General Aspects Of Hydrogen

Páginas: 15 (3617 palabras) Publicado: 30 de enero de 2013
Estudiante: Andrés Mauricio Ríos
Fecha: 09/11/2012
Materia:Energía e Impacto Ambiental
El hidrógeno, una alternativa de combustible vehicular.
General aspects of Hydrogen
Hydrogen, which comes from the Greek words “hydro” and “genes” meaning
“water” and “born of”, has been first identified as a distinct element by Henry
Cavendish after he separated hydrogen gas by reacting zinc metal withhydrochloric acid. After its discovery, Hydrogen has been considered the most
simple, lightest and common element in nature. Its molecule, H2, has multiple
characteristic such as the highest energy-mass (141.80MJ/Kg, equals to 39.4
kWh/Kg or 60,619 BTU/lb) relation of any know combustible molecule (gasoline
has 47.30MJ/Kg or 18,400 BTU/lb ) which is translated to more kilometers withoutrefilling the tank.

(Figure 1. Energy/mass relation for fuels, http://mae.ucdavis.edu/hypaul/overview.htm)

Even though hydrogen is not considered as a GHG (Green House Gas), recently it
has been demonstrated that it could compete with the process that removes
methane from the atmosphere, a potent GHG. H2 is therefore effectively an
indirect GHG. In the other hand, H2 is carbon free emissionsafter usage, it is a
nontoxic gas and after the combustion (or usage) for energy, its reaction produces
water, as shown in the following stoichiometric equation:

2H2+O2-> 2H2O + Energy

´(1)

There are some other characteristics of this molecule that determine the
advantages and disadvantage of the usage un hydrogen as fuel. For example the
mixtures of hydrogen and air burns within awide composition range. In other words
mixtures between the 4% of LEL (Low Explosion Level) (or 40.000ppm) and 75%
of UEL (Upper Explosion Level) (or 750.000ppm) of hydrogen plus an spark will
burn; for fossil fuel in air is between 1% LEL (or 10.000ppm) and 8% UEL (or
80.000ppm). Another of these points is that hydrogen has a very low volumeenergy ratio due to its low density (0.08988 g/L at 0°C, 101.325 kPa), this means
that large volumes of hydrogen are needed to be store to produce enough energy.
Somehow these problems could be solved using high pressure storage.
As a result of the above analysis:


For 1Kg of Hydrogen, which gives 141MJ, a container of 11.000 Liters (or
11m3) is needed to store the gas (in the same conditions).



For 1 gallon of diesel or gasoline,which gives 141MJ, a tank of 3,7 liters is
needed (1 kg of hydrogen is equivalent to 2.79 kg of diesel).

(Figure 2. Combustible zone for Hydrogen and Gasoline)

These qualities allocates the hydrogen as a candidate, full of advantages but
obviously with some barriers, for replacing the declining oil reserves and fossil fuel
as the base of our transportation necessity in the mid and longterm. In other words
Hydrogen has the potential to become a sustainable energy carrier of the future,
particularly for transportations, though the technological challenges that has to
minimize. As a result many initiatives have defined this phenomenon, of the fuel
transition, as the World Hydrogen Transition Model (WHTM) and Hydrogen
Economy.

Hydrogen production

Unfortunately, hydrogendoes not exist in its elemental form. As a consequence ,
hydrogen must be extracted from a hydrogen compound, such as fossil fuel or
water. Hydrogen could be produced in different ways and from different sources,
using various types of technologies considering that a separate energy source is
needed to extract the hydrogen from the compound, such as heat, light or
electricity.

Figure 3.Overview of assessed fuel production and supply pathways
(Transition to Hydrogen Pathways Toward Clean Transportation, Alexander Wokaun Erik
Wilhelm, 2006 )

Some of these involve well known industrial processes, such as electrolysis and
steam reforming from fossil fuels (which is the dominant source of industrial
hydrogen, http://www1.eere.energy.gov/hydrogenandfuelcells),

while others are...
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