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Show volatile organics sampling train (US EPA SW846 Method 10). The sample train isokinetically draws flue gas through a quartz nozzle and probe. Solid particulate in the flue gas sample is collected on a glass fiber filter. An oven housing the particulate filter is maintained at 250F to preclude condensation of water on the filter. Semi-volatile organic gaseous species which pass through the filter are absorbed with a porous polymeric resin (XAD-2). Sample train components were cleaned and organic species recovered using a 50/50 solution of methanol and methylene chloride. Extraction procedures and GC/MS analyses were performed in accordance with US EPA SW-846 Method 8280. RESULTS AND DISCUSSION The final objective of this test program was to develop an incineration operation strategy to minimize PCDD/PCDF emissions from RDF combustion units. Preliminary to strategy development was identification and examination of potential PCDD/PCDF formation mechanisms. PCDD/PCDF has been detected in refuse incinerator fly ashland Barton et al6 have shown a correlation between fly ash and PCDD/PCDF emissions from a full scale RDF incinerator. Therefore, a series of tests were conducted to investigate the role of fly ash in formation mechanisms. Impact of Downstream Hold Up Temperature. Vogg et al3 have observed a significant increase in the PCDD/PCDF content of MSW incinerator fly ash exposed to a flow of incinerator flue gas in laboratory studies. This increase was observed at temperatures ranging from 460F to 660F. To assess the impact of this PCDD/PCDF formation mechanism at pilot scale, flue gas samples were simultaneously sampled with a standard MM5 sampling train and a second MM5 train. The oven housing the particulate capture filter of the second train was maintained at 5 70F, near the midpoint of the downstream formation mechanism temperature range identified in the lab studies. This system was configured to simulate an RDF incinerator with a hot APCD. The oven housing the particulate filter in the standard MM5 train was maintained at 250F, well below the critical temperature range for the downstream formation. To verify that PCDD/PCDF recovered from the 250F filter trains were a result of furnace formation only, flue gas was sampled with a probe that quenched the sample gas to temperatures below 300F at the nozzle with injection of nitrogen. This sampling technique eliminated the possibility of PCDD/PCDF formation in fly ash captured in the probe. Simultaneous sampling of flue gas with a quench probe train and standard MM5 train demonstrated there was no detectable PCDD/PCDF formation in the fly ash captured by the standard MM5 sampling train via the downstream mechanism. Flue gas temperatures at the sampling location ranged from 660F to 800F, above the critical temperature range. Sampling duration was one hour for all tests. PCDD/PCDF levels in sample trains with the 570F filter were 8 to 20 fold higher than those captured by the 250F filter sample trains for a wide variety of furnace conditions. Typical results from these tests are shown in Figure 3. It appears that conversion of precursors, which survive the combustion zone, to PCDD/PCDF is highly favored in this temperature range. Laboratory data indicate that PCDD/PCDF are stable at temperatures below 660F, little decomposition is expected. These results indicate that the downstream formation mechanism can have a large 3 |