The use of solar energy to preheat natural gas before a city gate station (CGS) for reducing fuel consumption and environmental emissions is investigated in a real CGS. All analyses are conducted with a 1-h time-step throughout the entire year so that seasonal climate changes are accounted for precisely. A thermodynamic analysis of the hybrid system is performed with TRNSYS and verified with THERMOFLEX so as to ensure reliability. In addition, dynamic exergetic, exergoeconomic, and exergoenvironmental analyses for the proposed system are carried out. A life cycle assessment (LCA) based on Eco-indicator 99 is performed using SIMA PRO to compute the environmental impacts for each component of the system. The exergetic, exergoeconomic, and environmental analyses are performed in Engineering Equation Solver (EES) software. To perform the transient exergetic, exergoeconomic, and environmental analyses, the results of the thermodynamic analysis from TRNSYS are automatically imported into the EES code. The advanced exergetic, exergoeconomic, and exergoenvironmental analyses are performed to better determine components that have high potentials for improving the system; potentials are considered based on the exergy destruction, exergetic cost of destruction, and environmental impacts associated with exergy destruction.

The energy, exergy, and economic aspects are analyzed of a cycle consisting of a polymer fuel cell, a burner, a reformer, and a heat exchanger. Water is used for cooling the fuel cell, and the heated water is used for domestic consumption. The exergy and energy efficiencies of the cycle are calculated, and the effects of various cycle parameters on the exergy and energy efficiencies are investigated. To maximize the exergy efficiency while minimizing the cost of electricity generation by the fuel cell, the particle swarm optimization (PSO) algorithm is utilized. The results show that increasing the cooling water flow rate has the greatest effect on increasing the energy efficiency of the cycle, while increasing the burner temperature has the greatest effect on increasing the exergy efficiency of the cycle. Moreover, it is shown via multi-objective optimization of the proposed cycle that the exergy efficiency of the cycle increases by 31% and the cost of electricity generation decreases by 18% by applying optimized parameters.

In this study, the syngas composition exiting a biomass gasifier is investigated to determine the effect of varying selected gasification parameters. The gasification parameters considered are the mass flow rate of steam, the gasification agent, the mass flow rate of oxygen, the gasification oxidant, and the type of biomass. The syngas composition is represented by its hydrogen, carbon monoxide, carbon dioxide, and water fractions. The oxygen fed to the gasifier is produced using a cryogenic air separation unit (CASU). The gasifier and the air separation unit are modeled and simulated with aspen plus , where the gasification reactions are carried out based on the Gibbs free energy minimization approach. Finally, the syngas composition for the different types of biomass as well as the different compositions of the three types of the biomass considered are compared in terms of chemical composition. It was found that for each type of biomass and at a specified steam flow rate there is an air to the air separation unit where the gasification of the biomass ends and biomass combustion starts and as the volatile matter in the biomass increases the further the shifting point occur, meaning at higher air flow rate. It was found for the three considered biomass types and their four mixtures that, as the volatile matter in the biomass increases, more hydrogen is observed in the syngas. An optimum biomass mixture can be achieved by determining the right amount of each type of biomass based on the reported sensitivity analysis.

A novel solid–gas thermochemical sorption thermal energy storage (TES) system for solar heating and cooling applications operating on four steady-state flow devices and with two transient storage tanks is proposed. The TES system stores solar or waste thermal energy in the form of chemical bonds as the working gas is desorbed from the solid. Strontium chloride–ammonia is the working solid–gas couple in the thermochemical sorption TES system. Strontium chloride–ammonia has a moderate working temperature range that is appropriate for building heating and cooling applications. The steady-state devices in the system are simulated using Aspen Plus, and the two transient components are simulated using the ENGINEERING EQUATION SOLVER (EES) package. Multiple cases are examined of different heat and cold production temperatures for both heating and cooling applications for a constant thermal energy input temperature. Energy and exergy analyses are performed on the system for all simulated cases. The maximum energy and exergy efficiencies for heating applications are 65.4% and 50.8%, respectively, when the heat is generated at a temperature of 87 °C. The maximum energy and exergy efficiencies for cooling applications are 29.3% when the cold production temperature is 0 °C and 22.9% when it is −35 °C, respectively. The maximum heat produced per mass of the ammonia produced, for 100% conversion of the reactants in the chemical reaction, is 2010 kJ/kg at a heat production temperature of 87 °C, and the maximum cold energy generated is 902 kJ/kg at a temperature of 0 °C. Finally, the system is modified to operate as a heat pump, and energy and exergy analyses are performed on the thermochemical heat pump. It is found that the maximum energy and exergy coefficients of performance (COP) achieved by upgrading heat from 87 °C to 96 °C are 1.4 and 3.6, respectively, and the maximum energy and exergy efficiencies are 56.4% and 79.0%, respectively.

A thermodynamic analysis of the coupling of a reverse osmosis (RO) process with the gas turbine-modular helium reactor (GT-MHR) is presented in which the waste heat is utilized for the generation of steam as it is expanded in a steam turbine. A comprehensive parametric study is carried out to reveal the effect of some parameters such as compression ratio, turbine inlet temperature, recovery ratio, and preheated feed seawater inlet temperature on the exergy efficiencies of the RO process, electricity generation process, electricity generation without steam turbine work output, and overall system. The analysis shows that the exergy efficiency of the electric generation process is increased by 10.3%, if the waste heat from the reactor is utilized. The exergy efficiencies of the RO process, electricity generation process, electricity generation without steam turbine work output, and overall system are found to be 89.0%, 40.0%, 29.7%, and 41.0%, respectively.

Extraction–condensing steam turbines mix cold-condensing and cogeneration activities making the respective power and fuel flows not directly observable. A flawed assessment of the flows is causing confusion and bias. A steam expansion path on a Mollier diagram reveals the design characteristics of a thermal power plant and of its embedded combined heat and power (CHP) activities. State variable data on a unit mass of steam, entering the turboset as life steam and leaving it at one of the heat extraction exhausts, provide the roster of the power-heat production possibility set of the plant. The actual production possibilities are drawn from the roster by applying capacity data and constraints on the heat extraction points. Design power-to-heat ratios of CHP activities are univocally identified, allowing accurate assessments of cogenerated power. This information is needed for proper incentive regulation of CHP activities, pursuing maximization of CHP quality and quantity. Quality is gauged by the power-to-heat ratio, principally a design (investment) decision. Quantity is gauged by the operational amounts of recovered heat exhausts. Optimal regulatory specificity is attained through setting generic frameworks by technology, accommodating investment and operational decisions by plant owners. Our novel method is explained and applied with numerical data, also revealing the flaws in present regulations.

A new multigeneration system based on an ocean thermal energy conversion (OTEC) system equipped with flat plate and PV/T solar collectors, a reverse osmosis (RO) desalination unit to produce fresh water, a single effect absorption chiller, and proton exchange membrane (PEM) electrolyzer is proposed and thermodynamically assessed. Both energy and exergy analyses are employed to determine the irreversibilities in each component and assess the system performance. A parametric study is performed to investigate the effects of varying design parameters and operating conditions on the system energy and exergy efficiencies. In addition, an economic assessment of the multigeneration system is performed, and the potential reduction in total cost rate when the system shifts from power generation to multigeneration are investigated.

A hybrid photovoltaic (PV)-biomass system with energy storage options is investigated based on energy and exergy analyses. The hybrid system consists of a photovoltaic system, an electrolyser, and a biomass gasifier, which is integrated with a biomass-based gas turbine. The PV system is accountable for 56% of the annual exergy destruction in the hybrid system, while 38% of the annual exergy destruction occurs in the biomass-gas turbine (GT) system. The overall energy and exergy efficiencies of the hybrid PV-biomass system with energy storage options are 34.8% and 34.1%, respectively. A 29% increase in both energy and exergy efficiencies is reported with an increase in the steam-to-carbon ratio (SC) in the range of 1–3 mol/mol. The related specific carbon dioxide emission reduction is 1441–583 g/kWh. In contrast to SC, an increase in gas turbine inlet temperature results in a negative effect on the overall energy and exergy efficiencies, and it does not make a significant contribution to the reduction in specific carbon dioxide emission.

The entropy generation is investigated numerically in axisymmetric, steady-state, and incompressible laminar flow in a rotating single free disk. The finite-volume method is used for solving the momentum and energy equations needed for the determination of the entropy generation due to heat transfer and fluid friction. The numerical model is validated by comparing it to previously reported analytical and experimental data for momentum and energy. Results are presented in terms of velocity distribution, temperature, local entropy generation rate, Bejan number, and irreversibility ratio distribution for various rotational Reynolds number and physical cases, using dimensionless parameters. It is demonstrated that increasing rotational Reynolds number increases the local entropy generation rate and irreversibility rate, and that the irreversibility is mainly due to heat transfer while the irreversibility associated with fluid friction is minor.

A life cycle assessment of nuclear-based hydrogen production using thermochemical water splitting is conducted. The copper-chlorine thermochemical cycle is considered, and the environmental impacts of the nuclear and thermochemical plants are assessed. Environmental impacts are investigated using CML-2001 impact categories. The nuclear plant and the construction of the hydrogen plant contribute significantly to the total environmental impacts. The environmental impacts of operating the hydrogen production plant contribute much less. Changes in the inventory of materials or chemicals needed in the thermochemical plant do not affect significantly the total impacts. Improvement analysis suggests the development of more sustainable processes, particularly in the nuclear plant and construction of the hydrogen production plant.

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.

The combination of fuel cells with conventional mechanical power generation technologies (heat engines) promotes effective transformation of the chemical energy of fuels into electrical work. The implementation of solid oxide fuel cells (SOFCs) within gas turbine systems powered by natural gas (methane) requires an intermediate step of methane conversion to a mixture of hydrogen and carbon monoxide. State-of-the-art Ni-YSZ (yttria-stabilized zirconia) anodes permit methane conversion directly on anode surfaces, and contemporary designs of SOFC stacks allow this reaction to occur at elevated pressures. An exergy analysis of a gas turbine cycle integrated with SOFCs with internal reforming is conducted. As the efficiency of a gas turbine cycle is mainly defined by the maximum temperature at the turbine inlet, this temperature is fixed at 1573 K for the analysis. In the cycle considered, the high-temperature gaseous flow from the turbine heats the input flows of natural gas and air, and is used to generate pressurized steam, which is mixed with natural gas at the SOFC stack inlet to facilitate its conversion. This technological design permits avoidance of the generally accepted recirculation of the reaction products around the anodes of SOFCs, which reduces the capacity of the SOFC stack and the entire combined power generation system correspondingly. At the same time, the thermal efficiency of the combined cycle is shown to remain high and reach 65–85% depending on the SOFC stack efficiency. The thermodynamic efficiency of the SOFC stack is defined as the ratio of electrical work generated to the methane oxidized (through the intermediate conversion). For a given design and operating condition of the SOFC stack, an increase in the thermodynamic efficiency of a SOFC is attained by increasing the fuel cell active area. Achieving the highest thermodynamic efficiency of the SOFC stack leads to a significant and nonproportional increase in the stack size and cost. For the proposed steam generating scheme, increasing the load of the SOFC stack is accompanied by a decrease in steam generation, a reduction in the steam to methane ratio at the anode inlet, and an increased possibility of catalyst coking. Accounting for these factors, the range of appropriate operating conditions of the SOFC stack in combination with steam generation within a gas turbine cycle is presented.

In this paper, energy and exergy characteristics of wind energy are investigated. The effects of wind speed and air temperature and pressure at the inlet of a wind turbine on windchill temperature are examined. We also investigate energy and exergy efficiencies of the wind energy generating system and verify the models through a case study on a 100 kW wind generating system for 21 climatic stations in the province of Ontario, Canada. New energy and exergy efficiency maps of the wind energy generating system are introduced to provide a common basis for regional assessments and interpretations. These efficiency maps are plotted for 4 months of the year (January, April, July, October), which are taken to be representative months of the seasons. The results show that aerial differences between energy and exergy efficiencies are approximately 20%–24% at low wind speeds and approximately 10%–15% at high wind speeds.