Abstract:
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 BackgroundReliability, 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 MethodologyTo undertake a comprehensive reliability analysis of HRSG boilers, the study focuses on distinct subsystems, including:Feed-Water Storage SystemFeed-Water System (FWS)High-Pressure (HP) SectionLow-Pressure (LP) SectionCondensate SystemChemical 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 SystemConfigurations 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 modeFig2: Configuration of HRSG boiler water supply system in 4 pump mode Steps of optimizing the operational reliability (OPR)Step 1: Identifying Components Used in FWSStep 2: Determining Failure Rates for Each ComponentStep 3: Drawing a Reliability Block Diagram (RBD)Step 4: Evaluating Component ReliabilityStep 5: Calculating Overall Reliability for Each Configuration. ResultsTables 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 FindingsThe 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 ConclusionThis 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 ResearchAs 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.
Machine summary:
This article addresses how to model the water feed system of heat recovery steam generators (HRSG) using Reliability Block Diagram (RBD) in two states, part-load and full-load, and thereby evaluates the difference in the proposed design for them in terms of reliability.
Keywords HRSG Boilers, Reliability Block Diagram (RBD), Design Optimization Introduction The failure of sensitive industrial systems causes disruptions in their service and increases the risk of accidents and enormous losses.
In this study, the reliability of one of the main systems of the steam generation device (boiler) in combined cycle power plants is evaluated, and based on its results, the optimal configuration of this system has been determined.
Figure in the equipment failure rate database (refer to the page image) Drawing the Reliability Block Diagram (RBD) In this step, based on P&ID information, the arrangement of blocks was drawn in series or parallel according to the operational logic and a deep understanding of their functional requirements alongside each other.
Figure 7: Proposed 2-pump configuration option (2) for the boiler water feed system (Refer to the page image) Each of the operational states, full load, half load, or complete shutdown, can result from various combinations of block failures.
1. Mean Time Between Failures Figure 11: Block diagram of subsystems SS and S (Refer to the page image) Given that the health of at least two of them is required for system operation, its reliability is equal to the following value: Rs, = (0.
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