OCR Text |
Show Vaporization Reducing Environment \..... Nucleation Coagulation Condensation I /'~:. ':-.:: ;'.:- \ Reaction / /~ - , .. Co .' . ' ... ' .' 3 ~ . • If' ~ •• Particle-Size Distribution 0.2 10 Particle Size, Jlm Fuel. Char or Mineral Fusion Particle Fragmentation, ~ 0 0 J Shedding and 0 0 Trace Metal Coalescence 0 0 0 Entrapment Ce nosp he re Formation EERC CZ10448.CDR Figure 1. Trace metal transformations and partitioning. that trace metals in coal seem to follow during combustion or gasification include either transforming to a vapor phase or very fine aerosol or remaining entrapped with larger-sized major ash material. Trace metals that follow the vaporization or very fIne particulate path undergo either nucleation, coagulation, or condensation, developing a submicron fraction within the total entrained ash stream (8). Trace metals that react with, or become entrapped in, larger maj or ash constituents will show associations with ash particles in the larger-size fraction of entrained ash, bottom ash, or bed material. There does not appear to be a large amount of reported work in the area of trace metal emissions associated with gasification or heavily reducing environments to support these general coal trace metal transformation paths. It has been fairly well established that concentrations of volatile elements such as Hg, As, Cd, Ph, Se, and Zn will increase with decreasing particle size (1, 9-11) and that trace metals will follow distinct paths depending on |