Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02571622 2006-12-15
VENTED, GAS-FIRED AIR HEATER
Background of the Invention
The present invention is directed toward improvements in indirect fired,
vented air heaters.
There are generally two categories of gas-fired heaters, direct-fired and
indirect-fired (or vented) heaters. With a direct-fired heater, the products
of
combustion are released into the heated space. With an indirect-fired heater,
some form of heater exchanger is used to transfer the heat from the
combustion gases to the heated space. The combustion gases are vented
out of the heated area.
Gas-fired heaters used in temporary heating applications, such as on
construction sites, have generally been of the direct-fired type. There is
currently an increasing demand for indirect-fired heaters for such
applications.
There is also an increasing demand for more energy efficient heaters. As a
rule, heaters of higher efficiency are also much larger in size. The challenge
is to have a relatively small yet efficient heater that can be used in
temporary
applications. Since temporary heaters are used seasonally, a smaller size
would provide the benefit of reduced costs for off-season storage.
Summary of the Invention
The objects of this invention are to provide a heater that:
= has a highly efficient heat exchanger with enhanced heat transfer
characteristics.
= has an improved burner design providing a relatively short distance
between the burner inlet and the flame.
= provides a venturi action in the burner air flow at the burner head to
promote air and gas mixing and efficient burning in the combustion
chamber.
= is economical to produce and operate.
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= is compact in size, with a relatively small footprint.
= has a rugged construction that allows it to stand up to rigors both of
transportation between sites and of being used in applications such
as construction sites.
A gas burner in accordance with one aspect of the invention includes
an enclosure defining a path for movement of combustion air. A pair of
generally parallel burner plates are disposed transverse to the path of
combustion air travel. The burner plates are spaced apart to define a shallow
chamber therebetween and both plates have a plurality of openings therein
allowing for passage of combustion air therethrough. The openings in a first
one of said plates are aligned with respective ones of the openings in the
second plate to provide annular openings allowing exit of gaseous fuel from
the shallow chamber. A conduit supplies gaseous fuel into the shallow
chamber defined between said burner plates such that, in use, combustion air
moving along the path and through the aligned openings in said burner plates
mixes with gaseous fuel emerging from said chamber via said annular
openings thereby to provide a combustible fuel ¨ air mixture downstream of
said burner plates.
The openings in said plates are preferably in the form of short tubular
collars projecting from said plates with the tubular collars of both plates
being
aligned with and directed toward each other in confronting spaced apart
relation to provide said annular openings allowing exit of gaseous fuel
between the confronting spaced apart collars.
In another aspect of the invention, the first burner plate is located
upstream of the second burner plate relative to the flow direction of
combustion air when in use. The tubular collars of the first burner plate
define
flow passages of smaller diameter than those defined by the tubular collars of
the second plate thereby to create a venturi-like flow action as the
combustion
air passes through the aligned tubular collars thus promoting thorough mixing
of the air and the gaseous fuel being supplied via said annular gaps as well
as
allowing for reduced gas supply pressure to the shallow chamber between the
burner plates as the venturi action pulls the gas into the moving combustion
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air streams. This is the reverse of traditional venturi burners where higher
gas
pressures are used to draw combustion air in.
The short tubular collars are ideally integrally formed with their
respective burner plates.
The burner plates are preferably of generally circular outline, with said
conduit to supply gaseous fuel being connected centrally of said plates to
supply the fuel to the chamber defined between said plates. The conduit
preferably has an end portion centrally disposed between said burner plates
and having a plurality of radially arranged openings to assist in providing
even
distribution of gaseous fuel to said chamber.
The blower preferably includes a vaned rotor mounted for rotation on
an axis generally centered with said burner plates and extending normal
thereto. Air flow confining structures are shaped to direct the air flow from
said
rotor generally along said axis whereby to deliver a generally even and
balanced flow toward the burner plates to promote even flow distribution
through said openings therein.
In accordance with another aspect of the invention there is provided a
heat exchanger section comprising a pair of metal panels disposed in close
face-to-face relation to allow gases to flow therebetween from an inlet end to
an outlet end in a travel direction. The panels each have undulations or
corrugations therein whereby gases flowing between said panels in the travel
direction are forced to move in a turbulent fashion to enhance transfer of
heat
between said panels and the flowing gases.
In a preferred form of the invention said panels each have corrugations
therein angled relative to the travel direction and oppositely oriented with
respect to each other such that adjacent corrugations are in a criss-cross
relation to each other whereby gases flowing between said panels are forced
by the opposing corrugations to move in the form of a series of repeating
spirals from said inlet end to said outlet end to provide enhanced heat
transfer. The corrugations are preferably of a generally V-shaped or zig-zag
configuration when seen end-on and are disposed at a relatively shallow
acute angle relative to a line normal to the travel direction. In one
preferred
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=
embodiment, said acute angle is approximately 9 degrees with said adjacent
corrugations being at an angle of approximately 18 degrees relative to each
other.
An air heater combination in accordance with a further aspect of the
invention comprises a main housing having an air inlet and an outlet for
heated air and a combustion chamber located therein. A burner assembly is
connected to the combustion chamber to supply burning gases thereto. An
exhaust stack is provided and a heat exchanger is connected to said
combustion chamber and comprises a plurality of heat exchanger sections
having inlet ends connected to receive heated combustion gases from the
combustion chamber and outlet ends connected to said exhaust stack for
exhausting combustion gases after passage through the heat exchanger
sections. The heat exchanger sections are spaced apart to allow the passage
of air therebetween to effect heating of same. A blower assembly moves cool
air into said main housing via said air inlet and causes the air to travel
between the heat exchanger sections and thence outwardly of said outlet for
heated air.
The heat exchanger sections of the air heater each preferably
comprise metal panels having corrugations or undulations therein arranged to
cause combustion gases moving therethrough to move in a turbulent fashion
to enhance transfer of heat from the gases to the metal panels while also
causing turbulence in the air being heated as it travels between the heat
exchanger sections and enhancing heat transfer from the metal panels to the
air being heated.
In a typical embodiment, the heat exchanger sections are disposed, in
use, in vertically spaced horizontal planes to provide for said passage of air
along spaced horizontal planes during heating thereof.
Each said heat exchanger section in a preferred form of the invention
comprises a pair of metal panels disposed in close face-to-face relation to
allow gases to flow therebetween from the inlet ends to the outlet ends in a
travel direction. Said panels each have corrugations therein angled relative
to
the travel direction and oppositely oriented with respect to each other such
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that adjacent corrugations are in a criss-cross relation to each other whereby
gases flowing between said panels are forced by the opposing corrugations to
move in the form of a series of repeating spirals from said inlet end to said
outlet end to provide enhanced heat transfer.
The combustion chamber is preferably arranged in the main housing
such that cool air entering via said air inlet travels partly around the
combustion chamber exterior and receives heat therefrom prior to passing
between said heat exchanger sections.
An air heater according to a further aspect of the invention comprises a
main housing having an air inlet and an outlet for heated air, a combustion
chamber located therein, a burner assembly connected to the combustion
chamber to supply burning gases thereto, an exhaust stack, a heat exchanger
connected to said combustion chamber and comprising a plurality of heat
exchanger sections having inlet ends connected to receive heated
combustion gases from the combustion chamber and outlet ends connected
to said exhaust stack for exhausting combustion gases after passage through
the heat exchanger sections. Said heat exchanger sections are spaced apart
to allow the passage of air therebetween to effect heating of same. A blower
assembly moves cool air into said main housing via said air inlet and causes
the air to travel between the heat exchanger sections and thence outwardly of
said outlet for heated air. Said burner assembly includes an enclosure
connected to the combustion chamber and defines a path for movement of
combustion air toward the combustion chamber. A pair of generally parallel
burner plates are disposed transverse to the path of combustion air travel.
Said burner plates are spaced apart to define a shallow chamber
therebetween and both plates have a plurality of openings therein allowing for
passage of combustion air therethrough. The openings in a first one of said
plates are aligned with respective ones of the openings in the second plate to
provide annular openings allowing exit of gaseous fuel from the shallow
chamber. A conduit supplies gaseous fuel into the shallow chamber defined
between said burner plates such that, in use, combustion air moving along the
path and through the aligned openings in said burner plates mixes with
gaseous fuel emerging from said chamber via said annular openings thereby
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to provide a combustible fuel ¨ air mixture downstream of said burner plates,
which mixture, in use, is ignited to provide the supply of burning gases to
said
combustion chamber.
The air heater burner preferably is constructed such that said openings
in said plates are in the form of short tubular collars projecting from said
plates with the tubular collars of both plates being aligned with and directed
toward each other in confronting spaced apart relation to provide said annular
openings allowing exit of gaseous fuel between the confronting spaced apart
collars.
The air heater burner is typically arranged with said first burner plate
located upstream of the second burner plate relative to the flow direction of
combustion air when in use, and wherein the tubular collars of the first
burner
plate define flow passages of smaller diameter than those defined by the
tubular collars of the second plate thereby to create a venturi-like flow
action
as the combustion air passes through the aligned tubular collars thus
promoting thorough mixing of the air and the fuel being supplied via said
annular gaps.
The air heater burner plates may be of generally circular outline, with
said conduit to supply gaseous fuel being connected centrally of said plates
to
supply the fuel to the chamber defined between said plates, said conduit
having an end portion centrally disposed between said burner plates and
having a plurality of radially arranged openings to assist in providing even
distribution of gaseous fuel to said chamber.
The air heater typically employs a burner blower communicating with
said enclosure to provide for movement of combustion air along said path of
travel toward said burner plates and combustion chamber. The burner blower
preferably includes a vaned rotor mounted for rotation on an axis generally
centered with said burner plates and extending normal thereto, the burner
enclosure having a portion shaped to direct the air flow from said rotor
generally along said axis whereby to deliver a generally even and balanced
flow toward the burner plates to promote even flow distribution through said
openings therein.
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The air heater heat exchanger sections each preferably comprise metal
panels having corrugations or undulations therein arranged to cause
combustion gases moving therethrough to move in a turbulent fashion to
enhance transfer of heat from the gases to the metal panels. These heat
exchanger sections are disposed in a typical embodiment in vertically spaced
horizontal planes to provide for said passage of air along spaced horizontal
planes during heating thereof. The metal panels preferably have corrugations
therein angled relative to the travel direction and oppositely oriented with
respect to each other such that adjacent corrugations are in a criss-cross
relation to each other whereby gases flowing between said panels are forced
by the opposing corrugations to move in the form of a series of repeating
spirals from said inlet end to said outlet end to provide enhanced transfer of
heat.
Brief Description of the Drawinds
Fig. 1 is a longitudinal section view of the complete air heater taken in
a vertical plane.
Fig. 2 is a section view taken along line 2-2 of Fig. 1 in a horizontal
plane.
Fig. 3 is a section view of the burner assembly.
Fig. 4 is a partial section view of the burner assembly showing the
burner plates and gas feed assembly.
Fig. 5 is a bottom plan view of the burner plate structure of Fig. 4.
Fig. 6 is a further section view of the burner head assembly showing
gas/air flows.
Fig. 7 is a perspective view of the combustion chamber, heat
exchanger and exhaust stack assembly looking slightly from below.
Fig. 8 is a perspective view similar to Fig. 7 but looking somewhat
toward to the upper side.
Fig. 9 is a top plan view of a heat exchanger section.
Fig. 10 is a side elevation view of the heat exchanger section.
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Fig. 11 is a top plan view of a heat exchanger panel.
Fig. 12 is a view of the heat exchanger panel seen edge-on showing
the corrugations therein.
Fig. 13 is a diagrammatic view of a narrow slice of the heat exchanger
section taken longitudinally thereof illustrating the face-to-face
relationship of
the metal panels and the corrugations therein.
Fig. 14 is a diagrammatic plan view of a heat exchanger section
illustrating the panel corrugations therein and their criss-cross
relationship.
Detailed Description of Preferred Embodiment
The indirect fired, vented air heater 20 includes a rectangular box-like
main heater housing 22 having a burner assembly 24 mounted on an upper
portion thereof and with a vertically disposed combustion chamber 26
disposed within the main housing. A heat exchanger 28 is connected to the
combustion chamber 26 and extends laterally outwardly therefrom. The
combustion chamber is positioned vertically within the main housing 22 with
the burner assembly 24 positioned above and connected to the combustion
chamber with the lower end of the burner assembly projecting into the upper
end of the combustion chamber. The heat exchanger 28 includes a series of
vertically spaced formed sections 30 which will be described hereafter. These
sections 30 are connected in sealed relationship to slot-like openings in the
walls of the combustion chamber on one side and to slot-like openings which
are provided in the walls of a vertically arranged exhaust stack 32 located in
spaced relation to the combustion chamber. A blower assembly 34 in the
form of a pair of relatively large blower fans 36 is positioned to the side of
the
combustion chamber 26 which is opposite to the side where the heat
exchanger 28 is positioned. The inlet end of the main heater housing 22 is
provided with a rectangular inlet opening 38 for fresh cool air which is drawn
inwardly by the blower fans 36, forced around the exterior of the combustion
chamber and then caused to pass between the spaced apart heat exchanger
sections 30, with the heated air then passing through a similarly sized warm
air exit opening 40 in the exit or outlet end of the heater housing 22.
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It will be appreciated that the indirect fired heater being described may
be made in a variety of shapes and sizes while still retaining the basic
innovative features to be described in detail hereafter. For example, one
particular unit having a heating capacity of 1,500,000 BTU/hr., and fueled by
either natural gas or propane, had overall heater housing dimensions of
approximately 114 inches long by 32.5 inches wide by 77.5 inches high with a
weight of 1,875 lbs. The above-mentioned cool air and warm air inlet and
outlet openings 38, 40 at opposing ends of the housing were each 24 inches
high by 24 inches wide. The air flow provided by the above-mentidned
blowers 36 (without duct work and at 20 C) was in the order of 7300 ft3 per
minute. The air temperature rise (without duct work) was 95 C (171 F) while
the stack temperature rise was measured as 192 C (345 F). These figures
are given merely by way of example and will of course vary widely depending
on the size and exact design of the unit selected.
The gas burner assembly 24 (Fig. 3) includes a burner blower 44
positioned above the burner head 45. The burner blower 44 is provided with
suitable air flow confining structures 46 including flow straightening vanes
48
and conical section 49 defining a path for movement of combustion air
downwardly toward the burner head having a pair of generally parallel burner
head plates 50,52 and disposed transverse to the path of combustion air
travel. Burner plates 50, 52 are provided with upper and lower support plates
51, 53 respectively, to stiffen the burner head assembly and prevent warping
of same, etc. It will be seen that the vaned burner blower rotor 56 is mounted
for rotation on an axis defined by its vertical drive shaft 58 and is
generally
centered with the above-mentioned burner plates 50, 52 and extending
normal thereto. (The drive shaft motor is not shown). The air flow confining
structures 46 and vanes 48 are shaped to direct the air flow from the rotor 56
generally along this vertical axis thereby to deliver a generally even and
balanced flow toward the burner plates 50, 52 to promote even flow
distribution through the openings therein which will be hereafter described.
As best seen in Figs. 3-6, the burner plates 50, 52 are of generally
circular outline shape and they are spaced apart to define a shallow chamber
60 between them (Figs. 4 and 6). Both plates have a multiplicity of openings
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62, 64 therein allowing for passage of combustion air from the burner blower
44 therethrough. The openings 62 in a first one of the plates 50 are aligned
with respective ones of the openings 64 in the second plate 52 to provide
annular openings 66 allowing exit of gaseous fuel from the shallow chamber
60 defined between the plates. The gaseous fuel (either propane or natural
gas) is provided by way of a pipe 67 which is located just above the burner
plates 50, 52 and which is connected by a tee connection to a vertical conduit
68 having openings in its lower end to supply the gaseous fuel centrally of
the
burner plates 50, 52 in such a way as to provide a generally uniform supply to
them. As shown in the drawings (Figs. 3, 4, 6), this centrally connected
conduit 68 has a lower end portion disposed between the burner plates (50,
52) which is provided with a multiplicity of radially arranged openings 70 to
provide even distribution of gaseous fuel to the chamber 60 between the
plates 50, 52. During operation, combustion air moving along the path of
combustion air travel from the burner blower 44 enters through the aligned
openings 62, 64 in the burner plates and mixes with the gaseous fuel
emerging from between the burner plates via the above-mentioned annular
openings 66 thereby to provide a combustable fuel-air mixture downstream of
the burner plates.
The above-mentioned openings 62, 64 in the burner plates 50, 52 are
in the form of short tubular collars 74, 76 projecting from the plates with
the
tubular collars of both plates being aligned with and directed toward each
other in confronting spaced apart relation to provide the above-noted annular
openings 66 allowing exit of gaseous fuel between the confronting spaced
apart collars. In greater detail, the first burner plate 50 is located
upstream of
the second burner plate 52 relative to the flow direction of combustion air,
when in use, and it is important to note that the tubular collars 74 of this
first
burner plate 50 define flow passages which are smaller in diameter than those
defined by the tubular collars 76 of the second plate 52. Hence, by virtue of
their relationship as shown in the drawings and described above, there is
created a venturi-like flow action as the combustion air passes through the
aligned tubular collars 74, 76 of the two burner plates 50, 52 thus promoting
thorough mixing of the air and the gaseous fuel being supplied by the annular
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openings noted above and illustrated in Fig. 6 as well as allowing for reduced
gas supply pressure between the burner plates as the venturi action pulls the
gas into the moving combustion air streams.
The short tubular collars 74, 76 in the burner plates 50, 52 are
integrally formed with their respective burner plates as by a punching action
which need not be described in further detail. Alternatively the burner plates
may be made by a suitable casting process.
The diameter of the first or upper burner plate 50 is slightly larger than
that of the lower plate 52. The peripheral edges of both plates are formed or
turned inwardly toward each other with an annular gap 80 between them.
Some gas is allowed to leave the burner head through this annular gap 80
which then mixes with air flowing around the edge of the burner head.
It is noted that the positioning of the burner blower 44 in the manner
described above in relation to the burner head provides the benefits of
ensuring a balanced air flow all around and through the burner head plates
50, 52. This is in contrast to traditional power burners which require a very
much longer distance between the burner blower and the burner head to
ensure a balanced flow. The above-noted enclosures which define a path of
movement of combustion air from the blower are associated with the flow
straightener vanes 48 noted above to provide a smooth and uniform flow of air
to the burner head.
A conventional spark igniter part of which is shown as item 81 is
attached to the lower burner plate 52 and is used to light the burner in a
conventional fashion. During operation, the flames extend downwardly from
the burner head into the interior of the combustion chamber 26. The bottom
of the combustion chamber 26 is, of course, closed forcing the flames to turn
back with the hot combustion gases then made to flow around an elongated
metal shield 82 (Fig. 2) which is spaced a reasonable distance away from the
above-mentioned series of slot-like openings in the wall of the combustion
chamber 26, which openings lead into the heat exchanger sections 30 which
will be described hereinafter. It is also noted that although the combustion
chamber is shown in the drawings as being of hexagonal outline as seen in
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plan view, it is quite possible that other shapes, such as a circular shape,
might be chosen instead.
The heat exchanger 28 comprises a stack of metal exchanger sections
30 which extend away from the combustion chamber 26 and toward the
exhaust stack 32 in vertically spaced apart generally horizontal planes (Figs.
7
and 8). Each heat exchanger section is made from two metal panels 86,
preferably of stainless steel to resist corrosion, each metal panel 86
containing a series of parallel V-shaped corrugations 88 which are disposed
at an angle a to a line normal to the longitudinal axis of the heat exchanger
section 30. In the particular unit noted previously, this angle is in the
order of
9 although this angle can be varied considerably (e.g., as for different BTU
ratings). These metal panels 86 are attached together in face-to-face
relationship such that the peaks of the corrugations are touching or nearly
touching (Fig. 10). Because these panels are in close proximity, as the hot
combustion gases flow through each of the exchanger sections 30 between
the metal panels 86, these gases are forced to flow into the V-shaped
channels defined by the corrugations in the panels. It is important to note
that
the panels 86 are arranged so that the angles of the corrugations 88 therein
are oriented so as to be in opposing relationship as between the two panels of
each heat exchanger section 30. In other words, adjacent corrugations 88 are
in a "criss-cross" relationship to each other (Fig. 14). Thus, if the
corrugations
are at an angle of about 9 to a line normal to the longitudinal axis of the
exchanger section 30, adjacent corrugations 88 will be at an angle of twice
this amount, e.g. at about 18 relative to each other, keeping in mind as
noted
above that these 9 and 18 angles can easily be varied considerably by
several degrees. As a result of this relationship, the gases moving through
the heat exchanger sections from the combustion chamber 26 to the exhaust
stack 32 will be forced to move in a tortuous spiralling path. For example,
heated gases entering an upper channel will shift, e.g. towards the right,
while
gases entering the lower channel will shift toward the left. Eventually the
gases in an upper channel will be forced to move to a lower channel and vice
versa. Therefore, as these gases move through the heat exchanger sections
30, the gases are shifted right, down, left, and up in a repeating fashion
thus
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taking the form of a series of rough spirals while moving along through the
heat exchanger sections. This "spiralling" action of the gases allows for an
efficient transfer of heat from the combustion gases to the metal panels 86.
The combustion gases then leave the heat exchanger sections 30 and enter
through the slot like openings in the exhaust stack 32 and are vented
outwardly in any desired manner. The edge portions of the heat exchanger
sections 30 are of course sealed to prevent escape of combustion gases and
intermixing of same with the air as it is being heated.
The blower assembly 34 for the air to be heated, as mentioned above,
is positioned within the main housing 22 on the opposite side of the
combustion chamber 26 as the heat exchanger. Cold air is drawn into the
previously mentioned cold air inlet 38 in the end wall of the main housing and
is sucked into the blower wheels and then expelled from the blower into the
main housing interior such that the air first travels around the outside of
the
combustion chamber 26 (Fig. 2) thus receiving a certain amount of heat
therefrom, following which this air then enters the horizontal spaces between
the vertically spaced apart heat exchanger sections 30. Thus, this cold air
picks up heat from the walls of the combustion chamber 26 as well as the
panels 86 of the heat exchanger sections. As the air is flowing longitudinally
between the heat exchanger sections 30, the angled corrugations 88 of a heat
exchanger section above the air stream force the air in one direction while
the
corrugations in the section below force it in the opposite direction thus
creating a substantial amount of turbulence in the air being heated as it
travels lengthwise between the heat exchanger sections 30 thus further
improving the efficiency of the heat transfer process. The heated air then
exits the heat exchanger 28 and travels outwardly of the main housing 22 by
way of the previously mentioned hot air outlet 40 in the exit end of the main
housing. It will be obvious that the entrances and exits from the heat
exchanger are designed and well sealed to prevent any mixing of combustion
gases with the air being heated.
The blower assembly 34 position described above could be changed
such that the air travels first through the heat exchanger and then around the
combustion chamber. This could provide a more efficient heater but
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contact with it. Additionally, the upwardly rising warm air allows for some
preheating of the inlet air to the burner assembly thus further increasing
system efficiency.
A preferred embodiment of the invention has been described by way of
example. Those skilled in the art will realize that various modifications and
changes may be made while remaining within the scope of the invention.
Hence the invention is not to be limited to the embodiment as described but,
rather, the invention encompasses the full range of equivalencies as defined
by the appended claims as purposively construed.
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