Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02911796 2015-11-12
METHOD AND SYSTEM FOR EXTRACTING HEAT FROM A FLUE GAS
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of waste heat
recovery.
More particularly, the present invention relates to a method and system for
extracting
heat from flue gas that is exiting from a cooking appliance, such as for
instance a
commercial deep fryer or gas oven.
BACKGROUND
[0002] In the restaurant industry, and in other settings in which commercial
cooking
appliances are used, it is required to vent waste heat to the outside via an
exhaust
hood that is positioned above the cooking appliance. Unfortunately, this
practice
results in a very inefficient use of energy in the kitchen. For instance, the
flue gas
from a commercial deep flyer may be exhausted at a temperature in the range
700-
1100 F. At the same time, additional energy is consumed for space heating and
to
heat water for other applications in the kitchen, such as dish washing, hand
cleaning,
etc.
[0003] Various attempts have been made to partially recover the waste heat
that is
produced by commercial cooking appliances, to be used for other purposes such
as
space heating and/or production of hot water. In one approach a heat exchanger
is
located within the exhaust hood above the appliance for extracting heat from
the air as
it is being vented to the outside. This approach is not entirely satisfactory
because
grease and other particulates tend to build up rather quickly on the heat-
exchanger
surfaces, thereby insulating the surfaces and reducing the efficiency of the
system
over time. Further, the temperature of the air that enters the exhaust hood is
much
lower than the temperature of the air immediately after it exits the flue of
the cooking
appliance, and as such less heat is available to be extracted. In another
approach a
heat exchanger is introduced directly into the flue of the cooking appliance.
This
approach is also not entirely satisfactory because the heat exchanger is
subjected to
extremely high temperatures, which necessitates a very robust design and may
cause
solder joints etc. to fail relatively quickly. Additionally, modifying the
cooking
CA 02911796 2016-03-07
appliance to accept the heat exchanger within the flue may violate safety code
regulations and/or void manufacturer warranties.
SUMMARY OF THE INVENTION
[0004] In accordance with an aspect of at least one embodiment, there is
provided a
system for extracting heat from a flue gas exiting from a cooking appliance,
the
system comprising: a flue extension having an open first end and an open
second end
opposite the first end, the first end aligned with but spaced apart from a
flue of the
cooking appliance for receiving a flue gas at a first temperature as it exits
via the flue
of the cooking appliance, and the second end facing but spaced apart from an
exhaust
hood for discharging the flue gas at a second temperature to the exhaust hood,
the
second temperature being lower than the first temperature; a mount for
supporting the
flue extension within a space between the flue of the cooking appliance and
the
exhaust hood, the mount being secured to a surface that is proximate the
cooking
appliance and that is other than a surface of either the cooking appliance or
the
exhaust hood; and a heat exchanger assembly disposed within the flue extension
and
comprising a heat exchanger tube for circulating a volume of a thermal fluid,
the heat
exchanger tube comprising a plurality of substantially straight tube sections
that are
arranged substantially normal to a flow direction of the flue gas through the
flue
extension.
[0005] In accordance with an aspect of at least one embodiment, there is
provided a
system for extracting heat from a flue gas exiting from a cooking appliance,
comprising: a flue extension having an open first end, an open second end that
is
opposite the first end, and a central passageway extending between the first
and
second ends; a first heat exchanger assembly disposed within the central
passageway
of the flue extension; a mount for supporting the flue extension and the first
heat
exchanger within a space between a flue of the cooking appliance and an
exhaust
hood disposed above the cooking appliance, the mount being operable between: a
first
configuration in which the first end of the flue extension is aligned with but
spaced
apart from the flue of the cooking appliance by a first distance, and a second
configuration in which the first end of the flue extension is spaced apart
from the flue
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of the cooking appliance by a second distance that is greater than the first
distance; a
storage tank for containing a medium to be heated; a second heat exchanger
disposed
within the storage tank, the second heat exchanger being in fluid
communication with
the first heat exchanger; and a pump for circulating a thermal fluid within a
closed
circuit that includes the first heat exchanger and the second heat exchanger.
[0006] In accordance with an aspect of at least one embodiment, there is
provided a
method for extracting heat from a flue gas exiting a cooking appliance,
comprising:
using a mount, supporting a flue extension between a flue of the cooking
apparatus
and an exhaust hood disposed above the cooking apparatus, such that an open
first
end of the flue extension is aligned with but spaced apart from the flue of
the cooking
apparatus by a first distance, and wherein the mount is secured to a surface
that is
proximate the cooking appliance and that is other than a surface of either the
cooking
appliance or the exhaust hood; providing a heat exchanger assembly within the
flue
extension, the heat exchanger assembly including a heat exchanger coil;
receiving the
flue gas via the open first end of the heat exchanger, the flue gas being
constrained by
the flue extension to flow around the heat exchanger coil and out through an
open
second end of the flue extension along a direction generally toward the
exhaust hood;
and while the flue gas is being constrained to flow around the heat exchanger
coil,
circulating a heat transfer fluid within the heat exchanger coil, whereby heat
is
transferred from the flue gas to the thermal fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The instant invention will now be described by way of example only, and
with reference to the attached drawings, wherein similar reference numerals
denote
similar elements throughout the several views, and in which:
[0008] Fig. I is a block diagram showing the components of a system according
to
an embodiment.
[0009] Fig. 2 is a schematic diagram showing a system according to an
embodiment.
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[00101 Fig. 3 is a diagram showing the c'omponents of a sensing and control
sub-
system.
[0011] Fig. 4 is a perspective view of a flue extension secured to a mount.
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[0012] Fig. 5 is a side view showing the flue extension supported by the mount
when
the mount is in a first (operating) configuration.
[0013] Fig. 6 is a side view showing the flue extension supported by the mount
when
the mount is in a second (stowed) configuration.
[0014] Fig. 7 shows the flue extension supported by the mount in the first
(operating)
configuration, relative to an exhaust hood and cooking appliance.
[0015] Fig. 8 shows the flue extension supported by the mount in the second
(stowed) configuration, relative to an exhaust hood and cooking appliance.
[0016] Fig. 9 is a perspective view of a heat exchanger assembly that is
suitable for
use in a system according to an embodiment.
[0017] Fig. 10 is a side view of the heat exchanger assembly of Fig. 9.
[0018] Fig. 11 is a perspective view of an alternative heat exchanger
configuration.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0019] The following description is presented to enable a person skilled in
the art to
make and use the invention, and is provided in the context of a particular
application
and its requirements. Various modifications to the disclosed embodiments will
be
readily apparent to those skilled in the art, and the general principles
defined herein
may be applied to other embodiments and applications without departing from
the
scope of the invention. Thus, the present invention is not intended to be
limited to the
embodiments disclosed, but is to be accorded the widest scope consistent with
the
principles and features disclosed herein. Also, it is to be understood that
the
phraseology and terminology used herein is for the purpose of description and
should
not be regarded as limiting. The use of "including," "comprising," or "having"
and
variations thereof herein is meant to encompass the items listed thereafter
and
equivalents thereof as well as additional items. The phrase "heat exchanger
assembly" is used interchangeably with the term "coil" throughout the
description and
in the claims.
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[0020] Fig. 1 is a simplified block diagram showing the components of a system
100
according to an embodiment. A heat exchanger assembly 102 is disposed within a
flue extension 104, which is supported by a not illustrated mount within a
space 106
between a cooking appliance 108 and an exhaust hood 110. The heat exchanger
assembly 102 is in fluid communication with a second heat exchanger assembly
112,
which is disposed within a tank 114 containing a medium that is to be heated.
For
instance, tubing 116 and 118 are connected between the heat exchanger assembly
102
and the second heat exchanger assembly 112 for circulating a thermal fluid
therebetween. For simplicity, various elements including sensors, controllers,
manifolds, valves and pumps etc., which are described below with reference to
Fig. 2,
have been omitted from Fig. 1. The dashed lines in Fig. 1 represent data
communication paths for receiving feedback signals and for providing control
signals,
and are intended to be illustrative in nature. In this example, both the
medium that is
to be heated and the thermal fluid are water. Optionally, the thermal fluid is
another
fluid, such as for instance a water/propylene glycol mixture, e.g. 60%
propylene
glycol and 40% water. Optionally, the configuration of the second heat
exchanger
assembly 112 differs from the configuration of the heat exchanger assembly
102.
[0021] Fig. 2 is a more detailed schematic diagram of system 100. Controller
120
receives feedback signals from temperature sensors 200 and from flow sensors
202.
In the embodiment that is shown in Fig. 2, temperature sensors 200 are
located: (I) in
the tubing 118 before the inlet to the second heat exchanger assembly 112; (2)
in the
tubing 116 after the outlet from the second heat exchanger assembly 112; (3)
in the
cold water supply line before the inlet to the storage tank 114; and (4) in
the hot water
supply line after the outlet from the storage tank 114. A fifth temperature
sensor 200
is disposed within the flue extension 104. The fifth temperature sensor is
used to
detect a temperature increase in the flue extension 104, which causes the
system to
switch on and begin sensing other parameters, etc. For instance, a relay is
responsive
to an output signal from the fifth temperature sensor for switching on and off
a pump
206. Additionally, flow meters 202 are located in tubing 116 after the outlet
from the
second heat exchanger assembly 112 and in the cold water supply line before
the inlet
into the storage tank 114. Based on the signals that are received from the
temperature
CA 02911796 2015-11-12
sensors 200 and the flow meters 202, the controller 120 provides control
signals for
controlling various components of the system, such as for instance valves 204,
pumps
206, etc. Optionally, the temperature sensors 200 and/or flow meters 202
and/or
valves 204 and/or pumps 206 are disposed within the system 100 at other than
the
locations described above. Optionally, more or fewer temperature sensors 200
and/or
flow meters 202 and/or valves 204 and/or pumps 206 are utilized in the system
100.
[0022] Fig. 3 is a simplified schematic diagram showing the components of a
sensing
and control sub-system of the system 100. Controller 120 includes a plurality
of
analog inputs (numbered 2, 3, 5-7, 9-12 in Fig. 3), which receive signals that
are
generated by various sensing devices in response to sensed system parameters.
As
discussed supra with reference to Fig. 2, in this specific and non-limiting
example, the
controller 120 receives signals from two flow meters 202 and from five
temperature
sensors 200. A display device 300, such as for instance an LCD screen, is
provided
for displaying at least some of the data that are read from the temperature
sensors 200
and/or flow meters 202. Optionally, the display device 300 displays calculated
values
relating to the operation of the system 100, such as for instance the amount
of money
saved due to use of the system 100, the reduction in CO? emissions achieved,
the
amount of natural gas saved, etc.
[0023] Referring now to Fig. 4, shown is a perspective view of a mount 400
supporting flue extension 104. The mount 400 includes four wall-mounting
brackets
404 (three are visible in Fig. 4), for securing the mount 400 to a support
surface such
as a wall (not shown in Fig. 4). For instance, the mount 400 is secured to the
mounting surface using four 1/2" bolts (not shown in Fig. 4). The mount 400
includes
left and right single link pivoting assemblies 406, which support generally
vertical
movement of the flue extension 104 between a first (operating) configuration
in which
the lower end of the flue extension 104 is aligned with but spaced apart from
the flue
of the cooking appliance (not shown in Fig. 4) by a first distance, and a
second
(stowed) configuration in which the lower end of the flue extension 104 is
spaced
apart from the flue of the cooking appliance by a second distance that is
greater than
the first distance. For instance, the flue extension 104 is supported in the
first
configuration during operation, in order to maximize heat transfer from the
flue gas to
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the thermal fluid that is circulating within the heat exchanger assembly 102
(not
shown in Fig. 4). On the other hand, the flue extension 104 is supported in
the second
configuration during cleaning and/or maintenance of the heat exchanger
assembly 102
and/or cooking appliance and/or surrounding spaces. The single link pivoting
assemblies 406 are pivotally attached to left and right frame-members 408,
each of
which is secured to a respective pair of the wall-mounting brackets 404. A
handle
410 extends between the left and right single link pivoting assemblies 406,
and may
be grasped by a user when moving the flue extension 104 between the first and
second configurations.
[0024] Of course, the material that is used to fabricate the flue extension
104 and the
mount 400 must meet hygienic kitchen standards, must not corrode, and must be
able
to withstand the operating temperature of the cooking appliance 108. By way of
a
specific and non-limiting example, "403 stainless steel" is used.
[0025] Fig. 5 is a side view showing the flue extension 104 supported by the
mount
400 in the first configuration, and Fig. 6 is a side view showing the flue
extension 104
supported by the mount 400 in the second configuration. Additionally, Figs. 7
and 8
show the flue extension 104 installed adjacent to a surface 700 via the mount
400.
For improved clarity, the tubing 116 and 118 have been omitted from Figs. 7
and 8.
As is apparent, the mount 400 is supported entirely by the surface 700, which
in this
example is a wall that is situated behind the cooking appliance 108. None of
the
system components, including the mount 400, the flue extension 104, or the
heat
exchanger assembly 102, comes into contact with the cooking appliance 108 or
with
the exhaust hood 110. Accordingly, installing the system does not involve
making
any modifications to the cooking appliance 108 or to the exhaust hood 110.
[0026] Referring now to Fig. 9, shown is a perspective view of a heat
exchanger
assembly 102 that is suitable for use in the system 100 of Fig. 1. Fig. 10
shows a side
view of the heat exchanger 102. in this specific and non-limiting example, the
heat
exchanger assembly 102 comprises tubing 900 that is fabricated from 13 mm
(outside
diameter) seamless 310s stainless steel, with a wall thickness of 1.0 mm, and
with fins
902 that are made of 304 stainless steel. The tubing 900 is formed into an
elongated,
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double helical coil configuration, having a height H, and a length L that is
greater a
width W. The values of H, L and W are limited by inter alia the physical size
of the
space 106 between the cooking appliance 108 and the exhaust hood 110. In a
typical
application, the length L of the coiled assembly is in the range 203-381 mm,
and more
preferably in the range 292-381 mm. Of course, these values are examples only
and
assume a length-wise restriction imposed by a commercial cooking appliance 108
having a flue width of 425 mm. In the specific and non-limiting example that
is
shown in Figs. 9 and 10, the length L is approximately 304 mm, the width W is
approximately 127 mm, and the height H is approximately 304 mm. The uncoiled
length of the tubing 900 is approximately 6705 mm. Additionally, tube-end
connectors 904 and 906 are provided at the opposite ends of the tube 900, for
connecting the heat exchanger assembly 102 to the tubing 116 and 118. In
practice,
the tubing 116 and 118 may be standard flexible tubing, which may be routed or
plumbed throughout the building and then transitioncd to copper piping in the
kitchen
and finally to high temperature stainless steel flex lines for the final
connection to
inlets and outlets of the heat exchanger assembly 102.
[0027] In general, maximizing the outside diameter of the heat exchanger tube
900
and maximizing the number of turns of the coil, while also minimizing the wall
thickness of the heat exchanger tubes 900, results in greater heat transfer to
the
thermal fluid and accordingly produces a higher thermal fluid outlet
temperature. The
spacing between adjacent turns of the coil is limited by the maximum allowable
flue
gas flow rate reduction. That is to say, packing the turns of the double
helical coil too
closely together causes a flow restriction, and the flue gas venting may
become
inadequate. In the heat exchanger assembly 102 that is shown in Figs. 9 and
10, the
center of the double helical coil is substantially open and thereby ensures
adequate
flow through the structure.
[0028] Alternatively, a heat exchanger assembly having a different shape
and/or a
different configuration may be used in the system 100. For instance a common
"trombone-shaped" coil 1100, as shown in Fig. 11, may be used in place of the
heat
exchanger assembly 102 that is shown in Figs. 9 and 10. Further alternatively,
finless
tubing or tubing that is fabricated from a different material etc. is used.
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[0029] During operation the flue extension 104 is aligned above the flue 702
of the
cooking appliance 108, as is shown in Fig. 7. An optional gasket 704 (shown
using
dashed lines), which is fabricated from a heat resistant material, is disposed
between
the flue extension 104 and the flue 702. Pump 206 (not shown in Fig. 7)
circulates a
thermal fluid through the tubing 900 of the not illustrated heat exchanger
assembly
102. Flue gas is vented from the cooking appliance 108 via flue 702 and enters
into
the flue extension 104, optionally being guided by the gasket 704 when
present. The
flue gas flows around the finned tubing 900 of the heat exchanger assembly
102,
which results in transfer of energy (heat) from the flue gas to the thermal
fluid that is
being circulated within the heat exchanger assembly 102. More particularly,
the
finned heat exchanger tubing 900 comprises a plurality of substantially
straight tube
sections that are arranged substantially normal to a flow direction of the
flue gas
through the flue extension. Pump 206 then causes the heated thermal fluid to
flow
out of the heat exchanger assembly 102 and into the second heat exchanger
assembly
112, which is disposed within storage tank 114. Water stored within storage
tank 114
absorbs energy (heat) from the thermal fluid, thereby raising the temperature
of the
stored water and lowering the temperature of the thermal fluid. The cooled
thermal
fluid exits the second heat exchanger assembly 112 and is then returned to the
heat
exchanger assembly 102, and the cycle repeats.
[0030] When maintenance or cleaning is required, a user simply grasps the
handle
910 and pivots the flue extension 104 (including the optional gasket 704)
upward and
away from the flue 702 of cooking appliance 108. The flue 702 and/or
surrounding
surfaces etc., may then be cleaned, moved and/or maintained.
[0031] Providing a flue extension 104 in alignment with the flue 702 of the
cooking
appliance 108, and disposing the heat exchanger assembly 102 within the flue
extension 104, avoids the need modify either the flue 702 or the exhaust hood
110.
Further, the volume and pressure of the flue gas flow through the flue 702 and
exhaust
hood is substantially unaffected by the presence of the heat exchanger
assembly 102
within the flue extension 104. Further still, the heat exchanger assembly 102
and flue
extension 104 can be rapidly moved out of the way to provide access to the
flue 702
when required, including in emergency situations. The flue extension 104
channels
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the flue gas upward and toward the exhaust hood, limiting the amount of heat
that
escapes into the environment around the cooking appliance. Additionally, the
heat
exchanger assembly 102 removes some of the heat from the flue gas, thereby
lowering the temperature of the flue gas and further limiting the amount of
heat that
escapes into the environment around the cooking appliance.
[0032] Optionally, a different type of mount is used, such as for instance a
"drawer-
slider" type mount that support horizontal movement of the flue extension and
heat
exchanger assembly. Such a mount is appropriate when the vertical dimension of
the
space 106 between the cooking appliance 108 and exhaust hood 110 is limited.
Alternatively, the mount is stationary and the flue extension 104 is secured
to the
mount using quick-release fasteners, or the flue extension 104 simply "snaps"
into
place on the mount, such that the flue extension 104 and heat exchanger
assembly 102
may be removed from the mount for cleaning/maintenance purposes. Further
alternatively, the flue extension 104 and heat exchanger assembly 102 may be
suspended from the ceiling or from another support surface above the cooking
appliance, such as for instance using cables or chains.
[0033] While several inventive embodiments have been described and illustrated
herein, those of ordinary skill in the art will readily envision a variety of
other means
and/or structures for performing the function and/or obtaining the results
and/or one
or more of the advantages described herein, and each of such variations and/or
modifications is deemed to be within the scope of the invent of embodiments
described herein. More generally, those skilled in the art will readily
appreciate that
all parameters, dimensions, materials, and configurations described herein are
meant
to be exemplary and that the actual parameters, dimensions, materials, and/or
configurations will depend upon the specific application or applications for
which the
inventive teachings is/are used. Those skilled in the art will recognize, or
be able to
ascertain using no more than routine experimentation, many equivalents to the
specific inventive embodiments described herein. It is, therefore, to be
understood
that the foregoing embodiments are presented by way of example only and that,
within the scope of the appended claims and equivalents thereto, inventive
embodiments may be practiced otherwise than as specifically described and
claimed.
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Inventive embodiments of the present disclosure are directed to each
individual
feature, system, article, material, kit, and/or method described herein. In
addition, any
combination of two or more such features, systems, articles, materials, kits,
and/or
methods, if such features, systems, articles, materials, kits, and/or methods
are not
mutually inconsistent, is included within the inventive scope of the present
disclosure.
[0034] All definitions, as defined and used herein, should be understood to
control
over dictionary definitions, and/or ordinary meanings of the defined terms.
The
indefinite articles "a" and "an," as used herein in the specification and in
the claims,
unless clearly indicated to the contrary, should be understood to mean "at
least one."
The phrase "and/or," as used herein in the specification and in the claims,
should be
understood to mean "either or both" of the elements so conjoined, i.e.,
elements that
are conjunctively present in some cases and disjunctively present in other
cases.
[0035] Multiple elements listed with "and/or" should be construed in the same
fashion, i.e., "one or more" of the elements so conjoined. Other elements may
optionally be present other than the elements specifically identified by the
"and/or"
clause, whether related or unrelated to those elements specifically
identified. Thus, as
a non-limiting example, a reference to "A and/or B", when used in conjunction
with
open-ended language such as "comprising" can refer, in one embodiment, to A
only
(optionally including elements other than B); in another embodiment, to B only
(optionally including elements other than A); in yet another embodiment, to
both A
and B (optionally including other elements); etc.
[0036] As used herein in the specification and in the claims, "or" should be
understood to have the same meaning as "and/or" as defined above. For example,
when separating items in a list, "or" or "and/or" shall be interpreted as
being
inclusive, i.e., the inclusion of at least one, but also including more than
one, of a
number or list of elements, and, optionally, additional unlisted items. Only
terms
clearly indicated to the contrary, such as "only one of' or "exactly one of,"
or, when
used in the claims, "consisting of," will refer to the inclusion of exactly
one element
of a number or list of elements. In general, the term "or" as used herein
shall only be
interpreted as indicating exclusive alternatives (i.e. "one or the other but
not both")
when preceded by terms of exclusivity, such as "either," "one of," "only one
of," or
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"exactly one of." "Consisting essentially of," when used in the claims, shall
have its
ordinary meaning as used in the field of patent law.
[0037] As used herein in the specification and in the claims, the phrase "at
least
one," in reference to a list of one or more elements, should be understood to
mean at
least one element selected from any one or more of the elements in the list of
elements, but not necessarily including at least one of each and every element
specifically listed within the list of elements and not excluding any
combinations of
elements in the list of elements. This definition also allows that elements
may
optionally be present other than the elements specifically identified within
the list of
elements to which the phrase "at least one" refers, whether related or
unrelated to
those elements specifically identified. Thus, as a non-limiting example, "at
least one
of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at
least one
of A and/or B") can refer, in one embodiment, to at least one, optionally
including
more than one, A, with no B present (and optionally including elements other
than B);
in another embodiment, to at least one, optionally including more than one, B,
with no
A present (and optionally including elements other than A); in yet another
embodiment, to at least one, optionally including more than one, A, and at
least one,
optionally including more than one, B (and optionally including other
elements); etc.
[0038] It should also be understood that, unless clearly indicated to the
contrary, in
any methods claimed herein that include more than one step or act, the order
of the
steps or acts of the method is not necessarily limited to the order in which
the steps or
acts of the method are recited.
[0039] Numerical ranges include the end-point values that define the ranges.
For
instance, "between X and Y" includes both X and Y, as well as all temperature
values
between X and Y.
[0040] In the claims, as well as in the specification above, all transitional
phrases
such as "comprising," "including," "carrying," "having," "containing,"
"involving,"
"holding," "composed of," and the like are to be understood to be open-ended,
i.e., to
mean including but not limited to. Only the transitional phrases "consisting
of' and
"consisting essentially of' shall be closed or semi-closed transitional
phrases,
respectively.
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[0041] The foregoing description of methods and embodiments of the invention
has
been presented for purposes of illustration. It is not intended to be
exhaustive or to
limit the invention to the precise steps and/or forms disclosed, and obviously
many
modifications and variations are possible in light of the above teaching. It
is intended
that the scope of the invention and all equivalents be defined by the claims
appended
hereto.
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