In this study we have developed a unique method for synthesizing very reactive water splitting materials that will remain stable at temperatures as high as 1450 °C to efficiently produce clean hydrogen from concentrated solar energy. The hydrogen production for a laboratory scale reactor using a “Thermo-mechanical Stabilized Porous Structure” (TSPS) is experimentally investigated for oxidation and thermal reduction temperatures of 1200 and 1450 °C, respectively. The stability and reactivity of a 10 g TSPS over many consecutive oxidation and thermal reduction cycles for different particle size ranges has been investigated. The novel thermo-mechanical stabilization exploits sintering and controls the geometry of the matrix of particles inside the structure in a favorable manner so that the chemical reactivity of the structure remains intact. The experimental results demonstrate that this structure yields peak hydrogen production rates of 1–2 cm 3 /(min.g Fe3O4 ) during the oxidation step at 1200 °C and the 30 minute thermal reduction step at 1450 ° C without noticeable degradation over many consecutive cycles. The hydrogen production rate is one of the highest yet reported in the open literature for thermochemical looping processes using thermal reduction. This novel process has strong potential for developing an enabling technology for efficient and commercially viable solar fuel production.

Petroleum refining industry in the United States is the largest in the world operating 148 refineries. These refineries contribute a major economic value to the U.S. market for providing the chemical industry with vital products. The economic gain, however, is challenged by the increasing competitiveness within the refining sector as well as the unpredictable oil prices. Furthermore, environmental obligations also have been recently advocating low emission rates that may entail additional operating costs to refineries. In this study, we analyze hydrogen production and utilization in the U.S. oil and gas industry to characterize its key role and trends in this energy-intensive industry. We referred to U.S. Department of Energy data and statistics of hydrogen production rates as well as we considered other elementary factors of refineries productivity such as; economics of crude oil, power consumption and chemical outputs. Considering the fact that hydrogen-dependent processes in refining count as a key element in oil refining; it is certainly that efficient production and implementation of hydrogen in processes such as hydro-cracking and hydro-desulfurization will result in cost saving opportunities for refineries. From this point of view, we highlight the economic and environmental advantages of solar cracking of natural gas as an alternative way of hydrogen production. Hydrogen production in refineries could possibly benefit from utilizing this alternative method on both local and global levels. Economically, this study explains how solar cracking could save about $62 million in hydrogen production for U.S. refineries. Even though the momentum of desulfurization acts are not yet strong in the U.S., major European refining investments are in jeopardy if not soon to utilize enhanced desulfurization facilities in response to demands of lower sulfur content of refined products. A comprehensive expenditures model is presented in this study to monitor primary areas of saving in hydrogen production from the early stages of establishing a hydrogen production plant. Further alternatives showing potential are also included as future considerations for the refinery sector.

A two-step thermochemical cycle for hydrogen production using mixed iron oxides coated on silicon carbide substrates has been investigated. The water-splitting step proceeds at temperatures between 800 and 1000 °C while for the regeneration step temperatures around 1200 °C are needed. A deactivation of the material resulting in a decrease of the hydrogen production within the first couple of cycles was observed in preceding tests. For detailed investigations of the system composed of the redox-material and the substrate small scale samples were tested in a laboratory test-rig. For identification of material changes the samples were investigated via XRD and SEM-EDS analysis. The analysis revealed the reasons for the deactivation of the redox-material. Through parametric studies the influence of the regeneration parameters, namely regeneration temperature and time on the hydrogen production was analysed. A model for the regeneration step was developed describing the performance of the regeneration step as a function of temperature and time and additionally as a function of total regeneration time, i.e. the cumulated time the sample has been regenerated.

With the increasing concern of CO 2 emissions and climate change, efforts have grown to include solar technologies in chemical processes to manufacture products that can be used both as a commodity and as a fuel, such as hydrogen. This study focuses on a technique, referred to as “solar cracking” of natural gas for the co-production of hydrogen and carbon as byproduct with zero emission footprint via the following reaction: CH 4 →C(s) + 2H 2 (g). However, some portion of the incoming solar energy absorbed by the cavity greatly exceeds the surface absorption of the inner walls because of multiple internal reflections. Studies have shown that by seeding the reactor with micron-sized carbon particles, methane conversion improves drastically due to the radiation absorbed by the carbon particles and additional nucleation sites formed by carbon particles for heterogeneous decomposition reaction. This can maintain more heat at the core and can reduce the carbon deposits on the reactor walls. Present study numerically tries to investigate the above fact by tracking carbon particles in a Lagrangian frame-work. Initially, the numerical model is validated qualitatively by comparing the particle deposition on reactor window with the experimental observations. Effect of particle loading, particle emissivity, injection point location, and effect of using different window screening gases on a flow and temperature distribution inside a confined tornado flow reactor are studied. It is observed that the methane conversion substantially increases by particle seeding. The results of this research can be used in thermo-chemical reactor design.

COP15, Copenhagen, December 09, failed partly for lack of a credible, comprehensive vision for how we may, and must soon, “run the world on renewables”. We cannot, and should not try to, accomplish this entirely with electricity transmission. The world’s richest renewable energy (RE) resources — of large geographic extent and high intensity — are stranded: far from end-users with inadequate or nonexistent gathering and transmission systems to deliver the energy. Electricity energy storage cannot affordably firm large, intermittent renewables at annual scale, while gaseous hydrogen (GH2) and anhydrous ammonia (NH 3 ) fuels can: GH2 in large solution-mined salt caverns, NH 3 in surface tanks, interconnected via underground pipelines in RE systems for gathering, transmission, distribution, and end use. Thus, we need to think beyond electricity as we plan new “transmission” systems for bringing large, stranded RE resources to distant markets as annually-firm C-free energy, to empower subsequent efforts to COP15. Recent press has extolled the global RE vision, but without adequate attention to the diverse transmission and storage systems required for achievement. [21] At GW scale, renewable-source electricity from diverse sources can be converted to hydrogen and byproduct oxygen, and/or to NH 3 , pipelined underground to load centers for use as vehicle fuel and combined-heat-and-power generation on the wholesale or retail side of the customers’ meters. The ICE, CT, and fuel cell operate very efficiently on GH2 and NH 3 fuels. USA has extensive extant NH 3 pipeline and tank storage infrastructure.

This paper presents a thermo-economic assessment of three different hydrogen production processes using fossil fuels as feedstock. First, the paper provides process-step level energy and cost analysis for the solar reforming of natural gas. The same analysis is given for the solar cracking of natural gas. The results are compared with the thermo-economic process-step analysis of the steam reforming process. Based on the benchmark results, the paper discusses these three processes with respect to their economic viability. The data for the analysis is collected from literature, various vendors, and personal communications with people from industry and universities. The results are presented for unit hydrogen production by each technique and compared with the market price for hydrogen. An energy balance around each process-step is made to reveal the energy intensity of each process. Although the results show that the steam reforming of methane is still the most economical pathway for hydrogen production, it is only valid when the sequestration, storage, and transportation of hazardous emissions are not taken into account. Finally, this paper provides some ideas for the improvement of the most environmentally friendly hydrogen production technique; the solar cracking of natural gas.

In this work, we present a thorough reaction engineering analysis on the modeling of a vortex-flow reactor to show that commonly practiced one-plug reactor approach is not sufficient to explain the flow behavior inside the reactor. Our study shows that N-plug flow reactors in series is the best approach in predicting the flow dynamics based on the computational fluid dynamics (CFD) simulations. We have studied the residence time distribution using CFD by two different methods. The residence time distribution characteristics are calculated by approximating the real reactor as N-ideal reactors in series, and then estimated the number of ideal reactors in series for the model. We have validated our CFD model by comparing the simulation results with experimental results. Finally, we have done a parametric study with a different sweeping gas to identify the best screening gas to avoid carbon deposition inside the vortex-flow reactor. Our results have shown that hydrogen is a better screening gas than argon.

This research presents an approach for modeling and control of a hydrogen production plant based in steam reforming of methane (SRM). Many studies in the literature have established some important hydrogen production plant information related to sizing and optimization. This research shows a dynamic model integrated with an industrial control system, which will be able to represent the unified plant data for process variables (temperature, pressure, size, etc.). The plant was optimized using surface response methodology (SRM) to approach a maximum value of hydrogen and a minimum carbon monoxide concentration. The dynamic plant model exhibited high interactions and nonlinear behavior. Hence, a Model predictive control (MPC) strategy was design for the dynamic case, with very good results due to its centralized control structure. Steady-state and dynamic simulations were developed using HYSYS 2006.

The transient thermal behavior of two solar receiver-reactors for hydrogen production has been modeled using Modelica/Dymola. The simulated reactors are dedicated to carry out the same chemical reactions but represent two different development stages of the project HYDROSOL and two different orders of magnitude concerning reactor size and hydrogen production capacity. The process itself is a two step thermochemical cycle, which uses mixed iron-oxides as a redox-system. The iron-oxide is coated on a ceramic substrate, which is placed inside the receiver-reactor and serves on the one hand as an absorber for solar radiation and on the other hand as the reaction zone for the chemical reaction. The process consists of a water splitting step in which hydrogen is produced and a regeneration step during which the used redox-material is being reduced. The reactor is operated between these two reaction conditions in regular intervals with alternating temperature levels of about 800 °C for the water splitting step and 1200 °C for the regeneration step. Because of this highly dynamic process and because of fluctuating solar radiation during the day, a mathematical tool was necessary to model the transient behavior of the reactor for theoretical studies. Two models have been developed for two existing receiver-reactors. One model has been set up to simulate the behavior of a small scale test reactor, which has been built and tested at the solar furnace of DLR in Cologne. Results are very promising and show that the model is able to reflect the thermal behavior of the reactor. Another model has been developed for a 100 kW th pilot reactor which was set up at the Plataforma Solar de Almeri´a in Spain. This model is based on the first model but special geometrical features had to be adapted. With this model temperatures and hydrogen production rates could be predicted.

Biomass gasification process is simulated in order to determine the influence of the operating parameters on the quality of the gas produced. Furthermore, the hydrogen required to enrich the syngas is also established. The modeling and simulation showed that the gas obtained by gasification at atmospheric pressure is mainly composed of H 2 and CO; however, the molar ratio H 2 /CO is not favorable for synthesizing fuels such as methanol. This shows the need to enrich the syngas with additional hydrogen. For the case study developed, for each 100 kg / hr of biomass waste gasified, the amount of additional hydrogen required ranges between 2 to 6 kg / hr in order to obtain a molar ratio H 2 /CO close to 2. Using palm fiber, the amount of hydrogen required would be 4 kg / hr. This additional hydrogen could be derived from solar energy using thermoelectric modules with an effective area of solar radiation close to 400 m 2 per kg of biomass. The simulation was performed using ASPEN PLUS ®.

Process conditions for the direct solar decomposition of sulfur trioxide have been investigated and optimised by using a receiver-reactor in a solar furnace. This decomposition reaction is a key step to couple concentrated solar radiation or solar high temperature heat into promising sulfur based thermochemical cycles for solar production of hydrogen from water. After proof-of-principle a modified design of the reactor was applied. A separated chamber for the evaporation of the sulfuric acid, which is the precursor of sulfur trioxide in the mentioned thermochemical cycles, a higher mass flow of reactants, an independent control and optimisation of the decomposition reactor were possible. Higher mass flows of the reactants improve the reactor efficiency because energy losses are almost independent of the mass flow due to the predominant contribution of re-radiation losses. The influence of absorber temperature, mass flow, reactant initial concentration, acid concentration, and residence time on sulfur trioxide conversion and reactor efficiency have been investigated systematically. The experimental investigations was accompanied by energy balancing of the reactor for typical operational points. The absorber temperature turned out to be most important parameter with respect to both conversion and efficiency. When the reactor was applied for solar sulfur trioxide decomposition only, reactor efficiencies of up to 40% were achieved at average absorber temperature well below 1000 °C. High conversions almost up to the maximum achievable conversion determined by thermodynamic equilibrium were achieved. As the reradiation of the absorber is the main contribution to energy losses of the reactor a cavity design is predicted to be the preferable way to further raise the efficiency.

This paper gives a representative energy process-step model of hydrogen production in the U.S. Chemical Industry based on federal data. There have been prior efforts to create energy process-step models for other industries. However, among all manufacturing industries, creating energy flow models for the U.S. Chemical Industry is the most challenging one due to the complexity of this industry. This paper gives concise comparison of earlier studies and provides thorough description of the methodology to develop energy process-step model for hydrogen production in the U.S. Chemical Industry. Results of the energy process-step model of hydrogen production in the U.S. Chemical Industry show that steam allocations among the end-uses are: 68% to process cooling (steam injection to product combustion gases), 25% to process heating, and 7% to other process use (CO 2 converter). The model also shows that the major energy consuming step in hydrogen production is the reformer, which consumes approximately 16 PJ fuel. During the course of this study, the most recent U.S. federal energy database available was for the year 1998. Currently, the most recent available U.S. federal energy database is given for the year 2002 based on the data collected from 15,500 establishments.

In this paper, the potential benefits and technical advantages of using ammonia as a green fuel for transportation are analyzed based on performance indicators including the system effectiveness, the driving range, fuel tank compactness, and the cost of driving per km. Similar to hydrogen, ammonia is a synthetic product that can be obtained thermally, physically, chemically or biologically either from fossil fuels, biomass, or other renewable sources and can be used as a clean fuel. The refrigeration effect of ammonia is another advantage of it and is included in the efficiency calculations. The cooling power represents about 7–10% from the engine power, being thus a valuable side benefit of ammonia’s presence on-board. If the cooling effect is taken into consideration, the system’s effectiveness can be improved by about 20%. It is shown that if a medium size hydrogen car converted to NH 3 , it becomes more cost effective per driving range as low as CN$3.2/100 km.

The aim of this work is to reduce the refueling time of a metal hydride storage tank by improving its design, taking in account the total volumetric and mass capacity of the tank. A heat and mass transfer model is proposed and solved to obtain the charging curve for 1 kg hydrogen in a LaNi 5 reference storage tank. Compared to gas transport and reaction kinetics, heat transfer is found to limit the hydrogen charging dynamics of the storage tank. To improve the refueling time, it is found to be necessary to increase first of all the heat transfer inside the metal hydride bed, and subsequently the heat transfer from the metal hydride bed to the cooling fluid. Technical solutions such as the implementation of aluminum foam and/or internal heat exchanger tubes are investigated. By combining both solutions, the refueling time can be reduced from 400 minutes (reference tank) to 15 minutes. The tank volume still meets the DOE targets, but its mass remains a problem. Therefore, new materials with improved gravimetric capacity have to be developed. With this work it is now possible to improve the tank design for newly developed storage materials and to evaluate their potential for technical applications.

UT-3 thermochemical hydrogen production cycle has been studied, both theoretically and experimentally, and is one of the very few cycles studied on a pilot plant scale. The maximum operating temperature in this cycle is relatively lower than the temperatures in other cycles. Another advantage of this cycle is that it is comprised of four gas-solid reactions which simplify product separation. Although the cycle has several such advantages, one of the significant issues is the development of solid reactants that are chemically reactive and physically stable in cyclic operations between oxide and bromide forms, which have considerably different molar volumes. Acceleration of reaction rate as well as longer cyclic life time and durability of the solid reactant are important keys for the practicability of the cycle. Additionally, a simpler preparation step of the reactant is preferable. Therefore, in order to increase the surface area of the calcium oxide reactant and maintain reactivity as well as structure in cyclic transformations, porous calcium oxide films have been examined as candidates. The calcium oxide precursor was prepared by sol-gel chemistry following a metal alkoxide process and the film was fabricated by a dip coating procedure. The characterization of the calcium oxide film such as the structural changes in the film and compositional conversions due to the bromination reaction has been performed using SEM and EDS. Based on a preliminary experimental analysis as well as the advantages of a film type reactant, one can conclude that the calcium oxide film may be a feasible alternative to a pellet-type reactant.

This paper deals with an exergetic performance analysis of a gas turbine cycle integrated with SOFCs with internal reforming. As the efficiency of a gas turbine cycle is mainly defined by the maximum temperature at the turbine inlet, this temperature is fixed at 1573 K for the analysis. In the cycle considered, the high-temperature gaseous flow from the turbine heats the input flows of natural gas and air, and is used to generate pressurized steam which is mixed with natural gas at the SOFC stack inlet to facilitate its conversion. The application of SOFCs provides the opportunity to reduce the exergy losses of the most irreversible process in the system: fuel combustion. Depending on the SOFC stack efficiency, the energy efficiency of the combined cycle reaches 70–80% which compares well to the efficiencies of 54–55% typical of conventional combined power generation cycles. Parametric studies are also undertaken to investigate how energy and exergy efficiencies of the integrated system change with variations in operating conditions. An increase in the efficiency of SOFCs is attained by increasing the fuel cell active area. Achieving the highest efficiency of the SOFC stack leads to a significant and non-proportional increase in the stack size and cost, and simultaneously to a decrease in steam generation, reducing the steam/methane ratio at the anode inlet and increasing the possibility of catalyst coking. Accounting for these factors, likely operating conditions of the SOFC stack in combination with a gas turbine cycle are presented.