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Teledyne API - Model 200EH/EM Operation Manual Theory of Operation
205
10.3.8. OZONE SUPPLY AIR FILTER
The M200EH/EM uses ambient air as the supply gas for the O
3
generator and may produce a variety of
byproducts. Small amounts of water, ammonia and various sulfur oxides can combine to create ammonium
sulfate, ammonium nitrate, nitric acid and other compounds. Whereas sulfates and nitrates can create powdery
residues inside the reaction cell causing sensitivity drift, nitric acid is a very aggressive compound, which can
deteriorate the analyzer’s components. In order to remove these chemical byproducts from the O
3
gas stream,
the output of the O
3
generator flows through a special filter between the generator and the reaction cell.
Any NO
X
that may be produced in the generator (from reaction of O
2
or O
3
and N
2
in the air) and may cause an
artifact in the measurement, is calibrated out through the Auto-zero functionality, which checks the background
signal of the O
3
stream only once per minute.
10.3.9. OZONE SCRUBBER
Even though ozone is unstable and typically reacts to form O
2
, the break-down is not quite fast enough to ensure
that it is completely removed from the exhaust gas stream of the M200EH/EM by the time the gas exits the
analyzer. Due to the high toxicity and reactivity of O
3
, a special catalytic ozone scrubber is used to remove all of
the O
3
exiting the reaction cell. Besides its efficient destruction of O
3
, this catalyst does not produce any toxic or
hazardous gases as it only converts ozone to oxygen.
The O
3
scrubber is located inside the NO
2
converter housing next to the NO
2
converter in order to utilize residual
heat given of by the converter heater. Even though the catalyst is 100% efficient at scrubbing ozone at room
temperature, heating it significantly reduces the necessary residence time (the amount of time the gas must be
in contact with the catalyst) for 100% efficiency and full efficiency can be maintained at higher gas flow rates. As
this is a true catalytic converter, there are no maintenance requirements as would be required for charcoal-
based scrubbers.
A certain amount of fine, black dust may exit the catalyst, particularly if the analyzer is subjected to sudden
pressure drops (for example, when disconnecting the running pump without letting the analyzer properly and
slowly equilibrate to ambient pressure). To avoid the dust from entering the reaction cell or the pump, the
scrubber is equipped with sintered stainless steel filters of 20 µm pore size on either end and on some models,
an additional dust filter may be attached to the exhaust port.
04521C (DCN5731)