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Teledyne API - T100 UV Fluorescence SO2 Analyzer Principles of Operation
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The actual flow rate of gas through the orifice (volume of gas per unit of time), depends
on the size and shape of the aperture in the orifice. The larger the hole, the more gas
molecules, moving at the speed of sound, pass through the orifice. Because the flow rate
of gas through the orifice is only related to the minimum 2:1 pressure differential and
not absolute pressure the flow rate of the gas is also unaffected by degradations in pump
efficiency due to age.
The critical flow orifice used in the T100 is designed to provide a flow rate of 650
cm
3
/min.
13.4.2.2. SAMPLE PARTICULATE FILTER
To remove particles in the sample gas, the analyzer is equipped with a Teflon membrane
filter of 47 mm diameter (also referred to as the sample filter) with a 1 µm pore size. The
filter is accessible through the front panel, which folds down, and should be changed
according to the suggested maintenance schedule listed in Table 11-1.
13.4.3. HYDROCARBON SCRUBBER (KICKER)
It is very important to ensure that the air supplied sample chamber is clear of
hydrocarbons. To accomplish this task the T100 uses a single tube permeation scrubber.
The scrubber consists of a single tube of a specialized plastic that absorbs hydrocarbons
very well. This tube is located within outer flexible plastic tube shell. As gas flows
through the inner tube, hydrocarbons are absorbed into the membrane walls and
transported through the membrane wall and into the hydrocarbon free, purge gas flowing
through the outer tube. This process is driven by the hydrocarbon concentration gradient
between the inner and outer of the tubes.
INNER
TUBE
(Ambient Air)
OUTER TUBE
(Clean Air)
SAMPLE AI
R
FROM
PARTICULATE FILTER
CLEANED
SAMPLE AIR
TO
SAMPLE
CHAMBE
R
CLEAN
PURGE AIR
FROM
VACUUM MANIFOLD
USED PURGE AIR
TO
PUMP
AND
EXHAUST PORT
Figure 13-12: T100 Hydrocarbon Scrubber (Kicker)
In the T100 some of the cleaned air from the inner tube is returned to be used as the
purge gas in the outer tube (refer to Figure 13-12). This means that when the analyzer is
first started, the concentration gradient be
tween the inner and outer tubes is not very
large and the scrubber’s efficiency is relatively low. When the instrument is turned on
after having been off for more than 30 minutes, it takes a certain amount of time for the
gradient to become large enough for the scrubber to adequately remove hydrocarbons
from the sample air.
06807C DCN6650