Abstract:

Harmful gases such as NO _x (NO and NO₂) and N₂O are emitted during the production of dilute nitric acid by ammonia oxidation, which can lead to environmental problems such as photochemical smog (NO _x ), ozone layer depletion (NO _x and N₂O), and global warming (N₂O). It is imperative to remove NO _x and N₂O from the tail gas of nitric acid production. After introducing the generation pathways and control measures of NO _x and N₂O during nitric acid production, we summarized the main technological routes for simultaneous removal of NO _x and N₂O from the tail gas according to the research, development and application situations, including one-stage processes such as simultaneous SCR of NO _x and N₂O, SCR of NO _x and decomposition of N₂O over a composite catalyst, and two-stage processes such as catalytic N₂O decomposition followed by SCR of NO _x, SCR of NO _x followed by SCR of N₂O, and SCR of NO _x followed by catalytic N₂O decomposition. The principles and characteristics of different technological routes were analyzed. It was pointed out that the one-stage processes face challenges of improving the purification performance toward N₂O. The two-stage process of SCR of NO _x followed by catalytic N₂O decomposition, has advantages of low consumption of reducing agent and high purification efficiency of N₂O. Further research should focus on lowering the temperatures of both SCR of NO _x and catalytic N₂O decomposition and improving the tolerance of catalysts to co-existing gases (O₂, H₂O, etc.).

Key words: tail gas of nitric acid production, nitrogen oxide, greenhouse gas, selective catalytic reduction (SCR), N₂O decomposition, catalysts

摘要：

采用氨氧化法生产稀硝酸时会排放NO _x （NO和NO₂）和N₂O等有害气体，可导致光化学烟雾（NO _x ）、臭氧层消耗（NO _x 和N₂O）、全球变暖（N₂O）等环境问题，减少硝酸生产尾气中NO _x 和N₂O的排放势在必行。本文在分析硝酸生产过程中NO _x 和N₂O产生途径及减排措施的基础上，根据国内外研发和应用情况总结了联合脱除硝酸生产尾气中NO _x 和N₂O的主要技术路线，包括利用SCR催化剂同时催化NO _x 和N₂O还原和利用复合式催化剂同时催化NO _x 还原和N₂O分解等一段式工艺以及先催化N₂O分解后催化NO _x 还原、先催化NO _x 还原后催化N₂O还原和先催化NO _x 还原后催化N₂O分解等两段式工艺，分析了不同技术路线的原理、特点及面临的挑战。文中指出了一段式工艺主要存在N₂O净化性能有待提升的问题，两段式工艺中先催化NO _x 还原后催化N₂O分解的工艺在减少还原剂消耗量、促进N₂O去除等方面具有优势，未来需围绕同步降低SCR脱硝和N₂O分解所需温度、提高催化剂对共存气体（O₂、H₂O等）的耐受性等方面开展进一步研究。

关键词: 硝酸生产尾气, 氮氧化物, 温室气体, 选择性催化还原, N₂O分解, 催化剂