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

Abstract

Catalyst poisoning by SO_x has hindered the industrial application of selective catalytic reduction (SCR) technology for the DeNO_x 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 DeNO_x efficiency at low temperatures. Based on our previous pilot results, a DeNO_x project case was built before the desulfurization unit in a medium coking plant to explore the industrial feasibility of low temperature DeNO_x in the presence of SO_x. A new engineering process was considered and designed to overcome the problem of SO_x, 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% DeNO_x 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 SO_x. 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 DeNO_x efficiency and an increased pressure drop. A improved DeNO_x process with gravitational dust collectors was also proposed to upgrade the present DeNO_x project case for further continuous and stable operation.