What Is Flue Gas?
Flue gas analysis measures the composition of the gas leaving a combustion system. Unlike an emission compliance measurement, the focus here is combustion efficiency: by measuring oxygen, carbon dioxide, carbon monoxide and flue gas temperature, how completely combustion occurs and how much energy is lost are calculated.
Purpose of Flue Gas
The purpose is to optimise boiler and burner settings, reduce fuel consumption, and prevent carbon monoxide formation from incomplete combustion. It is also the basic measurement for periodic boiler inspections.
Which Products Is Flue Gas Applied To?
- Industrial and commercial boilers
- Burners and combustion systems
- Furnaces and dryers
- Cogeneration plants
- Central heating systems
In Which Sectors Is Flue Gas Used?
Standards Related to Flue Gas
- TS EN 15259 (measurement strategy and point)
- TS EN 15058 (CO tayini)
- TS EN 14792 (NOx tayini)
- TS EN 14789 (determination of oxygen)
- TS EN 12952-15 / EN 13384 (boiler efficiency and flue calculations)
Flue Gas Conditions
- Measurement point
- A representative point in the stack cross-section, away from air infiltration
- Steady operation
- Measurement is performed while the system is under steady load
- Reference
- Results are converted to the defined oxygen reference
- Temperature
- Flue gas and ambient temperature are measured for the efficiency calculation
Equipment for Flue Gas
- Portable flue gas analyser
- Electrochemical and NDIR sensors
- Temperature probe and draught gauge
- Pitot tube
Sample Requirements for Flue Gas
- Measurement is performed on site
- Fuel type and its analysis must be provided — the efficiency calculation depends on this
- Boiler capacity and operating load must be recorded
- The system must be brought to steady operation before measurement
Duration of Flue Gas
The field measurement is completed quickly. If measurement at different load stages is required, duration increases with the number of stages.
Flue Gas Procedure
- 1The system is run at steady load.
- 2The measurement point is determined and the probe is inserted.
- 3O2, CO2, CO and NOx concentrations are measured.
- 4Flue gas and ambient temperature are recorded.
- 5Draught and air infiltration are assessed.
- 6Combustion efficiency and flue gas loss are calculated.
Flue Gas Acceptance Criteria
The acceptance criterion is the minimum combustion efficiency and emission limit values set per boiler type and legislation. Values applicable in periodic boiler inspections are defined in national legislation; the manufacturer's specification may also state its own efficiency target.
Evaluation of Results
A high oxygen value means excess air and lowers efficiency; too low an oxygen value carries a risk of incomplete combustion and carbon monoxide formation. The optimum setting lies between these two. If air infiltrates at the measurement point, oxygen reads misleadingly high and the whole calculation is thrown off.
Flue Gas Report
- System identification, capacity and fuel information
- Measurement point and operating load
- O2, CO2, CO and NOx results
- Flue gas and ambient temperature
- Combustion efficiency and flue gas loss calculation
- Improvement recommendations
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- (EU) 2015/2193 Medium Combustion Plant Directive
- (EU) 2010/75 Industrial Emissions Directive
- 2009/125/EC Ecodesign Directive (for relevant product groups)
Environmental Analysis — What Does This Testing Field Cover?
The section below describes the field that the Flue Gas test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Environmental analysis determines the presence and concentration of pollutants in water, soil, waste, air and flue gas samples. The output of this family is usually part of a permit, a declaration or an inspection file; the result has direct legal consequences.
In this family SAMPLING is half the result, and this is the feature that most sets the field apart. A sample taken at the wrong time, in the wrong container, under the wrong preservation or from the wrong point gives an invalid result no matter how well it is analysed in the laboratory. In waste water a grab sample and a composite sample give different information; in soil, surface and depth produce different results. Sampling therefore has its own standards and its own accreditation scope.
On the water side, physico-chemical parameters (pH, conductivity, turbidity, COD, BOD, suspended solids), ions, heavy metals, organic pollutants and microbiological parameters are measured. Drinking water and waste water carry different parameter sets and different limits; the same laboratory method leads to a different decision under the two regimes.
In soil and waste, heavy metals, hydrocarbons, PAH and PCB compounds and LEACHING BEHAVIOUR are determined. The leaching test carries a logic peculiar to this field: it is not the total amount of a pollutant in soil but the fraction that can pass into water that determines the environmental risk. Waste classification and the disposal decision rest largely on this test.
On the emissions side, dust, sulphur dioxide, nitrogen oxides, carbon monoxide, oxygen, moisture and total organic carbon are monitored in flue gas. Measurement is made on site under operating conditions and must represent the plant's actual operating regime; a measurement taken at low load does not show the emissions at full capacity.
Continuous measurement systems are a separate body of work. In large plants emissions are monitored continuously and the accuracy of these systems is verified periodically by comparison with independent measurements; the quality assurance framework governs this.
Noise and vibration measurements complete the environmental impact side of the field: environmental noise mapping, workplace noise exposure and vibration exposure measurements produce evidence for both environmental and occupational health legislation.
Method groups in this field
Sampling
Separate sampling standards for water, waste water, soil, waste, flue gas and ambient air; grab, composite and continuous sampling techniques.
Water physico-chemical
pH, conductivity, turbidity, colour, suspended solids, COD, BOD, TOC, alkalinity, nitrogen and phosphorus species.
Elemental analysis
Determination of heavy metals and trace elements in water, soil and waste by ICP-OES and ICP-MS.
Organic pollutants
Volatile organic compounds, PAH, PCB and organochlorine pesticides by GC-MS; hydrocarbon oil index.
Flue gas
Measurement of dust, SO2, NOx, CO, O2, moisture and total gaseous organic carbon; quality assurance of automated measuring systems.
Leaching and waste characterisation
Leaching tests and waste classification parameters; the basis for the disposal decision.
Commonly confused in this field
- An analytical result cannot be used on its own without the sampling record; the time, point, conditions and chain of custody are part of the report.
- Total content and leachable amount give different information; in waste classification, leaching behaviour is what counts.
- Emission measurement must be made under representative operating conditions of the plant; a result taken at partial load is misleading.
- Drinking water and waste water limits are defined in different legislation; the same parameter carries a different threshold under the two regimes.
- A sample from a single point does not represent the whole area; assessment of a contaminated site requires a grid-based sampling plan.
Which decisions these results support
- Compliance with environmental permits and discharge limits
- Quality assurance of continuous emission measurement systems
- Contaminated site assessment and the remediation decision
- Waste classification and selection of the disposal method
- Workplace exposure measurements and occupational health obligations
Related Tests
Frequently Asked Questions About Flue Gas
Does flue gas analysis substitute for emission measurement?
No. The efficiency measurement with a portable analyser is for operational purposes; a regulatory compliance declaration requires an accredited emission measurement per EN 15259 and pollutant-specific standard methods.
Our CO value came out high — what does that mean?
It indicates incomplete combustion: it can stem from insufficient air, poor mixing, burner setting, or fouled heating surfaces. It is a finding that must be corrected for both safety and efficiency.