Sample Gas Preparation and Delivery DF-310E 33
6 Sample Gas Preparation and
Delivery
6.1 The STAB-EL Acid Gas System
With the STAB-EL system oxygen measurements in sample gases containing
varying amounts of acid gases are possible. As a general guide, the data in
Table 5-1 represents the maximum allowable limits of acid gases under
continuous operation that can be tolerated with the STAB-EL system.
Measuring Range Of
Analyzer
CO
2
*
%
SO
2
ppm
H
2
S
ppm
NO
X
ppm
Cl
2
ppm
HCL
ppm
0-50 ppm
0-100 ppm
0-500 ppm
0-1000 ppm
0-5000 ppm
0-10,000 ppm
0-5%
0-10%
0-25%
0.1
0.2
0.2
0.4
0.6
0.8
2.0
4.0
6.0
100
200
200
500
1000
1500
2600
4000
6000
100
200
200
500
1000
1500
2600
4000
6000
100
200
200
500
1000
1500
2600
4000
6000
50
100
100
200
400
800
1400
2000
3000
50
100
100
200
400
800
1400
2000
3000
* Concentrations of CO
2
are in percent. One percent is equivalent to 10,000
ppm.
Table 2: Maximum Allowable Acid Gas Limits
Contact the local Servomex Business Center for recommendations on using
the STAB-EL sensor on acid gases other than those listed above.
The STAB-EL limits shown in the table represent rough guidelines for
continuous exposure. In most cases, substantially higher acid gas levels can
be tolerated on a limited duty cycle basis. For example, a 0-100 ppm sensor
can be used to sample a 100% CO
2
background gas for a 15 minute period 3-4
times per week, and the balance of the time sampling from a clean gas like N
2
,
Ar, H
2
, etc. In general, a good guideline is to limit that the loading on the
STAB-EL system to not exceed the continuous limits if the total exposure is
averaged over a weekly period. Consult with Servomex for details.
There are applications where the acid gas components may exceed the upper
limits of the STAB-EL system on a continuous basis. In such circumstances a
sample dilution system can easily be fabricated to mix clean N
2
with the
sample gas in a 2:1 to 20:1 ratio using simple pressure control and flowmeter
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