The Effects of Extraneous Metal Oxides and Chlorides on the Partitioning of Toxic Metals in the Flames of a Pulverised Waste Fuel

Abstract

Measurements of metal partitioning between the submicron and supermicron particles produced during the combustion of a dried pulverised sewage sludge (DPSS) containing metal additives in extraneous forms with varying volatilities were made in a high heating rate (10⁵ K/s) Flat Flame Turbulent Jet (FFTJ) apparatus. The fate of metal oxides and chlorides was separately studied by introducing salts of Cd, Zn, Pb and Ni with the feed in the DPSS flame. The mass fraction of submicron particles in the sewage sludge flame was increased from 0.004 to 0.008 and 0.05, respectively, when metal oxides and chlorides were added to the fuel. The results suggest that the extraneous metal chlorides partition more to submicron particles as compared with the conditions where metal oxides were added. The observations show that the hypothesis that metal partitioning is primarily controlled by its vapour pressure is inadequate in the presence of large quantities of minerals and other processes such as fragmentation and mineral/metal interactions become increasingly important.

Keywords:

• Toxic metal emissions
• waste combustion
• particulate emissions