The modern combustion gas analyser is an electronic instrument that will extract a sample of gas from a burner flue continuously and test the concentrations of the individual gas components inside it. The combustion gas analyser also measures inlet air temperature and flue gas temperature in order to calculate the thermal efficiency of the system.
Using the results for oxygen and known parameters of the fuel it is possible to calculate the carbon dioxide concentration, as well as the excess air number. Efficiency and excess air number are the two main factors read from combustion gas analysers when adjusting a burner system.
The combustion gas analyser consists of a probe assembly that is placed inside the flue and contains a thermocouple to measure temperature in the flue gas stream. The gas will then travel through a filter and the suction pump, before passing to the sensors. It is important to remove all the condensate from the gas before it reaches the pump and other parts. The condensate will form an acidic solution with some of the gas components, and may leave tarry deposits that can block valves or other moving parts. The combustion gas analyser is generally fitted with electrochemical sensors for oxygen and carbon monoxide. These two components are the most commonly measured ones. Nitric oxide may also be fitted and there are combustion gas analysers containing a large number of sensors for other gases. The electrochemical sensors contain an electrolyte, so extremely high levels of water will cause damage, as will prolonged exposure to completely dry gases. Combustion gas analysers mostly have a water trap, but larger models, such as the GA-40Tplus, may be fitted with an integral gas dryer.
Combustion gas analysers make the work of adjusting and maintaining a burner system very much simpler.