ارزيابي قابليت اطمينان در بويلر بازياب با در نظر گرفتن شرايط عملكردي و محيطي، تعميرات و فرسودگي

RELIABILITY EVALUATION OF HRSG CONSIDERING OPERATIONAL AND ENVIRONMENTAL CONDITIONS, MAINTENANCE AND AGING EFFECTS

ارزيابي قابليت اطمينان بويلر بازياب به‌منظور پيش‌بيني احتمال وقوع خرابي و همچنين كاهش علل خرابي حايز اهميت است. در اين نوشتار به مدل‌سازي قابليت اطمينان، با در نظر گرفتن پديده فرسودگي، تاثير عمليات تعميرات و شرايط محيطي و عملكردي بر روي قابليت اطمينان پرداخته مي‌شود. سپس روشي براي تخمين پارامترهاي مورد نياز در مدل ارايه مي‌شود. با استفاده از روش معرفي شده، اطلاعات خرابي شش بويلر بازياب يك نيروگاه حرارتي، هركدام به ظرفيت 50 مگاوات، مورد ارزيابي قرار گرفته و پارامترهاي مدل ارايه شده براي اين نوع بويلر محاسبه مي‌شود. سپس رفتار توابع قابليت اطمينان بويلر بازياب مورد مطالعه در شرايط متفاوت مورد ارزيابي قرار گرفته و نهايتاً به بررسي علل وقوع خرابي در بويلرهاي بازياب پرداخته مي‌شود. به‌كمك مدل و روش ارايه شده در اين نوشتار مي‌توان قابليت اطمينان سيستم قدرت را در شرايط مختلف ارزيابي كرد.

Combined cycle power plants consist of three main sections, namely; gas turbine, Heat Recovery Steam Generator (HRSG) and steam turbine. Occurring failure in each part of them causes a reduction in power plant output power. As the main part, if HRSG fails, the steam turbine will be unusable and have no output power, so, the reliability assessment of HRSG has a great importance for forecasting the probability of occurring failure and also reducing failure causes. In this paper, the reliability of HRSG, considering the effects of the aging phenomenon, maintenance and working and operational conditions on reliability, are modeled. Weibull distribution is used in order to model the aging phenomenon. Proportional Age Setback (PAS) and Proportional Age Reduction (PAR) models are introduced to model the maintenance effects. Accelerated Life Model (ALM) and Proportional Hazard Model (PHM) are presented and the ALM model is used to model working conditions (operational and environmental conditions). Afterwards, a method to estimate the model parameters is introduced, which is based on the Maximum Likelihood Estimator (MLE) approach. Using the presented method, failure data of six HRSGs of a plant, each with a capacity of 50 MW, are analyzed and the model parameters are calculated. By the proposed method, the unique parameters are calculated for the whole six HRSGs. To ensure that the fitted distribution is true, the estimated parameters are assayed using the Chi-Square test. Then, the behavior of HRSG reliability related functions, hazard rate and reliability function are studied under different conditions. Finally, the HRSG failure causes are discussed. Using the presented method, one can evaluate the reliability of a power system under different conditions and decide how to choose the best maintenance policy. Results show that maintenance operations can reduce failures and consequently increase the reliability of HRSGs. The estimated Weibull parameters of the HRSG case study show that it is in the aging period and has an increasing hazard rate function.