Cold gas propulsion microthruster for feed gas utilization in micro satellites Appl. Energy (IF 7.182) Pub Date : 2018-03-21 R. Ranjan, K. Karthikeyan, F. Riaz, S.K. Chou
Micro spacecraft, which have gained huge popularity in the last decade, are termed as “CubeSats”, a well-known class of small satellites. The fast growing functionality and popularity of CubeSats have helped researchers push technology demonstration towards efficient performance and reliability needed for commercial and governmental applications. Keeping in mind the increasing space debris, dependence of satellite life on fuel, and the use of fossil fuels as propellants, recent efforts are being made to develop a cold gas propellant-based (CGP) micro propulsion system. The CGP system has various merits, namely, non-toxicity, easy to use, and low leakage concerns over other propulsion systems. Liquid propellant-based propulsion requires a liquid feed system, which uses pressurized gas (such as helium, argon and nitrogen) to pressure-feed liquid to the combustion or vaporization chamber so as to produce thrust. But once the liquid propellant is depleted, the pressurized gas is unusable while the system runs out of fuel. Thus, the proposed CGP system being studied, apart from being used as a normal cold gas propulsion system, also offers the advantage of being used as a propulsion system for a liquid fueled system, in the event the liquid fuel runs out. The present work reports on cold gas micro thruster development, utilization of feed gas in a liquid fueled thruster, and the experimental study on the CGP system in simulated vacuum conditions and under a range of pressure conditions. Pressure in the pressure feed gas system for a 1–50 kg category of satellites varies from 4 to 8 bar depending on the mission requirement. The pressure reduces as the liquid propellant gets exhausted. The experimental results are used to validate a computational fluid dynamics model of the system. Thrust values are obtained between the micro to milli-Newton range so as to fulfil the requirements of attitude and station keeping for CubeSats in the 1–50 kg dry mass range. Under vacuum conditions, we obtained thrust values of 0.8 mN at 1 bar feed pressure to 2.24 mN at 4 bar feed pressure. These thrust values are nearly twice those achieved for sea level tests for the corresponding feed pressure. Furthermore, the parameters such as Mach number, velocity vector, pressure, temperature, specific impulse, and nozzle efficiency are studied and reported for atmospheric and vacuum conditions.
Personalized thermal comfort inference using RGB video images for distributed HVAC control Appl. Energy (IF 7.182) Pub Date : 2018-03-07 Farrokh Jazizadeh, Wooyoung Jung
HVAC systems account for more than 40% of energy consumption in buildings to provide satisfactory indoor environments for occupants. The integration of personalized thermal comfort in the operation of HVAC systems has been shown to be highly effective in enhancing energy efficiency of buildings. To this end, research efforts have proposed personalized thermal comfort assessment through voting (i.e., occupant feedback) and profiling as well as physiological response measurement. In this study, we have proposed a novel approach for enabling RGB video cameras as sensors for measuring personalized thermoregulation states – an indicator of thermal comfort. If their feasibility for thermoregulation state inference could be established, optical cameras provide a cost-effective and omnipresent solution for distributed measurement of thermal comfort and consequently control of HVAC systems for energy saving. Accordingly, we have proposed a framework that draws on the concepts of thermoregulation mechanisms in the human body as well as the Eulerian video magnification approach. The framework is composed of several components including face detection, skin pixels isolation, image magnification. And calculation of detection index to infer subtle blood flow variations to the facial skin surface (i.e., blood perfusion), which is due to thermoregulation adjustments. In order to minimize the impact of variable illumination condition and the ambient noise on the results, different combinations of methods for framework components were taken into account. The feasibility assessments were conducted through an experimental study with 21 participants under low (20 °C) and high (30 °C) temperatures. In total, 16 positive cases out of 18 statistically significant cases were observed resulting in 89% of success rate using the most promising combinations of the methods. The results demonstrate that the proposed framework could contribute to realization of a non-intrusive, cost-effective, and ubiquitous distributed thermal comfort assessment that has been proven critical in increasing energy efficiency of the HVAC system through distributed control feedback.
Simultaneous production of CH4-rich syngas and high-quality tar from lignite by the coupling of noncatalytic/catalytic pyrolysis and gasification in a pressurized integrated fluidized bed Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Zhaohui Chen, Shiqiu Gao, Guangwen Xu
An integrated fluidized bed (IFB) reactor with a two-stage configuration has been developed to process small-size coal particles for the simultaneous production of CH4-rich syngas and high-quality tar, in which coal pyrolysis occurred in an upper transport bed (TB) within an atmosphere mixing steam and syngas generated by steam-oxygen gasification of coal or char in a lower fluidized bed (FB). The coupling effect was investigated by combining non-catalytic/catalytic pyrolysis and gasification in a pressurized IFB. Having TB pyrolysis obviously raised CH4 yield (also its content in producer gas) and tar yield. The respective contributions to CH4 formation from the TB pyrolysis and FB gasification were mainly relevant to operating pressure and Ca(OH)2 catalyst. Raising pressure facilitated CH4 formation. When lignite was treated without catalyst, the contribution from TB pyrolysis was greater than that from FB gasification as hydropyrolysis was intensified by pressure in H2-rich gas atmosphere from the FB gasifier. Adding catalyst into lignite reversed their contributions. The FB catalytic gasification formed more CH4 because Ca(OH)2 functioned well as a catalyst for CH4 formation in pressurized gasification. With elevated pressure or/and the addition of Ca(OH)2, pyrolysis tar yield decreased in different degrees but its quality was improved. With the combination effect of pressure and Ca(OH)2, producer gas from the tested IFB reactor was highly rich in CH4 to reach 10.8 vol%, with as well a high H2/CO ratio of 2.3 that is suitable for making SNG. The obtained tar had its light tar content as high as 95 wt%.
Brick : Metadata schema for portable smart building applications Appl. Energy (IF 7.182) Pub Date : 2018-02-23 Bharathan Balaji, Arka Bhattacharya, Gabriel Fierro, Jingkun Gao, Joshua Gluck, Dezhi Hong, Aslak Johansen, Jason Koh, Joern Ploennigs, Yuvraj Agarwal, Mario Bergés, David Culler, Rajesh K. Gupta, Mikkel Baun Kjærgaard, Mani Srivastava, Kamin Whitehouse
Buildings account for 32% of the energy use worldwide. A new regime of exciting new “applications” that span a distributed fabric of sensors, actuators and humans have emerged to improve building energy efficiency and operations management. These applications leverage the technological advances in embedded sensing, processing, networking and methods by which they can be coupled with supervisory control and data acquisition systems deployed in modern buildings and with users on mobile wireless platforms. There are, however, several technical challenges before such a vision of smart building applications and cyber-physical systems can be realized. The sensory data from and to the distributed systems end-points need significant curation before it can be used meaningfully. This is largely a manual, cost-prohibitive task and hence such solutions rarely experience widespread adoption due to the lack of a common descriptive schema. Recent attempts have sought to address this through data standards and metadata schemata but fall short in capturing the richness of relationships required by applications. This paper describes Brick , a uniform metadata schema for representing buildings that builds upon recent advances in the area. Our schema defines a concrete ontology for sensors, subsystems and relationships among them, which enables portable applications. We demonstrate the completeness and effectiveness of Brick by using it to represent the entire vendor-specific sensor metadata of six diverse buildings across different campuses, comprising 17,700 data points, and running eight unmodified energy efficiency applications on these buildings.
How to upgrade an enterprise’s low-carbon technologies under a carbon tax: The trade-off between tax and upgrade fee Appl. Energy (IF 7.182) Pub Date : 2017-07-25 Senyu He, Jianhua Yin, Bin Zhang, Zhaohua Wang
Reducing CO2 emissions is a hot topic, and an important policy to achieve this target is carbon tax. When an enterprise is subject to a carbon tax, it has to pay this extra fee for the long-term if it does not upgrade its production technology. It needs to pay a certain upgrade fee in the short-term if it chooses to upgrade its plant. Thus, it has been an important problem for enterprises seeking to balance the trade-off between the ‘long-term tax fee’ and the ‘short-term upgrade fee’. This paper explores how to optimise an enterprise’s production technology upgrade strategy based on existing low-carbon technologies, to minimise the total upgrade cost subject to an expected total cost per product. An integer programming model is proposed to formulate the problem, and a ‘multi-agent system – genetic algorithm’ method is presented for its solution. The model is applied to a numerical example and the results indicate that the proposed method is feasible. The impacts of carbon tax and enterprise’s expected cost on its technology upgrade strategy are further discussed.
Molecular dynamics simulations of the local structures and transport properties of Na2CO3 and K2CO3 Appl. Energy (IF 7.182) Pub Date : 2017-07-25 Jing Ding, Gechuanqi Pan, Lichan Du, Jianfeng Lu, Weilong Wang, Xiaolan Wei, Jiang Li
Molten alkali carbonates has been researched as one of the most promising thermal energy storage (TES) materials in Concentrating Solar Power (CSP) and received extensive attentions. Some attractive properties must be determined accurately, such as thermal conductivity, and viscosity. over a wide temperature range. However, these significant thermal and transport properties are difficult to be obtained for experiments on account of high-temperature extreme conditions. Molecular dynamics (MD) is an alternative way to predict these properties for molten salts. Systematic results including density, thermal conductivity and shear viscosity as a function of temperature from molecular dynamics simulations of molten alkali carbonates are presented in detail in this paper. Both reverse nonequilibrium molecular dynamics (RNEMD) and nonequilibrium molecular dynamics (NEMD) methods are tried for thermal conductivity and viscosity, and then the results are compared to experimental values. The temperature dependence are investigated and analyzed by correlating transport properties with local structures. The results show that the Tosi-Fumi potential predicts negative temperature dependences for both viscosity and thermal conductivity of the alkali carbonates. The simulation results are in good agreement with the experimental data available in the literature.
Measuring the transient airflow rates of the infiltration through the doorway of the cold store by using a local air velocity linear fitting method Appl. Energy (IF 7.182) Pub Date : 2017-07-21 Shen Tian, Yuping Gao, Shuangquan Shao, Hongbo Xu, Changqing Tian
The measurement of the infiltration airflow rates can support the calculation of the infiltration cooling load for the better understanding and optimizing the energy consumption of cold stores. However, the large temperature difference and the intense transient features make it difficult and complex to measure the airflow rates accurately. In this paper, a simple and practical method to measure the transient infiltration airflow rates is developed by using the local air velocity linear fitting. The proposed method is validated by the measurement results of the tracer gas decay method. It is concluded that the proposed method shows a good performance on the transient infiltration airflow rates measurement. The measurement errors are between ±10%. To enhance the application of this method, the layout of the measuring points of the air velocities are analyzed. The results show that, along the vertical layout direction, air velocity measuring points around the neutral level (where the cold and the warm air separate, about the middle height of the door) are not preferred when using this method. What’s more, the calculation of the infiltration cooling load by using this measuring method is also discussed.
Modeling, simulation and evaluation of biogas upgrading using aqueous choline chloride/urea Appl. Energy (IF 7.182) Pub Date : 2017-05-03 Chunyan Ma, Yujiao Xie, Xiaoyan Ji, Chang Liu, Xiaohua Lu
Biogas has been considered as an alternative renewable energy, and raw biogas needs to be upgraded in order to be used as vehicle fuels or injected into the natural gas grid. In this work, the conceptual process for biogas upgrading using aqueous choline chloride (ChCl)/urea (1:2 on a molar basis) was developed, simulated and evaluated based on the commercialized software Aspen Plus. Reliable thermophysical properties and phase equilibria are prerequisite for carrying out process simulation. In order to carry out the process simulation, the thermophysical properties of ChCl/Urea (1:2) and its aqueous solutions as well as the phase equilibria of gas-ChCl/Urea (1:2), ChCl/Urea (1:2)-H2O and gas-ChCl/Urea (1:2)-H2O were surveyed and evaluated. After evaluation, the consistent experimental data of these thermophysical properties were fitted to the models embedded in Aspen Plus. The properties needed but without available experimental results were predicted theoretically. The Non-Random Two-Liquid model and the Redlich-Kwong equation (NRTL-RK) model were used to describe the phase equilibria. The equilibrium approach was used for process simulation. Sensitivity analysis was conducted to determine the reasonable operating parameters. With a set of reasonable operating conditions, the effects of ChCl/Urea (1:2) content on the total energy utilization, the diameters and pressure drops of absorber and desorber as well as the environmental assessment of the process were studied. The simulation results showed that, with the addition of ChCl/Urea (1:2), the total energy utilization decreased by 16% compared to the process with pure water, and the diameters of both absorber and desorber decreased with increasing content of ChCl/Urea (1:2). The process using aqueous ChCl/Urea (1:2) was more environmentally benign than that with pure water. Therefore, aqueous ChCl/Urea (1:2) is a promising solvent for biogas upgrading.
Dynamic control strategy for the electrolyte flow rate of vanadium redox flow batteries Appl. Energy (IF 7.182) Pub Date : 2017-07-26 Tao Wang, Jiahui Fu, Menglian Zheng, Zitao Yu
The vanadium redox flow battery (VRB) is considered to be one of the most promising technologies for large-scale energy storage, with the electrolyte flow rate capable of significantly affecting the mass transfer, temperature rise, and pump power losses of the VRB system. Although the flow-rate optimization under constant current has been addressed in the literature, few studies have investigated the control strategy for the electrolyte flow rate under varying (dis-)charge power that is common in practical applications. Moreover, fewer studies have considered the concentration discrepancy of the active species in the tank and stack in the flow-rate optimization. In this paper, the electrolyte flow-rate optimization is investigated by incorporating the influences of the flow rate on the mass transfer, temperature rise, and required pump power. A transient model of the VRB system is developed to derive the total power losses (by which the overall system energy efficiency is determined; include losses resulting from overpotentials, ohmic drops, and required pump power) as a function of the applied current, concentration of the active species in the stack, and flow rate of the electrolyte. Based on this model, a dynamic flow-rate control strategy is proposed for determining the optimal flow rate under varying (dis-)charge power and state-of-charge conditions. The simulation results show that the proposed control strategy can deliver a high VRB system efficiency of 87.7%, and manage the electrolyte temperature to the safe range during mild summer days.
Explorative study on Compressed Air Systems’ energy efficiency in production and use: First steps towards the creation of a benchmarking system for large and energy-intensive industrial firms Appl. Energy (IF 7.182) Pub Date : 2017-07-29 Miriam Benedetti, Francesca Bonfa', Ilaria Bertini, Vito Introna, Stefano Ubertini
Compressed Air Systems (CAS) are one of the most common and energy intensive utilities in industry, representing up to 10% of the industrial energy needs. Thus, they can be considered as one of the main target systems while planning energy efficiency actions implementation in industry. Nevertheless, most of the available benchmarks of energy consumption are based on nominal data, thus referring to the quality of the design, while benchmarks based on measurements under actual operating conditions are not yet available. In accordance with the Italian transposition of the European Directive 2012/27/EU (i.e. Legislative Decree 102/2014), large and energy-intensive business organizations must perform energy audits at least every four years starting in 2015 and the Italian Energy, New Technology and Environment Agency (ENEA) has the task of collecting and analysing them. In this context, a data collection focused on CAS has been carried out and the subsequent data analysis, focused on nine most promising industrial sectors, has allowed to assess the current state of the art of CAS’s energy efficiency in Italy and to design a possible benchmarking system. Such a system is composed of a set of indicators and a benchmarking visual tool in the form of a matrix. In particular, results related to the Manufacturing of basic metals will be presented for sake of brevity. In this paper we present the results obtained from both the data analysis and the first application of the proposed benchmarking system, together with next steps for the creation of reliable sectorial and cross-sectorial benchmarks.
Techno-economic evaluation of biogas upgrading using ionic liquids in comparison with industrially used technology in Scandinavian anaerobic digestion plants Appl. Energy (IF 7.182) Pub Date : 2017-07-29 Yujiao Xie, Johanna Björkmalm, Chunyan Ma, Karin Willquist, Johan Yngvesson, Ola Wallberg, Xiaoyan Ji
The process of biogas upgrading with ionic liquids, i.e. pure 1-butyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide ([bmim][Tf2N]), aqueous choline chloride/urea (ChCl/Urea), and aqueous 1-allyl-3-methyl imidazole formate ([Amim][HCOO]), was simulated in Aspen Plus and compared with the conventional water scrubbing upgrading technique. The comparisons of the performances on the amount of recirculated solvents and energy usage show the following order: aqueous [Amim][HCOO] < aqueous ChCl/Urea < [bmim][Tf2N] < water. Six different co-digestion plants (anaerobic digestion, AD, plants) were surveyed to acquire data for comparison. The selected plants had different raw biogas production capacities and produced gas with differing methane content. The data confirmed the simulation results that the type of substrate and the configuration of AD process are two factors affecting energy usage, investment cost, as well as operation and maintenance costs for the subsequent biogas upgrading. In addition, the simulation indicated that the energy usage of the ionic liquid-based upgrading was lower than that of the conventional upgrading techniques in Scandinavian AD plants. The estimated cost including investment, operation and maintenance for the ionic liquid technology showed to be lower than that for the water scrubbing upgrading process.
Environmental impact of energy refurbishment of buildings within different district heating systems Appl. Energy (IF 7.182) Pub Date : 2017-07-29 T. Lidberg, M. Gustafsson, J.A. Myhren, T. Olofsson, L. Ödlund (former Trygg)
The refurbishment of existing buildings is often considered a way to reduce energy use and CO2 emissions in the building stock. This study analyses the primary energy and CO2 impact of refurbishing a multi-family house with different refurbishment packages, given various district heating systems. Four models of typical district heating systems were defined to represent the Swedish district heating sector. The refurbishment packages were chosen to represent typical, yet innovative ways to improve the energy efficiency and indoor climate of a multi-family house. The study was made from a system perspective, including the valuation of changes in electricity use on the margin. The results show a significant difference in primary energy use for the different refurbishment packages, depending on both the package itself as well as the type of district heating system. While the packages with heat pumps had the lowest final energy use per m2 of floor area, air heat recovery proved to reduce primary energy use and emissions of CO2-equivalents more, independent of the type of district heating system, as it leads to a smaller increase in electricity use.
A detailed study on phonon transport in thin silicon membranes with phononic crystal nanostructures Appl. Energy (IF 7.182) Pub Date : 2017-07-31 Qi Liang, Ya-Ling He, Qinlong Ren, Yi-Peng Zhou, Tao Xie
A common method to improve thermoelectric performance is to reduce thermal conductivity by enhancing phonon scattering. In this paper, a frequency-dependent phonon radiative transport equation (PRTE) solver, based on the discrete ordinates method, is developed to simulate phonon transport in thin silicon membranes with phononic crystal nanostructures. The influence of geometric parameters on phonon transport is discussed in detail. Besides, a nonlinear regression model is attained for predicting the thermal conductivity of thin silicon membranes with phononic crystal nanostructures using the non-linear least-squares method. The results indicate that thermal conductivity is reduced by phononic crystal nanostructures mainly due to the back scattering of phonons with pore boundaries, and phonons with larger mean free path have stronger back scattering. When the pore placement is fixed, pore configuration affects phonon transport in thin silicon membranes with phononic crystal nanostructures. In addition, thermal conductivity is primarily controlled by three geometric parameters, including r⊥, r||, and Au. Moreover, the obtained regression model reveals the relationship between thermal conductivity and geometric parameters well, which can offer useful suggestions for fabricating thin silicon membranes with low thermal conductivity.
Dynamic analysis of direct internal reforming in a SOFC stack with electrolyte-supported cells using a quasi-1D model Appl. Energy (IF 7.182) Pub Date : 2017-08-01 Jakub Kupecki, Konrad Motylinski, Jaroslaw Milewski
Solid oxide fuel cells (SOFC) offer several advantages that are accelerating the research and development of the technology. Recent advances include the improvement of materials and new fabrication techniques, as well as new designs, flow configurations, and applications. The large scale implementation of fuel cells, especially in distributed energy generation, is limited by several factors––one of which is their limited fuel flexibility. Changing fuel typically requires modifying the fuel processing unit to make it possible to effectively convert raw fuel into hydrogen-rich gas. One potential solution allows for the use of alternative fuels without the need for customization of the fuel processor. This solution requires the adaptation of the stack to operate with direct internal reforming (DIR) of the fuel on the surface of the anodes. The present study explores the potential to internally reform methane in the SOFC stack with electrolyte supported cells. The numerical model that was developed for the simulation of the 1300 W stack was validated using experimental data obtained from partial internal reforming. Later, the model was applied to simulate the operation of the stack with complete internal reforming of methane. It was observed that the strong effects of internal reforming on the temperature in the outlets are visible when the current exceeds 22 A. However, it was proven that the DIR-SOFC mode of operation is possible in the considered stack without exceeding the advised temperature limits in the core, and in the outlets of the anodic and cathodic compartments. The model was found to be accurate and the observed relative prediction error was in the range of 1.51–2.38%.
Substitution effect of renewable portfolio standards and renewable energy certificate trading for feed-in tariff Appl. Energy (IF 7.182) Pub Date : 2017-08-02 Qi Zhang, Ge Wang, Yan Li, Hailong Li, Benjamin McLellan, Siyuan Chen
The Feed-in Tariff (FIT) has been successfully used to promote the development of renewable energy; nevertheless, it may cause financial burden on the governments at the same time. Compared with FIT, Renewable Portfolio Standards (RPS) and the Renewable Energy Certificate (REC) trading have been considered to reduce the government’s expenditure caused by the subsidization. To examine the effectiveness of RPS and REC trading, the development of renewable energy and the environmental and economic benefits under different policies have been quantitatively investigated by using a multi-region power market model and China has been chosen as a case study. The obtained results show that: (i) REC trading can efficiently reduce the government’s expenditure on subsidies for the development of renewable energy; (ii) Compared to FIT, RPS and REC trading will reduce the power sectors’ profit; and (iii) RPS and REC trading may not be enough to achieve the target on renewable energy especially when the capital cost is high, therefore, RPS, REC trade and FIT subsidy should be implemented as complementary policies, not independent.
Multi-objective optimization research on the start condition for a parallel hybrid electric vehicle Appl. Energy (IF 7.182) Pub Date : 2017-08-02 Hongwen He, Xiaoguang Guo
One of the major issues for Parallel Hybrid Electric Vehicle (Parallel HEV) powertrain is the torsional vibration in the process of start condition, which is unavoidable. This article targets at reducing the damage caused by the torsional vibration with the method of Multi-Objective Optimization (MOO). The dynamic model of the parallel HEV powertrain is established by lumped mass method. Five design variables are selected from 19 parameters by the process of Design of Experiment (DOE), and are optimized by multi-objective downhill simplex optimization algorithm. Pareto Frontier is used to describe the relationship between the two objective functions, and one of the optimization data serves as the basics data for the powertrain modification. Finally, the results of optimization before and after optimization are compared by the test bench. Experimental results under the start condition show that the maximum torque of the optimized powertrain is decreased within the safe range, and the problem of shaft breaking on the originally powertrain is solved.
Performance evaluation of a low-grade power generation system with CO2 transcritical power cycles Appl. Energy (IF 7.182) Pub Date : 2017-08-04 Y.T. Ge, L. Li, X. Luo, S.A. Tassou
Globally, there are vast amounts of low-grade heat sources from industrial waste and renewables that can be converted into electricity through advanced thermodynamic power cycles and appropriate working fluids. In terms of the working fluid’s environmental impact, temperature match of cycle heat processes and system compactness, CO2 transcritical power cycles (T-CO2) were deemed more applicable for low-grade heat to power conversion. However, the system thermal efficiency of a T-CO2 requires further improvement. Subsequently, a test rig of the small-scale power generation system with T-CO2 power cycles was developed with essential connected components. These include a plate thermal coil CO2 supercritical heater, a CO2 transcritical turbine, a plate recuperator, an air-cooled finned-tube CO2 condenser and a CO2 liquid pump. Various preliminary test results from the system measurements are demonstrated in this paper. Meanwhile, the system model has been developed and applied to predict system performance at different operating conditions. The simulation results can therefore instruct further design and optimisation of system and components.
A non-stoichiometric equilibrium model for the simulation of the biomass gasification process Appl. Energy (IF 7.182) Pub Date : 2017-08-05 Agostino Gambarotta, Mirko Morini, Andrea Zubani
This paper presents a non-stoichiometric equilibrium model for the simulation of the biomass gasification process in downdraft gasifiers to be used within simulation models of complex energy systems. The chemical equilibrium is determined by minimizing the Gibbs free energy. The feedstock is composed of five elements, while fifteen chemical species are considered for the syngas. The model calculates the relative quantities of gasification products and the lower heating value of the syngas. An advantage of the non-stoichiometric approach is that it can easily calculate not only the concentrations of the main gasification products, but also the concentrations of minor products, especially the pollutant chemical species containing nitrogen and sulfur. To analyse the behaviour of the model, a sensitivity analysis of its process parameters is presented. The model is then validated by comparing its results with the results of the simulation carried out with equilibrium models and with experimental data found in literature. Finally, the model is applied to the study of the gasification of forest waste.
Effect of torrefaction on physiochemical characteristics and grindability of stem wood, stump and bark Appl. Energy (IF 7.182) Pub Date : 2017-08-07 L. Wang, E. Barta-Rajnai, Ø. Skreiberg, R. Khalil, Z. Czégény, E. Jakab, Z. Barta, M. Grønli
In this work, Norway spruce stem wood, stump and bark were torrefied in a bench scale tubular reactor at 225, 275 and 300 °C with two residence times (30 and 60 min). Effect of torrefaction on general properties, chemical composition, grindability and microstructure and morphology of biomass samples were studied. An increase in heating value and fixed carbon content of the torrefied biomass was observed for increasing torrefaction temperature and residence time. Chemical compositions of torrefied biomass samples considerably changed with increase of torrefaction severity. For the stem wood and stump, the relative hemicellulose content significantly decreased from respectively 42.3% and 29.8% to less than 1% after torrefaction at 300 °C for 60 min. The hemicellulose content of untreated bark decreased from 27.5% to 0.14% after torrefaction at the same conditions. Additionally, the cellulose content of the torrefied bark drastically decreased already to half the initial value at a torrefaction temperature of 275 °C, with only trace amounts left in the 300 °C torrefied products. The grindability of stem wood and stump were substantially improved after torrefaction treatment. The energy required for grinding stem wood and stump torrefied at 225 °C decreased to respectively 87 and 70 kWh/ton, which are less than 50% of the energy needed for grinding the untreated samples. For raw bark, much less grinding energy is required compared to those for raw stem wood and stump, and torrefaction has minor effects on the grindability of bark. The ground torrefied biomass samples have much smaller particles than those of the untreated ones. SEM analysis results show that particles from ground torrefied samples lose their fibrous structure with decrease of length-to-diameter ratios, compared to untreated biomass samples. It explains the shift in particle size distribution curves towards smaller particles as obtained from the sieving tests.
The water-food-energy nexus optimization approach to combat agricultural drought: a case study in the United States Appl. Energy (IF 7.182) Pub Date : 2017-08-07 Jie Zhang, Pietro Elia Campana, Tian Yao, Yang Zhang, Anders Lundblad, Forrest Melton, Jinyue Yan
The frequent recent drought events in the Great Plains of United States have led to significant crop yield reductions and crop price surges. Using an integrated water-food-energy nexus modelling and optimization approach, this study laid the basis for developing an effective agricultural drought management system by combining real-time drought monitoring with real-time irrigation management. The proposed water-food-energy simulation and optimization method is spatially explicit and was applied to one major corn region in Nebraska. The crop simulations, validated with yield statistics, showed that a drought year like 2012 can potentially reduce the corn yield by 50% as compared to a wet year like 2009. The simulation results show that irrigation can play a key role in halting crop losses due to drought and in sustaining high yields of up to 20 t/ha. Nevertheless, the water-food-energy relationship shows that significant investments on water and energy are required to limit the negative effects of drought. The multi-criteria optimization problem developed in this study shows that the optimal crop yield does not necessarily correspond to the maximum yield, resulting in potential water and energy savings.
Comparison of air-conditioning systems with bottom-supply and side-supply modes in a typical office room Appl. Energy (IF 7.182) Pub Date : 2017-08-07 Chenxiao Zheng, Shijun You, Huan Zhang, Wandong Zheng, Xuejing Zheng, Tianzheng Ye, Zeqin Liu
The growing energy consumption and thermal comfort of an air-conditioned room have attracted increasing public attention. As such, the performance of air-conditioning systems with two air supply modes for a simplified office room was studied by numerical simulation and physical experiment. An experimental investigation was developed in an environmental chamber to validate the simulation model. Numerical investigation was carried out subsequently for an office setting by the validated CFD model. The indoor thermal environment, human thermal comfort and energy utilization efficiency of two air supply modes were analyzed and compared in this study. The results showed that under both air supply modes, thermal stratification occurred in the model room, and the air flow velocity in the occupied zone was low. In addition, the results indicated that under 21 °C supply temperature, the air-conditioning system with bottom-supply mode provided better indoor thermal comfort of the occupied zone, but the energy consumption was higher than the side-supply mode.
Production of bio-jet fuel from corncob by hydrothermal decomposition and catalytic hydrogenation: Lab analysis of process and techno-economics of a pilot-scale facility Appl. Energy (IF 7.182) Pub Date : 2017-08-08 Yuping Li, Cong Zhao, Lungang Chen, Xinghua Zhang, Qi Zhang, Tiejun Wang, Songbai Qiu, Jin Tan, Kai Li, Chenguang Wang, Longlong Ma
Process design and techno-economic analysis of a pilot bio-jet fuel production facility were investigated using Aspen plus software and net present value method (NPV). This process include two-step hydrothermal decomposition of corncob to furfural (steam stripping of hemicellulose) and Levulinic acid (LA, acidic hydrolysis of cellulose), oxygenated precursor production via aldol condensation reaction of furfural and LA, and the subsequent hydro-processing for oxygen removal. Lab experiments on the major area of the process were carried out. The yields of furfural, LA, oxygenated precursor and bio-jet fuel-range hydrocarbons (C8–C15) were 59.5% (based on hemicellulose), 34.4% (based on cellulose), 75% (based on furfural and LA input) and 51 wt% (based on precursor) respectively. These values were used as the input information for the process simulation of a first-of-a-kind pilot facility for 1.3 ML/a bio-jet fuel production using this pioneering technology. The mass and energy analysis from Aspen plus model shows that the bio-jet fuel yield was 0.125 tonne/tonne dried corncob. 31.0% of carbon atoms and 47.6% of potential energy from carbohydrate compounds of corncob leave as bio-jet fuel. The estimated consumption of water, steam and electricity is relatively high of 12.3 kg, 63.7 kg and 1.22 KW h respectively due to small simulation scale and lack of process optimization. The total capital cost was ca. $3.96 MM for the 1.3 ML/a facility, of which 28% of equipment investment is spent for oxygenated precursor production. The total operation expense (OPEX) is $1.18/L bio-jet fuel, including variable and fixed costs. Expenses on corncob, catalytic catalyst and H2 contribute 23%, 19% and 16% respectively. Single point sensitivity analysis of the major breakdown of OPEX shows that catalyst lifetime is the priority factor. Economy of scale of minimum selling price of bio-jet fuel (MSPB) for different capacity facilities (1.3 ML/a, 6.5 ML/a and 13 ML/a) was investigated using different discount and tax rates, of which the lowest MSPB was $0.74/L with a subsidy of $0.31/L at 10% discount rate.
The novel perovskite-type Ni-doped Sr0.92Y0.08TiO3 as a reforming biogas (CH4 + CO2) for H2 production Appl. Energy (IF 7.182) Pub Date : 2017-08-09 Byeong Wan Kwon, Joo Hyeng Oh, Ghun Sik Kim, Sung Pil Yoon, Jonghee Han, Suk Woo Nam, Hyung Chul Ham
Tuning dry reforming of methane for F-T syntheses: A thermodynamic approach Appl. Energy (IF 7.182) Pub Date : 2017-08-10 Pengfei Cao, Stephen Adegbite, Haitao Zhao, Edward Lester, Tao Wu
In this research, a thermodynamic equilibrium model was established using FactSage to study the way to tune H2/CO ratio of syngas produced via dry (CO2) reforming of methane (DRM) for various F-T syntheses aiming at eliminating the use of a water–gas-shift unit. The effects of operating conditions, such as temperature, pressure and CH4/CO2 mole ratio, on CH4 and CO2 conversion, H2 and CO yield, and solid carbon yield in DRM were investigated. These operating conditions were studied in a wide range, i.e., 550–1200 °C for temperature, 0.05–5 MPa for pressure and 0.5–2 for CH4/CO2 mole ratio. The results showed that lower CH4/CO2 ratios favoured high CH4 conversion and CO selectivity, but hampered CO2 conversion and H2 selectivity. However, the increase in pressure hindered CH4 conversion, CO2 conversion, H2 selectivity and CO selectivity except for carbon yield. Since the deactivation of catalyst associated with coke formation is the major obstacle for the industrialization of DRM process, a carbon-free regime of DRM was identified as CH4/CO2 mole ratio = 1 and pressure = 0.1 MPa and temperature >1000 °C. Although the H2/CO ratio could be adjusted by adjusting CH4/CO2 mole ratio and/or pressure to satisfy the requirements of different F-T processes, the adjustment of CH4/CO2 mole ratio was found to be a more efficient way of tuning H2/CO mole ratio than adjusting operating pressure. The dependence of H2/CO ratio in syngas on operating conditions of the DRM process was also revealed in this research. With the assistance of this relationship, optimal operating conditions for DRM could be quickly determined based on the required H2/CO mole ratio for various typical F-T processes. It is shown that when the operating temperature of DRM was raised to over 700 °C, the H2/CO ratio obtained at CH4/CO2 ≤ 1 and P = 0.1 MPa was preferable for the synthesis of olefins, heavy hydrocarbons and oxygenated compounds. Otherwise the syngas was more suitable for the production of alkanes (C1–C5).
Evaluation of thermal stimulation on gas production from depressurized methane hydrate deposits☆ Appl. Energy (IF 7.182) Pub Date : 2017-08-10 Bin Wang, Hongsheng Dong, Yanzhen Liu, Xin Lv, Yu Liu, Jiafei Zhao, Yongchen Song
Natural gas hydrates have gained worldwide attention as an important potential non-conventional fossil fuel resource. Understanding the gas production behavior from hydrate deposits is critical to the utilization of the gas hydrate resource. In this study, the hydrate dissociation reaction was induced by depressurization in conjunction with thermal stimulation. Profiles of temperature, pressure, gas production rate, and cumulative gas production during the gas production processes were analyzed. The results show that the gas production process upon ice generation can be divided into five main stages: (1) a free gas release, (2) hydrate dissociation along the equilibrium curve driven by the reservoir sensible heat, (3) hydrate dissociation driven by the exothermic ice generation reaction, (4) ice melting and hydrate dissociation under ambient heat transfer, and (5) hydrate dissociation under ambient heat transfer. During the gas production process, two thermal stimulation methods—ambient heat transfer and warm water injection—were employed to supply heat for hydrate dissociation. The larger the heat flux supplied by ambient heat transfer, the greater the gas production. During the warm water injection process, the gas production time decreased as the temperature of the injected water increased. These two methods can effectively promote gas production from gas hydrate deposits. The findings of this study can provide some insight for designing and implementing optimal production techniques for use of hydrate resources.
Impacts on the solidification of water on plate surface for cold energy storage using ice slurry Appl. Energy (IF 7.182) Pub Date : 2017-08-10 Shengchun Liu, Hailong Li, Mengjie Song, Baomin Dai, Zhili Sun
Ice slurry has been widely used for thermal energy storage system due to its high cold energy storage capacity. To effectively improve the efficiency of ice slurry generator, it is essential to have a deeper understanding about the solidification mechanism on the plate surface of ice generator, which is affected by many factors, such as the roughness of surface and the apparent contact angle. This work studies the impacts of roughness and inhibitor concentration on the freezing temperature, subcooling and the heterogeneous nucleation energy at the surface of aluminum, copper and Teflon plates. Results show that both the roughness and the inhibitor concentration can clearly affect the freezing temperature of water droplet and the heterogeneous nucleation energy. In general, the freezing temperature rises and the subcooling and the heterogeneous nucleation energy drop as the surface roughness increases for all studied materials; and the heterogeneous nucleation energy also increases with the increase of inhibitor concentration. Since the heterogeneous nucleation energy is mainly determined by the substance and the roughness, while not by the surface material, it is important to increase the roughness in order to reduce subcooling and save energy, especially for copper and aluminum.
Experimental and numerical study on pressure drop and heat transfer performance of grille-sphere composite structured packed bed Appl. Energy (IF 7.182) Pub Date : 2017-08-12 Jingyu Wang, Jian Yang, Zhilong Cheng, Yan Liu, Yitung Chen, Qiuwang Wang
Packed beds are widely used in industries, in which the flow and heat transfer characteristics of the packed bed may have a significant effect on the energy efficiency of the whole system. The flow and heat transfer characteristics of packed beds are greatly dependent on their structures. Therefore, it is crucial to develop new packing structures to improve the overall heat transfer performance of packed beds. In the present paper, a grille-sphere composite structured packed bed (GSCSPB) was developed. The new structure aims at overcoming the shortcomings of both randomly packed beds and traditional structured packed beds. A naphthalene sublimation experiment is conducted to measure the pressure drop and heat transfer in GSCSPB and evaluations of the comprehensive heat transfer performance are made to compare the GSCSPB with the randomly packed bed and structured packed bed. A 3-D model is set up to analyze the mechanism of the heat transfer enhancement by using FLUENT 14.0. Results show that firstly, GSCSPB has an excellent design property to reduce the pressure drop of the randomly packed bed and enhance the heat transfer of the structured packed bed, obtaining the highest overall heat transfer performance among the compared packed beds. Secondly, it demonstrates that the existence of the grille wall can change the velocity and temperature distributions, thus the heat transfer is enhanced in GSCSPB compared with a similar configuration without the grille. Finally, it indicates that the grille will help to design a new packing configuration which could achieve a structured packed bed easily and improve the overall heat transfer efficiency.
Post combustion CO2 capture in power plant using low temperature steam upgraded by double absorption heat transformer Appl. Energy (IF 7.182) Pub Date : 2017-08-12 Dandan Wang, Sheng Li, Feng Liu, Lin Gao, Jun Sui
In CO2 capture retrofit unit of existing coal-fired power plants, energy level mismatch between extraction steam from turbines and CO2 regeneration process always results in large exergy destruction and low thermal efficiency. Thus, a new CO2 capture system driven by double absorption heat transformer is proposed. Through the absorption heat transformer, low-temperature steam is upgraded into a higher energy level to match the temperature of CO2 regeneration. Also, flue gas heat is partly recovered to preheat the circulating water from CO2 capture process to further decrease system energy penalty. Aspen Plus 11.0 is used to simulate the system and parameters of key processes are validated by experimental values. It is shown that with 90% CO2 capture, the thermal efficiency of the power plant with proposed CO2 capture system is enhanced by 1.25 percentage points compared with traditional method. And the efficiency enhancement of the proposed system has a trend of increase first and then decrease with CO2 capture rate growth. For a 350 MW coal-fired power plant, the optimum CO2 capture rate is 53.65% and the corresponding efficiency enhancement is 2.06 percentage points. Exergy analysis shows that the exergy destruction in CO2 separation and steam condensation process can decrease by 49.5% in the proposed system, and thereby the exergy efficiency is 1.85 percentage points higher than the conventional method. Furthermore, the cost of CO2 avoided and cost of electricity of the proposed system will be reduced by 10.7 $/t-CO2 and 1.9 $/MW h, respectively.
Industrial energy use and carbon emissions reduction in the chemicals sector: A UK perspective Appl. Energy (IF 7.182) Pub Date : 2017-08-12 Paul W. Griffin, Geoffrey P. Hammond, Jonathan B. Norman
The opportunities and challenges to reducing industrial energy demand and carbon dioxide (CO2) emissions in the Chemicals sector are evaluated with a focus on the situation in the United Kingdom (UK), although the lessons learned are applicable across much of the industrialised world. This sector can be characterised as being heterogeneous; embracing a diverse range of products (including advanced materials, cleaning fluids, composites, dyes, paints, pharmaceuticals, plastics, and surfactants). It sits on the boundary between energy-intensive (EI) and non-energy-intensive (NEI) industrial sectors. The improvement potential of various technological interventions has been identified in terms of their energy use and greenhouse gas (GHG) emissions. Currently-available best practice technologies (BPTs) will lead to further, short-term energy and CO2 emissions savings in chemicals processing, but the prospects for the commercial exploitation of innovative technologies by mid-21st century are far more speculative. A set of industrial decarbonisation ‘technology roadmaps’ out to the mid-21st Century are also reported, based on various alternative scenarios. These yield low-carbon transition pathways that represent future projections which match short-term and long-term (2050) targets with specific technological solutions to help meet the key energy saving and decarbonisation goals. The roadmaps’ contents were built up on the basis of the improvement potentials associated with various processes employed in the chemicals industry. They help identify the steps needed to be undertaken by developers, policy makers and other stakeholders in order to ensure the decarbonisation of the UK chemicals industry. The attainment of significant falls in carbon emissions over this period will depends critically on the adoption of a small number of key technologies [e.g., carbon capture and storage (CCS), energy efficiency techniques, and bioenergy], alongside a decarbonisation of the electricity supply.
A power dispatch model for a ferrochrome plant heat recovery cogeneration system Appl. Energy (IF 7.182) Pub Date : 2017-08-12 Lijun Zhang, Michael Chennells, Xiaohua Xia
A Organic Rankine Cycle waste heat recovery cogeneration system for heat recovery and power generation to relieve grid pressure and save energy cost for a ferrochrome smelting plant is investigated. Through the recovery and utilization of previously wasted heat from the facility’s internal smelting process off-gases, the cogeneration system is introduced to generate electrical power to supply the on-site electricity demand and feed electricity back to the utility grid when it is necessary and beneficial to do so. In addition, the cogeneration system generates cooling power through a lithium bromide-water solution absorption refrigeration cycle to meet the cooling requirements of the plant. The heat recovery process for power generation is modeled and the optimal power dispatching between the on-site loads and the utility grid is formulated as an economic power dispatching (EPD) problem, which aims to maximize the plant’s economic benefits by means of minimizing the cost of purchasing electricity from the utility and maximizing revenue from selling the generated electricity to the grid. Application of the developed model to a ferrochrome smelting plant in South Africa is presented as a case study. It is found that, for the studied case, more than $1,290,000 annual savings can be obtained as a result of the proposed heat recovery power generation system and the associated EPD model. In addition to this, more than $920,000 annual savings is obtained as a result of the generated cooling power via the proposed absorption refrigeration system. The combined cogeneration system is able to generate up to 4.4 MW electrical power and 11.3 MW cooling power from the recovered thermal energy that was previously wasted.
Modelling and optimisation of a hydrogen-based energy storage system in an autonomous electrical network Appl. Energy (IF 7.182) Pub Date : 2017-08-18 K.A. Kavadias, D. Apostolou, J.K. Kaldellis
The European Union’s 2020 climate and energy package (known as “20–20–20” targets) requests, among other key objectives, 40% of the electricity production in Greece to be supplied from Renewable Energy Sources by 2020. The main barriers for reaching this target is the intermittency of renewable energy sources combined with the penetration limits in the local electrical grids and the high seasonal demand fluctuations. In this context, the introduction of energy storage systems, comprises one of the main solutions for coping with this situation. One of the most promising technologies for storing the excess energy, that would be otherwise lost, is the production and storage of hydrogen through water electrolysis. Hydrogen can be used for supporting the electricity grid during periods of high demand but also as transportation fuel for hydrogen-based automobiles (e.g. fuel cell vehicles). For this purpose, a simulation algorithm has been developed, able to assess the specifications of the optimum sizing of hydrogen production storage systems. For the application of the algorithm, the area of the Aegean Sea has been selected, owed to the considerable renewable energy sources curtailments recorded in the various non-interconnected islands in the region. More specifically, the developed algorithm is applied to an autonomous electricity network of 9 islands, located at the SE area of the Aegean Sea and known as the “Kos-Kalymnos” electricity system. The results obtained designate the optimum size of the hydrogen-based configuration, aiming to maximize the recovery of otherwise curtailed renewable energy production.
Dynamic measurements of methane hydrate formation/dissociation in different gas flow direction Appl. Energy (IF 7.182) Pub Date : 2017-08-18 Pengfei Wang, Shenglong Wang, Yongchen Song, Mingjun Yang
Natural gas hydrate (NGH) is a clean energy with huge potential reserves. Therefore, it is essential to understand the hydrate formation and dissociation characteristics for NGH production. Methane hydrate formation under gas migration condition was studied as pre-exploratory step for hydrate reformation research. Vessel pressure changes, methane hydrate saturation (Sh) and residual aqueous water saturation (Sw) were measured and analyzed in this study. Residual aqueous water distribution is also illustrated by magnetic resonance imaging (MRI). We found that, when Sw0 was higher than 0.4, the capillary force affected the aqueous water migration more than when Sw0 was lower than 0.4. Hence, Sh-max had a positive correlation with Sw0 when Sw0 is lower than 0.4. In addition, an upward methane flow is more likely to cause aqueous water redistribution than a downward methane flow. Moreover, we found that the aqueous water distribution changes could not recover after hydrate dissociation. Furthermore, the shifting of the hydrate dissociation boundaries from the vessel wall towards the core can be observed from the MRI images.
Exploring the interactive effects of ambient temperature and vehicle auxiliary loads on electric vehicle energy consumption Appl. Energy (IF 7.182) Pub Date : 2017-08-18 Kai Liu, Jiangbo Wang, Toshiyuki Yamamoto, Takayuki Morikawa
The ability to accurately predict the energy consumption of electric vehicles (EVs) is important for alleviating the range anxiety of drivers and is a critical foundation for the spatial planning, operation and management of charging infrastructures. Based on the GPS observations of 68 EVs in Aichi Prefecture, Japan, an energy consumption model is proposed and calibrated through ordinary least squares regression and multilevel mixed effects linear regression. Specifically, this study focuses on how the ambient temperature affects electricity consumption. Moreover, the interactive effects of ambient temperature and vehicle auxiliary loads are explored. According to the results, the ambient temperature affects the energy efficiency significantly by directly influencing the output energy losses and the interactive effects associated with vehicle auxiliary loads. Ignoring the interactive effects between ambient temperature and vehicle auxiliary loads will exaggerate the energy consumption of the heater during warm conditions and underestimate the energy consumption of the air conditioner during cold conditions. The most economic energy efficiency was achieved in the range of 21.8–25.2 °C. The potential energy savings during proper usage of vehicle auxiliary loads is discussed later based on estimated parameters. As a result, a mean of 9.66% electricity will be saved per kilometre by eradicating unreasonable EV auxiliary loads.
Investigation on methane recovery from low-concentration coal mine gas by tetra-n-butyl ammonium chloride semiclathrate hydrate formation Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Dong-Liang Zhong, Wen-Chun Wang, Zhen-Lin Zou, Yi-Yu Lu, Jin Yan, Kun Ding
Thermodynamic investigations of the supercritical CO2 system with solar energy and biomass Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Xiaohe Wang, Qibin Liu, Zhang Bai, Jing Lei, Hongguang Jin
In this work, a supercritical CO2 system integrating solar energy and biomass is proposed to mitigate the emission of the greenhouse gases, and realize the stable and efficient operation of the system. The proposed system mainly contains three parts, i.e., solar island, biomass burner and power block. With the consideration of the variations of the solar irradiation and the complementation of the biomass, the on-design and off-design thermodynamic performances of this system are numerically studied. Results indicate that the solar-to-electric efficiency of the system can reach to 27.85% at the design point, and the ratios of solar heat supply in the power cycle in four representative days are in the range of 15.7–36.4%. The exergy analyses are implemented to investigate the irreversible losses and the variation of the exergy destruction in the energy conversion process. The economic evaluations are carried out to illustrate the feasibility of the proposed system, and the LCOE of the system is 0.085 $/kW h. Theoretical results indicate that the supercritical CO2 system with multi-energies input is a promising option for the efficient utilization of the abundant solar and biomass resources in western China.
State-of-health estimation for the lithium-ion battery based on support vector regression Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Duo Yang, Yujie Wang, Rui Pan, Ruiyang Chen, Zonghai Chen
Active and stable Ni based catalysts and processes for biogas upgrading: The effect of temperature and initial methane concentration on CO2 methanation Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Kristian Stangeland, Dori Yosef Kalai, Hailong Li, Zhixin Yu
CO2 hydrogenation to methane (CO2 methanation) is gaining increasing interest as a major chemical synthesis process for chemical storage of fluctuating renewable energy and producing synthetic natural gas by providing an effective process for biogas upgrading. In this study, a series of 12 and 20 wt% Ni/Al2O3 catalysts, either unpromoted or promoted by 0.5 wt% Ru, were prepared by the incipient wetness method for the CO2 methanation reaction from a feed of pure CO2 or biogas. The catalysts were characterized by N2 physisorption, XRD, TPR and H2 chemisorption. The activity for the 12 wt% Ni catalyst increased continuously in the temperature range from 250 °C to 400 °C. Increasing the Ni loading and Ru promotion greatly improved the activity of the catalyst. At 350 °C, the highest CO2 conversion of 82% and CH4 selectivity of 100% was achieved over the 20Ni0.5Ru/Al2O3 catalyst. Thereafter, methanation of a simulated biogas mixture was investigated over the 20Ni/Al2O3 and 20Ni0.5Ru/Al2O3 catalysts. The results showed that the CO2 conversion and CH4 selectivity were only mildly affected by the feed composition. Furthermore, the stability of the catalysts was similar regardless of the feed composition. This study demonstrates that high purity CH4 can be achieved from a biogas feed over our Ni based catalysts.
The use of electrical heating for the enhancement of gas recovery from methane hydrate in porous media Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Bo Li, Sheng-Dong Liu, Yun-Pei Liang, Hang Liu
The gas production behaviors of methane hydrate dissociation induced by depressurization and electrical heating are investigated in a Cuboid Pressure Vessel (CPV) with an effective volume of 1.5 L. The vertical well located at the axis of the vessel is used as the production well, and a resistance heating wire is distributed uniformly in the inner surface of the well for heat injection. Hydrate samples with the similar phase saturations are prepared and then decomposed under depressurization and electrical heating. A total of five experimental runs have been carried out with different production pressure (3.50, 4.50, and 5.50 MPa) and electrical heating power (0, 25, and 50 W). It is found that methane hydrate can be dissociated continuously in the CPV in each run, which proves the feasibility of the used method for hydrate exploitation in porous media. Compared with the pure depressurization case (run 3), both the gas production and hydrate dissociation rates could be increased to a much higher level when a relatively slow heat injection rate is supplied from the well. In addition, the net energy Enet can be recovered with a much faster rate under constant electrical heating rate, and the final amount of Enet is only a little lower than that of run 3. They all indicate that the production efficiency of depressurization can be greatly enhanced by employing the electrical heating simultaneously. A maximum Enet can be obtained in each case with constant electrical heating, and it is suggested that the production process should be terminated before Enet begins to drop. The gas production performance is generally more favorable under lower production pressure and a higher electrical heating rate.
Investigation on small-scale low pressure LNG production process Appl. Energy (IF 7.182) Pub Date : 2017-08-19 M.A. Ancona, M. Bianchi, L. Branchini, A. De Pascale, F. Melino, M. Mormile, M. Palella, L.B. Scarponi
With the increase of global energy demand, the natural gas will play a key role both for energy production and for transports. Typically, natural gas is extracted and liquefied in large-scale plants to be later transported by ship or, when it is possible, by pipeline. In this study, a plug & play solution for natural gas liquefaction to be directly installed at the vehicle’s filling stations, in order to avoid the transport costs of liquefied natural gas, is analyzed. The system analyzed in the paper consists in a single stage expansion process and the aim of the study is to improve the small-scale liquefaction process efficiency through the use of a cryogenic expander in replacement of a more common Joule-Thomson valve. A thermodynamic study has been carried out to optimize the process parameters with the aim of minimizing the energy consumption. This optimization study, starting from a reference case, allowed to identify an optimal case, which leads to a total energy saving of about 12% compared to the reference case. Furthermore, considerations relating to the cryogenic expander, which is a key component of the system, have been done. This device guarantees a higher thermodynamic efficiency than Joule-Thomson valve and it allows to integrate the produced shaft power into the process. This study represents a preliminary thermodynamic and parametric investigation on a low pressure LNG production process. The results of this study are the basis for the realization of a prototype which is actually under construction. Thus, further investigations by Authors will determinate the techno-economic feasibility of the optimized system also considering future experimental investigations.
Combustion modeling in RCCI engines with a hybrid characteristic time combustion and closed reactor model Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Dezhi Zhou, Wenming Yang, Jing Li, Kun Lin Tay, Markus Kraft
This study proposed a hybrid model consisting of a characteristic time combustion (CTC) model and a closed reactor model for the combustion modelling with detailed chemistry in RCCI engines. In the light of the basic idea of the CTC model of achieving chemical equilibrium in high temperature, this hybrid model uses the CTC model to solve the species conversion and heat release in the diffusion flame. Except for the diffusion flame, the auto-ignition in RCCI combustion is computed by a closed reactor model with the CHEMKIN library by assuming that the computational cells are closed reactors. The border of the transition between the CTC model and closed reactor model is determined by two criteria, a critical temperature and a critical Damköhler number. On the formulation of this hybrid model, emphasis is placed on coupling detailed chemistry into this hybrid model. A CEQ solver for species equilibrium calculations at certain temperature, pressure was embedded with CTC for detailed chemistry calculation. Then this combustion model was integrated with the CFD framework KIVA4 and the chemical library CHEMKIN-II and validated in a RCCI engine. The predicted in-cylinder pressure and heat release rate (HRR) show a good consistency with the data from the experiment and better accuracy than that computed from the sole closed reactor model. More importantly, it is observed that this model could save computational time compared with closed reactor model due to less stiff ordinary differential equations (ODEs) computation. A sensitivity analysis of the critical temperature and critical Damköhler number was conducted to demonstrate the effect of these two parameters in the current model.
Numerical investigation of heat transfer performance of a rotating latent heat thermal energy storage Appl. Energy (IF 7.182) Pub Date : 2017-08-19 Jundika C. Kurnia, Agus P. Sasmito
Performance of an electrical distribution network with Soft Open Point during a grid side AC fault Appl. Energy (IF 7.182) Pub Date : 2017-08-21 Avinash Aithal, Gen Li, Jianzhong Wu, James Yu
Soft Open Point (SOP) is a power electronic device installed in place of normally open points in electrical distribution networks. This paper investigates the dynamic performance of a medium voltage (MV) distribution network with a connected SOP, under grid side AC faults. Use of sequence networks was extended to include SOP, such that conventional fault analysis technique can be used on a distribution network with SOP. A Fault-Index was defined using symmetrical components of voltages measured at the grid connection point of the SOP. The network performance was investigated under a line-to-ground, a line-to-line and a three-phase fault. The behaviour of the network was analysed under different control schemes and various operating scenarios of the SOP. Furthermore, the dependence of the sequence voltages and currents on the SOP set points was investigated. Simulations were carried out on an 11 kV generic UK distribution network model developed in PSCAD/EMTDC. Results show that the convectional fault analysis technique is applicable on a network with SOP, regardless of the SOP control mode. The Fault-Index, defined based on the local voltage measurements, was effective in detecting the presence of an AC fault in the MV distribution network. In addition, the need for a non-current based detection method is illustrated.
Hydrodeoxygenation of lignin-derived phenoic compounds to hydrocarbon fuel over supported Ni-based catalysts Appl. Energy (IF 7.182) Pub Date : 2017-08-21 Xinghua Zhang, Wenwu Tang, Qi Zhang, Tiejun Wang, Longlong Ma
Ni-based catalysts supported on γ-Al2O3 and SiO2 were prepared by impregnation. Catalyst characterization was performed using XRD, NH3-TPD, H2-TPR and chemisorption. Effects of supports on catalytic performance were tested using the hydrodeoxygenation (HDO) of phenolic compounds as a model reaction. Experiment result shows that single phenolic compounds can be converted via HDO reaction over Ni/SiO2 and Ni/γ-Al2O3 catalysts at 300 °C. The hydrocarbon yields are in the range of 60–90%. The effect of supports on the reaction mechanism was also explored. It is found that hydrogenation of the aromatic ring preferentially occurs over Ni/SiO2 catalyst while the cleavage of CARO bond preferentially occurs over Ni/γ-Al2O3 catalyst in the HDO of phenol. Compared to Ni/γ-Al2O3 catalyst, Ni/SiO2 catalyst exhibits better repeatability and higher catalytic activity for hydrocarbon yield when mixed phenolic compounds were used as feedstock in the HDO reaction, and the carbon deposited on the surface of Ni/SiO2 catalyst is lower.
An adaptive Fuzzy logic-based approach to PID control of steam turbines in solar applications Appl. Energy (IF 7.182) Pub Date : 2017-08-21 S. Dettori, V. Iannino, V. Colla, A. Signorini
In Concentrated Solar Power Plants, steam turbines controlled with standard Proportional Integrative Derivative (PID) methods may suffer from performance downgrading in power generation when the steam conditions deviate from nominal ones. An enhancement of standard steam turbine controller can be the key to achieve optimal performance also in non-nominal steam conditions. This paper presents the improvement of the PID control concept by exploiting Fuzzy Logic, an artificial intelligence technique that allows taking into account the human experience and knowledge on the system behavior. A real Concentrated Solar Power Plant has been modeled focusing on generated power control loop, its stability and performance analysis, knowledge useful to design a Fuzzy Inference System. A fuzzy logic controller is proposed to continuously adapt the PID parameters, to improve the steam turbine governor action. Its performance is compared to the classical PID tuned according to three different approaches. The fuzzy logic PID controller extends the simplicity of PID and adapts the control action to actual operating condition by providing the system with a sort of “decision-making skill”. The possibility to design implementable algorithms on a Programmable Logic Controller, which have stringent computational speed and memory requirements, has been explicitly taken into account in the developed work, through the minimization of the controller complexity with a reduced number of fuzzy sets and fuzzy rules within the fuzzy inference system.
Investigation of thermo-fluidic performance of phase change material slurry and energy transport characteristics Appl. Energy (IF 7.182) Pub Date : 2017-08-23 F. Ma, P. Zhang, X.J. Shi
Thermal or cold storage is a promising way to alleviate the peak-valley difference of the electricity load and improve the energy efficiency. The thermal or cold storage by micro-encapsulated phase change material (MPCM) slurry is one of the effective measures to be implemented in waste heat recovery and heat transport system etc. due to its high energy storage density and excellent heat transfer performance. The thermo-fluidic performances of the MPCM slurry flowing through the horizontally circular pipe under constant heat flux are numerically investigated based on the Eulerian-Eulerian approach in the present study. It is found that the numerical results are in good consistence with the experimental results from the aspects of flow and heat transfer. The influences of particle diameter on solid volume fraction distribution, solid velocity distribution and pressure drop of the MPCM slurry are investigated under isothermal condition. And then the temperature distribution of the MPCM slurry and liquid volume fraction of the PCM in MPCM are presented to analyze the heat transfer performance of the MPCM slurry. The particle diameter also imposes significant influences on the heat transfer between the two phases and average heat transfer coefficient of the MPCM slurry. The largest pressure drop and the highest average heat transfer coefficient appear when the particle diameter of the MPCM decreases to 1 μm. Further investigations at different Reynolds numbers are carried out to study the variation of local heat transfer coefficient along the pipe. Finally, the comparison of energy transport performances between the MPCM slurry and water are presented based on the ratio of transported heat to pumping power. The MPCM slurry shows better energy transport performance than pure water when the Reynolds number is above 7865.
Co-digestion of sewage sludge and microalgae – Biogas production investigations Appl. Energy (IF 7.182) Pub Date : 2017-08-24 Eva Thorin, Jesper Olsson, Sebastian Schwede, Emma Nehrenheim
In municipal wastewater treatment plants (WWTPs), algae could be utilised for cleaning the water and, at the same time, produce a biomass that can be used for energy. Through anaerobic digestion, microalgae can contribute to biogas production when co-digested with sewage sludge. In this paper, previous published results on the co-digestion of sewage sludge and microalgae are summarised and reviewed, and any remaining knowledge gaps are identified. The batch tests currently documented in literature mostly concern digestion under mesophilic conditions, and studies investigating thermophilic conditions are less common. The average biochemical methane potential (BMP) for 29 different mixtures co-digested under mesophilic conditions is 317 ± 101 N cm3 CH4 gVS−1 while the result for 12 different mixtures investigated under thermophilic conditions is a BMP of 318 ± 60 N cm3 CH4 gVS−1. An evaluation of the heat required for increasing the temperature from mesophilic to thermophilic conditions shows that increased methane production under thermophilic conditions can be enough to create a positive energy balance. For a full-scale WWTP, using thermophilic digestion on sludge, or a combination of sludge and microalgae could therefore be of interest. This is dependent on the demands on sanitation of the sludge and the possibilities for heat recovery. Most of the mesophilic investigations indicate a synergetic effect for co-digestion, with enhancements of up to almost 70%. However, the results are uncertain since the standard deviations for some of the BMP tests are in the same order of magnitude as the identified enhancement. Neither of the presented publications provide an understanding of the basic mechanisms that led to higher or lower BMP when microalgae were mixed with wastewater sludge. We, therefore, call for care to be taken when assuming any effects related to the specification of substrates. Microalgae and wastewater sludge have several similarities, and the specific results of BMP in the mixtures relate more to the specifics of the respective materials than the materials themselves. Investigations into semi-continuous processes of co-digestion of microalgae and sludge are scarce. The yields for three co-digestion studies show high variation, with an average of 293 ± 112 N cm3 gVSin−1. The available results show strong potential for co-digestion of sewage sludge and microalgae. Further investigations are required to identify optimal conditions for biogas production, and analysis of microalgae implementation on wastewater treatment at a system level is also needed to identify the total mass balance of substrate and nutrient recovery.
High temperature gasification of high heating-rate chars using a flat-flame reactor Appl. Energy (IF 7.182) Pub Date : 2017-08-25 Tian Li, Yanqing Niu, Liang Wang, Christopher Shaddix, Terese Løvås
The increasing interest in gasification and oxy-fuel combustion of biomass has heightened the need for a detailed understanding of char gasification in industrially relevant environments (i.e., high temperature and high-heating rate). Despite innumerable studies previously conducted on gasification of biomass, very few have focused on such conditions. Consequently, in this study the high-temperature gasification behaviors of biomass-derived chars were investigated using non-intrusive techniques. Two biomass chars produced at a heating rate of approximately 104 K/s were subjected to two gasification environments and one oxidation environment in an entrained flow reactor equipped with an optical particle-sizing pyrometer. A coal char produced from a common U.S. low sulfur subbituminous coal was also studied for comparison. Both char and surrounding gas temperatures were precisely measured along the centerline of the furnace. Despite differences in the physical and chemical properties of the biomass chars, they exhibited rather similar reaction temperatures under all investigated conditions. On the other hand, a slightly lower particle temperature was observed in the case of coal char gasification, suggesting a higher gasification reactivity for the coal char. A comprehensive numerical model was applied to aid the understanding of the conversion of the investigated chars under gasification atmospheres. In addition, a sensitivity analysis was performed on the influence of four parameters (gas temperature, char diameter, char density, and steam concentration) on the carbon conversion rate. The results demonstrate that the gas temperature is the most important single variable influencing the gasification rate.
Microfluidics-based pH-differential reactor for CO2 utilization: A mathematical study Appl. Energy (IF 7.182) Pub Date : 2017-08-25 Xu Lu, Dennis Y.C. Leung, Huizhi Wang, Jin Xuan
This paper reports a mathematical model for calculating various losses in a pH differential microfluidic electrolytic cell (PMEC) for CO2 to formic acid conversion. The microfluidic characteristics of the cell were examined, and in respect of electro-chemical equilibrium states, major limiting factors such as mass transfer constraints, kinetic losses and overpotentials, were considered and acid–base interface and neutralisation losses therein identified. Losses of electrical resistance on electrodes and within micro-channels were quantified, and computational results were validated against previous experimental data. To the best of our knowledge, the model is the first for determining dual electrolyte arrangements and associated losses and can be used to develop parametric optimisation strategies.
Characterization of char from biomass gasification and its similarities with activated carbon in adsorption applications Appl. Energy (IF 7.182) Pub Date : 2017-08-26 Vittoria Benedetti, Francesco Patuzzi, Marco Baratieri
This study points out the similarities between gasification char and activated carbon and reviews its successful applications in the field of adsorption. Since only few data on char from biomass gasification are available in the literature, chars collected from six different commercial gasification plants have been characterized by different techniques. Similarities and differences of the six samples have been pointed out and eventually, three samples have been selected as the most suitable for further applications of char as activated carbon. Characterization results have been compared with data available in the literature and finally, effective examples of char applications as adsorbent have been reported.
Maximizing intermittency in 100% renewable and reliable power systems: A holistic approach applied to Reunion Island in 2030 Appl. Energy (IF 7.182) Pub Date : 2017-08-30 Nadia Maïzi, Vincent Mazauric, Edi Assoumou, Stéphanie Bouckaert, Vincent Krakowski, Xiang Li, Pengbo Wang
Technical constraints related to power systems management may limit the high integration of variable renewable energy sources in the power mix. This issue is addressed for the Reunion Island, which aims to reach energy independence by 2030 using 100 % renewables. To that end, a long-term power system analysis is proposed using a comprehensive and coherent approach based on a bottom-up TIMES model providing future production mixes according to different scenarios. A transient reliability indicator based on kinetic energy is proposed and endogenized within the model. In addition, a dedicated Kuramoto model describes the synchronism condition required for aggregating the kinetic energy embedded in the whole power system. For the case of Reunion island, this methodology draws the following conclusions: (i) to achieve the 100 % renewables target, the capacity to invest in the energy sector is doubled, and the level of reliability decreases considerably; (ii) the loss of reliability induced by higher intermittency— typically 50 % —in the power mix can be counter balanced and leveraged by implementing flexibility solutions (demand response and storage).
Coupling detailed radiation model with process simulation in Aspen Plus: A case study on fluidized bed combustor Appl. Energy (IF 7.182) Pub Date : 2017-08-31 Yukun Hu, Jihong Wang, CK Tan, Chenggong Sun, Hao Liu
While providing a fast and accurate tool for simulating fluidized beds, the major limitations of classical zero-dimensional ideal reactor models used in process simulations become irreconcilable, such as models built into commercial software (e.g. Aspen Plus®). For example, the limitations of incorporating heat absorption by the water wall and super-heaters and inferring thermal reciprocity between each reactor model/module. This paper proposes a novel modelling approach to address these limitations by incorporating an external model that marries the advantages of the zone method and Aspen Plus to the greatest extent. A steady state operation of a 0.3 MW atmospheric bubbling fluidized-bed combustor test rig was simulated using the developed modelling approach and the results were compared with experimental data. The comparison showed that the predictions were in agreement with the measurements. Further improvement is to be expected through incorporating more realistic zoned geometry and more complex reaction mechanisms. In addition, the developed model has a relatively modest computing demand and hence demonstrates its potential to be incorporated into process simulations of a whole power plant.
Life cycle sustainability assessment of grid-connected photovoltaic power generation: A case study of Northeast England Appl. Energy (IF 7.182) Pub Date : 2017-08-31 Tianqi Li, Anthony Paul Roskilly, Yaodong Wang
This paper proposes a comprehensive sustainability assessment model incorporating (a) life cycle approach and sustainability theory. In the model, sustainability is assessed from three categories: techno-economic, environmental and social. A total of thirteen indicators were included in the proposed model, with five evaluating the techno-economic performance, six evaluating the environmental performance, and two examining the social impact. The effectiveness of this model is then demonstrated through its application to a case study of solar photovoltaic in the North East region of England. Three types of the most commonly deployed solar photovoltaic electricity generation systems are included in the case study: monocrystalline (s-Si), polycrystalline (p-Si) and Cadmium telluride (CdTe) thin film. The multi-silicon solar photovoltaic system is found to be the most sustainable option for its high performance in the techno-economic and environmental categories; the CdTe based system is the least-favoured option across all three categories; and the polycrystalline system has the best performance across all categories. Energy conversion efficiency appears to be one of the most influential factors for the solar photovoltaic system’s sustainability performance. Despite being the least costly system among the three, the CdTe system appears to be the least financially viable option mainly due to its low energy-conversion efficiency. This study estimates the environmental impact of selected technologies using the CML2001 method and then employs ReCiPe method to cross-validate the estimated results. Identical results were found for all indicators apart from eutrophication potential, due to the difference in impact quantification methods between CML and ReCiPe.
Predictive air-conditioner control for electric buses with passenger amount variation forecast☆ Appl. Energy (IF 7.182) Pub Date : 2017-08-31 Hongwen He, Mei Yan, Chao Sun, Jiankun Peng, Menglin Li, Hui Jia
Air-conditioners (AC) usually consume the most electricity among all of the auxiliary components in an electric bus, over 30% of the battery power at maximum. On-board passengers carried by the electric bus are important but random heat sources, which are obsessional disturbances for the cabin temperature control and energy management of the AC system. This paper aims to improve the AC energy efficiency via passenger amount variation analysis and forecast in a model predictive control (MPC) framework. Three forecasting approaches are proposed to realize the passenger amount variation prediction in real-time, namely, stochastic prediction based on Monte Carlo, radial basis function neural network (RBF-NN) prediction, and Markov-chain prediction. A sample passenger number database along a typical bus line in Beijing is built for passenger variation pattern analysis and forecast. A comparative study of the above three prediction approaches with different prediction lengths (bus stops in this case) is conducted, from both the energy consumption and temperature control perspectives. A predictive AC controller is developed, and evaluated by comparing with Dynamic Programming (DP) and a commonly used rule-based control strategy. Simulation results show that all the three forecasting methods integrated within the MPC framework are able to achieve more stable temperature performance. The energy consumptions of MPC with Markov-chain prediction, RBF-NN forecast and Monte Carlo prediction are 6.01%, 5.88% and 5.81% lower than rule-based control, respectively, on the Beijing bus route studied in this paper.
How will sectoral coverage affect the efficiency of an emissions trading system? A CGE-based case study of China Appl. Energy (IF 7.182) Pub Date : 2017-08-31 Yaqian Mu, Samuel Evans, Can Wang, Wenjia Cai
This study contributes to the existing literature on optimal carbon mitigation policy by quantifying the impacts of various sectoral coverage options for the emissions trading systems (ETS) used to achieve China’s Intended Nationally Determined Contribution (INDC) targets for the Paris Agreement on climate change. The CHEER model, a computable general equilibrium (CGE) model of China with detailed representation of electricity and other energy intensive sectors, as well as a complete CO2 emissions accounting module and carbon market, is used in this study. Results show several important findings. First, China’s INDC targets can be achieved through an economy-wide ETS at an economic cost of 2.1% of real GDP by 2030. Second, including only the eight sectors proposed for initial implementation of the ETS in China is likely to result in a much larger mitigation cost than the economy-wide approach, estimated to be as high as 10.5% of 2030 real GDP. Thirdly, this study further indicates that the mitigation costs can be reduced to 3.3% of real GDP in 2030 if other energy-intensive sectors, accounting for additional 24.8% of total emissions, are included in the ETS. As a result, not all sectors are required to get close to the first-best mitigation option so long as critical sectors are not excluded. In addition, the temporal dimension of mitigation costs and air pollution co-benefits under different sectoral schemes of China’s ETS gives policy-makers a degree of short-run flexibility in terms of phasing in additional industries over time.
Performance assessment of a hybrid SOFC/MGT cogeneration power plant fed by syngas from a biomass down-draft gasifier Appl. Energy (IF 7.182) Pub Date : 2017-09-09 Alessandra Perna, Mariagiovanna Minutillo, Elio Jannelli, Viviana Cigolotti, Suk Woo Nam, Kyung Joong Yoon
Hybrid systems combine two or more power generating devices and make use of the synergism to generate maximum power and offer very high efficiencies. The aim of this work is to investigate the performance achievable from a small-scale hybrid power plant based on the integration between a micro gas turbine (MGT) and a solid oxide fuel cell (SOFC) fed by the syngas generated by a biomass downdraft gasifier (BG). The thermal energy needed to reach the turbine inlet temperature is supplied by the exhausts coming from a catalytic burner in which the SOFC anode and cathode off-gases are burnt. The hybrid BG-SOFC/MGT plant, based on a simplified configuration and realized considering components commercially available, is designed for optimizing not only the electric power generation, but also the thermal power production, in accordance with the promotion of decentralized CHP plants. The performance assessment has been carried out by means of a numerical model, based on thermodynamic/thermochemical approaches and realized by integrating the models of each plant section, developed by using the Aspen Plus software package. The models validation, performed by using experimental data, demonstrates that the results produced are close to those obtained from each unit, so that the overall integrated model can provide a sufficiently accurate prediction of the expected actual hybrid power plant. The effects of some operating parameters on cogeneration performances, such as the MGT pressure ratio and the S/C (steam to carbon) in the SOFC unit, have been evaluated and analyzed. Results show that the best performances are achieved by assuming the MGT pressure ratio equal to 4.5 and the S/C equal to 0. In this case the electric power is 262 kW (SOFC supplies 180 kW), the thermal power is 405 kW and the electric (AC) and cogeneration efficiencies are 35% and 88%, respectively.
Tolerance analysis of electrified vehicles on the motor demagnetization fault: From an energy perspective Appl. Energy (IF 7.182) Pub Date : 2017-09-12 Hongwen He, Nana Zhou, Jinquan Guo, Zheng Zhang, Bing Lu, Chao Sun
Due to possible overheat, abrasion or mechanical vibrations, demagnetization fault is inevitable in permanent magnet synchronous motors (PMSMs), which could greatly decrease the motor’s efficiency and hence an electrified vehicle’s performance. This paper, from an energy efficiency point of view, proposes to analyze the tolerance ability of different electrified vehicles on motor demagnetization faults, via PMSM flux density degradation modeling, efficiency estimation and dynamic programming (DP) based powertrain energy management. The relationship between different demagnetization levels and resultant motor efficiencies is obtained, and analyzed according to the motor operation area. Demagnetized PMSM is adopted in a pure electric vehicle (PEV), a hybrid electric vehicle (HEV) and a plug-in hybrid electric vehicle (PHEV) for energy efficiency analysis. Tolerance analysis indicates that the powertrain efficiency decrease caused by motor demagnetization is more severe under urban driving conditions, especially with PEV and PHEV configurations compared with HEV. A demagnetization threshold investigation is also given in this paper.
A comparison of radial-flow and axial-flow packed beds for thermal energy storage Appl. Energy (IF 7.182) Pub Date : 2017-09-14 J.D. McTigue, A.J. White
Packed-bed thermal reservoirs are an integral component in a number of electrical energy storage technologies. The present paper concentrates on packed beds where the heat transfer fluid travels along the radial co-ordinate. The governing energy equations and various mechanisms that cause exergetic losses are discussed. The radial-flow packed bed is compared to a dimensionally similar axial-flow packed bed. This approach provides a fair assessment of the underlying behaviour of the two designs. Multi-objective optimisation allows a wide range of design variables to be considered, and is employed to compare optimal radial-flow and axial-flow stores. Axial-flow stores that have been segmented into layers are also considered. The results indicate that radial-flow stores have a comparable thermodynamic performance, but that the additional volume required for by-pass flows leads to higher capital costs.
Lithium as energy carrier: CFD simulations of LI combustion in a 100 MW slag tap furnace Appl. Energy (IF 7.182) Pub Date : 2017-09-19 Pascal Maas, Martin Schiemann, Viktor Scherer, Peter Fischer, Dan Taroata, Günther Schmid
Designing high-order power-source synchronous current converters for islanded and grid-connected microgrids Appl. Energy (IF 7.182) Pub Date : 2017-09-21 Mahdi Ashabani, Hoay Beng Gooi, Josep M. Guerrero
This paper deals with development of a versatile and compact control strategy for voltage source converters in grid-connected and islanded microgrids using synchronous current converters technology. The key feature is its new integrated high-order controller/synchronizer with applicability to both operational modes without strategy rearrangement. Using high-order controllers, on the other hand, results in rather complex analysis and design process, therefore this paper aims at providing a general and simple theme for the design and parameter selection. The controller also provides adaptive and automated current-based grid synchronization. Moreover, the controller realizes a power-source current-controlled microgrid with minimum control loops, as compared to widely adopted voltage controlled microgrids in the literature, with advantages such as fault-ride-through and inherent droop-less power sharing capabilities. Adaptive current-based synchronization and smooth switching to islanding mode provides high flexibility, reliability and only-plug operation capability. Extensive simulation and experimental results are presented to demonstrate performance of the proposed control and management strategy.
Improvement of combustion performance and emissions in diesel engines by fueling n-butanol/diesel/PODE3–4 mixtures Appl. Energy (IF 7.182) Pub Date : 2017-09-21 Haozhong Huang, Qingsheng Liu, Wenwen Teng, Mingzhang Pan, Chang Liu, Qingxin Wang
Polyoxymethylene dimethyl ethers (PODEn) are an excellent biofuel with no CC bond and substantial soot-reduction potential. The effects of BMEPs on the characteristics of combustion performance and emissions in a four-cylinder direct injection diesel engine with n-butanol/diesel/PODE3–4 blends were investigated. Mechanism of the PODE blends on soot reduction is discussed. The experimental results indicate that upon adding PODE3–4 to the blend of n-butanol with diesel can improve the thermal efficiency and combustion efficiency with an increment in the brake specific fuel consumption (BSFC). As the BMEP increased, a decreasing trend was observed in the emissions of soot, CO, and THC, while increasing NOx formation. Under a BMEP of 1.2 MPa, the soot emissions from the combustion of BD20, BDP10, and BDP20 reduced by 61.5%, 80.7, and 91.1%, respectively, compared to that from pure diesel. Under equal BMEP value, adding PODE3–4 to n-butanol/diesel blend reduced the soot, CO and THC emissions, and the lowest soot and THC emissions were found for BDP20, followed by BDP10, BD20, and D100. The number concentration of the accumulated particulate matter as well as the mass concentration of total particulate matters can be decreased by adding PODE3–4. The chemical kinetics simulation results reveal that CO bonds break and CH2O is first produced in the pyrolysis of PODEn; as the value of n increases, more CH2O is produced and further oxidized to form HCO, which is finally transformed into CO and CO2, avoiding the production of soot precursors.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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