Patent Application
20200224879
The present invention generally relates to devices for burning fuel. More specifically, the present invention relates to an apparatus for burning biomass fuel sources, such as wood pellets, and/or granules of solid biomass.
Wood and other forms of biomass have been used as a heat source, such as for cooking, since virtually the beginning of civilization. However, past systems and devices, such as those employing wood logs and sticks for fuel have had low efficiency and poor heat transfer. When gas became available in the early 1800s, one of the first uses of gas was cooking, as a gas flame is clean and intense, and the cooking level may be easily controlled. However, gas and electric cooking require a sophisticated infrastructure for gas or power delivery, which is not practical in all locations. For example, half of the world's population is still cooking with biomass fires that are slow and inefficient, and which give off hazardous emissions. Wood and coal fire emissions are the cause of millions of premature deaths each year in developing countries.
Pellet burners are advantageous as compared to conventional stick wood burning devices. Such burners typically use a biomass fuel in the form of small pellets which are made from waste from wood processing industries. Wood pellets typically have a heat value of approximately 8300 BTU's per pound. Moreover, wood pellets give off substantially fewer emissions than traditional wood burners while achieving a higher efficiency. Therefore, most pellet burning stoves meet environmental emission standards. Wood pellets are easier to use than traditional sticks and logs, as they are purchased in pellet form and do not require chopping, splitting, or transporting logs. Moreover, because the wood pellets are processed prior to purchase and contain very little moisture, transporting wood pellets does not include the transport of bugs or pathogens associated with logs. Accordingly, home and industrial pellet burners are in wide use. On the other hand, recreational fires, camping fires, and backyard fires using stick wood are inefficient and produce harmful emissions. Replacing these types of wood stick fires with pellet fires would be more efficient as well as reduce emissions and harmful health effects. However, most pellet burning devices require the aid of a fan or blower to accomplish burning, making it difficult to use same without a power source and/or reducing the portability of the devices.
Pellet burners of the prior art include other disadvantages. For example, U.S. Pat. No. 4,471,751 to Hottenroth discloses a stove. The stove includes a primary air chamber and a secondary air chamber in addition to a combustion chamber. Air from the secondary chamber is directed into the combustion chamber via a plurality of air passageways that are located along the height of the combustion chamber. This configuration is inefficient, as secondary air reaching the combustion chamber does not include optimum burning properties. For example, secondary air of varying temperatures enters the combustion chamber. Moreover, the ratio of primary to secondary air is not as efficient as possible.
In other examples, United States Patent Application Publication No. 2007/0137634 to Traeger et al. discloses a pellet-fired cooking apparatus. United States Patent Application Publication No. 2012/0145139 to Deeds discloses a fire pit/barbeque adapted to transition between and enclosed fire pit configuration and an open configuration which serves as a portable barbecue. In addition, United States Patent Application Publication No. 2012/0196232 to Miller discloses a portable fire pit wherein particularly-sized fuel blocks are manually positioned in a square-shaped configuration around ventilation holds provided through the base of the barbecue pit. None of these devices are as efficient as possible as they do not include the introduction of secondary air into a combustion chamber. Therefore, the fuel and flammable gases obtained from the fuel are not allowed to burn to the fullest extent possible.
Accordingly, there exists a need in the art for a pellet burning device that may be used outdoors, such as for recreational, camping, and backyard fires that is as efficient as possible without the aid of a fan or blower. Moreover, the there exists a need for a device which burns as much of the fuel and gases therefrom as possible.
Provided is a fire pit comprising a burning chamber having a floor and an opening at the top. Also included is a secondary chamber having a bottom, at least one air intake, and at least one air escape. The air escape vents air from the secondary chamber to the burning chamber. The secondary chamber and the burning chamber may share a common wall. Furthermore, the at least one air intake is located in or near the bottom of the secondary chamber. The common wall includes a lower half and an upper half, and the air escape is located in the upper half of the common wall. The primary chamber top opening guides flames out of the burning chamber. In some embodiments of the present invention, the floor may be a grate. The grate may be 53% open to the air beneath the burning chamber. Moreover, in some embodiments of the present invention, the secondary chamber may include a roof, which may overhang a least a portion of the burning chamber, also. The secondary chamber may be located in the burning chamber. In some embodiments, an apparatus of the present invention may be round or cylindrical. Moreover, primary air may enter the burning chamber through the floor, and secondary air may enter the burning chamber though the at least one air escape. In some embodiments the ratio of secondary air intake area to secondary air escape outlet area is 18-41%.
Another embodiment of a fire pit of the present invention includes a burning chamber, the burning chamber having a floor at least partially open to the air below the burning chamber, a top at least partially open to the air above the burning chamber, and at least one wall common to a secondary chamber. The secondary chamber may surround the burning chamber, the secondary chamber including at least one outer wall, a bottom, and a roof. The common wall comprises a lower half, an upper half, and at least one secondary air escape. The lower half of the common wall is solid. Further, the secondary chamber outer wall includes at least one air intake inlet, which is located near the bottom of the secondary chamber, while the upper half of the outer wall is solid. In some embodiments, the fire pit may be cylindrical. In addition, the roof may cover at least a portion of the top of the burning chamber. Moreover, the floor may be 53% open to the bottom of the burning chamber. In many embodiments, the floor of the burning chamber allows primary air into the burning chamber, while the at least one air escape allows secondary air into the burning chamber. In some embodiments, the ratio of secondary air intake area to secondary air escape outlet area is 18-41%.
Yet another embodiment of the present invention includes a burning chamber having a floor which is a grate and a cylindrical inner wall and a secondary chamber that surrounds the burning chamber. The secondary chamber includes the cylindrical inner wall, a cylindrical outer wall, a secondary floor, and a roof. The cylindrical inner wall includes a plurality secondary air escape outlets, which are located near the roof of the secondary chamber. Moreover, the cylindrical outer wall includes a plurality of secondary air intake inlets, which are located near the secondary floor. The grate allows primary air to enter the burning chamber, while the at least one air escape allows secondary air to enter the burning chamber. The ratio of secondary air intake area to secondary air escape outlet area is 18-41%. Moreover, the secondary chamber roof may cover at least a portion of the burning chamber.
The following is a detailed description of an apparatus 100 for burning biomass fuels (sometimes “apparatus”). One particular use of such an apparatus 100 is as a pellet burning fire pit. For ease of discussion and understanding, the following detailed description may refer to the apparatus as a pellet burning fire pit, or simply a fire pit, and particularly a pellet burning fire pit designed to burn wood pellets. However, it will be appreciated by one skilled in the art that an apparatus 100 of the present invention may be used in any circumstance where a fire is to be made, including, but not limited to, for cooking, recreational fires, camping fires, and backyard fires. Moreover, an apparatus 100 of the present invention may be configured to employ any biomass fuel including but not limited to wood pellets and corn fuels.
Referring to
The common wall 108 also provides a wall or boundary to a secondary chamber 110 or manifold. In the illustrated embodiment, the secondary chamber 110 surrounds the burning chamber 102. However, it will be appreciated that the secondary chamber 110 may be located in any position. For example the secondary chamber 100 may be located inside the burning chamber 102 or beside the burning chamber 102. The secondary chamber 110 may include a roof 120, a bottom 130, and an outer wall 118. It will be understood that in some embodiments, the secondary chamber 100 may not include an outer wall 118 or a roof 120, such as embodiments wherein the secondary chamber 110 is located inside the burning chamber 102. The secondary chamber 110 includes at least one air intake and at least one air escape. The at least one air intake 112 may be located in the bottom 130 of the secondary chamber 110 and/or near the bottom 130 of the secondary chamber 110. In the illustrated embodiment, the secondary chamber 110 bottom 130 is at least partially open to the air below the apparatus 100. Specifically, the floor of the burning chamber 102 may be a grate which is also the bottom 130 of the secondary chamber. Furthermore, in the illustrated embodiment, the secondary chamber 110 includes a plurality of air intake inlets 112 located around the lower perimeter 116 or bottom of the secondary chamber 110 outer wall 118.
Furthermore, the secondary chamber 110 may include at least one air escape. The air escape may be located at the top of said secondary chamber 110 or near the top of said secondary chamber 110. For example, the common wall 108 may include an upper half 132 and a lower half 134 with the air escape located in the upper half. In the illustrated embodiment, the secondary chamber 110 includes a plurality of air escape outlets 114 located around the upper perimeter 117 or top of the common wall 108. However, as one of skill in the art will appreciate, the air escape need not be outlets 114. For example, the secondary chamber 110 may be open at the top, allowing air to escape. In addition, other configurations may be advantageous in embodiments wherein the secondary chamber 110 does not surround the burning chamber 102.
As discussed above, the secondary chamber 110 need not surround the burning chamber 102. For example, the secondary chamber 110 could be located inside the burning chamber 102 or at other locations. However, the secondary chamber 110 should be configured with the burning chamber 102 such that the burning chamber 102 heats the air inside the secondary chamber 110 and such that the air escape allows air from the secondary chamber 110 to contact the air from the burning chamber 102. As mentioned above, in some embodiments, the secondary chamber 110 may include a roof 120. Furthermore, the roof 120 may cover at least a portion of said burning chamber 102, as shown in
Turning to
Referring to
Moreover, the at least one air escape, which may be one or more air escape outlets 114, allows secondary air 124 to enter the burning chamber 102. As will be discussed in further detail below, the secondary air 124 may enter the secondary chamber 110 through the at least one air intake 112, the secondary chamber 110 bottom 130, or both. In preferred embodiments, discussed in further detail below, the ratio of secondary air intake area, including the area of air intake inlets 112 and the open bottom 106 beneath the secondary chamber 110, to secondary air escape outlet area is 18-41%, although any ratio may be employed. Moreover, the ratio may vary depending on the amount of fuel 135 in the burning chamber 102.
Referring again to
When the secondary air 124 enters the burning chamber 102, it meets the fuel gases, such as pyrolyzed gases, that were not burned during the primary combustion with the primary air 122. The secondary air 124 is fresh air which is full of oxygen and has been heated to a high temperature. Accordingly, when the secondary air 124 meets the fuel gases, the secondary air 124 ignites the fuel gases. In this way, a very efficient burning of the fuel source takes place, as fuel gases which may undergo combustion are not wasted. Moreover, as the air escape outlets 114 are located near the top of the inner wall 108, the flame caused by the secondary air 124 is at the top of the burning chamber 102. Furthermore, the opening 128 at the top of the burning chamber 102 may direct the flame out of the burning chamber 102. Therefore, the flames can be both felt and seen by a user. In addition, the apparatus 100 may operate employing natural airflow only. As one of skill in the art will appreciate, as the burning chamber 102 heats, the amount of secondary air 124 flowing through the secondary chamber 110 will increase. Therefore, heat output is increased. Moreover, the above-described configuration provides for air flow and flames 126 that primarily move upward, as shown in
The user may regulate the amount of heat by adjusting the amount of fuel in the apparatus 100, such as by adding wood pellets at the top of the burning chamber 102. Moreover, the amount of heat may be controlled by the quantity and size of air intake inlets 112 and air escape outlets 114, thereby regulating the flow of secondary air 124. As provided above, in a preferred embodiment, the inlets 112 and outlets 114, as well as the grated floor beneath the entire apparatus 100, are configured such that the ratio of secondary air intake area to secondary air escape outlet area is 18-41%. Moreover, in some embodiments, the roof 120 of the secondary chamber 110 may have a slight overhang 136 so as to cover a portion of the burning chamber 102, as shown in
Turning to
An apparatus 100 of the present invention provides a number of benefits, including, but not limited to, letting off very little smoke, being portable, requiring no power, burning wood pellets with low ash content after burning, and producing an aesthetically pleasing flame. Moreover, the configuration of the apparatus 100 provides for efficient burning of wood pellets in the burning chamber 102. Moreover, an apparatus 100 of the present invention may operate on natural air flow only. Accordingly, it is not necessary to utilize a fan or a blower, which provides for portability and eliminates the need for a power source. An apparatus 100 of the present invention also produces very low particulate emission levels and little airborne fly ash. The combustion air flow is naturally varied according to beat output.
Table 1 below provides dimensions for a number of exemplary preferred embodiments of an apparatus 100 of the present invention of various sizes, with the medium embodiment being most preferred. It should be understood that the embodiments below are provided for purposes of illustration only and are not intended to be limiting. It is anticipated that one skilled in the art could vary any of the dimensions without departing from the scope of the invention.
Although various representative embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of the inventive subject matter set forth in the specification and claims. Joinder references (e.g. attached, adhered, joined) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. Moreover, network connection references are to be construed broadly and may include intermediate members or devices between a network connection of elements. As such, network connection references do not necessarily infer that two elements are in direct communication with each other. In some instances, in methodologies directly or indirectly set forth herein, various steps and operations are described in one possible order of operation, but those skilled in the art will recognize that steps and operations may be rearranged, replaced, or eliminated without necessarily departing from the spirit and scope of the present invention. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.
Although the present invention has been described with reference to the embodiments outlined above, various alternatives, modifications, variations, improvements and/or substantial equivalents, whether known or that are or may be presently foreseen, may become apparent to those having at least ordinary skill in the art, Listing the steps of a method in a certain order does not constitute any limitation on the order of the steps of the method. Accordingly, the embodiments of the invention set forth above are intended to be illustrative, not limiting. Persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Therefore, the invention is intended to embrace all known or earlier developed alternatives, modifications, variations, improvements, and/or substantial equivalents.
This application is a divisional of U.S. Nonprovisional patent application Ser. No. 14/187,458, filed Feb. 24, 2014, the entire disclosure of which is hereby incorporated by reference. U.S. Nonprovisional patent application Ser. No. 14/187,458 claims priority from U.S. Provisional Application Ser. No. 61/769,376 filed Feb. 26, 2013 and entitled Pellet Burning Fire Pit.
| Number | Date | Country | |
|---|---|---|---|
| 61769376 | Feb 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14187458 | Feb 2014 | US |
| Child | 16830647 | US |
