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Show 100 f!- 80 >; u c UCD 60 !E w "i 40 >0 II Cyc+ESP E CD a: 20 liB Cyc+FF II WS+Cyc+FF o Hg Se Cd Sb Pb Cr Co As Mn V Ba PM Figure 6. Comparison of metals removal efficiencies across three APeD configurations on a pilot-scale slip-stream test faclility. The differences in metals removal efficiencies are indicative of the physicochemical mechanisms for metals collection. Figure 6 shows the data collected in a pilot-scale slipstream test facility. Three configurations of APCD were tested for metals removal efficiency. The results for cadmium and mercury are within the limits of error for the sampling and analytical methods and do not suggest a significant difference between the different APCD configurations. Selenium, on the other hand is collected with nearly 100 percent efficiency by the fabric filter baghouse, while 20 percent of selenium escapes the ESP. The difference in behavior between the APCDs and between these and the results in Figure 4 are attributable to the temperature of the particulate control device. In all cases, since the pilot-scale tests were conducted on a slip stream, the temperatures at the APCD were lower than on the full-scale ESP. In addition, however, the pilotscale baghouse was slightly cooler (ca. 20 - 40 OF) than the ESP, and when the scrubber was operating, the temperature dropped to within 20 OF of saturation at the baghouse. Figure 7 confirms the sensitivity of the selenium partitioning to temperatureover a somewhat narrower temperature range. These data were collected at the 615 MW power plant using two different Filter Temperature: D 1~C (325°F) 100 • 121°C (250°F) eo 1-----+--4 N ~.. 60 t----+--t So 5 40 0. ~ 20 o B Hg Se sampling methods to collect metals at the ESP inlet. Figure 7. Measured distribution of boron, mer-cury and selenium between the condensed and One set of data were collected with in-stack filters vapor phases at two filter temperatures for a that were at a temperature of 163°C (325 OF), the 615 MW coal-fired boiler. second set of data were collected using heated probes with filter boxes that were maintained at 121°C (250 OF). In each case the total metals concentrations were the same, however, the vapor-phase fractions of mercury and selenium were lower at the lower temperature. 11 |