BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:
FIG. 1 is a plan view of the board dryer of the present invention.
FIG. 2 is an elevational view showing the multi-deck dryer of the present invention.
FIG. 3 is a graph illustrating the relative cooling of the exposed and unexposed edges of transported boards using drying devices of the prior art.
FIG. 4 is a plan view of the delivery plenum and primary and bypass ducts of the drying apparatus of the present invention.
FIG. 5 is an elevational view taken the long line 5-5 of FIG. 4.
FIG. 6 is a detailed view of one of the edge cooling boxes of the present invention.
FIG. 7 is a perspective view of typical nozzle boxes distributing air over the board.
FIG. 8 is an alternative embodiment of the drying apparatus of the present invention.
FIG. 9 is a side elevational view of an alternative embodiment of the drying apparatus of the present invention.
Similar reference characters refer to similar parts throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention relates to an improved board drying apparatus and method. The invention involves delivering channels of warm air over the surface of a number of boards in a dryer. High temperature air in the outermost air channels can be partially displaced by cooler, unreheated air. The cooler air in these outermost channels is then directed to the areas of the boards most susceptible to overdrying. The various aspects of the present invention, and the manner in which they interrelate, will be described in greater detail hereinafter.
One of the objectives of the present invention is to prevent overdrying, thermal damage and discoloration to boards as they are being dried. In prior art dryers, such as gypsum board dryers, wet boards are transported through a dryer wherein warm air is delivered from a plenum and distribution nozzle boxes over the boards. This air is directed over top and/or bottom of the boards as they are being transported via a series of conveyors. These conveyors can be stacked on top of one another, six, eight, or more conveyors high, to maximize the residence time and evaporative capacity for the product traveling through the dryer (note FIG. 2). Additional drying capacity is achieved by orienting the boards upon the conveyor in a side-by-side relationship. For example, two, three or four boards can be arranged next to one another on the conveyor in an array. An example of a three board array is illustrated in FIG. 1. As illustrated, the respective longitudinal edges of the boards are parallel to one another. The two outermost boards each have one exposed longitudinal edge, while the innermost board, or boards, of the array has two unexposed edges.
While this arrangement has the advantage of increasing the number of boards being transported through the dryer, it has an undesirable thermodynamic effect. Namely, the air flowing over the innermost boards of the array contacts more board surface area than the air flowing over the outermost boards of the array. Because wet boards act as a heat sink, the air flowing over the innermost boards cools more rapidly. This thermodynamic phenomenon has the most effect upon the longitudinal edges of the boards. Thus, the exposed edges of the outermost boards of the array are least affected by the heat sink and the unexposed edges of the innermost boards are most affected. As a result, air flowing over the outermost exposed edges retains its heat over a greater distance which can result in overdrying. This drawback of prior art dryers is shown in the graph of FIG. 3. Namely, as air is delivered out of the plenum, the air impinging the inside edges of the boards cools more quickly than the air impinging upon the outside edges. Again, the result is an overdrying of the outside edges.
With reference now to FIG. 1, a plan view of the drying apparatus 20 of the present invention is depicted. The apparatus depicted is a gypsum board dryer. The invention, however, is applicable to any convection-dried product, including but not limited to wood fiber, perlite, composite, and mineral wool boards. In this figure, a number of boards 22, which in this example are positioned in a three board array, are being transported from a first location 24 to a second location 26 along a first direction of travel 28. FIG. 1 depicts just a single dryer or dryer zone 20. However, dryer 20 could be one in a number of sequentially arranged dryers. Plenums are located at the first and second locations (24 and 26) and mark the beginning and end of a drying zone. The first plenum is a return plenum 32 for collecting air to be used in drying boards 22. The second plenum is a delivery plenum 34 for routing high temperature air over boards 22. In the preferred embodiment, the air is delivered over boards 22 in channels that flow in a direction 35 that is opposite to the direction 28 of board travel. The principle described herein applies similarly well in dryer zones where the air flow is in the same direction as the product. Indeed, it is customary in most dryer zones to use parallel flow. As described more fully hereinafter in conjunction with FIG. 4, both a primary and a bypass duct (36 and 38) are used to interconnect two plenums 32 and 34. Although the depicted example is a three board array, the present invention can just as easily be a two, four or five board array. The use of even larger arrays is also within the scope of the invention, as is the use of a single board array, typically used in fiberboard and mineral wool dryers. Whatever the size of the array, the exposed edges 44 of the outermost boards 46 will be most susceptible to overdrying and thermal damage and the unexposed edges 48 of the innermost boards 52 are least susceptible.
In addition to positioning boards 22 in an array, board throughput can be increased further still by positioning the conveyors in a stack 54. FIG. 2 is an illustration of the multi-deck arrangement of the dryer of the present invention. Namely, a series of six conveyors are stacked one on top of another to increase the number of boards passing through dryer 20 at any given time. Although a six conveyor stack 54 is depicted, higher stacks can also be used. Delivery plenum 34 is used to supply an airflow over each of these conveyors.
The potential for overdrying exposed edges 44 in the array is eliminated via the use of primary and bypass ducts (36 and 38) as illustrated in FIG. 4. FIG. 4 is a plan view illustrating the primary and bypass ducts (36 and 38) that are used to interconnect the delivery and return plenums. The ducts and plenums are preferably located above the conveyor stack 54. As explained more fully hereinafter in conjunction with FIG. 5, a series of nozzle boxes 56 are used to redirect the air flow from above conveyor stack 54 to a direction over each of the individual conveyors. Air is gathered by the return plenum 32 and delivered to a heater or burner 68 via primary duct 36. One or more circulation booster fans 58 positioned within primary duct 36 help transport the heated air to delivery plenum 34. Delivery plenum 34 includes a series of vanes 62 that define a number of air channels. These air channels are both physically separate and may be thermally isolated. In the preferred embodiment, and again as depicted in FIG. 4, vanes 62 define three internal channels 64 and two external channels 66. Other channel arrangements can also be employed. The primary duct 36 delivers heated air into all of these channels.
Bypass duct 38 is employed to deliver a volume of cooler, unheated or cooler, unreheated air to external channels 66 of plenum 34. With continuing reference to FIG. 4, bypass duct 38 takes air from the return plenum 32 and delivers it directly to two edge cooling boxes 72. Bypass duct 38 is physically separate from primary duct 36 and is not exposed to burner 68 or any other heating element. Thus, the air delivered by bypass duct 38 is unreheated and therefore cooler than the air delivered by primary duct 36.
Each of the cooling boxes 72 functions to deliver unreheated air into external channels 66 of delivery plenum 34. FIG. 6 is a detailed view of one cooling box 72. As illustrated, the box includes a series of slots or vents 74 upon an outer face as well as an intake aperture 76 at its upper end. Air from bypass duct 38 is delivered into inlet 76 and is delivered to external channels 66 via slots 74. To achieve this, apertures 78 are formed through the wall of delivery plenum 34 to allow for the delivery of air from slots 74 of cooling box 72 to exterior channels 66. Slots 74 of cooling box 72 are thus in fluid communication with external channels 66 of delivery plenum 34. The area beyond slots 74 and within the external channels 66 is a blending point 82 where the warmer air from the primary duct 36 blends with the unreheated air from bypass duct 38. Each cooling box 72 further includes a temperature regulation mechanism. This mechanism takes the form of a temperature controller 84 and an associated damper 86. The mechanism controls the volume of unheated air leaving its respective cooling box 72. This, in turn, allows an operator to selectively control the amount of unreheated air that is ultimately delivered into the exterior channels 66. By regulating the temperature control mechanism, a user can make the temperature within the external channels 66 lower than the temperature of the air within the internal channels 64. Conversely if desired, the temperature control mechanism can be adjusted so that no unreheated air is delivered to the external channels 66, whereby the air in all of the channels (64 and 66) of delivery plenum 34 will be uniform.
The invention, therefore, provides a widely variable temperature control at the edges as needed by the specific dryer application. Any air temperature between the delivery plenum temperature and return plenum temperature can, therefore, be supplied to the outermost edges of the board. The apparatus is well suited not only for protecting the outer edges of board product during standard operation, but also in circumstance where the width of the boards passing through the dryer create more “outboard” space outside the outermost edges.
Air from delivery plenum 34 is then routed to a series of nozzle boxes 56. This routing is done with vanes to keep the air flowing in the respective channels (64 and 66). The arrangement of nozzle boxes 56 relative to the conveyors is illustrated with reference to FIG. 5. As depicted, nozzle boxes 56 are located at the second location 26 beneath delivery plenum 34 at positions both above and below each conveyor of the heater. For parallel flow dryer zones, the nozzles are located at the first plenum. As illustrated in FIG. 7, each nozzle box 56 includes vanes 88 that correspond to vanes 62 in delivery plenum 34 to maintain the integrity of the respective air channels. Thus, the heated air of internal channels 64 remains physically and thermally isolated from the cooler air of external channels 66. FIG. 5 illustrates the position of the nozzle boxes 56 and shows how the exiting air is delivered over boards 22 in a direction 35 that is, in this case, opposite to the direction of travel 28. By way of the drying apparatus 20 of the present invention, the cooler air from external channels 66 is delivered to the exposed edges 44 of the gypsum (or other) board while the warmer air from internal channels 64 is delivered to the unexposed edges 48 of the gypsum board. In this manner, the warmer air channel is delivered to the areas with the greatest heat sink and cooler air is delivered to the areas with less of a heat sink. Overdrying of the external edges is thus avoided.
FIGS. 8 and 9 illustrate an alternative drying apparatus 90. In most respects this apparatus is the same as the apparatus 20 of the primary embodiment depicted in FIGS. 1-7. However, the alternative embodiment 90 eliminates the need for separate cooling boxes 72. Air control dampers 92 are used to combine heated and unheated airstreams (94 and 96) at a blending point 98 that is upstream of delivery plenum 34. After the air is blended, a booster fan 102 is used to transport the air to external channels 66 via bypass duct 38. A primary duct 36 is still employed to transport warmed heated air to both the internal and external channels (64 and 66) of delivery plenum 34. This embodiment is the same in all other respects to the primary embodiment. Namely, the cooler air from external channels 66 is delivered via nozzle boxes 56 to the peripheral areas of the boards 22. However, in the alternative embodiment, the blending point is not located in delivery plenum 34.
Now that the invention has been described,
Patent Application
20080086905
