Note: Descriptions are shown in the official language in which they were submitted.
VACUUM DRYING KILNS AND CONTROL SYSTEMS THEREFORE
FIELD OF THE INVENTION
[0001] The present invention generally relates to drying kilns. In particular,
the present invention is
directed to Vacuum Drying Kilns and Control Systems Therefore.
BACKGROUND
[0002] Drying of organic materials such as hay, lumber, hemp, cotton,
cannabis, etc., have been
considered, for some time, more art than science. This is largely due to the
inherent variability of
organic materials. For example, even the same species of trees cut from the
same forest can have
differing water contents, and drying characteristics, which when dried using
traditional methods, can
result in wood that has different dryness or poor quality. Moreover, material
storage factors (e.g.,
time of storage, spacing/aeration techniques, storage conditions (covered,
enclosed, humidity
controlled, etc.)) can impact the water content of the material before drying.
[0003] The drying process not only reduces the weight of the material, but
also stabilizes the size and
finished characteristics of the product and reduces the chances of degradation
due to excess moisture.
The use of drying kilns is widespread for many materials. For example, drying
kilns are used to
prepare lumber for use in building furniture, flooring, and other applications
where warping of
lumber during and after incorporation in the product or structure is not
acceptable.
[0004] There are differing ways to dry materials, including: steaming,
dehumidification, air drying,
and kilns. Most of these methods take significant time, effort, and experience
to operate so as to
produce a desirable result.
[0005] Vacuum kilns are a specially designed type of kiln that can reduce
drying time from weeks to
days and from months to weeks, depending on the type and thickness of the
material/lumber to be
dried. Various forms of vacuum kiln drying have long been implemented on the
premise that the
boiling point of water is lowered when the surrounding atmospheric pressure is
reduced, thereby
reducing the energy required to dry the materials and a reduction of the
possibility of excessive heat
damaging the materials.
[0006] However, it has been found that even "cool" drying of the wood
accomplished by maintaining
a low ambient pressure during the drying process can result in material
degradation as the water is
CA 3012914 2019-01-23
boiled off. Moreover, the variations of water content in the materials can
result in inconsistent drying
from batch to batch or even within the same batch of materials placed in the
kiln.
[0007] Thus, there exists a need for a time, cost, and energy effective device
and control system for
drying materials, wherein such a device and control system are capable of
increasing yield (reducing
loss due to degrade).
SUMMARY OF THE DISCLOSURE
[0008] In a first exemplary aspect a drying control system for a vacuum based
drying system for
drying a material in a vacuum chamber is disclosed, the drying control system
comprising: a heat
control device; a plurality of first sensors in communication with the heat
control device, each of the
plurality of first sensors capable of sending a signal, representative of a
temperature of a fluid used to
heat the material, to the heat control device; and a plurality of second
sensors in communication with
the heat control device, each of the plurality of second sensors capable of
sending a signal,
representative of a temperature of the inside of the material, wherein the
heat control device controls
a rate of evaporation of moisture from the material by adjusting the
temperature of the fluid based
upon a temperature difference, the temperature difference being determined by
comparing a
difference to the signals from the plurality of second sensors, the difference
being determined from
the plurality of first sensors.
[0009] In another exemplary aspect, a vacuum drying system for drying a
material in need thereof is
disclosed, the vacuum drying system comprising: a vacuum chamber sized and
configured to receive
the material; a heating system coupled to the vacuum chamber and configured to
transfer heat to the
material, the heating system having an inlet temperature and an outlet
temperature; a plurality of
temperature probes coupled to the material, each of the temperature probes
measuring an internal
temperature of the material; and a drying control system comprising: a heat
control device; a first
sensor in communication with the heat control device, the first sensor capable
of sending a signal,
representative of a temperature of a fluid used to heat the material, to the
heat control device; and a
second sensor in communication with the heat control device, the second sensor
capable of sending a
signal, representative of a temperature of the inside of the material, wherein
the heat control device
controls a rate of evaporation of moisture from the material by adjusting the
temperature of the fluid
based upon a temperature difference, the temperature difference being
determined by comparing the
signal from the first sensors and the signal form the second sensor.
2
CA 3012914 2019-01-23
[0010] In yet another exemplary aspect a drying control system for use with a
vacuum
based drying system for drying materials, the vacuum based drying system
including a
vacuum chamber, a heating system having an inlet and an outlet, and a
plurality of
temperature probes coupled to the material is disclosed, the drying control
system
comprising: a heat control device including a processor, the processor
including a set
of instructions for adjusting the temperature of a fluid provided to the
vacuum
chamber, the instructions comprising: increasing the temperature of the fluid
when a
temperature difference is less than a predetermined amount; when the moisture
in the
material begins to boil, maintain the fluid at a first constant temperature;
when the
temperature of the material and the temperature of the temperature of the
fluid
entering the vacuum chamber are approximately equal, increasing the
temperature of
the fluid; and when the material is at the fiber saturation point, maintaining
the
temperature of the fluid at a second constant fluid temperature.
[0010A] In a further embodiment of the present invention, there is provided a
drying
control system for a vacuum based drying system for drying a material in a
vacuum
chamber comprising a heat control device; a plurality of first sensors in
communication with the heat control device, each of the plurality of first
sensors
capable of sending a signal, representative of a temperature of a fluid used
to heat the
material, to the heat control device; and
a plurality of second sensors in communication with the heat control device,
each of
the plurality of second sensors capable of sending a signal, representative of
a
temperature of the inside of the material,
wherein the heat control device controls a rate of evaporation of moisture
from the
material by adjusting the temperature of the fluid based upon a temperature
difference, the temperature difference being determined by comparing a
difference to the signals from the plurality of second sensors, the difference
being determined from the plurality of first sensors, and
wherein the heat control device further includes a processor, the processor
including a
set of instructions for adjusting the fluid temperature input to the vacuum
chamber comprising:
3
CA 3012914 2019-01-23
increasing the temperature of the fluid when the temperature difference
is less than a predetermined amount;
when the moisture in the material begins to evaporate, maintain the
fluid at a first constant temperature;
when the temperature of the material and the temperature of the fluid
entering the vacuum chamber are approximately equal,
increasing the temperature of the fluid; and
when the material is at the fiber saturation point, maintaining the
temperature of the fluid at a second constant fluid temperature.
[0010B] According to another aspect of the present invention, there is
provided a vacuum drying
system for drying a material in need thereof comprising a vacuum chamber sized
and configured to
receive the material; a heating system coupled to the vacuum chamber and
configured to transfer heat
to the material,; a plurality of temperature probes coupled to the material,
each of the temperature
probes measuring an internal temperature of the material; and a drying control
system comprising:
a heat control device; a first sensor in communication with the heat control
device, the first sensor
capable of sending a signal, representative of a temperature of a fluid used
to heat the material, to the
heat control device; anda second sensor in communication with the heat control
device, the second
sensor capable of sending a signal, representative of a temperature of the
inside of the material,
wherein the heat control device controls a rate of evaporation of moisture
from the material by
adjusting the temperature of the fluid based upon a temperature difference,
the temperature difference
being determined by comparing the signal from the first sensors and the signal
form the second
sensor.
[0010C] According to another aspect of the present invention, there is
provided a method of drying
materials in need thereof in a vacuum chamber, the method comprising heating
the materials under
vacuum; monitoring an internal temperature via at least one temperature sensor
inserted into at least
one or more of the materials; monitoring a fluid temperature entering and
exiting the vacuum
chamber; and adjusting the fluid temperature entering and exiting the vacuum
chamber based upon a
difference between the fluid temperature and the internal temperature.
[0010D] According to another aspect of the present invention, there is
provided a drying control
system for a vacuum based drying system for drying a material in a vacuum
chamber comprising:
4
CA 3012914 2019-01-23
a heat control device; a plurality of first sensors in communication with the
heat control device, each
of the plurality of first sensors capable of sending a signal, representative
of a temperature of a fluid
used to heat the material, to the heat control device; and a plurality of
second sensors in
communication with the heat control device, each of the plurality of second
sensors capable of
sending a signal, representative of a temperature of the inside of the
material, wherein the heat
control device controls a rate of evaporation of moisture from the material by
adjusting the
temperature of the fluid based upon a temperature difference, the temperature
difference being
determined by comparing a difference to the signals from the plurality of
second sensors, the
difference being determined from the plurality of first sensors, and wherein
each of the plurality of
second sensors is at least partially sealed inside the material.
[0010E] According to another aspect of the present invention, there is
provided a drying control
system for a vacuum based drying system for drying a material in a vacuum
chamber comprising:
a heat control device; a plurality of first sensors in communication with the
heat control device, each
of the plurality of first sensors capable of sending a signal, representative
of a temperature of a fluid
used to heat the material, to the heat control device; and a plurality of
second sensors in
communication with the heat control device, each of the plurality of second
sensors capable of
sending a signal, representative of a temperature of the inside of the
material, wherein the heat
control device controls a rate of evaporation of moisture from the material by
adjusting the
temperature of the fluid based upon a temperature difference, the temperature
difference being
determined by comparing a difference to the signals from the plurality of
second sensors, the
difference being determined from the plurality of first sensors, and wherein
the predetermined
temperature difference is less than 7 degrees Fahrenheit.
[0010F] According to another aspect of the present invention, there is
provided a vacuum drying
system for drying a material in need thereof comprising a vacuum chamber sized
and configured to
receive the material; a heating system coupled to the vacuum chamber and
configured to transfer heat
to the material; a plurality of temperature probes coupled to the material,
each of the temperature
probes measuring an internal temperature of the material; and a drying control
system comprising:
a heat control device; a first sensor in communication with the heat control
device, the first sensor
capable of sending a signal, representative of a temperature of a fluid used
to heat the material, to the
heat control device; and a second sensor in communication with the heat
control device, the second
sensor capable of sending a signal, representative of a temperature of the
inside of the material,
CA 3012914 2019-01-23
wherein the heat control device controls a rate of evaporation of moisture
from the material by
adjusting the temperature of the fluid based upon a temperature difference,
the temperature difference
being determined by comparing the signal from the first sensors and the signal
form the second
sensor, and wherein the drying control system determines when the material has
reached a fiber
saturation point, the fiber saturation point being when the material has a
moisture content of about
30%, and wherein, when the material is at the fiber saturation point, the
drying control system
maintains a substantially constant temperature of heating fluid provided to
the vacuum chamber until
a predetermined temperature differential is reached between the temperature of
the heating fluid
provided to the vacuum chamber and the temperature of the heating fluid
exiting the vacuum
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] For the purpose of illustrating the invention, the drawings show
aspects of one or more
embodiments of the invention. However, it should be understood that the
present invention is not
limited to the precise arrangements and instrumentalities shown in the
drawings, wherein:
FIG.1 i s a cut-away schematic of a vacuum kiln system according to an
embodiment of the present
disclosure;
FIG. 2 is a block diagram of an exemplary control system according to an
embodiment of the present
disclosure;
FIG. 3 is a process diagram of an exemplary process of drying materials using
a vacuum kiln
according to an embodiment of the present invention;
FIG. 4 is a diagram of a drying process according to an embodiment of the
present invention; and
FIG. 5 is a block diagram of an exemplary computing system suitable for use
with one or more of the
components discussed herein.
DESCRIPTION OF THE DISCLOSURE
[0012] A vacuum kiln according to the present disclosure provides for
consistent and efficient drying
of various materials. In certain embodiments, the vacuum kiln can use various
temperature
measurements to reduce the chance of overheating the materials. In certain
embodiments, a vacuum
kiln can use sensed information, such as the temperature differential across a
platen assembly or the
duty cycle of a vacuum pump, to determine when a large group of material has
reached a
6
CA 3012914 2019-01-23
substantially uniform dryness level. In certain embodiments, a vacuum kiln, as
disclosed herein, can
reduce checking, splitting, over-drying, and under-drying of material without
requiring parameters
from a user.
[0013] A general description of the operation of a vacuum kiln will now be
provided.
Typically, in a vacuum kiln, layers of lumber are either stacked on stickers
as in the dehumidification
kiln, or on hot plates or platens separating the layers of wood until the
desired stack is obtained. The
platens are typically large, flat hollow structures through which hot water is
circulated by means of a
hot water supply and conduits to and from the platens. Temperatures inside
these kilns are similar to
those reached in conventional dehumidification kilns. An airtight container
capable of handling
significant vacuums houses the lumber during the drying process. Also, the
container must be
constructed of an inert material such as stainless steel, due to the corrosive
nature of the acids which
are removed from the wood during the drying process.
[0014] After the stack of lumber has been placed inside the kiln container and
the door sealed, the
drying process may begin. A vacuum is created on the lumber by means of a
vacuum pump
connected with the interior of the kiln container and exhausting to the
outside. As the vacuum
increases, the moisture in the lumber is boiled out of the lumber at
temperatures below the boiling
point of water (if the vacuum is sufficiently high, the water will boil at
room temperature). The steam
or water vapor released by the lumber inside the container is passed through a
condenser and then
pumped to the outside of the container. As the moisture inside the lumber
boils and is released, the
temperature of the lumber drops. This is due to the fact that latent energy in
the moisture within the
wood turns to steam and leaves the wood. To compensate for this loss in
energy, heat must be added
to the container to prevent freezing of the wood or the slowing of the drying
process. Since heat does
not travel well through a vacuum, direct heating by contact with the layers of
lumber is accomplished
through the intervening platens.
[0015] Referring now to FIG. 1, there is shown an exemplary vacuum kiln system
100, according to
an embodiment of the present disclosure. Vacuum kiln system 100 includes a
sealable container 104
with a removable platen assembly 108. Platen assembly 108 is fluidly coupled
to a heating system
112, which in certain embodiments, directs water through the platen assembly
so as to heat up
materials contained within container 104. Container 104 is also coupled to a
depressurization system
116, which reduces the pressure within the container so as to assist with the
evaporation of moisture
7
CA 3012914 2019-01-23
of the materials contained within. Heating assembly 112 and depressurization
system 116 are each in
communication with a control system 120, which receives information from one
or more sensors
(discussed below) so as to direct the operation of heating assembly 112 and
depressurization system
116.
[0016] Platen assembly 108 includes plurality of platens 124 which are
selectively positioned in
between stacked layers of material 128. In an embodiment, platen assembly 108
includes a plurality
of square or rectangular platens 124 that are tillable with a fluid, such as
water. Typically, the size
and configuration of each platen 124 is similar in area to the layer of
material so as to provide for
even heat distribution to all areas of the material. Each of platens 124 are
connected on an inlet side
via tubes (not shown) and/or an input manifold (not shown) and rejoined at an
exit side via tubes (not
shown) and/or an exit manifold (not shown).
[0017] Heating assembly 112 is sized and configured to provide heat to platen
assembly 108 and
consequently to material 128 so as to facilitate evaporation of fluids in the
material. In an
embodiment, heating assembly 112 includes a boiler 132, heat exchanger 136, a
pump 140, and one
or more thermocouples 144 (e.g., thermocouples 144A and 144B). In an exemplary
embodiment,
boiler 132 is a steam boiler that is fluidly coupled to heat exchanger 136.
Heat exchanger 136
receives a heated fluid from boiler 132 and transfers the heat in the fluid to
the fluid that enters and
exits platen assembly 108. Heat exchanger 136 can be a shell-and-tube,
plate/fin, or any other type of
heat exchanger suitable to transfer heat from boiler 132 to platen assembly
108. Generally, for shell
and tube heat exchangers, one fluid flows through a set of metal tubes while a
second fluid passes
through a sealed shell that surrounds the metal tubes. Plate/fin heat
exchangers include a plurality of
thin metal plates or fins, which results in a large surface area for
transferring heat.
[0018] Pump 140 is a fluid pump capable of moving a fluid, typically water,
through the platen
assembly 108. The temperature of the fluid going to or coming from platen
assembly 108 is
measured by thermocouples 144A and 144B, respectively. Thermocouples 144 can
be most any type
of thermocouple that is capable of measuring fluid temperatures that are
typically below 200
Fahrenheit. As explained in more detail below, thermocouples 144 are coupled
to control system 120,
which uses the signals generated by the thermocouples, and other information,
to control the heat
coming from boiler 132 (typically via valve 146).
[0019] Depressurization system 116 creates a partial vacuum in container 104
so as to lower the
8
CA 3012914 2019-01-23
atmospheric pressure within the container and thereby facilitate evaporation
of fluids from material
128. In an embodiment, depressurization system 116 includes a condenser 148, a
first separator 152,
a vacuum pump 156, a condensate drain tank 160, a second separator 164, and
additional
thermocouples 144 (thermocouples 144C and 144D).
[0020] Condenser 148 removes liquids (namely, water) from air pulled from
container 104. As the
primary purpose of vacuum kiln drying system 100 is to dry material 128, the
liquid removed from
the materials is desirably evacuated so as to lower the humidity in container
104. In an embodiment,
condenser 148 is an air-cooled condenser whereby air from container 104 is
drawn into a plurality of
tubes or plates while a fan moves external air across the tubes or plates.
This process causes the air
inside the tubes or plates to cool, which precipitates liquids that can be
removed by separator 152.
Other types of condensers can be used, such as, but not limited to, water
cooled condensers or
evaporative condensers.
[0021] Separator 152 is fluidly coupled to condenser 148 and serves to remove
condensate generated
by condenser 148. Condensate separators come in a variety of types such as,
but not limited to,
chemical adsorption separators, gravitational separators, mechanical
separators, and vaporization
separators. In an exemplary embodiment, separator 152 is a gravitational
separator that allows the
condensate to flow to condensate drain tank 160. In operation, the condensate
stream from condenser
148 is passed into a large space, which decreases the transfer speed thereby
allowing the liquid
particles in the stream to sink from the condensate stream.
[0022] Vacuum pump 156 is sized and configured to create a partial vacuum in
container 104.
In an exemplary embodiment, vacuum pump is sized and configured to lower the
atmospheric
pressure in the container between about 400 and 700mmllg. In an embodiment,
vacuum pump 156 is
a liquid ring pump, which compresses gas by rotating an impeller disposed
within a cylindrical
casing. A fluid (usually water) is fed into the vacuum pump and, by
centrifugal acceleration, forms a
moving cylindrical ring against the inside of the casing, thereby creating
seals in the space between
the impeller vanes, which form compression chambers. Air from container 104 is
drawn into vacuum
pump 156 through an inlet port in the end of the casing, and then is trapped
in the compression
chambers formed by the impeller vanes and the liquid ring and exits through a
discharge port.
[0023] Air leaving vacuum pump 156 is sent to second separator 164, which
separates liquids from
the air. Separated liquid is returned for use in vacuum pump 156. In an
embodiment, second
9
CA 3012914 2019-01-23
separator 164 is a gravitational separator that passes the air leaving vacuum
pump 156 into a large
space, which decreases the transfer speed thereby allowing the liquid
particles in the air to be
separated.
[0024] Control system 120 is configured to adjust the depressurization of
chamber 104 and the
temperature of the fluid going through platen assembly 108 in response to the
real-time evaporation
conditions of the fluid in material 128. In an embodiment, control system 120
is in communication
with components of heating system 112 and depressurization system 116 so as to
control the rate of
evaporations from material 128.
[0025] An embodiment of a control system suitable for use with vacuum kiln
system 100 is shown in
FIG. 2 as control system 200. Control system 200 includes a programmable logic
controller (PLC)
204, which as shown, receives inputs from many different sensors, and sends
commands to others
components, based upon the inputs and the various software routines run by the
PLC 204. These
routines can be integrated with each other, as well as be discrete modules
which operate on their
own, or a combination of both.
[0026] As shown, PLC 204 is in electronic communication with a plurality of
sensors 208. For
example, sensors 208 can be temperature sensors 208A that provide a signal,
indicative of a
temperature, of:
= the fluid entering platen assembly 108;
= the fluid exiting platen assembly 108;
= the air exiting container 104;
= the air exiting condenser 148; and
= the temperature of material 128.
In a preferred embodiment, at least one temperature sensor is inserted into
one of material 128 such
that moisture can escape around the temperature sensor. For example, if
material 128 is a wood
board, a hole having a diameter sufficiently close to the diameter of the
temperature sensor such that
the insertion of the temperature sensor results in an unsealed compartment as
the wood dries (and
effectively shrinks). The desired result is that the internal temperature of
the material 128 is
effectively the wet-bulb temperature, which is the lowest temperature that can
be reached under
current ambient conditions by the evaporation of water only.
CA 3012914 2019-01-23
[0027] Having temperature sensors 208A inside material 128 (and preferably
multiple ones at
different locations within the stack of materials), and at different locations
related to heat inputs and
outputs (such as at the heating fluid entrance to platen assembly 108 and at
the heating fluid exit of
the platen assembly), and optionally, before and after condenser 148, allows
for determinations
regarding the state of evaporation of water from the materials. It should be
noted that humidity
sensors can be used in addition to or in certain embodiments substituted for
temperature sensors
208A.
[0028] Sensors 208 can also provide information related to the duty cycle of
vacuum pump 156 by
indicating when the vacuum pump is being used or when it is off. For example,
a duty cycle sensor
208B, which can be a frequency monitor, that is capable of sending a signal
representative of the
power usage by vacuum pump 156 to PLC 204.
[0029] Sensors 208 can also provide information related to the vacuum in
container 104.
Sensors 208 suitable for measuring the vacuum can include, for example,
pressure transmitters and
pressure transducers. In an embodiment, at least one pressure sensor 208C is
in electronic
communication with PLC 204, the pressure sensor sending a signal
representative of a pressure
inside container 104.
[0030] Inputs from sensors 208 can then be used to regulate a control valve
212 that is disposed
between boiler 132 and heat exchanger 136, thereby controlling the temperature
of the fluid going to
platen assembly 108. Input from sensors 208 can also be used to
increase/decrease the air flow
through condenser 148 so as to ensure efficient operation of the equipment and
vacuum pump 156.
[0031] PLC 204 can also monitor power consumption so as to determine the rate
of evaporation
occurring within container 104. For example, receiving information from sensor
208B can indicate
how often vacuum pump 156 is being actuated to maintain the desired pressure
within container 104.
It should be noted that the pressure within container 104 changes in response
to evaporation from
material 128 (gases have larger volumes than liquids). As such, sensor 208B
can provide an
indication of the power usage/duty cycle of vacuum pump 156.
[0032] While PLC 204 is shown as part of control system 120, it is understood
that multiple PLCs
can be employed and can contain software written to both act upon input
signals obtained from other
sensors or other components and ensure that the various different components
operate together.
11
CA 3012914 2019-01-23
[0033] In a preferred embodiment, PLC 204 is configured so as to efficiently
and effectively control
the evaporation of moisture from material 128. Efficient and effective
evaporation occurs, in an
embodiment, by monitoring the temperature of material 128 (or a representative
sample of the
materials) and adjusting the input temperature of the fluid going to platen
assembly 108. In a
preferred embodiment, the difference between the temperature of material 128
and the difference
between the input temperature of the fluid entering platen assembly 108 is
kept below about 7
degrees Fahrenheit.
[0034] Turning now to FIGS. 3 and 4, there is shown a process 300 suitable for
operating a vacuum
kiln system, such as vacuum kiln system 100, so as to achieve consistent and
efficient drying of
material 128, and a diagram 400 of heat input and material temperature over
time, which is reflective
of the results of process 300. Process 300 can be characterized as having 4
phases, shown as phases
404A-D in FIG. 4: a warm up phase 404A, a free water phase 404B, an
equalization phase 404C, and
a finishing phase 404D. It should be noted that the division into the phases
404 is used for illustrative
purposes only and more or fewer phases could be described and still come
within the scope of
process 400.
[0035] Prior to warm up phase 404A, material 128 are loaded into container 104
at step 304. In an
exemplary embodiment, layers of material 128 are separated by platens 124. One
or more
temperature sensors 208A are coupled to material 128 (before or after
loading). In an embodiment, at
least four temperature sensors 208A are inserted into holes drilled into the
ends of respective ones of
material 128.
[0036] The initial temperature of material 128 can vary depending on the
storage conditions, but
under any reasonable storage conditions the materials will be cooler than is
desired in order to cause
significant evaporation. In an embodiment, during warm up phase 404A, the
pressure in the container
is reduced using vacuum pump 156 and the temperature of material 128 is
brought to an evaporation
temperature 408 gradually using heating assembly 112 to avoid stressing the
materials (causing
excessive evaporation or uneven evaporation which can cause the materials to
degrade or deform).
As is known in the art, the temperature of evaporation (i.e., rapid transfer
of liquid to the gaseous
phase, e.g., boiling), is dependent upon pressure. Thus, the larger the vacuum
the lower the
temperature that is required to promote evaporation.
12
CA 3012914 2019-01-23
[0037] As shown in FIG. 4, input temperature 412 is the input temperature
coming from heat
exchanger 146 and material temperature 416 is the average temperature of
material 128. At step 308,
the input temperature is kept within a certain temperature range of the
average temperature of
material 128. In an embodiment, the desired temperature difference between the
input temperature
and the average temperature of material 128 is between about 3 F and about 7
F. In an
embodiment, the input temperature to platen assembly 108 is increased by a
predetermined amount
once the difference between the input temperature and the average temperature
of material 128 reach
a predetermined threshold. For example, the input temperature can be increased
by 3 F once the
difference between the input temperature and the average temperature of
material 128 is 3 F. As
another example, the input temperature can be increased by 7 F once the
difference between the
input temperature and the average temperature of material 128 is 0 F.
[0038] As shown in FIG. 4, during warm up phase 404A, the average temperature
of material 128
and the input temperature track each other fairly closely. This is largely due
to the lack of
evaporation occurring during warm up phase 404A (some is occurring, just as
wood left out in the
open will generally dry, but not at a significant rate). However, at a certain
point, moisture will begin
to be released from material 128. As mentioned previously, by inserting
temperature sensors inside
material 128, a seal is created. Thus, as material 128 begins to release
moisture, fluid will begin to
fill the hole around the temperature sensor and thereby lower the temperature
measured by the sensor
and thus lowering the average temperature value received by PLC 204 (although
it should be
understood the that actual material temperature may not have changed). Process
300 monitors for the
aforementioned change at step 312. At this point, the process shifts to the
next phase, free water
phase 404B.
[0039] Before discussing free water phase 404B, it is worth noting the
duration of warm up phase
404A may vary according to a number of factors including, but not limited to:
material 128's starting
temperature, type of material, water content in the material, amount of vacuum
applied, input
temperature difference maintained, and amount of material in the container. It
is also worth noting
that it is because of all these possible variables that prior art vacuum kiln
systems have failed to
repeatably and effectively dry materials without damaging the materials, under-
drying the materials,
or over-drying the materials.
[0040] As shown in FIG. 4, material temperature 412 drops fairly precipitously
once evaporation
13
CA 3012914 2019-01-23
begins at the beginning of free water phase 404B. In an embodiment, process
300, at step 316,
maintains a constant input temperature for a certain period of time. In this
embodiment, the average
temperature of material 128 is monitored and only when the average temperature
of the materials
approaches the constant input temperature (at step 320) does input temperature
again begin to be
increased at step 324. As with warm up phase 404A, the input temperature can
be adjusted in
accordance with the average temperature of material 128.
[0041] In an alternative embodiment, the process can be configured so as to
continue to have the
input temperature maintain a desired temperature difference from the average
temperature of material
128 throughout the entirety of free water phase 404B. The potential issue with
this process is that
allowing material 128 to cool can result in a decrease in the amount of
evaporation due to changes in
hardening material on its surface that can restrict the flow of fluids out of
it.
[0042] Free flow phase 404B continues until the steady convergence of the
input temperature and the
average material temperature begin to track each other closely (region
designated by 420, monitored
at step 328), i.e., increases in the input temperature result in concomitant,
albeit slightly delayed)
increases in the average material temperature. At this point it can be
presumed that the fluid entrained
in the material that is exterior to the cells of the structure (also referred
to in the art as the "free
water" in the material) has been substantially released (typically called the
fiber saturation point,
which is generally when the material has about 30% fluid).
[0043] Process 300 then proceeds to equalization phase 404C. During
equalization phase 404C, the
input temperature is maintained at a constant temperature (step 332) for a
predetermined amount of
time. As noted above, generally only certain ones of material 128 have a
temperature sensor inserted
in them, and even then, the insertion happens at the end of the materials.
Thus, while the temperature
sensor gives a temperature proximate the area of the material it resides,
material 128 may have
variations in dryness. Equalization phase 404C allows for the entire mass of
material to come to the
same dryness. In an embodiment, the input temperature is maintained at a
constant temperature for a
period of about 12 hours. In another embodiment or additionally to maintain a
constant temperature
for a predetermined amount of time, the input temperature can be maintained
until the inlet
temperature and the temperature at the outlet of platen assembly 108 converge
(step 336). This
convergence of temperatures is an indicator that material 128 is taking on no
new heat and thus it can
be presumed that all of material 128 is approximately at the same dryness. In
another embodiment or
14
CA 3012914 2019-01-23
additionally to maintain a constant temperature for a predetermined amount of
time, the duty cycle of
vacuum pump 156 is evaluated and used to determine whether material 128 has
all reached the same
dryness. Duty cycle can be used as a proxy because as less evaporation takes
place, the less vacuum
pump 156 needs to be turned on in order to keep a constant vacuum. In this
way, the duty cycle is a
proxy for the rate of evaporation occurring within container 104. In another
embodiment or
additionally to maintain a constant temperature for a predetermined amount of
time, the air inlet
temperature and the air outlet temperature proximate condenser 148 are
monitored. The closer these
two temperatures are to each other, the more likely that no new moisture is
being release from
material 128.
[0044] Process 300 then proceeds to finishing phase 404D. At step 332, the
inlet temperature is
increased, typically gradually, up to a maximum temperature (at step 340). In
an embodiment, the
inlet temperature is increases similarly as it was during warm up phase 404D.
In an embodiment, the
maximum temperature is between about 160 F and 170 F. In another embodiment,
the maximum
temperature is dependent upon the vacuum applied. In another exemplary
embodiment, the
maximum temperature is about 170 F at 600mmHg.
[0045] FIG. 5 shows a diagrammatic representation of one embodiment of a
computing device in the
form of a system 500 within which a set of instructions for causing a device,
such as control system
120 or PLC 204, to perform any one or more of the aspects and/or methodologies
of the present
disclosure may be executed, such as process 300. It is also contemplated that
multiple computing
devices may be utilized to implement a specially configured set of
instructions for causing the device
to perform any one or more of the aspects and/or methodologies of the present
disclosure. System
500 includes a processor 504 and a memory 508 that communicate with each
other, and with other
components, via a bus 512. Bus 512 may include any of several types of bus
structures including, but
not limited to, a memory bus, a memory controller, a peripheral bus, a local
bus, and any
combinations thereof, using any of a variety of bus architectures.
[0046] Memory 508 may include various components (e.g., machine readable
media) including, but
not limited to, a random-access memory component (e.g., a static RAM "SRAM", a
dynamic RAM
"DRAM", etc.), a read only component, and any combinations thereof. In one
example, a basic
input/output system 516 (BIOS), including basic routines that help to transfer
information between
elements within system 500, such as during start-up, may be stored in memory
508.
CA 3012914 2019-01-23
[0047] Memory 508 may also include (e.g., stored on one or more machine-
readable media)
instructions (e.g., software) 520 embodying any one or more of the aspects
and/or methodologies of
the present disclosure. In another example, memory 508 may further include any
number of program
modules including, but not limited to, an operating system, one or more
application programs, other
program modules, program data, and any combinations thereof.
[0048] System 500 may also include a storage device 524. Examples of a storage
device (e.g.,
storage device 524) include, but are not limited to, a hard disk drive for
reading from and/or writing
to a hard disk, a magnetic disk drive for reading from and/or writing to a
removable magnetic disk,
an optical disk drive for reading from and/or writing to an optical medium
(e.g., a CD, a DVD, etc.),
a solid-state memory device, and any combinations thereof. Storage device 524
may be connected to
bus 512 by an appropriate interface (not shown). Example interfaces include,
but are not limited to,
SCSI, advanced technology attachment (ATA), serial ATA, universal serial bus
(USB), IEEE 1494
(FIREWIRE , which is a registered trademark of Apple, Inc. of Cupertino,
California, USA), and
any combinations thereof. In one example, storage device 524 (or one or more
components thereof)
may be removably interfaced with system 500 (e.g., via an external port
connector (not shown)).
Particularly, storage device 524 and an associated machine-readable medium 528
may provide non-
volatile and/or volatile storage of machine-readable instructions, data
structures, program modules,
and/or other data for system 500. In one example, instructions 520 may reside,
completely or
partially, within machine-readable medium 528. In another example,
instructions 520 may reside,
completely or partially, within processor 504.
[0049] System 500 may also include an input device 532. In one example, a user
of system 500 may
enter commands and/or other information into system 500 via input device 532.
Examples of an input
device 532 include, but are not limited to, an alpha-numeric input device
(e.g., a keyboard), a
pointing device, a joystick, a gamepad, an audio input device (e.g., a
microphone, a voice response
system, etc.), a cursor control device (e.g., a mouse), a touchpad, an optical
scanner, a video capture
device (e.g., a still camera, a video camera), touch screen, and any
combinations thereof. Input
device 532 may be interfaced to bus 512 via any of a variety of interfaces
(not shown) including, but
not limited to, a serial interface, a parallel interface, a game port, a USB
interface, a FIREWIRE
interface, a direct interface to bus 512, and any combinations thereof. Input
device 532 may include a
touch screen interface that may be a part of or separate from display 536,
discussed further below.
16
CA 3012914 2019-01-23
Input device 532 may be utilized as a user selection device for selecting one
or more graphical
representations in a graphical interface so as to provide inputs to control
system 120. Input device
532 may also include, signal or information generating devices, such as
sensors 208. The output of
the input devices can be stored, for example, in storage device 524 and can be
further processed by
processor 504.
[0050] A user may also input commands and/or other information to system 500
via storage device
524 (e.g., a removable disk drive, a flash drive, etc.) and/or network
interface device 540. A network
interface device, such as network interface device 540 may be utilized for
connecting system 500 to
one or more of a variety of networks, such as network 544, and one or more
remote devices 548
connected thereto. Examples of a network interface device include, but are not
limited to, a network
interface card (e.g., a mobile network interface card, a LAN card), a modem,
and any combination
thereof. Examples of a network include, but are not limited to, a cloud-based
network, a wide area
network (e.g., the Internet, an enterprise network), a local area network
(e.g., a network associated
with an office, a building, a campus or other relatively small geographic
space), a telephone network,
a data network associated with a telephone/voice provider (e.g., a mobile
communications provider
data and/or voice network), a direct connection between two computing devices,
and any
combinations thereof. A network, such as network 544, may employ a wired
and/or a wireless mode
of communication. In general, any network topology may be used. Information
(e.g., data,
instructions 520, etc.) may be communicated to and/or from system 500 via
network interface device
540.
[0051] System 500 may further include a video display adapter 552 for
communicating a displayable
image to a display device, such as display device 536. Examples of a display
device include, but are
not limited to, a liquid crystal display (LCD), a cathode ray tube (CRT), a
plasma display, a light
emitting diode (LED) display, and any combinations thereof. Display adapter
552 and display device
536 may be utilized in combination with processor 504 to provide a graphical
representation of a the
evaporation process. In addition to a display device, a system 500 may include
one or more other
peripheral output devices including, but not limited to, an audio speaker, a
printer, and any
combinations thereof. Such peripheral output devices may be connected to bus
512 via a peripheral
interface 556. Examples of a peripheral interface include, but are not limited
to, a serial port, a USB
connection, a FIREWIRE connection, a parallel connection, and any combinations
thereof.
17
CA 3012914 2019-01-23
[0052] Exemplary embodiments have been disclosed above and illustrated in the
accompanying
drawings. It will be understood by those skilled in the art that various
changes, omissions and
additions may be made to that which is specifically disclosed herein without
departing from the spirit
and scope of the present invention.
18
CA 3012914 2019-01-23
