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NGA 2000 CLD
Instruction Manual
HAS60E-IM-HW
June 2007
3 - 14 Operation Emerson Process Management GmbH & Co.OHG
3-7 MEASUREMENT OF CONVERTER
EFFICIENCY
It is the responsibility of the user to measure efficiency of
the NO
2
-to-NO converter during initial startup and there-
after at intervals appropriate to the application (normally
once a month).
The reactant material used in the converter provides the
optimum combination of high conversion efficiency and
low ammonia interference. Unlike most competitive ana-
lyzers, the NGA 2000 CLD Analyzer Module utilizes a
reactant material that gradually becomes more efficient
at a given temperature. Thus, after a period of use, op-
eration at a lower temperature setpoint than initially re-
quired is possible.
a. Test Setup for Measurement of Conversion
Efficiency
A typical setup for measurement of conversion efficiency
is shown in figure 3-23. The test setup includes:
A cylinder on nitric oxide standard gas consisting of NO
in N
2
.
The concentration on NO in the standard gas should be
about the full-scale value of the range under test. The
test sample supplied to the analyzer should contain a
concentration of NO comparable to that in the samples
that are to be analyzed. Alternatively, a higher concen-
tration NO standard may be used if the test setup in-
cludes provision for diluting it appropriately with zero air.
Suitable standard gases are available from various sup-
pliers. Stainless steel cylinders are commonly used, but
specially treated aluminium is preferred for low parts-
per-million NO samples.
An ozone generator utilizing an ultraviolet lamp, not a
corona discharge.
A corona discharge ozone generator is undesirable be-
cause it may produce oxygen atoms, which can then
combine with atmospheric nitrogen to form NO. The re-
sult can erroneuosly high value for the measured con-
version efficiency.
b. Test Procedure
1. Measure converter temperature in the sub-menu
structure.
Note present reading as a reference for compari-
son with subsequent readings.
2. Lower converter temperature to 300 °C by setting
control parameters, and wait 15 minutes for tem-
perature equilibration.
3. Connect a Converter Efficiency Tester (e.g. Model
958) to the CLD Module (see figure 3-23), and fol-
low Steps 4 through 17 below:
4. Attach the NO/N
2
supply to C2, the air supply to
C1, and the CLD Module inlet fitting to C3.
5. With the variable transformer off, switch the CLD
Module to NO mode, and close valve MV1.
6. Open valve MV2 until the CLD Module SAMPLE
Pressure Gauge reaches operating pressure and
the BYPASS flowmeter indicates some bypass
flow. Wait until stable readings are obtained by the
CLD Module.
7. Zero and span the Analyzer output to indicate the
value of the NO concentration being used. This
value should be about 80 % of full-scale.
Record this concentration.
8. Open valve MV1 (air supply metering valve) and
adjust to blend enough air to lower the NO con-
centration (as noted above) about 10 %.
Record this concentration.
9. Power up the ozonator, and increase its supply
voltage until NO concentration noted in Step 8 is
reduced to about 20 percent of the concentration
noted in Step 7. Wait for stabilization. NO
2
is now
being formed from the NO+O
3
reaction. There
must always be at least 10 percent un-reacted NO
at this point. Record this concentration.
10. Switch the CLD Module to NO
x
mode. Total NO
x
concentration is now output to the network for dis-
play. Record this concentration.
11. Turn off the ozonator, and allow the Analyzer read-
ing to stabilize. Total NO
x
concentration of the di-
lute NO span gas initially used is displayed. Record
this concentration.