| abstract |
A multi-stage selective catalytic reduction (SCR) unit ( 32 ) provides efficient reduction of NOx and other pollutants from about 50-550° C. in a power plant ( 19 ). Hydrogen ( 24 ) and ammonia ( 29 ) are variably supplied to the SCR unit depending on temperature. An upstream portion ( 34 ) of the SCR unit catalyzes NOx+NH 3 reactions above about 200° C. A downstream portion ( 36 ) catalyzes NOx+H 2 reactions below about 260° C., and catalyzes oxidation of NH 3 , CO, and VOCs with oxygen in the exhaust above about 200° C., efficiently removing NOx and other pollutants over a range of conditions with low slippage of NH 3 . An ammonia synthesis unit ( 28 ) may be connected to the SCR unit to provide NH 3 as needed, avoiding transport and storage of ammonia or urea at the site. A carbonaceous gasification plant ( 18 ) on site may supply hydrogen and nitrogen to the ammonia synthesis unit, and hydrogen to the SCR unit. |