Manual D-LX-700 en.pdf - Durag Group

Page 20 D-LX 700
13.2 Purge and cooling air for the D-LL 704 fibre optic system
A flow volume of 7 Nm 3 /h will yield a flow velocity of approximately 10 m/s. This corresponds to an air
inlet pressure of approximately 50 mbar at the air connection on the fibre optic system. This flow rate
is sufficient for typical installations. If a higher level of particulate accumulation is expected, the airflow
should be increased to 15 Nm 3 /h (flow velocity of 20 m/s). This requires an inlet pressure of
approximately 250 mbar. Oil- and dust-free air must be used for the purge air supply.
If the fibre optic system must be cooled due to an ambient temperature higher than the tolerances of
the fibre optics, the airflow can be increased. For a flow velocity of 30 m/s, about 20 Nm 3 /h of air is
needed. This can be achieved if the air supply pressure at the air inlet port is approximately 600
mbar.
For higher ambient temperature applications, such as gas turbines, an additional guide tube should be
supplied on site to supply adequate cooling air to the fibre optic system.
The required air pressure at the inlet port for a given purge and cooling air volume can be determined
from the following graph. Pressure drops through the supply lines must be taken into account. The
curves on this graph do not compensate for any backpressure from the combustion chamber. The
supply pressure may need to be increased to achieve the same flow rate and compensate for the
furnace pressures on site.
LE703-06-001
(Fig. 12) Graph of purge and cooling air volume for the D-LL 704