Operating instructions

- 7-
7. Working principle of the conversion
The conversion of nitrogen dioxide NO
2
into nitrogen monoxide
NO occurs according to the following reaction equation:
2 NO
2
2 NO + O
2
The reaction equilibrium is shifted entirely 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 subject to a high expenditure of energy, i.e. temperature
(100% conversion at temperatures over 600 C). By using a
catalyst the activation energy of the above reaction is reduced
considerably so that conversion rates of 99% are possible at
temperatures below 400 C. A carbon-molybdenum mixture is used
as catalyst. The carbon supporting material guarantees optimal
contact between the gas to be converted and the surface of the
catalyst combined with a simultaneously low flow resistance.
The catalyst is supplied as a ready-to-use formatted cartridge.
Note!
For reasons associated with the filter effect of the catalyst filling
an appropriate gas conditioning system is to be mounted
upstream of the converters CG... in order to separate out
suspended particles and to dry the sample gas !
7.1 Selection of the appropriate catalyst temperature The
converter is pre-adjusted to 330 C in the factory. The catalyst
temperature can be adjusted continuously using the
temperature controller on the front of the converter (see 17.2).
The following table shows the recommended settings for
catalyst temperatures depending on the gas flow for a con-
version rate above 95%.
Gas flow[Nl/hr] Setting[ C]
30 330 C
60 330 C
90 340 C
Note!
Ammonia NH
3
in the sample gas converts a part of the NO
2
into
dinitrogen oxide N
2
O and elementary N
2
. Depending on the
ammonia concentration, this can cause a substantial reduction in
the conversion rate!
M&C Products Analysis Technology
9-2.0-MEUS