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• A biomass and solar energy based system is developed and comparatively evaluated. • The proposed system is analysed thermodynamically by energy and exergy approach. • Hydrogen, electricity, hot water for fish farming and cooling are major commodities. • The hydrogen production rate of 59.45 mol/s and power of 8.3 MW is produced. • The overall energy and exergy efficiencies are found to be 29.9% and 31.5%. A biomass and solar energy based system consisting of a gas turbine cycle, a reheat Rankine cycle, a solar heliostat field, four-step copper-chlorine cycle and absorption cooling system is newly proposed, analyzed and comparatively evaluated through energy and exergy approaches. The proposed system is designed for the multiple useful commodities of hydrogen, electricity, hot water for fish farming and cooling. The effects of different operating conditions and parameters, namely air flow rate, biomass flow rate, working fluid flow rate, direct normal irradiance, number of heliostats, evaporator exit temperature and ambient temperature are investigated for the performance of the designed system defined in terms of energy and exergy efficiencies, and energy and exergetic coefficients of performance. The combined system, excluding solar heliostat field and absorption cooling system, is simulated using the Aspen Plus while the subsystems are modeled using the engineering equation solver package. Heating and cooling are produced for community usage, and hydrogen can be employed for industrial purposes. Both design and cost analyses are also conducted using the Aspen Plus v9 and Aspen Plus economic analyzer v9. The energy efficiency of the overall system is determined as 29.9% while the corresponding exergy efficiency is obtained to be 31.5%. The additional findings and outcomes are also presented and discussed comprehensively. [ABSTRACT FROM AUTHOR]

Abstract In the present study, the solid anion exchange membrane and molten electrolyte entailing direct type ammonia fuel cells are uniquely developed, and their performances are investigated through energy and exergy efficiencies at varying operating conditions and state properties, based on the presently conducted experiments and datasets obtained. Both energy and exergy efficiencies are determined to be 12.1 ± 0.4% and 13.8 ± 0.4% respectively at the maximum power density value of 6.4 ± 0.2 W m−2 for the membrane based cell. Higher humidifier temperatures are observed to improve the performance of the fuel cell. The energy and exergy efficiencies of the molten alkaline electrolyte based cell are found to be 20.6 ± 0.6% and 23.3 ± 0.7% respectively at a temperature of 220 °C. The open circuit voltages are found as 278 ± 8 mV and 520 ± 16 mV for the anion exchange membrane and molten alkaline electrolyte based cells respectively. The open circuit voltage decreases and the short circuit current density increases with increasing electrolyte temperatures. Highlights • Membrane and molten electrolyte based direct ammonia fuel cells uniquely developed. • Membrane based cell has energy and exergy efficiencies of 12.1% and 13.8%. • Molten electrolyte based cell has energy and exergy efficiencies of 20.6% and 23.3%. • Open circuit voltages of 520 mV and 278 mV obtained for the two cells respectively. [ABSTRACT FROM AUTHOR]

A novel multi-generation integrated energy system is presented in this paper, consisting of a gas-steam combined cycle, four-step thermochemical copper-chlorine (Cu Cl) cycle, proton exchange membrane fuel cell (PEMFC) and a reverse osmosis (RO) desalination unit. Effective thermal management of waste heat is recognized as a key objective in the steel industry. Hydrogen, electricity, fresh water and heat are the useful outputs of the integrated system. The produced electricity supplies the electricity load required by the electrolyzer, compressor and pumps while the supplementary electricity is an additional system product. Aspen Plus and Engineering Equation Solver (EES) are used for modeling and simulation of the multi-generation system. The overall hydrogen production rate of the designed system is 51.8 kg/hr and the net power production is 1.7 MW. The overall energy efficiency of the multi-generation system is 63.3% and the exergy efficiency is 58.8%. Further sensitivity studies and outcomes are presented and discussed in this paper. [ABSTRACT FROM AUTHOR]

In this article, energy and exergy analyses are conducted for two integrated systems which can be used in HVAC applications. These two systems are analyzed for the cases of single generation, cogeneration and trigeneration, and their performances are evaluated through energy and exergy efficiencies. The parametric studies are performed to investigate the effects of using cogeneration and extended to trigeneration on the system performance. To perform the comparisons between the systems for multiple options, the same amounts of outputs (in terms of electricity, heating, cooling) are produced for all systems. The energy analyses of systems 1 and 2 show a great benefit for moving from single generation to trigeneration, with the trigeneration efficiencies of 83.5% and 87.2%, respectively, and single generation efficiencies of 47% for both systems. However, the exergy analyses show that trigeneration may not always become more efficient than single generation, particularly for system 1, due to the fact that the trigeneration exergy efficiency is 38.7% and the corresponding single generation efficiency is 44.3%. For system 2, the trigeneration exergy efficiency is 52.7% while the single generation efficiency becomes 44.3%. Depending on the type of cogeneration or cogeneration design, the system can be more efficient. [ABSTRACT FROM AUTHOR]

This paper presents an artificial neural network (ANN) approach of a smart grid integrated proton exchange membrane (PEM) fuel cell and proposes a neural network model of a 6 kW PEM fuel cell. The data required to train the neural network model are generated by a model of 6 kW PEM fuel cell. After the model is trained and validated, it is used to analyze the dynamic behavior of the PEM fuel cell. The study results demonstrate that the model based on neural network approach is appropriate for predicting the outlet parameters. Various types of training methods, sample numbers and sample distribution methods are utilized to compare the results. The fuel cell stack efficiency considerably varies between 20% and 60%, according to input variables and models. The rapid changes in the input variables can be recovered within a short time period, such as 10 s. The obtained response graphs point out the load tracking features of ANN model and the projected changes in the input variables are controlled quickly in the study. [ABSTRACT FROM AUTHOR]

This paper develops and analyzes a new photo electrochemical reactor that uses zinc sulfide as a photo catalyst to produce hydrogen, chlorine and sodium hydroxide. The effects of different parameters on the rate of hydrogen, chlorine and sodium hydroxide production are experimentally studied. The parameters include the applied voltage, varied from 4 V to 5 V, amount of catalyst, varied from 1 g/425 mL to 5 g/425 mL and light intensity, varied from 20 W/m 2 to 55 W/m 2 . A factorial design of experiments is applied and an analysis of variance (ANOVA) is used to examine the experimental results. Energy and exergy efficiencies are also calculated. An optimization is performed to find the optimal catalyst concentration. At the optimized catalyst concentration, salt water is used to check its effect on the rate of hydrogen production. [ABSTRACT FROM AUTHOR]

In this paper, a conventional solid oxide fuel cell (SOFC) is modeled, and its performance is assessed to investigate the main challenges that limit low temperature operation. SOFCs have numerous advantages over other fuel cell technologies; however, a major drawback of SOFCs is the high operating temperature (over 600 °C) which significantly reduces SOFCs lifetime and constrains manufacturing materials to costly produced composites. Therefore, the development of a low temperature solid oxide fuel cell (LT-SOFC) will improve the cost effectiveness of this technology and thereby enhance efficient energy utilization and contribute to CO 2 emission reduction. In this regard, a model is employed to predict the conventional SOFC performance under different operating and design conditions, in general, and at low operating temperatures, in particular. Furthermore, the contribution of each of the polarizations is evaluated. The model results are validated through a comparison with published experimental data and found to be in a good agreement with a maximum possible error value of 10.3% in cell potential and power density output. The results show that conventional SOFCs are vulnerable to a significant performance reduction when operating at low temperatures (below 600 °C). In addition, the polarization that SOFCs experience at low operating temperatures is mainly attributed to electrolyte ohmic loss. [ABSTRACT FROM AUTHOR]

A new integrated system, which combines three renewable energy sources and generates five different commodities as useful outputs, is proposed and analyzed energetically and exergetically. The mass, energy, entropy and exergy balance equations for the major components of the integrated system are written and analyzed. The energy and exergy efficiencies for the integrated system and its subsystems are defined and calculated. Parametric studies are conducted by varying dead state properties and operating conditions to investigate their effects on the system performance. Some meteorological and system data from various previous studies are used in the analyses and assessments. The results show that the energy and exergy efficiencies of the integrated system become 36.67% and 25.075% respectively. [ABSTRACT FROM AUTHOR]

Abstract: The study focuses on defining energy and exergy efficiencies based on three different types of approaches. For each of five key psychometric processes, such as heating or cooling, heating with humidification, cooling with dehumidification, evaporative cooling, and adiabatic mixing, parametric studies are carried out. Two efficiencies are newly proposed here in this study, and the third efficiency is taken from the literature for comparison purposes. The results show that for heating process exergy efficiency varies from 0.012 to 0.48 with rise in ambient temperature. Increasing ambient temperature results in variation of exergy efficiency from 0.014 to 0.29 for heating with humidification process. For cooling with dehumidification process exergy efficiency varies from 0.002 to 0.73 with rise in ambient temperature. The exergetic efficiency of evaporative cooling process varies from 0.64 to 0.03 with an increase in ambient temperature. For adiabatic mixing process, exergy efficiency varies from 0.65 to 0.94 with rise in ambient temperature. [Copyright &y& Elsevier]

SUMMARY In this paper, a comprehensive thermodynamic analysis of the triple-effect absorption-refrigeration system using ammonia-water solution is carried out in order to investigate the effect of different operating conditions on the coefficient of performance (COPs) and rate of heat input to the system. It is found that both energetic and exergetic COPs vary from 0.31 to 1.867 and 0.165 to 0.964, respectively, as the inlet temperature to the high-temperature generator (HTG), cooling load, and concentration of the strong solution are increased, while the rate of heat input varies from 65.5 to 71.5%. Moreover, increase in the mixture exit temperature from the HTG, concentration of the weak solution, and mass flow rate result in the variation of energetic and exergetic COPs from 2.49 to 0.68 and 1.0 to 0.23, respectively, which results in the change of rate of heat input from 7.1 to 28.5 kW. When the outdoor temperature is increased, the exergetic COP varies from 0.43 to 1.23. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyzes an integrated Cu–Cl thermochemical cycle, Kalina cycle and electrolyzer for hydrogen production. The system operating parameters such as mass fraction, pressure and temperature are varied to investigate their effects on the energy and exergy efficiencies of the with/without heat recovery and integrated system, rate of hydrogen production, and rate of oxygen production. A new Cu–Cl design layout is then presented with a heat exchanger network developed to recover heat within the Cu–Cl cycle in the most efficient manner. The exergy destruction rate in each component is determined and discussed. The results show that increasing the electrolyzer temperature is beneficial up to 328.6K, after which the performance of the cycle results in a negative trend. The exergy efficiency varies more significantly with operating parameters than the corresponding energy efficiency. The maximum exergy destruction in the Cu–Cl cycle occurs in the first separator (16.82kW) and in the heat exchanger of the Kalina cycle (48.05kW), so these components should be considered for performance improvement of the system. [Copyright &y& Elsevier]

Abstract: In this paper, we propose an integrated system, consisting of a heliostat field, a steam cycle, an organic Rankine cycle (ORC) and an electrolyzer for hydrogen production. Some parameters, such as the heliostat field area and the solar flux are varied to investigate their effect on the power output, the rate of hydrogen produced, and energy and exergy efficiencies of the individual systems and the overall system. An optimization study using direct search method is also carried out to obtain the highest energy and exergy efficiencies and rate of hydrogen produced by choosing several independent variables. The results show that the power and rate of hydrogen produced increase with increase in the heliostat field area and the solar flux. The rate of hydrogen produced increases from 0.006 kg/s to 0.063 kg/s with increase in the heliostat field area from 8000 m2 to 50,000 m2. Moreover, when the solar flux is increased from 400 W/m2 to 1200 W/m2, the rate of hydrogen produced increases from 0.005 kg/s to 0.018 kg/s. The optimization study yields maximum energy and exergy efficiencies and the rate of hydrogen produced of 18.74%, 39.55% and 1571 L/s, respectively. [Copyright &y& Elsevier]

SUMMARY This article develops the concept of renewable-energy-based multigeneration options for producing a number of outputs, such as power, heat, hot water, cooling, hydrogen, fresh water, and so forth; and discusses their benefits. Such multigeneration options obviously lead to improved system performance and reduced environmental impacts. First, single-generation (power generation only) and cogeneration systems are compared with respect to the energy utilization efficiency, exergy efficiency, green house gases (GHG) mitigation, and payback period. It is found that the cogeneration increases GHG mitigation about 2 to 4 times, whereas the payback time decreases about 2.8 times with respect to the single-generation case. Exergy efficiency is found to be between about 55% and 65%, depending on the degree of cogeneration. The exergy efficiency shows the maximum values for certain source temperatures. For the case studied here, the optimum source temperature is taken as 200°C for analysis purposes. The results show that multigeneration of energy systems helps increase both energy and exergy efficiencies, reduce cost and environmental impact, and increase sustainability. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new hybrid system for hydrogen production via solar energy is developed and analyzed. In order to decompose water into hydrogen and oxygen without the net consumption of additional reactants, a steady stream of reacting materials must be maintained in consecutive reaction processes, to avoid reactant replenishment or additional energy input to facilitate the reaction. The system comprises two reactors, which are connected through a proton conducting membrane. Oxidative and reductive quenching pathways are developed for the water reduction and oxidation reactions. Supramolecular complexes [{(bpy)2Ru(dpp)}2RhBr2] (PF6)5 are employed as the photo-catalysts, and an external electric power supply is used to enhance the photochemical reaction. A light driven proton pump is used to increase the photochemical efficiency of both O2 and H2 production reactions. The energy and exergy efficiencies at a system level are analyzed and discussed. The maximum energy conversion of the system can be improved up to 14% by incorporating design modification that yield a corresponding 25% improvement in the exergy efficiency. [Copyright &y& Elsevier]

SUMMARY The present study deals with a comprehensive thermodynamic modeling of a combined heat and power (CHP) system in a paper mill, which provides 50 MW of electric power and 100 ton h−1 saturated steam at 13 bars. This CHP plant is composed of air compressor, combustion chamber (CC), Air Preheater, Gas Turbine (GT) and a Heat Recovery Heat Exchanger. The design parameters of this cycle are compressor pressure ratio ( rAC), compressor isentropic efficiency ( ηAC), GT isentropic efficiency ( ηGT), CC inlet temperature ( T3), and turbine inlet temperature ( T4). In the multi-objective optimization three objective functions, including CHP exergy efficiency, total cost rate of the system products, and CO2 emission of the whole plant, are considered. The exergoenvironmental objective function is minimized whereas power plant exergy efficiency is maximized using a Genetic algorithm. To have a good insight into this study, a sensitivity analysis of the results to the interest rate as well as fuel cost is performed. The results show that at the lower exergetic efficiency, in which the weight of exergoenvironmental objective is higher, the sensitivity of the optimal solutions to the fuel cost is much higher than the location of the Pareto Frontier with the lower weight of exergoenvironmental objective. In addition, with increasing exergy efficiency, the purchase cost of equipment in the plant is increased as the cost rate of the plant increases. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel biomass-based hydrogen production plant is investigated. The system uses oil palm shell as a feedstock. The main plant processes are biomass gasification, steam methane reforming and shift reaction. The modeling of the gasifier uses the Gibbs free energy minimization approach and chemical equilibrium considerations. The plant, with modifications, is simulated and analyzed thermodynamically using the Aspen Plus process simulation code (version 11.1). Exergy analysis, a useful tool for understanding and improving efficiency, is used throughout the investigation, in addition to energy analysis. The overall performance of the system is evaluated, and its efficiencies become 19% for exergy efficiency and 22% energy efficiency while the gasifier cold gas efficiency is 18%. [Copyright &y& Elsevier]

Abstract: In this paper, we analyze the feasibility of using urea for onboard hydrogen production to improve the efficiency of vehicles. Here, hydrogen is used as an additive to the primary fuel (gasoline, diesel). Urea is generally obtained in large quantities by combining ammonia with carbon dioxide in industry. The reverse reaction of decomposing urea into ammonia and carbon dioxide is widely known and currently used for production of ammonia in diesel vehicles where it serves as a NOx reduction agent. In the present system, the vehicle is equipped with a tubular urea tank as placed in the vicinity of the exhaust pipes. The heat recovered from the exhaust gases is used for catalytic conversion of urea into ammonia. The resultant ammonia is further flown over a catalytic membrane where hydrogen is separated from nitrogen. The highly pure hydrogen is then mixed with the fuel and combusted in the engine. We also study how engine efficiency, specific shaft work, specific fuel consumption and costs are affected by this process. [Copyright &y& Elsevier]

Abstract: Solar based hydrogen production is a promising alternative to methods based on fossil fuels, such as steam methane reforming (SMR) and coal gasification. A more economically viable way of producing hydrogen from water is under active investigation by many researchers, to convert solar energy to chemical energy with higher efficiency. In this paper, supramolecular complexes developed by Brewer (2006) for photocatalytic hydrogen production are examined, particularly for larger scale engineering reactors that can use visible light to dissolve the photocatalysts in water, causing the splitting of water molecules into hydrogen and hydroxyl ions. This paper analyzes and optimizes the system parameters associated with this system. A predictive model for the reactor is developed for a batch type photocatalytic reactor. Results are presented and discussed to evaluate how the system parameters affect the hydrogen production rate, and solar to hydrogen efficiency, using a monochromatic LED array and Rhodium based photocatalysts. [Copyright &y& Elsevier]

Abstract: In this paper, an integrated process of steam biomass gasification and a solid oxide fuel cell (SOFC) is investigated energetically to evaluate both electrical and energy efficiencies. This system is conceptualized as a combined system, based on steam biomass gasification and with a high temperature, pressurized SOFC. The SOFC system uses hydrogen obtained from steam sawdust gasification. Due to the utilization of the hydrogen content of steam in the reforming and shift reaction stages, the system efficiencies reach appreciable levels. This study essentially investigates the utilization of steam biomass gasification derived hydrogen that was produced from an earlier work in a system combines gasifier and SOFC to perform multi-duties (power and heat). A thermodynamic model is developed to explore a combination of steam biomass gasification, which produces 70–75 g of hydrogen/kg of biomass to fuel a planar SOFC, and generate both heat and power. Furthermore, processes are emerged in the system to increase the hydrogen yield by further processing the rest of gasification products: carbon monoxide, methane, char and tar. The conceptualized scheme combines SOFC operates at 1000 K and 1.2 bar and gasifier scheme based on steam biomass gasification which operates close to the atmospheric pressure, a temperature range of 1023–1423 K and a steam-biomass ratio of 0.8 kmol/kmol. A parametric study is also performed to evaluate the effect of various parameters such as hydrogen yield, air flow rate etc. on the system performance. The results show that SOFC with an efficiency of 50.3% operates in a good fit with the steam biomass gasification module with an efficiency, based on hydrogen yield, of 55.3%, and the overall system then works efficiently with an electric efficiency of ∼82%. [ABSTRACT FROM AUTHOR]