Teledyne 6200T - Sulfides Analyzer - Manual (Page 301)

6200T Total Sulfur Analyzer Principles of Operation
Teledyen Analytical Instruments 301
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 6200T 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 6200T 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 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 13-12: 6200T Hydrocarbon Scrubber (Kicker)
In the 6200T 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 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