Abstract:
A method for transferring fuel includes flowing water to at least one nozzle of a main fuel circuit. Also included is flowing oil to the at least one nozzle of the main fuel circuit. Further included is flowing liquid fuel to the at least one nozzle of the main fuel circuit, wherein flowing water to the at least one nozzle of the main fuel circuit occurs prior to flowing oil to the at least one nozzle of the main fuel circuit and flowing liquid fuel to the at least one nozzle of the main fuel circuit.

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to turbine engines, and more particularly to a method for transferring fuel for a turbine liquid fuel system. 
     For large gas turbines, a combustion system typically employs multiple cans that are arranged circumferentially, with combustible fuel being delivered to each can for combustion. In order to produce sufficient combustion, the liquid fuel is often injected through a nozzle with atomization air assistance. If the atomization air is not used, the nozzle itself will be the atomizer. In this case, the combustion efficiency is related to the nozzle tip pressure drop. To ensure a high nozzle tip pressure drop, the combustion system typically employs two different fuel circuits, such as a pilot and a main, for example, because the fuel flow range from light off to base load is rather large. For dual orifice liquid fuel combustion systems, it is desirable to maintain a high tip pressure drop for each nozzle in the combustion system. Often, this requirement can be a challenge when the system transfers oil from the pilot circuit to the main circuit. During the transfer, some of the main nozzles do not have a pressure drop due to gravity head, which may hinder fuel flow. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a method for transferring fuel includes flowing water to at least one nozzle of a main fuel circuit. Also included is flowing oil to the at least one nozzle of the main fuel circuit. Further included is flowing liquid fuel to the at least one nozzle of the main fuel circuit, wherein flowing water to the at least one nozzle of the main fuel circuit occurs prior to flowing oil to the at least one nozzle of the main fuel circuit and flowing liquid fuel to the at least one nozzle of the main fuel circuit. 
     According to another aspect of the invention, a method for transferring fuel includes providing a pilot fuel circuit and a main fuel circuit to a combustion system, wherein the pilot fuel circuit and the main fuel circuit each comprise at least one nozzle. Also included is flowing pilot oil to the at least one nozzle of the pilot fuel circuit. Further included is flowing water to the at least one nozzle of the main fuel circuit. Yet further included is turning on the main fuel circuit, ramping up the main fuel circuit to a fixed position, and ramping down the pilot fuel circuit to a fixed position in about 10 seconds to about 40 seconds. 
     According to yet another aspect of the invention, a method for transferring fuel includes pre-filling a pilot manifold and a main manifold with oil. Also included is flowing oil to a plurality of nozzles of a pilot fuel circuit and ramping up a pilot control valve to about 80% to about 90% valve stroke. Further included is flowing water to a plurality of nozzles of a main fuel circuit. Yet further included is flowing oil to the plurality of nozzles of the main fuel circuit and ramping down the pilot fuel circuit. The method also includes flowing water to the plurality of nozzles of the pilot fuel circuit and operating under base load conditions. 
     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 flow diagram for a gas turbine liquid fuel system at a first stage of start-up; 
         FIG. 2  is a flow diagram for a gas turbine liquid fuel system at a second stage of start-up; 
         FIG. 3  is a flow diagram for a gas turbine liquid fuel system at a third stage of start-up; 
         FIG. 4  is a flow diagram for a gas turbine liquid fuel system at a fourth stage of start-up; 
         FIG. 5  is a flow diagram for a gas turbine liquid fuel system at a fifth stage of start-up; 
         FIG. 6  is a flow diagram for a gas turbine liquid fuel system at a sixth stage of start-up; 
         FIG. 7  is a flowchart illustrating a method for operating the gas turbine liquid fuel system. 
     
    
    
     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 
       FIG. 1  schematically illustrates a test set-up flow diagram for a gas turbine system  10 . Specifically, the gas turbine system  10  comprises a liquid fuel system  12  that is capable of transporting various fluids, such as oil, water, nitrogen, natural gas, and/or an emulsion. These are merely exemplary fluids that the liquid fuel system  12  is configured to operate with, and it is conceivable that other fluids may be employed within the liquid fuel system  12 . 
     The liquid fuel system  12  includes an oil source  14  comprising an oil tank  16  operably connected to an oil pump skid  18 . The oil pump skid  18  includes an oil filter  20  and an oil centrifugal pump  22 . The oil source  14  includes a plurality of oil lines  24  that operably connect the oil source  14  to a pilot fuel circuit  26  and a main fuel circuit  28 , with each of the plurality of oil lines  24  containing various valves and flow meters to monitor and regulate flow within the plurality of oil lines  24 . The liquid fuel system  12  also includes a water source  30  comprising a water tank  32  operably connected to a water pump skid  34 . The water pump skid  34  includes a water filter  36  and a water centrifugal pump  38 . The water flowing from the water source  30  is typically demineralized water, but other types of water may be employed. The water source  30  includes at least one water line  40  that operably connects the water source  30  to the pilot fuel circuit  26  and/or the main fuel circuit  28 , with the at least one water line  40  containing various valves, flow meters, and possibly other components to monitor and regulate flow within the at least one water line  40 . 
     The pilot fuel circuit  26  comprises at least one pilot manifold (not illustrated), at least one pilot oil control valve  44 , at least one pilot water valve  46 , and at least one nozzle  47  through which combustible fuel may be transferred. Similarly, the main fuel circuit  28  comprises at least one main manifold (not illustrated), at least one main oil control valve  50 , at least one main water valve  52 , and at least one nozzle  49  through which combustible fuel may be transferred. A mixing valve  48  is configured to deliver a mixture that includes combustible fuel to a combustor can (not illustrated). 
     Still referring to  FIG. 1 , one aspect of the invention provides a method for operating the liquid fuel system  12  of the gas turbine system  10 . Specifically, a start-up method for the liquid fuel system initially includes starting various pumps, including the oil centrifugal pump  22  and the water centrifugal pump  38 , as well as draining the main manifold of any water present. Subsequently, the main and pilot manifolds are each pre-filled with oil. 
     Referring to  FIG. 2 , the at least one, but typically a plurality of nozzles  47  associated with the pilot fuel circuit  26  begin to receive oil flow at a fixed valve position in order to facilitate light off flow. 
     Referring to  FIG. 3 , the oil flow through the pilot oil control valve  44  of the pilot fuel circuit  26  may then be switched to flow control and ramped up to about 80% to about 90% valve stroke. 
     Referring to  FIG. 4 , the main water valve  52  may be opened in order to initiate water flow to the at least one, but typically a plurality of nozzles  49  of the main fuel circuit  28 . The water flow to the at least one nozzle  49  may last for about five (5) to about ten (10) seconds. Flowing water to the at least one nozzle  49  of the main fuel circuit  28  protects the nozzle  49  from undesirable effects associated with initial oil flow thereto, such as coking buildup, for example. 
     Referring to  FIG. 5 , once the main fuel circuit  28  nozzle  49  has been provided with water, oil may begin to flow to the main fuel circuit  28 , thereby resulting in the provision of fuel to the nozzle  49  of the main fuel circuit  28 . The main oil control valve  50  is set at a fixed position and the pilot oil control valve  44  is ramped down to a fixed position in a timeframe of from about 10 seconds to about 40 seconds, depending on the application. 
     Referring to  FIG. 6 , the main oil control valve  50 , the pilot oil control valve  44 , and the main water valve  52  are switched to flow control and ramped up until system load conditions of about 50% to about 60% are satisfied, however, typically about a 60% load will be met. Once this load condition is attained, water flows to the pilot fuel circuit  26  by opening of the pilot water valve  46 . The fuel and water flow continue to ramp up toward full load, with a desired water/oil ratio of about in the range of about 0.9 to about 1.4. The system then operates at base load. 
     Referring to  FIG. 7 , the method for transferring fuel is described in conjunction with the illustrated flowchart, the method being generally referred to as  60 . Specifically, a startup sequence comprises draining the main manifold of water  62  and initiating the oil centrifugal pump and the water centrifugal pump  64 . The pilot manifold of the pilot fuel circuit and the main manifold of the main fuel circuit are pre-filled with oil  66  at a flow resulting from a fixed valve position of the pilot oil control valve. Subsequent to light off, the fixed valve position of the pilot oil control valve is then switched to a flow control operation during a transient ramp up process  68  of the pilot fuel circuit. The transient ramp up process  68  continues in the flow control operation until reaching about 80% to about 90% valve stroke of the pilot oil control valve. At this point, the main water valve is opened to initiate water flow  70  to at least one nozzle of the main fuel circuit. The water flow to the at least one nozzle lasts for about five (5) to about ten (10) seconds. Subsequent to the provision of water to the at least one nozzle, oil flows to the main fuel circuit  72 . The main oil control valve is set at a fixed position and the pilot oil control valve is ramped down to a fixed position in a timeframe of from about 10 seconds to about 40 seconds, thereby resulting in the pilot control valve reaching about 20% to about 35% valve stroke. The main oil control valve, the pilot oil control valve, and the main water valve are switched for flow control and ramped up until system load conditions of about 50% to about 60% are met, which may coincide with a main fuel flow rate of from about 14 lbs/second to about 35 lbs/second. Water then flows to the pilot fuel circuit  74  by opening of the pilot water valve. The fuel and water flow continue to ramp up toward full load  76 , with a desired water/oil ratio of about 0.9 to 1.4. The system then is operated at base load. 
     Advantageously, the method enables the dual circuit, two stage design without requiring atomization air assistance, instead relying on the nozzles as atomizers. To this effort, the nozzles are protected from coking buildup that inhibits effective fuel transfer, thereby leading to more efficient combustion. 
     Although the method has been described in a series of steps, it is conceivable that the order and nature of the steps may be modified as needed, depending on the specific application of operation of the liquid fuel system  12  of the gas turbine system  10 . 
     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.