Abstract: In view of the typical problems in the flue gas denitration system, such as poor flow uniformity, ammonia escape, air pre-heater clogging, failure of NO_x stable ultra-low emission in full load section, a comprehensive diagnosis and closed-loop optimization strategy for ultra-low emission of SCR is proposed. Combining with the 630 MW implementation case, with the online large data and performance testing as the base, numerical simulation and system diagnosis as the means, by means of simulation evaluation and test analysis, the improvement scheme is put forward, optimized, revised and implemented, and finally combined with the performance test to verify the effect. The comprehensive diagnosis and closed-loop optimization of the SCR system are performed with multiple means. Comparing before and after modification, the standard deviation of NO_x concentration field decreases from 18.6% to 4.89%, the denitration efficiency increases from 86.7% to over 89%, and the chimney NO_x emission concentration is steadily below 50 mg/m³, the ammonia escaping mass concentration at the outlet of the SCR system decreases from 16 mg/m³ to 0.75 mg/m³. The effect of ultra-low emission reconstruction is remarkable.

Key words: coal-fired power plant, flue gas denitrification, ultra-low emission reformation, comprehensive diagnosis, closed loop optimization