Abstract:
A conveyor for moving hot or cold material along a trough receiving the material. One or more heat transfer fluid flow tubes extend over the outer surface of a trough liner wall to indirectly cause cooling or heating of the liner wall. Fins or angled thin metal strips conductively interconnect the tube or tubes and the liner wall. A series of wear plates are clamped to a pushing side of a helical tube of an auger type conveyor, which tube can also receive a flow of heat transfer fluid. A mass of conductive beads can alternatively be used to transfer heat into or from the heat transfer fluid.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention concerns conveyors and more particularly, conveyors such as auger or recirculating chain flight conveyor used to convey hot (or cold) crushed or granular material, such as in cement plants, lime kilns, coal clinkers from power plants, etc. Conveyors for such hot materials have in the past had short service lives and were prone to failure. This is because of the effect of the high temperatures reached by the conveyor parts as a result of conduction of heat from the conveyed material. Such conveyors have sometimes incorporated liquid cooling jackets within a conveyor trough along which the hot material is conveyed by an auger extending along the length of the trough. The trough and jacket have been constructed as a weldment, and since the cooled liner is in direct contact with the hot material conveyed, the trough is severely stressed by gross thermal expansions and contractions.  
           [0002]    The resulting expansion and contraction of the trough and coolant jacket leads to cracking, buckling, weld failures and similar structural failures. Since very hot material is conveyed, liquid in direct contact with the cooling jacket wall is heated to boiling, so that vapor is generated in the jacket, greatly reducing the rate of heat transfer into the cooling liquid.  
           [0003]    Since the trough cooling jacket is constructed as a weldment, it often is not designed or approved for use as a pressure vessel, allowing only very low coolant pressures and flow rates.  
           [0004]    Similarly, conveying augers have also often been constructed as a weldment, with a central tube having radial spokes welded to a central tube forming a triangular cavity. Liquid coolant has sometimes been circulated through such a screw, with direct contact of the coolant in the metal screw in direct contact with the hot material conveyed, leading to the same problems described above in connection with the conveyor trough.  
           [0005]    Direct air cooling of the hot material requires dust collection equipment and baghouses and necessitates government permits, as pollutants may be mixed with the exhausted cooling air.  
           [0006]    Similar problems exist where a cool material is to be heated to elevated temperatures during the passage through the conveyor.  
           [0007]    It is an object of the present invention to provide a liquid cooled conveyor for hot material of the type described, in which direct contact of coolant with the structure defining a confinement of the hot material is avoided.  
           [0008]    It is a further object to provide a conveyor which avoids the use of a weldment structure subjected to thermal stresses induced by a large temperature differential between the conveyor and the material conveyed, and uses material that are capable of withstanding such thermal stresses.  
           [0009]    Yet another object is to provide a conveyor having heat exchange fluid passages which can withstand high pressures, and pass a high velocity flow of a heat transfer liquid to improve the heat conduction capacity of the unit.  
         SUMMARY OF THE INVENTION  
         [0010]    The above objects as well as other objects which will be understood upon a reading of the following specification and claims are achieved by a conveyor including a trough, with separate heat transfer fluid flow pressure vessels passing over an outside trough surface. The fluid flow vessels may be supported on an outer structural trough wall by heat conducting connections such as interposed heat fins, angled metal strips and curved thin metal standoffs, or conductive beads (aluminum or other) metal filling the air space. Optionally, air flow can be established over the fluid flow vessels, fins or beads to enhance the cooling (or heating) effect.  
           [0011]    Alternatively, noncontact cooling methods are employed including cooling fins attached to the trough, interposed metal beads, or high temperature heat conducting mediums.  
           [0012]    The heat transfer fluid flow vessels can be arranged in longitudinal or transverse loops or longitudinally extending straight sections can also be used, supplied with a heat transfer liquid from a manifold at one end of the conveyor trough.  
           [0013]    A helical auger tube used in an auger conveyor is constructed with mechanical connections to radial spokes to avoid thermally stressed welds. A side-to-side series of clamp-on wear plates of a durable material can be installed on the pushing side of the helical auger tube to prevent excessive wearing of the auger tube. Optionally, a heat transfer fluid can also be circulated through the helical auger tube, or a second tube can be inserted in a larger outer helical tube with fins or beads, conducting the heat between the outer tube and the heat transfer fluid in the inner tube. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a perspective view of an auger conveyor according to the present invention showing a portion of a helical tube auger included in the conveyor in broken lines.  
         [0015]    [0015]FIG. 2 is an enlarged partially broken away end view of the conveyor shown in FIG. 1.  
         [0016]    [0016]FIG. 3 is an end view of the conveyor of FIG. 1, with the trough outer wall partially broken away and showing further details of a coolant flow tubing installation for the trough.  
         [0017]    [0017]FIG. 4 is an end view of the conveyor with the outer wall broken away showing another form of coolant flow tubing installation for the trough.  
         [0018]    [0018]FIG. 5 is a perspective partially fragmentary view of another embodiment of the conveyor according to the present invention.  
         [0019]    [0019]FIG. 6 is an enlarged fragmentary perspective view of one end of the conveyor shown in FIG. 5 with the outer wall of the trough partially broken away.  
         [0020]    [0020]FIG. 7 is an enlarged perspective view of the end of the conveyor shown in FIG. 5 with both walls of the trough partially broken away to show the helical tube auger.  
         [0021]    [0021]FIG. 8 is a fragmentary perspective view of the helical tube auger shown in FIG. 7 with a single wear plate shown in solid lines and a phantom line depiction of the entire series of wear plates.  
         [0022]    [0022]FIG. 9 is an enlarged transverse section taken across the helical tube auger and clamp on pusher blade of the type shown in FIG. 7.  
         [0023]    [0023]FIG. 10 is an enlarged transverse sectional view across a square section form of the helical tube auger.  
         [0024]    [0024]FIG. 11 is an enlarged transverse sectional view of a trough coolant tube of the type shown in FIG. 7.  
         [0025]    [0025]FIG. 12 is a sectional view of an inner round tube nested within a round outer tube using an interposed mass of beads as the heat transfer medium.  
         [0026]    [0026]FIG. 13 shows an outer square tube having an inner tube carrying a heat transfer fluid, and with a mass of heat conductive beads interposed.  
         [0027]    [0027]FIG. 14 shows a double walled conveyor trough having a mass of interposed beads as a heat transfer medium.  
         [0028]    [0028]FIG. 15 is a diagram showing the relationship between thermal conductivity and the void space defined within a mass of heat conductive beads. 
     
    
     DETAILED DESCRIPTION  
       [0029]    In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims.  
         [0030]    Referring to the drawings and particularly FIG. 1, a conveyor  10  is shown which includes an inclined trough  12  provided with optional covers  14  installed except at a loading opening  16 .  
         [0031]    The trough  12  is supported to be upwardly inclined by means of frame supports  18 ,  20  at either end.  
         [0032]    A discharge chute  22  is at the upper end. A helically wound auger tube  24  is disposed lengthwise in the trough  14  and rotated by a rotary drive  26 . A heat transfer liquid is typically introduced at the discharge end through an axial inlet  32  and through a side inlet  34 , and exits outlets  28 ,  30  at the lower end of the conveyor  10 .  
         [0033]    A source  34 A,  32 A of heat exchange fluid such as a liquid coolant is respectively connected with each inlet  34 ,  32  and a coolant recycler (such as cooling towers) may be connected with each outlet  28 ,  30 .  
         [0034]    [0034]FIG. 2 shows further details. U-shaped loops of fluid flow tubing  36  are located between an inner trough wall  38  and an outer wall  40 . The inner wall  38  is made of heavy gauge metal to provide adequate structural support and durability as the conveyed material is in direct contact therewith and its weight supported thereby. The outer covering wall  40  can be of light gauge sheet metal or even mesh material as indicated.  
         [0035]    The flow tubing  36  is supported by transverse fins  42  contacting the tubing  36 , the outside of the inner wall  38  and the outer wall  40 . Thus, fluid does not directly contact the hottest surfaces, but rather there is an indirect heat conducting connection.  
         [0036]    The fins  42  may extend longitudinally so that an air flow can optionally be blown through the interwall space and over the fins  42 , from an air source  39 .  
         [0037]    Heat transfer fluid may also be circulated through the helical auger tube  24  introduced via a rotary fluid coupling  44  into a central support tube  46  rotated by the rotary drive  26  and supported by a rotary bearing  48  (FIG. 1).  
         [0038]    Fluid is directed into the helical tube  24  via a radial support tube  50  mechanically attached to the support/drive tube  46 . The support tube  46  is blocked so as to avoid circulation through the support tube  46 . Outlet flow is directed out into a support tube  46  at the lower of the conveyor.  
         [0039]    [0039]FIG. 3 shows another view of the trough fluid tubes showing the U-shaped loops and inlet, the loops extending transversely to the axis of rotation of the tube  24 , i.e., in circumferential directions, although occupying only a portion of the perimeter of the trough  12 .  
         [0040]    [0040]FIG. 4 shows a variation in which the fluid tube loops  36 A are arranged longitudinally, and the fins  42 A are oriented transversely.  
         [0041]    [0041]FIG. 5 shows another form of the conveyor  52  in which an inlet manifold  58  is connected to an inlet  60  at the upper end and an outlet manifold  54  is connected to an outlet  56 . A series of straight longitudinal flow tubes  62  (best seen in FIG. 6) extend the length of the trough  64  in the space between a inner wall  66  and outer wall  68 .  
         [0042]    As shown in FIG. 7, the tubes  62  are supported on the liner wall  66  by thin metal straight strips  70  and curved thin metal stand offs  72  (FIG. 11).  
         [0043]    Thus, the fluid does not directly contact the hottest surfaces, i.e., the trough liner wall  66 , but rather has an indirect heat conductive connection thereto. This prevents a loss of conductivity which would result from boiling of the cooling fluid.  
         [0044]    In order to reduce abrasion wear of the auger tube  74 , a series of wear plates  76  are clamped on the pushing side of the tube  74 , edge to edge along the length of the helical tube  74  (FIG. 8).  
         [0045]    The hot granular material  80  being conveyed could otherwise rapidly wear the tube  74  depending on the material characteristics, temperature, as well as the volume conveyed.  
         [0046]    [0046]FIG. 9 shows details of the attachment clamps for the wear plates  76  which are preferably constructed of a material such as an Nichrome alloy which is wear resistant at elevated temperatures.  
         [0047]    A U-bolt  82  passes through a clamping piece  84  and is secured by nuts  86 .  
         [0048]    A pair of opposing legs  88 ,  90  on the wear plate  76  and clamping piece  84  have cut outs mating with the auger tube  74 .  
         [0049]    [0049]FIG. 10 shows a square section tube  74 A, such that a flat wear plate  76 A and clamping piece  84 A can be secured with the U-bolt  82 A and nuts  86 .  
         [0050]    Both forms of wear plates  76  and  76 A can have an angled portion  94  to assist in effectively pushing the material by rotation of the auger tube  74  or  74 A. The clamp-on design avoids the problem of weld failure resulting from the high temperature experienced by the tube  74 .  
         [0051]    FIGS.  12 - 15  concern the use of an interposed mass of beads rather the fins to create a proper heat transfer path to a fluid coolant tube so as to not boil the fluid by a too rapid transfer of heat thereinto. In FIG. 12, a round tube  88  (used for auger tube  24 ) receives a smaller inner coolant circulating tube  90 . An intermediate space is filled with a mass  92  of heat conducting beads to establish a heat transfer path which can be controlled by controlling the proportion of void space, in turn varying with the bead size. The material would be selected depending on the selected design parameters, but would typically be a durable conductive material such as aluminum. The bead size would likewise be set to achieve the desired coefficient of thermal conductivity.  
         [0052]    A series of centering webs  94  should be provided to maintain the tubes centered with respect to each other while being loaded with the beads.  
         [0053]    [0053]FIG. 13 allows a round inner tube  96  and square outer tube  98  and centering webs  100 .  
         [0054]    [0054]FIG. 14 shows a portion of a trough inner wall  102  and outer wall  104  with an intervening space filled with a mass of beads  106 . Spacer webs  106  are also provided. This is intended to produce a controlled coefficient of thermal conductivity which does not cause boiling of the coolant and prevents the resultant loss of heat conductivity into the coolant.  
         [0055]    [0055]FIG. 15 shows the relationship between the proportion of void space and thermal conductivity.  
         [0056]    Loosely packed spherical particles will properly conduct the heat while still allowing relative movement without causing excessive stresses. Other shaped particles could be selected that serve the same basic purpose of controlling thermal conductivity.  
         [0057]    The proper selection of the spherical shaped particles involves diameter, material, and relative pipe sizes. If the space were filled with particles that would approximate air, the thermal conductivity would be very low. However, if the space were filled with very small particles, approaching a solid, the thermal conductivity would be high, approaching that of the solid. Somewhere between these two extremes is a void ratio that would be in line with the desired heat transfer characteristics. By properly selecting the pipe sizes, particle sizes and material and the overall geometry of the thermal screw, a desired design should be achieved.  
         [0058]    It should be noted that with proper design of connections, forces due to dimensional changes from thermal effects, as well as thermal stresses cause by thermal gradients within structural members should be effectively controlled.