Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Reexamination Certificate
1999-05-28
2001-06-12
Ferensic, Denise L. (Department: 3749)
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
C034S518000, C034S218000
Reexamination Certificate
active
06243970
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the drying of green lumber in a kiln and, more particularly, to a stack of lumber that is arranged to facilitate airflow therethrough as well as an associated method of drying lumber.
BACKGROUND OF THE INVENTION
Lumber which has recently been cut contains a relatively large percentage of water and is referred to as green lumber. Prior to being used in construction or other applications which demand good grades of lumber, the green lumber must be dried. Drying removes a large amount of water from the lumber and significantly reduces the potential for the lumber to become warped or cracked. Acceptable water content varies depending on the use of the lumber and type of wood; however, a moisture content of about nineteen percent, or less, is acceptable in many circumstances.
Although lumber may be dried in the ambient air, kiln drying accelerates and provides increased control over the drying process. In kiln drying, a charge of lumber is placed in a kiln chamber. A typical kiln chamber is a generally rectangular building which can be at least partially sealed to control the amount of air that is introduced to and exhausted from the kiln chamber. Further, such kiln chambers typically have reversible cans for circulating heated air through the chamber. The air may be heated in a number of ways, such as by a suspension furnace that exhausts hot air into the kiln chamber, or by heat transfer from steam-carrying pipes that extend through the chamber.
The charge of lumber placed in the kiln chamber typically consists of one or more rectangular stacks of lumber. It is conventional for each stack of lumber to consist of a number of vertically stacked, horizontal rows of lumber that are arranged such that cross-sections of the stack are generally rectangular. The horizontal rows are spaced apart with narrow wooden boards, or the like, referred to as “stickers.” The stickers are positioned between each horizontal row to space the rows apart and to allow air to flow between the rows. The stacks of lumber are placed on separate flat-bed cars that are moved upon railroad-type tracks. Kilns may have any desired number of such tracks, and multi-track kilns may accept several stacks of lumber during each drying cycle.
In operation, a charge of green lumber is initially placed in a kiln chamber. After at least partially sealing the chamber, the air within the chamber is heated to facilitate drying. The fans within the chamber circulate the heated air through the kiln chamber. Because the stickers provide spaces between the horizontal rows of lumber, the heated air passes between the rows of lumber and is in direct contact with both the upper and lower surfaces of individual pieces of lumber so that the lumber is dried.
FIG. 1
is a perspective view of a conventional stack of lumber
10
that is to be dried in a kiln in the manner generally described above. More specifically, the stack
10
includes a first side
12
and an opposite second side
14
, and multiple horizontally extending layers
16
of lumber that arc arranged one above the other and extend between the first and second sides. Each layer
16
includes multiple pieces of lumber
18
. Multiple stickers or spacers
20
, which are typically in the form of narrow pieces of lumber, are positioned between the layers
16
and extend between the opposite sides
12
and
14
, so that multiple passages
22
are defined between adjacent layers
16
and are open at the opposite sides. Only a few of the layers
16
, pieces of lumber
18
, spacers
20
and passages
22
are identified with a reference numeral in FIG.
1
. The stack
10
is positioned within the chamber of a kiln, and heated air is circulated in the chamber so that a flow of heated air is forced through each of the passages
22
.
A representative passage
22
is best seen in
FIG. 2
, which is a cross-sectional view of a portion of the stack
10
taken along line
2
—
2
of FIG.
1
.
FIG. 2
diagrammatically illustrates boundary layers
24
that form while airflow is forced into the passages
22
via openings of the passages that are at the first side
12
of the stack
10
. The direction of the airflow is generally designated by the arrows
23
in FIG.
2
.
Each of the passages
22
of the stack
10
are generally identical; therefore, the flow into the passage
22
that is illustrated in
FIG. 2
is generally representative of the flow into each of the passages
22
via the openings to the passages that are at the first side
12
of the stack
10
. Whereas
FIG. 2
has been described heretofore as being illustrative of airflow into the passages
22
via openings at the first side
12
of the stack
10
,
FIG. 2
is also illustrative of airflow into the passages via openings at the second side
14
of the stack, in which case
FIG. 2
is a cross-sectional view of a portion of the stack taken along line A—A of FIG.
1
.
As best seen in
FIG. 2
, for each of the passages
22
, airflow therethrough is such that viscous layers of air are developed proximate to the surfaces of the pieces of lumber
518
that face and define the passage. Those viscous layers are referred to as boundary layers
24
, which are not visible but are generally shown in dashed lines in FIG.
2
. More specifically, the boundary layers
24
, which are areas of retarded flow, are caused by the viscous interaction between the airflow through the passage
22
and the surfaces of the pieces of lumber
18
that define the passage, as well as interaction between the airflow and the lumber surfaces that are proximate to the inlet opening of the passage.
Each boundary layer
24
includes a protruding portion
26
that tapers to a generally planar portion
28
. For each of the boundary layers
24
, the protruding portion
26
is a portion of the boundary layer that has become separated from the surface or surfaces of the one or more pieces of lumber
18
that define the passage. The separation occurs because of interaction between the airflow and an edge or edges of the one or more pieces of lumber
18
that define the inlet to the passage.
As illustrated in
FIGS. 1 and 2
, it is conventional for the edges of the layers
16
to be aligned so that they extend in a common plane. As a result, for each of the passages
22
, the protruding portions
26
of the boundary layers
24
are aligned in a manner that is very restrictive to flow, since the boundary layers are regions of retarded flow and thereby tend to block flow into the passage
22
. More specifically, an unrestricted flow path exists only in that region between the boundary layers
24
of each of the passages
22
. Those unrestricted flow paths are characterized by generally inviscid flow. However, within each passage
22
, the protruding portions
26
are aligned to significantly restrict the flow such that the only unrestricted flow path is between the peaks of the protruding portions, as designated by the arrow
30
in FIG.
2
.
The resistance to flow through the stack
10
that results from the alignment of the protruding portions
26
reduces the speed at which the pieces of lumber
18
can be dried, which can be disadvantageous. The resistance to flow through the stack
10
that results from the alignment of the protruding portions
26
also requires significant pressure increases to maintain the flowrate; therefore, the kiln fans, which force the airflow through the stack, must work excessively, which is disadvantageous.
SUMMARY OF THE INVENTION
The present invention solves the above problems by providing a stack of lumber having a staggered arrangement, as well as a kiln system for drying a stack of lumber and methods for stacking and drying a stack of lumber. The staggered arrangement is such that the stack of lumber is capable of facilitating airflow therethrough, so that the stack of lumber can be efficiently dried.
In accordance with one aspect of the present invention, the stack of lumber includes a plurality of layers of lumber that are arranged one above the other. Each layer of lum
Culp George W.
Nagel Robert T.
Alston & Birds LLP
Culp George R.
Ferensic Denise L.
Mattera Michelle O.
LandOfFree
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