WO2017062963A1

WO2017062963A1 - Apparatus and method for burning a lean, pre-mixed flame

Info

Publication number: WO2017062963A1
Application number: PCT/US2016/056301
Authority: WO
Inventors: Robert K. CHENG; Peter THERKELSEN; Michael C. Tucker
Original assignee: The Regents Of The University Of California
Priority date: 2015-10-09
Filing date: 2016-10-10
Publication date: 2017-04-13
Also published as: US20180224120A1

Abstract

The present invention provides for an apparatus comprising a modified burner plate or a barrier, or both, and a method for burning a lean, premixed fuel/air mixture optionally with low NOx emission using the apparatus thereof.

Description

Apparatus and method for burning a lean, pre-mixed flame

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application Ser. Nos. 62/239,804, filed October 9, 2015; 62/249,890, filed November 2, 2015; and, 62/329,938, filed April 29, 2016; all of which are incorporated herein by reference.

STATEMENT OF GOVERNMENTAL SUPPORT

[0002] The invention was made with government support under Contract Nos. DE-AC02- 05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in the invention.

FIELD OF THE INVENTION

[0003] The present invention is in the field of an apparatus and method for stably burning lean, premixed fuel/air mixtures.

BACKGROUND OF THE INVENTION

[0004] There is a need to reduce indoor pollutant emissions and improve heat transfer from low velocity burners to equipment and processes needing heat. There is a need for an apparatus compring a natural draft combustion system capable of stabilizing premixed flames at low velocities in order to significantly reduce criteria pollutant emissions.

[0005] Currently there is no natural draft, ultra-low emission burner to operate at low velocities. As an example, cooktop ranges utilize a partially premixed natural draft flame stabilizer; but, because the fuel and air are only partially premixed, the emissions emitted by the flame are at levels unaceptable to the air quality goals of California as well as dangerous to human health in a home. Flames of current available technology is shown in Figure 1. Figure 2 shows an example of the ring burner technology.

[0006] The present invention is an improvement over the invention of U.S. Patent No.

5,516,280, issued May 14, 1996, which is incorporated by reference. SUMMARY OF THE INVENTION

[0007] The present invention provides for an apparatus comprising a burner plate or a barrier of the present invention, or both, and a method for burning a lean, premixed fuel/air mixture using the apparatus thereof.

[0008] The present invention provides for a burner plate comprising one or a plurality of port groups, wherein each port group comprises a primary port surrounded by a plurality of secondary ports, and each port has a maximum linear distance from another port of about 0.125 inch. In some embodiments, each secondary port has a maximum linear distance from the primary port of about 0.125 inch. In some embodiments, all of the secondary ports are spaced from the primary port and/or each secondary port is equally spaced from a nearest adjacent secondary port.

[0009] In some embodiments, the lean, premixed fuel/air mixture has a low NO_x emission.

[0010] In some embodiments, each port group further comprises one or more sets of tertiary ports, wherein each set of tertiary ports surrounds an outside border of the plurality of secondary ports or an outside border of another set of tertiary ports, such that the plurality of secondary ports and the one or more sets of tertiary ports form a series of concentric rings around the primary port; wherein each port has a maximum linear distance from another port of about 0.125 inch. In some embodiments, each tertiary port has a maximum linear distance from a secondary port, or a tertiary port of another set of tertiary ports, of about 0.125 inch. In some embodiments, all of the tertiary ports of set of tertiary ports are equally spaced from a secondary port or a tertiary port of another set of tertiary ports, and/or each tertiary port is equally spaced from a nearest adjacent tertiary port of the same set of tertiary ports. Figure 17 shows an embodiment of a primary port surrounded by plurality of secondary ports, which in turn is surrounded by a set of tertiary ports.

[0011] The present invention provides for a burner plate comprising one or a plurality of port groups, wherein each port group comprises a primary port surrounded by a plurality of secondary ports, and each port group has a maximum linear distance from another port group of about 0.125 inch. In some embodiments, the lean, premixed fuel/air mixture has a low NO_x emission. Figures 8A-8N depict embodiments of the burn plate.

[0012] The present invention also provides for an apparatus comprising a burner operating in free air to stably burn a premixed lean fuel/air mixture having a fuel/air equivalency ratio of less than unity to generate hot combustion products, and the burner plate of the present invention, the barrier of the present invention, or both, and optionally the apparatus does not contain a means to blow air and operates as a natural draft system.

[0013] The present invention also provides for a barrier (or "hot box") designed or configured to create an enclosure between a lean, pre-mixed flame and a heating target, such that heat loss from the space is reduced or minimized, wherein the barrier is constructed from a non-combustible material.

[0014] A method of burning a lean fuel/air mixture at substantially atmospheric pressure to generate hot combustion products, comprising: (a) providing a lean fuel/air mixture having a fuel/air equivalency ratio of less than unity; (b) directing the lean fuel/air mixture in a stream, the stream having a direction of flow, and an extent in a plane perpendicular to the direction of flow; (c) mounting a burner plate of the present invention in the stream of the fuel/air mixture to divide the stream into an inner portion and an outer portion having substantially similar flow velocities, through the primary ports and secondary ports respectively; and (d) igniting the stream of the lean fuel/air mixture at the eddies, whereafter the eddies recirculate a portion of the hot combustion products into the stream to continuously re-ignite the fuel/air mixture.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

[0016] Figure 1 shows flames of current available technology.

[0017] Figure 2 shows an example of the ring burner technology.

[0018] Figure 3 shows burner plates tested in Example 1 to determine port size.

[0019] Figure 4 shows an experimental setup assembled to test various burn plates.

[0020] Figure 5 shows the Forced Draft Test Results - Lean blowoff.

[0021] Figure 6 shows the Forced Draft Test Results - Emissions (NO_x). [0022] Figure 7 shows the Forced Draft Test Results - Emissions (CO).

[0023] Figure 8A shows the plan view of one embodiment of a burn plate.

[0024] Figure 8B shows an isometric view of the embodiment of the burn plate depicted in Figure 8A.

[0025] Figure 8C shows the plan view of another embodiment of a burn plate.

[0026] Figure 8D shows an isometric view of the embodiment of the burn plate depicted in Figure 8C.

[0027] Figure 8E shows the plan view of another embodiment of a burn plate.

[0028] Figure 8F shows an isometric view of the embodiment of the burn plate depicted in Figure 8E.

[0029] Figure 8G shows the plan view of another embodiment of a burn plate.

[0030] Figure 8H shows an isometric view of the embodiment of the burn plate depicted in Figure 8G.

[0031] Figure 81 shows the plan view of another embodiment of a burn plate.

[0032] Figure 8J shows an isometric view of the embodiment of the burn plate depicted in

Figure 81.

[0033] Figure 8K shows the plan view of another embodiment of a burn plate.

[0034] Figure 8L shows an isometric view of the embodiment of the burn plate depicted in Figure 8K.

[0035] Figure 8M shows the plan view of another embodiment of a burn plate.

[0036] Figure 8N shows an isometric view of the embodiment of the burn plate depicted in

Figure 8M.

[0037] Figure 9A shows an embodiment of a conventional cooktop, where a large portion of the heat is lost to the ambient air [0038] Figure 9B shows an embodiment of the invention, where most of the heat is contained near the heat target, such as a cooking vessel, such as a pot or pan (Figure 9B).

[0039] Figure 10 shows one embodiment of an adjustable aperture on the top.

[0040] Figure 11 shows an enclosure comprising a spiral wall.

[0041] Figures 12A shows one embodiments of one or a plurality of flames distributed across the heating area.

[0042] Figures 12B shows one embodiments of one or a plurality of flames distributed across the heating area.

[0043] Figure 13 shows an enclosure connected to a vent that directly removes combustion gases from the enclosure or heating area.

[0044] Figure 14 shows an enclosure comprising a heat exchanger to extract heat from the vented gases.

[0045] Figure 15 shows an enclosure is designed or configured to provide heat to the sides of the heat target.

[0046] Figure 16 shows an accessory for cleaning a specific pattern of a port group, and a burner plate with a plurality of port groups with the specific pattern.

[0047] Figure 17 shows an embodiment of a pattern of concentric rings of burner ports that can be turned on/off independently to fit the pot size or for more/less power.

[0048] Figure 18 shows an array of burner ports that covers the majority of a burner plate, such as a cooktop, and can be turned on/off individually or as clusters so that the user or automated system can configure the fired area's shape and size, and pattern anywhere across the burner plate, and adjust it to the pot shape/size.

[0049] Figure 19 shows an embodiment of a burner plate, and a corresponding grate for the burner plate. The grate has a flat top surface. In some embodiments, the grate has holes above each port group. Cookware, such as pots, can move seamlessly across the entire grate top surface, and the flames from each port group can reach the cookware without being blocked by the grate. In some embodiments, the grate is made of any material including those that allow it to be translucent or transparent, such as glass or ceramic, for visual access to the flames.

[0050] Figure 20 shows an embodiment of a burner plate wherein different combinations of port groups can be turned on to produce flame, such that more than one port group heat a cookware. A combination of port groups can be alternated so that a temporal pattern of flames is produced, such that one or more port groups are on while the rest of the port groups are off.

[0051] Figure 21 shows an embodiment of a grate comprising a plurality of concentric rings that extend down below a cookware/grate interface. These rings provide a dripline so any liquid which overflows from a cookware does not migrate to under the center of the cookware. The rings help keep burner ports under the cookware lit even if liquid drips down the sides of the cookware.

[0052] Figure 22 shows a series of posts or other stands that support cookware. Material with an array or singular burner ports that can be moved up and down such that the distance between the cookware supported by the posts or other stands and the burner ports is varied.

[0053] Figure 23 shows a burner plate with a singular or array of burner ports that is angled such that liquid or other materials will roll or run off and drain away.

DETAILED DESCRIPTION OF THE INVENTION

[0054] Before the invention is described in detail, it is to be understood that, unless otherwise indicated, this invention is not limited to particular sequences, expression vectors, enzymes, host microorganisms, or processes, as such may vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting.

[0055] As used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "port" includes a single port as well as a plurality of ports, either the same size or different sizes.

[0056] The term "about" refers to a value including 10% more than the stated value and 10% less than the stated value. [0057] In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings:

[0058] The terms "optional" or "optionally" as used herein mean that the subsequently described feature or structure may or may not be present, or that the subsequently described event or circumstance may or may not occur, and that the description includes instances where a particular feature or structure is present and instances where the feature or structure is absent, or instances where the event or circumstance occurs and instances where it does not.

[0059] The term "cooktop" as used herein means cooktop, range top, or other open-flame or covered-flame cooking device with one, multiple, or continuous burner areas.

[0060] In some embodiments, the primary and secondary ports have relatively blunt cross sectional shape such as circular or oval. In some embodiments, the number of port groups is 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, or 9 or more. In some embodiments, the primary port has a diameter of a value ranging from equal to or more than about 0.375 inch to equal to or less than about 0.4375 inch. In some embodiments, the secondary port has a diameter of a value ranging from equal to or more than about 15% to equal to or less than about 25% of the diameter of the primary port to which the secondary port is grouped. In some embodiments, within a port group, the length between the primary port to each secondary port is about 12.5% of the diameter of the primary port, or a value ranging from equal to or more than about 0.03 inch to equal to or less than about 0.06 inch, or a value ranging from equal to or more than about 0.035 inch to equal to or less than about 0.055 inch, or a value ranging from equal to or more than about 0.04 inch to equal to or less than about 0.05 inch, or a value about 0.045.

[0061] In some embodiments, the port groups on the burner plate are arranged in a pattern that has an at least 1-, 2-, 3-, 4-, 5-, or 6-fold reflectional symmetry. In some embodiments, the port groups on the burner plate are arranged in a pattern that has an at least 1-, 2-, 3-, 4-, 5-, or 6-fold rotational symmetry. In some embodiments, the burner plate has a uniform thickness in the portions wherein the port groups are located. In some embodiments, the uniform thickness is from about 0.3 mm to about 10 mm.

[0062] The apparatus can be configured to operate as a forced draft combustion system, or as a "natural draft" system. In some embodiments, the natural draft combustion system comprises a flow of one fluid, such as a compressed fuel (such a natural gas or propane gas) to entrain another fluid (such as ambient air) before both fluids enter the combustion burner and reaction zone. Forced air is used to increase the velocity of the reactants (fuel and air) prior to combustion. High velocity flows create flames that are easier to stabilize than low velocity flows. In some embodiments, the system utilizes a pressurized flow of gaseous fuel to entrain and mix with ambient air with the same combustion stability mechanism (the ring burner itself, may change slightly as compared to the original patent but those changes should be obvious) and operate at low velocities. The non-obvious change it to rely upon natural draft rather than forced draft for low velocity flows. Low emission premixed (fuel and air mixed before the burner) burners like the ring burner are by and large operated in forced draft mode. One application of this technology is thought to be for residential and commercial cooktops (ranges). While burners on these appliances are natural draft and operate at low velocities, they are not fully premixed and as a result emit large amounts of harmful pollutants. The perfectly premixed fuel and air stabilized by the ring burner will significantly (> 50%) reduce these pollutants. Additionally, the method of flame stabilization used by the incumbent burner technology creates a series of small flamelets that do not evenly heat food. The ring burner allows for natural draft operation at low velocities while maximizing flame surface area which promotes even cooking.

[0063] The present invention allows for the stable operation of a fully premixed flame at low velocities while producing ultra-low emissions. In some embodiments, the apparatus does not have or need an air blower, or is not configured to require an air blower. The apparatus is useful for the operation of low velocity burners without the need for energy consuming air blowers, thereby increasing system efficiency with maintaining low emissions.

[0064] The natural draft ring burner is made possible by using advanced fluid dynamics techniques to entrain ambient air with pressurized fuel. The coupling of the air entrainment with the ring burner technology requires advanced engineering work and innovation to ensure the premixed flow enters the ring burner in a way that the burner can stabilize the flame.

[0065] The present invention is an improvement over the ring stabilizer idea that uses geometry changes (ring stabilizers to hole stabilizers) and integration with a fuel venturi to enable natural draft operation while improving combustion efficiency, minimizing pollutant formation, increasing multi-burner design potential, and system stability at low Reynolds number operation. This development occurred as a result of our adaptation of the forced draft ring stabilizer to natural draft operation (see Example 1). The ring stabilizer geometry was determined not to provide the optimal geometry. The new burner reduces the amount of unburned fuel emitted by the burner at high load and is cheaper to manufacture than either the ring stabilizer or other lean premixed low Reynolds number burners. One aspect of the new burner is the small satellite holes (i.e. the secondary ports) that surround a primary fuel/air hole (i.e. the primary port). These satellite holes anchor the flame of the main hole in a more efficient way than the previous ring burner did. The satellite holes also allow for more distributed arrays of the burner to be made. The primary target application for this technology is for residential and commercial heating (e.g. cook tops, air heaters, water heaters, and ovens) and the application of industrial process heating.

[0066] In some embodiments, the heating target is a cooking vessel or cookware, such as a pot, pan, or wok. In some embodiments, the heating target has a round or flat bottom. In some embodiments, the non-combustible material is glass, ceramic, enamel, metal, or the like. In some embodiments, the top of the barrier is solid in order to facilitate cleaning. In some embodiments, the top of the barrier can span multiple enclosed burners, similar to induction or infrared cooktops. In some embodiments, the barrier top is translucent or transparent such that the burner flame is visible to the user. Figures 11 to 15 show variant enclosure designs.

[0067] Cooktops currently use rich flames (fuel-to-air stoichiometry of fuel/air mix coming into burner is fuel rich), and additional air diffuses/convects to the flame to complete combustion. This imposes a geometric requirement on the cooktop and cookware such that air diffusion is sufficient. Generally, unobstructed line-of-sight pathway between secondary ambient air and each flame is necessary. With the advent of lean flames (fuel-to-air stoichiometry of fuel/air mix coming into burner is air rich) for cooktops, this geometric requirement is relaxed, as the fuel/air mix has enough oxygen, and diffusion of secondary air to the flame is not necessary.

[0068] For this present invention, ambient air is separated from the cooking zone, enabling improved cooking in terms of homogenous heat distribution, fuel efficiency, and thermal transfer to the food (for example, reduced time to boil). Figures 9A and 9B compare an embodiment of the invention to a conventional cooktop. In the conventional cooktop, a large portion of the heat is lost to the ambient air (Figure 9A). In the invention, most of the heat is contained near the heat target, such as a cooking vessel, such as a pot or pan (Figure 9B). This containment results in a lower fuel consumption of the heat transfer to the heat target, such as food contained within the cooking vessel.

[0069] In some embodiments, the barrier defines an enclosure that confines a flame or flames, and hot cooking gas, and prevents or limits exchange between the hot cooking gas and ambient air, and touches or is in proximity to the heat target, such as a cooking vessel.

[0070] In some embodiments, the barrier comprises one or more vent airs, which when open permits forced air or natural air draft cooling, which extends the range of turn-down, or enable rapid cooling of the heat target, such as a cooking vessel, to, for example, prevent burning or overcooking of the food.

[0071] In some embodiments, the barrier is mounted on the cooktop, integrated into the heat target, or cooking vessel, or is a separate apparatus that is put in place before cooking.

[0072] In some embodiments, the heat target and the barrier are designed or configured for optimum performance such that the heat target and the barrier can "mate" together or have a tight fit.

[0073] In some embodiments, the barrier further comprises thermal insulation to reduce heat transfer with ambient air.

[0074] In some embodiments, the barrier comprises an adjustable aperture on the top to accommodate heat targets of various sizes, such as cooking vessels of different sizes. Figure 10 shows one embodiment of an adjustable aperture on the top.

[0075] In some embodiments, the barrier comprises a solid top, such as a griddle or grill.

[0076] In some embodiments, the barrier comprises a spiral wall to permit venting while retaining heat. Figure 11 shows a barrier comprising a spiral wall.

[0077] In some embodiments, the barrier is designed or configured to have one or a plurality of flames distributed across the heating area, such as a cooking area. Figures 12A and 12B shows embodiments of one or a plurality of flames distributed across the heating area. This permits flexibility in burner design in terms of cost, turn-down ratio, and size (such as Btu output) of each flame.

[0078] In some embodiments, the barrier connects to a vent that directly removes combustion gases from the enclosure or heating area. This circumvents a need for a range hood to exhaust heat, carbon monoxide, NOx, and other undesirable combustion by-products. Figure 13 shows a barrier connected to a vent that directly removes combustion gases from the enclosure or heating area.

[0079] In some embodiments, the barrier comprises a heat exchanger to extract heat from the vented gases. This can be used to preheat in coming fuel/air. Figure 14 shows a barrier comprising a heat exchanger to extract heat from the vented gases.

[0080] In some embodiments, the barrier is designed or configured to provide heat to the sides of the heat target. Figure 15 shows the barrier designed or configured to provide heat to the sides of the heat target.

[0081] In some embodiments, a heating system comprising the barrier uses an apparatus of the present invention or an apparatus taught in U.S. Patent No. 5,516,280, issued May 14, 1996, which is incorporated by reference, or any other burner. In some embodiments, the system uses a lean premixed flame including natural draft or forced draft.

[0082] The present invention also provides for an apparatus comprising protrusions which fit the ports of a port group. The apparatus can be an accessory of a burner plate. The apparatus is used to clean the hole pattern of a port group when food, or any matter, gets stuck in it. The protrusion can be solid, or comprise a wire brush, push-rod, or the like, optionally with multiple parts that fit into each hole in the burner pattern. Figure 16 shows an accessory for cleaning a specific pattern of a port group, and a burner plate with a plurality of port groups with the specific pattern.

[0083] In some embodiments, the port groups comprise one or more concentric rings of burner ports that can be turned on/off as needed to fit the pot size or for more/less power. Each ring may or may not have its own fuel supply system. Figure 17 shows of such an example.

[0084] In some embodiments, the burner plate is disposable. For example, when the burner plate is dirty, the user can throw it away.

[0085] In some embodiments, the burner plate is sized/shaped as desired, and optionally coated so that it can be washed by a dishwasher and is dishwasher wash.

[0086] In some embodiments, the burner plate comprises wall-to-wall burner ports that cover entire burner plate, or cooktop, wherein optionally each port group can be turned on/off individually or as clusters so that the user can configure a desired flame pattern anywhere across the cooktop, and adjust it to the cookware shape/size. A screen or touchpad can be used that identifies where the cookware is and allows high/low heat, cook-time, or other user commands, such that where the cookware is to be placed is not limited by a pre-determined factory-placement of a burner. The user can configure the burner pattern, heat, and other operation (including selected on/off pulse operation) as needed for each cooking session. Figure 18 shows of such an example.

[0087] In some embodiments, the burner plate is coated with enamel, glass, ceramic, or other coating to enable easy cleaning. In some embodiments, the burner plate is made of material capable of sustaining a high temperature without melting, such as cast iron, steel, ceramic, glass, or the like.

[0088] In some embodiments, the burner plate has a corresponding grate for cookware that is a single flat surface, and has holes above each burner port. Each cookware, such as a pot, can move seamlessly across the entire cooktop surface, and the flame can reach the cookware without being blocked by the grate. The grate is made of any material including those that allow it to be translucent or transparent, such as glass or ceramic for visual access to the flames. Figure 19 shows of such an example.

[0089] In some embodiments, a cooktop comprising the burner plate can comprise one or more of the features described herein. Sensors (IR, camera, weight, or the like) that determine where a cookware, such as a pot, is and light the associated burner ports. Optionally, the sensors can also detect hands, handles and other non-cookware items for safety. A grate for cookware comprising a single flat surface, and has holes above each burner port, wherein a subset of the flames (or a single flame) can be on, and the rest are off, such that the ones that are on can circulate around to intermittently warm the bottom of the pan (like doing the "wave"). The subset that is on can vary with time or is intermittent, such that a pattern of flames can move across or around the cooktop. The subset can circulate around or randomly turn on and off around to intermittently warm various sections of the bottom of the cookware. Figure 20 shows of such an example.

[0090] In some embodiments, the grate has concentric rings that extend down below the cookware/grate interface. These rings can provide a dripline so that liquid which overflows from the cookware does not migrate to under the center of the cookware. This helps keep burner ports under the cookware lit even if liquid drips down the sides of the cookware. Figure 21 shows of such an example.

[0091] In some embodiments, the burner plate can have a plate disposed below the burner plate comprising an array of holes such that it can be rotated to expose fuel flow to different subsets of ports in the burner plate.

[0092] Figure 22 shows a series of posts or other stands that support cookware. Material with an array or singular burner ports that can be moved up and down such that the distance between the cookware supported by the posts or other stands and the burner ports is varied.

[0093] Figure 23 shows a burner plate with a singular or array of burner ports that is angled such that liquid or other materials will roll or run off and drain away.

[0094] It is to be understood that, while the invention has been described in conjunction with the preferred specific embodiments thereof, the foregoing description is intended to illustrate and not limit the scope of the invention. Other aspects, advantages, and modifications within the scope of the invention will be apparent to those skilled in the art to which the invention pertains.

[0095] All patents, patent applications, and publications mentioned herein are hereby incorporated by reference in their entireties.

[0096] The invention having been described, the following examples are offered to illustrate the subject invention by way of illustration, not by way of limitation.

EXAMPLE 1

Optimized Reduced-Scale Ring-Stabilizer Port - Forced Draft

[0097] A goal is to optimize the configuration of a reduced-scale ring stabilizer port for operating at low Reynolds number flows. A goal is the determination of an optimal size and ring stabilizer configuration that is amenable to natural draft operation as well as scaling (via multi-port clustering approach) to the various shapes and sizes of residential and commercial heating appliances. The experiment involves a parametric study of the ring stabilizer to select designs that meet the metrics on operation, performance and ease of manufacturing.

[0098] The experiment tests the effect of reducing ring-stabilizer port size. The

manufacturing limitation (gap) is 0.60". The minimum port diameter is 0.375". This dimension is selected to minimize flashback potential. Figure 3 shows burner plates tested to determine port size.

[0099] Forced- Draft Ring-Stabilizer Test Stand Development

[00100] The test stand comprises: methane and air mass flow controllers, fuel and air mixing length, burner stand (plenum filled with glass beads to mitigate flashback events and straighten flow, and interface to quickly replace burner plates), emissions analyzer (for NO_x, CO, O₂, and CO₂), and custom control program with data logging capabilities. An experimental setup is assembled to test various burn plates (Figure 4).

[00101] Forced Draft Test Plan

[00102] The experiment tests for stability, lean blowoff (lowest amount of fuel possible before flame disappears), flashback (how slow can fuel/air exit burner before flame travels upstream of the burner port), emissions (enclosed so emissions are not diluted by ambient air), turndown (range of power outputs that burner can operate), and crossover ignition (spacing between burners that allows for ignition).

[00103] Forced Draft Test Results - Lean blowoff.

[00104] The results show consistent blowoff, lower velocity (i.e., lower temperature flame), and a large potential to match lower temperature flame of a 1" burner, and the possibility of reduced NO_x emissions (see Figure 5).

[00105] Forced Draft Test Results - Flashback

[00106] The results show flashback propensity increases with reduced velocity or increased flame temperature. This follows the expected relationships. The results also show that low velocity and flame temperature operation are not limited by flashback. The lowest velocity for the 1" burner is 0.4 m/s. See Tables 1 and 2. [00107] Table 1. 0.375" diameter ports (9 total)

[00108] Table 2. 0.4375" diameter ports (9 total)

[00109] Forced Draft Test Results - Emissions (NO_x)

[00110] The results show lower NOx than current cooktop emissions, and reduction of more than 80% (see Figure 6).

[00111] Forced Draft Test Results - Emissions (CO)

[00112] The results show CO emissions are only acceptable at lowest equivalence ratios, and the potential of lower equivalence ratio operation will further reduce CO emissions (see Figure 7).

[00113] Forced Draft Test Results - Turndown

[00114] The results show ring-Stabilizer show to have between 5: 1 and 3: 1 turndown, commercial systems have much higher turndown, additional engineering is required to increase turndown, and low turndown applications may include ovens, water heaters, and furnaces. See Tables 3 and 4.

[00115] Table 3. 0.375" diameter ports (9 total) Equivalence ratio Turndown ratio

0.80 3.0: 1

0.85 3.4: 1

0.90 4.0: 1

[00116] Table 4. 0.4375" diameter ports (9 total)

[00117] Forced Draft Test Results - Crossover Ignition

[00118] The results show various distances between ports, ignition at one end of burner plate, and self-igniting until port distance is too large.

[00119] Forced Draft Test Results - Crossover Ignition

[00120] The results show ports need to be less than 0.125" apart, and easy geometry to implement with low cost manufacturing techniques. See Tables 5 and 6.

[00121] Table 5. 0.375" diameter ports (9 total)

[00122] Table 6. 0.4375" diameter ports (9 total) Equivalence ratio Max edge distance (inch)

0.80 0.125

0.85 0.125

0.90 0.125

[00123] Conclusions

[00124] Scaled down Ring-Stabilizer burners operate at designed residential power thermal outputs (5,000 to 7,000 BTU/hr). Forced-draft burners are capable of meeting project goal of 80% NO_x reduction. Burner ports are able to ignite each other within geometric limits. Smaller port and gap size allow for more distributed heat release across burner plate.

[00125] While the present invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process step or steps, to the objective, spirit and scope of the present invention. All such modifications are intended to be within the scope of the claims appended hereto.

Claims

What is claimed is:

1. A burner plate comprising a plurality of port group, wherein each port group

comprises a primary ports surrounded by a plurality of secondary ports, and each port group has a maximum linear distance from another port group of about 0.125 inch.

2. A barrier designed or configured to create an enclosure between a lean, pre-mixed flame and a heating target, such that heat loss from the space is reduced or minimized, wherein the barrier is constructed from a non-combustible material.

3. An apparatus comprising a burner operating in free air to stably burn a premixed lean fuel/air mixture having a fuel/air equivalency ratio of less than unity to generate hot combustion products, and (a) a burner plate comprising a plurality of port group, wherein each port group comprises a primary ports surrounded by a plurality of secondary ports, and each port group has a maximum linear distance from another port group of about 0.125 inch, or (b) a barrier designed or configured to create an enclosure between a lean, pre-mixed flame and a heating target, such that heat loss from the space is reduced or minimized, wherein the barrier is constructed from a non-combustible material.

4. The apparatus of claim 3, wherein the lean, premixed fuel/air mixture has a low NO_x emission.

5. The apparatus of claim 3, wherein the apparatus does not contain a means to blow air and operates as a natural draft system.

6. The apparatus of claim 3, wherein the apparatus comprises the burner plate and the barrier.

7. A method of burning a lean fuel/air mixture at substantially atmospheric pressure to generate hot combustion products, comprising: (a) providing a lean fuel/air mixture having a fuel/air equivalency ratio of less than unity; (b) directing the lean fuel/air mixture in a stream, the stream having a direction of flow, and an extent in a plane perpendicular to the direction of flow; (c) mounting a burner plate in the stream of the fuel/air mixture to divide the stream into an inner portion and an outer portion having substantially similar flow velocities, through the primary ports and secondary ports respectively; and (d) igniting the stream of the lean fuel/air mixture at the eddies, whereafter the eddies recirculate a portion of the hot combustion products into the stream to continuously re-ignite the fuel/air mixture, wherein the burner plate comprises a plurality of port group, wherein each port group comprises a primary ports surrounded by a plurality of secondary ports, and each port group has a maximum linear distance from another port group of about 0.125 inch.

8. A method burning a lean fuel/air mixture at substantially atmospheric pressure to generate hot combustion products, comprising: (a) providing an apparatus comprising a burner operating in free air to stably burn a premixed lean fuel/air mixture having a fuel/air equivalency ratio of less than unity to generate hot combustion products, and

(i) a burner plate comprising a plurality of port group, wherein each port group comprises a primary ports surrounded by a plurality of secondary ports, and each port group has a maximum linear distance from another port group of about 0.125 inch, or

(ii) a barrier designed or configured to create an enclosure between a lean, pre-mixed flame and a heating target, such that heat loss from the space is reduced or minimized, wherein the barrier is constructed from a non-combustible material; (b) providing a lean fuel/air mixture to the apparatus; and (c) igniting the premixed lean fuel/air mixture to produce a lean, pre-mixed flame.

9. The apparatus of claim 8, wherein the lean, premixed fuel/air mixture has a low NO_x emission.

10. The apparatus of claim 8, wherein the apparatus does not contain a means to blow air and operates as a natural draft system.

11. The apparatus of claim 8, wherein the apparatus comprises the burner plate and the barrier.