Physical Properties of Hydrogen
Hydrogen is a colourless, odourless and completely non-poisonous gas. It has a specific gravity of 0.0899 g/l, (air is 14.4 times as heavy as hydrogen).
Hydrogen condenses at -252.77°C. Liquid-hydrogen has a specific gravity of 70.99 g/l. Because of that hydrogen has the highest energy density in relation to mass of all fuels and energy carriers: 1 kg hydrogen contains as much energy as 2.1 kg natural gas or 2.8 kg petrol (related to the lower heating value).
The energy density of liquid hydrogen referring to volume is a quarter compared to petrol and a third with reference to natural gas. The share of hydrogen in water is 11.2% by weight.
Ecological Advantages of Hydrogen
When burning hydrogen with air in internal combustion engines and gas turbines (when a suitable procedure is applied) only very few or negligible emissions are resulting.
Nitrogen monoxide emissions increase exponentially with calorific intensity. Therefore these emissions can be influenced by choosing a suitable process. As hydrogen, in contrast to other fuels, offers more freedom to influence the burning process, it is possible to decrease the Nox-emissions compared with natural gas or petroleum. To achieve this one can attain low calorific intensity e.g. by using a high air surplus.
By using hydrogen in low-temperature fuel-cells ( e.g. membrane fuel cells: PEMFC) emissions can be completely avoided. In the process of generating energy from hydrogen and air-oxygen water is the only reaction product (i.e. water without any minerals, like distilled water).
The use of hydrogen in fuel-cells operating at a higher temperature-level causes emissions a hundred times lower than in conventional power stations.
Hydrogen as a secondary energy carrier offers the possibility to introduce various renewable energies into the sector of combustibles and fuels in a flexible way.
To judge the relevance for the environment the complete fuel chain from the primary energy to the final implementation has to be considered.