Hydrogenoxygen steam generator for a closed hydrogen combustion cycle

The paper deals with the problems of hydrogen combustion in an oxygen environment to produce high-temperature steam to be used in electricity generation at various power stations including nuclear power plants (NPP). For example, the use of H₂/O₂ steam generator within a hydrogen energy complex may allow increasing the NPP power and efficiency under operating conditions due to hydrogen steam superheating of the main working fluid in a steam-turbine unit. In addition, the use of the hydrogen energy complex may allow adapting NPP to variable electric load schedules with the increasing share of such power stations as well as developing environmentally friendly technologies for electricity generation. In the paper, a new solution to the problem of the effective and safe use of hydrogen energy at NPP with a hydrogen energy complex has been proposed.Technical solutions to hydrogen combustion in an oxygen environment using direct injection of cooling water or water steam into combustion products may have a significant weakness, namely the “quenching” phenomenon occurring during water/water steam injection resulting in the recombination efficiency decrease during the cooling of combustion products which is reflected in the increased proportion of non-condensable gases. In this case, the supply of such mixture to the steam-power cycle may be unsafe, as it could result in the increased concentration of unburned hydrogen in the steam turbine flow path. In the paper, a closed hydrogen cycle along with the hydrogen steam superheating system on its basis has been proposed to solve this problem. The closed-circuit system of hydrogen combustion preventing hydrogen permeation into the working fluid of a steam cycle completely as well as ensuring its full oxidation due to some excess of circulating oxygen has been investigated by the authors.Two types of H₂/O₂ combustion chambers for the system of safe hydrogen steam superheating in NPP cycle by using the closed-circuit system of hydrogen combustion in an oxygen environment have been considered in the study. The required parameters of H₂/O₂ steam generator with regard to operating temperature conditions as well as the power range of H₂/O₂ steam generators with the proposed combustion chamber construction design have been determined by mathematical modeling of the combustion and heat-mass-exchange processes.     

Comprehensive assessment of system efficiency and competitiveness of nuclear power plants in combination with hydrogen complex

The strategy provides construction and commissioning of a number of new nuclear power units for the development of nuclear energy in Russia. The share of nuclear power plants increase in the energy systems of Russia is predicted from 19 to 22% in the future, up to 2050. Nuclear power plants planned to involve in the primary frequency control at the same time. All these circumstances exacerbate the problem of providing nuclear power plants with a basic electrical load in the night period, including during the daily period. The energy strategy of Russia provides for the production of hydrogen by low-carbon methods, one of which is water electrolysis using nuclear power. Hydrogen production is included in the development strategy of the at operating Russian NPPs. Hydrogen production planned at the Kola NPP by water electrolysis. Thus, the article provides a rationale for the effectiveness of combining nuclear power plants with a hydrogen complex based on the production of hydrogen by electrolysis of water. The effectiveness substantiated of the new principle of combination with overheating of the working fluid steam turbine cycle of the NPP taking into account the safety of handling hydrogen. A new system proposed for the combustion of hydrogen in oxygen, which makes it possible to overheat the working fluid of the NPP steam turbine cycle with undissociated steam, which significantly reduces the content of unreacted hydrogen in the working fluid flow. In addition, a system was developed and proposed for removing unreacted hydrogen and oxygen from the steam phase of the working fluid of the NPP steam turbine cycle. Thermodynamic and technical-economic new estimates are presented and analyzed of the efficiency of combining NPP with a hydrogen complex.     

Combined hydrogen production and power generation from aluminum combustion with water: Analysis of the concept

In this paper the combined production of hydrogen and power based on the aluminum combustion with water is investigated. Furthermore, a concept system is proposed that is potentially able to provide pressurized hydrogen and high temperature steam along with heat and work at the crankshaft. The system demonstrates high energy conversion efficiency, and it fully complies with environment sustainability requirements.     

Dynamic modelling of a solar hydrogen system for power and ammonia production

A new configuration of solar energy-driven integrated system for ammonia synthesis and power generation is proposed in this study. A detailed dynamic analysis is conducted on the designed system to investigate its performance under different radiation intensities. The solar heliostat field is integrated to generate steam that is provided to the steam Rankine cycle for power generation. The significant amount of power produced is fed to the PEM electrolyser for hydrogen production after covering the system requirements. A pressure swing adsorption system is integrated with the system that separates nitrogen from the air. The produced hydrogen and nitrogen are employed to the cascaded ammonia production system to establish increased fractional conversions. Numerous parametric studies are conducted to investigate the significant parameters namely; incoming beam irradiance, power production using steam Rankine cycle, hydrogen and ammonia production and power production using TEGs and ORC. The maximum hydrogen and ammonia production flowrates are revealed in June for 17th hour as 5.85 mol/s and 1.38 mol/s and the maximum energetic and exergetic efficiencies are depicted by the month of November as 25.4% and 28.6% respectively. Moreover, the key findings using the comprehensive dynamic analysis are presented and discussed.     

Operating maps of a combined hydrogen production and power generation system based on aluminum combustion with water

The performance of a novel hydrogen production and energy conversion system based on the aluminum-water reaction is addressed by means of a lumped and distributed parameter numerical approach. The interest on this type of technology arises because of the possibility of obtaining at the same time different secondary energy sources, such as hydrogen and heat and mechanical work, with very low pollutant and greenhouse gas emissions.In this paper the numerical models of the main components adopted in the system are developed, including the combustion chamber, the steam/hydrogen turbine and the heat exchangers. The behavior of the whole system is investigated for different configurations and energy conversion cycles, i.e. electric energy production only and combined heat and power production, in order to determine the operating maps in terms of efficiency, power output, pressure and temperature in the main sections, mass flow rates and the hydrogen yield. The numerical analysis of the thermo-dynamic behavior of the power unit is aimed at assessing the guidelines that will lead to the construction of a first prototype of this system.Finally, the use of a cogeneration system based on the aluminum combustion with water system for on-site small scale hydrogen production for feeding a hydrogen refueling station is explored. The proposed system is compared with other technologies as well as the case of large scale hydrogen production and delivery.     

Performance assessment of a direct steam solar power plant with hydrogen energy storage: An exergoeconomic study

Power generation and its storage using solar energy and hydrogen energy systems is a promising approach to overcome serious challenges associated with fossil fuel-based power plants. In this study, an exergoeconomic model is developed to analyze a direct steam solar tower-hydrogen gas turbine power plant under different operating conditions. An on-grid solar power plant integrated with a hydrogen storage system composed of an electrolyser, hydrogen gas turbine and fuel cell is considered. When solar energy is not available, electrical power is generated by the gas turbine and the fuel cell utilizing the hydrogen produced by the electrolyser. The effects of different working parameters on the cycle performance during charging and discharging processes are investigated using thermodynamic analysis. The results indicate that increasing the solar irradiation by 36%, leads to 13% increase in the exergy efficiency of the cycle. Moreover, the mass flow rate of the heat transfer fluid in solar system has a considerable effect on the exergy cost of output power. Solar tower has the highest exergy destruction and capital investment cost. The highest exergoeconomic factor for the integrated cycle is 60.94%. The steam turbine and PEM electrolyser have the highest share of exergoeconomic factor i.e., 80.4% and 50%, respectively.     

Thermodynamic analysis and assessment of an integrated hydrogen fuel cell system for ships

In this thermodynamic investigation, an integrated energy system based on hydrogen fuel is developed and studied energetically and exergetically. The liquefied hydrogen fueled solid oxide fuel cell (SOFC) based system is then integrated with a steam producing cycle to supply electricity and potable water to ships. The first heat recovery system, after the fuel cells provide thrust for the ship, is by means of a turbine while the second heat recovery system drives the ship's refrigeration cycle. This study includes energy and exergy performance evaluations of SOFC, refrigeration cycle and ship thrust engine systems. Furthermore, the effectiveness of SOFCs and a hydrogen fueled engine in reducing greenhouse gas emissions are assessed parametrically through a case study. The main propulsion, power generation from the solid oxide fuel cells, absorption chiller, and steam bottoming cycle systems together have the overall energy and exergy efficiencies of 41.53% and 37.13%, respectively.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

A hybrid fuel cell system integrated with methanol steam reformer and methanation reactor

In this paper, a hybrid fuel cell system integrated with methanol steam reformer and methanation reactor is demonstrated. Methanol steam reformer employed in this system is to produce hydrogen-rich reformate in connection with a methanation reactor to reduce the carbon monoxide content effectively, and the reformate gas is sent into a low-temperature polymer electrolyte fuel cell for direct electric power generation. The optimum conditions (temperature, water to methanol ratio, and space velocity) for methanol steam reforming (MSR) reaction and methanation (MET) reaction are verified by experiments. A comparison between pure hydrogen, reformate surrogate, and actual reformate is performed. The results show that the power density of this hybrid system achieves 245.2 mW/cm² while it achieves 268.8 mW/cm² when employing pure hydrogen as the fuel. An alternative novel method to solve the problem of hydrogen storage and transportation is provided and the in-situ hydrogen production and utilizing through low-temperature fuel cell system is realized, which is helpful to accelerate the commercialization process of the fuel cell.     

Geothermal‐based hydrogen production using thermochemical and hybrid cycles: A review and analysis

Geothermal‐based hydrogen production, which basically uses geothermal energy for hydrogen production, appears to be an environmentally conscious and sustainable option for the countries with abundant geothermal energy resources. In this study, four potential methods are identified and proposed for geothermal‐based hydrogen production, namely: (i) direct production of hydrogen from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated through geothermal power plant, (iii) by using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, and (iv) by using the heat available from geothermal resource in thermochemical processes. Nowadays, most researches are focused on high‐temperature electrolysis and thermochemical processes. Here we essentially discuss some potential low‐temperature thermochemical and hybrid cycles for geothermal‐based hydrogen production, due to their wider practicality, and examine them as a sustainable option for hydrogen production using geothermal heat. We also assess their thermodynamic performance through energy and exergy efficiencies. The results show that these cycles have good potential and attractive overall system efficiencies over 50% based on a complete reaction approach. The copper‐chlorine cycle is identified as a highly promising cycle for geothermal‐hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd.     

Energy and exergy analyses of a solar driven Mg–Cl hybrid thermochemical cycle for co-production of power and hydrogen

Analysis and performance assessment of a solar driven hydrogen production plant running on an Mg–Cl cycle, are conducted through energy and exergy methods. The proposed system consists of (a) a concentrating solar power cycle with thermal energy storage, (b) a steam power plant with reheating and regeneration, and (c) a hybrid thermochemical Mg–Cl hydrogen production cycle. The results show that higher steam to magnesium molar ratios are required for full yield of reactants at the hydrolysis step. This ratio even increases at low temperatures, although lowering the highest temperatures appears to be more favorable for linking such a cycle to lower temperature energy sources. Reducing the maximum cycle temperature decreases the plant energy and exergy efficiencies and may cause some undesirable reactions and effects. The overall system energy and exergy efficiencies are found to be 18.8% and 19.9%, respectively, by considering a solar heat input. These efficiencies are improved to 26.9% and 40.7% when the heat absorbed by the molten salt is considered and used as a main energy input to the system. The highest exergy destruction rate occurs in the solar field which accounts for 79% of total exergy destruction of the integrated system.     

Investigation of a multi-generation system using a hybrid steam biomass gasification for hydrogen, power and heat

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%.     

A hybrid aluminum/hydrogen/air cell system

A hybrid aluminum/hydrogen/air cell system is developed to solve the parasitic hydrogen-generating problem in an alkaline aluminum/air battery. A H₂/air fuel cell is integrated into an Al/air battery so that the hydrogen generated by the parasitic reaction is utilized rather than wasted. A systematic study is conducted to investigate how the parasitic reaction and the added H₂/air cell affect the performance of the aluminum/air battery. The aluminum/air sub-cell has an open circuit voltage of 1.45 V and the hydrogen/air sub-cell of 1.05 V. The maximum power density of the entire hybrid system increases significantly by ∼20% after incorporating a H₂/air sub-cell. The system maximum power density ranges from 23 to 45 mW cm⁻² in 1–5 M NaOH electrolyte. The hybrid system is adaptable in concentrated alkaline electrolyte with significantly improved power output at no sacrifice of its overall efficiency.     

Energetic and exergetic assessments of a novel solar power tower based multigeneration system with hydrogen production and liquefaction

In this article, a thermodynamic investigation of solar power tower assisted multigeneration system with hydrogen production and liquefaction is presented for more environmentally-benign multigenerational outputs. The proposed multigeneration system is consisted of mainly eight sub-systems, such as a solar power tower, a high temperature solid oxide steam electrolyzer, a steam Rankine cycle with two turbines, a hydrogen generation and liquefaction cycle, a quadruple effect absorption cooling process, a drying process, a membrane distillation unit and a domestic hot water tank to supply hydrogen, electrical power, heating, cooling, dry products, fresh and hot water generation for a community. The energetic and exergetic efficiencies for the performance of the present multigeneration system are found as 65.17% and 62.35%, respectively. Also, numerous operating conditions and parameters of the systems and their effects on the respective energy and exergy efficiencies are investigated, evaluated and discussed in this study. A parametric study is carried out to analyze the impact of various system design indicators on the sub-systems, exergy destruction rates and exergetic efficiencies and COPs. In addition, the impacts of varying the ambient temperature and solar radiation intensity on the irreversibility and exergetic performance for the present multigeneration system and its components are investigated and evaluated comparatively. According to the modeling results, the solar irradiation intensity is found to be the most influential parameter among other conditions and factors on system performance.     

Thermodynamic assessment of an electrically-enhanced thermochemical hydrogen production (EETHP) concept for renewable hydrogen generation

A novel concept for coupling a thermochemical cycle with an electrochemical separation device for the generation of hydrogen from steam is reported and a thermodynamic analysis of the system is presented. In a conventional thermochemical cycle, an oxygen carrier material is thermally reduced, cooled, and then reoxidized in steam thereby generating hydrogen. However, this process often requires high temperatures (>1700 K) and/or low oxygen partial pressures (<0.001 atm) in order to meet thermodynamic requirements. Such extreme conditions can adversely affect the stability of the reactive oxides, reactor materials, and system efficiency. In our proposed technology, we seek to decrease the required reduction temperature by several hundred degrees Kelvin by relaxing the requirement for spontaneous oxidation reaction at atmospheric pressure. This is accomplished by incorporating a proton-conducting membrane (PCM) to separate hydrogen produced at equilibrium concentrations from reactant steam. We also suggest the use of mixed ionic-electronic conducting (MIEC) oxygen carrier materials that reduce through a continuum of oxidation states at lower temperatures (～1200 °C). This concept allows the generation of a high-quality hydrogen stream while avoiding the challenging high temperatures/low partial pressures required in conventional water-splitting reaction schemes.     

A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications

A complete miniaturized methanol fuel processor/fuel cell system was developed and put into operation as compact hydrogen supplier for low power application. The whole system consisting of a micro-structured evaporator, a micro-structured reformer and two stages of preferential oxidation of CO (PROX) reactor, micro-structured catalytic burner, and fuel cell was operated to evaluate the performance of the whole production line from methanol to electricity. The performance of micro methanol steam reformer and PROX reactor was systematically investigated. The effect of reaction temperature, steam to carbon ratio, and contact time on the methanol steam reformer performance is presented in terms of catalytic activity, selectivity, and reformate yield. The performance of PROX reactor fed with the reformate produced by the reformer reactor was evaluated by the variation of reaction temperature and oxygen to CO ratio. The results demonstrate that micro-structured device may be an attractive power source candidate for low power application.     

Thermodynamic analysis and optimization of an integrated solar thermochemical hydrogen production system

In this study, thermodynamic analysis of solar-based hydrogen production via copper-chlorine (Cu–Cl) thermochemical water splitting cycle is presented. The integrated system utilizes air as the heat transfer fluid of a cavity-pressurized solar power tower to supply heat to the Cu–Cl cycle reactors and heat exchangers. To achieve continuous operation of the system, phase change material based on eutectic fluoride salt is used as the thermal energy storage medium. A heat recovery system is also proposed to use the potential waste heat of the Cu–Cl cycle to produce electricity and steam. The system components are investigated thoroughly and system hotspots, exergy destructions and overall system performance are evaluated. The effects of varying major input parameters on the overall system performance are also investigated. For the baseline, the integrated system produces 343.01 kg/h of hydrogen, 41.68 MW of electricity and 11.39 kg/s of steam. Overall system energy and exergy efficiencies are 45.07% and 49.04%, respectively. Using Genetic Algorithm (GA), an optimization is performed to evaluate the maximum amount of produced hydrogen. The optimization results show that by selecting appropriate input parameters, hydrogen production rate of 491.26 kg/h is achieved.     

A theoretical study of molten carbonate fuel cell combined with a solar power plant and Cu–Cl thermochemical cycle based on techno-economic analysis

A novel power and hydrogen coproduction system is designed and analyzed from energetic and economic point of view. Power is simultaneously produced from parabolic trough collector power plant and molten carbonate fuel cell whereas hydrogen is generated in a three-steps Cu–Cl thermochemical cycle. The key component of the system is the molten carbonate fuel cell that provides heat to others (Cu–Cl thermochemical cycle and steam accumulator). A mathematic model is developed for energetic and economic analyses. A parametric study is performed to assess the impact of some parameters on the system performance. From calculations, it is deduced that electric energy from fuel cell, solar plant and output hydrogen mass are respectively 578 GWh, 25 GWh and 306 tons. The overall energy efficiency of the proposed plants is 46.80 % and its LCOE is 7.64 c€/kWh. The use of MCFC waste heat allows increasing the solar power plant efficiency by 2.15 % and reducing the annual hydrogen consumption by 3 %. Parametric analysis shows that the amount of heat recovery impacts the energy efficiency of fuel cell and Cu–Cl cycle. Also, current density is a key parameter that influences the system efficiency.     

Combustion efficiency measurements and burner characterization in a hydrogen-oxyfuel combustor

Energy generation from renewable sources in the power sector keeps constantly increasing. This raises the demand for fast and flexible large-scale storage technologies. Steam generation via stoichiometric combustion of hydrogen and oxygen within a steam cycle is a promising way to recombine both gases, which can be generated by electrolysis utilizing excess renewable energy. At the same time, this technology could provide balancing and spinning network reserves. A crucial parameter of this approach is the combustion efficiency, since residual hydrogen or oxygen can damage downstream components of the power plant steam cycle. The current paper investigates the combustion of hydrogen and oxygen under steam diluted conditions. Flow field, mixing, flame types and combustion efficiency are assessed. The combustion efficiency measurement is very challenging in this case, as the combustor products consist mostly of pure steam and cannot be dried for conventional gas analysis. This is solved by an in-situ measurement method to quantify the combustion efficiency. Initial results of this approach are also presented in the current work.     

Experimental study of gaseous effluent and solid conversion in a fluidized bed hydrolysis reactor for hydrogen production

In this paper, new experimental data is presented for the hydrolysis of steam with CuCl₂ particles, in a high-temperature fluidized-bed reactor, which is a critical component of the Cu–Cl hydrogen production cycle. Results are obtained from large engineering-scale equipment built to perform the hydrolysis reaction using steam and CuCl₂. Experimental facilities are utilized for a boiler and superheater to supply steam for the endothermic reaction to proceed. This paper provides new insight into the hydrolysis operation by examining various issues involving the reaction rate and integrating the hydrolysis reactor into the Cu–Cl cycle. The results indicate a 40% reduction in the experimental reaction rate, during the initial 30 min of the reactor operation, as physical rate-controlling resistances develop in the process. This paper analyzes the process, in terms of chemical reaction rates, and limiting the physical resistances to efficient reaction rates within the reactor, as needed for the Cu–Cl cycle to become more economically competitive against other methods of hydrogen production.