Heat Recovery Steam Generator Performance Research Articles

Sensitivity and sustainability analysis of combined cycle plant with integrated LNG pressure energy recovery

Although combined cycle power plants (CCPPs) and liquefied natural gas (LNG) have arisen as solutions to the intermittent nature of renewable energy sources, they still need creative methods for performance enhancement and sustainability of the energy systems. Moreover, the energy efficiency of CCPPs is negatively impacted by environmental conditions, higher specific fuel consumption and a large quantity of waste heat released into the ambient. On the other hand, using seawater as a heating medium in LNG regasification circuits has a detrimental effect on the marine ecosystem. In this context, the LNG pressure energy recovery system through a direct expansion cycle (DEC) integrated with CCPP is proposed to improve sustainability, enhance exergetic performance and to reduce the heat recovery steam generator (HRSG) exhaust loss. To improve the cycle performance, low grade heat harnessed from CCPP is used as the heat source in the DEC rather than seawater. The system performance is analyzed by the energy and exergy method through a mathematical model. Moreover, the sensitivity analysis of the combined system is accomplished to examine the influence of LNG flow rate and ambient temperature on various performance indicators of the total system. It is observed that the integration of DEC boosts the HRSG performance by reducing the stack exergy loss and the efficiency is sensitive to LNG flow rate. The total integrated system energy efficiency ηtot, enhanced to 1.55% compared to the base case. Whereas, for ambient temperature in range of 15 – 45 °C, the system minimum and maximum exergetic efficiency ηex,tot is found to be 54.52 % and 55.94 %. Furthermore, the comparison of exergetic sustainability indicators is calculated and presented for three different simulation cases. The results demonstrate that increase in ηex,tot, affects the environment impact factor, ref and the sustainability index, θsi and improved 2.09 % compared to base case combined cycle.

Determination of optimal total area of heat recovery steam generator

Heat recovery steam generator (HRSG) plays a critical role in recovering waste heat from exhaust gas in a combined cycle. The performance of the steam cycle in the combined cycle depends on total HRSG area. This paper presents a comprehensive study on the determination of the optimal total area of single-pressure HRSG considering various factors such as exhaust gas temperature, main steam temperature, main steam pressure, reheat steam pressure, and reheat steam temperature. The research methodology involves the development of a mathematical model of HRSG that considers the key parameters affecting the HRSG performance. It is shown that, for given exhaust gas temperature and total HRSG area, there exists the set of steam parameters that yields the maximum net power output of the steam cycle. Furthermore, the power output increases monotonically with total HRSG area. However, the power output increases at a decreasing rate as total HRSG area increases. The optimal total HRSG area is shown to depend on the unit selling price of electricity, the unit cost of heat exchanger, the capacity factor of the power plant, and the acceptable payback period for the investment in the installation cost of HRSG.

Achieving Better Power Plant Guarantees Through a New Exergy-Based Approach for the HRSG

Abstract The best assurance an owner has to maximize the performance of the entire combined cycle power plant is the perfect alignment of heat recovery steam generator (HRSG) performance guarantee metrics to this goal. Currently, HRSG equipment performance guarantees include steam generation rates and steam temperature at each pressure level plus draft loss and reheater pressure drop. This profusion of guaranteed parameters with multiple bonus/liquidated damages (LD) rates is not always well correlated to the customer's ultimate goal of delivering power from the bottoming cycle since the behavior of each steam generation circuit is a complex function of steam pressure, steam turbine performance, and gas turbine exhaust temperature. This paper proposes a solution that normalizes and combines all HRSG performance measurements into a single value directly and reliably tied to the customer value metric (which may be different for fired and unfired operation or other load points). This is achieved by expressing the HRSG performance guarantee in terms of exergy recovered to steam and plant exergy loss attributable to the HRSG (gas side draft loss). This will be shown, with examples, to serve the goals of the customer to confirm by test that an HRSG delivers the promised steam exergy consistent with the plant level performance requirement.

Combined heat and power – multi-objective optimization with an associated petroleum and wet gas utilization constraint

Associated petroleum gas and wet gas are byproducts of oil field operations. The use of both gases as low-cost, low-quality fuel in oil field operations has several downfalls, such as a low Modified Wobbe Index and high hydrogen sulfide content. Modified Wobbe Index represents fuel interchangeability which affects gas turbine reliability. High hydrogen sulfide content may result in failures on the gas pipeline. The purpose of this research is to develop a multi-objective combined heat and power optimization by considering associated petroleum and wet gas utilization. The optimization model utilizes thermodynamic equations to represent gas turbine and heat recovery steam generator performance when subjected to low-quality fuel. Optimization also considers power system parameter as constraints. Three conflicting objective functions will be considered: cost vs. Modified Wobbe Index vs. hydrogen sulfide content. Optimization will use two algorithms for comparison purposes: Goal Attainment and NSGA-II. The result shows that the optimization model can analyze the tradeoffs between the three conflicting parameters.

Effects of Oxy-Fuel Combustion on Performance of Heat Recovery Steam Generators

The performance of steam power plants, utilizing recovered waste heat from air-fuel and oxy-fuel combustion, are compared. Temperature profiles in the heat recovery steam generator (HRSG), steam production rate, net-work output and energy efficiency are simulated for different conditions. Investigations are made into the effect of varying pinch point on HRSG performance, net-work and energy efficiency for power generation utilizing oxy-fuel combustion. It is found that with increased pinch point there is an associated decrease in HRSG and steam plant efficiencies. Exhaust gas composition influences the energy efficiency of the power plant. When air-fuel and oxy-fuel combustion are compared there is a reduced amount of nitrogen in the oxidant stream in the latter case. When comparing air-fuel and oxy-fuel combustion, a considerable deviation in HRSG and steam power plant performance is exhibited, with oxy-fuel combustion offering benefits in system efficiency and plant output. The exhaust gas composition at the HRSG inlet contributes significantly the performance characteristics of the system. Raising the HRSG inlet temperature also increases power generation and system efficiency. The results provide insights into the use of oxy-fuel combustion for systems utilizing HRSG for power generation while demonstrating the influence of gas composition, pinch point, and exhaust gas temperature on system performance, and suggest that oxy-fuel combustion can help enhance the contribution to sustainable development of some energy systems.

Thermodynamic Study of Multi Pressure HRSG in Gas/Steam Combined Cycle Power Plant

Combined cycle power plants have a combination of gas based topping cycle and steam based bottoming cycle through the use of Heat Recovery Steam Generator (HRSG). These HRSG may be either of single pressure (SP) or dual pressure (DP) or multiple pressure type. Here in this study thermodynamic analysis is carried out for optimal performance of HRSG using different types of HRSG layout for combined cycle efficiency improvement. Performance of single pressure HRSG and dual pressure HRSG, utilized in gas/steam combined cycle is analyzed and presented here. In comparison to single pressure, dual pressure HRSG offers 10 to 15% higher reduction in stack temperature due to greater heat recovery and thus improved plant efficiency.

Parametric study on effect of pinch and approach points on heat recovery steam generator performance at a district cooling system

Heat recovery steam generators are important equipment at district cooling plants. The capability of heat recovery steam generators in generating steam influences the steam absorption chiller's performance. The steam generation capability of the heat recovery steam generators in turn is linked to the values of pinch point and approach point. Hence, a study on the pinch point and approach point for the heat recovery steam generators would be useful in understanding the effects of varying pinch point and approach point values to the heat recovery steam generators' performance. In relation to this subject, a parametric study on the heat recovery steam generators was done. The study covered the effects of the pinch point and approach point on the following: mass flow rate of steam generated; exhaust heat temperature leaving the heat recovery steam generators; and the efficiencies of the heat recovery steam generators. The first law of thermodynamics was used for the analysis. Four scenarios were covered in the study: the effects of the pinch point and approach point on steam generation; the effects of the pinch point and approach point on the exhaust heat temperature leaving the heat recovery steam generators; the effects of the pinch point and approach point on the efficiency of the heat recovery steam generators; and the effects of the exhaust heat temperature of the gas turbine on the mass flow rate of steam. Operating data at Universiti Teknologi PETRONAS gas district cooling plant were used to validate the model. The results from the first scenario indicated that higher pinch point and approach point led to a decrease in the steam being generated. For the second scenario, the increase in pinch point and approach point resulted in higher exhaust heat temperature leaving the heat recovery steam generators. Meanwhile, for the third scenario, it was noted that there was only a minimal variation of the efficiency of the heat recovery steam generator when the pinch point and approach point were increased. The findings of the fourth scenario indicated that with higher gas turbine exhaust heat temperatures, there was an increase in steam being generated. Therefore, the findings could be useful for the plant to set the operating parameters for operating heat recovery steam generators. © Universiti Malaysia Pahang.

Exergy analysis of the dual pressure HRSG for varying physical parameters

Heat recovery steam generator (HRSG) is used to capture the heat of gas turbine exhaust gases for generating steam to run the steam turbine in gas/steam combined cycle power plant (CCPP). The performance of HRSG affects the steam turbine output and thus the overall combined cycle performance. The present study considers operating conditions of a 663MW, combined cycle power plant at Auraiya (U.P.), India for carrying out the exergy based investigation of a dual pressure HRSG. Different physical parameters of HRSG such as fin height, fin density and fin thickness are varied for analyzing exergy loss and exergy efficiency at different steam generation pressures. The exergy analysis shows how the exergy losses get lowered for LP evaporator and the exergy efficiency improves in LP economizer for higher fin heights and fin densities.

An Analysis of Energy and Carbon Intensities and Exergy Efficiency in Natural Gas Combined-Cycle Power Plants: A Case Study of Thailand

The objectives of this study were to estimate energy and carbon intensities of natural gas combined-cycle power plants and to improve the energy efficiency of power plants through an exergy analysis. Three plants in Thailand were evaluated as case studies in this research using data collected in 2013 – 2014. The results showed that the average carbon and energy intensities of three Combined-Cycle Power Plants were 0.436 kg CO 2 /kWh and 7.995 GJ/MWh, respectively. The range of the energy intensity in this study was slightly lower than that of other studies; however, the results of the carbon intensity were in the same range. The result of the exergy analysis illustrated that Heat Recovery Steam generator (HRSG) has the greatest exergy destruction due to the wide temperature range. To summarize, natural gas combined-cycle power plants require less energy and emit less carbon compared to other technologies or fuels. The exergy efficiency of HRSG was 60%, with an exergy destruction rate of 66.88 MW. One approach to improve the efficiency of power plants is to improve the efficiency and performance of HRSG.

Exergy analysis of dual pressure HRSG for different dead states and varying steam generation states in gas/steam combined cycle power plant

This paper deals with exergy analysis of a dual pressure (DP) heat recovery steam generator (HRSG) having steam generation at high pressure (HP) and low pressure (LP) in the range of 50–70 bar and 2–6 bar respectively in the gas/steam combined cycle power plant for varying dead states. The in-operation plant data for this study are taken from a gas/steam combined cycle power plant at Auraiya (U.P.), India. Results have been obtained for exergy loss and exergy efficiency with varying dead state temperatures for different HP and LP steam generation states in different sections of HRSG. The exergy analysis for chosen conditions/parameters helps in locating the particular sections of the HRSG having maximum exergy loss. It is found that at varying steam generation pressures the HP and LP super heater sections and at higher dead state temperatures the HP evaporator are found to act as major source of irreversibilities. The results obtained are useful in finding the thermodynamic states that will help in reducing the exergy destruction for enhancing HRSG performance which eventually improves the efficiency of combined cycle power plants.

Applying different optimization approaches to achieve optimal configuration of a dual pressure heat recovery steam generator

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Heat recovery steam generator performance and degradation in a 400 MW combined cycle

This article presents a research project carried out by the Thermochemical Power Group of the University of Genoa and is concerned with the monitoring of a three pressure level heat recovery steam generator (HRSG). The work consists of the development of an original computer code using Matlab software that calculates the performance of heat exchangers, at different power plant operating conditions. This kind of software was developed with a twofold objective: to calculate the actual gas path inside the HRSG starting from the available measurements, thus obtaining the current effectiveness of all the heat exchangers in the HRSG, and to estimate the expected performance of each heat exchanger to be compared with the actual ones. Once the actual effectiveness and the expected effectiveness of the heat exchanger are defined, non-dimensional performance parameters suitable for degradation assessment can be defined. As a result of the sensitivity analysis, each performance parameter is coupled with an accuracy factor. The developed methodology has been successfully applied to historical logged data (3 years) of an existing large size (400 MW) combined cycle, showing good capabilities in estimating the degradation of the HRSG throughout plant life.

Second law analysis of a waste heat recovery based power generation system

In the present paper the performance of a waste heat recovery power generation system based on second law analysis is investigated for various operating conditions. The temperature profiles across the heat recovery steam generator (HRSG), network output, second law efficiency and entropy generation number are simulated for various operating conditions. The variation in specific heat with exhaust gas composition and temperature are accounted in the analysis and results. The effect of pinch point on the performance of HRSG and on entropy generation rate and second law efficiency are also investigated. The second law efficiency of the HRSG and power generation system decreases with increasing pinch point. The first and second law efficiency of the power generation system varies with exhaust gas composition and with oxygen content in the gas. Approximating the exhaust gas as air, and the air standard analysis leads to either underestimation or overestimation of power plant performance on both first law and second law point of view. Actual gas composition and specific heat should be used to accurately predict the second law performance. The present results contribute further information on the role of gas composition, specific heat and pinch point influence on the performance of a waste heat recovery based power generation system based on first and second law of thermodynamics.

Performance simulation of heat recovery steam generators in a cogeneration system

The performance simulation of heat recovery steam generators in a cogeneration system has been investigated to see the effect of pinch and approach points on steam generation and also on temperature profiles across the heat recovery steam generator. The effects of operating conditions on steam production and also on exit gas temperature from the heat recovery steam generator are discussed. Low pinch point results in improved heat recovery steam generator performance due to reduced irreversibilites. The supplementary firing enhances the steam production. © 1998 John Wiley & Sons, Ltd.

Modeling of heat recovery steam generator performance

The performance of the heat recovery steam generator (HRSG) strongly affects the overall performance of a combined-cycle power plant. An accurate simulation of the performance of the HRSG is therefore necessary to analyze the effects of various design and operating parameters on the performance of combined-cycle power plants. Unfortunately, there are many sources of uncertainty and operational variance which prevent the accurate prediction of the HRSG performance. Furthermore, the prediction of heat-exchanger performance is based on assumptions about flow patterns. Empirical correction for departures from these assumptions is not possible in cases where the benefits of new geometrical configurations are to be explored. A numerical method was developed to predict the performance of the HRSG in a fashion that accounts, as much as possible, for the design and operation constraints, while keeping computational complexity manageable. The method is intended for use in performance-simulation models of advanced power cycles, since its accuracy is acceptable without requiring large computational resources. The method was used to simulate the pressure, temperature, steam quality and heat-flux distributions in a commercially available HRSG (operating under full- and part-load conditions). The predicted results were found to compare well with measurements obtained on full-scale units.