Selective catalytic reduction failure of low NH3-NOx ratio

doi:10.1016/j.cjche.2020.07.055

Abstract

Abstract: An insufficient amount of NH₃ (ammonia) will reduce the conversion efficiency of NO_x, which may lead to excess NO_x emissions, resulting in NH₃-SCR failure. In this article, SCR failure caused by a low NH₃-NO_x ratio is studied systematically by experiments. The main reasons for a low NH₃-NO_x ratio in SCR include insufficient urea injection, hydrothermal aging of catalysts and urea crystallization. It was found from an insufficient urea injection experiment that with the increase of NH₃-NO_x ratio, the NO_x conversion efficiency of the SCR system increased, but the ammonia leakage also increased. The main influencing factors of NO_x conversion efficiency are different under different NH₃-NO_x ratios. A flow reactor system was used in the catalyst hydrothermal aging experiment to investigate the effect of hydrothermal aging on catalyst activity. After a 24 h hydrothermal aging experiment at 800℃, the NO_x conversion efficiency of the copper-based zeolite catalysts decreased significantly at the boundary of medium and low temperature regions. And the NO₂-NO_x ratio in the mixture had a significant effect on the catalytic performance. Thermogravimetry coupled to Fourier transform infrared spectroscopy (TG-FTIR) was used to analyze the composition of urea deposits in a urea deposits analysis experiment. It was found that the main components of urea deposits were urea and isocyanic acid (HNCO). Preventing HNCO polymerization, especially the formation of CYA, can decrease the formation of urea deposits.

Key words: SCR, Low NH₃-NO_x ratio, Purification, Hydrothermal, Urea crystallization

摘要： An insufficient amount of NH₃ (ammonia) will reduce the conversion efficiency of NO_x, which may lead to excess NO_x emissions, resulting in NH₃-SCR failure. In this article, SCR failure caused by a low NH₃-NO_x ratio is studied systematically by experiments. The main reasons for a low NH₃-NO_x ratio in SCR include insufficient urea injection, hydrothermal aging of catalysts and urea crystallization. It was found from an insufficient urea injection experiment that with the increase of NH₃-NO_x ratio, the NO_x conversion efficiency of the SCR system increased, but the ammonia leakage also increased. The main influencing factors of NO_x conversion efficiency are different under different NH₃-NO_x ratios. A flow reactor system was used in the catalyst hydrothermal aging experiment to investigate the effect of hydrothermal aging on catalyst activity. After a 24 h hydrothermal aging experiment at 800℃, the NO_x conversion efficiency of the copper-based zeolite catalysts decreased significantly at the boundary of medium and low temperature regions. And the NO₂-NO_x ratio in the mixture had a significant effect on the catalytic performance. Thermogravimetry coupled to Fourier transform infrared spectroscopy (TG-FTIR) was used to analyze the composition of urea deposits in a urea deposits analysis experiment. It was found that the main components of urea deposits were urea and isocyanic acid (HNCO). Preventing HNCO polymerization, especially the formation of CYA, can decrease the formation of urea deposits.

关键词: SCR, Low NH₃-NO_x ratio, Purification, Hydrothermal, Urea crystallization

Piqiang Tan, Xiaoyu Li, Shiyan Wang, Zhiyuan Hu, Diming Lou. Selective catalytic reduction failure of low NH₃-NO_x ratio[J]. Chinese Journal of Chemical Engineering, 2021, 32(4): 231-240.

Piqiang Tan, Xiaoyu Li, Shiyan Wang, Zhiyuan Hu, Diming Lou. Selective catalytic reduction failure of low NH₃-NO_x ratio[J]. 中国化学工程学报, 2021, 32(4): 231-240.

References 30

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Selective catalytic reduction failure of low NH₃-NO_x ratio

Selective catalytic reduction failure of low NH₃-NO_x ratio

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