Sustainable urban energy system is an important support and driving force for the high-quality development of urban economy and society. In the context of addressing climate change and energy transformation, this paper summarizes the stylized facts of urban and energy system evolution. A sustainable urban energy system analysis framework is proposed to analyze the logical framework of the energy system from the physical, information, and value layers. Further, this paper proposes a comprehensive indicator system for quantitatively evaluating the degree of coordination between urban development and energy systems, and provides a method for assessing the comprehensive benefits of sustainable urban energy systems.
Gas hydrate, as an effective method for Carbon dioxide (CO2) capture, is facing the problem of the slow kinetics associated with hydrate formation. Adding promoters such as tetrahydrofuran(THF) and sodium dodecyl sulfate(SDS) has become a good solution to promote the formation. In this paper, the formation process of CO2 hydrate in the presence of 5.56mol% THF with and without 500ppm SDS has been studied combined with morphology. The experiments are carried at the temperature from 279K to 283K and the pressure of 3Mpa. The results show that the combination of THF and SDS has a better effect than adding THF alone. And it provides morphological changes during the formation process. When ΔT≤10K, the hydrates with needle-like morphology are observed and when ΔT>10K, there are dendrite-like crystals.
Large-scale wind farm has become an important factor affecting the transient stability of power system. In view of the lack of theoretical research on the transient power angle stability of multi-machine system connected with wind farm, this paper proposes a method to analyze the transient power angle stability of multi-machine system with doubly-fed induction generator (DFIG) based wind farm. By modifying and contracting the bus voltage matrix, thus the influence of wind farm on the mutual synchronization between synchronous generators is quantified to the variation of electrical distance between synchronous generators. Furtherly, according to the extended equal area criteria, the relation between the equivalent mechanical power of the system and wind farm’s power output or access position is derived, and finally the influence regularity of wind farm access location on transient stability of practical multi-machine power system is revealed, which provides a theoretical guidance for the scientific configuration of wind farm considering the LVRT scheme and access location synthetically. In simulation, the variation of electrical distances between synchronous generator nodes caused by different DFIG location is analyzed, and the power angle variation in the cases of two LVRT schemes of DFIG at different grid connection point are simulated and compared to verify the validity of proposed method.
Large-scale centralized charging of electric vehicles is likely to cause congestion phenomena such as line overload and voltage drop. A scheduling optimization scheduling strategy for distribution network congestion management considering electric vehicles charging load is proposed. Establish a multi-objective optimization model of three stakeholders including grid center, electric vehicle aggregator and electric vehicle user, and design the objective function according to their actual operating conditions. The non-dominated sorting genetic algorithm-II (NSGA-II) is used to solve the Pareto non-dominated solution set, and the Topsis method is used to determine the optimal solution. The case analysis part of the article proves that the proposed strategy can eliminate congestion by comparing the response results before and after optimization. The cost-benefit analysis proves that the strategy can reduce the running cost and increase the profit to some extent.
With the continually large-scale exploitation and utilization of renewable energy, China, especially in Western China, has faced serious hydropower, wind power and solar photovoltaic (PV) power curtailment difficulties since 2011. Especially in 2016, the amount of hydropower, wind power and solar PV power curtailment peaked. This paper summarizes the reasons for renewable energy power curtailment from four aspects of energy flow, and emphatically analyses the integrated multi-energy system (IMES) solution to reduce renewable energy curtailment. Statistical results show that these countermeasures achieved success in 2017 and 2018. Then, Longyangxia hydropower-PV integrated multi-energy project is used to prove the feasibility of IMES to reduce renewable energy power curtailment. And the successful case provides reference and guidance for the promotion of IMES in other areas of the nation.
In order to understand in depth that Diesel/Methanol Dual Fuel (DMDF) could gain ultra-low emissions and high thermal efficiency, P-V map and φ-T map were analyzed at full load @1660 r/min. Based on the analysis of P-V map, the reasons for the increase in thermal efficiency at DMDF mode are as follows: First, the effective work of DMDF mode reduced at DMDF mode. Then, methanol evaporated in the intake manifold and cylinder will absorb large amount of heat, which will achieve waste heat recovery; Finally, the energy carried away by the exhaust gases is reduced, which is due to low exhaust temperature.
In DMDF mode, the intersection of φ-T map and NO generation region is obviously reduced, compared with the diesel mode. Meanwhile, φ-T map of DMDF mode is not covered the highest NO generation rate region. This is the reason of achieving ultra-low NOx emissions. The φ-T map of DMDF mode avoids soot generation regions at CA05 and CA50. This is the key to achieve ultra-low soot emissions.