FLOX combustion technology has been developed for gaseous fuels, exhibiting ultra low NOx
-emissions, substantial energy savings and stable combustion for low calorific fuels.
Recently, application of this combustion technology to solid fossil fuels like pulverised coal has become of interest. The goal of ultra low NOx
-emissions is achieved by the separation of coal/primary air jet and secondary air jet as well as by avoiding of temperature peaks at the flame front.
The suppression of a stable flame front reduces NOx
-emissions via the thermal NO path (Zeldovich mechanism). Fuel-N contributes via the second governing path during combustion to NOx
-emissions. Experimental results have shown that low NOx
-emissions can be achieved by controlling the availability of oxygen in the burner vicinity.
Since combustion starts in fuel-rich, i.e. reducing conditions, drastic reduction of fuel-NO formation results. These combustion conditions are obtained by a fast heat up of coal and primary air over self-ignition temperature. Thus, devolatilisation takes place in the burner vicinity and devolatilised fuel-N reacts to N2
. Furthermore, lighter volatiles serve as fuel for reburning already existing NO. Dilution of injected secondary air results in a preheated high momentum jet, which oxidises remaining burnable molecules without a visible flame. Because of the wide spread reaction zone flameless oxidation is also known as volumetric combustion.
Former investigations of pulverised coal FLOX
burners shown the ability of very high burnout which means a high efficiency of the combustion process.
An additional advantage of the inexistent flame front is the reduced noise emission.