The present invention is directed to a power plant and, more particularly, to a system and method of determining leakage within a steam turbine.
Most steam turbines having opposing high pressure (HP) and intermediate pressure (IP) sections running at a hot reheat temperature in excess of 1050° F. (566° C.) require an external cooling system in order to maintain acceptable first reheat stage stress levels. As a result of an interaction between the cooling system and internal leakages between HP and IP sections, it is difficult to determine an amount steam leaking between the HP and IP sections. More specifically, in operation, a running clearance exists between a shaft interconnecting the HP and IP sections and a packing assembly that provides a seal about the shaft. The running clearance allows high pressure, high temperature steam to leak from the HP section, along the shaft, to the IP section. The high pressure, high temperature steam leakage affects an overall efficiency of the steam turbine. That is, as steam leakage increases, steam turbine performance decreases.
There have been numerous attempts to determine the amount of leakage in order to adjust the running clearance and packing geometry for enhanced steam turbine performance. At present, an inference method is employed to calculate the amount of leakage. The inference test relies upon measuring an effect on an exit portion of the IP section resulting from changes made to parameters at an inlet portion of the HP section. In essence, the inference method measures an indirect parameter in order to determine enthalpy changes in the exit portion of the IP section to estimate the amount of steam leaking along the shaft. Employing an indirect measurement to determine an amount of leakage results in a solution that is, at best, one step above a guess. Determining the amount of leakage will enable engineers to adjust the running clearance and packing geometry between the shaft and the packing assembly to create added efficiencies in steam turbine operation. Without knowing, within some level of certainty, the amount of high temperature, high pressure steam leaking along the shaft, adjusting the running clearance and packing geometry to enhance steam turbine performance will remain a time consuming, high cost, and inexact trial and error process.
A steam turbine constructed in accordance with exemplary embodiments of the present invention includes a first turbine section having a flow of high temperature steam, a second turbine section and a shaft operatively connecting the first turbine section and the second turbine section. The steam turbine further includes a packing assembly positioned about the shaft. The packing assembly limits an amount of the flow of high pressure steam passing along the shaft from the first turbine section to the second turbine section. A first conduit is fluidly connected to the packing assembly. The first conduit is configured to introduce a flow of low temperature, low pressure steam to the packing assembly. A second conduit is also fluidly connected to the packing assembly downstream from the first turbine section and upstream from the first conduit. The second conduit receives a portion of the high temperature, high pressure steam passing into the packing assembly from the first turbine section. A valve is fluidly connected to the second conduit. The valve is configured to be selectively operated so as to allow the high temperature, high pressure steam to mix with the low pressure, low temperature steam in the second conduit.
Exemplary embodiments of the present invention also include a method of determining a leakage within a steam turbine having first and second opposing turbine sections connected by a shaft surrounded by a packing assembly. The first turbine section leaks high temperature high pressure steam along the shaft within the packing assembly. The steam turbine includes a first and second conduits connected to the packing assembly with the second conduit being positioned between the first conduit and the first turbine section. The method includes guiding the high temperature, high pressure steam through the second conduit, and introducing a low temperature, low pressure steam into the first conduit. The low temperature, low pressure steam is passed along the shaft toward the second conduit. The method further requires operating a valve fluidly connected to the second conduit, and mixing the high temperature, high pressure steam and the low temperature, low pressure steam in the second conduit to form a combined steam flow. At least one parameter of the combined steam flow is measured, and the valve is adjusted until the at least one parameter of the combined steam flow drops relative to a corresponding parameter of the high temperature, high pressure steam flow. An amount of high temperature, high pressure steam leaking from the first turbine section along the shaft toward the second turbine section is calculated based on the combined steam flow.
Additional features and advantages are realized through the techniques of exemplary embodiments of the present invention. Other exemplary embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features thereof, refer to the description and to the drawings.
With initial reference to
First turbine section 4 receives a flow of high temperature/high pressure (ht/hp) steam 54 from a heat recovery steam generator (HRSG) 56. HT/HP steam 54 has a temperature of about 1050° F. and a pressure of approximately 2000 psia. During operation, a portion of ht/hp steam 54 flows along shaft 8 within packing assembly 10 towards second turbine section 6. HT/HP steam 54 entering second turbine section 6 impacts an overall efficiency of steam turbine 2. Towards that end, it is desirable to control leakage about shaft 8.
In order to determine the amount of leakage within packing assembly 10, steam turbine 2 includes a leakage measuring system 60 illustrated in
Reference will now be made to
Q=kAη
Where: k=flow coefficient base on packing type
At this point it should be appreciated that the present invention provides a system and method of determining steam leakage in a steam turbine using known values instead of inferred parameters. The use of known values increases measurement accuracy allowing engineers to establish an effective running clearance between the shaft and packing assembly to enhance operation of the steam turbine. It should also be appreciated that while the low temperature/low pressure steam is described as emanating from an IP bowl section of the IP turbine, various other sources of lt/lp steam having known temperatures and pressures can be employed. Finally, it should be appreciated that the temperatures and pressures described above are for exemplary purposes and can vary within the scope of exemplary embodiments of the present invention.
In general, this written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the exemplary embodiments of the present invention if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
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