Combined pre-reforming-desulfurization of high-sulfur fuels for distributed hydrogen applications

A major challenge facing the future Hydrogen Economy is the issue of hydrogen fuel delivery and distribution. In the near term, it may be necessary to deliver high-density hydrocarbon fuels (e.g., diesel fuel) directly to the end-user (e.g., a fueling station) wherein it is reformed to hydrogen, on demand. This approach has the advantages of utilizing the existing fuel delivery infrastructure, and the fact that more energy can be delivered per trip when the tanker is filled with diesel instead of liquefied or compressed hydrogen gas. Reforming high-sulfur hydrocarbon fuels (e.g., diesel, JP-8, etc.) is particularly challenging due to rapid deactivation of conventional reforming catalysts by sulfurous compounds. A new on-demand hydrogen production technology for distributed hydrogen production is reported. In this process, first, the diesel fuel is catalytically pre-reformed to shorter chain hydrocarbons (C₁-C₆) before being fed to the steam reformer, where it is converted to syngas and further to high-purity hydrogen gas. In the pre-reformer, most sulfurous species present in the fuel are converted to H₂S. Desulfurization of the pre-reformate gas is carried out in a special regenerative redox system, which includes an iron-based scrubber coupled with an electrolyzer. The integrated pre-reformer and sulfur-scrubbing unit operated successfully for 100 h at desulfurization efficiency of greater than 95%.     

Large-Scale Hydrogen Production

There is a growing need for hydrogen in processing heavier and dirtier fossil fuels and a future hydrogen economy is widely suggested as the next generation fuel/energy source once fossil fuels diminish in availability. Sustainable fuels are still regarded as too expensive given the large amounts of natural gas and a projected, ample supply of fossil fuels beyond the next twenty-plus years. Today, the steam reforming of hydrocarbons is the most favorable route to H₂. If CO₂ sequestration were ever to become widely practiced, fossil fuels would continue to play an important role in the future hydrogen economy.     

Biohydrogen Production from Organic Waste – A Review

Hydrogen fuel is a promising alternative to fossil fuels because of its energy content, clean nature, and fuel efficiency. However, it is not readily available. Most current producion processes are very energy intensive and emit carbon dioxide. Therefore, this article reviews technological options for hydrogen production that are eco-friendly and generate clean hydrogen fuel. Biological methods, such different fermentation processes and photolysis are discussed together with the required substrates and the process efficiency.     

Recent progress in hydrogenase and its biotechnological application for viable hydrogen technology

Despite increasing interest in hydrogen (H₂) as an alternative energy carrier, the current production of H₂ still depends on fossil fuels. Biotechnological hydrogen production can provide a more sustainable way to generate H₂. Hydrogenases are key enzymes involved in hydrogen metabolism of microorganisms with roles of H₂ oxidation or evolution. They have potential applications in H₂ production in vivo, in vitro and fuel cell. Important achievements have been made over the past decade in our understanding of hydrogenase and its biotechnological application as catalyst for H₂ production and fuel cell. This review summarizes recent progress in the study of hydrogenases, involving strategies for biosynthesis, maturation process, isolation of novel hydrogenases, heterologous expression system, structural feature of oxygen (O₂)-tolerant hydrogenases, and biotechnological applications for viable H₂ technology.     

制氢技术现状及展望

矿物燃料制氢是主要的制氢方法，其中以天然气蒸汽转化制氢的成本最低。重油部分氧化和煤气化曾经是制氢的重要方法，由于生产成本较高其发展有所减缓。这三种制氢过程制得合成气后还要经过变换完成进一步制氢，最后脱除CO2得到较纯的氢气，过程复杂。随着燃料电池的商业化进程的日益加快，低成本的、不含或少含CO的制氢技术受到广泛关注，其中铁蒸汽法和甲烷催化裂解法制得的氢气不含CO和CO2，过程得到简化。显然，矿物燃料制氢要向大气排放大量的温室气体，对环境不利。水电解制氢是较理想的制氢方法，不产生温室气体，但生产成本较高。因此水电解制氢适合电力资源如水电、风能、地热能、潮汐能以及核能比较丰富的地区。其他制氢技术如热化学制氢、太阳能制氢、生物质制氢以及等离子体制氢也在开发之中，相信是矿物燃料制氢与水电解制氢的有效补充。     

Recent applications of carbon nanotubes in hydrogen production and storage

Hydrogen is actually of great interest because it is the cleanest, sustainable and renewable energy carrier with a significantly reduced impact on the environment. In the future, hydrogen energy systems are expected to progressively replace the existing fossil fuels. Although hydrogen possesses significant advantages, it also exhibits major drawbacks in its utilization. The most important of them are production costs and storage characteristics. Carbon nanotubes (CNTs) have proven to possess ability as support for the fabrication of efficient heterogeneous catalysts in hydrogen production processes. Moreover, CNTs represent convenient adsorbent material that could form the basis of technologically viable hydrogen storage systems. This paper gives an overview of technologies used in the carbon nanotubes production and in the production and storage of hydrogen. In particular, it investigates the feasibility of CNTs and CNTs based catalyst materials in the mentioned processes. Our purpose is to overview the challenges of hydrogen production and storage technologies based on CNTs, to discuss and compare the different results published, and to emphasize recently developed modifications of CNTs that show potential to enhance hydrogen production and storage.     

Wind und Kohle: Die technische Photosynthese

The increasing energy demand, the associated CO₂ emissions, and the concurrently decreasing reserves of fossil fuels require new concepts for sustainable energy production. The so‐called Adam‐and‐Eve principle for CO₂‐free production of methanol from coal and nuclear energy is revisited and adapted to today's circumstances. Electrolysis of water using renewable electricity is applied for H₂ production. Simultaneously, coal and the oxygen formed during electrolysis are burned in an oxyfuel process, generating electricity and relatively pure CO₂. Hydrogen from electrolysis and CO₂ are converted to methanol, which can then be used as chemical‐ and energy feedstock.     

On-board plasma-assisted conversion of heavy hydrocarbons into synthesis gas

The fuel conversion performance of two gliding arc plasma reformers is investigated with the goal of syn-gas production on-board vehicles. In both systems, n-tetradecane (C₁₄H₃₀) fuel was reformed with plasma under partial oxidation conditions in the absence of metal catalysts and steam. A comparison of the performance of each device is made with regard to the hydrogen yield and energy conversion efficiency. The results show that gliding arc systems are capable of reforming heavy hydrocarbon fuels with high conversion efficiency and are an important piece of technology for on-board vehicular reforming systems that should be further developed and optimized.     

Combined Decarbonization of Electrical Energy Generation and Production of Synthetic Fuels by Renewable Energies and Fossil Fuels

Power generation from renewable energy sources and fossil fuels are integrated into one system. A combination of technologies in the form of a carbon capture utilization (CCU)-combined power station is proposed. The technology is based on energy generation from fossil fuels by a coal power plant with CO₂ recovery from exhaust gases, and pyrolysis of natural gas to hydrogen and carbon, completed by reverse water-gas shift for the conversion of CO₂ to CO, which will react with hydrogen in a Fischer-Tropsch synthesis for synthetic diesel. The carbon from the pyrolysis can replace other fossil carbon or can be sequestered. This technology offers significant CO₂ savings compared to the current state of technology and makes an environmentally friendly use of fossil fuels for electricity and fuel sectors possible.     

Hydrogen Supplied ICEs and Fuel Cells for Commercial Vehicles

In view of the limited availability of fossil fuels and the necessity to reduce the output of emissions of greenhouse gases in the long term, the transport sector needs efficient, environmentally compatible drive solutions. Hydrogen, as a clean and sustainable fuel, offers a high implementation potential and can be used both in internal combustion engines and in fuel cells. In urban deployment the fuel cell drive has specific advantages and is suitable for use in city buses. Integration of high‐power energy storage systems improves fuel consumption and can reduce the costs of the drive system. In May 2000 MAN presented its first fuel cell bus, which was successfully deployed in passenger transport in various cities. The next FC‐bus, using hybrid fuel cell propulsion, is planned under the framework of the Bavarian hydrogen project at Munich Airport and will be tested from spring 2004 on. The first deployment of pre‐series bus fleets with fuel cells using hydrogen as fuel can be expected from the end of this decade onwards.     

Möglichkeiten zur Wasserstoff-Erzeugung mit verminderter Kohlendioxid-Emission für zukünftige Energiesysteme

Hydrogen production possibilities for future energy systems with reduced carbon dioxide emission. All possible hydrogen production methods which are of technical importance or could become technically important have been systematically classified. The conventional processes based on fossil raw materials, as well as hydrogen production from biomass, are considered with a view to the separation of CO₂ or the minimization of CO₂ emission by using nuclear energy or solar energy, or by using electric energy generated from these primary energies. In addition, possibilities of hydrogen production with carbon separation are investigated. The nonfossil processes using thermal, electric or radiation energy are treated briefly, and water electrolysis is described in more detail. Finally, the hydrogenation of fossil raw materials is discussed, which would lead to mixed carbon-hydrogen energy systems.     

CO2 utilization in Eastern Canada: Sources,sites, and grid effects

Achieving net zero carbon dioxide (CO₂) emissions will require the cessation of fossil fuel emissions into the atmosphere, yet the need for ‘fuel’ and energy storage will remain. One solution could be a carbon-based fuel system where CO₂ of biogenic origin is converted to fuels using hydrogen generated by electrolysis powered by renewable energy sources. Methane has value as an initial target given its prevalence in biogas, use in home heating and in electricity generation. Sources of CO₂ in Eastern Canada are dominated by the iron and steel, cement, and aluminium industries, all of which have biogenic fuel options. Collecting all of the potentially biogenic CO₂ would displace 75% of current natural gas use and require a 50% increase in generating capacity. Initial efforts could site a carbon capture, utilization, and storage facility near Montreal, QC, with other large-scale facilities near Hamilton, ON, and Lac St-Jean, QC. These facilities would be grid connected and expected to operate ~6200 h annually. The most high-frequency electrolysis events would be 10 h of run time and 2 h of idle time. These periods would peak during the equinox months and be at a minimum during the winter solstice. These operational assumptions will all be subject to the increased variability caused by anthropogenic climate change and increased renewable generation on the grid. A closed-loop carbon-based fuel system would require an equivalent price of $250 per tonne CO₂.     

Adsorption of Off‐Gases from Steam Methane Reforming (H2, CO2, CH4, CO and N2) on Activated Carbon

Abstract

Hydrogen is the energy carrier of the future and could be employed in stationary sources for energy production. Commercial sources of hydrogen are actually operating employing the steam reforming of hydrocarbons, normally methane. Separation of hydrogen from other gases is performed by Pressure Swing Adsorption (PSA) units where recovery of high‐purity hydrogen does not exceed 80%.

In this work we report adsorption equilibrium and kinetics of five pure gases present in off‐gases from steam reforming of methane for hydrogen production (H₂, CO₂, CH₄, CO and N₂). Adsorption equilibrium data were collected in activated carbon at 303, 323, and 343 K between 0‐22 bar and was fitted to a Virial isotherm model. Carbon dioxide is the most adsorbed gas followed by methane, carbon monoxide, nitrogen, and hydrogen. This adsorbent is suitable for selective removal of CO₂ and CH₄. Diffusion of all the gases studied was controlled by micropore resistances. Binary (H₂‐CO₂) and ternary (H₂‐CO₂‐CH₄) breakthrough curves are also reported to describe the behavior of the mixtures in a fixed‐bed column. With the data reported it is possible to completely design a PSA unit for hydrogen purification from steam reforming natural gas in a wide range of pressures.     

Hydrogen Storage on Carbon-Based Adsorbents and Storage at Ambient Temperature by Hydrogen Spillover

Hydrogen storage is a crucially missing link to a future “hydrogen economy.” Extensive hydrogen storage studies have been focused on carbon-based adsorbents due to their light weight, high surface area, and tailorable structure. An overview/analysis of the progress on hydrogen storage on various carbon-based adsorbents is given in this review. Particularly, a recent, fast-developing research direction—hydrogen storage via spillover on carbons via added catalysts — is reviewed separately. A fundamental understanding of the factors that affect both H₂ and spillover hydrogen storage capacities, as well as strategies for improving the storage performance from the viewpoints of both hydrogen storage and materials chemistry, are discussed.     

A review on fermentative hydrogen production from dairy industry wastewater

Hydrogen (H₂) is one of the most promising alternative fuel sources for satisfying future energy demand, and fermentative hydrogen production is advantageous over other processes. In recent decades, considerable research has been conducted on H₂ production from carbohydrate‐rich materials since it is a cost‐effective approach and has the ability to generate intensive renewable energy from organic wastes. Dairy wastewater is a high volume industrial wastewater and with its immense carbohydrate content is an attractive candidate for sustainable fermentative H₂ production. The present paper provides comprehensive evaluation of recent reports on fermentative H₂ production from dairy wastewater. Important effective parameters and current bioreactor technologies for H₂ production from dairy wastewater are discussed. © 2014 Society of Chemical Industry     

Biohydrogen Production: Strategies to Improve Process Efficiency through Microbial Routes

The current fossil fuel-based generation of energy has led to large-scale industrial development. However, the reliance on fossil fuels leads to the significant depletion of natural resources of buried combustible geologic deposits and to negative effects on the global climate with emissions of greenhouse gases. Accordingly, enormous efforts are directed to transition from fossil fuels to nonpolluting and renewable energy sources. One potential alternative is biohydrogen (H₂), a clean energy carrier with high-energy yields; upon the combustion of H₂, H₂O is the only major by-product. In recent decades, the attractive and renewable characteristics of H₂ led us to develop a variety of biological routes for the production of H₂. Based on the mode of H₂ generation, the biological routes for H₂ production are categorized into four groups: photobiological fermentation, anaerobic fermentation, enzymatic and microbial electrolysis, and a combination of these processes. Thus, this review primarily focuses on the evaluation of the biological routes for the production of H₂. In particular, we assess the efficiency and feasibility of these bioprocesses with respect to the factors that affect operations, and we delineate the limitations. Additionally, alternative options such as bioaugmentation, multiple process integration, and microbial electrolysis to improve process efficiency are discussed to address industrial-level applications.     

Co-gasification of coal and wood in a dual fluidized bed gasifier

In the last decade the reduction of CO₂ emissions from fossil fuels became a worldwide topic. Co-gasification of coal and wood provides an opportunity to combine the advantages of the well-researched usage of fossil fuels such as coal with CO₂-neutral biomass. Gasification itself is a technology with many advantages. The producer gas can be used in many ways; for electric power generation in a gas engine or gas turbine, for Fischer-Tropsch synthesis of liquid fuels and also for production of gaseous products such as synthetic natural gas (bio SNG). Moreover, the use of the producer gas in fuel cells is under investigation. The mixture of coal and wood leads to the opportunity to choose the gas composition as best befits the desired process. Within this study the focus of investigation was of gasification of coal and wood in various ratios and the resulting changes in producer gas composition. Co-gasification of coal and wood leads to linear producer gas composition changes with linear changing load ratios (coal/wood). Hydrogen concentrations rise with increasing coal ratio, while CO concentrations decrease. Due to the lower sulfur and nitrogen content of wood, levels of the impurities NH₃ and H₂S in the producer gas fall with decreasing coal ratio. It is also shown that the majority of sulfur is released in the gasification zone and, therefore, no further cleaning of the flue gas is necessary. All mixture ratios, from 100 energy% to 0 energy% coal, performed well in the 100 kW dual fluidized bed gasifier. Although the gasifier was originally designed for wood, an addition of coal as fuel in industrial sized plants based on the same technology should pose no problems.     

Hydrogen production from liquid hydrocarbon fuels for PEMFC application

Lack of efficient hydrogen storage intermediate has boosted the development of fuel processor or economic onsite hydrogen production techniques for application to proton exchange membrane fuel cell promptly. Aiming to develop onsite hydrogen production techniques for proton exchange membrane fuel cell application using nickel-based reforming catalysts and stainless steel reactors, in this paper, a novel process for H₂ production from liquid hydrocarbon fuels was proposed and experimentally demonstrated on a lab scale. The main operations involved prereforming, autothermal reforming, high temperature water gas shift, low temperature water gas shift and H₂ enrichment by Pd membrane. The results indicated that prereforming introduction prior to autothermal reforming suppressed undesired gas phase reactions efficiently and made reforming reactions perform catalytically and smoothly, which was confirmed by a stable 500 h time-on-stream test of both prereforming and autothermal reforming catalysts. The air distributed feed applied in autothermal reforming reactor coupled the endothermic steam reforming and exothermic catalytic combustion reactions over the catalyst closely, maintaining an appropriate temperature distribution curve for autothermal reforming catalyst bed. During the process of H₂ enrichment by highly H₂ permeable Pd composite membrane, concentration polarization played an important role.     

Coal-derived methanol for hydrogen vehicles in China: Energy,environment, and economic analysis for distributed reforming

Hydrogen is considered an ideal energy carrier, but the storage and efficient delivery of hydrogen to vehicles still remain a challenging problem currently. This study analyzes the possibilities of using methanol as a hydrogen carrier in China, based on the distributed methanol reforming technology at forecourt refueling stations. A detailed well-to-tank life cycle analysis was applied to the hydrogen production from coal-derived methanol at refueling stations (onsite methanol pathway) from energy, environmental and economic performance aspects, followed by comparisons between the onsite pathway and conventional ones on the delivery cost of hydrogen, energy efficiency, and CO₂ emissions. The study shows that a coal-derived methanol pathway with distributed reforming utilities is well suited for China's specific energy situation, therefore it could play a key role in the transition process to a hydrogen economy in China.     

Thermodynamic analysis of glycerol dry reforming for hydrogen and synthesis gas production

A thermodynamic analysis of glycerol dry reforming has been performed by the Gibbs free energy minimization method as a function of CO₂ to glycerol ratio, temperature, and pressure. Hydrogen and synthesis gas can be produced by the glycerol dry reforming. The carbon neutral glycerol reforming with greenhouse gas CO₂ could convert CO₂ into synthesis gas or high value-added inner carbon. Atmospheric pressure is preferable for this system and glycerol conversion keeps 100%. Various of H₂/CO ratios can be generated from a flexible operational range. Optimized conditions for hydrogen production are temperatures over 975 K and CO₂ to glycerol ratios of 0-1. With a temperature of 1000 K and CO₂ to glycerol ratio of 1, the production of synthesis gas reaches a maximum, e.g., 6.4 mol of synthesis gas (H₂/CO = 1:1) can be produced per mole of glycerol with CO₂ conversion of 33%.