NGA 2000 CLD

Instruction Manual

HAS60E-IM-HW

June 2007

3-7 MEASUREMENT OF CONVERTER EFFICIENCY

It is the responsibility of the user to measure efficiency of the NO2-to-NO converter during initial startup and thereafter 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, operation at a lower temperature setpoint than initially required 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 N2.

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 concentration NO standard may be used if the test setup includes 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 because it may produce oxygen atoms, which can then combine with atmospheric nitrogen to form NO. The result can erroneuosly high value for the measured conversion 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/N2 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. NO2 is now being formed from the NO+O3 reaction. There must always be at least 10 percent un-reacted NO at this point. Record this concentration.

10.Switch the CLD Module to NOx mode. Total NOx 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 NOx concentration of the di- lute NO span gas initially used is displayed. Record this concentration.

3 - 14 Operation

Emerson Process Management GmbH & Co.OHG