A feasibility analysis of hydrogen delivery system using liquid organic hydrides

The paper discusses the techno-economic feasibility of a hydrogen storage and delivery system using liquid organic hydrides (LOH). Wherein, LOH (particularly cycloalkanes) are used for transporting the hydrogen in chemical bonded form at ambient temperature and pressure. The hydrogen is delivered through a catalytic dehydrogenation process. The aromatics formed in the process are used for carrying more hydrogen by a subsequent hydrogenation reaction. Cost economics were performed on a system which produces 10 kg/h of hydrogen using methylcyclohexane as a carrier. With proprietary catalysts we have demonstrated the possibility of hydrogen storage of 6.8 wt% and 60 kg/m³ of hydrogen on volume basis. The energy balance calculation reveals the ratio of energy transported to energy consumed is about 3.9. Moreover, total carbon footprint calculation for the process of hydrogen delivery including transportation of LOH is also reported. The process can facilitate a saving of 345 tons/year of carbon dioxide emissions per delivery station by replacing gasoline with hydrogen for passenger cars. There is an immense techno-economic potential for the process.     

A prototype truck powered by hydrogen from organic liquid hydrides

A prototype truck (17 tons, 6 cylinders, 150 kW(mech), ‘SAURER’) has been constructed to use a hydrogen-burning engine with H₂ injection under 10 bar pressure. The efficiency of the engine is ca 32%, the exhaust gas temperature ca 700°C and the power ca 150 kW(mech). The hydrogen (10 bar) is produced continuously by means of catalytic splitting of methylcyclohexane on board the truck.The reaction occurs under the following conditions: 10 bar pressure, 400°C, catalyst 0.25% Pt, 0.25% Re on alumina with an efficiency of ca 0.80 and a lifetime of several hundred hours, without hydrogen recycling. The approximate economics of the system, assuming ca 2 US¢ kWh^?1 (electric), results in ca 35 US¢ per litre of gasoline equivalent.     

A hydrogen-powered mass transit system

Hydrogen's application to mass transit systems is considered. A 21-passenger bus is converted to hydrogen using a Dodge engine which has been modified for high compression operation. Backfiring and nitric oxide pollution formation are controlled by a water injection technique. Hydrogen fuel storage for the experimental prototype is accomplished by two metal hydride containers using an iron-titanium alloy. Data are presented regarding equipment conversion and design, energy resource utilization, economics, and safety.     

Economic analysis of the seasonal storage of electricity with liquid organic hydrides

A future alternative for generating winter electricity is the seasonal storage of surplus summer electricity in the form of chemically bound hydrogen in liquid organic hydrocarbons using the MTH-system (Methylcyclohexane–Toluene–Hydrogen). This paper compares the economics of the MTH-system with the conventional production of electricity from fossil fuel sources.

Based on numerical modelling of the individual plants, simulations of several design alternatives of the MTH-system were performed for 1000 GWh of stored summer electricity and 80 MW output. The overall efficiencies η_tot and the economic results of these simulations are η_tot=0.40 and 0.26 $/kWh for the MTH-SOFC system alternative, η_tot=0.33 and 0.30 $/kWh for the MTH-MCFC and η_tot=0.25 and 0.36 $/kWh for the MTH-system with gas and steam turbines.

Compared with the cost of electricity production using fossil fuels (0.05–0.1 $/kWh), the electricity produced by the MTH-system is expensive. Therefore an economic comparison including an assumed carbon tax was made to account for a possible scarcity of energy or the environmental impact due to the use of fossil energy resources. It concludes that the MTH-system is not competitive for the levels of carbon tax under discussion, but compares with options for providing electricity from new renewables.

Due to the disparities in economics and carbon taxes, a best case study of the MTH-system was made to reduce its economic disadvantages. This results in a maximum efficiency of the MTH-system of 0.48 with corresponding winter electricity costs of 0.17 $/kWh.     

Carbon supports for the catalytic dehydrogenation of liquid organic hydrides as hydrogen storage and delivery system

The use of liquid organic hydrides as hydrogen carriers is a promising storage and delivery system due to the advantages of using liquid-based infrastructures and its economic feasibility compared to other conventional systems. The reversible dehydrogenation/hydrogenation of liquid organic hydrides is a key point for the development of highly performance reactors. In this study different carbon materials have been investigated as platinum supports, including carbon nanofibers, carbon black, carbon xerogel, activated carbon and ordered mesoporous carbon. To individuate the effect of the carbon support on the catalytic activity, platinum particles were synthesized by a microemulsion procedure. The analysis of the hydrogen evolution curves indicate that the support BET surface area plays a very important role on the initial catalytic activity, obtaining a maximum rate of 220 mmol g_Pt⁻¹ min⁻¹ when using an ordered mesoporous carbon with a surface area of 930 m² g⁻¹. Nevertheless, the analysis of catalytic activity at prolonged duration indicates a better behavior toward deactivation for supports characterized by wide pores and low graphitization degree like carbon black or carbon xerogel, despite their lower initial dehydrogenation rate (100–140 mmol g_Pt⁻¹ min⁻¹). The ultimate use in the dehydrogenation reactor as well as the operation conditions will define the best catalyst structure from the point of view of the carbon support.     

Hydrogen delivery through liquid organic hydrides: Considerations for a potential technology

Carrying hydrogen in chemically bounded form as cycloalkanes and recovery of hydrogen via a subsequent dehydrogenation reaction is a potential option for hydrogen transport and delivery. We have earlier reported a novel method for transportation and delivery of hydrogen through liquid organic hydrides (LOH) such as cycloalkanes. The candidate cycloalkanes including cyclohexane, methylcyclohexane, decalin etc. contains 6 to 8 wt% hydrogen with volume basis capacity of hydrogen storage of 60–62 kg/m³. In view of several advantages of the system such as transportation by present infrastructure of lorries, no specific temperature pressure requirement and recyclable reactants/products, the LOH definitely pose for a potential technology for hydrogen delivery. A considerable development is reported in this field regarding various aspects of the catalytic dehydrogenation of the cycloalkanes for activity, selectivity and stability. We have earlier reported an account of development in chemical hydrides. This article reports a state-of-art in LOH as hydrogen carrier related to dehydrogenation catalysts, supports, reactors, kinetics, thermodynamic aspects, potential demand of technology in field, patent literature etc.     

A novel batch-type hydrogen transmitting system using metal hydrides

In the case of transporting hydrogen by means of metal hydrides, a key problem is to reduce the weight of the portable container filled with metal hydrides. The paper describes a novel batch-type hydrogen transmitting system characterized by a portable light container filled with metal hydrides, which is not pressure-proof but only mechanically durable. Hydriding is performed by setting the portable light container in a fixed pressure-proof vessel and admitting hydrogen and nitrogen inside and outside the portable container, respectively, while adjusting the pressure difference between both gases to be zero. Using this system, 2.9 Nm³ of hydrogen can be stored in 14.3 kg of the total mass of the solid constituents including 3.5 kg of Mg-10% Ni alloy. The portable container contains twice as much hydrogen per unit weight and volume as a conventional compressed gas cylinder. Due to the advanced design of this portable container, the optimum hydrogen content could be around 5 wt % based upon the total mass of the container.     

A 70 MPa hydrogen-compression system using metal hydrides

The objective of this work was to develop a 70 MPa hydride-based hydrogen compression system. Two-stage compression was adopted with AB₂ type alloys as the compression alloys. Ti_0.95Zr_0.05Cr_0.8Mn_0.8V_0.2Ni_0.2 and Ti_0.8Zr_0.2Cr_0.95Fe_0.95V_0.1 alloys were developed for the compression system. With these two alloys, a 70 MPa two-stage hydride-based hydrogen compression system was designed and built with hot oil as the heat source, and composite materials formed by mixing hydrogen storage alloys with Al fiber were used to prevent hydride bed compaction and to prevent strain accumulation. The experimental results showed that Ti_0.95Zr_0.05Cr_0.8Mn_0.8V_0.2Ni_0.2 and Ti_0.8Zr_0.2Cr_0.95Fe_0.95V_0.1 alloys could well meet the requirements of compression system. Composite materials formed by mixing hydrogen storage alloys with Al fiber were an effective way to prevent strain accumulation for hydride compression. With cold oil (298 K) and hot oil (423 K) as the cooling and heating sources, the built compression system could convert hydrogen pressure from around 4.0 MPa to over 70 MPa.     

Conversion and testing of hydrogen-powered post office vehicle

A hydrogen-fueled post office jeep has been retrofitted for operation on hydrogen by the installation of a modified propane carburetor and by installation of an iron-titanium hydride storage vessel. The jeep was operated in the mail delivery system of the Independence, Missouri Post Office. Comparative data have been obtained by operating the jeep in tandem with a gasoline-fueled vehicle. Careful observation of fuel consumption for the two vehicles was closely monitored. Throughout the project, fuel consumption of the hydrogen vehicle was significantly less than the consumption of the gasoline version.     

Assessing customer preferences for hydrogen-powered street sweepers: A choice experiment

The large variety of potential hydrogen and fuel cell applications and the associated uncertainties of selecting a particular application pose a challenge for developers in the field: identifying and evaluating promising market niches. Therefore, we conducted an online survey comprising a choice experiment in Switzerland and Germany to assess fleet decision-makers’ preferences for hydrogen-powered street sweepers compared to (more) conventional diesel and compressed natural gas (CNG)/biogas vehicles. The findings indicate that the fleet decision-making structures and vehicle operating practices make street sweeper fleets a promising application for the early implementation of hydrogen fuel cell vehicles. Furthermore, the results show that a market niche for hydrogen-powered sweepers exists in both countries. The choice experiment was a useful approach for the identification of promising market niches and thereby reduces the uncertainties of application selection.     

Assessment of system variations for hydrogen transport by liquid organic hydrogen carriers

One option to transport hydrogen over longer distances in the future is via Liquid Organic Hydrogen Carriers (LOHC). They can store 6.2 wt% hydrogen by hydrogenation. The most promising LOHCs are toluene and dibenzyltoluene. However, for the dehydrogenation of the LOHCs – to release the hydrogen again – temperatures above 300 °C are needed, leading to a high energy demand. Therefore, a Life Cycle Assessment (LCA) and Life Cycle Costing are conducted. Both assessments concentrate on the whole life cycle rather than just direct emissions and investments. In total five different systems are analysed with the major comparison between conventional transport of hydrogen in a liquefied state of matter and LOHCs. Variations include electricity supply for liquefaction, heat supply for dehydrogenation and the actual LOHC compound. The results show that from an economic point of view transport via LOHCs is favourable while from an environmental point of view transport of liquid hydrogen is favourable.     

The development of a lean-burning carburettor for a hydrogen-powered vehicle

A simple lean-burning hydrogen carburettor system was developed and shown to be practical and no more complex than a normal throttled LPG-type carburettor. A beam LPG carburettor formed the basis of the hardware. The basic mechanism used to achieve the quality-controlled mixture delivery was to connect the pedal control to the valve which is normally used only for presetting the mixture strength and to deactivate the butterfly valve in the range down to an equivalence ratio of 0.25. The system was laboratory flow tested to ensure the correct characteristics. The engine requirements of optimum spark advance were measured and a mixture control, spark advance and throttle (i.e. mixture) control-linkage designed. After adjustment the vehicle was found to be slightly more driveable in the quality-controlled mode than in the normal quantity control mode and also showed a slightly better fuel consumption on an urban-type route. There was also reduced backflashing since the engine spends less time at stoichiometric.     

7-ethylindole: A new efficient liquid organic hydrogen carrier with fast kinetics

We report a discovery of a new member of the liquid organic hydrogen carrier (LOHC) family, 7-ethylindole (7-EID), with a low melting point of ?14 °C and a decent hydrogen content of 5.23 wt%. Hydrogenation of the compound was carried out over a commercial 5 wt% Ru/Al₂O₃ catalyst in the H₂ pressure range of 5–8 MPa and a temperature range of 120–160 °C, respectively. It was found that the hydrogenation rate positively correlates with the reaction temperature. However, the rate was barely effected by the H₂ pressure if the pressure exceeds 6 MPa. The estimated apparent activation energy of 7-EID hydrogenation is 51.5 kJ/mol. The fully hydrogenated product, octahydro-7-ethylindole (8H-7-EID), was used as the reactant for the dehydrogenation reaction at 170–200 °C over a 5 wt% Pd/Al₂O₃ catalyst. Full dehydrogenation of 8H-7-EID to 7-EID can be achieved within 270 min at 190 °C. The apparent activation energy of 8H-7-EID dehydrogenation was calculated to be 101.9 kJ/mol at 170–200 °C. The liberated H₂ was found to be of high purity, which meets the requirement of proton exchange membrane fuel cells.     

沼气发酵液开发生产高效有机花卉液肥

沼气发酵液虽是一种优质有机肥，但直接应用存在两大问题：其一，沼气发酵液本身具有抑制和促进两方面作用，不仅表现为促进农作物和牲畜生长，防治病虫害的作用，同时也具有抑制作用；其二，虽然沼气发酵液内营养物质丰富，但含量总体偏低。根据花卉生长、发育和繁殖所需的营养，以沼气发酵液为基础，补充适量的营养物质，通过pH值的调整消除抑制因素，从而开发出具有商品价值的高效有机花卉液肥。     

Investigation of catalytic activity of hydrides in the desulphurisation reactions of liquid hydrocarbon fuels

The sulphur content of liquid hydrocarbon fuels is an important index if their quality. The hydrides of Ni-Zr alloys are prospective catalysts for oil-product hydrodesulphurisation. They allow a higher degree of fuel purification from sulphur and they increase the equipment productivity.Test samples of the catalysts capsulate contacts are received and a method is developed for this process. Their catalytic activity both using the example of the demercaptanization reaction and the extraction of total sulphur from the kerosene fraction is studied. The processes occurring on Ni-Zr alloys due to the interaction with hydrogen are investigated by electron microscopy.     

Carbide-based fuel system for undersea vehicles

In underwater applications such as unmanned undersea vehicle (UUV) propulsion, mass and volume constraints often dictate system energy density and specific energy, which are targeted to exceed 300 Wh L⁻¹ and 300 Wh kg⁻¹, respectively, in order to compete with state-of-the-art battery technologies. To address this need, a novel carbide-based fuel system (CFS) intended for use with a solid oxide fuel cell (SOFC) is under development that is capable of achieving these energy metrics as well as sequestering carbon dioxide. The proposed CFS uses calcium carbide and calcium hydride that react with water to generate acetylene and hydrogen as the fuel and calcium hydroxide as a carbon dioxide scrubber. The acetylene is hydrogenated to ethane and then reformed to syngas (carbon monoxide and hydrogen) before being utilized by the SOFC. Carbon dioxide effluent from the SOFC is reacted with the calcium hydroxide to produce a storable solid, calcium carbonate, thus eliminating gas evolution from the UUV. A system configuration is proposed and discussion follows concerning energy storage metrics, operational parameters and preliminary safety analysis.     

Energy System Selection for Small Underwater Vehicles

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A portable power-pack fueled by carbonsilane-based chemical hydrides

Carbonsilanes have recently been demonstrated as new hydrogen storage materials for polymer electrolyte membrane fuel cells and have exhibited fast hydrogen-release kinetics, even at room temperature, by methanolysis in the presence of sodium methoxide as a catalyst. By building on prior results, we have developed an efficient hydrogen generator fueled by one of these carbonsilanes, 1,3,5-trisilacyclohexane, in this study. The H₂-generator exhibited a hydrogen generation rate up to 1.2 slm as well as fast load-following capability, with the response time of hydrogen production being 20–30 seconds. The as-developed hydrogen generator and 100 W_e PEMFC have been integrated into a portable power-pack whose capability as an off-grid power source has been tested.