Combustion analyzers

Combustion analyzers are instruments dedicated to monitoring pollutant emissions and combustion efficiency in boilers, burners, industrial furnaces and heating plant. They measure the main flue gas parameters simultaneously: oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), sulfur dioxide (SO2), unburnt hydrocarbons, flue gas temperature and draft (the differential pressure between flue and ambient). They automatically calculate combustion efficiency, stack losses, excess air and lambda, λ. They are used in the maintenance of heating plant, in mandatory periodic inspections, in environmental checks, in energy optimization and in the R&D of new burners.

Sensors used

The most widespread sensors are: electrochemical for O2, CO, NOx, SO2 and H2 (compact, accurate for standard industrial applications, with a service life of 1-3 years after which they must be replaced); NDIR for CO2 and hydrocarbons (virtually unlimited life, with no degradation); paramagnetic for high-precision O2; thermoresistive for HC (unburnt hydrocarbon sensors); type K thermocouples for flue gas temperature (range up to 1200 °C). The sensors are protected by particulate and condensate filters, with systems that drain accumulated condensate automatically.

Automatic calculations

Once the type of fuel is known (natural gas, diesel oil, LPG, biomass, coal and so on), the analyzer automatically calculates: combustion efficiency η (the efficiency of the combustion process, % – typically 85-95% for modern boilers); stack losses (% of heat lost with the flue gases); excess air λ (the ratio between actual and stoichiometric air – an optimum value of 1.1-1.4 for most fuels); the CO/CO2 ratio (an indicator of complete or incomplete combustion); and normalized values for comparison with regulatory limits. The built-in fuel database is extensive and can be customized.

Mandatory periodic inspections

In Italy, Presidential Decree 74/2013 governs the mandatory periodic inspections of heating plant used for winter climate control in buildings (boilers and other generators). The inspection involves measuring energy efficiency (with a combustion analyzer) and emission parameters, at intervals that vary with the plant’s output and fuel (typically every two or four years for residential installations, annually for high-output heating plant). The test report (the “bollino blu”) is mandatory and signed by a qualified technician. The rules are stricter for industrial plant and for atmospheric emissions under Legislative Decree 152/2006 (the environmental code).

Industrial applications

The industrial applications are: maintenance of domestic and industrial boilers; monitoring of the burners of industrial furnaces (firing kilns, heat treatment furnaces, steelworks furnaces); emission monitoring of cogeneration heating plants; optimization of combustion processes (reducing consumption and emissions); commissioning tests of new burners; monitoring of internal combustion engines (although specific analyzers are used for engines); and environmental inspections for AIA integrated environmental emission permits.

Reference standards

The main standards are: UNI 10389-1 (combustion analyzers – requirements); UNI EN 50543 (CO/CO2 detectors); in Italy, Presidential Decree 74/2013 (heating plant); Legislative Decree 152/2006 and subsequent amendments (the environmental code, atmospheric emissions); EN 14181 (QAL – Quality Assurance Level for continuous emission monitoring systems, CEMS). Analyzers are calibrated with ISO 17025 certified gas mixtures of known concentration, typically once a year or as the manufacturer specifies.

Selection criteria

The choice of combustion analyzer depends on: the parameters to be measured (simple for domestic use = O2/CO/T; complete for industrial use = adding NOx, SO2 and NDIR CO2); the concentration range (high for industrial applications above the 10,000 ppm CO/NOx range); the built-in fuel database; an integrated printer or wireless connectivity for immediate reports; compliance with UNI 10389-1; battery life for on-site service work; and an ISO 17025 traceable calibration service.