Investigation of selective catalytic reduction for control of nitrogen oxides in full-scale dairy energy production Mary Kay Camarillo a,⇑ , William T. Stringfellow b,c , Jeremy S. Hanlon b , Kyle A. Watson d a Civil Engineering Department, School of Engineering & Computer Science, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, USA b Ecological Engineering Research Program, School of Engineering & Computer Science, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, USA c Earth Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA d Mechanical Engineering Department, School of Engineering & Computer Science, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, USA highlights " Selective catalytic reduction reduced NO x emissions from a dairy biogas- fueled engine. " NO x production during combustion of dairy biogas was variable. " Performance was improved by real- time data collection and automated process control. " Air–fuel ratio impacted NO x removal; other engine conditions were less influential. " Catalysts demonstrated stable performance. graphical abstract article info Article history: Received 16 August 2012 Received in revised form 22 January 2013 Accepted 23 January 2013 Available online 28 February 2013 Keywords: Selective catalytic reduction (SCR) Nitrogen oxides (NO x ) Dairy manure Anaerobic digestion Combined heat power abstract Selective catalytic reduction (SCR) was used to reduce exhaust gas nitrogen oxides (NO x ) from the emissions of a 710 kW combined heat and power system fueled by dairy biogas. Exhaust gas NO x was reduced from 63.1 ± 31.9 to 14.2 ± 17.5 ppmvd @ 15% O 2 such that emissions were 0.33 ± 0.40 g kW 1 h 1 , based on data averaged over 15 min intervals. Online exhaust gas sensors with integrated process control algorithms were effective in improving NO x removal by automated control of urea, the ammonia source used for catal- ysis of NO x reduction reactions. Pre-SCR NO x was most strongly correlated with equivalence ratio (R 2 = 0.39), indicative of the air–fuel ratio. A concave relationship between NO x production and thermal conversion efficiency was not observed since lean-burn operation of the engine was consistent and only altered under low engine load. Following installation of pre- and post-SCR NO x sensors, average daily exhaust gas NO x reduction in the SCR was 82.6 ± 8.5%. Post-SCR NO x emissions were typically impacted by pre-SCR NO x (R 2 = 0.36), suggesting that altered operation of the anaerobic digesters or modifications to the engine would be effective in reducing NO x emissions as well as urea demand. After nearly three years of operation, the SCR catalyst remains in service without requiring replacement. Average daily urea demand was 31.8 ± 16.3 L d 1 for the system that produced 369 ± 136 kW of electricity. During the second year of observation the regulatory limit of 0.804 g kW 1 h 1 was met 94% of the time while the regulatory target of 0.201 g kW 1 h 1 was only met 45% of the time, based on data averaged over 15 min intervals. These results provide guidance for dairy energy projects in locations with stringent NO x emissions standards. Ó 2013 Elsevier Ltd. All rights reserved. 0306-2619/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.apenergy.2013.01.066 ⇑ Corresponding author. Tel.: +1 209 946 3056; fax: +1 209 946 3086. E-mail address: mcamarillo@pacific.edu (M.K. Camarillo). Applied Energy 106 (2013) 328–336 Contents lists available at SciVerse ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy