NOx-emissions from flameless coal combustionin air, Ar/O2 and CO2/O2

摘要

Flameless or ‘mild’ combustion is a well known measure to reduce Nox-emissions. This work aims atthe application of the technique to coal combustors. Experiments have been carried out with lignite as wellas bituminous coals showing an overall Nox-reduction capability with the current burner design of about20–50% depending on fuel type and the stoichiometry at the burner. The most important design feature is ahigh momentum of the combustion air inducing a strong recirculation which reduces the temperature variationsand temperature peaks in the combustion chamber and thus prevents thermal NO formation. Aninvestigation of Nox-emissions under Ar/O2 as well as CO2/O2 atmospheres was carried out in order toquantify the ratio of fuel- to thermal-NO. This investigation showed a high reduction of thermal NO inthe flameless combustion mode. It also showed an increase of fuel-NO which was primarily related tothe decrease of the peak flame temperature in flameless combustion. The intensive mixing in flameless combustionalso allows a reduction of the oxidiser oxygen concentration under oxyfuel conditions to 15 vol %as compared to 17 vol % with a standard swirl burner.