Patent Application
20070028947
The present application relates generally to gas turbines engines and more particularly relates to an improved on-line compressor water wash system for gas turbine engines.
An on-line water wash system is commonly used to remove contaminants from gas turbine compressors. The on-line system recovers gas turbine efficiency when the operating schedule does not permit shutdown time so as to perform a more effective off-line wash. For example, U.S. Pat. No. 5,011,540 to McDermott describes a commonly used on-line water wash system. The nozzles of the system are located in positions upstream or directly at the inlet to the compressor bellmouth casing. These nozzles create a spray mist of water droplets within a region of relatively low velocity air. When in operation, the spray mist is drawn through the bellmouth and into the compressor inlet by the negative pressure produced by the rotating compressor.
This known system, however, does not address the specific travel path of the mist droplets. As a result of this, erosion of the first stage rotating blade may occur at undesirable locations along the leading edge of the blade, including the root region. If erosion pits caused by the droplets exceed a critical flaw size, a total failure of the blade may occur. To prevent this event, monitoring of wash hours along with a blade inspection and repair program may be needed. These requirements, however, are time consuming and costly.
There is a desire, therefore, for an on-line water wash system that eliminates or reduces first stage rotor blade root erosion while still providing effective cleaning of the turbine compressor. It is preferred that the resultant cleaning will be as effective, if not more effective, then commonly known systems.
The present application describes an on-line water wash system for a compressor having a bellmouth casing with a region of known high velocity inlet airflow and a number of rotating blades. The water wash system may include a number of water nozzles positioned within the bellmouth casing about the region of known high velocity inlet airflow and a stream of water droplets. The stream of water droplets is targeted by the water nozzles so as to avoid the bellmouth casing and the rotating blades.
The water nozzles include a number of aft side water wash nozzles. The bellmouth casing includes an inlet and the water nozzles are positioned between the inlet and the rotating blades. The water nozzles may be aft nozzles. The compressor also may include a number of struts. The water nozzles may be positioned between the struts. There may be a nozzle for each pair of the struts. The stream of water droplets is targeted by the water nozzles so as to avoid wetting the struts. A pressure regulating valve may be in communication with the nozzles.
The present application further describes a method of on-line washing of a turbine having a compressor with an air inlet pathway for a high velocity air stream defined by a bellmouth casing and leading to a number of rotating blades. The method may include the steps of determining the location of the high velocity air stream, targeting the location of the high velocity air stream with a spray of water droplets, and providing the spray of water droplets to the location of the high velocity air stream such that the spray of water droplets stays in the air inlet pathway instead of coating the bellmouth casing or the rotating blades.
The compressor also may have a number of struts. The method further may include the step of providing the stream of water droplets such that the spray of water droplets stays in the air inlet pathway instead of coating the struts.
The present application further describes an on-line water wash system for a compressor having a bellmouth casing with a region of known high velocity inlet airflow, a number of rotating blades, and a number of struts. The water wash system may include a number of water nozzles positioned within the bellmouth casing, between a pair of the struts, and about the region of known high velocity inlet airflow. The water wash system includes a stream of water droplets. The stream of water droplets is targeted by the water nozzles so as to avoid the bellmouth casing, the rotating blades, and the struts.
These and other features of the present invention will become apparent to one of ordinary skill in the art upon review of the following detailed description of the embodiments when taken in conjunction with the drawings and the appended claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
As shown in
As is described above, both sets of nozzles 90 and 100 produce a spray mist of water droplets that are drawn into the air inlet pathway 20 by the negative pressure created by the rotating compressor blades 70. In traveling along the air inlet pathway 20, some droplets may strike the inside diameter wall of the bellmouth casing 40 and/or the bellmouth struts 60. A high concentration of these droplets may strike the root of the first stage rotating blades 70. The nozzles 90, 100, 115 described herein thus provide minimum targeting capability and, hence, less effective cleaning and possibly significant damage to the blades 70.
The nozzles 210 are positioned in a region of known high inlet air velocity where analysis and testing has confirmed that the spray mist efficiently enters the air inlet pathway 20 of the compressor 30. The specifics of the air velocity regions can be determined by aerodynamic modeling of the air inlet pathway 20, the inlet plenum 50, and the bellmouth casing 40. The positioning minimizes wetting of the walls of the bellmouth casing 40 and the struts 60 and reducing the amount of water reaching the root of the first stage blades 70.
Functionally, the aft side nozzles 210 are located about a position that provides targeting capability into the compressor air inlet pathway 20. The position about the high inlet air velocity results in the ability to optimize the direction of a spray of water droplets 220. Optimal spray coverage is defined as a full radial distribution of the spray droplets 220, with the exception of the roots of the blades 70. Actual targeting is achieved with consideration of the nozzle pressure ratio, the injection angles, and the nozzle tip design. As such, the vast majority of the spray droplets 220 remain in the free airflow path within the compressor air inlet pathway 20.
Both the size and the velocity profile of the spray droplets 220 will vary as the inlet velocity changes. With inlet air velocity being directly related to the geometry of the compressor 30 and the inlet air inlet pathway 20, the optimum design of the system 200 should be analyzed and defined for each specific gas turbine model. This optimization can achieved by system modeling, including computational fluid dynamics (CFD) and full scale wind tunnel (rig) testing. Velocity also may vary with ambient operating conditions, turbine loads, and other operating parameters.
With water supply pressure being a contributor to the nozzle pressure ratio, the system 200 also may include a pressure-regulating valve 230 and local pressure gauge 240 to insure that the pressure is maintained as desired level. A pressure transducer 250 also may be utilized.
It should be apparent that the foregoing description relates only to the preferred embodiment of the present invention and that numerous changes and modifications may be made herein without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.
