• the flame should be self-stabilizing, i.e. flameless zones must re-ignite automatically
within 2 to 3 seconds
Test measurements should be performed to optimize the burner setting and minimize
consumption.
Figure 9: Biogas stove in China
Photo: Grosch (gtz/GATE)
Gas demand
The gas demand can be defined on the basis of energy consumed previously. For example,
1 kg firewood then corresponds to 200 l biogas, 1 kg dried cow dung corresponds to 100 l
biogas and 1 kg charcoal corresponds to 500 l biogas.
The gas demand can also be defined using the daily cooking times. The gas consumption
per person and meal lies between 150 and 300 liter biogas. For one liter water to be cooked
30-40 l biogas, for 1/2 kg rice 120-140 l and for 1/2 kg legumes 160-190 l are required.
Biogas lamps
Efficiency of biogas lamps
In villages without electricity, lighting is a basic need as
well as a status symbol. However, biogas lamps are not
very energy-efficient. This means that they also get very
hot. The bright light of a biogas lamp is the result of
incandescence, i.e. the intense heat-induced luminosity of
special metals, so-called "rare earth" like thorium, cerium,
lanthanum, etc. at temperatures of 1000-2000°C. If they
hang directly below the roof, they cause a fire hazard. The
mantles do not last long. It is important that the gas and
air in a biogas lamp are thoroughly mixed before they
reach the gas mantle, and that the air space around the
mantle is adequately warm.
Light output
The light output (luminous flux) is measured in lumen (lm).
At 400-500 lm, the maximum light-flux values that can be
achieved with biogas lamps are comparable to those of a
normal 25-75 W light bulb. Their luminous efficiency
ranges from 1.2 to 2 lm/W. By comparison, the overall
efficiency of a light bulb comes to 3-5 lm/W, and that of a
fluorescent lamp ranges form 10 to 15 lm/W. One lamp
consumes about 120-150 liter biogas per day.
Figure 10: Biogas lamp in
Thailand
Photo: Kossmann (gtz/GATE)
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