Turbine Waste Heat Recovery Research Articles

Machine learning-based multi-objective optimization and thermal assessment of supercritical CO2 Rankine cycles for gas turbine waste heat recovery

Technologies for utilizing waste heat for power generation have attracted significant attention in recent years due to their potential to enhance energy efficiency and reduce greenhouse gas emissions. This research focuses on the comparative and optimization analysis of three supercritical carbon dioxide (sCO2) Rankine cycles (simple, cascade, and split) for gas turbine waste heat recuperation. The study begins with parametric analysis, investigating the significant effects of key variables, including turbine inlet temperature, condenser inlet temperature, and pinch point temperature, on the thermal performance of advanced sCO2 power cycles. To identify the most efficient cycle configuration, a multi-objective optimization approach is employed. This approach combines a Genetic Algorithm with machine learning regression models (Random Forest, XGBoost, Artificial Neural Network, Ridge Regression, and K-Nearest Neighbors) to predict cycle performance using a dataset extracted from cycle simulations. The decision-making process for determining the optimal cycle configuration is facilitated by the TOPSIS (technique for order of preference by similarity to the ideal solution) method. The study's major findings reveal that the split cycle outperforms the simple and cascade configurations in terms of power generation across various operating conditions. The optimized split cycle not only demonstrates superior power output but also exhibits enhanced net power output, heat recovery, system and exergy efficiency of 7.99 MW, 76.17 %, 26.86 % and 57.96 %, respectively, making it a promising choice for waste heat recovery applications. This research has the potential to contribute to the advancement and widespread adoption of waste heat recovery in energy technologies boosting system efficiency and economic feasibility. It provides a new perspective for future research, contributing to the improvement of energy generation infrastructure.

Dynamic Modeling and Control of Supercritical Carbon Dioxide Power Cycle for Gas Turbine Waste Heat Recovery

The gas turbine is a crucial piece of equipment in the energy and power industry. The exhaust gas has a sufficiently high temperature to be recovered for energy cascade use. The supercritical carbon dioxide (S-CO2) Brayton cycle is an advanced power system that offers benefits in terms of efficiency, volume, and flexibility. It may be utilized for waste heat recovery (WHR) in gas turbines. This study involved the design of a 5 MW S-CO2 recompression cycle specifically for the purpose of operational control. The dynamic models for the printed circuit heat exchangers, compressors, and turbines were developed. The stability and dynamic behavior of the components were validated. The suggested control strategies entail utilizing the cooling water controller to maintain the compressor inlet temperature above the critical temperature of CO2 (304.13 K). Additionally, the circulating mass flow rate is regulated to modify the output power, while the exhaust gas flow rate is controlled to ensure that the turbine inlet temperature remains within safe limits. The simulations compare the performance of PI controllers tuned using the SIMC rule and ADRC controllers tuned using the bandwidth method. The findings demonstrated that both controllers are capable of adjusting operating conditions and effectively suppressing fluctuations in the exhaust gas. The ADRC controllers exhibit a superior control performance, resulting in a 55% reduction in settling time under the load-tracking scenario.

Comparative analysis of supercritical CO2–ORC combined cycle for gas turbine waste heat recovery based on multi-objective optimization

To efficiently recover the waste heat of the gas turbine, this study introduces six innovative types of compound combined cycles, and proposes a multidimensional optimization method for the optimal cycle. In the combined cycle, the supercritical carbon dioxide cycle is used in the top cycle and the organic Rankine cycle is used in the bottom cycle. The working medium used in the organic Rankine cycle is the innovative mixture cyclopentane/R365mfc. Firstly, a parametric study is carried out for the proposed combined cycle to investigate the effects of system operating parameters on exergy efficiency, area per unit power output (APR) of the heat exchanger, and the levelized energy cost (LEC). The results show that the optimal values of objective function correspond to different systematic operating parameters. Secondly, the multi-objective optimization based on the genetic algorithm is used to obtain the optimal systematic parameters, and the six proposed composite combined cycles are optimized respectively. The comparison results show that the composite supercritical carbon dioxide regenerative cycle-organic Rankine simple cycle has the optimal performance parameters, and its exergy efficiency, APR and LEC are 55.68 %, 0.115 m2/kW and 4.23 cent/(kW·h), respectively. The layout of the composite cycle is that the supercritical carbon dioxide regenerative cycle and the organic Rankine simple cycle are used to recover the high temperature and low temperature of the gas turbine exhaust gas, while the organic Rankine simple cycle recovers the cooling heat of the supercritical carbon dioxide regenerative cycle. Finally, the superiority relative of the proposed combined system to the other cycles is also verified. This study has determined that the proposed combined system is appropriate for the waste heat recovery of gas turbines, with the advantages of deep utilization of waste heat, high efficiency, high compactness, and low cost.

Design and off-design performance analysis of supercritical carbon dioxide Brayton cycles for gas turbine waste heat recovery

The utilization of waste heat from marine gas turbines is an effective means of meeting future electric demands and achieving energy conservation and emission reduction. Meanwhile, the supercritical CO2 Brayton cycle, benefiting from its compact structure, is well-suited for power generation in limited spaces. Based on the reality that gas temperature and flow rate deviate from the design point with the variation of gas turbine operating conditions, this paper proposes a method for analyzing the off-design performance of supercritical CO2 cycles based on thermal source fluctuations rather than simply providing prescribed temperatures on the cycle side. This method allows for a clear understanding of the impact on the cycle when there are fluctuations in the thermal source. Firstly, the thermodynamic performance and economic viability of four types of supercritical CO2 cycles, namely simple regenerative, recompression, intercooling, and reheat, were optimized using a multi-objective genetic optimization algorithm. Subsequently, the off-design performance of these four cycles was investigated when the gas temperature and flow rate deviate from the design point. The results indicate that, compared to the decrease in gas temperature, the reduction in gas flow rate has a greater impact on the decline in cycle performance. Decreasing gas temperature enhances the exergy efficiency of all four cycles, while reducing gas flow rate initially increases and then decreases the exergy efficiency. The decrease in turbomachinery efficiency significantly contributes to the decline in cycle performance. When the gas flow rate exceeds 55% of the design value, it is recommended to adopt an intercooling cycle arrangement. Otherwise, a recompression cycle layout should be used.

Comparative assessment of the various split flow supercritical CO2 Brayton cycles for Marine gas turbine waste heat recovery

Supercritical CO2 Brayton cycle (sCO2 BC) can become easily utilized in marine gas turbine waste heat recovery applications due to their high efficiency, compact size, and low-cost advantages. In this study, the performance of the three different split flow sCO2 BCs, including turbine split flow-1 (TSF-1), turbine split flow-2 (TSF-2), and turbine split-3 (TSF-3), for the recovery of marine gas turbine waste heat is compared. The Engineering Equation Solver (EES) application is used to compare the three different split flow sCO2 BCs' performances. Moreover, to investigate the influence of important thermodynamic parameters on cycle performance, a parametric analysis is carried out. The effect of variable exhaust gas temperature, turbine input pressure, and compressor inlet pressure on net power, the energy efficiency of the system, system's exergy efficiency, and exergy destruction are examined. The results suggest that the energy efficiencies of the TSF-1 sCO2 BC, the TSF-2 sCO2 BC, and the TSF-3 sCO2 BC are calculated by 28.71%, 34.5%, and 29.42%, respectively. The TSF-2 sCO2 BC has more advantages in efficiency among all the cycle layouts while the TSF-3 sCO2 BC layout has better performance in the net power. In addition, the TSF-3 sCO2 BC has the highest exergy destruction at 99.71 kW, followed by the TSF-1 sCO2 BC at 91.83 kW and the TSF-2 sCO2 BC at 41.75 kW. It has been determined that the cycle's net power increases with rising exhaust gas temperature and turbine input pressure and decreases with compressor input pressure. Exhaust gas temperature and turbine inlet pressure have a positive effect on the performance of all split flow sCO2 BCs.

Multi-objective optimization of recompression S-CO2 cycle for gas turbine waste heat recovery

Recompression supercritical carbon dioxide Brayton cycle (RCSCBC) has important application prospects in the fields of gas turbine waste heat recovery. A RCSCBC model considering finite temperature difference heat transfer between heat reservoir and working fluid, irreversible compression, irreversible expansion and other irreversibility losses is established. Then the mass flow rate of the working fluid, cycle pressure ratio and the heat conductance distribution ratios of four heat exchangers are taken as optimization variables, the multi-objective coordinated optimization with net power output, exergy efficiency, thermal efficiency and ecological function as the goals is carried out, and an artificial neural network model is constructed to solve the problem of long optimization time. The results show that the decision-making result by Shannon Entropy method for the four-objective optimization has the lowest deviation index, and is the optimal. Compared with the initial design point, the thermal efficiency of the cycle for the optimization results by the Shannon Entropy method can reach 40.69%, which is increased by 29.8%. The net power output can reach 10.972 MW, which is increased by 9.5%. The ecological function can reach 7.265 MW, which is increased by 114.75%. The exergy efficiency can reach 74.72%, which is increased by 24.22%.

Thermodynamic, exergoeconomic, and exergoenvironmental analysis of a combined cooling and power system for natural gas-biomass dual fuel gas turbine waste heat recovery

Integrating biomass energy into existing fossil fuel power plants is a practical way to solve the current energy shortages and environmental problems considering system feasibility and economic benefits. In this work, a novel combined cooling and power (CCP) system is proposed for waste heat recovery of a natural gas-biomass dual fuel gas turbine (DFGT) based on the organic Rankine cycle (ORC) and absorption refrigeration cycle (ARC). Comprehensive thermodynamic, exergoeconomic, and exergoenvironmental performance and parametric analysis of this system are performed. Results show that under the design condition, thermal efficiency, exergy efficiency, levelized cost of exergy (LCOE), and levelized environmental impact of exergy (LEIOE) of the system are 68.88%, 42.10%, and 21.16 $/GJ, and 5208.82 mPts/GJ, respectively. Among all the components, combustion chamber has the highest exergy destruction rate. The parametric analysis indicates that the thermal and exergy efficiencies rise by increasing the gas turbine inlet temperature (GTIT) and ORC turbine inlet pressure or by decreasing the preheated air temperature (PAT) and exhaust gas outlet temperature at high-temperature vapor generator. The LCOE and LEIOE present similar trends in most cases, which are most affected by the PAT and GTIT. Finally, a tri-objective optimization is conducted using exergy efficiency, LCOE, and LEIOE as objective functions. Pareto frontier is obtained and the final optimum solution is recommended for engineering practice.

A triple cascade gas turbine waste heat recovery system based on supercritical CO2 Brayton cycle: Thermal analysis and optimization

• A new triple cascade gas turbine waste heat recovery system based on supercritical CO 2 Brayton cycle. • Evaluated the performance of an integrated system combining a gas turbine and a triple cascade cycle. • Analyze and optimize the system's thermodynamic and economic performance. A new triple cascade waste heat recovery system coupled with a supercritical CO 2 power cycle and transcritical CO 2 regenerative cycle is proposed for the high temperature exhaust waste heat generated during the operation of gas turbine, and thermodynamic and economic models are established to analyze the performance of the system, with the following performance indicators: the net output power is 5.67MW, the thermal efficiency is 24.94%, the exergy efficiency is 46.08%, the total investment cost rate is 126.06$/h, and the per unit energy cost is 6.31$/GJ. The thermal performance of the integrated system consisting of the gas turbine unit and the proposed triple cascade waste heat recovery system is evaluated, and the results show that the integrated system effectively utilizes the waste heat compared with the gas turbine unit alone, while the net output power of the integrated system is 22.17 MW and the thermal efficiency is 47.7%. Each component's exergy and cost analysis is performed. The heat exchanger accounts for a large percentage of the exergy destruction, and the investment cost rate of the turbine, compressor and other work-making components is high, indicating the direction of system optimization. The sensitivity analysis of the system's key parameters was carried out through the control variables method to reveal the influence of individual setting parameters on the system performance. Based on the research range of the set parameters, the system is optimized with multiple objectives, and the net output power, exergy efficiency and per unit energy cost are selected as the objective functions. The optimization results show that the combination of exergy efficiency and per unit energy cost resulted in better economic performance, with exergy efficiency of 50.37% and per unit energy cost of 4.66$/GJ. Comparing the system with the other two configurations proves the superiority of the proposed system.

Comparative Thermodynamic Environmental and Economic Analyses of Combined Cycles Using Air and Supercritical CO2 in the Bottoming Cycles for Power Generation by Gas Turbine Waste Heat Recovery

This study aims to improve existing fossil gas turbine power plants by waste heat recovery. These power plants function with an air simple cycle (ASC) and are implemented where water resources are limited. Modeling and simulation of ASC and two advanced energy conversion systems are performed. They are the gas turbine–air bottoming cycle (GT-ABC) and gas turbine–supercritical carbon dioxide bottoming cycle (GT-sc-CO2BC). The main intent is to assess the benefits of employing sc-CO2 as a working fluid in a closed Brayton bottoming cycle compared to air, based on the energetic and exergetic performance and economic and environmental impact. Analyses of ASC, GT-ABC, and GT-sc-CO2BC are performed for various topping gas turbine powers: large (plant 1); medium (plant 2); and low (plant 3). The results of the energetic and exergetic analyses indicate that there is a significant improvement in the output power (ranging from 22% to 25%); and energy and exergy efficiencies of GT-ABC and GT-sc-CO2BC (up to 8% and 11%, respectively) compared to that of ASC. To provide better insight into the behavior of these technologies and achieve their better integration, we investigate the influence of varying the bottoming compressor pressure ratio, the ambient temperature, and the gas flow rate in the bottoming cycle. The results of the environmental and economic analyses show that the amount of CO2 emissions in GT-sc-CO2BC is reduced by 10% more than in GT ABC. The results also show that GT-ABC improves the NPV between 17.69% and 30% but GT-sc-CO2BC improves it even more, between 25.79% and 33.30%.

How to identify trade-off of thermodynamic and economic performance of the S-CO2 cycle caused by the cycle structures?

Generally, the improvement of thermodynamic performance of supercritical CO2 Brayton cycles is realized by more complex cycle structures at the expense of expensive system cost. How to identify trade-off of the thermodynamic and economic performance of the S-CO2 cycle is a challenging issue because system structure is hard to be optimized with its nature of discrete variable. Therefore, taking the net power output and cost of electricity as the objective functions, this study tries to solve this issue by multi-objective optimization of superstructure of supercritical CO2 Brayton cycle for gas turbine waste heat recovery. Besides discussing the effect of heat source temperature and cooling temperature, the optimization results of the superstructure are compared with the traditional structures. The results show that at different heat source temperatures, the distribution regularities of the cycle structures on the Pareto-front are the same, and the structure of the trade-off solution tends to be the same. With the increase of heat source temperature, the costs of trade-off solutions are reduced by 8.86%, 11.16% and 16.51%, respectively. The change of cooling temperature has a great effect on the structure of the trade-off solution. In addition, superstructures have obvious advantages over the traditional structures in terms of trade-off solution performance and structure selection.

Ecological Function Analysis and Optimization of a Recompression S-CO2 Cycle for Gas Turbine Waste Heat Recovery.

In this paper, a recompression S-CO2 Brayton cycle model that considers the finite-temperature difference heat transfer between the heat source and the working fluid, irreversible compression, expansion, and other irreversibility is established. First, the ecological function is analyzed. Then the mass flow rate, pressure ratio, diversion coefficient, and the heat conductance distribution ratios (HCDRs) of four heat exchangers (HEXs) are chosen as variables to optimize cycle performance, and the problem of long optimization time is solved by building a neural network prediction model. The results show that when the mass flow rate is small, the pressure ratio, the HCDRs of heater, and high temperature regenerator are the main influencing factors of the ecological function; when the mass flow rate is large, the influences of the re-compressor, the HCDRs of low temperature regenerator, and cooler on the ecological function increase; reasonable adjustment of the HCDRs of four HEXs can make the cycle performance better, but mass flow rate plays a more important role; the ecological function can be increased by 12.13%, 31.52%, 52.2%, 93.26%, and 96.99% compared with the initial design point after one-, two-, three-, four- and five-time optimizations, respectively.

Optimal structure design of supercritical CO2 power cycle for gas turbine waste heat recovery: A superstructure method

The supercritical CO2 power cycle is an effective way for gas turbine waste heat recovery due to its compact system structure and high efficiency. The stepwise optimization of operating parameters and system structure in the early research results in a great limitation of the search space on the optimal structure, consequently, there are still huge challenges in determining the optimal structure of the supercritical CO2 power cycle for waste heat recovery. Therefore, this study proposed a new superstructure of supercritical CO2 cycle for waste heat recovery based on the concept of splitting, which could optimization system structure and design parameters simultaneously. Taking the net power output as the objective function, the optimal structure of supercritical CO2 cycle under different boundary conditions and equipment parameters are investigated. The results show that the superstructure method produces new cycle structures which are not reported before, which is mainly embodied in the flow split and compression structure of the cold end. Compared with traditional supercritical CO2 and steam Rankine cycles at the heat source temperature of 400–600 °C, the maximum net power output obtained by the superstructure method are increased by 4.09–6.94% and 11.65–21.23%, respectively.

Thermodynamic and exergoeconomic analysis of combined supercritical CO2 cycle and organic Rankine cycle using CO2-based binary mixtures for gas turbine waste heat recovery

Combined cycle system is an effective technical mean for waste heat recovery (WHR) of gas turbine to improve energy efficiency and decelerate environmental pollution. A combined cycle system including two supercritical CO2 (S-CO2) cycles and one organic Rankine cycle (ORC) using CO2-based binary mixtures for WHR of gas turbine is proposed. Firstly, thermodynamic and exergoeconomic analyses are conducted for the proposed system. Then parametric study is carried out to investigate the influences of decision parameters on the system performance including thermal efficiency, exergy efficiency and unit cost. Besides, optimization is performed for the system from the viewpoints of thermodynamics and exergoeconomic. The results indicate that the highest total exergy destruction and capital cost occur in the gas turbine subsystem, followed by two S-CO2 cycles and ORC. The obtained results demonstrate that using Propane as additive in CO2-based binary mixture can not only benefit thermodynamic performance, but also is conductive to its exergoeconomic characteristic. Moreover, thermal efficiency, exergy efficiency, unit cost and exergoeconomic factor of proposed system can achieve 48.56%, 51.90%, 3.66 cent/kWh and 28.30% after the optimization of exergoeconomic, respectively. Furthermore, the superiority of proposed systems is verified compared with other systems in the literatures.

Techno-economic-environmental evaluation of a combined cooling heating and power system for gas turbine waste heat recovery

With the development of the world economy, the energy crisis and environmental pollution have become global issues. Polygeneration systems, which have the advantages of energy saving and high efficiency, can alleviate them. This work proposed a novel combined cooling, heating, and power system structure composed of a gas turbine cycle, a supercritical CO2 (sCO2) cycle, an absorption refrigeration chiller, a steam generator, an organic Rankine cycle (ORC), and additional thermoelectric generator modules. The techno-economic-environmental performance of the proposed system was discussed through a comparative study of different integrated system structures. A parametric study was also conducted to analyze the effects of important decision variables, and then a multi-objective optimization was conducted to further study the system performance from different objectives. Finally, two different system structures were compared based on the optimal results. The results showed that the thermal efficiency was increased by 0.3% with the presence of a thermoelectric generator under design conditions, but it resulted in a higher cost rate of 0.45 $/h and larger emissions of approximately 0.19 kt CO2,eq. The optimal results revealed that the system had thermal efficiency of 67.88%, exergy efficiency of 42.62%, total cost rate of 10.60 $/h, and total emissions of 923.55 kt CO2,eq. Furthermore, a comparative study found that the proposed system structure exhibited excellent thermodynamic performance but worse economic performance than the integration of the sCO2 cycle and ORC.

Comparative investigation on the supercritical carbon dioxide power cycle for waste heat recovery of gas turbine

In this paper, a comparative investigation on the supercritical carbon dioxide power cycle for waste heat recovery of gas turbine is carried out. Four categories and six cycles are chosen to represent typical layout of supercritical carbon dioxide power cycle based on thorough literature reviews. The selected cycles are optimized and analyzed based on the results of single- and multi-objective optimization from the perspective of system efficiency, economic cost and configuration complexity. According to the exergy destruction analysis, several guidelines about the heat exchangers are proposed to enhance the thermal efficiency of gas turbine waste heat recovery system, including the avoiding of preheating, the utilization of partial heating layout, the employment of segmentation method and modified logarithmic mean temperature difference, the increase in the number of gas heater. The results indicate that turbine dominates the investment cost of power cycle. In conclusion, dual heated cascade cycle-II should be employed to pursue the maximized system efficiency. Otherwise, partial heating cycle is recommended due to its balanced overall performance.

Improvement design and analysis of a supercritical CO2/transcritical CO2 combined cycle for offshore gas turbine waste heat recovery

The supercritical CO2 (S–CO2) and transcritical CO2 (T-CO2) combined cycle is considered a promising technology for offshore gas turbine waste heat recovery. To further improve the thermodynamic and economic performances of the S–CO2/T-CO2 combined cycle for offshore gas turbine waste heat recovery, a new system layout is proposed in this paper. The net power output and net present value (NPV) are chosen as the objective functions of thermodynamic and economic performances, respectively. Compared to the basic systems presented by previous researchers, the new proposed S–CO2/T-CO2 combined cycle layout is modified in two aspects. One is that the residual heat of the topping S–CO2 cycle can be recovered by the bottoming T-CO2 cycle. The other is that a split flow branch is added in the bottoming T-CO2 cycle. The sensitivity analysis of different systems is carried out to explore the allowable ranges of independent parameters. Compared with the two basic layouts (Basic-I and Basic-II), the simulation results at the design point reveal that the proposed system has more than 10.53% increment on the net power output and 7.87% increment on the net present value (NPV). Besides, the multi-objective optimization results indicate the proposed system attains at least 8.30% increment on the optimized net power output and 3.79% increment on the optimized NPV at the same time. It is proved that the proposed system can be applied in some practical cases from the thermodynamic and economic views.

Exergoeconomic analysis of a novel trigeneration system containing supercritical CO2 Brayton cycle, organic Rankine cycle and absorption refrigeration cycle for gas turbine waste heat recovery

Poly-generation system is gaining more attentions recently due to its advantages of the effective promotion on energy utilization efficiency and deceleration of environmental pollution, as well as the security and reliable improvement on power supply. In this study, a novel trigeneration system composed of a gas turbine cycle (GTC), a regenerative supercritical carbon dioxide (sCO2) Brayton cycle, an organic Rankine cycle (ORC), and an absorption refrigeration cycle (ARC), is proposed. The waste heat exhausted from the GTC is firstly absorbed by sCO2 cycle and then utilized by ORC to generate power. The bottoming ARC is driven by the remaining heat to provide cooling capacity, while the hot water is provided by an intercooler in the GTC. The thermodynamic and exergoeconomic analyses are conducted to investigate the trigeneration system performance. Comparative study is carried out to evaluate the effects of ORC with different working fluids on the whole system performance. Besides, the performances of the proposed system are optimized and compared from the first law, second law of thermodynamics, and exergoeconomic viewpoints. Results show that the trigeneration system can generate 40.65 MW net power, 6.02 MW cooling capacity, and the 9.93 MW heating loads, with 20.17% overall exergoeconomic factor after the optimization on exergoeconomic aspect. Component combustion chamber presents the highest exergy destruction rate, while the subsystem GTC has the largest total exergy destruction and the highest total capital cost, successively followed by sCO2 cycle, ORC, and ARC. Compared with system using n-butane case, the total product unit costs increase by 0.27%, 1.09%, and 0.20% for fluids i-butane, n-pentane, and i-pentane cases, respectively, and the exergy efficiencies elevate correspondingly. However, the thermal efficiencies of above three cases decrease by 0.48%, 0.71%, and 1.06%, respectively. Moreover, combustion chamber is always the most important component for cost in the proposed trigeneration system optimized on the thermodynamic and exergoeconomic aspects, as well as the absorber being foremost in the bottoming ARC.

A comparative assessment of SPECO and MOPSA on costing of exergy destruction

This paper presents the comparison of specific exergy costing (SPECO) and modified productive structure analysis (MOPSA) method to test their abilities on costing of exergy destruction. MOPSA method is applied to a combined supercritical CO2 regenerative cycle and organic Rankine cycle using zeotropic mixtures for gas turbine waste heat recovery system. The results obtained with applying SPECO method to the system are taken from literature. The exergy destruction cost rate of overall system is obtained to be $86.08/h and $1,113.13/h for MOPSA and SPECO methods, respectively. The exergoeconomic factor of overall system is found to be 31.88% for SPECO method, while this value is found to be 85.82% for MOPSA method. The obtained results with applying MOPSA method for exergy destruction cost rate are significantly lower and more consistent compared to the results obtained by SPECO method.

A comparative assessment of SPECO and MOPSA on costing of exergy destruction

This paper presents the comparison of specific exergy costing (SPECO) and modified productive structure analysis (MOPSA) method to test their abilities on costing of exergy destruction. MOPSA method is applied to a combined supercritical CO2 regenerative cycle and organic Rankine cycle using zeotropic mixtures for gas turbine waste heat recovery system. The results obtained with applying SPECO method to the system are taken from literature. The exergy destruction cost rate of overall system is obtained to be $86.08/h and $1,113.13/h for MOPSA and SPECO methods, respectively. The exergoeconomic factor of overall system is found to be 31.88% for SPECO method, while this value is found to be 85.82% for MOPSA method. The obtained results with applying MOPSA method for exergy destruction cost rate are significantly lower and more consistent compared to the results obtained by SPECO method.

Design Performance Simulation of a Supercritical CO2 Cycle Coupling With a Steam Cycle for Gas Turbine Waste Heat Recovery

This study presents a train of thought and method for flue gas energy utilization management by connecting an optimized supercritical carbon dioxide (S-CO2) Brayton cycle with a selected steam/water Rankine cycle to recover the turbine exhaust gas heat with promising flue gas coupling capacity. Better performance over the currently used steam/water bottoming cycle is expected to be obtained by the combined bottoming cycle after the S-CO2 cycle is coupled with the high-temperature flue gas. The performances of several S-CO2 cycles are compared, and the selected steam/water cycle is maintained with constant flue gas inlet temperature to properly utilize the low-temperature flue gas. Aspen Plus is used for simulating the cycle performances and the flue gas heat duty. Results show that the recompression S-CO2 cycle with the reheating process is most recommended to be used in the combined bottoming cycle within the research scope. The suggested combined bottoming cycle may outperform most of the triple reheat steam/water cycles for the turbine exhaust temperature in the range of 602–640 °C. Subsequently, it is found that the intercooling process is not suggested if another heat recovery cycle is connected. Moreover, the specific work of the suggested S-CO2 cycles is calculated, and the bottoming cycle with the preheating cycle with the reheating process is found to be more compact than any other combined bottoming cycles.