Showing papers in "International Journal of Green Energy in 2005"

Latent Heat Storage Materials and Systems: A Review

Abstract: The use of a latent heat storage system using Phase Change Materials (PCM) is an effective way of storing thermal energy (solar energy, off-peak electricity, industrial waste heat) and has the advantages of high storage density and the isothermal nature of the storage process. It has been demonstrated that, for the development of a latent heat storage system, choice of the PCM plays an important role in addition to heat transfer mechanism. The information on the latent heat storage materials and systems is enormous and published widely in the literatures. In this paper, we make an effort to gather the information from the previous works on PCMs and latent heat storage systems. This review will help to find a suitable PCM for various purposes a suitable heat exchanger with ways to enhance the heat transfer, and it will also help to provide a variety of designs to store the heat using PCMs for different applications, i.e. space heating & cooling, solar cooking, greenhouses, solar water heating and waste heat recovery systems. Measurement techniques of thermophysical properties, studies on thermal cycles for long term stability, corrosion of the PCMs and enhancement of heat transfer in PCM are discussed. New PCM innovations are also included for the awareness of new applications. This paper contains a list of about 250 PCMs and more than 250 references.

Fatty Acids as Phase Change Materials (PCMs) for Thermal Energy Storage: A Review

Abstract: Thermal energy storage (TES) technologies in general and phase change materials (PCMs) in particular, have been topic in research for the last 20 years. Traditionally, available heat has been stored in the form of sensible heat (typically by raising temperature of water, rocks, etc). Latent heat storage on the other hand, is a novel and developing technology, which has found considerable interest due to its operational advantages of smaller temperature swing, smaller size, and lower weight per unit of storage capacity. The interest on thermal energy storage by using fatty acids as PCM has risen in recent times since they have desired thermodynamic and kinetic criteria for low temperature latent heat storage. An added advantage is that fatty acids are derived from the vegetable and animals oil that provides an assurance of continuous supply. This article will review the development of fatty acids as PCMs for solar thermal energy storage application.

Optimization of a Wind/PV Hybrid Power Generation System

Abstract: This study investigates the wind and solar electricity generation availability at the Solar Energy Institute of Ege University, Izmir, Turkey The main purpose of this study is to design an appropriate wind-PV hybrid system to cover the electricity consumption of the Institute In order to do this, monthly average solar irradiation and wind speed data are used, which were measured, consisting of hourly records over an eight-year period from 1995–2002 Simple models were developed to determine wind, solar, and hybrid power resources per unit area Correlations between the solar and wind power data were carried out on an hourly, daily, and monthly basis It is shown that the hybrid system can be applied for the efficient and economic utilization of these resources

Desorber Energy Consumption Amine Based Absorption Plants

Abstract: A computational model of the regeneration system of a monoethanolamine (MEA) based absorption plant for CO2 removal has been developed and used for an operational parameter study. Several parameters have been identified and varied over a given span in order to see the performance effects for the regeneration system, which determines the majority of the operational cost of the overall gas cleaning process. The results show that major energy savings can be realized by optimizing the loading level in the amine system as well as reboiler pressure. A more efficient heat exchanger followed by a flash prior to the desorber does not improve the overall stripping performance to a significant extent. The quality of equilibrium data is of crucial importance in the simulation and optimization of the desorber unit. They are much more important in the case for modeling the desorber compared to modeling the absorber.

CO2 Capture with Membrane Contactors

Abstract: This paper summarizes the development work for membrane gas/liquid contactors used for natural gas sweetening (CO2 and H2S removal), dehydration and CO2 removal from exhaust gas. Membrane gas/liquid contactors operate with liquid on one side of a membrane and gas on the other. Unlike gas separation membranes, where differential pressure across the membrane provides the driving force for separation, here the pressure is essentially the same on both sides of the membrane. Absorption into the liquid provides the driving force. The increased specific area of the membrane gas/liquid contactor allows for a 65-75% reduction in weight and size compared to conventional towers. The latest work has been a gas dehydration field test at a Duke Energy Field Services compressor station in Colorado. The project was performed in co-operation with Gas Technology Institute (GTI).

Anaerobic Digestion of Agricultural Solid Residues

Abstract: Agricultural residues can be converted to methane-rich gas mixture. Anaerobic biomethane production is an effective process for conversion of a broad variety of agricultural residues to methane to substitute natural gas and medium calorific value gases. Methane generating bacteria (methanogens) and other microbes that help digest dying plants in anaerobic conditions. Agricultural solid residues (ASR) represent a potential energy resource if they can be properly and biologically converted to methane.

A Constructal Approach to the Optimal Design of Photovoltaic Cells

Abstract: The constructal law is used for the minimization of the photovoltaic cells (PVC) electrical series resistance. In this paper we report a theoretical, step by step construction of optimal PVC, from the smallest, elemental cell to the largest assembly that relies on the minimisation of the maximum voltage drop subject to volume (material) constraints. This completely deterministic approach produces optimal geometric shape for each assembly level, the optimal number and orientation of constituents within each new, higher order assembly and the optimal size of each new collector (metallic) path.

Decision Support System to Assess Regional Biomass Energy Potential

Abstract: Biomass is a renewable source that accounts for nearly 33% of a developing country's energy needs. In India, it meets about 75% of the rural energy needs and the rural population constitutes 70% of the total population. Sustainable management of these resources requires better and timely decisions, which can lead to increased cost-efficiency and productivity. This would help in regional energy planning and conservation through appropriate decision interventions. To assist in strategic decision-making activities, considering spatial and temporal variables, Spatial Decision Support Systems (SDSS) are required. Spatial decision support system is an interactive computerized system that gathers data from a wide range of data sources, analyze the collected data, and then present it in a way that can be interpreted by the decision maker to deliver the precise information needed to make timely decisions. Decision support system (DSS) framework is designed and implemented to ease and speed up the use of environmental systems. In this regard, to assist planners to plan and manage bioresources in a sustainable way, Biomass Energy Potential Assessment (BEPA) decision support system is designed and is being implemented at regional levels through proper training. Overall objective of this DSS is the development of a set of tools aimed at transforming data into information and aid decisions for bioresources. This article outlines the design and implementation of DSS for assessment of biomass energy potential of a region considering the resources available and the demand. It is designed with user friendly GUI's (Graphic User Interface) using VB (Visual Basic) as frontend with Microsoft Access database as the backend. This helps to build executive information systems and reporting tools that tap vast data resources and deliver information in the context of daily processes. This tool can be used to form a core of practical methodology that will result in more resilience in less time and can be used by decision-making bodies to assess the impacts of various scenarios and to review cost and benefits of decisions to be made. It also offers means of entering, accessing and interpreting the information for the purpose of sound decision making.

A Novel Solar Thermal Cycle with Chemical Looping Combustion

Abstract: In this paper, we have proposed a thermal cycle with the integration of chemical-looping combustion and solar thermal energy with the temperature of about 500-600 C. Chemical-looping combustion may be carried out in two successive reactions between a reduction of hydrocarbon fuel with metal oxides and a reduced metal with oxygen in the air. This loop of chemical reactions is substituted for conventional combustion of fuel. Methane as a fuel and nickel oxides as an oxygen carrier were employed in this cycle. Collected high-temperature solar thermal energy is provided for the endothermic reduction reaction. The feature of the proposed cycle is investigated through Energy-Utilization Diagram methodology. As a result, at the turbine inlet temperature of 1200 C, the exergy efficiency of the proposed cycle would be expected to be about 4 percentage points higher than that of a conventional gas turbine combined cycle. Compared to the previous study of chemical-looping combustion energy systems, the proposed cycle with the integration of green energy and traditional hydrocarbon fuels will offer the possibility of both greenhouse gas mitigation, with green energy, and a new approach to the efficient use of solar energy.

Bio-Hydrogen Synthesis from Wastewater by Anaerobic Fermentation Using Microflora

Abstract: Biological hydrogen production was investigated using biomass in palm oil mill effluent (POME) and artificial wastewater containing 10g glucose under anaerobic fermentation in a batch process. Activated POME sludge and different types of composts were collected as sources of inocula for the study. The anaerobic microflora was found to yield significant amounts of hydrogen. The experimental results show that the gas composition contained hydrogen (66–68%) and carbon dioxide (32–34%). Through out the study, methane gas was not observed in the evolved gas. The hydrogen production was accompanied with the formation of acetate and butyrate. Furthermore, the cumulative hydrogen data were fitted to a simple model developed from Gompertz Equation, where the lag phase time, hydrogen production potential and hydrogen production rate at various conditions were quantitatively estimated.

Thermodynamic and Economic Aspects of the Hard Coal Based Oxyfuel Cycle

Abstract: The present study shows a new approach in modelling the hard coal fired Oxyfuel Cycle on the whole. The static process model comprises an Oxyfuel combustion principle applied to an existing state-of-the-art hard coal power plant located in Rostock, Germany. It includes the air separation unit and the flue gas liquefaction unit, which are modelled in detail. As one of the main advances to previous work, the closed simulation of all components in one model delivers a coherent solution with a significantly reduced number of assumptions. The model needs no interfaces between different stand alone simulation tools or manual iteration and transfer of internal variables. Results from a thermodynamic and economic feasibility study on this process are shown and areas relevant for future research are identified. The present study shows the feasibility and prospective key figures of the technology under realistic, comparable and reproducible assumptions and boundary conditions. The basic engineering of the process w...

Feedlot biomass co-firing: a renewable energy alternative for coal-fired utilities.

Abstract: The swiftly growing feedlot industry in the United States upshots in the production of manure from one or more animal species in excess of what can safely be applied to farmland, in accordance with nutrient management plans. Disposal of the vast quantity of manure produced as a by-product of the cattle feeding industry is one of the major operating tasks of the industry. Aside from the traditional means of disposal as fertilizer, an alternative and attractive way of overcoming this threat is to develop processes that make use of manure as an energy resource. In the present study, the feasibility of using manure as a fuel in existing coal fired power plants is considered and appropriately termed Feedlot Biomass (FB). The technology of co-firing coal: feedlot biomass facilitates an environment friendly utilization of animal waste for the production of valuable power/steam concurrently addressing the renewable energy, groundwater contamination, and greenhouse gas concerns. Co-firing tests were performed at t...

Policy, Institutional and Market Barriers to the Implementation of Clean Development Mechanisms (CDM) in China

Abstract: China is the second largest emitter of greenhouse gases (GHG) in the world, with potentially about two thirds of total Certified Emission Reductions (CERs) for Asia on the world carbon market (Grue ...

Theoretical and Experimental Investigation of a Novel Hybrid Heat-Pipe Solar Collector

Abstract: This article describes a novel flat plate heat-pipe solar collector, namely, the hybrid heat-pipe solar collector. An analytical model has been developed to calculate the collector efficiency as well as simulate the heat transfer processes occurring in the collector. The effects of heat pipes/absorber, top cover, flue gas channel geometry, and flue gas temperature and flow rate, on the collector efficiency were investigated based on three modes of operation, i.e., solar only operation, solar/exhaust gas combined, and solar, exhaust gas and boiler combined. Experimental testing of the collector was also carried out for each of these modes of operation under real climatic conditions. The results were used to estimate the efficiency of the collector and determine the relation between the efficiency and general external parameter. The modeling and experimental results were compared and a correlation factor was used to modify the theoretical predictions. It was found that the efficiency of the collect...

Optimization with Genetic Algorithms of a Gas Turbine Cycle with H2-Separating Membrane Reactor for CO2 Capture

Abstract: A gas turbine power process with CO2 capture through precombustion decarbonization, which employs a H2-separating membrane reactor is presented. Optimization with the process thermal efficiency as objective function is made through the use of genetic algorithms. The use of genetic algorithms enabled a division of the optimization parameters into two groups; one group where the values are at their optimum at the limit of the investigated parameter range, and one group where there actually is an optimum within the investigated range. It was found that the process has a severe efficiency penalty caused by the use of heat from hydrogen combustion for the reforming process. The process is a zero CO2 emission power process and also NOx emissions should be low, due to the inherent mixing of hydrogen with steam.

Feasibility Analysis of Wood Pellets Production and Utilization in China as a Substitute for Coal

Abstract: Wood pellets are regarded as one of the substitutes for fossil fuels like coal and oil for heating and co-generation. Wood pellets are a successful example of market penetration of renewable energy in some countries in Europe, e.g., Sweden. An analysis process is proposed in this paper and used to conduct a techno-economic assessment of wood pellets production and applications in some areas in China with the consideration of technology transfer from Sweden by examining their market competitiveness with coal in these areas. Financial indices such as net present value (NPV), internal return rate (IRR) and year-to-positive cash flow are calculated to investigate the profitability of the technology transfer. Four locations of applications in China have been considered as case studies. The result indicates that in the market-only-based scenario, wood pellets production will not be profitable in all selected areas. New scenarios from the analysis process show that reducing investment and increasing the amount o...

Investigations on the Packed Bed for High-Temperature Thermal Energy Storage

Abstract: Modeling and experimental studies were performed on a packed bed for high-temperature energy storage using Zirconium oxide pellets as the storage material. This is an advanced ceramic material that can withstand corrosion and high temperatures. Model predictions compare favorably with experimental results. Zirconium oxide demonstrated great potential as thermal energy storage material. More energy was recovered from the bed in the opposite direction than in the direction used during storage. The gas inlet temperature to the bed showed dominant influence on the uncertainty in the model predictions, implying that special attention should be paid to the measurement of this temperature.

Performance model for a horizontal tube falling film evaporator

Abstract: A model is developed to predict the evaporative heat transfer coefficient in a horizontal tube-falling evaporator and has been applied to evaluate overall performance of a desalination unit. Performance variation with different parameters like operation temperature, type of water distribution system, mass flow rate of distilled water inside the exchanger are analyzed. It has been observed that the model is able to predict the trends of heat transfer characteristics of the evaporator reasonably well. However, at low liquid film flow rate conditions, the model overpredicts the heat transfer characteristics marginally. In order to improve the evaporative exchanger performance, it is observed that preheating of the liquid film before injection into the evaporator is desirable. Calculations are also performed to estimate the value of overall heat transfer coefficient for a typical desalination unit.

Worldwide Tidal Current Energy Developments and Opportunities for Canada's Pacific Coast

Abstract: Recent rapid advances of tidal current energy extraction (TCEE) technologies and resource analyses suggest in excess of 20,000 GWh/annum of electricity may be realistically exploitable in the near term off Canada's West Coast. Moreover, because tidal currents have a semi-diurnal (or, in some locations, diurnal) periodicity, and can be predicted and quantified on a spatial and temporal basis, this resource confers a distinct advantage over most other renewables, and, therefore, may achieve supply security. In this study, TCEE technologies are assessed on the basis of energy delivered, environmental intrusion and economic viability. As such, relevant issues including resource characteristics, site selection, conversion efficiencies, capacity factors, power densities, hydrodynamic feedbacks, and grid integration are addressed.

Biomass Based Sorption Cooling Systems for Cold Storage Applications

Abstract: Controlled atmospheric storage is a widely popular technique for storage of fruits and vegetables. In this paper, the experimental studies on biomass powered absorption systems for cold storage applications using ammonia water as a working fluid pair is presented. The heat input to the absorption system is supplied by a producer gas obtained from a downdraft gasifier, using firewood as fuel. The system is designed and fabricated to store about 15 MT of fruits and vegetables, having a cooling capacity of 3 TR. The effect of sink temperature, solution flow rate, cooling water flow rate and biomass consumption on the performance of the system has been analyzed. It is found that the real co-efficient of performance of the system is around 0.35 - 0.2, considering the source-site factor for auxiliary power consumption. The operating Cost/h for the biomass based cold storage system is lower than the presently available conventional compression based units.

Experimental Investigation of Convective Heat Transfer Coefficient of Various Agricultural Products Under Open Sun Drying

Abstract: In this article, the convective heat transfer coefficients of various agricultural products were investigated under open sun drying conditions. Data obtained from open sun drying experiments for eight agricultural products, namely, mulberry, strawberry, apple, garlic, potato, pumpkin, eggplant, and onion were used to determine values of convective heat transfer coefficient. The value of convective heat transfer coefficient was determined as 1.861 W/m2°C for mulberry, 6.691 W/m2°C for strawberry, 11.323 W/m2°C for apple, 1.136 W/m2°C for garlic, 8.224 W/m2°C for potato, 8.613 W/m2°C for pumpkin, 6.981 W/m2°C for eggplant, and 6.767 W/m2°C for onion. The experimental error in terms of percent uncertainty was also calculated.

Zero Emission Technologies: An Option for Climate Change Mitigation

Abstract: The present paper briefly explores the scientific, technical and economical characteristics of Zero Emission Technologies, with a particular emphasis on the E-MATIANT cycle. It is shown that this latter provides a cost-effective option to mitigate CO2 emissions, with a cost of electricity generation comparable to the one of advanced coal/gas fired power plants with CO2 capture and competitive with renewable wind energy. The important energy policy question of whether it is more cost-effective to upgrade an existing plant with a capture unit or to build a ZET is also addressed by introducing the concept of Mitigation Cost.

Optimum Heat Conductance Distribution for Power Optimization of a Regenerated Closed Brayton Cycle

Abstract: In this paper, the power output of the cycle is taken as objective for performance optimization of an irreversible regenerated closed Brayton cycle coupled to constant-temperature thermal energy reservoirs in the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulae about the relations between power output and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible compression and expansion losses in the compressor and turbine, and the pressure drop loss in the piping. The maximum power output optimization is performed by searching the optimum heat conductance distribution corresponding to the optimum power output among the hot- and cold-side heat exchangers and the regenerator for the fixed total heat exchanger inventory. The influence of some design parameters, including the temperature ratio of the heat reservoirs, the total heat exchanger inventory, the efficienc...

Exhaust Emissions from a Gas-fuelled S.I. Engine

Abstract: Attempts to improve engine performance are often accompanied by increased emissions. An effective approach to reduce emissions without necessarily a significant penalty in fuel economy is through operating S.I. engines on a range of gaseous fuels, and either leaning the operating mixture or diluting it with some exhaust gases. The emission characteristics of an engine operated in turn on CH4, H2, CO and some of their mixtures are examined experimentally. The role of changes in some key factors affecting the production of the pollutants CO, NOx and unburned hydrocarbons were investigated. Guidelines for reducing the undesirable emissions are outlined.

Solar Assisted Small-Scale Biomass District Heating System in the Northern Part of Sweden

Abstract: This article presents a case study of a projected solar assisted biomass district heating system in the north of Sweden. It is generally known that a biomass district heating system combined with s...

Fluid mechanics of serpentine flow fields on a porous media

Abstract: Laminar flows are investigated in single and double parallel serpentine channels mounted on a porous media and it is found that significant convective transport occurs in porous media for practical fuel cell conditions. This transport increases with increasing flow Reynolds number, with decreasing land width, and most significantly with increasing channel length. Increasing the number of parallel channels significantly decreases the pressure drop across the fuel cell, but also significantly decreases the magnitude of convective transport in the porous media. Increased parasitic loads must be put in the context of the change in electrochemical performance. This paper presents both data and a methodology for beginning to think about flow field design from a hydrodynamic perspective.

Comparison Between Heat Pipe and Direct Heat Exchange Solar Louvre Collectors

Abstract: International concern about the environmental implications of climate change coupled with increasing demand for energy to fuel modern society has lead to growing interest in using renewable energy sources as alternatives to conventional sources. The work presented in this paper compares two types of solar collector integrated into louvred shading devices. In addition to protecting glazed spaces in buildings from excessive solar gain, the collector would provide the flexibility to produce systems customized for collecting heat over a temperature-range appropriate to particular building services applications at various climates/locations. This would allow considerable savings to be made in primary energy consumption and lead to a reduction in global warming impact. Two solar absorbers, based on different techniques of heat exchange, were tested experimentally. The first was based on a direct heat exchange technique, and the second used heat pipe technology. Various comparisons were made and it was concluded...

Control Issues in the Design of a Gas Turbine Cycle for CO2 Capture

Abstract: This article is concerned with control issues related to the design of a semi-closed O 2/CO 2 gas turbine cycle for CO 2 capture. Some control strategies and their interaction with the process design are discussed. One control structure is implemented on a dynamic simulation model using a predictive controller, and simulations assess the performance and compare its merits with a conventional PI structure. The results indicate that it can be advantageous for operability to allow a varying (as opposed to fixed) compressor inlet pressure, at the cost of a more expensive design. Furthermore, the results show that a predictive controller has some advantages with respect to the simpler conventional PI control structure, in particular in terms of constraint handling.

Energy Consumption in the Turkish Industrial Sector

Abstract: Turkey's primary energy resources seem limited as indigenous energy production meets nearly 31 % of the total primary energy demand. But the growth of Turkey's industry gives rise to a substantial increase in energy demand. Final energy consumption grew from 52.6 Mtoe (million tons of oil equivalent) in the year 1990 to 78.4 Mtoe in the year 2002. Industrial demand accounts for about 41.6 % of the final energy demand in Turkey. Basic metal industries, non-metallic material products and chemical and petroleum products have the highest energy consumption in industrial sector. In this work, industrial energy consumption and energy consumption of different indsutrial subsectors in Turkey are investigated.

Novel temperature control technique for a medicinal herb dryer system powered by a photovoltaic array.

Abstract: Each plant has its own optimal drying temperature, especially for the medicinal herbs, because they are sensitive to heat. If the drying temperature becomes more than the optimal value, some chemical reactions will occur and influence the quality of the dried herb, such as color, taste, and aroma. While if the drying temperature becomes lower than the optimal value, the drying process will slow down, and consequently an expected degradation in the quality of the herb may occur, due to insects and fungi infestation which increase in moist conditions. This paper presents a new temperature control technique for a medicinal herb dryer system. The technique fixes the drying temperature of the medicinal herbs at 40°C, even in cases of rapidly changing atmospheric conditions. The control of the dryer temperature is achieved through using the proportional integral (PI) controller. The designed dryer contains two systems, which are the thermal and the electrical systems. The thermal system is designed to heat the ...