Practical Guide
Industrial flue gas analysis

Major contributions to combustion optimization are made by

• The composition of fuel and combustion air (gas analysis field of application)

• The ignition behaviour and the combustion temperature

• The design of the burner and combustion chamber, as well as

• The fuel/combustion air ratio (gas analysis field of application).

The optimum ratio of fuel to combustion air (air ratio λ) for a given plant and a specific fuel can be determined from gas analysis readings using the combustion chart (see Figure 7). Here, the concentration progressions of the gas components CO, CO₂ and O₂ are shown in relation to the air ratio. The line of ideal combustion with 0 excess air is located at an air ratio of λ = 1. To the right, the excess air increases, while to the left lies the range of increasing air deficiency (insufficient air also means insufficient oxygen!).

ppm (abbreviation for parts per million) is a commonly used unit of concentration in the form of a mixing ratio; it has an equally common counterpart unit of mass concentration.

A specification in [ppm] can be converted to the corresponding unit of mass concentration [mg/Nm³] using the standard density of the gas in question as the factor for the formulae shown below. The "dilution" of the flue gas by air (from the excess air and where necessary from targeted additions of air or through possible leaks in the plant), of which the oxygen concentration is a measure, must also be taken into account. The readings must therefore generally be converted to a certain oxygen portion (called the "O₂ reference"). Only specifications with the same oxygen reference value are directly comparable! For this reason, the corresponding oxygen reference values are also always specified in the official requirements alongside the pollutants. In addition, the actual oxygen portion measured, which is a measure of the actual dilution, is also required for the conversion (O₂ in the denominator of the formula).