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Show This level of insight is now being applied to understanding differences between data collected in different combustors and under different test conditions. Figure 5 provides a summary of the data collected in the DOE program described earlier[3]. These data show that while total particulate lE-2~~----____________________________________ ~ lE-3 ~ lE-4 ......, lE-5 ~ lE-6 ell ell J: lE-7 o'"" IE-8 go IE-9 > e IE-IO ·S IE-II .0 :3 IE-12 =' $IE-13 IE-14 j I / ! i / Mercury ! ; I i i J l r J ; , 'u . I ranlum I I E-15 -t-----~----~--"""---_r------.,_----~----__f o 200 400 600 800 1000 1200 Temperature (deg C) matter removal across the Figure 4. Vapor pressures for mercury, selenium, boron and uranium as a ESP is essentially 100 per- function of temperature under conditions representative of coal combustion flues gases in the absence of chlorine or Hel. cent, removal efficiencies for selenium, boron, mercury, and several radionuclides are much lower. The presence of Cl2 and HCI immediately suggest the existence of volatile lead chloride that will be poorly collected by the ESP. Also, oxides of metals such as lead and some radionuclides, when present at sufficiently low concentra- Particulate Ra-226 PCDDIF B Pb-21 0 U-238 U-235 2,3,7,8 TCDD CI2 HCI Se C:;::::~~~ ___ =~>~~,~ tions, will volatilize completely in the combustion zone. Due to their low concentrations these species subsequently recondense at lower APCD temperatures into ultra-fine particulate matter that is much less effectively removed than typical fly-ash particles. Hg I I I I o 20 40 60 80 100 REMOVAL EFFICIENCY (0/0) Figure 5. Measured metals removal efficiencies across an ESP in a coalfired cell burner utility boiler. The low removal efficiency for boron is somewhat of a surprise. In these tests boron is present at about 5 mg/dscm, or roughly 5 ppm. The thermodynamic predictions shown in Figure 4 indicate that boron should have a substantially lower vapor pressure at APCD temperatures, and should have therefore condensed. 10 |