Turbine engines used in the electrical power generation industry typically include a compressor section, one or more combustors which may be arranged concentrically around the outside of the compressor section, and a turbine section which is located downstream from the compressor and the combustors.
Fuel is delivered into one or more combustion zones within the combustors via a plurality of fuel nozzles. The fuel nozzles are intended to deliver precisely controlled amounts of the combustible fuel, and to help mix the fuel with compressed air from the compressor section. The fuel air mixture is then ignited within the combustion zone, and the hot combustion gases exit the combustor into the turbine section to provide the motive power for the turbine engine.
Some turbine engines are designed to burn multiple different types of fuels. Regardless of the type of fuel being used, it is necessary to mix the fuel with a certain amount of air per unit volume of the fuel in order to achieve good combustion. If the local fuel/air ratio increases above an optimum value, meaning there is more than an optimum amount of fuel per unit volume of air, the mixture is said to be in fuel excess. Conversely, if the local fuel/air ratio decreases below the optimum value, meaning there is less than an optimum amount of fuel per unit volume of air, the mixture is said to be fuel lite.
When an engine is running with a local fuel excess in the combustion zone, meaning the local fuel/air ratio is higher than optimum, the local combustion temperature increases above the temperature that would exist if the fuel/air ratio were optimum. And the excess fuel/air ratio and the higher combustion temperature can lead to the generation of undesirable nitric oxide gases (NOX).
Conversely, when a turbine is running with a locally lite fuel/air ratio in the combustion zone, the combustion temperatures tend to be lower than the temperature that would exist if the fuel/air ratio was at optimum. And the lower then optimum fuel/air ratio and the lower local combustion temperature will be insufficient to burn out all of the undesirable CO gases.
Turbine engines used in the power generation industry must be capable of generating a range of power output so that the amount of electricity being generated can be matched to the demand. And this means that during some periods of time, the turbine will be lightly loaded, while during other periods of time, the turbine will be heavily loaded. In order to support these varying loads, one adjusts the amount of fuel being supplied to the combustors of the turbine.
Fuel is delivered into the combustors by a plurality of fuel nozzles that are mounted in each combustor. And it is relatively easy to vary the amount of fuel being delivered by the fuel nozzles into the combustors. However, it is more difficult to selectively vary the air splits being delivered at the combustion zone and downstream of the combustion zone.
When a turbine is being operated at high power, under a heavy load, the fuel nozzles must deliver a relatively large amount of fuel into the combustors so that the turbine can meet the load requirement. And because it is somewhat difficult control the amount of air being delivered into the combustion zone, this tends to result in the turbine running with an above optimum fuel/air mixture in the combustion zone. As noted above, this can result in a high combustion temperature, and the generation of undesirable NOX gases.
Conversely, when a turbine is operated at low power, to support a relatively light load, a relatively small amount of fuel is being delivered into the combustors by the fuel nozzles. And because it is difficult tovary the air splits to the combustion zone to properly match the amount of fuel being used, this tends to result in a less than optimum fuel/air mixture in the combustion zone. As noted above, this can result in a low combustion temperature. The lower combustion temperatures can result in not all of the CO gases being burned in the combustors, and the unburned CO gases are ultimately exhausted from the turbine, which is also undesirable.
Moreover, running with a locally less than optimum fuel/air mixture in the combustion zone can also negatively impact flame stability. Accordingly, when operating under leaner conditions, there is a danger that a combustor will experience a flameout.
Another somewhat related problem with fuel/air mixtures in turbine engines has to do with the fact that some turbines are designed to burn multiple types of fuel. In the past, turbines were generally run with relatively high heat value fuels, such as high methane content natural gases. In recent years, it has become more common for turbine operators to supply a turbine with a mixture of a relatively high heat value fuel such as natural gas and a relatively low heat value fuel such as syn-gas. Syn-gas and other low heat value fuels are generally less expensive. Also, syn-gas can be generated as a byproduct of waste treatment at a waste treatment plant. Thus, burning syn-gas in a power generating turbine is one way to recycle energy from waste.
In order to run a turbine at a certain load condition, it is necessary to use a greater volume of a low heat value fuel than of a high heat value fuel. Less air is required per unit volume of the low heat value fuel to achieve good complete combustion. Thus, for any given turbine load condition, when switching from a high heat value fuel to a lower heat value fuel, a greater volume of the low heat value fuel is required. Likewise, for certain lower heat content fuel, it may be desirable to use less air per unit volume of the lower heat value fuel to achieve good combustion.
As noted above, it is relatively easy to control the amount of fuel being delivered into a combustor via the fuel nozzles. As also noted above, it is difficult to vary the amount of air being supplied to the combustion zone.
During a typical turbine operation, the turbine would be started with a high heat value fuel, and the engine would be brought up to a steady state operational condition. Once that steady state condition has been achieved, the operator may begin to mix a certain quantity of a low heat value fuel into the high heat value fuel to create a mixture that is delivered into the combustor. Because a greater volume of the low heat value fuel is required to keep the engine at the load condition, a greater total volume of fuel will be delivered into the combustor. However, for the reasons given above, it may be desirable to simultaneously reduce the amount of air being supplied into the combustion zone per unit volume of fuel. Failure to reduce the amount of air per unit volume of fuel may result in an undesirably low fuel/air ratio in the combustion zone. And as noted above, this can result in flame instability, and incomplete burning of CO gases.
In a first aspect, the invention may be embodied in a fuel nozzle for a turbine engine that includes an elongated housing, a fuel delivery passageway that extends along at least a part of the length of the housing, an air delivery passageway that extends along at least a part of the length of the housing, and a fuel inlet that receives fuel from a fuel supply line and that communicates with the fuel delivery passageway. The fuel nozzle would also include an air regulation unit coupled to the fuel inlet, wherein the air regulation unit varies an amount of air that passes into the air delivery passageway based on a fuel pressure at the fuel inlet.
In a second aspect, the invention may be embodied in a combustor for a turbine engine that includes a combustor liner, a fuel nozzle mounted inside the combustor liner and coupled to a fuel supply line, and an air regulation unit coupled to the fuel supply line. The air regulation unit would act to vary a flow of air into a combustion zone of the combustor based on a fuel pressure in the fuel supply line.
In another aspect, the invention may be embodied in a method of controlling a flow of air into a combustion zone of a combustor of a turbine. The method would include sensing a fuel pressure in a fuel supply line that supplies fuel to the combustor, and varying a flow of air into the combustion zone based on the sensed fuel pressure.
Compressed air from the compressor section of the turbine is routed into the annular space located between the flow sleeve 30 and the combustor liner 40. The arrows 44 in
At the upstream end of the combustor, a plurality of fuel nozzles 60 are mounted in a concentric ring around a combustor cap assembly 50. In some turbines, a secondary fuel nozzle 70 is located at the center of the combustor. In other turbines, the secondary fuel nozzle is not present or in contrast to the figure, may be flush or recessed relative to the cap. Both the primary fuel nozzles 60 and the secondary fuel nozzle 70 penetrate the combustor cap assembly 50 and extend outside the combustor.
Air from the compressor section of the turbine can enter the combustion zone 99 via a plurality of different paths. As shown by the arrows 44, the compressed air travels up the annular space between the flow sleeve 30 and the combustor liner 40. The compressed air must turn 180°. The air can flow through the nozzles to enter a combustion zone 99, or the air can pass through apertures in the combustor cap 50 to enter the combustion zone 99. The apertures in the combustor cap 50 can be provided to cool the combustor cap. Likewise, annular spaces in the combustor cap 50 may surround each of the fuel nozzles, to allow a flow of the air to pass down the exterior of the nozzles to help cool the nozzles.
In addition, dilution holes 22 and cooling holes can be located in the transition piece 20. This allows some of the air from the compressor to pass from an exterior of the transition piece into the interior of the transition piece. Likewise, dilution holes 42 in the combustor liner 40 can allow air to enter the combustion zone 99.
Fuel supplied by the fuel nozzles 60, 70 mixes with the compressed air and the fuel air mixture is ignited in the combustion zone 99.
As explained above, it is sometimes desirable to vary the amount of air which is being locally mixed with the fuel supplied by the fuel nozzles to achieve optimum combustion. The proper mixture of fuel and air provides good combustion efficiency and also reduces the creation of undesirable combustion gases.
As explained above, when the load demand on a turbine increases, it is necessary to deliver a larger amount of fuel into the combustor to satisfy the higher load. As also explained above, when greater amounts of fuel are being delivered into the combustor, it is desirable to increase the amount of air being delivered into the combustion zone to avoid running the turbine at an undesirably high fuel/air ratio, which can lead to the generation of undesirable NOX gases. The first air regulation units 67 in the combustor illustrated in
Delivering a greater amount of fuel through the nozzles means that the pressure in the fuel lines will increase. Conversely, when lesser amounts of fuel are being delivered into the combustor, the fuel pressure decreases. Because fuel pressure varies depending on the rate at which fuel is being delivered into the combustor, the fuel pressure is used to actuate a mechanical mechanism in the first air regulation units 67 to selectively vary the amount of air being delivered into the upstream end of the combustor. The design of the air regulators can be such that air flow varies linearly or non-linearly with the fuel pressure as desired to optimize operation.
In the embodiment illustrated in
If the turbine is operated on high heat value fuel, such as natural gas, one would like to increase the amount of air being delivered into the combustion zone as the amount of fuel being delivered increases. And the varying pressure in the first fuel supply line 62 is used to accomplish this.
In the embodiment illustrated in
Although
An embodiment of the first air regulation unit 67 is illustrated in a functional fashion in
When an air regulation unit as illustrated in
The mechanical linkage illustrated in
The second air regulation unit 66 is designed to deal with the air supply problems than can occur when a turbine is run with low heat value fuel. As explained above, when a relatively low heat value fuel such as syn-gas is mixed with natural gas, or is used exclusively, it is necessary to use a greater volume of the low heat value fuel, as compared to the high heat value fuel, to maintain the turbine at a certain operating condition. It also may be desirable to use less air per unit volume of the low heat value fuel, depending on the fuel's composition, in the combustion zone to avoid running the turbine in an undesirably lean condition, which can result in flame instability and incomplete burning of undesirable CO gases. And the more low heat value fuel that is used, the more one may like to reduce the amount of air being supplied into the combustion zone.
The second air regulation unit is designed to selectively vary the air being introduced into the combustor based on the pressure in the second fuel delivery line 64, which provides the low heat value fuel to the fuel nozzles 60/70. As with the first air regulation units 67 described above, in an actual embodiment of a combustor, the second air regulation units 66 would be mounted in a ring around the exterior of the combustor. Also, additional second air regulation units 66 could be located downstream of the one shown in
A pressure line 65 couples the second fuel delivery line 64 to the second air regulation units 66. And the varying pressure is used to control a mechanical mechanism in the second air regulation unit 66 to selectively close off a supplemental air supply passage that admits air into the combustor. As the pressure of the low heat value fuel increases, indicating that greater amounts of the low heat value fuel are being mixed into the fuel delivered to the nozzles 60/70, the supplemental air passageway is gradually closed off.
The second air regulation unit 66 could be configured as illustrated in
As shown in
A device as illustrated in
The mechanisms illustrated in
For instance, in the embodiments described above, the air regulation units are located at the upstream end of the combustor. In alternate embodiments, the air regulation units could be located at the downstream end of the combustor, for instance, on the transition piece 20. However, when the air regulation units are located at the downstream end of the combustor, they would need to operate in the opposite fashion.
For instance, when an air regulation unit is located on the transition piece 20, and connected to the fuel supply line 62 that delivers high heat value fuel into the combustor, the air regulation unit would need to close off a supplementary air passage as the pressure of the high heat value fuel increases. This will reduce the amount of air entering the combustor at the downstream end, which will have the effect of increasing the amount of air entering at the upstream end, to avoid an undesirably rich fuel air ratio in the combustion zone.
Conversely, when an air regulation unit is located on the transition piece 20, and connected to the fuel supply line 64 that delivers low heat value fuel into the combustor, the air regulation unit would need to open a supplementary air passage as the pressure of the low heat value fuel increases. This will increase the amount of air entering the combustor at the downstream end, which will have the effect of decreasing the amount of air entering at the upstream end, to avoid an undesirably lean fuel air ratio in the combustion zone.
In the embodiments described above, the air regulation units directly control the amount of air flowing into the combustion zone 99. In alternate embodiments, similar air regulation units could be used to control the amount of air flowing through and/or around the exterior of the fuel nozzles themselves.
In the following description,
In many nozzles, air flows through the nozzle itself. The air may be mixed with fuel within the nozzle, or the air may exit the downstream end of the nozzle, and then mix with fuel outside the nozzle.
As shown in
A primary fuel delivery passageway 152 runs down the length of the nozzle. The primary fuel passageway 152 delivers fuel to a plurality of radially extending fuel injectors 140. Each of the radially extending fuel injectors 140 includes a plurality of fuel apertures 142. The fuel delivered through main fuel passageway 152 exits through the fuel apertures 142 directly into the flow of compressed air running down the exterior of the fuel nozzle. In alternate embodiments, the fuel apertures could be formed along exterior of the body, and/or the fuel apertures could be part of swirler mechanisms mounted on the exterior of the nozzle. The swirler mechanisms could induce air flowing along the exterior of the nozzle to swirl around the nozzle, which can help to mix the fuel with the air before it is ignited in the combustion zone.
In the embodiment illustrated in
The first air delivery passageway 156 is coupled to a first air regulation unit 162 and a second air regulation unit 164. An air inlet line 130 is coupled to the first and second air regulation units 162, 164. Although the air inlet line 130 is illustrated as coming from the side, as will be described later, in an actual nozzle, the air inlet might simply be an entrance opening in the nozzle that is positioned to receive a flow of compressed air from the compressor.
A first fuel supply line 110 supplies a high heat value fuel to the nozzle. A pressure line 112 connects the first air regulation unit 162 to the first fuel supply line 110. A fuel pressure within the first fuel supply line 110 is communicated to the first air regulation unit 162 via the pressure line 112. A rise in the fuel pressure in the fuel supply line 110 would cause the first air regulation unit 162 to increase the amount of air flowing into the air delivery passageway 156. A mechanism as illustrated in
A second fuel supply line 120 could be used to deliver a relatively low heat value fuel to the fuel nozzle. The pressure line 122 would communicate a fuel pressure in the second fuel supply line 120 to the second air regulation unit 164. An increase in the fuel pressure in the second fuel supply line 120 would cause the second air regulation unit 164 to decrease the amount of compressed air flowing into the air delivery passageway 156. A mechanism as illustrated in
The two air regulation units 162 and 164 would act to automatically adjust the amount of air passing through the nozzle and that is then introduced into the combustion zone of a combustor. The first air regulation unit 162 would act to introduce additional air when greater amounts of the high heat value fuel are being supplied, to avoid an above optimum fuel/air mixture. Likewise, when greater amounts of a low heat value fuel are being introduced into the combustor, depending on the composition of that fuel the second air regulation unit 164 could be utilized to decrease the amount of air being supplied to avoid operating with an undesirably lean fuel/air mixture.
In an actual fuel nozzle, one or more air regulation units could be positioned at the entrance of the nozzle to control the flow of air into the nozzle.
A leading or upstream end of the movable plunger 204 would be acted on by a high heat value fuel entering the nozzle. Under light load conditions, lesser amounts of fuel would act against the movable plunger 204, and the force of the biasing member would keep the plunger 204 positioned towards the upstream end of the nozzle. As a result, the downstream end of the movable plunger would partially block the entrance to the nozzle, limiting the amount of air passing through the nozzle.
When the turbine is more heavily loaded, and greater amounts of a high heat value fuel are flowing into the nozzle, the greater force of the fuel flow would act against the biasing member to push the movable plunger farther into the nozzle in the downstream direction. As shown in
In the embodiment illustrated in
When greater amounts of the low heat value fuel are entering the nozzle, the greater fuel pressure of the low heat value fuel will push the movable plunger 204 deeper into the nozzle, as illustrated in
The plunger mechanisms illustrated in
Likewise, the plunger could be moved within the nozzle in multiple different ways. The fuel could directly impact the upstream end of the plunger, as described above, or the pressure in a fuel delivery line could cause the plunger to move in some other fashion. Regardless, the concept is for the fuel pressure to act through a mechanical device to selectively vary the airflow. Airflow may be varied linearly or non-linearly with fuel pressure as desired to optimize performance.
The mechanisms illustrated in
The aperture 304 in which the nozzle is mounted has an angled surface such that a diameter of the aperture 304 increases as one progresses deeper into the aperture, in the downstream direction. The exterior of the nozzle also has an angled surface that matches the angled surface of the aperture 304.
The nozzle is movably mounted in the combustor cap 302 such that the nozzle can move in the direction of arrows 309. A biasing member would be provided to bias the nozzle toward the upstream direction. The force of a high heat value fuel would act upon the nozzle to cause the nozzle to move in the downstream direction. When a lesser amount of the high heat value fuel is flowing into the nozzle, the nozzle would be positioned towards the upstream end of its movable range, which would maintain a relatively small air gap 312 between the exterior of the nozzle and the aperture 304 in the combustor cap 302. This would ensure that a relatively small amount of air is allowed to flow through the air gap, and into the combustion zone of the combustor.
When greater amounts of the high heat value fuel are being delivered to the nozzle, the greater fuel pressure would cause the nozzle to move in the downstream direction, against the force of the biasing member. And when the nozzle moves in the downstream direction, the air gap 312 would increase, which would allow a greater amount of air to flow through the gap and into the combustion zone. Thus, the mechanism would selectively vary the airflow according to the pressure of a high heat value fuel, similar to the air regulation unit illustrated in
The mechanism illustrated in
When lesser amount of the low heat value fuel are flowing, the biasing member would hold the nozzle 322 at the upstream end of its travel, and a greater amount of air would be allowed to flow between the nozzle and the combustor cap. When the amount of the low heat value fuel increases, the pressure of the fuel would cause the nozzle to move in the downstream direction, which would act to reduce the gap between the exterior of the nozzle and the aperture in the combustor cap 302. Thus, as greater amounts of the low heat value fuel are burned, the amount of air flowing into the combustion zone would decrease. Thus, this mechanism would operate like the air regulation mechanism illustrated in
The mechanisms illustrated in
Also, in some embodiments, the entire nozzle might move with respect to the combustor cap, while in other embodiments, only the portion of the nozzle that is located in the aperture of the combustor cap might move. In still other embodiments, the nozzles themselves might remain stationary, and the combustor cap might move with respect to the nozzles.
In the mechanisms illustrated in
In the mechanism illustrated in
One or more simple mechanical mechanisms could be used to cause the movable collar 61 to move in the upstream and downstream directions based upon the pressures of high and low heat value fuels.
A first mechanical air regulation mechanism coupled to a high heat value fuel supply line would cause the movable collar 61 to move in the downstream direction when the pressure in the high heat value fuel line increases. This would increase the amount of air entering the combustion zone of the turbine.
A second air regulation mechanism coupled to a low heat value fuel supply line would cause the movable collar 61 to move in the upstream direction as the pressure in the low heat value fuel supply line increases. This would decrease the amount of air flowing into the combustion zone of the turbine.
Although the two mechanisms would act upon the movable collar in opposing directions, by providing both mechanisms, the airflow can be selectively varied based upon both the pressure of a high heat value fuel and the pressure of a low heat value fuel.
In alternate embodiments, the movable collar 61 could be coupled only to a high heat value fuel supply line, or only to a low heat value supply line. Further, some sort of biasing mechanism could ensure that the movable collar 61 always returns to a central or neutral position when the movable ring is not being moved in one direction or another by a pressure in a fuel delivery line.
For systems where the combustion zone is immediately at the nozzle exit such as in systems that do not include a centrally mounted secondary nozzle, the utilization of the mechanisms illustrated in
Devices similar to the ones described above could be utilized if instead of air, oxygen or oxygen enriched air is used, or if some other oxygen/air combination gas is used.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.