WO2003085243A1

WO2003085243A1 - Gas delivery system

Info

Publication number: WO2003085243A1
Application number: PCT/US2003/009603
Authority: WO
Inventors: David W. Dewis
Original assignee: Elliott Energy Systems, Inc.
Priority date: 2002-04-01
Filing date: 2003-04-01
Publication date: 2003-10-16
Also published as: AU2003226115A1

Abstract

A gas delivery system (10) and a method of metering combustible gas (B) to a combustor having a combustion chamber (14) and a nozzle (12) adapted to be in fluid communication with the combustion chamber (14). The nozzle (12) has an inner surface (18) defining a converging portion (20), a throat (22) and a diverging portion (24). The converging portion (20) is positioned upstream of the throat (22), and the diverging portion (24) is positioned downstream of the throat (22). The converging portion (20) of the nozzle (12) is adapted to be in fluid communication with a gas source (26) upstream of the converging portion (20). An end (32) of a conduit (30) is positioned at the throat (22), and the conduit (30) is adapted to be in fluid communication with a combustible gas source (34).

Description

GAS DELIVERY SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates generally to combustor gas delivery systems, and, in particular, to a low-pressure gas delivery system for an annular combustor.

2. Description of the Prior Art

[0002] In the field of compact electricity generating systems, the use of annular combustors and turbines is well-known. Typically, the annular combustor is used to generate the energy required to drive a turbine, thereby generating electricity. For example, see U.S. Patent No. 5,723,795, incorporated herein by reference, directed to an electricity generating system having an annular combustor.

[0003] In order to fuel the combustion process, a mixture of air and fuel (either liquid or gas) is fed to the combustion chamber via a nozzle. The introduction of a liquid or gas into another liquid or gas via a nozzle is disclosed, for example, in U.S. Patent Nos. 5,245,977; 4,483,805; 4,344,752; and 1,195,915. Once the fuel/air mixture is in the chamber, the mixture is ignited, creating the combustion process within the chamber. It is this combustion process that produces the gases that drive the turbines in an electricity generation system. [0004] One drawback of the prior art is the inaccurate mixing of the air and fuel prior to introduction into the combustion chamber. Another drawback of the prior art is the unknown stoichiometry that occurs when attempting to yield an efficient combustion process, i.e., a process that most efficiently and effectively utilizes the maximum amount of available air and fuel. Currently, the only manner in which to regulate the mixture of air and fuel, as well as to predict the stoichiometry of the mixture, is through trial and error. In most situations, it is undesirable to have an overly fuel rich mixture (wasting fuel) or an overly oxygen rich mixture (resulting in incomplete combustion). The introduction of both the fuel and the air into the system requires constant adjustment. It is, therefore, an object of the present invention to overcome the above-mentioned deficiencies by providing a low-pressure gas delivery system that allows for control of the air/fuel mixture.

SUMMARY OF THE INVENTION [0005] The present invention provides for a low-pressure gas delivery system that includes a combustor having a combustion chamber and a nozzle. The nozzle can be in fluid communication with the combustion chamber. The nozzle has an inner surface defining a converging portion, a throat and a diverging portion. The converging portion is positioned upstream of the throat, and the diverging portion is positioned downstream of the throat. The nozzle converging portion is adapted to be in fluid communication with a gas source, typically compressed air, upstream of the converging portion. The present invention also includes a conduit having an end positioned at the throat of the nozzle. This conduit is adapted to be in fluid communication with a low-pressure combustible gas source. [0006] The low-pressure gas delivery system of the present invention can also have a nozzle in fluid communication with the combustion chamber via a manifold. The manifold includes a plurality of injectors adapted to be in fluid communication at various locations with the combustion chamber. An air supply can optionally be fluidly connected to the manifold or to the combustion chamber.

[0007] The present invention also includes a method of metering low-pressure combustible gas to a combustor. The method includes the steps of providing a converging/diverging nozzle having an inner surface defining a converging portion, a throat and a diverging portion in fluid communication with a combustion chamber. The converging portion is positioned upstream of the throat and the diverging portion positioned downstream of the throat. The nozzle converging portion is adapted to be in fluid communication with a gas source upstream of the converging portion. Second, a conduit having an end positioned at the throat is also provided. The conduit is adapted to be in fluid communication with a combustible gas source. Third, gas from the upstream gas source is delivered into the converging portion of the nozzle at a pressure sufficient to cause choking of the gas at the throat of the nozzle. Lastly, the combustible gas from the combustible gas source is delivered through the conduit to the throat of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS [0008] A complete understanding of the present invention, both as to its construction and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing figures, wherein like reference characters identify like parts throughout.

[0009] Fig. 1 is a side sectional view, partially in section, of the first embodiment of a low- pressure gas delivery system according to the present invention;

[0010] Fig. 2 is a block diagram of a low-pressure gas delivery system according to the present invention; [0011] Fig. 3 is a side sectional view, partially in section, of a second embodiment of a low- pressure gas delivery system according to the present invention;

[0012] Fig. 4 is a partial-sectional elevational view of a portion of the low-pressure gas delivery system shown in Fig. 1 and an annular combustion chamber; [0013] Fig. 5 is a block diagram of a third embodiment of a low-pressure gas delivery system made in accordance with a the present invention; and

[0014] Fig. 6 shows a block diagram of a fourth embodiment of a low-pressure gas delivery system similar to that shown in Fig. 5, having an air supply in fluid communication with a combustion chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0015] Referring to Fig. 1, the present invention provides for a low-pressure gas delivery system 10 that includes a nozzle 12 in fluid communication with a combustion chamber 14 shown in Fig. 4. However, a plurality gas delivery system nozzles 12 can be in fluid communication at various locations with the combustion chamber 14 (not shown) in order to achieve a more evenly distributed air/fuel mixture into the combustion chamber 14. In order to allow fluid communication between the nozzle 12 and the combustion chamber 14, a fitting 16 may be utilized to attach the nozzle 12 either directly to the combustion chamber 14 or to another inlet 15 (shown in Fig. 4) attached to the combustion chamber 14. Referring back to Fig. 1, the nozzle 12 has a nozzle inner surface 18 which defines a converging portion 20, a throat 22, and a diverging portion 24. The converging portion 20 is positioned upstream of the throat 22, and the diverging portion 24 is positioned downstream of the throat 22. The nozzle 12 generally can be cylindrical in shape, and the converging portion 20 and the diverging portion 22 can be conical in shape.

[0016] Referring to Figs. 1 and 2, the converging portion 20 of the nozzle 12 is in fluid communication with a gas source 26, which is upstream of the converging portion 20. Typically, this gas source 26 is the oxygen source for the combustion reaction, namely compressed air. The gas source 26 may be connected to the nozzle 12 via a fitting 28. Specifically, the fitting 28 provides for the communication between the converging portion 20 of the nozzle 12 and the gas source 26. The flow of gas from the gas source 26 into the converging portion 20 of the nozzle 12 is represented by arrow A (shown in Fig. 1). As the gas A flows from the gas source 26 into the converging portion 20 of the nozzle 12, the gas A eventually encounters the throat 22 of the nozzle 12. [0017] With continued reference to Figs. 1 and 2, the gas delivery system 10 also includes a conduit 30 having an end 32 positioned at the throat 22 of the nozzle 12. h addition, the conduit 30 provides for fluid communication between a low-pressure combustible gas source 34 and the throat 22 of the nozzle 12. The flow of combustible gas from the combustible gas source 34 through the conduit 30 into the throat 22 is represented by arrow B. The combustible gas B can be methane or propane, but may be any other suitable combustible gas that can serve as a fuel to the combustion reaction. By "low-pressure" is meant the combustible gas B from the combustible gas source 34 is lower than the pressure of the gas A from the gas source 26.

[0018] Referring to Fig. 1, a fitting 36 can be used to physically connect the combustible gas source 34 to the nozzle 12. The fitting 36 can be secured to the nozzle 12 when threading or attaching the fitting 28 to the nozzle 12, thus creating an interface 37 between the fitting 36 and the nozzle 12. hi order to ensure a gas tight seal between the fitting 36 and the nozzle 12, at least one gasket 38 is positioned in a cavity 40. The gasket 38 can be an annular ring made of an elastomeric material. In order to further enhance the seal, a second gasket 42 positioned in a second cavity 44 may be provided. The conduit 30 extends directly through both the fitting 36 and nozzle 12, wherein the conduit end 32 terminates at the throat 22 of the nozzle 12.

[0019] In operation, gas A from the gas source 26 flows through the fitting 28 into the converging portion 20 of the nozzle 12 (shown in Figs. 1 and 2). The flow of gas A is accelerated due to the geometry of the converging portion 20, as explained by Bernoulli's Equation, wherein P + pv²/2g = constant. Thus, since v (velocity or flow) is increasing, P (pressure) must decrease. As the gas A from the gas source 26 flows through the converging portion 20 of the nozzle 12, inlet pressure Pi is converted to velocity v, reaching a maximum value at the throat 22. The diverging portion 24 of the nozzle 12 then slows the gas A down reconverting the velocity v back to approximately its original pressure. The pressure of the gas A decreases at the throat 22 reaching the critical flow pressure P₂, commonly referred to as "choking." Choking is characterized by the gas velocity v in the throat 22 being precisely equal to the speed of sound. Under these conditions, a fixed pressure ratio exists between the inlet pressure Pi and the throat pressure P₂ for all inlet pressures. By virtue of the sonic velocity at the throat 22, downstream pressure P₃ changes cannot affect the inlet pressure Pi, and the flow rate becomes dependent upon the inlet pressure Pi and temperature only. Because the inlet pressure Pi and temperature of the gas A from the gas source 26 can be known, this allows for a constant and known flow and pressure P₂ of the gas A at the throat 22 of the nozzle 12. Therefore, at throat 22, the pressure P and flow of the high pressure gas A is constant. By "high pressure gas" is meant that the inlet pressure Pi of the gas A from the gas source 26 is delivered into the nozzle 12 at a pressure sufficient to cause this "choking" of the gas A in the throat 22. A metering device, such as a pressure gauge or temperature gauge, can be used to measure the inlet pressure Pi and temperature of the gas A entering the nozzle 12, respectively.

[0020] Referring to Figs. 1 and 2, the combustible gas B is delivered from the combustible gas source 34 into the throat 22 of the nozzle 12. As with the gas A delivered from the gas source 26, combustible gas B can be metered into the throat 22 at a known flow rate and pressure. The combustible gas B and the gas A delivered from gas source 26 meet at the throat 22 of the nozzle 12 and, together, enter the diverging portion 24 of the nozzle 12. Due to the divergence of the diverging portion 24, the mixture of the combustible gas B from the combustible gas source 34 and the gas A from gas source 26 diffuses, decreases in flow, and increases in pressure with a minimum energy loss. Further, due to the turbulent flow that occurs in the diverging portion 24, the combustible gas B from the combustible gas source 34 and the gas A from the gas source 26 are thoroughly mixed. This air/fuel mixture, represented by arrow C (in box 46 in Fig. 2) is introduced into the combustion chamber 14. [0021] In this manner, a thoroughly mixed air/fuel mixture C is provided with known stoichiometry. Overall, due to the known parameters of both the low-pressure combustible gas B and the high pressure gas A at the throat 22 of the nozzle 12, the variability of the air/fuel mixture C is minimized. An angle of convergence α of the converging portion 20, the width of the throat 22, and an angle of divergence β of the diverging portion 24 are sized to achieve the proper "choking" and known flow and pressure of the gas (compressed air) through the gas delivery system 10.

[0022] A second embodiment according to the present invention is shown in Fig. 3, where like reference numbers are used for like elements, h the gas delivery system 10' of the second embodiment, the conduit 30' extends through the fitting 28, as opposed to the separate fitting 36 of the first embodiment. As with the gas delivery system 10, in this embodiment the end 32 of the conduit 30' terminates at the throat 22 of the nozzle 12. However, due to the positioning of the fitting 28, a conduit extension 48 is provided. This conduit extension 48 extends into an inner area of the fitting 28, through the converging portion 20, again terminating at the throat 22 of the nozzle 12. Any manner of allowing the combustible gas to enter the throat 22 is envisioned, as long as the combustible gas is introduced at the throat 22. [0023] In a specific example, the gas A delivered from gas source 26 is compressed air which enters the converging portion 20 of the nozzle 12 at a pressure of 4 bar (~ 58 psi). As the flow of the compressed air is accelerated in the converging portion 20, the pressure decreases and is "choked" at the throat 22. The combustible gas B is a gas fuel, such as methane, and is metered at the throat 22, where the velocity of the compressed air is at a maximum. The gas fuel, i.e. methane, is supplied at a lower pressure than what would otherwise be required had it not flowed into the diverging/converging nozzle. Hence, the present invention reduces the parasitic lost due to compressing the gas fuel as in prior art. The methane and the compressed air meet at the throat 22 and diffuse and mix through the diverging portion 24. This air/fuel mixture C is then available for combustion within the combustion chamber 14. [0024] A third and fourth embodiment according to the present invention are shown in Figs. 5 and 6, respectively, where like reference numbers are used for like elements. Figs. 5 shows an arrangement 50 that includes the low-pressure gas delivery system 10 as previously discussed having a nozzle 12 in fluid communication with the combustion chamber 14 via a manifold 52. The arrangement 50 can be used to evenly distribute an air/fuel mixture C within a combustion chamber 14. The manifold 52 includes a plurality of injectors 54, wherein each injector 54 can be fluidly connected at various locations to the combustion chamber 14. Referring to Fig. 5, an air supply 56 (shown in phantom) can optionally be in fluid communication with the manifold 52 in order to provide additional air to the air/fuel mixture C entering into the combustion chamber 14. Fig. 6 shows an arrangement 50' similar to arrangement 50, except that additional air may be supplied via an air supply 56' (shown in phantom) in fluid communication with the combustion chamber 14.

[0025] In operation, the air/fuel mixture C coming from the nozzle 12 of the gas deliver system 10 enters the manifold 52 (shown in Figs. 5 and 6). The air/fuel mixture C in the manifold 52 is then delivered through the injectors 54 to the combustion chamber 14 at various locations. For safety considerations, an overly rich fuel mixture (i.e., greater ratio of fuel to air) can be delivered to the manifold 52 from the nozzle 12. This fuel rich mixture can be above its Upper Explosive Limit (UEL) resulting in an air/fuel mixture that is too rich to burn (i.e., non-explosive). UEL is the highest concentration of fuel to air that can be ignited. Next, additional air from the air supply 56 is delivered to the manifold 52 (shown in Fig. 5) in order to achieve a proper ratio of air to fuel for combustion. The air/fuel mixture in the manifold 52 is then delivered through the injectors 54 to the combustion chamber 14 at various locations. However, a fuel rich mixture can be delivered from the manifold 52 to the combustion chamber 14, wherein additional air from the air supply 56' is delivered to the combustion chamber 14 (shown in Fig. 6) in order to achieve a proper ratio of air to fuel for combustion.

[0026] The fittings 16, 28, and 36 may be threadable fittings, allowing the nozzle 12 to be placed at any suitable inline position in the combustion system, as shown in Fig. 4. Further, the fittings 16, 28, and 36 may be threaded to the nozzle 12 or, alternatively, integrally formed with the nozzle 12.

[0027] The gas delivery systems 10 and 10' also provide a method of metering combustible gas to a combustor. First, a converging/diverging nozzle 12 as previously discussed is provided and adapted to be positioned in fluid communication with a combustion chamber 14. Second, an end 32 of a conduit 30 is positioned at the throat 22, and the conduit 30 is adapted to be in fluid communication with a combustible gas source 34. Third, gas A is delivered from the gas source 26 into a converging portion 20 of the nozzle 12 at a pressure sufficient to cause "choking" of the gas at the throat 22 of the nozzle 12. Fourth, combustible gas B is delivered from a combustible gas source 34 through the conduit 30 into the throat 22 of the nozzle 12. The combustible gas B from the combustible gas source 34 can be delivered at a pressure lower than the pressure of the gas A from the gas source 26 upstream of the converging portion 20. Finally, the upstream pressure and temperature of the gas A from the gas source 26 upstream of the converging portion can be measured. [0028] The present invention provides for a gas delivery system 10 and 10' that is a predictable system. By predictable system, it is meant that the gas delivery system 10 and 10' according to the present invention provides for the metered introduction of a fuel source with a gas source at known parametric conditions, yielding known stoichiometry. Further, the present invention allows for the thorough mixing of the gas A and the combustible gas B, enhancing combustion efficiency.

[0029] This invention has been described with reference to the preferred embodiments, obvious modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.

Claims

I CLAIM:

1. A combustor, comprising: a combustion chamber; a nozzle adapted to be in fluid communication with said combustion chamber, said nozzle comprising an inner surface defining a converging portion, a throat and a diverging portion, wherein said converging portion is positioned upstream of said throat and said diverging portion is positioned downstream of said throat, said nozzle converging portion adapted to be in fluid communication with a gas source upstream of said converging portion; and a conduit having an end positioned at said throat, said conduit adapted to be in fluid communication with a combustible gas source.

2. The combustor as claimed in claim 1, wherein said nozzle is fluidly connected to said gas source via a nozzle fitting.

3. The combustor as claimed in claim 1, wherein said conduit is fluidly connected to said combustible gas source via a fitting.

4. The combustor as claimed in claim 2, wherein said nozzle fitting is threadably fastened to said nozzle.

5. The combustor as claimed in claim 2, wherein said nozzle fitting intergally formed with said nozzle.

6. The combustor as claimed in claim 2, wherein said conduit extends through said nozzle fitting and said converging portion, wherein said conduit end terminates at said throat of said nozzle.

7. The combustor as claimed in claim 3, wherein said conduit extends through said fitting and said nozzle, wherein said conduit end terminates at said throat of said nozzle.

8. The combustor as claimed in claim 3, wherein said fitting having a sealing surface is secured to said nozzle, thereby forming a seal between said sealing surface and said nozzle.

9. The combustor as claimed in claim 8, wherein said sealing surface of said fitting further defines at least one cavity adapted to receive a gasket.

10. The combustor as claimed in claim 3, wherein said fitting is threadably fastened to said nozzle.

11. The combustor as claimed in claim 3, wherein said fitting is intergally formed with said nozzle.

12. A combustor, comprising: a combustion chamber; a manifold adapted to be in fluid communication with said combustion chamber; a nozzle adapted to be in fluid communication with said manifold, said nozzle comprising an inner surface defining a converging portion, a throat and a diverging portion, wherein said converging portion is positioned upstream of said throat and said diverging portion is positioned downstream of said throat, said nozzle converging portion adapted to be in fluid communication with a gas source upstream of said converging portion; and a conduit having an end positioned at said throat, said conduit adapted to be in fluid communication with a combustible gas source.

13. The combustor as claimed in claim 12, further comprising an air supply fluidly connected to said manifold.

14. The combustor as claimed in claim 12, wherein said manifold comprised a plurality of injectors adapted to be in fluid communication at various locations with said combustion chamber.

15. A method of metering combustible gas to a combustor, comprising the steps of:

(a) providing a converging/diverging nozzle in fluid communication with a combustion chamber, said nozzle comprising an inner surface defining a converging portion, a throat and a diverging portion, wherein said converging portion is positioned upstream of said throat and said diverging portion is positioned downstream of said throat, said nozzle converging portion adapted to be in fluid communication with a gas source upstream of said converging portion;

(b) providing a conduit having an end positioned at said throat, said conduit adapted to be in fluid communication with a combustible gas source;

(c) delivering gas from said upstream gas source into said converging portion of said nozzle at a pressure sufficient to cause choking of said gas at said throat of said nozzle; and

(d) delivering combustible gas from said combustible gas source through said conduit to said throat of said nozzle.

16. The method of metering combustible gas to a combustor as claimed in claim 15, further comprising the step of measuring upstream pressure and temperature of said gas from said gas source upstream of said converging portion.

17. The method of metering combustible gas to a combustor as claimed in claim 15, wherein said combustible gas from said combustible gas source is delivered at a pressure lower than the pressure of said gas from said gas source upstream of said converging portion.