A cycle capable of generating both hydrogen and power with “inherent” carbon capture is proposed and evaluated. The cycle uses chemical looping combustion to perform the primary energy release from a hydrocarbon, producing an exhaust of CO. This CO is mixed with steam and converted to H 2 and CO 2 using the water-gas shift reaction (WGSR). Chemical looping uses two reactions with a recirculating oxygen carrier to oxidize hydrocarbons. The resulting oxidation and reduction stages are preformed in separate reactors—the oxidizer and reducer, respectively, and this partitioning facilitates CO 2 capture. In addition, by careful selection of the oxygen carrier, the equilibrium temperature of both redox reactions can be reduced to values below the current industry standard metallurgical limit for gas turbines. This means that the irreversibility associated with the combustion process can be reduced significantly, leading to a system of enhanced overall efficiency. The choice of oxygen carrier also affects the ratio of CO versus CO 2 in the reducer’s flue gas, with some metal oxide reduction reactions generating almost pure CO. This last feature is desirable if the maximum H 2 production is to be achieved using the WGSR reaction. Process flow diagrams of one possible embodiment using a zinc based oxygen carrier are presented. To generate power, the chemical looping system is operated as part of a gas turbine cycle, combined with a bottoming steam cycle to maximize efficiency. The WGSR supplies heat to the bottoming steam cycle, and also helps to raise the steam necessary to complete the reaction. A mass and energy balance of the chemical looping system, the WGSR reactor, steam bottoming cycle, and balance of plant is presented and discussed. The results of this analysis show that the overall efficiency of the complete cycle is dependent on the operating pressure in the oxidizer, and under optimum conditions exceeds 75%.

A program for a hydrogen production by using a high temperature nuclear heat has been launched in Korea since 2004. Iodine sulfur (IS) process is one of the promising processes for a hydrogen production because it does not generate carbon dioxide and a massive hydrogen production may be possible. However, the highly corrosive environment of the process is a barrier to its application in the industry. Therefore, corrosion behaviors of various materials were evaluated in sulfuric acid to select appropriate materials compatible with the IS process. The materials used in this work were Ni based alloys, Fe–Si alloys, Ta, Au, Pt, Zr, SiC, and so on. The test environments were boiling 50 wt % sulfuric acid without/with HI as an impurity and 98 wt % sulfuric acid. The surface morphologies and cross-sectional areas of the corroded materials were examined by using the scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). From the results of the weight loss and potentiodynamic experiments, it was found that a Si enriched oxide is attributable to a corrosion resistance for materials including Si in boiling 98 wt % sulfuric acid. Moreover, the passive Si enriched film thickness increased with the immersion time leading to an enhancement of the corrosion resistance. Corrosion behaviors of the material tested are discussed in terms of the chemical composition of the materials, the corrosion morphology, and the surface layer’s composition.

A system analysis has been performed to assess the efficiency and carbon utilization of a nuclear-assisted coal gasification process. The nuclear reactor is a high-temperature helium-cooled reactor that is used primarily to provide power for hydrogen production via high-temperature electrolysis. The supplemental hydrogen is mixed with the outlet stream from an oxygen-blown coal gasifier to produce a hydrogen-rich gas mixture, allowing most of the carbon dioxide to be converted into carbon monoxide, with enough excess hydrogen to produce a syngas product stream with a hydrogen/carbon monoxide molar ratio of about 2:1. Oxygen for the gasifier is also provided by the high-temperature electrolysis process. The results of the analysis predict 90.5% carbon utilization with a syngas production efficiency (defined as the ratio of the heating value of the produced syngas to the sum of the heating value of the coal plus the high-temperature reactor heat input) of 64.4% at a gasifier temperature of 1866 K for the high-moisture-content lignite coal considered. Usage of lower moisture coals such as bituminous can yield carbon utilization approaching 100% and 70% syngas production efficiency.

This paper presents a review of recent advances in nuclear-based hydrogen production with a thermochemical copper-chlorine cycle. Growing attention has focused on thermochemical water decomposition as a promising alternative to steam-methane reforming for a sustainable future method of large-scale hydrogen production. Recent advances in specific processes within the Cu–Cl cycle will be presented, particularly for overall heat requirements of the cycle, preferred configurations of the oxygen cell, disposal of molten salt, electrochemical process of copper electrowinning, and safety/reliability assessment of the systems. An energy balance for each individual process is formulated and results are presented for heat requirements of the processes.

A commercially available natural gas fueled gas turbine engine was operated on hydrogen. Three sets of fuel injectors were developed to facilitate stable operation while generating differing levels of fuel∕air premixing. One set was designed to produce near uniform mixing while the others have differing degrees of nonuniformity. The emission performance of the engine over its full range of loads is characterized for each of the injector sets. In addition, the performance is also assessed for the set with near uniform mixing as operated on natural gas. The results show that improved mixing and lower equivalence ratio decrease NO emission levels as expected. However, even with nearly perfect premixing, it is found that the engine, when operated on hydrogen, produces a higher amount of NO than when operated with natural gas. Much of this attributed to the higher equivalence ratios that the engine operates on when firing hydrogen. However, even the lowest equivalence ratios run at low power conditions, higher NO was observed. Analysis of the potential NO formation effects of residence time, kinetic pathways of NO production via NNH, and the kinetics of the dilute combustion strategy used are evaluated. While no one mechanism appears to explain the reasons for the higher NO, it is concluded that each may be contributing to the higher NO emissions observed with hydrogen. In the present configuration with the commercial control system operating normally, it is evident that system level effects are also contributing to the observed NO emission differences between hydrogen and natural gas.

Korea Atomic Energy Research Institute is in the process of carrying out a nuclear hydrogen system by considering the indirect cycle gas cooled reactors that produce heat at temperatures in the order of 950 ° C . A coaxial double-tube hot gas duct (HGD) is a key component connecting the reactor pressure vessel and the intermediate heat exchanger for the nuclear hydrogen system. Recently, a preliminary design analysis for the primary and secondary hot gas ducts of the nuclear hydrogen system was carried out. These preliminary design activities include a preliminary decision on the geometric dimensions, a preliminary strength evaluation, and an appropriate material selection. In this study, a preliminary strength evaluation for the HGDs of the nuclear hydrogen system has been undertaken. Preliminary strength evaluation results for the HGDs showed that the geometric dimensions of the proposed HGDs would be acceptable for the design requirements.

Currently there are a number of Generation IV supercritical water-cooled nuclear reactor (SCWR) concepts under development worldwide. The main objectives for developing and utilizing SCWRs are (1) to increase the gross thermal efficiency of current nuclear power plants (NPPs) from 33–35% to approximately 45–50% and (2) to decrease the capital and operational costs and, in doing so, decrease electrical-energy costs (approximately US$ 1000 ∕ kW or even less). SCW NPPs will have much higher operating parameters compared to current NPPs (i.e., pressures of about 25 MPa and outlet temperatures of up to 625 ° C ). Additionally, SCWRs will have a simplified flow circuit in which steam generators, steam dryers, steam separators, etc. will be eliminated. Furthermore, SCWRs operating at higher temperatures can facilitate an economical cogeneration of hydrogen through thermochemical cycles (particularly, the copper-chlorine cycle) or direct high-temperature electrolysis. To decrease significantly the development costs of a SCW NPP and to increase its reliability, it should be determined whether SCW NPPs can be designed with a steam-cycle arrangement that closely matches that of mature supercritical (SC) fossil power plants (including their SC turbine technology). On this basis, several conceptual steam-cycle arrangements of pressure-channel SCWRs, their corresponding T ‐ s diagrams and steam-cycle thermal efficiencies are presented in this paper together with major parameters of the copper-chlorine cycle for the cogeneration of hydrogen. Also, bulk-fluid temperature and thermophysical properties profiles were calculated for a nonuniform cosine axial heat-flux distribution along a generic SCWR fuel channel, for reference purposes.

The development of a hydrogen-fueled engine using external mixture injection (e.g., using port or manifold fuel injection) with high efficiency and high power is dependent on the control of backfire. This work has developed a method to control backfire by reducing the valve overlap period while maintaining or improving engine performance. For this goal, a single-cylinder hydrogen-fueled research engine with a mechanical continuous variable valve timing system was developed. This facility provides a wide range of valve overlap periods that can be continuously and independently varied during firing operation. By using this research engine, the behavior of backfire occurrence and engine performance are determined as functions of the valve overlap period for fuel-air equivalence ratios between 0.3 and 1.2. The results showed that the developed hydrogen-fueled research engine with the mechanical continuous variable valve timing system has similar performance to a conventional engine with fixed valve timings, and is especially effective in controlling the valve overlap period. Backfire occurrence is reduced with a decrease in the valve overlap period, and is also significantly decreased even under operating conditions with the same volumetric efficiency. These results demonstrate that decreasing the valve overlap period may be one of the methods for controlling backfire in a hydrogen-fueled engine while maintaining or improving performance.

This paper proposes a novel, multifunctional energy system (MES), in which hydrogen and electricity are cogenerated and about 90% of CO 2 is removed. By integrating the methane/steam reforming reaction and combustion of coal, the natural gas and coal are utilized synthetically, and coal is burned to provide high-temperature thermal energy to the methane/steam reforming reaction. Afterwards, the resulting syngas enters a pressure swing adsorption (PSA) unit to separate about 70% of hydrogen, thereby significantly increasing the concentration of carbon dioxide from nearly 20% to 43% in the PSA tail gas. As a result, the overall efficiency of the new system becomes 63.2%. Compared to a conventional natural gas-based hydrogen plant and a coal-firing steam power plant without CO 2 removal (the overall efficiency of the two systems is 63.0%), the energy penalty for CO 2 removal in the new system is almost totally avoided. Based on the graphical exergy analysis, we propose that the integration of synthetic utilization of fossil fuel (natural gas and coal) and the CO 2 removal process plays a significant role in zero energy penalty for CO 2 removal and its liquefaction in the MES. The result obtained here provides a new approach for CO 2 removal with zero or low thermal efficiency reduction (energy penalty) within an energy system.

Hydrogen yield of conventional biomass gasification is limited by chemical equilibrium constraints. A novel technique that has the potential to enhance the hydrogen yield by integrating the gasification and absorption reactions has been suggested. The method involves gasification of biomass in presence of a C O 2 sorbent. Ethanol was used as the model biomass compound and CaO was the representative sorbent. Equilibrium modeling was used to determine the product gas composition and hydrogen yield. The analysis was done using ASPEN PLUS software (version 12.1) and the Gibbs energy minimization approach was followed. The effects of temperature, pressure, steam/ethanol ratio, and CaO/ethanol ratio on product yield were investigated. Three case studies were conducted to understand the effect of sorbent addition on the hydrogen yield. Thermodynamic studies showed that the use of sorbents has the potential to enhance the equilibrium hydrogen yield of conventional gasification by ∼ 19 % and reduce the equilibrium C O 2 content of product gas by 50.2%. It was also found that the thermodynamic efficiency of sorbent-enhanced gasification (72.1%) was higher than conventional gasification (62.9%). Sorbent-enhanced gasification is a promising technology with a potential to improve the yield and lower the cost of hydrogen production.

In this paper two options for H 2 production, by means of natural gas, are presented and their performances are evaluated when they are integrated with advanced H 2 /air cycles. In this investigation two different schemes have been analyzed: an advanced combined cycle power plant (CC) and a new advanced mixed cycle power plant (AMC). The two methods for producing H 2 are as follows: (1) steam methane reforming: it is the simplest and potentially the most economic method for producing hydrogen in the foreseeable future; and (2) partial oxidation of methane: it could offer an energy advantage because this method reduces the energy requirement of the reforming process. These hydrogen production plants require material and energetic integrations with power section and the best interconnections must be investigated in order to obtain good overall performance. With reference to thermodynamic and economic performance, significant comparisons have been made between the above introduced reference plants. An efficiency decrease and an increase in the cost of electricity has been obtained when power plants are equipped with a natural gas decarbonization section. The main results of the performed investigation are quite variable among the different H 2 production technologies here considered: the efficiency decreases in a range of 5.5 percentage points to nearly 10 for the partial oxidation of the natural gas and in a range of about 9 percentage points to over 12 for the steam methane reforming. The electricity production cost increases in a range of about 41–42% for the first option and in a range of about 34–38% for the second one. The AMC, coupled with partial oxidation, stands out among the other power plant solutions here analyzed because it exhibits the highest net efficiency and the lowest final specific CO 2 emission. In addition to this, economic impact is favorable when AMC is equipped with systems for H 2 production based on partial oxidation of natural gas.

In the last several years, gasification has become an interesting option for biomass utilization because the produced gas can be used as a gaseous fuel in different applications or burned in a gas turbine for power generation with a high thermodynamic efficiency. In this paper, a technoeconomic analysis was carried out in order to evaluate performance and cost of biomass gasification systems integrated with two different types of plant, respectively, for hydrogen production and for power generation. An indirectly heated fluidized bed gasifier has been chosen for gas generation in both cases, and experimental data have been used to simulate the behavior of the gasifier. The hydrogen plant is characterized by the installation of a steam methane reformer and a shift reactor after the gas production and cleanup section; hydrogen is then purified in a pressure swing adsorption system. All these components have been modeled following typical operating conditions found in hydrogen plants. Simulations have been performed to optimize thermal interactions between the biomass gasification section and the gas processing. The power plant consists of a gas-steam combined cycle, with a three-pressure-levels bottoming cycle. A sensitivity analysis allowed to evaluate the economic convenience of the two plants as a function of the costs of the hydrogen and electrical energy.

Steam methane reforming is the most common process for producing hydrogen in the world. It currently represents the most efficient and mature technology for this purpose. However, because of the high investment costs, this technology is only convenient for large sizes. Furthermore, the cooling of syngas and flue gas produce a great amount of excess steam, which is usually transferred outside the process, for heating purposes or industrial applications. The opportunity of using this additional steam to generate electric power has been studied in this paper. In particular, different power plant schemes have been analyzed, including (i) a Rankine cycle, (ii) a gas turbine simple cycle, and (iii) a gas-steam combined cycle. These configurations have been investigated with the additional feature of CO 2 capture and sequestration. The reference plant has been modeled according to state-of-the-art of commercial hydrogen plants: it includes a prereforming reactor, two shift reactors, and a pressure swing adsorption unit for hydrogen purification. The plant has a conversion efficiency of ∼ 75 % and produces 145,000 Sm 3 ∕ hr of hydrogen (equivalent to 435 MW on the lower-heating-volume basis) and 63 t ∕ hr of superheated steam. The proposed power plants generate, respectively, 22 MW (i), 36 MW (ii), and 87 MW (iii) without CO 2 capture. A sensitivity analysis was carried out to determine the optimum size for each configuration and to investigate the influence of some parameters, such as electricity, natural gas, and steam costs.

Low-calorific gases with a small portion of hydrogen are produced in various chemical processes, such as gasification of solid wastes or biomass. The aim of this study is to clarify the efficient usage of these gases in diesel engines used for power generation. Effects of amount and composition of low-calorific gases on diesel engine performance and exhaust emissions were experimentally investigated adding hydrogen-nitrogen mixtures into the intake gas of a single-cylinder direct-injection diesel engine. The results indicate that optimal usage of low-calorific gases improves N O x and Smoke emissions with remarkable saving in diesel fuel consumption.

In this paper, the thermodynamic potentialities and limits of the H 2 ∕ O 2 turbine cycles (afterward named only H 2 ∕ O 2 cycles) are investigated. Starting from the conventional gas turbine and steam turbine technology, the paper qualitatively tackles problems related to a change of oxidizer and fuel: from these considerations, an internal combustion steam cycle is analyzed where steam, injected into the combustion chamber together with oxygen and hydrogen, is produced in a regenerative way and plays the important role of inert. A proper parametric analysis is then performed in order to evaluate the influence of the main working parameters on the overall performance of H 2 ∕ O 2 cycles. All the results are carried out by neglecting the energy requirements for O 2 and H 2 production systems, but taking into account the work required by the O 2 and H 2 compression. This choice permits a great freedom in the definition of these thermodynamic cycles; moreover, it is possible to come to some general conclusions because the H 2 and/or O 2 production systems and their integrations with thermodynamic cycles do not have to be specified. Therefore, this paper can be framed in a context of centralized production of oxygen and hydrogen (by nuclear or renewable energy sources, for example) and their distribution as pure gases in the utilization place. By adopting some realistic assumptions, for example, a top temperature of 1350 ° C , the potentialities of H 2 ∕ O 2 cycles are very limited: the net efficiency attains a value of about 50%. Instead, by adopting futurist assumptions, for example, a top temperature of 1700 ° C , a different H 2 ∕ O 2 cycle scheme can be proposed and its performance becomes more interesting (the net efficiency is over 60%). The paper tackles the main thermodynamic and technological subjects of the H 2 ∕ O 2 cycles: for example, it is underlined how the choice of the working parameters of these cycles strongly influences the attainable performance.

The reliable prediction of the processes leading to autoignition during the rapid compression of an initially homogeneous mixture of fuel and air requires the coupled modeling of multidimensional fluid dynamics and heat transfer together with a sufficiently detailed description of the chemical kinetics of the oxidation reactions. To satisfy fully such requirements tends at present to be unmanageable. The paper describes an improvised approach that combines multidimensional fluid dynamics modeling (CFD KIVA-3) with derived variable effective global chemical kinetic data. These were generated through a fitting procedure of the corresponding results obtained while using a detailed chemical kinetic scheme; albeit with uniform properties, at constant volume and an initial state similar to that existing during the ignition delay. It is shown while using such an approach that spatially nonuniform properties develop rapidly within the initially homogeneous charge due to piston motion, heat transfer and any preignition energy release activity. This leads autoignition to take place first within the hottest region and a reaction front progresses at a finite rate to consume the rest of the mixture. The present contribution examines the compression ignition of hydrogen-oxygen mixtures in the presence of argon as a diluent. Validation of the predicted results is made using a range of corresponding experimental values obtained in a single-shot pneumatically driven rapid compression apparatus. It is to be shown that the simulation which indicates the build up of temperature gradients during the compression stroke, predicts earlier autoignition than that obtained with a single-zone simulation. Good agreement between predicted and experimental results is achieved, especially for lean and stoichiometric mixtures under high compression ratio conditions. The CFD-based simulation results are found to be closer to the corresponding experimental results than those obtained with an assumed reactive system of uniform properties and using detailed reaction kinetics.

To understand the occurrence of backfire in hydrogen fueled engines using an external (inducted) fuel supply, a fundamental study was completed using a modified experimental engine. A relation was found between the crevice volume in the combustion chamber and the occurrence of backfire. The results showed that the crevice around the spark plug electrode was not a major cause of backfire, but the combustion state of the mixture in the piston top land crevice, second land, and ring groove did have a direct affect on backfire occurrence. By increasing the top land crevice volume and the amount of blow-by gas, the equivalence ratio before backfire occurred was extended.

The Laboratory of Transport Technology (Ghent University) converted a GM/Crusader V-8 engine for hydrogen use. The engine is intended for the propulsion of a midsize hydrogen city bus for public demonstration. For a complete control of the combustion process and to increase the resistance to backfire (explosion of the air–fuel mixture in the intake manifold), a sequential timed multipoint injection of hydrogen and an electronic management system is chosen. The results as a function of the engine parameters (ignition timing, injection timing and duration, injection pressure) are given. Special focus is given to topics related to the use of hydrogen as a fuel: ignition characteristics (importance of electrode distance), quality of the lubricating oil (crankcase gases with high contents of hydrogen), oxygen sensors (very lean operating conditions), and noise reduction (configuration and length of intake pipes). The advantages and disadvantages of a power regulation only by the air-to-fuel ratio (as for diesel engines) against a throttle regulation (normal gasoline or gas regulation) are examined. Finally, the goals of the development of the engine are reached: power output of 90 kW, torque of 300 Nm, extremely low emission levels, and backfire-safe operation.