GE94-02: Repair Flow Testing and Calibration Procedures for ...

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GEN20‐10W. Control System Specification for Westinghouse Combustion Turbines. April 2002. This report embodies a general retrofit specification for Westinghouse simple cycle combustion turbine control systems. This document is not intended to be a purchase specification, but can be used as a guide in the preparation of more specific documents applicable to particular units and users. This document is not applicable to: combined cycles, SCRs, CEMs, industrial drives, nor to machines with dry low NOx or advanced combustion systems. GEN20‐17. Dry Low NOx Operation Impacts on Combustor Parts Wear. April 2002. CTC 2 members identified a potential problem with dry low NOX combustors and requested that a study be conducted to determine the extent, if any, of the dry low NOx combustors causing excessive wear of combustor parts. Structural Integrity Associates was contracted to survey CTC 2 members to determine their experiences with dry low NOX combustors and to identify which manufacturers units were experiencing excessive wear problems, what diagnostic tools could be used to detect wear on combustion components and estimate the economic impact of this problem on annual operating costs. Most of the members contacted had very little or no operating experience with dry low NOx combustion systems. Overall, the GE systems tended to have problems related to wear or fretting, particularly in the liner collar. One user is suggesting several fixes. The Westinghouse systems had problems with wear, fretting and cracking in the combustor baskets and transition pieces, with several reported cases of portions of these components entering the hot gas path and causing consequential damage. The one reported case of a Siemens V94.3a showed considerable wear after less than two years of service, requiring replacement of several combustion components. While it is factual that the dry low NOx (DLN) combustion system gives rise to pressure pulsations and the “humming” that accompanies these pulsations, problems with fretting, wear and transition piece cracking have been found on both Westinghouse and GE machines in the past, suggesting that DNL aggravates the situation, but is not necessarily the root cause of these problems.
Detection of these pressure pulsations and “humming” is accomplished by mounting piezo‐ electric transducers onto the outside of the combustion section of the turbine and monitoring both the frequency and magnitude of the signals over the load range of the unit. This is done by both GE and Westinghouse is developing a system that will permit users to monitor their machines in the future, but there has been no commercial offering as of this report. Very little information is provided to users as to the allowable magnitude and frequency of these pressure pulsations and the most common method of control is to reduce load when the “humming” becomes clearly audible. HRSG20‐14. Life Extension Techniques for HRSGs in Cycling Service. October 2001. With the advent of deregulated power generation, more and more combined cycle and cogeneration plants are being operated in a cycling mode. This can cause accelerated wear and tear on the heat recovery steam generator (HRSG), especially if it was not originally designed to accommodate cycling. This report reviews the negative impacts cycling can have on an HRSG. Those impacts can be grouped into two main categories: those related to thermal stress and those related to water chemistry. Thermal stress related problems are principally caused by either ramping at excessive rates or by thermally shocking metal parts during start‐up or shutdown. Water‐ related problems can ultimately almost all be traced back to poor lay‐up practices. This report describes techniques that can be employed to mitigate or even eliminate these problems. The techniques include both changes in operating procedures and modifications or additions to plant equipment. Recommendations for design changes are provided for both existing plants and for new, yet to be built, combined cycle plants. WE20‐06. For Sealing Blade Tips in Industrial Gas Turbine Compressors. December 2002. The efficiency of an axial compressor is reduced by loss of air through the gap between tips of the blades and the wall of the case. This loss can also reduce revenues from industrial gas turbines. Abradable coatings on the case wall can eliminate these losses by sealing this gap. As the turbine spins up the full speed, blades stretch and the tips cut a groove into the abradable material creating the airtight seal.
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GE94-02: Repair Flow Testing and Calibration Procedures for ...

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