9.2 NOx analyser quench checks
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - International Codes - NOx Technical Code (2008) - Technical Code on Control of Emission of Nitrogen Oxides from Marine Diesel Engines - Appendix 4 - Calibration of the analytical and measurement instruments - 9 Interference effects with CO, CO2, NOx and O2 analysers - 9.2 NOx analyser quench checks

9.2 NOx analyser quench checks

 The two gases of concern for CLD (and HCLD) analysers are CO2 and water vapour. Quench responses to these gases are proportional to their concentrations, and therefore require test techniques to determine the quench at the highest expected concentrations experienced during testing.

Parent topic: 9 Interference effects with CO, CO2, NOx and O2 analysers

9.2.1 CO2 quench check

  9.2.1.1 A CO2 span gas having a concentration of 80% to 100% of full scale of the maximum operating range shall be passed through the NDIR analyser and the CO2 value recorded as A. It shall then be diluted approximately 50% with NO span gas and passed through the NDIR and (H)CLD, with the CO2 and NO values recorded as B and C, respectively. The CO2 shall then be shut off and only the NO span gas be passed through the (H)CLD and the NO value recorded as D.

  9.2.1.2 The quench shall be calculated as follows:

 where:

  • A = the undiluted CO2 concentration measured with NDIR in percentage by volume;

  • B = the diluted CO2 concentration measured with NDIR in percentage by volume;

  • C = the diluted NO concentration measured with (H)CLD in ppm; and

  • D = the undiluted NO concentration measured with (H)CLD in ppm.

  9.2.1.3 Alternative methods of diluting and quantifying of CO2 and NO span gas values such as dynamic mixing/blending, can be used.

9.2.2 Water quench check

  9.2.2.1 This check applies to wet gas concentration measurements only. Calculation of water quench must consider dilution of the NO span gas with water vapour and scaling of water vapour concentration of the mixture to that expected during testing.

  9.2.2.2 A NO span gas having a concentration of 80% to 100% of full scale of the normal operating range shall be passed through the HCLD and the NO value recorded as D. The NO span gas shall then be bubbled through water at a temperature of 25°C ± 5°C and pass through the HCLD and record the NO value as C. The water temperature shall be determined and recorded as F. The mixture’s saturation vapour pressure that corresponds to the bubbler water temperature (F) shall be determined and recorded as G. The water vapour concentration (H in %) of the mixture shall be calculated as follows:

 The expected diluted NO span gas (in water vapour) concentration (De) shall be calculated as follows:

 For diesel engine exhaust, the maximum exhaust water concentration (in %) expected during testing shall be estimated, under the assumption of a fuel atom H/C ratio of 1.8/1, from the maximum CO2 concentration A in the exhaust gas as follows:

 and Hm is recorded.

  9.2.2.3 The water quench shall be calculated as follows:

 where:

D e = the expected diluted NO concentration in ppm;
C = the diluted NO concentration in ppm;
H m = the maximum water vapour concentration in %; and
H = the actual water vapour concentration in %.

  Note: It is important that the NO span gas contains minimal NO2 concentration for this check, as absorption of NO2 in water has not been accounted for in the quench calculations.

9.2.3 Maximum allowable quench

 The maximum allowable quench shall be:

  • .1 CO2 quench according to 9.2.1: 2% of full scale.

  • .2 Water quench according to 9.2.2: 3% of full scale.

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