船用氨燃料发动机尾气条件下Cu-SSZ-13催化性能研究

Study on the Catalytic Performance of Cu-SSZ-13 Under Exhaust Conditions of Marine Ammonia-Fueled Engines

摘要

为探究 Cu-SSZ-13 催化剂在氨燃料发动机高体积分数水蒸气排气条件下的催化性能,本文利用GT-SUITE 软件建立了一维反应器模型以及催化反应动力学模型,通过数值仿真的方法对 SCR 系统内化学反应进行了研究,分析了不同工况下高体积分数水蒸气对Cu-SSZ-13 催化性能的影响．模型在 Eley-Rideal 机理的基础上,首次引入了水蒸气的吸附与脱附反应,并设置水蒸气抑制函数来表征水蒸气对硝酸铵(NH₄NO₃)分解的促进作用以及对氨(NH₃)选择性氧化的抑制作用,同时补充了NH₃ 的非选择性氧化反应和氧化亚氮(N₂O)的还原反应来进一步完善该模型．结果表明：Cu-SSZ-13催化剂在230～450 ℃范围内具有较高的氮氧化物(NO_x)转化效率,在 350 ℃以下,水蒸气对NO_x 转化具有抑制作用,而在 350 ℃以上表现出促进作用．定义不同工况下NO_x转化效率超过95%的温度范围为高效温度窗口,发现较高的氨氮比与较低的空速均有助于高效温度窗口随水蒸气体积分数升高而拓宽,但同时也使得各水蒸气体积分数下的N₂O生成量有所增加．基于模拟结果,将230～450 ℃、氨氮比为1.2、空速为50 000 h^-1 定义为该催化剂的优化工况．研究发现,在优化工况下,水蒸气对NO_x 转化的不利影响显著降低,NO_x 转化效率均超过 98%．此外,在 550 ℃时,体积分数为 25%的水蒸气对NO_x转化效率的促进作用最为显著,相较于基准工况提升值达到8.6%．

Abstract

To investigate the catalytic performance of Cu-SSZ-13 catalyst under conditions involving water vapor emissions of high volume fraction,a one-dimensional reactor model and a catalytic reaction kinetics model were established using GT-SUITE software. The chemical reactions occurring within the SCR system were analyzed through simulation methods. The influence of water vapor of high volume fraction on the catalytic performance of Cu-SSZ-13 was analyzed under different operating conditions. The model was based on the Eley-Rideal mechanism and,for the first time,incorporated water vapor adsorption and desorption,as well as a water vapor inhibition function to characterize the promoting effect of water vapor on ammonium nitrate(NH₄NO₃)decomposition and its inhibitory effect on the selective oxidation of ammonia(NH₃). In addition,nonselective oxidation of NH₃ and reduction of nitrous oxide(N₂O)were supplemented to further improve the model. The results show that the Cu-SSZ-13 catalyst achieves high NO_x conversion efficiency in a temperature range of 230—450 ℃. Below 350 ℃,water vapor inhibits NO_x conversion,whereas above 350 ℃,it promotes conversion. The temperature range where NO_x conversion efficiency exceeds 95% is defined as the efficient temperature window. It was found that a higher ammonia-to-nitrogen ratio and a lower gas hourly space velocity can broaden this efficient temperature window when the volume fraction of water vapor increases. However,these conditions also cause increased formation of nitrous oxide (N₂O)at all the volume fractions of water vapor. Based on the simulation results,the optimized operating condition for the catalysts was identified as 230—450 ℃,ammonia-to-nitrogen ratio was 1.2,and gas hourly space velocity was 50 000 h^-1. Under these conditions,the detrimental effect of water vapor on NO_x conversion was significantly reduced,with the NO_x conversion efficiency consistently exceeding 98%. Furthermore,at 550 ℃,the water vapor with the volume fraction of 25% exhibited the most pronounced promotional effect on NO_x conversion efficiency,showing an improvement of 8.6% relative to the base-line condition.

关键词

船用氨燃料发动机 / 选择性催化还原 / 水蒸气 / 分子筛催化剂 / 数值模拟

Key words

marine ammonia-fueled engine / selective catalytic reduction / water vapor / molecular sieve catalyst / numerical simulation

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基金资助

国家自然科学基金资助项目(51976136)

国家自然科学基金资助项目(51576140)

移动源排放控制技术国家工程实验室开放基金资助项目(NELMS2019B01)

移动源排放控制技术国家工程实验室开放基金资助项目(NELMS2017A02)

清华大学汽车安全与节能国家重点实验室开放基金资助项目(KF1818)