On Degradation and Monitoring Tools for Gas and Steam Turbines

Sammanfattning: The revenue from a power plant is strongly dependent on the life cycle cost. Today, when the market conditions for power-producing companies have shifted from a protected market to a deregulated market, the need for tools to monitor power plants has increased significantly. In this new competitive market, targeted revenues and operational economy drive the need for advanced monitoring tools. In this thesis, monitoring tools for both the gas turbine and the steam turbine are described. The thesis gives a thorough description of the state-of-the-art model-based gas turbine flow path analysis system. The underlying mechanisms for degradation are also described, together with some remedying actions. The main intention of the thesis is to provide guidance for the user of the plant on how a model-based system works. The information is presented in general terms, since it is impossible to cover all gas turbine based power plant configurations. The tools presented here have different levels of sophistication, from the most simple to state-of-the-art heat and mass balance programs. The level of sophistication that is achievable is dependent on the extent of knowledge about a specific engine type. The highest level of sophistication is reserved for systems delivered by the manufacturing companies (OEMs). This level of model-based monitoring system requires detailed propriety turbine data that are not available outside the OEM. A system delivered by an OEM is more costly in general, but the additional know-how is a very valuable commodity. When working with the operational aspects of a power plant, one needs to make quantitative estimations of the effects of deteriorated components. Usually, the software for more detailed analysis are not available to the users since they use in-house code developed by the manufacturers. Besides being proprietary, such code is normally neither user-friendly nor adapted for this type of analysis. However, there are commercially available software packages on the market, but these do not usually provide the required level of off-design prediction capability. Thus, it was decided to develop a flexible tool with open structure that would enable both general power plant simulation useful for the plant owners, and detailed component analysis that is of special interest for research purposes. This work resulted in three different tools, a gas turbine performance deck or off-design performance prediction tool, a steam cycle analysis tool, and a reduced-order through-flow program. The gas turbine performance deck is suitable for both gas turbine and complete combined cycle analysis. This tool has also been used to analyze the off-design behavior of advanced wet gas turbine based cycles. The steam cycle analysis tool was developed for general steam cycle studies, and is suitable for highly loaded turbine components such as control stages at partial load. This tool was calibrated against high-quality data measured from test code (DIN) performance tests, and the results are well within expectation. The steam cycle calculation tool has been used by the project partners as a tool for generating data for ANN training purposes and general power plant off-design performance studies. The first two calculation models presented are at the component level ? where the performance of a component is simulated ? rather than dealing with an individual stage in a compressor or a turbine. As a complement, the author developed a reduced-order through-flow program, where more detailed analysis at the stage level can be performed. This software can be used for an arbitrary number of cooled and choked turbine stages. The code was validated against data measured from a turbine test rig, and the results show that the accuracy is well within the figures expected. This program is available at the department's website as open source code in Matlab?. The theories behind these calculation programs are presented in this thesis in Chapters 5, 6 and 7. Knowing the underlying degradation mechanisms, and with the possibility of including these in a condition-monitoring system, the potential for improving the economics of operation is significant. The availability of a plant can be increased if early warnings can be obtained. Also, in the case of component breakdowns, the cost of secondary replacement parts can be avoided entirely.