Open Tip Burner Assembly for Waste Gas Flares and Methods of Using the Same

This priority to U.S. Provisional Application No. 63/662,155 filed on Jun. 20, 2024. The entire content and disclosure of which is incorporated herein by reference in its entirety.

The field of the disclosure relates generally to burners for destroying a flammable waste gas, and more specifically, to burner assemblies for use in ultra-low nitrous oxide emission and high oxygen stack concentration waste gas burner applications.

Control of greenhouse gas (GHG) emissions in waste gas from landfills is mandated by the Environmental Protection Agency (EPA), and GHG reduction projects may be undertaken on other waste gas sources, such as anaerobic digesters and coal mines, to earn carbon dioxide credits. Various combustion devices exist that operate to reduce GHG emissions by combusting flammable gas (e.g., methane) present in the waste gas. Methane, on a ton per ton basis, has a Global Warming Potential (GMP) 25 to 85 times greater than carbon dioxide (CO). Landfill waste gas is typically about 50% methane (by volume, v/v), anaerobic digester waste gas is typically about 60% v/v methane, and coal mine waste gas is between 20 to 95% v/v methane. Burning one ton of methane (with a molecular weight of 16.04) produces 2.75 tons of CO(molecular weight of 44.01), resulting in a net GMP reduction of 22 to 82 tons of carbon dioxide equivalent.

Combusting methane produces primarily COand water. The methane combustion process also produces small amounts of nitrous oxides (NO) and carbon monoxide (CO). Landfill gas has trace amounts of various non-methane organic chemicals (NMOCs) that are not fully destroyed in the combustion process. State and federal air pollution laws regulate the allowable amount of NO, CO, and NMOCs in the exhaust of the combustion device. NOand CO emissions are typically expressed in either pounds per million BTUs combusted (#/MM BTU) or in terms of parts per million (ppm) measured in the stack, corrected to 3% stack oxygen.

Enclosed combustion devices, referred to herein as enclosed flares, produce fewer emissions as compared to open flame devices. This is due to the ability of the enclosed flare to control or limit total oxidant (e.g., air) flow that is introduced into the combustion process, using louvers for example. Enclosed flares typically include a burner that is enclosed by a flare stack or columnar structure. Waste gas (e.g., from a landfill, anaerobic digester, coal mine, or another suitable source) and an oxidant (e.g., air) are routed into the flare stack where they are mixed and ignited to initiate combustion. The flame is enclosed within an exhaust chamber of the flare stack and exhaust gases (e.g., CO, NO, water, NMOCs) flow through the exhaust chamber to an outlet of the device.

NOemissions from a methane burner may run as high as 0.15 #/MM BTU. Some enclosed combustion flares operate to produce ultra-low NOX (ULN) emissions, which are defined as equal to, or less than, 0.025 #/MM BTU. CO emissions on an ULN flare are typically 0.06 #CO/MM BTU. NOemissions from enclosed flares are primarily thermal NO, that is, NOproduced by atmospheric nitrogen combining with oxygen where air is used as the oxidant for combustion. Hotter flames produce more NO. NOemissions may be controlled in an ULN enclosed flare by limiting the flame temperature of the burner. The theoretical flame temperature of methane in air can be as high as 3640° F. Most enclosed flares operate between 1400° F. and 1700° F., and the lower operating flare temperature is achieved by introducing additional cooling air into the flare stack through louvers. The amount of cooling air is controlled using feedback from thermocouples that measure the process temperature, and modulating motors that open or close the air inlet louvers as required. Flare operational temperature is typically determined by an onsite source test, the final operational setpoint is determined by balancing NO, CO & NMOCs in the stack (hotter generally produces more NO, and reduces CO and NMOCs).

Various methods exist for controlling NOemissions, some of which are described in the EPA Technical Bulletin EPA 456/F-99-006R (November 1999), the contents of which are hereby incorporated by reference in their entirety. These include controls that limit NOproduced during combustion such as, inter alia, lean excess air (LEA), enriched oxygen as oxidant, flue gas recirculation, water or steam injection, reduced air preheating, air staging, fuel staging, and catalytic combustion. Add on NOemission controls are also used in some applications and include, inter alia, selective catalytic reduction, selective non-catalytic reduction (SNCR), and sorption (e.g., absorption or adsorption). Suitable combustion controls vary depending on the combustion process and application and can be used in varying combinations.

In the waste gas flare industry, the industry wide approach is to use a pre-mixed lean air mixture in combination with a short flame length to reduce NOduring combustion. Enclosed flares are operable with a relatively large amount of oxidant, unlike heat source technologies such as boilers and process heaters that may limit excess air to between 3 to 4% stack Oto maintain efficiency. In this regard, a lean air mixture approach for limiting NOemissions is usually adopted in waste gas flares because it is cost effective and reduces system complexity and footprint of the flare. The lean air mixture includes a relatively large amount of air to lower the flame temperature and limit thermal NO. The short flame length is typically achieved using a surface burner. Reducing the length of the flame may reduce NOby limiting the interaction between atmospheric nitrogen and oxygen during combustion.

Various problems are associated with conventional surface burner head technologies used in waste gas flares. For example, the surface burner may be susceptible to clogging from dirt brought in through the waste gas or air stream. Landfill gas can have dirt and other contaminants that may eventually occlude the surface burner. Landfills can be very dusty and every cubic foot of land fill gas is mixed with 7 or 8 cubic feet of air. The surface burner may be dependent on cooling from the air/gas mixture flowing through the burner, and if the surface burner clogs the element will get hot. In some instances, the surface burner may become hot enough to ignite the pre-mixed gas inside the burner, and if this happens the burner could detonate and self-destruct. To prevent these issues, the surface burner may be routinely cleaned and/or a filter bank may be used upstream of the flare for filtering contaminants from the waste gas and/or air. The filter bank introduces a pressure drop which increases as the filters become dirty and may negatively impact the air to fuel ratio (AFR) control system. As a result, the filter bank upstream of the blower may require routine service to ensure performance. The surface burner may also be susceptible to failure if the AFR is insufficiently lean or in the event of a backfire. The surface burner may also be susceptible to failure due to manufacturing fabrication techniques that result in parts of the burner with no cooling gas flow, and is relatively fragile and can be damaged in shipping or installation.

Accordingly, there exists a need for burners used in waste gas flares that provide adequate control of NOemissions and overcome at least some of the problems described above. In particular, there exists a need for burners that are operable using lean air mixtures for combustion and maintain the ULN capability of flares while overcoming the disadvantages associated with known surface burners used in ULN flare applications.

One aspect is a flare system for burning off flammable gas present in a waste gas stream. The flare system includes a flare stack having a first end and a second end, the flare stack defining a closed plenum at the first end and an open exhaust chamber at the second end; and a burner assembly positioned in the flare stack between the plenum and the exhaust chamber, the burner assembly and the flare stack defining an excess oxidant passage for routing excess oxidant between the plenum and the exhaust chamber. The burner assembly includes: a body having a first body end proximate the plenum and a second body end proximate the exhaust chamber, each body end being open, the body defining a central passage extending between the body ends through which oxidant and waste gas flow, the central passage being separated from the excess oxidant passage; a burner tip connected to the second body end and defining an open tip passage through which the oxidant and the waste gas flow from the central passage into the exhaust chamber; and a swirl plate positioned upstream of the burner tip. The flare system also includes an ignition source positioned in the exhaust chamber to ignite the oxidant and the waste gas flowing through the open tip passage and create a combustion flame. The swirl plate operates to direct and anchor the combustion flame.

Another aspect is a method of operating a flare system for burning off flammable gas present in a waste gas stream. The method includes: channeling a waste gas into a flare stack towards a burner assembly positioned in the flare stack; channeling an oxidant into the flare stack towards the burner assembly; mixing the waste gas and the oxidant using the burner assembly; flowing the waste gas-oxidant mixture through an open tip passage of the burner assembly into an exhaust chamber of the flare stack; igniting the mixture to create a combustion flame that produces exhaust gases that flow through the exhaust chamber and out of the flare stack; channeling excess oxidant to the exhaust chamber to cool the combustion flame; and controlling the combustion flame using a swirl plate positioned proximate the open tip passage, wherein the swirl plate directs and anchors the combustion flame.

Another aspect is a method of operating an ultra-low nitrous oxide (NO) emission flare system for burning off flammable gas present in a waste gas stream. The method includes: channeling the waste gas stream including the flammable gas into a flare stack towards a central passage of a burner assembly positioned in the flare stack; channeling an oxidant into the flare stack towards the central passage of the burner assembly, wherein the oxidant is channeled at a flow rate that is at least 12 times greater than a flow rate of the flammable gas; mixing the waste gas and a first portion of the oxidant within the central passage of the burner assembly; flowing the waste gas-oxidant mixture through an open tip passage of the burner assembly into an exhaust chamber of the flare stack, the open tip passage axially aligned with the central passage; igniting the mixture to create a combustion flame that produces exhaust gases that flow through the exhaust chamber and out of the flare stack; and channeling a second portion of oxidant to the exhaust chamber to cool the combustion flame and reduce an amount of NOin the exhaust gases to below 0.025 pounds per million BTU.

Corresponding reference numerals used throughout the drawings indicate corresponding parts.

The present disclosure relates to flare systems operable to destroy flammable gas present in a waste gas while achieving ultra-low nitrous oxides (NO) emissions. In the example embodiments of this disclosure, a flare system includes a flare stack that encloses a burner assembly that provides controlled combustion of a lean mixture of the waste gas and an oxidant (e.g., air) and excess air is added to the flare stack to cool the flare stack, which may maximize combustion chamber life by reducing thermal stresses on surrounding components and/or limit NO. Complete or substantially complete combustion occurs, with substantially all carbon in the waste gas being converted to COand substantially all hydrogen in the waste gas being converted to HO, resulting in a relatively low amount of unburned components (e.g., CO) in the exhaust. The lean waste gas-oxidant mixture and excess air result in a stack oxygen in the flare of 10% v/v or greater, with the oxidant/air flow rate through the burner being between 12 to 20 times greater than the flow rate of the flammable gas present in the waste gas. For example, if the waste gas stream includes 50% methane, the ratio of oxidant/air to waste gas flow rate is between 6:1 to 10:1 (6 to 10 standard cubic feet per minute (SCF) oxidant/air for every SCF waste gas). The flare system is operable with an output range of 5 to 150 MM BTU/hr. The flare temperature is lower than 1800° F., such as between 1400° F. to 1700° F.

The burner assemblies described herein include an “open” burner tip, rather than a surface burner that is typically used in waste gas flares. In one suitable embodiment, the burner assembly also includes a pre-mixing chamber with a static mixture that produces a pre-mixed lean air combustion mixture that is routed to the open burner tip. In another suitable embodiment, the burner assembly includes a tip mix configuration in which waste gas and oxidant are mixed at the open burner tip immediately before combustion. In the latter embodiment, the risk of flashback is reduced. In some embodiments, for both pre-mix and tip mix configurations, the open burner tip operates in conjunction with a swirl plate that controls a flow direction of the waste gas-oxidant mixture and anchors and directs the flame at the tip.

Surprisingly, it has been discovered that the burner assemblies of the present disclosure enable operating the flare using the open burner tip while producing ULN emissions without a surface burner. NOreduction is achieved by complete mixing of the waste gas and oxidant, providing a very lean waste gas-oxidant mixture that enables ULN emissions. The temperature of the flare, including the combustion temperature, is lowered using copious amounts of excess air that flows around the burner assembly and is introduced at the burner tip to cool the flame. In some embodiments, the lean waste gas-oxidant mixture approaches or even reaches the lean combustion limit of the flammable gas without extinguishing the flame. For example, where methane is the flammable gas, the lean waste gas-oxidant mixture may approach or reach 5% methane (e.g., a 20:1 ratio of oxidant to methane) without extinguishing the flame.

Moreover, the open tip burner assemblies of the present disclosure achieve ULN emissions without using a surface burner configuration that are commonly used in some ULN flare stacks in an attempt to lower NO. Surface burners operate by distributing a waste gas-oxidant mixture through small ports or apertures defined in an elongate burner head, which in some applications is also surrounded by a mat made from a high-temperature compatible metal alloy (e.g., a nickel alloy). The waste gas-oxidant mixture flows through the apertures (and, optionally, the mat) of the surface burner and the mixture is ignited to produce a short flame across a relatively large surface area. Unlike conventional surface burners, the “open tip” burner configurations of the present disclosure define an open tip passage through which the waste gas-oxidant mixture flows, without distributing the mixture through apertures across a large surface to reduce flame length. In the embodiments of the present disclosure, the waste gas-oxidant mixture is ignited at the outlet of the open tip passage, and excess oxidant dilution is used to create a very lean waste gas-oxidant mixture to achieve ULN emissions. The burner assemblies described herein advantageously avoid issues that may arise using surface burners, such as particle clogging of the small apertures that leads to overheating and increased pressure drops, frequent servicing, shorter runtime, backfiring and blowback, higher material costs, and damage to fragile components. Surface burners may be very sensitive to oxidant/waste gas ratios, and may fail if subjected to insufficiently lean conditions. The open tip burner assemblies described herein are more robust and will survive over a broad range of oxidant/waste gas ratios. Moreover, the open tip burner assemblies of this disclosure are used in a waste gas flares, rather than a heat source (e.g., boiler), which allows the use of nearly unlimited excess air up to the lean combustion limit. Boilers and other heating apparatus endeavor to hold excess air as low as possible (3 to 4% stack Ois typical) in order to maintain efficiency, in this application the stack Owill be 10% or greater, therefore, the excess air coming through the burner is free of efficiency constraints.

Referring now to the drawings,is schematic diagram of one suitable embodiment of a flare system (generally indicated by). The flare systemoperates to destroy or burn off flammable gas (e.g., methane, CH) present in a waste gas stream drawn from a waste gas sourcewhile achieving ultra-low nitrous oxides (NO) emissions. The waste gas sourcemay be a landfill, off spec natural gas, a renewable natural gas plant, a coal mine, an anaerobic digestion plant, or another source that produces flammable gas or gases in amounts suitable for burning off or destroying using the flare system. The waste gas stream, in the illustrated embodiment, is drawn towards a flare stackusing a blower, such as a centrifugal blower. A filtration vessel, such as a separation tank, is optionally included to remove contaminants or condensate from the waste gas stream upstream from the flare stack. One or more sensors, such as a flow sensor, a pressure sensor, and/or a composition analyzer, are located between the blowerand the flare stackfor monitoring conditions (e.g., flow rate) of the incoming waste gas stream. One or more valves, such as check valves, shut off valves, flame arrestors, and/or flow control valves, are also located between the blowerand the flare stackfor controlling or regulating the incoming waste stream and/or preventing blowback from the flare stack.

As illustrated in, the flare stackis a hollow columnar structure and includes a cylindrical sidewallthat extends between a first endand a second endof the flare stack. The sidewallencloses a hollow interior of the flare stack. In, the flare stackhas a vertical orientation, with the first enddefining a bottom of the flare stackand the second enddefining a top of the flare stack. In other suitable embodiments, the flare stackmay have a horizontal orientation with the first endand the second endbeing generally aligned along a horizontal plane. The flare stackmay have any orientation that enables the flare stack to function as described. The sidewalldefines a substantially cylindrical shape of the flare stackbetween the first endand the second end, as shown in. Alternatively, the flare stackmay have any other suitable shape that enables the flare stack to function as described.

The first endof the flare stackis closed, and the sidewalland the first enddefine a closed plenum. The second endof the flare stackis open, and the sidewallproximate the second enddefines an open exhaust chamber. A burner assemblyis positioned in the flare stackbetween the plenumand the exhaust chamber. In the illustrated embodiment, the flare stackis an “enclosed” flare stack in that the burner assemblyis located within the interior of the flare stackand surrounded by the sidewall.

With reference still to, the incoming waste gas stream from the sourceis routed into the flare stacktowards the burner assembly. One or more nozzlesare connected to the blowerand positioned in the flare stackto output the waste gas stream towards the burner assembly. The waste gas stream is mixed at the burner assemblywith an oxidant drawn from an oxidant source. The oxidant sourceincludes, for example, ambient air, enriched oxygen gas, and/or combinations thereof. The oxidant is drawn from the oxidant sourceinto the flare stackand is routed towards the burner assembly. The oxidant that is routed towards the burner assemblyis forced into the flare stackusing a blower, such as a fan or a blower. Like the input for the waste gas stream described above, one or more sensors, such as a flow sensor, a pressure sensor, and/or a composition analyzer, and one or more valves, such as check valves, shut off valves, flame arrestors, and/or flow control valves, are located between the blowerand the flare stackfor controlling or regulating the oxidant flow into the flare stackand/or preventing blowback from the flare stack. Excess oxidant (e.g., ambient air) is also drawn into the flare stack, entering into the plenumthrough shutters or louverslocated on the sidewallof the flare stack. The louversmay be modulated using motors that operate to open and close the louvers. The excess oxidant may be drawn into the plenumby vacuum or may be forced (e.g., blown) into the plenumusing fans for example.

In the illustrated embodiment, the burner assemblyincludes a pre-mixing chamberfor mixing the waste gas stream and the oxidant that is routed towards the burner assembly. The waste gas stream and the oxidant are mixed in the pre-mixing chamberusing a static mixerand flow through a tapered extensionof the burner assemblytowards a burner tip. In other suitable embodiments, the pre-mixing chamberis omitted and the waste gas stream and the oxidant remain separated until being mixed at or immediately prior to reaching the burner tip. An ignition sourceis located in the flare stackadjacent the burner tipand is operable to ignite a flame at the burner tip. The burner tipincludes an open tip passagethat allows the waste gas-air mixture to exit the burner assembly, and a flow directorpositioned in, or proximate to, the open tip passage. The flow directorcontrols the flow of the oxidant and/or the waste gas at or near open tip passageand operates to anchor and direct the flame at the burner tip. The flow directoris also referred to as a flame holder. The flow directorincludes one or more guide vanes for controlling fluid flow. In some embodiments, the flow directoris a swirl plate, also referred to as a swirl vane flame holder. The ignition sourceincludes a spark plug, pilot or any other suitable ignition device.

The excess oxidant circumvents the burner assembly, flowing in the flare stackaround the burner assemblybetween the plenumand the exhaust chamber. In particular, the excess oxidant is routed around the burner assemblyand is introduced at the burner tip, cooling the flare stackand the burner assemblyfor maximizing combustion chamber life by reducing thermal stresses on surrounding components in the flare stack. As seen in, to enable the excess oxidant to flow around the burner assemblyin the flare stack, the burner assemblysuitably has an outer dimension OD (e.g., an outermost diameter) that is smaller than an inner dimension ID (e.g., an inner diameter) of the adjacent region of the sidewall, such that an excess oxidant passageis defined between the burner assemblyand the sidewalland extends between the plenumand the exhaust chamber.

The flare stackalso includes sensorslocated on the sidewallfor monitoring operating conditions in the flare stack. The sensorsinclude, for example, temperature sensors and optical flame sensors (e.g., an ultraviolet or UV radiation detector or scanner). Some of the sensors(e.g., temperature sensors) are located along the sidewalland spaced between the burner assemblyand the second end. These sensorsmonitor the conditions (e.g., temperature) of the exhaust or combustion gases produced by the flame at the burner tipand flowing towards the open second end. Some of the sensorsalso include one or more flame monitoring sensors (e.g., a temperature sensor and/or a UV scanner) that provide feedback signals to enable controlling and maintaining the flame during operation. The flame monitoring sensorsare at any suitable location on and/or in the flare stack. For example, in various embodiments, the temperature sensor(s)and the UV scanner(s)used to monitor the flame are located in the plenumand/or the exhaust chamber.

The flare systemofalso includes a controllerthat controls various aspects and parameters of the systemduring operation. The controlleris communicatively connected to various components of the system, such as the blowers,, the louvers, the valves,, the sensors,,, and the ignition source. The controlleris a computer system that includes one or more processors and one or more memory devices that store programs or instructions that are executable by the processor(s) to perform the functions described for the controller. Although a single controlleris shown and described, the controllermay include multiple controllersthat may be centralized or decentralized. The controllerincludes a communication interface to communicatively couple the controller, via one or more connections, to one or more components of the systemvia a wired and/or wireless connection.

In operation of the flare system, the waste gas stream is routed from the waste gas sourceusing the blowertowards the burner assembly(e.g., towards the pre-mixing chamber) and the oxidant is also routed from the sourceusing the blowertowards the burner assembly(e.g., the premixing chamber). Excess oxidant enters into the plenumvia the louvers. In the illustrated embodiment, the waste gas stream is output at the nozzlesat or near the pre-mixing chamberand the waste gas stream and the oxidant are mixed in the pre-mixing chamberusing the static mixer, and the pre-mixture flows through the tapered extensiontowards the burner tip. In other suitable embodiments, the waste gas stream and the oxidant remain separated while flowing through the burner assembly, and are mixed at or near the burner tip. The mixture flows through the open tip passageof the burner tipand the ignition sourceis used to ignite the mixture at the burner tip, creating a flame that extends from the burner tipinto the exhaust chamber, with a flame length that is less than a length of the exhaust chamberbetween the burner tipand the second endof the flare stack. Alternatively stated, the flame at the burner tipterminates within the exhaust chamber, and does not extend to the second endof the flare stack. The flame is anchored and directed at the burner tipusing the swirl vane flame holderpositioned in the open tip passage. The sensors,, andcontinuously or periodically monitor conditions of the flare stack, and the controllerreceives signals from the sensors,, andto control the blowerand/or the blower, and/or the position of the louvers, to thereby adjust a composition of the waste gas-oxidant mixture flowing towards the burner tip.

The flare systemis operable using a lean mixture of the waste gas stream and the oxidant, with excess oxidant (e.g., air) also being introduced to cool the flare stackand/or to reduce or inhibit NOemissions by cooling the combustion flame. The burner assemblyalso enables complete combustion of the gas-oxidant mixture, which reduces or eliminates CO emissions. Advantageously, the flare systemoperates to burn off the flammable gas in the waste gas stream while achieving ultra-low NO(ULN) emissions (that is, NOemissions equal to, or less than, 0.025 pounds per million BTUs combusted, or #/MM BTU). The flare systemalso produces CO emissions equal to or less than 0.06 #/MM BTU. The flare temperature at the exhaust chamberis less than 1800° F., such as between 1400° F. and 1700° F. The relatively low flare temperature is achieved by introducing additional cooling air into the plenum(e.g., through the louvers). Final stack Oconcentrations will be between 10 to 15% O, some of the excess cooling air being introduced through the burner assembly(e.g., through the pre-mixing chamber), and the remainder into the plenumthrough the louvers. The amount of cooling air is controlled by the controllerusing feedback signals from the sensorsof the flare stackthat measure the process conditions (e.g., temperature). For example, the controller modulates the motors that open or close the louversto adjust the oxidant content in the flare stackas required. The oxidant/air flow rate through the burner assemblyin some examples is between 12 to 20 times greater than the flow rate of the flammable gas present in the waste gas. For example, if the waste gas stream includes 50% methane, the ratio of oxidant/air to waste gas flow rate is between 6:1 to 10:1 (6 to 10 standard cubic feet per minute (SCF) oxidant/air for every SCF waste gas). The flare stackin various examples has an output in the range of 5 to 150 MM BTU/hr.

are various views of a burner assemblyof one suitable embodiment that is used as the burner assemblyin the flare stackof. The burner assemblyincludes a mixer skirt, a tapered extension, and a burner tip. The mixer skirtextends into the pre-mixing chamber. The mixer skirtis cylindrical in shape, and defines a shape of the pre-mixing chamber. The shape of the mixer skirtvaries depending on the desired shape of the pre-mixing chamber. The mixer skirtextends from a first endto a second end, and is open at both ends,, defining a chambertherebetween. The mixer skirthas a flangeat the second endthat connects to the tapered extensiondescribed below. The mixer skirtalso includes a static mixerpositioned in the mixing chamber. The chamberforms the pre-mixing chamberand the static mixerforms the static mixerwhen the burner assemblyis used in the flare stackof. In the illustrated embodiment, the static mixeris positioned in the mixing chamberproximate the first end. Alternatively, the static mixermay be positioned in any suitable location in the pre-mixing chamberto enable the static mixerto function as described. The static mixeris described in more detail below with reference to.

The tapered extensionextends between a first endand a second endand has a tapered outer dimension between the first endand the second end. In the illustrated embodiment, the tapered extensionhas a frusto-conical shape. Alternatively, the tapered extensionhas another suitable frustum shape. The tapered extensionis open at both ends,and defines a central passagetherebetween. The central passageis axially aligned with the pre-mixing chamberrelative to a central axis A of the burner assembly. The cross section of the central passageis tapered correspondingly with the tapered outer dimension of the extension. Thus, in the illustrated embodiment, the central passagehas a tapered diameter that decreases from the first endto the second end. The diameter of the central passageat the first endis substantially equal to a diameter of the pre-mixing chamber. The tapered extensionhas a flangeat the first endthat connects to the flangeat the second endof the mixer skirt.

The tapered extensionalso has a flangeat the second endthat connects to a flangeof the burner tip. The burner tipincludes the flangeand a collarextending axially from the flange. The collardefines a central openingthat has substantially the same diameter as the central passageat the second endof the tapered extension. The central openingis axially aligned with the pre-mixing chamberand the central passagerelative to the central axis A of the burner assembly. The central openingforms the open tip passagewhen the burner assemblyis used in the flare stackof.

The burner assemblyalso includes a flame holderpositioned between the burner tipand the second endof the tapered extension. The flame holderforms the flame holderwhen the burner assemblyis used in the flare stackof. With additional reference to, the flame holderincludes a flangethat is seated between the flanges,of the tapered extensionand the burner tiprespectively. The flame holderalso includes swirl vanesextending radially inward from the flange. Each swirl vaneis set at an angle (e.g., between 15° to 60°, such as between 15° to 45°) relative to the flange. When the flame holderis positioned between the burner tipand the second endof the tapered extension, the swirl vanesare located at the junction of the central passageand the central opening, and extend circumferentially therein. The swirl vanesare supported by the flangeand a center retention ringof the burner tip. In particular, each swirl vaneis welded (e.g., spot welded or tack welded) to each of the flangeand the center retention ring. Alternatively, the flame holderand the swirl vanesare a single monolithic plate formed by removing material to free the swirl vanesand distorting the swirl vanesinto place. The center retention ringis located at or near the central axis A. The flame holderis also referred to as a swirl plate.

are various isolated views of the static mixer. The static mixerincludes an annular sidewallthat forms part of the mixer skirtand defines the first endof the mixer skirt. The static mixeris grated, having two rows of mixer vanes,extending between the sidewalland across the pre-mixing chamber(perpendicular to the central axis A). With specific reference to, a first row of mixer vanesextends between the sidewallin an X-axis direction and a second row of mixer vanesextends between the sidewallin a Y-axis direction, perpendicular to the X-axis direction. In other examples, the rows of mixer vanes,may extend at an oblique angle relative to one another.

With reference now to, each of the vanes,is also set at an angle a, relative to the central axis A. The angle a may be, for example, between 30° to 60°, such as between 40° to 50°, or 45°. The vanesof the first row are set at the angle a in the Y-axis direction and the vanesof the first row are set at the angle a in the X-axis direction. It will be appreciated that the vanes,may be set at different angles. Also, as shown in, the first row of mixer vanesare located closer to the first endof the mixer skirtthan the second row of mixer vanes. In the example orientation of the burner assembly, the second row of mixer vanesare located vertically above the first row of mixer vanes. The mixer vanes,are each welded to the sidewallof the static mixer, and the mixer vanesof the first row are also welded at cross jointed to the mixer vanesof the second row.

depict another suitable embodiment of a burner assemblythat can be used instead of the burner assemblyin the flare stackof. In this embodiment, the burner assemblyhas a tip mix configuration, in which the waste gas stream and the oxidant remain separated while flowing through a bodyof the burner assemblyand are mixed at or immediately before a burner tipof the burner assembly. Accordingly, a pre-mixing chamber and static mixer are omitted from this example.

The burner assemblyincludes the body, the burner tip, and an elongate waste gas ring(also referred to an annular waste gas can) positioned in the body. The bodyis cylindrical in shape, and defines a central axis Aof the burner assembly. The shape of the bodyvaries in other examples. The bodyextends from a first endto a second end, and is open at both ends,, defining an oxidant chambertherebetween. The central axis Aof the burner assemblyextends through the chamber.

The elongate waste gas ringis positioned in the chamberand extends between a first endand a second end. The second endof the waste gas ringis proximate the second endof the body. The first endof the waste gas ringis located in the oxidant chamberbetween the first endand the second endof the body. The first endof the waste gas ringis located either proximate the first endof the bodyor is spaced a distance from the first endof the body, relative to the central axis Atowards a middle region of the oxidant chamber. In some suitable embodiments, the first endof the waste gas ringis located in closer proximity to the second endof the bodythan the first end.

The waste gas ringhas an annular, cylindrical shape with a hollow interior that defines a waste gas passage. The waste gas ringcircumscribes a central passagewithin the oxidant chamber, and has an outer dimension OD(e.g., an outer diameter) that is smaller than an inner dimension ID(e.g., an inner diameter) of the body, such that a radially outer passageis defined between the waste gas ringand the body. The waste gas ringisolates the waste gas passagefrom the central passageand the radially outer passageof the oxidant chamber. The waste gas ringis closed at the first endand includes one or more outlets(e.g., openings or nozzles) at the second end. The waste gas ringis seated in the bodyand secured therein, for example, using one or more radially extending arms (not shown), e.g., spokes, that extend between the gas ringand the bodyand connect the gas ringto an inner surface of the body. The arms fix the waste gas ringin the bodyand maintain radial spacing therebetween for the radially outer passage. In some embodiments, the waste gas ringis removable from the body, enabling waste gas cansto be readily removed and replaced (e.g., depending on a type of waste gas and/or to replace a worn, spent, and/or damaged can).

Oxidant (e.g., air), indicated by the flow line, enters into the bodythrough the first endand flows through oxidant chambertowards the second end. Waste gas, indicated by the flow lines, enters into the waste gas passagevia a waste gas line. The waste gas lineis connected to a waste gas source (e.g., the waste gas sourceof) and the first endof the body is connected to an oxidant source (e.g., the oxidant sourceof). The waste gas and the oxidant may be forced into the waste gas passageand the oxidant chamber, respectively, using fluid displacement devices such as the blowers,of. The waste gasremains separated while flowing in the waste gas passagefrom the oxidantflowing in the central passageand the radially outer passage, and the waste gasis prevented from flowing towards the first endof the bodyby the closed first endof the waste gas ring. The waste gasis injected into the oxidant chambervia the outletsat or proximate the second endof the body, such that the waste gasmixes with the oxidantat or immediately prior to the burner tip.

The outletsare tuned to achieve a desired exit velocity of the waste gas. In particular, the size (e.g., diameter) and/or shape (e.g., circular, square, triangular) of the outletsmay be adjusted depending on the type of waste gasbeing used by the flare systemin order to achieve a desired mixing with the oxidant. For example, in some instances, a higher exit velocity is desired for richer, lighter gases (e.g., waste gas having a relatively higher concentration of flammable gas). In these instances, the size and/or shape of the outletsis adjusted to achieve a higher exit velocity of the waste gas(e.g., the diameter of the outletsis reduced). For more diluted, heavier gases, the size and/or shape of the outletsis adjusted to achieve a lower exit velocity of the waste gas(e.g., the diameter of the outletsis increased). As described above, the waste gas ringis removable in some embodiments, which allows for quick and efficient replacement of the waste gas ring(s)to adjust to the desired outletsize and/or shape for the type of waste gasbeing used.

The burner tipextends between a first endand a second end. The first endof the burner tipis connected to second endof the body. For example, the first endof the burner tipand the second endof the bodyhave complementing flanges or other complementing features that facilitate connecting the burner tipand the body. The burner tiphas a tapered outer dimension between the first endand the second end. In the illustrated embodiment, the burner tiphas a frusto-conical shape. Alternatively, the burner tiphas another suitable frustum shape. The burner tipis open at both ends,and defines a tip passagetherebetween. The tip passageforms the open tip passagewhen the burner assemblyis used in the flare stackof. The tip passageis axially aligned with the oxidant chamberand the central passagerelative to a central axis Aof the burner assembly. The cross section of the tip passageis tapered correspondingly with the tapered outer dimension burner tip. Thus, in the illustrated embodiment, the tip passagehas a tapered diameter that decreases from the first endto the second end. The diameter of the tip passageat the first endis substantially equal to a diameter of the oxidant chamber.

The burner assemblyalso includes a flame holder, also referred to as a swirl plate, positioned in the oxidant chamber. In the illustrated embodiment of, the flame holderis positioned in the central passage, proximate to and upstream from the second endof the waste gas ring. The flame holderis spaced an axial distance from the second endin this embodiment. In other embodiments, the flame holderis positioned in the central passageand flush with the second endof the waste gas ring. The flame holderforms the flame holderwhen the burner assemblyis used in the flare stackof. The flame holderis similar to the flame holderof the burner assemblydescribed above with reference to, and includes swirl vaneswhich are similar to the swirl vanesdescribed above for the flame holder. The swirl vanesare positioned in the central passageand extend in a circumferential pattern therein. The swirl vanesextend radially from a center retention ringto an outer portion or outer ringof the flame holder. As described above, each swirl vaneis set at an angle (e.g., between 15° to 60°, such as between 15° to 45°), and each swirl vaneis welded to the outer ringand the center retention ringof the flame holder. Alternatively, the flame holderand the swirl vanesare a single monolithic plate formed by removing material to free the swirl vanesand distorting the swirl vanesinto place. The center retention ringis located at or near the central axis A.

In this embodiment, the swirl plateoperates to redirect a flow direction of the oxidantupstream from the outletsof the waste gas ring. In particular, the swirl platedirects the oxidantto intersect or shear across the flow of the waste gasexiting the outlets. This enhances mixing of the oxidantand the waste gasat or proximate the second endof the body.

In another embodiment of the burner assembly, shown in, the flame holderis located downstream from the second endof the waste gas ringand more particularly, downstream from the outletsof the waste gas ring. In this embodiment, the flame holderis positioned between the burner tipand the second endof the body. The swirl vanesare thereby positioned between each passage,, andand the tip passage, and extend in a circumferential pattern therein and radially across an entirety or substantial entirety of the diameter at the junction of the oxidant chamberand the tip passage. In this way, the oxidantflowing through the passages,and the waste gasexiting the outletseach flow in a substantially similar flow direction and are redirected by the swirl vanesat or proximate the second endof the bodyto enhance mixing of the oxidantand the waste gas.

depict yet another suitable embodiment of a burner assemblythat can be used instead of the burner assemblyin the flare stackof. This example is similar to the burner assemblyof, with corresponding reference numerals indicating corresponding parts. In this embodiment, the waste gas ringincludes three concentric gas rings-that each respectively define a waste gas passage-and outlets-for injecting the waste gasinto the oxidant chamberat or proximate the second endof the body. An inner waste gas ring, having the smallest diameter, defines the central passageand an outer waste gas ringhaving the largest diameter, defines the outer radial passagewith the body. An intermediate waste gas ringis positioned between the inner and outer ringsand defines two intermediate oxidant passages,with the first and third ring,respectively. Oxidant flowing through the oxidant chamberflows through the oxidant passages,in addition to the central passageand the radially outer passage. This configuration of the waste gas ringmay be suitably used in relatively large sized burner assemblieswhere multiple (e.g., two, three, or more than three) concentric waste gas ringsare used to provide better radial distribution of the waste gasat or proximate the second endof the body, and thereby improve mixing of the waste gaswith the oxidantat or immediately prior to the burner tip. Any suitable number of waste gas ringsmay be included to enable the burner assemblyto function as described. In various embodiments, for example, the burner assembly includes two, three, four, five, six, or more than six gas rings.

In the illustrated embodiment of, a swirl plateis positioned in the central passageand a swirl plateis positioned in an intermediate passage,between adjacent waste gas rings. In this embodiment, there are three swirl platescorresponding to one central passageand two intermediate passages,. The number of swirl platesvaries depending on the number of waste gas ringsand, in particular, the number of intermediate passages between adjacent waste gas rings. In the illustrated embodiment, a first swirl plate, labeled asin, is positioned in the central passage, similar to the flame holderin. In addition, second and third swirl plates, respectively labeledandare respectively positioned in the oxidant passagesand. Each swirl plate-or flame holder-, is positioned proximate to and upstream from the second endof the waste gas ring, that is, each swirl plate-is spaced an axial distance from the second endin this embodiment. In other embodiments, one or more of the swirl plates-is flush with the second endof the waste gas ring. Each swirl plate-includes the swirl vanes, which extend radially from the center retention ringto the outer ringof the respective swirl plate-In this embodiment, the swirl plates-operate to redirect a flow direction of the oxidantupstream from the outlets-of the waste gas rings-such that the oxidantintersects or shears across the flow of the waste gasexiting the outlets-and the mixing of the oxidantand the waste gasat or proximate the second endof the bodyis enhanced.

shows another embodiment of the burner assemblyin which a single swirl plateis used and is similarly positioned as shown in the embodiment shown in. In this embodiment of the burner assembly, the single swirl plateis located downstream from each of the waste gas rings-and more particularly, downstream from the outlets-of the waste gas rings-and between the burner tipand the second endof the body. The swirl vanesof the swirl plateare thereby positioned between each passage,,-, andand the tip passage, and extend in a circumferential pattern therein and radially across an entirety or substantial entirety of the diameter at the junction of the oxidant chamberand the tip passage. In this way, the oxidantflowing through the passages,,,and the waste gasexiting the outlets-each flow in a substantially similar flow direction and are redirected by the swirl vanesat or proximate the second endof the bodyto enhance mixing of the oxidantand the waste gas.

In the burner assemblies,of, the swirl platemay be a fixed swirl plate or a floating swirl plate. A fixed swirl plateis secured via its outer retention ringand/or inner retention ringto an adjacent waste gas ring. A floating swirl plateis seated on an anchoring structure (e.g., one or more spokes extending within the oxidant chamber, e.g., within the central passage, one of the intermediate oxidant passages,, or at the junction of the oxidant chamberand the tip passage). Floating swirl platesare allowed to move axially or “float” in response to flow of the oxidant and/or the waste gas-oxidant mixture therethrough, and facilitate easier manufacturability and versatility of the burner assembly,.

Referring generally to, and with additional reference to, a methodof operating the flare systeminincludes channelinga waste gas into the flare stack(e.g., using the blower) towards the burner assembly, channelingan oxidant (e.g., air) into the flare stacktowards the burner assembly, and mixingthe waste gas and the oxidant using the burner assembly. The methodalso includes flowingthe waste gas-oxidant mixture through an open tip passageof the burner assemblyinto the exhaust chamberof the flare stackand ignitingthe mixture to create a combustion flame that produces exhaust gases that flow through the exhaust chamberand out of the flare stack. The combustion flame completely or substantially combusts the mixture to reduce CO emissions. The CO emissions are equal to or less than 0.06 #/MM BTU in some examples. The methodalso includes channelingexcess oxidant (e.g., air) to the exhaust chamberto cool the flare stackand/or reduce NOemissions by cooling the combustion flame. The NOemissions are within ULN requirements in some examples. For example, the NOemissions are equal to, or less than, 0.025 #/MM BTU. The methodalso includes controllingthe combustion flame using a flow director(e.g., a swirl vane flame holderor swirl plate) positioned proximate the open tip passage, where the flow directordirects and anchors the combustion flame. The flow directoroperates to stabilize the flame in very lean (high Ostack) conditions and limit or prevent the risk of extinguishing the flame at large oxidant/waste gas ratios (e.g., 10:1 or more). The flow directorallows the flame to survive, and maintains complete combustion, over a broad range of oxidant/waste gas ratios (e.g., from 6:1 to 10:1 for waste gas including 50% v/v flammable gas). In some embodiments, flow directorallows the lean waste gas-oxidant mixture to approach or even reach the lean combustion limit of the flammable gas without extinguishing the flame. For example, where methane is the flammable gas, the lean waste gas-oxidant mixture may approach or reach 5% methane (e.g., a 20:1 ratio of oxidant to methane) without extinguishing the flame.

In some suitable embodiments of the method, the Ostack concentration in the flare stackis 10% v/v or greater, such as between 10% v/v to 15% v/v. The oxidant is channeledat a greater flow rate than the flow rate at which the waste gas is channeled. For example, the oxidant is channeledat a flow rate that is 12 to 20 times greater than the flow rate of the flammable gas (e.g., methane) present in the waste gas being channeled. The ratio of oxidant/air to waste gas flow rate is between 6:1 to 10:1 in some examples. The ratio of oxidant to waste gas flow rate is greater than 10:1 in some examples, and less than 6:1 in other examples. The methodin some examples includes operating the flare stareat an output in a range of 5 to 150 MM BTU/hr. In some examples, the flare temperature during combustion is lower than 1800° F., such as between 1400° F. to 1700° F.