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Energies, Volume 2, Issue 2 (June 2009), Pages 180-476

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Research

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Open AccessArticle Optimal Fixed Bed Reactor Network Configuration for the Efficient Recycling of CO2 into Methanol
Energies 2009, 2(2), 180-189; doi:10.3390/en20200180
Received: 19 February 2009 / Revised: 2 April 2009 / Accepted: 3 April 2009 / Published: 7 April 2009
Cited by 2 | PDF Full-text (368 KB) | HTML Full-text | XML Full-text
Abstract
An optimal design strategy of a network of fixed bed reactors for Methanol Production (MP) is proposed in this study. Both methanol production and profit spanning a production period of eight years have been set as objective functions to find the optimal [...] Read more.
An optimal design strategy of a network of fixed bed reactors for Methanol Production (MP) is proposed in this study. Both methanol production and profit spanning a production period of eight years have been set as objective functions to find the optimal production network. The conservation of mass and energy laws on a heterogeneous model of a single industrial methanol reactor was first developed. The model was solved numerically and was validated with industrial plant data. Different reactor network arrangements were then simulated in order to find an optimal superstructure. It was found that a structure of four reactors (two in series in parallel with another two in series) provide maximum production rate. The application of the more realistic objective function of profit showed that a configuration of two parallel reactors is the best configuration. This optimal structure produces 92 tons/day more methanol than a single reactor. Full article
(This article belongs to the Special Issue Energy Solutions in the Era of Climate Change)
Open AccessArticle A Self-Supported Direct Borohydride-Hydrogen Peroxide Fuel Cell System
Energies 2009, 2(2), 190-201; doi:10.3390/en20200190
Received: 20 March 2009 / Revised: 2 April 2009 / Accepted: 8 April 2009 / Published: 14 April 2009
Cited by 8 | PDF Full-text (418 KB) | HTML Full-text | XML Full-text
Abstract
A self-supported direct borohydride-hydrogen peroxide fuel cell system with internal manifolds and an auxiliary control unit is reported. The system, while operating under ambient conditions, delivers a peak power of 40 W with about 2 W to run the auxiliary control unit. [...] Read more.
A self-supported direct borohydride-hydrogen peroxide fuel cell system with internal manifolds and an auxiliary control unit is reported. The system, while operating under ambient conditions, delivers a peak power of 40 W with about 2 W to run the auxiliary control unit. A critical cause and effect analysis, on the data for single cells and stack, suggests the optimum concentrations of fuel and oxidant to be 8 wt. % NaBH4 and 2 M H2O2, respectively in extending the operating time of the system. Such a fuel cell system is ideally suited for submersible and aerospace applications where anaerobic conditions prevail. Full article
(This article belongs to the Special Issue Fuel Cells)
Open AccessArticle The Optimal Operation Criteria for a Gas Turbine Cogeneration System
Energies 2009, 2(2), 202-225; doi:10.3390/en20200202
Received: 17 February 2009 / Revised: 27 March 2009 / Accepted: 27 March 2009 / Published: 16 April 2009
PDF Full-text (847 KB) | HTML Full-text | XML Full-text
Abstract
The study demonstrated the optimal operation criteria of a gas turbine cogeneration system based on the analytical solution of a linear programming model. The optimal operation criteria gave the combination of equipment to supply electricity and steam with the minimum energy cost [...] Read more.
The study demonstrated the optimal operation criteria of a gas turbine cogeneration system based on the analytical solution of a linear programming model. The optimal operation criteria gave the combination of equipment to supply electricity and steam with the minimum energy cost using the energy prices and the performance of equipment. By the comparison with a detailed optimization result of an existing cogeneration plant, it was shown that the optimal operation criteria successfully provided a direction for the system operation under the condition where the electric power output of the gas turbine was less than the capacity Full article
Open AccessArticle Fault Diagnosis on Medium Voltage (MV) Electric Power Distribution Networks: The Case of the Downstream Network of the AES-SONEL Ngousso Sub-Station
Energies 2009, 2(2), 243-257; doi:10.3390/en20200243
Received: 14 March 2009 / Revised: 21 April 2009 / Accepted: 22 April 2009 / Published: 27 April 2009
Cited by 8 | PDF Full-text (311 KB) | HTML Full-text | XML Full-text
Abstract
An analysis of the Medium Voltage (MV)electricity power distribution network operated by Cameroon’s AES-SONEL company shows that losses are very high due to energy which is produced but not distributed and that the duration of power interruptions as a result of these [...] Read more.
An analysis of the Medium Voltage (MV)electricity power distribution network operated by Cameroon’s AES-SONEL company shows that losses are very high due to energy which is produced but not distributed and that the duration of power interruptions as a result of these faults is long due to the time used in searching for the faults. Given that quick detection of faults is a sure means of improving availability and productivity in any company, we hereby propose a system of real-time diagnosis of the faults on AES-SONEL’s electric power distribution network. After an inventory of typical faults on electric power networks and the proposal of a tool for their identification, we propose a system for the detection and localization of these various failures. The implementation of the system on a Programmable Logic Controller (PLC) enables the performance of the system to be assessed. Full article
Open AccessArticle Air Gasification of Agricultural Waste in a Fluidized Bed Gasifier: Hydrogen Production Performance
Energies 2009, 2(2), 258-268; doi:10.3390/en20200258
Received: 17 April 2009 / Revised: 11 May 2009 / Accepted: 12 May 2009 / Published: 19 May 2009
Cited by 23 | PDF Full-text (250 KB) | HTML Full-text | XML Full-text
Abstract
Recently, hydrogen production from biomass has become an attractive technology for power generation. The main objective pursued in this work is to investigate the hydrogen production potential from agricultural wastes (coconut coir and palm kernel shell) by applying the air gasification technique. [...] Read more.
Recently, hydrogen production from biomass has become an attractive technology for power generation. The main objective pursued in this work is to investigate the hydrogen production potential from agricultural wastes (coconut coir and palm kernel shell) by applying the air gasification technique. An experimental study was conducted using a bench-scale fluidized bed gasifier with 60 mm diameter and 425 mm height. During the experiments, the fuel properties and the effects of operating parameters such as gasification temperatures (700 to 900°C), fluidization ratio (2 to 3.33 m/s), static bed height (10 to 30 mm) and equivalence ratio (0.16 to 0.46) were studied. It was concluded that substantial amounts of hydrogen gas (up to 67 mol%) could be produced utilizing agricultural residues such as coconut and palm kernel shell by applying this fluidization technique. For both samples, the rise of temperature till 900°C favored further hydrocarbon reactions and allowed an increase of almost 67 mol% in the release of hydrogen. However, other parameters such as fluidizing velocity and feed load showed only minor effects on hydrogen yield. In conclusion, agricultural waste can be assumed as an alternative renewable energy source to the fossil fuels, and the environmental pollution originating from the disposal of agricultural residues can be partially reduced. Full article
Open AccessArticle North American Natural Gas Supply Forecast: The Hubbert Method Including the Effects of Institutions
Energies 2009, 2(2), 269-306; doi:10.3390/en20200269
Received: 25 March 2009 / Revised: 13 May 2009 / Accepted: 19 May 2009 / Published: 22 May 2009
Cited by 15 | PDF Full-text (313 KB) | HTML Full-text | XML Full-text
Abstract
In this article, the U.S. and southern Canadian natural gas supply market is considered. An important model for oil and natural gas supply is the Hubbert curve. Not all regions of the world are producing oil or natural gas following a Hubbert [...] Read more.
In this article, the U.S. and southern Canadian natural gas supply market is considered. An important model for oil and natural gas supply is the Hubbert curve. Not all regions of the world are producing oil or natural gas following a Hubbert curve, even when price and market conditions are accounted for. One reason is that institutions are affecting supply. We investigate the possible effects of oil and gas market institutions in North America on natural gas supply. A multi-cycle Hubbert curve with inflection points similar to the Soviet Union’s oil production multi-cycle Hubbert curve is used to determine North American natural gas discovery rates and to analyze how market specific institutions caused the inflection points. In addition, we analyze the latest shale natural gas projections critically. While currently, unconventional resources of natural gas suggest that North American natural gas production will increase without bound, the model here suggests a peak in North American natural gas supplies could happen in 2013. Full article
Open AccessArticle Global Assessment of High-Altitude Wind Power
Energies 2009, 2(2), 307-319; doi:10.3390/en20200307
Received: 20 April 2009 / Revised: 15 May 2009 / Accepted: 18 May 2009 / Published: 26 May 2009
Cited by 61 | PDF Full-text (818 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The available wind power resource worldwide at altitudes between 500 and 12,000 m above ground is assessed for the first time. Twenty-eight years of wind data from the reanalyses by the National Centers for Environmental Prediction and the Department of Energy are [...] Read more.
The available wind power resource worldwide at altitudes between 500 and 12,000 m above ground is assessed for the first time. Twenty-eight years of wind data from the reanalyses by the National Centers for Environmental Prediction and the Department of Energy are analyzed and interpolated to study geographical distributions and persistency of winds at all altitudes. Furthermore, intermittency issues and global climate effects of large-scale extraction of energy from high-altitude winds are investigated. Full article
(This article belongs to the Special Issue Wind Energy)
Open AccessArticle Ethanol, Corn, and Soybean Price Relations in a Volatile Vehicle-Fuels Market
Energies 2009, 2(2), 320-339; doi:10.3390/en20200320
Received: 22 April 2009 / Revised: 22 May 2009 / Accepted: 25 May 2009 / Published: 2 June 2009
Cited by 44 | PDF Full-text (306 KB) | HTML Full-text | XML Full-text
Abstract
The rapid upward shift in ethanol demand has raised concerns about ethanol’s impact on the price level and volatility of agricultural commodities. The popular press attributes much of this volatility in commodity prices to a price bubble in ethanol fuel and recent [...] Read more.
The rapid upward shift in ethanol demand has raised concerns about ethanol’s impact on the price level and volatility of agricultural commodities. The popular press attributes much of this volatility in commodity prices to a price bubble in ethanol fuel and recent deflation. Market economics predicts not only a softening of demand to high commodity prices but also a positive supply response. This volatility in ethanol and commodity prices are investigated using cointegration, vector error corrections (VECM), and multivariate generalized autoregressive conditional heteroskedascity (MGARCH) models. In terms of derived demand theory, results support ethanol and oil demands as derived demands from vehicle-fuel production. Gasoline prices directly influence the prices of ethanol and oil. However, of greater significance for the fuel versus food security issue, results support the effect of agricultural commodity prices as market signals which restore commodity markets to their equilibriums after a demand or supply event (shock). Such shocks may in the short-run increase agricultural commodity prices, but decentralized freely operating markets will mitigate the persistence of these shocks. Results indicate in recent years there are no long-run relations among fuel (ethanol, oil and gasoline) prices and agricultural commodity (corn and soybean) prices. Full article
(This article belongs to the Special Issue Energy Economics)
Open AccessArticle Mesoscale Simulation of Year-to-Year Variation of Wind Power Potential over Southern China
Energies 2009, 2(2), 340-361; doi:10.3390/en20200340
Received: 27 April 2009 / Revised: 27 May 2009 / Accepted: 1 June 2009 / Published: 3 June 2009
Cited by 11 | PDF Full-text (1202 KB) | HTML Full-text | XML Full-text
Abstract
The objectives of this study are to combine historical observations and state-of-the-art numerical models (MM5/CALMET system) to map the spatial distribution of wind resources in high resolution, and to help foster a deeper understanding of the wind power potential over southern China [...] Read more.
The objectives of this study are to combine historical observations and state-of-the-art numerical models (MM5/CALMET system) to map the spatial distribution of wind resources in high resolution, and to help foster a deeper understanding of the wind power potential over southern China (Guangdong). Hourly wind fields were simulated for three entire years (2004-2006). It found that almost 70% of the time, the wind speed along the coast of Guangdong is over 5 m/s, which is deemed a baseline magnitude for typical wind turbines. Spatial plots of the wind speed and power and their variations over Guangdong Province for the three years are also presented. Full article
Open AccessArticle Transesterification of Vegetable Oils with Ethanol and Characterization of the Key Fuel Properties of Ethyl Esters
Energies 2009, 2(2), 362-376; doi:10.3390/en20200362
Received: 28 April 2009 / Revised: 24 May 2009 / Accepted: 3 June 2009 / Published: 5 June 2009
Cited by 39 | PDF Full-text (209 KB) | HTML Full-text | XML Full-text
Abstract
The transesterification reactions of four different vegetable oils (sunflower, rapeseed, olive oil and used frying oil) with ethanol, using sodium hydroxide as catalyst, were studied. The ester preparation involved a two-step transesterification reaction, followed by purification. The effects of the mass ratio [...] Read more.
The transesterification reactions of four different vegetable oils (sunflower, rapeseed, olive oil and used frying oil) with ethanol, using sodium hydroxide as catalyst, were studied. The ester preparation involved a two-step transesterification reaction, followed by purification. The effects of the mass ratio of catalyst to oil (0.25 – 1.5%), the molar ratio of ethanol to oil (6:1 – 12:1), and the reaction temperature (35 – 90 °C) were studied for the conversion of sunflower oil to optimize the reaction conditions in both stages. The rest of the vegetable oils were converted to ethyl esters under optimum reaction parameters. The optimal conditions for first stage transesterification were an ethanol/oil molar ratio of 12:1, NaOH amount (1% wt/wt), and 80 °C temperature, whereas the maximum yield of ethyl esters reached 81.4% wt/wt. In the second stage, the yield of ethyl esters was improved by 16% in relation with the one-stage transesterification, which was obtained under the following optimal conditions: catalyst concentration 0.75% and ethanol/oil molar ratio 6:1. The fuel properties of the esters were measured according to EN test methods. Based on the experimental results one can see that the ethyl esters do not differ significantly from methyl esters. Moreover, the results showed that the values of density, viscosity, and higher heating value of ethyl esters were similar to those of automotive and heavy duty engine diesel fuel. However, the CFPP values were higher, which may contribute to potential difficulties in cold starts. On the other hand, the flash points, which were higher than those of diesel fuel constituted a safety guarantee from the point of view of handling and storage. Full article
Open AccessArticle Influence of System Parameters on Fuse Protection Use in Regenerative DC Drives
Energies 2009, 2(2), 411-426; doi:10.3390/en20200411
Received: 20 April 2009 / Revised: 4 June 2009 / Accepted: 8 June 2009 / Published: 16 June 2009
PDF Full-text (323 KB) | HTML Full-text | XML Full-text
Abstract
Current limiting fuses are widely used to protect the thyristors in DC drive systems. One very important problem is the choice of the correct voltage rating for fuses protecting regenerative DC drives, where many types of fault may occur, which makes fuse [...] Read more.
Current limiting fuses are widely used to protect the thyristors in DC drive systems. One very important problem is the choice of the correct voltage rating for fuses protecting regenerative DC drives, where many types of fault may occur, which makes fuse protection difficult. In the event of a commutation failure while regenerating, the fuses need to interrupt the loop supplied by the AC and DC voltages acting in series, which is the most difficult case for protection by fuses. In this paper a detailed study of the complete interruption process has been investigated by modeling of arcing process of the fuse protection against the regenerative circuit internal commutation fault. The effect of varying the motor time constant, supply impedance, number of fuses used to clear the fault and DC machine rating on the total transient response is studied. The model of a 200 A fuse is employed in this study. Fuses in series with both the semiconductor devices (F1) and fuses in AC lines (F2) are considered. Comparison was made between arc energy produced for fuses protecting the regenerative circuit if failure occurs, with the arc energy produced in a standard AC test in order to investigate the required voltage rating for the fuse. Full article
Open AccessArticle A Microscale Modeling Tool for the Design and Optimization of Solid Oxide Fuel Cells
Energies 2009, 2(2), 427-444; doi:10.3390/en20200427
Received: 22 May 2009 / Revised: 9 June 2009 / Accepted: 10 June 2009 / Published: 23 June 2009
Cited by 13 | PDF Full-text (650 KB) | HTML Full-text | XML Full-text
Abstract
A two dimensional numerical model of a solid oxide fuel cell (SOFC) with electrode functional layers is presented. The model incorporates the partial differential equations for mass transport, electric conduction and electrochemical reactions in the electrode functional layers, the anode support layer, [...] Read more.
A two dimensional numerical model of a solid oxide fuel cell (SOFC) with electrode functional layers is presented. The model incorporates the partial differential equations for mass transport, electric conduction and electrochemical reactions in the electrode functional layers, the anode support layer, the cathode current collection layer and at the electrode/electrolyte interfaces. A dusty gas model is used in modeling the gas transport in porous electrodes. The model is capable of providing results in good agreement with the experimental I-V relationship. Numerical examples are presented to illustrate the applications of this numerical model as a tool for the design and optimization of SOFCs. For a stack assembly of a pitch width of 2 mm and an interconnect-electrode contact resistance of 0.025 Ωcm2, a typical SOFC stack cell should consist of a rib width of 0.9 mm, a cathode current collection layer thickness of 200–300 μm, a cathode functional layer thickness of 20–40 μm, and an anode functional layer thickness of 10–20 μm in order to achieve optimal performance. Full article
(This article belongs to the Special Issue Fuel Cells)
Figures

Open AccessArticle Biological Hydrogen Production from Corn-Syrup Waste Using a Novel System
Energies 2009, 2(2), 445-455; doi:10.3390/en20200445
Received: 31 May 2009 / Revised: 10 June 2009 / Accepted: 19 June 2009 / Published: 24 June 2009
Cited by 16 | PDF Full-text (276 KB) | HTML Full-text | XML Full-text
Abstract
The reported patent-pending system comprises a novel biohydrogen reactor with a gravity settler for decoupling of SRT from HRT. The biohydrogenator was operated for 100 days at 37 °C, hydraulic retention time 8 h and solids retention time ranging from 2.2–2.5 days. [...] Read more.
The reported patent-pending system comprises a novel biohydrogen reactor with a gravity settler for decoupling of SRT from HRT. The biohydrogenator was operated for 100 days at 37 °C, hydraulic retention time 8 h and solids retention time ranging from 2.2–2.5 days. The feed was a corn-syrup waste generated as a byproduct from an industrial facility for bioethanol production located in southwestern Ontario, Canada. The system was initially started up with a synthetic feed containing glucose at concentration of 8 g/L and other essential inorganics. Anaerobicaly-digested sludge from the St. Mary’s wastewater treatment plant (St. Mary, Ontario, Canada) was used as the seed, and was heat treated at 70 °C for 30 min to inhibit methanogens. After 10 days, when the hydrogen production was steady, the corn-syrup waste was introduced to the system. Glucose was the main constituent in the corn-syrup; its concentration was varied over a period of 90 days from 8 to 25 g/L. The change in glucose concentration was used to study the impact of variable organic loading on the stability of hydrogen production in the biohydrogenator. Hydrogen production rate increased from 10 L H2/L·d to 34 L H2/L·d with the increase of organic loading rate (OLR) from 26 to 81 gCOD/L·d, while a maximum hydrogen yield of 430 mL H2/gCOD was achieved in the system with an overall average of 385 mL H2/gCOD. Full article
Open AccessArticle Early Ideas in Underground Coal Gasification and Their Evolution
Energies 2009, 2(2), 456-476; doi:10.3390/en20200456
Received: 14 May 2009 / Revised: 10 June 2009 / Accepted: 12 June 2009 / Published: 24 June 2009
Cited by 24 | PDF Full-text (1717 KB) | HTML Full-text | XML Full-text
Abstract
This article follows the development of early UCG (underground coal gasification) ideas. Historical facts are discussed mainly from the technological perspective and early experiments in UCG are analyzed. Our search for the first successful UCG experiment brings to light a new finding, [...] Read more.
This article follows the development of early UCG (underground coal gasification) ideas. Historical facts are discussed mainly from the technological perspective and early experiments in UCG are analyzed. Our search for the first successful UCG experiment brings to light a new finding, which was commonly overlooked in previous reviews. We also outline the key role that engineer and inventor A. G. Betts played in introducing technologies utilizing unmined coal; his original ideas are visible in the first successful UCG experiments and in modern UCG technology. Full article
(This article belongs to the Special Issue Coal Gasification and Liquefaction)

Review

Jump to: Research

Open AccessReview Closing the Global Energy and Nutrient Cycles through Application of Biogas Residue to Agricultural Land – Potential Benefits and Drawback
Energies 2009, 2(2), 226-242; doi:10.3390/en20200226
Received: 3 March 2009 / Revised: 30 March 2009 / Accepted: 9 April 2009 / Published: 16 April 2009
Cited by 64 | PDF Full-text (121 KB) | HTML Full-text | XML Full-text
Abstract
Anaerobic digestion is an optimal way to treat organic waste matter, resulting in biogas and residue. Utilization of the residue as a crop fertilizer should enhance crop yield and soil fertility, promoting closure of the global energy and nutrient cycles. Consequently, the [...] Read more.
Anaerobic digestion is an optimal way to treat organic waste matter, resulting in biogas and residue. Utilization of the residue as a crop fertilizer should enhance crop yield and soil fertility, promoting closure of the global energy and nutrient cycles. Consequently, the requirement for production of inorganic fertilizers will decrease, in turn saving significant amounts of energy, reducing greenhouse gas emissions to the atmosphere, and indirectly leading to global economic benefits. However, application of this residue to agricultural land requires careful monitoring to detect amendments in soil quality at the early stages. Full article
Open AccessReview Direct Utilization of Liquid Fuels in SOFC for Portable Applications: Challenges for the Selection of Alternative Anodes
Energies 2009, 2(2), 377-410; doi:10.3390/en20200377
Received: 11 May 2009 / Revised: 30 May 2009 / Accepted: 2 June 2009 / Published: 12 June 2009
Cited by 51 | PDF Full-text (1439 KB) | HTML Full-text | XML Full-text
Abstract
Solid oxide fuel cells (SOFC) have the advantage of being able to operate with fuels other than hydrogen. In particular, liquid fuels are especially attractive for powering portable applications such as small power generators or auxiliary power units, in which case the [...] Read more.
Solid oxide fuel cells (SOFC) have the advantage of being able to operate with fuels other than hydrogen. In particular, liquid fuels are especially attractive for powering portable applications such as small power generators or auxiliary power units, in which case the direct utilization of the fuel would be convenient. Although liquid fuels are easier to handle and transport than hydrogen, their direct use in SOFC can lead to anode deactivation due to carbon formation, especially on traditional nickel/yttria stabilized zirconia (Ni/YSZ) anodes. Significant advances have been made in anodic materials that are resistant to carbon formation but often these materials are less electrochemically active than Ni/YSZ. In this review the challenges of using liquid fuels directly in SOFC, in terms of gas-phase and catalytic reactions within the anode chamber, will be discussed and the alternative anode materials so far investigated will be compared. Full article
(This article belongs to the Special Issue Fuel Cells)

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