Abstract:
A diffuser rod for use in a filter stalk having deflector disks rigidly mounted thereon to deflect liquid radially during the backwash process is disclosed. A backwashable filter element containing a diffuser plate that is located within the filter member at the end where the backwash fluid enters the filter member and a number of filter stalks with each filter stalk including a diffuser rod is disclosed. Finally, a method of backwashing a filter member that includes the step of introducing a diffuser rod and a diffuser plate to the filter assembly is disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     This invention relates to a filter system, and more specifically, to a backwashable filter system of the type utilized in petroleum refining applications. 
     Filter assemblies employing an array of individual filter stalks have long been utilized. Unfiltered fluid enters the filter assembly, passes through one of the slotted or perforated filter stalks arranged within the filter assembly, and exits the filter assembly as a filtered fluid. Solid contaminants are retained on the outer surface of the filter stalks as the fluid passes through the stalks. As more contaminants are retained against the filter stalks, the differential pressure across the filter medium increases and consequentially the flow decreases. 
     One method of cleaning filter stalks is a process known as backwashing. During backwashing, a cleaning fluid is forced through the filter assembly in a direction opposite to the normal operating flow. Backwashing alone, however, is of limited effectiveness. Even when a large amount of backwash fluid or an extended period of time are used, simple backwashing may clean only a portion of the filter stalks effectively. 
     To address this drawback, devices to supplement and enhance the backwashing process have been introduced. One such device is disclosed in U.S. Pat. No. 3,387,712, issued to Schrink. This patent discloses a backwash water diffuser for use within a filter stalk. The diffuser is made up of a shaft that extends the length of the filter stalk and that has a number of diffuser lugs mounted thereon. The diffuser lugs have an annular frusto-conical surface which faces the direction that the backwash fluid enters the filter, and, at least in one embodiment, are located within the seventy percent of the filter stalk adjacent to the backwash water inlet. 
     The present applicants have found that a rod which is mounted within a filter stalk and which has deflector disks that have a surface perpendicular to the rod and that are spaced along the rod enhances the backwashing action and, therefore, enhances cleaning of the filter stalk. The increased backwashing action results from the diversionary effect of the deflector disks and better distribution of the backwash fluid up and down the stalk. The result is improved removal of contaminants. In addition, applicants have found that the efficiency of the backwash process is enhanced when a diffuser plate that has apertures for the passage of fluid is mounted above the individual filter stalks. 
     Accordingly, it is the object of this invention to provide a diffuser rod with deflector disks rigidly mounted on said rod for use in a filter stalk to deflect liquid radially during the backwash process. 
     It is a further object of this invention to provide a backwashable filter assembly containing a number of filter stalks with each filter stalk including a diffuser rod as described above. 
     It is a further object of this invention to provide a backwashable filter assembly containing a diffuser plate that is located within the filter assembly at the end where the backwash liquid enters the filter assembly and is spaced from the filter stalks and that has a number of apertures corresponding to the number of filter stalks present within the filter assembly. 
     Finally, it is a further object of this invention to provide a method of backwashing a filter assembly that includes the step of introducing a diffuser rod and a diffuser plate to the filter assembly. 
     Further objects of this invention will be apparent to persons knowledgeable with devices of this general type upon reading the following description and examining the accompanying drawings. 
     SUMMARY OF THE INVENTION 
     A diffuser rod for use in a filter stalk, said rod having deflector disks rigidly mounted thereon to deflect liquid radially during the backwash process, is disclosed. A backwashable filter assembly containing a diffuser plate that is located within the filter assembly at the end where the backwash fluid enters the filter assembly and a number of filter stalks with each filter stalk including a diffuser rod is disclosed. Finally, a method of backwashing a filter assembly that includes the step of introducing a diffuser rod and a diffuser plate to the filter assembly is disclosed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith, and in which like reference numerals are used to indicate the parts in the various views: 
     FIG. 1 is a side elevation view of a filter array; 
     FIG. 2 is a view of one of the filter assemblies taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged vertical cross sectional view of the filter assembly of FIG. 2 taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a horizontal cross sectional view taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is a an enlarged vertical cross sectional view taken along line  5 — 5  of FIG. 4; and 
     FIG. 6 is an enlarged cross sectional view of the portion of FIG. 5 encompassed by the circle  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to FIG. 1, a filter array is designated generally by the numeral  10  and comprises a plurality of filter assemblies  12  which are mounted vertically in two parallel rows (one of which is visible in FIG. 1) between an outlet header line  16  located at the top end of the filter assemblies  12  and an inlet line  14  located substantially at the opposite end of the filter assemblies  12 . It is to be understood that header line  16  also serves as the backwash inlet line and thus serves multiple functions. The entire assembly is mounted on a framework designated generally by the numeral  18 . Framework  18  includes parallel vertical supports  20 , horizontal supports  21  and a bottom platform  22 . A backwash drain line  26  is also supported by framework  18 . The backwash drain line  26 , outlet header line  16  and inlet line  14  are in fluid communication with each of the filter assemblies  12 . A flush drain  28  extends from one end of the backwash drain line  26 . A plurality of purge inlets  30  extend from the outlet header line  16 . A plurality of controllers  32 , corresponding to the number of filter assemblies  12 , are mounted at one end of framework  18 . 
     Referring now to FIG.  2  and details of construction of the filter assemblies  12 , all of which are identical, each assembly  12  comprises a cylindrical housing  34  that terminates at its uppermost end in a flange  36  which is aligned with a corresponding flange  38  on a generally bell-shaped header  40 . Flanges  36  and  38  are held in alignment by a number of nut and bolt assemblies  42 . The bottom of cylinder  34  has an opening which receives an elbow  44  which is coupled with a backwash drain link  46  by means of a flanged coupling  48 . The backwash drain link  46  is in turn coupled with the backwash drain line  26 . The cylinder  34  has an opening near the bottom that receives an inlet branch  24  which is coupled to an inlet link  25  by means of a flange coupling  23 . The inlet link  25  is in turn coupled to the inlet line  14 . The header  40  receives an elbow  50  which is coupled with a link  52  by means of a flange coupling  54 . The link  52  is in turn coupled with the outlet header line  16 . It is to be understood that appropriate valving (not shown) well known to those skilled in the art is utilized to control the flow of fluid through the inlet and outlet headers as well as the backwash drain line. 
     A number of individual filter stalks  56  are disposed within the filter assemblies  12 , as shown in FIG.  3 . One end of each filter stalk  56  is fixedly attached to an assembly flange  58  which is sandwiched between the cylinder  34  and header  40 . The opposite end of the filter stalk  56  is supported by a support plate  60 . A diffuser rod  62  is disposed within each filter stalk  56 . One end of the diffuser rod  62  extends beyond the filter stalk  56  and the assembly flange  58  and is fixedly attached to an assembly plate  64 . Plate  64  is located at the open end of header  40 . The assembly plate  64  is held in alignment with the assembly flange  58  by nut and bolt assemblies  66  (see FIG.  4 ). A diffuser plate  68  is mounted above the assembly plate  64 . 
     As can be seen in FIG. 4, the assembly plate  64  contains a number of apertures  70  which correspond to the number of filter stalks  56  within cylinder  34 . One end of diffuser rod  62  extends through the apertures  70  and is fixedly attached to the assembly plate  64 . The assembly plate  64  also contains openings for the nut and bolt assemblies  66  that attach it to the assembly flange  58 . 
     Referring now to FIG.  5  and FIG.  6  and details of the filter stalk  56  and diffuser rod  62 , all of which are identical, each filter stalk  56  is comprised of a filter media  80  fixedly attached to a number of media supports  82 . The media supports  82  extend the length of the filter stalk  56 . The filter media  80  contains a plurality of slots or perforations through which fluid may pass but which will retain solids of a predetermined size or larger. The filter media  80  is formed such that the filter stalk  56  is cylindrical with a central open area  72 . A diffuser rod  62  is positioned substantially within the central open area  72  of the filter stalk  56 . A number of deflector disks  74  are fixedly attached to the rod  62  in spaced relation so that the surfaces of the deflector disks  74  are perpendicular to the rod  62 . The final deflector disk nearest to the support plate  60  is a centering disk  75  that has a diameter substantially corresponding to the diameter of the central open area  72  of the filter stalk  56  so that the diffuser rod  62  is prevented from moving radially (see FIG.  3 ). 
     With further reference to FIG. 6, a diffuser plate  68  is mounted above the assembly plate  64  and spaced apart from the assembly plate  64  by a ring  76  which is coupled to the diffuser plate  68 . The diffuser plate  68  contains a number of apertures  78  corresponding to the number of individual filter stalks  56  within cylinder  34 . The diffuser plate  68 , assembly plate  64  and assembly flange  58  are aligned so that apertures within each correspond. 
     The effectiveness of a specific diffuser rod in cleaning a particular filter stalk during a backwash cycle depends on certain dimensions of the filter stalk and diffuser rod. These dimensions may be derived from the formula below for filter stalks with an outside diameter ranging from 0.75 inches to 3 inches. 
     For a filter stalk with a central open area diameter of ID, the following formula provides a design constant, C D : 
     
       
           C   D =1.2·( ID /0.888) 2   
       
     
     which may be used in the following formula to determine the measurements of an effective diffuser rod for that filter stalk: 
     
       
           C   D =1 n ((( DD/ID ) 2  ·100)/( ST·SP )) 
       
     
     where DD is the diameter of the deflector disks, ST is the distance between the first deflector disk and the bottom of flange  58 , SP is the distance between each deflector disk, and ID, as stated above, is the diameter of the central open area of the filter stalk. SP, ST, and DD, may be derived from this equation, that is, SP may be derived for specific values of DD and ST, DD may be derived for specific values of ST and SP, and ST may be derived for specific values of DD and SP. For example, with these equations it is possible to determine the most efficient spacing for deflector disks of a specific diameter for use on a diffuser rod in a filter stalk with a known central open area diameter for various distances between the first deflector disk and the top of the filter stalk. 
     In operation, unfiltered product is introduced to the filter array  10  through the inlet header line  14 . The unfiltered product flows from the inlet header line  14  through the inlet link  25 , the inlet branch  24 , and into the filter assembly  12 . The only exit available for the product is through the elbow  50  attached to the header  40  which leads to the outlet header line  16 . In order to reach this exit, the product passes through the filter media  80  of the filter stalk  56  and through the apertures in the assembly flange  58 , the assembly plate  64  and diffuser plate  68 . As the product passes through the filter media  80 , all solid contaminants larger than a predetermined size are trapped outside and retained against the filter media  80 . 
     As more contaminants are retained against the filter stalks, the flow decreases. In order to clean the filter stalks  56 , backwash fluid is introduced to a particular assembly from backwash inlet line  16 . The backwash fluid flows through the link  52  coupled to the line  16  and into the elbow  50  attached to the assembly header  40  of the filter assembly  12 . As shown by arrow A in FIG. 6, the backwash fluid thereafter flows through the apertures  78  in the diffuser plate  68 . The apertures  78  in the diffuser plate  68  are relatively smaller than the apertures  70  in the assembly plate  64  so that a pressure differential is developed which evenly distributes the backwash fluid among the individual filter stalks  56  disposed within the filter assembly  12 . The backwash fluid then passes through the apertures  70  in the assembly plate  64  into the filter stalk  56 . Once in the filter stalk  56 , the backwash fluid encounters the deflector disks  74  and, as shown by arrow B in FIG. 6, a portion of the backwash fluid is deflected radially to the walls of filter stalk  56  where it carries away any solid contaminants adhering to those walls. After flowing the length of the filter assembly  12 , the backwash fluid drains through the elbow  44  attached to the bottom of the filter assembly  12  and through the backwash header link  46  into the backwash header drain  26  carrying the solid contaminants out of the filter assembly  12 . 
     The diffuser rod  62  described above and shown in the accompanying drawings causes the backwash fluid to deflect radially against the filter media  80  of the filter stalk  56 . The deflection of the backwash fluid causes the backwash cycle to be more efficient. The diffuser plate  68  described above causes the backwash fluid to distribute evenly among the filter stalks  56  arrayed within a filter assembly  12 . By causing an even distribution of the backwash fluid, the diffuser plate  68  also causes the backwash cycle to be more efficient. The increased efficiency of the backwash cycle results in decreased time for backwashing as well as increased time between backwashing and, therefore, decreases the time the filter assembly  12  is out of service. It also reduces the quantity of backwash fluid utilized which means less process fluid lost to the backwash process. 
     It will be seen from the foregoing that this invention is one well adapted to attain the ends and objects set forth above, and to attain other advantages which are obvious and inherent in the device. It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and within the scope of the claims. It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, all matter shown in the accompanying drawings or described hereinabove is to be interpreted as illustrative and not limiting.