نوع مقاله : مقاله پژوهشی

نویسندگان

• محمود شهرخی ¹
• محمد فرهادی ²

¹ دانشیار، گروه مهندسی صنایع، دانشکده مهندسی، دانشگاه کردستان، سنندج، ایران

² کارشناسی ارشد مهندسی صنایع، دانشکده مهندسی، دانشگاه کردستان، سنندج، ایران،

چکیده

در نیروگاه‌های سیکل‌ترکیبی تولید برق، به جای اینکه گازهای تولید شده از سوزاندن سوخت‌های فسیلی پس از چرخاندن توربین‌های گازی به اتمسفر رها شوند، جهت تولید بخار وارد بویلرهای بازیاب می‌شوند. بخار تولید شده توسط این بویلرها مجددا برای تولید برق در توربین‌های بخار استفاده می‌شوند. به این‌ترتیب راندمان تولید برق به نحو چشمگیری افزایش می‌یابد. بویلرهای بازیاب با صرف هزینه‌های زیاد ساخته شده و هرگونه خرابی آن‌ها موجب توقف بخشی از نیروگاه برق شده و هزینه‌های سرسام‌آوری را ایجاد می‌کنند؛ بنابراین بهینه‌سازی قابلیت‌اطمینان آن‌ها بسیار مهم می‌باشد. این مقاله به نحوه مدل‌سازی سیستم تغذیه آب بویلرهای بازیاب (HRSG) با استفاده از‌ ترسیم بلوک دیاگرام قابلیت‌اطمینان در دو حالت نیمه‌بار و تمام بار پرداخته و به این وسیله تفاوت دو طرح پیشنهاد شده برای آن‌ها را از نظر قابلیت‌اطمینان ارزیابی می‌کند. روش به کار رفته در این مقاله می‌تواند در ارزیابی و بهینه‌یابی قابلیت‌اطمینان بسیاری از سیستم‌های صنعتی دیگر نیز به کار رود.

کلیدواژه‌ها

• بویلرهای HRSG
• دیاگرام بلوکی قابلیت‌اطمینان (RBD)
• بهینه‌سازی طراحی

موضوعات

• ایمنی، خطر و قابلیت اطمینان

عنوان مقاله [English]

Optimization of design of HRSG boilers at cyclic power plants

نویسندگان [English]

• mahmoud Shahrokhi ¹
• Mohammad Farhadi ²

¹ Associate Professor, Department of Industrial Engineering, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran

² Master of Industrial Engineering, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran.

چکیده [English]

In combined cycle power plants, instead of releasing gases produced from burning fossil fuels, after turning the gas turbines, they enter into heat recovery steam generator (HRSG) boilers to produce steam. The produced steam by these boilers is used to generate electricity in steam turbines and thus, electricity generation efficiency is dramatically increased. In this way, the efficiency of electricity production increases significantly. These boilers are made at a great cost and also, any failures of them cause a power plant to stop and create enormous costs, so optimizing their reliability is very important. This paper deals with the modeling of the HRSG feed water system by using a block diagram for two states (i.e., half-time and full load), to evaluate the difference between the proposed alternative designs, by considering their reliability. The method used in this paper can be applied to evaluate and optimize the reliability of many other industrial systems.

Introduction

 In power generation, the reliability of industrial control systems is crucial, as failures can disrupt services, leading to accidents and damages. This study focuses on the reliability of Heat Recovery Steam Generator (HRSG) boilers in combined cycle power plants. These plants optimize electricity generation by redirecting gases from burning fossil fuels into heat recovery steam generators. HRSG boiler reliability is pivotal due to high construction costs and the potential for extensive downtime and expenses in case of malfunctions. Addressing this challenge, the research employs the underutilized Reliability Block Diagram (RBD) model, providing a graphical representation of system components and interactions. Specifically tailored to the needs of the Mapna Boiler Company, the study aims to assess and optimize the reliability of the steam production unit, i.e., the boiler, within combined cycle power plants.

Research Background

Reliability, in conjunction with factors such as availability and safety, stands as a cornerstone in ensuring the practical quality of any system. The application of Reliability Block Diagrams (RBD) is a well-established method for modeling and calculating the reliability of industrial systems. Numerous studies have applied RBDs across diverse domains, ranging from power substation automation and wind turbine reliability to error calculations in intelligent submarine power systems. However, despite the versatility of RBDs, a noticeable gap exists in the literature regarding their use for modeling boiler reliability, especially as a multi-state system.

Research Methodology

To undertake a comprehensive reliability analysis of HRSG boilers, the study focuses on distinct subsystems, including:

Feed-Water Storage System
Feed-Water System (FWS)
High-Pressure (HP) Section
Low-Pressure (LP) Section
Condensate System
Chemical Dosing System.

The Feed-Water System (FWS) is crucial for immediate boiler operation. The initial design involves a Four-Pump System (A2 design) for the FWS. A modification is proposed, removing one feed-water pump, prompting an examination of its impact on boiler reliability. Critical components are identified based on their role in potential disruptions, emphasizing parts causing immediate boiler shutdowns. Using expert knowledge and diagrams, a Reliability Block Diagram (RBD) is developed, visually highlighting weak points. The RBD assesses FWS reliability, comparing two configurations for optimization.

Calculation of HRSG Boiler Reliability as a Multistate System

Configurations of three-pump and four-pump setups for the Feed-Water System (FWS) are illustrated and analyzed using the Reliability Block Diagram (RBD). The reliability analysis entails a detailed process of data gathering, failure rate determination, and overall reliability calculation for diverse system configurations. The study incorporates probabilities for various operational states and introduces mathematical formulations to calculate the Mean Time Between Failures (MTBF) for water feed system configurations.
Fig1: Configuration of HRSG boiler water supply system in 3 pump mode
Fig2: Configuration of HRSG boiler water supply system in 4 pump mode
 

Steps of optimizing the operational reliability (OPR)

Step 1: Identifying Components Used in FWS
Step 2: Determining Failure Rates for Each Component
Step 3: Drawing a Reliability Block Diagram (RBD)
Step 4: Evaluating Component Reliability
Step 5: Calculating Overall Reliability for Each Configuration.

Results

Tables present Mean Time Between Failures (MTBF) for water feed system configurations, offering insights into the trade-offs between complete shutdowns and demi-capacity operations. The analysis suggests that the four-pump configuration, while experiencing fewer complete shutdowns, operates at half capacity more frequently compared to the three-pump configuration. The data-driven results highlight the nuances of system reliability and its dynamic nature.

Research Findings

The reliability assessment for boiler construction, considering the failure rates of components over a one-year period, indicates that the four-pump configuration is superior when component reliability is high; otherwise, the three-pump configuration may have an advantage. However, the decision to choose between these configurations necessitates an economic evaluation, accounting for construction costs, shutdown expenses, and half-capacity operation costs. The study underscores the importance of integrating economic considerations with reliability assessments for informed decision-making.

Discussion and Conclusion

This research offers valuable insights into vulnerable areas of the HRSG boiler water feeding system, guiding maintenance attention and informing decision-making processes. The study emphasizes the need for future research to consider repair times and incorporate fuzzy reliability values to enhance the robustness of reliability calculations. The holistic approach adopted in this study, combining technical assessments with economic considerations, lays the groundwork for a more comprehensive understanding of system reliability in industrial settings.

Suggestions for Future Research

As industries evolve, future research should tailor reliability models to specific contexts. Exploring different failure distribution functions beyond the constant-rate assumption opens avenues for investigation. Models like the Weibull mixture model, competitive risk models, compound models, and hybrid models offer promising directions. For instance, the study proposes exploring the application of a compound renewal model, known as complementary risk, for systems with parallel performance and independent components. The limited exploration of this model in the literature presents an opportunity for future research to uncover its potential applications and contributions to reliability modeling.

کلیدواژه‌ها [English]

• HRSG Boilers
• Reliability Block Diagram (RBD)
• Design Optimization