The performance of a once-through steam generator (OTSG) is bound to degrade due to fouling during its operation. The fouling will result in the degradation of the heat transfer between hot gas and water or steam on both sides of the tubes within the OTSG, thereby causing degraded OTSG performance. Such degradation could result in significant economic losses for a power plant where the OTSG plays a key role. Thus, it would be beneficial to develop a diagnostic method to quantify the fouling in an OTSG in order to support the condition monitoring and condition-based maintenance of the plant. In this study, a novel gas path diagnostic method for an OTSG based on Newton-Raphson method was developed to predict the OTSG degradation caused by fouling. The diagnostic method was applied to a model OTSG to test its effectiveness. The impact of measurement noise on the diagnostic accuracy was analyzed and discussed. A comparison between predicted and implanted degradation of a model OTSG demonstrated that the results are promising, and the method is satisfactory. Meanwhile, the diagnostic analysis of an OTSG based on real measurements has further proved that the developed diagnostic method works well and has a great potential to provide useful health information of OTSGs. In theory, the developed diagnostic method has the potential to be applied to different types of OTSGs.
The increasing demand for electricity and concern about global warming worldwide mean that electric power generation is required to be more efficient, cleaner, and more cost-effective. Combined-cycle power plants have gradually replaced their simple-cycle counterparts, where the energy of the exhaust gas from prime movers is recovered and used to generate steam and drive steam turbines to generate more useful power. There are two types of devices used to produce steam-one is the conventional drum-type heat recovery steam generator, and the other is the once-through steam generator (OTSG) that has no drum. The performance simulation of the former is relatively mature. However, the performance simulation for the latter is more difficult due to its multi-pressure circuits and moving boundaries between the economizer, evaporator, and superheater in the OTSG. In this research, a novel simulation method for the thermodynamic performance of a parallel dual-pressure OTSG under both design and off-design operating conditions has been developed. The method is applied to an OTSG operating in a combined-cycle gas turbine power plant at Manx Utilities, Isle of Man in the United Kingdom to demonstrate the effectiveness of the simulation method. Meanwhile, the OTSG performance variation caused by inlet gas energy variation and downstream steam turbine erosion are demonstrated. Compared with field data, the simulation results of the OTSG performance show that the novel performance simulation method is successful and provides details of the OTSG thermodynamic performance that may be useful for both OTSG designers and operation engineers.
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