Patent Publication Number: US-9835375-B2

Title: Hybrid continuous flow grain dryer

Description:
FIELD 
     The present disclosure relates to continuous flow grain dryers. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     Continuous flow grain dryers, such as those shown in U.S. Pat. Nos. 4,404,756, 4,268,971, and 5,467,535, which are incorporated herein by reference in their entirety, generally include two continuously moving columns of grain. One type of continuous flow grain dryer is known in the industry as a “mixed flow” grain dryer. Such grain dryers are commercially available from companies such as Cimbria, NECO, and Grain Handler USA. Other types of continuous flow grain dryers are also available. Each type of grain dryer has its own advantages and disadvantages. 
     For example, in most types of continuous flow grain dryers air discharged from a fan typically next passes through a burner and then through a grain column only once before being discharged or returned to the blower for recirculation. Recirculated air from volatile grains presents a risk of fire, since it typically needs to pass through the heater during the recirculation process where fines can be ignited. Such single pass airflow through the grain column, and such limitations on the ability to recirculate the air limits the efficiency of the grain drying operation. 
     One way to attempt to increase efficiency is to cause the heated air to pass through the grain column multiple times. Sometimes this can create challenges for dealing with grain fines within the grain column. For example, some continuous flow grain dryer types might tend to cause the fines to move to a particular position in the grain column (e.g., the edges). Some continuous flow grain dryer types might also recirculate the heated air into grain when the grain has not yet been sufficiently heated to minimize condensation on the grain kernel, which can cause fines to clump, or to stick to the grain dryer walls or diverters. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In one aspect of the disclosure a hybrid continuous flow grain dryer includes a pair of grain flow paths through which the grain flows downwardly under the influence of gravity in a grain column. Each grain flow path is defined by a pair of longitudinally extending side walls and a pair of transversely extending end walls. Each grain flow path has an upper portion including a plurality of upper elongated grain diverters extending transversely across the grain flow path between opposing inner faces of the pair of longitudinally extending side walls. The upper portion also includes an upper opening in the side walls associated with each upper grain diverter. Each grain flow path also has a lower portion including a plurality of lower elongated grain diverters extending longitudinally along alternating sides of the grain flow path between opposing inner faces of the pair of end walls. The lower portion also includes a longitudinally extending lower opening in the side walls associated with each lower grain diverter. 
     In another aspect of the disclosure a hybrid continuous flow grain dryer includes a pair of grain flow paths through which the grain flows downwardly under the influence of gravity in a grain column. Each grain flow path is defined by a pair of longitudinally extending side walls and a pair of transversely extending end walls. Each grain flow path has an upper portion including a plurality of upper elongated grain diverters extending transversely across the grain flow path between opposing inner faces of the pair of longitudinally extending side walls. The upper portion also includes an upper opening in the side walls associated with each upper grain diverter. Each grain flow path also has a lower portion including a plurality of lower elongated grain diverters extending longitudinally along alternating sides of the grain flow path between opposing inner faces of the pair of end walls. The lower portion also includes a longitudinally extending lower opening in the side walls associated with each lower grain diverter. In this aspect the upper elongated grain diverters are aligned substantially perpendicular in plan view to the longitudinally extending side walls, and the lower elongated grain diverters are aligned substantially parallel in plan view to the longitudinally extending side walls. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of one exemplary embodiment and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a perspective view of one exemplary grain dryer in accordance with the present disclosure; 
         FIG. 2  is a simplified cross-sectional view showing the grain flow paths and certain airflow paths within the exemplary grain dryer of  FIG. 1 ; 
         FIG. 3  is an internal view of one of the sub-plenums and showing the elongated airflow openings defined by the panels of the exemplary grain dryer of  FIG. 1 ; 
         FIG. 4  illustrates a loop paddle conveyor which can be used to feed grain into the top of the grain flow paths in exemplary grain dryer of  FIG. 1 ; 
         FIG. 5  illustrates a jump drag conveyor by which the output from each metering paddle conveyor can be joined to a single grain output in the exemplary grain dryer of  FIG. 1 ; 
         FIG. 6  is a simplified perspective view illustrating various airflow paths of the exemplary grain dryer of  FIG. 1 ; 
         FIG. 7  is a perspective view showing an outer shroud of the fan of the exemplary grain dryer of  FIG. 1 ; and 
         FIG. 8  is a partial perspective view illustrating the alignment of the upper diverters relative to the lower diverters (substantially perpendicular to each other) and relative to the longitudinal side walls and transverse end walls; and 
         FIG. 9  is a perspective view showing the airflow into, thru, and out of the grain column in an upper portion of the grain flow path. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Referring to  FIGS. 1 through 9 , an exemplary embodiment of a continuous flow grain dryer  10  of the present disclosure can generally include an induced draft burner  12  ( FIG. 6 ), and a double wide, double inlet centrifugal fan  14  ( FIG. 6 ) providing double pass airflow through a plurality of grain columns within grain flow paths  16  ( FIG. 2 ). 
     The illustrated embodiment includes four adjacent grain flow paths  16  that define four grain columns in use. In this exemplary embodiment, the adjacent grain flow paths  16  are longitudinally extending and therefore are completely separate from each other. Each grain flow path  16  is defined by a pair of longitudinally extending side walls  95  and a pair of end walls  94 . Adjacent grain flow paths  16 , however, can also exist in a circular grain dryer wherein opposing portions of a circular grain column can be considered to form adjacent grain flow paths  16 . 
     An upper portion of each grain flow path  16  includes a plurality of upper elongated grain diverters  88  extending transversely across the grain flow path  16 . These upper transverse grain diverters  88  can extend substantially perpendicular to the side walls  95  in a side (or elevation) view, or in a top (or plan) view, or in both side and plan views. These upper grain diverters  88  can have a generally inverted “V” or “U” shaped configuration and can be coupled to opposing side walls  95  at their opposing ends. 
     These upper transverse grain diverters  88  can be arranged in a plurality of substantially horizontal rows. The transverse diverters  88  of each horizontal row can be offset from each other by fifty percent. In other words, the transverse diverters  88  in alternating horizontal rows can be vertically aligned and the transverse diverters  88  of adjacent horizontal rows can be aligned along a plane that is angled to a horizontal plane as seen in  FIGS. 8 and 9 . 
     A generally triangular opening  89  in a side wall  95  can be associated with one end of each of the transverse diverters  88 . Specifically, the grain diverters  88  in one horizontal row can be coupled to a side wall  95  to surround the upper portion of a triangular opening  89  in the side wall  95  defining a grain flow path  16 . The upper transverse grain diverters  88  in adjacent horizontal rows can be coupled to the opposite side wall  95  defining the same grain flow path  16  to surround the upper portion of a triangular opening  89  in the opposite side wall  95 . 
     Such a configuration can create an airflow path through a grain column in the grain flow path  16  as illustrated in  FIG. 9 . It should be appreciated from  FIG. 9  that the air flows into the grain column through an inlet opening  89  in one side wall  95  at one transverse diverter  88  as indicated by arrow  47  and then can exit through an outlet opening  89  in the opposite side wall  95  associated with or at a different diverter  88  as indicated by arrow  49 . In addition, the inlet openings  89  can be provided at first alternating horizontal rows of transverse diverters  88   a , while the exit openings  89  can be provided at second alternating rows of the transverse diverters  88   b  interspersed therebetween. Although  FIG. 9  has been simplified to show only three rows of diverters, six or seven, or a different plurality of rows of diverters  88  and openings  89  can be provided. 
     Not only can this upper portion  17  of the grain flow paths  16  have the transverse diverters  88 , but the upper portion  17  can also have a relatively large cross-sectional area relative to the lower portion  19  (detailed hereinafter) of the grain flow paths  16 . This additional cross-sectional area can be provided by providing a larger transverse distance between the opposing side walls  95  defining each grain flow path  16  in the upper portion  17 , than in the lower portion  19 . This can enable a larger volume of grain to be resident in the upper portion  17  of the grain column  16  than in the lower portion  19 . The relatively larger cross sectional area of width can also enable a larger residence time per vertical foot of movement for the grain in the upper portion  17  of the grain column  16  than in the lower portion  19 . 
     In the lower portion  19  of each grain flow path  16  each of the grain columns can result from an undulating grain flow path  16 . The grain flow path  16  is defined by opposing sets of a plurality of longitudinally extending panels  18 . The longitudinally extending panels  18  have a lower portion that is angled transversely downwardly and toward the center of the grain flow path  16  to provide lower elongated grain diverters  98 , which act as moisture equalizers. 
     The lower grain diverters  98  extend longitudinally along alternating sides of the grain flow path  16  or grain column between the opposing pair of end walls that define the grain flow path  16 . The lower grain diverters  18  can extend longitudinally in a direction substantially parallel to the side walls  95  in a top (or plan) view. Thus, the lower grain diverters  18  can extend longitudinally in a direction that is substantially perpendicular to the longitudinal direction of the upper grain diverters  88  in top (or plan) view, or in side (or elevation) view, or in both side and plan views. 
     As should be apparent from the above description, the upper grain diverters  88  can tend to distribute grain fines along transverse lines extending the width of the upper portion  17  of the grain column, or substantially perpendicular to the side walls  95 . In contrast, the lower grain diverters  98  can tend to distribute grain fines along longitudinal lines substantially parallel to the side walls  95 . As a result, the grain fines can remain more evenly distributed throughout the grain column as the grain flows from the top of the grain flow path  16  to its bottom. 
     The angled panels  18  of each opposing side wall  95  are vertically spaced apart from each other forming upwardly facing elongated openings  20  (seen best in  FIG. 3  with grain present) between vertically adjacent panels  18 . Elongated openings  20  allow airflow to pass through one lateral side wall  95  of each grain flow path  16  between panels  18 , through centrally located undulating grain flow path  16 , and out of the grain flow path  16  through elongated openings  20  of the opposing lateral side wall  95 . 
     A central air plenum  22  is located in the space between a pair of grain flow paths  16  (a first and second grain flow path  16 ) on the left in  FIG. 2 . An additional central air plenum  22  is positioned in the space between another pair (a third and fourth grain flow path  16 ) on the right in  FIG. 2 . The sides of each central air plenum  22  are laterally defined by inner side walls  95  of adjacent grain flow paths  16  in the pair. 
     Each central air plenum  22  can include a divider  26  separating central plenum  22  into two sub-plenums. The upper sub-plenum can be a heat plenum  32 . The high pressure (or positive pressure), high heat airflow from fan  14  first flows into heat plenum  32  of central plenum  22 . Sub-plenum below heat plenum  32  can be a return plenum  34 . Air which has passed through a grain column in one of the grain flow paths  16  can be pulled from return plenum  34  to an inlet  36  of fan  14  via a return flow air duct  38 . Thus, the pressure in return plenum  34  can be below atmospheric pressure (negative pressure) during operation. 
     Enclosures  40 ,  42  are provided on sides of the grain flow paths  16  opposite that defining central plenum  22 . Outer enclosures  40  on opposing sides of the four grain columns can be defined by outer walls  44  ( FIG. 6 ). Inner enclosure  42  can be provided in the space between the pairs of grain flow paths  16  (between second and third grain flow paths  16  in this example). Sides of inner enclosure  42  are partially defined by sets of panels  18  forming the side wall  95  opposite those forming the sides walls  95  of the central plenum  22 . 
     Enclosures  40 ,  42  are positioned laterally adjacent a portion of high pressure, high heat plenum  32  to capture airflow passing through the lower portion of adjacent grain flow path  16  from heat plenum  32  via high heat airflow path represented by two-headed arrow  45 . Enclosures  40 ,  42  additionally define a portion of an airflow path represented by arrows  46  that once again passes through an adjacent grain flow path  16  before being ultimately exhausted to the atmosphere from the grain dryer  10 . 
     Enclosures  40 ,  42  further define a portion of a temper airflow path represented by arrows  48  that once again passes through an adjacent grain flow path  16  and into return plenum  34 . Thus, air entering central plenum  22  and passing through the grain flow path into one of the enclosures  40  and  42  makes two passes through a grain flow path  16  prior to (1) exiting to the atmosphere, or (2) returning via return plenum  34  to fan  14  via return duct  38  for recirculation. 
     Air also enters the grain columns from each heat plenum  32  at the upper portion of the grain flow paths  16  via the triangular inlet openings  89  of the side walls  95  defining the high pressure (or positive pressure), heat plenum  32  as indicated by double-headed arrows  47 . The air flows into the channel created below the associated generally triangular diverter  88 . The air then flows through the grain column as seen in  FIG. 9 , and then out a triangular outlet opening  89  of the opposing side wall  95  defining the grain flow path  16 . The air exiting of the upper portion  17  through the upper triangular outlet openings  89  is exhausted to the atmosphere directly or via exhaust plenum  28  between the pairs of grain columns above divider  24  defining enclosure  42 . This central exhaust plenum  28  is open to the atmosphere via openings  30  in the end walls  94  as best seen in  FIG. 1 . This provides a pre-heat zone in the upper portion  17  of the grain column as described hereinafter. 
     Referring to  FIG. 4 , a loop drag input conveyor  52  including grain paddles  54  can be provided. A motor  55  drives loop drag input conveyor  52 . Paddles  54  are positioned in a loop above two upper shelves  56  extending the length of the grain flow paths  16 . Each shelf  52  can include periodic openings  58  allowing grain to fall through the shelf  52 . Additionally or alternatively, each shelf  52  can include downwardly angled walls  60  along each side of shelves  52  or below openings  58 , with each angled wall  60  extending downwardly toward the top of one of the grain flow paths  16 . Thus, each downwardly angled wall  60  can be configured to direct grain from shelves  52  (e.g., over a side or through an opening  58 ) into the top of one of the grain flow paths  16 . A connecting shelf  62  can connect the two upper shelves together at each end of grain dryer  10  to complete the loop arrangement of drag conveyor  52 . 
     A cover can be provided over loop drag conveyor  52 , which includes a plurality of panels  64 . The loop arrangement of drag conveyor  52  allows grain to be added to the continuous flow dryer  10  at essentially any point along the loop. For example, any cover panel  64  can simply be removed to create a grain input opening to feed grain to loop drag conveyer  52  by which the pairs of grain flow paths  16  are fed. Alternatively, a cover panel  64  including a grain input opening therethrough (not shown) can simply be placed at any point along the loop to feed conveyor  52 . Thus, a grain input opening can be located at either end of grain dryer  10 , or at any point along either lateral side of grain dryer  10 . It can be desirable in some instances to dispose motor  55  opposite in the loop from the location of the grain input. For example, the both motor  55  and the grain input can be on opposite sides at one end of the grain dryer, so that the inputted grain flows along a “U” shape path prior to encountering motor  55  coupled to the paddle drive. 
     Referring to  FIG. 2 , shelves  56  and downwardly angled walls  60  by which grain flows into grain flow paths  16  can be seen. This allows grain to flow into each of the grain flow paths  16  between pairs of longitudinally extending side walls  95  of the upper portion  17 . The longitudinally extending side walls  95  of the upper portion  17  can be formed by a plurality of panels with openings  89  aligned in horizontal rows as previously described. Also as previously described, the upper portion  17  can have a larger cross-sectional area relative to the lower portion  19  of the grain flow column. 
     Opposing panels  18  forming side walls  95  and grain flow paths  16  can have a smaller width or cross-sectional area lower portion  19  below the upper portion  17  and adjacent return plenum  34  and the heat plenum  32 . In lower portion  19  of the grain flow path  16  the lateral spacing between opposing panels  18  forming each grain flow path  16  can be constant. In addition, the lower end of each panel  18  on one side can be vertically aligned with the lower end of opposing panels  18 . Thus, the fact that angled panels  18  define undulating grain flow paths  16  defining a grain column can be understood. 
     Horizontally extending elongated airflow openings  20  can also be defined by spaces between vertically adjacent panels  18  on each side of grain flow paths  16 . These airflow openings  20  between vertically adjacent panels  18  are present on opposing sides of each grain flow path  16 . Openings  20  enable airflow through one side of the grain flow path  16 , through a grain column in the path  16 , and out through opposing openings  20  of the other lateral side of the grain flow path  16 . The relationship between the airflow flowing through a grain column in to and out of various plenums of central plenum  22  is affected by the width of elongated openings  20  created by the spacing between vertically adjacent panels  18 . The width of openings  20  can also be sufficiently large that the exiting airflow speed through openings  20  is below that which lifts grain out of grain flow path  16  through openings  20 . Thus, there is no need for any screens on the openings  20 , despite the fact that the width of openings  20  is larger than the diameter of grain in grain flow path  16 . The width of openings  20  can be many times larger than the average diameter of the grain. For example, the width in some cases can be at least about 25 mm, at least about 50 mm, at least about 75 mm, or at least about 100 mm. 
     The divider  26  can also affect the relationship between the airflow flowing through grain columns in grain flow paths  16  into and out of the central plenum  22 . For example, the divider  26  can be coupled to one of angled panels  18  defining inner (or opposing) walls of adjacent grain flow paths  16 . This helps avoid any airflow path around dividers  24 ,  26  this is undesirably shortened, resulting in an undesirable short circuit of the airflow from heat plenum  32  to an adjacent part of central plenum  22 . The width of elongated openings  20  can also be varied in order to aid in reducing undesirably shortened airflow paths. Differences in the widths of various elongated openings at various locations along grain flow paths  16  can be seen in the drawings. Thus, in some instances the width (or height) of openings  20  might vary between 20 mm and 100 mm at various locations along grain flow paths  16 . 
     In addition, divider  26  can have a sloped or convex upper central surface and can be attached at an upper end of an angled panel  18  on each side. Thus, any grain that might possibly fall from one of elongated openings  20  will fall onto the sloped or convex upper surface of the divider  26 , which will guide the grain back into an adjacent grain flow path  16  via an adjacent elongated opening  20 . 
     Referring to  FIGS. 2 and 5 , an output metering drag conveyor  70  can be provided at the bottom of each pair of grain flow paths  16 . An exemplary metering drag conveyor  70  which can be used is described in detail in U.S. Pat. No. 6,834,442, incorporated herein, in its entirety, by reference. An terminal end of each output metering drag conveyor  70  can include an output that feeds a jump drag mechanism  72  that can joins the outputs of both metering drag conveyors  70  into a single grain output collection point. From there a discharge drag conveyor  74  or auger conveyor can be used to discharge the conditioned grain from the grain dryer  10 . 
     Referring to  FIGS. 1, 6 and 7 , a combined fan and burner assembly  76  can be positioned at one end of grain dryer  10 . Assembly  76  can include induced draft burner  12  positioned between an air intake  78  and centrifugal fan  14 . Thus, fan  14  pulls airflow through air intake  78  and into fan  14  through a fan inlet  36 . Fan  14  can be a double wheel, double intake centrifugal fan wherein there is a central fan intake  36  on each side of the fan  14 . A variable frequency drive motor (not shown) can drive fan  14  at variable speeds. 
     A shroud  80  on each side of assembly  76  provides airflow ducting from burner  12  to inlet  36  of fan  14 . Each shroud  80  also provides a portion of return airflow duct  38  for airflow coming from return plenum  34  to inlets  36  of fan  14 . Shroud  80  can include an outer member with a central opening  82  ( FIG. 7 ) adjacent the fan wheel bearings  84  ( FIG. 6 ). Central opening  82  in shroud  80  allows unheated air to flow over bearings  84  to cool them. This can greatly reduce negative effects on bearings  82  that might otherwise result from providing burner  12  immediately upstream from fan  14 . 
     Referring to  FIG. 6 , ambient air enters burner  12  via air inlet  78 . Air exiting burner  12  flows into inlets  36  at each side of fan  14 . The air is directed via shroud  80 , which defines an air duct between burner  12  and inlet  36  on each side of fan  14 . Thus, a burner airflow path flows through air inlet  78  to burner  12 , passes through burner  12 , and then from burner  12  flows to inlets  36  of fan  14 . 
     Return airflow paths represented by arrows  86  can provide additional air to inlets  36  of fan  38 . Each return airflow path  86  travels within a return air duct  38  from each of the return plenums  34  to one of the inlets  36  on either side of fan  14 . As noted above, shroud  80  can operate as part of the return air duct  38 , helping to direct air of the return airflow paths  86  into inlets  36  of fan  14 . As discussed above, shroud  80  can include a central opening  82  ( FIG. 7 ) providing a bearing cooling flow path to permit some cooler ambient air to additionally enter inlets  36  of fan  14  to flow over fan bearings  84  centrally located in the fan inlet  36 . Thus, despite the fact that highly heated air flows into fan inlets  36  directly from burner  12  via burner airflow path, and return warm air flows into inlets  36  of fan  14  via return airflow paths  86 , cool air can still flow over fan bearings  84  via central opening  82  in shroud  80 . 
     The air from these three flow paths can be thoroughly mixed in fan  14 , thereby outputting air that is of substantially uniform temperature. Fan output airflow paths represented by arrows  90  provide communication between outlet of fan  14  and each heat plenum  32 . Fan outlet airflow paths  90  can be provided by a dual duct  92  arrangement as seen in  FIG. 6 . 
     Referring to  FIG. 2 , the airflow through grain columns of each grain flow path  16  is shown in relation to the left pair of grain flow paths  16 . It should be understood, however, that the same airflow paths also flow through the other pair of grain columns within grain flow paths  16  in like manner during operation of grain dryer  10 . Air first enters heat plenum  32  via fan outlet flow path  86 . 
     From the lower portion of the heat plenum  32 , air flows outwardly through the grain columns of lower portions  19  of adjacent grain flow paths  16  into the surrounding enclosures  40 ,  42  as represented by double headed arrow  45 . In this case, the left outer enclosure  40  and the inner enclosure  42 . Thus, a heat zone is provided in the grain columns of the lower portion  19  of the grain flow paths  16  adjacent heat plenum  32  due to heat airflow paths  45 . 
     From the upper portion of the heat plenum  32 , air flows into the upper portion  17  of the grain flow path  16  via inlet openings  89  associated with alternating rows of upper transverse diverters  88   a  ( FIG. 9 ) as indicated by arrows  47 . After flowing through the grain column as shown in  FIG. 9 , the air can then exit the grain dryer  10  through openings  89  associated with the interspersed alternating rows of upper grain diverters  88   b  as indicated by arrows  49 . Thus, a pre-heat zone is provided in the grain columns of the upper portion  19  of the grain flow paths  16  adjacent heat plenum  32  due to preheat airflow paths  47 . 
     The relationship between the mass or volume of grain and the total cross-sectional area of the openings ( 89  and  20 ) in the upper and lower sections ( 17  and  19 , respectively) create a pressure drop ratio that is approximately 2:1 (upper section pressure drop:lower section pressure drop). Stated another way, the openings  89  and grain flow paths  16  are configured to distribute approximately twice the amount of air from the heat plenum  32  into the lower portion  19  than into the upper portion  17  of the grain flow path during operation. 
     The combination of lower airflow and greater grain mass or volume in the upper portion  17  of grain flow path  16  than in the lower portion  19 , results in the grain being gently preheated in the preheat zone of the upper portion  17 . The gentle heating of the grain in this pre-heat zone brings the moisture to the surface of the grain without causing it to be trapped within the grain. Likewise, this combination results in the grain being fully heated in the heat zone of the lower portion  19  to drive the moisture out of the grain without it being trapped therein. 
     Enclosures  40 ,  42  define portions of airflow paths  46 ,  48  causing the air to then flow again through one of the grain columns of a grain flow path  16  into the upper portion  17  or lower portion  19 , respectively. In this way, air passes into the grain columns or grain flow path  16  twice before being exhausted or returned to fan  14  for recirculation. 
     For example, enclosures  40 ,  42  define portions of preheat airflow path  46  through a grain column from enclosures  40 ,  42  which exits to the atmosphere, for example, through into exhaust plenum  28 . The air of preheat airflow path  46  is still warm. As a result of this warm airflow  46 , an extended preheat zone is provided in the grain columns of grain flow paths  16  adjacent exhaust plenum  28 . The preheat zone helps reduce thermal shock as the grain is being heated in grain dryer  10 . Air in the exhaust plenum  28  exits the grain dryer through exhaust opening  30  in the back wall  94  ( FIG. 1 ) of grain dryer  10 . 
     Enclosures  40 ,  42  also define portions of temper airflow path  48  through a grain column of adjacent grain flow paths  16  from enclosures  40 ,  42  into return plenum  34 . Air flowing through a grain column into return plenum  34  from enclosures  40 ,  42  into return plenum  34  is also still warm. This airflow occurs at an uppermost portion of the grain columns adjacent return plenum  34 , providing a temper zone. The temper zone helps reduce thermal shock as the grain is being cooled in grain dryer  10 . 
     A cooling zone is next created in grain columns adjacent below the temper zone as a result of ambient air being pulled into return plenum  34  below temper zone via cooling airflow path  50 . In cooling zone, ambient air is pulled into return plenum  34  via cooling airflow path  50  through adjacent grain columns via corresponding openings  20 . Air within return plenum  34  is pulled back into the fan  14  via return airflow path  86 . Thus, return air plenum  34  can typically be at a negative pressure during operation. 
     As a result of the various airflow paths  45 ,  46 ,  47 ,  48  and  50  through grain columns of grain flow paths  16  defining central plenum  22 , grain is first preheated in preheat zone as a result of airflow path  47 . Then, as grain moves down grain flow paths  16 , the grain is heated in heat zone as a result of airflow path  45 . Continuing down grain flow paths  16 , the grain is next subjected to a temper zone as a result of airflow path  48 , below which airflow path  50  creates a cooling zone portion of grain columns in grain flow paths  16  Thus, the grain can be subjected to at least four different treatment zones as it flows down through each grain flow path  16 . 
     Cooling airflow path  50 , temper airflow path  48 , or both, can pick up fines from the grain column and carry them into return plenum  34  and return airflow path  86  to fan  14 . After passing through fan  14 , any such fines are returned to the grain columns via return airflow paths  90  including fan output airflow paths  90 . Thus, return airflow path  86  and fan output airflow path  90 , including through fan  14 , define a recirculating airflow path in which fines might possibly be present. Since the airflow path through burner  12  is positioned outside the recirculating airflow path, any fines picked up flow through the recirculating airflow path without passing through burner  12 . As discussed above, only fresh ambient air flows through burner  12  on its way into the recirculating airflow path. Thus, there is no concern about igniting any fines pulled from a grain column. 
     Air flowing into the upper portion  17  of the grain column or grain flow path  16  from the central plenum  22  indicated by arrows  47  can pass through the grain as seen in  FIG. 9  and then out to the atmosphere as indicated by arrows  49 . Air entering via arrows  47  can also flow into exhaust plenum  28  and can exit grain dryer  10  to the atmosphere through exhaust opening  30  in a central location between the adjacent pairs of grain flow paths  16  defining exhaust plenum  28  above the central divider  24 . 
     Various methods should be apparent from the above discussion and should be considered part of the disclosure. For example, some methods disclosed herein can involve providing various components of grain dryer  10  disclosed herein. Other methods disclosed herein can involve arranging or connecting various components as disclosed herein. Further methods disclosed herein can involve providing components to create or creating various airflow paths as disclosed herein. Additional methods disclosed herein can involve operating various components as disclosed herein. Providing various components to create the various treatment zones in a grain column are also methods disclosed herein. Moreover, combinations including various aspects of the disclosed methods, including those listed as examples above, are further methods disclosed herein. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence of importance or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.