Patent Abstract:
Methods and systems for collecting dust produced in paper making involve an air inlet passage including an opening to receive dust laden air. The opening to the inlet passage may have a width approximately equal to a width of a paper web in a paper making machine. The air inlet passage is devoid of water injection. The dust collector may include a central vortex chamber and may be defined by an outer wall and an internal guide vane. There may be a water injector mounted in the outer wall and injecting water into the central vortex chamber, and there may be a discharge outlet of the central vortex chamber connectable to a water and air separator.

Full Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Patent Application Ser. No. 60/988,447 filed Nov. 16, 2007, which is incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to dust collection and, specifically, to the collection of paper dust generated by papermaking machines, such as tissue making machines. 
     Dust, e.g., paper fibers and other small air borne debris, is formed during the production of tissue paper and other types of paper. The amount of dust generated by paper making machines (e.g., tissue making machines) has increased as the speed increases of the paper webs passing through paper making machines. Greater amounts of dust tend to be created with paper machines that produce soft tissue paper and papers having high crepe ratios. 
     There is a need to remove dust produced during paper making processes. Dust removal is needed to avoid problems that may arise with dust collecting on the paper making machines and paper webs formed by these machines. Removal of substantial portions of the dust generated by paper making allows for improved paper quality and printability of the generated papers. 
     Conventional dust removal systems, such as disclosed in U.S. Pat. No. 6,176,898 (&#39;898 Patent), utilize various shapes of exhaust cross machine headers. Dust collectors typically uses large amount of exhaust air to evacuate the dust developed during the paper making process. The &#39;898 Patent discloses a dust collection cylinder having an interior air vortex and water spray that entrains dust laden air as soon as the air enters the collector. In the dust collector shown in the &#39;898 Patent, the inlet to the dust collector is short and recessed with respect to the cylindrical collector such that the dust laden air is immediately wetted by the vortex of air and water within the collector. 
     SUMMARY OF INVENTION 
     A novel dust collection and removal system has been developed that includes a volute center chamber within which a vortex of air, dust and water circulate and from which are discharged. The system may include an extended inlet to collect dust laden air. The inlet may include a narrow throat to accelerate the air. Downstream of the inlet is a curved passage into which or after which water is injected. The dust in the air may become entrained by water droplets. The mixture of air and water droplets with dust flow from the passage into the vortex formed in the center section of the volute. An outlet at one end of the center section may discharge the mixture of air, dust and water and may apply a suction to the center section to form the vortex. 
     In an embodiment, a novel dust collection and removal system includes an extended inlet allows the opening to the inlet to be positioned near a tissue web or other source of dust. The dust laden air that enters the inlet, may be accelerated into a high velocity stream. Water may be injected into or after the stream to entrain the dust. The air, dust and water flow into a vortex in the center of the system. From the center of the system, the mixture of air, dust and water is discharged where the air is separated from the dust and water mixture. An exhaust fan may apply a suction to the discharge outlet to create the vortex in the center of the system. The system may effectively collect air borne dust at or near a paper making machine, e.g., a tissue machine, mixes the dust with water, and may discharge the water and dust mixture for waste water processing. 
     In an embodiment, the dust collection and removal system may include a variable length inlet section that has a width that extends the full width of a tissue web so as to entrain the dust particles. Downstream of the extended inlet, the dust laden air may be showered with one or more water sprays to capture the dust particles in water droplets entrained in the air flow. The system may also allow from variation of the air inlet velocity at the opening to the inlet. A throat towards the back of the dust extractor may be adjust to control the velocity of the air entering the inlet. Inlet velocities can be controlled manually or automatically. This feature regarding inlet velocity control allows fine tuning to various machine speeds and paper grades. 
     In an embodiment, a method has been developed to collect and handle dust in a papermaking environment including: drawing dust-laden air into an opening of an inlet of a collector at a selected velocity, wherein a velocity of the air drawn into the opening is dependent on a cross-sectional area of the inlet slot; injecting water into the air flowing through the collector, wherein the water is introduced downstream of the inlet and dust in the air attaches to the injected water; inducing an vortex in the flow of water, dust and air in a chamber of the collector, and discharging the water, dust and air from the collector. 
     The inlet may be extendible, such as by a fixed or telescoping an opening of the inlet to an area proximate to a paper web or other source of dust. The injection of water may include spraying the water through one, two, or a row of water nozzles mounted to an outer wall of the collector. Further, the injection of water may be into an passage downstream of the inlet and upstream of the vortex. Alternatively, the injection of water may be downstream of an inlet. 
     The passage may be formed by an outer wall of the collector and an internal guide vane. The collector may include a volute, wherein the throat of the inlet is between an outer wall of the volute and an interior scroll of the volute. Further, the interior scroll may form a guide vane directing the air, dust and water to the vortex in a center chamber of the volute. 
     In an embodiment, a dust collector has been developed comprising: an air inlet passage including an opening to receive dust-laden air and a throat proximate to an outlet of the inlet, wherein the opening to the inlet passage has a width approximately equal to a width of paper web in a paper making machine and the throat has a cross-sectional area smaller than a cross-sectional area of the opening; an inlet guide vane passage extending from the throat to a central vortex chamber and defined by an outer wall of a volute and an internal guide vane of the volute, wherein the outer wall and internal guide vane are formed of a continuous sheet; a water injector mounted in the outer wall and injecting water into the passage; the central vortex chamber defined by the volute and coaxial with the volute, and a discharge outlet of the central vortex chamber connectable to a water and air separator and a source of air suction. 
     The cross-sectional area of the throat or inlet may be adjustable, such as by the use of a clamp extending between the outer wall of the collector and an internal guide vane. The inlet passage may be curved and substantially straight. The air inlet passage may be devoid of water injection. 
     In an embodiment, there is a dust collector comprising: an air inlet passage including an opening to receive dust laden air, wherein the opening to the inlet passage has a width approximately equal to a width of a paper web in a paper making machine, wherein the air inlet passage is devoid of water injection; a central vortex chamber and defined by an outer wall and an internal guide vane; a water injector mounted in the outer wall and injecting water into the central vortex chamber; and a discharge outlet of the central vortex chamber connectable to a water and air separator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-section diagram of an embodiment of the dust collection and removal system. 
         FIG. 2  is a schematic diagram showing a perspective view of an embodiment of a dust collection and removal system including a water supply, water and dust collector and a vacuum source. 
         FIG. 3  is a schematic cross-section diagram of the embodiment of the dust collection and removal system illustrated in  FIG. 2 . 
         FIG. 4  is a perspective view of an embodiment of the dust collection and removal system. 
         FIG. 5  is a perspective view of an embodiment of the dust collection and removal system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows in cross-section an embodiment of a dust collector and removal system  10  having an extended inlet  12  for dust collection and a volute section  14  for dust removal. Dust laden air  16  is pulled into an opening  18  of the inlet and passes through a dry, generally straight inlet section  20 . The section  22  of the inlet has a specific cross-sectional area that causes the velocity of the dust laden air passing through the inlet. The accelerated dust and air enter the volute section  14  where the fast moving dust laden air is mixed with a water spray and rotated to form a vortex. Water is injected tangentially by one or more water injectors  24 ,  26  arranged in the volute section. An internal vane guide  28  guides the dust laden air to form the vortex. The dust and water laden air is removed from the vortex section at one of the ends of the collector and removal section. 
     The collector and removal system  10  may be formed of a sheet metal, such as a galvanized steel to minimize corrosion. The interior surfaces of the system  10  may be optionally coated with a plastic material or be formed of a plastic liner to prevent water from leaking from joints in the system. 
     The inlet section  20  may be generally rectangular in cross-section, but other cross-sectional shapes such as race-track, oblong, oval, and elliptical may be suitable for particular applications. The cross-sectional area of the inlet is preferably constant from the opening Preferably, the width of the inlet section and particularly the opening  18  is approximately, e.g., within 10%, the width of the tissue machine or the tissue web being formed by the machine. Similarly, the length of the volute section  14  is preferably approximately the width of the inlet section and also approximately the width of the tissue machine. 
     The opening  18  of the inlet may be positioned adjacent the web or proximate a section of the machine that tends to generate dust. The inlet section may include an initial straight section  20 . The length of the straight section  20 , e.g., one foot to ten feet, is subject to design considerations, such as the position of the dust collector and removal system with respect to the tissue machine and an optimal location for the opening  18  to the inlet. 
     An extended inlet section  20  allows for the placement of the opening  18  for the dust collector and removal system  10  to at small or confined locations near the tissue web or machine that would not allow for the placement of the volute section  14 . The length of the inlet may be selected during a design phase of the dust collector and removal system  10 . Optionally, the length of the inlet may be adjusted, such as by telescoping the inlet which may be formed of multiple rectangular ducts which slide one into the other. The extended inlet allows the opening  18  to be positioned at locations where there may be insufficient space for the volute section. While the inlet  12  is shown as being straight, it may be curved, bent or otherwise shaped to fit into irregular spaces near the tissue machine and arranged to position the opening  18  proximate the tissue web or other source of dust on the machine. The opening may include a series of bars or a grid  19  that prevents large material, e.g., sections of a web, from being drawn into the opening  18  and entering the interior of the dust collector and removal system  10 . 
     The throat  22  of the inlet  12  may have a smaller cross-sectional area than does cross-section area of the straight section  20  of the extended inlet  12 . A reduced cross-sectional area of the throat may accelerate the dust laden air  16  passing through the dry inlet. The acceleration of the air creates a relatively high velocity air flow through the inlet section  22 . The acceleration and the high velocity air encourages mixing of the dust in the air, tends to prevent dust from accumulating on the sides of the inlet and imparts kinetic energy to the dust and the air flow. 
     The inlet  22  is between the section  20  and the volute section  14 . The throat  22  may have a curvature due to the curved internal guide vane  28  and the curved outside housing wall  30  of the volute section  14  of the dust collector and removal system  10 . The outside housing wall  30  may be formed from a metallic sheet wrapped to from a scroll, wherein an outer portion of the scroll defines the outside housing wall and an interior section of the scroll forms the internal guide vane  28 . 
     The cross-sectional area of the inlet  22 , e.g., the height of the inlet between the outside housing wall and the internal vane guide, may be selected to provide optimal acceleration of the air flow. Optionally, the cross-sectional area of the inlet may be adjusted to change the air flows, e.g., rate of air flow and velocity, to suit various operating conditions. 
     As the dust laden air passes through the inlet and enters the passage section  32  of the volute between the outer housing wall  30  and the internal vane guide  28 . In the illustrated embodiment, the expanded section is a curved passage between the throat and an open generally cylindrical chamber  34  at a center section  34  of the volute. The cross-sectional area of the expanded section may be generally larger than the cross-sectional area of the throat  22 . The cross-sectional area of the passage section  32  can be initially relatively small near the throat and increases as the passage curves around the volute and extends to a passage outlet  36 . As the dust laden air flows through the inlet passage section  36 , the air flow is turned to flow in a circular path and thereby to start a vortex air flow. At the outlet  36 , dust laden air flows into the center section  34  of the volute. The air flows in a circular path, e.g., a vortex, in the center section. The circular air flow path is initiated by the curvature of the inlet vane section. The vortex flow in the center section of the volute causes the dust laden air to circulate within the volute. 
     Water or other liquid is injected downstream of the throat  22  and into the air flow passing through the passage section  32 . The water is preferably injected by nozzle(s)  24  as a mist, spray or droplets that entrain the dust in the air flow. As the water mixes with the air, dust in the air attaches to the water. The water is preferably injected as sufficiently fine droplets and into an airflow at a sufficient velocity such that the water remains in the airflow. However, some water may accumulate on the interior walls of the passage section and the center section of the volute. The water on the walls tends to wash the walls and remove dust from the walls. 
     The water injector  24  may be multiple or single spray nozzles arranged to project water into the air flow in the passage section  32 . For example, the water injector may be a row of water nozzles mounted on the outside housing wall  30  and arranged to inject water tangentially into the curved passage  32 . The nozzles may be arranged along the entire length of the outer housing wall. Further the water injectors may be positioned slightly downstream, e.g., within six inches to two feet, of the narrow most section of the throat so that the water enters a relatively high velocity air flow. 
     The optional second water injector  26  may be mounted in the outer housing wall  30  and arranged to inject water directly into the center section of the volute  43 . The second water injector  26  may be one or multiple water nozzles arranged in the outer housing wall and projecting water into the center section. One or more water nozzles  26  may be arranged at one end of the center section such that water is sprayed into the vortex formed in that section. In this configuration, the water nozzles are mounted on an end wall  42  of the outer housing shown in  FIG. 2 . Alternatively or in addition to, the water nozzles  26  may be arranged in a row along the curved side wall  30  of the center section and inject water tangentially to the vortex flow in the center section. 
       FIG. 2  is a perspective view of an embodiment of the dust collector and removal system  10  showing a water pump  38  supply water to the water injectors  22 ,  26  from a water source  40 . The water pump provides water to the water injections, such as a row of water nozzles  26  and to a water nozzle  44  mounted on end wall  42 . 
     A second end wall  46 , opposite to the first end wall  42 , includes a water and air flow outlet  48  that may be a tapered duct coupled to the second end wall. A suction is applied to the outlet to draw air and water from the center section  34 . The suction at least partially creates the vortex within the center section. The vortex is also formed by the tangentially injected water sprays from injectors  24  and  26 , and the tangential flow of air from the passage section into the center section. 
     To create suction and to extract the air and water, a conduit  50  directs the dust and water laden air into a separator  52 , e.g., cyclone, that has an upper outlet coupled to a vacuum source such as a fan  54  and that has a lower drain that flows to a water and dust collector  56 . The dust may be filtered from the water using conventional water processing techniques. 
       FIG. 3  illustrates in cross-section an embodiment of a dust collector and removal system  100  having an extended inlet  108  for dust collection and removal. Dust laden air  102  is pulled into an opening  103  of the inlet and passes through a dry, generally straight inlet (e.g., throat) section  106 . The structure defining opening  103  may optionally be bell-shaped or otherwise curvilinear. The inlet  108  may have an approximately constant or variable cross-sectional area. As illustrated, the height of the inlet section may be 5 to 15% of the diameter of the substantially cylindrical chamber  108 . The dust and air tangentially enter a substantially cylindrical chamber  108  at the discharge of the inlet which is between wall  116  and the rear edge of internal guide vane  110 . There are one or more attachment mechanisms, e.g., bolts  107  as illustrated, that permit attachment of the dust collector and removal system  100  close and/or near a tissue or paper sheet. As illustrated, bolts  107  are near opening  103  along the generally straight inlet section  106 . 
     Dust-laden air enters the opening  103  of the inlet  108  and flows through the generally straight inlet section  106 . The air flows into a curved section of the inlet between the wall  116  of the cylindrical chamber  118  and the inlet guide vane  110 . The curvature of the inlet induces a rotational flow to the air that promotes a vortex in the chamber  118 . The air flow through the inlet may be fast, thus having a high potential energy. The curvature of the inlet directs the air flow such that the energy of the flow is effectively applied to create the vortex. 
     As the dust-laden air enters the cylindrical chamber  108 , water is injected tangentially by one or more water injectors  112  through nozzles  114 . Hinge  111  permits panel access to water injectors  112  and nozzles  114  so as to permit cleaning or repositioning of nozzles  114 , repairs, etc. An internal vane guide  110  guides the dust laden air to form a vortex. Hinge  111  also may facilitate access to the curved portion of inlet  108  defined by internal vane guide  110 . 
     The dust and water laden air is removed from the vortex section at one of the ends of the collector though exit  104 . As illustrated, exit  104  is disposed approximately perpendicularly to the center axis of the cylindrical chamber  108 , such that the dust and water laden air exits through an opening in the wall  116  (and not solely through an opening in the top or bottom of the cylindrical chamber). The substantially cylindrical shape of the chamber  108 , the tangential entry of the dust-laden air, and the tangential spray of water through nozzles  114  individually and collectively facilitate the formation of a vortex in the direction of the arrows illustrated in  FIG. 3 . 
     Water or other liquid is injected downstream of the inlet  108  and into the air flow passing into the substantially cylindrical chamber  108 . The water is preferably injected by nozzle(s)  114  as a mist, spray or droplets that entrain the dust in the air flow. As the water mixes with the air, dust in the air attaches to the water. The water is preferably injected as sufficiently fine droplets and into an airflow at a sufficient velocity such that the water remains in the airflow. The water may also wash the walls  116  of the substantially cylindrical chamber  108  so as to prevent dust build-up thereon. 
     The water injector  112  may include multiple or single spray nozzles arranged to project water into the air flow in chamber  108 . For example, the water injector may be a row of water nozzles mounted on the outside wall arranged to inject water tangentially in the same direction as the air flow exiting inlet  108 . The nozzles may be arranged along the entire length of the outer housing wall. 
     After exiting exit  104 , the mixture of dust, air, and water may be separated using a separator, e.g., a cyclone, that has an upper outlet coupled to a vacuum source and that has a lower drain that flows to a water and dust collector. The dust may be filtered from the water using conventional water processing techniques. 
       FIGS. 4 and 5  illustrate perspective views of collector  200  in accordance with an embodiment of the present invention. As illustrated, there is an opening  205  to collector  200  extending substantially along the entire length of the collector (e.g., matching the width of a sheet of tissue or paper). There is an exit  210  positioned at or near one end of the collector  200 . As illustrated, exit  210  may extend 10 to 20% from one end of collector  200  (i.e., its axial length), although in certain embodiments exit  210  may extend up to 100% of the axial length of the collector. Furthermore, there may be multiple exits positioned throughout the collector  200 . Furthermore, there are access panels  240  and hinges  230 , which facilitate access to water injectors and their nozzles (not shown). Attachment bolts  220  are similarly illustrated at or near the ends of collector  200 . 
     All numerical measurements and ranges as described and claimed are approximate and include at least some degree of variation. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Technology Classification (CPC): 3