Low Temperature Catalytic Reduction

Low Temperature Catalytic Reduction of NO via Selective Catalytic Reduction by Ammonia Catalytic Combustion and Catalytically Stabilized Combustion

 Student: Anand Krishnan

Sponsor: Federal Energy Technology Center and the US Department of Defense under cooperative agreement DE-FC22-92PC92162

Objective: To determine whether low temperature selective catalytic reduction of NOx could be combined with sorbent capture of SO2 in coal boiler flue gases.

Approach: The approach for simultaneous DeSOx-DeNOx is a variant on the Babcock & Wilcox SNRB process, in which sorbent injection upstream of a filter baghouse allows sulfur removal upstream of monolith supported NOx reduction catalysts. The monoliths are mounted within the filter bags, so that they are kept away from the sorbent and fly ash. Ammonia is also injected into the ductwork, and should pass through the filter bags and across the monoliths. In our version of this process, the flue gas temperature at the baghouse could be as low as 350øF and would be suitable for small scale industrial boilers with low flue gas temperatures. We performed characterization of catalyst selectivity and conversion efficiency for a range of synthetic flue gas compositions using an industrial low temperature SCR catalyst supplied by Engelhard Corporation.

Results: Selective catalytic reduction of nitric oxide with ammonia in synthetic low temperature flue gases has been investigated on a commercially available precious metal catalyst, NOxCAT 920 LTTM . It has been found that this catalyst is capable of achieving up to 90% conversion at temperatures below 300øC and low space velocities (12,000 hr-1), even in the presence of 20 ppm sulfur dioxide. The ideal ammonia concentration to reduce slip and achieve maximum conversion seems to be a stoichiometric match between ammonia concentration and nitric oxide concentration. A dual site model is proposed to explain the selectivity dependence on the presence of water vapor or sulfur dioxide.

Publications: Krishnan, A. T. and A. L. Boehman. Selective Catalytic Reduction of Nitric Oxide with Ammonia at Low Temperatures. Applied Catalysis B:Environmental, 18, 189-198 (1998).

Catalytic Reduction

Sketch of the Flow Reactor for SCR Catalyst Characterization