EN 14792 - Oxides of Nitrogen by Chemiluminescence Flashcards

1
Q

What is the principle of chemiluminescence?

EN 14792

A
  1. Based on reaction of NO with O3
  2. Reaction leaves NO2 molecules in excited state, emitting light radiation
  3. Amount of radiation is proportional to amount of NO in sample gas
  4. Radiation filtered by an optical filter and converted to electric signal by a photomultiplier tube.

BS EN 14792

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2
Q

Should the filter upstream of the sample line be heated?

EN 14792

A

Yes

EN 14792

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3
Q

What temperature must the gas be conditioned to?

EN 14792

A

Outlet temperature of ≤ 4°C

EN 14792

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4
Q

What is allowable for the zero check following zero and span gas calibration?

EN 14792

A

No significant change on the zero reading

EN 14792

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5
Q

What is the allowable deviation on the pre-test zero and span gas line checks?

EN 14792

A

< 2% of the span gas value

EN 14792

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6
Q

What specification of zero gas is required?

EN 14792

A

Nitrogen containing insignificant concentration of Nitrogen Oxides

EN 14792

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7
Q

What specification of span gas is required?

EN 14792

A

NO or NO / NO₂ mix
(Expanded uncertainty ≤ 2%)

EN 14792

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8
Q

What must the concentration of the span gas be for regulatory work?

EN 14792

A

Approximately at the half hourly ELV or 50 to 90% of the analyser range

EN 14792

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9
Q

What is maximum allowable analyser response time?

EN 14792

A

200 seconds to reach 90% of the range

EN 14792

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10
Q

What is the maximum allowable sample residence time?

EN 14792

A

< 60 seconds

EN 14792

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11
Q

What is the allowable lack of fit (linearity) and how often must the analyser be checked for lack of fit?

EN 14792

A

≤ 2% checked at least once a year

EN 14792

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12
Q

What is the allowable uncertainty at a 95% confidence interval?

EN 14792

A

± 10% of the daily ELV

EN 14792

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13
Q

How often must a NO₂ loss check be performed?

EN 14792

A

Every 3 months

EN 14792

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14
Q

What % of the NO₂ must the NOx converter be capable of converting to NO?

EN 14792

A

≥ 95%

EN 14792

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15
Q

What is a major source of cross interference in chemiluminescence analysers?

EN 14792

A

Carbon dioxide, particularly in the presence of water vapour due to quenching.

EN 14792

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16
Q

How can the effect know as “quenching” be combatted?

EN 14792

A

By using correction curves or by calibrating using gas containing same CO2 content in the stack.

EN 14792

17
Q

What is the state range of the method?

EN 14792

A

30 minute sampling periods:
0 to 1,300 mg/m³ for LCPD
0 to 400 mg/m³ for Waste Incineration

EN 14792

18
Q

What should the measurement range of a NOx analyser be able to cover?

EN 14792

A

Large enough to cover the peak emission and at least 150% of the half-hourly ELV

EN 14792