Page 47 - Advances in Eco-Fuels for a Sustainable Environment

24 Advances in Eco-Fuels for a Sustainable Environment

but still especially cheap for domestic heating nowadays). Wood could be considered
the ideal biomass as is readily and abundantly available, can be collected from the
ground, and is reasonably energy dense. Wood is actually more energy efficient than
many fuels, with about 70% of the energy content (10MJ/kg) recoverable, on average;
however, its downside is pollution. Not only does it produce more CO 2 than other fuels
such as methane, but it also produces other pollutants such as soot, smoke, and PAHs.
Industrial research had recently some success in producing stoves that burn wood and
o
derivatives at extremely high temperatures (>600 C), allowing the smoke itself to
burn, reducing emissions.
Still, more than 2 billion people across the world burn dried animal droppings for
energy daily. It is a cheap fuel found in areas were even wood is scarce; it is also
renewable and contains a reasonable amount of energy, about 50% methane and
30% carbon dioxide by mass when converted into biogas. If burned with 100% effi-
ciency, sow dung has an energy density of approximately 12MJ/kg. Unfortunately,
burning this matter efficiently is even more difficult than burning wood efficiently,
producing a number of pollutants, including dioxins and chlorophenols, and constitut-
ing a major health hazard where it is burned indoors with limited ventilation. Progress,
luckily, arranged for different biofuels to become more popular today.

2.3.1 Biogas and biomethane

Biogas is a mixture of combustible gases formed from anaerobic digestion (AD), a
biological process where the degradation of an organic substrate by bacteria occurs
in an anaerobic environment (Table 2.6). Its production comes mainly from MSW
landfills, sewage sludge AD, MSW organic fraction (MSWOF) codigestion, and zoo-
technical waste biogasification plants.
Europe as a continent is the major global producer of biogas (about 12Mtoe/year),
53% of which is generated in Germany. The United Kingdom (1.8Mtoe/year) is the
second-largest producer, followed by France (1.2Mtoe) and Italy (0.4Mtoe). Never-
theless, the sector’s contribution to the European biofuels market is limited to 0.3%.
3
Biogas with 60% CH 4 in volume has a lower heating value of 21.5MJ/Nm
3
(5.97kWh), biomethane (with CH 4 content>95%) 35.8MJ/Nm (9.94kWh). Biogas
has varied possible end uses such as domestic cooking, lighting, and heating. After

Table 2.6 Biogas composition [19]

Component gas Content (v/v)
Methane 40%–75%
Carbon dioxide 15%–60%
Hydrogen Traces
Nitrogen 0%–5%
Moisture 1%–5%
Hydrogen sulfide 0–5000ppm
Ammonia 0–500ppm