M&C TechGroup CG-2H-W_-2MH-W Operator's manual - Manual (Page 12)

12
Gas sampling and conditioning technology 9-0.2-ME
8.3 CROSS SENSITIVITIES AND INFLUENCE OF INTERFERING/CARRIER GAS
From operating experiences in different applications as well as laboratory measurements with differ-
rent CG-converter- and catalyst types we got a lot of experiences about influencing factors on the
NO
2
-NO conversion process. The following hints make no claim to be complete, but can help choosing
the adequate catalyst type as well as give an indication for the integration of the CG-converter into a
certain system environment.
In practice often several influencing factors have any effect at the same time. With their effect on the
NO
2
- conversion they are possibly interacting and therefore can complicate an explicit interpretation of
a certain device performance.
N O T E !
Carbon monoxide (CO)
In the conversion process from NO
2
to NO carbon monoxide is generated or
destroyed (oxydised). The hereby resulting CO-concentration downstream
the
converter depends on: catalyst type, NO
2
-concentration, O
2
-
concentration in the sample gas and can be some 10 ppm.
Therefore a CO-measurement should not be installed downstream the con-
verter but with a separate sample gas way to avoid faulty measurements.
N O T E !
Oxygen (O
2
)
In the conversion process, oxygen is generated proportional to the NO
2
con-
centration. This fact can lead to a faulty measurement in a downstream oxy-
gen trace measurement (ppm)!
N O T E !
Sulfur dioxide (SO
2
)
In the operating temperature range of the catalyst type SS of >600°C existing
concentrations of sulfur dioxide are partially destroyed (oxydised). This fact
can lead to faulty measurements in a downstream SO
2
-measurement. The
exact loss of concentration depends proportional on the oxygen concentra-
tion of the sample gas and can be up to 25% from the basic value.
Therefore a SO
2
-measurement should not be installed downstream the con-
verter with catalyst type SS but with a separate sample gas way.
N O T E !
Ammonia (NH
3
)
In the operating temperature range of the catalyst type SS of >600°C existing
concentrations of ammonia are almost completely transformed into NO if
–as
required for type SS- enough oxygen is in the sample gas. In the operating
temperature range of the catalyst type C around 350°C, Ammonia in concen-
trations >100ppm can alloy the NO
2
-No conversion.
N O T E !
Nitrous Oxide (N
2
O)
There was no influence of this gas detected on the NO
2
conversion with cata-
lyst type C or SS.