CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to co-pending U.S. Provisional Patent Application 62/464,699 entitled, "FIRE PIT" filed on February 28, 2017, which is hereby incorporated by reference in its entirety.

BACKGROUND

[0002] The present invention generally relates to apparatus for burning fuel, and more particularly to apparatus for burning biomass fuel, such as wood pellets, agricultural refuse, or sawdust granules.

[0003] Wood, coal, and other biomass fuels are burned to make heat for providing warmth and for cooking, as well as, to provide an aesthetic environment for relaxing. Various apparatus have been used to hold the biomass fuel sources when burning to contain the fire and to improve the burning efficiency. More recently, biomass pellets made from waste from wood processing industries have been used in apparatus specifically configured for burning wood pellets. Wood pellets typically have a heat value of about 8300 BTUs per pound. Further, wood pellet burning apparatus can emit substantially lower emissions than conventional wood burners while achieving higher efficiency. Because emissions from burning can be harmful to the environment and people in the vicinity, lower emissions are desirable.

[0004] One such prior wood pellet burning apparatus is a fire pit described in U.S. Patent Application Publication 2014/0238378 Al, entitled, "Pellet Burning Fire Pit," published August 28, 2014. This wood pellet burning

apparatus works well for its intended purpose. Still, there remains a need for a fire pit, or more generally a biomass fuel burning apparatus, that provides more efficient biomass fuel pellet burn to reduce harmful emissions and to increase heat output. There also is a need for a burning apparatus that provides extended burn times. Further, there is a need for a burning apparatus having increased wind resistance, so the burning fuel in the apparatus is less likely to be starved of oxygen or to be burned too fast. In addition, there is a need for a burning apparatus having lower outside wall temperatures during use to reduce opportunities for nearby persons to be burned, for a burning apparatus having increased stability, and for a burning apparatus having an alternate configuration when not in use to provide more efficient storage and shipping. Moreover, there is a need for a fire pit that captures ash, coals, and embers to reduce cleanup and to prevent burning material from escaping from the apparatus. Lastly, there is a need for a burning apparatus that limits fuel smoking and is easy to reload with fuel. One or more of these needs is addressed by the apparatus described below and shown in the accompanying drawings .

SUMMARY

[ 0005 ] In one aspect, a fire pit apparatus for burning biomass fuel comprises a base including a cylindrical shell surrounding a hollow interior and having an upper end and a lower end opposite the upper end. A flange extends outward from the upper end of the cylindrical shell, and a panel extends across the hollow interior of the cylindrical shell. An orifice extends through the cylindrical shell above the panel. The fire pit apparatus also comprises an upper body including a cylindrical enclosure having an upper end and a lower end opposite the upper end. A rim extends inward from the upper end of the enclosure. An inner cylindrical wall defining a burn chamber is mounted concentrically inside the cylindrical enclosure. The cylindrical wall extends downward from the rim thereby forming an annular passage between the cylindrical enclosure and cylindrical wall. A permeable plate extends across the cylindrical enclosure above the lower end of the cylindrical enclosure forming a recess sized and shaped for receiving the flange of the base when the permeable plate is positioned atop the flange of the base. An aperture extending through the cylindrical

enclosure adjacent the lower end of the cylindrical

enclosure permits air to enter the annular passage, and a port extending through the cylindrical wall adjacent the upper end of the cylindrical enclosure permits air to exit the annular passage and enter the burn chamber. When biomass fuel burns in the burn chamber, air is drawn into the hollow interior of the base through the orifice extending through the cylindrical shell and into the burn chamber through the permeable plate to feed primary burning. Air is drawn into the annular passage through the aperture. This air rises through the annular passage and enters the burn chamber through the port to feed secondary burning.

[ 0006 ] In another aspect, a fire pit apparatus for burning biomass fuel comprises a base including a shell surrounding a hollow interior. The shell has an upper end and a lower end opposite the upper end. A flange extends outward from the upper end of the shell, and a panel extends across the hollow interior of the shell above the lower end of the shell. A plurality of orifices extends through the cylindrical shell above the panel. The fire pit apparatus also comprises an upper body including an enclosure having an upper end and a lower end opposite the upper end. A rim extends inward from the upper end of the enclosure. An inner wall defining a burn chamber mounted inside the enclosure extends downward from the rim thereby forming a passage between the enclosure and wall. A permeable plate extends across the enclosure, and a plurality of apertures extends through the enclosure adjacent the lower end of the

enclosure permitting air to enter the passage. A plurality of ports extends through the wall adjacent the upper end of the enclosure permitting air to exit the annular passage and enter the burn chamber. When biomass fuel burns in the burn chamber, air is drawn into the hollow interior of the base through the plurality of orifices extending through the shell and into the burn chamber through the permeable plate to feed primary burning. Air is also drawn into the annular passage through the plurality of apertures. This air rises through the annular passage and enters the burn chamber through the plurality of ports to feed secondary burning.

[ 0007 ] Other aspects will be apparent in view of the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[ 0008 ] Fig. 1 is a perspective of a fire pit apparatus having a first configuration described below;

[ 0009 ] Fig. 2 is a top perspective of a base of the fire pit apparatus of Fig. 1;

[ 0010 ] Fig. 3 is a bottom perspective of a base of the fire pit apparatus of Fig. 1;

[ 0011 ] Fig. 4 is a top perspective of an upper body of the fire pit apparatus of Fig. 1 ;

[ 0012 ] Fig. 5 is an interior perspective of the upper body of Fig. 4 showing an interior wall of the body forming a burn chamber;

[ 0013 ] Fig. 6 is a bottom perspective of the upper body of Fig. 4;

[ 0014 ] Fig. 7 is a fragmentary perspective of the fire pit apparatus of Fig. 1;

[ 0015 ] Fig. 8 is a perspective of a fire pit apparatus having a second configuration described below;

[ 0016 ] Fig. 9 is a top perspective of a base of the fire pit apparatus of Fig. 8;

[ 0017 ] Fig. 10 is a bottom perspective of a base of the fire pit apparatus of Fig. 8; [ 0018 ] Fig. 11 is a top perspective of an upper body of the fire pit apparatus of Fig. 8;

[ 0019 ] Fig. 12 is an interior perspective of the upper body of Fig. 11 showing an interior wall of the body forming a burn chamber;

[ 0020 ] Fig. 13 is a bottom perspective of the upper body of Fig. 11; and

[ 0021 ] Fig. 14 is a fragmentary perspective of the fire pit apparatus of Fig. 8.

[ 0022 ] Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION

[ 0023 ] As illustrated in Fig. 1, fire pit apparatus of a first configuration for burning biomass fuels is designated in its entirety by a reference number 20. The apparatus 20 is formed in two pieces and includes an upper body

(generally designated 22) mounted on a base (generally designated by 24) . As shown in Figs. 2 and 3, the base 24 includes a cylindrical wall or shell 30 having a flange 32 extending radially outward from an upper end 34. A bottom panel 36 extends across the cylindrical wall 30 below the upper end 34. Although the bottom panel 36 may be attached to the cylindrical wall 30 in other ways such as braising or high-temperature adhesives, in the illustrated example the bottom panel is spot welded to the cylindrical wall. The wall 30 of the illustrated example has an outer diameter of about 10.75 inches, a height of about 6.25 inches, and is made from 20 gauge steel sheet. The bottom panel 36 of the illustrated example is made from 16 gauge steel sheet.

[ 0024 ] Racetrack-shaped holes or openings 40 extend through the cylindrical wall or shell 30 below the bottom panel 36, allowing air to circulate below the bottom panel. Other holes or orifices 42 extend through the cylindrical wall 30 above the bottom panel 36, providing an air passage to feed combustion as described in detail below. As shown in Fig. 2, these other holes 42 above the bottom panel may have decorative shapes, such as a trade name, or trademark.

Although the holes 42 may have other flow areas, in the illustrated example, the holes have a total flow area of about 2.86 square inches.

[ 0025 ] Figs. 4-6 illustrate the upper body 22. The upper body 22 comprises an outer cylindrical wall or enclosure 50 having a flange or rim 52 extending radially inward from an upper end 54. An inner cylindrical wall 56 is positioned concentrically inside the outer cylindrical wall as shown in Fig. 5. Although the inner cylindrical wall 56 may be attached to the radial flange 52 of the outer cylindrical wall 50 in other ways such as braising or high-temperature adhesives, in the illustrated example the inner cylindrical wall is spot welded to the flange. As further shown in Fig. 5, the radial flange 52 of the outer cylindrical wall 50 overlaps an upper end 58 of the inner cylindrical wall 56 and protrudes radially inward from the inner cylindrical wall. A grate or permeable plate 60 is attached to a lower end 62 of the inner cylindrical wall 56. Those skilled in the art will appreciate that a burn chamber 64 is formed in the upper body 22 above the grate 60 and inside the inner cylindrical wall 56 for burning biomass fuel pellets as described below. Although the grate 60 may be attached to the inner cylindrical wall 56 in outer ways such as braising or high-temperature adhesives, in the illustrated example the grate is spot welded to the lower end 62 of the inner cylindrical wall. In the configuration shown in Fig. 5, a narrow elongate hole or other marker 66 extends through the inner cylindrical wall 56 to indicate a level to which the burn chamber should be filled with biomass fuel pellets. Circular openings or ports 70 are provided through the inner cylindrical wall 56 to allow air to escape from an annular passage 72 formed between the inner and outer cylindrical walls 56, 50, respectively, and into the burn chamber. The outer cylindrical wall 50 of the illustrated example has an outer diameter of about 13.5 inches, a height of about 7.0 inches, and is made from 20 gauge steel sheet. The inner cylindrical wall 56 of the illustrated example has an outer diameter of about 12.125 inches and is made from 20 gauge steel sheet. In one example, the grate 60 of the illustrated example is replaced with a permeable plate such as described below with respect to Figs. 8-14. Although the openings 70 may have other flow areas, in the illustrated example, the openings have a total flow area of about 7.46 square inches. Further, although the openings 70 may have other sizes and configurations, the illustrated example has fifty equally spaced openings, each having an equal diameter of about 0.437 inches.

[ 0026 ] As shown in Fig. 6, a lower end 74 of the outer wall 50 extends below the inner cylindrical wall 56 and grate 60, forming a recess sized for receiving the flange 32 at the upper end 34 of the base 24 to retain the upper body 22 on the base during use. In the illustrated example, the recess has a height of about 0.625 inches. As further shown in Fig. 6, the grate 60 covers a bottom end of the annular passage 72. Because the grate 60 rests on the upper flange 32 of the base 24 in use, very little air enters directly into the bottom of the annular passage 72 in use. Circular openings or apertures 80 are provided through the outer cylindrical wall to allow air to enter the annular passage. Although the openings 80 may have other flow areas, in the illustrated example, the openings have a total flow area of about 8.51 square inches. Further, although the openings 80 may have other sizes and configurations, the illustrated example has 57 equally spaced openings, having equal diameters of about 0.437 inch.

[ 0027 ] In the configuration shown, the cylindrical wall 30 of the base 24 is sized to be received in the flange 52 of the upper body 22, so the apparatus 20 can be arranged with the base stacked inside the upper body to take less space during storage and transport. Further, although the upper body 22 and base 24 may be made from other materials, in some examples, these components are made from stainless steel or galvanized metal.

[ 0028 ] To use the apparatus 20 of the configuration shown in Figs. 1-7, a user positions the base 24 on a suitable surface and orients the base, so the flange faces upward. Next, the user orients the upper body 22, so the grate 60 faces downward and sets the grate on the flange 32 of the base 24, so the flange is received in the recess of the upper body. Biomass fuel pellets are loaded into the burn chamber 64 to the narrow slot 66 indicating the fill level previously described. The biomass fuel pellets are ignited using suitable conventional means. As the burning pellets heat air inside the burn chamber 64, air is drawn through the holes 40 above the bottom panel 36 of the base 24 and through the grate 60 to feed the fire as shown in Fig. 7. Those skilled in the art will appreciate that the cumulative area of the holes 40, 42 above the bottom panel 36 of the base 24 is less than the cumulative size of the openings in the grate 60. Thus, the holes 40 in the base 24 control airflow through the grate 60.

[ 0029 ] As the pellets continue to burn, air inside the annular passage 72 surrounding the burn chamber 64 is heated and begins to rise due to convection. The rising air in the annular passage 72 is delivered into the burn chamber 64 through the holes 70 in the inner cylindrical wall 56 of the upper body 22. Air leaving the annular passage 72 is replaced with cooler air drawn through the holes 80 provided in the outer cylindrical wall 50 at the lower end of the air passage. The cooler air cools the inner and outer

cylindrical walls, 56, 50, respectively, allowing the upper body 22 to withstand hotter fires in the burn chamber 64. As will be appreciated by those skilled in the art, air exiting the annular passage 72 through the holes 70 in the inner cylindrical wall 56 is warmed as it rises through the annular passage to reduce inefficiencies resulting from cool air entering the burn chamber. The air entering the burn chamber 64 from the annular passage 72 provides additional oxygen to the gases above the burning pellets, allowing those gases to be burned more thoroughly to improve the efficiency of the burn and reduce emissions from the fire. As will be appreciated by those skilled in the art, the flange 52 at the upper end of the burn chamber 64 directs air rising along the inner cylindrical wall 56 inward toward the center of the fire to further improve the secondary emissions burn. Ash falls onto the bottom panel 36 of the base 24 for disposal after the apparatus 22 cools.

[ 0030 ] As illustrated in Fig. 8, fire pit apparatus of a second configuration for burning biomass fuels is designated in its entirety by a reference number 120. The apparatus 120 of the second configuration is also formed in two pieces and includes an upper body 122 mounted on a base 124. As shown in Figs. 9 and 10, the base 124 of the second configuration is similar to the base 24 of the first configuration.

Additional racetrack-shaped holes or orifices 144 are provided through the cylindrical wall or shell 130 to allow additional air to pass through the wall. These holes 144 provide supplemental airflow over and above that provided by the decoratively shaped holes 42 of the first configuration. The wall 130 of the illustrated example has an outer diameter of about 15.375 inches, a height of about 8.125 inches, and is made from 20 gauge steel sheet. The bottom panel of the illustrated example is made from 16 gauge steel sheet. Although the holes 142, 144 may have other flow areas, in the illustrated example, the holes have a total flow area of about 32.44 square inches. [ 0031 ] Figs. 11-13 illustrate the upper body 122. The upper body 122 comprises an outer cylindrical wall or enclosure 150 having a flange 152 extending radially inward from an upper end 154. An inner cylindrical wall 156 is positioned concentrically inside the outer cylindrical wall 150 as shown in Fig. 14. Although the inner cylindrical wall 150 may be attached to the radial flange of the outer cylindrical wall in other ways such as braising or high- temperature adhesives, in the illustrated example the inner cylindrical wall is spot welded to the flange. As further shown in Fig. 14, the radial flange 152 of the outer cylindrical wall 150 overlaps an upper end 158 of the inner cylindrical wall 156 and extends radially inside the inner cylindrical wall. The outer cylindrical wall 150 of the illustrated example has an outer diameter of about 19.0 inches, a height of about 7.75 inches, and is made from 20 gauge steel sheet. The inner cylindrical wall 156 of the illustrated example has an outer diameter of about 16.75 inches and is made from 20 gauge steel sheet.

[ 0032 ] A plate 190 having a pattern of holes 192 is attached to a lower end 162 of the inner cylindrical wall 156. The plate 190 of the illustrated example is made from 16 gauge steel sheet. Although the holes 192 may have other flow areas, in the illustrated example, the holes have a total flow area of about 4.71 square inches. Further, although the holes 192 may have other sizes and

configurations, the illustrated example has 96 holes, each having an equal diameter of about 0.250 inches. A burn chamber 164 is formed above the plate 190 and inside the inner cylindrical wall 156 for burning biomass fuel pellets similarly to the first configuration. Although the plate 190 may be attached to the inner cylindrical wall 156 in other ways such as braising or high-temperature adhesives, in the illustrated example the plate is spot welded to the lower end 162 of the inner cylindrical wall. In the configuration shown in Fig. 14, a series of small holes or other marker 168 extends through the inner cylindrical wall 156

indicating a level to which the burn chamber 164 should be filled with biomass fuel pellets. As those skilled in the art will appreciate, providing the series of holes 168 at the fill line assists with primary combustion during startup by allowing air to flow over the top of the load instead of traveling upward through an entire load of pellets to reach the top surface where combustion occurs. This feature enhances ignition when additional fuel is loaded into the burn chamber 164 while a prior load is still burning.

Although the openings 168 may have other flow areas, in the illustrated example, the openings have a total flow area of about 0.44 square inches. Further, although the openings 168 may have other sizes and configurations, the illustrated example has nine equally spaced openings, each having an equal diameter of about 0.250 inches. Circular openings or ports 170 are provided through the inner cylindrical wall 156 near its upper end 158 to allow air to escape from an annular passage 172 formed between the inner and outer cylindrical walls 156, 150, respectively, and into a burn chamber 164. Although the openings 170 may have other flow areas, in the illustrated example, the openings have a total flow area of about 12.66 square inches. Further, although the openings 170 may have other sizes and configurations, the illustrated example has 46 equally spaced openings, each having an equal diameter of about 0.593 inches. In addition, smaller circular openings or inlets 194 through the inner cylindrical wall 156 near its lower end 162 to allow air to enter the burn chamber 164 near the plate 190. Although the openings 194 may have other flow areas, in the illustrated example, the openings have a total flow area of about 2.26 square inches. Further, although the openings 194 may have other sizes and configurations, the illustrated example has 46 equally spaced openings, each having an equal diameter of about 0.250 inches.

[ 0033 ] As in the first configuration, a lower end 174 of the outer wall 150 extends below the inner cylindrical wall 156 and plate 190, forming a recess sized for receiving the flange 132 at the upper end 134 of the base 124 to retain the upper body 122 on the base during use. In the

illustrated example, the recess has a height of about 0.625 inches. Racetrack-shaped openings or apertures 180 are provided through the outer cylindrical wall to allow air to enter the annular passage. Although the openings 180 may have other flow areas, in the illustrated example, the openings have a total flow area of about 18.60 square inches. As with the first configuration, the cylindrical wall 130 of the base 124 is sized to be received in the upper body 122, so the apparatus 120 can be arranged to take less space during storage and transport. Further, in some examples, the upper body 122 and the base 124 are made from stainless steel or galvanized metal.

[ 0034 ] The apparatus 120 of the second configuration is used similarly to the apparatus 20 of the first

configuration. The additional holes in the upper body 122 and the base 124 provide additional airflow pathways. Some of the air entering the annular passage 172 through the openings 180 in the outer wall 150 of the upper body 122 passes into the burn chamber 164 near the plate 190 to provide additional oxygen for the burning pellets. Further, air passes through openings 144 in addition to openings 140 and 142 to provide additional airflow. In contrast to the first configuration, the holes 192 in the plate 190 in the second configuration limit air passing through the plate.

[ 0035 ] As will be appreciated by those skilled in the art, biomass fuels other than wood pellets may be burned in the apparatus 20, 120 of the first and second

configurations, respectively. [ 0036 ] Apparatus 20, 120 described above provide several benefits. These benefits include producing very little smoke, portability, requiring no power, reduced residual ash, and/or producing an aesthetically pleasing flame.

Moreover, the configurations of the apparatus 20, 120 provide for efficient burning of wood pellets in the burning chamber. Apparatus 20, 120 described above may operate on natural airflow only, eliminating a need for a fan or a blower to enhance portability and to eliminate a need for a power source. Apparatus described above also produce very low particulate emission levels and little airborne ash.

[ 0037 ] As will be appreciated by those skilled in the art, airflow through the annular passages 72, 172 varies automatically with heat output. Thus, the pellets burn at a generally steady rate throughout the entire burn cycle. The sizes and locations of the holes and openings in the upper body 122 and base 124 were selected by trial and

experimentation to provide a constant burn rate through an entire load of wood pellets .

[ 0038 ] The bases 24, 124 of the first and second

configurations retain ash and embers to reduce cleanup and to prevent burning material from escaping from the

apparatus. The plate 190 of the second configuration reduces warping under high temperatures compared to the grate 60 of the first configuration. The plate 190 is also less

expensive to manufacture than the grate 60 of the first configuration. The plate 190 also improves wind resistance.

[ 0039 ] The openings 194 immediately above the plate 190 assist in igniting fuel when fuel is added to the apparatus 120. As will be appreciated by those skilled in the art, the placement of the openings 194 assists primary combustion, enhancing upward airflow toward the secondary combustion ports 170, which provides an even burn pattern at the top of the apparatus 120. Because the openings 194 enter the burn chamber 164 just above the plate 190, they ensure a cleaner burn during the latter third of the burn by enhancing combustion above the pellets.

[ 0040 ] The cylindrical bases 24, 124 of the first and second configurations provide stability to the apparatus 20. The cylindrical bases 24, 124 also shield the bottom of the grate 60 or plate 190 to prevent contact and reduce an opportunity for users to be burned. The bases also protect the burn chambers from downdraft, which may starve the fire and result in smoke.

[ 0041 ] The burn chamber 164 of the second configuration is larger than the chamber 64 of the first configuration. The increased volume is accomplished by increasing the height and diameter of the chamber 164. Increasing chamber size permits a larger volume of pellets to be loaded, which increases burn time.

[ 0042 ] Having described the drawings in detail, it will be apparent that modifications and variations are possible without departing from the scope of the application.

Further, it is envisioned that elements from one of the configurations described above may be substituted in the other configuration without departing from the scope of this description .

[ 0043 ] When introducing elements of the present

application, the articles "a, " "an, " "the, " and "said" are intended to mean that there are one or more of the elements. The terms "comprising, " "including, " and "having" are intended to be inclusive and mean that there may be

additional elements other than the listed elements.

[ 0044 ] As various changes could be made in the above constructions, products, and methods without departing from the scope of the application, it is intended that all matter contained in the above description and shown in the

accompanying drawings shall be interpreted as illustrative and not in a limiting sense .