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The industrial feasibility of low temperature DeNOₓ in the presence of SOₓ: a project case in a medium coking plant

Li, Changming, Yu, Jian, He, Yi, Yu, Chao, Li, Ping, Wang, Chao, Huang, Fulin, Gao, Shiqiu
RSC advances 2018 v.8 no.33 pp. 18260-18265
ammonia, catalysts, collectors, desulfurization, dust, filtration, flue gas, foams, industrial applications, operating costs, sulfur oxides, temperature
Catalyst poisoning by SOₓ has hindered the industrial application of selective catalytic reduction (SCR) technology for the DeNOₓ of low temperature flue gas for many decades. The current engineering process of placing the SCR unit after the desulphurization and dedusting units can lead to high project and operational costs owing to low DeNOₓ efficiency at low temperatures. Based on our previous pilot results, a DeNOₓ project case was built before the desulfurization unit in a medium coking plant to explore the industrial feasibility of low temperature DeNOₓ in the presence of SOₓ. A new engineering process was considered and designed to overcome the problem of SOₓ, including the elimination of SO₃ with NH₃ before the SCR reactor, the filtration of ash by a foam metal plate and in situ regeneration technology. The project case could run continuously for six months with above 70% DeNOₓ efficiency and less than 10 ppm NH₃ slip at 250 °C and a space velocity of 4000 h⁻¹ in the presence of 260–300 mg m⁻³ SOₓ. The activity loss for the catalyst itself was not obvious after it had been running for six months, but blocking of the honeycomb channels by the sedimentary ash on the honeycomb catalyst modules owing to the low linear velocity resulted in decreased DeNOₓ efficiency and an increased pressure drop. A improved DeNOₓ process with gravitational dust collectors was also proposed to upgrade the present DeNOₓ project case for further continuous and stable operation.