阅读说明：本技术 玻璃前炉氧燃料燃烧器 (Oxygen-fuel burner for glass forehearth ) 是由 M·D·达戈斯蒂尼 M·J·加拉赫尔 A·维诺德 于 2021-05-24 设计创作，主要内容包括：一种用于增加火焰湍流的燃烧器供气装置,该装置包含：导管,该导管特征宽度W,该导管由具有圆周方向和轴向方向的内表面界定,该轴向方向终止于界定喷嘴出口平面并且具有特征尺寸d的喷嘴,其中d≤W；以及三个钝体,每个钝体具有特征尺寸D-(bb-i),每个钝体从该内表面向该导管内突出长度L-(i),并且相邻钝体之间具有轴向间距X-(i)(在X-(1)的情况下,在下游钝体和喷嘴出口平面之间),其中0.5≤L-(i)/W≤1,并且其中X-(i)/D-(bb-i)≤30。(A burner gas supply apparatus for increasing flame turbulence, the apparatus comprising: a conduit of a characteristic width W, the conduit defined by an inner surface having a circumferential direction and an axial direction, the axial direction terminating in a nozzle defining a nozzle exit plane and having a characteristic dimension d, wherein d ≦ W; and three bluff bodies, each bluff body having a characteristic dimension D bb‑i Each bluff body protruding from the inner surface into the catheter by a length L i And adjacent blunt bodies have an axial spacing X i (at X) 1 In the case of (1), between the downstream bluff body and the nozzle outlet plane), where 0.5. ltoreq.L i W.ltoreq.1, and wherein X i /D bb‑i ≤30。)

1. A burner gas supply apparatus for increasing flame turbulence, the apparatus comprising:

a conduit having a characteristic width W defined by an inner surface having a circumferential direction and an axial direction, the axial direction terminating in a nozzle defining a nozzle exit plane and having a characteristic dimension d, wherein d ≦ W; and

a first bluff body having a characteristic dimension D_bb-1Protruding into the conduit from the inner surface by a length L₁Wherein L is more than or equal to 0.5₁W is less than or equal to 1, and the first blunt body is represented by X₁Is spaced from the nozzle outlet plane, wherein X₁/D_bb-1Less than or equal to 30; and

a second bluff body having a characteristic dimension D_bb-2Protruding into the conduit from the inner surface by a length L₂Wherein L is more than or equal to 0.5₂W ≦ 1, the second bluff body being further from the nozzle exit plane in the axial direction than the first bluff body and being X₂Is spaced apart from the first bluff body, wherein X₂/D_bb-2≤30；

A third bluff body having a characteristic dimension D_bb-3Protruding into the conduit from the inner surface by a length L₃Wherein L is more than or equal to 0.5₃W ≦ 1, the third bluff body being further from the nozzle exit plane than the second bluff body in the axial direction and being X₃Is spaced apart from the second bluff body, wherein X₃/D_bb-3≤30；

Wherein the first bluff body and the second bluff body are separated by a first spacing angle in the circumferential direction; and is

Wherein the second bluff body and the third bluff body are separated by a second angular interval in the circumferential direction.

2. The burner gas supply apparatus according to claim 1,

wherein 0.5 x (1+ d/W) is less than or equal to L₁/W≤1；

Wherein 0.5 x (1+ d/W) is less than or equal to L₂W is less than or equal to 1; and is

Wherein 0.5 x (1+ d/W) is less than or equal to L₃/W≤1。

3. The burner gas supply apparatus according to claim 1,

wherein L is more than or equal to 0.8₁/W≤1；

Wherein L is more than or equal to 0.8₂W is less than or equal to 1; and is

Wherein L is more than or equal to 0.8₃/W≤1。

4. The burner gas supply apparatus of claim 1 wherein 0.6 ≦ d/W ≦ 0.7.

5. The burner gas supply apparatus according to claim 1,

wherein X₁/D_bb-1≤5；

Wherein X₂/D_bb-2Less than or equal to 5; and is

Wherein X₃/D_bb-3≤5。

6. The burner gas supply apparatus of claim 1, wherein the first bluff body and the conduit are sized such that the first bluff body Reynolds number Re_bb-1=ρV_{An inlet}D_bb-1Mu is equal to or greater than 50; and is

Wherein the nozzle feature size d is sized to provide a jet Reynolds number Re_j=ρV_jd/mu is equal to or greater than the Reynolds number Re of the first blunt body_bb-1。

7. The burner gas supply apparatus of claim 1, wherein the first bluff body has a circular cross-section.

8. The burner air supply apparatus of claim 1, wherein the first and second spacing angles are each greater than 60 degrees and less than 180 degrees.

9. The burner air supply apparatus of claim 1, wherein the first and second angular intervals are each between 110 degrees and 130 degrees.

10. The burner air supply apparatus of claim 1, wherein the first and second angular intervals are each between 80 and 100 degrees.

11. The burner gas supply apparatus of claim 1, further comprising:

a fourth bluff body having a characteristic dimension D_bb-4Protruding into the conduit from the inner surface by a length L₄Wherein L is more than or equal to 0.5₄W is less than or equal to 1, and the fourth blunt body is arranged on the shaftIs further from the nozzle exit plane than the third bluff body in an upward direction and is at X₄Is spaced apart from the third bluff body, wherein X₄/D_bb-4≤30；

Wherein the third bluff body and the fourth bluff body are separated by a third angular separation in the circumferential direction.

12. The burner gas supply apparatus of claim 11, wherein the first, second, and third spacing angles are each between 80 and 100 degrees.

13. A burner, comprising:

the burner gas supply apparatus according to claim 1; and

a reactant conduit surrounding the burner gas supply;

wherein the burner gas supply is configured and arranged to supply one of a fuel and an oxidant; and is

Wherein the reactant conduit is configured and arranged to supply the other of the fuel and the oxidant.

Background

Efficient design of the burner requires control of flame characteristics, particularly flame length. Accurate knowledge of the flame length is particularly important because many burners are installed in a combustion chamber and flame characteristics cannot be visually inspected during operation.While experimental and engineering guidelines help predict flame length based on the design and operating parameters of the combustor and combustion chamber, it is well known that turbulent flames are more reliable in flame length prediction and control than laminar flames. While many factors may affect the transition point from a laminar flame to a turbulent flame, a dimensionless Reynolds number Re based on flow characteristics and combustor center jet geometry is typically employed_j. Its definition is shown in equation 1 below:

Re_j＝ρV_jD_j/μ (1)

in the formula, ρ is the central jet density on the nozzle exit plane; v is the center jet mean nozzle exit velocity, D is the nozzle diameter, and μ is the center jet kinetic viscosity, again determined by the conditions on the nozzle exit plane.

As an initial paper by Hawthorne et al ("Mixing and Combustion in Turbulent Gas Jets"),third party symposium of combustion, flame and explosion phenomenaPage 266-. Mixing in a laminar flame is controlled by the molecular diffusivity (which is a material property of the gases being mixed), while mixing in a turbulent flame is driven by turbulent "vortices". Unlike molecular diffusivity, so-called vortex diffusivity is not a material property, but is proportional to the product of the flame jet velocity and the nozzle exit plane diameter. FIG. 1 summarizes the effect of these different mixing modes on flame length. That is, the normalized length L/D of a laminar jet flame (L being the flame length and D being the nozzle exit plane diameter) increases with increasing nozzle flow rate, while the normalized length L/D of a turbulent jet flame remains unchanged.

As further seen in fig. 1, the maximum length of a laminar flame may be much longer than the maximum length of a fully turbulent flame. Thus, while flames may be primarily designed for turbulent operation, non-designed, low flow operation may result in flame lengths that exceed expectations, impacting the combustor end wall, resulting in premature failure of the wall insulation and structural materials or heat transfer surfaces.

Finally, in most practical combustion applications, the furnace interior environment is typically not stationary. In this case, long laminar flames tend to be relatively difficult to control because most of the fuel flow remains unreacted as the momentum dissipates. In contrast, turbulent jet flames mix rapidly, so the stability of the flame jet benefits from the increase in the velocity of the expanding hot gases. Laminar flames are therefore more easily deflected by furnace gas flow and incomplete combustion than turbulent flames, and these defects often result in performance and operational deficiencies related to reduced and/or misdirected flames to load heat transfer and reduced process fuel efficiency.

Disclosure of Invention

A burner is described herein comprising at least two bluff bodies in a burner gas supply conduit located at different axial positions upstream of an outlet plane. The use of multiple bluff bodies promotes the diffusion of turbulence by inducing vortices at multiple locations in the flow field, while the longitudinal spacing promotes the amplification of the turbulence effect produced by each upstream bluff body by flow field interaction.

Each bluff body may be introduced from a different circumferential location around the inner surface of the gas supply conduit. This direction produces vorticity with different axes (since vorticity is a vector) and thus a more efficient distribution of turbulence throughout the flow field.

Aspect 1: a burner gas supply apparatus for increasing flame turbulence, the apparatus comprising: a conduit having a characteristic width W, the conduit defined by an inner surface having a circumferential direction and an axial direction, the axial direction terminating in a nozzle defining a nozzle outlet plane having a characteristic dimension d, wherein d ≦ W; and a first bluff body having a characteristic dimension D_bb-1Said first bluff body protruding a length L from said inner surface into said catheter₁Wherein L is more than or equal to 0.5₁W is less than or equal to 1, and the first blunt body is separated from the outlet plane of the nozzle by X₁In the axial direction of (2), wherein X₁/D_bb-1Less than or equal to 30; and a second bluff body having a characteristic dimension D_bb-2Said second bluff body is driven from saidThe inner surface projects a length L into the conduit₂Wherein L is more than or equal to 0.5₂W ≦ 1, the second bluff body being further from the nozzle exit plane and being spaced from the first bluff body by an axial distance X than the first bluff body₂Wherein X is₂/D_bb-2Less than or equal to 30; a third bluff body having a characteristic dimension D_bb-3Said third bluff body protruding a length L from said inner surface into said catheter₃Wherein L is more than or equal to 0.5₃W ≦ 1, the third bluff body being further from the nozzle exit plane and being spaced from the second bluff body by an axial distance X than the second bluff body₃Wherein X is₃/D_bb-3Less than or equal to 30; wherein the first bluff body and the second bluff body are separated by a first angular interval in a circumferential direction; and wherein the second bluff body and the third bluff body are separated by a second angular separation in the circumferential direction.

Aspect 2: the burner gas supply apparatus according to aspect 1, wherein 0.5 x (1+ d/W) ≦ L₁W is less than or equal to 1; wherein 0.5 x (1+ d/W) is less than or equal to L₂W is less than or equal to 1; and wherein 0.5 x (1+ d/W) is less than or equal to L₃/W≤1。

Aspect 3: the burner gas supply apparatus according to aspect 1 or aspect 2, wherein 0.8. ltoreq.L₁W is less than or equal to 1; wherein L is more than or equal to 0.8₂W is less than or equal to 1; and wherein 0.8. ltoreq. L₃/W≤1。

Aspect 4: the burner gas supply apparatus according to any one of aspects 1 to 3, wherein d/W is 0.6. ltoreq. d/W.ltoreq.0.7.

Aspect 5: the burner gas supply apparatus according to any one of aspects 1 to 4, wherein X₁/D_bb-1Less than or equal to 5; wherein X₂/D_bb-2Less than or equal to 5; and wherein X3/Dbb-3 is ≦ 5.

Aspect 6: the burner gas supply apparatus according to any one of aspects 1 to 5, wherein the first blunt body and the duct are dimensioned such that a first blunt body reynolds number Re_bb-1＝ρV_{An inlet}D_bb-1Mu is equal to or greater than 50; and wherein the nozzle feature d is sized to provide a jet Reynolds number Re_j＝ρV_jd/mu is equal to or greater than the Reynolds number Re of the first blunt body_bb-1。

Aspect 7: the burner gas supply apparatus according to any one of aspects 1 to 6, wherein the first blunt body has a circular cross section.

Aspect 8: the burner air supply apparatus according to any one of aspects 1 to 7, wherein the first and second spacing angles are greater than 60 degrees and less than 180 degrees, respectively.

Aspect 9: the burner gas supply apparatus according to any one of aspects 1 to 8, wherein the first and second angular intervals are 110 degrees to 130 degrees, respectively.

Aspect 10: the burner gas supply apparatus according to any one of aspects 1 to 9, wherein the first and second angular intervals are 80 degrees to 100 degrees, respectively.

Aspect 11: the burner gas supply apparatus according to any of aspects 1 to 10, further comprising a fourth bluff body having a characteristic dimension D_bb-4Said fourth bluff body protruding a length L from said inner surface into said catheter₄Wherein L is more than or equal to 0.5₄W ≦ 1, the fourth bluff body being further from the nozzle exit plane and being spaced from the third bluff body by an axial distance X₄Wherein X is₄/D_bb-4Less than or equal to 30; wherein the third bluff body and the fourth bluff body are separated by a third angular separation in the circumferential direction.

Aspect 12: the burner gas supply apparatus according to aspect 11, wherein the third angular interval is 80 degrees to 100 degrees.

Aspect 13: a burner comprising a burner gas supply according to any one of aspects 1 to 12; and a reactant conduit surrounding the burner gas supply; wherein the burner gas supply is configured and arranged to supply one of a fuel and an oxidant; and wherein the reactant conduit is configured and arranged to supply the other of the fuel and the oxidant.

Drawings

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements:

FIG. 1 is a graph of flame height as a function of jet velocity, taken from Hottel and Hawthorne ("Diffusion in Laminar Jet Flames)",third party symposium of combustion, flame and explosion phenomenaPage 254-266, 1949).

Fig. 2A and 2B are shaded images showing a computational fluid dynamics model of laminar flame behavior in an oxy-fuel forehearth, where the lighter color indicates higher temperature: FIG. 2A shows laminar oxy-fuel flame bending due to cross flow of furnace gas at the outboard end upstream of the forehearth exhaust, where G denotes the direction of furnace gas flow; FIG. 2B shows the impingement of the wall stream flame on the upstream end of the forehearth.

FIG. 3 is a perspective end view schematic illustration of an exemplary burner tip having a plurality of small nozzles of diameter d to produce high velocity jets and increased surface area to enhance turbulent interaction with other gases within the furnace or exiting the burner.

FIG. 4 is a perspective end view schematic of a burner tip having a single nozzle with a diameter D to produce the same total cross-sectional area as the plurality of nozzles in FIG. 3, but with a single undisturbed jet.

FIG. 5 is a graph of Reynolds number and pressure drop as a function of multi-nozzle combustor nozzle aperture, as shown in FIG. 3.

FIG. 6 is a schematic end view showing the application of the multi-nozzle burner tip for oxy-fuel combustion as shown in FIG. 3, wherein fuel F flows through the multi-nozzle burner tip surrounded by an oxygen flow O-ring, and oxy-fuel combustion occurs between the fuel jets resulting in high temperatures on the nozzle face NF surfaces.

Fig. 7 is a schematic perspective view showing a qualitative flow structure resulting from flow through a truncated cylinder.

Fig. 8A and 8B are schematic diagrams showing an embodiment of a burner gas supply conduit having two bluff bodies protruding from the inner wall into the gas flow path upstream of the exit plane (left side of fig. 8A): FIG. 8A is a cross-sectional side view; fig. 8B is an end view.

Fig. 9A and 9B are schematic views showing an embodiment of a burner gas supply duct having four bluff bodies protruding from an inner wall into a gas flow path in which each adjacent bluff body is rotated circumferentially by 90 °: FIG. 9A is an end view; fig. 9B is a cross-sectional side view.

10A, 10B and 10C are cross-sectional side schematic views of three burner air supply ducts: FIG. 10A shows a baseline burner air supply conduit without features specifically designed to increase turbulence; FIG. 10B shows a burner air supply duct with cavity-driven nozzles; and figure 10C shows a burner air supply duct with a splitter nozzle.

Fig. 11 is a cross-sectional side schematic view showing the location of burner gas feed conduits as shown in fig. 8A through 10C for an experimental oxy-fuel combustion test to measure the transition reynolds number, pressure drop in the gas feed conduits, and flame length.

Fig. 12A and 12B show a schematic comparison of flame front in turbulent flames (fig. 12A), where turbulence fluctuations imposed on laminar flame front, resulting in the formation of small flames, and laminar flames (fig. 12B), where flame front is generally well defined.

FIG. 13 is a graph of experimentally measured transitional Reynolds number as a function of pressure drop in a gas supply duct.

FIG. 14 is a graph of experimentally measured flame length as a function of transitional Reynolds number for two embodiments of the present invention.

Detailed Description

Many glass manufacturing plants employ forehearths to provide slow but controlled cooling of the molten glass prior to forming at the cold end. Precise control of the cooling rate, which is achieved by balancing the heat loss from the forehearth wall and the heat input to the burner, is critical to prevent the formation of glass defects. Post-installation inspection of the burner flame is impractical because a single forehearth may use several hundred burners firing on a narrow passageway (typically 2-3 feet wide). Furthermore, the firing rate of oxy-fuel burners is relatively low and the flame jet reynolds number is typically in the range where low momentum laminar flames predominate. Furthermore, the effect of flame disturbance due to cross flow of combustion gases within the forehearth channel is significant. The detrimental effects of a large number of laminar flames in such an environment are shown in fig. 2A and 2B, which summarize the CFD simulation results for a forehearth oxy-fuel burner. As shown in fig. 2A, the flame bends most in the region most affected by the furnace gas flow G, whereas as shown in fig. 2B, the flame impinges on the opposite wall in the region where the combustion space is more stationary.

Because of the low firing rate requirements of the forehearth, oxy-fuel burners in the forehearth often produce laminar or transitional (from laminar to turbulent) jet-like flames. An undesirable aspect of laminar and transitional flames is that their flame length and stability vary very significantly as the burn rate increases or decreases. This can easily cause problems in forehearth operation, as the flame is difficult to observe from outside the forehearth and therefore may not be detectable.

Thus, as described herein, combustor characteristics have been determined to produce a transition to a turbulent flame at a lower reynolds number than naturally occurring in a typical combustor, while also avoiding any unnecessary increase in pressure drop. This design enables the oxy-fuel burner to operate in a forehearth with turbulent flame, providing better control and reliability.

Furthermore, the rapid mixing associated with the fully turbulent regime significantly reduces soot formation and flame temperature stratification, which helps to accurately control the temperature within the forehearth. Other features may include changes in the axial position of the central nozzle within the forehearth combustor furnace body, as well as the dynamic removal and replacement capabilities of the entire central nozzle assembly.

In the embodiments described herein, a central nozzle flows the combustion gases and is surrounded by an annular oxidant stream, typically comprising oxygen-enriched air or oxygen. The flow of gas through the central nozzle typically reduces the amount of unburned fuel. However, in a combustor with a central nozzle flowing oxidant and surrounded by an annular fuel gas stream, the same enhanced mixing benefits can be achieved.

The following detailed description merely provides preferred exemplary embodiments, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing detailed description of the preferred exemplary embodiments will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the invention. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the appended claims.

Various turbulence generators are used in combustion and related fields. Generally, as depicted in fig. 3, these devices enhance mixing by creating a high velocity jet array with N small nozzles in the combustor tip (note that the number of nozzles is merely exemplary, and the same concept applies to any number of nozzles in the combustor tip). The resulting consumption of pressure energy through such a device is significantly higher than the resulting consumption of a single jet of diameter D, as shown in FIG. 4, where D is²>Nd². For example, assume that a gas having a mass flow rate M, an absolute viscosity μ, and a density ρ flows through a nozzle having a single outlet with a diameter D and expands into a chamber having a larger cross-sectional dimension. Total pressure loss Δ P due to kinetic energy consumption at the nozzle outlet_{T, base line}And 1/2 ρ V²Proportional ratio, where V is the average nozzle velocity and the jet Reynolds number Re_j,_{Base line}Equal to ρ VD/μ. Suppose instead that the nozzle is configured with N holes of diameter D such that the combined cross-sectional area of the nozzle outlet is from A (where A is equal to π D²/4) reduction to A_d(wherein A is_dEqual to pi Nd²/4) and A)_d<A. A first order approximation indicates that the change in total pressure loss and jet Reynolds number relative to the baseline case for a single nozzle of diameter D is related to the reduction in nozzle area in equations 2 and 3:

ΔP_{t, reality}/ΔP_T,_{Base line}＝(A/A_d)² (2)

Re_{j, reality}/Re_j,_{Base line}＝(A/A_d)^0.5 (3)

These relationships are plotted as A in FIG. 5_dFunction of/A. FIG. 5 illustrates that as the nozzle flow area decreases, the undesirable increase in pressure loss greatly exceeds the desirable increase in Reynolds number. Further, if multiple orifices are used, as shown in FIG. 6, the nozzles will be separated for each orificeLocal combustion occurs at the surface. Since turbulence drives rapid combustion, oxy-fuel flame temperatures in excess of 5000 ° f, localized combustion can damage the combustor and shorten combustor life. It is for these reasons that the present burner is not configured as shown in fig. 5 and 6.

To be of practical industrial value, forehearth oxy-fuel burners should be capable of producing turbulent flames at low reynolds numbers while minimizing total pressure losses. The inventors have determined that an effective means of achieving this low reynolds number laminar to turbulent flame transition is a truncated bluff body in the central jet duct upstream of the nozzle exit plane. As used herein, the term "truncated" means that one end of the bluff body emanates from the flow boundary and the other end terminates within the flow field. The term "upstream" means a location away from the plane of the nozzle outlet, rather than a "downstream" location near the plane of the nozzle outlet. Fig. 7 shows a truncated cylinder in the flow field and the various forms of vorticity that result therefrom. These vortex structures may form at low reynolds numbers, which causes strategic placement of bluff bodies to produce a laminar to turbulent transition at the nozzle exit, which occurs at low reynolds numbers with low pressure losses.

In another alternative embodiment, the bluff body may be non-truncated, i.e. connected at both ends to the inner surface of the nozzle. Note that by comparison, a non-truncated bluff body has horseshoe vortices at each end of the cylinder, but neither tip nor wake vortices. Furthermore, the arched vortex is replaced by a twin scroll, the axis of which is aligned with the cylindrical axis. Although the flow structure of the non-truncated cylinder does not have the same three dimensions as the truncated cylinder, the inventors have found that the non-truncated cylinder can still be advantageously used in a combustor for the applications described herein.

The embodiments of the oxy-fuel burner described herein are based on the strategic placement of a plurality of bluff bodies to amplify the effect of vorticity formation at each bluff body and, in doing so, to catalyze the transition of the low reynolds number layer of the burner flame to turbulent flow. Thus, as shown in FIG. 8A, the present burner comprises at least two bluff bodies in a central conduit located at different axial positions upstream of the exit plane. The use of multiple bluff bodies promotes the diffusion of turbulence by inducing vortices at multiple locations in the flow field, while the longitudinal spacing promotes the amplification of the turbulence effect produced by each upstream bluff body by flow field interaction.

The burner of the invention has five important features which can be used alone and preferably in combination with one another:

first, the Reynolds number of each bluff body gas flow should be greater than the minimum Reynolds number at which Karman vortex streets are formed in its wake, as this can create flow instabilities and thus turbulence. For the burners described herein, a minimum bluff body Reynolds number (Re) of 50 is used_bb-i). For Re_bb-iAnd D_bb-iAnd i denotes a numerical index of each blunt body, as shown in fig. 8A and 9B.

The blunt body reynolds number is calculated according to equation 4:

Re_bb-i＝ρV_{an inlet}D_bb-i/μ (4)

Wherein velocity, V_{An inlet}And length scale D_bb-iWith respect to the mean free stream gas velocity near the bluff body and the ith bluff body dimension in the plane perpendicular to the main flow direction. In the case of a non-circular bluff body, the length dimension D_bb-iIndicating the width of the i-th bluff body in the flow plane as shown in figure 8B.

Secondly, the Reynolds number through each bluff body gas flow should also be less than the Reynolds number of the gas jet issuing from the nozzle, as calculated by equation 1 above, where D_jDefined as d in fig. 8A.

Therefore, combining the first and second characteristics, the following expression of the blunt body reynolds number in equation 5 is derived:

50≤Re_bb-i≤Re_j (5)

third, each bluff body should pass through a length L of 0.5 to 1.0 times the characteristic width W of the gas flow plane as shown in FIG. 8A_iAs shown in equation 6:

0.5≤L_i/W≤1.0 (6)

please note that in L_iIn the case of an edge of 1.0/W, the ith bluff body will pass completely through the central catheter and will not be truncated.

Fourth, the streamwise bluff body spacing is defined as the axial distance between two adjacent or neighboring bluff bodies divided by the upstream bluff body length dimension X_i/D_bb-i(i-2 case see fig. 8A), which should be less than or equal to 30 to ensure that the strong vorticity region generated by one bluff body lasts long enough to reach the next bluff body. As used herein, the term "adjacent" refers to two bluff bodies that are nearest neighbors in the axial direction.

Fifth, the normalized flow-direction spacing X between the furthest downstream bluff body and the nozzle exit plane₁/D_bb-1(see fig. 8A) should be less than or equal to 30.

In one embodiment of an oxy-fuel burner for forehearth applications, as shown in fig. 9A and 9B, each bluff body is introduced from a different circumferential location around the periphery of the central conduit and the flow direction or axial bluff body spacing is less than or equal to 10. The angular separation between adjacent bluff bodies in the circumferential direction generates vorticity with multiple axes, resulting in a more extensive turbulent distribution throughout the flow field, while ensuring low consumption of the vortex structure prior to interaction with adjacent downstream bluff bodies.

Preferably, four bluff bodies having a circumferential spacing angle of about 90 degrees between adjacent bluff bodies are employed, where about is defined as ± 10 degrees (i.e., the spacing between each adjacent pair of bluff bodies may be 80 to 100 degrees). Further, more preferably, the flow direction bluff body spacing is less than or equal to 5 and the bluff body extends across the diameter d of the outlet nozzle, as shown in fig. 8A and 8B. This requires adding a term to equation 6, resulting in equation 7:

0.5*(1+d/W)≤L_i/W≤1.0 (7)

equations 4, 5, 6 and 7 apply to the case where each bluff body may have different sizes and spacings. In the case where it is advantageous for all bluff bodies to have the same size and/or spacing, the term D is used for simplicity_bbL, X and Re_bbCan replace Db_b-i、L_i、X_iAnd Re_bb,i。

The purpose of this is to amplify the interaction between adjacent bluff wake flow fields, thereby desirably increasing the generation of turbulence.

Examples of the invention

Experimental comparisons were made for several embodiments of oxy-fuel burners, including the design principles set forth herein with four other configurations: a baseline nozzle without upstream turbulence-generating equipment (fig. 10A), a nozzle with single and double bluff bodies of the kind already described, a dual nozzle design with upstream turbulence generators (upstream turbulence generators are not of the bluff body kind), a nozzle with circumferential wall cavities (fig. 10B as shown in US 10,393,373), and a nozzle where the fuel is split internally into two streams which then converge vigorously (fig. 10C). Table 1 summarizes the nozzle design currently tested and the four comparative designs. Note that in the case of multiple bluff bodies, though L, D for each bluff body or the spacing between each bluff body_bbEqual to the value of X, in alternate embodiments of the present invention, each bluff body may employ its own L, D_bbAnd X values, but they are limited by equations 5, 6 and 7.

TABLE 1

An oxy-fuel combustion test was conducted in which fuel was introduced through the central nozzle design listed in table 1, which was inserted into an oxygen booster, as shown in fig. 11. The oxygen is of commercial grade (purity greater than 99%) and the fuel is pipeline natural gas.

Key parameters for relative evaluation of nozzles include:

first, the laminar to turbulent "transition" Reynolds number Re of the central jet_TR. Re was determined by deformation and time-motion initial appearance of the flame interface of fuel and oxygen streams_TR. FIGS. 12A and 12B schematically depict such a flame front appearance, sometimes referred to as a turbulent brush or small flame (see Turns forCombustion theory (An) Introduction to Combustion)2 nd edition, McGraw-Hill book company, new york, 2000).

Second, the total fuel pressure loss normalized by the nozzle outlet plane kinetic head loss, i.e., Δ P_{General assembly}/1/2ρV_{An outlet} ²。

Third, the flame length varies with the center nozzle flow rate. The flame length measurements disclosed herein were made by image analysis of flame photographs. The basis of the flame length determination is to identify the interface between the majority of the unreacted orange portion of the central fuel jet resulting from soot formation and the adjacent bluish color, these colors and C₂Associated with non-equilibrium, high-temperature emissions of C₂Are the so-called swan bands of the highly reactive part of the flame plume.

FIG. 13 compares the average transition Reynolds number and average total pressure loss for different nozzle designs, normalized by the corresponding values associated with the baseline nozzle. Two substantially parallel lines are added to the chart as the emphasis. The upper dashed line connects the results of the cavity-driven turbulence generator (name C in table 1), the single-bluff body and double-bluff body designs, and the splitter nozzle (name S in table 1). The lower solid line is a linear curve fit of the nozzle (3-BB and 4-BB-S) data described herein. Finally, the data points for the 4 bluff body long nozzle (4-BB-L) are below the solid line. A comparison of these data and curves strongly indicates that for a given pressure loss, the combustor with the inventive nozzle achieves a greater reduction in the transitional Reynolds number than the other test nozzles.

A greater reduction in the transitional Reynolds number for the 2-BB nozzle is expected, much like 3-BB rather than 1-BB. The inventors speculate that, without being bound by theory, 3-BB and 4-BB configurations may be more efficient because turbulence effects are amplified to a greater extent when the separation angle between adjacent blunts is about 120 degrees in the case of 3-BB (i.e., from 110 degrees to 130 degrees) or about 90 degrees in the case of 4-BB (i.e., from 80 degrees to 100 degrees). In a 2-BB configuration, due to the 180 degree separation angle, one or more vortices generated by the upstream bluff body may be better aligned with the downstream bluff body, resulting in less amplification. Thus, a 2-BB nozzle may be more effective in reducing the transitional Reynolds number if the circumferential spacing angle between two adjacent bluff bodies is greater than about 0 degrees and less than about 180 degrees, or greater than about 60 degrees and less than about 180 degrees.

Furthermore, in the test nozzles of the present invention, the reduction in the transitional Reynolds number at a given pressure loss was greatest for the nozzle employing the longer bluff body 4-BB-L. Further to this point, FIG. 14 shows a plot of flame length as a function of Reynolds number for examples 4-BB-S and 4-BB-L, both normalized to baseline nozzle 0. We note that the 4-BB-L data reflects a flame length that increases monotonically with Reynolds number, unlike the 4-BB-S data, which shows a longer flame just below the transition to turbulence. The behavior of 4-BB-S indicates the transition from molecular diffusion to eddy current diffusion, as explained previously and shown in FIG. 1. The 4-BB-L flame length was spike free, confirming the significant and unexpected enhancement of turbulence generation associated with the longer bluff body. Thus, this conclusion provides further evidence for enhanced performance of the longer bluff body inferred from the data in FIG. 13, which indicates that 4-BB-L has a lower transitional Reynolds number than the trend lines generated by 3-BB and 4-BB-S.

Although all of the tests were conducted with the fuel in the nozzle and oxygen passing through the annulus, it is apparent that similar beneficial results can be obtained by passing the fuel through the annulus by passing oxygen through the nozzle. Ensuring that the gas flowing through the nozzle exit plane is turbulent enough to promote mixing and achieve a turbulent flame.

While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this is done by way of illustration only and is not to be taken by way of limitation of the scope of the invention.