OCR Text |
Show the key objectives of the laboratory pilot tests was to demonstrate, on a continuous basis, particulate emissions in compliance with the NSPS requirement of 0.03 lb/million Btu. Of particular concern was the cleanability of the fully-integrated bag/catalyst assembly. Figure 4 illustrates the particulate removal results achieved throughout the SNRB laboratory pilot test program. Particulate emissions were determined using both the EPA Method 5 and 17 sampling techniques. As shown in the figure, particulate emissions less than 0.03 lb/million Btu were achieved for the majority of tests. Of equal importance was the fact that the bags could be repeatedly and reliably cleaned using conventional pulse-jet baghouse cleaning technology. The data collected after mid-December were obtained after the fabric filter bags had been removed from the baghouse. It is believed that some of the bags were damaged during their re-installation, leading to the higher particulate emission measured during the subsequent tests. The data points shown in February were obtained during tests with a low-sulfur coal, where inlet dust loadings were much lower than for the Ohio #8 coal tests. NOx Removal The primary NOx-related objective of the laboratory pilot tests was to detennine the design and operating specifications required to achieve at least 90% NOx removal. Of particular concern were the design of the catalyst and bag/catalyst supports, the required catalyst temperature and ammonia stoichiometry, and the amount of ammonia "slip". The NHYNOx stoichiometry is defined as the molar ratio of injected ammonia to the NOx in the 0.08 Method 5 flue gas, and ammonia slip refers to the amount of unreacted ammonia passing through the SNRB system and exiting the stack. To achieve this objective, the NHJlNOx ratio and catalyst temperature were varied over a range of operating conditions to maximize NOx reduction and minimize NH3 slip. The catalyst design - shape, formulation, and space velocity (flue gas flow rate divided by catalyst volume) - was also investigated during the tests. The effect of NHJlNOx ratio on NOx removal is illustrated in Figure 5. At NHJlNOx stoichiometries less than 1, the NOx removal increases from 70% to 90% as NHJI NOx stoichiometry increases from 0.8 to 1.0. At NHJI NOx stoichiometries greater than 1, NOx removals level off. In addition, operation at these higher stoichiometry levels also results in higher emissions of unreacted NH3. These results are also shown in Figure 5. This unreacted ammonia is primarily of concern due to the potential formation of troublesome ammonium bisulfate deposits as the flue gases pass through the downstream heat exchanger (air heater). At ammonia stoichiometries greater than 1.1, a sharp increase in NH3 slip was observed. At stoichiometries lower than 1.1, NH3 slip was typically less than 20 ppm. The catalyst design and arrangement have been modified for the field demonstration to reduce NH3 slip. Several tests were conducted to determine the effect of baghouse operating temperature on NOx removal performance. The bag house temperature was varied from 675" - 8S0"F to determine baghouse operating conditions for optimal NOx removal perfonnance. As indicated in Figure 6, NOx removal improved with increasing baghouse temperature up to about 8S0"F. Operation at temperatures ';;.'-"~' With Catalyst • Without Catalyst Method 17 ~~O~.0_3_I_b~s/_mv_J_II_io_~_B_t_u~(~N_S_P_S~) __ ----------------~rr~~ ~~~.---------~ ~ 1\\ 0.00 r-: I . I:. Bags Removed t\, I} ; . I -I _____ _________________ -+-I r~: t.l-----,·t!- li- ~! " \..::: ~ ... ' , ..: : . , I I . i " ~ . I SEP OCT NOV DEC JAN FEB Figure 4. Particulate Emissions Results 5 |