Abstract:
An apparatus for cleaning a rotating cylindrical wastewater screen of the type formed of tubular perforate wedgewire. The apparatus includes a frame, a rotatable cylindrical screen carried by the frame and having an axis of rotation and which is defined by a tubular perforate wedgewire sidewall having an interior wedgewire surface and an exterior wedgewire surface, a wastewater conduit having an opening disposed inside the wedgewire sidewall through which conduit effluent is discharged, a plurality of spray nozzles positioned along the length of the cylindrical screen from which fluid is ejected against the wedgewire sidewall to dislodge solids from the wedgewire sidewall, a control system coupled to the plurality of spray nozzles that controls the order that each nozzle of the plurality of spray nozzles ejects fluid and controls a duration of time that each nozzle of the plurality of nozzles ejects fluid, and a pump in fluid flow communication with a supply of the fluid for delivering the fluid to the plurality of spray nozzles.

Description:
This application is a continuation-in-part of U.S. application Ser. No. 09/500,860, filed Feb. 09, 2000, now U.S. Pat. No. 6,182,833 B1. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to cylindrical-type wastewater screens and more particularly to a sprayer for cleaning the cylindrical screen during operation. 
     BACKGROUND OF THE INVENTION 
     Presently, wastewater is a byproduct of many industrial processes that use water. For example, the food industry relies rather heavily on water for processing food. Water is used to clean vegetables, beef, fish, poultry, and other types of food often before the food is cooked, blanched or sterilized using other water. Unfortunately, after all this water is used it typically must also be processed to clean it so it can be either reused or inexpensively disposed. As a result of rather restrictive environmental laws and regulations that have made disposal of unprocessed wastewater prohibitively expensive, wastewater processing or preprocessing at the site of the food processing facility is desirable. 
     One apparatus that has proved particularly effective at treating wastewater is a cylindrical-type wastewater screen and such is shown and described in my U.S. Pat. No. 5,433,849, issued Jul. 18, 1995. As shown in that patent, a cylindrical-type wastewater screen has a cylindrical screen, typically comprised of perforate wedgewire, into which the wastewater is introduced while the screen is rotated. The wastewater passes radially outwardly through the screen after which it can be reused, further filtered, or disposed. Solids entrained in the wastewater that were filtered out of the wastewater can be cheaply disposed of as landfill or fertilizer. As shown, two cylindrical-type screens having successively finer screen media can be concentrically arranged to provide staged treatment of wastewater. 
     During operation, wastewater introduced within the cylindrical screen passes radially outwardly through perforations in the screen while most of the solids entrained in the wastewater is filtered by and retained in the screen because the perforations typically are no greater than about ten to twenty thousandths of an inch. The filtered solids often cling to the screen and the screen is rotated to cause gravity to encourage the solids to separate from the screen and fall to the bottom of the screen. A small flow of wastewater at the bottom of the screen carries the solids from the screen helping to keep the screen clean. 
     Many times, sticky solids, such as fat, connective tissue, coatings, starch, and other sticky residue will continue to cling to the screen despite rotation of the screen. The sticky solids can also cause other solids in the wastewater to stick to it and in general will significantly reduce the efficiency of the screen by partially or completely plugging perforations. Should too many perforations become plugged, the screen will have to be taken offline and cleaned. 
     Presently, to help keep the screen clean to prevent too many perforations from becoming plugged, fixed or stationary nozzles carried by a manifold which is disposed adjacent the screen can discharge cold water, hot water, steam or even air forcefully against the screen. Several spaced apart nozzles must be used to clean the screen along its entire axial length. Unfortunately, where water is used, each nozzle typically requires a flow of as much as about 3 gallons per minute such that a typical screen can use as much as 30 to 90 gallons of water per minute, depending on the number of nozzles required and the type of screening apparatus used. For example, where a double cylinder wastewater screen is used, such as is disclosed in U.S. Pat. No. 5,433,849 to Zittel, as many as 30 nozzles fixed to at least two manifolds are used to keep both cylinders clean. While the frequency of cleaning can vary with the type of solids entrained in the wastewater, each cleaning cycle nonetheless uses a lot of water which undesirably increases wastewater treatment costs. 
     While reciprocating sprayers have been used in some types of similar processing equipment, they have not been viewed as particularly well suited for use in cylindrical-type because of reliability considerations and because of concern they could not effectively clean the rather small perforations found in wastewater screens. For example, it is known to use a reciprocating sprayer to direct water against a perforate cylinder of a bean snipper to free the perforations of bean parts that have become lodged in them. However, the perforations in the cylinder of a bean snipper are much larger, typically at least {fraction (13/64)} (0.203) of an inch, the cylinder is made of polycarbonate, and a bean snipper is used to cut beans, not process wastewater. Moreover, it is not believed that the reciprocating sprayer used in bean snippers discharges water at a great enough pressure to completely pass through the exterior of the screen adjacent the sprayer and impact against the interior of the screen on the opposite side. Additionally, reciprocating sprayers can incorporate a rodless air cylinder system that uses an air cylinder. Such a system can require a sufficiently clean supply of air that may not be available at a plant utilizing a reciprocating sprayer. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for screening wastewater. The apparatus for screening wastewater includes a frame, a rotatable cylindrical screen carried by the frame and having an axis of rotation and which is defined by a tubular perforate wedgewire sidewall having an interior wedgewire surface and an exterior wedgewire surface, and a wastewater conduit having an opening disposed inside the wedgewire sidewall through which conduit effluent is discharged. The apparatus for screening wastewater further includes a plurality of spray nozzles positioned along the length of the cylindrical screen from which fluid is ejected against the wedgewire sidewall to dislodge solids from the wedgewire sidewall, a control system coupled to the plurality of spray nozzles that controls the order that each nozzle of the plurality of spray nozzles ejects fluid and controls a duration of time that each nozzle of the plurality of nozzles ejects fluid, and a pump in fluid flow communication with a supply of the fluid for delivering the fluid to the plurality of spray nozzles. 
     The plurality of nozzles can eject fluid under pressure sufficient to impinge against and pass through the outer surface of the wedgewire sidewall and then impinge against an inner surface of the wedgewire sidewall such that solids are dislodged at both regions of impingement. The plurality of spray nozzles can also eject fluid at a pressure of at least about 80 to 1000 psi. The plurality of spray nozzles can additionally eject fluid at a volume of about 5 to 20 gallons per minute based on the size of the screen and based on the water pressure supplied. The wedgewire sidewall of said cylinder can have openings of 10 to 20 thousands of an inch. 
     The apparatus for screening wastewater can further include a second cylindrical screen that is comprised of a tubular perforate wedgewire sidewall wherein the fluid from the plurality of spray nozzles is under sufficient pressure that it impinges against and passes through the outer surface of the cylindrical screen, the outer surface of the second cylindrical screen, the inner surface of the second cylindrical screen, and the inner surface of an opposite side of the cylindrical screen. The sprayer can be disposed about 4 to 6 inches away from the outer sidewall of the cylindrical screen. The plurality of spray nozzles can be arranged so that the fluid ejected from the spray nozzles against the wedgewire sidewall provides complete coverage of the cylindrical screen along the axis of rotation. 
     The apparatus for screening wastewater can further include a plurality of electrically actuated valves coupled to the plurality of spray nozzles positioned along the length of the cylindrical screen, wherein the controller can control the operation of the electrically actuated values to provide fluid to the plurality of spray nozzles. The valves can open and close in sequence to eject fluid from the spray nozzles to sequential areas of the cylindrical screen. 
     The apparatus for screening wastewater can further include a plurality of spray manifolds coupled to the plurality of spray nozzles, wherein each of the plurality of spray manifolds can be coupled to at least one of the plurality of spray nozzles. The apparatus for screening wastewater can further include an operator interface coupled to the control system. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     At least one preferred exemplary embodiment of the invention is illustrated in the accompanying drawings: 
     FIG. 1 is a perspective view of an exemplary apparatus for screening wastewater, certain parts being shown as broken away or removed for the sake of clarity in the drawings; 
     FIG. 2 is a transverse cross-sectional view, being more or less schematic in nature with certain parts removed, of the apparatus for screening wastewater shown in FIG. 1; 
     FIG. 3 is a view similar to FIG. 2 but showing a single cylinder arrangement; 
     FIG. 4 is a longitudinal sectional view through the apparatus for screening wastewater shown in FIG. 1 being more or less schematic in nature, with certain parts removed for the sake of clarity; 
     FIG. 5 is a fragmentary, enlarged view of the outer and also of the inner concentric wedgewire cylinders; 
     FIG. 6 is a longitudinal sectional view of the apparatus for screening wastewater shown in FIG. 1, with certain parts removed to highlight the sprayer according to a preferred embodiment; 
     FIG. 7 is a perspective view of an exemplary sprayer for a cylindrical wastewater screen according to a preferred embodiment; 
     FIG. 8 is a reverse angle perspective view of an exemplary sprayer for a cylindrical wastewater screen according to a preferred embodiment; and 
     FIG. 9 is an exemplary block diagram of a system for controlling a sprayer for a cylindrical wastewater screen according to a preferred embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an exemplary double cylindrical wastewater screen apparatus for cleaning wastewater  200  according to a preferred embodiment. The wastewater is introduced to the lower right-hand side of the machine via inlet  84  and conducted into the center of the inner cylindrical screen via conduit  82 . The general organization and function of the machine shown in FIG. 1 is described in some detail in U.S. Pat. No. 5,433,849, issued Jul. 18,1995, and reference may be had to that patent which forms a part of this specification. However, the following detailed description of the drum-type wastewater screen and apparatus is sufficient for purposes of describing the present invention as follows. 
     The apparatus for cleaning a wastewater  200  includes a fixed sprayer  300  (FIGS. 1-3 and  6 - 8 ) for cleaning cylindrical perforate screens  32  and  40  of a wastewater screening apparatus  34 . The sprayer  300  has nozzles  310  (FIGS. 2,  3 , and  6 - 9 ) that discharge a fluid  44  against the outer screen  32  (FIGS. 2,  3 ). Solids  46  (FIG. 4) which stick to or are attached to interior surfaces of the screens  32  and  40  are dislodged from the screens by the fluid  44  as the fluid  44  passes through the screens  32  and  40 . 
     The screening apparatus  34  is mounted on a frame  50  (FIG. 1) that carries the concentrically arranged screens  32 ,  40  and has legs  52  that space the apparatus above the ground. Also carried by the frame  50  is a housing  54  (FIGS. 2,  3 ) that encompasses the screens and the sprayer  30 . Four rollers  51  (FIGS. 1,  4 ) rotationally support the screens  32  and  40  and are driven by a motor and conventional belt and pulleys (not shown). Disposed below the screens is a trough  56  (FIGS. 1,  2 ,  4 ) that serves as a collection pan for collecting the wastewater after it has passed through the screens. The trough  56  has a drain  58  (FIGS. 1,  4 ) through which the screened wastewater is discharged. Collectively, the housing  54  and trough  56  ensure that the wastewater, as well as cleaning fluid (where the fluid is a liquid), is retained within the screening apparatus. 
     The inner screen  40  and outer screen  32  are part of a double screen assembly  60  (FIGS. 1,  2 ,  4 ) that includes two cylindrical screens  32  and  40 . FIG. 3 shows a single cylindrical screen arrangement. There is an effluent discharge end  62  (FIGS. 1,  4 ) at one end that preferably is at least partially open so that solids  46  screened from the wastewater can be discharged from the apparatus. To catch solids  46  filtered from the wastewater, there is a second trough  63  (FIG. 4) disposed below the screen assembly  60  adjacent the effluent discharge end  62 . To help urge solids  46  toward the effluent discharge end  62 , each screen preferably has a generally spiral-shaped or helical auger  100 ,  102  (FIGS. 1,  2 ,  4 ) inside the screen that preferably can be fixed to the screen. 
     The screen assembly  60  preferably is closed at its end opposite the discharge end by a disc-shaped drum head  64  (FIGS. 1,  4 ) to which one or both cylindrical screens  32 ,  40  preferably are fixed. In a preferred embodiment, such as is shown in FIGS. 1 and 4, both screens are fixed to the head  64  for rotation in unison therewith about a longitudinal axis of rotation  66  that preferably is a common axis of rotation. The outer screen  32  of the screen assembly  60  is rotatively supported on the frame by rollers or trunnions  51  (FIGS. 1,  4 ) that are received in spaced apart channels  70  or the like carried by the outer screen  32 . As is shown in FIGS. 1 and 4, a preferred embodiment of the apparatus has two pairs of spaced apart rollers or trunnions  51  with each pair of trunnions carried by an axle  72  journaled for rotation to the frame. 
     Wastewater to be cleaned is delivered to the machine as follows. A wastewater infeed  78  (FIGS. 1,  4 ) has an outlet  80  disposed inside the inner screen  40  for introducing the wastewater to be screened to the inner screen  40 . Where the screening apparatus  32  is of single screen construction, such as is depicted in FIG. 3, the infeed outlet  80  is disposed inside of screen  32  and directly introduces the wastewater therein. 
     In a preferred embodiment, the infeed  78  includes a vertical conduit or column  82  (FIGS. 1,  4 ) that communicates liquid to be screened from its inlet  84  to a generally horizontally extending conduit or trough  86  where the wastewater is discharged from the outlet  80  (FIGS. 1,  4 ) into the screen. The outlet  80  preferably is located adjacent the closed end (to the left in FIG. 1) of the screen assembly and each screen can be inclined such that the closed end is disposed at least slightly above the effluent discharge end to help spread the flow of wastewater more evenly over the entire axial length of each screen  32  and  40  and to help encourage flow of solids  46  out the discharge end. As is shown in FIG. 4, to help smooth flow of wastewater inside the infeed  78 , the infeed has an internal weir  88  with a lip  90  and a number of spaced apart internal baffles  92 ,  94  and  96 . To facilitate cleaning of the infeed, the horizontal conduit  86  can be equipped with a clean-out port  98 . 
     FIG. 5 depicts a fragmentary enlarged cross section of the outermost screen  32  and also the screen  40 . Preferably, each screen is comprised of wedgewire screens  105  which are less subject to becoming plugged or jammed than other types of screens. Each wedgewire screen is comprised of a plurality of wires  108  that are arranged to form a cylinder and which are held captive by spaced apart bands  110  that extend about the circumference of the screen. In a preferred embodiment, each wire  108  and band  110  is constructed of a metal that preferably is made of stainless steel. 
     Wire  108  has a preferred wire configuration of generally triangular or truncated triangular cross section. Where each axially extending wire  108  is of generally triangular or truncated triangular cross section, the base of each triangle formed is disposed (as shown in FIG. 5) toward the interior of the screen. In a typical screen arrangement, there are several circumferentially arranged bands  110  that are affixed to the wires to help form them into a screen that is a drum or cylinder. The wires  108  extend axially and the bands  110  circumferentially around the exterior of the wires. 
     The spacing between each pair of adjacent wires  108  is selected to permit liquid to flow therebetween while blocking solids  46  having a size about the same or bigger than the spacing. In a preferred embodiment, where the screen apparatus is a double-cylinder screen, the spacing between adjacent wires of the inner screen  40  is greater than the spacing between adjacent wires of the outer screen  32 . In a preferred double-cylinder embodiment, the wire-to-wire spacing of the inner drum  40  range from between about 0.040 inches and about 0.060 inches and the wire-to-wire spacing of the outer drum  32  range from between about 0.010 inches and about 0.020 inches depending upon the type and size of solids likely to be encountered. Where the apparatus  34 ′ (FIG. 3) is of single screen construction, the wire-to-wire spacing of the screen  32  ranges between about 0.030 inches and about 0.060 inches. 
     The outer screen  32  has an inner diameter of at least about 24 inches and typically no greater than about 60 inches and is at least about 48 inches long and no greater than about 168 inches long. Where the screen apparatus is a double drum screen, the inner screen  40  has an inner diameter of at least about 12 inches and typically no greater than about 48 inches and is at least about 24 inches long and no greater than about 60 inches long. 
     FIG. 6 is a longitudinal sectional view of the apparatus for screening wastewater  200  shown in FIG. 1, with certain parts removed to highlight the sprayer  300  according to an exemplary embodiment. The sprayer  300  includes spray nozzles  310 , spray manifolds  315 , electrically actuated valves  320  and hoses  325 . The valves  320  can include valves  321 ,  322  and  323 . As illustrated in FIGS. 2,  3 ,  4 , and  6 , the sprayer discharges a fluid, such as water, air, or the like, against the outer screen  32 . Solids  46  which stick to or are attached to surfaces of the screens  32  and  40  are dislodged from the screens by the fluid  44  as the fluid  44  passes through the screens  32  and  40 . In operation, the valves  320  are actuated to allow the fluid  44  to flow through the hoses  325  to the spray manifolds  315 . The spray manifolds  315  distribute the fluid  44  to the spray nozzles  310  to spray the fluid  44  against the screens  32  and  40 . 
     FIGS. 7 and 8 are opposite perspective views of an exemplary sprayer  300  for cylindrical wastewater screens  32  and  40  according to a preferred embodiment. FIGS. 7 and 8 illustrate the use of pipe coupling  330  for attaching the hoses  325  throughout the sprayer  300 . FIGS. 7 and 8 also illustrate a control system  350  coupled to the valves  320 . In operation, the control system  350  controls the actuation of the valves  320  to distribute fluid  44  to selected spray manifolds  315  and subsequently to the spray nozzles  310 . Thus, different valves  320  can be actuated at different times to spray fluid  44  against the screens  32  and  40 . The control system can control the order that the nozzles eject fluid and can control a duration of time that the nozzles eject fluid. The valves can open and close in a specified sequence to eject fluid from the spray nozzles to sequential areas of the screens  32  and  40 . 
     FIG. 9 is an exemplary block diagram of a system for controlling the sprayer  300  for a cylindrical wastewater screen according to a preferred embodiment. FIG. 9 illustrates the sprayer  300  including a pump  340  and a pump motor control  370 . FIG. 9 also illustrates the control system  350  including a programmable logic controller (PLC)  355 , an operator interface  360  and relays  361 ,  362 , and  363 . The operator interface  360 , the relays  361 - 363 , the pump motor control  370 , and the valves  320  are coupled to the PLC  355 . The pump motor control  370  is coupled to the pump  340  for controlling the pump  340 . The pump  340  is coupled to the valves  320  for providing fluid  44  to the valves and subsequently to the spray manifolds  315  and spray nozzles  310 . 
     In operation, a user can adjust a sequence pattern and timing to the PLC  355  for providing fluid  44  to sequential manifolds  315  by using the operator interface  360 . The  5  PLC  355  controls the valves  320  by triggering the relays  361 - 363  to open and close the valves  320  in a desired sequence. The valves  320  provide a feedback signal to the PLC  355  which informs the PLC  355  of proper operation of the valves  320 . Thus, the feedback signal can inform the PLC  355  of any necessary adjustments that may be made to correct the sequence and timing of the operation of the valves  320 . The PLC  355  can also control the timing of operation of the pump  340  by sending appropriate signals to the pump motor control  370 . Additionally, the PLC  355  can stop operation of the sprayer  300  if a valve fault is detected. All of the valves  320  can be set to open when the pump  340  is not running to act as a pressure relief for the system when the pump  340  starts back up. 
     The operator interface  360  displays a preset time and an elapsed time of each valve operation and an overlap time while the sprayer  300  is operating. For example, the valves can be set to operate in the order of first: valve  321 , second: valve  322 , and third: valve  323 . Additionally, the valves  320  can be set to operate for one minute each. Furthermore, the valves  320  can have an overlap time of five seconds. The user can adjust these settings by using the operator interface  360 . For example, the user can adjust the operation order, operation time, and/or the overlap time of the valves  320 . 
     By using the sprayer  300 , water usage can be minimized. For example, when three spray manifolds  310  are used, each manifold corresponding to a zone of the screens  32  and  40  can provide a necessary 10 gallons per minute when used sequentially. This provides water conservation over a situation where all manifolds are used in tandem and are providing 30 gallons per minute. 
     During operation, liquid at a pressure of at least about 350 pounds per square inch (psi) and no greater than about 1000 psi can be expelled from the nozzles toward the outermost screen. Where the wedgewire screen is a single cylindrical screen, liquid at a pressure of at least about 350 psi can be expelled from the nozzle at a flow rate of at least about 10 gallons per minute so that expelled liquid will pass completely through the rather small holes in one side of the screen disposed adjacent the nozzle and impact against an interior surface of the screen on an opposite side. As a result, solids clinging to the interior surface of the side of the wedgewire screen adjacent the nozzle are loosened and preferably dislodged from the screen. And solids clinging to the interior surface of the side of the screen opposite the nozzle are also loosened and dislodged from the screen. By this advantageous arrangement, cleaning of the screen is optimized, done more quickly, and with less water than in the past. 
     Where the screen is of double-cylinder construction, liquid at a pressure of at least about 1000 psi can be expelled from the nozzles  310  at a flow rate of at least about 6 gallons per minute so that expelled liquid will pass completely through the rather small holes or perforations in one side of the outer screen disposed adjacent the nozzles  310 , will pass through the rather small holes in one side of the inner screen disposed adjacent the nozzle  42 , will impact against an interior surface of the inner screen on a side opposite the nozzle, will pass through the small holes in the inner screen on the side opposite the nozzle  42 , and will impact against an interior surface of the outer screen on an opposite side. 
     Although the nozzles  310  are shown disposed in a general horizontal position relative to the force of gravity, the nozzles  310  preferably are disposed between about an eight o&#39;clock position and about an eleven o&#39;clock position. Where a double-cylinder screen is used, the nozzles  310  preferably are disposed between a nine o&#39;clock and about an eleven o&#39;clock position. Preferably, the nozzles  310  are disposed at about a ten o&#39;clock position to eject liquid at the same angle toward the outermost screen. 
     When the cleaning fluid discharged from the nozzles  310  is a gas, the nozzles  310  are located closer to the screen toward which it is pointed. Where the nozzles  310  are exteriorly disposed, the nozzles  310  are disposed no farther than about 2 inches from the outer surface of the screen toward which they are directed. 
     When the cleaning fluid is a gas, preferably air, the gas provided to the nozzles  310  has a pressure of at least 80 psi. In one preferred method of operation, gas is discharged from each nozzle of the system at a flow rate of at least about 25 cubic feet per minute (cfm). For particularly demanding cleaning applications, the gas has a pressure of at least 150 psi and a flow rate of at least 30 cfm. 
     Where gas is the cleaning fluid, the gas is provided to the nozzles  310  from a high pressure gas source. One preferred source is an air compressor, such as a rotary piston air compressor. Another preferred source is standard shop air, having a pressure of between 100 psi and 150 psi. A still further preferred gas source is a squirrel cage blower where the application involves higher volumes of air, but with lower impact force. This is particularly useful for very light product. 
     As a result of the aforementioned parameters and depending on the application, a preferred single drum screen can screen or filter at least about 4500 gallons per minute of wastewater. A preferred double drum screen can screen or filter at least about 3000 gallons. As a result of using the sprayer  300  of this invention, the flow of wastewater that can be screened or filtered is increased over a screen having a conventional spray arrangement. Moreover, because cleaning is more efficient, a screen equipped with a sprayer  300  of this invention is cleaned more thoroughly, decreasing downtime of the screen. 
     It is also to be understood that, although the foregoing description and drawings describe and illustrate in detail preferred embodiments of the present invention, to those skilled in the art to which the present invention relates, the present disclosure will suggest many modifications and constructions as well as widely differing embodiments and applications without thereby departing from the spirit and scope of the invention. The present invention, therefore, is intended to be limited only by the scope of the appended claims.