Calin Zamfirescu

Sustainable energy systems and applications

Thermodynamic fundamentals.- Introductory aspects of energy.- Energy conservation.- Fundamental concepts for sustainable process design.- Thermodynamic cycles.- Thermal and chemical devices.- Fossil fuels vs clean fuels.- Direct energy conversion.- System analysis through energy and exergy.- Renewable energy systems and applications.- Thermal energy storage systems and applications.- District energy systems.- Nuclear energy.- Hydrogen and fuel cell systems and applications.- Ammonia as a potential substance.- CO2 technologies.- Life cycle assessment.- Industrial ecology.- Sectoral energy and exergy utilization.- Sustainable energy policies.- Global warming and climate change issues and potential solutions.

Exergetic Performance Analysis of a Gas Turbine Cycle Integrated With Solid Oxide Fuel Cells

Energy and exergy assessments are reported of integrated power generation using solid oxide fuel cells (SOFCs) with internal reforming and a gas turbine cycle. The gas turbine inlet temperature is fixed at 1573 K and the high-temperature turbine exhaust heats the natural gas and air inputs, and generates pressurized steam. The steam mixes at the SOFC stack inlet with natural gas to facilitate the reformation process. The integration of solid oxide fuel cells with gas turbines increases significantly the power generation efficiency relative to separate processes and reduces greatly the exergy loss due to combustion, which is the most irreversible process in the system. The other main exergy destruction is attributable to electrochemical fuel oxidation in the SOFC. The energy and exergy efficiencies of the integrated system reach 70–80%, which compares well to the efficiencies of approximately 55% typical of conventional combined-cycle power generation systems. Variations in the energy and exergy efficiencies of the integrated system with operating conditions are provided, showing, for example, that SOFC efficiency is enhanced if the fuel cell active area is augmented. The SOFC stack efficiency can be maximized by reducing the steam generation while increasing the stack size, although such measures imply a significant and nonproportional cost rise. Such measures must be implemented cautiously, as a reduction in steam generation decreases the steam/methane ratio at the anode inlet, which may increase the risk of catalyst coking. A detailed assessment of an illustrative example highlights the main results.

Maximum intensity of rarefaction shock waves for dense gases

Modern thermodynamic models indicate that fluids consisting of complex molecules may display non-classical gasdynamic phenomena such as rarefaction shock waves (RSWs) in the vapour phase. Since the thermodynamic region in which non-classical phenomena are physically admissible is finite in terms of pressure, density and temperature intervals, the intensity of RSWs is expected to exhibit a maximum for any given fluid. The identification of the operating conditions leading to the RSW with maximum intensity is of paramount importance for the experimental verification of the existence of non-classical phenomena in the vapour phase and for technical applications taking advantage of the peculiarities of the non-classical regime. This study investigates the conditions resulting in an RSW with maximum intensity in terms of pressure jump, wave Mach number and shock strength. The upstream state of the RSW with maximum pressure drop is found to be located along the double-sonic locus formed by the thermodynamic states associated with an RSW having both pre- and post-shock sonic conditions. Correspondingly, the maximum-Mach thermodynamic and maximum-strength loci locate the pre-shock states from which the RSW with the maximum wave Mach number and shock strength can originate. The qualitative results obtained with the simple van der Waals model are confirmed with the more complex Stryjek–Vera–Peng–Robinson, Martin–Hou and Span–Wagner equations of state for selected siloxane and perfluorocarbon fluids. Among siloxanes, which are arguably the best fluids for experiments aimed at the generation and measurement of an RSW, the state-of-the-art Span–Wagner multi-parameter equation of state predicts a maximum wave Mach number close to 1.026 for D6 (dodecamethylcyclohexasiloxane, [O-Si-(CH3)2]6). Such value is well within the capacity of the measurement system of a newly built experimental set-up aimed at the first-ever demonstration of the existence of RSWs in dense vapours.

Clean Rail Transportation Options

This book will assess and compare several options for ammonia co-fueling of diesel locomotives with integrated heat recovery, multigeneration (including on-board hydrogen fuel production from ammonia), and emission reduction subsystems from energy, exergy, and environmental perspectives. Economic considerations will be presented to compare the cost of the proposed systems for different scenarios such as carbon-tax rates, diesel fuel cost and ammonia cost. Fossil fuel consumption and the associated negative environmental impact of their combustion is a significant global concern that requires effective, practical, and sustainable solutions. From a Canadian perspective, the Transportation Sector contributes more than 25% of national greenhouse gas emissions due to fossil fuel combustion, largely due to road vehicles (cars, light and heavy duty trucks). This is a complex and critical challenge to address, particularly in urban areas with high population density. There is a need to develop alternative energy solutions for mass passenger and freight transportation systems that will reduce both the traffic-volume of road vehicles as well as the emissions from the mass transportation systems. The book will be helpful to students in senior-level undergraduate and graduate level courses related to energy, thermodynamics, thermal sciences, combustion, Heating Ventilation Air Conditioning and Refrigeration (HVAC&R), etc. The quantitative comparative assessment of such alternative energy systems provided by this book will be useful for researchers and professionals interested sustainable development.

Chapter 3 – Fossil Fuels and Alternatives

In this chapter fossil fuels and alternatives are presented. Fuels have a major role in modern society, where they act as energy storage media for various applications including heating and power generation. Fossil fuels deplete and their use produces severe atmospheric pollution and induces global warming. Thus, alternatives to fossil fuels aim to seek solutions for energy security and environmental sustainability. In the first part of the chapter, the main categories of fuels are presented, together with the most important physical and chemical properties. Next, fossil fuels are analyzed in detail, starting with coal, which pollutes the atmosphere more than other fossil fuels. Lower and higher heating values and chemical exergies of coals are presented. Emissions factors are determined for coals by rank. Subsequently, other fossil fuels are analyzed, following the same approach as for coal. Alternative fuels derived from biomass and sustainable hydrogen sources are extensively discussed. Equations are given, based on literature studies, to estimate heating values and chemical exergy, starting with ultimate analysis of biomasses. Of major interest is converting biomass into liquid biofuels such as alcohols, ethers, esters, and oils. Hydrogen is also presented as the main potential fuel for the future; it can be produced in a multitude of sustainable ways. Novel developments show that hydrogen can be stored very well in various ammonia compounds, including metal amines or ammonia.

District Energy Systems

During the past decade, increasing local and global problems regarding energy, the environment, and the economy have created one of the biggest challenges for human beings to combat through sustainable solutions. District energy systems (DESs) for distributed heating and/or cooling, known also as district heating and cooling (DHC) systems, appear to be part of the solutions. In some situations, for example in the case of a major power plant, it may appear economically attractive to build a pipe network that distributes the ejected heat among a number of residential/commercial/industrial users covering a territory around the central power plant. Cogeneration, geothermal, or solar energy systems are the most suitable for being coupled to DHC. Steam, hot or cold water, or ice slurry can be used as heat-conveying fluids. The opportunity of using a DES must be judged first on an economic basis by comparison of the life-cycle cost (LCC) with the cost of other competing systems, such as electrically driven heat pumps at the user’s location.

Economic and Environmental Comparison of Conventional and Alternative Vehicle Options

This chapter presents an economic and environmental comparison of conventional and alternative vehicles and evaluates, based on actual cost data, the life cycle indicators for vehicle production and utilization stages. The vehicles analyzed include conventional gasoline vehicles, hybrid vehicles, electric vehicles, hydrogen fuel cell vehicles, hydrogen internal combustion vehicles, and ammonia-fueled vehicles. Hydrogen internal combustion vehicles and ammonia-fueled vehicles use hydrogen as a fuel in an internal combustion engine (ICE) and ammonia as a hydrogen fuel source to drive an ICE, respectively, both of which are zero polluting at fuel utilization stage during vehicle operation. When electricity is generated from renewable energy sources, the electric car is advantageous to the hybrid vehicle, and when electricity is generated from fossil fuels, the electric car remains competitive when it is generated onboard. The electric car is superior in many respects when the electricity is generated with an efficiency of 50–60% by a gas turbine engine connected to a high-capacity battery and electric motor. The various theoretical developments, consisting of novel economic and environmental criteria for quantifying vehicle sustainability, could prove useful in the design of modern light-duty automobiles, with superior economic and environmental attributes.

Thermochemical Water-Splitting Cycles

This chapter presents and analyzes thermochemical cycles, which are promising methods of nuclear produced hydrogen at a large scale. The introduction presents the origins of concepts and a historical perspective on the technology development. In the first part, the most important aspects and fundamental concepts for cycle modeling and synthesis are introduced and detailed. The discussion proceeds from single-step thermochemical water-splitting processes, to two-step and multi-step processes, followed by a presentation of hybrid cycles. Relevant analysis methods are introduced in the context of each type of cycle presentation. These concepts include chemical equilibrium, chemical kinetics, reaction rate and yield, and others. Analysis of the practicality of chemical reactions is established based on their yield. A large number of reactions and thermochemical cycles are compiled, categorized, and discussed. In total, the chapter presents 122 thermochemical cycles, 25 hybrid cycles, and six special cycles (assisted with photonic or nuclear radiation).

Residential Solar Power Generation Systems for Better Environment

The decline of the world’s fossil energy supply, the increase in energy consumption, and the continuous trend of global warming caused by greenhouse gas emissions enforce innovation and research efforts toward the implementation of a global economy based on renewable energy. As mentioned in many sources (e.g., Baneman, 2008), with the increasing price of fossil fuels and augmenting taxes placed by governments on emissions, renewable energies will become progressively competitive.

Evaluation of exergy and energy efficiencies of photothermal solar radiation conversion

In this paper, a new thermodynamic model for photothermal solar radiation conversion into mechanical through a heat engines is proposed. The developed equations allow for the energy and exergy contents of solar radiation to be found, as well as the energy and exergy efficiencies corresponding to concentration type solar-thermal heat engines operating under a range of conditions. The calculation method remains accurate to other published models when their assumed conditions are imposed to the newly developed model. The heat flux absorbed by the receiver (which is assumed to be a grey body and is placed in the focal point of the solar concentrator) depends on the hemispherical absorptivity and emissivity, concentration ratio and receiver temperature. The model is used to conduct a parametric study regarding the energy and exergy efficiencies of the system for assessing its performance. The use of a selective grey body receiver (having a reduced emissivity and a high absorptivity) for enhancing the conversion efficiency is also studied. If the absorptivity approaches one and the emissivity is low enough the photothermal conversion efficiency becomes superior to the known black body receiver limit of 0.853. It is found that in the limit of receiver emissivity tending to zero and absorptivity lending to one, the present model gives the exergy content of solar radiation because the work generated reaches its maximum. In this situation the energy efficiency approaches the exergy efficiency at 1-ITTIN0/TINS where TS and T0 are the sun and ambient temperatures, respectively. The influence of the ambient temperature on the exergy and energy efficiencies becomes apparent, with effects of up to 15%, particularly for high absorptivity and low emissivity. The heat transfer conductances at sink and source of the heat engine have a considerable impact on the efficiency of solar energy conversion. The present model is developed in line with actual power system operations for better practical acceptance. In addition, some irreversibility parameters (absorptivity, emissivity, heat transfer conductivity, etc.) are studied and discussed to evaluate the possible photothermal solar radiation conversion systems and assess their energy and exergy efficiencies.