Combustion without flames has always been known at low temperatures, whilst the discovery of flameless combustion happening at high temperatures is recent.
The phenomenon is created when the fuel temperature is above the ignition point or in general above 750°C .
In these conditions, if the fuel is injected directly into the furnace, at given levels of turbulence and velocity, and bypassing the mixer with combustion air, this generate an oxidation reaction which does not occur in the visible range, but still produces thermal energy.
In these conditions it is compulsory to disconnect the flame detection device as the flame is not visible anymore, and / or disconnect the ignition system: combustion will take place all the same.
|Thermal image with visible flame||Thermal image flameless|
|Max power: 400kW
T° furn = 1200°C T° air=500°C
Max T° flame = 1900°C
|Max Power: 400kW
T° furn = 1200°C T°air=500°C
Max T° flame = 1550°C
Combustion in flameless mode considerably reduces the formation of NOx as:
– Temperature peaks inside the flame are contained
– It is deleted the flame front, the separation surface between reactants and combustion products, which is the main zone of NOx formation.
– Lowers the relative concentration of oxygen in the flame, reducing the reaction speed of nitrogen in the air.
– part of previously formed NOx are carried back into the oxidation reaction, and burned again
ESA developed am optional kit for Flameless combustion available for different types of burners,