🌿 Oxygen (O₂) in waste gases — paramagnetic analyser (reference method)
In short
Continuous measurement of the volume concentration of oxygen in waste gases with a paramagnetic analyser fed through a probe, a filter, a line and a conditioning system; the standard reference method validated in the range 3–21 % for periods of 30 min, serving for the conversion of emission results to the reference oxygen content. The test is performed according to PN-EN 14789:2017-04 (EN 14789:2017); Range of validation: 3–21 % by volume O₂; sampling 30 min. The procedure comprises 5 steps; it is used for: Measurement of O₂ accompanying every emission measurement — the conversion of the concentrations of SO₂, NOx, CO and dust to the reference oxygen content, Calibration and control (QAL2, AST) of automated oxygen analysers (peripheral AMS) — the reference method under the regulation on measurements of emissions, Power boilers, waste incineration and co-incineration plants, industrial furnaces, engines and turbines.
At a glance
- Standard: PN-EN 14789:2017-04 (EN 14789:2017)
- Category: Environment
- Procedure steps: 5
- Range of validation: 3–21 % by volume O₂; sampling 30 min
- Result: volume concentration of O₂ in %; the basis for the conversions to reference O₂ and dry gas (273 K, 101.3 kPa)
- Performance characteristics: zero and span drift, linearity (lack of fit), interferences, response time t90 — in accordance with the criteria of the standard
Overview
EN 14789 specifies the standard reference method (SRM) based on the principle of paramagnetism for the determination of the concentration of oxygen in waste gases from ducts and stacks; it covers the gas sampling and conditioning system and the analyser. The standard gives the performance characteristics and the criteria for measuring systems, it is applied to periodic monitoring and to the calibration and control of automated measuring systems (AMS), and it lays down criteria for the equivalence of alternative methods (EN 14793). It was validated in field tests at incineration plants, co-incineration plants and large combustion plants and on a test rig for sampling periods of 30 min in the range 3–21 %. The concentrations of oxygen, expressed as volume concentrations, serve to standardise the results of emission measurements to the reference oxygen content and to dry gas required, for example, by Directive 2010/75/EU. The 2017 edition replaced EN 14789:2005. In Poland the regulation on the measurement of the quantity of emissions indicates PN-EN 14789 as the reference method for O₂ in the control of continuous measurements.
Method principle
The paramagnetic method makes use of the strong attraction of oxygen molecules by a magnetic field (paramagnetism), whereas the remaining components of waste gases are weakly paramagnetic or non-magnetic, which makes it possible to measure the oxygen selectively. The magnetic susceptibility of a gas is inversely proportional to its absolute temperature; a sample containing oxygen in a gradient of a magnetic field in a confined space flows in the direction of the field, and the magnitude of that flow depends on the concentration of oxygen — it is measured by various designs of analyser. The analyser is connected to an extractive sampling system and a gas conditioning system: the sample is taken from the stack with a probe and led through a sampling line and the conditioning to the analyser, and the readings are recorded electronically. The standard defines the performance characteristics of the analyser (zero and span drift, linearity, interferences, response time t90), which together with the combined uncertainty of the method must meet the criteria of the standard; the span gas is usually chosen at about 80 % of the upper limit of the range.
Applications
- Measurement of O₂ accompanying every emission measurement — the conversion of the concentrations of SO₂, NOx, CO and dust to the reference oxygen content
- Calibration and control (QAL2, AST) of automated oxygen analysers (peripheral AMS) — the reference method under the regulation on measurements of emissions
- Power boilers, waste incineration and co-incineration plants, industrial furnaces, engines and turbines
- Control of the combustion process (excess air) in the power industry and in industry
- Demonstration of the equivalence of alternative methods (e.g. electrochemical, zirconia) with respect to the SRM
Key parameters
| Parameter | Value |
|---|---|
| Range of validation | 3–21 % by volume O₂; sampling 30 min |
| Result | volume concentration of O₂ in %; the basis for the conversions to reference O₂ and dry gas (273 K, 101.3 kPa) |
| Performance characteristics | zero and span drift, linearity (lack of fit), interferences, response time t90 — in accordance with the criteria of the standard |
| Span gas | usually about 80 % of the upper limit of the range |
| Uncertainty | expanded, from the uncertainty budget, k = 2 (95 %) |
Standard
- Standard number
- PN-EN 14789:2017-04 (EN 14789:2017)
- Title (PL)
- Emisja ze źródeł stacjonarnych — Oznaczanie stężenia objętościowego tlenu — Standardowa metoda odniesienia: Paramagnetyzm
- Title (EN)
- Stationary source emissions — Determination of volume concentration of oxygen — Standard reference method: Paramagnetism
Step-by-step procedure
-
Planning
Plan the measurement in accordance with EN 15259 together with the measurements of the components for which the O₂ serves for the conversions; establish the range of the analyser and the span gas (about 80 % of the range).
-
Assembly and conditioning
Install the probe, the filter, the line and the conditioning system (removal of the water vapour — the result for dry gas); check the leak-tightness and heat the parts above the dew point.
-
Adjustment
Feed zero gas and span gas directly to the analyser and through the probe; check the response time and the linearity in accordance with the requirements of the standard.
-
Measurement
Record the concentration of O₂ continuously in parallel with the emission measurements over the averaging period (e.g. 30 min).
-
Drift check and calculations
After the measurement check the zero and the span; calculate the mean concentration of O₂ and use it to standardise the results for the other components to the reference oxygen content; draw up an uncertainty budget.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Paramagnetic O₂ analyser | designs measuring the flow induced paramagnetically (clause 5 of the standard) | — |
| Sampling probe with a particulate filter | inert materials, heated above the dew point | — |
| Sampling line and conditioning system | removal of the water vapour (a cooler, a permeation dryer) or a heated line | — |
| Test gases: zero (N₂) and span (O₂ in N₂ or air of a known composition) | with certificates | — |
| Data recording system | electronic recording of the readings of the analyser | — |
Health and safety (OHS)
- Secure and fasten the cylinders with test gases; span gas with an increased O₂ content increases flammability — keep it away from lubricants and sources of ignition
- The heated parts of the sampling system and work on the stack platform — heat-resistant gloves, protection against falling
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 14789:2017-04 (EN 14789:2017) — “Stationary source emissions — Determination of volume concentration of oxygen — Standard reference method: Paramagnetism”.
How does this method work?
The paramagnetic method makes use of the strong attraction of oxygen molecules by a magnetic field (paramagnetism), whereas the remaining components of waste gases are weakly paramagnetic or non-magnetic, which makes it possible to measure the oxygen selectively. The magnetic susceptibility of a gas is inversely proportional to its absolute temperature; a sample containing oxygen in a gradient of a magnetic field in a confined space flows in the direction of the field, and the magnitude of that flow depends on the concentration of oxygen — it is measured by various designs of analyser.
What is the measuring range and accuracy?
Range of validation: 3–21 % by volume O₂; sampling 30 min; Result: volume concentration of O₂ in %; the basis for the conversions to reference O₂ and dry gas (273 K, 101.3 kPa); Performance characteristics: zero and span drift, linearity (lack of fit), interferences, response time t90 — in accordance with the criteria of the standard; Span gas: usually about 80 % of the upper limit of the range.
How long does the test take?
The procedure comprises 5 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Paramagnetic O₂ analyser, Sampling probe with a particulate filter, Sampling line and conditioning system, Test gases: zero (N₂) and span (O₂ in N₂ or air of a known composition), Data recording system.
Where is this test used?
Measurement of O₂ accompanying every emission measurement — the conversion of the concentrations of SO₂, NOx, CO and dust to the reference oxygen content; Calibration and control (QAL2, AST) of automated oxygen analysers (peripheral AMS) — the reference method under the regulation on measurements of emissions; Power boilers, waste incineration and co-incineration plants, industrial furnaces, engines and turbines; Control of the combustion process (excess air) in the power industry and in industry; Demonstration of the equivalence of alternative methods (e.g. electrochemical, zirconia) with respect to the SRM.
What safety precautions apply?
Secure and fasten the cylinders with test gases; span gas with an increased O₂ content increases flammability — keep it away from lubricants and sources of ignition; The heated parts of the sampling system and work on the stack platform — heat-resistant gloves, protection against falling.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN 14789.