Patent Application
20250060097
The present invention relates to burners and particularly to industrial burners for gaseous fuels, and especially to the field of multi-fuel (two-fuel) burners.
In the prior art, many high-temperature melting or pre-heating furnaces are designed with an air-fuel burner in mind.
Due to increase in product demand or plant operational needs, manufacturers are looking to use burners, a means to provide energy to the process, that provide operational flexibility to the burners and in turn to the plants. Additionally for dual-fuel burners, there is a need of a burner that can be operated across a wide range of turndown, equivalence ratio, and/or flexibility to choose a fraction of heat supplied to the process from the two fuels. Furthermore, with increased focus on alternative fuels and availability of diverse gaseous fuels across geographical locations, there is a need for a burner that can operate for a wide range of fuels with minimal or no burner hardware change. It is particularly challenging to reliably start/ignite the burner at a low equivalence ratio (fuel lean start-ups), in particular in situations where one is unable to drop the air flow rate below a particular set point and one needs to flow at a minimum fuel flow rate.
There are several potential ways these challenges can be addressed.
First, fuel-flexible burners may be used, which can operate using any gaseous fuel such as natural gas (“NG”), liquefied petroleum gas (“LPG”), biogas, synthesis gas, hydrogen, ammonia or other gases, and meet the emissions and thermal performance criteria of the heating or melting furnace. Designing a fuel flexible gaseous fuel burner has several challenges depending on the burner type and design. Apart from wide variation in the combustion behavior of these fuels (well documented in combustion literature), e.g. the differences in heating value, reaction rates and flammability limits of the gaseous fuels creates a challenge when designing a burner.
Second, there generally is a challenge to further optimize the mixing of fuel and oxidants for partially-premixed burners.
Thirdly, there particularly is a challenge to reduce the length of the flame and to achieve a shorter flame that fits inside a compact/short reformer/furnace/combustion chamber.
Fourthly, a further general aim in the field of burners is to keep NOx emission low.
Fifth, there is a desire to operate the burner for a wide range of split of primary and secondary fuel.
It is therefore a first object of the present invention to provide an advantageous burner which alleviates or overcomes one or more of the above challenges.
Particular prior art designs of burners may be summarized as follows:
The present invention helps to solve above challenges by providing a new (non-premixed) multi-fuel (two fuel) burner.
In particular, the present invention provides burners having a unique special tip, and e.g. split main oxidant for partial pre-mixing of the first fuel (e.g. NG/LPG/H2/NH3 stream) and unique way to inject the primary and secondary fuels.
Burners of the present invention are regarded to allow for a more intimate mixing (e.g. from combined swirl and pre-mixing holes) leading to a shorter flame that fits inside a compact/short reformer/furnace/combustion chamber.
Specifically, the present invention relates to the subject-matter as defined in the claims.
Generally, the burners of the invention may e.g. be used in any application that needs high heating applications, specifically in applications like steam methane reforming, reheat furnaces in steel industry, or secondary melting furnaces.
In a general aspect, the invention provides a burner (1) comprising a primary fuel conduit (20) comprising a primary fuel outlet (22) having a multiplicity of primary fuel exit holes (23) for supply of a primary fuel into an ignition chamber (25), wherein the wall surrounding the ignition chamber (25) comprises a plurality of bleed holes (28), a main oxidant conduit (30) for supply of a main oxidant, comprising an intermediate annular conduit (35) in a downstream portion (5) of the burner, which intermediate annular conduit (35) is configured to allow splitting of the main oxidant, such that a first portion is introduced into the ignition chamber (25) via the plurality of bleed holes (28) to mix with the primary fuel.
Preferably, at least in the downstream portion (5) of the burner (1), in which primary fuel outlet (22), ignition chamber (25), intermediate annular conduit (35) and (if present) secondary fuel outlet (44) are present, the primary fuel conduit (20) is surrounded by the main oxidant conduit (30) and (if present) the secondary fuel conduit (40).
Further provided by the present invention are, among others, methods for operating said burners.
Particular (further) advantages of the burners of the present invention are disclosed herein below.
The present invention will hereinafter be described in conjunction with the appended figures wherein like reference numerals denote like elements.
The present invention generally provides burners and further subject-matter as defined in the claims.
The burner of the present invention overcomes above-described prior art challenges in various ways as already depicted above.
For example, this burner design enables rapid and thorough mixing of a portion of the air-fuel mixture at the point of ignition. This is enabled via air entrainment in the fuel jet through a unique burner cup tip (ignition chamber) design, thereby allowing reducing peak temperatures relative to common characteristics of non-premixed burners. The lower peak temperatures help to reduce thermal NOx formation as compared to conventional air-fuel non-premixed combustion.
Besides, the burner may be operated in a cold furnace (that is <400 F average temp during start-up sequence of the burner) without the need of oxygen assistance or a continuous ignition source. The burner may further be stably operated in a fuel lean, low flame temperature mode. The burner produces a stable flame (without any lift-off) over a very broad 30:1 turndown range, even with an equivalence ratio as low as 0.25. These features enable pre-heating of the process furnace at a controlled rate to allow the process to initiate and come to a steady-state condition within a time-frame dictated by process requirements.
This burner allows to start/ignite the burner at low equivalence ratio (fuel lean start-ups), in particular in situations where it is not possible to reduce the air flow rate below a particular set point while start-up fuel flow is simultaneously minimized for safety reasons. The equivalence ratio is defined as the ratio of the actual fuel/air molar ratio to the stoichiometric fuel/air molar ratio.
The burner allows operating the furnace over a wide range of the ratio of primary to secondary fuel total heating value (i.e. firing rate ratio).
Moreover, the oxidizer back pressure (e.g. air) in burners of the invention may be such that it is not required to have any external secondary compression device for these streams. This feature helps to reduce the burner operating costs and any maintenance involved with such activities.
In particular, in a first aspect herein, there is provided a burner (1) comprising a primary fuel conduit (20) comprising a primary fuel outlet (22) having a multiplicity of primary fuel exit holes (23) for supply of a primary fuel into an ignition chamber (25), wherein the wall surrounding the ignition chamber (25) comprises a plurality of bleed holes (28), a main oxidant conduit (30) for supply of a main oxidant, comprising an intermediate annular conduit (35) in a downstream portion (5) of the burner, which intermediate annular conduit (35) is configured to allow splitting of the main oxidant, such that a first portion is introduced into the ignition chamber (25) via the plurality of bleed holes (28) to mix with the primary fuel.
In preferred embodiments, the burner further comprises a secondary fuel conduit (40) for supply of a secondary fuel, having a secondary fuel outlet (44) at its downstream end, particularly wherein the secondary fuel outlet (44) comprises a secondary fuel distribution plate (45) having a multiplicity of secondary fuel exit holes (48). Preferably, the holes are staggered in a series of concentric circle patterns around the air annulus.
The inner diameter of the secondary fuel conduit (40) may be defined as D5.
Without intending to be bound by theory, the secondary fuel exit holes (48) located on progresively larger concentric circle pattern helps to achieve a more distributed combustion by a) reducing the heat release per unit area of injection plate and b) diluting the combustion through through the use of high velocity fuel injection. These factors are instrumental in lowering flame temperature of the tail gas combustion, which lowers thermal NOx emissions. NOx is further reduced by maximizing the radial separation between the tail gas and trim fuel combustion zones, represented by non-dimensional ratio D9/D5 and D8/D5.
Preferably, at least two sets of concentric holes are located at different radial dimensions.
Without intending to be bound by theory, the secondary fuel injection holes located on the innermost circle (the innermost extension of which is defined as D8) are regarded to be important for secondary fuel flame stability over a wide range of H2 concentration in the secondary fuel. This is regarded to ensure flexibility to supply total thermal input from the burner divided in different ratios between the primary and secondary fuels. The present inventors have found the maximum value of D8/D4 that ensures secondary flame stability under all conditions to be 1.4.
Without intending to be bound by theory, the tailgas injection holes located on the outermost circle (the outermost extension of which is defined as D9) are regarded important to lower the NOx emissions by enabling a distributed combustion. If the D9/D5 is too large, this leads to incomplete fuel combustion in a cold furnace (below autoignition temperature of the fuels). The present inventors have found the optimal range of D9/D4 that ensures complete combustion of secondary fuel while maintaining low NOx emissions is between 1.6 and 2.5.
Without intending to be bound by theory, the injection of the secondary fuel from secondary fuel injection holes located on several different circles around the primary oxidant pipe helps to achieve distributed combustion in the combustion space thereby helping to lower the NOx emissions from fuels that have tendency to form higher NOx example hydrogen and ammonia. Quantification of the degree of fuel distributedness is given by the porosity parameter, Δ, where:
(whereas the present inventors have found the optimal range of Δ is between 0.1 and 0.2).
In the first aspect, preferably at least in the downstream portion (5) of the burner (1), in which primary fuel outlet (22), ignition chamber (25), intermediate annular conduit (35) and optionally the secondary fuel outlet (44) are present, the primary fuel conduit (20) is surrounded by the main oxidant conduit (30) and optionally the secondary fuel conduit (40).
As used herein, a “downstream portion of the burner” in which certain outlets “are present” refers to a downstream portion that comprises all of said outlets. Moreover, the said portion may further comprise the swirler section and/or bleed holes.
The term “downstream portion” is used herein exchangeably herein with the term “downstream section”.
In preferred embodiments herein, at least in the downstream portion (5) of the burner (1), in which primary fuel outlet (22), ignition chamber (25), intermediate annular conduit (35), and (as the case may be) secondary fuel outlet (44) are present, the main oxidant conduit (30) and (as the case may be) the secondary fuel conduit (40) are arranged essentially concentrically around the primary fuel conduit (20).
In particular embodiments of the present invention, where one or more given conduits are arranged (concentrically) around one or more given other conduits, said conduit(s) are arranged around another in a section corresponding to at least 20%, preferably in at least 30%, particularly in at least 40%, especially in at least 50%, and in some embodiments in at least 75%, of the total length of the burner, wherein the said section includes the primary fuel outlet, main oxidant outlet, and secondary fuel outlet.
Moreover, in case that a swirler section and/or a bleed hole annulus is/are additionally present, the said portion preferably further includes the swirler section and/or bleed hole annulus.
Herein, the “total length” of the burner of the invention is determined by establishing the distance between the furthest upstream end of all conduits and the furthest downstream end of all conduits.
In a further preferred embodiment the primary fuel conduit, the main oxidant conduit and the secondary fuel conduit are arranged concentrically around the central ignition source along their full length.
In preferred embodiments of the invention, where a given conduit is arranged concentrically around another conduit, this results in the formation of a respective annulus.
Consequently, in preferred embodiments herein, the burner is configured in such a way that the one or more fuels or oxidants flow through at least one annulus. In the present invention, such annuli may further be characterized by containing further elements of the respective conduits (such as exit holes, bleed holes, a swirler section and suchlike) as defined elsewhere herein.
Likewise, in preferred embodiments herein, the burner is characterized in that one or more outlets of the conduits are configured as annular rings. In the present invention, such annular rings may be characterized by containing further elements (such as exit holes, bleed holes, a swirler section and suchlike) as defined elsewhere herein.
Generally, in the present invention, a certain conduit (is described as being “surrounded” by a certain other conduit (or several other conduits, respectively) if said conduit has a smaller diameter than said other conduit(s) and is arranged inside said other conduit(s).
However, for being “surrounded” by another conduit, a given conduit does not need to be entirely surrounded by the other, but may also extend further downstream and/or upstream from the other. Respective definitions apply herein, where a given element is said to be “arranged around” another element.
In preferred embodiments, a conduit that is described to be surrounded by (an) other conduit(s) shares its longitudinal axis with the other(s).
In preferred embodiments, the ignition chamber (25) is extending from the primary fuel conduit exit plane (55) to the intermediate annular conduit exit plane (56).
In certain preferred embodiments, the ignition chamber (25) is characterized by at least two (preferably by two or three) sections in its wall, wherein each step comprises a rows of bleed holes (28).
In certain preferred embodiments, the ignition chamber (25) comprises a section having an outer diameter that is smaller than or equal to the inner diameter of the primary fuel conduit (20).
In certain preferred embodiments, the ignition chamber (25) further comprises a section having an inner diameter that is greater than the outer diameter of the primary fuel conduit (20), but having an outer diameter that is smaller than the inner diameter of the intermediate annular conduit (35).
Generally, in particular embodiments, the ignition chamber (25) comprises an ignition cup (75) as well as a bleed cup (76). Preferably wherein the ignition cup (75) is comprised in a first section of the ignition chamber (25), and the bleed cup (76) is comprised in a second section of the ignition chamber (25), wherein the second section is located downstream of the first section.
More specifically, in one set of particularly embodiments, the burner is characterized in that the ignition chamber (25) is extending from the primary fuel outlet (22) to the intermediate annular conduit exit plane (56), wherein the wall surrounding the ignition chamber (25) comprises two sections, wherein i) the first section has an outer diameter smaller than or equal to the outer diameter of the primary fuel conduit (20) and comprises a plurality of bleed holes (28), wherein the wall surrounding the first section comprises a plurality of bleed holes (28), and wherein the first section further comprises means allowing the main oxidant to additionally enter the ignition chamber (25) in flow direction, ii) the second section has an inner diameter greater than the outer diameter of the primary fuel conduit (20), but the second section has an outer diameter smaller than the inner diameter of the intermediate annular conduit (35), and comprises a further plurality of bleed holes (28).
According to particularly preferred embodiments, as is e.g. also apparent from
In further detail, in particularly preferred embodiments, the distribution plates are recessed by L0+L1 or by L01+L1 length from the hot face of the burner. In more detail, a portion of primary oxidant (typically around 20% of the total) is introduced into the ‘ignition cup’ and ‘oxidant bleed cup’ enters via the peripheral wall of the chamber, which is at right angles to the fuel distribution nozzle. The first portion that enters the ‘ignition cup’ vigorously mix with a portion of the fuel and “ignition” oxidant such that the mixture composition in the ‘ignition cup’ allows to ignite the flame overall a broad range of flow rate of fuel and oxidant. The second portion that enters the ‘oxidant bleed cup’ mix with the fuel such that peak flame temperatures are reduced compared with typical diffusion flames. This is important for minimization of flame-generated NOx emissions. Moreover, the method of oxidant introduction also keeps the peripheral wall cooled by protecting it from direct contact with the flame. The first portion of fuel in ‘ignition cup’ mixes with ‘ignition oxidant’. The mechanical mixture plate breaks the fuel jets in this first section to mix with the ‘ignition oxidant’. The second portion of fuel through jets on plane 2 is recessed by L01+L1 in order to give sufficient length for the fuel jets to fully or partially develop and partially-premix with the “oxidant bleed cup” oxidant. This feature helps to stabilize the flame over a broad range of equivalence ratio.
Preferably, the burner further comprises a purge plate (73) with purge holes (32) present between the first section's outer diameter and inner diameter of the second section. Preferably, the burner further comprises a purge plate (73) with purge holes (32) present between the outer diameter of the second section and inner diameter of the intermediate annular conduit (35).
More specifically, in another set of particularly embodiments the ignition chamber (25) is extending from the primary fuel outlet (22) to the intermediate annular conduit exit plane (56), wherein the wall surrounding the ignition chamber (25) comprises two sections, wherein i) the first section is extending from the primary fuel outlet (22) to the primary fuel conduit end plane (24), wherein the primary fuel conduit wall (29) surrounding the section comprises a plurality of bleed holes (28), and ii) the second section has an inner diameter greater than the outer diameter of the primary fuel conduit (20), but the second section has an outer diameter smaller than the inner diameter of the intermediate annular conduit (35), and comprises a further plurality of bleed holes (28).
Preferably, the burner further comprises an oxidant purge plate (73) with purge holes (32) that extends between the first section's outer diameter and the inner diameter of the second section.
In an even further set of particularly embodiments, the ignition chamber (25) is extending from the primary fuel outlet (22) to the intermediate annular conduit exit plane (56), wherein the wall surrounding the ignition chamber (25) comprises at least two sections of annular conduits with increasing diameter, each of which comprises a plurality of bleed holes (28).
Preferably, the wall surrounding the ignition chamber (25) comprises two or three sections of annular conduits with increasing diameter, each of which comprises a plurality of bleed holes (28).
Generally herein, in certain preferred embodiments, the burner further comprises one or more mechanical mixer plates (74), wherein each mechanical mixer plate (74) is located downstream of and adjacent to the said two sections.
Preferably herein, a mechanical mixer plate (74) has a disk type structure that breaks the fuel flow coming out of fuel exit holes (23). In particular, the first mechanical mixer plate has a disk type structure (mechanical mixer 1) that breaks the fuel flow coming out of the ‘outer series’ of fuel exit holes (23). The disk breaks these fuel jets and help with quick mixing of fuel and air inside the ignition chamber.
Preferably herein, a purge plate (73) is a disc that comprises purge holes (32). More preferably, the plate/disk is present between the fuel conduit wall (29) and the intermediate conduit wall present inside the conduit (35).
In the present invention, the burner preferably further comprises an ignition source (10).
Preferably herein, the ignition source (10) terminates in the ignition chamber (25).
In certain embodiments, the ignition source (10) is a central ignition source having a central axis (15) and a conduit end plane (16).
In preferred embodiments herein, the main axis (2) of the burner (1) coincides with the central axis (15) of the ignition source (10).
Preferably, at least in said downstream portion (5) of the burner (1), the central ignition source (10) is surrounded by the primary fuel conduit (20), the main oxidant conduit (30) and the secondary fuel conduit (40).
In certain embodiments, the main axis (2) of the burner (1) coincides with the central axis (15) of the ignition source (10).
Further as to the ignition source (10), same may be designated herein as “pipe 1”.
The (central) ignition source may also be referred to herein simply as “igniter”.
Herein, the outer diameter of the ignition source (10) may be defined as D2.
Accordingly, the central ignition source wall (19) may have an outer diameter D2.
Furthermore, the central ignition source is preferably arranged in the center of the burner, preferably along its full length, particularly wherein the remaining conduits of the burner are arranged concentrically around the central ignition source.
Further as to the primary fuel conduit (20), same may be designated herein as “pipe 2”, which is a gaseous fuel pipe.
Herein, the inner diameter of the primary fuel conduit (20) may be defined as D3.
Accordingly, the primary fuel conduit wall (29) may have an inner diameter D3.
In certain embodiments, the primary fuel conduit end plane (24) corresponds to the ignition chamber end plane (26).
The primary fuel conduit (20) further comprises a primary fuel outlet (22). In certain embodiments, said primary fuel outlet (22) is configured as a plate (72) comprising primary fuel exit holes (23), particularly as a fuel plate (72) comprising primary fuel exit holes (23).
The primary fuel conduit (20) may further comprise a particular primary fuel connector (21).
Herein, the distance between the primary fuel outlet (22) and the primary fuel conduit end plane (24) and/or ignition chamber end plane (26) may be defined as L0. Accordingly, in certain embodiments, the primary fuel outlet (22) is recessed in upstream direction from the primary fuel conduit end plane (24) by a distance L0. Preferably, the primary fuel conduit end plane (24) corresponds to the ignition chamber end plane (26).
In the burners herein, the primary fuel conduit (20), more specifically the primary fuel outlet (22), further comprises primary fuel exit holes (23). Accordingly, the primary fuel outlet (22) may also be designated herein a “fuel distribution nozzle”. Said outlet/nozzle maybe described as having a multiplicity of holes introducing the primary-fuel into an ignition chamber.
Herein, the diameter of the primary fuel exit holes (23) may be defined as D0. Preferably, D0/D2 is between 0.05 and 0.6
In particular embodiments, the primary fuel exit holes (23) are located on concentric circles around the center of the primary fuel exit plate (72). Preferably the total number of concentric circles is in the range of 1-7, more preferably the total number of concentric circles is between 2 and 5. Preferably, the holes are of circular shape. The holes may be of any other shape such as stars, triangles, double-stars, rectangle, etc.
Without intending to be bound by theory, such size significantly contributes to the ability to quickly mix the fuel with surrounding air.
In the burners herein, the primary fuel conduit (20) further comprises bleed holes (28).
Herein, the inner diameter of the bleed holes (28) may be defined as P1. Preferably, P1/D2 is between 0.06 and 0.5.
In preferred embodiments herein, H/P1 is from 1.25 to 2.5, wherein H is the distance between the centers of two rows of bleed holes (28).
In particular embodiments, the bleed holes (28) are arranged in rows around the primary fuel conduit. Preferably the total number of concentric circles is in the range of 1-5. Preferably there will be no more than 5 rows of bleed holes; more preferably no more than 3 rows of bleed holes. Preferably, the holes are of circular shape. The holes may be of any other shape such as stars, triangle, double-stars, rectangle, etc.
Herein the axial distance between two rows of bleed holes (28) measured between their centers may be defined as H.
Herein, the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent bleed holes (28) may be defined as angle alpha.
In particular embodiments herein, the primary fuel conduit (20) further comprises air premixing holes (27), upstream of the primary fuel outlet (22).
Herein, the diameter of the air premixing holes (27) may be defined as P0. Preferably, P0/D2 is between 0.02 and 0.2.
In particular embodiments, the air premixing holes (27) are arranged in rows around the primary fuel conduit. Preferably there will no more than 5 rows of premixing holes. More preferably there will be no more than 3 rows of premixing holes. Preferably, the holes are of circular shape. The holes can be any other shape such as stars, triangles, double-stars, rectangles, etc.
Herein, the distance between the primary fuel conduit wall (29) (or the wall of the ignition cup (75), respectively,) and the intermediate annular conduit wall (37) may be defined as L4.
Herein, the distance between the wall of the oxidant bleed cup (76) and the intermediate annular conduit wall (37) may be defined as L5.
Further as to the main oxidant conduit (30), same may be designated herein as “pipe 3”, particularly as an air pipe.
Herein, the inner diameter of the main oxidant conduit (30) may be defined as D4.
Accordingly, the main oxidant conduit wall (39) may have an inner diameter D4.
In the present invention, the main oxidant is preferably air.
Herein, the distance between the intermediate annular conduit end plane (36) and the main oxidant conduit end plane (38) may be defined as L2. Accordingly, in certain embodiments, the intermediate annular conduit end plane (36) is recessed in upstream direction from the main oxidant conduit end plane (38) by a distance L2.
In the burners herein, the main oxidant conduit (30) further comprises an intermediate annular conduit (35).
In the present invention, the intermediate annular conduit (35) is configured to allow splitting of the main oxidant into two portions, such that a first portion is introduced into the ignition chamber (25) via a plurality of bleed holes (28) as defined above.
The first portion is preferably about 20% of the total volumetric flow. In particular embodiments, the first portion is in the range of 2%-40%, preferably the range is 10% to 25%.
In preferred embodiments herein, the first portion of the main oxidant enters into the ignition chamber at a right angle to the primary fuel outlet. (via the peripheral wall of the chamber).
Accordingly, in preferred embodiments herein, the first portion of the main oxidant enters into the ignition chamber in a direction that is perpendicular to the flow direction of the primary fuel.
Without intending to be bound by theory, this serves to vigorously mix the fuel and “ignition” air such that peak flame temperatures are reduced compared with typical diffusion flames. This is regarded important for minimization of flame-generated NOx emissions. Moreover, the method of air introduction also keeps the peripheral wall cooled by protecting it from direct contact with the flame.
Herein, the distance between the primary fuel conduit end plane (24) and the intermediate annular conduit end plane (36) may be defined as L1. Accordingly, in certain embodiments, the primary fuel conduit end plane (24) is recessed in upstream direction from the intermediate annular conduit end plane (36) by a distance L1.
In preferred embodiments of the present invention the burners are characterized in that the main oxidant conduit (30) further comprises a swirler section (33).
Accordingly, the intermediate annular conduit (35) is preferably configured to allow splitting of the main oxidant into two portions, wherein a second portion is introduced into a swirler section (33).
In particular, in preferred embodiments herein, the annular conduit (35) is configured to allow splitting of the main oxidant into two portions, such that a first portion is introduced into the ignition chamber (25) via the plurality of bleed holes (28) to mix with the primary fuel, and a second portion is introduced into a swirler section (33), which further comprises the main oxidant conduit.
Without intending to be bound by theory, the second portion of air introduced into the swirler section induces a strong tangential flow field in the combustion chamber that acts to increase the rate of mixing among the oxidant and fuel, while also creating a compact flame and one that does not contain appreciable soot.
Again without intending to be bound by theory use of a swirler to swirl the air is well-known in the field of combustion. The primary function of the swirl is to provide a tangential flow to e.g. the air exiting pipe 3 and create a recirculation zone at the center that brings in hot combustion gases back towards the burner exit plane thereby providing a continuous source of ignition to the fresh reactants. The upper and lower bound of the swirl angle is determined by the length of the furnace, and burner firing rate.
Preferably, the swirl angle is from 5 to 70 degrees, preferably from 30 to 45 degrees.
As used herein, a “swirl angle” is defined to be the angle between a plane that is nominally tangent to the outlet of the swirler blades and the plane parallel to the main axis of the burner.
Preferably herein, the strength of the swirl imparted to the fluid may be quantified by the Swirl number S, defined as the ratio of the axial flux of the angular momentum Gφ to the product of the axial thrust Gx and the exit radius R of the burner nozzle. When S=Gφ/GxR is less than 0.6, the fluid is in the weak swirl regime, and when S is greater than 0.6 the fluid is in the strong swirl regime. The swirl number is in the range from 0.1 to 1.5. This swirl number or strength can be produced by using either axial or radial or tangential swirler.
In certain embodiments, the main oxidant conduit (30) further comprises purge holes (32) located on the oxidant purge plate (73), particularly in flow direction parallel to the main axis (2) of the burner.
Herein, the diameter of the purge holes (32) may be defined as D1.
In particular embodiments, the purge holes (32) are arranged in a circular way on different concentric diameters as 1-7 series of diameters, preferably 1-3 concentric diameters of holes. Preferably, the holes are of circular shape. The holes may be of any other shape such as stars, triangle, double-stars, rectangle, etc.
The main oxidant conduit (30) may further comprise a particular main oxidant connector (31).
Further as to the secondary fuel conduit (40), same may be designated herein as “pipe 4”, which is a gaseous fuel pipe.
Herein, the inner diameter of the secondary fuel conduit (40) may be defined as D5.
Accordingly, the secondary fuel conduit wall (49) may have an inner diameter D5.
The burners of the present invention are designed to operate using any gaseous fuels like natural gas (NG), hydrogen (H2), LPG, biogas, synthesis gas, hydrogen, ammonia or other gases
Hence, in accordance with the present invention, the primary fuel used in the burner is any gaseous fuel. In preferred embodiments, it is selected from the group consisting of NG, H2, NH3, and LPG.
In accordance with the present invention, the secondary fuel is any gaseous fuel. In preferred embodiments, the secondary fuel is tailgas. In preferred embodiments, the secondary fuel is selected from the group consisting of PSA waste gas, H2, NG, NH3, LPG, syngas, H2/CO/CO2/CH4 mixture and H2/N2/NH3 mixture).
Generally herein, the specific nature of the fuels and oxidants to be used with the burner of the present invention is not particularly limited.
As used herein, an “outlet plane” of a given conduit designates a plane defined in direction perpendicular to the main axis of the conduit at a downstream location where the fuel or oxidant respectively is no longer restricted by two walls.
As used herein, a “conduit end plane” of a given conduit designates a plane defined in direction perpendicular to the main axis of the conduit at the downstream end of the conduit.
In preferred embodiments herein, D1/D2 is from 0.06 to 0.15.
In preferred embodiments herein, D3/D2 is from 1.5 to 5.0, in particular from 1.9 to 3.5.
In preferred embodiments herein, D4/D2 is from 2.0 to 12.0, in particular from 3.5 to 10.
In preferred embodiments herein, D5/D2 is from 5.0 to 25.0, in particular from 8 to 18.
In preferred embodiments herein, D6/D2 is from 1.5 to 6.0, in particular from 2.0 to 4.5.
In preferred embodiments herein, D8/D4 is from 1.1 to 1.4.
In preferred embodiments herein, D9/D4 is from 1.6 to 2.5.
In preferred embodiments herein, L0/D3 is from 0.2 to 2.0, in particular from 0.4 to 1.0.
In preferred embodiments herein, (L1+L2)/D3 is from 0.2 to 2.0, in particular from 0.4 to 0.7.
In preferred embodiments herein, (L01)/D3 is from 0.1 to 1.0, in particular from 0.3 to 0.8, wherein the length of the oxidant bleed cup is defined as L01.
In preferred embodiments L4/L1 is between 0.7 and 1.1.
In preferred embodiments L4/D3 is between 0.2 and 0.6.
In preferred embodiments L5/L1 is between 0.3 and 0.6.
Herein, the angle between the centers of two consecutive bleed holes (28) measured at the center of the conduit may be defined as angle alpha.
In preferred embodiments herein, angle alpha is from 10 to 20 degrees.
Without intending to be bound by theory, a lower range limit of angle alpha helps to separate the holes such that they are not too close to result in stream of oxidant with limited mixing with trim/primary fuel—and a higher range prevents the holes from being too far and ensures there is enough coupling between two jets to provide mixing of fuel-oxidant inside the mixing cup.
Each row may be symmetrically staggered to provide three dimensional mixing effects. This mixing may be important to provide a reliable ignition of the burner at lean equivalence ratio of as small as 0.25.
In preferred embodiments, 1.25<=H/P1<=2.5.
The ratio of area of all bleed holes in one row to the surface area of cylinder of height, P1 and inner diameter, D2 may be between 10% and 55%
Herein, the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent (oxidant) purge holes (32) may be defined as angle beta.
In preferred embodiments herein, angle beta is from 10 to 40 degrees.
Without intending to be bound by theory, a lower range of angle beta helps to separate the holes such that they are not too close to create air rich regions—and a higher range prevents the holes from being too far and ensures there is enough coupling between two jets to provide enough air for fuel-air mixing and create low velocity regions and recirculation zones to provide flame anchoring zone.
In preferred embodiments, the oxidant purge plate (73) has a porosity (defined by the total open area on the plate that allows the air to flow divided by cross-section area of the plate) in the range of 1% to 8%.
Herein, the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent secondary fuel exit holes (48) may be defined as angle gamma.
In preferred embodiments herein, angle gamma is from 10 to 90 degrees.
This angle may be the same or vary for holes located on each series of concentric hole pattern.
The total number of holes on each series of concentric hole pattern may be determined based on how the fuel amount is distributed, to reduce the NOx formation, across the different series of concentric hole pattern.
In preferred embodiments, the porosity of the secondary fuel distribution plate is in the range of 8% to 25%
Herein, the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent primary fuel exit holes (23) may be defined as angle theta.
In preferred embodiments herein, angle theta is from 10 to 50 degrees.
Without intending to be bound by theory, a lower range helps to separate the holes such that they are not too close to cause fuel rich regions and prevent from air-fuel mixing—and a higher range prevents the holes from being too far and ensures there is enough coupling between two jets to provide coupling effect of heat release from each jet for stable combustion.
In preferred embodiments, the primary fuel exit plate (72) has a porosity (defined by the total open area on the plate that allows the fuel to flow divided by cross-section area of the plate) in the range of 4% to 25%.
Generally herein, wherein the burner comprises different rows of holes, consecutive holes in different rows of holes may be staggered by half the included angle between the two consecutive holes in one row.
Preferably herein, wherein a given element of a burner, comprises different rows of holes, consecutive holes in different rows of holes are staggered by half the included angle between the two consecutive holes in one row.
In preferred embodiments, the burner (1) is configured in such a way that the velocity of the primary fuel at the exit of the primary fuel exit holes (23) is between 30 ft/s and 500 ft/s, particularly between 40 ft/s and 400 ft/s.
Without intending to be bound by theory, the velocity of primary fuel is determined to significantly contribute to the ability quickly mix the fuel with surrounding air. This velocity range provides a stable flame without any lift-off.
In preferred embodiments, the burner (1) is configured in such a way that the velocity of the main oxidant at the exit of the oxidizer pipe (34) is between 10 ft/s and 300 ft/s, particularly between 40 ft/s and 200 ft/s.
Without intending to be bound by theory, the maximum attainable main oxidant (preferably air) velocity is typically determined by the available pressure from the air blower. The present inventors found that these velocities provides sufficient mixing of the air with the two fuels and maintains a stable flame over a wide range of burner operations even in a cold furnace.
In preferred embodiments, the burner (1) is configured in such a way that the velocity of the secondary fuel is between 30 ft/s and 500 ft/s, particularly between 100 ft/s and 400 ft/s.
Without intending to be bound by theory, the velocity of the secondary fuel is maximized, within the constraints of stable and complete combustion, so as to, in turn, maximize entrainment of furnace gases in the fuel jets thereby diluting the combustion reactions. This helps to reduce tendency of the burner to form thermal NOx through lowering of the peak combustion temperature. Secondary fuel velocity that is below the low velocity limit can result in weak mixing, leading to unreacted fuel collecting near the furnace wall. This fuel can subsequently combust there causing over-heating of the reformer top wall.
In preferred embodiments, the burner of the invention is operated in such a way that
In preferred embodiments, the burner is configured in such a way that i) the volumetric flow rate of the ignition chamber oxidant, preferably of the bleed cup (76) oxidant, is about 5 to 25% of the total main oxidant flow rate; and/or ii) the volumetric flow rate of oxidant, preferably of the ignition cup (75) oxidant, is about 1-10% of the total main oxidant flow rate. In one particular conduit, the volumetric flow rate of any fluid is divided amongst different outlet by correlating individual exit cross-section area with the total exit cross-sectional area for that conduit. In doing so, the pressure of the fluid and pressure differential between two adjacent conduits are important criteria to determine the directional flow of fluid.
In particular embodiments herein, the equivalence ratio is between 1.0 and 0.25.
Further embodiments herein may be defined by areas of various holes and outlets. That is, for example in a sample area notation for oxidizer conduit, the cross-sectional area of bleed holes (28), purge holes (32), and oxidant section outlet (34) may be defined as A0, A1, and A2. Preferably, A0 is 5 to 25% of (A0+A1+A2).
Accordingly, in preferred embodiments herein (see e.g. also
Moreover, in certain embodiments, air premixing holes (27) enable fluid communication between primary air and primary fuel upstream of the fuel distribution plate (72). These holes (numbers and diameter, rows of holes) may be predetermined based on the area ratio of the holes A3 and air exit area, as well as the pressures of air and primary fuel. The pre-calculated ratio is dependent on the amount of air needed in the primary fuel during startup.
Generally herein, advantageous characteristics of the present invention include the following, all of which correspond to other preferred embodiments of the first aspect:
In a second aspect of the invention, there is provided a furnace comprising a burner according to the first aspect of the invention.
Preferred embodiments of the furnaces of the invention correspond to the embodiments of the burners of the invention described above. Hence, preferably, the furnace is further defined in line with any of the above embodiments of the burner as described in context with the first aspect.
This includes embodiments relating to the above described advantages of the burner of the first aspect, which are also envisaged herein regarding respective furnaces of the second aspect.
In certain preferred embodiments, the furnace is selected from the group consisting of a furnace for steam methane reforming, a reheat furnace in steel industries, and a secondary melting furnace.
In a third aspect of the invention, there is provided a method for operating a burner of the first aspect and/or for operating a furnace of the second aspect.
Said method is not particularly limited as will readily be appreciated by the skilled person.
In certain embodiments, the method comprises the steps of i) starting the burner, ii) ramping up the burner in firing rate, iii) starting the secondary fuel, iv) further changing the flow rate of primary, secondary fuel and burner equivalence ratio as required by the process.
In particular embodiments of the third aspect, step i) comprises starting the main oxidant, the igniter, and the primary fuel.
Generally, further preferred embodiments of the methods of the invention correspond to the embodiments of the burners of the invention described above, wherein the burner used in the method is further defined by further product features. In other words, preferably, the methods of the invention are further defined in line with any of the above embodiments of the burner as described in context with the first aspect.
Moreover, even further preferred embodiments of the methods of the invention involve further method features that are based on any features described above in context with the burners of the invention.
Moreover, advantages of the present invention include the following, all of which correspond to further preferred embodiments of the third aspect:
Moreover, generally herein, preferred embodiments of any of the second to fourth aspects correspond to preferred embodiments of the first aspect herein.
In general, the articles “a” and “an” as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of “a” and “an” does not limit the meaning to a single feature unless such a limit is specifically stated. The article “the” preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used. The adjective “any” means one, some, or all indiscriminately of whatever quantity.
Moreover, generally herein, if a certain embodiment is described by using the term “comprising” or suchlike terms, further embodiments are envisaged herein as well, which are described by using the term “consisting of” or suchlike terms instead of the said term “comprising” or suchlike terms.
The present invention particularly also relates to the following items:
Item 1: A burner (1) comprising a primary fuel conduit (20) comprising a primary fuel outlet (22) having a multiplicity of primary fuel exit holes (23) for supply of a primary fuel into an ignition chamber (25), wherein the wall surrounding the ignition chamber (25) comprises a plurality of bleed holes (28), a main oxidant conduit (30) for supply of a main oxidant, comprising an intermediate annular conduit (35) in a downstream portion (5) of the burner, which intermediate annular conduit (35) is configured to allow splitting of the main oxidant, such that a first portion is introduced into the ignition chamber (25) via the plurality of bleed holes (28) to mix with the primary fuel.
Item 2: The burner of item 1, wherein at least in the downstream portion (5) of the burner (1), in which primary fuel outlet (22), ignition chamber (25), and intermediate annular conduit (35) are present, the primary fuel conduit (20) is surrounded by the main oxidant conduit (30).
Item 3: The burner of item 1 or 2, wherein fuel exit holes (23) are located at least on two different planes.
Item 4: The burner of any one of the preceding items, wherein the ignition chamber (25) comprises at least two sections, particularly wherein the sections comprise different diameters.
Item 5: The burner of any one of the preceding items, wherein the ignition chamber (25) comprises an ignition cup (75) as well as an oxidant bleed cup (76).
Item 6: The burner of any one of the preceding items, wherein the burner further comprises a secondary fuel conduit (40) for supply of a secondary fuel, having a secondary fuel outlet (44) at its downstream end.
Item 7: The burner of item 6, wherein at least in the downstream portion (5) of the burner (1), in which primary fuel outlet (22), ignition chamber (25), intermediate annular conduit (35) and secondary fuel outlet (44) are present, the primary fuel conduit (20) is surrounded by the main oxidant conduit (30) and the secondary fuel conduit (40).
Item 8: The burner of any one of items 6 and 7, wherein the secondary fuel outlet (44) comprises a secondary fuel distribution plate (45) having a multiplicity of secondary fuel exit holes (48).
Item 9: The burner of any one of the preceding items, wherein the burner is characterized in that the ignition chamber (25) is extending from the primary fuel outlet (22) to the intermediate annular conduit exit plane (56), wherein the wall surrounding the ignition chamber (25) comprises two sections, wherein i) the first section has an outer diameter smaller than or equal to the outer diameter of the primary fuel conduit (20) and comprises a plurality of bleed holes (28), wherein the wall surrounding the first section comprises a plurality of bleed holes (28), and wherein the first section further comprises means allowing the main oxidant to additionally enter the ignition chamber (25) in flow direction, ii) the second section has an inner diameter greater than the outer diameter of the primary fuel conduit (20), but the second section has an outer diameter smaller than the inner diameter of the intermediate annular conduit (35), and comprises a further plurality of bleed holes (28).
Item 10: The burner of item 9, wherein the burner further comprises a purge plate (73) with purge holes (32) present between the first section's outer diameter and inner diameter of the second section. Preferably, the burner further comprises a purge plate (73) with purge holes (32) present between the outer diameter of the second section and inner diameter of the intermediate annular conduit (35).
Item 11: The burner of any one of the preceding items 1-8, wherein the ignition chamber (25) is extending from the primary fuel outlet (22) to the intermediate annular conduit exit plane (56), wherein the wall surrounding the ignition chamber (25) comprises two sections, wherein i) the first section is extending from the primary fuel outlet (22) to the primary fuel conduit end plane (24), wherein the primary fuel conduit wall (29) surrounding the section comprises a plurality of bleed holes (28), and ii) the second section has an inner diameter greater than the outer diameter of the primary fuel conduit (20), but the second section has an outer diameter smaller than the inner diameter of the intermediate annular conduit (35), and comprises a further plurality of bleed holes (28).
Item 12: The burner of item 11, wherein the burner further comprises an oxidant purge plate (73) with purge holes (32) that extends between the first section's outer diameter and the inner diameter of the second section.
Item 13: The burner of any one of the preceding items 1-8, wherein the ignition chamber (25) is extending from the primary fuel outlet (22) to the intermediate annular conduit exit plane (56), wherein the wall surrounding the ignition chamber (25) comprises at least two sections of annular conduits with increasing diameter, each of which comprises a plurality of bleed holes (28).
Item 14: The burner of item 13, wherein the wall surrounding the ignition chamber (25) comprises two or three sections of annular conduits with increasing diameter, each of which comprises a plurality of bleed holes (28).
Item 15: The burner of any one of the preceding items, wherein the burner (1) further comprises one or more mechanical mixer plates (74).
Item 16: The burner of item 15, wherein said one or more mechanical mixer plates (74) are each located downstream of and adjacent to one section of the ignition chamber (25).
Item 17: The burner of any one of the preceding items 15-16, wherein the mechanical mixer plate(s) (74) has/have a disk type structure that breaks the fuel flow coming out of fuel exit holes (23).
Item 18: The burner of any one of the preceding items, wherein the purge holes (32) are located on an (oxidant) purge plate (73).
Item 19: The burner of any one of the preceding items, wherein the burner comprises secondary fuel exit holes (48) that are located on a secondary fuel distribution plate (45).
Item 20: The burner of any one of the preceding items, wherein the burner further comprises an ignition source (10), wherein the outer diameter of the ignition source (10) is preferably defined as D2.
Item 21: The burner of item 20, wherein the ignition source (10) terminates in the ignition chamber (25).
Item 22: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the diameter of the primary fuel exit holes (23) is defined as D0 and wherein D0/D2 is between 0.05 and 0.6.
Item 23: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the inner diameter of the bleed holes (28) is defined as P1 and wherein P1/D2 is between 0.06 and 0.5.
Item 24: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the diameter of the air premixing holes (27) is defined as P0 and wherein P0/D2 is between 0.02 and 0.2.
Item 25: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the diameter of the purge holes (32) is defined as D1, and wherein D1/D2 is from 0.06 to 0.15.
Item 26: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the inner diameter of the primary fuel conduit (20) is defined as D3 and wherein D3/D2 is from 1.5 to 5.0, in particular from 1.9 to 3.5.
Item 27: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the inner diameter of the main oxidant conduit (30) is defined as D4, and wherein D4/D2 is from 2.0 to 12.0, in particular from 3.5 to 10
Item 28: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, The inner diameter of the secondary fuel conduit (40) is defined as D5 and wherein D5/D2 is from 5.0 to 25.0, in particular from 8 to 18.
Item 29: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the inner diameter of the oxidant bleed cup is defined as D6, and wherein D6/D2 is from 1.5 to 6.0, in particular from 2.0 to 4.
Item 30: The burner of any one of the preceding items, wherein the innermost extension of an inner circle of secondary fuel exit holes is defined as D8, the inner diameter of the main oxidant conduit (30) is defined as D4 and wherein D8/D4 is from 1.1 to 1.4.
Item 31: The burner of any one of the preceding items, wherein the outermost extension of an outer circle of secondary fuel exit holes is defined as D9, the inner diameter of the main oxidant conduit (30) is defined as D4 and wherein D9/D4 is from 1.6 to 2.5.
Item 32: The burner of any one of the preceding items 1, wherein the inner diameter of the primary fuel conduit (20) is defined as D3, the primary fuel outlet (22) is recessed in upstream direction from the primary fuel conduit end plane (24) by a distance L0, and wherein L0/D3 is from 0.2 to 2.0, in particular from 0.4 to 1.0
Item 33: The burner of any one of the preceding items, wherein the inner diameter of the primary fuel conduit (20) is defined as D3, the distance between the primary fuel conduit end plane (24) and the intermediate annular conduit end plane (36) is defined as L1, the distance between the intermediate annular conduit end plane (36) and the main oxidant conduit end plane (38) is defined as L2 and wherein (L1+L2)/D3 is from 0.2 to 2.0, in particular from 0.4 to 0.7.
Item 34: The burner of any one of the preceding items, wherein the inner diameter of the primary fuel conduit (20) is defined as D3, the length of the oxidant bleed cup is defined as L01, and wherein (L01)/D3 is from 0.1 to 1.0, in particular from 0.3 to 0.8.
Item 35: The burner of any one of the preceding items, wherein the outer diameter of the ignition source (10) is defined as D2, the diameter of secondary fuel exit holes is defined as D7 and wherein D7/D2 is between 0.05 and 0.6.
Item 36: The burner of any one of the preceding items, wherein the angle between the centers of two consecutive bleed holes (28) measured at the center of the conduit is defined as angle alpha, wherein angle alpha is from 10 to 20 degrees.
Item 37: The burner of any one of the preceding items, wherein the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent (oxidant) purge holes (32) is defined as angle beta, wherein angle beta is from 10 to 40 degrees.
Item 38: The burner of any one of the preceding items, wherein the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent secondary fuel exit holes (48) is defined as angle gamma, wherein angle gamma is from 10 to 90 degrees.
Item 39: The burner of any one of the preceding items, wherein the circumferential angle defined by the main axis (2) of the burner and the centers of two adjacent primary fuel exit holes (23) is defined as angle theta, wherein angle theta is from 10 to 50 degrees.
Item 40: The burner of any one of the preceding items, wherein the burner comprises at least one primary fuel exit plate (72), the porosity of which is particularly from 4% to 25%.
Item 41: The burner of any one of the preceding items, wherein the burner comprises at least one secondary fuel distribution plate (45), the porosity of which is particularly from 8% to 25%.
Item 42: The burner of any one of the preceding items, wherein the burner is configured in such a way that the velocity of the primary fuel is between 30 ft/s and 500 ft/s.
Item 43: The burner of any one of the preceding items, wherein the burner is configured in such a way that the velocity of the primary fuel is between 40 ft/s and 400 ft/s.
Item 44: The burner of any one of the preceding items, wherein the burner is configured in such a way that the velocity of the secondary fuel is between 30 ft/s and 500 ft/s, particularly between 100 ft/s and 400 ft/s.
Item 45: The burner of any one of the preceding items, wherein the burner is configured in such a way that the velocity of the main oxidant is between 10 ft/s and 300 ft/s, particularly between 40 ft/s and 200 ft/s.
Item 46: The burner of any one of the preceding items, wherein the main oxidant conduit (30) further comprises a swirler section (33).
Item 47: The of any one of the preceding items, wherein the intermediate annular conduit (35) is configured to allow splitting of the main oxidant into two portions, wherein a second portion is introduced into an oxidant section (33), such as a swirler section (33)
Item 48: The burner of any one of the preceding items 46-47, wherein the swirl angle is from 5 to 70 degrees, preferably from 30 to 45 degrees.
Item 49: The burner of any one of the preceding items, wherein the burner is characterized in that it provides improved mixing of main oxidant and primary fuel.
Item 50: The burner of any one of the preceding items, wherein the burner is characterized in that it allows operating the burner over a wide range of fuel composition.
Item 51: The burner of any one of the preceding items, wherein the burner is characterized by a primary fuel turndown ratio of 1:30.
Item 52: The burner of any one of the preceding items, wherein the burner is characterized in that it allows operation over a wide range of split of heat supplied from primary and secondary fuel.
Item 53: A method for operating a burner (1) in accordance with any one of items 1 to 52, the method comprising the steps of
Item 54: A method for operating a burner (1) in accordance with any one of items 1 to 52, the method comprising the steps of
Item 55: The method of item 53 or 54, wherein step i) comprises starting the main oxidant, the igniter, and the primary fuel.
Item 56: The burner of any one of the preceding items 53-55, wherein the burner (1) is configured in such a way that
Item 57: The method of any one of the preceding items 53-56, wherein the burner (1) is configured in such a way that during start-up, about 100% of the total thermal power of the burner is provided by the primary fuel.
Item 58: The method of any one of the preceding items 53-57, wherein the burner (1) is configured in such a way that during normal operation, about 0 to 70%, preferably 45 to 65% of the total thermal power of the burner is provided by the primary fuel.
Item 59: The method of any one of items 57 to 58, wherein the respective rest is provided by the secondary fuel.
Item 60: The method of any one of the preceding items 53-59, wherein the burner (1) is configured in such a way that
Item 61: The method of any one of the preceding items 53-60, wherein the burner (1) is configured in such a way that the volumetric flow rate of the ignition chamber oxidant is about 5 to 25% of the total main oxidant flow rate.
Item 62: The method of any one of the preceding items 53-61, wherein the burner (1) is configured in such a way that the volumetric flow rate of oxidant is about 1-10% of the total main oxidant flow rate.
Item 63: The method of any one of the preceding items 53-62, wherein the burner (1) is configured in such a way that, during normal operation, the burner can be turned down from 100% design firing rate to about 1:30 turndown, depending on the operation requirements.
Item 63: The method of any one of the preceding items 53-62, wherein the burner (1) is operated in such a way that the equivalence ratio is between 1.0 and 0.25.
The following example is provided to further illustrate aspects of the invention, but are by no means intended to be limiting in any way.
An examplary test burner with air as oxidant and natural gas as primary fuel (trim fuel) and a mixture of (H2, N2, NH3) as a low BTU value tailgas fuel was designed, manufactured, and tested in a laboratory test furnace.
The burner was operated over a wide range of operating conditions (Start-up, full load at heat-up, 100% design firing rate with both fuel, and 50% turndown condition with both fuel). The average furnace wall temperature under these conditions was in the range 450 F (during start-up and single fuel operation)-1600 F (dual fuel operation).
The plot in
The total burner firing rate, split of primary and secondary fuel thermal output, burner equivalence ratio, and composition of the primary fuel and secondary fuel are same for all the three burners. The three burners are identical except for the different way secondary fuel is injected through the burner. Table 1 (see also
Quantification of the flux of Thermal energy from secondary fuel is defined by:
The fact that the Burner C is able to produce significantly lower NOx as compared to Burner A and Burner B is regarded to be due to multiple unique features of the former burner as follows. First, the secondary fuel exit holes (48) located on progresively larger concentric circle pattern helps to achieve a more distributed combustion by radially separating the fuel injection holes away from the primary fuel flame. The increasing radial separation away from the primary fuel flame is important because this burner feature allows some fraction (50%) of the ‘secondary fuel’ to be injected and combust in a zone which is relatively lower temperature as compared to the primary flame temperature. In burners B and A, all of the secondary fuel is injected in a space that has higher temperature due to it's proximity to the primary fuel flame. The design of Burner C thus has lower tendency to form thermal NOx as compared to other designs. This effect is especially significant when secondary fuel has components like hydrogen and ammonia that have tendency to form higher NOx due to higher flame temperature and/or ability of the fuel to produce radical species that have chemical pathways to form NOx.
Second, the design exit velocity range for the secondary fuel allows entrainment of the furnace gases in the fuel jets thereby diluting the fuel jets. The composition and temperature of entrained gases changes as we move radially away from the oxidant conduit. Thermal NOx formation is primarily influenced by temperature and oxygen concentration. Temperature and oxygen concentration, in particular, reduces as we move radially out from the oxidant conduit because of increased radial seperation from the heat release region of the primary fuel flame and also, the oxidizer stream. As a result of this trend in temperature and furnace gas composition, the fuel jets that are located on outer series of holes would potentially entrain gases that have relatively lower temperature and oxygen concentration as compared to inner series of holes. This feature of entraining furnace gases to dilute the secondary fuel stream helps to reduce tendency of the burner to form thermal NOx by enabling distribution combustion, which helps to lower the peak combustion temperatures.
Lastly, the burner provides improved performance on NOx emissions. The bleed holes (28) provides air in the igniton cup that can be entrained by the fuel jets before the fuel leaves the exit plane of the burner. This enhanced mixing through a unique burner cup tip (ignition chamber) design thereby allows reducing peak temperatures relative to common characteristics of non-premixed burners. The lower peak temperature for this burner flame mimics that of a partially-premixed air-fuel combustion rather than non-premixed combustion.
Additionally to compare Burner B and Burner C, there is a practical higher limit by which a single series of secondary fuel injection holes can be radially seperated from the oxidant conduit (D8/D4). In Burner B, if the D8/D4 is increased to assist in NOx reduction, at a certain radial separation limit the plant operation to start secondary fuel injection below auto-ignition temperature of the secondary fuel is inhibited because it can lead to uncombusted fuel leaving the furnace. In the current invention Burner C, the secondary fuel exit holes (48) located on progresively larger concentric circle pattern allow combustion from fuel injected from inner series of holes to provide energy to initiate and combust the fuel injected from outer series of holes. This cascading combustion effect in Burner C allows plant operator to start the secondary fuel injection in a cold furnace (not above auto-ignition of secondary fuel) and still combusting all the fuel.
Furthermore, this cascading effect of combustion from inner series of holes to outer series of holes enable to combust a wide range of low Btu value fuel mixtures. A single series of secondary fuel injection holes (burner B and/or A) would not allow such fuel-flexibility without sacrifising on NOx emission. The current burner allows operating the burner over a wide range of fuel composition in a cold furnace. E.g. 5% H2-90% N2 to 90% H2-5% N2 and remaining constituents could be NH3, H2O. The total mole % of H2 and N2 could e.g. range from 50% to 95% of the total mixture. The secondary fuel injection holes located on the innermost circle (D8) are regarded important for flame stability over a wide range of H2 concentration in the secondary fuel.
The burner is able to produce stable flame at high turndown of 1:30 and at equivalence ratio of 0.25. This performance is because of the unique configuration of burner hardware that includes the location of air purge plate (73), step design aspect of it, and allowing the air to flow axially through the air purge plate (73) that provides a robust flame anchoring location. The burner provides multiple flame achoring location based on the total firing rate of the burner as illustrated in
The burner is able to produce a stable flame for a wide range of split of primary and secondary fuels. The primary fuel can supply 5% to 100% of the total burner thermal output and remaining balance coming from the secondary fuel. The main reason for this flexible performance is the strong flame anchoring zone for primary fuel provided by the air purge plate (73) as discussed above that allows the primary fuel heat input to be reduced to as low as 5% of the total thermal output.
The design features of the burner allow the oxidizer to be radially and axially purged in the ignition cup that keeps the peripheral wall cooled by protecting it from direct contact with the flame. The burner was operated in a plant setting reactor furnace and after one year of operation was found spotless without any damage to the burner hardware, in particular the ignition cup.
Finally, the burner ignites well at equivalence ratios as low as 0.25, even at cold furnace conditions. This is possible because of the unique design of ignition cup that provides a zone where local ignition can be initiated and sustained while the composite fuel-air mixture is still below the global burner lower flamibility limit of natural gas, which occurs at an equivalence ratio of approximately 0.48. Specifically, this is due to a portion of primary air being introduced into the ignition chamber, entering via the peripheral wall of the chamber, which is at right angles to the fuel distribution nozzle. This serves to vigorously mix the fuel and “ignition” air, creating numerous “pockets” of local fuel-air mixture having equivalence ratio within the flammable region, thereby enabling ignition to reliably and repeatably occur in spite of the composite gas mixture having a non-flammable fuel concentration.
