Abstract

The energy generation sectors in many countries around the world are experiencing a great transition period, moving away from fossil-based electricity to cleaner energy sources. Due to regulated emission limits and the integration of renewable energy sources, coal-fired power plants are heavily affected in terms of reduced operating hours and material life-time, lower efficiencies, higher operational expenses, and earlier retirement. By combining both literature review and analyzing real-time operational data from coal-fired power plants, this paper aims to provide an overview on: – The commercial and technological impacts of the energy transition in Europe (with a focus on Germany) – CO2 emission during stationary operations at two lignite-fired power plants. – CO2 emission during Start-up processes at a hard coal-fired power plant. – Potentials for reducing emission as well as lowering operational expenses.

Abstract

Potassium carbonate (K2CO3) is known to influence the kinetics of degradation of lignocellulosic biomass. Its effect has been studied in the literature on wood particles, but its catalytic effect on wood boards remains unexplored. In this work, beech wood blocks were impregnated with solutions having different concentrations ranging from 0 (demineralized water) to 0.012 M of K2CO3. After torrefaction at 300°C for 15 min, potassium impregnated samples were degraded up to 7.49 wt% (0.012 M) more than the raw one. The impregnation procedure and torrefaction changed the wood’s color, the desired aspect for construction. The increased HHV with torrefaction (around 24 MJ.kg-1 for 0.012 M impregnated samples) is attractive for energy production from end-of-life wood products. The obtained results validate the possibility of using potassium carbonate as a catalyst for wood torrefaction to reduce the torrefaction duration/temperature. Moreover, the torrefied wood has upgraded properties that make it useful for bioenergy production.

Abstract

The establishment of power system operation mode plays an important role in the safety, stability, economy and high quality operation of power grid. In order to enable the power grid operation mode staff can more quickly judge the advantages and disadvantages of the power flow of the operation mode according to the mode change and improve the flexibility and efficiency of the mode compilation, a fast evaluation method of the power flow based on the deep belief network is proposed. Firstly, considering the safety and stability guidelines of power system, the method establishes the evaluation index system of power flow state from three aspects of safety, stability and economy. Then the comprehensive evaluation method based on entropy-weight TOPSIS is adopted to comprehensively evaluate the evaluation indexes of multiple operation modes. Then, the index values of the above power flow evaluation system and the comprehensive evaluation results of entropy-weight TOPSIS are respectively used as the input and output data of the rapid evaluation model of power flow based on DBN. DBN algorithm based on RBM is used to extract deep features to complete unsupervised learning process, and then the supervised BP neural network is used as the conventional fitting layer to obtain the evaluation results. The flexibility and practicability of comprehensive assessment is effectively improved. In this paper, an example of IEEE39 nodes system is used to verify the effectiveness of the proposed model and algorithm.

Abstract

This paper presents a prototype of a pneumo-electromagnetic drive operating in reverse mode. Preliminary test results are presented. An example design is shown.

Abstract

With urban agglomerations becoming the core areas of economic development and carbon dioxide (CO2) emissions in China, the impact of the spatial structure of urban agglomerations, including monocentric and polycentric structure and reflecting the distribution of elements and resources among cities on CO2 emissions should be investigated. This paper empirically analyzed the impact of spatial structure of urban agglomeration on CO2 emissions and the inherent mechanism. The nightlight data is utilized to firstly evaluate the long-term evolution of the spatial structure of 19 urban agglomerations in China in terms of morphology. Then, econometric model is constructed, combining panel data of urban agglomerations during 2000-2018 to explore the relationship between spatial structure and CO2 emissions. What’s more, the mediation effect model is applied to trace the internal mechanism of industrial division. The results show that the polycentricity of the spatial structure of 19 urban agglomerations in China has increased since 2000, especially those on the coastal area. What’s more, polycentric spatial structure of urban agglomerations can help reduce carbon intensity, which is partly realized by promoting industrial division. Besides, spatial structure poses greater CO2 emission impact on core cities rather than non-core cities. Therefore, this paper could provide new insight into the realization of low-carbon urban agglomerations from the perspective of urban spatial planning and city positioning.

Abstract

With the increasing proportion of renewable energygeneration in the power system, its intermittence and volatility promote the development of Energy Storagesystems. Liquid Air Energy Storage (LAES) has attracted wide attention due to its many unique advantagesincluding high energy density, geographical-constraint free and a highly competitive capital cost. However, its efficiency is not high, mainly due to the lack of cold energy to cool the air, and the system’s liquid rate is low (about 70%). On the other hand, liquified natural gas (LNG) is an efficient and well-developed technology to store and transport natural gas after purification and liquefaction, which has a lot of cold energy that can be used to help cool the air. In this study, LNG is directly involved in the air-cooling process. According to the LNG inlet temperature, the recoverable energy cold in the discharging air is stored in different tanks. The thermodynamic model of the system is established, and the optimal mass flow rate of propane and LNG is studied. Performance of the system under different working conditions with or without LNG is analyzed. The result shows that it should increase the mass flow rate of propane on the premise of ensuring the temperature of the cold storage tank; The efficiency of the independent LAES system is still less than 51%, ignoring the disadvantages of high heat storage temperature under high energy storage pressure. However, under the optimal LNG supply mass flow rate, the recommended charging pressure is 8MPa, the energy release pressure is 16MPa, the liquid rate is up to 89.35%, and the system efficiency is 68.83%. In addition, optimal LNG flow rates under various operating pressures are provided to guide engineering practice.

Abstract

The growing interest in ecological energy sources is driving the dynamic development of energy storage. Increasing the efficiency of compressed air energy storage is associated with the efficiency of energy utilisation. This paper shows the possibilities of developing an energy utilisation component such as the compressed air engine. The authors present simulation results that show better engine performance when using a three-cylinder solution.

Abstract

Latent heat energy storage technology (LHES) has the advantages of high heat storage density, stable phase change temperature and easy process control. The development of high-performance phase change materials is crucial to the use of thermal energy storage. In this study, physisorption is used to create a variety of paraffin wax (PA) based composite phase change materials (PCMs), employing expanded graphite (EG) and aluminum nitride (AlN) nanoparticles as fillers. The thermal conductivity of composite samples at 25 °C is measured based on the principle of steady-state heat flow method. Thermal characterization of the composite PCM by differential scanning calorimetry (DSC) showes the effect of EG and nano-AlN on the specific heat capacity of paraffin. The thermal conductivities of the prepared PCMs are 6.4-11.8 times that of PA. This is a guiding meaning for the preparation of composite PCMs with high specific heat and thermal conductivity.

Abstract

A future building energy system is established with photovoltaic (PV) generation and hybrid storage system in a case in Hong Kong. The battery, electric vehicle (EV) and pump-hydro storage (PHS) system are considered. A technical feasibility study is conducted to assess the influence of different storage priorities. The PHS is shown to reduces the total energy efficiency by 7.16% at user side. The low self-sufficiency rate, 16.29% to 17.77% recommends the addition of remote renewable generation. The low usage rate of storage system, 31 to 58, annual equivalent battery cycle number emphasizes the need of grid charging.

Abstract

The current geopolitical situation and the Russian invasion in Ukraine have urgently increased the role of energy independence in national energy security. Nevertheless, the European Union, is still very dependent on imports of fossil fuels such as oil and natural gas, which are mainly sourced from neighboring Russia. Now more than ever, to accelerate Europe’s energy independence and transition to carbon neutrality, it is critical to restructure national energy infrastructures and promote the rapid development of local renewable energy resources. To understand whether the EU are ready to accelerate the decarbonization of their energy system by abandoning energy imports from Russia, it is necessary to assess what progress has been made so far in reducing net energy imports. In this study, Log-Mean Divisia Index (LMDI) decomposition analysis is used to examine the changes in net energy imports in the EU-27 during the period from 1995 to 2020. The change in net energy imports is measured by four main factors: changes in energy dependence, changes in energy intensity, changes in economic growth, and population. The results show that not only has no progress been made in reducing the EU’s energy import dependency, but the situation has actually worsened and become more unstable over the past five years.