Results 1 - 10 of 12
Results 1 - 10 of 12. Search took: 0.016 seconds
|Sort by: date | relevance|
[en] Highlights: • Four performance indexes of constant-sliding mode are the best. • Cooling capacity of constant-sliding mode is the strongest. • The exergy destruction of air storage chamber is the largest. • Three modes have similar variation tendencies of parameters of air storage chamber. - Abstract: The tri-generative system based on advanced adiabatic compressed air energy storage can simultaneously provide cooling energy, heating energy and mechanical energy. In order to study the discharge characteristics, three operation modes of expanders, which contain constant pressure, constant-sliding and sliding pressure, are proposed in this paper. By utilizing the numerical simulation method, the performance difference of three modes is compared with each other. The results show that four performance indexes of constant-sliding mode are all the biggest, which are respectively cycle efficiency 40.55%, thermal efficiency 80.06%, exergy efficiency 48.45% and exergy density 4.071 × 106 J·m−3, and cooling capacity of it is also the strongest, 8.386 × 109 J, among the three operation modes. Air storage chamber has the largest exergy destruction. Operation process of air storage chamber is similar for three operation modes. Meanwhile, the effects of heat exchanger effectiveness, ambient pressure and air storage chamber model on system performance are also investigated.
[en] This report documents findings from the Hybrid Systems Task Force of the U.S. Department of Energy's (DOE) Geothermal Technologies Office (GTO) Geothermal Vision Study (GeoVision Study). The GeoVision Study projects and quantifies the future electric and nonelectric deployment potentials of geothermal technologies within a range of scenarios in addition to their impacts on U.S. jobs, the economy, and environment. The Hybrid Systems Task Force is one of seven task forces within the GeoVision Study with the others being Exploration and Confirmation, Potential to Penetration, Thermal Applications, Reservoir Maintenance and Development, Institutional Market Barriers, and Social and Environmental Impacts. A summary of the study is captured in DOE’s report, GeoVision: Harnessing the Heat Beneath Our Feet. The Hybrid Systems Task Force investigated geothermal hybrid systems that have potential to increase the utilization of geothermal resources and/or decrease the costs of geothermal power generation. Applications evaluated include: hybrid thermal power generation in which geothermal energy is coupled with solar or fossil heat sources; use of geothermal energy to provide process heat for thermal desalination or CO2 capture from fossil power plants; analysis of compressed air energy storage augmented with geothermal energy; as well as an assessment of potential mineral recovery from geothermal brines. This report additionally discusses areas of research and development that should be pursued to enhance the ability of geothermal hybrid systems to provide valuable benefits in operational flexibility, reduction of project risks, increased energy security, and the ability to recover critical and strategic materials.
[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[en] Highlights: • Thermodynamic analysis is presented for a LAES system combined with packed bed units. • The LAES system round-trip efficiency is in the range 50–62%. • Cold box inlet temperature and discharge pressure have significant influence on system performance. • LAES system has smaller air storage volume and higher ASED compared with A-CAES system. - Abstract: Energy storage is a key technology required to manage intermittent or variable renewable energy, such as wind or solar energy. In this paper a concept of an energy storage based on liquid air energy storage (LAES) with packed bed units is introduced. First, the system thermodynamic performance of a typical cycle is investigated and temperature distribution in cold boxes is discussed. Then, the effects of inlet temperature of cold boxes, charge and discharge pressures on thermal behaviors of LAES system are analyzed, as well as the system round-trip efficiency. Finally, an overall comparison between this LAES system and an adiabatic compressed air energy storage (A-CAES) system is conducted. The system could achieve a round-trip efficiency in the range 50–62% depending on the values of process conditions. The system round-trip efficiency decreases with the increase of cold box inlet temperature, and increases with the rise of charge and discharge pressures. Although the round-trip efficiency of the present LAES system is a bit lower than the A-CAES system, however, the air storage volume decreases and the air storage energy density (ASED) increases remarkably for the same operational conditions. The main conclusions draw from this work is beneficial for future LAES development in particular the combination with the packed bed units and the fit with the requirements for large-scale energy storage.
[en] Highlights: • A grid-connected CCHP system with CAES and hybrid refrigeration is proposed. • A multi-objective assessment and optimization is presented. • Each component capacity of the CCHP system is determined by optimization. • A sensitivity analysis is conducted by the key parameters of the system. • Performance comparison with conventional CCHP system has been done. - Abstract: As one of attractive technology of energy conservation, combined cooling, heating and power (CCHP) system has brought about widespread attention. However, the variability of users demand has limited the application of CCHP system. To ensure stable and efficient operation, the compressed air energy storage is considered to be integrated with CCHP system. A grid-connected CCHP system with compressed air energy storage (CAES) and hybrid refrigeration is proposed in this paper. The power from grid is stored in CAES at off-peak time and released at on-peak time. The hybrid refrigeration system including LiBr absorption chiller and electric compression refrigerator provides cooling load to users. A multi-objective assessment and optimization synthetically considering energy, economy and environment are presented. The multi-objective indicator used as objective function to optimize each component capacity of the proposed CCHP system. A sensitive analysis of key parameters and performance comparison with conventional CCHP system have been carried out. The results shows that when the capacity of gas turbine is 691 kW, the comprehensive performance of the proposed CCHP system is the optimal performance. The power price, natural gas price, compression ratio and turbine inlet temperature of CAES have great influence on the performance of the proposed CCHP system. Meanwhile, the multi-objective indicator’s value of the proposed CCHP system is more than conventional CCHP system 4.85%.
[en] Highlights: • Techno-economic analysis is performed on a solid oxide electrolyzer cell. • Electrical and thermal energy of the electrolyzer is provided by dish collectors. • ORC system is used to recover energy from electrolyzer outlet streams. • Aperture diameter of dish collectors considerably affect the system performance. • Higher temperature of the cell benefits the system thermo-economically. - Abstract: Hydrogen is considered as one of the best alternatives for fossil fuels, especially when it is produced using renewable energy resources. In this paper, dish collector is used to provide the required energy of a solid oxide electrolyzer cell (SOEC) to produce hydrogen. Since dish collectors operate at high temperature, they would be an ideal match for high temperature electrolyzers. These electrolyzer cells need both thermal and electrical energy to produce hydrogen. A compressed air energy storage (CAES) system is used to produce electricity. To reduce its fuel consumption, it is combined with a dish collector. Another dish collector is also used to produce thermal energy. To analyze the system, both thermodynamic and economic analyses are conducted. The results showed that the system could produce 41.48 kg/day hydrogen. It is shown that efficiency of the power cycle and the electrolyzer cell is equal to 72.69% and 61.70%, respectively and levelized cost of hydrogen is 9.1203 . To study the effect of key parameters on the system performance, sensitivity analysis is performed. It was concluded that maximum and minimum pressure of air cavern in the CAES system have the highest effect on the levelized cost of hydrogen. Also higher operating temperature of the electrolyzer cell benefits the system both thermodynamically and economically.
[en] Highlights: • Integration of CAES with trigeneration characteristics enriches a CCHP system’s operation mode. • Integrated design method can solve operation mode uncertainty introduced by renewable energy. • Active storing strategy for CAES exhibits significant superiority in peak sheaving and efficiency increase. • Novel algorithm C-NSGA-II provides accurate and efficient solutions for the multi-objective optimization model. - Abstract: The inherent characteristics of renewable energy, such as highly random fluctuation and anti-peak, are essential issues that impede optimal design of a combined cooling, heating and power (CCHP) system. This study presents a novel hybrid CCHP system integrated with compressed air energy storage (CAES). The operation mode of the new system is enriched by the trigeneration characteristic of CAES when compared with a traditional CCHP system. Additionally, an integrated design method based on a tri-level collaborative optimization strategy is proposed for the new scheme. An active storing strategy is introduced to maximize the utility of the superiority of CAES for peak sheaving and efficiency increase. Thus, a novel algorithm based on a hybrid algorithm of Non-Dominated Sorting Genetic Algorithm-II and Multi-Objective Particle Swarm Optimization is employed to solve the multi-objective optimization model with the aim of minimizing the total cost and emissions. A case study shows the effectiveness of the above methods. The implementation of the study fundamentally improves the overall energy utilization degree and the ability for renewable consumption to thereby provide a guiding principle for CCHP system design.
[en] Highlights: • A high temperature PTES (HT-PTES) is proposed based on an electric heater. • The energy storage density of HT-PTES is more than twice that of PTES. • When combined with ORC the performance of HT-PTES improved significantly. • A novel parallel ORC is proposed to recover the heat at high temperature. • HT-PTES combined with parallel ORC is the most promising system in five types of storage systems. - Abstract: Pumped thermal electricity storage (PTES) using packed bed is an attractive large-scale energy storage technology. The performance of conventional PTES is limited by the existing technology of compressor, such as low isentropic efficiency and cannot bear high temperature. In this work, a high temperature PTES (HT-PTES) based on an additional electric heater is proposed to enhance the energy storage capacity of PTES. Waste heat, which produced due to the irreversibility of heating, compression and expansion process of both PTES and HT-PTES, is recovered by the organic Rankine cycle (ORC) to generate power. Air and argon (Ar) are investigated as working fluid for PTES and air is selected due to its high thermal performance and economy. Five types of PTES combined with ORC system namely, PTES, HT-PTES, PTES + ORC, HT-PTES + ORC and HT-PTES + parallel ORC are investigated based on transient analysis method. The simulation results show that combined with ORC is an effective approach to improve the round trip efficiency (RTE) of both PTES and HT-PTES. In the five types of combined systems, the HT-PTES + parallel ORC is considered as a more promising large-scale energy storage technology which advantages can be illustrated as follows: (1) it with an acceptable RTE of 47.67%, which is 5.68% higher that of HT-CAES and is only 2.46% lower than the maximum RTE of the five types; (2) it shows an appropriate operating pressure, which are 1.05 MPa for HT-PTES subsystem and 12.20 MPa for ORC subsystem (significantly lower than that of 31.2 MPa for ORC in the HT-PTES + ORC); (3) it presents a considerable energy storage density of 218.69 MJ/m3, which is more than twice that of PTES + ORC (88.14 MJ/m3).
[en] Highlights: • A novel isobaric A-CAES system based on volatile fluid has been proposed. • Waste heat has employed to make IA-CAES more efficient and stable. • Proposed IA-CAES is more efficient and capacity than A-CAES. • CO2 is selected as volatile fluid for its environmentally properties and high saturation pressure. • Mixtures contain CO2 are investigated to enhance the working temperature range of IA-CAES. - Abstract: Adiabatic compressed air energy storage (A-CAES) is regarded as a promising and emerging storage technology with excellent power and storage capacity. Currently, efficiencies are approximately 70%, in part due to the issue of exergy losses during the throttling of compressed air. To increase the performance of the system, a novel isobaric adiabatic compressed air energy storage (IA-CAES) is proposed on the base of volatile fluid. The air storage vessel is divided into two parts by a piston, one part for air storage and the other has introduced into suitable volatile fluid. The waste heat is utilized to keep the volatile in a desirable pressure in discharging process, which impairs the effect of ambient temperature on pressure of volatile and makes the IA-CAES system stable. CO2 is selected as the pure volatile fluid own to its environmentally properties and high saturation pressure, while the IA-CAES system based on the CO2 can work in the mid and high latitudes only, due to its low critical temperature (304.13 K). 3 binary mixtures namely CO2/HC-600, CO2/HFC-32 and CO2/HFO-1234ze(E) are investigated to improve the critical temperature of CO2, trends to adapt to a wide range of ambient temperatures for IA-CAES system. The thermodynamic analysis including energy analysis, exergy analysis and the parametric analysis are evaluated by using steady-state mathematical model and thermodynamic laws. The calculations show, when CO2 is selected as the pure volatile fluid and the ambient temperature is higher than 288.15 K (15 °C), the average of total exergy efficiency (TEE) of IA-CAES improves more than 4% compared with that of A-CAES. When the waste heat is considered as free, the round trip efficiency (RTE) improved more than 6% and power capacity increased by more than 49% compared to the conventional A-CAES system. The CO2/HC-600 mixture with the compositions 0.85/0.15 has been proposed as the mixture volatile fluid. Compare with the conventional A-CAES system, the RTE and discharge time improved 6.26% and increased by 56.44%, respectively. Meanwhile, a parametric analysis is also carried out to evaluate the effects of several key parameters on the system performance of the IA-CAES systems.
[en] Highlights: • The novelty of this research is using PCM microcapsules for thermal storage. • PCM Microcapsules absorb and release the compression heat at higher rates. • Air and tank wall temperatures during compression are predicted successfully. - Abstract: Compressed air energy storage is a useful means of storage since the stored compressed air can be used at any time as a source of mechanical energy for power production. However, if the heat generated during compression is not utilized, the process efficiency will be low, and consequently, additional heat is required to avoid frost formation during the expansion process. The generated heat during compression can be stored in the form of sensible heat in the wall of the high-pressure tank at an elevated temperature. However, this method is undesirable due to (1) less air can be compressed at higher temperatures and (2) heavy insulation would be required to prevent heat loss to the environment over extended time. A solution to this problem is to use Phase Change Material (PCM) which has a melting temperature close to ambient, and hence the heat could be stored as latent heat of melting. PCMs have low thermal conductivity and hence requires to have large contact area with the compressed air so as to be able to release its latent heat rapidly during rapid expansion. This could be achieved through the use of microencapsulated PCM, which provides very large surface area. In this work, a high-pressure tank (2 L, 200 bar) was used for air storage while the commercial microcapsules; Micronal® DS 5038X was used as the latent heat storage material. Both theoretical simulation and experimental measurements made on the system show that the use of PCM microcapsules reduces the maximum increase in air temperature from approximately 45 °C to 27 °C (150 g, Micronal® DS 5038X) during charging. While during discharging, the maximum decrease in temperature was reduced from 48 °C to 28 °C, which prevented air temperature from dropping to below 0 °C.