U.S. patent number RE31,633 [Application Number 06/443,539] was granted by the patent office on 1984-07-24 for lumber conditioning kiln.
Invention is credited to Donald C. Lewis.
United States Patent |
RE31,633 |
Lewis |
July 24, 1984 |
Lumber conditioning kiln
Abstract
A lumber conditioning kiln comprising an enclosure defining a
closed chamber for receiving a stack of lumber so positioned as to
provide space at the top and at the ends, a dehumidifier in said
chamber containing an evaporator, said dehumidifier defining a flow
path through the evaporator and a bypass passage around the
evaporator, a blower for inducing air flow into the flow path of
the dehumidifier for dehumidifying air and discharging dry air
therefrom, fans for effecting a circulation of air within the
chamber in a direction such that dry air from the dehumidifier is
conducted across the top of the stack to the far end and from there
reversely through the stack to the one end where the moisture-laden
air from the stack is induced into the flow path of the
dehumidifier and wherein there are dampers for reducing the air
flow over the evaporator and increasing the air flow through the
bypass.
Inventors: |
Lewis; Donald C. (Bangor,
ME) |
Family
ID: |
26684377 |
Appl.
No.: |
06/443,539 |
Filed: |
November 22, 1982 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
013059 |
Feb 21, 1979 |
04250629 |
Feb 17, 1981 |
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Current U.S.
Class: |
34/381;
34/77 |
Current CPC
Class: |
F26B
21/02 (20130101); F26B 21/086 (20130101); F26B
21/06 (20130101) |
Current International
Class: |
F26B
21/02 (20060101); F26B 21/08 (20060101); F26B
21/06 (20060101); F26B 003/06 () |
Field of
Search: |
;34/12,13.4,13.8,16.5,26,27,46,77,219,223 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2437372 |
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Feb 1975 |
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DE |
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1533651 |
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Nov 1978 |
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GB |
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Primary Examiner: Makay; Albert J.
Assistant Examiner: Joyce; Harold
Attorney, Agent or Firm: Gammons; Robert T.
Claims
What is claimed is:
1. In a kiln for drying lumber, means defining an enclosed chamber
for receiving a stack of lumber with a space above and at the ends
of the stack, dehumidifying means in the chamber including a
condenser, an evaporator and a compressor, means defining an
enclosure in the chamber within which the condenser and evaporator
are contained, said enclosure being provided with intake and outlet
openings through which moist air from the stack enters the
enclosure and dehumidified air leaves the enclosure, said
evaporator preceding the condenser in the flow path of the air
passing through the enclosure, said condenser being so positioned
in the enclosure that all of the air entering the enclosure must
pass through the condenser, means situated in the enclosure beyond
the condenser in the direction of flow for inducing flow through
the enclosure, damper means situated in the enclosure preceding the
evaporator, the position of which may be controlled to control the
flow of air entering the enclosure through the evaporator to
maintain the temperature of the evaporator at a predetermined level
and, hence, the load on the compressor and means for automatically
changing the position of the damper means in response to
temperature sensing means positioned in the path of the air leaving
the evaporator.
2. A kiln for drying lumber according to claim 1 wherein there are
fans arranged at one end of the stack for inducing circulation of
air from the one end across the top of the stack to the other end
and from thence through the stack to the one end.
3. A kiln according to claim 1 comprising means defining a bypass
for bypassing part of the air entering the inlet opening around the
evaporator.
4. A kiln according to claim 3 wherein the means for bypassing part
of the air comprises a bypass passage and a damper positioned in
the flow path of the bypass passage.
5. A kiln according to claim 1 comprising means for bypassing the
air comprising a bypass passage, a bypass damper positioned in the
bypass passage and means for effecting actuation of the bypass
damper which simultaneously closes said damper means and opens the
bypass damper.
6. A kiln according to claim 1 wherein the space above the stack
defines a flow path across the top and wherein the dehumidifier is
spaced from the end of the stack adjacent thereto sufficiently so
that some of the moisture-laden air leaving the stack at that end
re-enters the flow path of the air from the dehumidifier without
passing through the dehumidifier.
7. A kiln for drying lumber according to claim 6 comprising sensors
in the flow passage across the top of the stack.
8. A kiln for drying lumber according to claim 7 comprising a
controller connected to the sensors and to the compressor to effect
operation of the latter in response to said sensors.
9. A kiln for drying lumber according to claim 6 comprising dry and
wet bulb sensors in the flow passage across the top of the
stack.
10. A kiln for drying lumber according to claim 6 comprising
relative humidity and dry bulb sensors in the flow passage across
the top of the stack.
11. A kiln according to claim 1 wherein there is an exhaust fan in
the chamber and a supplemental heater in the dehumidifier for
heating the dehumidified air before it is discharged and the means
for circulating the air comprises fans positioned above the stack
at the one end and/or humidistat and dry bulb sensors positioned in
the path of the air flowing across the top of the stack, said
sensors operating in response to the temperature and moisture
content of the air flowing across the top of the stack to, on the
one hand, when there is insufficient moisture, stop the
dehumidifier unit and, on the other hand, when there is more than
enough moisture, to start the dehumidifier unit, and when the
temperature is excessive, to start an exhaust fan and when the
temperature is deficient, to stop the exhaust fan and start the
supplemental heater.
12. A kiln for drying lumber according to claim 1 comprising a
baffle at the top of the enclosure above the stack parallel to and
spaced from the top which defines a flow passage across the top of
the stack from one end of the stack to the other end thereof.
13. A kiln according to claim 1 wherein the means for controlling
the damper means comprises a motor and kinematic means connecting
the motor to the damper means.
14. A kiln according to claim 1 comprising a controller connected
to the sensor and to the compressor operable in response to the
sensor to start and stop the compressor.
15. The method of conditioning lumber comprising within a closed
chamber within which is a stack of lumber, circulating air in a
predetermined path which commences at one end of the chamber,
passes across the top of the stack to the other end and returns
through the stack to the one end, at the one end inducing a portion
of the air returning through the stack into a dehumidifier in a
flow path over the evaporator coil and controlling the flow of air
entering the dehumidifier in the event that the refrigerant flowing
from the evaporator to the compressor exceeds a predetermined level
to bypass the air .[.and.]. .Iadd.around .Iaddend.the evaporator.
.Iadd. 16. In a system for dehumidifying moisture-laden air which
has been circulated through a material to be dried, a dehumidifier
including a condenser, an evaporator, and a compressor, means
defining an enclosure within which the condensor and evaporator are
contained, said enclosure being provided with intake and outlet
openings through which the moisture-laden air enters the enclosure
and dehumidified air leaves the enclosure, said evaporator
preceding the condenser in the flow path of air passing through the
enclosure, said condenser being so positioned in the enclosure that
all of the air entering the enclosure must pass through the
condenser, means situated in the enclosure beyond the condenser in
the direction of flow inducing flow through the enclosure, damper
means situated in the enclosure preceding the evaporator, the
position of which can be controlled to control the flow of air
entering the enclosure through the evaporator to maintain the
temperature of the evaporator at a predetermined level and, hence,
the load on the compressor and means for automatically changing the
position of the damper means in response to the condition of the
cooling medium flowing from the evaporator to the compressor.
.Iaddend..Iadd. 17. A system according to claim 16 wherein said
last-named means is a temperature-sensing device located in the
flow path of the air through the evaporator. .Iaddend..Iadd. 18. A
system according to claim 16 wherein there is conductor means
interconnecting the condensor, evaporator and compressor and said
last-named means is a temperature-sensing device located in the
conductor means through which cooling medium flows from the
evaporator to the compressor. .Iaddend..Iadd. 19. A system for
removing the moisture content of materials comprising means
defining a closed chamber within which the material to be treated
is positioned, a dehumidifier positioned in the chamber including a
condenser, an evaporator, and a compressor, means defining an
enclosure in the chamber within which the condenser and evaporator
are contained, said enclosure being provided with intake and outlet
openings, means for inducing a flow of air from the outlet opening
of the enclosure through the material to be treated and back into
the enclosure through the intake opening, said evaporator preceding
the condenser in the flow path of the air passing through the
enclosure, said condenser being so positioned in the enclosure that
all of the air entering the enclosure must pass through the
condenser, damper means situated in the enclosure preceding the
evaporator, the position of which can be controlled to control the
flow of air entering the enclosure through the evaporator to
maintain the temperature of the evaporator at a predetermined level
and, hence, the load on the compressor, and means for automatically
controlling the position of the damper means in response to the
condition of the cooling medium flowing from the evaporator to the
compressor. .Iaddend..Iadd. 20. A system according to claim 19
wherein said last-named means is a temperature-sensing device
located in the flow path of the air through the evaporator.
.Iaddend..Iadd. 21. A system according to claim 19 wherein there is
conductor means interconnecting the condenser, evaporator and
compressor said last-named means is a temperature-sensing device
located in the conductor means through which the cooling medium
flows from the evaporator to the compressor. .Iaddend.
Description
BACKGROUND OF INVENTION
This invention relates to a process for kiln drying wood. In known
processes, air is circulated through the stacked wood in a kiln
chamber. The temperature and humidity of the air in the kiln are
controlled in accordance with established kiln schedules which have
been developed for various sizes, conditions and types of wood. A
typical schedule, taken from the U.S. Department of Agriculture
Handbook #.[.133.]. .Iadd.188.Iaddend., DRY KILN OPERATOR'S MANUAL,
for Eastern White Pine is shown below:
______________________________________ Moisture content Dry Bulb
Air Wet Bulb Air of wood at start Temperature Temperature of step
(in %) (in .degree.F.) (in .degree.F.)
______________________________________ Above 60% 130 115 60 130 110
50 130 105 40 130 100 35 130 95 30 140 105 25 150 115 20 160 125 15
160 can vary ______________________________________
Schedules such as the one shown above when closely followed can
result in good quality wood being dried in a reasonably fast time
with little or no damage. The schedule shown above would take about
one week to complete. The temperature is normally expressed in
.degree.F. or .degree.C. and the moisture content of the air is
usually expressed in .degree.F. or .degree.C. on a wet bulb
thermometer. The moisture content may also be expressed in some
other manner, such as relative humidity, dewpoint, moisture ratio,
etc.
There are several known processes for controlling the temperature
and humidity of the air in the kiln. This invention relates to the
dehumidification process. The prior art dehumidification systems do
not have the ability to operate over a wide range of temperature as
shown in the typical schedule above. This invention allows a
dehumidification system to operate at any temperature between
approximately 70.degree. F. dry bulb and 160.degree. F. dry bulb.
The prior art dehumidifiers have been generally limited to a
maximum operating temperature of approximately 120.degree. F. If
the temperature is limited to below 120.degree. F., the drying
process is much slower, the possibility of damage from mold and
stain increases, and kiln operators are required to ignore the
established kiln schedules. This invention allows the existing kiln
schedules to be used with only minor modifications. It also allows
a faster drying time because of the higher temperatures. Problems
related to mold are also reduced.
A dehumidification system uses a conventional refrigeration cycle.
In the known systems, air is drawn from the kiln chamber and it
passes over a cooling coil. It is cooled and dehumidified and then
the air passes over a heating coil where it is reheated. A fan is
used to draw the air over these coils and then the air is returned
to the kiln, heated and with the moisture removed. The cooling coil
is an evaporator of a conventional refrigeration cycle. The heating
coil is the condenser of a conventional refrigeration cycle and in
the refrigeration system there is also a compressor.
In the prior art, the cooling coil, condenser coil and compressor
are selected to operate within a certain range of temperatures. If
the temperature increases beyond design selection range, the
pressures that the compressor is required to maintain in the
evaporator and in the condenser also increase and the resulting
load would be beyond the design range for the compressor motor.
Also, as the temperature of the air going across the cooling coil
increases, the refrigerant leaving the cooling coil also increases
in temperature. Since the refrigerant cools the compressor in most
dehumidification systems, the warmer refrigerant may be unable to
provide the cooling the compressor motor requires.
This invention has for its purpose to provide for operating over a
wide range of temperatures, to increase the rate of drying thereby
to reduce damage from mold and stain, to allow existing kiln
schedules to be used with only minor modification and to vary the
amount of air passing over the cooling unit of the dehumidifier in
such a way as to prevent the compressor from being overloaded and
from being overheated.
SUMMARY OF THE INVENTION
A kiln for drying lumber comprising means defining an enclosed
chamber for receiving a stack of lumber with a space above the
stack and at the ends, a dehumidifier in the chamber containing an
evaporator, said dehumidifier defining a flow path through the
evaporator and a bypass passage around the evaporator, means for
inducing air flow into the flow path of the dehumidifier for
dehumidifying air entering the dehumidifier and discharging dry air
therefrom, means for effecting a circulation of air within the
chamber in a direction such that dry air from the dehumidifier is
conducted across the top of the stack to the far end and from
thence reversely through the stack to the one end and wherein
moisture-laden air from the stack is induced into the flow path of
the dehumidifier and means for decreasing the air flow over the
evaporator and correspondingly increasing the flow through the
bypass passage. There is a thermostat positioned to sense the
temperature of the evaporator and means operable by the thermostat
to effect actuation of the means for decreasing the flow of air
over the evaporator and increasing the flow through the bypass
passage. Optionally, the thermostat may be positioned to sense the
temperature of the refrigerant flowing from the evaporator to the
compressor. The means for decreasing the air flow over the
evaporator may comprise a damper arranged to be closed when the
temperature rises too high so as to bypass the air through the
bypass passage or a damper in the bypass passage for increasing the
flow through the bypass passage when the temperature rises too
high. Alternatively, the aforesaid means may comprise a primary
damper positioned in the flow path of the air to the evaporator and
a secondary damper in the bypass passage through which air is
diverted from the evaporator when the primary damper is closed.
When there are primary and secondary dampers, the means for
effecting the decrease in air flow over the evaporator and the
corresponding increase in the flow through the bypass passage
operates simultaneously to close the primary damper and open the
bypass damper.
A baffle coextensive with the top of the stack defines in
conjunction with the top of the chamber a flow path. The
dehumidifier is spaced from the end of the stack adjacent thereto
sufficiently so that a portion of the air leaving the stack at the
one end is recirculated without passing through the dehumidifier.
The means for effecting circulation of air in the chamber comprises
a fan positioned at the top of the chamber at the entrance to the
flow path at the one end and sensors positioned in the flow path of
the air across the stack, said sensors operating in response to the
temperature and moisture content of the air in the flow path, on
the one hand, when there is insufficient moisture, to stop the
dehumidifier and, on the other hand, when there is more than enough
moisture to start the dehumidifier and when the temperature is
excessive, to start an exhaust fan which exhausts air from the
chamber and when the temperature is deficient, to stop the exhaust
fan and start the supplemental heater in the dehumidifier.
There is a tray for collecting the condensate from the evaporator
and means for supplying a portion of it to sensors, and a portion
to an evaporator-type humidifier for restoring moisture to the
stack after a drying cycle to raise the moisture content to a
predetermined level.
The invention will now be described in greater detail with
reference to the accompanying drawings, wherein:
FIG. 1 is an elevation partly in section showing the kiln within
which the lumber to be conditioned is stacked, a dehumidifier at
one end of the chamber and the circulation set up within the
chamber; and
FIG. 2 diagrammatically illustrates an evaporator-type humidifier
for restoring a predetermined amount of moisture following a drying
cycle.
Referring to the drawings, the kiln comprises an enclosure 10 of
suitable size to receive a stack of lumber 12 for conditioning with
a space at one end between that and the adjacent end of the stack
of lumber for receiving a dehumidifying unit 14.
The enclosure 10 as herein illustrated is of substantially
rectangular, horizontal and vertical section and is provided near
the top with a horizontally-disposed baffle 16 which defines with
the underside of the top a flow passage across the top of the stack
12. At the end of the baffle adjacent the dehumidifying unit there
is a vertical extension 18 containing an opening 20 within which is
mounted a circulating fan or fans 22 for inducing air flow from the
dehumidifying unit through the opening 20 into the passage above
the baffle and forcing it to flow across the top of the baffle to
the end of the chamber remote from the dehumidifying unit and from
thence back to the one end of the chamber through the stack to the
one end of the chamber within which the dehumidifying unit is
situated and where a part of this air returned through the stack
enters the dehumidifying unit and a part is returned to the flow
path without passing through the dehumidifying unit. The air
passing through the dehumidifying unit is dried, ejected from the
top of the dehumidifying unit and, together with the untreated air,
is recirculated by the fan 22. The circulation is depicted in FIG.
1 by the arrows shown thereon. A baffle 23 is positioned at the top
of the chamber at the remote end to direct the air downwardly to
the end of the stack. An exhaust fan 49 is provided in one wall of
the chamber at the end within which the dehumidifier is
located.
The dehumidifying unit is, for the most part, of conventional
construction comprising a cooling coil or evaporator 24, a heating
coil or condenser 26, a compressor 28 which withdraws refrigerant
from the evaporator and supplies it to the condenser, and an
expansion valve 30 connecting the condenser to the evaporator. A
drain pan 32 supported below the evaporator provides for draining
water from the condenser. Above the condenser, there is a blower 34
for drawing air into the dehumidifying unit at the base and
discharging it from the top in line with the fan 22 which, in
conjunction with the fan 22, provides for the circulation of the
air. Above the blower 34, there is a supplemental heating coil 36
for reheating the dried air when necessary.
As herein illustrated, the dehumidifier unit defines a flow passage
38 through the evaporator and a bypass passage 40 around the
evaporator. A primary damper 38a and a bypass damper 40a are
mounted, respectively, in the passages 38,40 and so controlled that
when the primary damper 38a is open, the bypass damper 40a is
closed and vice versa. A damper motor M is provided and connected
to the dampers by suitable kinematic linkage to effect opening and
closing of the primary and bypass dampers in response to the
temperature of either the evaporator 24 or the temperature of the
refrigerant flowing from the evaporator to the compressor. Control
of the motor M is had by means of a thermostat T provided with a
sensor bulb 42 arranged in the path of the flow of air through the
evaporator or, alternatively, arranged in the pipe 44 extending
from the evaporator to the compressor.
A control system is thus provided by means of which the amount of
air passing over the evaporator coil can be varied as the
temperature increases. A sensor 42 located in the air path
immediately leaving the evaporator coil provides for closing the
damper over the evaporator coil and opening the bypass damper to
maintain a constant temperature leaving the evaporator coil of
approximately 60.degree. F. The dampers are modulated to maintain
temperature of the air approximately constant. The evaporation coil
is .[.circulated.]. .Iadd.circuited .Iaddend.so that the
refrigerant leaving the evaporation coil is approximately the same
as the air temperature. This provides refrigerant from the
evaporation coil cool enough to cool the compressor motor and a
constant pressure in the evaporator which prevents the compressor
from being overloaded and overheated.
The controls that position the dampers can be proportioning,
electric, pneumatic or electronic.
A controller 46 is provided for starting and stopping the
compressor motor 28 and responds to sensor means 48 connected
thereto by a line 50 which senses the condition of the air entering
the passage above the stack which is comprised of dry air from the
dehumidifying unit and the untreated air which bypasses the
dehumidifying unit. The sensor means 48 comprises wet and dry bulb
sensors. When the wet bulb indicates an excess of moisture in the
air, it starts the dehumidifying cycle by starting the compressor
motor. When the moisture is reduced to an acceptable level, the
dehumidifying cycle is stopped by stopping the compressor motor.
When the dry bulb sensor indicates an excess of temperature, it
starts the exhaust fan 49. However, when the temperature decreases
to an acceptable level, it stops the exhaust fan and starts the
supplemental heater 36. A humidistat may be used in place of a wet
bulb.
Optionally, the damper 40a may be omitted and the air flow
controlled solely by the damper 38a. When so constructed, closing
the damper 38a will divert the air through the bypass passage 40 so
as to increase the flow through the bypass passage and
simultaneously reduce or stop the flow through the flow passage 38.
Alternately, the damper 38a may be omitted and the damper 40a in
the bypass passage employed to control the flow, when open to
promote an increased flow through the bypass passage to thus reduce
flow through the flow path 38. In either instance, the damper or
dampers may be automatically or manually operated.
In conjunction with the dehumidifying unit, there is provided a
system to recover the water that is condensed from the air on the
evaporator coil and using it to restore some moisture to the stack
when conditions require it. This system is shown in FIG. 2 wherein
a drainpipe 52 conducts water from the drain pan 32 of the
dehumidifier into a condensate pump 54 which, in turn, pumps the
condensate through a conductor 56 to a storage tank 58. Water from
the storage tank is delivered by way of a conductor 60 and
adjustable valve V1 to a trough 62 within which are situated a dry
bulb and the wick of a wet bulb 64 and 66, respectively. A fan 68
maintains a circulation of air over the wick 66. In order to
alleviate a too dry condition in the kiln, a conductor 70 connected
to the bottom of the storage tank by way of a float valve 72 will
supply water from the tank to an evaporator-type humidifier 74
located within the base of the dehumidifier through a float valve
72 and is heated there by an electric heater 76 whenever the
humidity in the kiln is too low.
The system thus comprises circulating air through a stack of lumber
so as to remove excess moisture therefrom, dehumidifying the
moisture-laden air and recyling it. This provides certain
advantages over the prior art in that it enables operating over
wide ranges of temperature, increases the rate of drying, thereby
reducing the damage from mold and stain, allows existing kiln
schedules to be employed, and enables operating in such a way as to
prevent the dehumidifying unit from being overloaded and/or
overheated. Additionally, the system enables recovery of the water
from the drying operation and using it in an evaporator-type
humidifier to restore some of the moisture to the lumber following
the drying operation to relieve stresses that are developed during
the drying operation.
It should be understood that the present disclosure is for the
purpose of illustration only and includes all modifications or
improvements which fall within the scope of the appended
claims.
* * * * *