Fluid manifold

Abstract: A fluid manifold (41) comprises two annular chambers (42 and 46) in flow series and having a barrier (45) therebetween. A fluid is fed into the first larger annular chamber (42) and circulates circumferential therethrough before being passed through a plurality of apertures (44) in the barrier (45) to the second smaller annular chamber (46). The fluid circulates circumferentially through the second chamber (46) in the opposite direction prior to its discharge through apertures (50) in a final barrier (48). The apertures (50) in the final barrier (48) decelerate the fluid discharging therefrom to enhance mixing of air with the fluid downstream of the manifold (41).

Description: The present invention relates to a fluid fuel manifold as described in the preamble of claim 1. US-A-4 492 563 discloses the features of the preamble of claim 1. Industrial gas turbines are required to meet stringent emission levels. It is known that the production of NOx and CO is a function of the combustion flame temperature which in turn depends upon the combustor air inlet temperature, temperature rise of the combusting fuel/air mixture and the air inlet pressure. In order to limit the production of NOx and CO the temperature and residence time should be controlled. Series staged combustion controls the levels of NOx and CO produced. In series staged combustion a number of separate combustion zones are used, each being fed by the previous stage. The sequential nature of the staging, whereby combustion products from upstream flames become mixed with downstream flames, provides added benefit to emissions since the undesired combustion emissions from upstream have a chance to be converted to the desired combustion products in the downstream flame. Further the higher the number of stages, the smaller the temperature range required for each stage resulting in the lowest maximum temperature attained by each stage and hence minimum NOx. Each stage provides lean combustion, that is combustion of fuel in air where the fuel to air ratio is low. In multi-staged combustion chambers the fuel is premixed with air in separate premixing ducts for each stage. Fuel manifolds may be used to feed the fuel into the premixing ducts. The object of the present invention seeks to provide a fluid manifold which distributes a fluid fuel uniformly and which discharges the fuel at a velocity which enhances mixing of the fuel with air downstream of the manifold for use in the combustion chamber of a gas turbine engine. According to the present invention a fluid fuel manifold comprises a plurality of annular chambers in flow series and having barriers therebetween, means to supply fluid fuel into a first one of said annular chambers such that the fluid fuel flows therethrough before being passed through a said barrier to the next annular chamber, the fluid fuel flows through each annular chamber prior to its discharge through a final barrier which changes the velocity of the fluid fuel flow discharging therefrom, whereby the fluid fuel manifold is for use in a gas turbine combustion chamber and the means to supply fluid fuel into the first annular chamber comprises at least one pipe arranged at an angle of no more than 45° relative to the tangent of the circle at the point of the pipe attachment to the first annular chamber such that the fluid flows circumferentially through the first annular chamber four to eight times to produce a circular flow through the first annular chamber before being passed through the barrier to the next annular chamber, each barrier has a plurality of apertures to supply fluid fuel into the next annular chamber, the said plurality of apertures beeing arranged at an angle to the next annular chamber such that the fluid fuel flows circumferentially through the said next annular chamber to produce a circular flow through the next annular chamber prior to its discharge through the final barrier. In a preferred embodiment of the present invention the fluid manifold has two annular chambers in flow series, the first annular chamber being larger than the second annular chamber. The fluid flow in the first annular chamber circulates in the opposite direction to the fluid fuel flow in the second annular chamber. The barrier between the first and second annular chambers has a plurality of apertures therein. The apertures in the barrier between the first and second annular chambers are angled to increase the resistance to the passage of fluid fuel from the first annular chamber to the second annular chamber. The final barrier through which the fluid fuel discharges from the manifold has a plurality of small apertures therein which decelerate the fluid fuel. The apertures may be angled radially to remove any swirl from the fluid discharged from the manifold. Preferably the fluid fuel manifold may be used with a liquid or gaseous fuel. A manifold in accordance with the present invention is for use in a combustion chamber of a gas turbine engine. In particular the manifold is for use in a combustion chamber having multiple combustion chambers in flow series. Each manifold is located in a premix duct of one stage of a multi-staged combustion chamber. The manifold is located by swirler vanes in the premix duct which swirl air, the swirled air mixing with the fuel discharged from the manifold in the premixing duct. A preferred embodiment will now be described with reference to the accompanying drawings in which:- Figure 1 is a schematic view of a gas turbine engine having a combustion chamber and fuel manifolds in accordance with the present invention. Figure 2 is a cross-sectional view through the combustion chamber shown in figure 1. Figure 3 is an enlarged cross-sectional view through one of the fuel manifolds shown in figure 2. Figure 4 is a cross-sectional view through part of a fuel manifold in accordance with the present invention. An industrial gas turbine engine 10, shown in figure 1, comprises in axial flow series an inlet 12, compressor 14, a combustion chamber assembly 16, turbine section 18, power turbine section 20 and an exhaust 22. The turbine section 18 is arranged to drive the compressor section 14 via one or more shafts (not shown). The power turbine section 20 is arranged to drive an electrical generator 26 via a shaft 24. The combustion chamber assembly 16 is shown more clearly in figure 2 and comprises a plurality of tubular combustion chambers 30. The axes of the tubular combustion chambers 30 are arranged to extend in a generally radial direction. The inlets to the tubular combustion chambers 30 are at their radially outmost ends and the outlets 60 at their radially innermost ends. Combustion of the fuel is staged in three zones A, B & C which are in flow series. To control the combustion flame temperature and hence NOx and CO levels fuel is premixed with air in separate premixing ducts 32, 36, & 38 for each stage. In the primary combustion zone fuel and air are mixed in a primary premix duct 32. Fuel is also injected from a central injector 33 located in the upstream wall 31 of each tubular combustion chamber 30 just upstream of the exit of the primary premix duct 32. Several fuel orifices (not shown) are distributed around the injector 33. The number, size and location of the orifices are determined so as to provide best stability and combustion efficiency. A torch igniter 34, which is lit by two spark ignitors (not shown), is provided in the centre of the central injector 33 of each tubular combustor 30. A diffusion flame, initially lit by the torch ignitor 34, is fuelled by the central injector 33. The flame is contained in the primary zone A and stabilised by a recirculating flow generated by the primary premix ducts 32. The diffusion flame is intended for starting and minimum power situations only ie. at power settings below 30% of maximum load. For power settings between 30-50% of maximum load fuel is also injected into secondary premix ducts 36 forming a uniform mixture which begins burning in the secondary zone B. Finally for power settings from 55-80% of maximum load fuel is also injected into a tertiary premix ducts 38 forming a uniform mixture which begins burning in the tertiary zone C. The secondary and tertiary premix ducts 36 and 38 each supply a fuel/air mixture to the burner in a ring of jets which penetrate and mix with the gases from the upstream stages. To create the discrete jets, each premix duct 36 and 38 ends with aerodynamic partitions 39, wedges, whose base form part of the combustor liner. Swirlers 40 are provided at the inlet to the secondary and tertiary ducts 36 and 38. The swirlers 40 are of an efficient aerodynamic design to accelerate the air passing therethrough. The swirlers 40 have a counter-swirling configuration so that they produce a shear layer which gives good mixing of the air and fuel. The inlet to the secondary and tertiary ducts 36 and 38 is at a large radius from the burner centerline. To minimise the length of the ducts 36 and 38 the most vigorous method was sought to mix premix gas with the air. Vigorous mixing is achieved by injecting the fuel at a low velocity into the shear layer formed between the air flows from the counter-rotating swirlers 40. The partition between the counter-rotating swirlers 40 is a manifold 41 to which premix fuel is supplied. The external profile of the manifold 41 has been optimised to give the air passing over it the best aerodynamic performance. The internal configuration of the manifold 41 is designed to even out any non-uniformities in the fuel flow and fed the fuel in a uniform manner into the premix duct 36. The internal configuration of a fuel manifold 41 in accordance with the present invention is shown in more detail in figures 3 & 4. Each manifold 41 consists of a large annular chamber 42 fed by one of more feed pipes 43. The feed pipes 43 are attached to the circumference of the manifold 41 at an angle. In the preferred embodiment of the present invention three feed pipes 43 are attached to the circumference of the manifold 41. Each feed pipe 43 is attached at the same angle relative to the tangent of the circle at the point of attachment and the feed pipes 43 are equally spaced around the circumference. In this way the fuel flowing into the annular chamber 42 is given a strong circumferential motion. Each feed pipe makes an angle of no more than forty five degrees so that the majority of the fluid momentum goes into the circular motion rather than raising the local static pressure. The dimensions of the annular chamber 42 are such that relative to the speed of the circulating flow the fluid fuel residence time is several times greater than the time it would take the average fluid fuel element to circumnavigate the chamber 42. The fluid fuel swirls around the circumference of the large annular chamber 42 four-eight times. On an interior wall 45 of the manifold, opposite where the feed pipes 43 are attached, are numerous identical and equally spaced exit holes 44. The holes 44 are orientated at an angle such that the flow entering one of the holes 44 makes a turn of about one hundred and thirty five degrees. Due to this acutely sharp turn the hole 44 entrance has an effective flow area much smaller than its geometric area. In this way the problem of making many holes with very small identical flow areas is diminished. Furthermore this orientation makes the holes less sensitive to being located near a feed pipe 43 since any momentum hitting a hole from a nearby feed pipe 43 will be perpendicular to the hole direction. The fluid fuel passes from the large annular chamber 42 thorough the holes 44 in interior wall 45 to a smaller annular chamber 46 where it circulates in the opposite direction. The fluid fuel then passes though small radial holes 47 in a wall 48 to a plurality of separate cavities 50. Fluid fuel is fed from the cavities 50 to etched diffusers 51 and discharges from the trailing edge of the fuel manifold 41 into the premix duct 36. The largest pressure drop in the fluid fuel manifold 41 takes place between the two chambers 42 and 46 and the radial holes 47 in the wall 48 discourage swirl at the entry to the diffusers 51. The slits 49 decelerate the fluid fuel and is discharged from the trailing edge of the fluid fuel manifold 41 into the premix ducts. The fluid fuel discharges from the trailing edge of the manifold 41 and is mixed with the counter-swirling flows of air from the swirlers 40 located in the inlet of the premix ducts 36 and 38. The fuel/air mixture from the premix ducts 36 and 38 penetrates and mixes with the gases from the upstream combustion stages. The sequential nature of the staging, whereby combustion products from upstream flames become mixed with downstream flames provides added benefit to emissions since the undesired combustion emissions from upstream have a chance to be converted to the desired combustion products in the downstream flame. It will be further appreciated by one skilled in the art that a manifold 41 in accordance with the present invention may have any number of annular chambers 44 and 46 provided a uniform circumferential distribution of the fluid fuel is achieved. If several annular chambers are to be implemented to obtain the required uniformity the holes 44 and 47 should decrease in size and increase in number with each stage. The manifold residence time and the pressure drop should decrease with each stage. Circumferential flow is eliminated in the last stage by making its feed holes radial. Similarly the manifold 41 could decelerate or accelerate the fluid fuel discharged therefrom.

Claims: A fluid fuel manifold (41) comprising a plurality of annular chambers (42,46) in flow series and having barriers (45) therebetween, means to supply fluid fuel (43) into a first one of said annular chambers (42) such that the fluid fuel flows therethrough before being passed through a said barrier (45) to the next annular chamber (46), the fluid fuel flows through each annular chamber (42,46) prior to its discharge through a final barrier (48) which changes the velocity of the fluid fuel flow discharging therefrom, characterised in that the fluid fuel manifold is for use in a gas turbine combustion chamber whereby the means to supply fluid fuel into the first annular chamber (42) comprises at least one pipe (43) arranged at an angle of no more than 45° relative to the tangent of the circle at the point of the pipe attachment to the first annular chamber (42) such that the fluid fuel flows circumferentially through the first annular chamber (42) four to eight times to produce a circular flow through the first annular chamber (42) before being passed through the barrier (45) to the next annular chamber (46), each barrier (45) has a plurality of apertures (44) to supply fluid fuel into the next annular chamber (46), the said plurality of apertures (44) being arranged at an angle to the next annular chamber (46) such that the fluid fuel flows circumferentially through the said next annular chamber (46) to produce a circular flow through the next annular chamber (46) prior to its discharge through the final barrier (48). A fluid fuel manifold as claimed in claim 1 having two annular chambers (42,46) in flow series, the first annular chamber (42) being larger than the second annular chamber (46). A fluid fuel manifold as claimed in claim 1 or claim 2 in which the fluid fuel in the first annular chamber (42) circulates in the opposite direction to the fluid fuel in the second annular chamber (46). A fluid fuel manifold as claimed in any of claims 1-3 in which the barrier (45) between the first and second annular chambers (42,46) has a plurality of apertures (44) therein. A fluid fuel manifold as claimed in claim 4 in which the apertures (44) in the barrier (45) between the first and second annular chambers (42,46) are angled to increase the resistance to the passage of fluid fuel from the first annular chamber (42) to the second annular chamber (46). A fluid fuel manifold as claimed in any preceding claim in which the final barrier (48) through which the fluid fuel discharges from the fluid fuel manifold (41) has a plurality of small apertures (47,50) therein which decelerate the fluid fuel. A fluid fuel manifold as claimed in claim 6 in which the apertures (47) are angled radially to remove any swirl from the fluid fuel discharged from the manifold (41). A fluid fuel manifold in accordance with any preceding claim for use with a liquid or gaseous fuel. A fluid fuel manifold as claimed in claim 8 for use in a combustion chamber (16) of a gas turbine engine (10). A fluid fuel manifold as claimed in claim 9 wherein the combustion chamber (16) comprises a primary combustion zone (A), a secondary combustion zone (B) and a tertiary combustion zone (C) arranged in flow series. A fluid fuel manifold as claimed in claim 10 wherein the combustion chamber (16) comprises a primary premix duct (32) to supply a fuel and air mixture to the primary combustion zone (A), a secondary premix duct (36) to supply a fuel and air mixture to the secondary combustion zone (B) and a tertiary premix duct (38) to supply a fuel and air mixture to the tertiary zone (C). A fluid fuel manifold as claimed in claim 11 wherein the fluid fuel manifold (41) supplies fuel into the secondary premix duct (36) or the tertiary premix duct (38). A fluid manifold as claimed in claim 12 wherein the fluid fuel manifold (41) is arranged between a first swirler (40A) and a second swirler (40B), the first and second swirlers (40A, 40B) are arranged to swirl in opposite directions. A fluid manifold as claimed in claim 13 wherein the fluid fuel manifold (41) is arranged between a first radial swirler (40A) and a second radial swirler (40B) and the fluid fuel manifold (41) discharges the fluid fuel radially. A fluid fuel manifold as claimed in any of claims 1 to 14 wherein the pipe (43) is arranged at an angle of no more than 45° and the apertures (44) in the barrier (45) are arranged at an angle of about 135°.

Inventors: ALLAN FREDERIC JAMES, ALLAN, FREDERIC JAMES
Applicants: ROLLS ROYCE PLC, ROLLS-ROYCE PLC
Application year: 1998
Main classification: F02C7
IPC codes: F23C6, F23R3, F02C7