Abstract:
There is provided an improved method and apparatus for renewal of a plurality of faces across which gas enters a panel of a granular material. The panel is for contacting the gas and granular material with each other to effect physical or chemical treatment of at least one of them (for example, to filter dust from a gas or to remove a constituent from a gas by means of adsorption or absorption). In the panel, gas-entry faces are transversely disposed, upwardly spaced, and held in place by supporting members. These supporting members are subjected to a sharp motion in a direction toward the gas-entry faces, causing body movement of the granular material toward the faces, thereby causing moieties of granular material to fall away therefrom. Removal of these moieties and exposure of previously underlying granular material renew the faces. Flat-plate louvers are preferred supporting members.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/698,982, filed Jul. 14, 2005, which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the intimate contacting of a gas and a loose granular solid material for the purpose of chemically or physically treating one or both of the gaseous and solid substances, for example: to filter fine particulate matter (“dust”) from the gas; to effect a chemical change in gas or solid; to remove a chemical constituent of the gas by absorption, adsorption, or chemical reaction; to heat a cold gas by contact with a hot solid. The invention also relates to the countercurrent contacting of a gas and a granular solid material. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 6,783,326 (Aug. 31, 2004), which the instant application incorporates by reference, broadly discusses uses of a panel of granular material: for filtration of a dusty gas, assisted by an accumulation of deposits of dust (filter cakes) upon gas-entry faces of the panel; for countercurrent contacting of the granular material with a gas. 
     The referenced patent discloses means for renewing gas-entry faces of a panel of a granular material in which faces are transversely disposed, upwardly spaced, and held in place by supporting members. One means is to provide a surge flow of gas toward the faces (a “puffback”), which produces a body movement of the granular material toward the faces, thereby producing spills of moieties of the material from the faces and concomitantly exposing previously underlying material, thereby renewing the faces. Another means is to strike the panel with the blow of a hammer, the blow being directed either upward or downward. The blow also gives rise to a body movement of granular material toward gas-entry faces, producing spills of moieties of material therefrom. 
     These means are admirably effective in renewing gas-entry faces when a supporting member is a louver seen in vertical cross-section to comprise two segments: an outer segment sloping upward from its outer edge (e.g., sloping at an angle of 9° to horizontal) and an inner segment sloping upward toward the louver&#39;s inner edge at, preferably, an angle not less than ˜45° to horizontal (where “outer” refers to the outside limit of the gas-entry side of the granular-bed panel, and “inner” refers to a location within the interior of the panel). 
     A disappointment, however, has been performance of these means when tested for renewal of gas-entry faces resting upon transversely disposed upwardly spaced flat-plate louvers. Following a puffback of flat-plate louvers (inclined upward from their outer edges at 9°), a narrow, sand-free region appears beneath each louver, extending to its upper, inner edge. A similar, sand-free region appears after subjecting flat-plate louvers to a sharp upward or downward motion; this region is even wider than the narrow sand-free region seen following puffback. 
     The appearance of this region is undesirable for two reasons. First, following gas-entry face renewal, granular material moves downward in a space between inner edges of support louvers and a panel&#39;s gas-exit side, the downward motion making good losses of granular material from the panel&#39;s gas-entry faces. If the panel is tall, at flat-plate louvers near its top, the downward motion pulls granular material away from part of gas-entry faces close by their inner edges. If the panel is employed for filtering dust from a gas, such pulling away of moieties of gas-entry-face material hurts filtration efficiency. Second, in an application requiring countercurrent contacting (i.e., an application requiring relatively wide flat-plate louvers), extension of a sand-free region to a louver&#39;s inner edge spoils the desired countercurrenticity of contacting in the granular material lying beneath this region. 
     Yet flat-plate louvers have important advantages over louvers comprising outer and inner segments, the latter sloping upward at 45°: flat-plate louvers afford significantly lower pressure drops and lower costs for fabrication. 
     SUMMARY OF THE INVENTION 
     A primary object of the invention is to provide an improved method and apparatus for renewing gas-entry faces of a panel of granular material in which the members supporting the faces are inexpensive flat-plate louvers. 
     Another object is to provide an improved method and apparatus for bringing a gas and a granular material into intimate contact to effect physical or chemical treatment of at least one of them, wherein an application of the method or apparatus entails lowered costs and lesser pressure loss of the gas. 
     Another object is to achieve countercurrenticity in the contacting of a gas and a granular material at low cost and low gas pressure loss. 
     Another object is to provide an improved filter for removing fine particulate matter (“dust”) from a gas. 
     Another object is to provide an improved technique for periodically removing granular material adjacent to gas-entry faces of a panel-form gas-powder contactor. 
     The present invention relates to an improved method for renewal of a plurality of faces across which gas enters a panel of granular material for contacting the gas and the granular material with each other to effect physical or chemical treatment of at least one of them. The gas-entry faces are transversely disposed, upwardly spaced, and held in place by supporting members. The members are subjected to a sharp motion in a direction toward the gas-entry faces, this direction having a predominant horizontal component. The motion causes body movement of the granular material toward the faces, thereby causing moieties of granular material to fall away from the faces. Falling-away of the moieties and concomitant exposure of previously underlying granular material renews the faces. 
     Flat-plate louvers are preferred for usage as members supporting gas-entry faces. In one embodiment of the invention, the louvers are intermittently subjected to a sharp motion, thereby producing an intermittent body movement of the granular material toward the gas faces. This body movement and the flow of the gas in the opposite direction cause the contacting of the gas and granular material to be substantially countercurrent. 
     The present invention also relates to an improved apparatus for renewal of a plurality of gas-entry faces across which gas enters a panel of granular material for contacting the gas and the granular material with each other to effect physical or chemical treatment of at least one of them. The gas-entry faces are transversely disposed, upwardly spaced, and held in place by supporting members. Means are provided for subjecting the members to a sharp motion in a direction toward the gas-entry faces, this direction having a predominant horizontal component. The motion causes body movement of the granular material toward the faces, thereby, causing moieties of granular material to fall away from the faces. Falling-away of the moieties and concomitant exposure of previously underlying granular material renews the faces. Flat-plate louvers are preferred for usage as members supporting gas-entry faces. 
     The means for subjecting the members to sharp motions includes a pressure chamber and a cylinder within the chamber that travels vertically. A first stop limits the cylinder&#39;s upward motion at a point where the cylinder divides the chamber into upper and lower regions. A substantially vertical rod depends from the cylinder. A substantially horizontal plate is situated beneath the cylinder and is capable of traveling vertically. The rod passes through a central opening in the plate and has a larger diameter below the plate than above it. A second stop limits the plate&#39;s downward motion. An electromagnetic device is supplied with electric current and holds the plate at a point where it forms the bottom closure of the lower region of the pressure chamber. 
     A hammer head is connected to the bottom of the rod. Beneath the hammer head lays a target. A blow of the hammer head against the target is translated by linkage rods and hinges below the target into a sideways thrust. This sideways thrust is applied to pads situated at central points on the gas discharge side of panels of granular material containing gas-entry faces. This thrust produces a sharp motion in the supporting members towards the gas-entry faces. 
     Gas at elevated pressure flows from a source through orifice means into the lower region of the pressure chamber, then into the upper region of the pressure chamber, and from there to the exterior of the chamber. The orifice means create an elevated pressure in the lower region of the pressure chamber a different elevated pressure in the upper region. The elevated pressure in the lower region is sufficiently higher than the elevated pressure in the upper region so as to hold the cylinder against the first stop. 
     The invention has a means for interrupting the electric current to the electromagnetic device, allowing the pressurized gas in the lower region of the pressure chamber to drive the plate downwards against the second stop. The gas in the lower region then discharges suddenly to the exterior of the chamber, allowing the pressurized gas in the upper region of the chamber to drive the cylinder sharply downward. This causes the hammer head to strike the target, which limits the downward motion of the cylinder. 
     The invention also has a means for renewing the electric current to the electromagnetic device. When the electric current is restored, the electromagnetic device lifts the plate upward, closing off the lower region of the pressure chamber. The flow of gas at an elevated pressure then restores the pressure levels in the upper and lower regions of the pressure chamber to their original levels. When the pressures return to normal, the cylinder is again lifted against the first stop. 
     The apparatus of the instant invention is suitable for renewing gas-entry surfaces in a panel of the filter trays, disclosed in utility application Ser. No. 10/303,739, now matured as U.S. Pat. No. 7,033,556 (Apr. 25, 2006) which the instant application incorporates by reference. 
     These and further other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings, and U.S. Pat. No. 6,783,326 and application Ser. No. 10/303,739 incorporated in the instant application by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more particularly described in conjunction with the following drawings wherein: 
         FIG. 1  is a vertical section illustrating an arrangement for imparting a sharp lateral motion to gas-entry-face support members of a panel of granular material. 
         FIG. 2  is a horizontal section of the arrangement of  FIG. 1 . 
         FIG. 3  is a vertical section illustrating a portion of a preferred design of a panel of granular material for use in filtering a dusty gas. 
         FIG. 4  is a vertical section illustrating a portion of a preferred design of a panel of granular material for effecting countercurrent contacting of a gas and the material. 
       One diagram in  FIG. 5  illustrates a performance flaw revealed by tests of a panel of flat-plate louvers intended for use in a panel filtering a dusty gas, the panel equipped for puffback or hammer-blow renewal of gas-entry faces; alongside, a second diagram illustrates a bent louver answering this flaw. 
       One diagram in  FIG. 6  illustrates a performance flaw revealed by tests of a panel of flat-plate louvers intended for use in a panel effecting countercurrent contacting of a gas and the material, the panel equipped for puffback or hammer-blow renewal of gas-entry faces; alongside, a second diagram illustrates a bent louver answering this flaw. 
         FIG. 7  is a vertical section illustrating a panel of filter trays for which application of the arrangement of  FIG. 1  is suitable for purpose of gas-entry-face renewal. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the several figures, like reference numerals refer to like parts having like functions. 
     In  FIG. 1 , dashed lines provide a schematic representation (in vertical cross-section) of a tall, narrow granular material panel  1  presenting gas-entry faces at  2  and a porous gas-exit wall at  3 . Similar dashed lines are a schematic representation of a second tall, narrow granular material panel  4  presenting gas-entry faces at  5  and a porous gas-exit wall at  6 . Black arrows indicate flows of a gas entering the two panels and open arrows indicate gas flows leaving the panels. The latter flows enter a space  7  bounded vertically by the two panels. The space  7  is provided with a bottom closure  8 , a portion of which is pleated, facilitating lateral motion of the two panels  1 , 4 . 
     A beam  20  supports a pressure chamber  21 , which a cylinder  22  divides into upper and lower regions  23 ,  24 . The lower region  24  is bounded at the bottom by a plate  25  held in place by an electromagnet  26 . The cylinder  22  centrally supports an upper vertical rod  27 . The upper rod  27  passes through a central hole in the plate  25 . The upper rod  27  has a diameter slightly larger below the plate  25  than above it. The upper rod  27  carries at its bottom end a hammer head  28 . Gas at elevated pressure enters an inlet pipe  29  and flows through an orifice  30  into a delivery pipe  31 , which carries the gas into the lower region  24 . Gas enters the upper region  23  from the lower region  24  by flowing across the cylinder  22  through a conduit  33  via an orifice  34 . Gas leaves the upper region  23 , flowing to the outside of the chamber  21  through a conduit  35  via an orifice  36 . The orifices  30 ,  34 ,  36  are at sizes such that a difference between gas pressures in the lower region  24  and the upper region  23  is sufficient to maintain the cylinder  22  in position against stops  37 , while the pressure in the upper region  23  is significantly higher than a pressure outside of the chamber  21 . 
     In the described condition of the aforesaid equipment items in  FIG. 1 , they are “cocked” to deliver a blow of the hammer head  28  upon a target  38 . Such a blow drives a lower vertical rod  39  downward, and a linkage of its downward motion via linkage rods  40 ,  41 ,  42 ,  43  connected by hinges  44 ,  45 ,  46  delivers a sidewards thrust via pads  47 ,  48  upon the panels  1 ,  4 . The pads  47 ,  48  are located at central positions on the porous gas-exit walls  3 ,  6 . An upper frame  49  supports an upper vertical guide cylinder  50 , which maintains strict verticality of the downward motion of the upper rod  27 . The upper vertical guide cylinder  50  supports a lower frame  51 , which in turn supports a lower vertical guide cylinder  52  and horizontal guide cylinders  53 ,  54 . The lower vertical guide cylinder  52  maintains strict verticality of the downward motion of lower rod  39 , while horizontal guide cylinders  53 ,  54  ensure strict horizontality of the sidewards thrust that the linkage rods  42 ,  43  exert upon the pads  47 ,  48 . 
     Electric current reaches the electromagnet  26  via wires  55 ,  56 . A sequence of events causes the hammer head  28  to deliver a blow upon the target  38  when a switch control  57  opens an electricity switch  58 , interrupting the flow of electricity to the electromagnet  26 . Pressure in the lower region  24  drives the plate  25  downward against the stops  59 . The downward motion of the plate  25  has two effects: the motion forces the upper rod  27  downward and releases gas from the lower region  24  to the outside of the pressure chamber  21 . Lowering of the pressure in the lower region  24  creates a pressure difference between the upper region  23  and lower region  24 , the larger pressure present in the former region. This pressure difference increases the downward velocity of the cylinder  22 . A blow of the hammer head  28  upon the target  38  stops the downward motion of the cylinder  22 . Shortly after the blow is struck, the switch control  57  closes the electricity switch  58 , commencing a new flow of electricity to the electromagnet  26 , which lifts the plate  25  into its former position, closing the lower region  24 . The action of a spring  60  serves to restore the panels  1 ,  4  to their original positions. Gas flow from the inlet pipe  29  (never interrupted) gradually restores the earlier pressure levels in the upper and lower regions  23 ,  24 , and the equipment is “cocked” to deliver another hammer blow when operation of the panels  1 ,  4  requires it. 
       FIG. 2  depicts schematically the horizontal cross-section A-A in  FIG. 1 . Side-closures  9 ,  10 , like the bottom closure  8  seen in  FIG. 1 , have pleated portions facilitating lateral motion of the two panels  1 , 4 . 
       FIG. 3  is a schematic vertical cross-sectional drawing of a segment of a panel  101  employing supporting members in the form of flat-plate louvers  102 , the preferred form for practice of the invention. A sidewards thrust upon the panel  101 , such as the arrangement of  FIG. 1  is capable of creating, causes granular material in the panel  101  to move en masse toward the louvers  102 , thereby causing moieties of the material to fall away from gas-entry surfaces  103 , renewing the surfaces. The panel of  FIG. 3  is suitable for filtering a dusty gas, the filtration performance being assisted by an accumulation of filter cakes upon the gas-entry surfaces  103 . Granular material is supported on the panel&#39;s gas-exit side by closely-spaced horizontal louvers  104 . The vertical space between the neighboring horizontal louvers  104  can be a few times greater than substantially the smallest particle in the granular material. The space should be not greater than about one-sixth the width of one of the louvers  104 . 
     Note that an inner edge  105  of the gas-entry face  103  does not extend to the inner edge of a superjacent support louver. At the inner edge  105  location seen in  FIG. 3 , a downward motion of granular material in a space  106 , making good losses of material from the gas-entry surfaces  103  following a sidewards thrust upon the louvers  102 , does not pull away material from gas-entry surfaces near the top of a tall panel, causing such pulled-away material to enter the space  106 . 
     The space  106  communicates with an overhead supply of granular material in a manner to be seen by consulting U.S. Pat. No. 6,783,326, incorporated in the instant application by reference. 
       FIG. 4  is a schematic vertical cross-sectional drawing of a segment of a panel  201  employing supporting members in the form of flat-plate louvers  202 . The panel of  FIG. 4  is suitable for achieving countercurrent contacting of a gas and a granular material, through periodic action of a sidewards thrust upon the panel  201  causing body movement of the material toward gas-entry faces  203 . Granular material is supported on the panel&#39;s gas-exit side by closely-spaced horizontal louvers  204 . 
     The left-hand drawing in  FIG. 5  is a fragmentary vertical cross-section of flat-plate louvers  302 , similar to the louvers  102  seen in  FIG. 3 . The drawing illustrates a flaw in the performance of a panel employing flat-plate louvers when either puffback or a vertical hammer blow is employed for renewal of gas-entry faces  303 . A face is seen to extend all the way to a rear edge  304  of a superjacent louver  302 , so creating an empty space, narrow in the vertical direction, between the face and the superjacent louver  302 . The presence of such a narrow space is undesirable in a tall panel for filtration of a dusty gas, because of the danger that the downward motion of granular material inner from the rear edge  304  will pull material away from faces near the top of the panel. The right-hand drawing in  FIG. 5  illustrates a louver design  313  adopted to avoid this danger; both puffback and a vertical hammer blow are effective in renewing gas-entry faces of a panel using this type of louvers. The design  313 , however, is disadvantageous in two respects in a comparison with a flat-plate louver design. First, it costs more, both because it requires more metal and because it requires an extra step in fabrication, a step producing the bend seen in the drawing. Second, there is a greater loss in pressure in a gas flowing across the panel. 
     The left-hand drawing in  FIG. 6  is a fragmentary vertical cross-section of flat-plate louvers  402 , similar to the louvers  202  seen in  FIG. 4 . The drawing illustrates a flaw in the performance of a panel employing the louvers  402  when either puffback or a vertical hammer blow is employed for renewal of gas-entry faces  403 . A face is seen to extend all the way to rear edge  404  of a superjacent louver  402 , so creating an empty space, narrow in the vertical direction, between the face and the superjacent louver  402 . The presence of this space, of course, prevents the use of the flat-plate louvers  402  in a panel intended to provide countercurrenticity of contacting of gas and granular material. The right-hand drawing in  FIG. 6  illustrates a louver design  413  adopted to afford countercurrenticity. The design  413  is appropriate for either puffback or hammer-blow renewal of gas-entry faces. It suffers the same two disadvantages in respect to flat-plate louvers as those cited in the discussion of  FIG. 5 . 
       FIG. 7  is a schematic vertical cross-sectional drawing of a segment of a panel  501 , suitable for filtering a dusty gas. In the panel  501 , gas-entry-face supporting members  502  are porous and are inclined at an angle to the horizontal approaching the angle of repose of the supported granular material but shallower than this angle. A supported gas-entry face  503  is substantially parallel to a supporting member  502 . Advantageously, a supporting member comprises an array of closely-spaced parallel plates, as the drawing illustrates. Distance across the granular bed  504 , in a direction perpendicular to the supporting member  502 , is substantially constant. 
     Gas entering the gas-entry face  503  flows downward in a direction substantially perpendicular to the supporting member  502 , leaving the bed  504  across the member. A plate  505 , lying between the supporting member  502  and the subjacent gas-entry face  503 , directs gas in a direction toward the upper end of the member  502 . The arrangement of  FIG. 1  is appropriately employed for imparting a sharp motion of the support member  502  toward the gas-entry face  503 , the motion having a dominant horizontal component. The sharp motion produces spills of granular material from the face  503 . 
     A row of segmented, vertical pipes  506 , extending in a direction perpendicular to the drawing of  FIG. 7 , supplies fresh granular material to the bed  504 , making good losses of the material from the bed. Gas directed by the plate  505  is free to flow laterally across openings between neighboring pipes, as the open arrow seen at the right in the  FIG. 7  drawing indicates. The general arrangement depicted in  FIG. 7  is the filter tray disclosed in U.S. Pat. No. 7,033,556, which the instant application incorporates by reference. 
     While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.