Energy and exergy analyses of a new four-step copper–chlorine cycle for geothermal-based hydrogen production

In this paper, energy and exergy analyses of the geothermal-based hydrogen production via thermochemical water decomposition using a new, four-step copper–chlorine (Cu–Cl) cycle are conducted, and the respective cycle energy and exergy efficiencies are examined. Also, a parametric study is performed to investigate how each step of the cycle and its overall cycle performance are affected by reference environment temperatures, reaction temperatures, as well as energy efficiency of the geothermal power plant itself. As a result, overall energy and exergy efficiencies of the cycle are found to be 21.67% and 19.35%, respectively, for a reference case.     

The evaluation of hydrogen production via a geothermal-based multigeneration system with 3E analysis and multi-objective optimization

In this study, a novel geothermal-based multigeneration system is designed and evaluated in energy, exergy and economic (3E) analyses. Besides 3E analyses, multi-objective optimization has been assessed to reach the highest exergetic effectiveness and the lowest total cost rate. To evaluate the designed plant, thermodynamic balance equations are assigned to all sub-systems found in the design. These equations are solved by using Engineering Equation Solver (EES) software. According to the analyses' results, with base parameters, total power production is 1951 kW, the hydrogen generation rate is 0.0015 kg/s, and the whole energy and exergy efficiencies are 59.53% and 53.17%. The economic analysis performed for the multigeneration system indicates that the total cost rate is 186 $/h, and the levelized energy cost is 0.102 $/kWh. These results indicate that the designed geothermal-based multigeneration system performs better than a single-generation plant in terms of efficiency and cost.     

Thermodynamic and exergo-economic assessments of a new geothermally driven multigeneration plant

In this paper, a new geothermal-based multigeneration system is designed and investigated in both thermodynamic and economic analyses. The reason to select the geothermal source is that geothermal power is a renewable and sustainable power resource, and also it is not weather dependent. The proposed geothermal-based multigeneration plant is able to produce power, heating, cooling, swimming pool heating, and hydrogen. The main idea in this renewable-based multigeneration system is to create valuable products by using waste heat of subsystems. Then, by applying thermodynamic analyses, the energy and exergy performances of proposed multigeneration system are computed. Also, parametric work has been performed in order to see the impacts of the reference temperature, geothermal fluid temperature, and geothermal water mass flow rate. Finally, exergo-economic analysis based on exergy destruction or thermodynamic losses is done to gain more information about the system and to evaluate it better. According to the calculations, the overall plant's energy and exergy performances are 32.28% and 25.39%. Economic analysis indicates that hydrogen production cost can be dropped down to 1.06 $/kg H₂.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

A review on biomass‐based hydrogen production and potential applications

In this paper, a detailed review is presented to discuss biomass‐based hydrogen production systems and their applications. Some optimum hydrogen production and operating conditions are studied through a comprehensive sensitivity analysis on the hydrogen yield from steam biomass gasification. In addition, a hybrid system, which combines a biomass‐based hydrogen production system and a solid oxide fuel cell unit is considered for performance assessment. A comparative thermodynamic study also is undertaken to investigate various operational aspects through energy and exergy efficiencies. The results of this study show that there are various key parameters affecting the hydrogen production process and system performance. They also indicate that it is possible to increase the hydrogen yield from 70 to 107 g H₂ per kg of sawdust wood. By studying the energy and exergy efficiencies, the performance assessment shows the potential to produce hydrogen from steam biomass gasification. The study further reveals a strong potential of this system as it utilizes steam biomass gasification for hydrogen production. To evaluate the system performance, the efficiencies are calculated at particular pressures, temperatures, current densities, and fuel utilization factors. It is found that there is a strong potential in the gasification temperature range 1023–1423 K to increase energy efficiency with a hydrogen yield from 45 to 55% and the exergy efficiency with hydrogen yield from 22 to 32%, respectively, whereas the exergy efficiency of electricity production decreases from 56 to 49.4%. Hydrogen production by steam sawdust gasification appears to be an ultimate option for hydrogen production based on the parametric studies and performance assessments that were carried out through energy and exergy efficiencies. Finally, the system integration is an attractive option for better performance. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of hydrogen production with iron-based chemical looping fed by different biomass

In this study, the iron-based chemical looping process driven by various biomasses for hydrogen production purposes is studied and evaluated thermodynamically through energy and exergy approaches. The overall system consists of some key units (combustor, reducers and oxidizer) a torrefier, a drying chamber, an air separation unit, a heat exchanger, and auxiliary units as well. The biomasses considered are first dried and torrified in the drying chamber and sent to reactors to produce hydrogen. The exergy and energy efficiencies of the iron based chemical looping facility are investigated comparatively for performance evaluation. The maximum exergy destruction and entropy production rates are calculated for the torrefaction process as 123.15 MW and 4926 kW/K respectively. Under the steady–state conditions, a total of 8 kg/s hydrogen is produced via chemical looping process. The highest energy efficiency is obtained in the looping of rice husk with 86% while the highest exergy efficiency is obtained in the looping using sugarcane bagasse with 91%, respectively.     

Ranking locations for producing hydrogen using geothermal energy in Afghanistan

Geothermal energy is a type of renewable energy with high availability and independence from climatic and atmospheric conditions. It has been shown that geothermal energy is technically, economically and environmentally more suitable for hydrogen production than other renewable sources. Hydrogen has wide applications in many fields including cooling, oil, gas, petrochemical, nuclear, and energy industries. Afghanistan has significant potential in geothermal power generation and also several hydrogen-consuming industries that provide opportunities for geothermal-based hydrogen production. This study attempted to find suitable locations for the construction of geothermal power plant for hydrogen production in Afghanistan. Given the multitude of criteria involved in the choice of location, evaluations and comparisons were performed using multi-criteria decision-making methods. Nine criteria were used to evaluate 17 Afghanistan provinces in terms of suitability for geothermal-based hydrogen production. The SWARA (Stepwise Weight Assessment Ratio Analysis) method was used to weight the criteria and then the ARAS (Additive Ratio Assessment) method was used to rank the provinces. The results were validated. The results showed that Sari pul, Balkh and Herat are the most suitable Afghanistan provinces and Zabul, Ghor and Kandahar are the least suitable Afghanistan provinces for geothermal-based hydrogen production. The three methods produced almost identical rankings with only minor differences in the overall ranking of some provinces.     

Electrolyzer-fuel cell combination for grid peak load management in a geothermal power plant: Power to hydrogen and hydrogen to power conversion

This study provides comprehensive energy, exergy, and economic evaluations and optimizations of a novel integrated fuel cell/geothermal-based energy system simultaneously generating cooling and electricity. The system is empowered by geothermal energy and the electricity is mainly produced by a dual organic cycle. A proton exchange membrane electrolyzer is employed to generate the oxygen and hydrogen consumed by a proton exchange membrane fuel cell utilized to support the network during consumption peak periods. This fuel cell can be also used for supplying the electricity demanded by the network to satisfy the loads at different times. All the simulations are conducted using Engineering Equation Solver software. To optimize the system, a multi-objective optimization method based on genetic algorithm is applied in MATLAB software. The objective functions are minimized cost rate and maximized exergy efficiency. The optimum values of exergy efficiency and cost rate are found to be 62.19% and 18.55$/h, respectively. Additionally, the results reveal that combining a fuel cell and an electrolyzer can be an effective solution when it comes to electricity consumption management during peak load and low load periods.     

Thermodynamic evaluation of hydrogen and electricity cogeneration coupled with very high temperature gas-cooled reactors

Hydrogen production using thermal energy, derived from nuclear reactor, can achieve large-scale hydrogen production and solve various energy problems. The concept of hydrogen and electricity cogeneration can realize the cascade and efficient utilization of high-temperature heat derive for very high temperature gas-cooled reactors (VHTRs). High-quality heat is used for the high-temperature processes of hydrogen production, and low-quality heat is used for the low-temperature processes of hydrogen production and power generation. In this study, two hydrogen and electricity cogeneration schemes (S1 and S2), based on the iodine-sulfur process, were proposed for a VHTR with the reactor outlet temperature of 950 °C. The thermodynamic analysis model was established for the hydrogen and electricity cogeneration. The energy and exergy analysis were conducted on two cogeneration systems. The energy analysis can reflect the overall performance of the systems, and the exergy analysis can reveal the weak parts of the systems. The analysis results show that the overall hydrogen and electricity efficiency of S1 is higher than that of S2, which are 43.6% and 39.2% at the hydrogen production rate of 100 mol/s, respectively. The steam generators is the components with the highest exergy loss coefficient, which are the key components for improving the system performance. This study presents a theoretical foundation for the subsequent optimization of hydrogen and electricity cogeneration coupled with VHTRs.     

Thermodynamic analysis of a parabolic trough solar power plant integrated with a biomass-based hydrogen production system

In the current study, a solar energy power plant integrated with a biomass-based hydrogen production system is investigated. The proposed plant is designed to supply the required energy for the hydrogen production process along with the electrical energy generation. Thermochemical processes are used to obtain high-purity hydrogen from biomass-based syngas. For this purpose, the simulation of the plant is performed using Aspen HYSYS software. Thermodynamic performance evaluation of the hybrid system is conducted with exergy analysis. Based on the obtained results, the exergy efficiencies of the hydrogen production process and power generation systems are 55.8% and 39.6%, respectively. The net power output of the system is obtained to be 38.89 MWe. Furthermore, the amount of produced hydrogen in the integrated system is 7912.5 tons/year with a flow rate of 10.8 tons/h synthesis gas for 7500 h/year operation. Results show that designing and operating a hybrid high-performance energy system using two different renewable sources is an encouraging approach to reduce the environmental impact of energy conversion processes and the effective use of energy resources.     

Analysis and performance assessment of a combined geothermal power-based hydrogen production and liquefaction system

In this paper, the thermodynamic study of a combined geothermal power-based hydrogen generation and liquefaction system is investigated for performance assessment. Because hydrogen is the energy of future, the purpose of this study is to produce hydrogen in a clear way. The results of study can be helpful for decision makers in terms of the integrated system efficiency. The presented integrated hydrogen production and liquefaction system consists of a combined geothermal power system, a PEM electrolyzer, and a hydrogen liquefaction and storage system. The exergy destruction rates, exergy destruction ratios and exergetic performance values of presented integrated system and its subsystems are determined by using the balance equations for mass, energy, entropy, energy and exergy and evaluated their performances by means of energetic and exergetic efficiencies. In this regard, the impact of some design parameters and operating conditions on the hydrogen production and liquefaction and its exergy destruction rates and exergetic performances are investigated parametrically. According to these parametric analysis results, the most influential parameter affecting system exergy efficiency is found to be geothermal source temperature in such a way that as geothermal fluid temperature increases from 130 °C to 200 °C which results in an increase of exergy efficiency from 38% to 64%. Results also show that, PEM electrolyzer temperature is more effective than reference temperature. As PEM electrolyzer temperature increases from 60 °C to 85 °C, the hydrogen production efficiency increases from nearly 39% to 44%.     

Exergetic assessment of solar hydrogen production methods

Hydrogen is a sustainable fuel option and one of the potential solutions for the current energy and environmental problems. Its eco-friendly production is really crucial for better environment and sustainable development. In this paper, various types of hydrogen production methods namely solar thermal (high temperature and low temperature), photovoltaic, photoelecrtolysis, biophotolysis etc are discussed. A brief study of various hydrogen production processes have been carried out. Various solar-based hydrogen production processes are assessed and compared for their merits and demerits in terms of exergy efficiency and sustainability factor. For a case study the exergy efficiency of hydrogen production process and the hydrogen system is discussed in terms of sustainability.     

Analysis and assessment of a novel hydrogen liquefaction process

In the present study, a novel supercritical hydrogen liquefaction process based on helium cooled hydrogen liquefaction cycles to produce liquid hydrogen is thermodynamically analyzed and assessed. The exergy analysis approach is used to study the exergy destruction rates in each component and the process efficiency. The energy and exergy efficiencies of liquefaction process are found to be 70.12% and 57.13%, respectively. In addition, to investigate the process efficiency more comprehensively to see how it is affected by varying process parameters and operating conditions, some parametric studies are undertaken to examine the impacts of different design variables on the energy efficiency, exergy efficiency and exergy destruction rates of the hydrogen liquefaction process. The results show that the increases in the cycle pressure of hydrogen and helium result in increasing hydrogen liquefaction process exergy efficiency and providing a smaller pinch point temperature difference of catalyst beds related with the heat transfer surface area and more efficiently process.     

Thermodynamic and economic assessment of a PEMFC-based micro-CCHP system integrated with geothermal-assisted methanol reforming

A micro-combined cooling heating and power (CCHP) system integrated with geothermal-assisted methanol reforming and incorporating a proton exchange membrane fuel cell (PEMFC) stack is presented. The novel CCHP system consists of a geothermal-based methanol steam reforming subsystem, PEMFC, micro gas turbine and lithium bromide (LiBr) absorption chiller. Geothermal energy is used as a heat source to drive methanol steam reforming to produce hydrogen. The unreacted methanol and hydrogen are efficiently utilized via the gas turbine and PEMFC to generate electricity, respectively. For thermodynamic and economic analysis, the effects of the thermodynamic parameters (geothermal temperature and molar ratio of water to methanol) and economic factors (such as methanol price, hydrogen price and service life) on the proposed system performance are investigated. The results indicate that the ExUF (exergy utilization factor the exergy utilization factor), TPES (trigeneration primary energy saving) and energy efficiency of the novel system can be reached at 8.8%, 47.24% and 66.3%, respectively; the levelized cost of energy is 0.0422 $/kWh, and the annual total cost saving ratio can be reached at 20.9%, compared with the conventional system. The novel system achieves thermodynamic and economic potential, and provides an alternative and promising way for efficiently utilizing abundant geothermal energy and methanol resources.     

A review on solar-hydrogen/fuel cell hybrid energy systems for stationary applications

There are several methods for producing hydrogen from solar energy. Currently, the most widely used solar hydrogen production method is to obtain hydrogen by electrolyzing the water at low temperature. In this study, solar hydrogen production methods, and their current status, are assessed. Solar-hydrogen/fuel cell hybrid energy systems for stationary applications, up to the present day are also discussed, and preliminary energy and exergy efficiency analyses are performed for a photovoltaic-hydrogen/fuel cell hybrid energy system in Denizli, Turkey. Three different energy demand paths – from photovoltaic panels to the consumer – are considered. Minimum and maximum overall energy and exergy efficiencies of the system are calculated based on these paths. It is found that the overall energy efficiency values of the system vary between 0.88% and 9.7%, while minimum and maximum overall exergy efficiency values of the system are between 0.77% and 9.3% as a result of selecting various energy paths. More importantly, the hydrogen path appears to be the least efficient one due to the addition of the electrolyzer, the fuel cells and the second inverter for hydrogen production and utilization.     

Energy and exergy analysis and optimization of biomass gasification process for hydrogen production (based on air,steam and air/steam gasifying agents)

Growing the consumption of fossil fuels and emerging global warming issue have driven the research interests toward renewable and environmentally friendly energy sources. Biomass gasification is identified as an efficient technology to produce sustainable hydrogen. In this work, energy and exergy analysis coupled with thermodynamic equilibrium model were implemented in biomass gasification process for production of hydrogen. In this regard, a detailed comparison of the performance of a downdraft gasifier was implemented using air, steam, and air/steam as the gasifying agents for horse manure, pinewood and sawdust as the biomass materials. The comparison results indicate that the steam gasification of pinewood generates a more desired product gas compositions with a much higher hydrogen exergy efficiency and low exergy values of unreacted carbon and irreversibility. Then the effects of the inherent operating factors were investigated and optimized applying a response surface methodology to maximize hydrogen exergy efficiency of the process. A hydrogen exergy efficiency of 44% was obtained when the product gas exergy efficiency reaches to the highest value (88.26%) and destruction and unreacted carbon efficiencies exhibit minimum values of 7.96% and 1.9%.     

Exergoeconomic analysis of hydrogen production from biomass gasification

In this study, we investigate biomass-based hydrogen production through exergy and exergoeconomic analyses and evaluate all components and associated streams using an exergy, cost, energy and mass (EXCEM) method. Then, we define the hydrogen unit cost and examine how key system parameters affect the unit hydrogen cost. Also, we present a case study of the gasification process with a circulating fluidized bed gasifier (CFBG) for hydrogen production using the actual data taken from the literature. We first calculate energy and exergy values of all streams associated with the system, exergy efficiencies of all equipment, and determine the costs of equipment along with their thermodynamic loss rates and ratio of thermodynamic loss rate to capital cost. Furthermore, we evaluate the main system components, consisting of gasifier and PSA, from the exergoeconomic point of view. Moreover, we investigate the effects of various parameters on unit hydrogen cost, such as unit biomass and unit power costs and hydrogen content of the syngas before PSA equipment and PSA hydrogen recovery. The results show that the CFBG system, which has energy and exergy efficiencies of 55.11% and 35.74%, respectively, generates unit hydrogen costs between 5.37 $/kg and 1.59 $/kg, according to the internal and external parameters considered.     

A renewable energy based waste-to-energy system with hydrogen options

A pressurized gasification combined system is studied in a novel integration with geothermal energy to produce hydrogen-enriched syngas. This system utilizes dewatered sludge, which leaves the biological wastewater treatment facility during the wastewater treatment process and is used as a feedstock to produce hydrogen as a useful output. The hydrogen produced is transformed in a proton-exchange fuel cell to electricity for community use. This system also incorporates a wind farm with a hydrogen storage system to meet societies’ energy need when the energy demand fluctuates. The integrated system is then analyzed with thermodynamic-based energy and exergy approaches. The Greater Toronto area is chosen as the case study location and comprehensive thermodynamic analysis and simulation are completed on the Aspen Plus and Engineering Equation Solver softwares while the annual wind speed data are obtained from the RETScreen software. The daily total energy delivered to the community from this proposed system is recorded to be 2.1 GWh. In addition, the hydrogen production ratio at the gasification system is observed to be 0.12 through the sludge utilization where the energy and exergy efficiencies of the integrated gasification combined cycle were calculated to be 24% and 28%, in this order. The highest energy and exergy efficiency with 38.6% and 42.2%, respectively, are observed in January where the wind farm operated at a capacity of 41.7% and the average wind speed was 6.3 m/s for Greater Toronto Area. The overall energy and exergy efficiencies of this waste-to-energy system are calculated as 32.7% and 36.6%, respectively.     

Life cycle assessment of H2 generation with high temperature electrolysis

Water electrolysis is a well-established process for hydrogen production but requires efficiency improvements to reduce costs. High temperature electrolysis (HTE) as a means to higher efficiency was advanced in the EU project RelHY. Through Life Cycle Assessment (LCA), also the environmental performance of five HTE-based hydrogen production systems was evaluated: operation with power and steam from a nuclear plant, continuous and intermittent operation with wind power and water, intermittent operation with natural gas or biogas reforming as back-up. Large scale natural gas reforming (NGR) was used as a reference. The LCA aims to identifying environmental hotspots of HTE plants and comparing their operation. The results show that stack manufacturing has the strongest impact during construction of the HTE plant while the impacts during H₂ production are largely due to power supply. All HTE variants studied lead to less life cycle CO₂-equivalent emissions than NGR. However, only the wind powered HTE variants without back-up use less energy than NGR. The other impacts and flows show different patterns. The results and limitations of the study are discussed.     

Thermodynamic investigation and comparison of selected production processes for hydrogen and hydrogen-derived fuels

The results are reported of comparisons based on energy and exergy analyses of a wide range of production processes for hydrogen and hydrogen-derived fuels (HDFs). A commercial process-simulation computer code, previously enhanced by the author for exergy analysis, is used in the analyses. Depending on the process and the efficiency definition used, overall efficiencies are determined to range widely, from 21 to 92% for energy efficiencies and from 19 to 83% for exergy efficiencies. The losses for all processes are found to exhibit many common factors. Energy losses associated with emissions account for 100% of the total energy losses, while exergy losses associated with emissions account for 4 to 11% of the total exergy losses. The remaining exergy losses are associated with internal consumptions. It is anticipated that the results will prove useful to those involved in the improvement of existing and design of future production processes for hydrogen and HDFs.