Overview and status of post-combustion NOx control: SNCR, SCR and hybrid technologies

Requirements for reduced NOx emissions have required that emissions reduction technologies move beyond combustion controls alone. Post combustion NOx control technologies that are being applied to coalfired utility boilers include selective non catalytic reduction (SNCR), selective catalytic reduction (SCR), and combined SNCR/SCR systems (hybrid SNCR/SCR). This paper reviews these technologies from the standpoint of their history of application, limitations in terms of NOx reduction and balance of plant impacts. The paper also includes a brief discussion of future developments that are ongoing for these post combustion NOx control technologies.