SWIRL BURNER FOR AMMONIA COMBUSTION

FIELD OF THE DISCLOSURE

The disclosure relates to ammonia combustion and more specifically, to swirl burners used to combust ammonia.

BACKGROUND

Ammonia is unsuitable for direct replacement of current hydrocarbon fuels used in burners such as propane or natural gas. Its flame speed is far lower than these hydrocarbon fuels, therefore it must be burned in a manner that accommodates that flame speed. For ammonia to be competitive for replacement of hydrocarbon fuels in existing combustion devices, its flame speed must be enhanced.

For ammonia, flame speed enhancement is commonly achieved by blending with another fuel such as hydrogen or hydrocarbon fuels (natural gas, propane, gasoline, etc.) For the case of hydrogen blending, hydrogen usually forms nearly half (by volume) of the total fuel charge, meaning ammonia is not the primary fuel source.

SUMMARY

Disclosed herein is a swirl burner for combusting ammonia with little to no hydrogen blending. The swirl burner receives flowing combustion oxidizer gas and gaseous ammonia into a mixing chamber. The ammonia enters tangentially to the flow of oxidizer gas to induce turbulent swirl. A nozzle introduces the combustion mixture of fuel and oxidizer gas into a flame holder in which the mixture combusts.

In general, an aspect disclosed herein is a method of burning gaseous ammonia including receiving a oxidizer gas into a chamber body such that the oxidizer gas generally flows in direction that extends along a longitudinal axis of the chamber body; introducing gaseous ammonia into the chamber body such that swirl is introduced into the gaseous ammonia; mixing the oxidizer gas and the gaseous ammonia to form a combustion mixture; igniting the combustion mixture, combusting the combustion mixture for a duration such that the gaseous ammonia is converted to combustion products.

Examples may include one or more of the following features. At least 50% of the gaseous ammonia can be converted to combustion products. At least 98% of the gaseous ammonia can be converted to combustion products. At least 99.9% of the gaseous ammonia can be converted to combustion products. The method may include combusting the combustion mixture for the duration to produce a resultant level of NO_xthat can be below a threshold value. The threshold value can be 10 ppm. The threshold value can be 2.5 ppm. The method may include combusting the combustion mixture for the duration to produce a resultant level of N₂O that can be below a threshold value of 10 ppm. Igniting the combustion mixture may include igniting the combustion mixture at a gas pressure in a range from 50 psi to 200 psi. Igniting the combustion mixture may include igniting the combustion mixture at a gas pressure in a range from 10 PSI to 20 PSI. The method may include introducing, during introducing gaseous ammonia, a flow of gaseous hydrogen into the chamber body at less than 25% v/v to the gaseous ammonia. The method may include terminating, following the igniting, the flow of gaseous hydrogen. The gaseous ammonia can be introduced into the chamber body in a direction normal to the longitudinal axis.

In general, an aspect disclosed herein is an ammonia combustion system a plurality of ammonia burners, each ammonia burner including a cylindrical chamber body; an intake conduit having a first end for receiving oxidizer gas and a second end coupled to one open end of the chamber body and the second end defining an opening having a cross-sectional area that is larger than a maximum cross-sectional area of the chamber body; a nozzle connected to an end of the chamber body opposing the oxidizer gas intake, the nozzle having an inlet opening and an outlet opening, where the outlet opening is enlarged or reduced in size relative to the inlet opening; a plurality of inlets extending through a sidewall of the chamber body, configured to receive gaseous ammonia at an angle relative to a central axis of the chamber body such that when oxidizer gas passes through the chamber body, swirl is induced in the gaseous ammonia; a flame holder surrounding the outlet opening of the nozzle and configured to confine a flame exiting the outlet opening, where an inner dimension of the flame holder is proportional to the opening angle of the nozzle; a fuel manifold, configured to receive pressurized gaseous ammonia and deliver gaseous ammonia at a reduced pressure to the plurality of inlets of each of the plurality of burners.

Examples may include one or more of the following features. The plurality of ammonia burners can be configured to receive pressurized gaseous ammonia from the fuel manifold. The plurality of ammonia burners can be configured to receive substantially unpressurized gaseous ammonia from the fuel manifold. The fuel manifold can enclose the chamber body of each of the plurality of burners. The fuel manifold can be configured to deliver the gaseous ammonia at a plurality of pressures to the plurality of burners. The chamber body can have a cylindrical shape. The chamber body can have a conical shape. The plurality of inlets can extend through the sidewall of the chamber body at an angle relative to a longitudinal axis. The inlets can be configured to form an acute angle with respect to an inner wall of the chamber body. The inlets can be configured to achieve a swirl number of at least 0.5. The oxidizer gas scoop, chamber body, and nozzle can be a unitary body. The nozzle can have an opening angle in a range from −20 to 20 degrees. The flame holder can be configured such that a flame exiting the outlet opening of the nozzle impinges an inner wall of the flame holder at a distance such that at least 50% of ammonia present in the flame can be combusted. A distance the nozzle extends into the flame holder can be configured induce toroidal reburn in uncombusted ammonia exiting the flame. The flame holder can define an internal volume configured to combust the gaseous ammonia. The flame holder may include a metal or a ceramic material. A sidewall of the flame holder can define a plurality of perforations. The chamber body can include a static turbine which may include a plurality of vanes. Each vane of the static turbine can be shaped such that an edge nearest the oxidizer gas intake forms a 0 degree angle with respect to the central axis of the chamber body and an edge nearest the nozzles forms a 60 degree angle with respect to the central axis of the chamber body. The flame holder can be configured to confine a flame exiting the outlet opening, where an inner dimension of the flame holder can be proportional to the opening angle of the nozzle. The flame holder can have a cross-sectional area that can be larger than the maximum cross-sectional area of the chamber body. The flame holder may include a thermal, chemical, and/or mechanical surface modification to a wall, an inner surface of a wall, or both.

Particular implementations of the subject matter described in this specification can be implemented so as to realize one or more of the following technical advantages.

The disclosed burner achieves extremely high thermal throughput (kW/Vol) compared to similar examples by using a nearly 100% unobstructed tube to introduce oxidation gas from an upstream flow.

The burner produces low levels of ammonia combustion products, such as unburned ammonia (NH₃), nitrogen oxide (NO_X), and nitrous oxide (N₂O) through swirl mixing of the fuel and combustion oxidizer gas and a flame holder designed to facilitate near-complete ammonia combustion.

The burner generates swirl without external energy input from electrical or mechanical sources, reducing the energy input into the system and increasing the stand-alone capabilities of the burner.

The burner can be designed to receive both pressurized and non-pressurized ammonia and oxidizer gas which increases the flexibility of deployment in various configurations.

The burner combusts ammonia without the need for hydrogen as a secondary fuel.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of an ammonia swirl burner system.

FIG. 2A is a schematic illustration of an ammonia swirl burner.

FIG. 2B is an exploded-view schematic illustration of the ammonia swirl burner of FIG. 2A.

FIGS. 3A and 3B are perspective-view schematic illustrations of an intake conduit.

FIG. 4A is a side-view schematic illustration of a chamber body including ports in the sidewall.

FIG. 4B is a cut-away side-view schematic illustration of the chamber body of FIG. 4A.

FIG. 4C is a cut-away top-view schematic illustration of the chamber body along the plane of the ports.

FIG. 4D is a cut-away side-view schematic illustration of a chamber body including a static turbine.

FIG. 5A is a perspective-view schematic illustration of a nozzle.

FIG. 5B is a cut-away side-view schematic illustration of the nozzle of FIG. 5A.

FIGS. 6A and 6B are diagrammatic illustrations of diverging and converging nozzles, respectively, and the flames produced by each.

FIG. 7A is a diagrammatic illustration of how three angles of a diverging nozzle define three recirculation zone volumes.

FIGS. 7B-7D are diagrammatic illustrations of the three recirculation zones of each of the three angles shown in FIG. 7A.

FIG. 8 is a diagrammatic illustration of a flame holder having perforated regions and secondary oxidizer gas flow interacting with the perforated regions.

FIG. 9 is a flow chart diagram of a method of burning gaseous ammonia.

In the figures, like references indicate like elements.

DETAILED DESCRIPTION

The systems and devices described herein facilitate ammonia fuels, or ammonia-hydrogen fuel blends, to be used as drop-in replacements for existing hydrocarbon burners, such as natural gas, propane, and butane-fueled burners. These hydrocarbon burners are already used around the world for any process that needs heating, such as duct burners for heat recovery steam generators, for material drying, or for boilers.

The systems and devices described herein can be used for any type of process heater where there is forced convection of oxidizer gas or lean combustion exhaust that constitutes an oxidizer gas. This burner could also be used in the case where compressed oxidizer gas is used, such as from an oxidizer gas compressor, or a turbine driven compressor like a turbocharging assembly in a vehicle or a chemical processing plant. Lastly, using the compressed fuel to induce an oxidizer gas could be used in non-forced convection applications, such as torches and burners.

This method of additional oxidizer gas entrainment through fuel jets from the ports creates circumstances where the swirl burner can be overfired purposely, with additional fuel entraining the required mixture for complete combustion. The ammonia swirl burner design described herein can pull additional fuel, e.g., gaseous ammonia, through the chamber body by adjusting the angle of entry of the tangential fuel ports. While tangential entry occurs perpendicular to the flow of oxidizer gas through the chamber body, adjusting the angle from 90° to <90° entrains additional oxidizer gas and pulls it through the chamber body using pre-existing fuel pressure. Burners with this off-tangent port angling can be tuned to have a broad range of low-emission operating heat rates and be turned up or down to match heating demand under variable circumstances.

With this technology, hydrogen is optionally introduced with the gaseous ammonia to enhance flame properties, such as flame speed, but at much lower percent volume rates (0-10%) to achieve the same efficiency and emissions benefits. The technology provides similar efficiency as hydrocarbon burners, while achieving low criteria emissions (e.g., N₂O, NO_x) and negating CO₂emissions. Optionally, hydrogen can be used as a pilot fuel to begin combustion or can be omitted entirely.

FIG. 1 is a schematic illustration of a combustion system 100 which includes an array of swirl burners 110. One of the swirl burners 110 is denoted specifically, though the array includes five swirl burners 110, each having the same configuration. The combustion system 100 is configured to receive environmental oxidizer gas at standard temperature and pressures, though in some examples, the combustion system 100 can be arranged to receive flowing oxidizer gas from a fan, from an oxidizer gas manifold, or from a pressurized source (e.g., a compressor). In an example, the oxidizer gas is air.

In other examples, the combustion system 100 illustrated in FIG. 1 is arranged to receive lean combustion exhaust with an oxygen volume fraction in the range of 10% to 20.9% as an oxidizer gas. In this case, the oxidizer gas could be at elevated temperatures in the range of 100 to 1000 degrees Celsius (° C.) and at non-standard pressure (e.g., greater or lower than atmospheric pressure). The combustion system 100 could be arranged to receive lean combustion exhaust in a duct located downstream of a combustor, gas turbine, or reciprocating engine.

Each of the swirl burners 110 includes an intake conduit 130 which receives the oxidizer gas. The intake conduit 130 directs the oxidizer gas into a combustion chamber body (shown with reference to FIG. 2).

A fuel manifold 120 is present if there is an array of swirl burners 110, as in FIG. 1 and distributes fuel to the chamber body of the individual swirl burners 110 for mixing with the oxidizer gas to create the combustion mixture. The fuel manifold 120 has inlets 122 which receive fuel from external sources at a gas pressure in a range from 50 PSI to 200 PSI and an inner chamber which distributes the received fuel. The fuel manifold 120 encloses the mixture chamber body of each of the swirl burners 110 such that fuel enters through the ports in the walls of the mixture chamber body. The fuel manifold 120 can optionally be divided into multiple chambers to separate different fuels or fuel streams at different pressures.

The ports of the chamber body introduce the ammonia at an angle with respect to the flow direction of the combustion, substantially parallel with the longitudinal axis of the swirl burners 110. The angle at which the ammonia is introduced induces turbulent swirl in the ammonia and oxidizer gas which increases the mixture rate and uniformity of the resultant combustion mixture.

A mixture of fuel and oxidizer gas flows through a nozzle and into a flame holder 140 within which the mixture is combusted in a flame. The flame holder 140 is designed to encompass the flame during combustion of the ammonia and extends from the nozzle by a distance sufficient to enclose the entirety of the flame based on the exit angle of the nozzle and the flow rate of the combustion mixture. The flame holder 140 increases the combustion time of the ammonia flame and protects the flame from cooling effects of secondary oxidizer gas in the surrounding environment, e.g., gas not flowing through the swirl burners 110. By prolonging a combustion duration of the flame and protecting the flame from cooling effects, ammonia can burn near-completely (e.g., >98% combustion, e.g., 99.9% efficiency), resulting in low emissions, high efficiency (e.g., a mass ratio between fuel burned and fuel supplied, e.g., kg_burned/kg_supplied), and high power density (e.g., kW/liter displacement volume of the burner, e.g., power/volume) compared to hydrocarbon flames. The combustion of ammonia generates heated gas which exits the flame holder 140 along the flow path direction.

Ignition of the combustion mixture takes place either within the flame holder 140, or adjacent an exhaust opening of the flame holder 140. This prevents combustion from occurring within the main chamber body 150 and prevents transfer of combustion heat to the body 150 which may reduce the flame energy for mixture combustion.

In general, the combustion mixture is ignited within the burners 110 by an ignition source such as, but not limited to, a spark (e.g., a spark plug or electrode), a hot surface ignitor (e.g., a glow plug, or silicon-carbide element), a jet igniter, or a pilot flame. The ignition source can be mounted to the flame holder 140 (e.g., through a wall or at a rim of the flame holder 140), or adjacent the flame holder 140. In some examples, ignition occurs by adjacent lit burners (e.g., a flame jumps from an opening of one flame holder 140 to the opening of an adjacent unlit burner. The ignited flame propagates down through the flame holder 140 to the nozzle, where it then reaches a steady operating point, e.g., sustained combustion.

In some examples, the combustion system 110 is ignited by a flame lance, where a flame jet is directed perpendicular to the direction of flow of the flame holder 140 of each burner 110. The flame jet is directed to all the burners 110 in the system 100 thereby igniting the combustion mixture.

Referring now to FIGS. 2A and 2B, the swirl burner 110 is shown in a perspective view and an exploded view, respectively. The swirl burner 110 is configured to mix gaseous ammonia fuel with entrained oxidizer gas and combust the mixture to produce heated gas with low combustion emissions, high energy density, and near-complete combustion of the ammonia. Examples of combustion emissions which are reduced by the swirl burner include, but are not limited to, NH₃, NO_X, and N₂O. The swirl burner 110 can produce a level of combustion emissions below a threshold level which can depend on the type of combustion emissions measured. For example, the swirl burner can produce a level of NO_Xbelow a threshold value of 10 ppm (e.g., below 5 ppm, below 2.5 ppm, below 2 ppm, or below 1 ppm). In another example, the swirl burner can produce a level of N₂O below a threshold value of 1 ppm (e.g., below 0.5 ppm, or below 0.25 ppm). The orientation of the swirl burner 110, shown as the dashed line through FIGS. 2A and 2B, defines a flow path 170 from the intake conduit 130 to the flame holder 140 which substantially is parallel with the longitudinal axis of the swirl burner 110 when assembled.

The swirl burner 110 receives oxidizer gas through the intake conduit 130 arranged at one end of the swirl burner 110. The intake conduit 130 has a hollow trumpet-like geometry which is open on both ends, e.g., one end of the intake conduit 130 has a larger opening cross section than the opposing end. The inlet 132 “scoop” should be the largest cross section of the burner 110 and reduces to the chamber body 150 cross section. The cross section can then further decrease at the nozzle 160 before the flow enters the flame holder 140 volume. Oxidizer gas enters the larger opening having a dynamic pressure (e.g., which is proportional to velocity) and a static pressure. The oxidizer gas travels through the intake conduit 130 to the smaller opening during which the static pressures increases and the dynamic pressure of the gas decreases, e.g., some of the dynamic pressure is converted to static pressure which pushes the gas through the device from the intake conduit 130 toward the flame holder 140.

The intake conduit 130 is connected to the mixing chamber body 150 such that oxidizer gas exiting the smaller end of the intake conduit 130 enters the inner volume of the chamber body 150. The chamber body 150 provides a mixing volume in which oxidizer gas entering the chamber body 150 from the intake conduit 130 is mixed with gaseous ammonia to create the combustion mixture.

The overall ratio of cross sections between the inlet 132 and the chamber body 150, defined as the cross-sectional area of the inlet 132 to the cross-sectional area of the chamber body 150, can vary with the ambient oxidizer gas pressure. If the ambient oxidizer gas is at a lower pressure, a slightly larger inlet 132 cross-sectional area relative to the main body can be used. This has to do with the conversion of dynamic pressure to static pressure. The gas is compressed more when starting from a lower pressure. The opposite can be considered when the oxidizer gas starts at a relatively higher pressure. The conversion of dynamic to static pressure still happens, but the change in oxidizer density is relatively less. The inlet 132 cross section can be relatively larger than the chamber body 150 cross section to cause a compression of the oxidizer gas due to Bernoulli's principle. The conversion of dynamic pressure to static pressure helps overcome the pressure restrictions of the nozzle and combusting mixture downstream. The densification of the oxidizer gas can keep power (kW) output of the burner relatively higher than not compressing the oxidizer gas.

The chamber body 150 includes ports 152 around the circumference. The ports 152 are holes through the wall of the chamber body 150 which connect the ammonia in the surrounding fuel manifold 120 to the inner volume of the chamber body 150. The ports 152 are configured to introduce the fuel into the chamber body 150 at an angle with respect to the flow path 170 which induces turbulent swirl in the oxidizer gas flow. The induced swirl increases the mixing speed of the oxidizer gas and the gaseous ammonia beneficially increasing the rate of fuel oxidation in the mixture, thereby generating increased heat, and achieving maximal combustion efficiency when the mixture is combusted.

The end of the chamber body 150 opposing the intake conduit 130 is connected to a nozzle 160, which constricts the flow of the combustion mixture to increase the static pressure. The combustion mixture exits the nozzle 160 through an outlet opening 162. The shape of the outlet opening 162 determines the shape of the ammonia flame when the combustion mixture is ignited. The outlet opening 162 can be converging, or diverging, with respect to the flow path 170 which influences the combustion duration of the ammonia flame.

The swirl burner 110 includes a cylindrical or conical cup-shaped flame holder 140 which protects the flame from secondary oxidizer gas which can cause cooling of the flame and incomplete combustion of the fuel/oxidizer mixture, known as quenching. The nozzle 160 extends through a base by a distance and the combusted gases exit through an opening 142. The flame holder 140 can be composed of a durable material which is resistant to effects from the heat of ammonia combustion, e.g., a metal or a ceramic material. Implementations of the flame holder 140 can include solid sidewalls, perforated sidewalls, or a combination. Implementations of the flame holder 140 can include modifications which perform catalytic functions. The modifications can include thermal or chemical surface treatments, coatings, or inserts which are attached to or contained by the flame holder 140. The modifications can enhance combustion rate, and/or help maintain steady combustion through reactions of fuel and/or oxidizer.

The flame holder 140 is cylindrical, or conical, to maintain a toroidal swirling motion of the oxidizer gases in a recirculation zone between the inner wall of the flame holder 140 and the nozzle 160. The recirculation zone consists of the inner volume of the flame holder 140 below where the flame cone impinges the inner wall. The revolved profile of the flame holder 140 influences the degree of toroidal recirculation and consequent reburn and can be rectangular, rounded, or trapezoidal to generate cylindrical, toroidal, and conical geometries of the inner volume.

The combustion mixture exiting the nozzle 160 is ignited and the flame is encircled within the flame holder 140. The dimensions of the flame holder 140 are sufficient to contain the entire flame within the inner volume and can be designed dependent on several factors. For example, a flame holder 140 with a large length along the flow path fully encloses a flame produced from a combustion mixture exiting the nozzle 160 at high velocities. In another example, a flame holder 140 with a wide diameter allows the flame to near-fully combust the gaseous ammonia in the combustion mixture before the flame contacts the inner wall of the flame holder 140.

The internal volume of the flame holder 140 is a factor in determining the permitted burn duration of the combustion mixture. Without wishing to be bound by theory, burn duration can be quantified as the time between fuel entering the flame-front (e.g., initiation) to the time where the mixture no longer produces heat through reaction (e.g., flame extinction). The permitted burn duration should be equal to or exceed the time needed to fully combust fuel and oxidizer gas under all operating conditions. In general, flame extinction can occur inside the flame holder or outside the flame holder after flame mixes with secondary oxidizer gas stream. The diameter of the flame holder 140 affects the relative volume of the flame recirculation zone. The diameter of the flame holder 140 is sufficient to produce a recirculation zone no smaller than 10% of the total flame holder volume. Further, in general, the flame holder 140 has a diameter sufficient to allow no less than 50% of the gaseous ammonia present in the combustion mixture to combust before the resulting flame contacts the inner wall. In some examples, between 50% and 75% of the gaseous ammonia combusts before contacting the inner wall. Significant combustion activity continues to occur above the impact point in the remaining volume of the flame holder. The heated combustion products escape the end of the flame holder 140 furthest from the nozzle 160 and continue along the flow path 170.

Further details of the components of the combustion system 100 are discussed with reference to the following figures. FIGS. 3A and 3B show two perspective angles of the intake conduit 130. The intake conduit 130 has a trumpet-like geometry having an inlet 132 and an exhaust 134. Other examples can include a cone, or a frustum. In geometry, a frustum is defined as the portion of a solid (e.g., a pyramid, or a cone) that lies between two parallel planes cutting this solid. In the case of a pyramid, the base faces are polygonal, the side faces are trapezoidal.

The inlet 132 has a larger opening area than the exhaust 134 such that the dynamic and static pressure of oxidizer gas received into the inlet 132 is increased before exiting the exhaust 134. Said another way, the inlet 132 has a higher maximum cross-sectional size relative to the exhaust 134, and/or maximum cross-sectional area of the inner volume of the chamber body 150. In some examples, the opening area of the inlet 132 has a ratio of 1:1 with the area of the exhaust 134. In more examples, the ratio of the inlet 132 to the exhaust 134 areas is less than 4:1. For an intake conduit 130 having a circular cross section, an intake 132 having twice the diameter of the exhaust 135 is preferred. The inlet 132 being larger than the exhaust 134 primarily allows some conversion of dynamic pressure to static pressure to maintain the same flow velocity throughout the chamber body 150 of the swirl burner. The flow velocity through the chamber body 150 and nozzle 140 is maintained relative to the free-stream outside the burner 110 as free-stream velocity is approximately the highest achievable flow velocity and results in the highest potential power density. For reference, the free-stream oxidizer gas generally refers to the oxidizer gas upstream of and surrounding an aerodynamic body, such as the burner 110, that is, before the body has a chance to deflect, slow down or compress the oxidizer gas.

The inlet 132 has a curved trapezoidal shape, e.g., a portion of a circular segment. In other examples, the inlet 132 can be circular, triangular, oval, arcuate, or polygonal in cross section. Polygonal examples can be regular or irregular. The exhaust 134 has a circular shape which matches the cross-sectional shape of the chamber body 150. The intake conduit 130 can be formed, cast, machined or 3-D printed from a metallic, polymeric, or ceramic material. In one example, the intake conduit 130 is formed from stainless steel which increases the durability of the intake conduit 130. The flow path length of the intake conduit 130 can be varied to suit a particular application. In some examples, the intake conduit 130 is angled relative to the chamber body 150. Angling the intake conduit 130 relative to the main chamber body 150 offers the ability to keep the intake 132 scoop normal to the flow of oxidizer gas and facilitates positioning the opening 142 at an angle relative to the flow of free-stream oxidizer gas. This allows increased homogeneity in the exhaust mixture from the combustion system 100 having short burner 110 length.

A high overall burner 110 length is desirable to promote laminar flow within the nozzle 140. Laminar flow helps the tangential fuel jets reliably induce turbulent swirl, and/or induce a consistent swirl in a chamber body 150 having a fixed swirl-vane (as shown herein with respect to FIG. 4D). A low overall burner 110 length may be desired for physical size constraint reasons, or to minimize pressure loss from wall friction between oxidizer gas and the intake conduit 130.

The chamber body 150 provides a chamber in which the oxidizer gas received from the intake conduit 130 is mixed with fuel to produce a combustion mixture. The chamber body 150 includes an arrangement of ports 152 configured to induce swirl in the combustion fuel mixtures. FIGS. 4A-4C show various views of the mixing chamber body 150 including the ports 152 which connect the surrounding fuel manifold 120 to the inner volume of the mixing chamber body 150. FIG. 4A is a side-view of the chamber body 150 and the ports 152 and FIG. 4B is a cut-away of the chamber body 150 through two ports 152. Oxidizer gas is received from the intake conduit 130 along the flow path 170 having a substantially streamlined, or laminar, flow having low turbulence. As the oxidizer gas follows the flow path 170 and the passes the ports 152, gaseous ammonia from the fuel manifold 120 enters the chamber body 150 and is mixed with the flowing oxidizer gas. The vapor pressure of the ammonia fuel from the manifold 120 drives the fuel into the chamber body 150.

The chamber body 150 of FIGS. 4A-4C is cylindrical in shape and has a circular cross sectional profile transverse to the flow path 170, though other geometries are possible including non-uniform cross-sectional profiles. Some implementations of the chamber body 150 have a conical, rectangular, or frustum-like shape. Some examples of the cross-sectional profile of the chamber body 150 have a larger opening at one end of the chamber body 150 than the other end, e.g., an expanding cross-sectional profile.

The ports 152 are holes machined into the sidewall of the chamber body 150 connecting the inner volume 154 to the environment surrounding the ports 152. The port 152 convert static pressure (e.g., measurable PSI) of the fuel into dynamic pressure (e.g., velocity/momentum) and to impart swirling motion in the fuel within the chamber body 150. The ports 152 can be cylindrical to minimize flow resistance of fuel entering the inner volume 154 of the chamber body 150 and create a flow of fuel having momentum in the direction of the ports 152 are oriented. The number, geometry, and orientation of the ports 152 can be configured to achieve high fuel flow rates and high mixing swirl turbulence when combined with the oxidizer gas in the chamber body 150. Examples of variable geometry parameters of the ports 152 include cross-sectional shape (e.g., circular, oval), or greatest dimension (e.g., diameter). The inlet ports 152 are angled such that the fuel flow impinges the inner wall of the chamber body near to the opening of the ports 152. The resultant fuel jets induce swirl upon impact of the inner wall of the chamber body 150 and change direction to continue moving along the inner wall. Impact with the wall causes the jets to redirect in a circular manner, inducing swirl.

In some examples, the ports 152 can be shaped to form nozzles having convex or concave openings into the inner volume of the chamber body 150. In yet more examples, the ports 152 can include injectors which extend from the inner wall of the chamber body 150 into the inner volume to cause the ammonia to enter at a point radially closer to the flow path 170. The ports 152 can be formed to include nozzles to cause or increase a jet-like flow of fuel into the chamber body 150. In some examples, the nozzles can be a straight section of small-diameter tubing to create a tube where the length (L) of the ports 152 is greater than the diameter (D), e.g., L>D.

Ports 152 having a converging (concave) opening into the inner volume of the chamber body 150 restricts flow to create a more-narrow, higher-speed jet in which conversion of static-pressure to dynamic pressure (velocity) of fuel occurs. Higher velocity jets increase fuel momentum transfer in the tangential direction of where the ports 152 are aligned, relative to a wider and slower jet. Ports 152 having a diverging (convex) opening into the inner volume of the chamber body 150 induce diffuse flow compared to straight-walled or concave openings. In some examples, diverging openings are beneficial in examples in which the chamber body includes a fixed-vane swirler installed.

In FIG. 4B, a planar cross-sectional view of the chamber body 150 parallel with the flow path 170 is shown. The ports 152 are circumferential around a plane (dotted line) perpendicular to the flow path 170, though in some examples the ports 152 are not oriented on a common plane. In FIG. 4C, a planar cross-sectional view of the chamber body 150 parallel with the plane, e.g., perpendicular to the flow path 170, is shown.

Referring now to FIGS. 4B and 4C, the angling of the ports 152 relative to the flow path 170 causes turbulent swirl when the fuel enters the chamber body 150 through the ports 152 and mixes with the oxidizer gas. The ammonia entering the chamber body 150 has momentum in the direction of the ports 152, which are angled at θ and ϕ with respect to the flow path 170. Equations for calculating swirl number are known in the art, though examples can be found in at least Swirl Flows and Combustion Aerodynamics (see Gupta, A. K., Lilley, D. G., and Syred, N., Swirl Flows, Abacus Press, Kent, England (1984), and Beer, J. M., and Chigier, N. A., Combustion Aerodynamics, Applied Science Publishers, London, England (1972), which are incorporated herein by reference).

Implementations in which the ports 152 are angled with respect to the flow path 170 entrain more oxidizer gas which can change the heat rate of the burner (e.g., overfiring, e.g., more fuel and/or oxidizer gas has been provided to the burner 110 over and above a designed limit) without substantially increasing emissions or reducing efficiency. Values of θ closer to parallel with the flow path 170 can entrain more oxidizer gas and provide a larger range of heating rates. In some examples, the burner 110 can be “overfired” by 10% for example, if the fuel flowrate were increased. Values of θ near to perpendicular to the flow path 170 increase swirl to increase efficient combustion. The angles θ and ϕ determine the momentum components of the fuel along flow path 170 (a linear momentum component) and transverse to flow path 170 (an angular momentum component), respectively.

Without wishing to be bound by theory, angular momentum transfer is governed by the angle ϕ as shown in FIG. 4C. At an angle value of 0°, fuel enters the chamber body 150 normal to the walls of the cavity containing flow path 170. This radial entry, e.g., an angle value of 0°, imparts no angular momentum and no swirl induction. As you increase ϕ, the angular momentum and swirl of the flow of fuel increases.

The theoretical maximum angle ϕ is governed by the geometry of the chamber body 150 cavity which creates flow path 170 and the wall thickness of the chamber body 150. The maximum angular momentum is achieved at a ϕ angle of ϕ=sin⁻¹r₁/r₂. At this angle, which increases for larger diameter tubes, the flow of fuel enters at an angle of ϕ relative to normal of the outer radius and enters at 90 degrees relative to normal of the inner radius. The inner radius is the radius from the flow path 170 to the inner wall of the chamber body 150 while the outer radius is the radius from the flow path 170 to the outer wall of the chamber body 150. There is a different maximum ϕ angle relative to the outer wall to get a tangent flow at the inner wall depending on a thickness of the wall. At this angle, all momentum from the fuel flow is converted to angular momentum in the swirling fuel and oxidizer gas mixture. The possible range of ϕ includes

$0 \leq ϕ \leq \sin^{- 1} \frac{r_{1}}{r_{2}}, e . g ., (0.33 * (\sin^{- 1} \frac{r_{1}}{r_{2}}) \leq ϕ \leq \sin^{- 1} \frac{r_{1}}{r_{2}}, 0.5 * (\sin^{- 1} \frac{r_{1}}{r_{2}}) \leq ϕ \leq \sin^{- 1} \frac{r_{1}}{r_{2}}, or 0.75 * (\sin^{- 1} \frac{r_{1}}{r_{2}}) \leq ϕ \leq \sin^{- 1} \frac{r_{1}}{r_{2}}) .$

Without wishing to be bound by theory, the swirl number, S, is defined as proportional to a ratio of the angular momentum to the linear momentum in which higher angular:linear ratios have higher S values. Increasing the value of θ increases the dynamic pressure of the combustion mixture and entrains additional oxidizer gas from the intake conduit 130. Increasing ϕ increases the swirl number, e.g., a measure of the angular velocity, of the combustion mixture. In general, the chamber body 150 inducing a swirl number of at least 0.5 (e.g., at least 0.75, at least 1, or at least 2) in the combustion mixture along the flow path 170.

In general, θ is a positive value indicative of the linear momentum component of the fuel along the flow path 170 and ϕ is a positive value indicative of the angular momentum component orthogonal the flow path 170. The upper values of θ and ϕ are limited by the sidewall thickness of the chamber body 150 and the diameter of the ports 152, though θ can be in a range from 0° to 60° (e.g., from 20° to 60°, from 25° to 50°, from 30° to 40°, or from 35° to) 55° and ϕ can be in a range within 10° from tangent to the interior wall of the chamber body 150 (e.g., from 20° to 60°, from 25° to 50°, from 30° to 40°, or from 35° to) 55°. In some examples, θ is zero and the fuel enters the chamber body 150 parallel to the plane of the ports 152.

In some implementations, the chamber body 150 includes a static turbine (e.g., a stator) to induce tangential swirl in the oxidizer gas flow in addition to the swirl induced by the angular orientation of the ports 152. FIG. 4D shows the chamber body 150 having a static turbine 180 along the flow path 170 upstream of the ports 152. The turbine 180 includes two example vanes 182 oriented to form an angle with respect to the flow path 170 (shown by the arrow). The turbine 180 can have any number of vanes 182 and a vane angle (α) in a range from 0° to 60° (e.g., 10° to 50°, 15° to 45°, 25° to 50°, or 35° to) 55°. Steeper vane angles result in high degree of flow disturbance, restrict flow through the chamber body 150, and induce higher S values, which are beneficial to clean and efficient combustion. In some examples, the vane angle is progressive, starting from parallel to the flow (0°) and increasing to a maximum vane angle over the length of the vanes 182. The turbine 180 may be attached to an opening of the chamber body 150 (e.g., between the chamber body 150 and the intake conduit 130), or pressed into the chamber body 150, such as in FIG. 4D.

The chamber body 150 may be necked or expanded to affect the oxidizer gas flow rate through the tube. Said another way, the ratio of the opposing opening areas of the chamber body 150 may be greater than 1, or less than 1. In one example, the opening of the chamber body 150 receiving oxidizer gas from the intake conduit 130 is larger than the opening providing the combustion mixture which increases entrainment into the chamber body 150 and increases the dynamic pressure at the combustion mixture end. In some examples, the chamber body 150 may contain a concentric tube to introduce additional fuel into the oxidizer gas charge, in addition to the fuel introduced by the ports 152.

The combustion mixture exits the chamber body 150 along the flow path 170 and enters the nozzle 160 through an inlet opening 166. Some examples of the chamber body 150 and nozzle 160 include male and female threading such that the chamber body 150 can be reversibly secured to the inlet opening 166. FIGS. 5A and 5B show perspective and cross-sectional views of the nozzle 160, respectively.

The chamber body 150 is secured within the nozzle 160 to a depth, e.g., the depth of the female threads. The inner wall 164 can converge or diverge from parallel to the flow path 170 through the length of the nozzle 160. Said another way, the inner wall 164 can narrow or widen between the inlet opening 166 and the outlet opening 162. In the example of FIG. 5B, the inner wall 164 converges to a throat 168 having a smaller radius than the receiving end of the nozzle 160. The throat 168 converges further into the outlet opening 162 producing a convergent nozzle 160. The angle of the outlet opening 162 with respect to the tangent of the flow path 170, shown as a, generally corresponds to the shape of the combustion flame such that a convergent nozzle 160 produces a converging flame, while a diverging nozzle 160 produces a divergent flame. In the example of FIG. 5B, a is less than 90° for a convergent nozzle 160, while a is greater than 90° for a divergent nozzle 160A. A convergent nozzle 160 results in increased angular velocity of the swirled oxidizer gas-fuel mixture, a larger recirculation zone (described further with respect to FIG. 7), and restricts the flow of gas through the swirl burner 110, resulting in lower burning rate, e.g., power level. A divergent nozzle 160 creates reduced pressure restriction and permits a greater oxidizer gas-fuel mixture ratio. In general, the angle of the walls should be within 20° of the direction of the flow path 170, corresponding to values of a in a range from 70° to 110°.

To illustrate the flames produced by convergent and divergent nozzles and provide illustrative examples of the nozzle 160, two example nozzles, nozzle 660 and nozzle 662, are shown in FIGS. 6A and 6B along with flames produced by the respective nozzles 660, 662. The nozzle 660 is a divergent nozzle which results in a diverging flame. The nozzle 662 is a converging nozzle which results in a flame having convergent portion exiting the nozzle 662 and a divergent portion past a convergence point. As an example, the flame exiting the nozzle 662 includes a combusting flow of fuel which is combusting at or near atmospheric pressure (e.g., within 10 psi of local atmospheric pressure, within 5 psi of local atmospheric pressure, e.g., in a range from 10 psi to 20 psi, e.g., about 15 psi).

The angle of the outlet opening 162 changes where the flame impinges on the flame holder 140, which affects flame quenching, e.g., heat-loss of the flame to the flame holder 140, among other things. Referring now to FIGS. 7A-7D, schematic illustrations depicting the revolved profile of an exemplary diverging nozzle 760 and a flame holder 740 are shown. The nozzle 760 and flame holder 740 can provide the nozzle 160 and flame holder 140 of the swirl burners 110. The view of FIG. 7A shows the revolved profile as a radial cross section between the flow path 770 to the flame holder 740 and the recirculation zone 790, which radially surrounds the nozzle 760. The recirculation zone 790 is an area within the flame holder 740 between where the flame impinges the flame holder 740 and the outlet opening of the nozzle 760, shown in shaded regions in FIGS. 7A-7D. The circular arrow represents the induced reburn circulation pattern as a portion of the combustion mixture which impinges the inner wall of the flame holder 740 is cooled and returns to the nozzle along the flame holder 740. The induced reburn pattern is toroidal and surrounds the nozzle 760, forming an induced toroidal reburn of uncombusted ammonia exiting the flame. The toroidal reburn beneficially consumes nitrogen oxides and nitrous oxide in a secondary zone of turbulent mixing which promotes complete combustion.

FIG. 7A illustrates three exemplary opening angles, a, of the nozzle which produce different recirculation zone volumes. FIGS. 7B-7D are schematic illustrations of a recirculation zone 790 at three opening angles of FIG. 7A, showing the comparative size (e.g., the shaded regions including the circular arrow) at α₁, α₂, α₃, respectively. The height, h, of the nozzle 760 relative to the base of the flame holder 740 changes the volume of the recirculation zone 790. Larger h values create higher volumes and increase toroidal recirculation.

The opening angle of the nozzle 760 is shown as angles α₁, α₂, α₃. All three values of a are >90° which defines the nozzle 760 as a divergent nozzle 760. Higher opening angles with respect to the flow path 770 produce wider flames and lower impingement points against the inner wall of the flame holder 740. For example, the highest depicted angle, α₁, shown in FIG. 7B, produces the smallest recirculation zone 790, while the lowest angle, α₃, produces the largest recirculation zone 790. The geometry of the flame holder 140 facilitates a shaped flame by protecting the flame from external secondary oxidizer gas flow and inducing a degree of recirculation of combustion products, helping to prolong combustion duration and decrease emissions.

As mentioned herein, some examples of the flame holder 140 include perforations in the sidewall. Referring to FIG. 9, a schematic illustration of a diverging nozzle 860 is shown extending into a flame holder 840 by a distance, h, and producing a flame. The volume of the flame holder 740 enclosed below where the flame impinges the inner wall of the flame holder 840 and the nozzle 860 is the recirculation zone 890.

The flame holder 840 includes perforated regions 842 and 844 which are portions of the sidewall which include perforations. Examples of the perforations can be slots, or circular holes, or the regions 842 and 844 can be formed of perforated structures such as foams or meshes. The perforations fluidically connect the volume of the flame holder 840 to secondary oxidizer gas surrounding the flame holder 840, labelled as “Oxidizer gas flow” in FIG. 8.

The perforated region 842 is above the point at which the flame impinges the flame holder 840 and allows a small diffusion of oxidizer gas from the free stream around the flame holder 840 into the reaction zone which promotes clean (e.g., high efficiency) combustion without increasing nitrogen oxides or quenching the flame. In one example, the primary oxidizer gas and fuel entering from the swirling chamber are fuel-rich, and an additional quantity of oxidizer gas is beneficial to complete the burn.

The perforated region 844 is below the point at which the flame impinges the flame holder 840 and fluidically connects the recirculation zone 890 to the secondary oxidizer gas flow. The secondary flow can provide the recirculation zone 890 with secondary oxidizer gas to increase the efficiency of the toroidal reburn.

A method of burning gaseous ammonia which can be used in the systems and devices described herein is shown in the flowchart diagram of FIG. 9. The method includes receiving an oxidizer gas into a chamber body such that the oxidizer gas, e.g., oxidizer gas, flows along a longitudinal axis of the chamber body (step 902). The oxidizer gas can be introduced into the chamber body by a flow of gas from an intake conduit, e.g., intake conduit 130. In some examples, the intake conduit receives atmospheric oxidizer gas. In other examples, the intake conduit received lean combustion exhaust.

The method includes introducing gaseous ammonia into the chamber body in a direction normal to the longitudinal axis such that swirl is introduced into the gaseous ammonia and the oxidizer gas and the gaseous ammonia form a combustion mixture (step 904). A fuel, e.g., gaseous ammonia, is introduced through ports in the sidewall of the chamber body which fluidically connect the chamber body inner volume to the surrounding environment. In implementations in which an array of burners is present, a fuel manifold surrounds the chamber bodies of the burners and provides fuel to the inlets of each of burners.

The fuel is introduced at an angle with respect to the longitudinal axis of the burner, also known as the flow path 170. The angle at which the fuel is introduced induces an amount of turbulent swirl in the fuel and the oxidizer gas. In some further examples, the angle at which the fuel is introduced induces additional flow of oxidizer gas into the chamber body from the intake. The mixing of the gaseous ammonia fuel and the oxidizer gas creates a combustion mixture.

The systems and devices described herein are designed to efficiently and completely combust gaseous ammonia fuel in the absence of additional hydrogen gas. However, a percentage (e.g., 10% v/v) of hydrogen gas introduced with the gaseous ammonia can increase the flame speed of the ammonia flame and increase the combustion efficiency of the reaction, thereby reducing the levels of undesirable emissions in the hot gas exiting the flame holder. Optionally, the method includes introducing a flow of gaseous hydrogen with the gaseous ammonia (step 906). The flow of gaseous hydrogen can remain below a maximum threshold for the duration of the combustion, or solely for ignition. In one example, the ratio of hydrogen gas to gaseous ammonia is 25% v/v or less (e.g., 10% or less, 5% v/v or less, or 2% v/v or less). The flow of hydrogen is reduced (e.g., eliminated) once the flame is lit.

The method includes igniting the combustion mixture (step 908). The combustion mixture can be ignited with a spark at an outlet opening of a nozzle, such as with an affixed electrically-sparked spark plug, hot surface ignitor (e.g., glow plug), or pilot flame.

Optionally and in methods employing step 906 in which hydrogen was introduced, the method includes terminating the flow of hydrogen gas (step 910).

The method includes permitting the combustion mixture to combust for a duration such that the gaseous ammonia is converted to combustion products (step 912). The combustion duration is a measure of the time the combustion reaction is allowed to take place in which the combustion mixture is combusted to form the combustion products, by-products, and heat. The combustion duration depends on parameters of the swirl burners, such as the geometry of the flame holder, the nozzle opening geometry, the distance by which the nozzle extends into the flame holder, the amount of swirl induced in the combustion mixture, and the dynamic pressure of the combustion mixture exiting the nozzle.

As gaseous ammonia has a low laminar flame speed (e.g., ˜7.0 cm/s) compared to other combustion fuel gases, such as hydrogen (e.g., ˜250 cm/s), the combustion duration is higher than comparable fuels.

While this specification contains many details, these should not be construed as limitations on the scope of what may be claimed, but rather as descriptions of features specific to particular examples. Certain features that are described in this specification in the context of separate implementations can also be combined. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple embodiments separately or in any suitable sub-combination.

SWIRL BURNER FOR AMMONIA COMBUSTION

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