Second law analysis and heat integration of a CCGT using hybrid NSGA-II and SA optimisation

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.

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.

A novel hybrid system coupled liquid dehumidification with absorption refrigeration driven by solar energy is proposed. Traditional and advanced exergy and exergoeconomic analyses of the system are conducted to ascertain the degree of irreversibility and potential improvement for each component. Based on the advanced exergy and exergoeconomic analyses, the effects of air humidity, segment temperature, and refrigeration temperature on the total exergy destruction and cost rates of the system are obtained. The total avoidable exergy destruction rate, avoidable exergy destruction cost rate, and avoidable investment cost rate of the system are selected as objective functions and optimized by using nondominated sort genetic algorithm-II. The results show that the total exergy destruction rate and the total exergy destruction cost rate reach 262.39 kW and 8.563 $/h, respectively. The generator and regenerator have higher cost rates of the irreversibility overall system, achieving the values 3.536 and 2.430 $/h, respectively. The absorber has the highest investment cost rate in the whole system. The endogenous parts of the exergy destruction and cost rates are much higher than the exogenous parts in the system. Multiobjective optimization results show that optimal values for the total avoidable exergy destruction rate and the exergy destruction cost rate are 50.99 kW and 1.60 $/h, which are 4.15 and 9.14% lower than those calculated by single-objective optimization, respectively. This study provides a potential way to utilize solar energy for dehumidification and refrigeration.

A new approach for optimization of combined cycle system based on first level of exergy destruction splitting

In this study, energy, exergy, and environmental (3E) assessments have been conducted on a proposed combined-cycle power plant (CCPP) with three pressure levels of the HRSG and reheating process. 3E design approaches cross-link mechano-electric and environmental objectives. Herewith, the suggested combined-cycle is formed by a gas unit, condenser, steam turbines, triple-pressure heat recovery steam generator (HRSG) and also utilizes reheat facilities and auxiliary components. It is observed that more than 56% of total exergy destruction occurs in the combustor, followed by HRSG (15.29%), steam turbines (roughly 15.02%), gas turbine (8.93%), air compressor (1.79%), and condenser (0.66%). A parametric study is also presented that examines the sensitivity of performance indicators to various environmental states, steam pressures, pinch points, and steam mass flow rates. Moreover, it is presented that the implementation of Siemens SGT-100-1S over other GT configurations can considerably reduce deficiency of the overall cycle. The effects of each contaminant mass flowrate (NOx, CO, UHC, and CO2) and adiabatic flame temperature (AFT) are also studied when the gas unit operates under partial power and incomplete combustion conditions. In conclusion, a number of potential causes of irreversibilities and corrective optimization guidance are offered for each main equipment of the CCPP.

Thermodynamic and thermoeconomic optimization of an integrated gas turbine and organic Rankine cycle

This article aims to model and optimize the fire tube Heat Recovery Steam Generator (HRSG) used in a gas microturbine cogeneration of heat and power system. Here, six cases including a finless and finned tube (solid and serrated) HRSGs with the inline and staggered arrangements are optimized and compared using techno‐economic assessment. Optimization of HRSG was carried out by applying two objective functions of minimizing the total annual cost as well as maximizing the exergy efficiency. Nondominated Sorting Genetic Algorithm II is used to find out the optimal values of design variables. The TOPSIS decision‐making process is employed to choose the optimum point of the Pareto front. A 600 kW gas microturbine cogeneration plant is considered as a case study. The results revealed that the finless tube HRSG with an inline arrangement has the lower pinch and approach temperatures (3.5°C and 3.1°C, respectively), the higher steam mass flow rate (12.7%), the lower total annual cost (64 096$/year), and the higher exergy efficiency (60.6%). It is also found that using the staggered arrangement tube banks along with the solid fins in HRSG leads the total annual cost, the steam mass flow rate, and exergy efficiency increase up to 41.6%, 100%, and 12.6%, respectively. This means that the thermodynamic performance improvement will compensate the total annual cost increment. Furthermore, it is demonstrated that HRSG with solid fins and staggered arrangement with total annual costs of (90 810$/year), exergy efficiency of (73.2%), and steam mass flow rate of (4680 kg/h) has the best performance in comparison with other finned tube cases.

In the present article, thermodynamic and thermoeconomic analysis are applied to find the optimum values of design parameters for water-tube heat recovery steam generators (HRSGs) in combined cycle power plants. Design variables optimized in this article are pinch point and gas-side velocity. Optimization is carried out based on two different objective functions. The first one is thermodynamic, which is the summation of exergy loss due to an outflow of hot gas escaping from the HRSG through stack, and exergy destruction due to internal irreversibility inside the HRSG. The second one is a thermoeconomic objective function, which is the summation of exergy loss and destruction in terms of expenses including the cost of fuel and electricity, and the capital cost of HRSG in terms of the future value of money according to the interest rate. The capital cost of HRSG includes procurement and erection of piping and insulation, electrical panels and wiring, control and instrumentation equipment, insurance, tax, engineering, and supervision. The effects of pinch point and gas-side velocity on the components of objective functions are investigated in details. The pinch point and gas-side velocity that make these objective functions minimum are called optimum values.

Parametric study and multi-criteria optimization of total exergetic and cost rates improvement potentials of a new geothermal based quadruple energy system

Evaluation of supply boiler repowering of an existing natural gas-fired steam power plant

Changes of inlet temperature, mass flow rate and composition of flue gas, or of water/steam pressure and temperature in heat recovery steam generator (HRSG), all will modify the amount of waste heat recovered from flue gas; this brings forward a desire for the optimization of the design of HRSG. For single pressure HRSGs with given structures and specified values of inlet temperature, mass flow rate and composition of flue gas, the steam mass flow rate and gas outlet temperature of the HRSG are analyzed as functions of several parameters. This analysis is based on the laws of thermodynamics, incorporated into the energy balance equations for the heat exchangers. Those parameters are superheated steam pressure and temperature, feedwater temperature and pinch point temperature difference. It was shown that the gas outlet temperature could be lowered by selecting appropriate water/steam parameters and pinch point temperature difference. While operating with the suggested parameters, the HRSG can generate more high-quality steam, a fact of great significance for waste heat recovery from wider ranges of sources for better energy conservation.

This study proposes a hybrid Multi-Objective Optimization (MOO) approach that integrates the Non-dominated Sorting Genetic Algorithm II (NSGA-II) and the Evaluation by an Area-based Method of Ranking (EAMR) to optimize the design of a two-stage helical gearbox featuring a split input stage. The optimization simultaneously targets two conflicting objectives: minimizing the base area of the gearbox housing and maximizing the transmission efficiency. A parametric design model was developed to capture the key geometrical and performance parameters, while ensuring compliance with the practical constraints related to gear strength and manufacturing limitations. The NSGA-II algorithm was employed to generate a set of Pareto-optimal solutions, which were subsequently ranked using the EAMR method to support decision-making. The results demonstrate the effectiveness of the hybrid approach in identifying high-performance design alternatives that offer an optimal balance between compactness and efficiency. This is the first study to apply a combination of NSGA-II and a Multi-Criteria Decision-Making (MCDM) method to the dual-objective optimization of a two-stage gearbox with a split input stage. In particular, the proposed approach successfully identifies the optimal design parameters across a wide range of transmission ratios, thereby facilitating the initial selection of appropriate gearbox transmission ratios in the early-stage design. This study also provides valuable design guidelines for engineers seeking to improve space utilization and performance in gear transmission systems.

ABSTRACTCombined power plants are among the most attractive options to optimally utilise conventional fuel energy with respect to energy conversion and the environment. In the present study, a dual-pressure heat recovery steam generator (HRSG) used in a gas/steam combined cycle power plant is investigated. This paper presents exergy and economic analysis of a dual-pressure HRSG. The parameters used for the investigation of the exergo-economic study are pinch point, fuel price, cost of exergy losses, gas turbine inlet temperature and cycle pressure ratio. A parametric study shows that the considered parameters have a huge impact on the total annual cost per unit exergy of steam produced in the HRSG. It is seen that best exergo-economic conditions are obtained at the pinch point value of 10 K to get the total annual cost per unit exergy of steam produced to be the minimum.

In this article, we conducted a new hybrid method between Non-dominated Sorting Genetic Algorithm II (NSGA-III) and SPEA/R (HNSGA-III&SPEA/R). This method is implemented to find the optimal values of the powertrain mount system stiffness parameters. This is the task of finding multi-objective optimization involving six simultaneous optimization goals: mean square acceleration and mean square displacement of the powertrain mount system. A hybrid HNSGA-III&SPEA/R has proposed with the integration of Strength Pareto evolutionary algorithm-based reference direction for Multi-objective (SPEA/R) and Many-objective optimization genetic algorithm (NSGA-III). Several benchmark functions are tested, and results reveal that the HNSGA-III&SPEA/R is more efficient than the typical SPEA/R and NSGA-III. Powertrain mount system stiffness parameters optimization with HNSGA-III&SPEA/R is simulated. It proved the potential of the HNSGA-III&SPEA/R for powertrain mount system stiffness parameter optimization problem.

The product form evolutionary design based on multi-objective optimization can satisfy the complex emotional needs of consumers for product form, but most relevant literatures mainly focus on single-objective optimization or convert multiple-objective optimization into the single objective by weighting method. In order to explore the optimal product form design, we propose a hybrid product form design method based on back propagation neural networks (BP-NN) and non-dominated sorting genetic algorithm-II (NSGA-II) algorithms from the perspective of multi-objective optimization. First, the product form is deconstructed and encoded by morphological analysis method, and then the semantic difference method is used to enable consumers to evaluate product samples under a series of perceptual image vocabularies. Then, the nonlinear complex functional relation between the consumers’ perceptual image and the morphological elements is fitted with the BP-NN. Finally, the trained BP-NN is embedded into the NSGA-II multi-objective evolutionary algorithm to derive the Pareto optimal solution. Based on the hybrid BP-NN and NSGA-II algorithms, a multi-objective optimization based product form evolutionary design system is developed with the electric motorcycle as a case. The system is proved to be feasible and effective, providing theoretical reference and method guidance for the multi-image product form design.