Supercritical CO2 Cycle Research Articles

Comprehensive analysis and multi-objective optimization of an innovative power generation system using biomass gasification and LNG regasification processes

The biomass-based systems have considerable feasibility to design a co-generation with different subsystems. This paper presents a novel biomass-based gas turbine with a modified Kalina cycle, supercritical-CO2 cycle, and LNG regasifying subsystems. A turbine is installed in the LNG regasifying subsystems to produce more power. Energy, advanced exergy, including thermal and mechanical exergies, and economic analyses are applied to assess the system's performance. Three double-objective and two triple-objective optimizations are carried out to obtain the system's operation mode at the optimum state. The results reveal that the combustion chamber and supercritical-CO2 cycle's condenser have the highest exergy destruction. Also, the compressors and turbines have the main portion of the investment cost rate of about 79.91%. The design system provides 7560 kW net power, 41.75% exergy efficiency, and 6.2 years payback period. Regarding the parametric study, the system's performance indexes are mainly affected by the air compressor's pressure ratio. Furthermore, considering the net power-sum unit cost of production as the optimization goal represents the best performance of 7830 kW net power, 42.97% exergy efficiency, and 7.262 $/GJ sum unit cost of products.

Multi-objective optimization of hydrogen production system based on the combined supercritical cycle and gas turbine plant

In this paper, considering the hydrogen production cycle coupled with the supercritical CO2 cycle, hydrogen is produced as a clean fuel along with power and heat production. Also, the world's need for clean energy doubles the solutions to achieve clean hydrogen energy. The investigated cycle has a supercritical CO2 cycle with a combustion chamber where enriched fuel is introduced. Combustion products produce work in the gas turbine, and further hydrogen separation is formed with the help of water gas shift reaction and hydrogen separation membrane. In the thermodynamic analysis, combustion chamber known as the most irreversible member of set, where the most exergy is lost. The energy and exergy efficiency for whole set are 64.82%, 52.46% respectively. Produced hydrogen mass flow rate calculated 46.8 kg/h. Also, multi-objective optimization based on genetic algorithm were done and the results were reported. All calculation and optimization method has been done in MATLAB software.

Multi-objective optimisation of a power generation system integrating solid oxide fuel cell and recuperated supercritical carbon dioxide cycle

This article presents an advanced power generation system that integrates a solid oxide fuel cell (SOFC) module with a recuperated supercritical CO2 (s-CO2) cycle. The waste heat generated by the exhaust of the SOFC module is utilised to drive the s-CO2 cycle, resulting in enhanced energy efficiency. The performance of the system was investigated through thermodynamic and economic analyses and optimised using response surface methodology. The optimisation process focused on two objectives: maximising the energy efficiency of the integrated system and minimising the levelised cost of electricity. The study meticulously analysed the effects of important variables such as current density, fuel utilisation factor, and operating temperature of the fuel cell. The optimisation efforts yielded impressive results, achieving an energy efficiency of 64% and a levelised cost of electricity (LCOE) of 0.18£/kWh. The proposed system surpassed traditional natural gas-fuelled power plants in terms of efficiency and specific emissions. Furthermore, the system's performance was evaluated when operated with green hydrogen fuel, which led to a substantial improvement in efficiency, estimated at 73.37%. However, it was found that the LCOE of the system is relatively higher and approximately 15% higher than the methane-based alternative.

Development and assessment of a novel multigeneration plant combined with a supercritical CO2 cycle for multiple products

Multigenerational energy conversion plants are one of the most promising solutions for tackling environmental challenges and making efficient use of energy sources. In this regard, a newly designed multigeneration plant integrated with a methane-based Brayton cycle, a steam Rankine cycle, a supercritical CO2-based Brayton cycle, a multi-effect desalination process, a PEM unit, a domestic water heater process, and two thermoelectric generators is integrated, proposed and analyzed. The thermodynamic and environmental assessments of the developed paper are conducted and examined with energy and exergy efficiencies as well as CO2 emission rate. Similarly, a parametric study is executed and reported, by the way, to define the impact of the various significant factors on the developed plant's efficiency. In the end, the CO2 emission rate is determined and compared according to different energy conversion plants. In light of the analysis results, the net power, hydrogen, and freshwater production capacities of the reference study are calculated to be 1336 kW, 0.002004 kgs−1, and 0.954 kgs−1, respectively. Additionally, it is found that the developed study's energetic and exergetic performances are 55.76% and 52.17%. According to emission analysis results, the multigeneration system emits 272.2 kg/MWh less CO2 emissions than the single energy conversion system.

Simulation of gas-solid combustion characteristics in a 1000 MW CFB boiler for supercritical CO2 cycle

Supercritical CO2 (S-CO2) power cycle has become one of the most efficient and low-pollution cycle schemes to improve thermal power generation efficiency and reduce energy consumption around the world. In this study, the 3D physical model of a 1000 MW S-CO2 circulating fluidized bed (CFB) boiler with annular furnace is established to simulate the gas-solid combustion process based on the MP-PIC method under the Eulerian-Lagrangian framework. By comparing with the conventional water steam CFB boiler, the S-CO2 CFB boiler has a smooth and stable gas-solid flow pattern with good uniformity of the particle concentration and velocity distribution, indicating that the annular structure and the layout of the heating surfaces is conducive to the gas-solid flow uniformity. The gas-solid phase temperature distributes uniformly basically without sudden rise or sudden drop, and the temperature difference between the solid phase and the gas phase is not large, which reflects the good combustion uniformity of the S-CO2 CFB boiler. Compared with 300 MW and 600 MW S-CO2 CFB boilers, the 1000 MW one shows a higher carbon conversion rate, lower desulphurization effect, and lower nitrogen removal performance with the CO, NO, and SO2 outlet concentration of 0.002%, 5.8 mg/m3, and 125 mg/m3, respectively.

Improved coordinated control strategy of coal-fired power units with coupled heat storage based on supercritical carbon dioxide cycle

With the rapid development of intermittent renewable energy sources, operating a power generation system, like coal-fired power plants that can ensure supply stability, has become increasingly challenging. In this study, an additional supercritical CO2 (sCO2) cycle is incorporated into coal-fired power units to improve load regulation capability. First, a dynamic model of the coal-fired power unit with the additional sCO2 cycle is established. Two improved coordinated control systems are designed to improve the power ramp rate, i.e., a switching controller and a dual controller. Finally, a 330 MW coal-fired power plant was simulated. The results show that the proposed control method could effectively improve the load response characteristics. The integral of the absolute error (IAE) index and integral of the time square error (ITSE) index, of the coordinated control system based on dual control, were superior to those of the standard coordinated control system. The automatic generation control (AGC) performance indicators were found to be 9.03 and 8.76 in the load rise and decrease stages, respectively. Thus, the study provides a new direction for the application of sCO2 cycles in the field of coal-fired power generation.

Multimode operation control strategy for improving part-load performance of supercritical CO2 Brayton cycle

The recompression supercritical CO2 (S-CO2) Brayton cycle is regarded as one of the most promising energy conversion systems owing to its high efficiency and compactness. Because the recompressor impairs the performance of a system at low loads, the concept of multimode operation by switching the recompressor on or off is proposed to improve the part-load performance. In this study, a dynamic model of the recompression S-CO2 cycle with reheating is developed, and three control strategies, including turbine throttle valve control, turbo-alternator-compressor (TAC) speed control, and inventory control, are selected to follow the part-load. Subsequently, the action mechanism of the multimode operation and the effects of different control strategies on the part-load performance of the system under multimode operation is investigated and compared. Simulation results indicate that the improved thermal efficiency by switching operation modes is due to improvement in the thermal match inside the high-temperature recuperator and reduced degradation of the recompressor. Moreover, switching the system to Mode 2 by switching off the recompressor at 20% load under TAC speed control, turbine throttle valve control, and inventory control can improve thermal efficiency by 1%, 3.5%, and 5.4%, respectively. This result can serve as a guideline for the efficient operation of the recompression cycle under part-load.

Corrosion of Potential First Stage Blade Materials in Simulated Supercritical CO2

ABSTRACT Global power consumption is predicted to double by 2050, notably driven by the transportation and energy sectors necessitating limitations of emissions. Due to its compact turbomachinery, better thermal efficiency, and simpler layout, supercritical-CO2 cycles have received attention, with numerous variations proposed (either indirect-fired/closed cycles or direct-fired-open cycles). One technical challenge is degradation pathway quantification of turbine materials in sCO2 as selection is crucial to successfully and economically operate new plants. This requires degradation assessment in representative environments simulating the Allam cycle. Laboratory tests were conducted on a first stage turbine blade alloy, CM247, with either an environmentally resistant coating or bond coat/thermal barrier coat at one atmosphere and 800°C, with potential exposure including (O2, H2O, N2, SO2) for up to 1000 h. Weight change and metallographic measurements tracked scale development. Scanning electron microscopy/energy dispersive X-ray spectroscopy studied scales and internal precipitates. Locations of contaminant element in the CO2-rich environment were investigated.

Performance comparison of basic and parallel double evaporator Organic Rankine Cycle integrated with solar based supercritical CO2 cycle

Performance comparison of basic organic Rankine cycle (ORC) and parallel double evapora-tor ORC (PDORC) integrated with solar power tower (SPT) driven intercooled cascade sCO2 (supercritical carbon dioxide) cycle was carried out in present study. The intercooled cascade sCO2 cycle/ORC (configuration-1) and the intercooled cascade sCO2 cycle/PDORC (configu-ration-2) were considered for comparison on basis of parametric analysis. The effects of SPT design parameters such as solar irradiation, solar receiver emittance, and concentration ratio on system performance were investigated. It was concluded that the addition of basic ORC and PDORC to the intercooled cascade sCO2 cycle improved the thermal efficiency by 2.26% and 6.66% respectively at solar irradiation of 950 W/m2. In the case of basic ORC and PDORC, the waste heat recovery ratios were 0.1197 and 0.1775, respectively. It was also discovered that configuration-2 performed better than configuration-1 in terms of waste heat recovery. The combined cycle’s performance can be improved even more by lowering solar emittance and increasing the concentration ratio.

Conversion of medical waste into value-added products using a novel integrated system with tail gas treatment: Process design, optimization, and thermodynamic analysis

The COVID-19 pandemic has generated substantial medical waste (MW), posing risks to society. Based on widespread MW incineration, this study proposes an integrated system with tail gas treatment to convert MW into value-added products with nearly zero emissions. Herein, steam generators and supercritical CO2 cycles were used to recover energy from MW to produce high-temperature/pressure steam and electricity. A simple power generation cycle achieved a net electricity efficiency of 22.4% through optimization. Thermodynamic analysis revealed that the most energy and exergy loss occurred in incineration. Furthermore, a pressurized reactive distillation column purified the resultant tail gas. The effects of inlet temperature, pressure, liquid/gas ratio, and recycle ratio on the removal and conversion efficiencies of NO2 and SO2 were evaluated. Nearly 100% of the SO2 and 75% of the NO2 generated by the incineration of MW have been converted into their acid forms. Based on the proposed tail gas treatment unit, high-purity CO2 (∼98% purity) was finally obtained.

Biomass-to-energy integrated trigeneration system using supercritical CO2 and modified Kalina cycles: Energy and exergy analysis

One of the main global challenges is to produce energy in a sustainable way, for example, from renewable energy sources. This study proposes a novel system for trigeneration of cold, heat, and electricity, driven by biomass gasifier. The proposed solution consists of a modified Kalina cycle and a supercritical CO2 power cycle. The input energy of the system is provided by the gasification of municipal solid wastes. In addition to electricity generation, the cold is produced at the sub-zero temperature in the modified Kalina cycle, and the absorbed heat is recovered by a heating unit in the supercritical CO2 cycle. The high thermal energy of the exhaust gases is used to increase the temperature of CO2 entering a gas turbine and then is directed to a boiler to run the Kalina cycle. The thermodynamic relations governing the gasifier, CO2 and Kalina cycles are developed using the engineering equation solver (EES) software. As a result of thermodynamic modeling, from 3.683 kg/s of syngas the energy and exergy efficiency at 71.45% and 55.43% can be achieved, respectively. Furthermore, the highest exergy loss is found to be 7.604 kW and 2.839 kW in the gasifier and combustion chamber, respectively.

Performance analysis and optimization of a novel geothermal trigeneration system with enhanced Organic Rankine cycle, Kalina cycle, reverse osmosis, and supercritical CO2 cycle

The present investigation analyzes in deep a multi-generation system producing power, heating, and domestic consumable water. The system is based on renewable energy sources with approaches utilizing subterranean geothermal reservoir, allocating a considerable potential for means of generation. The system is comprised of a single-flash geothermal system, a dual-turbine Kalina cycle, an Organic Rankine Cycle with an internal heat exchanger and an open feed open heater, a supercritical CO2, and a reverse osmosis cycle. The analyzes carried out include energy, exergy, entransy, and exergoeconomic evaluation. Considering the base mode, the values are derived as 46.08%, 56.04%, 333.1MWK, and 16.89$/GJ for energy efficiency, exergy efficiency, entransy loss, and the sum unit cost of products. The coupling of the cycles demonstrated a novel configuration aimed at generating power, heating, and freshwater as a multi-generation system with substantial output potential. The outputs are total power output, heating load, and freshwater as 130.068 MW, 30.79 MW, and 44.97 kg/s, respectively. The remainder of the study includes four multi-objective optimization scenarios aimed at identifying the optimum conditions associated with energy efficiency, exergy efficiency, entransy loss, and the sum unit cost of products. The present investigation uses the Engineering Equation Solver to simulate the conditions of the concept.

Superstructure-free synthesis and multi-objective optimization of supercritical CO2 cycles

The optimization of the supercritical CO2 cycle structures is mostly experience-intensive and computation-demanding. Using the superstructure-free method can effectively realize computer-aided intelligent construction and optimization of cycle configurations. In this paper, an improved superstructure-free algorithm is proposed which goes beyond the state-of-the-art methods by expanding the searching space and evaluation matrices. The improved algorithm can intelligently and simultaneously optimize the cycle structure and design parameters by considering both the net power output and specific investment cost as objective functions. By applying the algorithm, several previously unseen cycle structures were retrieved, and the maximum net power output increases by a range of 15.45% to 37.71%. The optimal cycle obtained by entropy weight and TOPSIS analysis of the Pareto solution set is a cascaded configuration of a double compression intercooling cycle and a basic cycle through sharing cooling process, which achieves a net power output of 37.75 kW and a specific investment cost of 5.33 $/W. The improved superstructure-free algorithm can also be applied to other thermodynamic cycles and can greatly contribute to the intelligent configuration design and optimization of similar thermodynamic cycles.

Techno-economic assessment of biomass and coal co-fueled chemical looping combustion unit integrated with supercritical CO2 cycle and Organic Rankine cycle

This study evaluates the effect of co-combustion of woody biomass and coal on the techno-economic performance of a 300 MWth in-situ gasification chemical looping combustion power plant. The circulating fluidized bed reactor system was designed and a modified macroscopic model was applied to predict the fuel conversion and the CO2 capture efficiency. The supercritical CO2 cycle and the Organic Rankine cycle were integrated with the heat sources for power generation. The results showed that increasing biomass share in the input thermal power, in addition to enhancing the CO2 capture efficiency, improves the coal conversion. Moreover, negative CO2 emissions are achieved as the biomass share exceeds 50 MWth. The net electrical efficiency of the plant is about 43.89% and grows slightly for higher biomass shares. For biomass share of 150 MWth, the CO2 capture efficiency increases from 79.27% to 90.87%. Also, the levelized cost of electricity (LCOE) rises by 15.9%–108.262 $/MWh due to higher biomass price. Despite this increased fuel cost, the LCOE is still lower than that value for the coal-fired power plant with conventional CO2 capture technology. Biomass utilization becomes more cost-effective than coal if the carbon tax is above 30 $/tCO2.

Optimization and performance analysis of a near-zero emission SOFC hybrid system based on a supercritical CO2 cycle using solar energy

Renewable energy represented by solar energy has the characteristics of intermittency and fluctuation. To ensure that the grid can operate safely and stably after the large-scale grid connection of renewable energy power, a new hybrid system consisting of a solid oxide fuel cell (SOFC), a solar power tower plant, and a supercritical CO2 (S-CO2) Brayton cycle is proposed in this study from the perspective of energy, exergy, and economy. By utilizing the cold source loss of the S-CO2 cycle to provide part of the energy required for the alkaline electrolyzer, it can efficiently produce and store hydrogen, achieving zero greenhouse gas emissions while increasing efficiency. Meanwhile, the high-temperature exhaust gas from SOFC is recovered by the S-CO2 cycle. The system considers two operation modes, switching two types of S-CO2 cycle configurations to efficiently utilize solar energy according to the variation of solar radiation energy. The thermal efficiency of the proposed system is improved by 16.61% and 6.88% compared with the other two typical S-CO2 cycle power generation systems, and the net power output reaches 8.0 MW. A parameter study shows that increasing the split ratio is beneficial to improve the thermodynamic performance of the system. However, at a split ratio less than 0.76, it is beneficial to the total cost rate of the system. The results of multi-objective optimization show that the exergy efficiency of the combined system and the total system cost rate reach 56.86%, 513.10$/h and 56.45%, 481.59$/h for the system with an additional simple S-CO2 cycle and the system with an additional recompression S-CO2 cycle, respectively, and the optimum point is selected by the TOPSIS and LINMAP methods.

Thermodynamic analysis of combined cycle system based on supercritical CO2 cycle and gas turbine with reheat and recuperation

ABSTRACT The gas turbine combined cycle (GTCC) system has the advantages of high power density, high efficiency, and fast start-stop control, which will occupy an important position in the next-generation power system. In this paper, two groups of reheat cycle gas turbines with different thermal parameters are compared and the reheat and recuperative cycle is constructed by adding a recuperator to the recommended reheat cycle. Two typical sCO2 cycles are selected to construct a combined cycle system with simple cycle, reheat cycle, reheat, and recuperative cycle, respectively. In the range of gas turbine pressure ratio of 32–56, the parameters of GTCC with turbine inlet temperature of 1750°C are optimized based on the system calculation method of total physical properties, and the thermodynamic performance of the GTCC system was evaluated. The research shows that the reheat cycle with a TRIT (inlet temperature of the turbine after reheat) of 1250°C has higher efficiency and lower specific net work than the reheat cycle with a TRIT of 1750°C, and the relatively low exhaust temperature is more suitable for the sCO2 bottoming cycle. In addition, compared with the simple cycle, the optimal topping cycle thermal efficiency of the reheat and regenerative cycle is only reduced by 0.1%, but the exhaust temperature is higher. Under the same sCO2 cycle form, the combined cycle efficiency is improved by 1.5–2.0%. The thermal efficiency of the reheat and regenerative cycle gas turbine combined cycle (RCRHCC) studied in this paper can reach up to 67.53%, which has the potential to become the next generation of GTCC units.

A novel system integrating water electrolysis and supercritical CO2 cycle for biomass to methanol

In order to improve the efficiency of conventional biomass to methanol, a novel cogeneration system is designed that couples an electrolytic water subsystem with a s-CO2 cycle and a conventional biomass to methanol system. The novel cogeneration system uses syngas converted from biomass gasification and hydrogen obtained by water electrolysis for methanol synthesis, and it uses a supercritical CO2 cycle to improve its performance. The proposed process was modeled and calculated using Aspen Plus and MATLAB as the main simulation software to analyze its energy efficiency, exergy efficiency and economics, and to illustrate the advantages of the system compared with the conventional biomass to methanol system from a thermodynamic point of view. Taking a biomass with a mass flow rate of 2.78 kg/s for example, the energy efficiency of the new process was increased by 19.89% for the same biomass consumption conditions. The results show that the system has an energy efficiency of 67.98% and an exergy efficiency of 64.82%. The irreversibility comes from two main components: the gasifier and the electrolyzer. The project is expected to achieve a net present value of $22,948,830 over its 20-year life cycle.

Thermodynamic analysis of SOFC–CCHP system based on municipal sludge plasma gasification with carbon capture

To solve the environmental problems associated with municipal sludge incineration and landfilling, a combined cooling, heating, and power (CCHP) system integrating plasma gasification, solid oxide fuel cell (SOFC), gas turbine, supercritical carbon dioxide (S-CO2) cycle, and double-effect absorption refrigeration cycle (ARC) is proposed. Additionally, the CO2 generated in the system is captured to reduce the environmental impact. Energy, exergy, and sensitivity analyses of the developed system are conducted. Key parameters such as the SOFC temperature, SOFC pressure, and fuel utilization rate affecting the system performance are studied. The results show that net electrical efficiencies of the SOFC and the system are 41.96 % and 50.00 %, respectively. The exergy efficiency and comprehensive energy utilization rate of the system are 47.04 % and 87.59 %, respectively. The system can generate a power of 175.03 kW, cooling of 45.70 kW, and heating of 85.82 kW under the design conditions, accounting for 67.46 %, 21.23 %, and 11.31 % total energy output of system, respectively. The three main sources of exergy destruction of the system are the plasma gasification, SOFC, and supercritical CO2 cycle subsystems, accounting for 36.8 %, 12.2 %, and 10.7 % exergy destruction, respectively. The system performs the best when the SOFC temperature is 910 °C and the fuel utilization rate is between 0.85 and 0.90. The SOFC pressure has little effect on the system performance. In addition, the carbon capture rate of the system can reach 97.50 %. The CCHP system has high thermodynamic efficiency and hence can convert municipal sludge efficiently into clean energy; therefore, this study provides a new concept for resource treatment of urban sludge.

NaNO3-KNO3-KCl/K2CO3 with the elevated working temperature for CSP application: Phase diagram calculation and machine learning

Mixed nitrates with relative low melting point have widely been used as thermal storage medium in the concentrated solar power stations. However, their maximum working temperatures aren’t high enough to integrate with more efficient power generation systems such as the supercritical CO2 cycle. In the present work, mixed nitrates with elevated working temperature were obtained by adding KCl/K2CO3. With the help of FactSage software and back-propagation (BP) algorithm combined with genetic algorithm (GA), the eutectic compositions and melting points of NaNO3-KNO3-KCl and NaNO3-KNO3-K2CO3 were predicted, and the validity of BP algorithm combined with GA was verified. Based on DSC and TG curves, the melting points of the as-prepared NaNO3-KNO3-KCl and NaNO3-KNO3-K2CO3 are 206.12 °C and 207.24 °C, respectively, which are in agreement with predicted values. Moreover, their decomposition temperatures were increased to more than 640 °C. In addition, the specific heat capacity of both mixed molten salts was measured, and it also was calculated by using FactSage software. This work provides two new ternary molten salts based on nitrates with higher working temperature and develops the prediction method on phase diagram calculation and machine learning.

Performance evaluation of an integrated cooling and power system combining supercritical CO2, gas turbine, absorption refrigeration, and organic rankine cycles for waste energy recuperating system

This study proposes and explores a unique integrated cooling and power system in which waste heat from a gas turbine (GT) cycle is collected and used to generate electricity via a supercritical CO2 (sCO2) recompression Brayton cycle (sCO2RBC) and an organic Rankine cycle (ORC). An absorption refrigeration cycle (ARC) recovers waste heat from the sCO2RBC in order to provide a cooling impact. An energy analysis is carried out where mathematical modelling has been performed by a validated one-dimensional Python code. For working fluids e.g., air, combustion/exhaust gas, and NH3–H2O solution, property equations are used for obtaining the properties of respective state points. Impacts of different parameters are investigated on the total power output, net cooling effect and net energy utilization. The work emphasizes on modeling a novel integrated cooling and heating power system that utilizes the next generation sCO2 cycle, as well as other conceivable combinations, to effectively and reliably recover the waste heat. The analysis reveals that except for difference in the temperature in the hot side of the generator, all of the parameters increase resulting in an increase in net work done. The increase in temperature at inlet of GT, pressure ratio of the RBC, the decrease in GT pressure ratio, isentropic efficiency of GT, and lastly the temperature variation in the hot side of absorption refrigeration cycle generator affects the co-efficient of performance (COP) & energy utilization factor (EUF) of combined system. The EUF achieves a highest value of 49.09% and COP of 0.72.