OCR Text |
Show ) stack emission rates and the Tier II emissions levels are presented in Table 2. The results show that the measurement of hexavalent chromium was necessary to prove that the emission levels were acceptable. Measurement of total chromium only along with the required conservative assumption that all chromium was hexavalent chromium would have given an emission level above the proposed limit. Although lead emissions were acceptable, they approached within 31% of the allowable levels. Since the concentration of lead in the waste material was a moderate 180 ppm, the measured emission rates show that waste materials containing high concentrations of lead may have excessive emission rates. Metals Partitioning Concentrations -- The results of the analyses of the different residues, which are presented in Table 3, showed that metal concentrations varied greatly. Hexavalent chromium was not detected in the kiln ash or stack particulates but hexavalent chromium was found in the cyclone ash and separator sludge. The analyses showed that about 17% to 19% of the chromium in the cyclone ash had converted to hexavalent chromium. However, only minor quantities of hexavalent chromium, equivalent to about 1% to 2% of the total chromium, were detected in the . ~eparator sludge. Concentrations of chromium and arsenic remained reasonably constant in the different residue streams. The metals that form low boiling point compounds i.e. cadmium, lead, and mercury, had much lower concentrations in the kiln ash and cyclone ash residues than in the waste feed. Also cadmium and lead exhibited much lower concentrations in the cyclone ash than in the kiln ash. The concentrations of cadmium and lead were about 12% to 33% in the kiln ash and about 1 to 2% in the cyclone ash compared to the waste. Mercury .was not detected in either the kiln ash or cyclone ash. This data is in general agreement with the equilibrium predictions for mercury and lead presented in Reference 6. However, the behavior of arsenic, which also forms low boiling point compounds, was anomalous. As shown in Table 3, cadmium and lead concentrated in the separator sludge at levels of 5 to 16 times greater than the concentrations in the waste feed. This concentrating phenomenon was even greater in the stack emissions. Lead concentrations were about 50 times; cadmium about 65 times; and mercury about 85 to 90 times greater than in the waste. The above behavior is consistent with evaporation of low boiling point compounds in the hot part of the incineration system (1700oF in kiln, 21000F in SCC) followed by condensation of the compounds in the cool part of the system (190oF) [2]. A proportionately greater mass of material condenses on the lower weight small diameter particles due to their higher surface to volume ratio. As illustrated by the particle size distribution data presented in Table 4, the coarsest particles are removed at each stage of particulate removal in the MIS. Since coarse particulates are removed more efficiently by the air pollution control devices than the fine particles and fine particles contain greater amounts of condensed volatile materials, the concentration of volatile metals increases with each stage of particulate removal. 7 |