Carbon Dioxide Transcritical Cycle Research Articles

Introducing and performance evaluation of a novel Multi-Generation process for producing Power, fresh Water, oxygen and nitrogen integrated with liquefied natural gas regasification and carbon dioxide removal process

The objective of this paper is to develop and evaluate a new integrated multigenerational system comprised of cryogenic air separation, hydrate-based desalination, combined cycle and oxyfuel power plants, carbon dioxide amine absorption, and transcritical carbon dioxide power cycle, employing liquefied natural gas cold energy. This integrated multi-generation system, applicable for liquefied natural gas importer terminals with access to seawater, produces approximately 2,533 MW net output power and 1,985 kg/h fresh water. In addition, this integrated multi-generation process produces 16,735,861 kg/h high-purity liquid oxygen (100 mol%), 4,773,633 kg/h liquid nitrogen with 99.71 mol% purity, more than 31,724,465 kg/h high-purity gaseous nitrogen (99.9 mol%), and 90,903,230 kg/h low-purity gaseous nitrogen (83.38 mol%). About 5907.3 MW of produced power is generated by liquefied natural gas expander. The performance of this system is evaluated by energetic methods. The results of energy analysis show the specific energy consumptions of the air separation products are 0.551 kW/kg and 1.93 kW/kg for liquid oxygen and nitrogen, respectively. Moreover, in the hydrate-based desalination subsystem, the specific energy consumption is 0.5 kW/m3 for produced pure water. The combined cycle power plant includes two gas turbines, three steam turbines, and a three-pressure level heat recovery steam generation. The thermal efficiencies of gas turbine cycles (Bryton), steam turbine cycles (Rankine) and combined power cycles are 26.3 %, 29.6 %, and 36.2 %, respectively. The flue gases from power plants enter the carbon dioxide amine absorption subsystem. The separated carbon dioxide is used as a working fluid to produce 372.1 MW power in transcritical carbon dioxide cycle. The results of energy analysis for carbon dioxide amine absorption subsystem show that the specific energy consumption, the ratio of captured carbon dioxide per unit mass of liquefied natural gas and the carbon dioxide removal efficiency are 6.60 kW/kg, 33.91 kg/tone, and 90.06 %, respectively. Approximately 2,905,000 kg/h of liquid carbon dioxide is obtained as the byproduct of this multi-generation process. Additionally, sensitivity analysis is conducted to determine key parameters influencing the main energetic indexes. Finally, the amount of attainable regasified natural gas reaches 257,523 tone/h by applying this multi-generation system with total 86 % energy efficiency.

A novel designation of LNG solid oxide fuel cells combined system for marine application

This paper presents a pioneering multigeneration system for marine vessel applications, involving the integration of solid oxide fuel cells (SOFCs) fueled by liquefied natural gas (LNG), coupled with LNG cold energy utilization cycles and exhaust gas heat recovery systems. The system comprises a tandem arrangement of organic Rankine cycle (ORC) and trans-critical carbon dioxide cycle (TCO2), specifically engineered to harness the cold energy released during LNG regasification process. The elevated temperature exhaust gases emanating from the SOFC are efficiently recuperated through a series of components including a gas turbine (GT), regenerative, steam Rankine cycle (SRC), and waste heat boiler (WHB). The proton exchange membrane fuel cells (PEMFC) is designed to enhance the overall operational flexibility and responsiveness of the multigeneration system. The Aspen Hysys V12.1 is used to simulate the propose system and numerical method is employed to parameter optimize of system. The first and second laws of thermodynamics are applied to establish the thermodynamics equations and calculated the system performances. The described system is estimated to obtain energy efficiency of 69.32 % and exergy efficiency of 33.85 %. The high-temperature exhaust gas harvesting integrated systems are sufficiently generated 2091.24 kW which accounted 35.49 % of entire power generate. Furthermore, the parametric researches are implemented to examine the influence of current density, β values to the performance indicators of systems. The WHB is designed to generate 1081 kg/h of superheated vapor at 170 °C and 405 kPa for various purposes of seafarers and equipment's onboard ship. The economic feasibility is performed to view the possibility of investment, maintenance cost and payback period for the described system.

Thermodynamic Analysis of an Increasing-Pressure Endothermic Power Cycle Integrated with Closed-Loop Geothermal Energy Extraction

The thermodynamic analysis of an increasing-pressure endothermic power cycle (IPEPC) integrated with closed-loop geothermal energy extraction (CLGEE) in a geothermal well at a depth from 2 km to 5 km has been carried out in this study. Using CLGEE can avoid some typical problems associated with traditional EGS technology, such as water contamination and seismic-induced risk. Simultaneous optimization has been conducted for the structural parameters of the downhole heat exchanger (DHE), the CO2 mixture working fluid type, and the IPEPC operating parameters. The CO2-R32 mixture has been selected as the optimal working fluid for the IPEPC based on the highest net power output obtained. It has been found that, when the DHE length is 4 km, the thermosiphon effect is capable of compensating for 53.8% of the pump power consumption. As long as the DHE inlet pressure is higher than the critical pressure, a lower DHE inlet pressure results in more power production. The power generation performance of the IPEPC has been compared with that of the organic Rankine cycle (ORC), trans-critical carbon dioxide cycle (t-CO2), and single-flash (SF) systems. The comparison shows that the IPEPC has more net power output than other systems in the case that the DHE length is less than 3 km, along with a DHE outer diameter of 0.155 m. When the DHE outer diameter is increased to 0.22 m, the IPEPC has the highest net power output for the DHE length ranging from 2 km to 5 km. The application scopes obtained in this study for different power generation systems are of engineering-guiding significance for geothermal industries.

The 4E emergy-based analysis of a novel multi-generation geothermal cycle using LNG cold energy recovery

Over the last decade, the increasing demand for sustainable energy sources has led to the development of innovative approaches in geothermal power plant cycles. In this study, a novel combined geothermal power plant cycle (GTPPC) that integrates the Kalina cycle, transcritical Carbon Dioxide (T-CO2) cycle, with the injections of the Liquid Natural Gas (LNG) stream and geothermal water (GTW) stream is proposed in order to provide cold and hot sources of the system. The performance of the system is evaluated using emergy analysis, an evaluation factor based on thermodynamic principle and solar energy with the aid of emergoeconomic and emergoenvironmental factors. The injection of LNG stream leads to significant improvements: enhancing the net output power and overall emergoeconomic and emergoenvironmental efficiencies of the cycle. By conducting improvement priority and parametric studies, crucial stream points and the system's performance's optimization is identified. Our results indicate that the Kalina sub-cycle has a greater impact on performance, and the exergy destruction in the LNG stream will be minimized. At the optimal point, the GTPPC achieves high thermal efficiency and emergy-based metrics, indicating its sustainability and viability as a geothermal power generation solution. By the injection of LNG stream, the net output power, and overall emergoeconomic and emergoenvironmental efficiencies of the cycle, improved by 1.79 MW, 14 %, and 16 %, respectively. According to the obtained results, the performance of the Kalina sub-cycle has more effect than the Carbon Dioxide sub-cycle, and destructing exergy in the LNG stream will have irreparable effects on the operation of the GTPPC. At the optimum point of the system performance, the GTPPC will operate with the thermal efficiency, ψ, and φ of 15.4 %, 94.3 %, and 98.5 %, respectively.

Energy, exergy and economic analysis of ammonia-water power cycle coupled with trans-critical carbon di-oxide cycle

Energy, exergy and economic analysis of ammonia-water power cycle coupled with trans-critical carbon di-oxide cycle

Estudio comparativo de un ciclo transcrítico de dióxido de carbono alimentado por un único ciclo geotérmico flash en los modos de funcionamiento con/sin economizador

Renewable energy, particularly geothermal energy, is on the rise globally. It has been demonstrated that recovering heat lost during geothermal cycles is essential due to the inefficiency of these cycles. This paper pproposes a combined power generation cycle using EES software to model a single-flash geothermal cycle, and a trans-critical carbon dioxide cycle. The study compares the system's performance during its "Without Economizer" and "With Economizer" operational stages. The impact of the economizer on the system's output metrics, including the net power output, energy efficiency, and exergy efficiency, was examined. The results show that the "With Economizer" system's net power output increased from 451.3 kW to 454 kW. The energy efficiency difference between the two systems is based on the first law of thermodynamics, where the value ofthe "Without Economizer" system is 6.036%, and the "With Economizer" system is 6.075%. The system without an economizer had an exergy efficiency value of 26.26%, whereas the system with an economizer reached 26.43%, based on the second law of thermodynamics. Installing the economizer increased the total economic cost rate of the system from 0.225M$/Year to 0.2294M$/Year, which increased the product cost rate from 15.82$/GJ to 16.02$/GJ.

Performance analysis of a CO2 near-zero emission integrated system for stepwise recovery of LNG cold energy and GT exhaust heat

Combined cooling, heating and power (CCHP) system can further improve energy utilization efficiency while meeting diversified energy demands, and the rational use of the CCHP system is an effective way to alleviate the energy crisis. An innovative cascaded CCHP system based on the transcritical carbon dioxide cycle (TRCC) and organic Rankine cycle (ORC) has been proposed, which is designed to recover the cold energy of liquefied natural gas (LNG) and the exhaust heat from the gas turbine (GT), while achieving near-zero CO2 emissions. The simulation result demonstrates that the system achieves energy utilization efficiency, exergy efficiency and net electrical efficiency of 87.3%, 56.9% and 55.39%, respectively, with a CO2 capture rate of 79.2 kg/h under the design condition. Compared to the mentioned cogeneration systems that recover LNG cold energy and GT waste heat, the proposed system exhibits improvements in energy utilization efficiency, exergy efficiency and net electrical efficiency by 9.84%, 4.37% and 3.4%, respectively. The parameter sensitivity analysis reveals that increasing the pressure ratio of the TCO2 turbine and ORC turbine or reducing the air compressor feed temperature can improve the overall performance of the system. If the focus is solely on energy utilization efficiency and exergy efficiency, appropriately increasing the air compressor pressure ratio or reducing the gas turbine pressure ratio would be beneficial. The proposed system in the study is environmentally friendly and energy-saving, which especially suggests a direction for cold energy cascade utilization in LNG stations integrated with CCHP.

A new multi‐objective optimization of refrigeration cycles (Case study: “Optimization of transcritical carbon dioxide cycle”)

AbstractFor store and maintain products, ingredients, and other perishables at a safe temperature, there is a growing need for low‐temperature refrigeration systems. In this study, a new multi‐objective exergetic criterion is proposed for the optimization of refrigeration cycles, the conventional coefficient of performance (COP) maximization method results in high evaporator temperature, which is in contrast with the philosophy of the invention and design of refrigeration cycles. Thus, it is not a suitable platform for comparing different refrigeration cycles. This research aims to define a practical performance analysis parameter for designing and comparing refrigeration cycles. The novelty of this research is incorporating the impact of evaporator temperature into the COP concept. A performance comparison of the multi‐objective optimization is drawn with that of the maximum COP state on a transcritical carbon dioxide refrigeration cycle. According to the comparison, the evaporator temperature at the optimal state of multi‐objective exergetic optimization was 44 K lower than that of the maximum COP state, which demonstrates the excellent performance of the method. The results of the new multi‐objective exergetic optimization can be used to design low‐temperature evaporation refrigeration cycles. In the end, the flowchart of the suggested performance optimization is presented. Exergy of power at the optimal point of exergetic optimization is about 77% higher than the maximum COP. A comparison of the results obtained from maximum performance coefficient with optimal point of exergetic optimization suggests that the performance coefficient at optimum state of exergetic optimization is about 58% lower than the maximum COP.

Proposal and analysis of a novel CCHP system based on SOFC for coalbed methane recovery

To utilize the waste heat from coalbed methane, this study presents a novel solid oxide fuel cell (SOFC) system combined with a transcritical carbon dioxide cycle, lithium bromide absorption refrigeration cycle, ammonia vapor compression refrigeration cycle, and water heating cycle to provide power, cooling, and heating. An Aspen Plus model is developed to perform thermodynamic and exergy analyses, assessing system performance. The results indicate that critical parameters such as current density and operating temperature of the SOFC have a significant influence on the overall system. Increasing current density and air preheating temperature enhance thermal efficiency while raising the SOFC operating temperature reduces it. For the specified coalbed methane flow, the system achieves electrical efficiency, thermal efficiency, and exergy efficiency of 52.46%, 86.30%, and 75.58%, respectively. Additionally, the cooling capacity, power generation, and heat production are obtained as 1567.72 kW, 4879.1 kW, and 2476.43 kW, respectively. The SOFC system has the largest exergy destruction, accounting for 48.8% of the total exergy destruction, but the overall exergy efficiency remains at around 75%. The results illustrate that the proposed integrated system provides a high level of efficiency and reliability, thereby offering a new avenue for the efficient and rational utilization of CBM.

Multi objective optimization and 3E analyses of a novel supercritical/transcritical CO2 waste heat recovery from a ship exhaust

Waste heat recovery systems are a promising solution to reduce the overall energy consumption. These systems are capable of producing energy from both high grade and low-grade waste heat without producing any pollution. This paper proposes a novel waste heat recovery system installed on a ship that can produce power and cooling by supercritical/transcritical CO2 waste heat recovery. For this purpose, supercritical and transcritical carbon dioxide cycles are integrated in a special configuration to recover the highest amount of energy in the ship. To analyze the system, 3E analyses (Energy, Exergy, and Economic) are utilized. Then, to achieve the best performance, the most important and influential parameters have been optimized with the aim of increasing energy, exergy efficiency, and reducing the capital cost. Based on the obtained results, energy, exergy efficiency, and capital cost of the plant reaches 69.6%, 42.3%, and 2.5 M$ respectively in the best condition. Finally, at design condition, the system produces a net power of 9.061 kW and 19.522 kW of cooling.

Recurrent machine learning based optimization of an enhanced fuel cell in an efficient energy system: Proposal, and techno-environmental analysis

Real hybrid energy systems based on developing fuel cell (FC) technology are promising in addressing energy and environmental problems. Before looking at the research investigations, the earlier review studies are briefly examined to spot any gaps in the literature. In the present study, a novel scheme of fuel cells is introduced with higher efficiency and compatibility. The exhaust gases are then introduced to the transcritical carbon dioxide cycle for the production of more power and to extract heat from the intercoolers. The system is analyzed from the multiple objective functions aspect, and the net present value method is occupied for determining the system's payback period. The important design conditions are then put to the test to seek their effect on the overall system. The genetic algorithm is applied for the sake of optimization, and the efficiency is maximized while minimization of environmental impact and the cost of the system. The results indicate that maximum ηII and minimum of LCOP and ζ at the ideal point which equals to 73.8%, 0.24 $/MWh and 0.07 kg/kWh, can be reached correspondingly. Also, by changing the selling price of electricity from 0.19 $/kWh to 0.22 $/kWh, the net present value and the payback period reach 1329000 $ and 6.24 years, respectively.

Exergy analyses and optimization of a single flash geothermal power plant combined with a trans-critical CO2 cycle using genetic algorithm and Nelder–Mead simplex method

Compared with conventional fossil fuel sources, geothermal energy has several advantages. The produced geothermal energy is safe for the environment and suitable for meeting heating power needs. Because the hot water used in the geothermal process can be recycled and used to generate more steam, this energy is sustainable. Furthermore, the climate change does not affect geothermal power installations. This study suggests a combined power generation cycle replicating using the EES software that combines a single flash cycle with a trans-critical carbon dioxide cycle. The findings demonstrate that, in comparison to the BASIC single flash cycle, the design characteristics of the proposed system are greatly improved. The proposed strategy is then improved using the Nelder–Mead simplex method and Genetic Algorithm. The target parameter is exergy efficiency, and the three assumed variable parameters are separator pressure, steam turbine outlet pressure, and carbon dioxide turbine inlet pressure. The system’s exergy efficiency was 32.46% in the default operating mode, rising to 39.21% with the Genetic Algorithm and 36.16% with the Nelder–Mead simplex method. In the final step, the exergy destruction of different system components is calculated and analyzed.Graphical

Optimization of a Single Flash Geothermal Power Plant Powered by a Trans-Critical Carbon Dioxide Cycle Using Genetic Algorithm and Nelder-Mead Simplex Method

The usage of renewable energies, including geothermal energy, is expanding rapidly worldwide. The low efficiency of geothermal cycles has consistently highlighted the importance of recovering heat loss for these cycles. This paper proposes a combined power generation cycle (single flash geothermal cycle with trans-critical CO2 cycle) and simulates in the EES (Engineering Equation Solver) software. The results show that the design parameters of the proposed system are significantly improved compared to the BASIC single flash cycle. Then, the proposed approach is optimized using the genetic algorithm and the Nelder-Mead Simplex method. Separator pressure, steam turbine output pressure, and CO2 turbine inlet pressure are three assumed variable parameters, and exergy efficiency is the target parameter. In the default operating mode, the system exergy efficiency was 32%, increasing to 39% using the genetic algorithm and 37% using the Nelder-Mead method.

A combined cooling and power transcritical CO2 cycle for waste heat recovery from gas turbines

• A combined cooling and power cycle working with CO 2 is proposed for waste heat recovery from a gas turbine. • Efficiencies of the combined system and its COP are evaluated for three configurations (simple, split and cascade) versus different cycle parameters. • Although the split configuration has the highest net power generation at high and moderate heat source temperatures, in the case of low temperature waste heat from the gas turbine (less than 420 °C), net power of the simple cycle surpasses and the split cycle gives the lowest net power. • The split configuration yields the highest thermal efficiency between the three investigated configurations except at low condenser pressures. • The split cycle has a slight supremacy in heat recovery efficiency at intermediate and high gas turbine exhaust temperatures. This supremacy persists over all the investigated cycle parameters. • For low CO 2 mass fractions into the refrigeration part, cascade configuration has the highest COP. • For high CO 2 mass fractions into the refrigeration part, simple configuration has the highest COP. • The split cycle is the most efficient configuration regarding the total system efficiency. Hence, it can be selected as the candidate cycle configuration for further optimization in a future study. A transcritical carbon dioxide (T-CO 2 ) cycle is analyzed for waste heat recovery from a gas turbine. The cycle is proposed to produce combined power and cooling using carbon dioxide as a single pure working fluid. Simple, cascade and split cycle configurations are compared for power generation using a recuperator while a low-temperature loop is added for the cascade and split cycles. In a previous report in the literature the power generation part alone was presented for the three configurations and it was concluded that the split cycle can produce the highest power among the three systems. Here, the same configurations are studied combined with a compression refrigeration cooling effect with the same working fluid, and a parametric study is conducted. The power cycle is a T-CO 2 cycle which absorbs the waste heat from a gas turbine. The effect of different parameters like cooling load, splitters mass fractions, turbine pressure and condenser pressure are investigated and a comparison between the three configurations are demonstrated. It is shown that, for instance, in case of higher temperatures of gas turbine exhaust the split configuration has the highest net power production while using gas turbine exhaust flow of temperatures less than 420 °C the simple configuration produces the maximum output power. From the cooling perspective, for values of turbine inlet pressure higher than 222 bar, abs. the cascade cycle indicates the best cooling performance while the split one takes this position at lower turbine inlet pressures.

Thermo-economic analysis and optimization of a cascade transcritical carbon dioxide cycle driven by the waste heat of gas turbine and cold energy of liquefied natural gas

• A cascade transcritical CO 2 cycle is proposed to recover waste heat and cold energy. • The cascade transcritical CO 2 cycle is condensed by LNG at different pressures. • The effects of thermodynamic parameters on the system performance are studied. • The maximum exergy efficiency is 49.24% according to the optimization result. In this paper, a cascade transcritical carbon dioxide cycle is proposed to utilize the waste heat of gas turbine and the cold energy of liquefied natural gas (LNG). In the proposed system, the carbon dioxide of the bottom cycle and the top cycle are condensed at different pressures by LNG. Meanwhile, the LNG absorbs heat from carbon dioxide at different temperatures, leading to smaller temperature difference. The detailed models are established and the simulation results are discussed from the viewpoints of thermodynamics and economics. Under the design condition, the exergy destruction of the low-pressure condenser is the largest, followed by the high-pressure condenser. The investment cost of the high-temperature turbine is the highest. The exergy efficiency of the proposed cascade transcritical CO 2 cycle first rises then drops as the split ratio and the pressure of high-pressure condenser increase. Moreover, the system exergy efficiency would increase as the inlet temperature of high-temperature turbine rises and decrease as the pressure of low-pressure condenser rises. Finally, the optimization results indicate that the maximum exergy efficiency of the proposed cascade transcritical carbon dioxide cycle is 49.24%. The net power output of the optimal case is 15.53 MW, which is 6.14 MW higher than the reference system.

Transcritical carbon dioxide cycle as a way to improve the efficiency of a Liquid Air Energy Storage system

The article deals with the subject of energy storage. This important issue relates to the ongoing transformation toward renewable energy sources. Liquid Air Energy Storage (LAES) is a mechanical energy storage technology that is suitable for large-scale energy storage. The article presents a method to increase the efficiency of LAES by coupling it with the transcritical carbon dioxide cycle. To this end, the paper presents a numerical analysis of two Kapitza LAES systems with the transcritical CO2 cycle: in parallel and subsequent mode. In both cases, maximizing CO2 pressure contributes to greater overall efficiency. It is only profitable to direct residual heat to the CO2 cycle. In contrast, lowering the air temperature prior to expansion in hopes of providing a greater amount of heat to the CO2 cycle actually delivers worse results. Parallel system implementation can add 5–6% to storage efficiency, depending on other factors. In comparison, the subsequent system only adds some 3.5%–5% to storage efficiency.

Experimental demonstration of comminution with transcritical carbon dioxide cycles

A new comminution technology that can reduce energy consumption when compared to traditional grinding of rock is presented. The process is based on pulverization driven by transcritical CO2 cycles, resulting in tensile fracture inside the particle rather than compression from outside. Tensile strength of many rocks is approximately 10 times lower compared to compressive strength offering significant potential for saving energy. In this apparatus, comminution can occur over multiple cycles to enhance rock breakage without extracting and refeeding rock between cycles. The test rig depicts test conditions to capture and to recycle the CO2.Limestone is utilized as an example material in a lab-scale experimental apparatus. Within the apparatus, the temperature and pressure are raised to supercritical conditions. A rapid release of the CO2 into a decompression chamber results in an expansion of supercritical CO2 inside the pores and fractures rock from tension instead of compression. Results show a significant fraction of the limestone is comminuted in three consecutive CO2 pressure cycles. A majority of the resulting particles exhibit larger fragments from 5 mm to 13.2 mm. 6.2% of the feed material was directly transferred to fine material <300 μm without many intermediate progeny particles. Initial results indicate a larger ratio of the pressure before and after burst, and longer soak times aid pulverization. A single rock is also analyzed, where it is noted that breakage occurs along visible fractures, and this behavior is noted over consecutive cycles.

Experimental evaluation of a transcritical CO[formula omitted] refrigeration facility working with an internal heat exchanger and a thermoelectric subcooler: Performance assessment and comparative

The use of carbon dioxide in transcritical state has become one of the most used solutions to comply with the F-Gas directive and reduce greenhouse gases emissions from refrigeration systems at high ambient temperatures. For low-medium power units, the commonly used solutions to improve the efficiency such as the ejector, multiple compressor arrangements, mechanical subcooler, etc., add complexity and increase the cost of the refrigeration facility, which is not ideal for small units. In this low-medium power range, two technologies stand out to increase the performance of a carbon dioxide transcritical cycle: the internal heat exchanger and the thermoelectric subcooler. This study brings a complete research in which both solutions have been tested in the same experimental transcritical carbon dioxide refrigeration facility under the same working conditions. It focuses on the real performance of both systems and discusses the strengths and weaknesses of using an internal heat exchanger or a thermoelectric subcooler. The results show that the thermoelectric subcooler outperforms the internal heat exchanger in both the coefficient of performance and the cooling capacity while also being a more controllable and flexible solution.

Evaluation of the performance and economy for a hybrid energy storage system using hydrogen and compressed carbon dioxide as the energy carrier

A green concept of hybrid energy storage system with hydrogen and compressed carbon dioxide as the energy carrier has been proposed in this paper. The integration of the two energy storage methods leads to a hybrid efficient storage way, which can have higher energy density and lower pressure tank volume compared to the compressed carbon dioxide, and has higher energy storage efficiency compared with the hydrogen one. The ratio of the two energy storage is determined by the hydrogen consumption way. In this paper, the hydrogen fueled gas turbine with carbon dioxide as the working fluid (Allam cycle) is used for large amounts of the hydrogen consumption, and the mass flow rate ratio of hydrogen and CO2 is 0.0048 at the design point. The combined system can be used for inter-regional power dispatching, peak and frequency modulation and so on. A basic system form is firstly introduced, and the round trip efficiency (RTE) and levelized cost of electricity (LCOE) are 42.41% and 0.2075 $/kWh at the design point, respectively. In addition, two improved types are proposed. The effect of key parameters, including the CO2 compressor outlet pressure, the CO2 compressor inlet pressure and the CO2 mass flow rate, on the system performance is performed. The multi-objective optimization is also conducted. The comparison reveals that the improved form-I performs with a lower LCOE and a weaker RTE. In contrast, the improved form-II owns a better RTE but a higher LCOE. It can be concluded that the improved form-I can improve the economic performance of the energy storage system through the optimization of the compressed carbon dioxide high pressure storage subsystem. And the improved form-II can enhance the thermodynamic performance by adding the transcritical carbon dioxide cycle branch. Potential solutions to improve the system economic performances are also discussed and the results indicate that technology development, subsidies and electricity market transaction premium would be beneficial for the large-scale promotion of the system in practical.

Study on a near-zero emission SOFC-based multi-generation system combined with organic Rankine cycle and transcritical CO2 cycle for LNG cold energy recovery

This study proposes a near-zero emission SOFC based multi-generation system integrated with organic Rankine cycle and transcritical carbon dioxide cycle, and a LNG cold energy utilization system is also introduced in order to realize CO2 condensation and cryogenic capture. In the proposed system, the unreacted anode gas of SOFC is burned with pure oxygen instead of cathode gas by which it can provide the possibility for the follow-up CO2 capture at low energy consumption assisted by LNG cold energy utilization. The novel poly-generation system can realize the cooperative production of the energy (cooling, heating and power output), and the matter (condensate recovery and captured CO2). The energy and exergy analysis are performed to investigate the proposed system performance based on the established steady-state model. The results reveal that, under the design conditions, the thermal efficiency, net electrical efficiency and exergy efficiency of the proposed system achieve 90.99%, 55.01% and 53.07%, respectively. And the amount of CO2 captured, condensate recovery, and natural gas supply reach 5219.21 ton/year, 1324.83 ton/year and 4273.13 ton/year, respectively. Moreover, the exergy analysis shows that the exergy loss proportion of SOFC top cycle accounts for 47.3% of the total losses. Parameters analysis indicate that the electrical efficiency and the exergy efficiency are increased first and then decreased, and achieve the maximums at the SOFC inlet temperature of 554.4℃ and the operating pressure of 650 kPa, respectively. In addition, it is observed that the variation of steam-to-carbon ratio (STCR) has little effect on electrical efficiency and exergy efficiency, but has obvious effect on thermal efficiency. It is also found that the cooling, heating and power output are increased, but all the efficiencies are decreased as current density increases.