Civil Engineering Reference
In-Depth Information
7.6
D
L
(13-23)
3.6
1
D
where
L
equivalent length of straight pipe, feet (m)
D
pipe diameter, inches (cm)
The loss in globe valves is about:
11.4
D
L
(13-24)
3.6
1
D
where
L
and
D
are as defined above.
Carbon dioxide absorption systems often consist of a grid of perforated pipe sub-
merged in the water. The recommended minimum depth of submergence is 8 feet (2.5
m). With lesser depths of submergence some undissolved CO
2
will escape at the water
surface. Properly designed absorption systems will put into solution 85 to 100 percent
of the applied CO
2
. PVC pipe is suitable for the perforated CO
2
grid pipes. Current
practice is to use
3
⁄
16
-inch (5 mm)-diameter orifices drilled in the bottom of the pipe
at an angle of 30 degrees to the right of the vertical centerline, then 30 degrees to the
left, alternating at a spacing of about 3 inches (75 mm) along the centerline of the
pipe. Another arrangement is to point the orifices straight up at the top of the pipe
and to direct a jet of water from a header down at the CO
2
orifice, in order to form
fine bubbles of the gas, which dissolves more readily in the water than larger bubbles.
Because PVC does not corrode under acidic conditions, the openings are not subject
to plugging as they are in metal pipes.
If
3
⁄
16
-inch (0.48-cm) orifices are used, each opening is often rated at 1.1 to 1.65
cu ft / min (0.03 to 0.05 m
3
/ min), which corresponds to headlosses through the orifice
of 3 and 8 inches (75 to 200 mm) of water column, respectively. This is sufficient loss
through the orifice to ensure good distribution of the CO
2
to each opening. Carbon
dioxide laterals must be laid with the same depth of submergence on each orifice. If
the size of the pipe changes, then eccentric reducers should be used to keep the bottom
of the pipe level (assuming that the holes are in the bottom of the pipe). Horizontal
spacing between CO
2
diffusion laterals should be at least 1.5 feet (0.46 m) in order
to get good absorption. To convey cool, dry CO
2
, plain steel or cast-iron pipe may be
used; but for hot, moist CO
2
gas, the use of stainless steel or other acid-resistant metal
is suggested. Special pipe is also required to convey liquid CO
2
in water; a 1.5-inch
(38.0-mm) cotton fabric hose with openings of controlled size or porosity has been
used successfully. Basin hydraulics must take into account raised water levels caused
by CO
2
injection.
CARBON DIOXIDE REACTION BASINS OR
INTERMEDIATE SETTLING BASINS
Contrary to many early reports in the literature, the recarbonation reaction is not in-
stantaneous. Although about 90 percent of the applied CO
2
does dissolve in its very
