Air supply systems for combustion of batch-loaded biomass fuels

Abstract

A stove is configured to burn solid biomass fuels. A method of controlled burning of the solid fuel in the stove comprises injecting intake air directed at a first portion of the solid fuel and then, without moving the solid fuel, reducing injection of intake air directed at the first portion and initiating increasing injection of intake air directed at a second portion of the solid fuel.

Description

Attorney Docket No. 19925.004W01AIR SUPPLY SYSTEMS FOR COMBUSTION OF BATCH-LOADED BIOMASS FUELS FIELD OF THE INVENTION

[0001] The present disclosure relates to solid fuel combustion, and more specifically to air supply systems to improve the emissions performance of combustion apparatuses burning solid fuel.BACKGROUND

[0002] Worldwide, combustion apparatuses burning solid fuel are used extensively for cooking, heating, and power generation. One example is solid fuel stoves, such as wood log stoves, which Eire popular in residential applications for heating due to their low-cost, locally available fuel, and aesthetic benefits. These devices use tree branches, split logs, or briquettes made from sawdust or agricultural residues for fuel. A batch of fuel is loaded into the stove periodically and bums according to the airflow properties of the stove. Wood heaters such as these have been used traditionally and offer a way to heat buildings with the low carbon footprint of renewable biomass compared to gas and oil fossil-fuel stoves. Other examples of combustion apparatuses burning a batch of solid fuel such as wood logs or biomass briquettes include hydronic heaters and forced air furnaces.

[0003] However, combustion apparatuses burning solid fuel such as wood are not without their shortcomings. One major concern is the emissions they produce. Combustion exhaust can release carbon monoxide (CO), particulate matter with a diameter of 2.5 microns and smaller (PM2.5), and other products of incomplete combustion into the atmosphere, contributing to air pollution and potentially affecting air quality, climate, and human health. Many countries have regulations on the pollutant emissions of wood stoves used for heating. The emissions depend on the stove design, the type of fuel, the operation of the stove, the way the stove is installed in a home or building, and the local weather. Therefore, while combustion apparatuses burning solid fuel such as wood offer a more sustainable heating and cooking option compared to some alternatives, there is a need to improve the emissions performance to mitigate their environmental drawbacks.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The present application can be best understood by reference to the following descriptions taken in conjunction with the accompanying drawing figures, in which like parts may be referred to by like numerals.Attorney Docket No. 19925.004W01

[0005] Fig. 1A illustrates a schematic perspective view of an example combustion apparatus burning solid fuel.

[0006] Fig. IB illustrates a schematic cross-section view taken along line 1B-1B of Fig.1A.

[0007] Fig. 1C illustrates a schematic cross-section view of another example combustion apparatus burning solid fuel indicating the airflow pattern within the combustion apparatus.

[0008] Fig. ID illustrates a schematic cross-section view of yet another example combustion apparatus burning solid fuel indicating the airflow pattern within the combustion apparatus.

[0009] Fig. 2A illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0010] Fig. 2B illustrates a schematic top-down view of the air supply system of Fig. 2A.

[0011] Fig. 2C illustrates a schematic bottom view of the air supply system of Fig. 2A.

[0012] Fig. 2D illustrates a schematic cross-section view taken along line 2D-2D of Fig.2B.

[0013] Fig. 3A illustrates a schematic perspective view of an air supply system in operable position inside an exemplary combustion apparatus burning solid fuel, in accordance with some embodiments.

[0014] Fig. 3B illustrates a schematic cross-section view taken along line 3B-3B of Fig.3A, showing an airflow pattern.

[0015] Fig. 3C illustrates a schematic cross-section view taken along line 3C-3C of Fig.3A, showing an airflow pattern.

[0016] Fig. 4A illustrates a schematic cross-section view of an air supply system supplying secondary air to one location in the combustion chamber, in accordance with some embodiments.

[0017] Fig. 4B illustrates a schematic cross-section view of an air supply system supplying secondary air to an alternate location in the combustion chamber, in accordance with some embodiments.

[0018] Fig. 4C illustrates a schematic cross-section view of an air supply system supplying secondary air simultaneously in a plurality of locations in the combustion chamber, in accordance with some embodiments.

[0019] Fig. 5 illustrates a schematic cross-section view of an air supply system supplying primary and secondary air simultaneously in a plurality of locations in the combustion chamber, in accordance with some embodiments.Attorney Docket No. 19925.004W01

[0020] Figs. 6A-6E illustrate a schematic cross-section view of an air supply system supplying primary air at different locations of the combustion chamber in sequence to concentrate burning of a batch of solid fuel starting and one end and transitioning to the other, in accordance with some embodiments.

[0021] Figs. 7A-7C illustrate a schematic cross-section view of an air supply system operating a re-load sequence to establish and maintain combustion in a batch of solid fuel, in accordance with some embodiments.

[0022] Figs. 8A-8D illustrate a schematic cross-section view of an air supply system operating an alternate re-load sequence to establish and maintain combustion in a batch of solid fuel in accordance with some embodiments.

[0023] Fig. 9A illustrates a schematic block diagram of an air control assembly, in accordance with some embodiments.

[0024] Fig. 9B illustrates a schematic block diagram of an air control assembly, in accordance with some embodiments.

[0025] Fig. 9C illustrates a schematic block diagram of an air control assembly, in accordance with some embodiments.

[0026] Fig.9D illustrates a schematic block diagram of an air control assembly, in accordance with some embodiments.

[0027] Fig. 10A illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0028] Fig. 10B illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0029] Fig. 10C illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0030] Fig. 11 A illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0031] Fig. 1 IB illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0032] Fig. 11C illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.

[0033] Fig. 1 ID illustrates a schematic perspective view of an air supply system, in accordance with some embodiments.Attorney Docket No. 19925.004W01

[0034] Figs. 12A-12B illustrate a schematic cross-section view of an r supply system supplying primary air and secondary air at a plurality of locations in the combustion chamber in sequence, in accordance with some embodiments.

[0035] Fig. 13 illustrates a graph of experimental results showing particulate matter emissions and firepower over time, in accordance with some embodiments.SUMMARY

[0036] In accordance with one embodiment, the present specification provides a method of controlled burning of a solid fuel in a stove, comprising injecting intake air directed at a first portion of the solid fuel and then, without moving the solid fuel, reducing injection of intake air directed at the first portion and initiating increasing injection of intake air directed at a second portion of the solid fuel.

[0037] In accordance with another embodiment, the present disclosure provides a combustion apparatus configured to bum a batch of solid fuel, comprising a combustion chamber and a fuel support structure configured to support the batch of solid fuel thereupon within the combustion chamber. The batch of solid fuel bums substantially without moving. A first group of primary air nozzles can be positioned at or adjacent a first portion of the fuel support structure. A second group of primary air nozzles can be positioned at or adjacent a second portion of the fuel support structure. An air control assembly can be configured to selectively supply air to the first and second groups of primary air nozzles.

[0038] Some such embodiments can comprise a first plenum and a second plenum, the first group of primary air nozzles communicating with the first plenum, and the second group of primary air nozzles communicating with the second plenum. In further embodiments, each of the first plenum and second plenum comprises an upper surface, and the fuel support structure comprises the upper surface of the first plenum and second plenum. In other further embodiments the first plenum and second plenum are on the sides of the batch of solid fuel and direct primary air to impinge on the sides of the batch of solid fuel. In still other further embodiments, the first plenum and second plenum are above the fuel support structure and direct primary air down to impinge on the batch of solid fuel from above.

[0039] In additional embodiments the air control assembly is configured to deliver an individually controllable amount of primary air to the first and second group of primary air nozzles. In some such embodiments the air control assembly comprises one or more individually controllable fans that delivery air at positive pressure. In additionalAttorney Docket No. 19925.004W01embodiments, the air control assembly additionally comprises valves. In yet other embodiments the air control assembly comprises valves to regulate the flow of primary air. Yet further embodiments can additionally comprise a flue gas extractor fan.

[0040] Still further embodiments additionally comprise one or more groups of secondary air nozzles positioned at or adjacent the fuel support structure. In some such embodiments, the air control assembly delivers is configured to deliver an individually controllable amount of secondary air to the one or more groups of secondary air nozzles. In some embodiments the apparatus is configured so that the location and amount of secondary air introduced into the combustion chamber is coordinated with the location and amount of primary air introduced into the combustion chamber.

[0041] Yet further embodiments can comprise 3 or more groups of primary air nozzles positioned at or adjacent 3 or more portions of the fuel support structure.

[0042] In some embodiments the solid fuel is biomass. In further embodiments the biomass is wood.

[0043] In accordance with another embodiment the present disclosure presents a method of controlled burning of a batch of stationary solid fuel in the combustion chamber of a combustion apparatus. The method can comprise injecting primary air substantially toward a first portion of the batch of solid fuel where combustion is occurring and substantially not at a second portion whereby combustion is concentrated near the first portion of the batch of solid fuel. The method can further comprise shifting the primary air injection substantially toward the second portion of the batch of solid fuel, and substantially not at the first portion, whereby combustion is concentrated near the second portion of the batch of solid fuel.

[0044] In some embodiments the combustion chamber of the combustion apparatus comprises one or more primary air nozzles grouped into a plurality of adjacent primary air injection locations wherein primary air is injected substantially from a first primary air injection location at an edge of the combustion chamber where combustion is occurring, but substantially not at other primary air injection locations. In such embodiments the method can include shifting the primary air injection substantially from the first primary air injection location to the next adjacent primary air injection location, but substantially not at other primary air injection locations. The method can further include shifting the primary air injection substantially from the second primary air injection location to the next adjacent primary air injection location further away from the first primary air injection location, but substantially not at other primary air injection locations. The method can yet further include continuing to shift the location of primary air injection to the next adjacent primary airAttorney Docket No. 19925.004W01injection location in linear series from one edge of the combustion chamber to the other, whereby the primary air and the concentrated combustion location of the stationary batch of solid fuel progresses from one end of the combustion chamber to the other.

[0045] Additional embodiments can additionally comprise injecting secondary air at a location in the combustion chamber.

[0046] In accordance with a yet further embodiment, the present specification provides a method of controlled burning of a solid fuel in a stove. The method can comprise injecting intake air at a first position adjacent a first portion of the solid fuel but not at a second position adjacent a second portion of the solid fuel nor at a third position adjacent a third portion of the solid fuel. Later, the method can include injecting intake air at the second position but not at the first position nor at the third position. Still later, the method can include injecting intake air at the third position but not at the second position.

[0047] Some embodiments comprise injecting air at the second position after injecting air at the first position, and injecting air at the third position after injecting air at the second position.

[0048] In some embodiments, the second position is between the first position and the third position. In other embodiments the stove has an entry, and the first position is closer to the entry than is the second position.

[0049] Some embodiments can comprise injecting air at the first position at a second flow rate while injecting intake air at the third position at a first flow rate, the second flow rate being less than the first flow rate.

[0050] Further embodiments additionally comprise injecting a secondary air at a secondary air injection position spaced vertically above the first, second and third positions. Still further embodiments additionally comprise injecting the secondary air while injecting air at the first position, while injecting air at the second position, and while injecting air at the third position.

[0051] In some embodiments the combustion chamber volume available for loading a batch of solid fuel is less than 6 cubic feet.

[0052] In additional embodiments the maximum rated firepower is less than 30 kW.

[0053] In further embodiments the combustion chamber volume available for loading a batch of solid fuel is less than 35 cubic feet.

[0054] In yet further embodiments the maximum rated firepower is less than 130 kW.DETAILED DESCRIPTIONAttorney Docket No. 19925.004W01

[0055] The following detailed description discusses features and advantages of inventive subject matter in accordance with multiple embodiments. Although the detailed description includes many specific embodiments, these are provided by way of example only and should not be construed as limiting the scope of the embodiments disclosed herein.

[0056] Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosed embodiments belong. Any methods and materials similar to, or equivalent to, those described herein can be used in the practice or testing of the described embodiments.

[0057] The following description sets forth exemplary methods, parameters and the like. It should be recognized, however, that such description is not intended as a limitation on the scope of the present disclosure but is instead provided as a description of exemplary embodiments.

[0058] Numeric ranges provided herein are inclusive of the numbers defining the range.

[0059] With reference to Fig. 1 A, a schematic perspective view of an exemplary combustion apparatus 100 is illustrated. The represented apparatus is a heating stove, specifically resembling model 2469E produced by US Stove Company of South Pittsburg Tennessee, configured to heat a room or other space by burning solid fuel 102 in a combustion chamber 104. The combustion chamber 104 has a door 106 (shown in an open position) that permits access to the combustion chamber for introducing fuel 102, initiating combustion, and removing ash. The flue gasses are extracted out of the combustion chamber 104 by buoyant natural draft of the chimney 108 which is configured to conduct the flue gasses out of the room where the heater is installed. The fire in the combustion chamber 104 heats the exterior surface of the stove 110, whereby heat is transferred to the room primarily by radiation and convection.

[0060] In the illustrated embodiment, and in other embodiments discussed herein, the solid fuel 102 is introduced into the combustion chamber 104 as a batch, and the solid fuel bums substantially without moving.

[0061] A batch of solid fuel is a predetermined amount of fuel that is loaded into the combustion chamber and bums substantially before additional fuel is added to the combustion chamber. In some embodiments preferably at least 50% of the mass of one batch of fuel is consumed by combustion before the next batch of fuel is added. In some embodiments where the solid fuel is cordwood logs the batch of solid fuel may comprise a single wood log or any number of wood logs that may partially fill or substantially fill the volume of the combustion chamber. This is in contrast to fuel that is fed continuously orAttorney Docket No. 19925.004W01semi continuously where new fuel is added to the combustion chamber before the previously added fuel bums substantially.

[0062] Solid fuel that bums substantially without moving is solid fuel that is not substantially moved by a feed mechanism nor by the action of gravity. This is in contrast to solid fuel that is moved through a combustion chamber by a moving grate such as a traveling grate or a reciprocating grate. Configurations wherein the fuel feed mechanism advances the fuel bed with the introduction of new fuel into the combustion chamber, such as underfeed stokers, are also considered to move the solid fuel during combustion. Gravity feed systems where fuel is stored outside the combustion chamber and falls by the action of gravity into the combustion chamber are examples of configurations with moving fuel.

[0063] The depicted combustion apparatus 100 is but one example of an apparatus that bums a batch of solid fuel substantially without moving. Other examples include additional styles of heating stoves which may have alternate airflow patterns as will be described below. Yet other examples include heaters that use a heat transfer medium such as water or air to heat a room other than where the combustion apparatus is located, such as hydronic heaters and forced air furnaces. Boilers to produce hot water or steam for heat, power generation, or other purpose can also be considered.

[0064] Fig. IB illustrates a schematic cross-section view of the exemplary commercially available combustion apparatus 100 of Fig. 1A. A batch of solid fuel 102 is supported by the floor of the combustion chamber 104. The floor in this figure functions as a fuel support structure. Primary air 112 enters through holes in the door 106 and through a slit underneath the door. Secondary air 114 passes through a secondary air conduit 116 that runs underneath the floor of the combustion chamber 104 and then through the combustion chamber to where the secondary air is released from a group of nozzles above the fuel. The primary air 112 passes over the combusting fuel 102 to form flames, flammable vapors, and products of combustion herein referred to flue gases 118 that circulate throughout the combustion chamber 104. The baffle 120 guides the flue gases back towards the door 106 where the secondary air 114 is introduced. The secondary air 114 facilitates further combustion of the flu gases, which are drawn into a secondary combustion zone 122 and then into the chimney 108 by the buoyant natural draft of the said chimney. As the flue gasses 118 pass through the combustion chamber 104 and secondary combustion zone 122 heat is transferred to the exterior surface of the stove 110 and into the environment surrounding the apparatus. There are no air controls on the example stove such as dampers, or valves to control the flow of primary air 112 and secondary air 114. The airflow throughAttorney Docket No. 19925.004W01the stove is determined by the buoyant natural draft in the chimney 108 and the physical properties of the flow path such as the geometry of the primary air nozzles and the secondary air nozzles.

[0065] Fig. 1C illustrates a schematic cross-section view of another example combustion apparatus burning solid fuel. A combusting batch of solid fuel 102 is supported by the floor of the combustion chamber 104. Primary air 112 enters through the door 106. There may be a valve (not shown) on the primary air inlet to adjust the amount of primary air entering the combustion chamber 104. The primary air 112 passes over the batch of burning solid fuel 102 to create flue gases which are drawn out of the combustion chamber 104 into the chimney 108.

[0066] Fig. ID illustrates a schematic cross-section view of yet another example combustion apparatus burning solid fuel. A combusting batch of solid fuel 102 is supported by a grate 124 that allows primary air 112 to flow upwardly and through the fuel, creating flue gasses 118. The door 106 comprises a glass viewing window 126 that allows observation of the burning solid fuel in the combustion chamber 104. Air 128 is directed downward along the window 126 to prevent accumulation of soot and other deposits on the viewing window glass. This air 128 is herein referred to as airwash air. The airwash air 128 also contributes primary air to the combustion process. Secondary air 114 is introduced below a baffle 120 that directs the secondary air 114 and flue gasses 118 toward the chimney 108 and out of the combustion chamber 104. Various forms of valves and dampers may be used to control the flow of primary air 112, airwash air 128 and secondary air 114.

[0067] In the airflow configurations exemplified by Fig. IB - Fig. ID, the primary air 112 or flue gasses 118 pass substantially over and around the batch of solid fuel 102 so that the entire batch of fuel is heated and participates in combustion substantially at the same time.

[0068] With reference next to Figs. 2A-2C,an embodiment of an air supply system 130 comprises five different plenums 132A - 132E that are in fluid communication with respective conduits 134A - 134E so that one conduit is in communication with one plenum of like letter. For example, plenum 132A is in fluid communication with conduit 134A. Each plenum comprises a group of nozzles 136 formed in the upper surface of the plenum 138. The nozzles 138 can be as simple as a hole through the plenum wall in some embodiments, but in other embodiments can include flow-shaping structures of various complexities.Attorney Docket No. 19925.004W01

[0069] Fig. 2D illustrates an example wherein conduit 134C is delivering primary air along an airflow path 140 in which the primary air flows to plenum 132C and further through nozzles 136 into the combustion chamber.

[0070] With reference next to Figs. 3A-3C, air supply system 130 is placed in an operable position inside the combustion chamber 104 of exemplary combustion apparatus 100 burning solid fuel 102. In this embodiment the air supply system 130 also functions as the floor, or fuel support structure, of the combustion chamber 104. The door 106 preferably is configured to seal around the protruding conduits 134 and prevent the inlet of primary air 112 through and under the door. The air control assembly 142 is in fluid contact with conduits 134 and is configured to individually control the flow of air into each conduit 134 and plenuml32 of air supply system 130. The air supply system in this example is configured as a retrofit, modifying an existing stove. Of course, the function of the illustrated exemplary embodiment can be integrated into combustion apparatus designs and included at the time of manufacture.

[0071] Fig. 3B shows the apparatus 103 in a configuration in which primary air 112 is supplied through sealed conduit 134C to plenum 132C and further into the combusting portion 143 of solid fuel 102, which is resting on the upper surfaces 138 of the plenums 132. In the illustrated configuration, the combusting portion 143 is the most forward (i.e., towards the door) portion of the solid fuel 102. Flue gases 118 comprising flames, flammable vapors, and products of combustion are guided toward the secondary combustion zone 122 by the buoyant natural draft in the chimney 108 and the baffle 120. Secondary air 114 is guided by the secondary air conduit 116 and is released above the fuel. In this configuration, substantially no - or at least substantially less - primary air is being provided to the other plenums 132A, 132B, 132D, 132E, and thus primary combustion is directed at the combusting portion 143 rather that at the entire batch of solid fuel 102.

[0072] Changing the location and manner of introducing the primary air into the combustion chamber 104 changes the flow path of the flue gases 118 as compared to, for example, Fig. IB. In Fig. IB the primary air 112 and flue gasses 118 pass substantially over and around the batch of solid fuel as the flue gasses recirculate around the combustion chamber 104. In contrast, in Fig. 3B the primary air 112 impinges substantially only on the portion of the solid fuel that is above the active plenum 132C. This concentrates the solid fuel primary combustion to the region above the active plenum 132C. The flue gasses 118 then are drawn away from the rest of the batch of solid fuel 102 and do not pass substantially over and around the other parts of the batch of solid fuel whereby combustionAttorney Docket No. 19925.004W01is concentrated in one portion of the solid fuel and not in other portions. Over time the primary air 112 impinging on the combusting portion of the solid fuel 143 bums the solid fuel down to charcoal and ash.

[0073] With reference next to Fig. 3C, after the portion of burning solid fuel 143 above planum 132C has burned down to charcoal and ash 144, the primary airflow through plenum 132C can be stopped, or at least substantially reduced. Primary air 112 supply is then switched to conduit 134D and emitted from plenum 132D impinging on the portion of solid fuel above plenum 132D, and thus causing the portion of the batch of solid fuel 102 that is burning 143 to shift to the portion of fuel above the active plenum 132D. The flue gases 118 continue to be guided by the baffle 120 and buoyant natural draft in the chimney 108 away from the remaining batch of solid fuel 102 whereby combustion is concentrated in one portion of the batch of solid fuel relative to other portions. The sequence of directing primary air 112 first from one plenum 132C and then shifting the primary air 112 to the adjacent plenum 132D at a later time causes more concentrated combustion in a portion of the batch of solid fuel 102 that progressed from one end of the batch of solid fuel towards the other; from the side of the combustion chamber 104 closer to the door 106 towards the side of the combustion chamber under the chimney 108. Such a progression of switching primary air supply from one plenum to the next plenum controls combustion of the solid fuel 102 in a desired manner.

[0074] Various structures and methods of supplying primary and secondary air can be employed. For example, Fig. 4A illustrates a schematic cross-section view of an air supply system supplying secondary air 114 to one location in the combustion chamber 104, of a combustion apparatus 100. The secondary air 114 is released from the air supply system plenum 132A in front of the batch of solid fuel 102. The secondary air 114 interacts with the flue gases 118 comprising flames, flammable vapors, and combustion products but substantially does not impinge on the solid fuel 102 itself. Even though the air released from plenum 132A is on the floor of the combustion chamber 104 it substantially does not contribute to primary combustion of the solid fuel 102, instead contributing to secondary combustion of the flue gasses. Thus, air released into the combustion chamber 104 is classified as primary air or secondary air based on the role it has in combustion, not on the relative position in the firebox such as below the solid fuel 102 or above the solid fuel. An- released from the air plenums 132 can be primary air or secondary air depending if the air impinges on the solid fuel 102.Attorney Docket No. 19925.004W01

[0075] Fig. 4B illustrates a schematic cross-section view of an air supply system supplying secondary air 114 to an alternate location in the combustion chamber 104 of a combustion apparatus 100. Secondary air 114 is released from the secondary air conduit 116 above the batch of solid fuel 102. The secondary air 114 interacts with the flue gases 118 comprising flames, flammable vapors, and combustion products but substantially does not impinge on the solid fuel 102.

[0076] Fig. 4C illustrates a schematic cross-section view of an air supply system supplying secondary air 114 simultaneously in a plurality of locations in the combustion chamber 104, of a combustion apparatus 100. Secondary air 114 is released from the secondary air conduit 116 above the batch of solid fuel 102. The secondary air 114 interacts with the flue gases 118 but substantially does not impinge on the solid fuel 102. Secondary air 114 is released from the air supply system plenum 132A in front of the batch of solid fuel 102. The secondary air 114 interacts with the flue gases 118 and substantially does not impinge on the solid fuel 102.

[0077] Fig. 5 illustrates a schematic cross-section view of another embodiment of a firebox comprising an air supply system supplying primary air 112 and secondary air 114 simultaneously in a plurality of locations in the combustion chamber. Primary air 112 is released from plenum 132B and impinges on solid fuel 102 creating an actively burning region 143 and creating flue gases 118. Secondary air 114 is released from the secondary air conduit 116 above the batch of solid fuel 102. The secondary air 114 interacts with the flue gases 118 but substantially does not impinge on the solid fuel 102. Secondary air 114 is released from the air supply system plenum 132A in front of the batch of solid fuel 102. The secondary air 114 interacts with the flue gases 118 and substantially does not impinge on the solid fuel 102.

[0078] With reference next to Fig. 6A-Fig. 6E, an embodiment is illustrated in which an air supply system supplies primary air 112 at different locations of the combustion chamber 104 in sequence to concentrate burning of a batch of solid fuel 102 around a certain region of the fuel batch 143.

[0079] With reference to Fig. 6A, combustion is initiated in the batch of solid fuel 102 at the side of the combustion chamber 104 where the flue gases 118 exit the combustion chamber. Primary air 112 is released by plenum 132B under the solid fuel 102 concentrating combustion of the solid fuel to the region 143 around where the primary air is introduced and impinges on the solid fuel. Secondary air 114 is released from plenum 132A in front of the concentrated combustion region 143 and contributes to secondary combustion of theAttorney Docket No. 19925.004W01flue gases 118. Additional secondary air 114 is released above the concentrated combustion region 143 from the secondary air conduit 116.

[0080] Fig. 6B is at a later time when the primary air 112 released from plenum 132B has at least partially consumed the solid fuel burning in concentrated combustion region 143. In some embodiments it is preferred to continue releasing primary air 112 at the concentrated combustion region 143 until the volatile component of the solid fuel has been substantially consumed. Secondary air 114 released from plenum 132A and conduit 116 continues to contribute to secondary combustion of flue gases 118.

[0081] Fig. 6C is at a later time when the solid fuel above plenum 132B has been reduced to ash and charcoal 144. Primary air 112 is then released from adjacent plenum 132C further away from the flue gas outlet to shift the concentrated combustion region 143 to the portion of the batch of solid fuel 102 where the primary air is released and impinges on the solid fuel. The air released from plenum 132B is reduced while secondary air 114 from plenum 132A and conduit 116 continue.

[0082] Fig. 6D is at a later time when the solid fuel above plenum 132C is reduced to ash and charcoal 144. Primary air 112 is then released from the adjacent plenum further away from the flue gas outlet 132D to shift the concentrated combustion region 143 to the portion of the batch of solid fuel 102 where the primary air is released and impinges on the solid fuel. The air released from plenum 132C is reduced.

[0083] Fig. 6E is at a later time when the solid fuel above plenum 132D is reduced to ash and charcoal 144. Primary air 112 is then released from the adjacent plenum further away from the flue gas outlet 132E to shift the concentrated combustion region 143 to the portion of the batch of solid fuel where the primary air is released and impinges on the solid fuel. The air released from plenum 132D is reduced. In some embodiments it is preferred to reduce the air released from plenum 132A at this stage in the bum where the active combustion region 143 is near the opposite side of the combustion chamber 104.

[0084] The illustrated sequence of releasing primary air from adjacent plenums in series to move a concentrated combustion zone from one end to the other of a substantially stationary batch of solid fuel within a combustion chamber can be conducted in various ways. For example, releasing primary air from the adjacent plenums can proceed from left to right, from right to left, front to back, back to front, and top to bottom. Initiating combustion on the side of the batch of solid fuel closest to the flue gas exit is preferred whereby the solid fuel that is not in the active combustion zone is less affected by the flue gasses. This sequence can be conducted with two or more primary air plenums. In someAttorney Docket No. 19925.004W01embodiments it is preferred to reduce the primary air released from a plenum after devolatilization of the solid fuel is complete to conserve the charcoal residue to facilitate ignition of the next batch of solid fuel. Also, it is to be understood that, as combustion continues, adjacent plenums may be providing primary air simultaneously, and the volume of air provided by a first plenum may reduce as the volume provided by a second plenum may increase. Thus, in some embodiments there can be a transition when switching from one plenum to the next. For example, the flow of air through one plenum can be gradually reduced while the flow of air to the next plenum can be gradually increased until the air supply is completely switched to the next plenum.

[0085] With reference next to Fig. 7A-Fig. 7C, and example sequence is depicted demonstrating an an air supply system embodiment operating a re-load sequence to establish and maintain combustion in a batch of solid fuel.

[0086] In Fig. 7A solid fuel residue of burning charcoal and ash 144 is above plenum 132B releasing primary air 112 such as at the end of the bum sequence illustrated in Fig. 6. To begin the reload sequence as illustrated in Fig. 7B the solid fuel residue 144 of burning charcoal is moved over plenum 132A where primary air 112 is released and air is stopped being released from plenum 132B. A new batch of solid fuel 102 is placed on top of plenums 132A and 132B. At a later time in Fig. 7C the burning charcoal from the residues of the previous batch of solid fuel has ignited a concentrated combustion zone 143 in the portion of the solid fuel 102 above plenum 132A where the primary air 112 impinges on the fuel. The sequence of shifting primary air to adjacent regions of the batch of solid fuel to advance the concentrated combustion region may continue as illustrated in Fig. 6.

[0087] Fig. 8A-Fig. 8D illustrates a schematic cross-section view of an air supply system operating an alternate re-load sequence to establish and maintain combustion in a batch of solid fuel. Solid fuel residue of burning charcoal and ash 144 is above plenum 132B releasing primary air 112 such as at the end of the bum sequence illustrated in Fig. 6. To begin the reload sequence as illustrated in Fig. 8B a batch of solid fuel 102 is placed on top of plenums 132A and 132B and primary air 112 is released from both plenums. The primary air 112 released from plenum 132B into burning residual charcoal 144 causes flue gases 118 to flow over the batch of fuel 102. With reference to Fig. 8C at a later time the flue gases 118 and primary air 112 from both plenums 132A and 132B have ignited the batch of solid fuel 102 to establish a concentrated combustion zone 143 above both plenums. At later time in Fig. 8D air is reduced from plenum 132B and primary air 112 continues being released from plenum 132A to continue burning the concentrated combustion zone 143 establishedAttorney Docket No. 19925.004W01over plenum 132A with the batch of solid fuel 102 above plenum 132B conserved for continuing the burn sequence illustrated in Fig. 6. This alternate ignition method may be preferred in some embodiments for the convenience of not moving the charcoal residue 144 before loading the batch of solid fuel 102. This method also redirects the combustion zone from, for example, the back of a combustion chamber to the front of a combustion chamber, which may be desired when the outlet is disposed above the front of the combustion chamber. As noted above, in some embodiments it is preferred to sequence the combustion zone of the solid fuel in a direction away from the combustion chamber outlet.

[0088] The air control assembly 142 can be configured to manipulate a plurality of valves and / or fans to control delivery of primary air as discussed herein. For example, Fig.9 A illustrates a schematic block diagram of the air control assembly 142 wherein a controller 146 adjusts two or more individually controllable fans 148A and 148B to selectively release air to conduits 134A and 134B to supply combustion air to the combustion chamber 104 of combustion apparatus 100.

[0089] Fig. 9B illustrates a schematic block diagram of an air control assembly 142 wherein controller 146 adjusts one individually controllable fan 148 and two or more individually controllable valves 150A and 150B to release air to conduits 134A and 134B to selectively supply combustion air to the combustion chamber 104 of combustion apparatus 100.

[0090] Fig. 9C illustrates a schematic block diagram of an air control assembly 142 wherein controller 146 adjusts two or more individually controllable valves 150A and 150B to release air to conduits 134A and 134B to supply combustion air to the combustion chamber 104 of combustion apparatus 100.

[0091] Fig.9D illustrates a schematic block diagram of an air control assembly 142 wherein controller 146 adjusts two or more individually controllable valves 150A and 150B to release air to conduits 134A and 134B to supply combustion air to the combustion chamber 104 of combustion apparatus 100. Controller 146 additionally controls a flue gas extractor fan 152 which evacuates flue gases from chimney 108.

[0092] Notably, sensors and the like can be disposed within the combustion chamber 104 in order to identify the location and intensity of combustion zones. Such sensors can relay such information to the controller 146, which can use such information to determine when and how to direct the air control assembly 142 to deliver air to particular locations within the combustion chamber.Attorney Docket No. 19925.004W01

[0093] Fig. 10A illustrates a schematic perspective view of an alternate embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 that impinges on the sides of the batch of solid fuel 102.

[0094] Fig. 10B illustrates a schematic perspective view of another embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 that impinges on the sides of the batch of solid fuel 102.

[0095] Fig. 10C illustrates a schematic perspective view of an alternate embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 that impinges on the sides of the batch of solid fuel 102.

[0096] Further, although plenums can be on opposing walls of the firebox, in some embodiments the plenums may be on one wall of the firebox. And, in yet additional embodiments, plenums on opposing walls of the firebox may be offset from one another so as not to direct air toward an opposing plenum.

[0097] Fig. 11 A illustrates a schematic perspective view of an alternate embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 downward that impinges on the top of the batch of solid fuel 102.

[0098] Fig. 1 IB illustrates a schematic perspective view of an alternate embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 downward that impinges on the top of the batch of solid fuel 102.

[0099] Fig. 11C illustrates a schematic perspective view of an alternate embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 upward that impinges on the bottom of the batch of solid fuel 102.

[0100] Fig. 1 ID illustrates a schematic perspective view of an alternate embodiment of air supply system 130 wherein air conduits 134 are connected to plenums 132 with nozzles 136 that release primary air 112 that impinges on the sides of the batch of solid fuel 102. This embodiment can be operated to facilitate combustion from the top of the batch of solid fuel downward from plenum 132A to plenum 132B to plenum 132C.

[0101] Fig. 12A-12B illustrates a schematic cross-section view of an air supply system supplying primary air and secondary air at a plurality of locations in the combustion chamber in sequence. In Fig. 12A secondary air is released from plenum 132A and conduit 116A to bum flue gasses 118. Primary air 112 is released from plenum 132B and impingesAttorney Docket No. 19925.004W01on concentrated combustion zone 143 of solid fuel batch 102. No air is released from plenum 132C or conduit 116B. At a later time in Fig. 12B the solid fuel above plenum 132B has burned down to charcoal and ash residues and the air released from 132B acts as secondary air 114 to support secondary combustion of the flue gases 118. Primary air 112 is emitted from plenum 132C to maintain the concentrated combustion region 143. Secondary air 114 is released from conduit 116B. No air is emitted from conduit 116A or plenum 132A. This sequence is preferred in some embodiments to maintain the secondary air release in close proximity to the concentrated combustion region 143 as it is shifted to different portions of the batch of solid fuel 102.

[0102] Fig. 13 illustrates a graph of experimental results showing particulate matter emissions and firepower over time, and is discussed below with reference to the examples.

[0103] In some embodiments the solid fuel 102 comprises biomass, charcoal, coal, or combinations thereof. In some embodiments the solid fuel comprises biomass. In some embodiments the biomass comprises agricultural waste or residues, forestry waste or residues, municipal waste or residues, or combinations thereof. In some embodiments the biomass comprises agricultural waste or residues. In some embodiments the biomass comprises forestry waste or residues. In some embodiments the biomass is derived from trees. In some embodiments the biomass comprises wood. In some embodiments the biomass comprises split wood logs suitable for use as firewood, commonly known as cordwood. In some embodiments the biomass comprises compressed briquettes of sawdust or agricultural residues or combinations thereof. In some embodiments the biomass comprises dimensional lumber or carpentry residues.

[0104] Based on example embodiments as described herein, a combustion apparatus can be modified, created, and / or operated in a way to reduce the emissions and increase the efficiency of the combustion apparatus. These improvements are made available by certain features disclosed herein, which can, in some embodiments, include one or more of the following: (i) initiating combustion of a batch of solid fuel in one region near the exit of flue gases from the combustion chamber; (ii) releasing primary air to impinge on a particular region of the batch of solid fuel whereby combustion is concentrated in the region of impinging primary air; (iii) shifting the location of primary air release to adjacent regions of the batch of solid fuel in linear sequence to progressively bum the solid fuel batch.Attorney Docket No. 19925.004W01EXAMPLES

[0105] The following examples are intended to illustrate, but not limit, embodiments described herein. These examples were performed using a particular structure, but of course additional embodiments can employ different specific structures. For all the runs summarized below (Example 1 and Example 2), the stove, the specific combustion apparatus that was used in the experiments, was fueled with split Douglas Fir wood logs approximately 16 inches in length.

[0106] Experimental Methods and Calculations:

[0107] For each test run in Example 1 and Example 2 the key stove operation parameters and performance metrics are reported in Table 1 and Table 2. The meaning of the terms and the methods of calculation of the data in Table 1 and Table 2 are herein explained. The number of wood logs is the number of pieces of split wood that were placed into the stove. The mass of wood kindling as fired reported in kilograms [kg] is the measured mas of the wood kindling as it was burned in the stove including the unbound moisture content. The mass of wood logs as fired reported in kilograms [kg] is the measured mas of the wood logs as they were burned in the stove including the unbound moisture content. The average wood log moisture content reported in percent wet basis [% WB] is the mass of the unbound water in the wood logs divided by the sum of the mass of the unbound water and the mass of the dry wood multiplied by 100. The average wood log moisture was found by measuring the dry basis moisture content (mass of unbound water in the wood divided by the dry wood mass) in three places of each log using a Delmhorst J-2000 pin-type resistance moisture meter and taking the mean over all the wood logs used in both batch 1 and batch 2 of a test run, and converted from dry-basis into wet-basis moisture content as is known in the art. The mass of starting charcoal reported in kilograms [kg] is the measured mass of charcoal at the beginning of the bum phase. The mass of ending charcoal reported in kilograms [kg] is the mass of charcoal left in the stove at the end of a bum phase. Energy equivalent mass of dry wood consumed reported in kilograms [kg] is a calculated metric that takes into account the mass of wood loaded into the stove, the moisture content of the wood, and the charcoal that was consumed or produced during the bum phase that allows different test runs with different wood loads to be compared. This metric is the mass of dry wood multiplied by the lower heating value of the fuel (19,314 kilojoules per kilogram [kJ / kg] for Douglas Fir) minus the energy required to boil away the unbound moisture in the wood, minus the change in charcoal mass between the start and end of the bum phase multiplied by the lower heating value of the charcoal (31,300 kilojoules per kilogram [kJ / kg]) all divided by theAttorney Docket No. 19925.004W01lower heating value of the dry fuel (19,314 [kJ / kg]) which gives the mass of dry fuel completely burned away during the test phase that would have an equivalent energy release to the moist logs and residual char balance that actually occurred. The test duration reported in minutes [min] is the elapsed time during a bum phase from ignition to the stopping criteria of the test protocol of measuring 160 degrees Celsius [°C] in the chimney. The time average firepower reported in kilowatts [kW] is the energy equivalent mass of dry wood consumed, multiplied by the lower heating value of the dry fuel (19,314 [kJ / kg]) divided by the test duration. The HHV efficiency reported in percent [%] is the useful heating energy delivered to the room divided by the total fuel energy loaded into the stove (using the HHV energy content of 20,634 [kJ / kg]) multiplied by 100. The HHV efficiency is calculated by the stack loss method as is known in the art. The energy content of the exhaust is considered lost, and the balance of the energy released by the fuel is assumed to have been transferred into the room. To calculate the energy content of the exhaust gas, the exhaust gas volume was calculated as is known in the art based on measurements of the velocity and exhaust temperature in the center of the chimney about 10 pipe diameters above the stove. The velocity was measured using an S-type pitot static probe and a Honeywell HSC 1” W.C. range pressure transducer. The pressure sensor is corrected for drift over the measurement period by taking a pre- and post-test zero reading and assuming a linear drift. The average velocity is calculated from the center velocity for a turbulent velocity profile with a Reynolds number of about 6000. The density and specific heat of the dry exhaust gas is based on reference tables for air and the measured temperature of the gas. The energy needed to heat and evaporate the water in the fuel results in a reported loss in efficiency. The energy that is lost by the emission of CO results in a reported loss in efficiency.

[0108] The mass of different pollutants in the stove exhaust stream were determined for each test run: carbon monoxide (CO); particles with a diameter less than 2.5 microns known as fine particulate matter or PM2.5 (or “PM2.5”); and carbon dioxide (CO2 or "CO2"). CO, PM2.5, and CO2 were measured as is known in the art. CO and CO2 were measured continuously (sampling rate = 1Hz, at one-second intervals) and PM2.5 was measured using a gravimetric filter for each run at a given configuration. CO, PM2.5, and CO2 were measured with the aid of a 4000 Series Laboratory Emissions Monitoring System (LEMS), commercially available from Aprovecho Research Center of Cottage Grove, OR, and operated according to the manual "Instructions for Use of the Laboratory Emissions Monitoring System (LEMS)", Aprovecho Research Center, updated November 2018, for ISO 19867-1. The total mass of pollutants was divided by the elapsed time of the bum phaseAttorney Docket No. 19925.004W01to calculate the time-average emissions rate. The time average PM emissions rate is reported in grams per hour [g / hr] is the measured mass of PM2.5 emissions divided by the elapsed time of the bum phase in hours. The time average CO emissions rate is reported in grams per minute [g / min] and is the measured mass of CO emissions released during the bum phase divided by the elapsed time of the bum phase in minutes. The time average CO2 emissions rate reported in grams per minute [g / min] is the measured mas of CO2 released during the burn phase divided by the elapsed time of the bum phase in minutes. Emissions factors are the mass of pollutant emitted during a bum phase divided by the dry wood mass consumed during the bum phase. The dry wood mass is the wood mass as-fired minus the moisture content minus 1.5 times the change in charcoal mass between the end and beginning of the test. The mass average PM emissions factor reported in grams PM per kilogram of dry wood mass [g / kg] is the mass of PM emitted during a bun phase divided by the dry mass of fuel burned during the bum phase. The Mass average CO emissions factor reported in grams CO per kilogram of dry wood mass [g / kg] is the CO mass emitted during the bum phase divided by the dry wood mass consumed during the bum phase. The molar CO / CO2 ratio reported in percent [%] is the ratio of measured mass of CO emitted from the stove converted to moles CO and the measured mass of CO2 emitted from the stove converted to moles CO2 multiplied by 100. The carbon balance reported in percent out / in [%] is the mass of carbon measured in the exhaust leaving the stove as CO and CO2 divided by the mass of the carbon in the fuel put into the stove assuming that the fuel is 50% carbon by mass. This serves as a general data quality check. Carbon balance agreement within 20% (i.e. carbon balance of 80% to 120%) is generally considered acceptable within the art. The range of carbon balance measured for all bum phases ranged between 121% and 6% indicating good agreement and acceptable experimental uncertainty.

[0109] The values reported in the average column of Table 1 and Table 2 is the time-weighted average for the emissions rates (sum of pollutant mass emitted from the bum phases in the table divided by the sum of the elapsed time of the bum phases in the table) and is the mass-weighted average for the emissions factors and thermal efficiency (sum of pollutant mass emitted from the bum phases in the table divided by the sum of the dry fuel mass from all bum phases in the table).

[0110] The values of the emission rates for CO, PM2.5, and CO2 described above, measured for a particular combustion device (e.g., a US Stove 2469E) operating under specified conditions (such as selected for the baseline emissions performance determination described here) can be used to characterize the emissions performance of the particularAttorney Docket No. 19925.004W01device operating under the specified conditions and to assess the emissions performance against certain regulatory requirements in certain jurisdictions. In certain other jurisdictions and / or against certain other regulatory requirements, a corresponding emission factor is more preferably used to characterize emissions performance.

[0111] Example 1: Baseline Emissions Performance

[0112] Baseline emissions performance was measured as an example of emissions performance of a representative combustion apparatus, a commercial wood stove, model 2469E, available from the United States Stove Company of South Pittsburg, TN, represented in Fig. 1A and Fig. IB, and operated according to the owner's manual.Approximately 80 inches of single-wall metal chimney pipe with a diameter of 6 inches was used for all test tuns. There are no operator adjustable air controls on the baseline 2469E stove. Air supply was controlled by the buoyant natural draft of the chimney maintaining the stove firebox at negative pressure relative to ambient and drawing in primary air through the fixed dimensions of the fuel feed door directed towards the fuel load and secondary air into the flames through the secondary air plenum. The stove was operated according to a prescribed test protocol representing a realistic real-world use case that includes ignition, reload, and burnout emissions. The stove is loaded with kindling and three Douglas fir cordwood logs including bark. Bum phase one starts when the kindling is lit with three tablespoons of denatured ethanol accelerant. The stove door is then closed, and the fuel charge bums down to charcoal. Once the chimney temperature reaches 160°C bum phase one ends and the remaining charcoal is weighed. The still-glowing charcoal is then placed at the front of the stove and two more logs are placed on the char. Bum phase two starts when the door of the stove is closed after reloading, and ends when the wood bums down to char and the temperature in the chimney falls to 160°C. The remaining charcoal at the end of the test is then weighed. The complete test run consisting of the two loads of fuel lasts 4 to 5 hours. In Table 1 each column of data reports results for a particular bun phase. For example, run 1.1 is the ignition burn of test run 1 and run 1.2 is the reload bum of run 1. At a different time once the stove body had equilibrated to the ambient temperature run 2 was conducted with sequential bums of run 2.1 and 2.2. The average performance for the two test runs, four bum phases, is then reported on a time-weighted average or dry-fuel-mass-weighted-average as explained above. The other data table entries specify the specific operating conditions and performance for each burn phase.

[0113] Table 1: Baseline Operation and PerformanceAttorney Docket No. 19925.004W01

[0114] Example 2: Emissions Performance of Examples of Certain Embodiments

[0115] Stove Modification and Setups

[0116] The US Stove Company 2469E stove used to determine baseline emissions performance, as described above, was modified in order to test and characterize emissions performance of specific examples of certain embodiments. The air supply system 130, as described by the detailed description regarding Fig. 2A-Fig. 2D, was added to the combustion chamber 104 of the combustion apparatus 100 (specifically stove model 2469E in this example) as characterized by the detailed description above regarding Fig. 3 A. The plenums 132A-132E each have and array of thirty air nozzles 136 arranged as a 3x10 grid. Each nozzle was formed by a 5 / 64-inch drill bit in the top surface 138 of the plenums 132 and has a diameter of about two millimeters. The horizontal spacing between the nozzles is about 1.2 inches and the vertical spacing between nozzles is about 1.325 inches. All of the five plenums 132A-132E are made from one-inch tall by four-inches wide steel tubing with a wall thickness of 1 / 8thinch and are about 12.15 inches wide. All of the conduits 134A-134E are made from one-inch square tubing.

[0117] Experimental Protocols and Operation

[0118] The same test protocol used in Example 1 was followed for testing the performance of certain embodiments with two changes. First, the mass of wood kindling forAttorney Docket No. 19925.004W01ignition was reduced and charcoal was added as specified in Table 2. Second, a human operator continuously adjusted the five individually controlled fans coupled to the five conduits 134A-134E throughout the test runs. One fan was coupled to one conduit to control the air released from one plenum. The fans used to control the front two plenums (132A and 132B) in Example 2 were Coleman brand Quickpump model 2120 adjusted by Router Speed Control Item 43060 from Harbor Freight. The adjustment knob was varied from minimum up until the position of the letter “M” on the dial or turned off completely. The fans used to control the back two air plenums in Example 2 (132D and 132E) are SSM model YY5020H12S controlled by a variable speed 5-volt USB to 12-volt controller also from SSM. The adjustment knob was varied from minimum to maximum or turned off completely. The fan for the middle plenum (132C) was a 5-volt fan of similar construction and performance to the model YY5020H12S fan and it was controlled by an external power supply that varied the supply voltage from Ov (of!) to 8v. The fans were turned on and off and adjusted to focus the burning to one area of the fuel load where the air exiting the plenums impinges on the fuel load as described in the detailed description regarding Fig. 3B-Fig.3C. The position of the concentrated air was changed throughout the burn phase as described in the detailed description regarding Fig. 6A-Fig.6E during the ignition runs 3.1, 4.1, and 5.1. For reload runs 3.2, 4.2, and 5.2 the ignition process was as in the detailed description regarding Fig. 7A-Fig. 7C and the controlled burning process was as described regarding Fig. 6A-Fig. 6E. Throughout all runs the secondary air conduit 116 was operable as in the baseline unmodified condition releasing secondary air 114 according to the buoyant natural draft of the chimney and geometry of the conduit and air nozzles. .

[0119] The meaning of the Table 2 data entries is the same as defined above and in Table 1.

[0120] Table 2: Operation and Performance of Examples of Certain EmbodimentsAttorney Docket No. 19925.004W01

[0121] By comparing Table 1 and Table 2 the operating parameters of fuel mass, moisture content, and firepower are all similar in all test runs. However, the PM emissions from the certain embodiments of Example 2 are reduced by 85% from baseline, CO emissions reduced 12% from baseline, and the HHV efficiency increased by 7% from baseline indicating that the certain embodiments of Example 2 have notably improved performance compared to the baseline stove, and in fact have improved performance to a surprising extent.

[0122] Particulate matter emissions (PM2.5) and firepower over time (minutes elapsed from the start of the test) from Example 1 run 1.1 and 1.2 and Example 2 run 3.1 and 3.2 are depicted in graphical form in Fig. 13. Data line 150 is the PM2.5 emissions from run 1.1 and data line 152 is the PM2.5 emissions from rim 1.2. Dat line 154 is the PM2.5 emissions from run 3.1 and data line 156 is the PM2.5 emissions from run 3.2. All PM2.5 data refers to the left axis of PM emissions in grams per hour [g / hr]. Data line 158 is the firepower from run 1.1 and data line 160 is the firepower from run 1.3. Data line 162 is the firepower from run 3.1 and data line 164 is the firepower from run 3.3. All firepower data refers to the right axis of firepower in kilowatts [kW]. As is apparent from the data the PM2.5 emissions of run 3.1 and 3.2 employing specific examples of certain embodiments as described herein especially reduce the peak and / or duration of the PM2.5 emissions during startup and reload contributing to the average reduction in PM2.5 of 85%. Comparing the firepower data, lineAttorney Docket No. 19925.004W01162 generally has a shorter and broader peak of about 15 kW than data line 158 which indicates a more stable and even heat release which is a desirable attribute of the specific examples of certain embodiments as described herein. Comparing the firepower data, line 164 indicates a longer bum duration than data line 160 which is another desirable attribute of the specific examples of certain embodiments as described herein.

[0123] Although the foregoing inventive subject matter has been described in some detail by way of illustration and examples for purposes of clarity of understanding, it will be apparent to those skilled in the art that certain changes and modifications may be practiced without departing from the spirit and scope of the invention, which is delineated in the appended claims. Therefore, the description should not be construed as limiting the scope of the invention. For example, structures supplying primary air from side walls as depicted in Figs. 10A-10C can employ sequential delivery of primary air as discussed in other embodiments, and in any embodiment secondary air can sometimes be provided by the same source that, at other times, provides primary air.

[0124] A person of ordinary skill in the art will recognize that any process or method disclosed herein can be modified in many ways. The process parameters and sequence of the steps described and / or illustrated herein are given by way of example only and can be varied as desired. For example, while the steps illustrated and / or described herein may be shown or discussed in a particular order, these steps do not necessarily need to be performed in the order illustrated or discussed.

[0125] The various exemplary methods described and / or illustrated herein may also omit one or more of the steps described or illustrated herein or comprise additional steps in addition to those disclosed. Further, a step of any method as disclosed herein can be combined with any one or more steps of any other method as disclosed herein.

[0126] Unless otherwise noted, the terms “connected to” and “coupled to” (and their derivatives), as used in the specification and claims, are to be construed as permitting both direct and indirect (i.e., via other elements or components) connection. In addition, the terms “a” or “an,” as used in the specification and claims, are to be construed as meaning “at least one of.” Finally, for ease of use, the terms “including” and “having” (and their derivatives), as used in the specification and claims, are interchangeable with and shall have the same meaning as the word “comprising”.

[0127] As used herein, the term “or” is used inclusively to refer items in the alternative and in combination.

[0128] As used herein, characters such as numerals refer to like elements.Attorney Docket No. 19925.004W01

[0129] Embodiments of the present disclosure have been shown and described as set forth herein and are provided by way of example only. One of ordinary skill in the art will recognize numerous adaptations, changes, variations and substitutions without departing from the scope of the present disclosure. Several alternatives and combinations of the embodiments disclosed herein may be utilized without departing from the scope of the present disclosure and the inventions disclosed herein. Therefore, the scope of the presently disclosed inventions shall be defined solely by the scope of the appended claims and the equivalents thereof.

[0130] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entireties for all purposes and to the same extent as if each individual publication, patent, or patent application were specifically and individually indicated to be so incorporated by reference.

Claims

Attorney Docket No. 19925.004W01CLAIMSWHAT IS CLAIMED IS:

1. A combustion apparatus configured to bum a batch of solid fuel, comprising: a combustion chamber;a fuel support structure configured to support the batch of solid fuel thereupon within the combustion chamber;wherein the batch of solid fuel bums substantially without moving;a first group of primary air nozzles positioned at or adjacent a first portion of the fuel support structure;a second group of primary air nozzles positioned at or adjacent a second portion of the fuel support structure; andan air control assembly configured to selectively supply air to the first and second groups of primary air nozzles.

2. The apparatus of Claim 1, comprising a first plenum and a second plenum, the first group of primary air nozzles communicating with the first plenum, and the second group of primary air nozzles communicating with the second plenum.

3. The apparatus of Claim 2, wherein each of the first plenum and second plenum comprises an upper surface, and the fuel support structure comprises the upper surface of the first plenum and second plenum.

4. The apparatus of Claim 2, wherein the first plenum and second plenum are located horizontally adjacent to the batch of solid fuel and direct primary air horizontally to impinge on the batch of solid fuel.

5. The apparatus of Claim 2, wherein the first plenum and second plenum are above the fuel support structure and direct primary air down to impinge on the batch of solid fuel from above.

6. The apparatus of Claim 1, wherein the air control assembly is configured to deliver an individually controllable amount of primary air to the first and second group of primary air nozzles.

7. The apparatus of Claim 6, wherein the air control assembly comprises one or more individually controllable fans that deliver air at positive pressure.

8. The apparatus of Claim 7, wherein the air control assembly additionally comprises valves.Attorney Docket No. 19925.004W019. The apparatus of Claim 6, wherein the air control assembly comprises valves to regulate a flow of primary air.

10. The apparatus of Claim 9, wherein the air control assembly additionally comprises a flue gas extractor fan.

11. The apparatus of Claim 1, additionally comprising one or more groups of secondary air nozzles positioned at or adjacent the fuel support structure.

12. The apparatus of Claim 11, wherein the air control assembly is configured to deliver an individually controllable amount of secondary air to the one or more groups of secondary air nozzles.

13. The apparatus of Claim 12, configured so that a location and amount of secondary air introduced into the combustion chamber is coordinated with the location and amount of primary air introduced into the combustion chamber.

14. The apparatus of Claim 1, comprising 3 or more groups of primary air nozzles positioned at or adjacent 3 or more portions of the fuel support structure.

15. The apparatus of Claim 1, wherein the solid fuel is biomass.

16. The apparatus of Claim 15, wherein the biomass is wood.

17. A method of controlled burning of a batch of stationary solid fuel in a combustion chamber of a combustion apparatus, the method comprising;injecting primary air substantially toward a first portion of the batch of solid fuel where combustion is occurring and substantially not at a second portion whereby combustion is concentrated near the first portion of the batch of solid fuel; andshifting the primary air injection substantially toward the second portion of the batch of solid fuel, and substantially not at the first portion, whereby combustion is concentrated near the second portion of the batch of solid fuel.

18. The method of claim 17, wherein the combustion chamber of the combustion apparatus comprises one or more primary air nozzles grouped into a plurality of adjacent primary air injection locations wherein primary air is injected substantially from a first primary air injection location at an edge of the combustion chamber where combustion is occurring, but substantially not at other primary air injection locations;shifting the primary air injection substantially from the first primary air injection location to the next adjacent primary air injection location, but substantially not at other primary air injection locations;Attorney Docket No. 19925.004W01shifting the primary air injection substantially from the second primary air injection location to the next adjacent primary air injection location further away from the first primary air injection location, but substantially not at other primary air injection locations; andcontinuing to shift the location of primary air injection to the next adjacent primary air injection location in linear series from one edge of the combustion chamber to the other, whereby the primary air and the concentrated combustion location of the stationary batch of solid fuel progresses from one end of the combustion chamber to the other.

19. The method of claim 17, additionally comprising injecting secondary air at a location in the combustion chamber.

20. A method of controlled burning of a solid fuel in a stove, comprising:injecting intake air directed at a first portion of the solid fuel; and without moving the solid fuel, reducing injection of intake air directed at the first portion and increasing injection of intake air directed at a second portion of the solid fuel.

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