U.S. patent application number 13/744980 was filed with the patent office on 2013-07-25 for low emission, wood fueled hydronic heater.
This patent application is currently assigned to HAWKEN ENERGY, INC.. The applicant listed for this patent is HAWKEN ENERGY, INC.. Invention is credited to Gary Bird, Donald Squire, Warren W. Walborn, Daniel Walton.
Application Number | 20130186313 13/744980 |
Document ID | / |
Family ID | 48796170 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130186313 |
Kind Code |
A1 |
Walborn; Warren W. ; et
al. |
July 25, 2013 |
LOW EMISSION, WOOD FUELED HYDRONIC HEATER
Abstract
A wood burning hydronic heater comprises a primary firebox into
which the wood is loaded and wherein initial combustion occurs. The
heater also includes a secondary combustion chamber below the
primary firebox into which the combustible gases from the primary
firebox are forced and into which a fresh air stream is passed to
burn the gases. A primary heat exchanger downstream of the
secondary combustion chamber is adapted to reduce the temperature
of the exhaust exiting from the secondary combustion chamber. A
catalytic combustor, located in a chamber downstream of the
secondary combustion chamber and primary heat exchanger, completes
combustion and reduces emissions.
Inventors: |
Walborn; Warren W.; (Shelby,
MI) ; Squire; Donald; (New Era, MI) ; Walton;
Daniel; (Rothbury, MI) ; Bird; Gary;
(Muskegon, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HAWKEN ENERGY, INC.; |
Shelby |
MI |
US |
|
|
Assignee: |
HAWKEN ENERGY, INC.
Shelby
MI
|
Family ID: |
48796170 |
Appl. No.: |
13/744980 |
Filed: |
January 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61588723 |
Jan 20, 2012 |
|
|
|
Current U.S.
Class: |
110/345 ;
110/309; 122/16.1; 122/19.2 |
Current CPC
Class: |
F24H 1/108 20130101;
F23B 90/08 20130101; F24H 2230/02 20130101; F23J 15/02 20130101;
F24H 1/22 20130101; F23B 90/06 20130101; F24H 9/1845 20130101; F23B
50/06 20130101; F24H 9/0026 20130101; F23G 7/07 20130101; F23B
10/02 20130101 |
Class at
Publication: |
110/345 ;
122/16.1; 122/19.2; 110/309 |
International
Class: |
F24H 1/10 20060101
F24H001/10; F24H 9/18 20060101 F24H009/18; F23J 15/02 20060101
F23J015/02; F24H 9/00 20060101 F24H009/00 |
Claims
1. A wood burning hydronic heater comprising: a primary firebox
into which the wood is loaded and wherein initial combustion
occurs; a secondary combustion chamber into which the combustible
gases from the primary firebox are directed and into which an air
stream is passed to burn the gases; a primary heat exchanger
downstream of the secondary combustion chamber adapted to reduce
the temperature of the exhaust exiting from the secondary
combustion chamber; and a catalytic combustor located in a chamber
downstream of the secondary combustion chamber.
2. The heater of claim 1 further comprising a secondary heat
exchanger that extracts heat from the exhaust gases such that the
exiting stack temperature of exhaust gases is about 250.degree. to
300.degree. F.
3. The heater of claim 2, wherein the catalytic combustor is
located in a chamber between the primary heat exchanger and a
secondary heat exchanger.
4. A wood burning hydronic heater comprising: a primary firebox
into which the wood is loaded and wherein initial combustion
occurs; a secondary combustion chamber below the primary firebox
into which the combustible gases from the primary firebox are
directed; vertical channels providing fluid communication between
the firebox and the secondary combustion chamber below the firebox;
an air blower; and a brick combustion plenum disposed between the
primary firebox and secondary combustion chamber, the brick
combustion plenum having an upper channel and a lower channel,
wherein the upper channel forces air into an upper portion of the
primary firebox and the lower channel forces air into the vertical
channels.
5. The heater of claim 4 further comprising downwardly inclined
slots that pass air from the lower channel to the vertical
channels.
6. The heater of claim 5, wherein the downwardly inclined slots act
as nozzles to introduce air at a downward angle for combustion in
the secondary burn combustion.
7. The heater of claim 5, wherein there are four vertical
channels.
8. The heater of claim 5 further comprising a pair of side airflow
paths on each side of the firebox in fluid communication with the
lower channel to pass air to each side of the firebox.
9. The heater of claim 5, wherein the primary firebox has a floor
constructed of arranged bricks, the vertical channel formed in a
brick forming the floor of the primary firebox.
10. The heater of claim 9, wherein the bricks further comprise the
downwardly inclined slots formed in each that pass air from the
lower channel to the vertical channels.
11. The heater of claim 4, wherein one of the bricks between the
primary firebox and the secondary combustion chamber has a
horizontal channel forming a horizontal airflow path with the lower
channel.
12. The heater of claim 4, wherein the primary firebox has a floor
constructed of arranged bricks, and one of the arranged bricks has
a horizontal channel extending along the length of the one of the
arranged bricks to provide for fluid communication with the lower
channel to allow air to flow to each side of the firebox.
13. The heater of claim 1, wherein the emissions from the heater is
less than 0.32 pounds particulate per 1,000,000 BTU output.
14. A wood burning hydronic heater comprising: a primary firebox
into which the wood is loaded and wherein initial combustion
occurs; a secondary combustion chamber into which the combustible
gases from the primary firebox are directed and into which an air
stream is passed to burn the gases; a primary heat exchanger
downstream of the secondary combustion chamber adapted to reduce
the temperature of the exhaust exiting from the secondary
combustion chamber; a catalytic combustor located in a chamber
downstream of the primary heat exchanger; and a secondary heat
exchanger located downstream of the catalytic combustor that
extracts heat from the exhaust gases such that the exiting stack
temperature of exhaust gases is about 250.degree. to 300.degree.
F.
15. The heater of claim 14 further comprising an air blower in
fluid communication with the primary firebox through an air opening
in a rear wall of the primary firebox and a removable firebox air
channel mounted to the rear wall of the primary firebox by a pair
of brackets, whereby air is introduced into the primary firebox via
the air blower into the rear of the primary firebox through the air
opening in the rear wall, upwards through the air channel and out
the exit opening into upper portion of the primary firebox.
16. The heater of claim 15, wherein the air channel comprises a
flat rectangular steel stamping formed into an open box having a
closed bottom end and an upper end, and an exit opening and tab
disposed at the upper end; and wherein one of the pair of brackets
is located just below the air opening and is shaped is snuggly
accept the closed bottom end of the air channel and the other one
of the pair of brackets is situated above the air opening and is
shaped is snuggly accept the tab.
17. A method of reducing the smoke emissions of a wood burning
hydronic heater, the method comprising the steps of: providing a
primary firebox into which the wood is loaded and wherein initial
combustion occurs; providing a secondary combustion chamber into
which the combustible gases from the primary firebox are directed,
during which an air stream is passed to burn the gases at extreme
temperatures to maintain high combustion efficiency; directing the
combusted gases to a primary heat exchanger to reduce the
temperature of the exhaust to a temperature suitable for use with
catalytic combustion; and directing the exhaust gas to a catalytic
combustor located in a chamber downstream of the primary heat
exchanger.
18. The method of claim 17 further comprising the step of providing
a secondary heat exchanger that extracts heat from the exhaust
gases such that the exiting stack temperature of exhaust gases is
about 250.degree. to 300.degree. F.
19. The method of claim 18, wherein the catalytic combustor is
located in a chamber between the primary heat exchanger and a
secondary heat exchanger.
20. The method of claim 19, wherein the emissions from the heater
is less than 0.32 pounds particulate per 1,000,000 BTU output.
Description
CLAIM OF PRIORITY
[0001] Applicants hereby claim the priority benefits under the
provisions of 35 U.S.C. .sctn.119(e), basing said claim of priority
on related provisional U.S. patent application Ser. No. 61/588,723,
filed on Jan. 20, 2012.
FIELD OF THE INVENTION
[0002] The present invention generally relates to wood fueled
hydronic heaters and more particularly to a low emission, wood
fueled hydronic heater incorporating a catalytic convertor.
BACKGROUND OF THE INVENTION
[0003] Wood burning furnaces, and particularly hydronic heaters
(also called outdoor wood heaters or outdoor wood boilers), are
increasingly being used in a multiple of residential and commercial
applications. Specifically, wood burning hydronic heaters are used
in place of natural gas, oil, propane, and other fossil fuel
burning applications, particularly for furnaces that are used to
heat water. Water is circulated through a heat exchanger in the
furnace and piped to a nearby building, providing both heat and hot
water to the building. The heat energy from the heated water is
then transferred to the residential or commercial application
through either a water-to-water heat exchanger or water-to-air heat
exchanger. Such furnaces are often housed in a small shed provided
with an exhaust vent. Most hydronic heaters are used in rural, cold
climate areas where wood is readily available, but can also be
found throughout North America.
[0004] Given the emissions inherent in the burning of wood or
wood-related products, such as wood pellets or, for example, corn,
there is an increasing interest to decrease smoke emissions,
especially particulate emissions, while maintaining if not
improving the efficiency of the combustion process. However, the
water jacket surrounding the fire tends to lower the temperature
within the firebox, thus interfering with the ability to obtain a
relative hot fire and improving the efficiency of the combustion
process. The present disclosure presents an effort to decrease the
smoke emissions of a wood burning hydronic heater without
compromising efficiency or performance.
SUMMARY OF THE INVENTION
[0005] According to one aspect of the present invention, a wood
burning hydronic heater includes a primary firebox into which the
wood is loaded and where initial combustion occurs. A secondary
burn or combustion chamber below the primary firebox is provided
into which the combustible gases from the primary firebox are
directed and into which an air stream is passed to additionally
burn the smoke-filled gases at extreme temperatures to maintain
high combustion efficiency. The heater further includes a primary
heat exchanger to reduce the temperature of the hot exhaust from
the extreme temperature in the secondary combustion chamber to a
temperature suitable for use with a catalytic combustor. The
catalytic combustor, located in a chamber between the primary heat
exchanger and a secondary heat exchanger, burns particulate matter
and improves the resulting combustion products. The heater finally
includes a secondary heat exchanger that extracts heat from the
exhaust gases such that the exiting stack temperature of exhaust
gases is about 250.degree. to 300.degree. F.
[0006] Another aspect of the invention includes a method of
reducing the smoke emissions of a wood burning hydronic heater that
includes a primary firebox into which the wood is loaded and where
initial combustion occurs. A secondary combustion chamber below the
primary firebox is provided into which the combustible gases from
the primary firebox are directed and into which an air stream is
passed to burn the gases at extreme temperatures to maintain high
combustion efficiency. The method further includes directing the
combusted gases to a primary heat exchanger to reduce the
temperature of the hot exhaust from the extreme temperature to a
temperature suitable for use with a catalytic combustor. The gas is
then directed to a catalytic combustor located in a chamber between
the primary heat exchanger and a secondary heat exchanger for
reducing particulate matter and improving the combustion process.
The method finally includes directing the heated gas to a final
heat exchanger that extracts heat from the exhaust such that the
exiting stack temperature of exhaust gases is about 250.degree. to
300.degree. F.
[0007] These and other aspects, objects, and advantages of the
present invention will be further understood and appreciated by
those skilled in the art by reference to the following written
specification, claims, and appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] In the drawings:
[0009] FIG. 1 is a schematic representation of the structure and
method associated with the disclosed low emission, wood hydronic
heater;
[0010] FIG. 2A is a front view of the low emission, wood hydronic
heater;
[0011] FIG. 2B is a side view of the low emission, wood hydronic
heater;
[0012] FIG. 3 is a perspective, exploded view of the heat shield
and openable door of the low emission, wood hydronic heater;
[0013] FIG. 4 is a perspective view of the brick combustion plenum
for delivering air into the low emission, wood hydronic heater;
[0014] FIG. 5 is another perspective view of the brick combustion
plenum for delivering air into the low emission, wood hydronic
heater;
[0015] FIG. 6 is yet another perspective view of the brick
combustion plenum for delivering air into the low emission, wood
hydronic heater, wherein several of the bricks have been removed
for clarity;
[0016] FIG. 7 is still another perspective view of the brick
combustion plenum for delivering air into the low emission, wood
hydronic heater;
[0017] FIG. 8 is an additional perspective view of the brick
combustion plenum for delivering air into the low emission, wood
hydronic heater, wherein one of the bricks has been removed for
clarity;
[0018] FIG. 9 is a perspective view of the horizontally slotted
brick for directing air within the brick combustion plenum;
[0019] FIG. 10 is a perspective view of the vertically slotted
brick within the brick combustion plenum having air channels to
introduce air at a downward angle into the vertical channels in the
brick for combustion in the secondary combustion chamber of the low
emission, wood hydronic heater;
[0020] FIG. 11 is a perspective view of the primary firebox of the
low emission, wood hydronic heater with the removable air channel
removed;
[0021] FIG. 12 is a perspective view of the removable air channel
of the low emission, wood hydronic heater;
[0022] FIG. 13 is a perspective view of the rear of the low
emission, wood hydronic heater with the rear panel removed and the
fan assembly removed from the fresh air inlet;
[0023] FIG. 14 is a perspective view of the fan assembly of the low
emission, wood hydronic heater removed from the fresh air
inlet;
[0024] FIG. 15 is a perspective view of the fresh air inlet of the
low emission, wood hydronic heater with the fan assembly
removed;
[0025] FIG. 16 is a side view of the chamber into which the
catalytic combustor is placed;
[0026] FIG. 17 is a perspective view of the secondary heat
exchanger;
[0027] FIG. 18 is a perspective view of the base of the low
emission, wood hydronic heater;
[0028] FIG. 19 is a front view of the water level indicator of the
low emission, wood hydronic heater in the full position; and
[0029] FIG. 20 is a front view of the water level indicator of the
low emission, wood hydronic heater in the less than full
position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0030] For purposes of description herein, the terms "upper,"
"lower," "right," "left," "rear," "front," "vertical,"
"horizontal," and derivatives thereof shall relate to the invention
as oriented in FIG. 2A, with reference to a viewer facing the front
of the furnace. However, it is to be understood that the invention
may assume various alternative orientations and step sequences,
except where expressly specified to the contrary. It is also to be
understood that the specific parts, devices and processes
illustrated in the attached drawings and described in the following
specification are simply exemplary embodiments of the inventive
concepts defined in the appended claims. Hence, specific dimensions
and other physical characteristics relating to the embodiments
disclosed herein are not to be considered as limiting, unless the
claims expressly state otherwise.
[0031] Further, where a range of values is provided, it is
understood that each intervening value, to the tenth of the unit of
the lower limit unless the context clearly dictates otherwise,
between the upper and lower limit of that range, and any other
stated or intervening value in that stated range, is encompassed
within the invention. The upper and lower limits of these smaller
ranges may independently be included in the smaller ranges, and are
also encompassed within the invention, subject to any specifically
excluded limit in the stated range. Where the stated range includes
one or both of the limits, ranges excluding either or both of those
included limits are also included in the invention.
[0032] Referring to the Figures, the reference numeral 100
generally designates a wood burning hydronic heater comprising
several components, including: (1) a primary firebox 102; (2) a
brick combustion plenum 104; (3) a secondary combustion chamber
106; (4) a primary heat exchanger 108; (5) a catalytic combustor
110; and (6) a secondary heat exchanger 112.
[0033] The primary firebox 102 is generally a brick or ceramic
lined chamber formed within a steel compartment 114, as shown in
FIG. 1. Wood is loaded through an opening 116 that may be accessed
via an openable, fire-resistant door 118. After being loaded, the
wood may be ignited. The door 118 preferably comprises an inner
stainless steel door or heat shield 120 and an outer door 122, as
shown in FIG. 3. The inner door 120 protects the user from blowback
when the door is opened and protects the outer door 122 and
non-water-jacketed door frame 124 from heat. The primary firebox
102 includes a brick combustion plenum 104 that forms a brick floor
126 and brick inclined side walls 128, where the plenum 104 is
comprised of a plurality of slotted, refractory bricks intermixed
therein with conventionally constructed refractory bricks. Thus,
the wood fuel only sits on firebrick. This design minimizes
corrosion of steel and increases burn temperatures, in part owing
to the ability of refractory bricks to absorb and retain heat
energy. A first set of horizontally slotted bricks 130 have a
plurality of slots that form horizontal or transverse channels 132,
as best shown in FIG. 9, and a second set of vertically slotted
bricks 134 have a plurality of slots that cooperate to form
vertical or downwardly-directed channels 136, as best shown in FIG.
10. The second set of vertically slotted bricks 134 also has a
plurality of downwardly inclined slots 138 in fluid communication
with the vertical channels 136, as discussed further below and as
also seen in FIG. 10.
[0034] The secondary combustion chamber 106 is disposed below the
primary firebox 102 and plenum 104. The secondary combustion
chamber 106 is fully brick-lined front to back within the secondary
combustion chamber 106 to enable complete combustion of all
remaining gases, as shown in FIGS. 4-8. The brick lining is fully
insulated to protect the steel compartment 114 and still retain
sufficient heat to maintain high combustion efficiency. Also, it is
has been found that high temperature combustion is desirable. Smoke
is essentially an unburned carbon. At temperatures above
1200.degree. F., this carbon is consumed and no smoke is produced.
Thus, temperatures reaching 2000.degree. F. in the secondary
combustion chamber 106 are sought to enable the unit to burn at
high temperatures and therefore operate very cleanly with no
visible smoke produced.
[0035] Outside fresh air is delivered to the brick combustion
plenum 104, which includes the channels 132 and 136 and slots 138
to form airflow paths 146, 148, 152, and 154, via two separate air
delivery channels 140 and 142, as shown in FIG. 4, from an external
fan assembly 156. Preferably, both channels 140 and 142 are
relatively short enough to allow ready cleaning access. The first
channel 140 forces the air up, where it is vented into an upper
portion 144 of the otherwise sealed primary firebox 102. The second
channel 142 forces air into a first of a pair of side airflow paths
146, 148 created on each side of the firebox 102 between the brick
floor 126 and brick inclined side walls 128 and the insulating
brick liner 150 of the steel compartment 114, as shown in FIG. 5.
Horizontal airflow paths 152 formed by the horizontal channels 132
in the horizontally slotted bricks 130 allow air to flow to the
opposite side of the firebox 102, as shown in FIGS. 6 and 7. Thus,
fresh air is introduced to each of the pair of side airflow paths
146, 148.
[0036] Vertical or downwardly-directed airflow paths 154 in the
vertically slotted bricks 134 provide fluid communication between
the firebox 102 and secondary combustion chamber 106 below the
firebox 102, as shown in FIG. 6. It is to be noted that in the view
of FIG. 6, several vertically slotted bricks 134 have been removed
to provide a clearer view of the vertical channels 136. As air is
forced into the upper portion 144 of the firebox 102, the smoke of
the burning wood is forced into the vertical or downwardly-directed
channels 136 and into the secondary combustion chamber 106 below.
The vertically-oriented channels 136 in the brick preferably form
four vertical or downwardly-directed airflow paths 154, each
preferably 0.625 inches deep by 6.0 inches wide by 4.5 inches high
(the height of standard firebrick). The four constricted channels
136 force highly combustible gases through the airflow paths 154 at
high velocity, similar to a constricted burner tip on a propane
torch. The downwardly inclined slots 138 likewise force fresh air
into the downwardly-directed channels 136, and also act as nozzles
to introduce and direct air at a downward angle, into the secondary
combustion chamber 106, below the pyrolysis zone in the firebox 102
(or the area where combustible gases are created), as shown in FIG.
6.
[0037] The fan assembly 156 preferably comprises a blower 158,
damper 160, and solenoid 162. The blower 158, damper 160, and
solenoid 162 are preferably mounted together to create an easily
removable fan assembly 156, as shown in FIGS. 13 and 14, that may
be preferably removed by detaching a clip (not shown) for ease of
cleaning the inlet 224 and channels 140 and 142, as shown in FIG.
15. Solenoid 162 is attached to the damper 160 that seals shut
against an air opening 161 that provides air to the primary firebox
102 when the blower 158 is deactivated. Preferably, the solenoid
162 is mounted away from the airflow to prevent smoke backflow and
protect the blower 158.
[0038] Preferably, a removable firebox air channel 163 is mounted
to a rear wall 149 of the primary firebox 102 by a pair of brackets
151, 153. The air channel 163 preferably comprises a flat
rectangular steel stamping formed into an open box measuring about
3 inches wide and 2 inches deep having a closed bottom end 165 and
an upper end 167, at which an exit opening 169 and tab 171 is
situated. The lower bracket 151 is located just below the air
opening 161 and is shaped is snuggly accept the closed bottom end
165 of the air channel, as shown in FIG. 11. Similarly, the upper
bracket 153 is situated above the air opening 161 and is shaped is
snuggly accept the tab 171. Air may thus be introduced into the
primary firebox 102 via the fan assembly 165 into the rear of the
primary firebox 102 through the air opening 161 in the lower rear
wall 149, upwards through the air channel 163 and out the exit
opening 169 into upper portion of the primary firebox 102.
[0039] The removable firebox air channel 163 is particularly useful
where unseasoned wood is used or in warmer weather when the unit
tends to cycles off more frequently, where creosote can accumulate
in this channel and restrict airflow. The results of such
accumulations are reduced combustion, more creosote, and in some
cases failure. As noted above, the air channel 163 is preferably
located at the rear and inside the primary firebox 102. To remove
it, the user may reach through the door 118 into the primary
firebox 102 after it has cooled and simply lift the removable
firebox air channel 163 from the brackets 151, 153. With a rear air
channel 161 removed, the user can clean and replace the rear air
channel 161 quite easily, particularly since no brick needs to be
removed in this process.
[0040] It has been found that moving the air through the brick as
described herein, not above or below the brick, creates optimal
conditions for gasification of the smoke entering the secondary
combustion chamber 106. That is, as the combustible gases laden
with smoke pass from the primary firebox 102 to the secondary
combustion chamber 106, fresh air is introduced into the gases as
these gases pass through the brick, which greatly enhances
combustion of the smoke upon entering the secondary combustion
chamber 106 and the amount of heat energy that is harvested from
the wood. Since these passages are constricted, the gases are
forced to pass through the vertical channels 136 at relatively high
velocity for increased combustion and efficiency. Moreover, air is
introduced into the firebox 102 through dual channels, which
provide optimal air supply both up into firebox 102 and into the
in-brick air channels as described herein.
[0041] A sealed steel reservoir 166 is situated around the primary
firebox 102. A cavity or water jacket 168 is formed between the two
compartments 114 and 166 and is filled with water that is
preferably constantly circulated between the furnace and the
building. The heated water delivered to the building is then passed
through a radiator or heat exchanger, such as in the path of a
forced air generator, where the heat is extracted from the water
and distributed through the building to be warmed. Ideally, the
water exiting the heater 100 is at 180.degree. F. and the
temperature returning to the heater from the building is
160.degree. F. The water jacket 168 is open to the atmosphere and
provided with a water level indicator 170, as shown in FIG. 1 and
FIGS. 19 and 20. The water level indicator 170 is fitted to the
water level indicator fitting 172 on the top of the heater 100 and
comprises a support 174, float 176, indicator 178, and indicator
scale 180. An orifice 218 at the bottom of the support 174 and an
orifice 220 at the top of the support 174 receive a metal rod 222.
The float 176 is attached to a lower end of the rod 222 and the
indicator 178 is formed at the upper of the rod 222 and is adjacent
the indicator scale 180 so that the water level may be conveniently
determined. As the water level in the water jacket 168 drops, the
float 176 and indicator 178 will drop as well, as shown in FIG. 20.
If the water level is deemed to be low, a tap (not shown) can be
opened to provide additional water to the water jacket 168 as
necessary, which will in the turn raise the float 176 and indicator
178 relative to the indicator scale 180 to the "FULL" location, as
shown in FIG. 19.
[0042] The fan assembly 156 is situated to provide additional air
flow to the furnace and is provided with a thermocouple that
measures the temperature of the water leaving the water jacket 168.
The fan assembly 156 is activated whenever this temperature drops
below 160.degree. F., thus stoking the ignited wood in the primary
firebox 102 and forcing air into the brick combustion plenum 104 to
further combust the smoke passing from the primary firebox 102
through the vertical channels 136 and into the secondary combustion
chamber 106 to release more thermal energy to the water jacket.
When the temperature returns to 180.degree. F., the fan assembly
156 is deactivated and the fire is allowed to return to a
smoldering level. This cycle repeats to maintain the temperature of
the water delivered to the building. Wood is added at regular
intervals once or twice a day to maintain the delivery of heated
water to the building.
[0043] The exhaust gas is then forced into the primary heat
exchanger 108 situated at the rear and above the secondary
combustion chamber 106 and adjacent the primary firebox 102. The
primary heat exchanger 108 preferably comprises a set of nine tubes
184, each having a diameter of 1.6 inches, disposed in the water
jacket 168, as shown in FIG. 1. The purpose of the primary heat
exchanger 108 is to reduce the temperature of the hot exhaust from
about 2000.degree. F. to around 600.degree. F.
[0044] Further, the presently disclosed hydronic heater is capable
of being fitted with a catalytic combustor 110 for emissions
control. Thus, after passing through primary heat exchanger 108,
the exhaust gas is passed to a catalytic combustor 110. The
catalytic combustor 110 is located in a chamber 188 situated
between the primary heat exchanger 108 and secondary heat exchanger
112, as shown in FIGS. 1 and 16. The catalytic combustor 110
reduces the concentration of invisible particulate matter and
significantly improves the combustion process. However, the
catalytic combustor 110, constructed from materials such as
platinum or palladium, requires a minimum temperature of
400.degree. F. to function properly, but will be destroyed if
operated at temperatures above 1600.degree. F. Generally, exhaust
exiting the primary heat exchanger 108 and entering the catalyst
combustor 110 at 600.degree. F. will exit at 800.degree. F., since
the catalytic process generates heat.
[0045] Since the catalytic combustor 110 is situated downstream of
the primary heat exchanger 108, the temperatures of the relatively
cool exhaust gas allow use of a catalytic combustor, which has not
been known to have been used in a hydronic heater prior to the
presently disclosed hydronic heater. As shown in FIG. 16, the
catalytic combustor chamber 188 includes deflector 190, cover 192,
and sides 194, as well as a holder 196 on the air deflector 190
that holds the catalyst disk 198 at an angle that maximizes air
flow through the catalytic combustor 110. This structure also
protects the surrounding steel by directing the flow of hot exhaust
gases away from non-water-jacketed steel. Since the device is
preferably made of stainless steel, this is advantageous. Also, the
shown structure allows the catalyst disk 198 to be easily removed
for cleaning or replacement.
[0046] The exhaust gas is finally passed through the secondary heat
exchanger 112 that extracts heat from the exhaust such that the
exiting stack temperature of the exhaust gases is around
250.degree. F. to 300.degree. F. This improves efficiency
tremendously. The secondary heat exchanger 112 preferably comprises
a set of eight U-shaped tubes 202, best seen in FIG. 17, also
disposed in the water jacket 168, as shown in FIGS. 1 and 2. Each
of the tubes 202 has an inlet 204 and an outlet 206 from which the
exhaust gas exits the secondary heat exchanger 112 and enters the
stack 208 and is vented to the atmosphere.
[0047] The disclosed hydronic heater enjoys several advantages. It
employs a compact design owing to the unique flow patterns of the
exhaust gas within. An inverted burning process is used, which
passes combustible gases downward through the wood coals. Air is
fed into the firebox 102 through dual airflow paths 146, 148, as
shown in FIG. 6. Upward flowing air is pushed up an upper region
144 of the primary firebox chamber 102 to create rolling combustion
that then must go down. Combustion within the secondary combustion
chamber 106 is also directed from the front to the back of the
secondary combustion chamber 106. Gases then move upward through
the primary heat exchanger tubes 184 creating a bottom to top flow
of combustion gases after the secondary combustion chamber 106. The
result is a reduction in creosol build-up and back-draft into the
fan assembly 156, which improves the durability of the blower 158,
particularly in combination with the fan assembly damper 160 that
is actuated by the solenoid 162 to the closed position when the
blower 158 is deactivated. The unique construction of the disclosed
hydronic heater allows the emissions to reach 0.14 pounds
particulate per 1,000,000 BTU output, which is less than the target
of 0.32 pounds particulate per 1,000,000 BTU output established by
the U.S. Environmental Protection Agency's Phase 2 Hydronic Heater
Voluntary Partnership Program.
[0048] The construction methods for the presently disclosed
hydronic heater 100 includes mainly cast bricks, bolted assemblies,
and bent tube heat exchangers. For example, the heat exchangers 108
and 112 (see FIG. 1) are simply bent tubes to transfer heat from
the gases to the water. The primary subassemblies of the presently
disclosed hydronic heater include a front panel 210, bent tubes
202, vertical tubes 184, refractory brick frame 212, water jacket
168, and base assembly 214, as shown in FIGS. 2A and 2B. This allow
for ease of construction, cost-containment, and manufacturing
repeatability. Bolts are preferably used to attach the lower base
assembly 214 to the upper water jacket assembly 168, as shown in
FIGS. 2A and 2B. Silicone caulk is preferably used as a sealant.
The bolted-together components are those that are not required to
be watertight. Bolted-together components also reduce welding and
fabrication costs and enable "modularity" or the ability to replace
components in the future should a component wear out. Finally, the
presently disclosed hydronic heater 100 employs a pallet base
design, as shown in FIG. 18, has perpendicularly oriented forklift
access receivers 216, which makes lifting the hydronic heater 100
possible with a standard pallet jack or forklift. Preferably, the
presently disclosed hydronic heater 100 may be lifted from at least
three sides to facilitate shipping.
[0049] It is to be understood that variations and modifications can
be made on the aforementioned structure without departing from the
concepts of the present invention, and further it is to be
understood that such concepts are intended to be covered by the
following claims unless these claims by their language expressly
state otherwise. As discussed herein, the embodiments of the
present invention include, but are not limited to, any combination
or sub-combination of elements or steps or portions of steps
described herein and the various claims presented herein.
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