Note: Descriptions are shown in the official language in which they were submitted.
3~ 3
BACKGROUND OF THE INVENTION
The present invention relates to wood fired com-
; bustion heaters.
It is an important object of the invention to
effectively utilize wood as a fuel for heating residencesrfactories, greenhouses, warehouses, and other buildings or
spaces.
It is a further object of the invention to sub-
stantially completely consume all combustibles of a wood
fuel charge consistent with the preceding object.
It is a further object of the invention to provide
economy of operation consistent with one or more of the pre-
ceding objects.
It is a further object of the invention to provide
effective burning rate and temperature controls consistent with
one or more of the preceding objects.
It is a further object of the invention to separate
heat production from heat removal and to have the hottest
possible fire box environment for greater efficiency consiste~
with one or more of the preceding objects.
. It is a further object of the invention to pre-heat
all the intake combustion air utilizing the normal radiant
energy available from the firebox walls consistent with one or
more of the preceding objects.
; 25 It is a further object of the invention to minimize
pollutant generation consistent with one or more of the pre-
ceding objects.
It is a further object of the invention to provide
good usage of space in terms of effective heating ob~ained,
consistent with one or more of the preceding objects of the
invention.
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It is a further object of the invention to provide
a fail-safe and useful mode of operation in the event of
electrical power failure consistent with one or more of the
preceding objects.
It is a further object of the invention to adapt
to conventional or existing hot air duct work systems for
spreading heated air throughout an installation.
It is a further object of the invention to provide
a long time, at least eight hours, between stokings of the
burner, consistent with one or more of the preceding objects.
It is a further object of the invention to substan-
tially reduce hea-t loss up the chimney to below 250 consis-
tent with one or more of the preceding objects.
It is a further object of the invention to reclaim
energy spent to vaporize water from green wood by recondensa-
tion consistent with one or more of the preceding objects.
It is a further object of the invention to dry out
chimney gases to avoid harming chimneys by freezing out
consistent with one or more of the preceding objects.
It is a further object of the invention to provide
apparatus consistent with one or more of the preceding objects
which is economical, transportable and easily installed and
substantially maintainable by unskilled personnel and con-
veniently.
It is a further object to electrically ignite any
unburned smoke content in the exhaust.
It is a further object to provide for drainage of
recondensed water from the burner of green wood.
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SUM~r~Y OF THE INVENTION
According to the above objects, from a broad aspect,
the present invention provides a cornbustion heater comprising
means defining a combustion chamber with a lower space for
holding an elongated solid fuel charge and means for feeding
primary air and combustion gas products therefrom so that the
charge burns from a forward towards a rear end. Means also
defines an elongated combustion gas products conduit running
above and substantially parallel to the fuel charge space and
within the flame produced thereby. Means defines a heat ex-
changer for receiving the exhaust of the conduit and extract-
ing heat therefrom. Means is further provided for injecting
secondary air into the combustion chamber outside of and adja-
cent to the exhaust conduit to enhance flame coverage thereof.
Accord:iny to a further broad aspect of the present
invention, there is provided a combustion heater with an S-
draft gas flow pattern being established merely by an elon-
gated solid fuel burning gradually back along its length and
comprising means for lirniting combustion air to establish
such gradual lengthwise burning.
According to a still further broad aspect of the
present invention, there is provided a combustion heater com-
prising primary combustion chamber means including means for
injecting a limited amount of air therein to burn with a solid
fuel charged therein~ A heat exchanger means is provided.
Conduit means is provided for conducting combustion products
from the primary combustion chamber to the heat exchanger.
Means is also provided for producing after-burning secondary
combustion in the conduit means b-y injecting secondary ~ir
therein to burn with gaseous fuel content of the combustion
products.
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1132~323
~ ccording to a further broad aspect of the present
invention, there is provided an improved furnace capable of
burning moisture-containing wood comprising means defining a
primary combustion chamber for burning such wood and convert-
ing moisture therein to water vapor and generating combustion
product from the wood per se. Means is also provided defining
a separate heat exchanger for heat transfer between the
water-vapor-containing combustion products and a flaming
ambient via separating walls. The heat exchanger is con-
structed and arranged to chill combustion gas therein tobelow 212F and recondense water vapor therein and drain the
water vapor to avoid re-evaporation. Means is also provided
for exhausting combustion products from the heat exchanger.
According to a still further broad aspect of the
present invention, there is provided a method of heating gas
comprising burning moisture-containing wood in one zone to
produce water vapor-containing combustion products of wood
, combustion. The combustion products are conveyed to a separate
heat exchanger through multiple tubes in the heat exchanger.
Gas to be heated is passed over the tubes for indirect heat
exchange with the moisture vapor-containing combustion pro-
ducts. The vapor is condensed and drained. The combustion
products are conducted away from the heat exchanger as an
exhaust and the yas to be heated is conducted away from the
heat exchanger to a point of use.
Further, in accordance with the invention, a primary com-
bustion chamber is provided for insertion of logs, preferably
of standard four foot cordwood length (an economical way to
buy or cut firewood). 'rhe elongated combustion chamber is
preferably fed from the front. ~n exhaust tube is provided
therein in a high portion thereof, above and generally parallel
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to the logs, and has an opening at the rear of the combustionchamber. Air admission is limited so that the logs burn from
front to back, rather than entirely along their lengths at once.
The resultant air and combustion product moves along an S-
shaped flow path (including transit of the exhaust gassesthrough the after-burner tu~e). Within the after-burner tube,
additional air is injected to create a new combustion therein.
Secondary air is injected into high regions of the combustion
chamber parallel to the exhaust/after-burner tube so that there
will be flames bathing the tube. In contrast, without such
secondary air admission, there would be just smoke and hot air
of considerably lower temperature around that tube.
Electric spark or glowplug ignition is provided
within ~he exhaust/after-burner tube to maintain continuous
af~erburning Whenever products of incomplete combustion are
present.
The air for combustion is pre-heated and moved by
passing around the combustion chamber itself (in heat exchange
relation) before admission thereto, p;eferably through an
annulus surrounding the combustion chamber with flow-directing
ribs therein to assure a longitudinal component of flow and
reduce hot spots in the firebox. The hot combustion creates
suction draw of pre-heated combustion air and the forced
drafting as a whole eliminates common chimney problems and
allows for precise thermostatic control of temperature of the
heated air. The pre-heating of air is used for all of the
primary air, the secondary air and the after-burning air
admission described above. Multiple fans are provided for
force drafting, one running at all times to provide limited
- 30 capacity air intake to barely sustain combustion ("idling"
- glow) and one or more other fans cut in to provide addition~l
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AJc/KAcL P01 air to supplement the limited capacity first fan in response to alO/8/77 thermostat's signal call for higher room temperature or more
air. The fans are electrically operated, but in the event of
a power failure, the furnace itself maintains sufficient heat from its
high mass and natural suction draw to operate for a while.
The exhaust/after-burner tube exits immediately into
an indirect heat exchanger comprising an inlet plenum, an
outlet plenum and, therebetween, a multiplicity of tubes with
a high surface area to a volume ratio of exhaust gas passage.
Domestic air to be heated passes over such tubes and then into
the regions of the room to be hea~ed. In addition to ductwork
conveying the heated air to various locations desired to be
heated, the structure of the combustion chamber itself and of
the heat exchanger comprise a source of significant heat for
the surrounding room area. Such structures are made massive
to constitute a built-in heat reservoir (or virtual flywheel
effect) to evenly dissipate heat over a wide time span pro-
viding a more constant room temperature at any given control
setting of air admissions. The primary control is through
electrically varying one or more of the above described forced
draft fans. This is adjusted by the remote control thermostat.
Also, an automatic shut-down of combustion at the end of the
fuel supply is provided through monitoring exhaust temperature
through a thermostat on the wall of the final exhaust tube to
shut off air supplies and to shut down electrical ignition upon
consumption of fuel an alarm or indicator to show that more
stoking ~wood reloading) is necessary can also be activated by
the thermostat.
The primary chamber combustion produces a total com-
bustion of solids and results in a light gray to white powderash, indicative of an extremely lean and thorough burn. Minor
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unburned solids remain at times. Moisture and volatile gasses
contained within the wood fuel are continuously driven off.
Air admitted for the primary combustion and secondary combustion
described above is pre-heated beyond the wood ignition tempera-
ture per se and ignites many of the volatile gasses for more
complete heat production and to avoid chimney and pollution
problems. Hot oxygen-rich air is provided to lean flame tips
to produce a blue lazy tipped flame resulting in measurable
increase in heat output and observed improvement in color and
reduction of exhaust emissions at the chimney. The exhaust is
clear and cool.
Because of high combustion efficiency and heat trans-
fer efficiency and large wood charge, typical models made in
accordance with the invention can burn for 12-36 hours without
stoking, variable by control of inlet air. Efficiency is
further enhanced by extracting almost all the imparted heat
from exhaust gas. It is chilled to well below 212F. Moisture
from the wood is converted to water vapor (steam) in the
primary combustion chamber and after-burner and is recondensed
2Q in the heat exchanger and rapidly drained to avoid re-evapora-
tion. The final exhaust is dry and doesn't condense out on
the chimney to any substantial degree. The condensation
represents a return of heat to the system to make up to the
system, at least in part, the energy originally used to vapor-
ize the moisture content of wood.
The primary combustion chamber, including a pre-
heating annulus -therein for inlet air, and the heat exchanger
constitute an easily transportable, p~e-assembled, easily
installed structure.
In accordance with a particular em~odiment of the
invention a combustion heater comprises: first means defining
1~3~Z~3
a combustion chamber with inner and outer walls and an annulus
therebetween and with a lower spa_e within the inner wall
having a forward end and rear end for holding an elongated
solid fuel charge and means for feeding primary air thereto and
combustion gas products therefrom both at said forward end so
that the charge burns from said forward towards said rear end
of said chamber, second means defining an elongated com~ustion
gas products conduit running above and substantially parallel
to the fuel charge spa_e and within -the flame produced thereby
. 10 and having an entrance for combustion gas products of said
first means, said first and second means being arranged to
define an S-draft gas flow pa-th, means defining a principal
heat exchanger for receiving the exhaust of said conduit and
extracting heat therefrom, and means for injecting secondary
air into the combustion chamber outside of and adjacent to the
exhaust conduit at multiple points along the length thereof
to enhance flame coverage thereof, means for producing after-
burning in said conduit by injecting secondary air therein at
a point downstream of the conduit entrance, and means for pre-
heating the primary air and secondary air and after-burner air
in counter-current heat exchange in said combustion chamber
annulus by injection to said annulus at the combustion chamber
rear end and movement to said forward end.
Other objects, features and advantages of the
invention will be apparent from the following detailed
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~AB KAL P01 description of preferred embodiments thereof, taken in
10/8/77 connection with the accompanying drawing, in which,
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a longitudinal section of a preferred
embodiment of the invention and
FIG. 2 is a lateral cross section thereof, taken
as indicated at 2-2 in FIG. 1.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to FIGS. 1 and 2, there is shown the
above described primary combustion chamber 10 and the above
' described heat exchanger 20 and air and exhaust gas ductwork
30. ~ 31 + 32 + 23.
The primary combustion chamber 10 comprises an
inner chamber 12, an outer wall 14, with an annulus 16 there-
between containing longitudinally extending fins 15 fordirecting air (which enters at inlet 11) essentially longi-
tudinally along the outer wall of inner chamber 12. Inner
chamber 12 has a lower region 121 containing logs L and an
upper region 122~ Within the inner chamber upper portion 122,
there is an after-burner/exhaust tube 18. Primary air for
combustion comes to the primary combustion chamber via annulus
16 and two or more spaced pipes 161 (elbows). Secondary air
- for the upper portion 122, comes from annulus 16 via two or
more spaced pipes 162 (elbows). Similarly, the elbow pipe 163
provides the after-burnerair from space 16to tube 18. The
second~ry air pipes 162have holes along their lengths as they run
parallel to the e~haust/after-burner tube. Air fed into these
pipes induces the complete combustion which causes flames to
reach out and touch the pipe 18 as indicated at FL in FIG. 2.
In the absence of the secondary air, the flames would be lower
and less consistent inreaching pipe 18 to maintain it very hot.
Z3
JC/rc Inlet air comes through pipes llA and llB, each of which have
10/8/77 a fan F therein, one of which continually operates and the
other which is selectively controlled. Both are electrically
driven. The idle air provided by the continuous fan provides
` 5 just enough combustion air to maintain a rekindleable fire
(glow) and the second fan provides to the fire more than
twice as much air as the idle situation to speed up combustion,
producing greater flames and heat. A circulator fan (not
shown~ is provided in the heat exchanger system and can be set
10 to run at one speed, at different selected C.F.~I.
The heat exchanger 20 comprises an inlet plenum 21,
an exhaust plenum 22 for waste gasses and an exit 23 to the
smokestack and air inlet and outlet passages 31 and 32,
respectiveIy. An electric spark igniter for the after-burner
15 is indicated at I and has an electrical power supply PS
externally (which may be alternating or a connection to house
power via a transformer). Preferably it operates con-
tinuously, but it may be provided with a switch for selective
use of the exhaust after-burning.
Typical dimensions and construction parameters for
a unit which has been operated effectively are -- one-half
inch thick steel, 100% welded primary chamber and a 3/8 inch
thick steel 100% welded heat exchanger. The primary and
secondary chambers are about 4.5 ft. long each and each is
less than 3 ft. in diameter. They have a total weight of the
two of about one and one-half tons.
A front plate Pl of the primary chamber contains
a loading door Dl of about 17 X 12 inches, within a cleanout
- door of circular form and about 23 inches diameter, both being
hinged. Typically, the circulator/blower will handle 2,000 cu.
ft. per minute up to 100 ft. of 12" ductwork or equivalent.
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AB KAL POl The furnace described above can be integrated with
JC/rc
10/8/77 other heating systems or used for purposes other than domestic
heating, and in turn, can borrow from existing components for
implementation at any given installation.
It is evident that those skilled in the art, once
given the benefit of the foregoing disclosure, may now make
numerous other uses and modifications of, and departures from
the specific embodiments described herein without departing
from the inventive concepts. Consequently, the invention is
to be construed as embracing each and every novel feature and
novel combination of features present in, or possessed by, the
apparatus and techniques herein disclosed and limited solely
by the ecope and spirit of the appended claims.
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