Interesterification optimization of waste cooking oil and ethyl acetate over homogeneous catalyst for biofuel production with engine validation Appl. Energy (IF 7.9) Pub Date : 2018-09-18 Sathaporn Chuepeng, Cholada Komintarachat
Analysis and forecasting of the carbon price using multi—resolution singular value decomposition and extreme learning machine optimized by adaptive whale optimization algorithm Appl. Energy (IF 7.9) Pub Date : 2018-09-18 Wei Sun, Chongchong Zhang
Precise prediction of carbon prices by means of single forecasting models may be difficult due to the inherent non-stationary and nonlinearity characteristics of the carbon price. This paper i proposes an innovative hybrid model for predicting the carbon price. The prediction was made through the extreme learning machine optimized by the adaptive whale optimization algorithm based on the multi-resolution singular value decomposition. The multi-resolution singular value decomposition was used to eliminate the high frequency components of the previous carbon price data. Afterwards, the carbon price was successfully decomposed into two time series—the approximation series and the detailed series. The partial auto-correlation function was employed in the approximation series for determining the input variables of the extreme learning machine. The adaptive whale optimization algorithm was utilized to optimize both the input weight matrix and the bias matrix to improve the robustness and accuracy of extreme learning machines. The empirical simulation based on four diverse types of carbon prices under carbon trading pilot programs in China found that the proposed model outperformed the other benchmark methods. Four different matured carbon future prices under the European Union national emissions trading scheme (EU ETS) were also selected for forecasting. The results showed that the proposed model performed fairly well in forecasting the EU carbon price.
Failure probability estimation of the gas supply using a data-driven model in an integrated energy system Appl. Energy (IF 7.9) Pub Date : 2018-09-18 Xueqian Fu, Gengyin Li, Xiurong Zhang, Zheng Qiao
Probabilistic security evaluation is one of the academic frontiers in the research on energy system reliability. It is very important to evaluate the impact of gas systems on the power/heat system for practical engineering in gas turbine engine-based integrated energy systems. This paper proposes a data-driven model instead of a physical model to estimate the probabilities of the incident of insufficient gas supply suffered from weather uncertainty, which affects the reliability of gas turbine engine-based integrated energy systems. According to actual energy projections, it can be assumed that the uncertainty of intermittent wind power, load fluctuations, and variations in gas deliverability derives from fluctuating weather conditions such as the temperature and wind. The wind power, load, and gas consumption data in the integrated energy system and the gas supply data of the station are sufficient to accurately build a data-driven model. Traditional methods based on physical models include the Iman and Stein methods, the first-order reliability method, and the mixed Monte Carlo algorithm to judge the effectiveness of the proposed method. The results from three cases are a testimony to the accuracy and engineering feasibility of the proposed method. The calculation of a data-driven model is easier than that of a physical model, and its simplification is conducive to failure probability estimation in a real application.
Performance optimization of single and two-stage micro/nano-scaled heat pumps with internal and external irreversibilities Appl. Energy (IF 7.9) Pub Date : 2018-09-18 Wenjie Nie, Ke Lü, Aixi Chen, Jizhou He, Yueheng Lan
Based on the thermosize effects of a confined ideal Maxwellian gas, we established a model of micro/nano-scaled heat pump including two isothermal and two isobaric processes, where the Joule-like heating effect was analyzed in detail by using the nonequilibrium thermodynamic theory. Further, in order to improve the performance of a single thermosize device, a model of two-stage micro/nano-scaled heat pump with multiple micro/nano components is for the first time put forward. The general expressions of heating load and coefficient of performance for the single and the two-stage heat pump are derived. The influences of the internal and external irreversibilities of the system, i.e., Fourier heat flow and the Joule-like heating and the finite rate heat transfer with the reservoirs, on the performance characteristic of thermosize devices are studied in detail. Moreover, we also discuss the effect of the allocation the thermosize components on the optimal performance of the two-stage micro/nano-scaled heat pump cycle. It is found that in the presence of the internal and external irreversibilities, the two kinds of the micro/nano-scaled heat pump can achieve specific heating performance. In particular, when the total number M of the thermosize components is fixed, both the maximum of the optimal coefficient of performance Φopt,max and the maximum of the heating load Πopt,max corresponding to the optimal coefficient of performance appear near n=M/2 with n being the number of the thermosize elements of the top stage. The results obtained here show several main irreversibility source of the micro/nano-scaled heat pump and have potential applications in the efficient utilization and conversion of energy in the microchannel system using gas.
An improved supercritical coal-fired power generation system incorporating a supplementary supercritical CO2 cycle Appl. Energy (IF 7.9) Pub Date : 2018-09-18 Cheng Xu, Qiang Zhang, Zhiping Yang, Xiaosa Li, Gang Xu, Yongping Yang
Large superheat degree of the steam bleeds from regenerative heaters as well as the large heat transfer temperature difference during the air preheating process is not thermodynamically satisfactory in advanced supercritical power plants with the aim of high power generation efficiency. In this study, an improved supercritical coal-fired power generation system, which integrates a supercritical CO2 (S-CO2) power cycle to utilize the superheat of the steam bleeds as well as to heat the combustion air, was proposed. In the proposed system, the heat transfer temperature difference within the steam regenerative trains and air preheating process could be reduced, leading to less exergy destructions. Moreover, less required heat for flue gas air heaters makes it possible to adopt a low-temperature economizer (LTE) between the arranged two-stage flue gas air heaters, saving part of the steam bleeds, even if the exhaust flue gas temperature is kept constant. The detailed exergy distributions within the regenerative heaters and air pre-heating process were discussed using the graphical exergy analysis. The mass and energy balance of the proposed system and the overall system performance were determined using the process simulation. The economic viability and the implementation feasibility of the proposed system was also analyzed. Results showed that the exergy destruction of the regenerative heaters and air preheating process could be reduced by 4.47 MW and 11.95 MW, respectively. The gross electric power output from the proposed system was 1007.79 MW with a satisfactory energy efficiency at 46.0%, 0.4 percentage point higher than the reference power plant. The payback period of the proposed system is slightly longer than that of the reference plant at the current market condition and it will be more profitable as the S-CO2 cycle becomes more commercially mature.
A critical review of heat and mass transfer in vegetative roof models used in building energy and urban enviroment simulation tools Appl. Energy (IF 7.9) Pub Date : 2018-09-18 Sergio Vera, Camilo Pinto, Paulo Cesar Tabares-Velasco, Waldo Bustamante
Vegetated or green roofs are sustainable roofing systems that have become increasingly widespread across the world in recent decades. However, their design requires accurate numerical modeling to fully realize the benefits of this technology at the building and larger scales. For this reason, several heat and mass transfer models for vegetated roofs have been developed over the last 36 years. This paper provides a critical review of more than 23 heat transfer vegetative roof models developed between 1982 and 2018 that have been used for building energy or urban modeling purposes. Findings of the study include the following: (i) more than 55% of the vegetated roof models have been developed and validated using data from warm temperate climate zones; (ii) green roof validation efforts vary and do not follow a common verification and validation framework; (iii) four of the reviewed models have not been subjected to any simulation process; (iv) no model has been validated for semi-arid conditions or cold climates or during cold winter conditions; (v) the most common variable reported for validation (in more than half of the models) is substrate surface temperature; however, surface temperature does not fully test the accuracy of a model to represent all heat and mass transfer phenomena; (vi) practitioners access to these models is limited since only five of the 23 models have been implemented in whole-building energy models, such as EnergyPlus, TRNSYS, ESP-r, and WUFI; finally, (vii) despite the extensive studies on the impacts of vegetative roofs on building energy performance and urban temperature reduction, no studies have validated the model using whole-building energy data or at larger scales.
Biofuel-water-land nexus in the last agricultural frontier region of the Brazilian Cerrado Appl. Energy (IF 7.9) Pub Date : 2018-09-17 Renata del G. Rodriguez, Bridget R. Scanlon, Carey W. King, Fabio V. Scarpare, Alexandre C. Xavier, Fernando F. Pruski
The sustainability of biofuels depends on considering the environmental consequences of using water and land resources for bioenergy production. The objective of this study was to assess the potential for biofuel crop expansion by combining water footprint, water availability, and land availability in the last agricultural frontier region of Brazil using the Corrente Basin as a case study. Results show that the water footprint (ratio of water consumption to biomass or energy production) of sugarcane is low (114–190 m3 Mg−1) reflecting high water consumption (∼9000 m3 ha−1) divided by high crop yield (∼50–80 Mg ha−1), including millable stalks. However, water consumption for sugarcane grown in this area (9370 m3 ha−1) exceeds water availability in much of the basin (90th percentile of streamflow), which limits sugarcane expansion. In contrast, the water footprint of soybeans (900–2600 m3 Mg−1) is 8–14 times higher than that of sugarcane, reflecting much lower water consumption (∼1500–3800 m3 Mg−1) and even lower crop yield (0.7–4.3 Mg ha−1), limited to grains, relative to sugarcane. The low water consumption of soybeans allows expansion under rainfed agriculture during the wet 1st harvest season over 22% of the region and under irrigation during the dry 2nd harvest season over 13% of the region, without the need for deforestation of the Cerrado biome. This soybean expansion represents ∼20 × 106 GJ of energy supply per year, ∼4 times current production. Surface water availability for irrigation extends into the dry season because of substantial groundwater discharge to streams during the dry season. Irrigation increases biofuel crop yield of sugarcane and soybeans, reducing land area required to produce an equivalent amount of biomass by 2 to 4 times relative to rainfed management. Therefore, water can be traded for land by expanding irrigated biofuel production, conserving more native Cerrado vegetation. Considering water and land requirements relative to availability for bioenergy crops provides data on potential increases in bioenergy production while minimizing clearing of native vegetation in the Brazilian agricultural frontier.
An electrostatic discharge based needle-to-needle booster for dramatic performance enhancement of triboelectric nanogenerators Appl. Energy (IF 7.9) Pub Date : 2018-09-17 Cong Zhai, Xiujian Chou, Jian He, Linlin Song, Zengxing Zhang, Tao Wen, Zhumei Tian, Xi Chen, Wendong Zhang, Zhichuan Niu, Chenyang Xue
Numerical simulation and experimental validation of the solar photovoltaic/thermal system with phase change material Appl. Energy (IF 7.9) Pub Date : 2018-09-17 Weiqi Yuan, Jie Ji, Mawufemo Modjinou, Fan Zhou, Zhaomeng Li, Zhiying Song, Shengjuan Huang, Xudong Zhao
A PV/T system faces the difficulty of high-temperature dissipation as a result of low heat-exchange efficiency and winter freezing challenges that badly influence the performance of the system and even damage the PV/T. These problems can be addressed by using of the PCM in a PV/T system. The PCM can absorb heat in the daytime to reduce the operating temperature of the PV cell, and release heat at night to prevent the system from freezing in winter. In this study, a PV/T with PCM was designed and constructed by the authors. A series of experiments were done to compare the performance of the PV/T with PCM with a normal water-pipe-based PV/T during the daytime and night respectively. Physical-mathematical models were developed to simulate the transient performance of the PV/T with PCM. The data was analyzed, compared and validated with the experimental results. The results for the daily electrical efficiencies of the PV/T with PCM and water-pipe-based PV/T are 12.1% and 11.9% respectively, while the thermal efficiencies of two systems are 42.3% and 44.5% respectively. Also, the temperature of the PV/T with PCM is obviously higher at night in winter. This shows that PCM can improve the performance of a PV/T system. The results reveal good agreements between model simulation and experimental measurement with sufficient confidence. The design parameter analysis shows that the PV/T with single melting-temperature PCM panels can hardly meet the two requirements which are cooling the collector during daytime and preventing it from freezing at night. The study also reveals that increasing the thickness of the PCM can improve the collector’s antifreeze function.
Parameter identification of lithium-ion battery pack for different applications based on Cramer-Rao bound analysis and experimental study Appl. Energy (IF 7.9) Pub Date : 2018-09-15 Ziyou Song, Heath Hofmann, Xinfan Lin, Xuebing Han, Jun Hou
This paper presents an experimental study on the parameter identification of a battery pack, which determines the relationship between identification accuracy and measurement data. Parameter identification of the lithium-ion battery is poor when the input-output data, i.e., the input current and output voltage, is not appropriate. In addition, selection/optimization of an appropriate data set for estimation needs to adapt to different applications. A first-order equivalent circuit model is adopted to model a battery pack, and the identification accuracy is analyzed for both the single-parameter and multi-parameter identification scenarios. It is found that the accuracy of different identification scenarios is influenced by the voltage noise, the current amplitude, and the current frequency. Three experiments using sine waves with different frequencies are then performed to characterize a lithium-ion battery pack. Experimental results show that the current profile with the optimal frequency content achieves the best identification performance. Therefore, it is validated that the identification accuracy can be improved when the current excitation satisfies certain criteria.
Possible design with equity and responsibility in China’s renewable portfolio standards Appl. Energy (IF 7.9) Pub Date : 2018-09-14 Bing Wang, Yi-Ming Wei, Xiao-Chen Yuan
Feed-in tariff and renewable portfolio standards are two major policies for renewable power generation and China is the first country to adopt both policies at the national level. The black box for regional allocation of renewable portfolio standards, however, may lead to the instability and inefficiency of this policy. This paper introduces the principles of Management by Objective to build a clear policy framework for renewable portfolio standards in China and employs the entropy method to equally and reasonably assign regional responsibility for renewable energy development. A comparison is made between our allocation and the goal-directed policy to determine whether historical responsibility and infrastructure construction should be further considered in crafting renewable portfolio standards. The trends for regional renewable quotas are influenced by the twin-track approach of nearby utilization and external transmission. Finally, based on our analysis, the policy implications behind the new incentive are presented to urge the establishments of supporting facilities.
Modelling transport modal shift in TIMES models through elasticities of substitution Appl. Energy (IF 7.9) Pub Date : 2018-09-14 Raffaele Salvucci, Jacopo Tattini, Maurizio Gargiulo, Antti Lehtilä, Kenneth Karlsson
Several efforts have been directed lately towards the endogenisation of transport modes competition in Energy/Economy/Environment/Engineering (E4) models. TIMES-DKEMS is a novel methodology paving the way for applying elasticities of substitution to incorporate transport modal shift into TIMES (The Integrated MARKAL-EFOM System) models. Substitution elasticities are defined for four transport demand aggregates, each corresponding to a different distance range class. Within an aggregate, modal demands can adjust their levels according to the defined substitution elasticity and in response to changes of their shadow prices relative to a reference case. The total volume of the transport demand over the aggregate is conserved and modal shift potentials are implemented to guarantee realistic dynamics. The behavior of TIMES-DKEMS is tested under an arbitrary environmental policy, an increasingly stringent bound on CO2 emissions. Modal shares are compared with the standard version of TIMES-DK. Results show that in 2050, 11% of car mobility demand is substituted by more efficient and less costly modes such as train and coach. A sensitivity analysis on the values of substitution elasticities indicates that higher absolute values correspond to larger modal shift. Finally, other model constraints, such as mode-specific travel patterns, interact with the substitution mechanism resulting in a modal shift containment.
Modeling, simulation and evaluation of biogas upgrading using aqueous choline chloride/urea Appl. Energy (IF 7.9) 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.
Data-driven model predictive control using random forests for building energy optimization and climate control Appl. Energy (IF 7.9) Pub Date : 2018-04-21 Francesco Smarra, Achin Jain, Tullio de Rubeis, Dario Ambrosini, Alessandro D’Innocenzo, Rahul Mangharam
Model Predictive Control (MPC) is a model-based technique widely and successfully used over the past years to improve control systems performance. A key factor prohibiting the widespread adoption of MPC for complex systems such as buildings is related to the difficulties (cost, time and effort) associated with the identification of a predictive model of a building. To overcome this problem, we introduce a novel idea for predictive control based on historical building data leveraging machine learning algorithms like regression trees and random forests. We call this approach Data-driven model Predictive Control (DPC), and we apply it to three different case studies to demonstrate its performance, scalability and robustness. In the first case study we consider a benchmark MPC controller using a bilinear building model, then we apply DPC to a data-set simulated from such bilinear model and derive a controller based only on the data. Our results demonstrate that DPC can provide comparable performance with respect to MPC applied to a perfectly known mathematical model. In the second case study we apply DPC to a 6 story 22 zone building model in EnergyPlus, for which model-based control is not economical and practical due to extreme complexity, and address a Demand Response problem. Our results demonstrate scalability and efficiency of DPC showing that DPC provides the desired power curtailment with an average error of 3%. In the third case study we implement and test DPC on real data from an off-grid house located in L’Aquila, Italy. We compare the total amount of energy saved with respect to the classical bang-bang controller, showing that we can perform an energy saving up to 49.2%. Our results demonstrate robustness of our method to uncertainties both in real data acquisition and weather forecast.
Evaluation of thermal stimulation on gas production from depressurized methane hydrate deposits☆ Appl. Energy (IF 7.9) 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.
Tuning dry reforming of methane for F-T syntheses: A thermodynamic approach Appl. Energy (IF 7.9) 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).
Experimental and numerical study on pressure drop and heat transfer performance of grille-sphere composite structured packed bed Appl. Energy (IF 7.9) 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.
Industrial energy use and carbon emissions reduction in the chemicals sector: A UK perspective Appl. Energy (IF 7.9) 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.
Post combustion CO2 capture in power plant using low temperature steam upgraded by double absorption heat transformer Appl. Energy (IF 7.9) 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.
A power dispatch model for a ferrochrome plant heat recovery cogeneration system Appl. Energy (IF 7.9) 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.
Exploring the interactive effects of ambient temperature and vehicle auxiliary loads on electric vehicle energy consumption Appl. Energy (IF 7.9) 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.
Dynamic measurements of methane hydrate formation/dissociation in different gas flow direction Appl. Energy (IF 7.9) 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.
Modelling and optimisation of a hydrogen-based energy storage system in an autonomous electrical network Appl. Energy (IF 7.9) 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.
State-of-health estimation for the lithium-ion battery based on support vector regression Appl. Energy (IF 7.9) Pub Date : 2017-08-19 Duo Yang, Yujie Wang, Rui Pan, Ruiyang Chen, Zonghai Chen
The use of electrical heating for the enhancement of gas recovery from methane hydrate in porous media Appl. Energy (IF 7.9) 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 methane recovery from low-concentration coal mine gas by tetra-n-butyl ammonium chloride semiclathrate hydrate formation Appl. Energy (IF 7.9) Pub Date : 2017-08-19 Dong-Liang Zhong, Wen-Chun Wang, Zhen-Lin Zou, Yi-Yu Lu, Jin Yan, Kun Ding
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 7.9) 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.
Numerical investigation of heat transfer performance of a rotating latent heat thermal energy storage Appl. Energy (IF 7.9) Pub Date : 2017-08-19 Jundika C. Kurnia, Agus P. Sasmito
Thermodynamic investigations of the supercritical CO2 system with solar energy and biomass Appl. Energy (IF 7.9) 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.
Investigation on small-scale low pressure LNG production process Appl. Energy (IF 7.9) 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 7.9) 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.
An adaptive Fuzzy logic-based approach to PID control of steam turbines in solar applications Appl. Energy (IF 7.9) 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.
Performance of an electrical distribution network with Soft Open Point during a grid side AC fault Appl. Energy (IF 7.9) 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 7.9) 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.
Investigation of thermo-fluidic performance of phase change material slurry and energy transport characteristics Appl. Energy (IF 7.9) 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 7.9) 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 7.9) 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 7.9) 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 7.9) 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 7.9) 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).
How will sectoral coverage affect the efficiency of an emissions trading system? A CGE-based case study of China Appl. Energy (IF 7.9) 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.
Life cycle sustainability assessment of grid-connected photovoltaic power generation: A case study of Northeast England Appl. Energy (IF 7.9) 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.
Coupling detailed radiation model with process simulation in Aspen Plus: A case study on fluidized bed combustor Appl. Energy (IF 7.9) 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.
Predictive air-conditioner control for electric buses with passenger amount variation forecast☆ Appl. Energy (IF 7.9) 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.
Performance assessment of a hybrid SOFC/MGT cogeneration power plant fed by syngas from a biomass down-draft gasifier Appl. Energy (IF 7.9) 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 7.9) 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 7.9) 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 7.9) Pub Date : 2017-09-19 Pascal Maas, Martin Schiemann, Viktor Scherer, Peter Fischer, Dan Taroata, Günther Schmid
Improvement of combustion performance and emissions in diesel engines by fueling n-butanol/diesel/PODE3–4 mixtures Appl. Energy (IF 7.9) 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.
Numerical investigation of the effect of two-stage injection strategy on combustion and emission characteristics of a diesel engine Appl. Energy (IF 7.9) Pub Date : 2017-09-22 Hanzhengnan Yu, Xingyu Liang, Gequn Shu, Yuesen Wang, Xiuxiu Sun, Hongsheng Zhang
This work assessed two types of two-stage injection strategies for the operation of a diesel engine: pilot and early injection. The effects of the two-stage injection interval and the first-stage fuel injection proportion on the combustion and emission characteristics when employing these two injection strategies were investigated by numerical modeling, dividing the in-cylinder zone into three different regions. Variations in the NOx, soot, HC and CO emissions in each region were determined at various values of two-stage injection interval and first-stage fuel injection proportion for both strategies. The results demonstrate that, considering both the engine combustion and emission characteristics, a two-stage injection strategy in conjunction with an injection interval of 30–40°CA and a first-stage fuel injection proportion of 30–60% is advisable.
EGR control on operation of a tar tolerant HCCI engine with simulated syngas from biomass Appl. Energy (IF 7.9) Pub Date : 2017-09-28 Subir Bhaduri, Hervé Jeanmart, Francesco Contino
In combined heat and power plants operated with biomass syngas, the removal of condensible tars is a necessary but expensive step (up to one third of the installation and maintenance costs). This step is required because the syngas has to be cooled down to avoid knocking in the spark ignition engines traditionally used in such plants. To remove the tar condensation problem, we developed an alternative system based on an Homogeneous Charge Compression Ignition (HCCI) engine operated at intake temperatures above the tar dew point. To address the challenge of power derating of such engine setups, the current paper focuses on the application of Exhaust Gas Recirculation (EGR) as a control parameter that would indirectly allow the improvement of the engine performance. Based on a conservative estimate of tar dew points, HCCI combustion was studied at an intake temperature of 250 °C using synthetic biomass syngas and synthetic EGR on a mono-cylinder HCCI engine operated at 1000 RPM. The effects of charge dilution, thermal and kinetic damping due to the EGR gases were also analysed to understand their main effects. The use of EGR successfully increased the maximum achievable Indicated Mean Effective Pressure from 2.5 bar at EGR = 0% up to 3.3 bar at EGR = 25%, through damping the maximum pressure rise rate and allowing higher equivalence ratios.
Analysis of depressurization mode on gas recovery from methane hydrate deposits and the concomitant ice generation Appl. Energy (IF 7.9) Pub Date : 2017-09-28 Bin Wang, Zhen Fan, Pengfei Wang, Yu Liu, Jiafei Zhao, Yongchen Song
Natural gas hydrates have garnered worldwide attention as an important potential non-conventional fossil fuel resource. When extracting natural gas from gas hydrate deposits via depressurization, problematic ice generation and hydrate reformation can occur under conditions of fast depressurizing and low production pressures, due to insufficient heat transfer in the surrounding sediments. In this work we conduct in situ magnetic resonance imaging (MRI) visualization and analysis of hydrate decomposition behavior for different depressurization modes; we visually determine the volumetric and spatial characteristics of the hydrate decomposition during depressurization induced gas production operation. Our results indicate that fast depressurization rate can result in a fast hydrate decomposition rate, therefore, a rapid gas production rate. In addition, the radial extension behavior of the decomposition front confirms that ambient heat transfer is a critical factor driving hydrate decomposition into free gas and liquid water. Obvious hydrate reformation and ice generation phenomenon, seen in some of the sudden depressurization experiments, can be effectively avoided using piecewise and continuous depressurization methods. The findings of this study clearly demonstrate how production pressures affect the gas production behavior from hydrate deposits and provide further insight for establishing optimal production techniques for utilizing hydrate resources in the field.
Techno-economic analysis of photovoltaic battery system configuration and location☆ Appl. Energy (IF 7.9) Pub Date : 2017-09-28 Amin Lahnaoui, Peter Stenzel, Jochen Linssen
The techno-economic analysis investigates first the impact of tilt angle and orientation on the production profile of a rooftop solar generator and the related performance of a photovoltaic battery storage system for single family houses at a specific location in Germany. Then, a technical comparison to a different location in Almeria in Spain is performed. The calculations are model-based and take into consideration the consumer load profile, technical and economic photovoltaic battery storage system parameters as well as the framework of regulations for the case of Germany. The parameters “share of self-consumption”, “degree of autarky”, and “economic efficiency in terms of levelized cost of electricity” make up the focus of the modelling results. It is concluded that self-consumption and degree of autarky are strongly and inversely related. In terms of system design, a trade-off has to be made between aiming for high self-consumption and a high degree of autarky. Key findings from the modelling results reveal that in Lindenberg in Germany, a south orientation gives the highest degree of autarky and the lowest levelized cost of electricity, but with the lowest share of self-consumption as well. For rooftops oriented towards east/west, an interesting possibility could be to split the total installed capacity (equally) between the two orientations. This makes it possible to benefit from the high self-consumption of the east orientation and the high degree of autarky of the west orientation. In general, it has to be considered that the optimum orientation strongly depends on the consumer load profile. The technical analysis shows that changing the location to Almeria increases degree of autarky and decreases share of self-consumption for south orientation with different magnitude that depends on the load profile. Finally, the results show opposite impacts that depend on orientation and location when switching from a tilt angle of 30° to 45°. For a south orientation in Almeria and Lindenberg, the degree of autarky is increased when approaching the optimum tilt angle, while for west and east orientations in Lindenberg self-consumption increases.
Cost–benefit analysis of China’s Intended Nationally Determined Contributions based on carbon marginal cost curves Appl. Energy (IF 7.9) Pub Date : 2017-09-29 Xi Yang, Fei Teng, Xiaoqian Xi, Egor Khayrullin, Qi Zhang
The prohibitive cost of carbon abatement has put large pressure on China’s government during its carbon mitigation process to meet the country’s target for Intended Nationally Determined Contributions (INDC). Previous studies mostly focus on the cost analysis of China’s INDC. This study fills the gap between the cost of carbon mitigation and auxiliary benefits, and attempts to answer the following key questions associated with China’s INDC: (1) How much of the mitigation cost can be offset by environmental benefits? (2) What is the break-even carbon mitigation rate? (3) Is China’s INDC carbon reduction target cost effective? In this study, carbon tax is added into China-Multi-Pollutant Abatement Planning and Long-term Benefit Evaluation (China-MAPLE). The corresponding carbon mitigation rate is calculated to construct the marginal abatement cost curves (MACCs). The environmental co-benefit from air pollutant abatement is evaluated by the health damage avoided, and the benefit is added into the revised MACCs. Several conclusions are drawn from analysis based on MACC and China-MAPLE model. First, the net cost of carbon abatement can be substantially reduced when considering environmental benefits. When mitigation rate in normal end-of-pipe control (NEPC) scenario is below 16.8%, carbon mitigation cost is fully compensated by environmental benefits. Second, if strict end-of-pipe control (EPC) measures are implemented, then environmental benefits can be sternly influenced but can continue to fully compensate the cost when mitigation rate is below 3%. Third, the carbon mitigation target of China’s INDC is achievable and cost effective under the NEPC scenario. Carbon mitigation cost is 0.08% of the GDP loss, which is compensated by the 0.14% environmental benefit of the GDP. As a result, a net benefit of 0.06% of the GDP is obtained. The cost effectiveness of China’s INDC is largely dependent on the stringency of EPC measures. However, even in the strict EPC scenario, 0.02% of the GDP loss accounting for the mitigation cost is partially offset by environmental benefits. These results strongly support the implementation of China’s serious de-carbonization effort toward its INDC and serve as a good reference for other developing countries.
Assessment of uncertainties of laminar flame speed of premixed flames as determined using a Bunsen burner at varying pressures Appl. Energy (IF 7.9) Pub Date : 2017-10-02 S. Hu, J. Gao, C. Gong, Y. Zhou, X.S. Bai, Z.S. Li, M. Alden
Laminar methane/air premixed flames at different pressures in a newly developed high-pressure Bunsen flame rig are studied using detailed numerical simulations and laser diagnostics. In the numerical simulations, one-dimensional and two-dimensional axisymmetric configurations were considered employing detailed transport properties and chemical kinetic mechanisms. In the measurements, OH PLIF was employed. The aims are to improved the understanding of the structures of the flames at varying pressures, to measure the laminar flame speed at different pressures, and to quantify the accuracy of the Bunsen flame method for measurement of laminar flame speed at different pressures. The stoichiometric and fuel-rich flames were found to exhibit a two-reaction-zone structure: an inner premixed flame in which the fuel was converted to CO and H2, and an outer diffusion flame in which CO and H2 were oxidized further to form combustion products. With increasing pressure, the inner premixed flame becomes thinner and the flame as a whole has the tendency to become unstable. Using the numerical and the experimental data, the methods of flame-cone-angle and flame-area were used to extract the laminar flame speed for different equivalence ratios and pressures. The flame-cone-angle method showed slightly better accuracy than the flame-area method did. The accuracy of both methods became lower under high pressure conditions. The inlet velocity of the burner was shown to affect the accuracy of the extracted laminar flame speed. For a stoichiometric atmospheric flame it was found that the most suitable inlet velocity for the fuel/air mixture was about 6 times the laminar flame speed, yielding a flame length about 7 times the radius of the burner. With appropriate flame length, the mid-height of the flame showed a rather low flame stretch rate, the laminar flame speed being in close agreement with the unstretched laminar flame speed, the error being less than 6% for the flames that were studied.
A CFD decompression model for CO2 mixture and the influence of non-equilibrium phase transition Appl. Energy (IF 7.9) Pub Date : 2017-10-03 Bin Liu, Xiong Liu, Cheng Lu, Ajit Godbole, Guillaume Michal, Anh Kiet Tieu
Carbon Capture and Storage (CCS) is widely seen as an effective technique to reduce what is perceived as excessive CO2 concentration in the atmosphere. This technique includes transporting CO2 from source point to the storage site, usually through high-pressure pipelines. In order to ensure safe transport (i.e. to prevent the contents from being released into the atmosphere), it is important to estimate the required pipe toughness in the design stage. This requires an accurate prediction of the speed of the ‘decompression wave’ in the fluid, which is created when the high-pressure fluid escapes into the ambient. In this paper, a multi-phase Computational Fluid Dynamics (CFD) model is presented to simulate the decompression of high-pressure pipelines carrying CO2 mixtures. A ‘real gas’ Equation of State (EOS), the GERG-2008 EOS, is incorporated into the CFD code to model the thermodynamic properties of the fluid in both liquid and vapour states. The non-equilibrium liquid/vapour transition is modelled by introducing ‘source terms’ for mass transfer and latent heat. The model is validated through simulation of a ‘shock tube’ test. A ‘time relaxation factor’ is used to control the inter-phase mass transfer rate. The measured decompression wave speed is compared with that predicted using different values of the time relaxation factor. It is found that the non-equilibrium phase transition has a significant influence on the decompression wave speed. Also, the effects of delayed bubble formation and of various impurities on the decompression wave speed are investigated.
Do all sectors respond to oil price shocks simultaneously? Appl. Energy (IF 7.9) Pub Date : 2017-10-06 Shupei Huang, Haizhong An, Xuan Huang, Yue Wang
Sector stock indices respond to oil price fluctuations with temporal heterogeneities based on their oil dependence and multiple transmission mechanisms. Additionally, such heterogeneities may not persist across time scales due to their inherent multiscale features. Aiming to explore the lead-lag effects among oil-stock nexuses at sectoral level and further identify the transmission path of oil price shocks to different stock sectors chronologically across time scales, we propose an integrated research framework combining the wavelet transform, cross correlation coefficients and the network analysis together. We take the Brent oil price and Morgan Stanley Capital International (MSCI) world sector stock indices (Materials, Industrials, Consumer Discretionary, Consumer Staples, Health Care, Financials, Telecommunications, Utilities, Transportation and Metals & Mining) from January 2000 to January 2016 as data samples. We find that the number of oil-stock nexuses involved in lead-lag effects and the maximum time lags grow as the length of the time horizon. Each sector may lead or lag behind other sectors in different frequencies to move with an oil price shock, but Transportation, Utilities and Consumer Discretionary are sectors have higher probability to lag behind other sectors, while Materials and Telecommunications are the sectors with higher possibility to lead other sectors. In addition, The oil-stock nexuses of Utilities, Telecommunication and Consumer Staples work as key points in the frequencies of 8, 64, and 128 days, whereas the Brent-Transportation nexus control more information in the frequency of 256 days. Finally, we infer that the complexity of the interaction between oil price and the stock market is triggered by different causes across time scales. In the short term, such complexity is caused by high fluctuations of the oil-stock nexuses happening simultaneously because there are fewer lead-lag relationships among nexuses. In the long term, the relationships of oil-stock nexuses are more stable, but the time lags among nexuses become longer, which could overlap the impacts of oil price from different time points.
Powering an island system by renewable energy—A feasibility analysis in the Maldives Appl. Energy (IF 7.9) Pub Date : 2017-10-16 Jiahong Liu, Chao Mei, Hao Wang, Weiwei Shao, Chenyao Xiang
Water and energy supply systems are essential parts of the infrastructure on islands. For small islands that are far from continents, water shortage is usually the main constraint on economic and social development. In order to maintain island water security, desalination plants are built to supply fresh water. The plants need a great deal of energy, which increases demand for energy and the cost of transportation. Thus, it is necessary to design a new island system driven by renewable energy. This study investigated the existing type of water and energy supply systems in some typical islands of the world, and analyzed their advantages and disadvantages. The energy supply systems can be classified into three categories: imported conventional energy supply system (ICESS); imported conventional energy & renewable energy supply system (ICE&RESS); and integrated energy supply system (IESS). Water supply systems can also be classified into three categories: imported water supply system (ImWSS); imported water and unconventional water supply system (IW&UWSS); and integrated water supply system (InWSS). The nexus of energy and water is very complicated on islands. This paper presents a framework for an interconnected energy and water system on an island. The new framework reveals a roadmap from “full input of energy & water (FIEW)” through “semi-input of energy & water (SIEW)” to “zero input of energy & water (ZIEW)”, which leads an island's energy and water resources to become gradually independent from the mainland. The new framework also reduces transportation costs and carbon emissions. The proposed framework is applied to the Maldives to aid design of a renewable energy-driven water supply system. The characteristics and mutual adaptability of three types of renewable energy (solar, wind, and biomass energy) and water supply systems is discussed. The results show that a ZIEW system can be realized in the Maldives with a reduction in the cost of renewable energy. ZIEW system has great potential for application in island regions in the future.
Thermodynamic analysis and optimization of multistage latent heat storage unit under unsteady inlet temperature based on entransy theory Appl. Energy (IF 7.9) Pub Date : 2017-10-21 Y.K. Liu, Y.B. Tao
An optimization model for a multistage latent heat storage (LHS) unit with unsteady heat transfer fluid (HTF) inlet temperature was proposed. Thermodynamic analysis and optimization were performed based on the entransy theory. The expressions of the optimum phase change material (PCM) melting temperatures (Tm,opt) were derived. The effects of geometric parameters and unsteady HTF inlet temperature on the optimum phase change temperatures were investigated. The results indicate that with the increase of stage number (n), Tm1,opt increases and Tmn,opt decreases, which is beneficial to extend the selection range of PCM. For fixed entransy dissipation condition, increasing n will not change the fluctuation of the HTF outlet temperature; however a nearly uniform HTF outlet temperature can be obtained by increasing unit length (L). The unsteady HTF inlet temperature has great effects on the optimum phase change temperature. For a 3-stage LHS unit, the optimum phase change temperature of each stage increases by 14.9 K, 26.4 K and 38.0 K respectively with respect to the values obtained by steady method, which causes the heat storage capacity decreases by 6.1% and entransy dissipation decreases by 10.6%. The present work can provide guidance for the design of the multistage LHS unit with unsteady HTF inlet temperature.
Numerical study of gas production from methane hydrate deposits by depressurization at 274 K Appl. Energy (IF 7.9) Pub Date : 2017-10-21 Minghao Yu, Weizhong Li, Lanlan Jiang, Xin Wang, Mingjun Yang, Yongchen Song
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