Abstract:
A reciprocating power sprayer for cleaning a rotating cylindrical wastewater screen of the type formed of tubular perforate wedgewire. The spray is reciprocated on an elongated pneumatic cylinder which is arranged in parallelism along the cylinder wastewater screen. Controls are provided for automatically controlling the reciprocation of the spray.

Description:
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 
     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. 
     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 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. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a reciprocating sprayer is provided that discharges liquid from a spray nozzle and through a cylindrical screen so as to dislodge solids on the interior surface of the screen adjacent the sprayer, and also from the interior surface of the screen on the diametrically opposite side of the cylinder. The invention also provides a reciprocating sprayer that discharges liquid from a traveling spray nozzle through a pair of concentrically arranged cylindrical-type screens of a double cylindrical-type screen in a manner that dislodges solids from both screens. 
     Other objects, features, and advantages of the present invention include a reciprocating sprayer which is rugged, simple, flexible, reliable, and durable, and which is of economical manufacture and is easy to assemble, install, and use. 
    
    
     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 dual cylindrical-type wastewater screen, 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 dual cylinder screen arrangement 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 dual screen arrangement 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 schematic perspective, fragmentary view showing the waste water machine and showing the traveling spray mounted thereon; 
     FIG. 7 is a perspective, fragmentary view of the traveling spray shown in the center portion of FIG. 6, but on an enlarged scale; 
     FIG. 8 is a perspective view of the spray mechanism shown in FIG. 6, but from the opposite side thereof; 
     FIG. 9 is an enlarged, fragmentary view of the sensor, air flow valve, and bracket at the left-end of the control apparatus as shown in FIG. 6; 
     FIG. 10 is a fragmentary perspective view of the sensor, air flow valve, and bracket as shown at right-end portion of FIG. 6 but shown on an enlarged scale; 
     FIG. 11 is an enlarged cross-sectional view taken transversely in FIG. 12 of the spray nozzle and its carriage for reciprocating along its cylinder rail; 
     FIG. 12 is an enlarged, longitudinal view partially in section, through the spray carriage; and 
     FIG. 13 is a schematic view of the traveling spray including its control circuit. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a double cylindrical waste water screen for cleaning waste water which 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 my 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. It is believed sufficient to say, however, that the following detailed description of the drum-type wastewater screen and apparatus is sufficient for purposes of describing the present invention as follows. 
     A reciprocating sprayer  30  (FIGS. 2,  6 ,  7 ,  8 , and  12 ) for cleaning cylindrical perforate screens  32  and  40  of a wastewater screening apparatus  34 . The sprayer has a carriage  36  (FIGS. 2,  6 ,  7  and  8 ) that reciprocates along a rodless air cylinder  38  (FIGS. 1,  2 ,  3 ,  9 ,  10   12 ) which is located in parallelism for long stroke requirement* alongside the outer screen  32  and inner screen  40  of a double-cylindrical type screening apparatus. The carriage  36  has a nozzle  42  (FIGS. 2,  3 ,  4 ,  8 ,  9 ,  10 ,  11 ,  12 ,  13 ) that discharges a fluid  44  against the outer screen  32  (FIGS. 2,  3 ) as the carriage reciprocates back and forth alongside the screen. Solids  46  (FIG. 4) which stick to or are attached to interior surfaces of the screens are dislodged from the screens by the fluid as the fluid passes through the screen. 
     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 and are driven by a motor and conventional belt  55  and pulleys (not shown). Disposed below the screens is a trough  56  (FIGS. 1,  2 ,  4 ,  5 ) that serves as a collection pan for collecting the wastewater after it has passed through the screens. The trough  56  has a drain  58  (FIG. 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 . FIGS. 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  (FIGS. 3,  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  (FIG. 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 FIG. 1, a preferred embodiment of the apparatus has two pairs of spaced apart rollers or trunnions  51  (FIGS. 1,  4 ) 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 its 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 FIGS. 1 and 4) 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 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 a 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  10  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. 4) 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 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 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. 
     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 reciprocating sprayer  30  of this invention discussed in more detail below, the flow of wastewater that can be screened or filtered is increased over a screen having a conventional non-reciprocating spray arrangement. Moreover, because cleaning is more efficient, a screen equipped with a sprayer  30  of this invention is cleaned more thoroughly, decreasing downtime of the screen. 
     Reciprocating Sprayer 
     FIGS. 6-13 illustrate a preferred embodiment of a sprayer  30  of this invention that discharges a cleaning fluid toward and through the screen or screens. The previously mentioned nozzle  42  of the sprayer  30  discharges cleaning fluid toward a screen and can be disposed so as to discharge cleaning fluid through the sidewalls of two screens. The nozzle  42  is part of carriage  36  that reciprocates along rodless cylinder  38 , permitting the nozzle  42  to move relative to the screen or screens being cleaned. As is shown in FIG. 6, a flexible conduit  122 , extends from a water manifold  124  (FIG. 6) via swivel joints  123  to the carriage  36 , with the fluid ultimately being communicated to the nozzle  42 . The carriage  36  preferably comprises a manifold  125 . 
     Manifold  125  and nozzle  42  ultimately receives fluid from a conventional pressurized fluid source (not shown). 
     In the preferred embodiment shown in FIGS. 6-13, the rodless cylinder  38  extends substantially along the length of the cylindrical screen. The rodless cylinder  38  has end caps  114  that having mounting and porting means formed integrally therein. 
     The end caps  114  are constructed and arranged to dispose the rodless cylinder  38  and nozzle  42  about three inches from the screen surface of the screen  32  toward which it is directed. The outermost screen surface comprises the exterior surfaces of the wedgewires  108  that makeup the outermost screen. 
     Spray Nozzle Carriage 
     A fluid such as air is used to move the carriage  36  and nozzle  42  along the cylinder  38  in one direction or the other. 
     Referring to FIGS. 9,  10 ,  11 ,  12 , and  13 , each end cap  114  carries a threshold sensor  115  that detects when the carriage  36  which is attached to and moved by piston  140  (FIGS. 11 and 12) has reached a desired limit of travel and enables its direction of travel to be reversed. The threshold sensor provides pneumatic feedback information on the position of the carriage on pneumatic cylinder  38 . For example, as shown in FIG. 12, each end of the piston  140  has a cylinrical bore  141  which slides over the projection  142  having a central passage  145  that communicates via passage  146  with the sensor  115 . This connection  141 - 142  acts to throttle the air and cushions the end of the stroke of the piston  140 . Thus, these devices monitor the back pressure of the cylinder&#39;s exhausting chamber. When the cylinder stops, the back pressure drops and the threshold sensor provides the desired output. The sensors  115  are each operatively connected to an air flow control valve  143  (FIGS. 6,  9 ,  10 ,  11  and  13 ) that causes the direction of air flow propelling the carriage  36  to be reversed. Thus, the carriage  36  is moved by air in one direction until it reaches the end of the cylinder. This causes the four-way main air valve  150  (FIG. 13) to move to a second position that changes the air flow to the cylinder  38  causing the carriage to move in the opposite direction. A conventional air lubricator  152  and an air regulator  154  (FIGS. 6 and 13) are provided in the circuit. 
     Operation 
     During operation, liquid at a pressure of at least about 350 pounds per square inch (psi) and no greater than about 1000 psi is expelled from the nozzle toward the outermost screen. Where the wedgewire screen is a single cylindrical screen, liquid at a pressure of at least about 350 psi is 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 is expelled from the nozzle  42  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 nozzle  42 , 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 nozzle is shown disposed in a general horizontal position relative to the force of gravity, the nozzle preferably is 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 nozzle preferably is disposed between a nine o&#39;clock and about an eleven o&#39;clock position. Preferably, the nozzle is disposed at about a ten o&#39;clock position to eject liquid at the same angle toward the outermost screen. 
     Where the cleaning fluid discharged from the nozzle  42  is a gas, the nozzle is located closer to the screen toward which it is pointed. Where the nozzle  42  is exteriorly disposed, the nozzle  42  is disposed no farther than about  2  inches from the outer surface of the screen toward which it is directed. 
     Where the cleaning fluid is a gas, preferably air, the gas provided to the nozzle  42  has a pressure of at least 80 psi. In one preferred method of operation, gas is discharged from each nozzle  42  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 nozzle  42  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. 
     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.