Frontiers in Energy

ISSN 2095-1701

ISSN 2095-1698(Online)

CN 11-6017/TK

Postal Subscription Code 80-972

2018 Impact Factor: 1.701

   Online First

Administered by

, Volume 13 Issue 3

For Selected: View Abstracts Toggle Thumbnails
REVIEW ARTICLE
An overview of the development history and technical progress of China’s coal-fired power industry
Weiliang WANG, Zheng LI, Junfu LYU, Hai ZHANG, Guangxi YUE, Weidou NI
Front. Energy. 2019, 13 (3): 417-426.  
https://doi.org/10.1007/s11708-019-0614-2

Abstract   HTML   PDF (806KB)

As the main power source of China, coal-fired power industry has achieved a great progress in installed capacity, manufacturing technologies, thermal efficiency, as well as pollutant control during the past century. With the fast development of renewable energies, coal-fired power industry is experiencing a strategic transformation. To specify the development of coal-fired power industry, its development history is reviewed and the technical progresses on aspects of thermal efficiency, pollutants control and peaking shaving capacity are discussed. It is concluded that the role of China’s coal-fired power source would be transformed from the dominant position to a base position in power source structure. Considering the sustainable development of coal-fired power industry in energy conservation, emission control, and utilization of renewable energies, it is suggested that the national average thermal efficiency should be improved by continual up-gradation of units by using advanced technologies and eliminating outdated capacity. Moreover, the emission standard of air pollutants should not be stricter any more in coal-fired power industry. Furthermore, the huge amount of combined heat and power (CHP) coal-fired units should be operated in a decoupled way, so as to release more than 350 GW regulation capacity for the grid to accept more renewable energy power.

Figures and Tables | References | Related Articles | Metrics
A comprehensive review of greenhouse shapes and its applications
Ravinder Kumar SAHDEV, Mahesh KUMAR, Ashwani Kumar DHINGRA
Front. Energy. 2019, 13 (3): 427-438.  
https://doi.org/10.1007/s11708-017-0464-8

Abstract   HTML   PDF (346KB)

Greenhouse technology is a practical option for the production and drying of agricultural products in controlled environment. For the successful design of a greenhouse, the selection of a suitable shape and orientation is of great importance. Of various shapes of greenhouses, the even-span roof and the Quonset shape greenhouses are the most commonly used for crop cultivation and drying. The orientation of greenhouses is kept east–west for maximum utilization of solar radiations. Hybrid and modified greenhouse dryers have been proposed for drying of products. The agricultural products dried in greenhouses are found to be better in quality as compared to open sun drying because they are protected from dust, rain, insects, birds and animals. Moreover, various greenhouses shapes along with their applications have been reviewed.

Figures and Tables | References | Related Articles | Metrics
RESEARCH ARTICLE
A numerical study of non-Darcy flow in EGS heat reservoirs during heat extraction
Wenjiong CAO, Wenbo HUANG, Guoling WEI, Yunlong JIN, Fangming JIANG
Front. Energy. 2019, 13 (3): 439-449.  
https://doi.org/10.1007/s11708-019-0612-4

Abstract   HTML   PDF (1289KB)

Underground non-Darcy fluid flow has been observed and investigated for decades in the petroleum industry. It is deduced by analogy that the fluid flow in enhanced geothermal system (EGS) heat reservoirs may also be in the non-Darcy regime under some conditions. In this paper, a transient 3D model was presented, taking into consideration the non-Darcy fluid flow in EGS heat reservoirs, to simulate the EGS long-term heat extraction process. Then, the non-Darcy flow behavior in water- and supercritical CO2 (SCCO2)-based EGSs was simulated and discussed. It is found that non-Darcy effects decrease the mass flow rate of the fluid injected and reduce the heat extraction rate of EGS as a flow resistance in addition to the Darcy resistance which is imposed to the seepage flow in EGS heat reservoirs. Compared with the water-EGS, the SCCO2-EGS are more prone to experiencing much stronger non-Darcy flow due to the much larger mobility of the SCCO2. The non-Darcy flow in SCCO2- EGSs may thus greatly reduce their heat extraction performance. Further, a criterion was analyzed and proposed to judge the onset of the non-Darcy flow in EGS heat reservoirs. The fluid flow rate and the initial thermal state of the reservoir were taken and the characteristic Forchheimer number of an EGS was calculated. If the calculated Forchheimer number is larger than 0.2, the fluid flow in EGS heat reservoirs experiences non-negligible non-Darcy flow characteristic.

Figures and Tables | References | Related Articles | Metrics
Theoretical modeling and experimental verifications of the single-compressor-driven three-stage Stirling-type pulse tube cryocooler
Haizheng DANG, Dingli BAO, Zhiqian GAO, Tao ZHANG, Jun TAN, Rui ZHA, Jiaqi LI, Ning LI, Yongjiang ZHAO, Bangjian ZHAO
Front. Energy. 2019, 13 (3): 450-463.  
https://doi.org/10.1007/s11708-018-0569-8

Abstract   HTML   PDF (2486KB)

This paper establishes a theoretical model of the single-compressor-driven (SCD) three-stage Stirling-type pulse tube cryocooler (SPTC) and conducts experimental verifications. The main differences between the SCD type and the multi-compressor-driven (MCD) crycooler are analyzed, such as the distribution of the input acoustic power in each stage and the optimization of the operating parameters, in which both advantages and difficulties of the former are stressed. The effects of the dynamic temperatures are considered to improve the accuracy of the simulation at very low temperatures, and a specific simulation example aiming at 10 K is given in which quantitative analyses are provided. A SCD three-stage SPTC is developed based on the theoretical analyses and with a total input acoustic power of 371.58 W, which reaches a no-load temperature of 8.82 K and can simultaneously achieve the cooling capacities of 2.4 W at 70 K, 0.17 W at 25 K, and 0.05 W at 10 K. The performance of the SCD three-stage SPTC is slightly poorer than that of its MCD counterpart developed in the same laboratory, but the advantages of lightweight and compactness make the former more attractive to practical applications.

Figures and Tables | References | Related Articles | Metrics
Effect of 2,5-dimethylfuran addition on ignition delay times of n-heptane at high temperatures
Zhenhua GAO, Erjiang HU, Zhaohua XU, Geyuan YIN, Zuohua HUANG
Front. Energy. 2019, 13 (3): 464-473.  
https://doi.org/10.1007/s11708-019-0609-z

Abstract   HTML   PDF (1526KB)

The shock tube autoignition of 2,5-dimethylfuran (DMF)/n-heptane blends (DMF0-100%, by mole fraction) with equivalence ratios of 0.5, 1.0, and 2.0 over the temperature range of 1200–1800 K and pressures of 2.0 atm and 10.0 atm were investigated. A detailed blend chemical kinetic model resulting from the merging of validated kinetic models for the components of the fuel blends was developed. The experimental observations indicate that the ignition delay times nonlinearly increase with an increase in the DMF addition level. Chemical kinetic analysis including radical pool analysis and flux analysis were conducted to explain the DMF addition effects. The kinetic analysis shows that at lower DMF blending levels, the two fuels have negligible impacts on the consumption pathways of each other. As the DMF addition increases to relatively higher levels, the consumption path of n-heptane is significantly changed due to the competition of small radicals, which primarily leads to the nonlinear increase in the ignition delay times of DMF/n-heptane blends.

Figures and Tables | References | Related Articles | Metrics
Flexible liquid metal coil prepared for electromagnetic energy harvesting and wireless charging
Shen GUO, Peng WANG, Jichuan ZHANG, Wenpeng LUAN, Zishuo XIA, Lingxiao CAO, Zhizhu HE
Front. Energy. 2019, 13 (3): 474-482.  
https://doi.org/10.1007/s11708-019-0632-0

Abstract   HTML   PDF (2861KB)

This paper reported a study on a flexible liquid metal coil (LMC) for electromagnetic collection from the transmission line for self-powered sensor and electromagnetic generation for wireless charging of cellular telephone. The room temperature liquid metal of Galinstan was perfused to elastic silicone tube, which is then terminated with gallium-plated copper wire. The as-prepared liquid metal wire can sustain stretching, twisting, and bending with large deformation, and has a good electrical contact stability with the external circuit. The LMC based magnetic energy harvester was then designed and demonstrated to collect the magnetic field energy induced by a wire carrying alternating current. The power of 260 mW was obtained for the wire carrying current of 10 A. The flexible toroidal inductor was fabricated and tested for magnetic energy harvesting. The flexible spiral-shaped LMC was also designed and demonstrated to power cellular telephone through wireless charging. The present study opens the way for further applications of elastic LMC in electromagnetic energy harvesting and charging.

Figures and Tables | References | Related Articles | Metrics
Pre-chamber turbulent jet ignition of methane/air mixtures with multiple orifices in a large bore constant volume chamber: effect of air-fuel equivalence ratio and pre-mixed pressure
Xiang LI, Wenzheng ZHANG, Zhong HUANG, Dehao JU, Li HUANG, Mingzhi FENG, Xingcai LU, Zhen HUANG
Front. Energy. 2019, 13 (3): 483-493.  
https://doi.org/10.1007/s11708-019-0631-1

Abstract   HTML   PDF (5075KB)

Liquefied natural gas (LNG), mainly composed of methane, is in progress to substitute diesel fuel in heavy-duty marine engine for practical, economic, and environmental considerations. However, natural gas is relatively difficult to be ignited in a large bore combustion chamber. A combustion enhancement technique called pre-chamber turbulent jet ignition (TJI) can permit combustion and flame propagation in a large-bore volume. To investigate the effect of air-fuel equivalence ratio and pre-mixed pressure on pre-chamber TJI of methane/air mixtures with multiple orifices in a large bore volume, experimental tests and computational simulations were implemented to study the discharge of hot turbulent jets from six orifices of the pre-chamber. Different initial pressures and air-fuel equivalence ratios were considered to analyze the characteristics of TJI. The asymmetry of the turbulent jet actuated from six different orifices were found due to the asymmetric orientation of the spark plug, resulting in the inhomogeneous distribution of combustion in the constant volume chamber, which should be considered seriously in the marine engine design. Besides, as the premixed pressure increases, it has more effect on the flame propagation and plays a more important role, as it further increases.

Figures and Tables | References | Related Articles | Metrics
Feasibility of using wind turbines for renewable hydrogen production in Firuzkuh, Iran
Ali MOSTAFAEIPOUR, Mojtaba QOLIPOUR, Hossein GOUDARZI
Front. Energy. 2019, 13 (3): 494-505.  
https://doi.org/10.1007/s11708-018-0534-6

Abstract   HTML   PDF (1663KB)

The present study was conducted with the objective of evaluating several proposed turbines from 25 kW to 1.65 MW in order to select the appropriate turbine for electricity and hydrogen production in Firuzkuh area using the decision making trial and evaluation (DEMATEL) and data envelopment analysis (DEA) methods. Initially, five important factors in selection of the best wind turbine for wind farm construction were determined using the DEMATEL technique. Then, technical-economic feasibility was performed for each of the eight proposed turbines using the HOMER software, and the performance score for each proposed wind turbine was obtained. The results show that the GE 1.5sl model wind turbine is suitable for wind farm construction. The turbine can generate 5515.325 MW of electricity annually, which is equivalent to $ 1103065. The average annual hydrogen production would be 1014 kg for Firuzkuh by using the GE 1.5sl model turbine.

Figures and Tables | References | Related Articles | Metrics
Renewable energy resources, policies and gaps in BRICS countries and the global impact
Lakshmi PATHAK, Kavita SHAH
Front. Energy. 2019, 13 (3): 506-521.  
https://doi.org/10.1007/s11708-018-0601-z

Abstract   HTML   PDF (1524KB)

This paper presents comparative yet extensive analysis of existing non-conventional renewable resources, energy policies and gaps in BRICS countries. An intelligent transformation to green economy to maintain natural resources is noted. Brazil has stable energy policies and is the leading producer of biofuels following hydropower until 2014 but supported wind and solar power development by tendering specific tariffs for energy generation from solar and wind. Russia needs improvement in its legal and regulatory framework with more incentives in energy policies. China is improving upon wind and hydropower but it needs strong policy measures to put cap on increased CO2 emissions. India needs revision in energy policy and requires extra incentives and consumer specific energy policies for research-infrastructure and energy generation technologies. South Africa requires lessons to increase renewable energy and reduce coal mining. Moreover, BRICS countries need to redefine their energy policies based upon their existing geographical, economical, societal and environmental conditions which will help in shaping global energy policies and more financial stability. This paper recognizes the potential of BRICS to reshape the global system paralleled with minimizing CO2 emissions. The concerted role of BRICS needs to be recognized as the leading contributor of global renewable capacity where the developed world is geared and busy to address the environmental issues.

Figures and Tables | References | Related Articles | Metrics
Usability perceptions and beliefs about smart thermostats by chi-square test, signal detection theory, and fuzzy detection theory in regions of Mexico
Pedro PONCE, Therese PEFFER, Arturo MOLINA
Front. Energy. 2019, 13 (3): 522-538.  
https://doi.org/10.1007/s11708-018-0562-2

Abstract   HTML   PDF (439KB)

It is well known that smart thermostats (STs) have become key devices in the implementation of smart homes; thus, they are considered as primary elements for the control of electrical energy consumption in households. Moreover, energy consumption is drastically affected when the end users select unsuitable STs or when they do not use the STs correctly. Furthermore, in future, Mexico will face serious electrical energy challenges that can be considerably resolved if the end users operate the STs in a correct manner. Hence, it is important to carry out an in-depth study and analysis on thermostats, by focusing on social aspects that influence the technological use and performance of the thermostats. This paper proposes the use of a signal detection theory (SDT), fuzzy detection theory (FDT), and chi-square (CS) test in order to understand the perceptions and beliefs of end users about the use of STs in Mexico. This paper extensively shows the perceptions and beliefs about the selected thermostats in Mexico. Besides, it presents an in-depth discussion on the cognitive perceptions and beliefs of end users. Moreover, it shows why the expectations of the end users about STs are not met. It also promotes the technological and social development of STs such that they are relatively more accepted in complex electrical grids such as smart grids.

Figures and Tables | References | Related Articles | Metrics
Energy supply for water electrolysis systems using wind and solar energy to produce hydrogen: a case study of Iran
Mostafa REZAEI, Ali MOSTAFAEIPOUR, Mojtaba QOLIPOUR, Mozhgan MOMENI
Front. Energy. 2019, 13 (3): 539-550.  
https://doi.org/10.1007/s11708-019-0635-x

Abstract   HTML   PDF (450KB)

Due to acute problems caused by fossil fuels that threaten the environment, conducting research on other types of energy carriers that are clean and renewable is of great importance. Since in the past few years hydrogen has been introduced as the future fuel, the aim of this study is to evaluate wind and solar energy potentials in prone areas of Iran by the Weibull distribution function (WDF) and the Angstrom-Prescott (AP) equation for hydrogen production. To this end, the meteorological data of solar radiation and wind speed recorded at 10 m height in the time interval of 3 h in a five-year period have been used. The findings indicate that Manjil and Zahedan with yearly wind and solar energy densities of 6004 (kWh/m2) and 2247 (kWh/m2), respectively, have the greatest amount of energy among the other cities. After examining three different types of commercial wind turbines and photovoltaic (PV) systems, it becomes clear that by utilizing one set of Gamesa G47 turbine, 91 kg/d of hydrogen, which provides energy for 91 car/week, can be produced in Manjil and will save about 1347 L of gasoline in the week. Besides, by installing one thousand sets of X21-345 PV systems in Zahedan, 20 kg/d of hydrogen, enough for 20 cars per week, can be generated and 296 L of gasoline can be saved. Finally, the RETScreen software is used to calculate the annual CO2 emission reduction after replacing gasoline with the produced hydrogen.

Figures and Tables | References | Related Articles | Metrics
Will Germany move into a situation with unsecured power supply?
Harald SCHWARZ
Front. Energy. 2019, 13 (3): 551-570.  
https://doi.org/10.1007/s11708-019-0641-z

Abstract   HTML   PDF (6330KB)

Together with a huge number of other countries, Germany signed the Paris Agreements in 2015 to prevent global temperature increase above 2°C. Within this agreement, all countries defined their own national contributions to CO2 reduction. Since that, it was visible that CO2 emissions in Germany decreased, but not so fast than proposed in this German nationally determined contribution to the Paris Agreement. Due to increasing traffic, CO2 emissions from this mobility sector increased and CO2 emission from German power generation is nearly constant for the past 20 years, even a renewable generation capacity of 112 GW was built up in 2017, which is much higher than the peak load of 84 GW in Germany. That is why the German National Government has implemented a commission (often called “The German Coal Commission”) to propose a time line: how Germany can move out of coal-fired power stations. This “Coal Commission” started its work in the late spring of 2018 and handed over its final report with 336 pages to the government on January 26th, 2019. Within this report the following proposals were made: ① Until 2022: Due to a former decision of the German Government, the actual remaining nuclear power generation capacity of about 10 GW has to be switched off in 2022. Besides, the “Coal Commission” proposed to switch off additionally in total 12.5 GW of both, hard coal and lignite-fired power plants, so that Germany should reduce its conventional generation capacity by 22.5 GW in 2022. ② Until 2030: Another 13 GW of German hard coal or lignite-fired power plants should be switched off. ③ Until 2038: The final 17 GW of German hard coal or lignite-fired power plants should be switched off until 2038 latest. Unfortunately the “Coal Commission” has not investigated the relevant technical parameter to ensure a secured electric power supply, based on German’s own national resources. Because German Energy Revolution mainly is based on wind energy and photovoltaic, this paper will describe the negligible contribution of these sources to the secured generation capacity, which will be needed for a reliable power supply. In addition, it will discuss several technical options to integrate wind energy and photovoltaic into a secured power supply system with an overall reduced CO2 emission.

Figures and Tables | References | Related Articles | Metrics
China’s pre-2020 CO2 emission reduction potential and its influence
Hailin WANG, Jiankun HE
Front. Energy. 2019, 13 (3): 571-578.  
https://doi.org/10.1007/s11708-019-0640-0

Abstract   HTML   PDF (244KB)

China achieved the reduction of CO2 intensity of GDP by 45% compared with 2005 at the end of 2017, realizing the commitment at 2009 Copenhagen Conference on emissions reduction 3 years ahead of time. In future implementation of the “13th Five-Year Plan (FYP),” with the decline of economic growth rate, decrease of energy consumption elasticity and optimization of energy structure, the CO2 intensity of GDP will still have the potential for decreasing before 2020. By applying KAYA Formula decomposition, this paper makes the historical statistics of the GDP energy intensity decrease and CO2 intensity of energy consumption since 2005, and simulates the decrease of CO2 intensity of GDP in 2020 and its influences on achieving National Determined Contribution (NDC) target in 2030 with scenario analysis. The results show that China’s CO2 intensity of GDP in 2020 is expected to fall by 52.9%–54.4% than the 2005 level, and will be 22.9%–25.4% lower than 2015. Therefore, it is likely to overfulfill the decrease of CO2 intensity of GDP by 18% proposed in the 13th FYP period. Furthermore, the emission reduction potentiality before 2020 will be conducive to the earlier realization of NDC objectives in 2030. China’s CO2 intensity of GDP in 2030 will fall by over 70% than that in 2005, and CO2 emissions peak will appear before 2030 as early as possible. To accelerate the transition to a low-carbon economy, China needs to make better use of the carbon market, and guide the whole society with carbon price to reduce emissions effectively. At the same time, China should also study the synergy of policy package so as to achieve the target of emission reduction.

Figures and Tables | References | Related Articles | Metrics
Optimization of the power, efficiency and ecological function for an air-standard irreversible Dual-Miller cycle
Zhixiang WU, Lingen CHEN, Yanlin GE, Fengrui SUN
Front. Energy. 2019, 13 (3): 579-589.  
https://doi.org/10.1007/s11708-018-0557-z

Abstract   HTML   PDF (660KB)

This paper establishes an irreversible Dual-Miller cycle (DMC) model with the heat transfer (HT) loss, friction loss (FL) and other internal irreversible losses. To analyze the effects of the cut-off ratio (ρ) and Miller cycle ratio (rM) on the power output (P), thermal efficiency (η) and ecological function (E), obtain the optimal ρopt and optimal rMopt, and compare the performance characteristics of DMC with its simplified cycles and with different optimization objective functions, the P, η and E of irreversible DMC are analyzed and optimized by applying the finite time thermodynamic (FTT) theory. Expressions of P, η and E are derived. The relationships among P, η, E and compression ratio (ε) are obtained by numerical examples. The effects of ρ and rM on P, η, E, maximum power output (MP), maximum efficiency (MEF) and maximum ecological function (ME) are analyzed. Performance differences among the DMC, the Otto cycle (OC), the Dual cycle (DDC), and the Otto-Miller cycle (OMC) are compared for fixed design parameters. Performance characteristics of irreversible DMC with the choice of P, η and E as optimization objective functions are analyzed and compared. The results show that the irreversible DMC engine can reach a twice-maximum power, a twice-maximum efficiency, and a twice-maximum ecological function, respectively. Moreover, when choosing E as the optimization objective, there is a 5.2% of improvement in η while there is a drop of only 2.7% in P compared to choosing P as the optimization objective. However, there is a 5.6% of improvement in P while there is a drop of only 1.3% in η compared to choosing as the optimization objective.

Figures and Tables | References | Related Articles | Metrics
Optical performance analysis of an innovative linear focus secondary trough solar concentrating system
Xiliang ZHANG, Zhiying CUI, Jianhan ZHANG, Fengwu BAI, Zhifeng WANG
Front. Energy. 2019, 13 (3): 590-596.  
https://doi.org/10.1007/s11708-018-0602-y

Abstract   HTML   PDF (1073KB)

The parabolic trough solar concentrating system has been well developed and widely used in commercial solar thermal power plants. However, the conventional system has its drawbacks when connecting receiver tube parts and enhancing the concentration ratio. To overcome those inherent disadvantages, in this paper, an innovative concept of linear focus secondary trough concentrating system was proposed, which consists of a fixed parabolic trough concentrator, one or more heliostats, and a fixed tube receiver. The proposed system not only avoids the end loss and connection problem on the receiver during the tracking process but also opens up the possibility to increase the concentration ratio by enlarging aperture. The design scheme of the proposed system was elaborated in detail in this paper. Besides, the optical performance of the semi and the whole secondary solar trough concentrator was evaluated by using the ray tracing method. This innovative solar concentrating system shows a high application value as a solar energy experimental device.

Figures and Tables | References | Related Articles | Metrics
COMMUNICATION
Fabrication of layered structure VS4 anchor in 3D graphene aerogels as a new cathode material for lithium ion batteries
Lijun WU, Yu ZHANG, Bingjiang LI, Pengxiang WANG, Lishuang FAN, Naiqing ZHANG, Kening SUN
Front. Energy. 2019, 13 (3): 597-602.  
https://doi.org/10.1007/s11708-018-0576-9

Abstract   HTML   PDF (1756KB)

VS4 has gained more and more attention for its high theoretical capacity (449 mAh/g with 3e transfer) in lithium ion batteries (LIBs). Herein, a layered structure VS4 anchored in graphene aerogels is prepared and first reported as cathode material for LIBs. VS4@GAs composite exhibits an exceptional high initial reversible capacity (511 mAh/g), an excellent high-rate capability (191 mAh/g at the 5 C), and an excellent cyclic stability (239 mAh/g after 15 cycles).

Figures and Tables | References | Supplementary Material | Related Articles | Metrics
16 articles