US20120272876A1 - Maple syrup evaporator with biomass burner - Google Patents

Abstract

A burner using biomass combustibles, namely pellet fuel, for a maple syrup evaporator. Compared to wood or oil burning heat sources, pellet fuel is less costly, burns more efficiently and generates the heat necessary to properly evaporate maple sap. The burner includes a burn pit defining a plurality of holes for allowing air to communicate between a combustion chamber and a primary air plenum formed between a base and an underside of the burn pit. An air supply conduit supplies air supply to the primary air plenum. A fuel conduit in communication with the combustion chamber supplies the pellet fuel for combustion within said burn pit. A secondary plenum in pneumatic communication with the primary air plenum receives and cools a portion of the primary air supply. A plurality of injectors in communication with the secondary plenum inject the cooled air into the combustion chamber.

Description

FIELD OF THE INVENTION
• 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
• 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 (NO_x) and Sulphur Dioxide (SO_x).
• 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
• 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 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
• FIG. 1 is a perspective view of a maple sap evaporator, according to a preferred embodiment of the present invention;
• FIG. 2 is a cross-sectional side view of the maple sap evaporator ofFIG. 1;
• FIG. 3 is a rear perspective view of a burner assembly in accordance with an illustrative embodiment of the present invention;
• FIG. 4 is a front perspective view of a burn pit insert of the burner assembly ofFIG. 3 in accordance with an illustrative embodiment of the present invention;
• FIG. 5 is a cross-sectional side view of the burner assembly ofFIG. 3;
• FIG. 6 is a front perspective view of the burner assembly ofFIG. 3; and
• FIG. 7 is a cross-sectional view alongline7 of burner assembly ofFIG. 3.
DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS
• The present invention is illustrated in further details by the following non-limiting examples.
• Now referring toFIG. 1, there is provided an evaporator for the evaporation of maple sap in the production of maple syrup generally referred to using the reference numeral10. The evaporator comprises a maplesap evaporating section12 and a maple syrup forming section14 both illustratively comprising horizontally extendingpans16, which are shown inFIG. 2, provided with partitions in which maple sap travels. The evaporator10 further comprises a hood as in18 for eachsection12,14 and vapour outlets as in20 for directing the water vapour evaporated from the sap to atmosphere.
• Now referring toFIG. 2, in addition toFIG. 1, extending beneath the maplesap evaporating section12 and the maple syrup forming section14 is a heating housing22 comprising aheating chamber24 for exposingheated air26 and flames28 to the undersides of the horizontally extendingpans16. The heating housing22 is illustratively formed from an enclosed space beneath the horizontally extendingpans16 enclosed by sheets of stainless steel or the like. As the undersides of the horizontally extendingpans16 are heated, heat is transferred to maple sap30 travelling along its upper surface of the horizontally extendingpan16 to cause its evaporation. In accordance with an illustrative embodiment of the present invention, theheated air26 and flames28 are generated by abiomass burner32 illustratively connected to the front of the evaporator10.
• Still referring toFIG. 2, thebiomass burner32 comprises a housing34 enclosing aburner assembly36. A front38 of the housing34 comprises anaccess opening39 capable of being enclosed by adoor40, and a rear42 connected to the heating housing22. Illustratively, the housing34 and thedoor40 are formed from a double layered walled44 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 theburner assembly36. The access opening39 in the housing34 is covered by the hingeddoor40 to provide a user access to theburner assembly36 for cleaning, repair, ignition, and maintenance when opened, and for confining the heat and flames28 to within theburner assembly36 when closed. The rear42 of the housing34 is in open connection with theheating chamber24 such that heat and flames28 generated within theburner assembly36 are directed to withinheating chamber24, in a manner as will be described hereinbelow, for the heating of the horizontally extendingpans16.
• Still referring toFIG. 2, theburner assembly36 generates heat from the combustion of combustible materials burned therein, such as wood pellets, vegetable matter, agri-pellets or other forms of pellet fuel46 which may be employed for heating theair26 in theheating chamber24 such that anunderside48 of the horizontally extendingpans16 is heated. Illustratively, the pellet fuel46 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 theburner assembly36 for combustion therein. A plurality ofsteps50 are provided as part of theheating chamber24 to direct theheated air26 upwardly and to generate turbulence so that theunderside48 of the horizontally extendingpans16 is evenly heated. In addition to heat, theburner assembly36 comprises combustion by-products such as carbon monoxide and the like which are directed and expelled from theheating chamber24 to atmosphere via achimney52.
• Now referring toFIG. 3, in addition toFIG. 2, theburner assembly36 illustratively comprises a structure formed from abase54 and asemi-cylindrical dome56 connected to the top of thebase54 by welding, rivets, screws or the like. Thesemi-cylindrical dome56 comprises an open front end60 for communication with theaccess front opening39 and which is enclosed by thedoor40. Thesemi-cylindrical dome56 further comprises anopen rear58 in open communication with theheating chamber24 for providing a direct exhaust channel from theburner assembly36 into theheating chamber24. Thebase54 is illustratively comprised of asolid box housing62 for receiving a burner insert64 at its open top. The space defined above the burner insert64 and below thedome56 is thecombustion chamber66 where pellet fuel46 undergoes combustion in a manner as described hereinbelow. Thebox housing62 and thedome56 are illustratively formed from bent stainless steel sheets or the like and 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 thebiomass burner32. For instance, the ceramic wool may be affixed to the inner surface of thebase54 and thedome56 by tack welding at intermediate points along the inner surface or may be contained within a doubled walled layer structure of thebase54 anddome56 if provided. The provision of insulation ensures a thermal resistance against the deformation of thedome56 and thebase54 caused by the intense heat generated during a high burn intensity operation of thebiomass burner32. Of note, such construction of theburner assembly36 also prevents expansion of theburner assembly36 when subjected to intense heat and remains free of deformation once cooled during inoperation.
• Now referring toFIG. 4, in addition toFIG. 2 andFIG. 3, theburner insert64 comprises a perforated box like structure formed from bent plate sheet metal to form aburn pit68 for containing the pellet fuel46 during combustion thereof. Illustratively, theburner insert64 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 thebiomass burner32. Theburn pit68 is configured and sized sufficiently large enough to hold the pellet fuel46 required for a maximum heat output given the size of the evaporator10. Of note, the sizing of theburn pit68 and thebiomass burner32 may be varied depending on the application.
• Now referring toFIG. 5, in addition toFIG. 3 andFIG. 4, a plurality ofholes70 formed in thewalls72 and floor74 of the bent plate forming theburn pit68 provide air communication between a primary air plenum76 formed between thewalls72 and floor74 of theburn pit68 and the inner sides of thebox housing62. Theholes70 ensure that aprimary air supply78 from within the primary plenum76 are preferably evenly distributed across the pellet fuel46 deposited within theburn pit68 in a uniform manner so as to create an equal rate of combustion of the pellet fuel46. With this configuration, theair holes70 are provided in a patterned configuration to ensure sufficient amounts of oxygen are supplied to thecombustion chamber66 such that an efficient burn of the pellet fuel46 results.
• Still referring toFIG. 4 andFIG. 5, pellet fuel46 is supplied to theburn pit68 via afuel supply inlet80 provided for in theside wall72 of theburner insert64. As pellet fuel46 is received therein, ahollow divider82 projecting upwardly from the floor74 of theburner insert64 and also comprising a plurality of holes as in70 acts to distribute the pellet fuel46 received from thefuel supply inlet80 into twoseparate sub-burn pits84 formed by thehollow divider82 andadjacent walls72. This W cross-sectional shape of theburn pit68 advantageously improves the distribution and surface exposure of the pellet fuel46 for a maximum exposure to oxygen from theprimary air supply78 required to generate a maximum energy output and rapid combustion. Thehollow divider82 is illustratively formed by a bend in the burner insert64 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 theburn pit68 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 fuel46. On the other hand, the number and shape of these projections would reduce the amount of pellet fuel46 that is available in theburn pit68, therefore these need to be designed according to design requirements.
• Still referring toFIG. 4 andFIG. 5, the double combustion burn pit configuration maximises the combustion and the quality of the combustion of the fuel pellets46 by maximizing the combustion area of the pellets supplied with oxygen. Of note, the combustion efficiency of theburner assembly36 can be controlled by regulating the amount ofprimary air supply78 entering the primary plenum76 which in turn passes through theair supply holes70. Additionally, while onehollow divider82 has been illustratively shown, additional dividers may also be provided for improving combustion. Thehollow divider82 also promotes combustion by ensuring that all points within eachsub-burn pit84 are supplied with oxygen with theprimary air supply78.
• Still referring toFIG. 5, in addition toFIG. 2 andFIG. 3, there is further provided aconical cone86 connected to theopen rear58 for directingheated air26 and flame28 from thecombustion chamber66 into theheating chamber24. Advantageously, theconical cone86 also acts to increase the air pressure within thecombustion chamber66 which aids in directing or funnelling of the combustion flames28 to within theheating chamber24. Illustratively, thecone86 directs the flames28 are funnelled at a generally horizontal direction from thecombustion chamber66 and directed into theheating chamber24 for contact with theunderside48 of the horizontally extendingpans16 and for heating theair26 contained therein. The increase in pressure also acts to increase the rate at which exhaust and flames28 are expelled from theburner assembly36 and into theheating chamber24. Theinner surface88 of theconical cone86 is illustratively fabricated from heat resistant reflective material which minimizes the heat retention within thecombustion chamber66 and promotes the transfer of energy to within theheating chamber24. Additionally, thecone86 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 flame28.
• Referring back toFIG. 2, in addition toFIG. 1,FIG. 3 andFIG. 5, thebase54 of theburner assembly36 further comprises a plurality of inlets for receiving air and fuel. Illustratively, the air and fuel are illustratively provided to theburner assembly36 by twoair conduits90 and afuel conduit92, respectively, which originate from an area beneath theheating chamber24 enclosed within the heating housing22. Illustratively, air is supplied to the primary plenum76 viaair conduits90 throughinlets94 in the side of thebase54. Air may be illustratively drawn from the atmosphere exterior to the evaporator10 by one or more electrically powered air blowers96 such as a fan or the like connected to an air intake98 on the side of evaporator10. Air supply to the primary plenum76 can be illustratively controlled by controlling the operation of the of the air blowers96 or by providing achoke valve100 or the like for controlling the air supply to thecombustion chamber66 and in turn for controlling the burn rate of the pellet fuel46. The amount of air within eachair conduit90 can be individually controlled via the control of the air blower96 or thechoke valve100, either manually or automatically by a feedback controlled system (not shown) for example.
• Now referring toFIG. 6, in addition toFIG. 2 andFIG. 5, air received from theair conduits90 in the first plenum76 also supplies asecondary plenum102 formed within thedoor40 via second air inlets as in104 (illustratively, fourinlets104 are shown) for pneumatically connecting the primary plenum76 with thesecondary plenum102. Whenprimary air supply78 enters thesecondary plenum102 it is cooled therein before being forced or injected intocombustion chamber66 at a point illustratively aboveburn pit68 via a plurality ofinjectors106 formed from holes provided for within the inner side of thedoor40. Theinjectors106 may be formed from projecting tubes (not shown) in the inside of thedoor40 and projecting into thecombustion chamber66 for directingsecondary air108 directly into thecombustion chamber66 at specific directions. Theinjectors106 provide a stream ofsecondary air supply108 to further contribute to the combustion process within thecombustion chamber66 and to create the turbulence of the air within thecombustion chamber66 to further complete the combustion of non-combusted gas of the burn process. Illustratively, theinjectors106 are strategically sized and placed within thedoor40 so as distribute thesecondary air108 to the areas within thecombustion chamber66 which favour a complete combustion. Of note, additional channels (not shown) carryingsecondary air108 may also be directed over thecone86 to help cool it and to further provide oxygen for combustion at the flame as it exits theburner assembly36.
• Still referring toFIG. 5 andFIG. 6, prior to thesecondary air108 passing into thecombustion chamber66, thesecondary air108 undergoes a cooling as thedoor40 and thesecondary plenum102 is thermally insulated from thecombustion chamber66. Ceramic wool may be provided on the interior of thedoor40 to reflect heat from thecombustion chamber66. In addition to providing a source of secondary oxygen for completing the burn process within thecombustion chamber66, the configuration of theinjectors106 aids in controlling the direction of the flame28 and heated gas towards the open rear58 through thecone86 and towards theheating chamber24. A plurality ofwindows110 may be provided for in thedoor40 for viewing thecombustion chamber66 for monitoring the combustion of pellet fuel46.
• Now referring back toFIG. 2,FIG. 3 andFIG. 5, thefuel conduit92 supplies pellet fuel46 to theburn pit68 via thefuel supply inlet80 and afuel inlet112 in the side of thebase54. Illustratively, pellet fuel46 is supplied to theburn pit68 by anauger screw114 provided within thefuel conduit92 to form a screw conveyor in communication with a fuel storage bay116. Theauger screw114 comprises a pitch spacing so as to allow a precise control of fuel for combustion to be supplied. Fuel pellets46 may be supplied to the fuel storage bay116 by ahopper118 provided for on the side of the evaporator10. The rotation of theauger screw114 transports fuel pellets46 from the fuel storage bay116 through thefuel conduit92 and to theburn pit68 in a manner as is generally known in the art of variable rate feeders. The rotational speed of theauger screw114 is illustratively controlled by the modulation of an electric motor120 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 thebiomass burner32 by monitoring the consumption of the fuel pellets46, the level of oxygen in the combustion exhaust in theheated air26, the burn temperature within theheating chamber24 and other parameters collected at various points of the evaporator10. Such feedback control also provides an automatic fuel supply and precision control of fuel to thecombustion chamber66. By regulating the supply of air and fuel to the interior of thecombustion chamber66 in such a manner the amount of heat generated by thebiomass burner32 can be accurately controlled.
• Now referring back toFIG. 2 andFIG. 5, in operation of theburner assembly36, theauger screw conveyor114 feeds fuel pellets46 from the fuel storage bay116 to within theburn pit68 wherein the fuel pellets46 are divided into two separatesub-fire pits84 by thehollow divider82. The air blowers96 supply air to the primary plenum76 andsecondary plenum102 for supplying the fuel pellets with the required oxygen for combustion. The fuel pellets46 may be illustratively ignited by a user accessing theburn pit68 via thedoor40 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 pellets46 occurs within theburn pit68 by oxygen supplied from theprimary air supply78 passing through theholes70.
• A second burn of the non-combusted gases occurs in the upper portion of thecombustion chamber66 from oxygen supplied from the cooledsecondary air108 supplied via theinjectors106. The forcedsecondary air108 additionally directs the flame28 and gases towards thecone86 which funnels and accelerates the flame28 and exhaust gases towards theheating chamber24 whereheated air26 and flames28 heat theunderside48 of the horizontally extending pans16. As a result, intense heat reaching upwards of2000 degrees Fahrenheit at the exit of theburner assembly36 is generated. Air and combustion exhaust in theheating chamber24 is eventually expelled via thechimney52. Advantageously, the feeding of pellet fuel46 by theauger114 and the supply of air by the air blowers96 provide a controlled and stable source of heat for the evaporator10. The high intensity burn of the fuel pellets46 within thecombustion chamber66 advantageously results in a minimum amount of burn residue, a reduced emission of NO_x, SO_x, 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.
• Of note, while thebiomass burner32 has been illustrated as a heat source to the maple sap evaporator10, thebiomass burner32 may also be employed for other furnace use applications. Additionally, while asingle biomass burner32 has been illustrated, the maple sap evaporator10 can utilize one or more burners to generate the heat needed for different capacity equipment which serves to evaporate water from maple sap.
• Although the present invention has been described hereinabove by way of specific embodiments thereof, it can be modified without departing from the spirit and nature of the subject invention as defined by the appended claims.

Claims (10)

1. A biomass burner (32) for a maple sap evaporator comprising:

a burner assembly (36) comprising a base (54) and a top for forming a combustion chamber (66) therein, said top defining an entrance and an exit;

a burn pit (68) disposed within said base (54) and defining a plurality of holes (70) for allowing air to communicate between said combustion (66) chamber and a primary air plenum (76) formed between said base (54) and an underside of said burn pit (68);

an air supply conduit (90) for supplying a primary air supply to said primary air plenum (76);

a fuel conduit (92) in communication with said combustion chamber (66) for supplying a pellet fuel (46) for combustion within said burn pit (68);

a secondary plenum (102) in pneumatic communication with said primary air plenum (76) for receiving and cooling a portion of said primary air supply; and

a plurality of injectors (106) in communication with said secondary plenum (102) for injecting said cooled air into said combustion chamber (66);

wherein when said pellet fuel (46) undergoes combustion with said primary air supply, a generated heat is directed towards said exit by said injected cooled air.

2. The biomass burner ofclaim 1, wherein the a plurality of holes (70) of the burn pit (68) are evenly distributed thereon.

3. The biomass burner ofclaim 1, wherein said top is a semi-circular dome (56).

4. The biomass burner according toclaim 1, wherein said exit comprises a cone (86) for accelerating said heat out of said combustion chamber (66).

5. The biomass burner according toclaim 1, further comprising a hollow divider (82) projecting from said burn pit (68) into said combustion chamber (66) for dividing said supplied pellet fuel into two sub-burn pits.

6. The biomass burner according toclaim 1, further comprising a door (40) for sealing said entrance.

7. The biomass burner ofclaim 6, wherein said door (40) is hollowed for providing said secondary air plenum (102), said door (40) comprising an inlet for pneumatic communication of said primary air plenum (76) and said secondary air plenum (102) and defining a plurality of holes formed within said door (40) for forming said injectors (106).

8. The biomass burner according toclaim 1, wherein said pellet fuel (46) is supplied to said burn pit (68) by an auger screw conveyor (114) provided in said fuel conduit (92).

9. The biomass burner according toclaim 1, wherein said primary air supply is supplied to said primary and said secondary air plenums (76,102) via an air blower (96) connected to said air supply conduit (90).

10. The biomass burner according toclaim 1, wherein said pellet fuel is wood pellet fuel.

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