method of washing the screen surface  26  to remove debris is to close the effluent port  31  and open the purge valve  35  which creates a pressure that keeps the liquid from going through the screen  25 . The liquid on the screen surface  26  will wash debris  61  from the screen face  26  and down into the debris receptacle  33  of the vessel  13 . The debris  61  can then be removed from the debris receptacle  33  through use of the purge valve  35  which can be operated manually or on a timed interval.  
         [0032]    It is therefore to be understood that while preferred forms form of invention are herein set forth and described, various modifications and changes may be made therein without departing from the spirit and scope of the present invention as defined by the appended claims and reasonable equivalents thereof.