Note: Descriptions are shown in the official language in which they were submitted.
CA 02717531 2010-10-13
HEAT ACTIVATED CIRCULATION FAN
FIELD OF THE INVENTION
The present invention pertains to a heat activated electrical fan for
distributing heated
air within an enclosed environment, such as a service building. The fan has
particular
application in cold climates for circulating air in remotely located
structures such as
compressor stations and service buildings associated with the oil and gas
industry
operation and maintenance. The fan has been adapted for use in association
with
explosion-proof catalytic heaters as are commonly used in such service
buildings.
BACKGROUND OF THE INVENTION
Pipelines, which convey fluids and fluidized materials, have been built in
virtually all
parts of the globe. In colder reaches of the north and south hemispheres,
steps must
be taken to ensure that the fluids conveyed in pipelines do not freeze. While
the
pipelines themselves may be heavily insulated when exposed above ground, or
are
buried below ground beyond the reach of freezing temperatures, or any
combination
of both, some portions of the pipelines must be accessible for maintenance or
operational purposes. Such accessible facilities include compressor stations,
monitoring stations, pressure reduction stations and maintenance facilities.
Typically,
such facilities are housed in above ground structures. Structures which are
located
near populated regions normally have access to the electrical grid and,
whether staffed
or simply automated, allow a full array of required electrical instrumentation
and
heaters. However, many other such stations are in remote areas unconnected to
the
electrical grid. Where such remote facilities are staffed, electrical
generators may be
activated as required. However, in remote, non-staffed locations, service
structures
must still be heated in cold weather. In areas of extreme cold weather,
service
structures which are heated often experience stratification of the heated air
depending
upon the design and location of the heat source. Often in such remote
locations,
catalytic heaters are utilized, often in the absence of any service personnel,
to provide
required heat to the structure. Nonetheless, given the size of structure
normally
required to house compressor stations and maintenance facilities, there is a
tendency
of air to stratify over the vertical extent of the structure. This is a
consequence of
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insufficient convection currents being generated by the heater to result in
uniform heat
distribution throughout the structure, thereby permitting temperature
stratification and
ventilation dead spots. In consequence of stratification of air within service
structures, there is a tendency for condensation and resulting ice formation
and build-
up within the structure, which ultimately hampers equipment operation and, in
extreme cases, can result in failure of the equipment. A fan device to cause
air
movement within the structure and overcome stratification of air is clearly
desirable.
Heretofore, thermal electric modules or generators (TEMs or TEGs) have been
used
in association with space heaters and other heating units such as wood and
fossil fuel
combustion burning stoves. One such heat transfer fan, called an EcoFan
manufactured by Caframo Ltd. of Wiarton, Canada utilizes TEM means connected
to
a motor and fan to circulate air. As disclosed in U.S. Patent 5,544,488, the
EcoFan
device relies purely on heat transfer by conduction. The TEM is sandwiched
between
a collection plate (hot side) and heat sink (cold side) with the collection
plate in direct
contact with the upper horizontal surface of the stove. The device also
includes heat
avoidance structures to avoid thermal damage to the TEM. This unit cannot be
used
in hazardous locations.
In United States published Patent Application 2008/0087315 Al, there is
disclosed a
thermal electric fan for use with catalytic heaters. The fan utilizes a
thermoelectric
module in a fan housing which is positioned in front of a heater face. As the
heat sink
required to operate the thermoelectric module is also in front of the heater
face, the
fan is directed to blow against the heat sink to cool it, and care must be
taken to
insulate the heat sink from the heater face. The fan orientation causes air to
blow
across the heater face, thereby distorting and adversely affecting combustion,
and
potentially causing the heater to operate outside the manufacturer's
specifications.
This unit can be used in hazardous locations.
In order to avoid the adverse consequences of a fan structure blowing against
the
heater while utilizing radiant heat, the present invention involves the use of
a low
voltage electric motor driven fan wherein the electrical current is generated
by a
thermal electric module or generator (TEM or TEG) heated by a conductor plate
(heat
harvester plate, or HHP) which receives radiant, convective and conductive
heat
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energy from a catalytic heater and conveys it to the receiving surface of the
thermal
electric generator. A heat sink contacting the opposite surface of the TEG is
at a
cooler temperature. The temperature gradient between opposed surfaces of the
thermal electric module induces an electrical current sufficient to operate an
electric
motor and fan. The fan is preferably positioned above the catalytic heater,
and blows
heated air together with by-products of combustion generated by the catalytic
heater
away from the heater face and throughout the building structure, thereby
preventing
or reducing stratification of air and hence reducing or eliminating ice build-
up within
the structure.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electric drive fan
means to
circulate air in a heated, enclosed structure where no electric grid service
is available.
It is a further object of the invention to utilize a building heat source to
generate an
electric supply to operate a fan means.
It is another object of the invention to utilize a thermal electric generator
(TEG),
activated by a catalytic heater, to provide the electrical service to the fan.
It is a further object of the invention to utilize a heat collector and
conductor to supply
heat to one surface of a TEG, whereby the heat collector or harvester does not
interfere with the operation and dissipation of heat from the catalytic
heater.
It is still a further object of the invention to provide an explosion-proof
electric fan
activated by a TEG and explosive proof catalytic heater for use in hazardous
locations
involving combustible environments.
Catalytic heaters generally have a vertical orientation, with combustion
extending
over a vertical catalyst face. The circulation fan device of the present
invention is
adapted for use with such a heater, preferably an explosion-proof catalytic
heater.
The fan device utilizes a collector plate or heat harvester plate (HHP) as a
receiver to
collect radiative and convective heat transfer components from a discrete area
of the
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heater face, and to conduct heat to the input plate of a thermal electric
generator. The
upper portion of the receiver HHP is sitting directly on the heater's case,
additionally
extracting more heat that is conducted towards the TEGs. The fan is
strategically
positioned as rising heat and by-products of combustion including water vapor
and
carbon dioxide are forced away from heater area promoting more even heat
distribution inside a service structure. This position minimizes ice formation
in the
vicinity of a heating unit and reduces stratification effect inside facility.
As is known in the art, TEGs utilize the direct conversion of temperature
differentials
to electric voltage (the Seebeck effect). The present device uses one or more
TEGs
sandwiched between a heat harvester plate (HHP) and an output plate or heat
sink
generally at ambient room temperature to produce a voltage difference and
generate a
current sufficient to operate an appropriate electric motor which is used to
drive the
circulating fan blades.
In particular, the present invention is adapted for use in remote locations
where there
is no electric grid power or manned generator. When used in an oil or gas
pipeline
application, a compressor station or maintenance facility will normally be
housed in a
building structure. Because of the volatile nature of oil and gas fumes, an
explosion-
proof heater is utilized during winter months for a source of heat with the
structure.
Preferably, the explosion-proof, gas fired heater is self-activating, such as
Cata-
DyneTM Heating Systems manufactured by CCI Thermal Technologies, Inc. of
Edmonton, Canada. Further, the TEG and electric motor circuit is a low
voltage/low
current device. As a result, low powered devices such as the present invention
do not
have sufficient energy to ignite petroleum products including natural gas,
propane,
solvents and other compounds. Therefore it is capable of working safely in
those
environments.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to assist in understanding of the invention, preferred embodiments
will now
be described with reference to the accompanying drawings, wherein:
FIG. I is a schematic perspective view of the circulating fan device of the
invention;
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FIG. 2 is a general location view of the present circulating fan device
associated with
a catalytic heater within an oil pipeline service structure, portions of which
are
cutaway for illustration purposes;
FIG. 3 is a schematic of the circulating fan device with portions of a
catalytic heater,
illustrating air flows during operation.
DESCRIPTION OF PREFERRED EMBODIMENTS
Figure 1 illustrates a preferred embodiment of the present invention, and the
circulating fan device 1. The device comprises a heat collector and conductor
plate,
(i.e. the heat harvester plate or HHP) 2 and a heat sink 4. Sandwiched between
HHP
2 and heat sink 4 is a thermal electric generator 6 comprising one or more TEG
units.
Heat sink 4 is generally at or slightly above the ambient temperature of the
air within
the confines of a building structure 20 (see Figure 2) but below the
temperature of the
HHP. Reduction of heat sink temperature below the HHP temperature results from
cooler floor level air being circulated and drawn across the heat sink. An
electric
motor 8 is positioned atop the heat sink and activated by electric current
generated by
the TEG 6. A fan 10 may be directly affixed to the shaft of electric motor 8,
or geared
indirectly thereto.
Circulating fan device 1 is positioned atop a catalytic heater 22 as seen in
Figure 2.
One preferred type of heater is a Cata-Dyne Model No. NG WX 12x24 explosion-
proof heater. When the heater is in operation, heat is radiated into the
interior space
of structure 20, and heats the relevant pipeline machinery 24 to temperatures
sufficient to avoid freezing. However, in extremely cold environments, air
within
structure 20 may tend to stratify, resulting in a temperature differential
between
ceiling and floor, with floor temperatures sufficiently low as to permit
freezing and
ice build-up. The rotating fan 10 of device 1 causes further circulation of
air which
disrupts the stratification and aids in generating convection currents
sufficient to
produce a more uniform temperature throughout the building, thereby inhibiting
or
eliminating condensation and/or ice build-up.
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As may be seen in Figures 1 and 2, conductor or heat harvester plate 2 is
generally
shaped as a right angle flange member whereby the vertical flange element 12
extends
partially over the generally vertical face 26 of the explosion-proof, gas
fired, catalytic
heater. The minor amount of overlap is in the order of 15% or less and
provides
sufficient heat supply to flange 12 without adversely interfering with the
operation of
the heater 22. Any overlap exceeding 20% is not considered to be minor for the
purposes of this invention and may well adversely interfere with operation of
the
heater. The heater is normally designed to operate on natural gas or propane.
With
the above-referenced Cata-Dyne heater, the burner surface is about 12 inches
by 12
inches (1 square foot). The depending flange 12 is about 5 inches by 4 inches,
thereby overlapping about 15% of the surface area of the heater face 26. This
limited
overlap is important in order to maintain proper exposure of the radiant
surface of the
heater to combustion air. Blockage of the catalytic surface 26 can cause
production of
carbon monoxide, lower combustion efficiency, slow combustion-air delivery,
slow
removal of combustion products such as carbon dioxide and water vapor), and
thus is
to be avoided.
Heat harvesting plate 2 receives infrared heat as well as convective heat on
lower
flange 12 and conducts it through to the generally horizontal upper flange
element 14.
Further, upper flange 14 sits directly in contact with the heater 22 and
receives
conductive heat from the heater. Upper flange 14 is in direct contact with the
bottom
input surface 16 of TEG 6. Upper surface 18 of TEG 6 in contact with the
bottom
surface of heat sink 4 and is generally maintained at the cooler ambient
temperature of
the heat sink, creating a temperature differential from the heated HHP flange
14 and
the associated input surface 16 of TEG 6. The TEG 6 is sealed between the HHP
flange 14 and the bottom of heat sink 4 in order to inhibit potential
corrosion from the
ambient atmosphere, which can include sour gas, sulphur dioxide, petroleum
products, etc. The sealing compound is also designed to avoid direct
conductivity
between the flange 14 and the heat sink 4, thereby keeping the temperature
gradient of
the TEG as high as possible.
Several models of TEGs are satisfactory. Therma-TECTM manufactured by Laird
Technologies, Model Number HT6-12-40 and HT8-12-40, as well as a TEG
manufactured by Watronix Inc., Model Number INBC1-127-08HT, have proven
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effective to run a Pittman Motor Model Number 9234S004, which has proven
effective to operate a fan of about 10" diameter at 400-1,200 r.p.m. range. A
further
advantage of the present invention is that the generated power is so low that
no
current or voltage limiting device is required for use in hazardous locations.
Heat sink 4 may be of any adequate design sufficient to shed heat and to be
cooled by
an airflow. As illustrated in Figures 1 and 3, heat sink 4 has a plurality of
internal and
external radiating fins, generally aligned horizontally to inhibit a
descending air flow
and promote horizontal air flow past the heater face 26.
As may be seen in Figure 3, while radiant energy represented by arrow A is
directed
horizontally from the heater face 26 or heater 22, thereby heating the room
and
vertical flange 12 of the heat harvesting plate 2, the fan 10 draws air
horizontally
(arrows B) past heat sink 4, maintaining the upper (cool) surface 18 of the
TEG at an
ambient temperature cooler than lower heated surface 16 of the TEG in contact
with
HHP 2. Horizontal airflow B from the fan 10 passes over the top of heater 22,
and
avoids the undesirable degradation of the catalytic combustion process as a
consequence of air being directed against the radiant surface 26 of the
catalytic heater.
Furthermore, the fan device of this invention does not adversely affect burner
temperature of the heater 22, which can operate in full accordance with the
manufacturer's standards.
In one test of the present invention, temperature stratification in a
structure relying
simply on natural convection resulted in significant vertical temperature
differential of
7 C to 8 C between floor and ceiling of structure 20, use of the circulating
fan of the
present invention resulted in significant reduction, in the order of 2 C to 3
C (and with
virtual elimination of freezing temperatures. The above numbers are specific
for
tested location and are not generic. Depending of ambient and facility type
(size,
insulation, number of heaters, etc), temperature differential will be
different.
While the foregoing invention has been described in relation to embodiments
using
the circulating fan mounted on top of the heater, other locations may also be
satisfactory. Depending on the application and location, the fan may be
mounted to
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the side of the heater, or may be mounted below a suspended heater. As well,
depending on the application, multiple fan units may be used.
The terms and expressions which have been employed in the foregoing
specification
are used therein as terms of description and not of limitation, and there is
no intention
in the use of such terms and expressions to exclude equivalents of the
features shown
or described, it being recognized that the scope of the invention is defined
and limited
only the claims which follow.
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