NOx attenuation in flue gas by •OH/SO4•--based advanced oxidation processes
2020
Chen, Hongyu | Wang, Cuicui | Zhang, Jiahao | Shi, Yijie | Liu, Yuexian | Qian, Zhi
The combustion of fossil fuels has resulted in rapidly increasing emissions of nitrogen oxide (NOₓ), which has caused serious human health and environmental problems. NO capture has become a research focus in gas purification because NO accounts for more than 90% of NOₓ and is difficult to remove. Advanced oxidation processes (AOPs), features the little secondary pollution and the broad-spectrum strong oxidation of hydroxyl radicals (•OH), are effective and promising strategies for NO removal from coal-fired flue gas. This review provides the state of the art of NO removal by AOPs, highlighting several methods for producing •OH and SO₄•⁻. According to the main radicals responsible for NO removal, these processes are classified into two categories: hydroxyl radical-based AOPs (HR-AOPs) and sulfate radical-based AOPs (SR-AOPs). This paper also reviews the mechanisms of NO capture by reactive oxygen species (ROS) and SO₄•⁻ in various AOPs. A HiGee (high-gravity) enhanced AOP process for improving NO removal, characterized by intensified gas-liquid mass transfer and efficient micro-mixing, is then proposed and discussed in brief. We believe that this review will be useful for workers in this field. Graphical abstract
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