Summary

Two major environmental problems that limit combustion processes in furnaces are emission of nitrogen oxides and emission of fine particles. Mechanisms of nitrogen oxide pollutant formation and destruction have been researched for many decades. The chemical kinetics are now well understood, and this understanding has led to pollutant abatement measures such as staged combustion and reburning. Not currently available is a quantitative understanding of the coupling between flame aerodynamics/mixing and NOx formation/destruction kinetics. This paper presents research results describing how poor, non ideal mixing, such as are obtained in diffusion flames, can be exploited to allow NOx reduction by reburning under overall fuel lean conditions, where premixed kinetic mechanisms suggest reburning to be ineffective. One especially interesting result was that the transition from laminar to turbulent diffusion flames affected the apparent order of NO reduction with respect to NO.

The other problem that is of environmental concern is that of fine particle emissions. This paper describes results on the partitioning of trace metals in fine particles during the combustion of coal. A relatively new result is that the particle size distribution from coal combustion can be trimodal, rather than bimodal, as has been reported in the literature hitherto. Also important is the partitioning of toxic metals during the combustion process, and how this depends on the form in which the metal is first introduced into the furnace. This research has been coupled with health effects research in an attempt to link the combustion process with the health effects of the fine particles emitted. Results from an international project involving collaboration between multiple laboratories and multiple disciplines, show that the composition of particles produced from co-combustion of a mixture of municipal sewage sludge (MSS) and coal caused potential severe long-term respiratory distress in mice. Ash particles from combustion of coal alone, or MSS alone, appeared to show short term, inflammatory effects common to all particles.