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Model T101 Instruction Manual Principles Of Operation
257
10.3.5. HYDROCARBON SCRUBBER (KICKER)
It is very important to make sure the air supplied to sample the chamber is clear of
hydrocarbons. To accomplish this task the T101 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 the 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 partial pressure
gradient between the inner and outer tubes.
INNER
TUBE
(Ambient Air)
OUTER TUBE
(Clean Air)
SAMPLE AIR
FROM
PARTICULATE FILTER
CLEANED
SAMPLE AIR
TO
SAMPLE
CHAMBER
CLEAN
PURGE AIR
FROM
VACUUM MANIFOLD
USED PURGE AIR
TO
PUMP
AND
EXHAUST PORT
Figure 10-9. T101 Hydrocarbon Scrubber (Kicker)
In the T101 some of the cleaned air from the inner tube is returned to be used as the
purge gas in the outer tube (Figure 10-9). This means that when the analyzer is first
started, the concentration gradient between 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.
10.3.6. SO
2
SCRUBBER
In order to ensure that no ambient SO
2
interferes with the analyzer’s H
2
S measurement
the sample gas stream is passed through a chemical scrubber that removes SO
2
from the
sample stream before it is passed though the catalytic converter (see Figure 10-7).
The SO
2
scrubber is a Teflon encased, stand-alone unit containing a room-temperature
tube mounted in the front right side of the analyzer case (see Figure 3.8) near the
instrument’s on/off switch.
The SO
2
scrubber material is consumed as it removes SO
2
. If the expected
concentrations of SO
2
are very high, the lifetime of the scrubber will be short. The
expected life of the scrubber is approximately 1000 ppm-hours. See Section 8.3.3 for
information on when and how to replace the SO
2
scrubber material)
07266B DCN6485