• Energy Research
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Abstract The industrial exhaust flue gas contains tremendous waste heat that cannot be efficiently recovered by conventional condensing heat exchanger. This paper proposes a novel full-open absorption heat pump for the total heat recovery of flue gas. The recovered heat is used for district heating. By applying direct-contact heat and mass transfer without solid transfer interfaces, the novel system can save considerable metallic tube or plate materials and therefore the initial investment can be reduced substantially. A prototype full-open absorption heat pump is developed and tested, achieving the COP (coefficient of performance) of 1.621 and the exit flue gas dew point of 36.2 °C at most. A detailed theoretical model in Eulerian–Lagrangian formulation is established, involving in conjugate heat and mass transfer and particle dynamics. The numerical simulation agrees well with the experiment results. On the basis of the validated model, three critical parameters, including excess air coefficient of the burner, moisture content of the objective flue gas and return water temperature of the district heating network, are selected to study their effects on system performances. As a controlled variable, especially, the excess air coefficient plays an important role by influencing the regeneration of the liquid absorbent in the generator. The full-open absorption heat pump outperforms the condensing heat exchanger by 19.7–178.1% in heat recovery capacity as the return water temperature increases from 40 to 55 °C.

In recent years, transient voltage instability occurs occasionally in large-scale AC/DC mixed receiving systems which may cause serious economic losses and adverse social impact. Therefore, how to evaluate transient voltage stability when the system suffers serious disturbances poses a great challenge for safe operation of modern power systems, hi this paper, firstly the mechanism of transient voltage instability in a typical receiving-end power system, i.e., Guangzhou power grid, is discussed based on in-depth analysis. Secondly, we propose a quantitative assessment method to determine the transient voltage stability of actual large-scale power grid. The key to the quantitative evaluation method is the definition of various voltage sag indexes based on the transient voltage stability criterion under large disturbances. Based on these well-defined voltage sag indexes, the various influencing factors of transient voltage instability have been identified, including the model of comprehensive load and the type of fault As a case study, the Guangzhou power grid is used to verify the proposed method. This huge receiving-end system is simulated with PSD-BPA and the voltage sag indices are worked out under different operating conditions and disturbances to evaluate its transient voltage stability and the crucial influencing factors. The simulation results demonstrate the effectiveness of the proposed method and indices for quantitative assessment of transient voltage stability of large-scale actual system. They also give an intuitive and quantitative measure of the influence of fault type and load model on transient voltage stability.

China is confronted with an unprecedented water crisis regarding its quantity and quality. In this study, we quantified the dynamics of China?s embodied water use and chemical oxygen demand (COD) discharge from 2010 to 2015. The analysis was conducted with the latest available water use data across sectors in primary, secondary and tertiary industries and input?output models. The results showed that (1) China?s water crisis was alleviated under urbanisation. Urban consumption occupied the largest percentages (over 30%) of embodied water use and COD discharge, but embodied water intensities in urban consumption were far lower than those in rural consumption. (2) The ?new normal? phase witnessed the optimisation of China?s water use structures. Embodied water use in light-manufacturing and tertiary sectors increased while those in heavy-manufacturing sectors (except chemicals and transport equipment) dropped. (3) Transformation of China?s international market brought positive effects on its domestic water use. China?s water use (116?80 billion tonnes (Bts))(9) and COD discharge (3.95?2.22 million tonnes (Mts)) embodied in export tremendously decreased while its total export values (11?25 trillion CNY) soared. Furthermore, embodied water use and COD discharge in relatively low-end sectors, such as textile, started to transfer from international to domestic markets when a part of China?s production activities had been relocated to other developing countries.

Abstract To study the concentration characteristics of mechanical vapor compression (MVC) technology on the wastewater concentration process, a single-effect MVC system for concentrating dimethylacetamide wastewater was investigated. The performance of the MVC experimental system was evaluated under different levels of distillation pressure and concentrations of the raw solution. We demonstrated that under conditions of atmospheric distillation (evaporating temperature was 100 °C), the COP and distilled water production rate of the experimental system reached 20.17 and 70.80 kg/h, respectively. In the distillation operating cycle, the DMAC solution was concentrated from 6% to 83.5%. In addition, when the system was under vacuum conditions (evaporating temperature was 55.8 °C), the COP and distilled water production rate were 5.44 and 18.2 kg/h, respectively, and the concentration of the DMAC dilute solution was only 0.2%.

Abstract How to increase clean energy utilization is a key issue in household energy consumption analysis aimed at alleviating air pollution and improving the health of residents. Clean energy substitution is a complex decision process between related stakeholders, and is affected by a combination of factors such as geographical location and household income. To evaluate the potential of clean energy promotion to contribute to better policy decisions and measures, an agent-based household energy consumption model is established to capture the group habits of different stakeholders and the impact mechanism of critical influential factors. Multi-layered structures including various types of households and energy consumption devices are modeled. The experimental results of several scenario analyses show that increased income, improved technology and subsidies from local governments can influence clean energy substitution in the household in various ways. These findings provide a better understanding of the energy cleaning process and decision-making support for governments.

According to the U.S. Department of Energy, about 40% of total energy is consumed on buildings in industrialized countries, among which 68% is electricity. Recently research shows that 20%∼30% of building energy consumption can be saved with optimized operation and management without changing building structure and hardware configuration of energy supply system significantly. Therefore, there is a huge potential for building energy savings through efficient operation.

Abstract The Accelerator Driven Subcritical Reactor System (ADS) has a strong ability to transmute minor actinides (MAs) and it has inherent safety because of its subcritical core. However, the removal of decay heat is a major problem for the ADS and the design of spallation target is still a difficulty. Therefore, this paper presents a design of gas-cooled ADS with passive safety to attain the good performance of removing decay heat and transmutation. For the design of the target, the helium-cooled tungsten target is decided to adopt, and it is modelled into the cone structure to strengthen the convective heat transfer. A series of numerical experiments have been made to determine the optimal parameters of the target using the MCNP and CFX code. In the design of core, the subcritical core is divided into fast neutron region which the MAO2 is placed in and thermal neutron region which the UO2 is placed in to improve the performance of the transmutation. Two methods are proposed in this paper for the thermal-hydraulic calculation in the steady-state analysis, and the results show its good thermal performance.

Abstract Identifying the appropriate amount of subsidy is crucial to spur the development of low carbon electricity technologies such as wind power that are currently not competitive with conventional coal-fired power on the basis of levelized cost. Though essential for formulating subsidy policy, most of the existing planning tools have not been tailored for policymakers, especially at the sub-national level. In this paper, we introduce an integrated renewable power planning (IRPP) model that is both practical and flexible. This model integrates resource databases, equipment databases and levelized cost calculation module to generate supply curves for wind and solar and evaluate potential subsidy to achieve a certain installation target. A case study focused on wind power planning in Fujian Province is performed. Under the wind power feed-in-tariff of 0.61 yuan/kWh, the generation can reach about 3.7 TWh, and total subsidy will be about 260 million yuan (including subsidies already paid to existing projects). Sensitivity analysis shows that this number will significantly increase if capital cost of wind is reduced or external cost of coal-fired power is internalized.