Abstract

The low-melting alloys composed of Sn, Bi, Pb, Cd, In, Ga and Sb show good application prospect in phase change heat sink and heat storage system. Thereby, a well understanding of the melting behaviors of low melting-alloys is crucial to design efficient thermal heat storage appliances or heat sinks. In this paper, a one-dimensional enthalpy-based model is established to explore the melting process of an alloy bar. As the results, the effect of mushy zone temperature range which can be reflected by phase change temperature interval and average phase change temperature is discussed on the motion of mushy zone. The results indicates that the increase of surface temperature is significantly delayed by the release of latent heat. Moreover, the duration of mushy zone gradually increases along the vertical direction, which attributes to the increase of thermal resistance. Reducing the average temperature of mushy zone instead of increasing the temperature interval is an effective way to improve the thermal performance of alloy. Specifically, the effective protection time increases 22% with the average temperature decreases from 70 to 50 oC. The calculated results provide theoretical guidance for selecting the working medium of the thermal heat storage appliances or heat sinks.

Abstract

Zero emissions of waste gas and water from coal-fired power plants are one of the pathways for cleaner electricity production in China. It is expected to achieve low-cost zero discharge of flue gas desulfurization (FGD) wastewater by applying multi-effect distillation (MED) or multi-stage flash (MSF) technologies and matching different heat sources from the power plant. In the present work, four different integration schemes were proposed for FGD wastewater recovery by concentration and deep desalination. The thermo-economics of different schemes were analyzed in terms of gained output ratio (GOR) and energy cost. The results showed that the cost of auxiliary steam driven MED could be lowered by the integration of thermal vapor compression (TVC). The GOR of MED could be increased by 10%-100% while the energy cost was reduced by approximately 10%-50%. In contrast, the pump electricity consumption should be reduced when MED was driven by flue gas. Moreover, the MSF distillation had stronger adaptability to salt concentration than MED. The energy cost of flue gas driven MSF could be remarkably reduced by lowering the flash temperature difference.

Abstract

Handling the variability of renewable energies is a key for power systems towards de-carbonization and sustainability, and hybrid power system (HPS) is a promising solution for enhancing power generation by aggregating various energy resources. Meanwhile, the development, implementation and influence of variable speed pumped storage technology has been increasing all over the world. In this paper, a preliminary study on dynamic performance of variable speed unit (VSU) for hybrid photovoltaic-pumped storage power system is conducted. The main method here is numerical simulation based on timescale of seconds, by adopting MATLAB/Simulink. First, a mathematical model of the HPS is established, and a VSPSP and a photovoltaic power system are included. Then, the dynamic performance of the VSU in the HPS is simulated and discussed based on a quantitative comparison between the VSPSP and the FSPSP. The focus is to assess the two aspects: combined power output of the HPS and actuator movement. The results demonstrate the capability and advantage of applying the VSPSP for balancing photovoltaic power variation. Meanwhile, there is no fundamental distinction between the VSU and the fixed-speed unit (FSU) for the regulation movements that indicates wear and tear, despite the physical process and mechanism of active power regulation are different for the two types of pumped storage unit. The model and results could provide understandings on the detailed dynamic behaviors of HPS with VSPSP and photovoltaic power systems, for further supporting the operation and performance evaluation of HPS with multiple renewable energies.

Abstract

In this work a hardware-in-the-loop simulator of a novel micro combined heat and power system is discussed and its potential presented. The plant under investigation consists of a concentrated Linear Fresnel Reflectors solar field, a 2kWe/18kWt Organic Rankine Cycle unit and an advanced latent heat thermal energy storage tank equipped with reversible heat pipes.
Because of the complexity of the integrated system, various control strategies are requested for its optimized operation. However, the evaluation of the different control logics and optimizations in real-time can be complex due to technical and reliability issues. Hence, a hardware-in-the-loop simulation framework based on Matlab/Simulink has been developed and validated to assess the dynamics operation of the different subsystems with varying control strategies and set-points. As an example of the validation procedure, the use of the simulator is illustrated by means of the switch among the different operation modes of the plant with varying ambient conditions. The scientific approach proposed can be extended to any function block of the developed controller.

Abstract

Microgrids and peer-to-peer (P2P) energy trading are important technical and market arrangements to deal with the challenges brought by the increasing penetration of distributed energy resources (DERs). In this paper, a P2P energy trading hierarchy was proposed for microgrids in distribution networks. Hierarchical P2P markets were established for facilitating the energy trading between prosumers and consumers. A two-stage matching method, including bilateral and pool-based matching, was proposed to match the generation and demand in the hierarchical P2P markets. An extended Mid-Market Rate (MMR) pricing method was further proposed for clearing the hierarchical P2P markets. The proposed hierarchy and matching and pricing methods were tested on a distribution network adapted from a practical network in Neath Port Talbot, Wales, UK. Simulation results demonstrate the operation of the proposed hierarchy, and indicate that the proposed hierarchy, with the proposed matching and pricing method, has the potential to bring greater social welfare compared to the conventional market paradigm.

Abstract

Accurate capacity estimation is of vital importance for lithium-ion battery management. In this paper, an adaptive battery capacity estimation method based on incremental capacity analysis (ICA) is proposed. First of all, the second-order central least squares method is employed to smooth the charging data and obtain the incremental capacity (IC) curve. Then some battery experiments, including the complete charging and partial charging, are designed and conducted. For the complete charging, the relationship between the features of IC curves and battery capacity fading is investigated. For the limitation of ICA on partial charging, the correction method considering the charging initial SOC and battery aging status is proposed. Finally, the algorithm framework of the adaptive capacity estimation based on ICA is put forward.

Abstract

Amorphous silicon (a-Si) have a lower thermal coefficient, but the electrical performance is undermined by the fact of Staebler-Wronski (S-W) effect. Study on the effects of temperature on a-Si cells shows that a-Si cells can obtain higher electrical output at higher operating temperatures. This property makes a-Si cells more suitable for photovoltaic/thermal (PV/T) system where the operating temperature can easily reach higher level. At present, a-Si cells have attracted less attention in the PV/T application, but are promising photovoltaic (PV) materials for PV/T system. Research on the effects of temperature on a solo a-Si cell is already available, but the long-term impact on the a-Si PV/T system is still lacking. In a PV/T system, the operating temperature not only affects the electrical and thermal performance, but also the technical and thermodynamic reliability. To investigate the effect of temperature on the performance of a-Si PV/T system, long-term outdoor experiments of two identical a-Si PV/T systems operating at medium temperature (60°C) and low temperature (30°C) have been conducted from December 2017 to June 2019. At the initial phase of the long-test test, the electrical efficiency of the a-Si PV/T system operating at 30°C is 6.14%, which is much higher than that at 60°C (5.69%). During the long-term operation, both the electrical performances at 30°C and 60°C show an obvious download trend owing to the S-W effect. The initial difference in the electrical efficiency between 30°C and 60°C is 0.47%, while the gap eventually narrows to only 0.13%. In the past year and a half, the two a-Si PV/T systems operated stably without significant degradation in thermal and electrical performance. Through the long-term performance monitoring at different operation temperatures, it is demonstrated that a-Si cells are suitable for the PV/T application.

Abstract

Effectively treating industrial SO2 emissions depends on the synergy of different factors from the industrial SO2 generation source to the end of treatment. This study proposes a multi-region decomposition and attribution analysis approach to analyze the contributions of SO2 emissions treatment. The approach can decompose industrial SO2 emissions into six specific driving factors, including three whole process treatment (WPT) dimensions (i.e. source prevention, process control, and end-of-pipe treatment). This provides more detailed information about each factor’s treatment effect from both temporal and spatial perspectives, and the contribution of each region to the key driving factors. The empirical study across 30 regions in China using data from 2005-2015 shows that the end-of-pipe treatment is the dominant dimension for decreasing industrial SO2 emissions, of which Shandong, Inner Mongolia and Guangdong are the main contributors. The energy structure is the main factor promoting industrial SO2 emissions reduction in the source prevention dimension. The treatment emphases are different among regions, and regions can be classified into four categories. Based on the empirical results, this paper identifies the policy implications of promoting China’s industrial SO2 emissions reduction.

Abstract

Durability is a major issue against the commerciali-zation of proton exchange membrane fuel cells (PEMFC). Several mechanisms play an important role on the deg-radation of the cathode catalyst layer (CCL) by deterio-rating the transport properties of reactants in the CCL mainly. A pseudo three-dimensional (P3D), two-phase, and non-isothermal model is used to study the effects of cell degradation on transport properties of the CCL. Ac-curacy of the model is verified by comparing the polari-zation curves from the model with the experimental ones reported in the literature. The model is used to investi-gate the effects of CCL transport properties and agglom-erate parameters on cell performance. Results demon-strate that the cell performance is improved for thinner ionomer film around agglomerates, smaller agglomer-ates, higher exchange current density, lower transport resistance and higher proton conductivity of the CCL. The transport parameters of the CCL are varied to fit the po-larization curves to the experimental ones for an acceler-ated stress test. It is found that the transport resistances increase exponentially with the carbon loss in the CCL.

Abstract

Process simulation with stoichiometric mass, energy and exergy balance analysis of a pilot bio-light olefin production facility via gasification and methanol synthesis from forestry residues were investigated using Aspen Plus software. The mass yield of the process was 0.127kg light olefins per kg dry feedstock, which was comparable to the current status for biofuel production. 40.7% of potential energy of the forestry residue feedstock leaves as bio-light olefin, together with 2.33% as electricity export. The exergetic analysis of the whole process indicated that 22.6%, 22.2% and 11.5% of feedstock exergy were irreversible lost in the boiler/turbogenerator, gasifier and light olefin separation. And the exergetic efficiency of light olefins was 32.1%. The calculation procedure and balance evaluation criterial presented offered a valuable theoretical basis for improving process performance for bio-light olefin production application.