Hydrogen, space, natural laws and a lot of time – that’s all it took to create everything around us.
It all started with hydrogen
Everything that surrounds us on Earth, indeed all the matter of the universe known to us, is basically nothing other than the history of the transformation of hydrogen.
Hydrogen is omnipresent in its diverse compounds, but we only find hydrogen in its pure form in places that are hidden from our direct view and are therefore often only known to the scientific community.
How important is hydrogen for the engineering office Ruth?
Since Ruth deals with the production of synthetic fuels using CO₂ filtered from exhaust gases, hydrogen is of particular importance to us as a synthesis component.
Hydrogen is a core element and an essential building block that we need to manufacture our synthetic fuels. The range of renewable energies, either from wind power or photovoltaics, enables us to convert the “excess” electricity, which cannot be fed into the grid in times of overproduction, into hydrogen via electrolysis and thus into a storable energy carrier. Since a power grid cannot store the electricity, when it is converted into a liquid, storable and transportable energy carrier it can be reconverted anywhere and at any time.
The first step is to convert electricity into hydrogen via electrolysis. Further conversion steps, for example the conversion of this hydrogen into synthetic fuel, can then be carried out as required.
Since the production and intermediate storage of hydrogen is not always advisable for certain synthesis steps, the equipment required for electrolysis must be specifically optimized and adjusted to our applications, be it modular use in the maritime sector or decentralized stationary applications, and this will also depend in many ways on the desired process chain.
What is important to us at engineering office Ruth:
Dealing with the energy carrier hydrogen in connection with fuel cell technology means that we can make our future energy supply in this area CO₂-free. With the gradual introduction of fuel cell technology, e.g. transitionally with LNG as a fuel cell energy source, an economic transformation process can be easier to achieve because it builds on existing infrastructures.
What can be made from hydrogen?
The sun is able to convert hydrogen into helium. People have not yet mastered this art, which is why we have to be content with other forms of energy generation and storage.
However, hydrogen can be used to generate electricity using the fuel cell technology currently available on the market, be it PEM or SOFC. Hydrogen can also be burned directly (gas firing) or used as fuel in modified conventional gasoline engines. The current problem associated with using hydrogen is and remains the storage of the hydrogen. In the short and medium term we therefore do not consider the use of hydrogen in the maritime sector to be expedient due to the low volume energy density and the insufficient infrastructure.
Methane as a “transport carrier” for green hydrogen:
Since ships with diesel engines can be converted to LNG, and this has been happening increasingly in recent years plus direct methanization from renewable energies is becoming more and more cost-effective, by using synthetically produced methane (e-LG) we see a way in both the short and medium term to constructively support the transformation of the energy sector required by the German government by 2050. We see retrofitting fuel cells that are currently operated with LNG, but in the medium term can be operated with e-LG and in the future with hydrogen, as another approach to increasing the efficiency of energy supply concepts in the maritime sector. This would enable a gradual shift towards renewable energy sources in the maritime sector at reasonable expense.
Characteristics of hydrogen:
Hydrogen has a lower volume-related energy density compared to many hydrocarbons (approx. 1/3 of natural gas). A tank roughly three times the size is required to store comparable amounts of energy in liquid form. For storage in a gaseous state, this disadvantage can be partially countered by storing it at high pressure (currently up to 700bar is achieved for H2 in the automotive sector).
However, due to its low molar mass, hydrogen has a comparatively high mass-based energy density (H2 has more than twice the mass-based energy density of natural gas). Because of this high mass-based energy density H2 is being considered as aviation fuel, especially for novel large-volume aircraft.
Here is a comparison of the mass-based energy density of different fuels:
• 1 kg of liquid hydrogen provides heat of approx. 120 MJ (33.33 kWh)
• 1 kg of liquid LNG provides heat of approx. 32 to 45 MJ (8.89 to 12.5 kWh)
• 1 kg of liquid gasoline provides heat of approx. 40 to 42 MJ (11.11 to 11.66 kWh)
• 1 kg of liquid diesel provides heat of approx. 43 MJ (11.94 kWh)
In addition to the mass-based energy density analysis listed above, a volume-based energy density analysis of various types of fuel is presented here for comparison:
• 1 litre of liquid hydrogen provides heat of approx. 8.5 MJ (2.36 kWh)
• 1 litre of liquid LNG provides heat of up to 23.4 MJ (up to 6.5 kWh)
• 1 litre of liquid gasoline provides heat of up of 30.6 MJ (up to 8.5 kWh)
• 1 litre of liquid diesel provides heat of approx. 34.9 MJ (9.7 kWh)
How can we store hydrogen?
During cryogenic hydrogen liquefaction, thermal insulation losses cause hydrogen to vaporize and outgas.
Hydrogen (liquid, cryogenic) weighs 71 kg/m³
The amount of energy required for storage is:
• Compression approx. 12 %
• Liquefaction approx. 20 %
Storage volumes
• Cryogenic storage at 20 K ≈ −253 °C: 70.82 kg/m³ are equivalent to 14.12 L/kg. This offers the greatest storage density!
• 700 bar pressurized storage at 15 °C: 40 kg/m³ (real gas) are equivalent to 25 L/kg; this is equivalent to 7.5MJ/ltr. (In comparison: gasoline with roughly 31 MJ/ltr.)
• 200 bar pressurized storage at 15 °C: 14.5kg/m³ (real gas) are equivalent to 69 L/kg
• Feasible pressurized storage: currently (as of 2020) it is assumed with current technology that storage pressure of 1200 bar is feasible
H2 tanks:
The colour coding of H2 cylinders:
Hydrogen is stored in red steel cylinders or grey cylinders with a red neck. Flammable gases are stored in red steel cylinders.
As a gas:
• Carbon fibre reinforced plastic (CFRP)
As a liquid:
• Thermally insulated steel tanks
Chemical bonding:
• Chemisorption
• … one way is the transformation into synthetic fuels
As a solid:
• Metal hydride storage: One cubic metre of metal hydride contains more hydrogen atoms than one cubic metre of liquified hydrogen!
The mere cost of transporting H2, excluding investment costs:
Investment costs for transporting H2:
What special properties does hydrogen have?
Physics:
• Hydrogen is the element with the lowest density
• Molecular hydrogen (H2) is approximately 14.4 times less dense than air
• Liquid hydrogen weighs 70.8 grams per litre
• Its melting point is 14.02 K (−259 °C)
• Its boiling point is 21.15 K (−252 °C)
• Hydrogen has the highest diffusivity of all gases at room temperature
• Hydrogen has the highest thermal conductivity of all gases at room temperature
• Hydrogen has the highest effusion velocity of all gases at room temperature
• Only triatomic or polyatomic real gases, such as n-butane, have a lower viscosity
• The mobility of hydrogen in a solid matrix is very high, due to the small molecular cross-section.
Some technical applications for hydrogen:
• in oil refinieries for desulphurization
• in large-scale chemical syntheses (ammonia, methanol, oxysyntheses, hydrogenation of organic intermediates)
• hydrogenation of heavy fuel oil (HFO)
• hydrogenation of coal
• mineral oil processing
• in the direct reduction of Fe2O3 or also of CuO
• as a reduction gas, protective gas (special metals, sintering processes, silicon chemistry, float glass)
• in the hardening of fats (margarine production)
Advantages of using hydrogen:
• Hydrogen mixes with air very quickly after leaving the storage tank. With sufficient ventilation, hydrogen gas evaporates very quickly.
• In hot environments, hydrogen burns off at a concentration of 4 % which is why it is not that easy for an explosive mixture to accumulate in this way.
The hazards of hydrogen (special risks):
• A mixture of hydrogen and air is highly flammable.
• Hydrogen can ignite when it is discharged, for example through electrostatic processes at high pressures.
• Only a very low ignition energy is required for it to ignite, for example by the friction of water droplets on hydrogen gas particles.
• When hydrogen is discharged from the storage tanks, a very high-pitched whistling sound may occur.
• A hydrogen flame is not visible in daylight.
• The invisible flame is over 2000 degrees centigrade and can have lengths of up to 30 m depending on the discharge pressure.
• Hydrogen flames emit only a small amount of heat radiation. Therefore, there is a danger of unconsciously getting too close to the flame.
• Hydrogen gas ignites within a very wide range of between 4 – 78 volume % in air.
• An explosive mixture (oxyhydrogen) is formed at a volume of 18% in air.
• Hydrogen mixes intensively and rapidly with air.
• Hazard in enclosed spaces: Hydrogen accumulates throughout the available space, especially up at the ceiling in a room as it is much lighter than air.
• The explosion radius for H2 truck trailer tanks is: 750m
• Liquified and cryogenic hydrogen lingers for a long time at the exit point and can be recognized by the formation of mist in its vicinity, but evaporates quickly.
• Cryogenic hydrogen separates liquid oxygen from the ambient air and is therefore even more dangerous than gaseous hydrogen.
• Cryogenic hydrogen can lead to cold burns.
• When cryogenic hydrogen is discharged, mist is formed. This is condensed air moisture.
• Rooms where hydrogen can escape must not be protected with a CO2 system, since carbon dioxide can ignite hydrogen when it is discharged.