Abstract:
A filtration apparatus comprises a casing defining an inner cavity with an upper cylindrical portion and a lower hopper portion. An inlet feeds gas and solids into the inner cavity and causes movement of the solids in a downward spiral path in the casing. A solids outlet at a bottom of the lower hopper portion outlets the solids from the casing. A gas outlet exhausts gases from the casing. An annular arrangement of ports in a wall of the lower hopper portion of the casing injects an other gas in the inner cavity. The ports are oriented to guide the other gas into following a partially vertical path into the inner cavity to disrupt the movement of the solids in the downward spiral path to allow a capture of the solid particles by the capturing solids. A gas source is connected to the arrangement of ports.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present patent application claims priority on a Canadian patent application filed on Mar. 30, 2010, the serial number of which has not been disclosed at the time of filing. 
       FIELD OF THE APPLICATION 
       [0002]    The present application relates to a filtration apparatus of the type used in processes and systems in which bulk materials are transformed into a smaller uniform format, such as granules, pellets, or the like. 
       BACKGROUND OF THE ART 
       [0003]    It is commonly known to process bulky materials to convert these to a given format. For example, in the animal-feed industry, the feed is often produced as a mass of raw material, and must be converted to a suitable particle format (granules, balls, pellets, among many other possibilities) to be edible by animals. As another example, in the production of fuel from biomass, it is desired to produce pellets as pellets are well suited for efficient combustion. 
         [0004]    Accordingly, various systems and processes are commonly used for such transformation. However, such systems and processes may always be improved in terms of energy efficiency, whereas waste resulting from the transformation must be minimized. 
       SUMMARY OF THE APPLICATION 
       [0005]    It is therefore an aim of the present disclosure to provide a novel filtration apparatus. 
         [0006]    Therefore, in accordance with the present application, there is provided a filtration apparatus for filtering solid particles from a gas, with capturing solids, comprising: a casing defining an inner cavity with an upper cylindrical portion, and a lower hopper portion connected to the upper cylindrical portion; at least one inlet in the upper cylindrical portion for feeding a flow of gas and solids into the inner cavity, the at least one inlet being positioned with respect to the casing to cause movement of the solids in a downward spiral path in the casing; a solids outlet at a bottom of the lower hopper portion for outletting the solids from the casing; a gas outlet in the upper cylindrical portion to exhaust gases from the casing; an annular arrangement of ports in a wall of the lower hopper portion of the casing to inject an other gas into the inner cavity, the ports being oriented so as to guide the other gas into following a path at least partially vertical when entering the inner cavity to disrupt the movement of the solids in the downward spiral path to allow a capture of the solid particles by the capturing solids; and a gas source connected to the arrangement of ports for the injection of the other gas into the inner cavity. 
         [0007]    Further in accordance with the present application, there is provided a method for filtering solid particles from exhaust air in a process of the type in which raw material is transformed into elements of predetermined shape, the process using drying air to remove at least one of moisture and heat from the mass of raw material, with air exhausted from the process having solid particles of the raw material in suspension, comprising: supplying a flow of the exhaust air having solid particles of the raw material in suspension, and parts of the raw material to a filtration apparatus; inducing a mixing of the exhaust air and of the raw material in the filtering apparatus for the raw material to capture solid particles; outletting the raw material with captured solid particles from the filtering apparatus; and outletting the exhaust air without the captured solid particles separately from the raw material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a system using a filtration apparatus in accordance with the present disclosure; 
           [0009]      FIG. 2  is a schematic sectional view of the filtration apparatus used in the system of  FIG. 1 ; and 
           [0010]      FIG. 3  is a perspective view of a sustentation ring of the filtration apparatus of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0011]    Referring to the drawings and more particularly to  FIG. 1 , there is illustrated a gas filtration apparatus  10  in accordance with the present disclosure. The filtration apparatus  10  is illustrated in any appropriate system or process requiring the separation of a solid from a gas, such as a feed-producing system A of  FIG. 1 . Among numerous possibilities, the filtration apparatus  10  may be used to recuperate energy from a gas or from a solid, to allow a reaction between a solid and solids in suspension in the gas, to allow the absorption of moisture by the solids. The possibilities will be related to the process with which the filtration apparatus  10  is used. 
         [0012]    Referring to  FIG. 2 , the filtration apparatus  10  is shown in greater detail. The filtration apparatus  10  has a casing  12  defining an inner cavity in which the filtration process takes place. The casing  12  has an upper cylindrical portion  14 , and a lower hopper portion  16 . The lower hopper portion  16  has an inverted conical shape, whereby the casing has a circular section (or arcuate) along its vertical axis. An elliptical section may also be considered for the casing  12 . 
         [0013]    An inlet  18  merges into a wall of the cylindrical portion  14  so as to be in fluid communication with the inner cavity of the casing  12 . The inlet  18  may be tangentially oriented with respect to the cylindrical portion  14 , as it is desired to create a cyclonic flow in the inner cavity of the casing  12 . Although a single inlet  18  is illustrated in  FIG. 2 , the casing  12  may have two or more inlets, for instance in accordance with the process or system using the filtration apparatus  10 . The inlet  18  is preferably provided in the upper half of the cylindrical portion  14  of the casing  12 . 
         [0014]    A solids outlet  20  is provided at a bottom end of the hopper portion  16 , for instance at the tip of the inverted conical shape, and is thus in fluid communication with the inner cavity of the casing  12 . Solids therefore exit the casing  12  via the solids outlet  20  by the effect of gravity. A valve may close the solids outlet  20  to maintain a given pressure or flow conditions in the inner cavity of the casing  12 . For instance, the valve  21  is a rotary valve. 
         [0015]    A gas outlet  22  is provided in the top of the cylindrical portion  14 , and is also in fluid communication with the inner cavity of the casing  12 . The gas outlet  22  may be connected to a side wall of the cylindrical portion  14 , or to the top wall of the cylindrical portion  14 . Filtrated gas therefore exits the casing  12  through the gas outlet  22 . 
         [0016]    The inner cavity of the casing  12  is divided into two compartments by a support wall  24 . The support wall  24  supports filters, whereby the unfiltered gas and solids circulate in the compartment below the support wall  24 , whereas the filtered gas circulates in the compartment above the support wall  24  to exit the casing  12 . 
         [0017]    In  FIG. 2 , the support wall  24  has throughbores, with cages  26  hanging from each throughbore. The cages  26  therefore extend into the lower compartment of the casing  12 , although they could also be arranged to extend in the upper compartment of the casing  12 . 
         [0018]    Filtering membranes  28  are retained by the cages  26 , and are selected to filter out given sizes of solid particles. The filtering membranes  28  cover any free space in the cages  26  to prevent solids from exiting the casing  12  through the gas outlet  22 . According to an embodiment, the filtering membranes  28  are sleeves slipped onto the cages  26 . For instance, the membranes  28  are made of a polyester, although any other suitable material may be used. Any other type of filtering member may be used as an alternative to the filtering membranes  28 . For instance, it is considered to position a circular filtering mesh or screen directly in each throughbore of the support wall  24 . 
         [0019]    A protection skirt  30  projects downwardly from the support wall  24  and encompasses the cages  26  and filtering membranes  28 . According to an embodiment, the skirt  30  has a circular section, whereby the wall of the cylindrical portion and the protection skirt concurrently form an annular plenum. The annular plenum may enhance the cyclonic flow of gas in the inner cavity of the casing  12 , as described hereinafter. 
         [0020]    Still referring to  FIG. 2 , nozzles  32  may be provided in the throughbores of the support wall  24 . The nozzles  32  are of the Venturi type and increase the velocity of a blowback flow into the filtering membranes  28 . The blowback flow is produced by jets  34 . The jets  34  are connected to a pressure source (e.g., compressed air network, a compressor, etc.), and oriented to outlet a flow of compressed air toward the nozzles  32 . The blowback flow may be periodically performed. Alternatively, a pressure differential may be measured on opposed sides of the filtering membranes  28 , with the blowback being automatically performed if the pressure differential is above a given threshold value. 
         [0021]    Referring to  FIGS. 2 and 3 , a sustentation ring  40  is provided about the wall of the casing  12  at the level of the hopper portion  16 . The sustentation ring  40  is positioned on the wall of the hopper portion  16  to blow air into the inner cavity of the casing  12 . In an embodiment, the sustentation ring  40  is approximately located midway along a vertical axis of the hopper portion  16 . However, the sustentation ring  40  may be located at other heights along the vertical axis, notably about the midway line. Accordingly, the sustentation ring  40  is in fluid communication with the inner cavity through a plurality of relatively small ports  42 . 
         [0022]    The ports  42  are arranged in a ring in the wall of the casing  12 , and therefore inject a gas (e.g., air) into the inner cavity, with an upward vector component. Accordingly, the solids blown along a downward cyclonic path in the inner cavity of the casing  12  will be lifted by the gas injected by the sustentation ring  40 . A pressure source (not shown), such as a blower, fan or compressor, is in fluid communication with an inlet  44  of the sustentation ring  40 . The pressure of air injected by the ports  42  may be controlled by adjusting the level of actuation of the pressure source. By controlling the pressure of air injected by the ports  42 , a residence time of the solids in the inner cavity of the casing  12  may be increased or decreased. 
         [0023]    In an embodiment, the ports  42  are sized (e.g., between 0.25 and 0.375 in for an inner diameter between 16 and 18 in for the ring  40 ) to inject gas at a flow rate of about 2 CFM per port, with a velocity ranging between 3500 and 4000 FPM. There are a plurality of ports  42  (e.g., between 40 and 60 ports), spread over the full circumference of the hopper portion  16 . 
         [0024]    Now that various components of the filtration apparatus  10  have been described, a reaction taking place in the filtration apparatus  10  is described. 
         [0025]    Solids and gases to be separated are fed to the casing  12  via the inlet  18 , or inlets  18 . In an embodiment, the solids and liquid are mixed in a same pipe upstream of the inlet  18 , and hence enter the inner cavity of the casing  12  concurrently. Typically, the solids are in a granular or aggregate form, whereas the gases may be filled with solid particles in suspension. Moreover, the solids and gases may be a different temperatures, and may have different levels of humidity/moisture content. 
         [0026]    The solids and gases enter the inner cavity of the casing  12 , and follow a downward cyclonic path. More specifically, the inlet of gases  18  is oriented with respect to the casing  12  so as to create a circular flow of the gas into the inner cavity. Because of the effect of gravity, the solids conveyed by the gas will move in a spiral toward the solids outlet  20 , i.e., along a downward cyclonic path. 
         [0027]    Upon reaching the height of the ports  42 , the gas injected by the sustentation ring  40  will lift the solids, increasing their residence time in the casing  12 . According to some embodiments, it may be desired to increase the residence time of the solids. For instance, the increased residence time may result in a temperature or moisture-content adjustment for the solids. If the gas is hotter or more humid than the solids, the solids may be heated, or may absorb humidity from the gas. Moreover, there may be some reaction between the solids and solid particles in suspension in the gas. Accordingly, an increased residence time may increase the level of solid particles captured by the solids. Accordingly, the raw material is a capturing solid that captures the solid particles from the gas. 
         [0028]    The solids then reach the solids outlet  20 , while the gas follows a straight cyclonic upward path toward the filtering membranes  28 . Solid particles remaining in the gas are filtered out of the gas by the filtering membranes  28 , whereby the gas exits the lower compartment of the casing  12  with a filtered level of solid particles. 
         [0029]    The filtration apparatus  10  is readily cleaned. More specifically, as the inner cavity of the filtration apparatus  10  has very few edges, corners, cavities and components, the use of a pressurized fluid may be sufficient to remove unwanted particles from the surfaces of the inner cavity. 
         [0030]    Referring to  FIG. 1 , the filtering apparatus  10  may be used in any applicable systems/processes, such as thermo-transformation, roasting, feed production, biomass production, etc., in which a raw material (e.g., in a bulky, chunky state) is transformed into smaller elements of a generally uniform shape. The system A of  FIG. 1  is equipped to perform a feed production. Feed must be in the form of pellets within a predetermined size range. The system A is used to convert feed from a bulk chunk state to pellets, having a predetermined moisture content and temperature. 
         [0031]    A bulk feed hopper  50  outlets the feed in the bulk chunk state into an air conveyor  52 . The air conveyor  52  is, for instance, a pipe in which a gas flows, thereby entraining the feed from the hopper  50 . Although not shown, an appropriate valve (e.g., rotary valve) may be provided at the outlet of the hopper  50  to control the amount of feed entering the air conveyor  52 . A rotary valve may, for instance, separate the outlet into small batches of bulk feed. 
         [0032]    The air conveyor  52  is in fluid communication with the inlet  18  of the filtration apparatus  10 . The treatment of the gas and feed in the filtration apparatus  10  will be described hereinafter. The feed exits the filtration apparatus  10  via the solids outlet  20  of the casing  12  with an increased temperature and/or moisture content, and thus in a softened state. 
         [0033]    The feed is then directed to an extruder unit  54  that converts the bulky feed to pellets. To direct the feed from the filtering apparatus  10  to the extruder unit  54 , another air conveyor  56  is used in conjunction with an extruder hopper  58 . The air conveyor  56  may have its own blower, or may use residual pressure flow from the filtration apparatus  10 . 
         [0034]    The extruder unit  54  receives the feed from the hopper  58 , via inlet  60 , in the softened state. Steam may be injected into the feed to further soften it with a view to being transformed. The extruder unit  54  may for instance be a Bliss™ unit, or any appropriate shaping unit that converts bulky feed into an appropriate format. The extruder unit  54  has an endless screw portion  62  pressing the feed against an extrusion disc (not shown). Accordingly, the feed pressed against the extrusion disc will be converted to pellets by passing through holes in the extrusion disc. 
         [0035]    A drying unit  64  receives the feed pellets from the extruder unit  54 . The feed pellets are in the softened state, and thus have relatively high moisture content and/or temperature. In the drying unit  64 , the feed pellets are therefore dried, and cooled if necessary. Any appropriate drying unit may be used. For instance, a Law-Marot™ drying unit (e.g., Milpro™) may be used. 
         [0036]    The drying unit  64  typically uses a flow of air to dry the feed pellets. The drying unit  64  may be of the type having a reciprocating sieve into which air is blown against a descending mass of feed pellets. Alternatively, the drying unit  64  may feature a mesh conveyer or the like, also allowing air to be blown against the feed pellets. Therefore, once the feed pellets are dried, they exit the system A, for instance via outlet conveyor  66 . 
         [0037]    The air exiting the drying unit  64 , namely the exhaust air, is humid and warm, as it has contacted the feed pellets to dry and cool them. Moreover, the air typically has a non-negligible level of solid particles in suspension. Accordingly, the drying unit  64  is connected to the filtration apparatus  10  by the air conveyor  52 . This will allow the exhaust air to be used as conveying gas for the air conveyor  52  to convey the bulky feed from the bulk feed hopper  50 . 
         [0038]    The filtration apparatus  10  allows the bulk feed to be preheated by the exhaust air. Moreover, the bulk feed is usually drier than the exhaust air, whereby the bulk feed absorbs humidity from the exhaust air. The preheating and moisturizing of the bulk feed will soften the amount of steam required by the extruder unit  54 . Also, the solid particles in suspension in the exhaust air may adhere to the bulk feed in the filtration apparatus  10 . Therefore, the filtration apparatus  10  allows the recuperation of waste heat, humidity and solids from the exhaust air, simultaneously cleaning the exhaust air for its exhaust to the atmosphere, via the gas outlet  22 . A heat exchanger  68  may be provided in the gas outlet  22  to absorb more heat from the air exiting the filtration apparatus  10 . A refrigerant circulates in the heat exchanger  68 . The refrigerant may be any one of a synthetic refrigerant, alcohol-based refrigerant (e.g., glycol), or heat-transfer fluid (i.e., cooling fluid). The recuperated heat may be used in any appropriate way. For instance, it may be used to preheat the water of a boiler producing the steam for the extruder unit  54 . According to another embodiment of the system A, the filtration is performed by an endless screw unit, in which the exhaust gas and bulky feed are mixed. The rotational speed of the endless screw unit is controlled to adjust the residence time of the exhaust gas and bulky feed therein, to allow the bulky feed to absorb some humidity and heat from the exhaust gas, and to capture solids in suspension.