Abstract:
A particulate filtration device comprising filter media having upstream and downstream surfaces, a gas-moving device for moving gas through the filter media from the upstream surface toward the downstream surface, and a cleaning assembly including a blow pipe having a plurality of cleaning nozzles for directing a flow of cleaning gas toward the filter media. A first one of the cleaning nozzles comprises a structural characteristic (e.g., throat size, exit angle, exit size) that is different than a second one of the cleaning nozzles. In one embodiment, the filter media comprises a filter bag corresponding with each nozzle, and both the first one and the second one of the cleaning nozzles are spaced substantially the same distance from the corresponding filter bag. The cleaning assembly can also include a plurality of blow pipes (e.g., each having a plurality of cleaning nozzles) coupled to a gas-pressurized manifold, and a valve positioned between the manifold and each blow pipe to control gas flowing from the manifold to the blow pipes. In this configuration, it is preferred that the nozzle nearer the manifold has a larger throat size, smaller exit angle, and larger exit size than the nozzle farther from the manifold.

Description:
BACKGROUND 
       [0001]    The present invention generally relates to the field of particulate filtration assemblies and, more particularly, to systems for cleaning filters within such assemblies. 
         [0002]    Particulate filtration assemblies function to remove contaminates from the air or other fluid medium. One type of particulate filtration assembly is a dust collector for filtering dust particles out of the air. Dust collectors mainly use a filter media, such as a filter bag, to trap dust particles and allow cleaned air to pass through the filter. Over time the trapped dust particles build up a dust cake on the upstream side (e.g, outside) of the filter media, greatly reducing the efficiency of the dust collector. 
         [0003]    Dust collectors typically include a system for cleaning the filter media when it gets clogged with particulate. Such cleaning systems commonly are designed to shoot or force pressurized pulses of air into the opening of the filter media from downstream (e.g., inside) of the media. The air is often forced through a cleaning nozzle that accelerates the air to supersonic speeds prior to being forced toward the filter media. The cleaning air momentarily flows through and agitates the filter media by reversing the oncoming fan air, resulting in particulate dislodging and falling into a particulate removal system, such as a hopper. 
         [0004]    Cleaning systems for dust collectors commonly utilize a single blowpipe for providing compressed air to multiple (e.g., as many as sixteen) nozzles. Each nozzle is positioned to provide high-velocity air to a corresponding filter media. As pressurized air is provided to one end of the blowpipe from a manifold, all nozzles attached to the blowpipe will function to direct air to all corresponding filter media. 
       SUMMARY 
       [0005]    When pressurized air is provided from the manifold to one end of the blowpipe, the pressure pulse travels the length of the blowpipe until it contacts the opposing, closed end of the blowpipe. At that time, the pressure in the blowpipe quickly builds, starting at the closed end of the blowpipe and progressing back toward the manifold. As the pressurized air travels the length of the blowpipe and sequentially provides pressurized air to the nozzles, the pressure of the air reduces slightly. As a result, the pressure provided to the nozzle closest to the manifold is slightly less than the pressure provided to the nozzle farthest from the manifold. This results in a difference in performance of the various nozzles positioned on the same blowpipe. This phenomenon is illustrated in  FIG. 7 , which shows the pressure at three different nozzles after providing 100 psig air from the manifold to the blow pipe. After an initial period of time of about 0.074 seconds, the pressure at the nozzle farthest from the manifold is higher than the pressure of the nozzle closest to the manifold, and remains that way until the pressures have subsided. These test results show that there is a pressure differential of about 9.5% between the nearest and farthest nozzles. 
         [0006]    The present invention recognizes this phenomenon and modifies the nozzles accordingly in order to reduce the difference in performance of nozzles positioned on the same blowpipe. More specifically, the present invention provides a particulate filtration device comprising filter media having an upstream surface and a downstream surface, a gas-moving device for moving gas through the filter media from the upstream surface toward the downstream surface, and a cleaning assembly including a blow pipe having a plurality of cleaning nozzles for directing a flow of cleaning gas toward the filter media. A first one (e.g., a plurality) of the cleaning nozzles comprises a structural characteristic (e.g., throat size, exit angle, exit size) that is different than a second one (e.g., a plurality) of the cleaning nozzles. 
         [0007]    In one embodiment, the filter media comprises a filter bag corresponding with each nozzle, and both the first one and the second one of the cleaning nozzles are spaced substantially the same distance from the corresponding filter bag. The cleaning assembly can also include a plurality of blow pipes (e.g., each having a plurality of cleaning nozzles) coupled to a gas-pressurized manifold, and a valve positioned between the manifold and each blow pipe to control gas flowing from the manifold to the blow pipes. In this configuration, it is preferred that the nozzle nearer the manifold has a larger throat size, smaller exit angle, and larger exit size than the nozzle farther from the manifold. 
         [0008]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a cut-away perspective view of a particulate filtration device embodying the present invention. 
           [0010]      FIG. 2  is an enlarged partial view of the device of  FIG. 1  during a cleaning operation. 
           [0011]      FIG. 3  is a partially cut-away end view of another particulate filtration device embodying the present invention and having more filter bags. 
           [0012]      FIG. 4  is a section view taken along line  4 - 4  in  FIG. 3 . 
           [0013]      FIG. 5  is a section view taken along line  5 - 5  in  FIG. 4 . 
           [0014]      FIG. 6  is an enlarged section view of a nozzle used in the embodiment of  FIG. 5 . 
           [0015]      FIG. 7  is a chart that illustrates the phenomenon described in the Summary. 
       
    
    
     DETAILED DESCRIPTION  
       [0016]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
         [0017]      FIGS. 1 and 2  illustrate a particulate filtration system, which in the preferred embodiment is a dust collector  10  designed to remove particulates  14 , such as dust, from the air. The illustrated dust collector  10  includes a support assembly  18 , a particulate removal assembly  22  positioned within the support assembly  18 , a filtering assembly  26  positioned on top of the support assembly  18 , and a cleaning assembly  30  positioned on top of the filtering assembly  26 . 
         [0018]    The illustrated support assembly  18  includes support members  34  that provide a rigid frame to which the remaining assemblies may be mounted. The illustrated support assembly  18  is generally square-shaped, and the support members  34  include four legs positioned at the four corners of the square and diagonal braces that provide extra rigidity to the frame. In other constructions, the support assembly  18  may be different shapes and may have more or less support members  34  of the same or different shape. In addition, more than four or less than four legs are conceivable. 
         [0019]    The illustrated particulate removal assembly  22  is positioned within the support assembly  18  and is attached to the filter assembly  26  such that the particulate removal assembly  22  receives the particulates  14  that are removed from the air by the filter assembly  26 . The particulate removal assembly  22  includes a door (not shown) and a hopper  36  with a generally conical shape that funnels the particulates  14  into a container (not shown). The door is positioned in the hopper  36  and is movable between an open position and a closed position. While in the closed position, the particulate removal assembly  22  inhibits air flow out of the particulate removal assembly  22  and collects the particulates  14  that are removed from the air by the filter assembly  26 . In the open position, the particulate removal assembly  22  allows the collected particulates  14  to escape the hopper  36  and be emptied into a container for disposal. In other constructions, the particulate removal assembly may have other arrangements. For example, the hopper  36  may have a different profile and the door may be replaced with a powered louver. Other arrangements are also conceivable and are known by those skilled in the art. 
         [0020]    The illustrated filter assembly  26  is positioned above the particulate removal assembly  22  and mounted on top of the support assembly  18 . The filter assembly  26  includes an intake  38 , a screen  40  covering the intake  38  and promoting an equal distribution of airflow in the filter and preventing large objects from entering the filter assembly  26 , a classifier section  42 , filter media  43  (e.g. filter bags), and a filter assembly enclosure  44 , which includes four vertical walls, and a top  46 , commonly referred to as a “tubesheet”. The bottom of the filter assembly  26  is open to provide access to the particulate removal assembly  22  such that the particulates  14  collected in the filter assembly  26  are allowed to fall into the particulate removal assembly  22 . The classifier section  42  is a space between the filter assembly enclosure  44  adjacent the screen  40  and the filter media  43  closest to the screen  40 . The classifier section  42  is illustrated as an empty space and provides an area for larger particulates  14  to drop out of the air thereby reducing the load on the filter media  43 . In addition, baffles could be added to the classifier section  42  to further remove particulates  14 . The top  46  defines one or more openings  54  aligned with the filter media  43  and through which filtered air can flow out of the filter assembly  26  and into the cleaning assembly  30 . To escape the filter assembly  26 , the air must pass through the filter media  43  to gain access to the openings  54  and pass into the cleaning assembly  30 . A fan  56  moves air through the dust collector  10 . In other constructions, different filter media  43  may be used and the filter assembly may be arranged differently as is known by those skilled in the art. For example, the classifier section may have a different arrangement or may be removed. 
         [0021]    The illustrated cleaning assembly  30  is positioned on top of the filter assembly  26  and includes a cleaning assembly enclosure  58 , an exhaust  62 , and an advanced cleaning system  66 . The cleaning assembly enclosure  58  includes four vertical walls and a top. The illustrated exhaust  62  is attached to the side of the cleaning assembly enclosure  58  and directs cleaned air out of the dust collector  10 . In other constructions, the exhaust  62  may be arranged differently and may be attached to a different side of the cleaning assembly enclosure  58 . 
         [0022]    As is best seen in  FIG. 2 , the advanced cleaning system  66  includes a primary distribution member  70 , one or more secondary distribution members in the form of blowpipes  74  attached to the primary distribution member  70 , and one or more nozzles  110  coupled to the blowpipes  74 . The primary distribution member  70  distributes bursts of pressurized air to the blowpipes  74 , which in turn supply the nozzles  110  with bursts of pressurized air. As the pressurized air passes through the nozzles  110 , it is directed into a stream of cleaning air  114  which is directed into the openings  54  and downward though the filter media  43 . 
         [0023]    In operation, air including particulates  14  enters the filtration assembly  26  of the dust collector  10  through the intake  38  where the screen  40  inhibits large particulates  14  from entering the filter assembly enclosure  44 . Once inside the filter assembly enclosure  44  the air moves in a “downflow” air pattern toward the filter media  43 . First, the air will pass through the classifier section  42  where more particulates  14  will drop out. After the classifier section  42 , the air enters into contact with the filter media  43 , and the remaining particulates  14  are trapped on the filter media  43  before the clean air exits through the openings  54  and enters the cleaning assembly  30  and exits the dust collector  10 . 
         [0024]    The filtering assembly  26  provides several advantages due to the “downflow” air pattern, the geometry of the openings  54 , and other features not mentioned. The “downflow” air pattern guides the particulates  14  down to the bottom of the filter assembly  26  and into the particulate removal assembly  22 . This causes more particulates  14  to fall out in the classifier section  42  and fewer particulates  14  to be deposited on the filter media  43 . Due to the geometry of the openings  54 , the particulates  14  that are trapped by the filter media  43  tend to build up a more even dust cake along the entire length of the filter media  43 . This even dust cake promotes a better filtering efficiency and allows for more thorough cleaning with lower bag wear. In addition, the resulting dust cake produces a lower pressure drop between the filtering assembly  26  and the cleaning assembly  30  because there is no restriction (venturi) at the top of the bag opening. The lower pressure drop and higher filter efficiency allow the dust collector  10  to function at high efficiency and volume with significantly less filter media  43 . 
         [0025]    When a significant amount of particulate  14  covers the filter surface  32 , the filter media  43  should be cleaned. During the cleaning operation (as is best seen in  FIG. 2 ), the cleaning assembly  30  uses bursts of high velocity air to clean the filter media  43  thus increasing efficiency and prolonging the life of the filter media  43 . In the illustrated embodiment, the pressurized air is provided to each blowpipe  74  and directed to each nozzle  110  on the blowpipe  74 . Each nozzle  110  directs bursts of high velocity air into the mouth of the filter media  43  through the opening  54 . The high velocity air is slowed before entering the opening  54  by a pluming effect, such that the air reaches the mouth of the filter media  43  at ideal cleaning velocities. In one embodiment, the ideal cleaning velocity is between about one-hundred-fifty and two-hundred-fifty feet per second at the opening  54 . In other embodiments, different velocities may be ideal as is known by those skilled in the art. 
         [0026]    The illustrated dust collector  10  does not need to stop operation to perform a cleaning operation. The low pressure drop created between the filtering assembly  26  and the cleaning assembly  30  is easily overcome by the stream of cleaning air  114  even while the filtering assembly  26  is running. The cleaning operation forces high pressure air through the primary distribution member  70  where the high pressure air is distributed to the blowpipes  74 , and forced thorough the nozzles  110  and directed into streams of cleaning air  114  that are directed into the mouth of the filter media  43  through the openings  54 . The streams of cleaning air  114  are shot into the filter media  43  in bursts so as to rapidly inflate the filter media  43  and produce a shock or upset that causes the particulates  14  that are trapped on the filter media  43  to dislodge and fall to the filter assembly floor  50  and then down to the particulate removal assembly  22 . 
         [0027]    The nozzles  110  are high velocity supersonic nozzles designed to provide a greater volume of induced cleaning air and a more even bag inflation. The greater volume of induced cleaning air produces a larger stream of cleaning air  114  and increases cleaning potential. The even bag inflation allows the filter media  43  to be cleaned more thoroughly, with less shock to the filter media  43 . This results in lower wear and longer life for the filter media  43 . 
         [0028]      FIGS. 3 and 4  illustrate a much larger dust collector  200  having two-hundred-fifty-six filter bags  202 . The duct collector  200  includes an upper bin  204  defining a clean air chamber, a lower bin  206  defining a dirty air chamber, and a hopper  208  for directing particulate removed from the bags  202 . A rotary air lock  210  ( FIG. 3  only) is mounted to the bottom of the hopper  208  for the discharge of collected particulate. 
         [0029]    The duct collector  200  further includes a manifold  212  for providing compressed air to a series of diaphragm valves  214 . Each diaphragm valve  214  is controlled to selectively provide compressed air to a series of blow pipes  216 . 
         [0030]    Referring to specifically to  FIG. 4 , each blow pipe  216  extends substantially the full width of the upper bin  204  and includes sixteen cleaning nozzles  218 , 220 . Each cleaning nozzle  218 , 220  is aligned with the opening  222  of a corresponding filter bag  202 . Due to the phenomenon described above in the Summary of the Invention, the pressure of the air provided to the nozzles  218 , 220  on a particular blow pipe  216  is not consistent along the length of the blow pipe  216 . That is, the pressure experienced by the nozzles on the end of the blow pipe  216  nearest the manifold  212  (“nearest nozzles  218 ”) is typically lower than the pressure experienced by the nozzles farthest from the manifold  212  (“farthest nozzles  220 ”). In order to account for this difference in pressure, the configuration of the nearest nozzles  218  is different than the configuration of the farthest nozzles  220 . 
         [0031]    In the illustrated embodiment, the goal was to modify the configuration of the nearest nozzles  218  so that they achieve a flow rate (i.e., weight flow rate of air) that is closer to that of the flow rate of the farthest nozzles  220 , even though the pressure of the air provided to the nearest nozzles  218  is less than the pressure of the air provided to the farthest nozzles  220 . In order to achieve this, three nozzle characteristics were modified: throat size A, exit angle α, and exit size B. In the illustrated embodiment, two different nozzle configurations were used, one for the eight nearest nozzles  218 , and the other for the eight farthest nozzles  220 . It should be understood that a larger number of different nozzle configurations could be used. For example, 16 different nozzle configurations could be used along the length of the blow pipe  216  to achieve a more uniform flow rate through the different nozzles. 
         [0032]    Referring to  FIG. 5 , in the illustrated embodiment, each filter bag  202  is cylindrical in shape and the opening  222  of each bag  202  has a diameter C of about 4.7906 inches. The center of each blow pipe  216  is positioned a distance D of about 18.0 inches from the open end of the corresponding filter bag  202 . Each nozzle includes a converging section  230 , a throat  232 , and a diverging section  234 . The throat  230  is positioned a distance E of about 16.9638 inches from the open end of the corresponding filter bag  202 . 
         [0033]    The throat size A is defined as the size of the narrowest portion of the nozzle between the converging section  230  and the diverging section  234 . The exit angle α is defined as an angle at which the air exits the nozzle, and is commonly referenced as a half angle. The exit size B is the size of the nozzle at the nozzle exit. The nozzles also include an inlet length F, an outlet length G, and an overall length H. In the illustrated embodiment, because a cross-section of the nozzles at any location along the length of the nozzle produces a circular interior configuration, the throat size A and exit size B are commonly given as a diameter. 
         [0034]    Referring to  FIG. 6 , in the illustrated embodiment, the eight nearest nozzles  218  have a throat size/diameter A of about 0.324 inches, an exit angle α of about 7.5 degrees, an exit size/diameter B of about 0.382 inches, an inlet length F of about 0.180 inches, an outlet length G of about 0.220 inches, and an overall length H of about 0.400 inches. The eight farthest nozzles  220  have a throat size/diameter A of about 0.3125 inches, an exit angle α of about 7.5191 degrees, an exit size/diameter B of about 0.3750 inches, an inlet length F of about 0.180 inches, an outlet length G of about 0.237 inches, and an overall length H of about 0.417 inches. It should be understood that the present invention is not limited to the specific dimensions listed above. In fact, depending on the parameters that one is trying to achieve, the dimensions listed above could be quite different and/or other dimensions could be modified to achieve the desired goal. 
         [0035]    Thus, the invention provides, among other things, a unique combination of nozzles on a blowpipe that achieves a more equalized flaw rate between the nozzles. Various features and advantages of the invention are set forth in the following claims.