Combined Cycle Power Generation System Research Articles

An optimization of efficient combined cycle power generation system for fusion power reactor

Fusion power plants can meet the energy demands of the world. The high thermal performance of a power generation system is still a challenge and one of the developing trends with a fusion reactor due to the high outlet temperature. A combined cycle system has been optimized to work at high outlet temperature and pressure of fusion power reactor with thermal power of 2500 MWth and its input parameter has been optimized along with impact of partial load to achieve high thermal performance very first time. The combined cycle based on the concept of two stages of expansion in the closed-Brayton-cycle and two reheaters in the Rankine cycle named Schematic-IV with the higher thermal performance of 58.19% as compared to Schematic-I, II and III has been proposed for a fusion power reactor. The increase in more than one expansion stage and reheat stage is not economical because it increased the thermal performance by about half of performance as compared to one. The effect of isentropic efficiency of compressor and heat rate have been investigated to validate the thermodynamic model and calculations. The optimized thermal performance of the combined cycle is 58.19% at a feed water mass flow rate of 592 kgs−1 and steam outlet temperature of 277 °C in the combined cycle. The heat rate decreased and thermal performance increased with the mass flow rate verifying that the thermodynamic model is correct. The thermodynamic analysis of the combined cycle-based nuclear reactor provides insights for better system thermal performance and reveals the effect of key parameters on the system performance.

Dynamic simulation analysis of molten salt reactor-coupled air–steam combined cycle power generation system

Dynamic simulation analysis of molten salt reactor-coupled air–steam combined cycle power generation system

Exergy destruction analysis of a power generation system utilizing the cold energy of LNG

The purpose of this research is in-depth understanding of the internal causes of exergy destruction in various parts of the system and to identify potential improvements for the components. The focus is on a combined cycle power generation system that utilizes the organic Rankine cycle (ORC) and direct expansion cycle (DEC). To investigate the primary sources of exergy destruction in each component, advanced exergy analysis (AEA) is utilized. The result demonstrates that the net out power of the proposed system can reach 106.64 kW with energy efficiency of 11.22%, and exergy efficiency of 21.40%. The heat exchanger is identified as the primary contributor to exergy destruction, constituting 81.70% of the total ratio. Specifically, the condenser exhibits the highest exergy destruction ratio at 59.82%, indicating a need for prioritized optimization efforts. The findings of AEA reveal that the primary source of component irreversibility stems from the endogenous part. This shows that, while most exergy destruction is unavoidable, there remains room for system improvement. Regarding the turbine, its exergy destruction is primarily attributed to inefficiencies, leading to irreversibility. Nevertheless, there is exergy destruction that may be avoidable and can be reduced by 25.93 kW, which is 2.5 times greater than that of the heat exchanger. This finding underscores the high potential for improvement in ORC and DEC turbines, making them a priority for optimization efforts.

Sulfidation performance of unsupported and SBA 15-supported Ca-based mixed metal oxides

Coal is the most widely used fossil fuel resource, and clean coal technologies allow an increase in the efficiency of clean energy production. Gasification-based combined cycle power generation systems, for example, aim to produce a mixture of CO and H2 (syngas) formed from coal and biomass. However, H2S is an undesired gasification product of fossil fuels with their high sulfur content. Hot gas desulfurization (HGD) reduces the sulfur contents of the gasification products by eliminating thermal losses of endothermic syngas formation processes. This study aims to develop efficient sorbents to remove H2S from hot flue gas. Unsupported and SBA 15-supported Ca-based binary mixed metal oxides (CuO, FeO, MnO, ZnO) were synthesized as sulfur sorbents by the wet impregnation method. The crystal structure of the sorbents was determined by X-ray diffraction (XRD), while BET analysis was used to determine the surface area and pore size distribution of the sorbents. The results of the XRD and BET analyses revealed mixed metal oxide formation and a high surface area of SBA 15-supported sorbents, respectively. Mixed metal oxide formation was also confirmed by Fourier transform infrared radiation (FTIR) spectroscopy. The desulfurization performance of the sorbents was examined by a simulated gas mixture at 800 °C. A gas chromatography analyzer equipped with a flame photometric detector was used to follow the H2S concentration. SBA 15-supported CaO–MnO exhibited the best desulfurization performance at 800 °C with a breakthrough sulfur capacity (BSC) of 43.38 g S/100 g sorbent in the longest breakthrough time of 1077 min.

Concept design, parameter analysis, and thermodynamic evaluation of a novel integrated gasification chemical-looping combustion combined cycle power generation system

Integrated gasification chemical-looping combustion (IGCLC) is a potential combustion technology with innate CO2 separation for solid fuels. Coupling this technology with coal-fired power plants is expected to greatly alleviate the high efficiency penalty induced by CO2 capture. This study proposes an innovative system called integrated gasification CLC combined cycle (IGCLCCC) that highly integrates a gasification system, a CLC system, a combined cycle, an ultra-supercritical steam cycle, and a CO2 capture system. In the proposed system, the oxygen-depleted stream from air reactor and flue gas from fuel reactor enter the combined cycle and ultra-supercritical steam cycle, respectively, for power generation. The energy and mass balances of the proposed system are determined by process simulation. The relationship between the performance of subsystems and system efficiency is studied by parameter analysis. Results indicate that the net efficiency penalty (0.3 percentage points) of the proposed system is 4.3 to 13.2 percentage points less than those of the conventional CO2 capture power plants, and the power consumption of specific CO2 capture is minimized to 8.3 kWeh/t. Besides, its net efficiency is as high as 45.0%, which is comparable to that of the natural gas combined cycle power plant with a 90% CO2 capture rate. This work provides a new sight into the design of the low-carbon and efficient power generation system.

Energy and Exergy Analysis on a Blast Furnace Gas-Driven Cascade Power Cycle

Blast furnace gas is the major combustible by-product produced in the steel industry, where iron ore is reduced by coke into iron. Direct combustion of blast furnace gas after simple treatment for power generation is a common utilization method nowadays. However, this method suffers from low efficiency and high carbon intensity. The use of gas-steam combined cycle is an excellent method to improve the efficiency of blast furnace gas for power generation. However, there is a problem of insufficient utilization of low product heat, and the addition of CCS system can further reduce the power efficiency. To solve these issues, a new blast furnace gas power generation system with a Brayton cycle with supercritical CO2 and a Rankine cycle with transcritical CO2 is proposed in this work. The new system is then thermodynamically simulated by Aspen Plus, after the sub-modules are validated. The effects of molar ratio of steam to carbon, selexol/CO2 mass ratio, compression ratio, turbine import temperature and turbine inlet pressure on the system are investigated. A comparison is also performed between the new combined cycle system and the traditional combined cycle power generation system. The results show that in the new power generation system, net power efficiency of 53.29%, carbon capture efficiency of 95.78% and sulfur capture rate of 94.46% can be achieved, which is significantly better than the performance of the conventional combined cycle.

A low energy consumption de-carbonization natural gas combined cycle power generation system based on LiBr/H2O absorption heat transformer

An integrated system of natural gas combined cycle (NGCC) with monoethanolamine-based (MEA-based) CO2 capture was proposed in this study aiming to reduce the efficiency penalty of CO2 mitigation. In the proposed system, three measures were adopted: (1) utilizing absorption heat transformer (AHT) and ejector to recover the waste heat as well as providing suitable steam for solvent regeneration; (2) recirculating part of reboiler condensate to fully utilize the superheat degree of the extracted steam, and (3) injecting reboiler condensate into the regenerative system of power cycle to reuse the surplus heat of reboiler condensate. Thermodynamic benefits and economic viability of the proposed system were compared with the de-carbonization NGCC power plant without integration. Results indicated the efficiency penalty of CO2 capture in the proposed system decreased by 2.67 percentage points. Meanwhile, the cost of electricity and the cost of CO2 avoided were reduced by 4.73% and 15.08%, respectively, while the adopted additional devices caused an increase of the investment by 19.12 M$.

Emergy evaluation of the integrated gasification combined cycle power generation systems with a carbon capture system

An Integrated Gasification Combined Cycle (IGCC) power generation system has a significant effect on improving resource utilization efficiency. Carbon capture and storage (CCS) has been widely adopted to control greenhouse gas emissions. The integration of the two systems can further reduce CO2 emissions but cause elevated investment costs. As an effective tool to evaluate resource utilization efficiency and environmental impact, emergy analysis on coal and biomass based IGCC power generation systems with/without CCS is conducted in this paper. The coal based IGCC systems are simulated in Aspen plus to obtain the electricity generated under different CCS scales. For other systems, the data for emergy evaluation are from references. The sustainabilities under different CO2 tax values are compared. The factors impacting the sustainabilities are discussed. The results show that when CCS is not considered, all IGCC systems are superior to coal and biomass direct-fired systems in terms of sustainability. After CCS is integrated, the sustainability of biomass based IGCC system is still higher than that of biomass direct-fired systems, while coal based IGCC systems are less sustainable than coal direct-fired systems under low CO2 tax. The sustainabilities of Texaco-IGCC systems increase with CCS scales when CO2 tax is higher than 0.0220 $/kg, emphasizing CCS at a larger scale. For the Shell-IGCC systems, a higher CO2 tax (0.3880 $/kg) is preferred for the promotion of large scale CCS. In the scenario that the cost emergy transformity improves, the CO2 tax value at the point of sustainabilities reversal will decrease.

Simulation of a new biomass integrated gasification combined cycle (BIGCC) power generation system using Aspen Plus: Performance analysis and energetic assessment

A new biomass integrated gasification combined cycle (BIGCC), which featured an innovative two-stage enriched air gasification system coupling a fluidized bed with a swirl-melting furnace, was proposed and built for clean and efficient biomass utilization. The performance of biomass gasification and power generation under various operating conditions was assessed using a comprehensive Aspen Plus model for system optimization. The model was validated by pilot-scale experimental data and gas turbine regulations, showing good agreement. Parameters including oxygen percentage of enriched air (OP), gasification temperature, excess air ratio and compressor pressure ratio were studied for BIGCC optimization. Results showed that increase OP could effectively improve syngas quality and two-stage gasification efficiency, enhancing the gas turbine inlet and outlet temperature. The maximum BIGCC fuel utilization efficiency could be obtained at OP of 40%. Increasing gasification temperature showed a negative effect on the two-stage gasification performance. For efficient BIGCC operation, the excess air ratio should be below 3.5 to maintain a designed gas turbine inlet temperature. Modest increase of compressor pressure ratio favored the power generation. Finally, the BIGCC energy analysis further proved the rationality of system design and sufficient utilization of biomass energy.

Effects of thermophysical and thermochemical recuperation on the performance of combined gas turbine and organic rankine cycle power generation system: Thermoeconomic comparison and multi-objective optimization

In this paper, effects on the performance of a combined gas turbine and organic Rankine cycle (GT/ORC) system of using thermophysical and thermochemical recuperation based on methane steam reforming (MSR) process is investigated from the viewpoint of thermoeconomics. For this purpose, three power generation systems consisting of simple GT/ORC, GT/ORC with thermophysical recuperators (TPR) and GT/ORC with thermophysical and thermochemical recuperators (TPCR) are proposed and compared thermodynamically and economically. In addition, the multi-objective optimization using genetic algorithm is conducted for the systems and the systems characteristics at the final optimum design points are compared. Resultsreveals that the thermodynamic, economic and environmental performance of all three proposed power generation systems are enhanced as the combustion temperature raises. In addition, the power generation system with TPR shows the best performance from the thermodynamic perspective with the 22.86% and 27.52% improvement in the exergy efficiency compared to the simple GT/ORC and GT/ORC with TPCR, respectively. However, under the operating thermodynamic conations obtained by the multi-objective optimization approach, the product cost associated with the system using TPCR is less than that of the other configurations.

Emergy evaluation of power generation systems

With the increasing demand of power sources, it is of great significance to evaluate different power generation systems and optimize the energy structure. The emergy is proved to be a comprehensive and powerful way to evaluate the sustainability of a system. In this paper, emergy is used to compare ten power generation systems by two calculation methods of emergy indices. The emergy data of integrated gasification combined cycle and wind power generation systems are gathered from the studies of life cycle assessment, while those of the other eight systems are taken from existing emergy evaluations and converted to the same baseline. The study of hydropower generation systems shows the influence of technical progress and geographical location to the sustainability. The comparison of ten power generation systems shows that the hydropower generation system has the best sustainability while the wind and solar systems demonstrate relatively low sustainability. Besides, the sustainability is relative to the carbon dioxide tax. The sustainability of wind and concentrated solar power generation systems is tend to be better than that of integrated gasification combined cycle power generation system with an increase in the carbon dioxide tax. The results indicate that the technology, investment cost and carbon dioxide emission are essential factors to sustainability of power generation systems.

Simulation Analysis of Performance of Nuclear-Gas Combined Cycle Power Generation Systems

For the low cycle thermal efficiency of Pressurized Water Reactor(PWR) nuclear power units and the growing demand on the nuclear power peaking capacity of the power grid, using Ebsilon software, based on the thermodynamic system model of the secondary loop of Daya Bay Nuclear Power Station, the nuclear-gas combined cycle power generation thermodynamic system is established. Taking the gas turbine cycle efficiency and the combined cycle efficiency as the index of the heat economy, the performance of the combined cycle system is evaluated. At the same time, the effect of ambient temperature, pressure and gas turbine load on the system performance is analyzed. The results show that, the thermal efficiency of the nuclear-gas combined cycle system increased by 13.15% compared with the original nuclear power unit, the output power of the steam turbine increased by 75.49%, and the working environment of the steam turbine is improved obviously; The fall of ambient temperature will increase the efficiency and the power of the gas turbine, and the drop in ambient pressure will decrease the efficiency of the gas turbine and the combined cycle efficiency. When reducing the load of the gas turbine, the inlet temperature of nuclear reactor remains unchanged by afterburning the natural gas, and the steam turbine can still have high output power. The adjustable range of the load is from 56.57 % to 100%.

Oxide Layer Rumpling Control Technology for High Efficiency of Eco-Friendly Combined-Cycle Power Generation System

Combined-cycle power generation is a high-efficiency power generation method using natural gas that can reduce the emissions of carbon dioxide and other harmful substances by increasing the power generation efficiency. Therefore, the turbine inlet temperature should be increased to improve the power generation efficiency. However, given that the operating environment becomes extreme as the turbine inlet temperature increases, ensuring the sufficient durability of the gas turbine components is a necessity. Thermal barrier coatings (TBCs) applied to ensure the durability of the gas turbine components in a high temperature environment can peel off by stress generated through the difference in the thermal expansion coefficient of each layer. Because internal gas turbine components are damaged if peeling occurs, it is essential to ensure sufficient durability of the TBC. In particular, to enhance the efficiency of the combined-cycle power plant, and to withstand higher operating temperatures, it is essential to develop a TBC with an improved durability performance, when compared with currently commercialized TBCs. In this study, we attempted to improve the durability of the TBCs by mitigating the stress concentration phenomenon by gently controlling the rumpling of the oxide layer. For this purpose, the vertical crack design conditions required to reduce the buckling stress were derived through a finite element analysis. Isothermal degradation and thermal fatigue tests were conducted on the fabricated specimens to verify whether the oxide layer rumpling of the designed TBC was controlled gently and whether the durability was improved. Base on the results, a TBC structure with improved durability using oxide layer rumpling control technology is proposed.

A conceptual chemical looping combustion power system design in a power-to-gas energy storage scenario

Increasing global energy demand and the continued reliance on non-renewable energy sources, especially in developing countries, will cause continued increases in greenhouse gas emissions unless alternative electricity generation methods are employed. Although renewable energy sources can provide a clean way to produce electricity, the intermittent nature of many existing renewable energy sources, such as energy from the wind or sun, can cause instability in the energy balance. Energy storage systems such as power-to-gas may provide a clean and efficient way to store the overproduced electricity. In this work, a power-to-gas energy storage system coupled with a chemical looping combustion combined-cycle power generation system is proposed to provide base and intermediate load power from the unused electricity from the grid. Enhanced process integration was employed to achieve optimal heat and exergy recovery. The simulation results using ASPEN Plus V8.8 suggest that electric power generation with an overall energy efficiency of 56% can be achieved by using a methane chemical looping combustion power generation process with additional hydrogen produced from a solid oxide electrolysis cell. The proposed system was also evaluated to further improve the system's total energy efficiency by changing the key operating parameters.

Energy and Exergy Analysis of Power Generation Systems with Chemical Looping Combustion of Coal

AbstractCoal direct (CD) chemical looping combustion (CLC) and coal gasification (CG) CLC processes are two basic approaches to the application of CLC with coal. Based on these two approaches, two different combined cycle power generation systems were proposed and simulated by using the ASPEN Plus software. The performance of those two combined cycles was evaluated based on energy and exergy analyses. The results indicate that the circulation ratio of the oxygen carrier in the CG‐CLC process is smaller than that in the CD‐CLC process, but the CD‐CLC combined cycle offers advantages of higher net power efficiency, exergy efficiency, and carbon capture efficiency.

Investigation of the thermodynamic behavior of an apple juice waste- and sugarcane bagasse-fuelled combined-cycle power generation system

ABSTRACTThe paper presents an account of research findings dealing with the development of a thermodynamic equilibrium model based on chemical reactions resulting from gasification of solid wastes, apple juice waste and sugarcane bagasse. The existing data has been analyzed with respect to the effects of gasifier pressure and gas turbine inlet temperature (GTIT) on the lower heating value of syngas as well as on first- and second-law efficiencies of a solid waste-fuelled combined power cycle. Both these parameters for the combined power cycle decrease with an increase in gasifier pressure but increase with an increase in turbine inlet temperature. The observations also clearly indicate that the first-law efficiency is higher than the second-law efficiency, and this may be attributed to higher exergy content (biomass fuel) compared to the energy content. Further, compared to the sugarcane bagasse-fuelled cycle, improved performance in the context of higher first- and second-law efficiencies and lower CO2 and H2O emissions results from the apple juice waste-fuelled combined cycle.

Fuel Composition in Pressurized SOFCs

Introduction Pressurized SOFC system combined with gas and steam turbine will achieve high power generation efficiency approaching 70% as the triple combined cycle power generation system. It has been reported that operating SOFCs under high pressure can make cell power output higher (1,2). However, there are only a limited number of studies available on the fuel composition for pressurized SOFCs. In general, fuel gas consists of carbon, hydrogen and oxygen, so that the C-H-O equilibrium composition determines anode performance. In this study, fuel gas composition on the anode side of pressurized SOCFs was derived by thermochemical equilibrium calculation for considering various operating conditions in terms of carbon deposition and each gas molar fraction affecting power generation characteristics, all described in the C-H-O diagrams. Calculation Procedure We calculated carbon deposition region and each gas molar fraction under various equilibrium conditions upon suppling fuels composed of carbon, hydrogen and oxygen. Thermochemical calculations were carried out using three approaches: (i) calculation with equilibrium constants, using (ii) HSC Chemistry (Version 9.0.5, Outotec Research Oy, Finland) and (iii) FactSage (Version 6.3.1, Thermfact Ltd., Canada). As the first approach, we defined main reactions within the fuel and solved the system of equations using relational expression of equilibrium constants and elements ratios by Mathematica (Version 10.4.1, Hulinks Inc., Japan). HSC Chemistry and FactSage are both thermochemical equilibrium calculation software based on Gibbs free energy minimization, containing various databases. It has been known that the major constituents of equilibrium products are H2(g), H2O(g), CO(g), CO2(g), CH4(g), and C(s) (graphite) (3). The line specifying the carbon deposition region means the equilibrium concentration of C(s) equal to 10-6 of the initial carbon content in the fuel. The C-H-O diagrams are described in such a way between 100 and 1000oC, and between 1 and 30 bar. Results and discussion Comparing Fig. 1 with Fig. 2, carbon deposition region boundaries vary with respect to temperature and pressure. The C-H-O diagrams clearly show that carbon deposition region expands on the oxygen-rich side and contracts on the hydrogen-rich side with decreasing temperature and/or increasing total pressure. It can be explained by the chemical equilibrium reactions (I) and (II): CH4↔C(s)+2H2 (I) 2CO↔C(s)+CO2 (II) Reaction (I) is an endothermal reaction; on the hydrogen-rich side, equilibrium reaction (I) shifts to the left side, preventing carbon deposition at lower temperatures. With increasing total pressure, the equilibrium also shifts to the left side due to the decrease in the number of molecules. In the same way, Reaction (II) is an exothermal reaction and the number of molecules is lower on the right side, so that the equilibrium reaction shifts to the right side to promote carbon deposition. The C-H-O diagrams of various gases and the corresponding theoretical open circuit voltage are also calculated. These results suggest, for example, a decrease in the fraction of H2and CO under higher total pressure.

Coupled analysis of performance and costs of segmented-in-series tubular solid oxide fuel cell for combined cycle system

Integrated approaches that combine numerical modeling and economic evaluations were developed to investigate the potential widespread use of integrated solid oxide fuel cell (SOFC) systems. A coupled model analysis of the cell performance and production costs of a segmented-in-series tubular solid oxide fuel cell (SST-SOFC) system was performed for a combined cycle power generation system integrating an SOFC and a gas turbine. The SST-SOFC cell-stack performance was investigated using a finite element method (FEM), and cost analysis of the SST-SOFC module production was conducted based on process-integration modeling. The impact of the cell-stack dimensions and material properties on the cell-stack performance was evaluated using FEM-based numerical modeling simulation. Cost analysis was performed in terms of cell dimension, the production process, and cell performance, based on the results of the FEM-based model simulation. We used a 250 kW combined cycle system, i.e., a 220 kW SST-SOFC module with a 30 kW micro gas turbine, to explore quantitative technological innovation pathways. The base-case production cost was ca. 240 JPY/W (ca. 2.4 USD/W), which can be reduced to ca. 110 JPY/W (ca. 1.10 USD/W) by increasing the production scale. In addition, the present method showed the innovation pathway to achieve a break-even point for grid electricity cost (14 JPY/kWh (0.14 USD/kWh)).

Thermal efficiency of advanced integrated coal gasification combined cycle power generation systems with low-temperature gasifier, gas cleaning and CO2 capturing units

Advanced integrated coal gasification combined cycle (A-IGCC) systems have been proposed to obtain higher thermal efficiency than that of IGCC systems by recuperating exhaust heat from a gas turbine to provide the heat source for a gasifier. The performances of the A-IGCC systems with a low-temperature dual-bed fluidized bed gasifier, gas cleaning, CO2 capturing, and the most advanced (1650°C-class) gas turbine units were evaluated using Aspen Plus®. Net thermal efficiency of the A-IGCC model with hot gas desulfurizing unit using ZnO and TiO2 was 53.6% and that with cold gas desulfurizing unit using Selexol® process was 52.0% without CO2 capturing when the cold gas efficiency (CGE) in the gasifier was 80.1%. The net thermal efficiency can be increased to 54.7–57.2% by improving CGE from 80.1 to 85.0%, suggesting the improvement of cold gas efficiency in the gasifier is critical. CO2 emission factors of the A-IGCC system are 505–520kg-CO2/MWh (CGE=80.1%) and 468–490kg-CO2/MWh (CGE=85.0%), and can be decreased to 39.7–112kg-CO2/MWh with 80–95% of CO2 capturing. Compliance to the CO2 emission factor target (<499kg-CO2/MWh) for coal-fired power generation systems can be achieved without CO2 capturing by developing gasifiers whose CGE is 85.0% and integration with 1650°C-glass gas turbine.

5-12.石炭ガス化複合発電実現のための新しい技術開発(Session(5)実用化を迎える石炭利用技術)

5-12.石炭ガス化複合発電実現のための新しい技術開発(Session(5)実用化を迎える石炭利用技術)