BVT-Merkblatt zu Abwasser- und Abgasbehandlung

Example 3
Highly effective SCR to control high initial NO x content.
[Comments from France to Draft 2]
Annexes
Production high performance abrasive grit for the manufacture of grinding wheels
and sand paper
Production process Norton SG process using nitric acid and emitting highly concentrated
nitrous waste gas
Conditions: waste gas stream 800 Nm 3 /h, NOx concentration 10000 ppm
NOx abatement chosen SCR process
Alternative abatement process Scrubbing with peroxide / water, conversion of NOx to nitric acid
Rationale of decision in favour of
SCR
� investment and operating costs of SCR seem to be reasonable
� no more polluting effluents
� operation and maintenance of SCR are easy
Abatement process The gas (70-90 °C) is first diluted to reduce the NOx concentration to
less than 5000 ppm. The mixture is heated to about 240 °C, the
stoichiometric amount of NH3 (NH3/NOx up to 1.24) sprayed as 25 %
ammonia solution into it. The mixture is immediately led across the
catalyst bed of granules. Finally, the waste gas is again diluted with
air by a factor >10 (reduction of NOx concentration from 200 mg/Nm3
to 20 mg/Nm3) to eliminate any rust that colours the flue gas.
Performance data
Catalyst temperature upstream: 215-225 °C
NOx concentration downstream catalyst: 1240-1450 ppm
NOx concentration after dilution: 50-100 ppm
ratio NH3/NOx (mol/mol): 1.17-1.24
NH3 leakage: up to 15 mg/Nm 3
NOx conversion: 93.1-96.2 %
Costs
Investment costs 2.4 million FFR
equipment and civil engineering 1.755 million FFR
design 0.645 million FFR]
Annual operating costs 2176 FFR/t converted NOx
Overall cost 5182 FFR/t abated NOx
Waste Water and Waste Gas Treatment 349