Clean coal technology is a key way to ensure the energy security and sustainable development of China. Supercritical water gasification of coal is a representative clean coal technology, which can be integrated within thermal power plants. In this study, adapted layouts of power generation system based on supercritical water gasification of coal were proposed to further enhance the system energy efficiency. Models of adapted systems were developed by Aspen Plus, and their performance was simulated. The results showed that the efficient system layout increased the energy efficiency by 8.72%- pts to 48.24% in contrast to its comparison layout. This improvement is mainly due to the 40% decrease of exergy destruction in superheater of the systems through adaption, as well as higher inlet parameters of turbine.
The use of SF6/N2 or SF6/CO2 mixture gas as a potential alternative to SF6 has attracted wide attention due to the easy availability of N2 and CO2, stable chemical and physical properties, non‐toxicity, nonflammability, and non‐combustion. In this paper, the simulation study of the arc formation process in the circuit breaker is carried out from a microscopic point of view. The simulation is based on the gas dynamics equation considering the complex collisions between charged particles and neutral molecules and obtaining the time‐varying law of the micro‐parameters such as the electron density and average electron energy in the arc forming process of SF6/N2 and SF6/CO2 mixture gas. The results can help us understand the characteristics of the mixture gas arc from the microscopic level, and provide a theoretical basis for the design and manufacture of the new circuit breaker.
Hydrogen-based energy systems are a viable solution to perform long-term storage of excess intermittent renewable energy. However, such systems are rarely considered in energy system optimization. Moreover, whenever these technologies are considered, the model parameters are considered known and fixed, which can result in suboptimal designs, sensitive to uncertainty. To evaluate the inclusion of a hydrogen-based system in a global energy system and to address the uncertainty on its techno-economic performance, we performed an optimization under uncertainty of a solar-powered, grid-connected household, supported by batteries and hydrogen storage. This paper illustrates the effect of the hydrogen-based energy system on the uncertainty of the predicted levelized cost of electricity. The inclusion of the hydrogen system decreases the standard deviation of the levelized cost of electricity by 4.3 €/MWh (13%) at the expense of an increase in mean levelized cost of electricity by 100 €/MWh (28%). Consequently, despite the gain in robustness, including a hydrogen-based storage system in the considered urban area is not beneficial overall. Future works will focus on including remote areas, to fully exploit the gain in robustness induced by hydrogen-based storage systems.
A novel SOFC-MHR (metal hydride reactor)-Engine hybrid energy conversion system fueled with alternative fuels is proposed and modelled in this present study. The MHR is introduced into the hybrid system for H2 addition by waste heat recovery. The dynamic modelling is performed to investigate the transient response of the proposed hybrid energy conversion system. The results show that the SOFC has a relatively slow dynamic behavior while the engine has the fast dynamic behavior. Besides, the SOFC dominates the transient responses of the hybrid system because that the engine fuel directly comes from the FC off-gas. Therefore, it is found that the addition of H2 by MHR not only extends the system power output, but also improves the dynamics of the hybrid system due to the enhanced autonomy of the engine with fast transient response. When the H2 addition is χ=2.0, the hybrid system can quickly reach the stable power output within 5 s, indicating that the hybrid system presents superior dynamic behaviors and is promising for mobile applications.
The performance of simultaneous charging and discharging process of a thermal energy storage system is experimentally investigated in this study. The microencapsulated phase change material (MEPCM) is used as the energy storage medium. The different combinations of the inlet cooling/heating water flow rates are adopted when the PCM in the ESU is initially in solid phase and melted, respectively. During the experiment, the system shows a high heat transfer rate between the cooling water and the heating water due to the thermal enhancement by the carbon fiber. The final states of the ESU are different under the same working condition with different initial states. The results of this experiment shows a great potential of the system in the practical application scenarios where the request of heat exchange and energy storage needs to be both satisfied.
A dispatch method with synergy and interaction between integrated energy hub and users was put forward aimed at the problems of failure to consider the thermal storage characteristics of building envelopes and demand response subsidy mechanisms for users during the operation and dispatch of integrated energy hub. First of all, a building virtual storage model was established with the indoor air and building envelope as the main part of heat transfer through comprehensive consideration of influences of indoor and outdoor disturbances on thermal process, and a mathematical model of building virtual storage with equivalent storage and discharge power was put forward; secondly, a typical equipment composition structure of integrated energy hub with supply of cooling, heating and power systems and a multi-agent interactive transaction relationship among external power companies, integrated energy hub and users were established, and a stimulating demand response mechanism based on user subsidy was put forward; thirdly, an optimized economic dispatch model of integrated energy hub was established with the maximum earnings of power station as the target, containing external power purchase expenses, incomes through selling power to users, and subsidies and with the flexible comfort level of users as constraints, and the CPLEX solver was adopted to solve the problems; finally, the practicability and effectiveness of the expressed model and method was verified through examples.
An industrial furnace with a thermochemical heat recuperation (TCR) system by steam methane reforming is considered. A method for determining the TCR systems efficiency is proposed. The methodology is based on the determination of the heat recuperation rate. A distinctive feature of the method is taking into account the work losses due to flow-dynamic drag in a packed bed of a thermochemical recuperator. The total recuperated heat and the recuperated heat in the steam generator and the reformer as well as work losses due to flow-dynamic drag are calculated. It is established that the efficiency of the TCR system depends on the methane conversion and with increasing temperature, the efficiency of the TCR system increases. It is shown that work losses due to flow-dynamic drag do not have a significant effect on the energy balance in the TCR systems. It is established that the maximum recuperation rate is for 700°C and H2O:CH4=2.
Organic Rankine cycle (ORC) coupled with biomass combustion boiler is an appealing and promising technology for small scale combined heat and power (CHP) plants. The aim of this paper is to investigate thermodynamic analysis and economic assessment of biomass-fired ORC CHP system, especially from the perspective of pinch point location. The thermoeconomic model of bioenergy cogeneration system has been developed, in which the pressurized boiler hot water is worked as heat source for ORCs and the condensation heat can be fully utilized to supply domestic hot water. Results show that pinch point location from vaporization start point to preheating start point is observed with increasing boiler hot water temperature or decreasing evaporation temperature in evaporator. The pinch point location has slight influence on thermodynamic performance, while it has significant effect on economic assessment in this bioenergy system. The same optimal boiler hot water temperature with the specific evaporation temperature can be achieved in terms of total investment (INVtot), dynamic payback period (DPP) and profit ratio of investment (PRI).
In this paper, molecular dynamics method was employed to investigate the wetting and electrowetting behaviors of nano-droplet of ionic liquid on a solid substrate with different wettability. The results show that the anion and cation groups are distributed in layers above the wall. The static contact angle decreases obviously when epsilon increases from 0.1 to 0.6 On the hydrophobic surface (ε=0.1), the droplet shows an asymmetric wetting when the imposed vertical electric field is in positive and negative direction. While on the hydrophilic surface (ε=3.0), the wetting of ILs droplet becomes nearly asymmetric because the strong solid attraction tend to dominate the wetting process. Through analyzing the distribution of coarse particles, it’s found that the asymmetric wetting is caused by the fact that the diffusion of cations on the substrate surface is stronger than that of anions.
The simulation and experiment of two 400 W low-speed direct-drive permanent magnet synchronous generators (PMSGs) installed in a Floating Kuroshio Turbine (FKT) was implemented. We used ANSYS Maxwell design tool to design the 400 W low-speed direct-drive PMSG and simulate the interior magnetic field at different conditions. The test of FKT was carried out in the towing tank in National Taiwan University. The result shows generated power is more than 800 W in direct current (DC) at 1.5 m/s flow rate. The energy conversion efficiency of the PMSG measured from the testing platform is about 0.85. The power coefficient of FKT is about 0.4. It means FKT has high efficiency and stable power output.