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Energies, Volume 5, Issue 10 (October 2012), Pages 3723-4250

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Open AccessArticle Effects of a Green Space Layout on the Outdoor Thermal Environment at the Neighborhood Level
Energies 2012, 5(10), 3723-3735; doi:10.3390/en5103723
Received: 3 August 2012 / Revised: 17 September 2012 / Accepted: 17 September 2012 / Published: 25 September 2012
Cited by 5 | PDF Full-text (2324 KB) | HTML Full-text | XML Full-text
Abstract
This study attempted to address the existing urban design needs and computer-aided thermal engineering and explore the optimal green space layout to obtain an acceptable thermal environment at the neighborhood scale through a series of building energy and computational fluid dynamics (CFD) simulations.
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This study attempted to address the existing urban design needs and computer-aided thermal engineering and explore the optimal green space layout to obtain an acceptable thermal environment at the neighborhood scale through a series of building energy and computational fluid dynamics (CFD) simulations. The building-energy analysis software eQUEST and weather database TMY2 were adopted to analyze the electric energy consumed by air conditioners and the analysis results were incorporated to derive the heat dissipated from air conditioners. Then, the PHOENICS CFD software was used to analyze how the green space layout influences outdoor thermal environment based on the heat dissipated from air conditioners and the solar heat reemitted from the built surfaces. The results show that a green space located in the center of this investigated area and at the far side of the downstream of a summer monsoon is the recommended layout. The layouts, with green space in the center, can decrease the highest temperature by 0.36 °C. Full article
(This article belongs to the Special Issue Energy Efficient Buildings and Green Buildings)
Open AccessArticle Transient Analysis of Large Scale PV Systems with Floating DC Section
Energies 2012, 5(10), 3736-3752; doi:10.3390/en5103736
Received: 27 July 2012 / Accepted: 13 September 2012 / Published: 26 September 2012
Cited by 10 | PDF Full-text (868 KB) | HTML Full-text | XML Full-text
Abstract
The increasing penetration of renewable sources with power-electronic interfaces in power systems is raising technical problems and the overall efficiency of photovoltaic systems can decrease dramatically. In this context, the optimal layout for the photovoltaic system is required. The most adequate strategy to
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The increasing penetration of renewable sources with power-electronic interfaces in power systems is raising technical problems and the overall efficiency of photovoltaic systems can decrease dramatically. In this context, the optimal layout for the photovoltaic system is required. The most adequate strategy to connect the renewable system to the electrical power grid or to supply the end users must be adopted. The present paper proposes a design layout of a PV plant using a DC bus system to improve the overall energy conversion efficiency. An analysis of steady-state system stability, voltage drop and DC cable conduction losses is conducted. The leakage currents to the ground are investigated through simulations. Experimental results are shown focused on the analysis of optimal layout of photovoltaic systems under particular operating conditions. Full article
Open AccessArticle Collection of Thermal Energy Available from a Biogas Plant for Leachate Treatment in an Urban Landfill: A Sicilian Case Study
Energies 2012, 5(10), 3753-3767; doi:10.3390/en5103753
Received: 31 July 2012 / Revised: 20 September 2012 / Accepted: 21 September 2012 / Published: 26 September 2012
Cited by 4 | PDF Full-text (641 KB) | HTML Full-text | XML Full-text
Abstract
The landfill of Bellolampo is located in northern Sicily and serves the greater area of Palermo (Sicily). In the recent past, the landfill has been progressively renovated in order to align the waste disposal process with the state-of-the-art technology. During the past years,
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The landfill of Bellolampo is located in northern Sicily and serves the greater area of Palermo (Sicily). In the recent past, the landfill has been progressively renovated in order to align the waste disposal process with the state-of-the-art technology. During the past years, the site had been equipped with seven biogas engines, fuelled with the biogas produced at the oldest part of the landfill. More recently, another two engines of the same type have been installed for a total of 9 MW electrical power installed at the landfill. The landfill of Bellolampo faces a significant leachate disposal problem. Some 250 m3 of contaminated leachate are produced daily and transported by ships and trucks to an area about 1000 km away before being treated and disposed. The disposal of this extremely polluting fluid causes significant nuisance in the integrated waste management process and significant disposal expenses (in excess of € 60 per ton of fluid disposed and € 4.5 mln per year). Furthermore, the recent legislation strongly suggests the landfill manager to activate fully integrated systems and 100% landfill auto-sustainability. On the other hand, the above mentioned biogas engines produce a great quantity of unused thermal energy yearly. This study demonstrates that this energy could be effectively and efficiently used to enable the sustainable in-house treatment of the leachate. The treatment is aimed to significantly reduce leachate volume in order to reduce fluid disposal costs. A thorough economical analysis is also performed. The study demonstrates that a medium sized landfill can sustainably and cost-effectively be managed through a fully integrated system thus producing substantial economies. Full article
(This article belongs to the Special Issue Waste to Energy Technologies)
Open AccessArticle Minimization of Losses in Smart Grids Using Coordinated Voltage Control
Energies 2012, 5(10), 3768-3787; doi:10.3390/en5103768
Received: 4 July 2012 / Revised: 21 August 2012 / Accepted: 19 September 2012 / Published: 27 September 2012
Cited by 10 | PDF Full-text (1555 KB) | HTML Full-text | XML Full-text
Abstract
This article deals with the influence of distributed generation (DG) on distribution line losses with respect to voltage profile. The article focuses on the development of a control strategy to minimize the grid losses and assure fairness regarding reactive power contributions. As retail
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This article deals with the influence of distributed generation (DG) on distribution line losses with respect to voltage profile. The article focuses on the development of a control strategy to minimize the grid losses and assure fairness regarding reactive power contributions. As retail customers typically have no choice where they are located along a feeder, it seems unfair that only some of them bear all the burden and responsibility for the voltage rise. On the basis of new technologies, which are capable of fast communication and data processing, a new control system has been proposed that combines classical centralized and local control. The heart of the control system is a load‑flow algorithm, which estimates the voltage drop using a modeled network. Different control solutions were evaluated by means of computer simulations. The simulated network is an actual Slovenian medium-voltage distribution network which covers a large area with diverse feeders and thus gives relatively general results. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle Study of Pea Accessions for Development of an Oilseed Pea
Energies 2012, 5(10), 3788-3802; doi:10.3390/en5103788
Received: 25 August 2012 / Revised: 7 September 2012 / Accepted: 14 September 2012 / Published: 27 September 2012
Cited by 3 | PDF Full-text (247 KB) | HTML Full-text | XML Full-text
Abstract
Global interest in stable energy resources coupled with growing demand for bio-oils in various conventional and arising industries has renewed the importance of vegetable oil production. To address this global interest, oilseed production has been increased in recent decades by different approaches, such
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Global interest in stable energy resources coupled with growing demand for bio-oils in various conventional and arising industries has renewed the importance of vegetable oil production. To address this global interest, oilseed production has been increased in recent decades by different approaches, such as extending the cultivation area of oil crops, or breeding and growing genetically modified plants. In this study, pea (Pisum sativum L.) accessions were screened for lipid content using a rapid extraction method. This method quantifies lipid concentration in pea seeds and was developed by assessing and comparing the results of existing extraction methods used for canola and soybean, the top two Canadian oilseeds. Seeds of 151 field pea accessions were grown to maturity in 2009 and 2010 at McGill University (Quebec, Canada). Overall, lipid concentration in pea seeds ranged from 0.9 to 5.0%. Among several seed characteristics, only seed shape (wrinkled verses round) had a significant effect on the total lipid production in the seeds. Peas are a valuable source of protein and starch, but the lipid concentration in their seeds has been undervalued. This research supports the idea of developing a novel dual-purpose oilseed pea that emulates the protein and oil production in soybean seeds while being conveniently adapted to a colder climate. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Characterization of Woodchips for Energy from Forestry and Agroforestry Production
Energies 2012, 5(10), 3803-3816; doi:10.3390/en5103803
Received: 21 August 2012 / Revised: 18 September 2012 / Accepted: 18 September 2012 / Published: 27 September 2012
Cited by 20 | PDF Full-text (165 KB) | HTML Full-text | XML Full-text
Abstract
We set out to determine the particle-size distribution, the fiber, the bark and the leaves content, the heating value, the CNH and the ash content of a wide sample of wood chips, collected from 10 forestry and 10 agroforestry production sources. This sampling
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We set out to determine the particle-size distribution, the fiber, the bark and the leaves content, the heating value, the CNH and the ash content of a wide sample of wood chips, collected from 10 forestry and 10 agroforestry production sources. This sampling focused on two main production types: forestry (Full Tree System—FTS—and logging residues—LR) and agroforestry (Short Rotation Coppice—SRC). For the forestry production wood chips from coniferous and broadleaf species were considered. For the agroforestry production wood chips from poplar plantations were examined (different clones with two different harvesting intervals). Overall, we collected 400 samples. Particle size distribution was determined with an automatic screening device on 200 samples. The higher heating value was determined on 200 subsamples using an adiabatic bomb calorimeter. The CNH and the ash content was ascertained on another 200 subsamples. FTS and SRC (with three year old sprouts) offered the best quality, with high fiber content (71%–80%), favorable particle-size distribution and good energetic parameters. On the contrary, both logging residues and SRC (with two year old sprouts) presented a high bark content (18%–27%) and occasionally a mediocre particle-size distribution, being often too rich in fines (6%–12%), but the energetic parameters are in the normal range. Full article
(This article belongs to the Special Issue Wood to Energy)
Open AccessArticle Integrated Coordinated Optimization Control of Automatic Generation Control and Automatic Voltage Control in Regional Power Grids
Energies 2012, 5(10), 3817-3834; doi:10.3390/en5103817
Received: 19 April 2012 / Revised: 23 July 2012 / Accepted: 30 August 2012 / Published: 27 September 2012
Cited by 2 | PDF Full-text (720 KB) | HTML Full-text | XML Full-text
Abstract
Automatic Generation Control (AGC) and Automatic Voltage Control (AVC) are key approaches to frequency and voltage regulation in power systems. However, based on the assumption of decoupling of active and reactive power control, the existing AGC and AVC systems work independently without any
[...] Read more.
Automatic Generation Control (AGC) and Automatic Voltage Control (AVC) are key approaches to frequency and voltage regulation in power systems. However, based on the assumption of decoupling of active and reactive power control, the existing AGC and AVC systems work independently without any coordination. In this paper, a concept and method of hybrid control is introduced to set up an Integrated Coordinated Optimization Control (ICOC) system for AGC and AVC. Concerning the diversity of control devices and the characteristics of discrete control interaction with a continuously operating power system, the ICOC system is designed in a hierarchical structure and driven by security, quality and economic events, consequently reducing optimization complexity and realizing multi-target quasi-optimization. In addition, an innovative model of Loss Minimization Control (LMC) taking into consideration active and reactive power regulation is proposed to achieve a substantial reduction in network losses and a cross iterative method for AGC and AVC instructions is also presented to decrease negative interference between control systems. The ICOC system has already been put into practice in some provincial regional power grids in China. Open-looping operation tests have proved the validity of the presented control strategies. Full article
(This article belongs to the Special Issue Electrical Power and Energy Systems)
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Open AccessArticle Investigation of Site-Specific Wind Field Parameters and Their Effect on Loads of Offshore Wind Turbines
Energies 2012, 5(10), 3835-3855; doi:10.3390/en5103835
Received: 27 July 2012 / Revised: 3 September 2012 / Accepted: 24 September 2012 / Published: 8 October 2012
Cited by 9 | PDF Full-text (4298 KB) | HTML Full-text | XML Full-text
Abstract
The main contributing factors to unsteady loading of Offshore Wind Turbines (OWT) are wind shear, turbulence, and waves. In the present paper, the turbulence intensity and the wind shear exponent are investigated. Using data from the FINO 1 research platform, these parameters are
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The main contributing factors to unsteady loading of Offshore Wind Turbines (OWT) are wind shear, turbulence, and waves. In the present paper, the turbulence intensity and the wind shear exponent are investigated. Using data from the FINO 1 research platform, these parameters are analyzed and compared with the proposed wind field parameters in the IEC standard 61400-3. Based on this analysis, aeroelastic simulations are performed to determine the effect of wind field parameters on the fatigue and the extreme loads on the rotor blades. For the investigations, the aeroelastic model of a 5 MW OWT is used with a focus on design load cases in an operating state (power production). The fatigue loads are examined by means of the damage-equivalent load-range approach. In order to determine the extreme loads with a recurrence period of 50 years, a peak over threshold extrapolation method and a novel method based on average conditional exceedance rates are used. The results show that the requirements of the IEC standard are very conservative for the design of the rotor blades. Therefore, there could be a large optimization potential for the reduction of weight and cost of the rotor blades. Full article
(This article belongs to the Special Issue Wind Turbines)
Open AccessArticle Preliminary Design of a Multi-Column TLP Foundation for a 5-MW Offshore Wind Turbine
Energies 2012, 5(10), 3874-3891; doi:10.3390/en5103874
Received: 12 August 2012 / Revised: 24 September 2012 / Accepted: 1 October 2012 / Published: 15 October 2012
Cited by 13 | PDF Full-text (1392 KB) | HTML Full-text | XML Full-text
Abstract
Currently, floating wind turbines (FWTs) may be the more economical and suitable systems with which to exploit offshore wind energy in deep waters. Among the various types of floating foundations for offshore wind farms, a tension leg platform (TLP) foundation can provide a
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Currently, floating wind turbines (FWTs) may be the more economical and suitable systems with which to exploit offshore wind energy in deep waters. Among the various types of floating foundations for offshore wind farms, a tension leg platform (TLP) foundation can provide a relatively stable platform for currently available offshore wind turbines without requiring major modifications. In this study, a new multi-column TLP foundation (WindStar TLP) was developed for the NREL 5-MW offshore wind turbine according to site-specific environmental conditions, which are the same as the OC3-Hywind (NREL) conditions. The general arrangement, main structure and mooring system were also designed and investigated through hydrodynamic and natural frequency analyses. The complete system avoids resonance through the rotor excitations. An aero-hydro-servo-elastic coupled analysis was carried out in the time domain with the numerical tool FAST. Statistics of the key parameters were obtained and analysed and comparisons to MIT/NREL TLP are made. As a result, the design requirements were shown to be satisfied, and the proposed WindStar TLP was shown to have favourable motion characteristics under extreme wind and wave conditions with a lighter and smaller structure. The new concept holds great potential for further development. Full article
Open AccessArticle A Numerical Corrosion Rate Prediction Method for Direct Assessment of Wet Gas Gathering Pipelines Internal Corrosion
Energies 2012, 5(10), 3892-3907; doi:10.3390/en5103892
Received: 16 July 2012 / Revised: 25 September 2012 / Accepted: 25 September 2012 / Published: 15 October 2012
Cited by 8 | PDF Full-text (461 KB) | HTML Full-text | XML Full-text
Abstract
The paper introduces a numerical internal corrosion rate prediction method into the internal corrosion direct assessment (ICDA) process for wet gas gathering pipelines based on the back propagation (BP), the genetic algorithm (GA) and BP, and the particle swarm optimization and BP artificial
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The paper introduces a numerical internal corrosion rate prediction method into the internal corrosion direct assessment (ICDA) process for wet gas gathering pipelines based on the back propagation (BP), the genetic algorithm (GA) and BP, and the particle swarm optimization and BP artificial neural networks (ANNs). The basic data were collected in accordance with the terms established by the National Association of Corrosion Engineers in the Wet Gas Internal Corrosion Direct Assessment (WG-ICDA) SP0110, and the corrosion influencing factors, which are the input variables of the ANN model, are identified and refined by the grey relational analysis method. A total of 116 groups of basic data and inspection data from seven gathering pipelines in Sichuan (China) are used to develop the numerical prediction model. Ninety-five of the 116 groups of data are selected to train the neural network. The remaining 21 groups of data are chosen to test the three ANNs. The test results show that the GA and BP ANN yield the smallest number of absolute errors and should be selected as the preferred model for the prediction of corrosion rates. The accuracy of the model was validated by another 54 groups of excavation data obtained from pipeline No. 8, whose internal environment parameters are similar to those found in the training and testing pipelines. The results show that the numerical method yields significantly better absolute errors than either the de Waard 95 model or the Top-of-Line corrosion model in WG-ICDA when applying the approach to specific pipelines, and it can be used to investigate a specific pipeline for which the data have been collected and the ANN has been developed in WG-ICDA SP0110. Full article
Open AccessArticle Visions, Scenarios and Action Plans Towards Next Generation Tanzania Power System
Energies 2012, 5(10), 3908-3927; doi:10.3390/en5103908
Received: 25 June 2012 / Revised: 3 September 2012 / Accepted: 27 September 2012 / Published: 16 October 2012
Cited by 7 | PDF Full-text (4199 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents strategic visions, scenarios and action plans for enhancing Tanzania Power Systems towards next generation Smart Power Grid. It first introduces the present Tanzanian power grid and the challenges ahead in terms of generation capacity, financial aspect, technical and non-technical losses,
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This paper presents strategic visions, scenarios and action plans for enhancing Tanzania Power Systems towards next generation Smart Power Grid. It first introduces the present Tanzanian power grid and the challenges ahead in terms of generation capacity, financial aspect, technical and non-technical losses, revenue loss, high tariff, aging infrastructure, environmental impact and the interconnection with the neighboring countries. Then, the current initiatives undertaken by the Tanzania government in response to the present challenges and the expected roles of smart grid in overcoming these challenges in the future with respect to the scenarios presented are discussed. The developed scenarios along with visions and recommended action plans towards the future Tanzanian power system can be exploited at all governmental levels to achieve public policy goals and help develop business opportunities by motivating domestic and international investments in modernizing the nation’s electric power infrastructure. In return, it should help build the green energy economy. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
Open AccessArticle Some Chemical Compositional Changes in Miscanthus and White Oak Sawdust Samples during Torrefaction
Energies 2012, 5(10), 3928-3947; doi:10.3390/en5103928
Received: 13 July 2012 / Accepted: 19 September 2012 / Published: 16 October 2012
Cited by 7 | PDF Full-text (1137 KB) | HTML Full-text | XML Full-text
Abstract
Torrefaction tests on miscanthus and white oak sawdust were conducted in a bubbling sand bed reactor to see the effect of temperature and residence time on the chemical composition. Process conditions for miscanthus and white oak sawdust were 250–350 °C for 30–120 min
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Torrefaction tests on miscanthus and white oak sawdust were conducted in a bubbling sand bed reactor to see the effect of temperature and residence time on the chemical composition. Process conditions for miscanthus and white oak sawdust were 250–350 °C for 30–120 min and 220–270 °C for 30 min, respectively. Torrefaction of miscanthus at 250 °C and a residence time of 30 min resulted in a significant decrease in moisture—about 82.68%—but the other components—hydrogen, nitrogen, sulfur, and volatiles—changed only marginally. Increasing torrefaction temperatures to 350 °C with a residence time of 120 min further reduced the moisture content to 0.54%, with a significant decrease in the hydrogen, nitrogen, and volatiles by 58.29%, 14.28%, and 70.45%, respectively. Regression equations developed for the moisture, hydrogen, nitrogen, and volatile content of the samples with respect to torrefaction temperature and time have adequately described the changes in chemical composition based on R2 values of >0.82. Surface plots based on the regression equation indicate that torrefaction temperatures of 280–350 °C with residence times of 30–120 min can help reduce moisture, nitrogen, and volatile content from 1.13% to 0.6%, 0.27% to 0.23%, and 79% to 23%, with respect to initial values. Trends of chemical compositional changes in white oak sawdust are similar to miscanthus. Torrefaction temperatures of 270 °C and a 30 min residence time reduced the moisture, volatiles, hydrogen, and nitrogen content by about 79%, 17.88%, 20%, and 5.88%, respectively, whereas the carbon content increased by about 3.5%. Full article
(This article belongs to the Special Issue Biomass and Biofuels 2012)
Open AccessArticle Forecasting Annual Power Generation Using a Harmony Search Algorithm-Based Joint Parameters Optimization Combination Model
Energies 2012, 5(10), 3948-3971; doi:10.3390/en5103948
Received: 21 August 2012 / Revised: 24 September 2012 / Accepted: 5 October 2012 / Published: 16 October 2012
Cited by 1 | PDF Full-text (410 KB) | HTML Full-text | XML Full-text
Abstract
Accurate power generation forecasting provides the basis of decision making for electric power industry development plans, energy conservation and environmental protection. Since the power generation time series are rarely purely linear or nonlinear, no single forecasting model can identify the true data trends
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Accurate power generation forecasting provides the basis of decision making for electric power industry development plans, energy conservation and environmental protection. Since the power generation time series are rarely purely linear or nonlinear, no single forecasting model can identify the true data trends exactly in all situations. To combine forecasts from different models can reduce the model selection risk and effectively improve accuracy. In this paper, we propose a novel technique called the Harmony Search (HS) algorithm-based joint parameters optimization combination model. In this model, the single forecasting model adopts power function form with unfixed exponential parameters. The exponential parameters of the single model and the combination weights are called joint parameters which are optimized by the HS algorithm by optimizing the objective function. Real power generation time series data sets of China, Japan, Russian Federation and India were used as samples to examine the forecasting accuracy of the presented model. The forecasting performance was compared with four single models and four combination models, respectively. The MAPE of our presented model is the lowest, which shows that the proposed model outperforms other comparative ones. Especially, the proposed combination model could better fit significant turning points of power generation time series. We can conclude that the proposed model can obviously improve forecasting accuracy and it can treat nonlinear time series with fluctuations better than other single models or combination models. Full article
Open AccessArticle Residential Solar-Based Seasonal Thermal Storage Systems in Cold Climates: Building Envelope and Thermal Storage
Energies 2012, 5(10), 3972-3985; doi:10.3390/en5103972
Received: 21 August 2012 / Revised: 26 September 2012 / Accepted: 8 October 2012 / Published: 16 October 2012
Cited by 4 | PDF Full-text (320 KB) | HTML Full-text | XML Full-text
Abstract
The reduction of electricity use for heating and domestic hot water in cold climates can be achieved by: (1) reducing the heating loads through the improvement of the thermal performance of house envelopes, and (2) using solar energy through a residential solar-based thermal
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The reduction of electricity use for heating and domestic hot water in cold climates can be achieved by: (1) reducing the heating loads through the improvement of the thermal performance of house envelopes, and (2) using solar energy through a residential solar-based thermal storage system. First, this paper presents the life cycle energy and cost analysis of a typical one-storey detached house, located in Montreal, Canada. Simulation of annual energy use is performed using the TRNSYS software. Second, several design alternatives with improved thermal resistance for walls, ceiling and windows, increased overall air tightness, and increased window-to-wall ratio of South facing windows are evaluated with respect to the life cycle energy use, life cycle emissions and life cycle cost. The solution that minimizes the energy demand is chosen as a reference house for the study of long-term thermal storage. Third, the computer simulation of a solar heating system with solar thermal collectors and long-term thermal storage capacity is presented. Finally, the life cycle cost and life cycle energy use of the solar combisystem are estimated for flat-plate solar collectors and evacuated tube solar collectors, respectively, for the economic and climatic conditions of this study. Full article
Open AccessArticle A Two-Dimensional Numerical Study of Hydrodynamic, Heat and Mass Transfer and Stability in a Salt Gradient Solar Pond
Energies 2012, 5(10), 3986-4007; doi:10.3390/en5103986
Received: 24 May 2012 / Revised: 25 September 2012 / Accepted: 8 October 2012 / Published: 18 October 2012
Cited by 4 | PDF Full-text (7555 KB) | HTML Full-text | XML Full-text
Abstract
In this work, the problem of hydrodynamic, heat and mass transfer and stability in a salt gradient solar pond has been numerically studied by means of computational fluid dynamics in transient regime. The body of the simulated pond is an enclosure of height
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In this work, the problem of hydrodynamic, heat and mass transfer and stability in a salt gradient solar pond has been numerically studied by means of computational fluid dynamics in transient regime. The body of the simulated pond is an enclosure of height H and length L wherein an artificial salinity gradient is created in order to suppress convective motions induced by solar radiation absorption and to stabilize the solar pond during the period of operation. Here we show the distribution of velocity, temperature and salt concentration fields during energy collection and storage in a solar pond filled with water and constituted by three different salinity zones. The bottom of the pond is blackened and the free-surface is subjected to heat losses by convection, evaporation and radiation while the vertical walls are adiabatic and impermeable. The governing equations of continuity, momentum, thermal energy and mass transfer are discretized by finite–volume method in transient regime. Velocity vector fields show the presence of thin convective cells in the upper convective zone (UCZ) and large convective cells in the lower convective zone (LCZ). This study shows the importance of buoyancy ratio in the decrease of temperature in the UCZ and in the preservation of high temperature in the LCZ. It shows also the importance of the thickness of Non-Convective Zone (NCZ) in the reduction of the upwards heat losses. Full article
(This article belongs to the Special Issue Solar Energy Systems and Materials)
Open AccessArticle Computation of Electromagnetic Torque in a Double Rotor Switched Reluctance Motor Using Flux Tube Methods
Energies 2012, 5(10), 4008-4026; doi:10.3390/en5104008
Received: 19 August 2012 / Revised: 22 September 2012 / Accepted: 4 October 2012 / Published: 18 October 2012
Cited by 9 | PDF Full-text (1874 KB) | HTML Full-text | XML Full-text
Abstract
With their highly robust nature and simple design, switched reluctance machines are finding their way into numerous modern day applications. However, they produce oscillatory torque that generates torque ripple and mechanical vibrations. A double rotor structure to maximize the flux linkage and thereby
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With their highly robust nature and simple design, switched reluctance machines are finding their way into numerous modern day applications. However, they produce oscillatory torque that generates torque ripple and mechanical vibrations. A double rotor structure to maximize the flux linkage and thereby increase the torque generating capability is proposed. As the machine operates close to saturation, the torque computation depends heavily on the energy conversion as the rotor rolls over the stator for a fixed pole pitch. The flux linkage characteristics are highly non-linear, hence estimation of the magnetic and mechanical parameters is extremely cumbersome. Magnetic circuit analysis by interpretation of the number of flux tubes using integration techniques at different positions of the machine to develop the flux linkage characteristics of the double rotor structure is presented. Computation of the inductances during the movement of rotor from unaligned to aligned is crucial in determining the generated torque. Relevant equations of calculations for inductance and flux linkages in the aligned, partially aligned and unaligned positions are computed. The partially aligned computation is based on the average on two intermediate positions, namely the 1/4th aligned and 3/4th aligned conditions. The static torque characteristics based on the energy conversion principles are used to compute the torque value. Results from simulation and experiments used for performance evaluation of the proposed flux tube analysis for computation of the electro-magnetic torque are presented. Full article
Open AccessArticle Magnetic Decoupling Design and Experimental Validation of a Radial-Radial Flux Compound-Structure Permanent-Magnet Synchronous Machine for HEVs
Energies 2012, 5(10), 4027-4039; doi:10.3390/en5104027
Received: 27 August 2012 / Revised: 15 September 2012 / Accepted: 16 September 2012 / Published: 19 October 2012
Cited by 4 | PDF Full-text (561 KB) | HTML Full-text | XML Full-text
Abstract
The radial-radial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), integrated by two concentrically arranged permanent-magnet electric machines, is an electromagnetic power-splitting device for hybrid electric vehicles (HEVs). As the two electric machines share a rotor as structural and magnetic common part, their magnetic paths
[...] Read more.
The radial-radial flux compound-structure permanent-magnet synchronous machine (CS-PMSM), integrated by two concentrically arranged permanent-magnet electric machines, is an electromagnetic power-splitting device for hybrid electric vehicles (HEVs). As the two electric machines share a rotor as structural and magnetic common part, their magnetic paths are coupled, leading to possible mutual magnetic-field interference and complex control. In this paper, a design method to ensure magnetic decoupling with minimum yoke thickness of the common rotor is investigated. A prototype machine is designed based on the proposed method, and the feasibility of magnetic decoupling and independent control is validated by experimental tests of mutual influence. The CS-PMSM is tested by a designed driving cycle, and functions to act as starter motor, generator and to help the internal combustion engine (ICE) operate at optimum efficiency are validated. Full article
Open AccessArticle Natural Gas Prices on Three Continents
Energies 2012, 5(10), 4040-4056; doi:10.3390/en5104040
Received: 17 April 2012 / Revised: 8 October 2012 / Accepted: 9 October 2012 / Published: 19 October 2012
Cited by 4 | PDF Full-text (400 KB) | HTML Full-text | XML Full-text
Abstract
We investigate the pricing formation of natural gas markets on three different continents (Europe, Asia and North America). We find that natural gas markets showed a strong relationship with the crude oil market between 1992 and 2001 and natural gas prices tended to
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We investigate the pricing formation of natural gas markets on three different continents (Europe, Asia and North America). We find that natural gas markets showed a strong relationship with the crude oil market between 1992 and 2001 and natural gas prices tended to thermal parity with crude oil prices. From 2002 natural gas markets exhibited a less pronounced relationship with the crude oil market and major natural gas markets were severely underpriced compared to crude oil. A globally integrated natural gas market, comparable to the global oil market, has not evolved. The main natural gas markets, however, exhibit some level of integration, especially over a longer time. The European market exhibits the strongest levels of integration, while the North American market exhibits the weakest. Full article
Open AccessArticle A Nonlinear Elastic Model for Triaxial Compressive Properties of Artificial Methane-Hydrate-Bearing Sediment Samples
Energies 2012, 5(10), 4057-4075; doi:10.3390/en5104057
Received: 28 June 2012 / Revised: 1 October 2012 / Accepted: 16 October 2012 / Published: 19 October 2012
Cited by 12 | PDF Full-text (354 KB) | HTML Full-text | XML Full-text
Abstract
A constitutive model for marine sediments containing natural gas hydrate is essential for the simulation of the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, the triaxial compressive properties of artificial methane-hydrate-bearing sediment samples reported in an earlier work
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A constitutive model for marine sediments containing natural gas hydrate is essential for the simulation of the geomechanical response to gas extraction from a gas-hydrate reservoir. In this study, the triaxial compressive properties of artificial methane-hydrate-bearing sediment samples reported in an earlier work were analyzed to examine the applicability of a nonlinear elastic constitutive model based on the Duncan-Chang model. The presented model considered the dependences of the mechanical properties on methane hydrate saturation and effective confining pressure. Some parameters were decided depending on the type of sand forming a specimen. The behaviors of lateral strain versus axial strain were also formulated as a function of effective confining pressure. The constitutive model presented in this study will provide a basis for an elastic analysis of the geomechanical behaviors of the gas-hydrate reservoir in the future study, although it is currently available to a limited extent. Full article
Open AccessArticle Vehicle to Grid Services: Potential and Applications
Energies 2012, 5(10), 4076-4090; doi:10.3390/en5104076
Received: 15 August 2012 / Revised: 2 October 2012 / Accepted: 9 October 2012 / Published: 19 October 2012
Cited by 27 | PDF Full-text (230 KB) | HTML Full-text | XML Full-text
Abstract
Electric Vehicle (EV) technology is expected to take a major share in the light-vehicle market in the coming decades. Charging of EVs will put an extra burden on the distribution grid and in some cases adjustments will need to be made. On
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Electric Vehicle (EV) technology is expected to take a major share in the light-vehicle market in the coming decades. Charging of EVs will put an extra burden on the distribution grid and in some cases adjustments will need to be made. On the other hand, EVs have the potential to support the grid under various conditions. This paper studies possible potential and applications of Vehicle to Grid (V2G) services, including active power services, which discharge the EV batteries, and power quality services, which do not engage the battery or require only small amounts of battery charge. The advantages and disadvantages of each service and the likelihood that a given service will be effective and beneficial for the grid in the future are discussed. Further, the infrastructure cost, duration, and value of V2G services are compared qualitatively. Full article
(This article belongs to the Special Issue Vehicle to Grid)
Open AccessArticle Intrusion Detection of NSM Based DoS Attacks Using Data Mining in Smart Grid
Energies 2012, 5(10), 4091-4109; doi:10.3390/en5104091
Received: 5 September 2012 / Revised: 9 October 2012 / Accepted: 12 October 2012 / Published: 19 October 2012
Cited by 6 | PDF Full-text (661 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we analyze the Network and System Management (NSM) requirements and NSM data objects for the intrusion detection of power systems; NSM is an IEC 62351-7 standard. We analyze a SYN flood attack and a buffer overflow attack to cause the
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In this paper, we analyze the Network and System Management (NSM) requirements and NSM data objects for the intrusion detection of power systems; NSM is an IEC 62351-7 standard. We analyze a SYN flood attack and a buffer overflow attack to cause the Denial of Service (DoS) attack described in NSM. After mounting the attack in our attack testbed, we collect a data set, which is based on attributes for the attack. We then run several data mining methods with the data set using the Waikato Environment for Knowledge Analysis (WEKA). In the results, we select the decision tree algorithms with high detection rates, and choose key attributes in high level components of the trees. When we run several data mining methods again with the data set of chosen key attributes, the detection rates of most data mining methods are higher than before. We prove that our selected attack attributes, and the proposed detection process, are efficient and suitable for intrusion detection in the smart grid environment. Full article
(This article belongs to the Special Issue Smart Grid and the Future Electrical Network)
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Open AccessArticle Retrofitting Domestic Hot Water Heaters for Solar Water Heating Systems in Single-Family Houses in a Cold Climate: A Theoretical Analysis
Energies 2012, 5(10), 4110-4131; doi:10.3390/en5104110
Received: 20 July 2012 / Revised: 15 October 2012 / Accepted: 15 October 2012 / Published: 22 October 2012
Cited by 9 | PDF Full-text (699 KB) | HTML Full-text | XML Full-text
Abstract
One of the biggest obstacles to economic profitability of solar water heating systems is the investment cost. Retrofitting existing domestic hot water heaters when a new solar hot water system is installed can reduce both the installation and material costs. In this study,
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One of the biggest obstacles to economic profitability of solar water heating systems is the investment cost. Retrofitting existing domestic hot water heaters when a new solar hot water system is installed can reduce both the installation and material costs. In this study, retrofitting existing water heaters for solar water heating systems in Swedish single-family houses was theoretically investigated using the TRNSYS software. Four simulation models using forced circulation flow with different system configurations and control strategies were simulated and analysed in the study. A comparison with a standard solar thermal system was also presented based on the annual solar fraction. The simulation results indicate that the retrofitting configuration achieving the highest annual performance consists of a system where the existing tank is used as storage for the solar heat and a smaller tank with a heater is added in series to make sure that the required outlet temperature can be met. An external heat exchanger is used between the collector circuit and the existing tank. For this retrofitted system an annual solar fraction of 50.5% was achieved. A conventional solar thermal system using a standard solar tank achieves a comparable performance for the same total storage volume, collector area and reference conditions. Full article
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Open AccessArticle Effect of CH4–Air Ratios on Gas Explosion Flame Microstructure and Propagation Behaviors
Energies 2012, 5(10), 4132-4146; doi:10.3390/en5104132
Received: 18 August 2012 / Revised: 24 September 2012 / Accepted: 18 October 2012 / Published: 22 October 2012
Cited by 7 | PDF Full-text (1846 KB) | HTML Full-text | XML Full-text
Abstract
To reveal the inner mechanism of gas explosion dynamic behavior affected by gas equivalent concentration, a high speed Schlieren image system and flow field measurement technology was applied to record the gas explosion flame propagation and flame structure transition. The results show that
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To reveal the inner mechanism of gas explosion dynamic behavior affected by gas equivalent concentration, a high speed Schlieren image system and flow field measurement technology was applied to record the gas explosion flame propagation and flame structure transition. The results show that a flame front structure transition occurs, followed by a flame accelerating propagation process. The laminar to turbulence transition was the essential cause of the flame structure changes. The laminar flame propagation behavior was influenced mainly by gas expansion and fore-compressive wave effect, while the turbulent flame speed mostly depended on turbulence intensity, which also played an important role in peak value of the explosive pressure and flame speed. On the condition that the laminar-turbulent transition was easier to form, the conclusion was drawn that, the lowest CH4 concentration for maximum overpressure can be obtained, which was the essential reason why the ideal explosive concentration differs under different test conditions. Full article
Open AccessArticle Synthesis of Alcohols and Alkanes from CO and H2 over MoS2/γ-Al2O3 Catalyst in a Packed Bed with Continuous Flow
Energies 2012, 5(10), 4147-4164; doi:10.3390/en5104147
Received: 25 August 2012 / Revised: 4 October 2012 / Accepted: 11 October 2012 / Published: 22 October 2012
Cited by 6 | PDF Full-text (1232 KB) | HTML Full-text | XML Full-text
Abstract
Effects of reaction conditions on the production of alcohols (AOHs) and alkanes (Alk) from CO and H2, which can be obtained from the gasification of biomass, using a molybdenum sulfide (MoS2)-based catalyst of MoS2/γ-Al2
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Effects of reaction conditions on the production of alcohols (AOHs) and alkanes (Alk) from CO and H2, which can be obtained from the gasification of biomass, using a molybdenum sulfide (MoS2)-based catalyst of MoS2/γ-Al2O3 were studied. A high-pressure fixed packed bed (HPFPB) was employed to carry out the reaction. The results indicate that the conversion of CO (XCO) and specific production rates of alcohol (SPRAOH) and alkane (SPRAlk) are highly depended on temperature (T). In T = 423–573 K, maximum yield of alcohols (YAOH) and SPRAOH occur at T = 523 K. In the meantime, well performance gives the selectivity of ethanol (SEtOH) of 52.0 C%. For the studies on varying H2/CO mole ratio (MH/C) from 1 to 4 at 523 K, the appropriate MH/C to produce EtOH is 2, giving higher ratios of SPRAOH/SPRAlk and YAOH/YAlk than those with other MH/C. As for varying the total gas flow rates (QG) of 300, 450, 600 to 900 cm3 min−1 tested at T = 523 K and MH/C = 2, the lower QG provides longer reaction time (or gaseous retention time, tR) thus offering higher XCO, however lower productivity. For setting pressure (PST) = 225–540 psi, a supply of higher pressure is equivalent to providing a larger amount of reactants into the reaction system, this thus suggests the use of higher PST should give both higher XCO and productivity. The assessment of the above results indicates that the MoS2/γ-Al2O3 catalyst favors the production of alcohols over alkanes, especially for ethanol. The information obtained is useful for the proper utilization of biomass derived gases of CO and H2. Full article
Open AccessArticle Short Term Electric Production Technology Switching Under Carbon Cap and Trade
Energies 2012, 5(10), 4165-4185; doi:10.3390/en5104165
Received: 1 September 2012 / Revised: 24 September 2012 / Accepted: 10 October 2012 / Published: 23 October 2012
Cited by 9 | PDF Full-text (276 KB) | HTML Full-text | XML Full-text
Abstract
This study examines fuel switching in electricity production following the introduction of the European Union’s Emissions Trading System (EU ETS) for greenhouse gas emissions. A short-run restricted cost equation is estimated with carbon permits, high-carbon fuels, and low carbon fuels as variable inputs.
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This study examines fuel switching in electricity production following the introduction of the European Union’s Emissions Trading System (EU ETS) for greenhouse gas emissions. A short-run restricted cost equation is estimated with carbon permits, high-carbon fuels, and low carbon fuels as variable inputs. Shadow values and substitution elasticities for carbon-free energy resources from nuclear, hydroelectric and renewable sources are imputed from the cost equation. The empirical analysis examines 12 European countries using monthly data on fuel use, prices, and electricity generation during the first phase of the European Emissions Trading System. Despite low emission permit prices, this study finds statistically significant substitution between fossil fuels and carbon free sources of energy for electric power production. Significant substitution between fossil fuels and nuclear energy also was found. Still, while 18 of the 20 substitution elasticities are statistically significant, they are all less than unity, consistent with limited substitution. Overall, these results suggest that prices for carbon emission permits relative to prices for carbon and carbon free sources of energy do matter but that electric power producers have limited operational flexibility in the short-run to satisfy greenhouse gas emission limits. Full article
Open AccessArticle Parabolic Trough Photovoltaic/Thermal Collectors: Design and Simulation Model
Energies 2012, 5(10), 4186-4208; doi:10.3390/en5104186
Received: 30 July 2012 / Revised: 25 September 2012 / Accepted: 16 October 2012 / Published: 23 October 2012
Cited by 16 | PDF Full-text (417 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a design procedure and a simulation model of a novel concentrating PVT collector. The layout of the PVT system under investigation was derived from a prototype recently presented in literature and commercially available. The prototype consisted in a parabolic trough
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This paper presents a design procedure and a simulation model of a novel concentrating PVT collector. The layout of the PVT system under investigation was derived from a prototype recently presented in literature and commercially available. The prototype consisted in a parabolic trough concentrator and a linear triangular receiver. In that prototype, the bottom surfaces of the receiver are equipped with mono-crystalline silicon cells whereas the top surface is covered by an absorbing surface. The aperture area of the parabola was covered by a glass in order to improve the thermal efficiency of the system. In the modified version of the collector considered in this paper, two changes are implemented: the cover glass was eliminated and the mono-crystalline silicon cells were replaced by triple-junction cells. In order to analyze PVT performance, a detailed mathematical model was implemented. This model is based on zero-dimensional energy balances. The simulation model calculates the temperatures of the main components of the system and the main energy flows Results showed that the performance of the system is excellent even when the fluid temperature is very high (>100 °C). Conversely, both electrical and thermal efficiencies dramatically decrease when the incident beam radiation decreases. Full article
Open AccessArticle Adsorption of Thiophenic Compounds from Model Diesel Fuel Using Copper and Nickel Impregnated Activated Carbons
Energies 2012, 5(10), 4233-4250; doi:10.3390/en5104233
Received: 18 July 2012 / Revised: 13 September 2012 / Accepted: 20 September 2012 / Published: 23 October 2012
Cited by 12 | PDF Full-text (1453 KB) | HTML Full-text | XML Full-text
Abstract
Adsorption of sulfur compoundsby porous materials is an effective way to produce cleaner diesel fuel.In this study, adsorption of refractory thiophenic sulfur compounds, i.e., benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in single-solute systems from n-hexane solutions onto metal-impregnated activated carbons
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Adsorption of sulfur compoundsby porous materials is an effective way to produce cleaner diesel fuel.In this study, adsorption of refractory thiophenic sulfur compounds, i.e., benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in single-solute systems from n-hexane solutions onto metal-impregnated activated carbons was investigated. A hydrogen-treated activated carbon fiber was selectively loaded with Ni, NiO, Cu, Cu2O, and CuO species to systematically assess the impact of each metal species on the adsorption of thiophenic compounds (TC). Metal-loaded adsorbents had the same total metal contents and similar microporosities, but contained different types of copper or nickel species. All metal-loaded adsorbents showed enhanced adsorption of tested TC. Cu2O- or NiO-loaded adsorbents exhibited the highest uptakes, due to more specific interactions between Cu+ or Ni2+ species and TC molecules. The theoretical monolyer coverage of TC on the exposed Cu+ sites was estimated and compared with that calculated from the experimental data. Results suggested catalytic conversion of TC molecules to other compounds on the Cu+ sites, followed by adsorption of reaction products onto the carbon surface or multilayer accumulation of TC molecules on the Cu+sites. TC adsorption uptake of the majority of adsorbents followed the order of: 4,6-DMDBT > DBT > BT due to higher intensity of specific and non-specific interactions of larger TC molecules with adsorbents. Full article

Review

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Open AccessReview Ash Management Review—Applications of Biomass Bottom Ash
Energies 2012, 5(10), 3856-3873; doi:10.3390/en5103856
Received: 18 July 2012 / Revised: 13 September 2012 / Accepted: 20 September 2012 / Published: 9 October 2012
Cited by 37 | PDF Full-text (210 KB) | HTML Full-text | XML Full-text
Abstract
In industrialized countries, it is expected that the future generation of bioenergy will be from the direct combustion of residues and wastes obtained from biomass. Bioenergy production using woody biomass is a fast developing application since this fuel source is considered to be
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In industrialized countries, it is expected that the future generation of bioenergy will be from the direct combustion of residues and wastes obtained from biomass. Bioenergy production using woody biomass is a fast developing application since this fuel source is considered to be carbon neutral. The harnessing of bioenergy from these sources produces residue in the form of ash. As the demand for bioenergy production increases, ash and residue volumes will increase. Major challenges will arise relating to the efficient management of these byproducts. The primary concerns for ash are its storage, disposal, use and the presence of unburned carbon. The continual increase in ash volume will result in decreased ash storage facilities (in cases of limited room for landfill expansion), as well as increased handling, transporting and spreading costs. The utilization of ash has been the focus of many studies, hence this review investigates the likely environmental and technological challenges that increased ash generation may cause. The presence of alkali metals, alkaline earth metals, chlorine, sulphur and silicon influences the reactivity and leaching to the inorganic phases which may have significant impacts on soils and the recycling of soil nutrient. Discussed are some of the existing technologies for the processing of ash. Unburned carbon present in ash allows for the exploration of using ash as a fuel. The paper proposes sieve fractionation as a suitable method for the separation of unburnt carbon present in bottom ash obtained from a fixed-bed combustion system, followed by the application of the gasification technology to particle sizes of energy importance. It is hoped that this process will significantly reduce the volume of ash disposed at landfills. Full article
(This article belongs to the Special Issue Waste to Energy Technologies)
Open AccessReview A Review on Waste to Energy Processes Using Microwave Pyrolysis
Energies 2012, 5(10), 4209-4232; doi:10.3390/en5104209
Received: 29 June 2012 / Revised: 6 September 2012 / Accepted: 12 October 2012 / Published: 23 October 2012
Cited by 53 | PDF Full-text (658 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents an extensive review of the scientific literature associated with various microwave pyrolysis applications in waste to energy engineering. It was established that microwave-heated pyrolysis processes offer a number of advantages over other processes that use traditional thermal heat sources. In
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This paper presents an extensive review of the scientific literature associated with various microwave pyrolysis applications in waste to energy engineering. It was established that microwave-heated pyrolysis processes offer a number of advantages over other processes that use traditional thermal heat sources. In particular, microwave-heated processes show a distinct advantage in providing rapid and energy-efficient heating compared to conventional technologies, and thus facilitating increased production rates. It can also be established that the pyrolysis process offers an exciting way to recover both the energetic and chemical value of the waste materials by generating potentially useful pyrolysis products suitable for future reuse. Furthermore, this review has revealed good performance of the microwave pyrolysis process when compared to other more conventional methods of operation, indicating that it shows exceptional promise as a means for energy recovery from waste materials. Nonetheless, it was revealed that many important characteristics of the microwave pyrolysis process have yet to be raised or fully investigated. In addition, limited information is available concerning the characteristics of the microwave pyrolysis of waste materials. It was thus concluded that more work is needed to extend existing understanding of these aspects in order to develop improvements to the process to transform it into a commercially viable route to recover energy from waste materials in an environmentally sustainable manner. Full article
(This article belongs to the Special Issue Waste to Energy Technologies)

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