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 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.     

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.     

Seasonal storage of hydrogen in stationary systems with liquid organic hydrides

A comparison of energy storage media for carbon free systems was made on a cost and weight basis for application with renewable energy sources such as hydropower. On a seasonal timescale (summer to winter), storage of hydrogen in liquid organic hydrides was equivalent to other carbon free alternatives and superior to zero emission systems like batteries.Seasonal energy storage is illustrated by the methylcyclohexane-toluene-hydrogen (MTH) system. Low cost summer electricity is used for water electrolysis to yield hydrogen for hydrogenation of toluene. Dehydrogenation in winter gives hydrogen for heat and power generation by fuel cells with an estimated overall electrical efficiency of 41%. Recent laboratory results using commercial, dehydrogenation catalysts in fixed bed reactors show how catalyst efficiency was increased (low by-products) to reduce the carbon emissions to 0.01 kgC/kWh_e. Hydrogen separation membranes and new molecular reactions are being investigated to further increase efficiencies. Economic analyses show that the seasonal storage of hydroelectric power with hydrogen by the MTH system is economically competitive with new hydropower projects.     

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.     

Analysis of the seasonal energy storage of hydrogen in liquid organic hydrides

This analysis considers the techno-economic potential of the seasonal storage of electricity with chemically bound hydrogen in liquid organic hydrocarbons in the methylcyclohexane-toluene-hydrogen (MTH) system. It is shown that the efficiency of the electric power plant is the most important system parameter in the complete MTH system. The heat integration and efficiency of the re-electrification were estimated with energy and exergy analyses. A more accurate analysis by simulation and thermodynamic calculations of parts of the MTH system allows a considerable improvement in the cost estimation. Sensitivity analyses show the parameters which strongly influence the costs. From these analyses it follows that the costs of winter electricity amount to $0.23/kWh at a total efficiency of 0.39 for the overall system.     

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.     

Economic analysis of hydrogen-powered data center

The data center needs more and more electricity due to the explosive growth of IT servers and it could cause electricity power shortage and huge carbon emission. It is an attractive and promising solution to power the data center with hydrogen energy source. The present work aims to conduct an economic analysis on the hydrogen-powered data center. Configurations of hydrogen-powered and traditional data centers are compared and the differences focus on backup power system, converter/inverter, fuel cell subsystem, carbon emission, hydrogen and electricity consumptions. Economic analysis is conducted to evaluate the feasibility to power the data center with hydrogen energy source. Results show that electricity price increasing rate and hydrogen cost are the main factors to influence economic feasibility of hydrogen-powered data center. When the electricity price keeps constant in the coming two decades, the critical hydrogen price is about 2.8 U.S. dollar per kilogram. If the electricity price could increase 5% annually due to explosive growth of electric vehicles and economy, critical hydrogen price will become 6.4 U.S. dollar per kilogram. Hydrogen sources and transportation determine the hydrogen price together. Hydrogen production cost varies greatly with hydrogen sources and production technologies. Hydrogen transport cost is greatly influenced by distances and H₂ consumptions to consumers. It could be summarized that the hydrogen-powered data center is economic if hydrogen could be produced from natural gas or H₂-rich industrial waste streams in chemical plant and data center could not be built too far away from hydrogen sources. In addition, large-scale hydrogen-powered data center is more likely to be economic. Solar hydrogen powered data center has entered into a critical stage in the economic feasibility. Solar hydrogen production cost has restrained the H₂ utilization in data center power systems now, since it could be competitive only when more strict carbon emission regulation is employed, hydrogen production cost reduces greatly and electricity price is increasing greatly in the future. However, it could be expected solar hydrogen-powered system will be adopted as the power source of data centers in the next few years.     

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.     

Refueling equipment for liquid hydrogen vehicles

We are introducing a newly developed mobile filling station for liquid hydrogen for refuelling cars and buses. With a combined approval as a road tanker and as a filling station, it can be used for demonstration purposes at various places. Due to the employment of lately developed components like solenoid valves, couplings and steerings, the refuelling operation could be made safer and faster.     

On-board equipment for liquid hydrogen vehicles

The paper focuses on liquid hydrogen-powered vehicles such as passenger cars and buses. It describes recent solutions for the on-board storage and supply of the liquid fuel for different vehicles and driving systems, for example in internal combustion engines and fuel cells.In addition to optimized storage facilities and particular safety components, systems for improved pressure management and a new device supplying an engine with fuel at a constant low temperature are presented. Initial testing of these components is described.     

Characterization of metal hydrides for thermal applications in vehicles below 0 °C

Metal hydrides promise great potential for thermal applications in vehicles due to their fast reaction rates even at low temperature. However, almost no detailed data is known in literature about thermochemical equilibria and reaction rates of metal hydrides below 0 °C, which, though, is crucial for the low working temperature levels in vehicle applications.Therefore, this work presents a precise experimental set-up to measure characteristics of metal hydrides in the temperature range of −30 to 200 °C and a pressure range of 0.1 mbar–100 bar. LaNi_4.85Al_0.15 and Hydralloy C5 were characterized. The first pressure concentration-isotherms for both materials below 0 °C are published. LaNi_4.85Al_0.15 shows an equilibrium pressure down to 55 mbar for desorption and 120 mbar for absorption at mid-plateau and −20 °C. C5 reacts between 580 mbar for desorption and 1.6 bar for absorption at −30 °C at mid-plateau.For LaNi_4.85Al_0.15, additionally reaction rate coefficients down to −20 °C were measured and compared to values of LaNi₅ for the effect of Al-substitution. The reaction rate coefficient of LaNi_4.85Al_0.15 at −20 °C is 0.0018 s⁻¹. The obtained data is discussed against the background of preheating applications in fuel cell and conventional vehicles.     

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.     

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.     

Burner-heated dehydrogenation of a liquid organic hydrogen carrier (LOHC) system

For a hydrogen-based economy, safe and efficient hydrogen storage is essential. Compared to other chemical hydrogen storage technologies, such as ammonia or methanol, liquid organic hydrogen carrier (LOHC) systems allow for a reversible storage of hydrogen while being easy to handle in a diesel-like manner. In our contribution, we describe for the first time the successful utilization of the exhaust gas enthalpy of a porous media burner to directly supply the dehydrogenation heat for a kW-scale dehydrogenation of the hydrogen-rich LOHC compound perhydro dibenzyltoluene (H18-DBT). Our setup demonstrates the dynamics of the dehydrogenation unit at a realized maximum hydrogen power of 3.9 kW_th, based on the lower heating value of the released hydrogen. For the intended applications with fluctuating hydrogen demand, e.g. a hydrogen refueling station (HRS) or stationary heating in buildings, a dynamic hydrogen supply from LOHC is important. Methane, e.g. from a biogas plant, is utilized in our scenario as a fuel source for the burner. Hydrogen is released within 30 min after cold start of the system. The dehydrogenation unit exhibits a power density relative to the reactor volume of about 0.5 kW_therm l⁻¹ based on the lower heating value of the hydrogen and a catalyst productivity of up to 0.65 g_H2 g_Pt⁻¹ min⁻¹ for hydrogen release from H18-DBT. An analysis of the by-products and reaction intermediates shows low by-product formation (e.g. maximum 0.6 wt.-% for high boilers and 0.9 wt.- % for low boilers) and uniform distribution of intermediates after the reaction. Thus, a relatively homogeneous temperature distribution and a uniform LOHC flow in the reaction zone can be assumed. Our findings illustrate the dynamics (heating rates of about 10 K min⁻¹) and performance of direct heating of a release unit with a burner and represent a significant step towards LOHC-based hydrogen provisioning systems at technically relevant scales.     

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.     

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.