Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 This invention relates to a bio-mass burner
construction provided with a unique grate structure
which permits substantially smokeless operation and,
more particularly, to such a burner and method of opera-
5 tion which will solve many of the current energy problems
brought about especially by the rapid rise in th~ price
of fuel oil.
BACKGROUND OF THE INVENTION
Heretofore it has been quite common to use fuel
oil as a source of energy because of its relative abun-
dance and relatively inexpensive price. The almost
meteoric price rises within the p3st decade have put an
end to this condition and necessitated a search for alter-
nate sources of fuel. The present invention, while not
meeting all the world's energy needs, does satisfy a
substantial number of them~ particularly in industrial
and residential heating requirements. The invention,
however, is not limited to the afor~mentioned specific
uses since it may be widely used wherever an inexp~nsive
fuel product is required.
SUMMARY OF THE INVENTION
. . . _ .
In particular, the present invention utilizes
a bio-mass fuel product which may be varied substantially
in size, moisture content and heat content. Sawdust, for
examplej makes an excellent fuel and has been burned
1 ~uite successfully in the burner of the present invention.
Many other fuel products such as wood chips, wood pellets
and pulveri2ed coal may be used. A11 sorts of agricul-
tural products, normally deemed to be waste products,
S may be used. For example, shredded corn stalks~ shredded
straw, shredd a soy bean stems, shredded tobacco stems
and hulls, and peanut hul's may be used just to mention
a few. The reason for shredding these agricultural
, products is to make them easier to feed continuously on
demand to the burner of the present invention. Thus,
the term "bio-mass" is used to describe these readily
availa~le biologically oriented and derived fuel products.
The invention is deemed to be applicable to all known
solid fuels necessitating only accommodating changes in
lS feeding the product to the burning chamber and supporting
it therein for combustion.
The presen-t invention contemplates that the
bio-mass fuel product will be fed substantially continu-
ously on demand to the burner. As far as determining
the demand, the controls necessary to start and stop
the feeding~ to start and stop the sources of primary
and secondary air and to start and stop any auxiliary
heating means are all deemed to be conventional, within
the known state of the art, and do not form a part of
the present invention. Also the term "air" is used
1 herein merely to indicate a source of oxygen which will
support combustion and is to be construed in its broadest
context so as not to exclude ~he metering of gases,
including oxygen, which will support combustion.
In the preferred form of the burner construction
of the present invention, a bio-mass fuel produc-t as pre-
viously defined is fed continuously on demand to the top
of a first combustion chamber where it is directed by
baffle means toward a novel grate structure. The grate
itself has crisscrossed tubular members extending between
opposing manifolds so as to support the ~uel product~
If the fuel itself is sufficiently crushed or pulverized
so as to sift between the tubular members of the grate
structure, an auxiliary or supplemental grate in the form
of expanded metal, for example, may be used to insure
containment of the fuel for combustion. Means are em-
ployed for supplying primary air under pressure to the
underside of the grate means so as to support combustion
within the ~irst combustion chamber.
A uni~ue application of a venturi tube i5
employed to receive secondary air which is supplied
to the hollow grate structure and to direct the secondary
air into a secondary burning chamber. This secondary
air is superheated by the time it reaches the second
combustion chamber after passing through the hollow
-
nonporous tortuous path of the grate means. Auxiliary
means may be employed to preheat the grate bringing it
up to temperature so that ignition occurs in the first
and second combustion chambers without producing any
substantial quantity of smoke at the outlet stack. The
venturi tube means cooperates with the baffle structure
to create a decrease in pressure beneath the baffle
arrangement whereby any as yet unburned products of
combustion are directed into the secondary burning
chamber. The fuel product is fed by any suitable means
substantially continuously on demand into the top of
the first burning chamber and -the rate of combustion
equals the rate of feed of the fuel product.
The novel steps of the method of the present
invention will be evident upon considering the following
principal steps thereof:
1. feeding a bio-mass fuel substantially con-
tinuously on demand into a first combustion chamber;
2. feeding that fuel product by gravity onto
a grate structure positioned within the first combustion
chamber, the grate structure being hollow and having
nonporous~ walls;
3. providing a primary source of air to the
underside of the grate structure;
1 4. establishing a Elow of unburned products
of combustion from the first combustion chamber to a
second combustion chamber;
5. and providing a secondary source of air
in the second combustion chamber with the secondary air
being heated sufficiently to cause re-ignition of any
unburned products of combustion in the second combustion
chamber~
Additional steps of the method invention include
the superheating of the secondary source of air in the
first combustion chamber, positioning baffl~ means for
redirecting the fuel product toward the grate structure
and for impeding the flow of smoke fxom the first com~
bustion chamber, passing the secondary air through the
lS hollow, nonporous grate structure, and using a venturi
tube which is in fluid communication with the outlet of
the hollow grate structure in order to establish the -flow
of unburned products of combustion from the first combus-
tion chamber to the second combustion chamber.
The inherent advantages and improvements of
the present invention will become more readily apparent
upon considering the following detailed description of
the invention and by reference to the drawings wherein:
Fig. 1 is an elevational view taken in vertical
cross section illustrating the burner construction and
grate means therefor of the present invention;
.
1 Fig. 2 is a pla,n view taken in horizontal
cross section along line 2-2 of Fig. l;
Figa 3 is an elevational view taken in vertical
cross section showing a modified form of the burner con-
struction and grate means therefor;
Fig. 4 is a plan view taken in horizontalcross section along line 4-4 of Fig. 3;
Fig. S is a perspective view illustrating
, the grate means of Fig. 3;
Fig~ 6 is an elevational view, schematic in
nature~ illustrating the means for feeding the fuel
product to the burner construction of the present
invention; and
Fig. 7 is a fragmentary elevational view,
schematic in nature, illustrating a rnodified form of
the present invention.
Referring now to Figs. 1 and 2 of the drawings,
a burner is indicated generally at 10 which provides a
first combustion chamber 12 for a bio-mass fuel productO
Hollow grate means are suitably supported within the
first combustion chamber 12 and designated generally
by the numeral 14. The burner 10 is illustrated to have
an open top 16 through which the fuel product may be
supplied by gravity feed. The chamber 12 has opposed
side walls 18 and a bottom 20.
1 Adjacent the top of the combustion chamber 12
are downwardly and inwardly projecting baffle means 22, 2~.
These baffle means direct a fuel product which is supplied
to the burner by any suitable means, preferably continu-
ously on demand, toward the grate structure 14.
As seen both in Figs. 1 and 2, the grate
structure 14 comprises a first manifold Z6 which is
supplied with air under pressure from a fan 28 located
exteriorly of the burner 10. A first set of tubes 30
extend upwardly and transversely to a second manifold 32
which is adjacent an opposed side wall 18~ A second set
of tubes 34 extend transversely in the reverse direction
and upwardly in fluid communication with a third manifold
36 which is preferably located above the first manifold
26. A venturi tube 3~ in fluid communication with the
third manifold extends upwardly and has an end portion
thereof 40 which extends into an outlet tube 50.
When the fuel product is sufficiently pulver-
i~ed or comminuted so as to sift between the spaces of
adjace~t tubes 30, 34 of the grate structure 14, it is
desirable to use a supplemental grate 42 to contain the
fuel for combustion. One such supplemental grate 42
was made from expanded metal. ~ source of primary air
is supplied under pressure by means of a fan 44 with
the ~uantity of air being varied by the setting of
suitable valve means 4~.
1 The outlet tube 50 which defines at least the
beginning of a secondary combustion chamber or zone is
attached to the wall 18 so as to align an aperture in
the wall 18 with the diameter of the outlet tube ~0.
An inner flange 52 facilitates bolting of the outlet
tube to the burner 10. The outlet tube 50 i5 Eurther
provided with an outer flange 54 which is conveniently
bolted onto another burning chamber such as i5 shown
at ~8 in Fig. 7. In the first wor~ing model of the
present invention, the entire exterior of the burner 10
and outlet tube 50 were covered with an insulation
material 56 such as Kaowool. Any suitable insulation
material can be used to be certain that the burner
retains its heat and this insures that the fuel product
will burn. Also in the first working model a single fan
with two outlets was used in place of fans 28, ~4.
Referring now to Figs. 3 and 4, a more com-
mercial form of the invention is illustrated for the
~urner 10. In particular, the grate construction 19
in these figures is preferably made from rectangularly-
shaped manifolds such as are shown at 25a, 32a, and 36a.
The sets of tubes 30, 34 remain circular in cross
section and provide the desired tortuous path from the
source of secondary air provided by fan 28 leading from
the first manifold 26a through the second manifold 32a
via the set of tubes 30 and then hack to the third
manifold 36a by means of the set of tubes 34. This
arrangement is most clearly illustrated in Fig. 5.
Because many of the fuel products have an
ignition temperature in excess of 400F., it is necessary
to briny the temperature level within the grate to that
temperature as rapidly as possible, especially if it is
desired to avoid smoking of the burner. For this pur-
pose, a pre-heater or auxiliary burner 60 is employed
with suitable controls 62 to recycle the auxiliary burner
and start it and stop it as desired. The use of con-
trols 62 may include cadmium cells or the like which
sense whether or not there is a flame in the grate
structure 14 and if so the auxiliar~ or pre-heater
burner is turned off. For example, if an oil burner
is used, it may have as small a tank as five gallons
to work satisfactorily for this purpose. Other fuels
can be used in place of an oil burner and they include
methane, propane, ethane, natural gas and others. Eow-
eVer, propane may tend to accumulate in the bottom o~the burner 10 and is not preferred.
In the commercial model illustrated in
Figs. 3 - 5 inside insulation also in the form of
Kaowool is shown at 64 and a metal covering is shown
at 66. The exterior of the unit is also insulated again
1 with Kaowool at 56 and a sheet metal trim ~8 is used
for a more pleasing appearance. To provide longer
wearing characteristics, a ceramic lining 51 or stain-
less steel or other non~reactive lining may be used to
line outlet tube 50.
In both embodiments previously illustrated
and described, a fuel product is preferably fed con-
tinuously on demand from a source of fuel such as ~rom
a hopper or bin 70 illustrated in Fig. 6 onto a suitable
feeding means with fuel product being shown at 72~ A
conveyor 74 is illustrated with a suitable drive means 76
for the sprockets of the conveyor. Such a device was
actually used in the original model; however, a screw
feed device or any other suitable feed means may be
employed. In additionl it may be desirable to agitate
the fuel 72 within the hopper or bin 70 so as to prevent
coalescing or bridging of fuel within the hopper or bin 70.
Thus, in operation, fuel 72 is fed substantially
continuously on demand from a bin 70 by means of feed
means 74 until the fuel falls by gravity into the top
of burner 10 directed by baffle means 22, 24 onto the
grate structure 14. The crisscross arrangement of the
sets of tubular members 30, 34 together with any auxiliary
grate as needed contains the fuel product in a first
combustion zone within the burner 10. Primary air is
l supplied under pressure by means of fan 44 to the
underside of grate 14 and secondary air is supplied by
means of fan 28 to the first manifold 26 then trans-
versely through the first set of tubes 30 to a second
manifold 32, then through the second set of tubes 34
to a third manifold 36, and then finally through the
venturi tube 38 which has its outlet 40 directed toward
the second combustion zone which begins in the outlet
tube 50 and may continue in an expanded chamber such
as the chamber provided by an oil burner such as is
shown at 78 in FIg. 7. That is to say, the present
inv~ntion may also be used to retrofit existing oil
burner constructions by simply taking out the fuel nozzle
arrangement in the burner construction and attaching the
outlet tube 50 thereto with the aid of flange 54. Igni-
tion temperatures for bio-mass fuel products having a
lower ignition range of 450F. to 5t)0F. up to about
800F., principally depending upon the amount of moisture
content, must be reached to permit full combustion of
the bio-mass fuel product. When this occurs, there is a
roar-like sound emitted from the burner construction.
In Fig. 7 an oil burner is illustrated at 78
without the burner nozzle employed and the unit of
Figs. 3 - 5 bolted thereto. The oil burner is shown
with a suitable stack means 80. In the embodiment shown
12
1 in Fig. 7, the fan 28 supplies secondary air to a coil 82
which is spirally wound around the inside of the outlet
tube 50, and connected to the venturi tube 38 whose out-
let 40 is directed toward the second combustion zone.
Thus, the heat of combustion of the products passing
through the outlet tube 50 is used to superheat the air
within coil 82~ A conventional grate 14a is employed
with the fan 44 providing primary air to the conventionaL
grate 14a. While it is possible to wind coil 82 exte-
riorly of outlet tube 50 and to have it connected influid communication with venturi tube 38, this modifi~
cation is less efficient than that shown. A suitable
access to ashes may be provided such as a door 84.
A number of other modifications can be made
from the structure illustrated in the drawings. Thus,
it is possible to use a plurality of venturi tubes 38
to supply secondary air depending upon the desired oùt-
put in BTU per pound. Also heating jets may be used in
the outlet tube 50 in place of the hollow grate construc-
tion and venturi tube arrangement. Also the venturitube can be a nozzle so as to increase the velocity of
the secondary air.
It is desirable to provide an excess of air
both for the primary combustion and the secondary com-
bustion. Thus, the undergrate air may be 125~ in excess
of that re~uired and the secondary air may be in theorder of magnitude 200% of excess air. This insures
smokeless operation of the burner following ignitlon.
In the original construction of this burner, a single
fan supplied both the primary and secondary air. It
was found~ however, that a substantial pressure had to
be employed so that the secondary air was sufficient to
travel through the tortuous path provided by the hollow
grate and still provide sufficient air at the outlet 40
of the venturi tube 38 to provide complete combustion of
the unburned products. Similarly, a four inch diameter
tube was ini~ially used for outlet tube 5~ and this did
not work. A six inch diameter tube did work and larger
diameter tubes may have to be employed depending upon
lS the feed rate and the amount of air re~uixed to complete
combustion in the secondary combustion zone. Also, as
has already been mentioned, a plurality of venturi tu~es
ma~ be employed to increase the secondary air directed
into the secondary hea-ting zone.
With a feed rate of about 60 pounds per hour
approximately 420,000 sTu per hour is produced by the
burner construction of the present invention using wood
as the bio-mass fuel product. The quantity of air
required is directly proportional to the rate of feed.
Also, the taller stack employed on the burner in which
14
1 the secondary combustion occurs, -the more suction is
provided and therefore less undergrate air is required.
The burner unit itself may be quite compact.
In the original model the unit was 3~ inches tall and
length and width dimensions of 12 inches each. Larger
sizes may be employed for achieving greater BTU outputs.
It is preferred from a practical standpoint to
use low ash fuels in the practice of this invention so
khat the fuel will not clog the grate structure. There-
fore, the apparatus can run continuously for extended
periods of time. Temperatures within the combustion
chambers in excess of 1800~F. have been measured. Because
the rate of the substantially continuous feed must equal
the rate of combustion, batch loading procedures such
~5 as are common in existing pot belly or wood burning
stoves cannot be used. Ignition would nvt occur if an
attempt was made to start the burner with a large amount
of fuel on the grate means. Similarly, if the fuel is
not fed on a substantially continuous basis at a rate
of feed equal to the rate of combustion, the fire will
go out.
While presently preferred embodiments of the
invention have been illustrated and described, it will
be recognized that the invention may be otherwise variously
embodied and practiced within the scope of the claims
which ~ollow.
