Patent Publication Number: US-8123150-B2

Title: Variable area fuel nozzle

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a variable area fuel nozzle. 
     Dry Low NOx (DLN) combustors are widely used for power generation as well as oil and gas production applications and are mainly designed for use with natural gas fuel and/or liquid fuels. New applications of the combustors are, however, beginning to demand that the combustors exhibit wider fuel flexibility. For example, in many cases currently operating combustors must have the capability to operate on natural gas fuels and then switch to low British Thermal Unit (BTU) fuels where fuel flow rates double and still meet emissions and operability requirements. 
     In these cases, as fuel flow rates of the alternate fuels can be significantly greater than those of other fuels, additional circuits need to be installed to maintain fuel side pressure ratios to satisfy fuel delivery specifications. These additional circuits often require active controls, purge circuits and/or additional equipment and are, therefore, expensive and costly to maintain. In addition, dynamics effects due to varying pressure levels within the circuits can be problematic. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a nozzle is provided and includes a circuit by which fuel is delivered to a nozzle part and a valve, interposed between the circuit and the nozzle part and upon which the fuel impinges, an opening and closing of the valve being passively responsive to a fuel pressure in the circuit such that the valve thereby modulates a size of an area through which a corresponding quantity of the fuel flows from the circuit to the nozzle part. 
     According to another aspect of the invention, a nozzle is provided and includes a selectively operated circuit, including a body formed to define an orifice, by which fuel is delivered to a nozzle part and a valve, interposed between the circuit and the nozzle part and upon which the fuel impinges, which passively opens and closes the orifice in response to a fuel pressure in the circuit, the opening and closing of the orifice by the valve thereby modulating a size of an area through which a corresponding quantity of the fuel flows from the circuit to the nozzle part. 
     According to yet another aspect of the invention, a nozzle is provided and includes a selectively operated circuit, including a body formed to define one or more orifices, by which fuel is delivered to a nozzle part and a valve associated with each of the orifices, each valve being interposed between the circuit and the nozzle part and upon each of which the fuel impinges, which passively opens and closes the respective orifice in response to a fuel pressure in the circuit, the opening and closing of the respective orifices by each of the valves thereby modulating a size of an area through which a corresponding quantity of the fuel flows from the circuit to the nozzle part. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side sectional view of a fuel nozzle; 
         FIG. 2  is a side sectional view of a fuel nozzle according to embodiments; 
         FIG. 3  is a side sectional view of a fuel nozzle according to further embodiments; 
         FIG. 4  is a side sectional view of a fuel nozzle according to further embodiments; 
         FIG. 5  is a perspective view of an end cover with a multi-fuel nozzle; and 
         FIG. 6  is a perspective view of a valve according to embodiments. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A dual gas fuel nozzle allows for use of a relatively wide range of molecular wobbe index fuels in hardware geometries. This dual gas fuel nozzle can burn up to about 100% natural gas fuel to low British Thermal Unit (BTU) fuels having about 100 to about 400 BTUs per standard cubic foot, like high reactivity syngas or low reactivity highly diluted streams, by utilizing passively or actively controlled multiple internal fuel passages located within the fuel nozzle. For example, two circuits may be employed and joined internally to a fuel nozzle where one fuel stream provides shielding to the other and prevents it from direct exposure and ingestion of hot combustor flame or combustion products that, if remain unpurged, could result in hardware damage. 
     At least one of these circuits provides for a variable flow area that is regulated passively or actively actuated by the fuel side pressure. As the pressure in the fuel circuit rises due to increased mass flow, a valve or some other suitable device disposed with respect to the circuit opens and provides variable fuel flow area to meet the flow demand while maintaining reasonable fuel feed stream pressures. Valve settings and features can be custom designed based on the application demands. 
     With reference to  FIG. 1 , a fuel nozzle  10  is provided. The fuel nozzle  10  may be employed for various applications including, but not limited to, dry low NOx (DLN) combustors of gas turbine engines. The fuel nozzle  10  includes a first fuel circuit  20  and a second fuel circuit  30  by which first and second fuels are delivered to nozzle part  40 . The first fuel is delivered to nozzle part  40  through fixed slots and the second fuel is delivered to nozzle part  40  by way of a valve  50 . The valve  50  is interposed between the second fuel circuit  30  and the nozzle part  40  with the second fuel impinging on the valve  50  at a second fuel pressure. The valve  50  is passively responsive to this second fuel pressure and thereby modulates a size of an area  55  through which a corresponding quantity of the second fuel flows from the second fuel circuit  30  to the nozzle part  40 . The flow of the second fuel maintains the valve  50  in a substantially equilibrated state as long as the second fuel circuit  30  is operated. 
     In accordance with embodiments, the second fuel is a relatively low BTU fuel as compared to the first fuel. For example, the first fuel may include natural gas or a combination of natural gas and synthetic gas (Syngas) whereas the second fuel may include only Syngas. The second and the first fuel can also be the same fuel such as low BTU Syngas. The second fuel circuit  30  may be selectively operated in accordance with internal and external conditions, such as the availability of certain fuels and, in a case where the fuel nozzle  10  is a component of a gas turbine engine, turbine loads that require a given level of energy production from the available fuels. 
     The first fuel circuit  20  and the second fuel circuit  30  may each be annular in shape with the second fuel circuit  30  disposed within the first fuel circuit  20 . Each may terminate at similar axial locations proximate to the nozzle part  40 . The second fuel circuit  30  may be defined through a circuit body  31  with the first fuel circuit  20  being defined through an annular space between the circuit body  31  and annular casing  21 . The nozzle part  40  includes section  41  aligned with the annular casing  21  and partially surrounding an end of the circuit body  31 . 
     The valve  50  may be spring-loaded and linearly responsive to a change in the second fuel pressure. That is, the valve  50  may open and close in direct proportion to increases or decreases in the second fuel pressure. In alternate embodiments, the valve  50  may be non-linearly responsive to the second fuel pressure changes. Here, the valve  50  opens and closes more or less responsively as the second fuel pressure increases or decreases significantly. In still further embodiments, the valve  50  may be linearly responsive to relatively small or large second fuel pressure changes and non-linearly responsive to relatively large or small second fuel pressure changes. In a similar manner, the spring-loaded valve  50  may be configured to at least one of linearly and non-linearly modulate the size of the area in passive response to second fuel pressure changes. 
     With reference now to  FIGS. 1-4 , the valve  50  may passively open and close an orifice  60  in response to a fuel pressure change in the second circuit  30  to thereby modulate a size of the area through which a corresponding quantity of the second fuel flows from the second circuit  30  to the nozzle part  40 . The circuit body  31  may include a valve seat  32  with the orifice  60  defined through the valve seat  32  as a passage having a substantially axial component  70  in some cases. With reference to  FIGS. 5 and 6 , the circuit body  31  may include an endcover  140  formed to define the orifice  60  as a passage having a radial component  142  and an axial component  143 . 
     Referring to  FIG. 1 , the valve  50  may include an upstream head  81  and a downstream head  82 , upon each of which the second fuel impinges, an axle  83 , which extends between the upstream and downstream heads  81  and  82 , and which is supported by the valve seat  32  to be axially movable in accordance with the second fuel pressure and a first elastic member  84 . The first elastic member  84  may be a spring and may be at least one of linearly and non-linearly responsive to the second fuel pressure. The first elastic member  84  biases the downstream head  82  toward a downstream surface of the valve seat  32  to urge closure of the orifice  60 . 
     With this construction, the valve  50  admits second fuel to the nozzle part  40  at a predefined second fuel pressure sufficient to energize the first elastic member  84  and continues to admit increasing quantities of the second fuel as the second fuel pressure increases and the downstream head  82  recedes from the valve seat  32 . 
     As shown in  FIG. 2 , the valve seat  32  and the valve  50  may each include complementary stepped profiles  100 ,  101  at the orifice  60 . In this way, at position A, the profiles  100 ,  101  are formed such that the valve seat  32  and the valve  50  abut one another and do not admit second fuel to the nozzle part (i.e., the orifice  60  is closed). However, as the second fuel pressure increases and the valve  50  approaches positions B and C, the valve seat  32  and the valve  50  have space in between them and second fuel can be admitted to the nozzle part  40  (i.e., the orifice  60  is opened). Moreover, since the C position is characterized by a larger opening that the B position more fuel can pass through the C position opening. Thus, whether the valve  50  is linearly or non-linearly responsive to the second fuel pressure, the valve  50  may admit different quantities of the second fuel at increasing second fuel pressures. In an alternate embodiment, as shown in  FIG. 3 , the valve seat  32  and the valve  50  may each include complementary continuously variable surface profiles  110 ,  111  at the orifice  60 . 
     With reference to  FIG. 4 , a downstream circuit  120  may be formed to extend axially from the circuit body  31  to deliver the second fuel, having passed through the orifice  60 , to a surface  130  of the nozzle part  40  for impingement cooling thereof The downstream circuit  120  is thus partially disposed within the conical section  41  of the nozzle part  40  and includes sidewalls  121  extending from the valve seat  32  and an end portion  122  proximate the surface  130 , which is formed to define through-holes  123  that direct second fuel toward the surface  130 . 
     As mentioned above and with reference to  FIGS. 5 and 6 , the circuit body  31  may include an endcover  140  formed to define a fuel channel groove  141  with the orifice  60  being defined as a passage between the fuel channel groove  141  and the nozzle part  40 . The orifice  60  thus includes a radial component  142  extending radially inwardly from a sidewall of the fuel channel groove  141  and an axial component  143  in communication with the radial component  142  and extending axially toward the nozzle part  40 . 
     The valve  50  may include a boss  150  disposed along the orifice  60 , a valve body  160  having a surface  161 , upon which the second fuel impinges, and a second elastic member  170 , which may include a spring and which is passively responsive to the second fuel pressure. The second elastic member  170  serves to bias the valve body  160  toward the boss  150  to thereby urge closure of the orifice  60 . 
     With this construction, the closure of the orifice  60  is achieved at predefined second fuel pressures insufficient to energize the second elastic member  170  such that complementary surface profiles  171 ,  172  of the valve body  160  and the boss  150  abut one another. The valve  50  admits second fuel to the nozzle part  40  at a predefined second fuel pressure sufficient to energize the second elastic member  170  and continues to admit increasing quantities of the second fuel as the second fuel pressure increases and the valve body  160  recedes from the boss  150 . 
     Although the valve  50  is illustrated in  FIGS. 5 and 6  as being disposed within the axial component  143  of the orifice  60 , it is understood that this is merely exemplary and that the valve  50  may also be disposed within the radial component  142 . It is further understood that the valve  50  may be provided in pairs with each valve  50  of the pair disposed in the radial and axial components  142 ,  143 . In this case, each of the pair of valves  50  may be opened and closed at similar or varied second fuel pressures. 
     The boss  150  may be formed as a component of an insert  180  that is removably insertable into the radial or the axial component  142 ,  143 . In this case, the insert  180  may include a screw-top  181  and both the insert and the sidewall of the orifice  60  may include complementary threading such that the insert  180  can be screwed into the orifice  60  for fastening. This is, of course, merely exemplary and it is understood that other fastening systems for the insert  180  may be provided. 
     The second elastic member  170  may be anchored to a second boss  190  downstream from the boss  150 . Here, the second boss  190  may be formed as part of the sidewall of the orifice  60  or as a further separate component. In any case, the second boss  190  supports the second elastic member  170  and the valve body  160  against the second fuel pressure. 
     As shown in  FIG. 5 , endcover  140  may have one or more multi-nozzle assemblies  42 . In this case, the valve  50  and the orifice  60  may each be plural in number and arrayed at plural locations relative to the second circuit  30 . In particular, the valves  50  and the orifices  60  may be arrayed with substantially uniform spacing and/or complementary directionality around the circuit body  31 . Moreover, the valves  50  may each be oriented at least one of radially and axially within the orifices  60 . 
     The descriptions provided above can be applied to eliminate air purge requirements for DLN and/or multi-nozzle quiet combustors (MNQC), single nozzle arrays or any fuel nozzle that requires multiple fuels circuits in the combustor. Eliminating purge circuits and equipments can provide significant hardware and contractual cost savings that can multiply at fleet level. Also, passively controlled valves provide variable area geometry for changing a fuel wobbe index throughout the operating range of a system to thereby increase fuel flexibility of the system. Moreover, variable area geometries mitigate dynamics effects due to reduced fuel side pressure fluctuations. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.