Teledyne 9110T instruction manual Pneumatic Sensors, Ozone Supply Air Filter, Ozone Destruct

Model 9110T NOx Analyzer Principles of Operation

To provide a dry purge gas for the outer side of the Nafion tube, the 9110T returns some of the dried air from the inner tube to the outer tube. This means that any time the analyzer is turned on after having been OFF for 30 minutes or more, the humidity gradient between the inner and outer tubes is not very large and the dryer’s efficiency is low. Since it takes a certain amount of time for the humidity gradient to become large enough for the Perma Pure® Dryer operate efficiently, in such cold start cases the O3 Generator is not turned on until 30 minutes has passed in order to ensure that it is not operating until its air supply is properly dry. During this 30 minute duration the O3 GEN OVERRIDE menu displays “TMR” on the front panel screen.

Note	When rebooting the instrument within less than 30 minutes of power-
	down, the generator is turned on immediately.

The Perma Pure® Dryer used in the 9110T is capable of adequately drying ambient air to a dew point of

≤-5˚C (~4000 ppm residual H2O) at a flow rate of 1 standard liter per minute (slpm) or down to ≤ -15˚C (~1600 ppm residual H2O) at 0.5 slpm. The Perma Pure® Dryer is also capable of removing ammonia from the sample gas up to concentrations of approximately 1 ppm.

13.2.3.3. Ozone Supply Air Filter

The 9110T uses ambient air as the supply gas for the O3 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 O3 gas stream, the output of the O3 generator flows through a special filter between the generator and the reaction cell.

The small amount of NOX produced in the generator (from the reaction of O2 or O3 and N2 in the air) will not affect the 9110T’s ability to measure NOx, NO and NO2 as it is accounted for and removed from the concentration calculations by the analyzer’s Auto Zero feature (see Section 13.1.4).

13.2.3.4. Ozone Destruct

Even though ozone is unstable and typically reacts to form O2, the break-down is not quite fast enough to ensure that it is completely removed from the exhaust gas stream of the 9110T by the time the gas exits the analyzer. Due to the high toxicity and reactivity of O3, a highly efficient catalytic converter scrubs or converts all of the O3 from the gas exiting the reaction cell. The conversion process is very safe. It only converts ozone to oxygen and does not produce any toxic or hazardous gases.

The O3 destruct is located just inside the NO2 converter. As this is a true catalytic converter, there are no maintenance requirements as would be required for charcoal-based ozone destructs.

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 prevent the dust from entering the reaction cell or the pump, the ozone destruct is equipped with a quartz wool filter material.

13.2.4. PNEUMATIC SENSORS

Note	The 9110T displays all pressures in inches of mercury absolute (in-Hg-A),
	i.e. absolute pressure referenced against zero (a perfect vacuum).

Teledyne Analytical Instruments 335