Environmental Control Devices — Combined SO2 and NOx Removal

Environmental Control Devices — Combined SO2 and NOx Removal

In the SNOX (a trademarked name) process (Fig. 6), demonstrated at Ohio Edison’s Niles Station in Niles, Ohio, flue gas first passes though a high-efficiency fabric filter baghouse to minimize fly ash fouling of downstream equipment. Ammonia is then added to

the flue gas, which passes to a catalytic reactor where the ammonia reacts with NOx to form nitrogen gas and water. The next step is a catalytic reactor, which oxidizes SO2 to SO3. The presence of this reactor oxidizes any unreacted ammonia to N2 and water, thus preventing the formation of ammonium sulfate, which can form deposits that foul down­stream equipment. The oxidation catalyst also vir­tually eliminates CO and hydrocarbon emissions. The gas then flows to a condenser for the recovery of sulfuric acid and then to the stack. Sulfur removal is about 95% and NOx removal averages 94%. The sulfuric acid exceeds federal specifications for Class I acid. The fabric filter removes over 99% of the particulates.

Another demonstration combining SO2 and NOx removal was the SOx-NOx-Rox Box (SNRB) project at Ohio Edison’s R. E. Burger Plant. The SNRB process combines the removal of SO2, NOx, and particulates in one unit, a high-temperature fabric filter baghouse (Fig. 7). SO2 removal is effected by injecting a calcium – or sodium-based sorbent into the flue gas upstream of the baghouse. Ammonia is also injected into the flue gas to react with NOx and to form N2 and water over the SCR catalyst, which is installed inside the bags in the baghouse. Particulate removal occurs on the high – temperature fiber filter bags. Sulfur removal with calcium-based sorbents was in the 80-90% range at a Ca/S ratio of 2.0. NOx removal of 90% was achieved.

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