Mineral Matter Transformations During the Oxygen-Enriched Combustion of Sewage Sludge

摘要

Combustion of sewage sludges was studied in a laboratory-scaled drop tube furnace to investigate their combustibility and evolution of mineral matters in the oxygen-enriched atmosphere. The experimental results indicated that, at low oxygen content, the major mineral compounds in sludge, including calcium oxide, phosphorus oxide and aluminosilicate, mainly underwent coalescence within char to form the large molten agglomerates. Increasing oxygen content resulted in the rapid decomposition of sludge, and accordingly, many droplets were firmed and condensed into fine panicles. Additionally, the vaporization model for both sodium and zinc was built considering the internal diffusion of both two elements with char and their reaction with phosphates. The simulation results had a fairly good consistence with experiments. Sodium was released mainly under the controlling of its internal mass-transfer diffusion within ash layer. Conversely, zinc was released under the controlling of both internal mass-transfer diffusion and its reaction of with molten phosphate salts. Improving oxygen content mitigated the diffusion resistance in ash layer, and hence, more sodium and zinc were vaporized.