Note: Descriptions are shown in the official language in which they were submitted.
CA 02409066 2002-10-18
APPARATUS FOR BULK DRYING OF SLICED AND GRANULAR MATERIALS
This application is a continuation-in-part to U.S. applications serial nos:
60/339254,
filed Oct. 26, 2001, for which a petition under 37 CFR 1.53 has been filed to
convert to non-
provisional status; to 09/592,333, filed 06/13/00, now issued patent no.
6,438,862; and to
09/021,360, filed 2/10/1998, now issued patent no. 6,202,321.
BACKGROUND OF THE INVENTION
TECHNICAL FIELD OF THE INVENTION
This invention most generally relates to methods and apparatus for drying
sliced and
granular materials and small fruit crops with a heated airflow, and more
particularly to
distributed airflow containers and airflow circulation systems with simple
open loop airflow
circuits and complex open and closed loop airflow circuits for batch drying of
diced, sliced
or granular materials up to berry size to reduce the moisture content.
BACKGROUND
The drying or reduction in moisture content of berries, cherries, grapes,
nuts, whole
fruits, sliced fruits, meats, and bulk materials provided in the form of
granules or slices or
small pieces is an old and well informed field of art. For example, the art of
harvesting and
processing coffee beans from tree-borne "cherries" to the green coffee bean of
commerce
consists of two principle methods, the "dry" method and the "wet" method.
Either method
must result in moisture content equivalent to one third or more of the bean's
weight being
2 5 removed, to produce a commercial product.
The dry method is the more ancient and rudimentary. The cherries are hand-
picked all
in one picking, washed, and sun-dried on drying ground or concrete slabs~~in
thin layers,
usually for a period of two to three weeks. The beans are heated by solar
radiation from above
1
CA 02409066 2002-10-18
and by secondary radiation from the already warmed concrete slab below, while
natural
circulation of relatively dry air over the top of the beans slowly leaches out
the moisture. The
beans ferment during the process, and are tamed several times a day to promote
even drying.
They are covered at night to protect them from reabsorbing moisture during the
night time
dew point and temperature changes.
In the wet method, only the ripe cherries are picked in any one picking of a
tree. It
may take three to five sequential pickings in a season over the time it takes
between the
earliest and the latest chernes to ripen. After the cherries are washed, the
outside fruit pulp is
removed by machines and the berries are then placed into large concrete tanks
to ferment for
twelve to twenty-four hours, then poured into concrete sluiceways or washing
machines to be
thoroughly washed in constantly running water. Then they are dried in much the
same way as
in the dry method, except that the drying time is shorter. These beans are
then processed
through hulling machines to remove the remaining layers of skin.
Problems with either method of this art include the inefftcient, labor-
intensive and
lengthy sun-drying time of beans arranged on open air slabs. There have been
introduced over
the years, other manual, passive solar methods and devices attempting to
promote and control
air movement in combination with heat, to remove the moisture from bulk crops.
Most
2 0 typically, the beans or other materials being dried, are supported on a
foramenous surface or
in a container having at least foramenous bottom surface or screen, to permit
a greater degree
of circulation or air flow in contact with the underside as well as the
topside of the bulk
materials.
2 5 Various electrical powered and/or fuel-fired dryer systems have also been
used to try
to accelerate the drying time and prevent mold problems. There are many
patents that
describe related technologies and devices. Most of these alternatives add
expense and
complexity to an otherwise simple process. Failing to safeguard the beans from
excess
moisture, in particular the formation of mold during the drying process is
crucial as the value
CA 02409066 2002-10-18
of the crop drops dramatically if mold occurs. Over drying can also occur
using accelerated
methods; this also affects the quality and value of the crop. A sampling of
the art of
convective and low pressure air drying systems is included to provide context
for the
reader:
Stokes' US4,490,926 (1980 discloses a solar drying device and method for
lumber,
tobacco and grain. It includes a solar collector, a drying chamber, and a
dehumidification
system. The background section mentions solar heated kilns and dryers with
easy access
and containerized methods, wheeled vehicles or carts, for moving materials
into and out of
the dryer. Insulation and double glazing of light-admitting sheet materials is
discussed, as
is passing air between a drying chamber and a dehumidifying chamber. The focus
is on
drying and reusing the air.
Sutherland's US5,584,127 (1996) is a recent patent for a solar powered fruit
dryer.
The focus of the apparatus design is on recirculation of a portion of the
drying gas. It refers
to air circulating through perforated shelves (col. 4, line 32) upon which the
materials are
arranged. Column 4, line 60, describes the physical embodiment in some detail,
including
air flow volumes.
Andrassy's US5,001,846 (1991) is a solar drying apparatus with a translucent
sloping top and means for evacuating the condensation from the moist air. The
specification describes a perforated or porous tray on which the materials are
arranged for
dying. A solar powered fan forces drying air vertically through the porous
tray.
2 5 Mullin's US4,099,338 ( 1978) shows an elaborate, solar-assisted dryer for
tobacco,
onions, titanium dioxide drying, polyester fiber setting, and roasting nuts
and cereals. The
focus appears to be on ratios of solar heated makeup air in the circulation
system to save
fuel. The material is dried on a foraminous conveyor belt.
3
CA 02409066 2002-10-18
O'Hare's US4,501,074 (1985) is a convection powered solar food dryer that
discloses a solar collector on the inlet side for heating intake air, and a
vertical solar tower
or column to accelerate the convection of warm air through the system by
suction. The
actual drying chamber can be removed from the solar devices at each end of the
convection
system. The materials are arranged on shelves in the drying chamber.
Steffen's US4,045,880 (1977) is a solar grain drying apparatus. It discloses a
fan
forced down draft eave inlet solar roof heating system, that then drives the
drying air up
through the perforated floor of the central drying chamber. The air is then
exhausted
upwards roof exhaust fans in the drying chamber ceiling.
It~iuller's US 1,556,86 (1923) is a solar powered dryer system for vegetable
matter,
consisting of a series of circumfecential racks with inlet perforations in the
sidewalls and
internal shelf brackets in the corners for holding drying shelves or trays.
The racks are
configured for interlocked stacking underneath a solar collector roof which
has a central
exhaust vent.
Pietraschke's US4,391,046 (1983) is a solar heated grain drying system
featuring an
inlet manifold receiving multiple collector pipes and a fan blowing the intake
air up
through a perforated floor in the drying chamber.
Sweeny's US278,199 (1883) is a coffee roaster showing perforated drums for
containing the coffee beans, configured to revolve within a heated chamber.
The drums are
feed by hoppers through the ends. The drums use internal vanes to distribute
the beans or
other materials lengthwise, particularly for loading and unloading the drums.
Heating is by
other than solar means.
4
CA 02409066 2002-10-18
Danford's US4,263,721 (1981) is a tobacco curing and drying structure that is
configured for adding makeup air, using a heat exchanger and means for partial
recirculation.
The drying of coffee beans is exemplary of the prior art. The drying or
dehydrating
of fruits, nuts, vegetables and other food crops and naturally granular or
crushed or sliced
materials is a much frequented subject in the prior art. It is noteworthy that
a sliced and
dried piece of fruit has a significantly higher value than the freshly
harvested product.
While coffee and related bulk crops were the subject of the parent
applications, the
principles disclosed there are extended in both content and application in the
disclosure
that follows.
5
CA 02409066 2002-10-18
SUMMARY OF THE INVENTION
The invention in it's simplest form is a low pressure airflow dryer or
dehydrator
system for reducing the moisture content in berries, cherries, grapes, nuts,
whole fruits,
sliced fruits and garden foods, sliced meats, and bulk materials in the form
of small pieces or
granules or slices, and sliced crops in particular. Materials for which the
invention is
suitable can be divided into three categories by size and shape. The first
category
encompasses granular or crushed crops and whole nuts and berries; such as
rice, whole
coffee beans, cocoa beans, vanilla beans, crushed coconut, blueberries,
strawberries,
cranberries, and other seeds, pods, grains and materials having naturally
occurring small
specimens, or being easily reduced to small pieces by crushing, chipping,
cutting, freezing
and breaking, or other mechanical means, of a nominal average diameter between
one
quarter and about one inch, and having sufficient structural integrity to be
disposed at least
several inches deep, preferably as deep as three or four feet, without damage
that would
affect its dried value. In the case of relatively hard granular bulk materials
such as coffee
beans, commercial embodiments may utilize much greater depths in combination
with
complex airflow circuits and automated loading and unloading mechanisms.
The second category is bulk materials including fruits, vegetables and other
crops,
specimens of which can be easily reduced to slices of uniform thickness
between about one
quarter and one inch, and still have sufficient structural integrity to be
stacked edgewise at
least several inches and preferably to as high as three to four feet within
the apparatus of
the invention for drying, without damage that would affect its dried value.
Examples
include fruits such as apples, pears, mango, papaya, and carrots.
The third category is bulk materials including crops, specimens of which can
be
easily reduced to slices of uniform thickness as described above, but which
may not have
sufficient structural integrity to be stacked vertically on edge, and so are
preferably handled
6
CA 02409066 2002-10-18
in a horizontal plane without stacking. Examples include crops such as
tomatoes, peaches,
watermelon and bananas.
At the core of the system, there is a specialized bulk crop container
specially
configured to form a system of open wall airway channels uniformly distributed
throughout
the container and hence the selected bulk material when it is added to the
container, the
airways connecting through openings in the top and bottom or through opposing
sides of
the container as airflow inlets and outlets connecting to a closed or semi-
enclosed primary
airflow circulation system so that a distributed airflow can be directed
through the airway
network of the container to leach excess moisture efficiently from the bulk
material. The
container may be integral to the dryer system or removable.
The primary airflow system has a heater to elevate the air temperature so as
to be
able to absorb more moisture. The heater may be a heat exchanger of any type
or a heat
7. 5 generator such as an electric heating element. The airflow is maintained
by an air mover of
any n-pe, most typically a simple fan. The flow rates and pressure drop across
the container
are not excessive, generally within the range of standard 11VAC (heating,
ventilation and
air conditioning) industry practices.
2 0 A more limited secondary or exterior airflow or circulation path provides
a partial
exhaust and makeup air supply to the primary airflow system, so that moisture
levels are
kept below the saturation level. A heat exchanger using the inlet and exhaust
airflows of
the secondary airflow system may be employed to elevate the temperature of the
inlet or
makeup air so as to hold more moisture, by scavenging heat from the exhaust
airflow.
The key to creating an open-wall airway network distributed throughout the
container is the use of an internal structural network of minimal volume that
provides an
array of open face grooves or channels spanning the height and width of the
container. The
width of the open face each groove or channel is specified to be sufficiently
narrow to
7
CA 02409066 2002-10-18
prevent more than partial penetration into the groove by an average size
granular type
material being dried, and still pass a useful volume and rate of drying air
without undue
restriction or pressure drop. The parallel set of dividing partitions between
the airflow
channels provides an adequate surface area and sufficiently closely spaced
support grid to
support the sliced materials being dried. The depth of the groove or channel
is sufficient to
assure an airflow passageway will remain open the full length of the groove or
channel,
when the container is full of the bulk or sliced material.
An efficient form of the required internal structure of the container is a
series of
parallel partitions or airflow plates, dividing the container into a parallel
set of uniformly
thin bays or compartments, preferably in the order of three Bights to one inch
in width. The
bays may be arranged in the vertical plane or the horizontal plane. In either
case the
opposing faces of each bay feature a parallel set of grooves running the full
height or width
of the partition, and terminating at or actually projecting through a
foramenous end wall or
bottom panel such that the airway formed by the groove is accessible to an
airflow that is
ducted or channeled to that wall or bottom panel. It will be apparent that the
partitions
themselves consume width in the container between compartments, in order to
provide the
unobstructed, uniformly distributed air channels that are a hall mark of the
invention.
2 c) As described, each groove or channel has an open face exposed to the bulk
material, while being sufficiently narrow to prevent the pieces or slices of
materials from
penetrating into the groove. This provides a significant surface area of the
material with
direct or near direct exposure to the drying effects of the airflow in the
groove or channel.
Closely adjacent airflow channels or grooves on each airflow plate, and
closely spaced
2 5 airflow plates uniformly distributed within the container volume, assure a
uniform and
relatively quick penetration of the drying effects of the airflow as to the
material in the
container.
8
CA 02409066 2002-10-18
Practical embodiments of partition material, as will be discussed more fully
below,
include ribbed panels, where both sides of a panel are configured with
parallel sets of
raised ribs, the spaces in between which are grooves; and corrugated panels,
where both
sides of the panel present to their respective bays or compartments, a
parallel array of
ridges and grooves. Raised ribs or round corrugations, rather than sectional
or box
corrugations with flats, have a further benefit of offering only a tangential
point of contact
to the materials being contained. Other forms and embodiments of the internal
structure are
within the scope of the invention.
The preparation of fruit or other materials needing to be sliced for loading
and
drying requires the fruit to be sliced into uniformly thick slices that will
fit closely within
the width of the drying compartments and slide into a closely packed
arrangement without
binding. There is no particular orientation required of the fruit for slicing,
so the slicing can
be easily automated or semi-automated for speedy slicing. In the case of
category two
vertical orientation of the bays and vertical stacking for drying, the
edgewise oriented
column of slices in the compartments must not be so tall as to seriously crush
the slices at
the bottom. However, this has not been a problem with containers suitably
sized for manual
handling and compartments in the order of three eighths or one half inches
wide and up to
30 inches tall. Containers for category three sliced materials are arranged
with partitions in
2 0 the horizontal plane, so that each partition acts as a ribbed tray for the
bay above it,
suspending the slices sufficiently on the air channel partitions to permit
drying airflow
beneath the slices as well as over them.
The cycle of loading and unloading of the bulk materials into and out of the
dryer
2 5 system may be enhanced by configuring the container or containers with
bottom panel gates
or sliding gates which can be opened to dump the contents of each bay, and
closed for refill
and operation of the dryer, without removing the container from the system. An
optional
vibrator may be attached to the container or framework of the apparatus to aid
in filling and
emptying the container. The vertical bay container may be manually filled with
sliced
CA 02409066 2002-10-18
materials through the open top, more akin to how granular bulk crops such as
coffee beans
are loaded, with greater speed and efficiency by carefully metering the sliced
materials out of
a dispensing container so as to flow the slices into the open end of the
container with an
orientation parallel to the partitions.
An alternative method for loading of materials, and in particular category
three
materials, is to arrange the container so that the airflow plates are in the
horizontal plane. The
grooved plates or panels can then be removed sequentially or collectively
through an open
end of the container for manual or automated placement of a single layer of
slices on each
panel and reinsertion into the receiving slots of the container. A loading
rack may be used to
receive and deliver the full set of plates to and from the container. The
loading and unloading
may be further automated for higher volume conunercial practices.
During the drying process, there may be some tendency for some types of fruit
or
other materials to stick lightly to the panels. When the drying cycle is
complete, a light sweep
over the panel surface releases any stuck slices. If desired, an antistick
coating may be
applied to the plates prior to use, or the plates may be fabricated with a non-
stick surface.
As is apparent from the above description, by arrangement of the airflow
panels or
2 0 partitions, or by reorientation of the container, the airflow through the
container with
vertical bays can be arranged to be vertical or horizontal; whereas in a
container configured
with horizontal bays, the airflow is constrained to horizontal although it may
be in either of
the two orthogonal horizontal axis. Upwardly vertical airflow is particularly
useful for very
low airflow pressure systems such as passive solar systems where thermally
generated
2 5 connective airflow with minimal head pressure can be applied to a single
level container.
Not withstanding, short horizontal airflows may also used.
Alternatively, a user may, by using a forced airflow system, provide a much
greater
pressure and volume of air through the container than typical passive solar
systems. This
CA 02409066 2002-10-18
makes the larger container systems with horizontal airflow plates useful,
whether
configured with vertical or horizontal drying bays. Forced air circulation
with or without a
supplemental heat source for adding more heat to the air, speeds up the
process. Using a
heat pump as the air mover and dryer adds significant efficiency to the
process with its
ability to cycle air temperature so as to squeeze out the moisture and then
reheat and
recirculate the air. The user may obtain either faster drying time of a small
batch of
materials by pushing more air through the dryer, up to a maximum useful rate
of extraction
of moisture; or greater batch capacity by using larger and more complex
containers with
either vertical or horizontal airflow networks, interconnected with ductwork
to link the
containers.
The container is scalable and adaptable to smaller and larger dryer systems
utilizing
heat exchangers, solar radiation or other power sources for generating a warm,
relatively
dry, low to moderate pressure airflow. The container, inserted or connected to
the airflow
plenum of the system for both inlet and exhaust, absorbs the full flow of
drying air through
its interior. The internal construction provides a baffle effect on the
pressure side of the
container, which promotes very uniform distribution of airflow through the
materials and
even drying, overcoming a significant disadvantage of other systems.
Z ~ IIl the passive solar drying of bulk crops such as coffee and grains, nuts
and berries,
and sliced fruits and vegetables, airflow is generally more limited than heat,
due to the
relatively low differential pressure that can be generated in low cost,
practical, solar
radiation dryers. It takes many hours or days to affect a significant
reduction in moisture
levels in the passive solar drying of crops. The relative amount of airflow to
which the
2 5 crops are directly exposed has been demonstrated in passive solar dryers
to be the more
significant factor to the dryer's utility and efficiency, than simply adding
heat. Too much
heat with too little air will do more damage than good. It is therefore
important to configure
solar powered dryers to obtain maximum flow from a relatively dry air source,
and
11
CA 02409066 2002-10-18
maximum exposure of the materials to the dry air flow, while retaining a low
cost structure
and a simple bulk container handling system.
The principle functional components of a primary dryer system of the invention
are
a warm, dry airflow generator, a bulk materials container configured to
provide the
uniformly distributed open channel airways network of the invention, structure
for
supporting the container within the primary dryer system in such a way as to
constrain air
flow to flowing through the airways of the container, and features of the
container by
which it can be filled and emptied.
As introduced above, a further aspect of the invention provides a complex
airflow
system with a closed primary loop and an open secondary loop. As distinguished
from the
simpler case above, there is a closing of the circulation loop or path of the
primary airflow
system through the container as a recirculating airflow with a good airflow
rate and
pressure drop through the airflow plates of the drying container and hence
through a larger,
lower airflow rate, mixing plenum, the pressure and airflow rate being
maintained by
airmover mechanisms. The airflow is heated by any suitable means and the
overall
enclosure may be insulated to conserve heat. Added to that is a secondary,
open airflow
circulation loop of more limited airflow rate that provides for partial
exhaust and makeup
2 0 air to the primary closed loop airflow path for removing excess moisture.
This permits
configuring the total system to optimize each functional element of the
process at the
lowest total energy cost, as will be further described below.
Still other objects and advantages of the present invention will become
readily
2 5 apparent to those skilled in this art from the following detailed
description, wherein I have
shown and described only a preferred embodiment of the invention, simply by
way of
illustration of the best mode contemplated by me on carrying out my invention.
12
CA 02409066 2002-10-18
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a side view of a preferred embodiment solar dryer of the invention,
showing the rack,
solar powered convective generator, container housing, container and
transparent top
assembly.
Fig. 2 is a perspective view of the container of Fig. 1, showing the filling
of the
compartments of the container with a bulk crop.
Fig. 3 is a partial edge view of a corrugated airflow plate.
Fig. 4 is a partial perspective view of the corrugated airflow plate of Fig.
3.
Fig. S is a partial plan view of a slotted bottom panel as used in the
container of Fig. 2.
Fig. 6 is an edge view of the panel of Fig. 5, after the edges are folded to
right angles.
Fig. 7 is a partial perspective view of the panel of Fig. 6, with airflow
plates installed in the
slots of the panel.
Pig. 8 is a partial perspective view of three of the Fig. 6 panels, configured
as a bottom panel
for the container of Fig. 2.
Fig. 9 is a left rear perspective view of a preferred embodiment dryer, with a
partial cut away
2 5 revealing the bulk material container and general airflow pattern.
Fig. 10 is a lefr front perspective view of the embodiment of Fig. 1, the
front and left side of
the enclosure and the enclosed portion of the container shown in phantom. ,
13
CA 02409066 2002-10-18
Fig. 11 is a perspective view of a slotted V brace for supporting airflow
plates in a container.
Fig. 12 is a cross section view of a vertical airflow plate container
employing the slotted V
brace
of Fig. 11 in support of the airflow plates.
Fig. 13 is a cross section view of a horizontal airflow, corrugated airflow
plate, commercial
dryer system employing the slotted panels of Figs. 5 - 8 for retaining the
airflow plates.
Fig. 14 is a plan view of a commercial dryer system employing the dryer of
Fig. 13.
Fig. 15 is a perspective partial view of an airflow plate partially removed
from the dryer of
Fig. 13.
Fig. I6 is a diagrammatic cross section view of a two chamber dryer system of
the invention
separated by a materials drying container, with an air dryer in the low
pressure chamber and a
primary airflow fan between the chambers.
Fig. 17 is a diagraincnatic cross section view of a dryer similar to that of
Fig. 16, but having a
2 0 fan forced secondary airflow of makeup and exhaust air vents in the low
pressure chamber
rather than an air dryer.
Fig. 18 is a diagrammatic cross section view of a dryer similar to that of
Fig. 17, except that
the exhaust air outlet is in the high pressure chamber so that secondary
airflow is generated
2 5 by the air pressure differential beriveen chambers.
Fig. 19 is a diagrammatic cross section view of a dryer similar to that of
Fig. 18, except that
an air to air heat exchanger is added to scavenge exhaust air heat for heating
makeup air.
14
CA 02409066 2002-10-18
Fig. 20 is a diagrammatic cross section view of a dryer similar in function to
that of Fig. 19,
except that in incorporates solar heating of the primary airflow, and the air
to air heat
exchanger and secondary airflow path is fan forced.
S Fig. 21 is a diagrammatic cross section view of a multiple container
embodiment of the
invention, each container having its own high pressure chamber and sharing a
common low
pressure chamber.
Fig. 22 is a diagrammatic cross section view of a three chamber dryer with two
banks of
materials containers sharing a common low pressure chamber.
Fig. 23 is a diagrammatic cross section view of a multiple container
embodiment similar to
that of Fig. 21, except that it includes air to air heat exchangers and fans
in the secondary
airflow circuit.
CA 02409066 2002-10-18
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Fig. l, there is illustrated an open loop solar powered dryer
system 10
with a removable, vertical airflow, bulk materials container 100. Rack
assembly 1 is made
of pipe material secured to the ground or a base of some sort, and passive
solar convective
airflow generator 2 is attached to it. Top assembly solar collector 3,
consisting of a frame
with a translucent top surface, is attached to sidewalls 4, forming plenum 5.
The top
assembly is equipped with a circulation fan 8 powered by solar cell 9, which
boosts the
convective airflow through the dryer system. Container 100 is manually
insertable through
an opening in the upper end of plenum 5, by the use of handles 102.
Container 100 is configured with an interior airway network structure of
uniformly
distributed, vertical, open wall, airflow passageways which open through the
bottom panel
to admit the connective airflow generated by airflow generator 2. The channels
defining
the open wall airways are too deep to be obstructed by pieces or slices of
materials being
held in parallel alignment with the partition walls and too small to be filled
by the grains or
kernels of the bulk crops placed in the container for drying. The container
can be filled to
the top of the airvrray strucriue, the fruit slices or bulk material enjoying
a distributed flow
of air from bottom to top, as will be further explained in the later figures.
2C
The interior sidewalls of plenum S are configured with sidebars and side
skirts upon
which container 100 is supported. This contact serves to divide the plenum
into upper and
lower chambers, and to constrain the vertical airflow to flowing from the
lower chamber
through the internal airways in the container into the upper chamber.
Referring now to Figs. 3 - 8, container 100 has an interior network of
vertical
airflow plates 116, uniformly spaced and parallel to each other, extending
across the width
of the container. The airflow plates are held in position by slotted top
support brackets 112,
oriented at right angles to the airflow plates, and slotted bottom panels 114.
16
CA 02409066 2002-10-18
The fruit or bulk material is added as shown in Fig. 3, to container 100, to a
nominally full state, about level with the tops of airflow plates I 10. There
is a ventilated
bottom panel, not shown, permitting airflow through the bottom panel and to
the airflow
plates.
Airflow plates 110 are variously fabricated as shown in Figs. 3 and 4, of
stainless
steel sheets of 0.010 to 0.015 inches thick, into corrugated airflow plates
116. Aluminum is
also useful material for airflow plates. Other materials can be used,
including other metals
or plastic. A surface coating such as Teflon can be added to metal airflow
plates to reduce
sticking of fiuit slices.
The width and depth of the channels provided by the corrugations is determined
by
the size of the grains or kernels of the bulk crop being dried, when the bulk
crop is granular
in nature. When the container is intended for the dying of coffee beans, the
depth D of the
corrugations is about one eighth (1/8) inch. The width W of the corrugations
is about one
sixth (1/6) inch. In embodiments using these airflow channel dimensions,
granular bulk
crops of average grain diameter of greater than one quarter (1/4) inch can
also be
processed. This corrugation size also works well with sliced fruit, although a
somewhat
larger scale to the corrugations will work, also, up to one quarter (1/4) inch
in width and
2 0 depth. Larger scale airflow channels consume more space in the container
than is necessary
for effective drying when several airflow plates are used, and reduce the
useful volume for
the materials being processed. The dimension of the airflow plate in the
direction of the
airflow channels is about 8 inches. This provides a sufficiently short airflow
path for
assuring low static pressure across the container from inlet to outlet. Longer
dimensions
2 5 may be preferred for some applications or where greater airflow pressures
are available.
It should be reiterated that the airflow plates need not and preferably are
not
perforated. Uniform distribution of airflow through the materials is initiated
at the inlet
baffling structure of the airplate end supports, whether bottom or sidewall of
the container,
17
CA 02409066 2002-10-18
between the protruding airflow plate ends and airflow plate support dividers.
The airflow
plate structure and contents of the container resist airflow so as to provide
a small static
pressure head in the inlet plenum that exerts uniform pressure across the face
of the inlet
structure. The airflow is then segregated by the airflow plates so as to
maintain the uniform
cross section distribution of airflow through the container such that the
materials are
uniformly dried.
Referring to Figs. 5 - 8, stainless steel sheet is slotted as in Fig. 5, and
folded at the
edges to fabricate edge panels 114 as in Fig. 6, which may be used at the
bottom or side
depending on container configuration, so as to hold the ends of corrugated
airflow plates in a
uniformly spaced, parallel relationship as in Fig. 7. The panels are arrayed
as shown in Fig. 8
to form a bottom for a vertical airflow container. The bottom edges of
corrugated airflow
plates 116 are inserted into the slots from above, held at equidistant spacing
in the container
by the slots, and rest on the folded slot ends, as in Fig. 7. The channels of
the slightly
protruding airflow plates are thus open to airflow from beneath the container
when the
container is filled with bulk granular or sliced materials. A container
configured for
horizontal airflow would use the same panels 114 incorporated as side panels
as in the
container of Fig. 13.
Referring to Figs. 9 and 10, an airflow dehydrator 20, consists of enclosure
22,
configured with front side discharge door 23, a sloping discharge plate 24,
and an airflow
inlet 25 on the back side, which is a large, air manifold that can be
connected to a solar, oil,
gas or wood fired furnace, a solar hot air panel, or other source of warm air.
Hinged top 26
is configured with exhaust ports 28, to which powered exhaust fans may be
readily adapted
if desired. Vertical airflow container 101 is supported within enclosure 22 so
as to seal off
air flow from inlet 24 to exhaust port 28, except as may pass through the
airflow
passageways of container 101, as further described below. Hinged top 26 may be
opened
for access to and filling of container 101. Bulk material, when dry and
allowed to fall
18
CA 02409066 2002-10-18
through the bottom of container 101, is directed by sloping discharge plate 25
towards
discharge door 23 for collection.
Containers for dryers such as dehydrator 20, such as container 101, are
similar, in that
in both cases the bottom panels are ventilated in some fashion to connect the
vertical airflow
plates to the airflow source or supply. However, container 101 is
distinguished from container
100 by having an openable bottom panel system, so that bulk materials can be
loaded through
the top and emptied when dry, through the bottom. With this arrangement, the
container can
be left more or less stationary in the dryer. Alternatively, the elements or
functional
components of container I01 can simply be integrated directly into the
dehydrator 20 design,
if desired.
For vertical airflow containers using parallel airflow plates, it is desirable
to reduce or
eliminate top side support brackets so that the bulk materials can be loaded
more easily to the
top of the airflow plates. Referring to Figs. 11 and 12, slotted and inverted
V braces 118,
uniformly spaced and attached to opposing sides of container I01, provides an
open top
spacing and lateral support system for a full compliment of corrugated airflow
plates 116.
The airflow plates are seated in the bottom of the inverted V slot. The V
brace height
coincides with the top of the airflow plates, permitting easy loading and
leveling of the bulk
2 0 materials in the container. On the bottom side of the container, the dump
gates are oriented to
close and open the space between the V braces. The open space within the
inverted V brace
118 is lost as to container volume, but does assure even greater penetration
of the sliced or
granular bulk materials by the drying effect of the airflow entering from
underneath, and
exiting out the top of the container. V braces I 18 are preferably fabricated
of stainless steel.
Dryers 10 and 20 above are illustrative of small batch dryers, using
relatively small
containers, and employing an open loop airflow circuit where a dry airflow
from a source is
directed by an airmover of any sort through the container of the invention to
scavenge
moisture from the contents, and then e:chausted to atmosphere. They can be
scaled upwards
19
CA 02409066 2002-10-18
within practical limits of materials. Very low pressure convective airflow
pressure, such as
generated by solar devices, will effectively penetrate up to a foot or more of
material depth in
a vertical airflow container. The benefits of these devices include low cost,
simplicity, easy
operation and adaptability. Greater capacity can be had by simply duplicating
the apparatus as
many times as desired. These devices can be configured to employ containers
configured for
horizontal airflow, or even downward directed vertical airflow, but would
preferably include
a powered fan or airmover device.
Referring to Fig. 13, there is illustrated a cross section view of a preferred
embodiment, open airflow circuit, horizontal airflow commercial dryer system
30, especially
suitable for drying sliced materials such as fruits and vegetables. System 30
incorporates a
container 32, employing the slotted panel 114 of Figs. 5 - 8, for retaining
corrugated airflow
plates 116 in a horizontal airflow configuration at a materials depth of up to
about four feet,
and a width for airflow penetration of materials of about eight inches.
Container length, or
module length, can be up to two feet without special consideration. Inlet 34
feeds plenum 36
and the inflow side of container 32. The horizontal airflow exits the outflow
side of container
32 into plenum 38 and is exhausted out of outlet 40. Legs 42 support system 30
sufficiently
high to permit opening of dump gate 44 and discharge of the bulk materials
into the user's
collection system. Referring to Fig. 1 ~, airtlow plates I 16 can be manually
removed for
2 0 inspection, cleaning or other service access, and reinstalled. The airflow
supply for system 30
is presumed to be fan powered on the inlet and/or outlet side, and auxiliary
heat may be
added to the airflow on the inlet side of the container.
System 30 may be configured and operated as a single container unit, or ganged
with
2 5 ductwork as in the Fig. 14 plan view for larger operations. The Fig. 14
system includes three
bays of three end to end modules 30, with ductwork 50 connecting the inlets
and outlets.
Dehumidifier 52 and/or hot air furnace 54 are connected in the upstream side
of the airflow.
Exhaust fan ~6 is connected on the downstream side of the airflow. System 30
is here
illustrated as an open airflow circuit system, but note that airflow control
valve 58 enables the
CA 02409066 2002-10-18
primary airflow circuit to be closed for recirculation of the air for heat
conservation, where
exhaust fan 56 functions as a recirculation fan, and where dehumidifier 52 is
used to remove
excess moisture. Dehumidifier 52 and furnace 54 can be replaced with a heat
pump,
obtaining the greater efficiency of using a significant range of thermal
cycling of the air for
moisture removal and recirculation. Also note that in the system of Fig. 14,
and in all cases
where airflow is predominately controlled by fans and contained by ductwork,
the distributed
airway system may be configurzd to permit the airflow direction to be
reversed. This is
readily apparent in horizontal flow dryers, but is also applicable to vertical
airflow dryers of
the invention, without a significant increase in back pressure, due to the
presence of the
airivays. This airflow switching technique enhances the drying process by
offering quick
penetration of the drying effect of the airflow on the materials from the top
down as well as
from the bottom up, or left and right in the case of horizontal airflow,
thereby more quickly
drying the entire volume of material. In an open airflow circuit system,
reversed airflow will
require a heater on each end of the container if heated airflow is required in
both directions.
The embodiment of Fig. 13 extends to containers or material holding sections
of very
tall connnercial drying systems for small, relatively hard granular bulk
materials such as
coffee beans. Systems with materials container sections having vertical depths
of up to I 6
feet and greater, fillable from the top and configured with hinged or slide
gate bottoms for
self emptying, adapted with automated filling and collection mechanisms,
enable efficient
drying of conunercial size batches of beans or other materials. The systems
may incorporate
vibrators to promote easy filling and drainage of the container section. The
16 foot long
corrugated airflow plates of this preferred embodiment remain limited to eight
inches in
width, consistent with the above description of airflow channel orientation
and length. This
2 5 dimension assures a minimal static pressure drop across the container from
inlet to outlet
with respect to the drying airflow. Such containers are likely to be
incorporated into the more
complex airflow systems described in Figs. 14 and 16-23, than in simpler open
loop airflow
systems.
21
CA 02409066 2002-10-18
Referring back to Figs. I, 13 and 14, while the heat generated in a simple
solar
collector is adequate for a basic open airflow circuit dryer of the invention,
the minimal head
pressure of a relatively short solar powered airflow generator combined with
the resistance of
the distributed array of airflow channels through the container may result in
a less than
optimal volume of drying airflow through the container. Any boost to the
airflow inlet
pressure or flow rate through the container is found to improve the
performance of the
dryer. A passive, solar-generated air flow can be boosted by the addition of
circulation fans
at various places on the dryer, including in the convective generator section,
in the
upstream or source air plenum, or in the exhaust plenum. Of course, fans are
often used
exclusive of any passive solar contribution, in many commercial dryer
installations.
Auxiliary heat, supplied by heaters, heat exchangers, or the injection of
supplemental hot air, can also be added anywhere to the air flow path upstream
of the
container. Sensors may be added to the container or dryer to monitor pressure,
airflow,
humidity, time, and/or temperature; indicators may be provided locally or
remotely. A local
or remote, automated or programmable control means may be added for better
control
and/or recording of the process. Pressure sensors can be utilized to monitor
the weight of
the container or dryer to calculate the progress and amount of moisture
reduction.
2 0 While these elements are not core components of the instant invention, use
of the
invention enhances the benefit provided by greater pressure and more heat, up
to the point
of maximum drying effect in a given configuration for a given bulk product.
The division
and distribution of the airflow through the bulk materials assures uniformity
and rapidity of
drying, thereby improving the quality of the end product and the efficiency of
the system.
The method of the invention includes low temperature drying as may be done
with
the use of heat pumps and cooling coils. System components may be augmented
for
addition cooling capacity for removing moisture from the low temperature
primary airflow
circuit. The invention is further adaptable to freeze drying methodologies.
22
CA 02409066 2002-10-18
Now referring to Figs. 16 - 23, there are shown several preferred embodiments
incorporating a complex airflow circuit feature, where the primary airflow
circuit is a
closed loop airflow path within the system, analogous to the recirculation
operation of the
system of Fig. 14. There is common to all embodiments of Figs. 16 - 23 at
least one drying
container, and a low pressure plenum connected to the outlet side of the
container and
divided by an airmover or fan from a high pressure plenum on the inlet side of
the
container. The airflow through the container is maintained by the fan, and the
air
temperature is maintained by a heater of some sort, so as to pass a continuous
flow of
warm air through the container.
In Fig. 16, an insulated enclosure 160 houses a removable container 161 of the
invention, the outlet of which connected to low pressure plenum 162 which is
divided by
fan 163 in wall 169 from high pressure plenum 164 which is connected to the
inlet side of
container 161. This path defines the primary airflow circuit through container
161. Electric
heater 165 is positioned on the intake side of fan 163 to heat the primary
airflow.
Dehumidifier 166 within enclosure 160 removes moisture fCOIll the airflow, and
emits it at
condensate outlet 167. Container 161 rides on rails 168 for removal from
enclosure 160
for filling and emptying of materials being dried, and seats when fully
inserted against
2 0 partition 169 to seal its inlet to high pressure plenum 164. The benefit
here is that the
airflow and temperature can be balanced with the best moisture removal rate
from the
materials, and the dehumidifier sized and operated to remove excess moisture
from the
primary airflow and keep the moisture level in the love pressure plenum at a
suitable level.
2 5 There may be substituted for dehumidifier 166 in this embodiment or other
embodiments similar in this regard, any type of air dryer or means for
removing moisture
from the closed primary airflow, as for example a desiccant dryer of
sufficient capacity
such as a desiccant wheel dryer.
23
CA 02409066 2002-10-18
Fig. 17 is the same as Fig. 16 except that enclosure 170 incorporates an open
secondary airflow circuit in lieu of dehumidifier 166, through exhaust fan 176
and
adjustable inlet 177 servicing low pressure plenum 162. This permits the
primary airflow
through the container to be set at a higher rate for most effective drying
action, and a lower
secondary airflow rate, which is adequate to remove the accumulated moisture
by
continuously replacing a small portion of the relatively moisture ladened
total primary
airflow volume with dry air. The total energy cost for heating and moving air
so as to dry
the contents of the container is improved over the single open circuit system
of the earlier
described systems.
Fig. 18 is the same as Fig. 17 except that enclosure 180 incorporates outlet
vent 186
in the high pressure plenum 164 and adjustable inlet vent 187 in the low
pressure plenum
162 in lieu of the exhaust fan 176 and inlet 177 of Fig. 17, as defining the
secondary
airflow circuit. The pressure differential maintained between plenums 162 and
164 by fan
15 163 enables the secondary circuit, with balancing between primary and
secondary airflow
circuits provided by the adjustability of inlet vent 187.
Fig. 19 is the same as Fig. 18, except that the secondary airflow circuit
incorporates
air to air heat exchanger 191, where a partial outflow from high pressure
plenum 164 enters
20 heat exchanger 191 at inlet 192 and exits at adjustable outlet 196, and
make up air enters
heat exchanger at inlet 197 and exits heat exchanger at outlet 193 within low
pressure
plenum 162.
Fig. 20 is visually different but functionally the same as Fig. 19, except for
the
following. Enclosure 200 consists of a solar panel section 204 and insulated
walls 205 for
providing solar heating of the primary airflow in low pressure plenum 162. As
in the
previous Figs. 16 - 19, the closed loop primary airflow circuit is through
container 161, low
pressure plenum 162, fan 163, high pressure plenum 164 and again through
container 161.
Heater 16~ adjacent fan 163 is option where solar heating is sufficient. The
secondary
24
CA 02409066 2002-10-18
airflow circuit in this embodiment is moved by its own airmover device rather
than by the
differential pressure between plenums. It consists of air to air heat
exchanger 201, where a
partial outflow from low pressure plenum 162 enters heat exchanger 191 at an
inlet (not
shown) and exits at exhaust fan outlet 206, and make up air enters heat
exchanger 20I at
inlet 207 and exits heat exchanger within low pressure plenum 162. The
utilization of
passive solar heat for heating the primary airflow further reduces the system
operating cost
at a minimal further capital cost. As in the prior embodiments, the drying
efficiency of the
system for drying the materials in the airflow plate container 161 may be
optimized for
drying time and energy consumption by suitably balancing the primary airflow
rate and
temperature, and the percentage of secondary airflow for exhausting moist air
and
supplying pre-heated make up ambient air. Heat exchanger 201 is configured
within low
pressure plenum 162 and behind solar panel section 204 so as to derive further
benefit from
direct passive solar heating that adds heat to the secondary airflow circuit
makeup air.
Fig. 21 is visually distinguished but functionally the same as the embodiment
of
Fig. 20, except for the following. Enclosure 210 is a green house, having a
solar permeable
exterior 214, by which passive solar heating of the primary airflow is
accomplished, and a
convenient access door 21 ~. The primary airflow circuit serves two airflow
plate containers
161, which each have a fan 163 and high pressure plenum 164, but sharing a
common low
2 0 pressure plenum 162, which consumes most of the interior volume of the
enclosure.
Optional heaters 16~ are optimally positioned adjacent fans 163 for further
heating
capacity. The heaters can be solar hot water heaters, or electric or wood or
fossil fuel
heaters intended to augment the solar heat during night or times of extended
cloudiness.
The secondary airflow circuit is produced by two exhaust fans 216 diagonally
positioned
2 S on opposite corners of the enclosure, and interspersed with two adjustable
inlets 217 on the
other two opposite corners of the enclosure. The two containers 161 can each
be a line of
containers 161, each served with its own fan 163 and high pressure plenum 164,
for the
length of the enclosure. Secondary airflow capacity must be altered
accordingly.
CA 02409066 2002-10-18
Fig. 22 is visually distinguished but functionally the same as the embodiment
of
Fig. 18, except for the following. Enclosure 220 is a green house, having a
solar permeable
exterior 224, by which passive solar heating of the primary airflow is
accomplished. The
interior is divided by two partitions 169 into three plenums, a center low
pressure plenum
162 sandwiched between two high pressure plenums 164. Each of two airflow
plate
containers 161 are sealed to a respective partition 169. Fans 163 in each
partition 169 pull
the primary airflow through containers 161, hence through the common low
pressure
plenum 162, and divide and push it into high pressure plenums 164 and back
into
containers 161. Optional heaters 165 provide for additional airflow heating
capacity. The
secondary airflow circuit is provided by adjustable inlet vent 227 in low
pressure plenum
162 and outlets 226 in each of high pressure plenums 164. Enclosure 220 has
three
convenient access doors 215, one serving each plenum. It will be appreciated
that the fan
direction, primary airflow, and secondary vent orientation can be reversed. It
will be further
appreciated that each partition 169 and container 161 can be a long partition
and several
1 S containers for the length of enclosure 220. Vents and airmovers would have
to be sized and
positioned accordingly.
Fig. 23 is visually distinct but functionally the same as the embodiment of
Fig. 20,
except for the following. Enclosure 2 30 is a green house, having a solar
permeable exterior
2 0 234, by which passive solar heating of the primary airflow is
accomplished. The interior is
principally dedicated to low pressure plenum 162. Each of two airflow plate
containers
161 are coupled with high pressure plenums 164 configured with fans 163 for
maintaining
the primary airflow. Optional heaters 165 adjacent fans 163 provide for
additional airflow
heating capacity. The secondary airflow circuit in this embodiment is moved by
its own
2 5 airmover device rather than by the differential pressure between plenums
as in some
embodiments. It consists of two vertically oriented air to air heat exchanger
231, where a
partial outflow from low pressure plenum 162 enters heat exchanger 231 at an
inlet (not
shown) and exits at exhaust fan outlet 236, and make up air enters heat
exchanger 231 at
inlet 237 and exits heat exchanger within low pressure plenum 162. Heat
exchangers 231
26
CA 02409066 2002-10-18
are configured within solar permeable section 234 so as to derive further
benefit from
direct passive solar heating that adds heat to the secondary airflow circuit
makeup air. It
will be further appreciated that each container 161 and plenum 164 with its
fan 163 can be
a line of such assemblies as long as the length of enclosure 230. Secondary
airflow circuit
heat exchangers, vents and exhaust fans would have to be sized and positioned
accordingly.
The design configuration of the closed primary airflow circuit dryer enclosure
and
the airflow plate containers can be scaled and varied as required for drying
various batch
quantities of crops or other materials, always incorporating appropriate
vertical and/or
horizontal airway partitioning elements uniformly distributed throughout the
container. The
drying effect radiates outward by convective and conductive means into the wet
granular or
sliced materials from each airway passage on each airflow plate in the
container, and
uniformly over time reduces the moisture content of the materials, carrying
the moisture
out evith the primary airflow to where it is removed from the dryer system by
air dryers or
the secondary airflow air exchange.
The bottom of the airflow plate container can be configured with a releasable
door
or dump gate assembly that is ventilated as necessary to permit airflow to the
airplates,
while closing off the bottom opening of the bays or compartments which hold
the sliced or
2 0 bulk material being dried. The gates can be easily opened, manually or
remotely if so
configured, to dump or empty the container without the need to turn it over.
The containers
can be configured for easy manipulation for being withdrawn from the dryer
enclosures for
emptying and refilling, including the use of mechanisms for sliding, rolling,
and/or rotating
the containers, and combinations of such actions, and the use of drop gates,
doors and
2 5 plungers to clear the containers of contents.
The airflow plate container and in particular the embodiments of Figs..l6 - 23
of the
invention are quite suitable for drying apple slices, for example. Other foods
and fruits or
articles of other types having a significant moisture content and that are of
the correct
27
CA 02409066 2002-10-18
thickness or are susceptible of reduction into slices of uniform thickness
that will still hold a
suitable degree of rigidity for edge stacking between airflow plates, can be
dried in the
vertical slots of the containers. For slices that tend to stick to the airflow
panels in the drying
process, manual or automated removal forks and light combing or sweeping of
the airflow
plates can be employed to release the slices. The combing or scrubbing action
can be
accomplished by a simple grid that is laid over the top of the container so as
to place a bar or
gate over each open compartment, so that lifting of an airflow plate partially
out of its slot
causes a combing action by the bar that releases any sticking fruit slices to
fall back into the
container. Alternatively, an automated plunger system can be used to evacuate
the container
after the bottom gate is opened.
For slices of food, fruit, or other articles less tolerance of vertical
stacking, such as
sliced tomatoes or bananas, container and system embodiments using grooved or
corrugated
panels with slots oriented in the horizontal plane, resembling a stack of
corrugated trays, are
useful. The horizontal plane airflow plate embodiments are less critical as to
the thickness of
slices, as well, and some foods and fruits are better suited to being dried in
relatively thin
slices.
There are other and numerous embodiments of the invention. For example, there
is a
2 0 dryer system for drying materials of uniform thickness, meaning to include
granular materials
of relatively uniform diameter such as coffee beans, berries, nuts and the
like, as well as slices
of uniform thickness of fruit and other wet materials from which moisture is
desired to be
removed. The dryer system may consist of a container for holding the materials
for drying, a
high pressure plenum communicating with a first ventilated surface of the
container, a low
2 5 pressure plenum communicating with an opposing ventilated surface of the
container; and
a plurality of parallel and uniformly spaced airflow plates disposed within
the container so
as to form bays of uniform widths sufficient to accommodate the sliced
materials of
uniform thickness. The airflow plates are configured with open wall airflow
channels
connecting the inlet plenum to the outlet plenum.
28
CA 02409066 2002-10-18
There is a primary airflow circuit consisting of a connecting airway running
from
the low pressure plenum to the high pressure plenum and hence through the
container and
into the low pressure plenum, and a primary airflow sustainable by an air
mover such as a
fan. There may be means for heating the primary airflow including airflow
heaters of any
or all types, and there may be incorporated control mechanisms and airflow
coolers for
controlling the average temperature of the airflow. There are also means for
removing
moisture from the primary airflow, such as air dryers of any or all types or
secondary
airflows partially exhausting wet air and providing relatively drier makeup
air. There are
means for sustaining the secondary airflow, such as solar heated plenums,
flues or the use
of electric fans. There may be an inlet for the make up air configured in a
low pressure
plenum and an outlet for exhaust air configured in the high pressure plenum,
with at least
one being adjustable for controlling the rate of said secondary airflow
relative to the
pressure differential between the inlet and the outlet. In the case of coffee
beans in
particular, the ba3-s detined by the airflow plates may be vertically oriented
and extend to
much more than four feet, even up to 16 feet and higher.
As another example, there is a dryer system expressly for drying sliced
materials of
uniform thickness, consisting of a container for holding the sliced materials
for drying, an
2 0 inlet plenum communicating with a first ventilated surface of the
container, an outlet
plenum communicating with an opposing ventilated surface of the container; a
plurality of
parallel and uniformly spaced airflow plates disposed within the container so
as to define a
parallel set of bays of uniform thickness sufficient to accommodate a layer of
the sliced
materials, where the airflow plates are configured with open wall airflow
channels
2 5 connecting the inlet plenum to the outlet plenum. There is means for
exerting a pressure
differential between the inlet plenum and the outlet plenum so as to maintain
an airflow
through the container. There may be means for controlling the airflow
temperature,
including means for heating and/or cooling airflow to higher than ambient
temperature or
such other temperature as may be useful for the materials being dried. The
airflow plates
29
CA 02409066 2002-10-18
may be oriented as horizontal bays within the container and the airflow
channels be
horizontal, or the airflow plates may be oriented as vertical bays within the
container with
the airflow channels being horizontal or vertically oriented. The container
may be
configured for top feeding and underside removal of the sliced materials,
which may be
sliced fruit.
The descriptions and figures of the preferred embodiments are illustrative of
the
invention, but other embodiments within the scope of the invention and the
claims below, as
will be readily apparent to those skilled in the art.
