Progress and prospects of flue gas deNOx technology for the iron and steel industry

Nitrogen oxides (NO_x) are the primary air pollutant in China. The iron and steel industries have become the primary industrial sources of NO_x emissions in China. The NO_x emissions from iron and steel industries account for 27.3% of all industrial NO_x emissions from sources nationwide, surpassing thermal power generation and cement manufacturing. Over the past ten years, China’s iron and steel industry has achieved tremendous results in flue gas desulfurization, but a huge gap in denitrogenate (deNOx) still remains. In 2019, the Ministry of Ecology and Environment and other departments jointly issued “Opinions on Promoting the Implementation of Ultra-low Emission in the Iron and Steel Industry”, which promoted the retrofitting of ultra-low emission in the iron and steel industry. Sintering, pelleting, coking, and other processes are the focus of retrofitting for NO_x emissions. Because their low-temperature flue gas contains several contaminants that differ from the flue gas of thermal power plants, they cannot completely copy the existing deNOx technology for the coal-fired boiler flue gas of thermal power plants. At present, selective catalytic reduction (SCR), activated carbon (AC) adsorption catalysis, ozone (O₃) oxidation and absorption, and other technologies are used in sintering, pelleting, and coking processes. These technologies have achieved good results. Herein, we investigated the existing flue gas deNOx technologies for sintering, pelleting, and coking processes in iron and steel industries and analyzed the advantages and disadvantages of SCR technology, AC adsorption catalysis, and O₃ oxidation and absorption technologies. The SCR technology has high efficiency and reliable performance, but the operation process requires heating of the flue gas, which uses large amounts of blast furnace gas or coking oven gas, and the service life of the catalyst is typically approximately three years. The waste SCR catalysts are recognized as HW50 hazardous waste. AC adsorption catalytic technology can simultaneously desulfurize and deNOx; its operating temperature is low without flue gas reheating. The by-product of H₂SO₄ can be utilized, and the waste AC produced can be directly used for sintering or coking, while its deNOx efficiency is low. O₃ oxidation and absorption technologies have a low initial investment cost and require little floor space. However, their operating cost is relatively high, and the coabsorption of NO_x and SO₂ makes the desulfurization ash mixed with nitrate, which increases the difficulty of comprehensive utilization. Finally, we analyzed the application possibilities of SCR and other technologies, providing a reference for the development and selection of deNOx technologies for flue gas from the iron and steel industry.