Århus Maskinmesterskole 1 Hydrogen for the future?

Århus Maskinmesterskole 2 Hydrogen was produced first by Cavendish in 1766 by reacting metals with acids. Hydrogen storage… ∙HYDROGEN (H2) – The simplest and lightest element in the universe, which exists as a gas except at low cryogenic temperatures. Hydrogen gas is color-less, odorless and highly flammable gas when mixed with oxygen over a wide range of concentrations. Hydrogen forms water when combusted, or when otherwise joined with air, as within a fuel cell. Hydrogen molecules in which both protons have the same spin are known as “orthohydrogen”. and those in which the protons have opposite spins are known as “parahydrogen”.

Århus Maskinmesterskole 3 Hydrogen storage FuelMJ/kgkWh/kg H2H Natural Gas Gasoline Diesel Hydrogen is one of the most common substances in the Universe. However, we need to produce it from either fossil fuels (reforming), water (by electrolysis) or biomass (for instance gasification).

Århus Maskinmesterskole 4 Hydrogen Storage Issues... Tank Fuel H 2 in Metal Hydrides MeOH Gasoline H 2 (liquefied) H 2 (compressed) System Weight [kg] System Volume [liters] 1500 Fuel equivalents to 45 liters of gasoline:

Århus Maskinmesterskole 5 DOE Freedom Car H2 Storage Targets... Note: Not only the H 2 weight% matters!!

Århus Maskinmesterskole 6 DOE Freedom Car H 2 Storage Targets... Some extremely important remarks from DOE… Useful constants: kWh/MJ, ~ 8.8kWh/liter gasoline equivalent. ”The targets that were developed are system-level targets and are customer- driven, based on achieving similar performance and cost levels as current gasoline fuel storage systems. The storage system includes the tank, storage media, safety system, valves, regulators, piping, mounting brackets, insulation, added cooling capacity, and any other balance-of-plant components”. “In order to achieve system-level capacities of 2 kWh/kg system (6 wt.% hydrogen) and 1.5 kWh/L (0.045 kg hydrogen/L) in 2010, the gravimetric and volumetric capacities of the material alone must clearly be higher than the system-level targets”. Also note that standards are made for U.S. vehicles!! Quotes from:

Århus Maskinmesterskole 7 Hydrogen for the future?

Århus Maskinmesterskole 8 H2 Storage Capacity of Various Compounds… FormulaFormula wt.% Hydrogen CH H 3 BNH LiBH (CH 3 ) 4 NBH NH Al(BH 4 ) Mg(BH 4 ) C 2 H 5 OH (Ethanol/Crude Ethanol)13.1 Diesel Oil13.0 LiH12.6 CH 3 OH (Methanol)12.5 Gasoline (depending on composition) Biodiesel12.0 (Note the favorable O 2 content) H2OH2O11.2 LiAlH NaBH AlH MgH NaAlH Problem is not to get a high wt% H 2 but to have the hydrogen released at a fast rate with low energy consumption. Furthermore, process must be reversible so that the system can adsorb and desorb hydrogen at low cost at low temperatures and pressures!

Århus Maskinmesterskole 9 Comparison of storage methods: (Note Light/Heavy Hydrides compared with H 2 -content!) Source: Alex Züttel

Århus Maskinmesterskole 10 Metal Hydride Storage (With Metal Hydride Powder) Hydrogen adsorption: Exothermic (heat must be removed) Hydrogen desorption: Endothermic (heat must be added) Source: FACE8, 2004

Århus Maskinmesterskole 11 Hydrogen Storage (MeH): ∙Vehicles must be refilled rapidly, so both heat and hydrogen should be moved quickly! ∙Material production cost must be low ∙Physisorption (physical storage in nanostructures) results in low binding energy – easy to release hydrogen but suffers from low volumetric density! ∙Chemisorption (chemical bonding with metals) – higher storage densities but require higher release energy! Binding energy in H 2 must be broken! ∙Optimum might be a combination of both! Smalley 1996 Li, Nature, 1999

Århus Maskinmesterskole 12 Rapid progress within metal hydrides! 70s 80s 90s NaAlH 4 LiNH 2 TiZrVCr Low temperature hydrides Specific Mass H 2 (%) Light metal alloys Complex hydrides

Århus Maskinmesterskole 13 Source: Freedom car project, 2004

Århus Maskinmesterskole 14 Hydrogen for the future?

Århus Maskinmesterskole 15 Compression of Hydrogen: Isothermal compression from bar consumes 21.5MJ/kg Complicated multistage compressor and severe wear on parts It is significantly cheaper to compress methane – however the energy content is only half of that of hydrogen (In the case of steel) Source: Andreas Züttel, 2003

Århus Maskinmesterskole 16 Cost of Compressed Storage Vessels

Århus Maskinmesterskole 17 Hydrogen for the future?

Århus Maskinmesterskole 18 Liquid Hydrogen? h [kJ/kg] T [ ° C ] 10 bar 6 bar 3 bar 1,013 bar 0,2 0,4 0,6 0,8 T,h-diagram for Hydrogen

Århus Maskinmesterskole 19 Liquefaction of Hydrogen: Theoretical limit (from 1 bar) is 14.1 MJ/kg and 10.1 MJ/kg from 20 bar (many electrolysers deliver at higher pressures) Practical Claude large-scale process ~ 24 MJ/kg 1 kWh = 3.6 MJ

Århus Maskinmesterskole 20 Theoretical Liquefaction (Not a very efficient method in general!)

Århus Maskinmesterskole 21 Expanding a gas: The Joule-Thompson Effect (Inversion Curves) The Joule-Thompson effect is of special interest in a liquefaction process. Throttling a real gas through an adiabatic valve, results in the reduction of its pressure with a concurrent change in its temperature. The temperature may increase or decrease depending on the substance and its initial temperature. The JT inversion curve, a locus of points in a pressure-temperature plot at which the drop in pressure has no effect on the temperature dictates whether the temperature will increase or decrease during expansion. dh=0

Århus Maskinmesterskole 22 The Linde process: Accomplished by cooling a gas to a temperature in the 2-phase region (4) through the cycle. Some liquid is formed (5) in each cycle. The simple cycle is impossible to realise for hydrogen since pressure would be extremely high (staged compression with intercooling)! Furthermore, hydrogen needs to be precooled below the upper JT inversion temperature at 1 atm (-69°C) before expanding to get maximum cooling.

Århus Maskinmesterskole 23 The LN 2 pre-cooled Linde Process

Århus Maskinmesterskole 24 The Claude-process (2-stage compression version): Staged Compression Introducing a Turbine Cooling with LN 2 Heat Exchanger