CFD-based Design and Installation of Cost-effective ROFA/Rotamix System for NOx Reduction at RPU Silver Lake Unit 4

摘要

This paper summarizes the design and application of Nalco Mobotec’s Rotating Opposed Fired Air(ROFA~?) and Rotamix~? systems at Rochester Public Utilities (RPU) Silver Lake Unit 4, a 55 MW B&W front-wallfired pulverized coal boiler. Computational Fluid Dynamics (CFD) simulation was used to analyze combustionperformance and to evaluate NOx reduction performance in the design process of the ROFA/Rotamix system. Basedon baseline modeling and initial ROFA modeling, the final optimized ROFA ports were located and the air flowrequirements were determined. Rotamix SNCR (selective non-catalytic reduction) modeling was performed todesign the Rotamix urea injection system. After the installation and tuning of the ROFA/Rotamix systems at RPUSilver Lake Unit 4, a field performance test was carried out. At 44 MW gross without ROFA or Rotamix system inservice, the baseline NOx was averaged to be 0.43 lb/MMBtu. With ROFA system only in service, a NOx level of0.23 lb/MMBtu was achieved. Rotamix system with urea injection further reduced NOx to 0.15 lb/MMBtu or lessfor the entire boiler load range with less than 1 ppm ammonia slip at the stack. Due to the enhanced combustion, theimplementation of ROFA/Rotamix systems added additional benefit of reducing unburned carbon in the fly ash.These field results are consistent with the modeling results.