Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02738432 2012-12-10
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TITLE OF THE INVENTION
BIOMASS BURNER FOR A MAPLE SYRUP EVAPORATOR
FIELD OF THE INVENTION
[001] The present invention relates to a biomass burner. In particular, the
present invention relates to a biomass burner comprising a fuel and air supply
system to provide a high efficiency burner for a maple syrup evaporator.
BACKGROUND OF THE INVENTION
[002] Maple syrup evaporators used for evaporating water contained in maple
sap generally employ wood or oil burning heat sources for causing evaporation.
One drawback of such burners is the high cost of the wood or oil fuel, their
energy conversion inefficiencies, and environment impacts associated with the
pollutants emitted during combustion of the fuel such as particulate matter,
Nitrogen Oxide (N0x) and Sulphur Dioxide (SOO.
[003] What is therefore needed, and one aspect of the present invention, is a
burner for maple sap evaporators that uses biomass combustibles which are less
costly, burn more efficiently and which generate the heat necessary to
properly
evaporate maple sap. Additionally, what is needed is a biomass burner that
provides all the benefits of an oil burner, for instance autonomous operation,
ease
of use, automatic and constant supply of fuel, and easy ignition, which
minimizes
the carbon dioxide emissions and other pollutants to reduce environmental
impacts on the surrounding environment.
SUMMARY OF THE INVENTION
[004] According to the present invention, there is provided a biomass burner
for
a maple sap evaporator comprising: a burner assembly comprising a base and a
top for forming a combustion chamber therein, said top defining an entrance
and
an exit; a burn pit disposed within said base and defining a plurality of
holes for
allowing air to communicate between said combustion chamber and a primary air
plenum formed between said base and an underside of said burn pit; an air
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,
plenum formed between said base and an underside of said burn pit; an air
supply conduit for supplying a primary air supply to said primary air plenum;
a fuel
conduit in communication with said combustion chamber for supplying a pellet
fuel for combustion within said burn pit; a secondary plenum in pneumatic
communication with said primary air plenum for receiving and cooling a portion
of
said primary air supply; a plurality of injectors in communication with said
secondary plenum for injecting said cooled air into said combustion chamber;
wherein when said pellet fuel undergoes combustion with said primary air
supply,
a generated heat is directed towards said exit by said injected cooled air.
BRIEF DESCRIPTION OF THE DRAWINGS
[005] FIG.1 is a perspective view of a maple sap evaporator, according to a
preferred embodiment of the present invention;
[006] FIG. 2 is a cross-sectional side view of the maple sap evaporator of
FIG.
1;
[007] FIG. 3 is a rear perspective view of a burner assembly in accordance
with
an illustrative embodiment of the present invention;
[008] FIG. 4 is a front perspective view of a burn pit insert of the burner
assembly of FIG. 3 in accordance with an illustrative embodiment of the
present
invention;
[009] FIG. 5 is a cross-sectional side view of the burner assembly of FIG. 3;
[010] FIG. 6 is a front perspective view of the burner assembly of FIG. 3; and
[011] FIG. 7 is a cross-sectional view along line 7 of burner assembly of FIG.
3.
DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS
[012] The present invention is illustrated in further details by the following
non-
limiting examples.
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[013] Now referring to FIG. 1, there is provided an evaporator for the
evaporation of maple sap in the production of maple syrup generally referred
to
using the reference numeral 10. The evaporator comprises a maple sap
evaporating section 12 and a maple syrup forming section 14 both
illustratively
comprising horizontally extending pans 16, which are shown in FIG. 2, provided
with partitions in which maple sap travels. The evaporator 10 further
comprises a
hood as in 18 for each section 12, 14 and vapour outlets as in 20 for
directing the
water vapour evaporated from the sap to atmosphere.
[014] Now referring to FIG. 2, in addition to FIG. 1, extending beneath the
maple
sap evaporating section 12 and the maple syrup forming section 14 is a heating
housing 22 comprising a heating chamber 24 for exposing heated air 26 and
flames 28 to the undersides of the horizontally extending pans 16. The heating
housing 22 is illustratively formed from an enclosed space beneath the
horizontally extending pans 16 enclosed by sheets of stainless steel or the
like.
As the undersides of the horizontally extending pans 16 are heated, heat is
transferred to maple sap 30 travelling along its upper surface of the
horizontally
extending pan 16 to cause its evaporation. In accordance with an illustrative
embodiment of the present invention, the heated air 26 and flames 28 are
generated by a biomass burner 32 illustratively connected to the front of the
evaporator 10.
[015] Still referring to FIG. 2, the biomass burner 32 comprises a housing 34
enclosing a burner assembly 36. A front 38 of the housing 34 comprises an
access opening 39 capable of being enclosed by a door 40, and a rear 42
connected to the heating housing 22. Illustratively, the housing 34 and the
door
40 are formed from a double layered walled 44 structure formed from stainless
steel or the like and lined with or enclosing an insulating material, such as
high
temperature insulation wool like ceramic fibre, amorphous Alkaline Earth
Silicate
(AES) wool, Aluminum Silicate Wool (ASW), or the like, and which is capable of
resisting high temperatures generated within the burner assembly 36. The
access
opening 39 in the housing 34 is covered by the hinged door 40 to provide a
user
access to the burner assembly 36 for cleaning, repair, ignition, and
maintenance
when opened, and for confining the heat and flames 28 to within the burner
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assembly 36 when closed. The rear 42 of the housing 34 is in open connection
with the heating chamber 24 such that heat and flames 28 generated within the
burner assembly 36 are directed to within heating chamber 24, in a manner as
will be described hereinbelow, for the heating of the horizontally extending
pans
16.
[016] Still referring to FIG. 2, the burner assembly 36 generates heat from
the
combustion of combustible materials burned therein, such as wood pellets,
vegetable matter, agri-pellets or other forms of pellet fuel 46 which may be
employed for heating the air 26 in the heating chamber 24 such that an
underside
48 of the horizontally extending pans 16 is heated. Illustratively, the pellet
fuel 46
is typically a wood fuel generally comprised of saw dust as is known in the
art
which permits high combustion efficiency. The high density and compact size of
the wood pellets allows for space efficient storage and further allows for
precise
control of the amount of fuel able to be supplied to the burner assembly 36
for
combustion therein. A plurality of steps 50 are provided as part of the
heating
chamber 24 to direct the heated air 26 upwardly and to generate turbulence so
that the underside 48 of the horizontally extending pans 16 is evenly heated.
In
addition to heat, the burner assembly 36 comprises combustion by-products such
as carbon monoxide and the like which are directed and expelled from the
heating chamber 24 to atmosphere via a chimney 52.
[017] Now referring to FIG. 3, in addition to FIG. 2, the burner assembly 36
illustratively comprises a structure formed from a base 54 and a semi-
cylindrical
dome 56 connected to the top of the base 54 by welding, rivets, screws or the
like. The semi-cylindrical dome 56 comprises an open front end 60 for
communication with the access front opening 39 and which is enclosed by the
door 40. The semi-cylindrical dome 56 further comprises an open rear 58 in
open
communication with the heating chamber 24 for providing a direct exhaust
channel from the burner assembly 36 into the heating chamber 24. The base 54
is illustratively comprised of a solid box housing 62 for receiving a burner
insert
64 at its open top. The space defined above the burner insert 64 and below the
dome 56 is the combustion chamber 66 where pellet fuel 46 undergoes
combustion in a manner as described hereinbelow. The box housing 62 and the
dome 56 are illustratively formed from bent stainless steel sheets or the like
and
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may be heat insulated with a ceramic wool (not shown) tacked to their outer
surfaces to help reduce radiated heat loss to the exterior of the biomass
burner
32. For instance, the ceramic wool may be affixed to the inner surface of the
base
54 and the dome 56 by tack welding at intermediate points along the inner
surface or may be contained within a doubled walled layer structure of the
base
54 and dome 56 if provided. The provision of insulation ensures a thermal
resistance against the deformation of the dome 56 and the base 54 caused by
the intense heat generated during a high burn intensity operation of the
biomass
burner 32. Of note, such construction of the burner assembly 36 also prevents
expansion of the burner assembly 36 when subjected to intense heat and
remains free of deformation once cooled during inoperation.
[018] Now referring to FIG. 4, in addition to FIG. 2 and FIG. 3, the burner
insert
64 comprises a perforated box like structure formed from bent plate sheet
metal
to form a burn pit 68 for containing the pellet fuel 46 during combustion
thereof.
Illustratively, the burner insert 64 is fabricated from a heat resistant
material such
as nickel, stainless steel, cast metal or the like capable of resisting
deformation
between operation and inoperation of the biomass burner 32. The burn pit 68 is
configured and sized sufficiently large enough to hold the pellet fuel 46
required
for a maximum heat output given the size of the evaporator 10. Of note, the
sizing
of the burn pit 68 and the biomass burner 32 may be varied depending on the
application.
[019] Now referring to FIG. 5, in addition to FIG. 3 and FIG. 4, a plurality
of
holes 70 formed in the walls 72 and floor 74 of the bent plate forming the
burn pit
68 provide air communication between a primary air plenum 76 formed between
the walls 72 and floor 74 of the burn pit 68 and the inner sides of the box
housing
62. The holes 70 ensure that a primary air supply 78 from within the primary
plenum 76 are preferably evenly distributed across the pellet fuel 46
deposited
within the burn pit 68 in a uniform manner so as to create an equal rate of
combustion of the pellet fuel 46. With this configuration, the air holes 70
are
provided in a patterned configuration to ensure sufficient amounts of oxygen
are
supplied to the combustion chamber 66 such that an efficient burn of the
pellet
fuel 46 results.
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[020] Still referring to FIG. 4 and FIG. 5, pellet fuel 46 is supplied to the
burn pit
68 via a fuel supply inlet 80 provided for in the side wall 72 of the burner
insert
64. As pellet fuel 46 is received therein, a hollow divider 82 projecting
upwardly
from the floor 74 of the burner insert 64 and also comprising a plurality of
holes
as in 70 acts to distribute the pellet fuel 46 received from the fuel supply
inlet 80
into two separate sub-burn pits 84 formed by the hollow divider 82 and
adjacent
walls 72. This W cross-sectional shape of the burn pit 68 advantageously
improves the distribution and surface exposure of the pellet fuel 46 for a
maximum exposure to oxygen from the primary air supply 78 required to generate
a maximum energy output and rapid combustion. The hollow divider 82 is
illustratively formed by a bend in the burner insert 64 plate which also
increases
the rigidity of the structure to resist deformation under exposure to the
intense
heat produced during combustion. Those skilled in the art will understand that
other configurations besides W cross-sectional shape of the burn pit 68 could
be
provided For example, further projections having different shapes and
configurations may be provided to increase the distribution and surface
exposure
of the pellet fuel 46. On the other hand, the number and shape of these
projections would reduce the amount of pellet fuel 46 that is available in the
burn
pit 68, therefore these need to be designed according to design requirements.
[021] Still referring to FIG. 4 and FIG. 5, the double combustion burn pit
configuration maximises the combustion and the quality of the combustion of
the
fuel pellets 46 by maximizing the combustion area of the pellets supplied with
oxygen. Of note, the combustion efficiency of the burner assembly 36 can be
controlled by regulating the amount of primary air supply 78 entering the
primary
plenum 76 which in turn passes through the air supply holes 70. Additionally,
while one hollow divider 82 has been illustratively shown, additional dividers
may
also be provided for improving combustion. The hollow divider 82 also promotes
combustion by ensuring that all points within each sub-burn pit 84 are
supplied
with oxygen with the primary air supply 78.
[022] Still referring to FIG. 5, in addition to FIG. 2 and FIG. 3, there is
further
provided a conical cone 86 connected to the open rear 58 for directing heated
air
26 and flame 28 from the combustion chamber 66 into the heating chamber 24.
Advantageously, the conical cone 86 also acts to increase the air pressure
within
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the combustion chamber 66 which aids in directing or funnelling of the
combustion flames 28 to within the heating chamber 24. Illustratively, the
cone 86
directs the flames 28 are funnelled at a generally horizontal direction from
the
combustion chamber 66 and directed into the heating chamber 24 for contact
with
the underside 48 of the horizontally extending pans 16 and for heating the air
26
contained therein. The increase in pressure also acts to increase the rate at
which exhaust and flames 28 are expelled from the burner assembly 36 and into
the heating chamber 24. The inner surface 88 of the conical cone 86 is
illustratively fabricated from heat resistant reflective material which
minimizes the
heat retention within the combustion chamber 66 and promotes the transfer of
energy to within the heating chamber 24. Additionally, the cone 86 may be of
variable dimension so as to modulate the size of its opening as depending on
the
type and the length of the required flame 28.
[023] Referring back to FIG. 2, in addition to FIG. 1, FIG. 3 and FIG. 5, the
base
54 of the burner assembly 36 further comprises a plurality of inlets for
receiving
air and fuel. Illustratively, the air and fuel are illustratively provided to
the burner
assembly 36 by two air conduits 90 and a fuel conduit 92, respectively, which
originate from an area beneath the heating chamber 24 enclosed within the
heating housing 22. Illustratively, air is supplied to the primary plenum 76
via air
conduits 90 through inlets 94 in the side of the base 54. Air may be
illustratively
drawn from the atmosphere exterior to the evaporator 10 by one or more
electrically powered air blowers 96 such as a fan or the like connected to an
air
intake 98 on the side of evaporator 10. Air supply to the primary plenum 76
can
be illustratively controlled by controlling the operation of the of the air
blowers 96
or by providing a choke valve 100 or the like for controlling the air supply
to the
combustion chamber 66 and in turn for controlling the burn rate of the pellet
fuel
46. The amount of air within each air conduit 90 can be individually
controlled via
the control of the air blower 96 or the choke valve 100, either manually or
automatically by a feedback controlled system (not shown) for example.
[024] Now referring to FIG. 6, in addition to FIG. 2 and FIG. 5, air received
from
the air conduits 90 in the first plenum 76 also supplies a secondary plenum
102
formed within the door 40 via second air inlets as in 104 (illustratively,
four inlets
104 are shown) for pneumatically connecting the primary plenum 76 with the
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secondary plenum 102. When primary air supply 78 enters the secondary plenum
102 it is cooled therein before being forced or injected into combustion
chamber
66 at a point illustratively above burn pit 68 via a plurality of injectors
106 formed
from holes provided for within the inner side of the door 40. The injectors
106
may be formed from projecting tubes (not shown) in the inside of the door 40
and
projecting into the combustion chamber 66 for directing secondary air 108
directly
into the combustion chamber 66 at specific directions. The injectors 106
provide a
stream of secondary air supply 108 to further contribute to the combustion
process within the combustion chamber 66 and to create the turbulence of the
air
within the combustion chamber 66 to further complete the combustion of non-
combusted gas of the burn process. Illustratively, the injectors 106 are
strategically sized and placed within the door 40 so as distribute the
secondary
air 108 to the areas within the combustion chamber 66 which favour a complete
combustion. Of note, additional channels (not shown) carrying secondary air
108
may also be directed over the cone 86 to help cool it and to further provide
oxygen for combustion at the flame as it exits the burner assembly 36.
[025] Still referring to FIG. 5 and FIG. 6, prior to the secondary air 108
passing
into the combustion chamber 66, the secondary air 108 undergoes a cooling as
the door 40 and the secondary plenum 102 is thermally insulated from the
combustion chamber 66. Ceramic wool may be provided on the interior of the
door 40 to reflect heat from the combustion chamber 66. In addition to
providing a
source of secondary oxygen for completing the burn process within the
combustion chamber 66, the configuration of the injectors 106 aids in
controlling
the direction of the flame 28 and heated gas towards the open rear 58 through
the cone 86 and towards the heating chamber 24. A plurality of windows 110 may
be provided for in the door 40 for viewing the combustion chamber 66 for
monitoring the combustion of pellet fuel 46.
[026] Now referring back to FIG. 2, FIG. 3 and FIG. 5, the fuel conduit 92
supplies pellet fuel 46 to the burn pit 68 via the fuel supply inlet 80 and a
fuel inlet
112 in the side of the base 54. Illustratively, pellet fuel 46 is supplied to
the burn
pit 68 by an auger screw 114 provided within the fuel conduit 92 to form a
screw
conveyor in communication with a fuel storage bay 116. The auger screw 114
comprises a pitch spacing so as to allow a precise control of fuel for
combustion
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to be supplied. Fuel pellets 46 may be supplied to the fuel storage bay 116 by
a
hopper 118 provided for on the side of the evaporator 10. The rotation of the
auger screw 114 transports fuel pellets 46 from the fuel storage bay 116
through
the fuel conduit 92 and to the burn pit 68 in a manner as is generally known
in the
art of variable rate feeders. The rotational speed of the auger screw 114 is
illustratively controlled by the modulation of an electric motor 120 either by
a user
manually controlling the RPM of the motor via a control dial (not shown) or
the
like or by a feedback control system (also not shown). The feedback control
system can automatically provide for an accurate control of the heat
generation
by the biomass burner 32 by monitoring the consumption of the fuel pellets 46,
the level of oxygen in the combustion exhaust in the heated air 26, the burn
temperature within the heating chamber 24 and other parameters collected at
various points of the evaporator 10. Such feedback control also provides an
automatic fuel supply and precision control of fuel to the combustion chamber
66.
By regulating the supply of air and fuel to the interior of the combustion
chamber
66 in such a manner the amount of heat generated by the biomass burner 32 can
be accurately controlled.
[027] Now referring back to FIG. 2 and FIG. 5, in operation of the burner
assembly 36, the auger screw conveyor 114 feeds fuel pellets 46 from the fuel
storage bay 116 to within the burn pit 68 wherein the fuel pellets 46 are
divided
into two separate sub-fire pits 84 by the hollow divider 82. The air blowers
96
supply air to the primary plenum 76 and secondary plenum 102 for supplying the
fuel pellets with the required oxygen for combustion. The fuel pellets 46 may
be
illustratively ignited by a user accessing the burn pit 68 via the door 40
which is
subsequently closed during operation, or by providing a small pilot flame
assembly (not shown) therein. As a result of the combustion, a first burn of
the
fuel pellets 46 occurs within the burn pit 68 by oxygen supplied from the
primary
air supply 78 passing through the holes 70. A second burn of the non-combusted
gases occurs in the upper portion of the combustion chamber 66 from oxygen
supplied from the cooled secondary air 108 supplied via the injectors 106. The
forced secondary air 108 additionally directs the flame 28 and gases towards
the
cone 86 which funnels and accelerates the flame 28 and exhaust gases towards
the heating chamber 24 where heated air 26 and flames 28 heat the underside 48
of the horizontally extending pans 16. As a result, intense heat reaching
upwards
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of 2000 degrees Fahrenheit at the exit of the burner assembly 36 is generated.
Air and combustion exhaust in the heating chamber 24 is eventually expelled
via
the chimney 52. Advantageously, the feeding of pellet fuel 46 by the auger 114
and the supply of air by the air blowers 96 provide a controlled and stable
source
of heat for the evaporator 10. The high intensity burn of the fuel pellets 46
within
the combustion chamber 66 advantageously results in a minimum amount of burn
residue, a reduced emission of NOR, SON, and volatile organic compounds, while
providing an energy release comparable to that of oil at a fraction of the
cost, in
addition to a controllability of the burn process that is comparable to that
of oil.
[028] Of note, while the biomass burner 32 has been illustrated as a heat
source
to the maple sap evaporator 10, the biomass burner 32 may also be employed for
other furnace use applications. Additionally, while a single biomass burner 32
has
been illustrated, the maple sap evaporator 10 can utilize one or more burners
to
generate the heat needed for different capacity equipment which serves to
evaporate water from maple sap.
