M&C CG-2 - Operating Principle of Conversion

www.mc-techgroup.com CG-2 | 1.04.00 11
8 OPERATING PRINCIPLE OF THE CONVERSION
The conversion of nitrogen dioxide NO
2
into nitrogen monoxide NO passes according to the following
reaction equation:
2 NO
2
2 NO + O
2
The reaction equilibrium is shifted at room temperature onto the side of the original material NO
2
. A shift
of the equilibrium towards the products and the resultant high product yield can only be achieved as
subject to a high-energy input, i.e. increase of temperature.
A nearly 100 % conversion of NO
2
and therefore a complete conversion to NO is achieved with a car-
tridge filled with a metal catalyst within a temperature range of 620 to 680 °C [1148 to1256 °F].
The energy input can be reduced explicitly by using a carbon-molybdenum based catalyst. With this
type of catalyst, a nearly complete conversion of NO
2
to NO is achieved within a temperature range of
320 to 380°C [608 to 716 °F].
The catalyst is supplied as a ready-to-use formatted cartridge.
NOTE!
Dust-loaded gases may choke up the catalyst filling. For this reason, an ap-
propriate gas conditioning system is to be mounted upstream of the convert-
ers CG... in order to separate out suspended particles!
NOTE!
For converters with unheated sample gas in- and outlet at dew points above
10 °C [50 °F] a sample gas drying/cooling shall be provided!
To minimize the loss of NO
x
in the sample gas conditioning, according to DIN EN 14792:2005 (descrip-
tion of the NO
x
reference measuring method) the usage of sample gas coolers is not allowed in case
the NO
2
fraction is higher than 10 % of the NO
x
content (note: because of the high solubility of NO
2
).
If the dew point simultaneously is higher than 10 °C [50 °F], a converter with heated in- and outlet has
to be used (‘hot gas converter’).