Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02479070 2004-08-25
MULTI-ZONE, MULTI-CONVEYOR DRYER AND CONVERSION
METHODS AND HIT
BACKGROUND
The present invention relates generally to conveyor material dryers and
particularly to mufti-conveyor material dryers and relates specifically to
mufti-zone,
mufti-conveyor dryers and in the most preferred form to conversion kits for
converting
single-zone, mufti-conveyor dryers into mufti-zone, mufti-conveyor dryers.
In conveyor type dryers, the material to be dried is transported through a
dryer
chamber, and the material is dried by causing the drying air to be passed
vertically
through the material on the conveyor as the material moves through the drying
chamber. To increase residence time while shortening the chamber length,
multiple
conveyors are provided in the drying chamber where the material to be dried is
transferred from one conveyor to anothex conveyor moving in the opposite
direction. It
can be appreciated that an even number of conveyors can be included such as in
the
1 S event that material is desired to be introduced and exit in the same end
of the drying
chamber or an odd number of conveyors can be included such as in the event
that
material is desired to be introduced and exit in opposite ends of the drying
chamber.
It should be appreciated that a dryer is one component in a production line
for
any given product such as a breakfast cereal or a snack product. Additionally,
the
through put of the production line is limited by the maximum capacity of each
of the
individual components which make up the production Iine. Thus, there is always
an
attempt to increase the capacity of the component in the production line which
has the
smallest capacity in potential through put. Significant strides have been made
in
increased efficiency and through put in components upstream and downstream of
the
dryer in the production Line. 'Thus, there also exists a need for dryers
having increased
efficiency and through put so that the dryer is not the component which limits
the
through put of the production Line.
Further, the ability to replace an existing dryer with a dryer of increased
capacity may be restricted for a vaxiety of reasons. A typical way to increase
drying
capacity is to add additional dryers and/or increase the size of the dryer
chamber and
the total conveyor length. The problem is that this may not be possible
because of the
inability to fit additional and/or larger dryers in the production line due to
facility size
or constraints, production line restraints, or the like. Further, even if
possible, it would
CA 02479070 2004-08-25
typically be necessary to shut down the production line during the time that
the dryers
are added and/or substituted which can be for an extended period of time in
the order of
several weeks, resulting in loss of product production and profits.
Additionally, dryers
involve considerable investment of capital, so that it is more desirable to
increase the
efficiency of existing dryers rather than replace the existing dryers with new
dryers.
It is well known that higher temperatures result in faster drying. It is also
recognized that although higher temperatures can be utilized during the start
of the
drying process when the material has higher moisture content, higher
temperatures can
result in damage to the material at the end of the drying process when the
material has
lower moisture content. In particular, if drying temperatures exceeded
240° at the end
of the drying process, material being dried may have a frosting or white sugar
glaze
which may be undesirable. Thus, single-zone dryers operated at temperatures
below
240°F. However, two-zone dryers have been created allowing drying
initially at higher
temperatures and final drying at lower temperatures. For a variety of reasons
including
lower costs and sufficient capacity when installed, many production lines
utilize single
zone dryers. However, because of increased efficiency and through put of the
remaining components in the production line, such single zone dryers become
the
through put limiting component.
For the reasons previously set forth, a need exists to increase the capacity
of
existing dryers and in preferred aspects to convert existing single zone
dryers to two
zone dryers.
SUMMARY
The present invention solves this need and other problems in the field of
multi-
zone, mufti-conveyor dryers by providing, in preferred aspects . . .
It is thus an object of the present invention to provide a novel mufti-zone,
multi-
conveyor dryer.
It is further an object of the present invention to provide such a novel multi-
zone, mufti-conveyor dryer converted from a single-zone, mufti-conveyor dryer.
These and further objects and advantages of the present invention will become
clearer in light of the following detailed description of an illustrative
embodiment of
this invention described in connection with the drawings.
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DESCRIPTION OF THE DRAWINGS
The illustrative embodiment may best be described by reference to the
accompanying drawings where:
Figure 1 shows a diagrammatic side view of a conventional material dryer, with
portions broken away to show internal details.
Figure 2 shows a diagrammatic side view of a mufti-zone, mufti-conveyor dryer
according to the preferred teachings of the present invention, with portions
broken
away to show internal details.
Figure 3 shows a diagrammatic top view of the mufti-zone, mufti-conveyor
dryer of Figure 2, with portions broken away to show internal details.
Figure 4 shows a diagrammatic side view of a second heat source utilized in
the
mufti-zone, mufti-conveyor dryer of Figure 2.
All figures are drawn for ease of explanation of the basic teachings of the
present invention only; the extensions of the figures with respect to number,
position,
relationship, and dimensions of the parts to form the preferred embodiment
will be
explained or will be within the skill of the art after the following
description has been
read and understood. Further, the exact dimensions and dimensional proportions
to
conform to specific force, weight, strength, and similar requirements will
likewise be
within the skill of the art after the following description has been read and
understood.
Where used in the various figures of the drawings, the same numerals designate
the same or similar parts. Furthermore, when the terms "side", "end",
"bottom",
"first", "second", "inside", "upper", "lower", "intermediate" and similar
terms are used
herein, it should be understood that these terms have reference only to the
structure
shown in the drawings as it would appear to a person viewing the drawings and
are
utilized only to facilitate describing the illustrative embodiment.
DESCRIPTION
A method utilizing a preferred apparatus for converting a single zone, multi-
conveyor dryer to a mufti-zone, mufti-conveyor dryer according to the
preferred
teachings of the present invention is shown in the drawings. Specifically,
dryer I O as
shown includes a first, upper conveyor 12 for receiving material to be dried
and for
transporting it through a heat chamber 14 in a first conveying direction.
Material falls
from first conveyor 12 onto a second conveyor 16 which transports it through
heat
chamber 14 in a second, intermediate conveying direction parallel to, below,
and in the
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opposite direction to first conveyor 12. Material falls from second conveyor
16 onto
third, lower conveyor 18 which transports it through heat chamber 14 in a
third
conveying direction parallel to, below, and in the opposite direction to
second conveyor
16 and parallel to, below, and in the same direction as first conveyor 12.
Material falls
from third conveyor 18 for exiting from dryer 10. Material spends
approximately the
same amount of time in heat chamber 14 on conveyors 12, I6 and 18. It should
be
appreciated that dryer 10 includes suitable provisions such as slitted plastic
sheeting to
minimize air flow around the ends of conveyors 12, 16 and 18. Conveyors 12, 16
and
18 can be of a variety of forms and do not form a part of the present
invention.
IO Likewise, although three conveyors 12, 16 and 18 have been shown, dryers 10
according to the teachings of the present invention can include two or four or
more
conveyors 12, 16, and 18.
Dryer 10 further includes an air plenum 20 for directing air flow into and out
of
heat chamber 14 shown in the most preferred form as a parellepiped on both
sides of
heat chamber I4 and conveyors 12, I6 and 18. Additionally, air plenum 20 is
divided
in the most preferred form by a wall 21 into two halves which for purposes of
explanation are labeled a front half 20a and a rear half 20b. Each half 20a
and 20b
includes a source 22 of heat which typically is in the form of steam coils
located
generally perpendicular to the conveying directions and midway in each half
20a and
20b. A device of circulating air 24 which typically is in the form of a fan is
located in
or associated with each half 20a and 20b. Dryer 10 further includes suitable
provisions
for removing moisture laden air and replacing the removed moisture Laden air
with
heated, dried air, which provisions can be of a variety of forms and do not
form a part
of the present invention. In this regard, approximately 10% of the circulating
air is
typically drawn off to remove moisture, while 90% of the air is simply
recirculated.
In conventional dryers, air is removed from heat chamber 14 through an exit
opening 26 above the upper row of first conveyor 12 and through an exit
opening 28
below the upper run of second conveyor 16 and above the upper run of third
conveyor
18. In this regard, air can be removed through exit opening 28 from below the
lower
run of second conveyor 16 or from intermediate the upper and lower runs of
conveyor
16. Air passes from exit openings 26 and 28 through heat source 22 (under the
influence of air circulating device 24) where it is heated and passes into
heat chamber
14 through an entrance opening 30 located below the upper run of first
conveyor 12
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and above the upper run of second conveyor 16 and through an entrance opening
32
located below the upper run of third conveyor 18. In this regard, air can be
introduced
through opening 30 below the lower run of first conveyor 12 or including
intermediate
the upper and lower runs of conveyor 12 and through opening 32 below the lower
run
of third conveyor 18 or including intermediate the upper and lower runs of
conveyor
18. In the most preferred form, openings 30 and 32 of halves 20a and 20b are
located
adjacent to each other and are located intermediate openings 26 and 28 of
halves 20a
and 20b. It should be appreciated that there is no significant difference in
temperature
between halves 20a and 20b between portions of heat chamber 14. Likewise, air
plenums 20 are located on both sides of heat chamber 14 of an identical
construction.
It should be appreciated that based upon the assumption that air will take the
path of
least resistance inside of chamber 14 between entrance openings 30 and 32 and
exit
openings 26 and 28, air will flow through the upper run and the material
thereon of the
associated conveyor 12, 16 and 18.
Dryer 10 according to the teachings of the present invention includes several
improvements which result in a different mode of operation. In particular, a
division
plate 40 is installed in heat chamber 14 and divides heat chamber 14 into an
upper zone
14a and a lower zone 14b. In the preferred form, material on conveyor 12 is
located in
upper zone 14a, and material on conveyors 16 and 18 is located in lower zone
14b. In
the most preferred form, plate 40 is located intermediate the upper and lower
runs of
conveyor 12, but plate 40 could also be positioned below the lower run of
conveyor 12
according to the teachings of the present invention. Plate 40 is impervious to
air flow
and thus generally prevents air passage between zones 14a and 14b therethrough
such
that air movement between the upper and lower zones 14a and 14b is minimized.
In dryer I O according to the teachings of the present invention, air is
removed
from heat chamber 14 through an exit opening 42 above plate 40 and below the
upper
run of conveyor I2, through an exit opening 44 below plate 40 and above the
upper run
of conveyor 16, and through an exit opening 46 below the upper run of conveyor
18.
In the preferred form, opening 42 is located in front half 20a on a first side
of dryer 10
and in rear half 20b in the opposite side of dryer 10. Likewise, openings 44
and 46 are
located in rear half 20b on the first side of dryer 10 and front half 20a in
the opposite
side of dryer 10. Air passes from exit opening 42 through heat source 22
(under the
influence of air circulating device 24) where it is heated and passes into
heat chamber
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14 through an entrance opening 52 located above the upper run of conveyor 12.
Air
passes from exit openings 44 and 46 through heat source 22 (under the
influence of air
circulating device 24) where it is heated and passes into heat chamber 14
through an
entrance opening 54 located below the upper run of conveyor 16 and about the
upper
run of conveyor 18. In most preferred form and to generally match exit
openings 44
and 46, an extension 56 is provided through wall 21. In particular and in the
preferred
form, extension 56 includes upper and lower plates 56a having a horizontal
extent
outward from heat chamber 14 generally equal to that of wall 14 and has a
horizontal
extent parallel to the conveying direction generally equal to but slightly
less than the
I O spacing of heat source 22 from wall 21. Extension 56 also includes a
vertical plate 56b
extending between the outer edges of plates 56a. Thus, in the first side of
dryer 10
shown in the drawings, extension 56 and opening 54 extend from wall 21 into
front
half 20a and in the opposite side of dryer 10, extension 56 and opening 54
extends
from wall 2I into rear half 20b.
It should be appreciated that openings 42 and 52 in the respective half 20a
and
20b communicate only with zone 14a and generally not with zone I4b to
substantially
prevent air flow with zone 14b. Similarly, openings 44, 46 and 54 in the
respective
half 20a and 20b communicate only with zone 14b and generally not with zone
14a to
substantially prevent air flow with zone 14a. According to the teachings of
the present
invention, halves 20a and 20b including openings 42 and 52 and thus zone I4a
is
heated to a greater temperature than halves 20a and 20b including openings 44,
46 and
54 and thus zone 14b. In the most preferred form, air flowing into zone 14a
has a
temperature in the order of 300°F whereas air flowing into zone 14b has
a temperature
in the order of 2I0-240°F. It should also be appreciated that in the
embodiment shown,
only conveyor 12 is located in zone 14a whereas two conveyors 16 and 18 are
present
in zone 14b such that the residence time in zone 14b is roughly double that in
zone 14a.
It should be appreciated that especially for halves 20a and 20b including
openings 42 and 52 having a higher temperature than that of conventional
dryer, heat
source 22 of the conventional dryer may be insufficient to deliver sufficient
heat to
result in the desired temperature of zone 14a. Thus, according to the
preferred form,
the present invention, two heat sources 22 and 22a are provided horizontally
between
openings 42 and 52.
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It should be appreciated that material dust and other debris tends to be
carried
by the air movement and after lodges or otherwise collects on heat source 22.
Thus, to
increase heat transfer efficiency and to reduce the risk of burning, it is
necessary to
clean heat source 22. To increase the areas of openings 42 and 52, it is
desired to
decrease the horizontal spacing therebetween, with heat source 22 being
positioned in
the horizontal spacing between openings 42 and 52. Thus, when multiple heat
sources
22 and 22a are utilized, it is necessary to place them close together, which
can make
cleaning very difficult. In the most preferred form, the first heat source 22
is mounted
in a stationary manner generally perpendicular to the conveying directions as
in
conventional dryers. However, the second heat source 22a is mounted in a
pivotal
manner about a vertical axis in the preferred form such that second heat
source 22a is
pivotal between an operative position generally perpendicular to the conveying
directions and parallel to and slightly spaced from first heat source 22 and a
cleaning
position generally parallel to the conveying directions and at a nonparallel
angle and
preferably perpendicular to first heat source 22. In the most preferred form
where heat
source 22 is in the form of steam radiators, the inlet and outlet 22b to heat
source 22a
have a vertical orientation and are arranged in rotary unions or swivel joints
22c which
allow passage of steam therethrough but allow relative pivotal movement about
an axis
defined by inlet and outlet 22b. Additionally, in the preferred form where
steam is the
source of heat, the steam control valves are opened approximately 90% of the
time for
heat sources 22 and 22a for intake zone 14a but are opened approximately 40%
of the
time for heat sources 22 for lower zone 14b.
As heat transfer is a function of air speed, air circulating devices 24
according
to the preferred teachings of the present invention are operated at higher
flow rates in
the order of 8700 cubic feet per minute, with air circulating devices 24 of
conventional
dryers providing about 75% of the rate of the present invention. In the most
preferred
form, the conventional air circulating device 24 are utilized but are rotated
at speeds of
roughly 1200 RPM as compared to about 8-900 RPM for conventional dryers. To
provide the increased RPM, dryer 10 of the most preferred form utilizes
replacement
motors of greater power in air circulating devices 24 and specifically in the
most
preferred form having 20 horsepower in comparison to 15 horsepower for
conventional
dryers.
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Now that the basic construction of dryer 10 according to the preferred
teachings
of the present invention has been set forth, some of the advantages of dryer
10
according to the present invention can be highlighted. Specifically, in the
most
preferred form, a conventional single-zone, mufti-conveyor dryer is converted
into
dryer 10 according to the teachings of the present invention. In particular,
plate 40 can
be prefabricated for insertion into heat chamber 14 relative to conveyor I2 to
divide
chamber 14 into zones 14a and 14b. Similarly, panels which define the division
between chamber 14 and plenum 20 and including openings 42, 44, 46, 52 and 54
can
be prefabricated for replacement of corresponding locations in the
conventional dryer.
Likewise, extension 56 can be prefabricated and inserted into plenum 20 after
a
corresponding opening is cut in wall 21. Heat source 22a, if needed, is
prefabricated
for installation into the conventional dryer. Likewise, higher powered motors
can be
purchased and replaced for the motors of air circulating devices 24 of the
conventional
dryer.
According to the preferred teachings of the present invention, each of the
improvements can be replaced while the conventional dryer is in position and
can be
rapidly performed such as over a weekend, preferably when the production line
is
down for other reasons. It should be appreciated that the major portion of the
conventional dryer remains in place without replacement such that a
conventional dryer
can be converted to dryer 10 according to the teachings of the present
invention with
lesser investment of capital. The overall size of dryer 10 of the present
invention is
generally the same as the conventional dryer from which it was converted.
Additionally, the conversion can be accomplished in considerable less time
than if a
tear-out and total replacement were performed. Thus, the down time for the
production
line as a result of the dryer conversion is minimized.
Additionally, because of the provision of two-zone heating, the capacity of
dryer 10 is considerably increased and in the preferred form is doubled. In
particular,
drying time utilizing dryer 10 of the preferred form is about half of the
drying time for
a conventional dryer, with a residence time of material in dryer 10 according
to the
most preferred form being 2 to 3 minutes versus 3 to 8 minutes for a
conventional dryer
of the same physical size. Residence time can be reduced by increasing the
conveying
speeds of conveyors 12, 16, and 18 such that material thereon spends less time
in heat
chamber 14. Typically, material entering dryer 10 will have a moisture content
of IO-
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12%, and it is desired to have material leave dryer 10 having a 2% moisture
content.
Material leaving conveyor 12 of dryer 10 typically will have a moisture
content of
approximately 5% according to the preferred teachings of the present invention
versus
8 to 9% for conventional, single-zone dryers. The quicker and larger reduction
of
moisture content is the result of the higher temperature of the intake zone
14a of multi-
zone dryer 10 according to the present invention.
Now that the basic construction and advantages of dryer 10 according to the
preferred teachings of the present invention has been explained, many
extensions and
variations will be obvious to one having ordinary skill in the art. For
example,
although dryer 10 according to the preferred teachings of the present
invention has
been set forth created from the conversion of a conventional single-zone
dryer, which
conversion took considerable invention, dryer 10 according to the teachings of
the
present invention could be created as an original article of manufacture.
Similarly, conventional dryer can be of a variety of forms and types, with
only
one of such conventional forms being described. However, a person skilled in
the art
may apply the teachings of the present invention to other forms and types of
conventional dryers.
Thus since the invention disclosed herein may be embodied in other specific
forms without departing from the spirit or general characteristics thereof,
some of
which forms have been indicated, the embodiments described herein are to be
considered in all respects illustrative and not restrictive. The scope of the
invention is
to be indicated by the appended claims, rather than by the foregoing
description, and all
changes which come within the meaning and range of equivalency of the claims
are
intended to be embraced therein.
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