Agriculture Reference
In-Depth Information
Photo 9.2.
CO
2
generator that produces CO
2
by combustion.
the air supply (by a factor of 1.6) to avoid
incomplete combustion. The supply of
external air to the burner (by means of a fan)
avoids these problems.
The use of small burners is usually
imprecise. If they are used just to heat the
air, they may produce very high CO
2
levels,
which are undesirable sometimes; whereas
if there is no need to heat, their use involves
an undesired thermal supply.
at night. Dissipating it to the exterior
(air, underground water) is not advisable
due to the environmental impact.
9.2.4
Distribution of CO
2
It is important to achieve a homogeneous
distribution of CO
2
in the whole greenhouse,
without differences between the beginning
and end of the supply lines (horizontal gra-
dient), and also avoiding vertical gradients
(low concentration inside the canopy). The
distribution ducts may be located inside the
crop, laying over the soil, so the enriched
air crosses the canopy before it reaches the
roof vents.
There are two main methods for the
distribution of pure CO
2
. In the first
instance, the liquid CO
2
is evaporated by
means of specialized equipment and then
forced by its own pressure through a dis-
tribution network of pipes and delivered
through perforated PE tubes along or under
(when raised gutters are used) the rows of
plants; this method is popular in northern
countries (Nederhoff, 1995). The second
method is to inject CO
2
in the airflow of a
fan, which is connected with a pipeline of
large-diameter perforated air-circulation
CO
2
enrichment from a central boiler
In a centralized heating system, the com-
bustion gases originating in the boiler can
be used for CO
2
supply, if the gases are
pure enough. The advantage is that the
supply of CO
2
and the heating can be done
separately in the greenhouse. As the boiler
is larger, a better control of the combustion
is possible. Besides, the water vapour con-
tained in the combustion gases can be
extracted, avoiding their entrance in the
greenhouse.
When CO
2
is produced by combustion
in a central boiler, the destination of the
heat can be: (i) to use it directly for heat-
ing; (ii) to dissipate it inside the green-
house to get rid of it (maintaining a low
pipe temperature); and (iii) to store it
during the daytime and use it for heating
