Abstract:
A system for draining fuel from the combustion chamber of a gas turbine engine in the event of a false start includes associated passageways and a straight through flow pilot air actuated poppet valve. The valve is normally open and actuated by the pilot air to close off the combustion chamber from the drain. A return spring biases the valve to open upon release of pilot air pressure acting on the valve. The valve housing has a piston section with a pilot air chamber and a section defining the passageways for the drain. The drain passageway extends along a straight path at an oblique angle to a piston axis along which a piston actuator moves in response to the return spring and/or the pilot air pressure. The valve also includes a position feedback system for detecting the state of the valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims benefit to U.S. provisional application Ser. No. 60/487,026 filed Jul. 14, 2003. 

   STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to valves, and in particular, to valves for draining the combustion area of turbine engines. 
   2. Description of the Related Art 
   Gas turbine engines are commonly used in power generation and propulsion applications. Gas turbine engines have a set of rotating turbine blades to compress air leading to one or more combustors into which fuel is injected and ignited. Fuel is delivered through metering orifices to burners in the combustors under pressure through a fuel line. Combustion of the fuel turns a downstream set of blades, used for energy extraction or propulsion, and which can be used to drive the compressor blades. 
   Gas turbine engines typically burn gaseous fuel, such as natural gas, and ignite using liquid fuel (such as diesel fuel). Some turbine engines are capable of sustained operation burning either gas or liquid fuel. Cost, clean burning and other considerations usually dictate that natural gas is the primary fuel for sustained operation, particularly for power generation applications. However, as mentioned, liquid fuel is often used for ignition or as a backup fuel supply in the event of a disruption in the natural gas line. 
   Gas turbine engines are designed for lengthy continuous operation, particularly in the case of power generation. Since they ordinarily run on natural gas, the liquid fuel system is often left unused for long periods. The heat and pressure associated with combustion of the gaseous fuel can cause “coking”, which occurs when the volatile components of the fuel are driven off by heat such that only a tarry deposit remains. Among other things, the coke deposits can build up on the liquid fuel burners and/or inhibit proper conduit of the liquid fuel when the engine is returned to fuel mode. When this happens at ignition, the combustion can fail causing a false start of the turbine. This false start can leave unspent liquid fuel in the combustor(s). Large gas turbines, such as those used in power generation, can have several combustion cans which can consume many gallons (35 gallons or more in some cases) of liquid fuel at ignition. This large volume of unspent liquid fuel must be drained from the combustors before ignition can be attempted again in order to prevent excessive combustion. Drain lines and collection wells are provided for this purpose. 
   Valving is used to open the combustors to the drain after a false start and keep the drain isolated during operation so that compression can be sustained. Conventional valves have several disadvantages particularly with regard to high pressure drops and resisting the effects of contamination. For example, common gate or globe type valves used for this purpose require the drained fuel to follow a non-linear path as it passes through the valve. This change in direction of the flow presents at least two distinct problems, namely, it causes a higher pressure drop across the valve and presents locations for the liquid fuel to collect, particularly given that the drain flow is usually not under pressure. Since the collected fuel is still in a high heat environment, it can cause a safety concern if combined with air, and it also can lead to coke deposits on the valve. 
   Ball-type valves are sometimes employed to allow for straight through flow of the drained fuel. The straight flow reduces the pressure drop and also alleviates some of the pooling of fuel inside the valve. However, it is still susceptible to other adverse effects of contamination. In particular, contaminants and coking deposits can arise on the non-sealing surface of the ball valve during operation (when the valve closes the drain). However, the deposit can be transferred onto the sealing surface of the valve seat when the valve is actuated. Specifically, as the ball is rotated to open, the build-up on the outer wall of the valve can rub against the valve seat. Once this occurs, the seal is compromised and turbine compression can be diminished by leakage through the valve to the drain. This in turn reduces the efficiency of the engine. 
   Accordingly, an improved drain valve is needed for draining liquid fuel from the combustors of gas turbine engines. 
   SUMMARY OF THE INVENTION 
   The present invention is a valve system for draining the combustion can(s) of a gas turbine engine to a drain collector, particularly after a false start. The valve system is arranged to provide for straight through flow of the drained fuel through the valve, while minimizing the adverse effects of contaminants on the sealing features of the valve. The valve is preferably normally open and actuated closed to seal off the combustion can from the drain during normal operation. After a false start of the engine, the valve is returned to open so that the unspent fuel can pass straight through the valve to the drain. 
   In one aspect, the drain valve includes a housing defining a drain passageway extending along a drain axis with an inlet for communicating with the combustion chamber and an outlet for communicating with the drain collector. The housing contains a valve that can move along a valve axis, which intersects the drain axis at an oblique angle, from an open position in which the valve is essentially clear of the drain passageway to a closed position in which the valve seals off communication between the inlet and outlet. 
   In another aspect, the invention is a drain valve having a valve housing with a pilot air inlet in communication with an air chamber and a drain passageway isolated from the air chamber and in communication between the combustion area and the drain collector. A piston has a valve and an enlarged head disposed in the air chamber of the piston housing. The piston is movable along a piston axis by application of pilot air into the air chamber acting against the piston head to seat the valve in the drain passageway at an oblique angle relative to the drain passageway and close off communication between the combustion area and the drain collector. 
   In another aspect the invention is a drain valve including a housing having a piston section and a drain coupler section. The piston section extends along a piston axis and defines a pilot air inlet in communication with an air chamber. The drain coupler section defines a passageway in communication with the combustion chamber and the drain collector that extends obliquely relative to the piston axis. The valve also includes a piston disposed in the piston section of the housing having a valve and an enlarged head disposed in the air chamber to be movable along the piston axis by application of pilot air into the air chamber, which acts against the piston head to seat the valve in the drain passageway and close off communication between the combustion chamber and the drain collector. The piston is biased to unseat the valve from the drain passageway upon release of the pilot air from the air chamber. 
   In still another aspect, the invention provides a fuel drain system. The system includes a drain passageway and a poppet valve aligned to allow for straight flow of the drained fuel. The drain passageway includes an inlet for communicating with the turbine engine combustion chamber and an outlet for communicating with the drain collector. The inlet and outlet are axially aligned along a drain axis. The poppet valve moves along a valve axis that intersects the drain axis at an oblique angle. In an open position, the valve is essentially clear of the drain passageway (inlet and outlet passageways), and in a closed position the valve prevents flow the drain passageway between the inlet and outlet. 
   The valve of the present invention is thus designed for use in the extreme pressure and temperature environment of turbine engines. The oblique angular arrangement of the drain passageway and the axis of valve movement allows the drain passageway to follow a straight path through the valve and permits the valve to move straight into and out of the drain passageway when seating and unseating. This allows for straight through flow of the drained fuel with minimal pressure drop. It also allows a poppet type valve to be used to seal the drain passageway with minimal susceptibility to contamination or coking at the sealing surfaces. 
   A crush seal can be provided about the drain passageway and concentric with the valve axis that is entirely isolated from the heat and pressure of operation of the turbine. Any contamination or coking build-up will occur at the non-sealing face of the valve. After a false start event in which the valve is opened, because of the oblique angle orientation, the valve passes straight away from the seal without any contaminated surface of the valve coming near or in contact with the sealing surface of the seal. To make the valve further resistant to contaminants, the seal is preferably of a soft material relative to that of the likely contaminants. Any small hard particles can embed themselves into the seal without interfering with the valve/seal interface. 
   These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is a preferred embodiment of the present invention. To assess the full scope of the invention the claims should be looked to, as the preferred embodiment is not intended as the only embodiment within the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side elevational view of the drain valve of the present invention; 
       FIG. 2  is a top plan view thereof; 
       FIG. 3  is an end view thereof; 
       FIG. 4  is a cross-sectional view through line  4 — 4  of  FIG. 2  showing the valve in an open position; and 
       FIG. 5  is a cross-sectional view similar to  FIG. 4  albeit showing the valve closing off a drain passageway. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1–3  of the drawings, a combustor drain valve  10  of the present invention includes a body with a main housing  12 , an actuator housing  14  and a position feedback housing  16 . The body can be constructed of one or more separate sections joined together as needed. In the preferred form shown, the actuator housing  14  has an end cap  18  (see  FIG. 4 ) welded to an end to which the position feedback housing  16  bolts. A retainer ring  20  is bolted in place to secure the other end of the actuator housing  14  to the main housing  12 . 
   As shown in  FIGS. 1 and 4 , the main housing  12  is in part formed of two sections  22  and  24  bolted together at respective flanges  25  and  27 . These two sections  22  and  24  define respective inlet  26  and outlet  28  sections of a drain passageway  30 . The inlet  26  and outlet  28  have open ends that are designed to accept fittings or other couplers for joining the valve to lines leading from the combustion can(s) of a turbine engine and a drain collector, respectively. The inlet  26  and outlet  28  are aligned along a drain axis  32  thereby defining a straight flow path through the drain passageway  30 . This drain axis  32  is aligned to intersect at an oblique angle a valve or piston axis  34 . 
   The piston axis  34  extends essentially through the center of the long axis of the valve body and is the axis along which a piston  36  travels between the open position shown in  FIG. 4  and the closed position shown in  FIG. 5 . A preferred form of the piston  36  includes a poppet valve  38 , which is press fit into one end of an elongated tubular body  40 , onto the other end of which is mounted a piston head  42 . A return spring  44  fits around the tubular body  40  and presses against the back of the piston head  42  and a retainer  45  for an annular seal  46 , which is preferably made of graphite filled Teflon. The seal  46  seals against the outer circumference of the tubular body  40  to isolate the drain side of the valve from the inside of the actuator housing  14 . The actuator housing  14  has a smooth cylindrical inner wall section against which a piston seal  48  on the piston head  42  slides. A pilot air inlet port  50  provides air communication into the actuator housing  12 , particularly into an air chamber within the cylindrical section between the piston head  42  and the end cap  18 . The pilot air inlet port  50  is coupled to an air line (not shown) to pressurize the air chamber and drive the piston  36  against the spring  44  along the piston axis  34  toward the drain passageway  30 . In one form, the spring  44  is preloaded at approximately 60 lbs. in the open position of  FIG. 4  and is at approximately 100 lbs. at the closed position in  FIG. 5 . The pilot air pressure in this case is some pressure higher than 100 psi, 150 psi for example, so that it can overcome the spring force and maintain the valve securely in the closed position during operation. When the pilot air pressure is released sufficiently, the spring  44  will drive the piston back along the piston axis  34  and return it to the open position. 
   The pilot air pressure moves the piston  36  along the piston axis  34  until the poppet valve  38  ends up in the closed position shown in  FIG. 5  in which the angled sealing surface  52  of the poppet valve  38  seats against the angled seat  54  of a seal  56 . The seal  56  preferably forms a crush seal between the flanges  25  and  27 . This is accomplished by using a seal of softer material than that of the housing flanges and also by undersizing the groove holding the seal such that when the flanges are bolted together the seal will compress and create high bearing loads against the flanges to form a tight seal. In a preferred form, the housing sections of the valve body are steel, and the seal is a softer metal, such as copper, which has sufficient heat resistant capabilities. The softer, crush seal is also advantageous because small, hard particles that may come in contact with the seal when the valve is in the open position can become embedded into the seal, rather that become lodged between the valve and seat interface, thereby promoting a better seal in a contaminated environment. 
   As can be seen in  FIG. 5 , the seal  56  is supported and protected at opposite faces by virtue of its position between the flanges  25  and  27 , leaving only the angled seat  54  of the seal  56  exposed when the poppet valve  38  is unseated. When seated, however, the entire seal  56  is isolated from the inlet  26  by virtue of the sealing surface  52  of the poppet valve  38  seating against the seat  54  of the seal  56 . The face of the poppet valve  38  remains exposed to the inlet  26  when closed, however, its sealing surface  52  is not. As noted above, the seal  56  and the poppet valve  38  are disposed at an oblique angle relative to the drain passageway  30 . This not only allows for a straight drain passageway, and thus low pressure drop, but also allows the poppet valve  38  to unseat from the seal  56  by moving straight back along the piston axis  34 . This in turn prevents the face surface of the poppet valve  38 , which is exposed to contaminants and likely to have coke build-up after prolonged operation of the engine, from coming into contact with the sealing surface of the seat  52  when the poppet valve  38  is opened. This maintains the integrity of the valve seal in an otherwise extreme heat and contaminated environment. A tight seal is critical to prevent leaking of engine compression to drain, and thereby maintain the efficiency of the engine. 
   As shown in  FIGS. 4 and 5 , the valve  10  also includes a position feedback system including a pair of sensors, such as proximity sensors  60 , that detect (via magnetic flux) the presence of a magnetic switch  62 , preferably of a ferrous metal, which is mounted to an elongated indicator rod  64 . The indicator rod  64  extends along the piston axis  34  through a sealed opening in the end cap  18  and the tubular body  40  of the piston  36 . One end is threaded into the back of the poppet valve  38  and the other end fits through an opening in housing  16  to extend outside the valve body when in the open position of  FIG. 4 . This end provides visual indication of the state of the valve. 
   As mentioned, the preferred application for the valve of the present invention is in the drain system for a gas turbine engine. Specifically, the valve is designed to isolate a combustion chamber or can of the engine from the drain so that engine compression can be maintained during normal operation, in which conventional engines burn gaseous fuel. Typically, there are several combustion cans for each turbine. Some conventional power generation turbine engines have 14 combustion cans coupled in upper and lower pairs. Thus, a total of seven valves of the present invention would be used to control the draining of fuel from each of the seven combustion can pairs. 
   In any event, the valve stays in the closed state shown in  FIG. 5  for prolonged periods of operation, particularly when the turbine is used for power generation. The inlet side of the valve is thus open to the high temperature and pressure environment of the combustion chambers for prolonged periods. Fuel contaminants and coking can build up at the inlet side, however, as described above, not on the seal  56  or the sealing surface of the poppet valve  38 . Coking and contaminants can also build up on the valves delivering liquid fuel to the combustion cans for start up, and in some cases, when the fuel supply is changed “on the fly” during operation. As is common, after the turbine is shut down after long periods of use, the attempted re-start can fail due to the contamination of the burner nozzles or other fuel delivery components. The large volume of unspent liquid fuel delivered to the combustion cans are drained by opening the drain valve  10  to the position in  FIG. 4 . This is accomplished by releasing or venting the pilot air pressure in the air chamber and allowing the spring  44  to return the piston/valve to its normally open position. 
   As mentioned, the oblique arrangement of the drain and piston axes allows the drained fuel to pass straight through the valve. Thus, very little pressure drop occurs across the valve and the fuel will drain without collecting inside the valve, which greatly reduces the opportunity for coking or other contaminant build up inside the valve. And, the straight axial movement of the poppet valve  38  from the oblique drain passage prevents contaminants from the exposed areas of the poppet valve from contacting and being transferred to the sealing seat of the seal when actuated. Thus, the valve provides for high seal integrity in a contaminated environment. 
   It should be appreciated that merely a preferred embodiment of the invention has been described above. However, many modifications and variations to the preferred embodiment will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced.